JP2002246021A - Method of producing lithium-containing composite nitride for negative electrode for non-aqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium contained composite nitride which gives high capacity and superior cycle characteristic to an electrode for a non-aqueous electrolyte secondary battery. SOLUTION: This method of producing the lithium-containing composite nitride comprises a first step of baking a mixture of a lithium nitride powder and a transition metal powder in an atmosphere having nitrogen at 450 deg.C or higher and lower than 650 deg.C and then cooling it down to 100 deg.C or lower, and a second step of re-baking a product obtained in the first step at 650 deg.C or higher and 800 deg.C or lower.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a lithium-containing composite nitride used for a negative electrode of a non-aqueous electrolyte secondary battery and a method for producing the same. The present invention also relates to a negative electrode made of a lithium-containing composite nitride and a nonaqueous electrolyte secondary battery having the negative electrode.

[0002]

2. Description of the Related Art In recent years, a lithium secondary battery has been used as a main power source for mobile communication devices and portable electronic devices because a high voltage and a high energy density can be obtained. However, along with the miniaturization and high performance of these devices, further higher performance of lithium secondary batteries is required, and in particular, the demand for higher capacity is increasing.

[0003] Various transition metal oxides and chalcogen compounds have been proposed as positive electrode materials for non-aqueous electrolyte secondary batteries, and their capacity has been studied.

On the other hand, various materials have been studied for the negative electrode, and carbon materials and aluminum alloys have been put to practical use as the negative electrode material. Among them, carbon materials are widely used because of their high performance. However, the carbon material is already used at a capacity close to the theoretical capacity (about 370 mAh / g), and it is difficult to further increase the capacity.

Therefore, a lithium-containing composite nitride composed of lithium, nitrogen, and a transition element has been proposed as a negative electrode material capable of greatly increasing the capacity of a lithium secondary battery in the future. In the lithium-containing composite nitride, the potential at which lithium insertion and desorption occurs is about 0. 0 on average with respect to lithium.
It is 8 V, and has a high capacity that is much higher than that of a carbon material.
This material is represented by the general formula Li _3-XY M _X N, and has a hexagonal crystal structure.

In the above general formula, M is mainly Co, N
i, at least one transition element selected from the group consisting of Cu and Zn, wherein X and Y are each 0.1 ≦ X
≦ 0.8 and 0 ≦ Y ≦ 2-X. X <0.
In case of 1, the capacity of the material is extremely reduced, and in case of 0.8 <X, a single-phase material cannot be obtained. However, preferably 0.3 ≦ X
≦ 0.6. When 2-X <Y, the potential of the negative electrode of the lithium secondary battery becomes 1.5 V or more, and the battery voltage decreases.

In the above general formula, the composition of Y = 0 is a stoichiometric composition, which is a general composition. Therefore,
Hereinafter, Y is abbreviated and described as Li _3-X M _X N.

This lithium-containing composite nitride is produced by mixing lithium nitride and cobalt and firing in a nitrogen atmosphere or a nitrogen atmosphere containing a small amount of hydrogen. Conventionally, it is general to perform one-stage baking at a temperature of about 700 ° C.

[0009]

However, a lithium secondary battery using a lithium-containing composite nitride produced by a conventional one-stage calcination method as a negative electrode material has a very high capacity, There is a problem with the characteristics.

[0010]

According to the present invention, a first step of firing a mixture of lithium nitride powder and transition metal powder in an atmosphere containing nitrogen at 450 ° C. or more and less than 650 ° C., and then cooling the mixture to 100 ° C. or less. And a second step of firing the product of the first step again at 650 ° C. or higher and 800 ° C. or lower, and a method for producing a lithium-containing composite nitride for a negative electrode of a nonaqueous electrolyte secondary battery.

Here, the transition metal powder is composed of Co, Ni, C
It is preferable that the material be at least one selected from the group consisting of u and Zn. The transition metal powder may be a simple substance or an alloy. The average particle size of the lithium nitride powder is 45 μm or less, and the average particle size of the transition metal powder is 15 μm.
It is preferable that the average particle diameter be 50 μm or less, since a lithium-containing composite nitride having an average particle diameter of 50 μm or less can be efficiently obtained.

The nitrogen-containing atmosphere is, for example, a gas atmosphere in which the partial pressure of N ₂ is 1.0 × 10 ⁴ Pa or more.

[0013] The present invention also relates to a lithium-containing composite nitride for a negative electrode of a non-aqueous electrolyte secondary battery obtained by the above production method. Among them, a lithium-containing composite nitride having an average particle diameter of 50 μm or less is preferable.

According to the above process, it has a hexagonal crystal structure, the powder X-ray reflection peak intensity of (001) plane in the diffraction pattern (I ₀₀₁₎ of the (101) reflection peak intensity by plane (I ₁₀₁₎ Is _{less than} I ₀₀₁ / I ₁₀₁ ≦
A lithium-containing composite nitride satisfying 0.20 can be obtained. Further, according to the above production method, the powder has a hexagonal crystal structure, and the reflection peak intensity (I ₁₁₁ ) on the (111) plane in the powder X-ray diffraction pattern is smaller than the reflection peak intensity (I ₁₀₁ ) on the (101) plane. The ratio is I ₁₁₁ / I ₁₀₁
A lithium-containing composite nitride satisfying ≦ 0.10 can be obtained. The half width of the reflection peak due to the (101) plane is
More preferably, it is 0.25 ° or less.

The present invention further relates to a negative electrode for a non-aqueous electrolyte secondary battery comprising the above-mentioned lithium-containing composite nitride. Further, the present invention provides a non-aqueous electrolyte secondary battery including a positive electrode capable of reversibly occluding and releasing lithium, a negative electrode composed of the lithium-containing composite nitride, and a non-aqueous electrolyte interposed between the positive electrode and the negative electrode. About.

[0016]

DETAILED DESCRIPTION OF THE INVENTION Composition _{Li 3-X M X N (} 0.1 ≦ x ≦
When the lithium-containing composite nitride having 0.8) is used as a negative electrode active material of a nonaqueous electrolyte secondary battery, its charge / discharge characteristics and cycle characteristics are greatly affected by the initial crystal structure of the lithium-containing composite nitride. You. For example, the initial capacity of the lithium-containing composite nitride increases or decreases due to crystallinity, and the subsequent reversible capacity is determined by the initial capacity. In the initial state immediately after production, the lithium-containing composite nitride has a hexagonal crystal structure, but becomes amorphous during the first Li elimination reaction. After that, even if the charge / discharge reaction is repeated, it remains in an amorphous state.

However, even in the amorphous state, the order in a minute region is maintained, and it is considered that the initial crystal structure has a great influence on the cycle characteristics. For example, when materials having different specific peak intensity ratios in the powder X-ray diffraction pattern are used, a difference occurs in electrode characteristics.

More specifically, the intensity ratio (I) of the peak reflected by the (001) plane to the peak reflected by the (101) plane.
₀₀₁ / I ₁₀₁₎ but is good cycle characteristics can be obtained if 0.20 or less, deterioration of the cycle characteristics becomes large in this range. Similarly, when the intensity ratio (I ₁₁₁ / I ₁₀₁ ) of the reflection peak of the (111) plane to the reflection peak of the (101) plane is 0.10 or less, good cycle characteristics can be obtained. Outside, the deterioration of the cycle characteristics becomes large.

I ₀₀₁ / I ₁₀₁ ≦ 0.20 and I ₁₁₁ / I ₁₀₁ ≦
FIG. 1 shows an example of a powder X-ray diffraction pattern of Li _2.5 Co _0.5 N as an initial lithium-containing composite nitride satisfying 0.10.

It is considered that the above-mentioned peak intensity ratio changes due to the difference in the position where the transition metal element M exists in the crystal structure of the lithium-containing composite nitride (Li _3-x M _x N). The lithium-containing composite nitride has a hexagonal crystal structure, and has a layered structure in which an A layer composed of only cations and a B layer composed of cations and anions are alternately laminated.
The peak intensity ratio changes depending on the position occupied by the transition metal element M in the layer A and the layer B and the difference in the occupancy.

For example, when the transition metal element M exists only in the layer A, the intensity ratio I ₀₀₁ / I ₁₀₁ ≦ 0.2 is satisfied,
The crystal structure is stable. However, when the raw material is fired at a high temperature in order to increase the initial capacity, the crystal structure in which the transition metal element M penetrates into the B layer is likely to occur, and the cycle characteristics deteriorate. In this case, the intensity ratio I ₀₀₁ / I ₁₀₁ becomes large. The peak intensity ratio also changes depending on the presence of defects in the crystal structure.

The details of the effect of the crystal structure of the lithium-containing composite nitride on the electrode characteristics are unknown, but the stability at the time of insertion and extraction of lithium differs depending on the crystal structure, and the cycle characteristics differ. it is conceivable that.

As described above, the powder X-ray diffraction pattern of the lithium-containing composite nitride after the charge / discharge reaction shows an amorphous pattern, but the crystal structure is maintained in a small region, and as a result, the reversible It is considered that a proper charge / discharge reaction is possible. However, when the crystallinity of the initial lithium-containing composite nitride is low, the atomic arrangement in the microscopic region is also disordered, so that a sufficient amount of lithium cannot be inserted or released, and the charge / discharge capacity decreases. It is thought that. Therefore, the crystallinity of the initial lithium-containing composite nitride is preferably higher.

The degree of crystallinity can be determined by the half width of the peak of the powder X-ray diffraction pattern. Specifically, in the powder X-ray diffraction pattern, when the half width of the reflection peak by the (101) plane is 0.25 ° or less, it is considered that the crystallinity is sufficiently high, and a high capacity is obtained. . The half width of the reflection peak due to the (101) plane is 0.25.
If it exceeds °, sufficient capacity cannot be obtained.

As described above, when a lithium-containing composite nitride is used as a negative electrode active material of a lithium secondary battery, it is necessary to control the initial crystal state, and for that purpose, the firing temperature of the raw material is important. High firing temperature, for example 650 ° C
At the above temperature, the intensity ratio I ₀₀₁ / I ₁₀₁ becomes large in the powder X-ray diffraction pattern of the obtained product. 650 so that the intensity ratio does not increase.
If it is calcined at a temperature lower than ℃, the crystallinity of the product will be low and sufficient capacity cannot be obtained. Therefore, in the present invention, initially firing the raw material at a low temperature of less than 650 ° C., the intensity ratio I ₀₀₁
/ I ₁₀₁ ≦ 0.2 or after forming crystals satisfying I ₁₁₁ / I ₁₀₁ ≦ 0.1, from once to via cold 650
Refire at a temperature of at least ℃. By performing the two-stage calcination in this manner, I ₀₀₁ / I ₁₀₁ ≦ 0.2 or I ₁₁₁ / I ₁₀₁
It satisfies ≦ 0.1 and has high crystallinity, so that a lithium-containing composite nitride having high capacity and excellent cycle characteristics can be obtained.

If the firing temperature at the first low temperature is lower than 450 ° C., the formation reaction of the lithium-containing composite nitride becomes very slow, so that the firing temperature must be 450 ° C. or higher.
On the other hand, when the second high-temperature baking temperature exceeds 800 ° C., it is difficult to control the content of Li, which has a low melting temperature and is easily evaporated, in the nitride.

If the average particle diameter of the raw material lithium nitride powder and transition metal powder is large, a uniform solid solution cannot be obtained at the time of firing at a low temperature, and the crystalline state of the final product becomes non-uniform. Characteristics deteriorate. Therefore, it is preferable to use a raw material in which the average particle diameter of the lithium nitride powder is 45 μm or less and the average particle diameter of the transition metal powder is 15 μm or less.

When the temperature of the first baking is increased or the second baking is performed without passing through the normal temperature, the particle growth during the solid solution formation reaction becomes severe, and the particle size of the final product becomes large. There is a problem that it becomes. In particular, 650
Since the remarkable particle growth occurs at temperatures above ℃, setting the first firing temperature as described above means that after firing the raw materials at a temperature of 650 ° C or less, the temperature is once lowered to normal temperature to complete the solid solution generation reaction. There is also a meaning to make it. And 650
By refiring the solid solution at a high temperature of not less than ° C., a final product reflecting the particle size of the raw material powder is obtained. Therefore, according to the present invention, it is easy to control the particle size of the final product.

Since the control of the particle size is easy, the operations of pulverizing and classifying the final product can be simplified, and the production cost is reduced. For example, if the average particle size is 45
Using lithium nitride powder of μm or less and cobalt powder having an average particle size of 15 μm or less as the raw material, firing the raw material at less than 650 ° C., and performing re-firing at 650 ° C. or higher via room temperature,
A powdery final product having an average particle size of 50 μm or less can be obtained efficiently.

The temperature of refiring is 5 times lower than the initial firing temperature.
A temperature higher than 0 ° C. is preferable in that the crystallinity of the final product can be sufficiently increased.

From the viewpoint of obtaining a lithium-containing composite nitride composed of a uniform solid solution phase, the first calcination is preferably performed over 2 hours. However, if the initial baking time is too long, the production cost increases, so it is preferable that the baking time is 50 hours or less.

On the other hand, the re-firing time is preferably 2 to 24 hours. If the re-firing time is too short, the crystallinity of the product cannot be sufficiently improved, and if it is too long, it becomes difficult to control the predetermined peak intensity ratio in the powder X-ray diffraction pattern to a preferable range.

In the firing step, the rate of temperature rise and the rate of temperature fall are not particularly limited, but since heat is uniformly transmitted to the reactants and the synthesis reaction easily proceeds uniformly, 1 to 20 ° C.
Preferably, the temperature is raised and lowered at a rate of / min. In addition, the firing step is preferably performed while stirring the reactants.

As the transition metal powder, Co, Ni, C
Although u, Zn, and the like are preferably used, these metals include those having a hexagonal close-packed crystal structure and those having a cubic close-packed crystal structure. Among these, when a transition metal having a hexagonal close-packed crystal structure is used, a lithium-containing composite nitride having higher reactivity and a favorable crystal structure can be obtained.

Although the lithium-containing composite nitride obtained by the method of the present invention cannot be distinguished from the composition, it has a different crystal structure or phase structure from the lithium-containing composite nitride obtained by the conventional method, and has excellent electrode activity. It is a new material that can be used as a substance.

The lithium-containing composite nitride of the present invention is used, for example, as a negative electrode active material of a battery. The negative electrode active material is
It is used as a negative electrode mixture by mixing with materials such as a conductive agent and a binder. However, the lithium-containing composite nitride of the present invention,
Since the surface is covered with a conductive material, it is possible to obtain an electrode that functions effectively without adding a conductive agent.

The conductive agent may be any material as long as it is an electron conductive material. Examples of the electron conductive material include natural graphite such as flake graphite, graphite such as artificial graphite and expanded graphite, carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black. Examples include conductive fibers such as fibers and metal fibers, metal powders such as copper and nickel, and organic conductive materials such as polyphenylene derivatives. These may be used alone or in combination of two or more. Among these conductive agents,
Artificial graphite, acetylene black and carbon fiber are particularly preferred.

The amount of the conductive agent is not particularly limited,
1 to 50 based on 100 parts by weight of lithium-containing composite nitride
Part by weight is preferred, and 1 to 30 parts by weight is particularly preferred.

As the binder, a thermoplastic resin, a thermosetting resin or the like is used. For example, polyethylene, polypropylene, polytetrafluoroethylene, polyvinylidene fluoride, styrene butadiene rubber, tetrafluoroethylene-hexafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer Polymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer, polychlorotrifluoroethylene, vinylidene fluoride-pentafluoropropylene copolymer Coal, propylene-tetrafluoroethylene copolymer, ethylene-chlorotrifluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene-tetra Fluoroethylene copolymer, vinylidene fluoride-perfluoromethylvinyl ether-tetrafluoroethylene copolymer, 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 Na ion crosslinked product, ethylene-methyl methacrylate copolymer or its Na ion crosslinked product. These may be used alone or in combination of two or more. Among 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 Na ion crosslinked product, ethylene-methyl methacrylate copolymer or its Na ion crosslinked product are preferred.

The negative electrode mixture is made into a paste using a dispersion medium, applied to a negative electrode current collector, and dried to obtain a negative electrode. The negative electrode current collector may be any electronic conductor that does not cause a chemical change in the configured battery. As a material for the negative electrode current collector, for example, stainless steel, nickel, copper, titanium, carbon, a conductive resin, or the like can be used. Copper and stainless steel surfaces treated with carbon, nickel or titanium may also be used. Further, the surfaces of these materials can be oxidized and used. As a material of the negative electrode current collector, copper or a copper alloy is particularly preferable. In addition, it is desirable that the surface of the current collector be provided with irregularities. The shape of the negative electrode current collector is a foil, a film, a sheet, a net, a punched material, a lath body, a porous body, a foamed body, a formed body of a fiber group, and the like. It is 500 μm.

When the obtained negative electrode is combined with battery components such as a positive electrode capable of reversibly inserting and extracting lithium, a non-aqueous electrolyte, and a separator, a non-aqueous electrolyte secondary battery having high capacity and excellent cycle characteristics is obtained. Can be obtained. The positive electrode is also made of a positive electrode mixture containing a positive electrode active material, a conductive agent, a binder and the like.

The positive electrode active material contains or does not contain lithium.
A compound having an organic compound can be used. For example, Li_XCo
O_Two, Li_XNiO_Two, Li_XMnO_Two, Li_XCo_YNi_1-Y
O_Z, Li_XCo_YM_1-YO_Z, Li_XNi_1-YM_YO_Z, Li_X
Mn_TwoO_Four, Li_XMn_2-YM_YO _Four (M = Na, Mg, S
c, Y, Ti, Mn, Fe, Co, Ni, Cu, Zn,
Selected from the group consisting of Al, Cr, Pb, Sb and B
At least one). Where x = 0
1.2, y = 0 to 0.9, z = 2.0 to 2.3.
The value x is a value before the start of charge / discharge, and
Increases or decreases according to However, transition metal chalcogenides,
Nadium oxide and its lithium compound, niobium oxide
And its conjugates using lithiated and organic conductive materials
-Based polymers, Chevrel phase compounds, etc. can also be used
It is. In addition, mixing and using different materials
Is also possible.

The average particle size of the positive electrode active material particles is not particularly limited, but is preferably 1 to 30 μm. However,
When a lithium-containing compound represented by Li _X CoO ₂ is used as a positive electrode active material and a lithium-containing composite nitride is used as a negative electrode active material to form a battery, a treatment for previously removing lithium from one of the positive electrode and the negative electrode is necessary.

The conductive agent for the positive electrode may be any electronic conductive material that does not cause a chemical change in the charge and discharge potential of the positive electrode material. For example, natural graphite such as flake graphite, graphite such as artificial graphite, carbon blacks such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black, and conductive materials such as carbon fiber and metal fiber. Fibers,
Examples thereof include 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. These may be used alone or in combination of two or more. Among these, artificial graphite and acetylene black are particularly preferred.

The amount of the conductive agent is not particularly limited,
The amount is preferably 1 to 50 parts by weight, particularly preferably 1 to 30 parts by weight, per 100 parts by weight of the positive electrode active material. However, in the case of carbon or graphite, 2 to 15 parts by weight is particularly preferable.

As the binder for the positive electrode, a thermoplastic resin,
A thermosetting resin or the like is used. Specifically, for example,
Polyethylene, polypropylene, polytetrafluoroethylene, polyvinylidene fluoride, styrene butadiene rubber, tetrafluoroethylene-hexafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-perfluoroalkylvinyl ether copolymer , Vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer, polychlorotrifluoroethylene, vinylidene fluoride-pentafluoropropylene copolymer, Propylene-tetrafluoroethylene copolymer, ethylene-chlorotrifluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoro Tylene copolymer, vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene copolymer, 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 Na ion crosslinked product, 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 positive electrode current collector used in the present invention may be any electronic conductor that does not cause a chemical change in the charge / discharge potential of the positive electrode material. Examples of the material of the positive electrode current collector include stainless steel, aluminum, titanium, carbon, and a conductive resin. Of these, aluminum or an aluminum alloy is particularly preferred. A material obtained by treating the surface of aluminum or stainless steel with carbon or titanium may be used. The surface of these materials can be oxidized and used. In addition, it is desirable to form irregularities on the current collector surface. The shape of the current collector is a foil, a film, a sheet, a net, a punched material, a lath body, a porous body, a foam, a fiber group, a molded body of a nonwoven fabric, and the like, and the thickness is not particularly limited. 1 to 500 μm
It is.

For the positive electrode mixture and the negative electrode mixture, in addition to a conductive agent, a binder, and a dispersion medium, fillers, ion conductors, pressure enhancers, and other various additives can be used. 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 3 with respect to the electrode mixture.
0% by weight is preferred.

The positive electrode and the negative electrode are arranged in the battery such that at least the positive electrode mixture surface and the negative electrode mixture surface face each other.

The non-aqueous electrolyte is composed of, for example, a non-aqueous solvent and a lithium salt dissolved in the solvent. As the non-aqueous solvent, for example, ethylene carbonate, propylene carbonate, butylene carbonate, cyclic carbonates such as vinylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, chain carbonates such as dipropyl carbonate, methyl formate, methyl acetate, methyl acetate , Aliphatic carboxylic acid esters such as methyl propionate and ethyl propionate,
γ-lactones such as γ-butyrolactone, 1,2-dimethoxyethane, 1,2-diethoxyethane, chain ethers such as ethoxymethoxyethane, tetrahydrofuran, cyclic ethers such as 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolan, formamide, acetamide, dimethylformamide, dioxolan, acetonitrile, propylnitrile, nitromethane, ethyl monoglyme, phosphoric acid 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.

As the lithium salt dissolved in the non-aqueous solvent,
For example, LiClO_Four, LiBF_Four, LiPF₆, LiAl
Cl_Four, LiSbF₆, LiSCN, LiCl, LiCF
_ThreeSO _Three, LiCF_ThreeCO_Two, Li (CF_ThreeSO_Two)_Two, Li
AsF₆, LiN (CF_ThreeSO_Two)_Two, LiB_TenCl_Ten, Low
Lithium aliphatic carboxylate, LiCl, LiBr, L
iI, lithium chloroborane, lithium lithium tetraphenylborate
And imides. These alone
They may be used, or two or more kinds may be used in combination.
Of these, LiPF₆Is particularly preferred.

Specifically, as the non-aqueous electrolyte, an electrolyte containing at least ethylene carbonate and ethyl methyl carbonate and containing LiPF ₆ is preferable.

The amount of lithium salt dissolved in the non-aqueous solvent is not particularly limited, but is preferably from 0.2 to 2 mol / l, particularly preferably from 0.5 to 1.5 mol / l.

The amount of the nonaqueous electrolyte added to the battery is not particularly limited, but the required amount varies depending on the amounts of the positive electrode material and the negative electrode material, the size of the battery, and the like.

As the non-aqueous electrolyte, a solid electrolyte as described below can be used. Solid electrolytes are classified into inorganic solid electrolytes and organic solid electrolytes. Among the inorganic solid electrolytes, nitrides, halides and oxyacid salts of Li are well known. Among them, Li ₄ SiO ₄ and Li
_{4 SiO 4 -LiI-LiOH, xLi} 3 PO 4 - (1-
_{x) Li 4 SiO 4, Li} 2 SiS 3, Li 3 PO 4 -Li 2
_{S-SiS 2, Li 3 M} 2 (PO 4) 3 (M is Sc and I
n), oxynitride phosphate, phosphorus sulfide compound, and the like are effective. In the organic solid electrolyte, for example, polyethylene oxide, polypropylene oxide, polyphosphazene, polyaziridine, polyethylene sulfide, polyvinyl alcohol,
Polymer materials such as polyvinylidene fluoride, polyhexafluoropropylene and the like, or derivatives, mixtures and composites thereof are effective.

It is also effective to add the following compounds to the non-aqueous electrolyte for the purpose of improving the charge / discharge characteristics of the battery. For example, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme,
Pyridine, hexaphosphoric acid triamide, nitrobenzene derivatives, crown ethers, quaternary ammonium salts, ethylene glycol dialkyl ether, and the like can be used.

As the separator used in the battery, an insulating microporous thin film having a high ion permeability and a predetermined mechanical strength is used. The separator preferably has a function of closing the pores at a certain temperature or higher and increasing the resistance. A sheet, nonwoven fabric or woven fabric made of an olefin-based polymer or glass fiber using a material such as polypropylene or polyethylene alone or in combination from the viewpoint of organic solvent resistance and hydrophobicity is used. The pore size of the separator is desirably in a range where the positive electrode material and the negative electrode material detached from the electrode sheet do not pass through, for example, 0.01
It is desirably about 1 μm. The thickness of the separator is
Generally, it is 10 to 300 μm. The porosity is
It is determined according to the electron and ion permeability, the material, and the film pressure, but generally it is preferably 30 to 80%.

A polymer material holding a non-aqueous electrolyte is contained in a positive electrode mixture and a negative electrode mixture, and a porous separator made of the polymer material holding a non-aqueous electrolyte is used as a positive electrode.
It is also possible to configure a battery integrated with the negative electrode. At this time, any polymer material can be used as long as it can hold the non-aqueous electrolyte, but a copolymer of vinylidene fluoride and hexafluoropropylene is particularly preferable.

The non-aqueous electrolyte secondary battery of the present invention can be used for portable information terminals, portable electronic devices, household small power storage devices, motorcycles, electric vehicles, hybrid electric vehicles, etc., but is not particularly limited thereto. It is not done. There are coin type, button type, sheet type,
There are a laminated type, a cylindrical type, a flat type, and a square type.

[0060]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below based on embodiments. However, the present invention is not limited to these examples.

Example 1 Li using Co as transition metal
The lithium-containing composite nitride of _3-X Co _X N will be described.

Li _3-X Co _X N is prepared by mixing lithium nitride powder having an average particle diameter of 36 μm and cobalt powder having an average particle diameter of 12 μm at a predetermined ratio, and is mixed in a nitrogen atmosphere of 1.0 × 10 ⁵ Pa. By performing two-stage firing. The mixing ratio of the raw materials was such that the x value was 0.3, 0.4, 0.5 or 0.6, respectively.

First, the temperature of the first firing was examined. That is, in the first firing, the raw material is heated at 450 ° C.
Raise the temperature to 0 ° C, 550 ° C, 600 ° C or 650 ° C,
After heating for an hour, the temperature is once lowered to room temperature, and then
The temperature was raised to 00 ° C. and re-baked for 2 to 3 hours.

Next, the temperature of refiring was examined. That is, in the first baking, after heating the raw material at 550 ° C. for 8 hours, the temperature is once lowered to normal temperature, and then again at 600 ° C.
The temperature was raised to 650 ° C., 700 ° C., or 800 ° C., and rebaked for 2 to 3 hours.

As a comparative example, the raw materials were not heated at 450 ° C., 500 ° C., 550 ° C., 600 ° C.,
Samples that were only fired at 800C or 800C for 8 hours were also prepared. In either case, the rate of temperature rise and fall is
10 ° C./min.

The obtained sample was analyzed by powder X-ray diffraction.
Reflection peak intensity of (101) plane of the reflection peak intensity (I ₀₀₁₎ by (001) plane of the hexagonal calculated from X-ray diffraction pattern ratio (I ₁₀₁₎ (I ₀₀₁ /
I ₁₀₁ ) and the half width of the reflection peak due to the (101) plane are shown in Table 1.

[0067]

[Table 1]

As shown in Table 1, the first firing of the raw material was performed at a temperature of 450 ° C. or more and less than 650 ° C., the temperature was lowered to room temperature, and
When the two-stage baking is performed at a temperature of 50 ° C. or more and 800 ° C. or less, I ₀₀₁ / I ₁₀₁ ≦ 0.20 is satisfied,
It can be seen that a lithium-containing composite nitride having a half-value width of a reflection peak by the (101) plane of 0.25 or less can be obtained.

Sample obtained (composite nitride containing lithium)
Was used to produce a coin-type test cell shown in FIG. 2, and its cycle characteristics were evaluated.

First, a lithium-containing composite nitride powder;
The weight ratio (100: 20: 5) of artificial graphite (KS6) as a conductive agent and polytetrafluoroethylene as a binder
, And integrally molded on a current collector 2 installed in a case 3 to obtain a test electrode 1. The test electrode 1 was sufficiently dried at 80 ° C. under reduced pressure. Next, a porous polyethylene sheet 7 as a separator was placed on the test electrode 1. Then, a solution obtained by dissolving lithium hexafluorophosphate in a 1: 1 mixed solvent of ethylene carbonate and diethyl carbonate at a concentration of 1 mol / liter was poured into the case 3 as a non-aqueous electrolyte. On the other hand, the lithium foil 4 as a counter electrode is
Current collector 5 installed inside sealing plate 6 for sealing
Was crimped. Then, the sealing plate 6 having the gasket 8 around it was placed on the case 3 and then swaged with a press sealing machine to obtain a coin-type battery. The weight of the lithium-containing composite nitride in the test electrode was adjusted to be 25 mg. The counter-electrode lithium foil is in a sufficient excess with respect to the capacity of the test electrode.

Next, the charge / discharge cycle of the test cell was repeated. Charging and discharging were performed at a constant current of 0.5 mA / cm ² in a voltage range of 0 to 1.5 V. And
The charge / discharge cycle characteristics were evaluated based on the capacity maintenance ratio (%) at the 50th cycle from the initial stage. FIG. 3 shows the relationship between the I ₀₀₁ / I ₁₀₁ peak intensity ratio and the capacity retention ratio. In addition, FIG.
The relationship between the half width of the reflection peak by the (101) plane and the battery capacity in the case of 0.4 is shown.

In FIG. 3, when I ₀₀₁ / I ₁₀₁ is 0.15 or less, the capacity retention ratio in the 50th cycle is 97% or more and 0.
When it is 20 or less, it is as good as 95% or more.
If it exceeds 20, the capacity retention rate is significantly reduced. Also, FIG. 4 shows that when the half width of the reflection peak by the (101) plane exceeds 0.25 °, the capacity is significantly reduced.

Example 2 In this example, powder X-ray diffraction
Reflection peak intensity by (111) plane of pattern
(I ₁₁₁) Reflection peak intensity by (101) plane
(I₁₀₁) To the ratio (I₁₁₁/ I_{1 01}) And the cycle
The relationship with the characteristics was discussed. Materials reviewed (Lichiu
Is the same as that used in Example 1.
You.

Table 2 shows the intensity ratio I ₁₁₁ / I ₁₀₁ calculated from the X-ray diffraction pattern.

[0075]

[Table 2]

As shown in Table 2, the first firing of the raw material was performed at a temperature of 450 ° C. or more and less than 650 ° C., the temperature was lowered to room temperature, and
It can be seen that when the two-stage baking is performed at a temperature of 50 ° C. or more and 800 ° C. or less, a lithium-containing composite nitride satisfying I ₁₁₁ / I ₁₀₁ ≦ 0.10.

FIG. 5 shows the relationship between the intensity ratio I ₁₁₁ / I ₁₀₁ and the capacity retention ratio.

In FIG. 5, when I ₁₁₁ / I ₁₀₁ is 0.05 or less, the capacity retention ratio at the 50th cycle is 97%, 0.10
In the following, it is as good as 85% or more, whereas 0.10
When the ratio exceeds, the capacity retention rate sharply decreases. Therefore,
It is considered that good cycle characteristics can be obtained when the value of I ₁₁₁ / I ₁₀₁ is 0.10 or less.

Example 3 In this example, lithium nitride powder and cobalt powder having various average particle diameters were used as raw materials.

The average particle size is 50 μm, 45 μm or 40
A lithium-containing composite nitride was synthesized using a lithium nitride powder having a size of not more than μm and a cobalt powder having a size of not more than 20 μm, 15 μm, or 10 μm. At this time, the first firing is 6
The firing was carried out at 00 ° C. for 8 hours, the temperature was once lowered to room temperature, and re-firing was performed at 700 ° C. for 2 to 3 hours.

As a comparative example, a sample obtained by performing one-step firing at 700 ° C. and a sample obtained by firing at 600 ° C., and then raising the temperature to 700 ° C. without lowering the temperature to normal temperature and re-baking. The prepared sample was prepared. Then, the average particle size of the obtained final product was measured. Table 3 shows the relationship between the average particle size of the raw material and the average particle size of the final product obtained by performing the two-stage calcination at room temperature.

When firing at 700 ° C. in one stage and re-firing at 700 ° C. without passing through normal temperature, the final product is a sintered body and does not become powder. Was.

[0083]

[Table 3]

As shown in Table 3, when the average particle size of the lithium nitride powder was set to 45 μm or less and the average particle size of the cobalt powder was set to 15 μm or less, and the two-stage calcination was performed at room temperature, the average particle size of the final product was obtained. It can be seen that the diameter can be controlled to 50 μm or less. On the other hand, in the case of the comparative example, since it became a sintered body, it is understood that it is difficult to obtain even a powder.

Example 4 In this example, Ni, Cu or Zn was used as the transition metal, and Li _2.6 Ni _0.4 N, L
i _2.6 Cu _0.4 N or Li _2.6 Zn _0.4 N was synthesized.

Various samples were prepared under the same conditions as in Example 1 except that nickel powder, cobalt powder or zinc powder classified to 15 μm or less was used as a raw material and the x value was 0.4. Then, Example 1 was performed using the obtained sample.
A coin-type battery was prepared in the same manner as in Example 1 and evaluated.

The intensity of the reflection peak (I ₀₀₁ ) due to the hexagonal (001) plane calculated from the X-ray diffraction pattern was (10)
Table 1 shows the ratio (I ₀₀₁ / I ₁₀₁ ) to the reflection peak intensity (I ₁₀₁ ) due to the (1) plane, and the half width of the reflection peak due to the (101) plane.

[0088]

[Table 4]

As shown in Table 4, the first firing of the raw material was performed at a temperature of 450 ° C. or more and less than 650 ° C., the temperature was lowered to room temperature, and
When the two-stage baking is performed at a temperature of 50 ° C. or more and 800 ° C. or less, I ₀₀₁ / I ₁₀₁ ≦ 0.20 is satisfied,
It can be seen that a lithium-containing composite nitride having a half-value width of a reflection peak by the (101) plane of 0.25 or less can be obtained.

In the one-stage firing, the final product was not a powder but a sintered body as in the case of Example 3, and it was difficult to control the particle size.

FIG. 6 shows the relationship between the intensity ratio I ₀₀₁ / I ₁₀₁ and the capacity retention ratio.

[0092] In Figure 6, Ni as transition metals, in the case of using a Cu or Zn, I ₀₀₁ / I ₁₀₁ is 0.20 or less in the 50 th cycle capacity retention rate of 96% or more, 0.1
5 or less is as good as 95% or more, whereas 0.2
When it exceeds 0, the capacity retention rate sharply decreases. This indicates that good cycle characteristics can be obtained when the value of I ₀₀₁ / I ₁₀₁ is 0.20 or less even when Ni, Cu or Zn is used as the transition metal. As in the case of Co, when the value of I ₁₁₁ / I ₁₀₁ was 0.10 or less, good cycle characteristics were obtained.

In this embodiment, the case where the transition metal is used alone has been described. However, it is considered that the same effect can be obtained by using a mixture of two or more metals.

In this example, the test was performed using a coin-type battery. However, it is considered that similar results can be obtained in a test using a cylindrical battery or a stacked battery using a polymer electrolyte.

[0095]

According to the present invention, lithium nitride powder and transition metal powder are mixed and mixed in an atmosphere containing nitrogen.
After firing at a temperature of 0 ° C. or more and less than 650 ° C., the temperature is lowered to room temperature, and firing is performed at a temperature of 650 ° C. or more and 800 ° C. or less. A lithium-containing composite nitride that gives an excellent electrode can be obtained.

[Brief description of the drawings]

FIG. 1 is an X-ray powder diffraction pattern of an example of a lithium-containing composite nitride.

FIG. 2 is a cross-sectional view of a test cell for evaluating a negative electrode for a non-aqueous electrolyte secondary battery.

FIG. 3 is a diagram showing the relationship between the peak intensity ratio I ₀₀₁ / I ₁₀₁ of the sample of Example 1 and the capacity retention ratio.

FIG. 4 is a diagram showing a relationship between a half width of a reflection peak by a (101) plane of a sample (x = 0.4) of Example 1 and a battery capacity.

FIG. 5 is a view showing the relationship between the peak intensity ratio I ₁₁₁ / I ₁₀₁ of the sample of Example 2 and the capacity retention ratio.

FIG. 6 is a diagram showing the relationship between the peak intensity ratio I ₀₀₁ / I ₁₀₁ of the sample of Example 4 and the capacity retention ratio.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Test electrode 2 Current collector 3 Case 4 Lithium foil 5 Current collector 6 Sealing plate 7 Separator 8 Gasket

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shinji Kasamatsu 1006 Kadoma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Yoshiaki Nitta 1006 Odakadoma Kadoma City, Osaka Pref. F-term (Reference) 5H029 AJ03 AJ05 AK03 AK05 AK15 AK16 AK18 AL01 AM02 AM03 AM04 AM05 AM07 AM12 AM16 BJ03 BJ12 CJ02 CJ08 DJ16 DJ17 HJ05 HJ13 HJ14 5H050 AA07 AA08 BA17 CA08 CA09 CA11 CA19 FA05

Claims (10)

[Claims] 1. A first step of firing a mixture of lithium nitride powder and transition metal powder at 450 ° C. or more and less than 650 ° C. in an atmosphere containing nitrogen, and then cooling the mixture to 100 ° C. or less, and a product of the first step A second step of re-baking at 650 ° C. or more and 800 ° C. or less for a negative electrode of a non-aqueous electrolyte secondary battery. 2. The method according to claim 1, wherein the transition metal powder is Co, Ni, Cu.
The method for producing a lithium-containing composite nitride for a negative electrode according to claim 1, comprising at least one selected from the group consisting of Zn and Zn. 3. The lithium nitride powder has an average particle size of 45.
μm or less, and the average particle size of the transition metal powder is 15 μm.
The method for producing a lithium-containing composite nitride for a negative electrode according to claim 1, which is not more than m. 4. A lithium-containing composite nitride for a negative electrode of a non-aqueous electrolyte secondary battery obtained by the production method according to claim 1. 5. An average particle size of 50 μm or less.
The lithium-containing composite nitride for a negative electrode according to the above. 6. A powder X-ray diffraction pattern having a hexagonal crystal structure, wherein the ratio of the reflection peak intensity (I ₀₀₁ ) on the ( ₀₀₁ ) plane to the reflection peak intensity (I ₁₀₁ ) on the (101) plane is I _{5. The} lithium-containing composite nitride for a negative electrode according to claim 4, wherein ₀₀₁ / I ₁₀₁ ≤0.20 is satisfied. 7. has a hexagonal crystal structure, the ratio of the reflection peak intensity of (101) plane of the reflection peak intensity in the powder X-ray diffraction pattern by (111) plane (I ₁₁₁₎ (I ₁₀₁₎ is, I _The lithium-containing composite nitride for a negative electrode according to claim 4, which satisfies ₁₁₁ / _I101 ≤ 0.10. 8. The lithium-containing composite nitride for a negative electrode according to claim 6, wherein the half width of a reflection peak by the (101) plane is 0.25 ° or less. 9. A negative electrode for a non-aqueous electrolyte secondary battery, comprising the lithium-containing composite nitride according to claim 4. 10. A non-aqueous electrolyte secondary battery comprising a positive electrode capable of reversibly inserting and extracting lithium, a negative electrode according to claim 9, and a non-aqueous electrolyte interposed between the positive electrode and the negative electrode.