JP3289262B2 - Method for producing negative electrode active material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to is a method of manufacturing a negative active material for a secondary battery, the negative electrode active especially having a high energy density, and charging and discharging capacity is large, moreover a long battery characteristics cycle life The present invention relates to a method for producing a substance .

[0002]

2. Description of the Related Art In recent years, electronic devices have become smaller, lighter and more portable, and there has been a demand for the development of batteries having a high energy density as power sources. As a battery that meets such demands, a lithium secondary battery is expected.

[0003] Lithium secondary batteries are basically various types of commercially available secondary batteries, for example, nickel cadmium batteries,
It has higher voltage and higher energy density than lead storage batteries and the like. However, in general, lithium secondary batteries using lithium metal as the negative electrode active material generate needle-like lithium during charging, lithium is cut off during discharging, and falls off from the electrode substrate, producing dead lithium that does not contribute during charging and discharging. I do. For this reason, a battery using lithium metal as the negative electrode active material has a problem that the cycle life is short.

As a new negative electrode active material replacing lithium metal, carbonaceous materials such as natural graphite and artificial graphite and Nb
₂ O ₅ , MoO ₂ , TiS ₂ , Li ₃ FeN ₂ , Li ₇
Inorganic materials such as MnN ₄ and Li _2.5 Co _0.5 N have been studied. These materials utilize the lithium ion intercalation reaction, which retains lithium in an ionized state in the skeletal structure, thereby eliminating the dendrite generation seen with lithium metal and improving cycle life. Is done. Among them, the carbonaceous material can stably insert and desorb lithium ions in the range of a negative electrode potential of 0 to 1 V with respect to the lithium metal reference electrode,
It has a charge / discharge capacity of 200 to 370 mAh / g. In fact, lithium ion secondary batteries using a carbonaceous material as the negative electrode active material have been put to practical use.

[0005]

However, the above-mentioned carbonaceous material and inorganic material have a smaller capacity than lithium metal, and the energy density of a battery using the above-mentioned carbonaceous material or inorganic material for the negative electrode is also lower than that of lithium metal. There is a problem that the size is considerably smaller than that of the battery used for the negative electrode. In addition, among these inorganic negative electrode active materials , Li ₃ FeN ₂ , L ₃
Lithium-containing transition metal nitrides such as i ₇ MnN ₄ and Li _2.5 Co _0.5 N have very high reducing power like lithium metal. There is a problem that it is not possible to obtain excellent battery characteristics. In addition, since lithium is included in the constituent elements, when the firing temperature is high, lithium evaporates and separates, and a substance having a desired composition cannot be obtained. Further, since these lithium-containing nitrides have a high reducing power, they react with a solvent or the like used at the time of lithium elimination, and thus have a problem that battery characteristics are deteriorated.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art and to provide a method for producing a negative electrode active material having a high energy density, a large charge / discharge capacity, and a cycle life having battery characteristics. Is to provide.

[0007]

To achieve Means for Solving the Problems] Such objects, composition formula _{Li 3-x-y M x} N ( where, M represents an element belonging to the transition metal, x is 0.1 to 0.5 in the range, y is expressed by some) in the range of 0.8 to 1.9 negative
The active material composition formula _{Li 3-x M x} N (where, M represents an element belonging to the transition metal, x is in the range of 0.1 to 0.5) forming a precursor represented by And a step of desorbing lithium ions from the precursor. Moreover, precursor represented by the composition formula _{Li 3-x M} x N is, Li metal or lithium nitride starting material (L
i ₃ N) and a transition metal or a transition metal nitride,
It is formed by firing in a nitrogen gas atmosphere or a nitrogen-hydrogen mixed gas atmosphere in a temperature range of 00 to 800 ° C. Further, as a method of desorbing lithium ions from the precursor, a chemical reaction or an electrochemical reaction is used.
You.

The present invention will be described below in more detail.

As described above, in the present invention, the composition formula L
i _3-xy M _x N (where M represents an element belonging to a transition metal, x is in the range of 0.1 to 0.5, and y is 0.8
Negative electrode active substance represented by any) in the range of 1.9 has a composition formula _{Li 3-x M x} N (where, M represents an element belonging to the transition metal, x is 0.1 to 0.5 A negative electrode active material having excellent battery characteristics can be obtained by using a method that is manufactured through a step of forming a precursor represented by the following formula) and a step of desorbing lithium ions from the precursor. This was confirmed by experiments. In particular, by using Li metal or lithium nitride (Li ₃ N) and a transition metal or a transition metal nitride as starting materials , and firing in a nitrogen gas atmosphere or a nitrogen-hydrogen mixed gas atmosphere at a temperature range of 500 to 800 ° C. The composition formula Li _3-x having high crystallinity, no impurities, small composition deviation, and good material properties.
Experiments have confirmed that a precursor represented by M _x N can be produced. Moreover, the a method for desorbing lithium ions from the precursor, and more the use of the chemical reaction or electrochemical reaction, the structure explosion or surface deterioration (oxidation film formation) I
Experiments have confirmed that a good quality negative electrode active material can be produced. Moreover, by using the production method of the present invention,
In the following electrode potential 1.5V against lithium reference electrode has a discharge area of the high capacity, stability can be inserted deintercalating lithium ions, a negative showing a long cycle life
It has been found through experiments that a polar active material can be obtained, and the present invention has been completed based on the recognition.

The transition metal referred to in the present invention has an element number of 2
1 from Sc of element number 30, Zn of element number 30, Y of element number 39, Cd of element number 48, La of element number 57, and Hg of element number 80.

A process for forming a precursor represented by a composition formula Li _3-x M _x N (where M represents an element belonging to a transition metal and x is in the range of 0.1 to 0.5) explain. First, the precursor is prepared by using lithium (L
i) or lithium nitride (Li ₃ N) and a transition metal or a transition metal nitride.
According _{3-x M} x N, it weighed a predetermined amount, after mixing,
It can be synthesized by putting in an alumina crucible and firing.

In the above-mentioned composition formula, when x is less than 0.1, the insulating property becomes high, and the battery characteristics are deteriorated.
Decomposition may occur, while if it exceeds 0.5, solid solution of the transition metal becomes difficult. The firing temperature is suitably from 500 to 800 ° C., and when the firing temperature is lower than 500 ° C., the starting metal, Li metal, lithium nitride (Li ₃ N), transition metal, or transition metal nitride is in an unreacted state. remains and can not form a composition formula _{Li 3-x M} x N of interest. On the other hand, when the temperature exceeds 800 ° C., the evaporation and dissipation of lithium increase, and the amount of lithium decreases by about 10% by weight or more as compared with the amount of lithium before firing, so that a precursor according to the composition formula cannot be formed. The atmosphere is suitably a nitrogen gas atmosphere or a nitrogen-hydrogen mixed gas atmosphere.
The amount of hydrogen in the hydrogen mixed gas atmosphere is suitably 30% or less. If the hydrogen concentration is higher than this, nitrogenation is not sufficiently performed, and a precursor according to the composition formula cannot be formed.

Next, lithium ions are removed from the precursor.
Apart, composition formula _{Li 3-x-y M x} N ( where, M represents an element belonging to the transition metal, x is in the range of 0.1 to 0.5, y is from 0.8 to 1.9 negative represented by the range of)
The step of forming the pole active material will be described. As a result of trying various methods of desorbing lithium ions, for example, a method of desorbing lithium ions from a precursor by a chemical reaction and a method of desorbing lithium ions from a precursor by an electrochemical reaction have good characteristics. Obtained. As a method of desorbing lithium ions by an electrochemical reaction, a nonaqueous electrolyte containing a lithium metal salt as a precursor and a lithium metal as an electrolyte and a lithium salt as an electrolyte, for example, a volume ratio of ethylene carbonate and dimethyl carbonate is used. 1: 1 mixed solvent
An oxidation-reduction system using a solution of M LIPF ₆ was assembled, charged with a predetermined amount of electricity (in the direction of removing lithium ions from the working electrode), washed with anhydrous 2-methyltetrahydrofuran, and washed in a nitrogen atmosphere. There is a method of drying.

On the other hand, as a method of desorbing lithium ions by a chemical reaction, a predetermined amount of iodine (I ₂ ) is dissolved in dehydrated acetonitrile, and the precursor is added thereto.
There is a method of stirring, filtering and drying in a nitrogen atmosphere.

In the above-mentioned composition formula, when y is less than 0.8, the battery characteristics deteriorate and the capacity decreases. On the other hand, 1.
If it exceeds 9, the structure of the negative electrode active material is destroyed, and the battery reaction becomes difficult.

As described above, by using the method for producing a negative electrode active material of the present invention, a precursor having high crystallinity, containing no impurities, having a small composition deviation, and having good material properties can be produced. , structure explosion or surface deterioration of the negative electrode active material (oxide film) is not, it can be produced a high-quality of the negative electrode active material. In addition, the negative electrode active synthesized using the manufacturing method of the present invention.
The material has a high capacity charge / discharge region at an electrode potential of 1.5 V or less with respect to the lithium reference electrode, can insert and remove lithium ions stably, and has a long cycle life. Properties can be obtained. Therefore,
By using the method for producing a negative electrode active material of the present invention, a lithium secondary battery having a high energy density, a large charge / discharge capacity, safety, and a long cycle life can be provided.

Hereinafter, the present invention will be described in more detail with reference to examples.

[0018]

EXAMPLE 1 First, a precursor represented by a composition formula Li _2.6 Co _0.4 N was used as a starting material, and lithium nitride (Li ₃ N) was used as a starting material.
And Co metal at 650 ° C. for 8 hours in a mixed gas atmosphere of nitrogen (98%)-hydrogen (2%) for synthesis. FIG. 1 shows an X-ray diffraction pattern. The tube is Cuka
The measurement was performed at a tube current of 100 mA and a tube voltage of 30 kV. As is clear from FIG. 1, Li _2.6 Co _0.4 N
Was obtained, and no impurity peak was observed. As a result of the composition analysis, the composition after firing was
Li _2.59 Co _0.41 N, and almost no evaporation of lithium was recognized. Next, from this precursor, lithium ions were converted to 1.5
9 Li / mol desorbed, composition formula Li _1.0 Co _0.4 N
A negative electrode active material represented by was synthesized. FIG. 2 shows an X-ray diffraction pattern. The tube is Cukα and the tube current is 100m
A, Measurement was performed at a tube voltage of 30 kV. Since the negative electrode active material undergoes a phase change from crystalline to amorphous due to lithium desorption, the diffraction pattern disappears. As is clear from FIG. 2, no diffraction peak was observed in the range of 10 to 70 ° in 2θ, and no generation of lithium metal and other impurities was observed.

Next, the battery characteristics of the negative electrode active material thus manufactured were evaluated. FIG. 3 is a cross-sectional view of a test cell used for evaluating the performance of the negative electrode active material according to the present invention. In FIG. 3, reference numeral 1 denotes a counter electrode case which is formed by drawing a stainless steel plate. Reference numeral 2 denotes metallic lithium, which is obtained by stamping a lithium metal foil having a predetermined thickness into a diameter of 16 mm and pressing it. 3 is a non-aqueous electrolyte,
LiClO ₄ was added to a mixed solvent of C and DEE at a volume ratio of 1: 1.
Is dissolved at 1 mol / liter. Reference numeral 4 denotes a separator made of a porous film of polypropylene or polyethylene. Reference numeral 5 denotes a working electrode case formed by drawing a stainless steel plate. 6 is L synthesized by the above-described production method.
This is a working electrode configured using i _1.0 Co _0.41 N. This working electrode is composed of the synthesized amorphous Li _1.0 Co
_0.41 N, acetylene black as a conductive agent, and polytetrafluoroethylene as a binder in a weight ratio of 70: 2.
Mixing and rolling at 5: 5 to produce a sheet, 16 mm in diameter
It was punched out. Reference numeral 7 denotes a current collector made of Ti net, which is spot-welded to the working electrode case 5 while covering the working electrode 6. Reference numeral 8 denotes a gasket which keeps electrical insulation between the counter electrode case 1 and the working electrode case 5, and hermetically seals and seals the battery contents by bending the working electrode case opening edge inward and crimping it. I have.

The test cell was subjected to a charge / discharge test in a voltage range of 0.0 to 1.4 V and a current of 1 mA. FIG. 4 shows a charge / discharge curve of the third cycle at this time. As is clear from FIG. 4, Li _1.0 Co _0.41 N is 0.0 to 1.4.
A capacity of 30 mAh was obtained when charge / discharge was repeated stably in the voltage range of V. Also, no rapid decrease in capacity due to charge / discharge was observed, and charge / discharge was repeated stably for 100 cycles or more. After the completion of the charge / discharge test, the test cell was disassembled, and the surface of the working electrode was observed by SEM. However, no deposition of lithium metal or growth of dendrites on the surface of the working electrode could be recognized. The working electrode was analyzed by an X-ray diffractometer, but no X-ray diffraction pattern of lithium metal was observed.

[0021]

Example 2 In the step of forming a precursor in Example 1, the precursor was synthesized by changing the firing temperature to 700 ° C. As a result of X-ray diffraction, the diffraction pattern was the same as in FIG.
Only a diffraction pattern of _2.6 Co _0.4 N was obtained, and no impurity peak was observed. As a result of composition analysis, the composition after firing was Li _2.586 Co _0.414 N
And almost no evaporation of lithium was recognized. The step of desorbing lithium ions from the precursor is the same as in Example 1, except that lithium ions are removed at 1.586 Li /
By mol desorption, a negative electrode active material represented by a composition formula of Li _1.0 Co _0.414 N was synthesized.

A test cell was prepared using this negative electrode active material . Except for the working electrode 6, it is the same as the first embodiment. The test cell was subjected to a charge / discharge test in a voltage range of 0.0 to 1.4 V and a current of 1 mA. This Li _1.0 Co _0.414 N is also
In the voltage range of 0.0 to 1.4 V, 29 mAh was obtained when the charge and discharge were repeatedly performed stably. Also, no rapid decrease in capacity due to charge / discharge was observed, and charge / discharge was repeated stably for 100 cycles or more. After the completion of the charge / discharge test, the test cell was disassembled, and the surface of the working electrode was observed by SEM. However, no deposition of lithium metal or growth of dendrites on the surface of the working electrode could be recognized. The working electrode was analyzed by an X-ray diffractometer, but no X-ray diffraction pattern of lithium metal was observed.

[0023]

Embodiment 3 In the step of forming the precursor of Embodiment 1, the mixture ratio of the nitrogen-hydrogen mixed gas atmosphere was changed to nitrogen (95%).
%)-Hydrogen (5%) instead of a mixed gas to synthesize a precursor. As a result of X-ray diffraction, the diffraction pattern was the same as that in FIG. 1. Only a diffraction pattern of Li _2.6 Co _0.4 N was obtained, and no impurity peak was observed. As a result of the composition analysis, the composition after firing was Li _2.590 Co
_0.410 N, and almost no lithium evaporation was observed. The step of desorbing lithium ions from the precursor is the same as in Example 1, except that lithium ions are removed from the precursor in the same manner as in Example 1.
59 Li / mol desorbed, with the composition formula Li _1.0 Co
A negative electrode active material represented by _0.41 N was synthesized.

A test cell was prepared using this negative electrode active material . Except for the working electrode 6, it is the same as the first embodiment. The test cell was subjected to a charge / discharge test in a voltage range of 0.0 to 1.4 V and a current of 1 mA. This Li _1.0 Co _0.41 N is also
A capacity of 31 mAh was obtained when charge and discharge were repeated stably in a voltage range of 0.0 to 1.4 V. Also, no rapid decrease in capacity due to charge / discharge was observed, and charge / discharge was repeated stably for 100 cycles or more. After the completion of the charge / discharge test, the test cell was disassembled, and the surface of the working electrode was observed by SEM. However, no deposition of lithium metal or growth of dendrites on the surface of the working electrode could be recognized. The working electrode was analyzed by an X-ray diffractometer, but no X-ray diffraction pattern of lithium metal was observed.

[0025]

Example 4 The process of forming the precursor is the same as that of Example 1. In the step of desorbing lithium ions from the precursor of Example 1, the composition was changed by changing the desorption amount to 1.0 Li / mol. Negative electrode active material represented by the formula Li _1.59 Co _0.41 N
Synthetic quality . FIG. 5 shows an X-ray diffraction pattern. The tube was Cukα, and the measurement was performed at a tube current of 100 mA and a tube voltage of 30 kV. Since the negative electrode active material having this composition was in the process of undergoing a phase change from crystalline to amorphous due to lithium elimination, a diffraction pattern having a small intensity and a wide half width was recognized.
As is apparent from FIG. 5, no diffraction peaks other than the negative electrode active material were observed in the range of 10 to 70 ° in 2θ,
No generation of lithium metal or other impurities was observed.

A test cell was prepared using this negative electrode active material . Except for the working electrode 6, it is the same as the first embodiment. This test cell was subjected to a charge / discharge test in a voltage range of 0.0 to 1.0 V and a current of 1 mA. This Li _1.59 Co _0.41 N is
A capacity of 21 mAh was obtained when charge and discharge were repeated stably in a voltage range of 0.0 to 1.0 V. Also, no rapid decrease in capacity due to charge / discharge was observed, and charge / discharge was repeated stably for 200 cycles or more. After the completion of the charge / discharge test, the test cell was disassembled, and the surface of the working electrode was observed by SEM. However, no deposition of lithium metal or growth of dendrites on the surface of the working electrode could be recognized. The working electrode was analyzed by an X-ray diffractometer, but no X-ray diffraction pattern of lithium metal was observed.

[0027]

Embodiment 5 The step of forming a precursor is the same as that of Embodiment 1. In the step of desorbing lithium ion from the precursor of Embodiment 1, the lithium ion is removed by using the above-mentioned electrochemical reaction. .59 Li / mol desorbed, composition formula Li
A negative electrode active material represented by _1.0 Co _0.41 N was synthesized. FIG. 6 shows an X-ray diffraction pattern. The tube was Cukα, and the measurement was performed at a tube current of 100 mA and a tube voltage of 30 kV.
Since this negative electrode active material undergoes a phase change from crystalline to amorphous due to lithium desorption, the diffraction pattern disappears. FIG.
As is clear from the above, no diffraction peak was observed in the range of 10 to 70 ° in 2θ, and no generation of lithium metal and other impurities was observed.

A test cell was prepared using the negative electrode active material . Except for the working electrode 6, it is the same as the first embodiment. The test cell was subjected to a charge / discharge test in a voltage range of 0.0 to 1.4 V and a current of 1 mA. This Li _1.0 Co _0.41 N is also
In the voltage range of 0.0 to 1.4 V, the capacity was 30 mAh when the charge and discharge were repeated stably. Also, no rapid decrease in capacity due to charge / discharge was observed, and charge / discharge was repeated stably for 100 cycles or more. After the completion of the charge / discharge test, the test cell was disassembled, and the surface of the working electrode was observed by SEM. However, no deposition of lithium metal or growth of dendrites on the surface of the working electrode could be recognized. The working electrode was analyzed by an X-ray diffractometer, but no X-ray diffraction pattern of lithium metal was observed.

[0029]

Example 6 A negative electrode active material was produced by changing the starting material of Example 1 from Co metal to Cu metal. First, the composition formula Li
_2.6 A precursor represented by Cu _0.4 N was prepared by using lithium nitride (Li ₃ N) and Cu metal as starting materials at a temperature of 650 ° C. for 8 hours using nitrogen (98%)-hydrogen (2 %) In a mixed gas atmosphere. FIG. 7 shows an X-ray diffraction pattern. The tube was Cukα, and the measurement was performed at a tube current of 100 mA and a tube voltage of 30 kV. As is clear from FIG.
Only the diffraction pattern of i _2.6 Cu _0.4 N is obtained, the peak of the impurity was observed. As a result of composition analysis, the composition after firing was Li _2.58 Cu _0.42 N, and almost no lithium was evaporated and dissipated.
Next, 1.58 Li / mol of lithium ions were desorbed from this precursor using the above-mentioned chemical reaction, and the composition formula Li
A negative electrode active material represented by _1.0 Cu _0.42 N was synthesized. FIG. 8 shows an X-ray diffraction pattern. The tube was Cukα, and the measurement was performed at a tube current of 100 mA and a tube voltage of 30 kV.
Since this negative electrode active material undergoes a phase change from crystalline to amorphous due to lithium desorption, the diffraction pattern disappears. FIG.
As is clear from the above, no diffraction peak was observed in the range of 10 to 70 ° in 2θ, and no generation of lithium metal and other impurities was observed.

A test cell was prepared using this negative electrode active material . Except for the working electrode 6, it is the same as the first embodiment. This test cell was subjected to a charge / discharge test in a voltage range of 0.0 to 1.0 V and a current of 1 mA. This Li _1.0 Cu _0.42 N is also
In the voltage range of 0.0 to 1.4 V, the capacity was 30 mAh when the charge and discharge were repeated stably. Also, no rapid decrease in capacity due to charge / discharge was observed, and charge / discharge was repeated stably for 100 cycles or more. After the completion of the charge / discharge test, the test cell was disassembled, and the surface of the working electrode was observed by SEM. However, no deposition of lithium metal or growth of dendrites on the surface of the working electrode could be recognized. The working electrode was analyzed by an X-ray diffractometer, but no X-ray diffraction pattern of lithium metal was observed.

[0031]

Comparative Example 1 In the step of forming the precursor of Example 1, the precursor was synthesized by changing the firing temperature to 480 ° C. The X-ray diffraction pattern is shown in FIG. In addition to the diffraction pattern of Li _2.6 Co _0.4 N, the starting material lithium nitride (Li
_{3 N)} or the peak of unidentifiable impurities were observed many. As in Example 1, lithium ions were eliminated from the precursor to synthesize a negative electrode active material .

A test cell was prepared using this negative electrode active material . Except for the working electrode 6, it is the same as the first embodiment. The test cell was subjected to a charge / discharge test in a voltage range of 0.0 to 1.4 V and a current of 1 mA. This Li _1.0 Co _0.4 N is _0.1 .
In the voltage range of 0 to 1.4 V, an initial capacity of 29 mAh was obtained, but the capacity rapidly decreased with charging and discharging, the cycle life was 20 cycles, and the cycle characteristics were significantly deteriorated.

[0033]

Comparative Example 2 In the step of forming the precursor of Example 1, the precursor was synthesized by changing the firing temperature to 830 ° C. As a result of X-ray diffraction, the diffraction pattern was the same as in FIG.
Only a diffraction pattern of _2.6 Co _0.4 N was obtained, and no impurity peak was observed. However, as a result of composition analysis, the composition after firing was Li _2.36 Co _0.64
N, and violent lithium evaporation was observed. As in Example 1, lithium ions were desorbed from the precursor,
A negative electrode active material was synthesized.

A test cell was prepared using this negative electrode active material . Except for the working electrode 6, it is the same as the first embodiment. The test cell was subjected to a charge / discharge test in a voltage range of 0.0 to 1.4 V and a current of 1 mA. This Li _1.0 Co _0.64 N is
In the voltage range of 0.0 to 1.4 V, the initial capacity is 29 mA.
However, the capacity decreased with charge and discharge, and thereafter, the charge and discharge were stably performed 200 times or more, but the stable capacity was 15 mAh.
And the capacity was significantly reduced.

[0035]

Comparative Example 3 The step of forming a precursor was the same as in Example 1. In the step of removing lithium ions from the precursor of Example 1, an attempt was made to remove lithium ions by acid treatment. Specifically, the acid is 1M hydrochloric acid (HC
l) A predetermined amount of the precursor was added thereto and stirred with an aqueous solution, but the precursor reacted violently with an acid, and the desired negative electrode active material could not be recovered.

[0036]

As described above, the composition formula Li
_{3-x-y M x N} ( where, M represents an element belonging to the transition metal, x is in the range of 0.1 to 0.5, y is 0.8
Negative electrode active substance represented by any) in the range of 1.9, the composition formula _{Li 3-x M x} N (where, M represents an element belonging to the transition metal, x is 0.1 to 0.5 A method for producing a negative electrode active material having excellent battery characteristics can be obtained by using a method that is manufactured through a step of forming a precursor represented by the following formula) and a step of desorbing lithium ions from the precursor. it can. In particular, by using Li metal or lithium nitride (Li ₃ N) and a transition metal or a transition metal nitride as starting materials, and firing in a nitrogen gas atmosphere or a nitrogen-hydrogen mixed gas atmosphere at a temperature range of 500 to 800 ° C. , High crystallinity, no impurities, small composition deviation,
It can be produced the precursor with good material properties. Further, a method for desorbing lithium ions from the precursor,
More using the chemical reaction or electrochemical reaction, structure
High quality negative electrode active without structural damage or surface deterioration (oxide film formation)
Materials can be manufactured. Moreover, by using the production method of the present invention, the electrode has a high-capacity charge / discharge region at an electrode potential of 1.5 V or less with respect to the lithium reference electrode, and can stably insert and desorb lithium ions. A negative electrode active material having a long cycle life can be obtained.

Therefore, the present invention provides a high energy density
In addition, there is an excellent effect that a negative electrode active material having a large charge / discharge capacity and a cycle life having battery characteristics can be provided.

[Brief description of the drawings]

FIG. 1 shows an X-ray diffraction pattern of a precursor according to Example 1.

FIG. 2 is a view showing an X-ray diffraction pattern of a negative electrode active material according to Example 1.

FIG. 3 is a sectional view of a test cell used in the present invention.

FIG. 4 is a view showing a third cycle charge / discharge curve of a test cell using a negative electrode active material according to Example 1 as a working electrode.

FIG. 5 is a view showing an X-ray diffraction pattern of a negative electrode active material according to Example 4.

FIG. 6 is a view showing an X-ray diffraction pattern of a negative electrode active material according to Example 5.

FIG. 7 is a view showing an X-ray diffraction pattern of a precursor according to Example 6.

FIG. 8 is a view showing an X-ray diffraction pattern of a negative electrode active material according to Example 6.

FIG. 9 is a view showing an X-ray diffraction pattern of a precursor according to Comparative Example 1.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Counter electrode case 2 Counter electrode 3 Non-aqueous electrolyte 4 Separator 5 Working electrode case 6 Working electrode 7 Current collector 8 Gasket

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Junichi Yamaki 1-6, Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (56) References JP-A-7-78609 (JP, A) Hei 7-320720 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 4/58 H01M 4/02-4/04 C01G 3/00 C01G 51/00 C01G 53/00 JICST File (JOIS)

Claims (4)

(57) [Claims] 1. A composition formula Li _3-xy M _x N (where M represents an element belonging to a transition metal, x is in the range of 0.1 to 0.5, and y is 0.8 to 1). The negative electrode active material represented by the composition formula Li _3-x M _x N (where M represents an element belonging to a transition metal, and x falls within a range of 0.1 to 0.5). A method for producing a negative electrode active material , comprising: a step of forming a precursor represented by the following formula: and a step of desorbing lithium ions from the precursor. 2. The method according to claim 1, wherein the negative electrode active material represented by the composition formula Li _3-xy M _x N is Li _3-xy Co _x N, Li
_3-xy Ni _x N or Li _3-xy Cu _x N
(Where x is in the range of 0.1 to 0.5 and y is 0.8
1.9). The method for producing a negative electrode active material according to claim 1, wherein 3. The precursor represented by the composition formula Li _3-x M _x N is prepared by using lithium metal or lithium nitride (Li ₃ N) and a transition metal or a transition metal nitride as starting materials, and 2. The method according to claim 1 , wherein the sintering is performed by baking in a nitrogen gas atmosphere or a nitrogen-hydrogen mixed gas atmosphere in a temperature range of ° C.
2. The method for producing a negative electrode active material according to any one of 2 . 4. The method according to claim 1, wherein a chemical reaction or an electrochemical reaction is used as a method for removing lithium ions from the precursor .
A method for producing a negative electrode active material .