JP2002313334A - Negative electrode material for use in nonaqueous electrolyte secondary battery and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a negative electrode material for use in a nonaqueous electrolyte secondary battery having large capacity and high reliability, by improving capacity recovering characteristics after being overdischarged by using an alkali metal-added and lithium-containing composite nitride as a negative electrode active material. SOLUTION: This negative electrode material comprises the alkali metal added and lithium-containing nitride composite expressed by Li3-x-y Ay Mx N (where, A is an alkali metal other than lithium, M is a transition metal, and 0.2<x<=0.8, 0.0<y<=0.8), or it is coated on the surface of a center particle comprising a lithium-containing composite nitride expressed by Li3-x Mx N (where, M is a transition metal, 0.2<x<=0.8) to obtain this negative electrode material having enhanced oxidation resistant decomposition characteristics and improved capacity recovering characteristics when overdischarged.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in resistance to oxidation decomposition of a negative electrode material capable of providing a high capacity nonaqueous electrolyte secondary battery. More specifically, the present invention relates to a non-aqueous electrolyte secondary battery having excellent overdischarge recovery characteristics.

[0002]

_2. Description of the Related Art In recent years, lithium ion batteries using LiCoO ₂ for the positive electrode and a carbon material for the negative electrode have been widely used as power sources for portable equipment. With the miniaturization and weight reduction of electronic devices, these batteries are desired to have a higher energy density, and various materials are being actively studied. Until now, in addition to LiCoO ₂ , as a positive electrode material of a non-aqueous electrolyte secondary battery,
LiMn ₂ O ₄ , LiFeO ₂ , LiNiO ₂ , V ₂ O ₅ , C
Transition metal oxides such as r ₂ O ₅ , MnO ₂ , TiS ₂ and MoS ₂ and chalcogen compounds have been proposed. On the other hand, various materials have been studied for the negative electrode, and a carbon material has been put to practical use as a negative electrode material, and is generally widely used. However, carbon materials have already reached their theoretical capacity (about 370 m
(Ah / g), and a new negative electrode material having a high capacity is desired in order to achieve a higher energy density.

Here, Japanese Unexamined Patent Publication No. 9-102311 discloses a material capable of increasing the energy density of a secondary battery.
Formula: A _x MyN (where A is Na, K, Mg, Ca, A
g, at least one selected from the group consisting of Cu, Zn and Al, M is a transition metal element (M ≠ A), 0.0
<X, y ≦ 3.0 is satisfied. It has been proposed to use the nitride represented by) for the negative electrode active material holder. And
It is shown that the nitride can insert and desorb the element represented by A in the above formula, and can also insert and desorb lithium ions. However, the material does not contain lithium at the time of its synthesis. In order to insert and desorb lithium as a negative electrode active material of a lithium ion battery, the element A in the above formula is desorbed by some method to secure a lithium site or to be directly inserted into a crystal lattice. Will be needed.

[0004] Therefore, the simplicity of lithium ion battery fabrication, the structural stability during charge and discharge, and the reversibility of charge and discharge are
As proposed in JP-A-7-78609,
It is considered that the case where the composite nitride containing lithium is used is more excellent. The lithium-containing composite nitride proposed in JP-A-7-78609 has a formula:
Li _a M _b N (where, M is a transition metal, a is a content of lithium in the active material and is a variable that changes by charge and discharge), and includes lithium inserted and desorbed by charge and discharge from the beginning. It is synthesized in the state. The average working electrode potential is around 0.8 V based on the lithium potential, and the reversible capacity when this is used as a negative electrode is much larger than that of a carbon material. That is, it is a material that can be expected to increase the capacity of the battery.

[0005]

DISCLOSURE OF THE INVENTION The present inventors have proposed a method in which lithium has been electrochemically desorbed from a positive electrode material in advance.
It was manufactured using CoO ₂ and a lithium-containing composite nitride represented by the formula: Li _3-x M _x N (where M is a transition metal, 0.2 <x ≦ 0.8) as a negative electrode material. As a result of evaluating the battery, there was no problem under normal use conditions and environments. However, when the battery was over-discharged and gas was generated, the battery swelled and the recovery characteristics thereafter were not sufficient. In addition,
Here, the reaction in which lithium is occluded in the active material used for the negative electrode (that is, the lithium-containing composite nitride) is referred to as charging, and the reaction in which lithium is released is referred to as discharging.

The mechanism of gas generation in the overdischarge state is presumed as follows. Unlike the carbon material, the lithium-containing composite nitride immediately after the synthesis is in a state of being filled with lithium. This state corresponds to a charged state of a battery using the lithium-containing composite nitride for the negative electrode. Therefore, the lithium-containing composite nitride in a discharged state from which lithium has been desorbed has a lower stability than the initial charged state and is in a more reactive state. This is considered to have affected gas generation. Here, when the present inventors analyzed the generated gas, nitrogen was the main component. Therefore, it is presumed that this gas is not a gas generated by decomposition of the electrolytic solution, but a gas derived from the lithium-containing composite nitride, that is, a gas generated by decomposition of the lithium-containing composite nitride.

[0007] The electric charge of the lithium-containing composite nitride at the time of discharge is compensated by a change in the valence of the contained transition metal element as lithium is released from the lithium-containing composite nitride. Thus, it is considered that the electrical neutrality of the lithium-containing composite nitride is maintained. However, when the amount of desorbed lithium increases, the charge cannot be compensated for only by the change in the valence of the transition metal, and it is expected that a load is applied to the nitrogen element. For example, when the composition of the lithium-containing composite nitride is represented by the formula: Li _2.6 Co _0.4 N, lithium is desorbed and the formula: Li _1.0 Co _0.4 N
It is said that the composition is represented by

The initial state of this compound (Li _2.6 Co
_0.4 N), formally, the oxidation number of Li (lithium) is +1 valence, the oxidation number of Co (cobalt) is +1 valence, and the oxidation number of N (nitrogen) is -3 valence.
When o is responsible, the oxidation number of cobalt in the discharged state (Li _{1. 0} Co _0.4 N) becomes a pentavalent. This oxidation number indicates a high oxidation state that is not normally considered. Therefore, in such a state, it is considered that nitrogen also plays a role of charge compensation by donating electrons, but in an overdischarge state in which the nitride is oxidized, the nitrogen in the lithium-containing composite nitride is further reduced. It is presumed that the bond became very unstable, leading to decomposition. Therefore, an object of the present invention is to
An object of the present invention is to solve the above problem and to realize a highly reliable battery having excellent recovery characteristics by avoiding an overdischarge state.

[0009]

In order to solve the above-mentioned problems, the present invention provides a method of formula (1): Li _3-xy A _y M _x N (where
A is an alkali metal other than lithium; M is a transition metal;
2 <x ≦ 0.8, 0.0 <y ≦ 0.8) Provided is a negative electrode material for a non-aqueous electrolyte secondary battery, comprising a lithium-containing composite nitride represented by the following formula: Here, A is
Effectively, it is at least one selected from the group consisting of Na and K. M is Co, Cu,
It is effective that it is at least one selected from the group consisting of Ni, Fe, and Mn.

Further, the present invention provides a compound of the formula (2): Li _3-x M _x N
(Wherein, M is a transition metal, 0.2 <x ≦ 0.8) a central particle composed of a lithium-containing composite nitride represented by 0.2 <x ≦ 0.8, and a material that suppresses oxidative decomposition of the central particle. A negative electrode material for a non-aqueous electrolyte secondary battery, comprising a covering surface layer. Here, the surface layer is
Formula (1): Li _3-xy A _y M _x N (where A is an alkali metal other than lithium, M is a transition metal, and 0.2 <x ≦ 0.
8, 0.0 <y ≦ 0.8) is effective. A is Na
And at least one member selected from the group consisting of K. Further, M is Co, Cu, N
It is effective that it is at least one selected from the group consisting of i, Fe, and Mn.

Further, the present invention provides a compound of the formula (2): Li _3-x M _x
A step of synthesizing a central particle composed of a lithium-containing composite nitride represented by N (where M is a transition metal, 0.2 <x ≦ 0.8), and comprising a material that suppresses oxidative decomposition of the central particle. Mixing a fine powder with the central particles to obtain a mixture,
And a method for producing a negative electrode material for a non-aqueous electrolyte secondary battery, comprising a step of applying mechanical energy to the mixture and fusing the material to the surface of the central particle by a mechanochemical reaction to form a surface layer.

Further, the present invention provides a compound of the formula (2): Li
_3-x M _x N (where M is a transition metal, 0.2 <x ≦ 0.8)
A step of synthesizing a central particle composed of a lithium-containing composite nitride represented by, a step of mixing the central particle and an alkali metal or a nitride of the alkali metal to obtain a mixture, and subjecting the mixture to a temperature of 450 ° C. or higher. A method for producing a negative electrode material for a non-aqueous electrolyte secondary battery, comprising the step of re-firing to form a surface layer made of a material that suppresses oxidative decomposition on the surface of the central particle.

In this case, the alkali metal is at least one selected from the group consisting of Na and K, and the nitride of the alkali metal is at least one selected from the group consisting of Na ₃ N and K ₃ N. Is effective. The present invention also provides a nonaqueous electrolyte secondary battery including a negative electrode using the above negative electrode material, a nonaqueous electrolyte, and a positive electrode capable of inserting and extracting lithium.

[0014]

DETAILED DESCRIPTION OF THE INVENTION Regarding the Negative Electrode Material of the Present Invention As described above, in order to solve the above problems, it is necessary to suppress the oxidative decomposition of the material in an overdischarged state. Therefore, the present inventors have conducted intensive studies and found that the formula (1): Li _3-xy A _y M _x N (where A is an alkali metal other than lithium, M is a transition metal, and 0.2 <x ≦ 0.8,
When y is a lithium-containing composite nitride represented by 0.0 <y ≦ 0.8) as a negative electrode active material, gas generation due to oxidative decomposition in an overdischarge state is suppressed, and the recovery characteristics of the battery are improved. The inventors have found that the present invention can be performed, and have completed the present invention.

Further, the formula (2): Li _3-x M _x N (where M
Is a transition metal, a material containing lithium-containing composite nitride represented by 0.2 <x ≦ 0.8) as a central particle and suppressing oxidative decomposition of the central particle, for example, the above-mentioned formula (1): Li _3-xy A _y
M _x N (where A is an alkali metal other than lithium, M is a transition metal, 0.2 <x ≦ 0.8, 0.0 <y ≦ 0.8)
It has been found that a negative electrode material for a non-aqueous electrolyte secondary battery having a surface layer formed by covering the surface with a lithium-containing composite nitride represented by the formula (1) also exhibits the same effect.

The lithium-containing composite nitride represented by the above formula (1) is synthesized with a composition mainly composed of lithium at the time of synthesis, has a large capacity, and is excellent in charge / discharge reversibility and oxidation decomposition resistance. Can be solved. When lithium is released from the lithium-containing composite nitride with the discharge of the battery, it is considered that the charge is basically compensated for by the change in the valence of the transition metal. But,
It is presumed that even in the final stage of discharge, even nitrogen forming a hybrid orbital with the transition metal participates in charge compensation, disrupting the charge balance and causing instability of the composite nitrogen compound.

When the potential of the negative electrode material composed of the lithium-containing composite nitride was actually scanned to an overdischarge region not used in a normal charge / discharge cycle and to a region nobler than a certain potential, the potential of the negative electrode material was reduced. It was found that the part decomposed to generate nitrogen gas. The reason that the battery is inferior in capacity recovery characteristics after overdischarge is that the overdischarge causes the negative electrode potential to reach the decomposition potential region, a part of the lithium-containing composite nitride is decomposed, gas is generated, and the amount of the negative electrode material decreases. This is considered to be due to the fact that the gas removes the electrolyte from the surroundings of the negative electrode material, and the gas is present between the positive electrode and the negative electrode to inhibit the electrode reaction.

When the behavior of the electrode potential during battery discharge was examined in more detail, the difference between the open circuit potential and the closed circuit potential,
In other words, it was clarified that the overvoltage rapidly increased at the end of discharge, and that gas was generated when the closed circuit voltage reached the decomposition potential region during overdischarge. Although the cause of the overvoltage increase is not clear, it is considered that the electron conductivity was lowered at the end of discharge on the surface of the negative electrode material, which is a reaction field in the charge transfer process of the electrode reaction. From the above, the present inventors have focused on improving the electron conductivity at the end of discharge on the surface of the negative electrode material to suppress an increase in overvoltage, and have solved the problem.

In the lithium-containing composite nitride represented by the above formula (1), when at least one selected from the group consisting of Na (sodium) and K (potassium) is added as the alkali metal A, especially overdischarge occurs It was found that the time recovery characteristics were improved. Although the reason is not clear, it is considered as follows. That is, the ionization energies of Li (lithium), Na (sodium) and K (potassium) are 520 kJ / mol and 4 kJ / mol, respectively.
96 kJ / mol and 419 kJ / mol (L
i (lithium)> Na (sodium)> K (potassium)). That is, it can be said that sodium and potassium are more easily ionized and emit electrons than lithium.

Therefore, sodium and potassium added to the lithium-containing composite nitride are not occluded / released by charge / discharge like lithium, but serve as electron donors at the end of discharge, causing a decrease in electron conductivity and an increase in overvoltage. It is supposed that this suppresses the electrode potential from reaching the decomposition region in the overdischarge state and suppresses the oxidative decomposition of the lithium-containing composite nitride. In addition, sodium and potassium act as electron donors and participate in charge compensation, preventing the transition metal from becoming a highly oxidized state and preventing electrons from being extracted from nitrogen which forms a hybrid orbit with the transition metal, and thereby balances the charge. It also contributes to stabilization. As a result, it is presumed that the stability of the lithium-containing composite nitride is also improved.

In the above formula (1), the addition amount y of the alkali metal A other than lithium in Li _3-xy A _y M _x N is 0.0
It is preferable that <y ≦ 0.8. As described above, if at least one selected from the group consisting of sodium and potassium is added as the alkali metal element A, there is an effect that oxidative decomposition is suppressed, but when y exceeds 0.8, This is because the alkali metal element does not completely solidify in the nitride and an impurity phase is generated.
Above all, it is more preferable to satisfy 0.01 <y ≦ 0.6. Sodium and potassium may be added alone, or both may be added.

Further, the negative electrode material of the present invention has the formula (1)
It may have a surface layer represented by At this time, the central particle (nucleus) is represented by the following formula (2): Li _3-x M _x N
(Wherein M is a transition metal, 0.2 <x ≦ 0.8) lithium-containing composite nitride represented by the formula (2), and oxidation of the lithium-containing composite nitride represented by the formula (2) is performed on the surface thereof. It is preferable to provide a surface layer made of a nitride represented by the formula (1) having an effect of suppressing decomposition.

[0023] In particular, the surface layer has a formula (1): Li
_3-xy A _y M _x N (where A is an alkali metal other than lithium, M is a transition metal, 0.2 <x ≦ 0.8, 0.0 <y ≦
0.8), and A is preferably at least one selected from the group consisting of sodium and potassium. This is because the addition of an alkali metal element has an effect of suppressing oxidative decomposition, but when y exceeds 0.8, the alkali metal does not completely form a solid solution in the nitride and an impurity phase is generated. As described above, more preferably, 0.01 <y ≦ 0.6.

The lithium-containing composite nitride to which an alkali metal element is added has a sufficiently larger capacity than the carbon material currently used for the negative electrode material of the lithium ion battery. However, the capacity is slightly lower than that of the lithium-containing composite nitride before addition. Therefore, a large capacity formula (2): Li _3-x M _x N (where M is a transition metal, 0.
2 <x ≦ 0.8) A lithium-containing composite nitride represented by the following formula (1): Li _3-xy A _y M _x N (where A is An alkali metal other than lithium, M is a transition metal, 0.2 <x ≦ 0.8,
By forming the surface layer of the lithium-containing composite nitride represented by 0.0 <y ≦ 0.8), a very large effect of obtaining a high capacity and excellent resistance to oxidation decomposition can be obtained.

Formula (2) constituting the central particle: Li _3-x M _x
The lithium-containing composite nitride represented by N (where M is a transition metal and 0.2 <x ≦ 0.8) is lithium nitride (Li ₃
It can be obtained by substituting a part of lithium in N) with transition metal M. As the transition metal M, copper, iron, manganese, cobalt, nickel and the like are preferable because a lithium-containing composite nitride having a particularly high capacity and excellent reversibility of charge and discharge can be realized.

The lithium-containing composite nitride may contain only one type of transition metal, or may contain two or more types of transition metals. Further, the composition such as the transition metal and the substitution amount thereof may be different between the surface layer and the central particle. In particular, the formula in which the transition metal M is cobalt: Li
_The lithium-containing composite nitride represented by _3-x Co _x N exhibits particularly excellent charge / discharge reversibility. When x is 0.2 or less, the conductivity in the negative electrode becomes insufficient, and when x exceeds 0.8, the capacity of the negative electrode becomes insufficient.

The method of providing the surface layer by coating the surface of the center particle is not particularly limited. However, after the lithium-containing composite nitride is synthesized in advance to obtain the center particle, the fine powder of the material constituting the desired surface layer is obtained. And a method using a mechanochemical reaction in which mechanical energy is applied to a mixture of the center particles and the center particles to fuse the surfaces of the center particles to form an alloy. Specific methods utilizing such a mechanochemical reaction include, for example, a hybridization method,
Examples include the mechanofusion method, theta composer method, mechanomill method, and ball mill method.

After the lithium-containing composite nitride as the center particle is synthesized in advance, the center particle and the alkali metal element A (preferably at least one selected from the group consisting of Na and K) or a nitride thereof (preferably Is mixed with Na ₃ N or K ₃ N), and the resulting mixture is refired at 450 ° C. or higher. When the refiring temperature is lower than 450 ° C., the solid solution reaction of the alkali metal element does not sufficiently proceed.

Although the boundary between the surface layer and the central particle may be clear, it is more preferable that the composition continuously changes (inclines) from the surface layer to the central particle.
By using the above-described coating method, it is possible to synthesize a negative electrode material in which the composition continuously changes, that is, the size of the crystal lattice changes continuously. By having such a composition that changes continuously, there is no discontinuity in the conduction path of lithium ions, and the diffusion of lithium ions in the solid phase is less hindered. As a result, polarization is reduced, and improvement in oxidation resistance and charge / discharge characteristics of the battery can be expected.

When the surface layer is formed on the negative electrode material of the present invention by the above method, the surface layer is formed under an atmosphere containing as little moisture and oxygen as possible, such as high-purity nitrogen gas or argon gas. Is preferred. This is because the lithium-containing composite nitride has high reactivity with moisture and is deteriorated by moisture. Also, it is for preventing oxidation of the obtained negative electrode material.
Particularly, in the formation of the surface layer by refiring, it is more preferable to perform the formation in a high-purity nitrogen gas.

The thickness of the surface layer in the negative electrode material of the present invention is preferably 0.01 μm or more. Furthermore, 0.
It is particularly preferred that the thickness be 1 μm or more. If the thickness is less than 0.01 μm, the effect of suppressing the oxidative decomposition of the lithium-containing composite nitride is reduced. However, when the surface layer is formed of a lithium-containing composite nitride to which an alkali metal element represented by the above formula (1) is added, the upper limit of the thickness is not particularly limited. In order to further improve the stability, the thickness of the surface layer may be increased, and in order to further increase the capacity, the surface layer may be minimized. That is, the thickness can be arbitrarily set according to the intended battery characteristics.

On the other hand, the ratio of the surface layer covering the surface of the central particle may be 20% or more of the total surface area from the viewpoint of exhibiting a sufficient effect of suppressing oxidative decomposition. Further, it is preferably at least 80%, and it is particularly preferable to provide a surface layer over the entire surface. The thickness and the covering ratio of the surface layer were determined by X-ray photoelectron spectroscopy (ESC
A), it can be confirmed by precision analysis using an electronic probe (EPMA) and scanning electron microscope (SEM).

A negative electrode material comprising a nitride which is hardly oxidized and decomposed by the formula (1) and has a surface layer comprising the nitride and central particles comprising a lithium-containing composite nitride obtained as described above. A negative electrode is manufactured using the negative electrode material, and a nonaqueous electrolyte secondary battery can be assembled. Hereinafter, components of the non-aqueous electrolyte secondary battery will be described.

B. Regarding Other Battery Components The negative electrode mixture may include a binder in addition to the negative electrode material (active material) and the conductive agent. As the binder, those conventionally used for a negative electrode mixture of a nonaqueous electrolyte secondary battery may be used. For example, polyvinylidene fluoride, styrene-butadiene rubber, polyvinylidene difluoride, or the like can be used. In order to obtain a negative electrode mixture, an active material, a conductive agent, and a binder may be mixed. At that time, if a solvent is added and kneaded, a uniformly mixed paste mixture can be obtained. The obtained paste is applied to a current collector such as a metal foil, and this is rolled and processed into a desired form to obtain an electrode.

As the solvent used at this time, it is desirable to use a highly dehydrated one. This is because the lithium-containing composite nitride contained in the negative electrode has high reactivity with moisture and is deteriorated by moisture. For example, it is preferable to use dehydrated toluene or the like. The obtained negative electrode is not particularly limited, for example, lithium occlusion and storage of lithium-containing composite nitrides such as lithium cobaltate and lithium nickelate.
A non-aqueous electrolyte secondary battery can be formed by a normal manufacturing method in combination with a positive electrode made of a material that can be released.

The negative electrode conductive agent used in the present invention is not particularly limited as long as it is an electron conductive material. For example,
Conductive fibers such as natural graphite (flaky graphite, etc.), graphite such as artificial graphite and expanded graphite, acetylene black, Ketjen black, channel black, furnace black, lamp black, carbon black of thermal black, carbon fiber and metal fiber , Copper and nickel metal powders, and organic conductive materials such as polyphenylene derivatives. These can be used alone or in any combination. Among these conductive agents, artificial graphite, acetylene black and carbon fiber are particularly preferred.

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

The binder for the negative electrode used in the present invention may be either a thermoplastic resin or a thermosetting resin. Preferred binders in the present invention include, for example, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PV
DF), styrene butadiene rubber, tetrafluoroethylene-hexafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer (FE
P), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, ethylene-
Tetrafluoroethylene copolymer (ETFE resin), polychlorotrifluoroethylene (PCTFE), vinylidene fluoride-pentafluoropropylene copolymer, propylene-tetrafluoroethylene copolymer, ethylene-
Chlorotrifluoroethylene copolymer (ECTFE),
Vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, vinylidene fluoride-perfluoromethylvinyl ether-tetrafluoroethylene copolymer, ethylene-acrylic acid copolymer and its (Na ⁺ ) ion crosslinked product, ethylene- Methacrylic acid copolymer and its (Na ⁺ ) ion crosslinked product, ethylene-methyl acrylate copolymer and its (Na ⁺ ) ion crosslinked product, ethylene-methyl methacrylate copolymer and its (Na ⁺ ) ion crosslinked product And the like, and these can be used alone or in combination.

Of these, styrene butadiene rubber, polyvinylidene fluoride, ethylene-acrylic acid copolymer and its (Na ⁺ ) ion cross-linked product, ethylene-methacrylic acid copolymer and its (Na
⁺ ) Ion crosslinked product, ethylene-methyl acrylate copolymer and its (Na ⁺ ) ion crosslinked product, ethylene-methyl methacrylate copolymer and its (Na ⁺ ) ion crosslinked product.

The current collector for the negative electrode used in the present invention is not particularly limited as long as it is an electron conductor which does not cause a chemical change in the battery constituted. As a material constituting the current collector for the negative electrode, for example, stainless steel, nickel, copper,
In addition to titanium, carbon, and a conductive resin, those obtained by treating the surface of copper or stainless steel with carbon, nickel, or titanium are used. In particular, copper or a copper alloy is preferable.

The surface of these materials can be oxidized and used. Further, the surface of the current collector may be made uneven by surface treatment. As the shape, in addition to a foil, a film, a sheet, a net, a punched material, a lath body, a porous body, a foamed body, a molded body of a fiber group, and the like are used. The thickness is not particularly limited, but a thickness of 1 to 500 μm is used.

As the positive electrode material used in the present invention, a lithium-containing transition metal oxide can be used. For example,
Li _x CoO ₂ , Li _x NiO ₂ , Li _x MnO ₂ , Li _{x
Co y Ni 1-y O 2} , Li x Co y M 1-y O z, Li x Ni 1-y
_{M y O z, Li x Mn} 2 O 4, Li x Mn 2-y M y O 4 (M is N
a, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu,
At least one of Zn, Al, Cr, Pb, Sb and B, x = 0 to 1.2, y = 0 to 0.9, z = 2.0
To 2.3).

Here, the value of x is a value before the start of charging / discharging, and increases / decreases due to charging / discharging. However, it is also possible to use other positive electrode materials such as transition metal chalcogenides, vanadium oxides and lithium compounds thereof, niobium oxides and lithium compounds thereof, conjugated polymers using organic conductive substances, and chevrel phase compounds. . It is also possible to use a mixture of a plurality of different positive electrode materials. The average particle size of the positive electrode active material particles is not particularly limited, but is preferably 1 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 at the charge / discharge potential of the positive electrode material used. For example, graphite such as natural graphite (flaky graphite, etc.), artificial graphite, etc.
Acetylene black, Ketjen black, channel black, furnace black, lamp black, carbon black of thermal black, conductive fibers such as carbon fiber and metal fiber, metal powders such as carbon fluoride and aluminum, zinc oxide, potassium titanate, etc. Conductive whiskers, conductive metal oxides such as titanium oxide, and organic conductive materials such as polyphenylene derivatives. These can be used alone or in combination.

Among these conductive agents, artificial graphite and acetylene black are particularly preferred. The addition amount of the conductive agent is not particularly limited, but is preferably 1 to 50% by weight, and particularly preferably 1 to 30% by weight based on the positive electrode material. For carbon and graphite, 2 to 15% by weight is particularly preferred.

The binder for the positive electrode used in the present invention may be either a thermoplastic resin or a thermosetting resin. In the present invention, preferred binders include, for example, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), styrene butadiene rubber, tetrafluoroethylene-hexafluoroethylene copolymer, tetrafluoroethylene -Hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkylvinyl ether copolymer (PFA), vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, ethylene -Tetrafluoroethylene copolymer (ETFE resin), polychlorotrifluoroethylene (PCTFE), vinylidene fluoride-pentafluoropropylene copolymer, propylene-tetrafluoroethylene Polymer, ethylene - chlorotrifluoroethylene copolymer (ECTFE), vinylidene fluoride - hexafluoropropylene - tetrafluoroethylene copolymer, vinylidene fluoride - perfluoromethyl vinyl ether - tetrafluoroethylene copolymer,
Ethylene-acrylic acid copolymer and its (Na ⁺ ) ion crosslinked product, ethylene-methacrylic acid copolymer and its (Na ⁺ ) ion crosslinked product, ethylene-methyl acrylate copolymer and its (Na ⁺ ) ion crosslinked , Ethylene-methyl methacrylate copolymer and (Na ⁺ )
An ionic crosslinked body can be used, and these can be used alone or as a mixture. Among these materials, more preferred materials are polyvinylidene fluoride (PVDF), polytetrafluoroethylene (P
TFE).

The current collector for the positive electrode used in the present invention is not particularly limited as long as it does not cause a chemical change in the charge / discharge potential of the positive electrode material used. As a material constituting the positive electrode current collector, for example, in addition to stainless steel, aluminum, titanium, carbon, and a conductive resin, a material obtained by treating the surface of aluminum or stainless steel with carbon or titanium is used. In particular, aluminum or an aluminum alloy is preferable. The surface of these materials can be oxidized and used. In addition, it is desirable to make the current collector surface uneven by surface treatment. The shape is
In addition to the foil, a film, a sheet, a net, a punched material, a lath body, a porous body, a foam, a group of fibers, a molded article of a nonwoven fabric, and the like are used. The thickness is not particularly limited, but a thickness of 1 to 500 μm is used.

The electrode mixture includes a conductive agent and a binder,
Fillers, dispersants, ionic conductors, pressure enhancers and other various additives can be used. The filler is not particularly limited as long as it is a fibrous material that does not cause a chemical change in the configured battery. 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. The configuration of the negative electrode plate and the positive electrode plate in the present invention,
It is preferable that the negative electrode mixture surface exists at least on the surface opposite to the positive electrode mixture surface.

The non-aqueous electrolyte used in the present invention is composed of a solvent and a lithium salt (solute) dissolved in the solvent. Examples of the non-aqueous solvent include ethylene carbonate (EC), propylene carbonate (PC),
Cyclic carbonates such as butylene carbonate (BC) and vinylene carbonate (VC), chain carbonates such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC) and dipropyl carbonate (DPC), methyl formate;
Aliphatic carboxylic acid esters such as methyl acetate, methyl propionate and ethyl propionate, γ-lactones such as γ-butyrolactone, 1,2-dimethoxyethane (DM
E), chain ethers such as 1,2-diethoxyethane (DEE) and ethoxymethoxyethane (EME), cyclic ethers such as tetrahydrofuran and 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-
Non-protic organic solvents such as imidazolidinone, 3-methyl-2-oxazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ethyl ether, 1,3-propanesultone, anisole, dimethylsulfoxide, N-methylpyrrolidone and the like. These can be used alone or in combination. Among them, a mixed solvent of a cyclic carbonate and a chain carbonate, or a mixed solvent of a cyclic carbonate, a chain carbonate and an aliphatic carboxylic acid ester is preferable.

Examples of lithium salts dissolved in these solvents include LiClO ₄ , LiBF ₄ , LiPF ₆ , LiPF
AlCl ₄ , LiSbF ₆ , LiSCN, LiCl, Li
CF ₃ SO ₃ , LiCF ₃ CO ₂ , Li (CF ₃ SO ₂ ) ₂ ,
LiAsF ₆ , LiN (CF ₃ SO ₂ ) ₂ , LiB ₁₀ C
l ₁₀ , lithium lower aliphatic carboxylate, LiCl, Li
Examples thereof include Br, LiI, lithium chloroborane, lithium tetraphenylborate, and imide, and these can be used alone or in combination as dissolved in an electrolytic solution or the like. In particular, it is more preferable to include LiPF ₆ . Particularly preferred in the present invention is an electrolyte containing at least ethylene carbonate and ethyl methyl carbonate, and containing LiPF ₆ as a lithium salt.

The amount of the electrolyte added to the battery is not particularly limited, but can be appropriately selected depending on the amounts of the positive electrode material and the negative electrode material and the size of the battery. The amount of lithium salt dissolved in the nonaqueous solvent is not particularly limited, but is preferably 0.2 to 2 mol / l. In particular, 0.5 to
More preferably, it is 1.5 mol / l.

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

As the separator used in the present invention,
Has a large ion permeability, has a predetermined mechanical strength,
An insulating microporous thin film is used. Further, it is preferable to have a function of closing a hole at a certain temperature or higher to increase resistance. From the viewpoints of resistance to organic solvents and hydrophobicity, sheets, nonwoven fabrics and woven fabrics made of one or more olefin polymers such as polypropylene and polyethylene, or glass fibers are used.

The pore diameter of the separator is desirably in a range in which the positive and negative electrode materials, the binder, and the conductive agent detached from the electrode sheet do not pass, and for example, desirably 0.01 to 1 μm. The thickness of the separator is generally 10 to
300 μm is used. The porosity is determined according to the electron and ion permeability, the material, and the film pressure, but is generally preferably 30 to 80%.

A mixture of a polymer material and an organic electrolyte composed of a solvent and a lithium salt dissolved in the solvent is absorbed and held in the positive electrode mixture and the negative electrode mixture. It is also possible to configure a battery in which a porous separator made of a retained polymer is integrated with a positive electrode and a negative electrode.

The shape of the battery can be any of a coin type, a button type, a sheet type, a laminated type, a cylindrical type, a flat type, a square type, and a large type used for electric vehicles. 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. Hereinafter, the present invention will be described more specifically with reference to Examples, but the present invention is not limited thereto.

[0057]

Examples << Examples 1 to 5 and Comparative Examples 1 and 2 >> The overdischarge recovery characteristics of lithium-containing composite nitrides with various amounts of alkali metal added were compared. First, the lithium-containing composite nitride according to the present invention was synthesized as follows. Here, an example in which cobalt (Co) is used as a transition metal will be described. However, other transition metals shown in the present invention could be similarly synthesized.

As a starting material, lithium nitride (Li
₃ N) powder, cobalt (Co) powder, and sodium nitride (Na ₃ N). Then, the ratio of Li (lithium), Na (sodium) and Co (cobalt) is
2.60: 0.00: 0.40 respectively (Comparative Example 1),
2.595: 0.005: 0.4 (Example 1), 2.5
9: 0.01: 0.4 (Example 2), 2.5: 0.1:
0.4 (Example 3), 2.0: 0.6: 0.4 (Example 4), 1.8: 0.8: 0.4 (Example 5) or 1.
6: 1.0: As will be 0.4 (Comparative Example 2), Li ₃
N powder, Na ₃ N powder and Co powder are mixed well,
Seven mixtures were obtained.

Each of these was put into a crucible, and a high purity (9
(9.9% or more) in a nitrogen atmosphere at 700 ° C. for 8 hours to obtain Li _2.60 Co _0.4 N (Comparative Example 1), Li _2.595 Na
_0.005 Co _0.4 N (Example 1), Li _2.59 Na _0.01 Co
_0.4 N (Example 2), Li _2.5 Na _0.1 Co _0.4 N (Example 3), Li _2.0 Na _0.6 Co _0.4 N (Example 4), Li _1.8
Na _0.8 Co _0.4 N (Example 5) and Li _1.6 Na _1.0 C
A lithium-containing composite nitride powder (negative electrode material) represented by o _0.4 N (Comparative Example 2) was obtained.

The synthesis process is carried out at low humidity (dew point -20
C. or less) in a high-purity nitrogen atmosphere (oxygen concentration 100 ppm or less). As a result of a powder X-ray diffraction measurement of the obtained lithium-containing composite nitride, Li _1.6 Na _1.0 Co _0.4
Only for N (Comparative Example 2), a peak considered to be based on the impurity phase was observed, and it was not uniformly dissolved. However, for the others, the same hexagonal pattern as lithium nitride (Li ₃ N) was observed, and it was confirmed that there was no impurity peak. The synthesis in the case where the transition metal substitution amount was other than x = 0.4 or the transition metal species was other than Co alone was also studied. .

Next, a coin-shaped test battery shown in FIG. 1 was prepared using the above-mentioned negative electrode material, and its electrochemical characteristics such as recovery characteristics upon overdischarge were evaluated. The lithium-containing composite nitride powder synthesized as described above, artificial graphite (KS-6) as a conductive agent, and styrene butadiene rubber as a binder are mixed at a predetermined ratio, and these are dispersed in dehydrated toluene. Thus, a slurry-like negative electrode mixture was obtained. The negative electrode mixture is
It was applied to a copper foil (thickness: 14 μm) as a negative electrode current collector using a doctor blade, and was sufficiently dried at 80 ° C. under reduced pressure. Next, the coated current collector was rolled through rollers. From the negative electrode sheet thus obtained, a diameter of 15
mm disk-shaped negative electrode was punched out.

On the other hand, LiCoO ₂ powder, carbon powder as a conductive agent, and polyvinylidene fluoride resin as a binder were mixed at a weight ratio of 90: 7: 3, and the resulting mixture was dehydrated into n-methyl-2. -Dispersed in pyrrolidinone to obtain a slurry-like positive electrode mixture. Next, the positive electrode mixture was applied to an aluminum foil (thickness: 20 μm) serving as a positive electrode current collector using a doctor blade, dried, and rolled between two rollers. From the positive electrode sheet thus obtained, a disk-shaped positive electrode having a diameter of 14 mm was punched. Using this positive electrode plate in advance, a coin battery with a counter electrode of lithium metal was assembled and charged, and then the battery was disassembled to produce a positive electrode from which lithium was electrochemically desorbed.

For these test cells, a current density of 0.
After 10 cycles of charge / discharge at 65 mA / cm ² in a voltage range of 2.3 to 4.0 V, the discharge was performed to 0 V, and the system was left for one day. After that, charge again between 4.0V and 2.3V
Of the 10th cycle of the discharge capacity when discharging to 2.
The ratio to the discharge capacity up to 3 V was defined as the capacity recovery rate.
Table 1 shows the results.

[0064]

[Table 1]

When the negative electrode material of the present invention was used, it was found that the battery did not swell due to gas generation after overdischarge and the capacity recovery rate was superior to Comparative Example 1 in which no alkali metal was added. . The negative electrode potential during overdischarge was confirmed by producing a model cell, and in Comparative Example 1, the voltage reached 2.4 V on the lithium basis.
5 all reached a potential lower than 2.0 V, and the effect of adding an alkali metal was observed. Although the case where potassium or both sodium and potassium were added as an alkali metal element was also examined, the capacity recovery rate after overdischarge was improved as in Example 1.

<< Examples 6 to 10 and Comparative Example 3 >> The overdischarge recovery characteristics when the surface of the center particle was coated with a lithium-containing composite nitride in which the added amount of the alkali metal was changed and when the surface was not coated were compared. The surface layer composed of the five kinds of alkali metal-substituted lithium-containing composite nitrides represented by the formula (1) synthesized in the same manner as in Examples 1 to 5 was coated with the lithium-containing composite nitride Li _2.6 Co _0.4 N as the central particle. On the surface of
It was formed using a mechanofusion method, which is a method using a compression grinding type fine pulverizer. Here, FIG. 2 is a diagram partially and schematically showing the structure of the compression attrition type pulverizer used in the present embodiment. FIG. 3 is a diagram schematically showing a state of compression and grinding acting between the respective particles in the pulverizer.

The coating mechanism of this device will be briefly described. The cylindrical case 1 rotates at a high speed around the fixed shaft 3 and the lithium-containing composite nitride particles (base particles) which become the central particles due to the centrifugal force generated thereby. ) And a mixture of the alkali metal-substituted lithium-containing composite nitride particles (child particles) to be the surface layer are pressed against the inner wall of the case 1. At the same time, the mixture pressed against the case 1
The pressing force of the operation piece 2 fixed to the plate acts. Thus, the child particles are coated on the surface of the base particles while being rolled. In addition, by scraping the mixture from the inner wall of the case with the scraping pieces 6 and stirring and mixing, the surface of the base particles is efficiently coated with the child particles. Particles subjected to this coating treatment,
That is, FIG. 4 schematically shows a cross section of the central particle 4 having the surface layer 5. FIG. 5 is an enlarged view of a portion X in FIG.

A sample in which the surface of the lithium-containing composite nitride, which is the central particle, was coated with the alkali metal-substituted lithium-containing composite nitride was produced by such a coating treatment method. The processing conditions can be set as appropriate, but here, 180 g of the lithium-containing composite nitride Li _2.6 Co _0.4 N of the central particle and 20 g of the lithium-containing composite nitride of the above-mentioned composition and various alkali metal-substituted are charged. , Rotation speed 180
0 rpm and the processing time were 10 minutes. Case 1
The closest distance between the inner wall of the target and the working piece 2 fixed to the fixed shaft was set to 3 mm.

Li_2.595Na_0.005Co_0.4Represented by N
Anode material having a surface layer made of lithium-containing composite nitride
(Example 6), Li_2.59Na_0.01Co_0.4Represented by N
Having surface layer made of lithium-containing composite nitride
Material (Example 7), Li_2.5Na_0.1Co_0.4Represented by N
Negative electrode having surface layer made of lithium-containing composite nitride
Material (Example 8), Li_2.0Na_0.6Co_0.4Represented by N
Negative electrode having surface layer made of lithium-containing composite nitride
Material (Example 9), and Li_1.8Na_0.8Co _0.4In N
Having a surface layer composed of a lithium-containing composite nitride represented
Negative electrode materials (Example 10) were obtained. Also, Li
_1.6Na_1.0Co_0.4Lithium-containing composite nitride represented by N
Negative electrode material (Comparative Example 3) having a surface layer made of
Was.

The coating area and the thickness of the surface layer were determined by X-ray photoelectron spectroscopy (ESCA), precision analysis using an electronic probe (EPMA), and scanning electron microscope (S
EM), it was about 80% of the total surface area and the thickness was about 0.3 μm in each case. Next, a coin-shaped test battery shown in FIG. 1 was prepared, and the electrochemical characteristics such as the recovery characteristics at the time of overdischarge were measured in Example 1.
The evaluation was performed in the same manner as described above. Table 2 shows the results. In addition,
The results of Comparative Example 1 having no surface layer are also shown.

[0071]

[Table 2]

As described above, it was found that the negative electrode material having the surface coated with the lithium-containing composite nitride to which the alkali metal was added also exhibited better capacity recovery characteristics than the conventional lithium-containing composite nitride.

Examples 11 to 15 Next, the composition of the surface layer was Li _2.5 Na _0.1 Co _0.4 N, and the composition of the central particles was Li.
_The recovery characteristics were compared by changing the coating ratio of the surface layer as _2.6 Co _0.4 N. The method for coating the surface layer was the same as in Example 6, and the method for producing the electrodes and the evaluation battery was the same as in Example 1. However, the coating ratio was adjusted by changing the conditions for coating by the mechanofusion method. The coating ratio was 15% of the total surface area (Example 11), 20%
(Example 12), 50% (Example 13), 80% (Example 14), and 100% (Example 15). Table 3
Figure 11 shows the evaluation results. The results of Comparative Example 1 having no surface layer are also shown.

[0074]

[Table 3]

In the battery of Example 11 having a covering area of 15%, although the characteristics were slightly improved as compared with the battery of Comparative Example 1 not covered, the battery was insufficient. On the other hand, when the coating area ratio was 20% or more, the characteristics were significantly improved, and particularly when the coating area ratio was 80% or more, the characteristics were excellent.

Examples 16 to 19 Next, the composition of the surface layer was Li _2.5 Na _0.1 Co _0.4 N, and the composition of the central particles was Li.
_The recovery characteristics were compared by changing the coating thickness of the surface layer as _2.6 Co _0.4 N. The method for coating the surface layer was the same as in Example 6, and the method for producing the electrodes and the evaluation battery was the same as in Example 1. However, the coating thickness is adjusted by changing the conditions when coating is performed by the mechanofusion method, and the X-ray photoelectron spectroscopy (ESCA) and the scanning electron microscope (S
EM). The coating thickness is 0.005μ
m (Example 16), 0.01 μm (Example 17), 0.
1 μm (Example 18) and 1 μm (Example 19). Table 4 shows the evaluation results. The results of Comparative Example 1 having no surface layer are also shown.

[0077]

[Table 4]

In the case of the battery of Example 16 having a coating thickness of 0.005 μm, although the characteristics were slightly improved as compared with the battery of Comparative Example 1 in which the coating was not made, it was insufficient. On the other hand, when the coating thickness was 0.01 μm or more, a significant improvement in characteristics was observed. If the thickness is more than this,
The result is similar to.

Examples 20 to 24 Next, a negative electrode active material was prepared by mixing potassium nitride (K ₃ N) with a lithium-containing composite nitride having a composition serving as central particles of Li _2.6 Co _0.4 N and refiring. The material was synthesized. Using this, an electrode and an evaluation battery were prepared and evaluated in the same manner as in Example 1. The amount of K ₃ N added was determined by XPS or the like from various conditions studied, where K (potassium) was solid-dissolved from the surface to 0.1 μm and the composition of the surface layer was almost Li _2.5 K _0.1 Co. _0.4 N
It was adjusted to be. The temperatures of the refiring were 350 ° C. (Example 20), 450 ° C. (Example 21), 500 ° C. (Example 22), 700 ° C. (Example 23), and 800 ° C.
(Example 24) Table 5 shows the results. In addition,
The results of Comparative Example 1 are also shown.

[0080]

[Table 5]

At 350 ° C., the solid content of K (potassium) was not sufficient, and the desired active material could not be synthesized.
It has been found that the active material of the present invention synthesized at a temperature of not less than ° C. has excellent capacity recovery characteristics during overdischarge. As described above, for Examples 6 to 24, similar tests were performed by changing the alkali metal species to be added and the ratio thereof, or the transition metal species and the composition of the surface layer and the central particle in various ways. When the material was used, the result that the recovery characteristic after overdischarge was improved was obtained.

[0082]

According to the present invention, by using a lithium-containing composite nitride to which an alkali metal is added as a negative electrode active material, the capacity recovery characteristics after overdischarge of a battery are improved, and high capacity and high reliability are obtained. A negative electrode material for a non-aqueous electrolyte secondary battery can be provided.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a test battery used for evaluating a negative electrode for a non-aqueous electrolyte secondary battery.

FIG. 2 is a vertical cross-sectional view schematically showing a mechanism of a compression attrition type pulverizer used for a coating treatment in an embodiment of the present invention.

FIG. 3 is a view schematically showing a state of compression and grinding by a compression grinding type fine grinding machine of FIG. 2;

FIG. 4 is a cross-sectional view of particles coated with a lithium-containing composite nitride or the like to which an alkali metal has been added.

FIG. 5 is an enlarged view of a portion X in FIG. 4;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Case of compression grinding type fine crusher 2 Working piece 3 Fixed shaft 4 Base particle 5 Child particle 6 Scraping piece 11 Test electrode 12, 15 Current collector 13 Case 14 Lithium foil 16 Electrolyte 17 Separator 18 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 AJ05 AK02 AK03 AK05 AK16 AK18 AL01 AM02 AM03 AM04 AM05 AM07 BJ03 CJ02 CJ08 CJ22 DJ16 DJ17 HJ02 HJ13 HJ14 5H050 AA04 AA07 BA17 CA02 CA08 CA09 CA11 CA20 CA29 CB01 FA17 FA18 FA17

Claims (11)

[Claims] 1. Formula (1): Li _3-xy A _y M _x N (wherein
A is an alkali metal other than lithium; M is a transition metal;
2. A negative electrode material for a non-aqueous electrolyte secondary battery, comprising a lithium-containing composite nitride represented by the following formula: 2 <x ≦ 0.8, 0.0 <y ≦ 0.8). 2. The negative electrode material for a water electrolyte secondary battery according to claim 1, wherein the A is at least one selected from the group consisting of Na and K. 3. The negative electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein said M is at least one selected from the group consisting of Co, Cu, Ni, Fe, and Mn. material. 4. A central particle comprising a lithium-containing composite nitride represented by the formula (2): Li _3-x M _x N (where M is a transition metal, 0.2 <x ≦ 0.8) A negative electrode material for a non-aqueous electrolyte secondary battery, comprising a material that suppresses oxidative decomposition of the central particles and a surface layer that covers the central particles. 5. The method according to claim 1, wherein the surface layer has a formula (1): Li _3-xy A _y.
M _x N (where A is an alkali metal other than lithium, M is a transition metal, 0.2 <x ≦ 0.8, 0.0 <y ≦ 0.8)
The negative electrode material for a nonaqueous electrolyte secondary battery according to claim 4, comprising a lithium-containing composite nitride represented by the following formula: 6. The negative electrode material for a non-aqueous electrolyte secondary battery according to claim 4, wherein A is at least one selected from the group consisting of Na and K. 7. The non-aqueous electrolyte according to claim 4, wherein said M is at least one selected from the group consisting of Co, Cu, Ni, Fe, and Mn. Anode material for secondary battery. 8. A central particle comprising a lithium-containing composite nitride represented by the formula (2): Li _3-x M _x N (where M is a transition metal, 0.2 <x ≦ 0.8) A step of synthesizing, a step of mixing a fine powder made of a material that suppresses oxidative decomposition of the center particles with the center particles to obtain a mixture, and applying mechanical energy to the mixture, and applying a mechanochemical reaction to the surface of the center particles. A method for producing a negative electrode material for a non-aqueous electrolyte secondary battery, comprising a step of forming a surface layer by fusing the above materials with each other. 9. A central particle comprising a lithium-containing composite nitride represented by the formula (2): Li _3-x M _x N (where M is a transition metal, 0.2 <x ≦ 0.8) Synthesizing, mixing the central particle with an alkali metal or a nitride of the alkali metal to obtain a mixture, and mixing the mixture with 450
A method for producing a negative electrode material for a non-aqueous electrolyte secondary battery, comprising a step of forming a surface layer made of a material that suppresses oxidative decomposition on the surface of the central particles by refiring at a temperature of not less than ° C. 10. The alkali metal is at least one selected from the group consisting of Na and K, and the nitride of the alkali metal is at least one selected from the group consisting of Na ₃ N and K ₃ N. The method for producing a negative electrode material for a non-aqueous electrolyte according to claim 9. 11. A non-aqueous electrolyte secondary battery comprising at least a negative electrode using the negative electrode material according to claim 1, a non-aqueous electrolyte, and a positive electrode capable of inserting and extracting lithium.