JP2001266893A - Non-aqueous electrolytic solution secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress a decomposition on a lithium containing compound nitride of non-aqueous electrolytic solution or the like at a high temperature storage, and prevent the generation of gas and the reduction of battery capacity by self-discharge in a battery which uses lithium containing composite nitride for a negative electrode. SOLUTION: This is equipped with a positive electrode, negative electrode and nonaqueous electrolytic solution, and the negative electrode which is composed of lithium containing compound nitride expressed in a general formula Lix, Mv, N (M: transition metal, 0<=x<=3, 0.1<=y<=0.8), and, is configured from particulate materials having a phase that contains Li2CO3 in a surface layer part or a phase in which the content of M is smaller than that of inside in the surface layer part.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a non-aqueous electrolyte secondary battery using a lithium-containing composite nitride as a negative electrode material.

[0002]

2. Description of the Related Art In recent years, lithium ion batteries using lithium cobalt oxide for a positive electrode and a carbon material for a negative electrode have been widely used as power supplies for portable equipment. These batteries are
As electronic devices become smaller and lighter, higher energy densities are desired. Therefore, in order to increase the capacity of a battery, it has been proposed to use a lithium-containing composite nitride as an electrode material for an electrochemical element such as a non-aqueous electrolyte secondary battery.
78609. This lithium-containing composite nitride has an operating electrode potential of about 0 with respect to the Li potential.
２2 V, and its use as a negative electrode material is also considered. When the lithium-containing composite nitride is used as the negative electrode, the reversible capacity is extremely large, and a battery with a high energy density can be realized.

[0003] Among them, a lithium-containing composite nitride represented by the general formula Li _x M _y N, wherein cobalt is used for M and y
= 0.4 to 700 mAh for a material with a composition of 0.4
/ G of reversible capacity. In the above equation, the value x is
Indicates the content of Li in the active material, and is a variable that changes with charging and discharging. This value is the theoretical capacity (about 370 mA) of a carbon material used as a negative electrode material of a normal lithium ion battery.
h / g). Therefore, when a lithium-containing composite nitride is used, the battery capacity can be dramatically improved, and a lithium secondary battery with extremely high energy density can be obtained.

[0004]

The capacity of a battery using a lithium-containing composite nitride as a negative electrode is much larger than that of a battery using a carbon material.
There is a problem that the capacity is reduced due to self-discharge and the battery is swollen due to gas generation. An object of the present invention is to provide a non-aqueous electrolyte secondary battery which solves these problems, has excellent storage characteristics, is easily obtained, and has a low production cost.

[0005]

SUMMARY OF THE INVENTION The present invention comprises a positive electrode, a negative electrode and a nonaqueous electrolyte, wherein the negative electrode has the general formula Li _x M _y
N (M: transition metal, 0 ≦ x ≦ 3, 0.1 ≦ y ≦ 0.8)
And a non-aqueous electrolyte secondary battery comprising a particulate material having a phase containing Li ₂ CO ₃ in a surface portion thereof. By using the particulate material, the storage characteristics of the non-aqueous electrolyte secondary battery can be improved. The phase containing Li ₂ CO ₃ is preferably present in a region from the surface of the particulate material to a depth of 30 nm. The content of Li ₂ CO ₃ in the particulate material is preferably 0.01 to 20% by weight.

[0006] The present invention further includes a positive electrode, a negative electrode and a nonaqueous electrolyte, wherein the negative electrode has the general formula Li _x M _y N (M:
A transition element, composed of a lithium-containing composite nitride represented by 0 ≦ x ≦ 3, 0.1 ≦ y ≦ 0.8), and having a phase in which the amount of M is smaller than that of the inside in the surface layer portion The present invention relates to a non-aqueous electrolyte secondary battery comprising a material. Even when the particulate material is used, the storage characteristics of the nonaqueous electrolyte secondary battery can be improved.

[0007] Of the particulate materials, M in the above general formula
Is an element from Sc of element number 21 to Zn of element number 30, for example, in XPS analysis, the peak intensity (I _a ) based on the 2p spectrum of M when the outermost surface of the particle is measured, and the particle Was etched by argon ion irradiation, and the peak intensity (I based on the 2p spectrum of M when the inside of a depth of 50 nm was measured from the surface was measured.
₅₀ ) have a relationship of I _a <I ₅₀ . The peak intensity (I _a ) based on the 2p spectrum of M when measuring the outermost surface of the particle, and the depth of 50 nm from the surface by etching the particle by irradiating with argon ions.
Preferably has a relationship of (I _a ) / (I ₅₀ ) ≦ 0.3 with the peak intensity (I ₅₀ ) based on the 2p spectrum of M when the inside of the sample is measured.

In the above general formula, M is cobalt,
It is preferably at least one selected from the group consisting of iron, manganese, copper and nickel.

[0009]

The negative electrode used in the nonaqueous electrolyte secondary battery of the embodiment of the present invention have the general formula Li _x M _y N (M: transition metal, 0
.Ltoreq.x.ltoreq.3, and 0.1.ltoreq.y.ltoreq.0.8).

In the above general formula, the transition metal M includes, from Sc of element number 21 to Zn of element number 30 and Y of element number 39.
To Cd of element number 48 and Hg of element number 80 to La from element number 57. The transition metal M is preferably at least one selected from the group consisting of cobalt, iron, manganese, copper and nickel, with cobalt being particularly preferred. These transition metals are used because a high-capacity electrode material can be obtained.

The lithium-containing composite nitride powder is prepared by, for example, mixing a predetermined amount of a starting material, Li ₃ N powder, and a transition metal powder, which is a substitute species, and firing the mixture in a high-purity nitrogen atmosphere. Obtainable.

The above-mentioned particulate material has Li on its surface layer._TwoCO_ThreeTo
It has a phase containing. That is, the particulate material
Is Li_TwoCO_ThreeWherein the phase containing
It is formed on the surface layer of the particles, and the surface layer is
It has a function as a protective film layer. Such a structure
Can cause gas generation during high-temperature storage.
Suppresses the reaction between titanium-containing composite nitride and organic electrolyte
It becomes possible. This is Li_TwoCO_ThreeIs the organic electrolyte
And very low reaction with lithium-containing composite nitride
Is it a stable substance and effective as a component of the surface protective film layer?
It is. Li _TwoCO_ThreeProtective layer consisting of a phase containing
High qualitative Li_TwoCO_ThreeIs the main component, and Li
_TwoO, LiOH and the like may be contained. In addition,
The structure may be either crystalline or amorphous.

In order to obtain the effect of the present invention, it is preferable that at least 30%, more preferably at least 50%, of the surface of the lithium-containing composite nitride particles is covered with a phase containing Li ₂ CO ₃ . More preferably, Li is applied to the entire surface of the particles.
It is preferred to form a phase containing ₂ CO ₃ . Where L
The area covered with the phase containing i ₂ CO ₃ was determined by electron microscopy,
It is determined using electron beam diffraction or the like.

The phase containing Li ₂ CO ₃ is preferably present in a region from the surface of the particulate material to a depth of 30 nm. That is, it is desirable that Li ₂ CO ₃ be present at a depth of 30 nm from the surface of the lithium-containing composite nitride particles. Li ₂ to a depth exceeding 30 nm from the surface
If there is a large amount of CO _{3, the} portion that cannot be charged or discharged increases, and battery characteristics tend to decrease. On the other hand, even when Li ₂ CO ₃ is present in a region from the surface to a depth of 30 nm, the storage characteristics can be improved without affecting the charge / discharge characteristics of the battery. Here, as a method of examining how deep Li ₂ CO ₃ exists from the surface, analysis by XPS is preferable.

The content of Li ₂ CO ₃ in the particulate material is preferably 0.01 to 20% by weight. L
If the content of i ₂ CO ₃ is less than 0.01% by weight, the effect of the present invention cannot be obtained. If the content exceeds 20% by weight, the battery capacity decreases. Here, the weight ratio of Li ₂ CO ₃ can be determined by analysis such as weight reduction by thermal analysis or quantification of carbonate by chemical analysis.

The average particle size of the particulate material (50% particle size:
In the weight distribution, the particle size that just divides coarse particles and fine particles into 50% each) is preferably 1 to 50 μm, more preferably 2 to 30 μm. Here, the average particle size is determined by measurement using a laser diffraction type particle size distribution analyzer.

[0017] Another negative electrode used in the nonaqueous electrolyte secondary battery of the present invention also, the general formula Li _x M _y N (M: transition metal, 0 ≦ x
.Ltoreq.3, 0.1.ltoreq.y.ltoreq.0.8). And, the particulate material has a phase in which the content of M is smaller in the surface layer portion than in the inside. By making the transition metal content of the surface layer portion of the lithium-containing composite nitride particles lower than the internal transition metal content, the number of active sites for decomposing organic substances such as an electrolyte solution and a binder decreases, and the particle surface has This is because the decomposition of the electrolytic solution or the like can be suppressed. In addition,
The elucidation of the degradation reaction mechanism at high temperatures in non-aqueous electrolyte secondary batteries using lithium-containing composite nitride as the anode material is insufficient, but the transition metal dissolved in the lithium-containing composite nitride decomposes organic matter. It is considered that this is the active point.

The transition metal content in the surface layer is smaller than that in the interior
For example, particulate materials composed of lithium-containing composite nitrides
For example, as described above, the surface portion of the lithium-containing composite nitride particles
To Li _TwoCO_ThreeCan be obtained by forming a protective film layer of
However, it is not limited to this method. Various other surface treatments
The surface layer of the particles is Li_TwoO, LiOH, Li_ThreeSimple such as N
It may be modified to a single or mixed phase. Also, another surface treatment
Low transition metal content or total transition metal
The particles may be coated with a single phase or a mixed phase that does not contain much.
In addition, the transition metal
Change to particles with a gradient in transition metal concentration so that the amount increases
May be quality.

As the particulate material, for example, in the above general formula, M is from element number 21 Sc to element number 30 Z
n, and in the XPS analysis, the peak intensity (I _a ) based on the M 2p spectrum when the outermost surface of the particle is measured and the M 2p spectrum when the inside of the particle is measured. And the peak intensity (I _b ) based on
I _a <those having a relationship of I _b, more M between the peak intensity based on 2p spectrum (I _a), the depth 50nm from the surface of the particles were etched by argon ion irradiation when measuring the top surface of the particle M when measuring the inside of
And the peak intensity (I ₅₀ ) based on the 2p spectrum of
_a <I ₅₀ . I ₅₀ is, for example, an acceleration voltage of 500 V, an angle of 90 degrees, and an ion current density of 3
² μA / cm ² , etching rate about 10 ° / min
Etching with argon ions is performed for 50 minutes under the conditions of (SiO ₂ conversion), and the peak intensity based on the 2p spectrum of the transition metal M when measuring the inside of the particle after removing the surface layer by 50 nm may be used.

In the XPS analysis, for example, when M is cobalt, it is 810-770 eV, and when M is iron, it is 740-770 eV.
700 eV, 662 to 631 eV for manganese, 975 to 925 eV for copper, 888 for nickel
What is necessary is just to compare the peak intensities of the 2p spectra appearing within the range of ８848 eV.

The effect of the present invention can be obtained if the transition metal content of the surface layer is smaller than that of the inside. Among them, M in the above general formula is an element from Sc of element number 21 to Zn of element number 30. And a peak intensity (I _a ) based on a 2p spectrum of M when measuring the outermost surface of the particle;
The peak intensity (I ₅₀ ) based on the 2p spectrum of M when the particles were etched by irradiation with argon ions and the inside at a depth of 50 nm from the surface was measured was (I _a ) / (I _a ).
₅₀ ) It is preferable to have a relationship of ≦ 0.3.

The positive electrode and the negative electrode used in the nonaqueous electrolyte secondary battery of the present invention include, for example, a positive electrode material and a negative electrode material capable of electrochemically and reversibly inserting and releasing lithium ions, a conductive agent, a binder and the like. It can be produced by applying an electrode mixture to the surface of the current collector. Here, the particulate material is used as the negative electrode material.

The conductive agent for a negative electrode used in the present invention may be any material as long as it is an electron conductive material. For example, graphites such as natural graphite (flaky graphite, etc.), artificial graphite, expanded graphite, carbon blacks such as acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, carbon fibers, metal fibers Conductive fibers such as copper, nickel and the like, and organic conductive materials such as a polyphenylene derivative can be used alone or as a mixture thereof. Among them, artificial graphite, acetylene black and carbon fiber are particularly preferred.

The amount of the negative electrode conductive agent is not particularly limited, but is 1 to 50% by weight, and more preferably 1 to 50% by weight, based on the negative electrode material.
~ 30% by weight is preferred. Further, since the particulate material according to the present invention itself has electronic conductivity, it can function as an electrode without adding a conductive agent.

As the binder for the negative electrode used in the present invention, either a thermoplastic resin or a thermosetting resin may be used. Preferred binders in the present invention, for example, polyethylene, polypropylene, polytetrafluoroethylene,
Polyvinylidene fluoride, styrene butadiene rubber, tetrafluoroethylene-hexafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-perfluoroalkylvinyl ether copolymer, vinylidene fluoride-hexafluoropropylene copolymer Polymer, vinylidene fluoride
Chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer, polychlorotrifluoroethylene, vinylidene fluoride-pentafluoropropylene copolymer, propylene-tetrafluoroethylene copolymer, ethylene-chlorotrifluoroethylene copolymer Polymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, vinylidene fluoride-perfluoromethylvinyl ether-tetrafluoroethylene copolymer, ethylene-acrylic acid copolymer or its (Na ⁺ ) ion crosslinked product , An ethylene-methacrylic acid copolymer or its (Na ⁺ ) ion crosslinked product, ethylene-
Examples thereof include a methyl acrylate copolymer or a (Na ⁺ ) ion crosslinked product thereof, and an ethylene-methyl methacrylate copolymer or a (Na ⁺ ) ion crosslinked product thereof. These may be used alone or in combination of two or more. Of these, styrene butadiene rubber,
Polyvinylidene fluoride, ethylene-acrylic acid copolymer or its (Na ⁺ ) ion crosslinked product, ethylene-methacrylic acid copolymer or its (Na ⁺ ) ion crosslinked product, ethylene-methyl acrylate copolymer or its (N
a ⁺ ) ion crosslinked product, ethylene-methyl methacrylate copolymer or its (Na ⁺ ) ion crosslinked product is preferred.

As the current collector for the negative electrode used in the present invention, any collector may be used as long as it does not cause a chemical change in the constructed battery. As the material of the current collector, for example, stainless steel, nickel, copper, titanium, carbon, conductive resin, or a material obtained by treating the surface of copper or stainless steel with carbon, nickel, titanium, or the like is used. Among these, copper or a copper alloy is particularly preferable. Further, the surfaces of these materials may be oxidized and used, or the surface of the current collector may be made uneven by surface treatment. As a form of the current collector, for example, a foil, a film, a sheet, a net,
Punched materials, lath bodies, porous bodies, foams, molded articles of a fiber group, and the like can be given. The thickness of the current collector is not particularly limited, but a thickness of 1 to 500 μm is used.

[0027] For the positive electrode material used in the present invention, it is possible to use a general lithium-containing transition metal oxides, for example _{Li p CoO 2, Li p NiO} 2, Li p MnO 2, Li
_{p Co q Ni 1-q O} 2, Li p Co q M 1-q O r, Li p Ni 1-q
_{M q O r, Li p Mn} 2 O 4, Li p Mn 2-q M q O 4 ( provided that, M is Na, Mg, Sc, Y, Mn, Fe, Co, N
i, Cu, Zn, Al, Cr, Pb, Sb or B, 0
≦ p ≦ 1.2, 0 ≦ q ≦ 0.9, 2 ≦ z ≦ 2.3). Here, the p value is a value before the start of charge / discharge, and increases / decreases due to charge / discharge. However, transition metal chalcogenide, vanadium oxide and its lithium compound,
It is also possible to use other positive electrode materials such as niobium oxide and its lithium compound, a conjugated polymer using an organic conductive substance, and a Chevrel phase compound. It is also possible to use a mixture of a plurality of different positive electrode materials. Although the average particle diameter of the positive electrode active material particles is not particularly limited,
It is preferably from 30 to 30 μm.

The conductive agent for the positive electrode used in the present invention may be any electronic conductive material which does not cause a chemical change in the charge and discharge potential of the positive electrode material used. For example, graphites such as natural graphite (flaky graphite, etc.), artificial graphite, acetylene black, Ketjen black, channel black, furnace black, lamp black,
Carbon blacks such as thermal black, carbon fiber,
Conductive fibers such as metal fibers, metal powders such as carbon fluoride and aluminum, conductive whiskers such as zinc oxide and potassium titanate, conductive metal oxides such as titanium oxide, and organic conductive materials such as polyphenylene derivatives Materials. These may be used alone or in combination of two or more. Among these, artificial graphite and acetylene black are particularly preferred. The addition amount of the conductive agent is not particularly limited, but is 1 to 50 with respect to the positive electrode material.
% By weight, more preferably 1 to 30% by weight. In the case of carbon or graphite, 2 to 15% by weight is particularly preferable.

The binder for the positive electrode used in the present invention may be either a thermoplastic resin or a thermosetting resin. Preferred binders in the present invention, for example, polyethylene, polypropylene, polytetrafluoroethylene,
Polyvinylidene fluoride, styrene butadiene rubber, tetrafluoroethylene-hexafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-perfluoroalkylvinyl ether copolymer, vinylidene fluoride-hexafluoropropylene copolymer Polymer, vinylidene fluoride
Chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer, polychlorotrifluoroethylene, vinylidene fluoride-pentafluoropropylene copolymer, propylene-tetrafluoroethylene copolymer, ethylene-chlorotrifluoroethylene copolymer Polymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, vinylidene fluoride-perfluoromethylvinyl ether-tetrafluoroethylene copolymer, ethylene-acrylic acid copolymer or its (Na ⁺ ) ion crosslinked product , An ethylene-methacrylic acid copolymer or its (Na +) ion crosslinked product, ethylene-
Examples thereof include a methyl acrylate copolymer or its (Na +) ion crosslinked product, and an ethylene-methyl methacrylate copolymer or its (Na +) ion crosslinked product. These may be used alone or in combination of two or more. Of these, polyvinylidene fluoride and polytetrafluoroethylene are preferred.

The current collector for the positive electrode used in the present invention may be any electronic conductor that does not cause a chemical change in the charge and discharge potential of the positive electrode material used. As the material of the current collector, for example, stainless steel, aluminum, titanium, carbon, a conductive resin, a material obtained by treating the surface of aluminum or stainless steel with carbon or titanium, or the like is used. Among these, aluminum or an aluminum alloy is particularly preferable. Further, the surface of these materials may be oxidized and used, and it is desirable to make the current collector surface uneven by surface treatment. Examples of the form of the current collector include a foil, a film, a sheet, a net, a punched material, a lath body, a porous body, a foam, a fiber group, and a non-woven fabric. The thickness of the current collector is not particularly limited, but a thickness of 1 to 500 μm is used.

For each electrode mixture, a filler, a dispersant, an ion conductor, a pressure enhancer, and other various additives can be used in addition to a conductive agent and a binder. As the filler, any fibrous material that does not cause a chemical change in the configured battery can be used. Usually, fibers such as olefin-based polymers such as polypropylene and polyethylene, glass, and carbon are used. The addition amount of the filler is not particularly limited, but is 0 to 30% by weight based on the electrode mixture.
Is preferred.

In the present invention, the negative electrode plate and the positive electrode plate are preferably provided such that the negative electrode mixture surface is present on the surface opposite to the positive electrode mixture surface.

The non-aqueous electrolyte used in the present invention comprises a solvent and a lithium salt dissolved therein.
Examples of the solvent include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate and vinylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, chain carbonates such as dipropyl carbonate, methyl formate, methyl acetate, and propion. Methyl acid,
Aliphatic carboxylic acid esters such as ethyl propionate, γ-lactones such as γ-butyrolactone, 1,2-
Chain ethers such as dimethoxyethane, 1,2-diethoxyethane and ethoxymethoxyethane, cyclic ethers such as tetrahydrofuran and 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolan, formamide, acetamide, dimethylformamide, dioxolan , Acetonitrile, propyl nitrile, nitromethane, ethyl monoglyme, phosphate triester,
Trimethoxymethane, dioxolane derivative, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, 3-methyl-2-oxazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ethyl ether, 1,3-propane sultone, Aprotic organic solvents such as anisole, dimethylsulfoxide, N-methylpyrrolidone and the like can be mentioned. These may be used alone or in combination of two or more. Among them, a mixture of a cyclic carbonate and a chain carbonate or a mixture of a cyclic carbonate, a chain carbonate and an aliphatic carboxylic acid ester is preferable.

Lithium salt (supporting salt) dissolved in the above-mentioned solvent
For example, LiClO ₄ , LiBF ₄ , LiP
F ₆ , LiAlCl ₄ , LiSbF ₆ , LiSCN, Li
Cl, LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , Li (CF ₃
SO ₂ ) ₂ , LiAsF ₆ , LiN (CF ₃ SO ₂ ) ₂ , Li
B ₁₀ Cl ₁₀ , lithium lower aliphatic carboxylate, LiC
1, LiBr, LiI, lithium chloroborane, lithium tetraphenylborate, imides and the like. These may be used alone or in combination of two or more. Among these, in particular, LiPF
₆ is preferred.

A particularly preferred nonaqueous electrolyte in the present invention contains at least ethylene carbonate and ethyl methyl carbonate, and contains LiPF ₆ as a supporting salt. The amount of these electrolytes to be injected into the battery is not particularly limited, but a required amount is used according to the amounts of the positive electrode material and the negative electrode material and the size of the battery. The amount of the supporting salt dissolved in the solvent is not particularly limited, but is preferably 0.2 to 2 mol / L, and more preferably 0.5 to 1.5 mol / L.

In addition to the non-aqueous electrolyte, a solid electrolyte is also used.
Can be Solid electrolytes consist of inorganic solid electrolytes and organic
It is divided into solid electrolytes. Li is used as the inorganic solid electrolyte.
Well-known nitrides, halides, oxyacid salts, etc.
I have. Above all, Li_FourSiO_Four, Li_FourSiO_Four-LiI
-LiOH, xLi_ThreePO_Four-(1-x) Li_FourSiO _Four,
Li_TwoSiS_Three, Li_ThreePO_Four−Li_TwoS-SiS_Two, Sulfide
Compounds are effective. For organic solid electrolytes, for example
Polyethylene oxide, polypropylene oxide
, Polyphosphazene, polyaziridine, polyethylene
Sulfide, polyvinyl alcohol, polyvinyl fluoride
Den, polyhexafluoropropylene and their
Polymer materials such as derivatives, mixtures, and composites are effective.
You.

It is also effective to add another compound to the electrolyte for the purpose of improving the discharge capacity and charge / discharge characteristics. Examples of the other compounds include triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, pyridine, hexaphosphoric triamide, nitrobenzene derivatives, crown ethers, quaternary ammonium salts, ethylene glycol dialkyl ether and the like. Can be mentioned.

As the separator used in the present invention,
An insulating microporous thin film having high ion permeability and predetermined mechanical strength is used. Further, it is preferable to have a function of closing a hole at a certain temperature or higher to increase resistance. As the material of the separator, a sheet, a nonwoven fabric, a woven fabric, or the like made of an olefin polymer such as polypropylene or polyethylene, glass fiber, or the like is used from the viewpoint of organic solvent resistance and hydrophobicity. The pore diameter of the separator is desirably a size that does not allow the passage of the positive electrode material, the negative electrode material, the binder, and the conductive agent detached from the electrode sheet, and is desirably, for example, 0.01 to 1 μm. The thickness of the separator is generally from 10 to 300 μm. In addition, the porosity is determined according to the electron and ion permeability, the material, the film pressure, and the like, but is generally preferably 30 to 80%.

A positive electrode mixture or a negative electrode mixture containing a non-aqueous electrolyte absorbed and retained in a polymer material, or a porous separator made of a polymer having a non-aqueous electrolyte absorbed and retained is integrated with the positive and negative electrodes. It is also possible to configure a battery that has been turned off.

The form of the non-aqueous electrolyte secondary battery of the present invention is not particularly limited. For example, coin type, button type, sheet type, laminated type, cylindrical type, flat type, square type, large type used for electric vehicles, etc. And the like. In addition, the nonaqueous electrolyte secondary battery of the present invention can be used for portable information terminals, portable electronic devices, home small power storage devices, motorcycles, electric vehicles, hybrid electric vehicles, and the like, but is not particularly limited thereto. Not necessarily.

[0041]

The present invention will be described in more detail with reference to the following examples. However, the present invention is not limited to these examples.

Example 1 First, a particulate material used for a negative electrode was produced as follows. As starting materials, lithium nitride (Li ₃ N) powder and cobalt (Co) powder were used. After sufficiently mixing these powders so that the ratio of Li to Co becomes 2.6: 0.4, the mixture is put into a crucible,
8 at 700 ° C in nitrogen atmosphere of high purity (99.9% or more)
After firing for a time, a lithium-containing composite nitride powder having a composition formula of Li _2.6 Co _0.4 N was obtained. The resulting powder was stirred for 5 minutes in carbon dioxide gas with a dew point of -5 ° C to obtain Li ₂ C
A phase containing O ₃ was formed on the surface layer of the particles to obtain a particulate material for a negative electrode.

When the outermost surface of the particulate material for a negative electrode was analyzed by XPS, peaks attributed to carbonate were observed around 290 eV and 532 eV. Where X
For the PS analysis, XPS-7000 manufactured by Rigaku Denki Kogyo was used, and the X-ray source was Mg-Kα, voltage 10 kV, current 10
It was measured under the condition of mA. The charge correction was performed for 1 s based on a very small amount of hydrocarbon carbon adsorbed on the sample surface.
Electrons (285.0 eV), gold were deposited, and the bonding energies of 4f _7/2 electrons (83.8 eV) of gold and 2p electrons (242.3 eV) of argon used for ion etching were used as a reference.

An acceleration voltage of 500 V, an angle of 90 °, an ion current density of 32 μA / cm ² , an etching rate (S
(Io ₂ conversion: value converted when SiO ₂ was etched under the above conditions) Argon ion etching was performed under the condition of about 10 ° / min, and the same measurement was performed. The peaks attributed to the carbonates show the etching for 2 minutes and 4 minutes, respectively.
It was observed in the measurements after 10 and 28 minutes, but not in the measurements after 30 and 50 minutes. Therefore, it is presumed that the phase containing Li ₂ CO ₃ exists in a region from the surface to a depth of 28 to 30 nm. Further, under the same conditions, when peaks attributed to 2p of Co appearing around 778 eV and around 791 eV were observed, no peak was observed on the outermost surface, but was observed in the measurement after etching for 50 minutes. Accordingly, the peak intensity I _a and I _{5 0} has a relationship of _{(I a) / (I 50} ) = 0. The particulate material for the negative electrode was handled in a high-purity nitrogen atmosphere except for the step of stirring in carbon dioxide gas.

Next, a method of manufacturing a coin-shaped battery used for evaluating the performance of the particulate material for a negative electrode will be described with reference to a longitudinal sectional view of the coin-shaped battery shown in FIG. A weight ratio of the particulate material for negative electrode, graphite as a conductive agent and styrene butadiene rubber (SBR) as a binder was 100: 2.
The mixture was mixed at a ratio of 5: 5 and dispersed and dissolved in dehydrated toluene so as to have an appropriate viscosity to prepare a slurry. This is thickness 2
It was applied to a 0 μm current collector copper foil using a doctor blade, dried, and then rolled. The electrode sheet thus produced was punched into a disk having a diameter of 15 mm,
Test electrode 3 was used.

The test electrode 3 was pressed on a stainless steel mesh 2 welded to the inner surface of the case 1 and an electrolyte was injected. Put a polypropylene separator 4 on it,
Further, the sealing plate 6 was covered with a gasket 7 interposed therebetween, and the end of the case was swaged and sealed to obtain a coin-type battery for evaluation. Note that a current collector 8 is provided on the inner surface of the sealing plate 6, and a disk-shaped metal lithium electrode 5 serving as a counter electrode is crimped thereto. The electrolyte used was a mixture of ethylene carbonate and ethyl methyl carbonate (EMC) in which lithium hexafluorophosphate (LiPF ₆ ) was dissolved at a concentration of 1 mol / liter as an electrolyte.

Example 2 Instead of stirring in carbon dioxide gas,
Except that the lithium-containing composite nitride particles were allowed to stand for 30 minutes in a dry air atmosphere at a dew point of -5 ° C, a particulate material for a negative electrode was obtained in the same manner as in Example 1 to produce a coin-type battery. When the particulate material for a negative electrode was analyzed by XPS in the same manner as in Example 1, a peak of carbonate was confirmed. The peak attributed to carbonate was observed in the measurement after etching for 2 minutes, but was not observed in the measurement after 4 minutes and 50 minutes, respectively. Therefore, it is estimated that the phase containing Li ₂ CO ₃ exists in a region from the surface to a depth of 2 to 4 nm. Further, XPS measurement was performed on Co in the same manner as in Example 1, and the peak intensity ratio (I _a ) /
When (I ₅₀ ) was determined, the value was 0.27.

Comparative Example 1 A negative electrode particulate material was obtained in the same manner as in Example 1 except that stirring in carbon dioxide gas was not performed, and a coin-type battery was manufactured. That is, the lithium-containing composite nitride particles were handled only in a high-purity nitrogen atmosphere containing no carbon dioxide gas. When the particulate material for a negative electrode was analyzed by XPS in the same manner as in Example 1, no carbonate peak was observed on the outermost surface of the lithium-containing composite nitride particles, and the presence of a phase containing Li ₂ CO ₃ was confirmed. Did not. Further, XPS measurement was performed on Co in the same manner as in Example 1 to determine the peak intensity ratio (I _a ) / (I ₅₀ ).
Its value was 1.

Example 3 Instead of stirring in carbon dioxide gas,
A particulate material for a negative electrode was obtained in the same manner as in Example 1 except that the battery was left in the air (atmosphere) containing carbon dioxide at room temperature of 20 ° C. for 5 hours, to produce a coin-type battery. When the particulate material for a negative electrode was analyzed by XPS in the same manner as in Example 1, a peak of carbonate was confirmed. However, peaks attributed to carbonate were also observed in the measurements after etching for 20 minutes and 40 minutes, respectively. Therefore, Li ₂ CO ₃
Is presumed to exist also in a region whose depth from the surface is 40 nm or more.

For the coin-shaped batteries of Examples 1 and 2 and Comparative Examples 1 and 2, a charge / discharge test was performed at a constant current of 1 mA under the conditions of an upper limit cut voltage of 1.5 V (for lithium) and a lower limit cut voltage of 0.1 V. went. Here, the reaction proceeding in the direction of inserting lithium into the lithium-containing composite nitride is referred to as charging, and the reaction proceeding in the direction of releasing lithium is referred to as discharging.

The discharge capacities of the particulate materials for negative electrodes were 810 mAh / g and 805 mAh / g in Examples 1 and 2, respectively.
g and Comparative Example 1 were 815 mAh / g, which were almost the same. From this, it was confirmed that there was almost no capacity reduction due to the inclusion of Li ₂ CO ₃ in Example 1 and Example 2 as the particulate material for the negative electrode. However, the discharge capacity of the particulate material for a negative electrode of Comparative Example 2 was 505 mAh / g, and it was confirmed that when the protective film containing Li ₂ CO ₃ was too thick, the battery capacity was significantly reduced.

Next, 10 coin-type batteries of Examples 1 and 2 and Comparative Example 1 were prepared and charged / discharged for 3 cycles under the above-described test conditions to be charged (lithium inserted). It was stored for 3 days in a thermostat at ℃. Table 1 shows the average value of the discharge capacity and the capacity retention ratio immediately before storage and immediately after storage.

[0053]

[Table 1]

Table 2 shows the average values of the total heights of the batteries before storage and immediately after storage.

[0055]

[Table 2]

As is clear from Table 1, the discharge capacity retention rate of the battery after storage was higher in Examples 1 and 2 than in the battery of Comparative Example 1.
Batteries are larger. Also, as is clear from Table 2,
The total height of the battery after storage was 2.12 mm for the battery of Comparative Example 1, and the swelling due to gas generation was large.
It is 1.71 mm in the battery of No. 3, which indicates that the swelling of the battery is greatly suppressed.

[0057] Incidentally, although this embodiment described the cell using the Li _2.6 Co _0.4 N lithium-containing composite nitride represented by the general formula The same test Li _x M _y N (M: cobalt,
At least one transition metal selected from the group consisting of iron, manganese, copper, and nickel, 0 ≦ x ≦ 3, 0.1 ≦ y ≦
The same effect was obtained when the test was performed with lithium-containing composite nitrides having various compositions represented by 0.8).

As can be seen from the above results, by forming a phase containing lithium carbonate or a phase having a lower transition metal content than the inside in the surface layer of the lithium-containing composite nitride particles used for the negative electrode, It can be seen that the battery is prevented from swelling due to gas generation and has a high capacity retention rate during high-temperature storage.

[0059]

According to the present invention, the decomposition of the electrolytic solution due to the reaction between the lithium-containing composite nitride and the organic electrolytic solution is suppressed, the self-discharge and gas generation are small, and the high-temperature storage characteristics are excellent and the reliability is high. A non-aqueous electrolyte secondary battery can be provided.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of an evaluation coin-shaped battery used in an example of the present invention.

[Explanation of symbols]

 1 Case 2 Stainless steel mesh 3 Test electrode 4 Separator 5 Metal lithium electrode 6 Sealing plate 7 Gasket 8 Current collector

Continued on the front page (72) Inventor Masaki Hasegawa 1-1, Matsushita-cho, Moriguchi-shi, Osaka Matsushita Battery Industrial Co., Ltd. (72) Inventor Junichi Yamaura 1-1-1, Matsushita-cho, Moriguchi-shi, Osaka Matsushita Battery Industrial Inside the company (72) Inventor Yoji Sakurai 2-3-1 Otemachi, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (72) Inventor Sou Arai 2-3-1 Otemachi, Chiyoda-ku, Tokyo Nippon Telegraph Telephone Co., Ltd F-term (reference) 5H029 AJ04 AK03 AL03 AM03 AM04 AM05 AM07 AM12 AM16 DJ08 DJ16 EJ03 HJ01 HJ02 HJ13 5H050 AA10 BA17 CA08 CA09 CB03 DA03 EA01 FA17 FA18 HA01 HA02 HA13

Claims (7)

[Claims] 1. A battery comprising a positive electrode, a negative electrode and a non-aqueous electrolyte,
The negative electrode, the general formula Li _x M _y N (M: transition metal, 0 ≦ x
≦ 3, 0.1 ≦ y ≦ 0.8), and a particulate material having a phase containing Li ₂ CO ₃ in the surface layer portion. Water electrolyte secondary battery. 2. The method according to claim 1, wherein the phase containing Li ₂ CO ₃ exists in a region from the surface of the particulate material to a depth of 30 nm.
The non-aqueous electrolyte secondary battery according to the above. 3. The non-aqueous electrolyte secondary battery according to claim 1, wherein the content of Li ₂ CO ₃ in the particulate material is 0.01 to 20% by weight. 4. It comprises a positive electrode, a negative electrode and a non-aqueous electrolyte,
The negative electrode, the general formula Li _x M _y N (M: transition metal, 0 ≦ x
≦ 3, 0.1 ≦ y ≦ 0.8), and a particulate material having a phase in which the M content is smaller than the inside in the surface layer. Non-aqueous electrolyte secondary battery. 5. The XPS analysis of the particulate material (wherein, in the general formula, M is a transition element from Sc of the element number 21 to Zn of the element number 30), the M.P. And the peak intensity (I _a ) based on the 2p spectrum and the M in the case where the particles were etched by irradiation with argon ions to measure the inside at a depth of 50 nm from the surface.
And the peak intensity (I ₅₀ ) based on the 2p spectrum of
_a <Non-aqueous electrolyte secondary battery according to claim 4, further comprising a relation of I _50. 6. In the XPS analysis of the particulate material,
6. The non-aqueous electrolyte secondary battery according to claim 5, having a relationship of (I _a ) / (I ₅₀ ) ≦ 0.3. 7. The non-aqueous electrolyte secondary battery according to claim 1, wherein M is at least one selected from the group consisting of cobalt, iron, manganese, copper, and nickel.