JP2002075358A - Positive electrode material for lithium ion secondary battery and manufacturing method of the material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a new positive electrode material for a lithium ion battery having excellent battery characteristics. SOLUTION: The positive electrode material for lithium ion battery consists of a lithium-containing composite oxide expressed by LiMn1-yFeyO2, (0<y<0.5) substantially formed from a rhombic phase, and is manufactured through such processes that lithium compound, oxidizing agent, and alkali are added to and mixed with a solution containing manganese ions (II) and iron ions (III) and then the obtained mixture solution is subjected to a hydrothermal treatment at a temperature of 400 deg.C or below.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a positive electrode material for a lithium ion secondary battery and a method for producing the same.

[0002]

2. Description of the Related Art Lithium-ion secondary batteries have attracted attention as a secondary battery mounted on portable devices such as portable telephones and notebook personal computers because of their outstanding energy density. The application of lithium ion secondary batteries to large batteries such as electric vehicles and power load leveling systems is being studied in the future, and their importance is increasing more and more.

[0003] In a lithium ion secondary battery currently in practical use, a lithium cobalt oxide (LiC) is used as a positive electrode material.
Carbon materials such as graphite are used for the oO ₂ ) material and the negative electrode material, respectively, and an organic electrolyte is used as the electrolyte.
Among them, the cathode material is used to improve the battery performance such as the operating voltage of the battery (the difference between the oxidation-reduction potential of the transition metal in the cathode and that of the anode element) and the charge / discharge capacity (the amount of Li that can be removed and inserted from the cathode). It is a component that has a great influence.

[0004] However, the lithium cobalt oxide as the positive electrode material uses cobalt, which is a rare metal, and thus is one of the factors that hinder the cost reduction of the production of lithium ion secondary batteries. Therefore, lithium manganese oxide (L
The development of iMn ₂ O ₄ and LiMnO ₂ ) has attracted attention.

[0005] Among LiMn ₂ O ₄ is greater and the oxidation reduction potential of about 4V, is a material that has attracted the currently most attention may retrieve up to theoretically MnO ₂ composition than the chemical formula L
The i amount is 0.5, which is only half of 1.0 of LiMnO ₂ , and there is a limit in increasing its capacity.

On the other hand, the operating voltage of LiMnO ₂ is about 3 V
However, a higher capacity can be expected as compared with LiMn ₂ O ₄ . The low operating voltage of LiMnO _{2 has} a disadvantage in comparison with LiMn ₂ O ₄ , but does not cause a serious problem in an actual battery. This is because the decomposition of the organic electrolytic solution is less likely to occur than in the case of the 4 V system, which can contribute to the improvement of the safety of the battery. By the way, this L
Although iMnO ₂ has an orthorhombic phase which is a stable phase and a monoclinic phase which is a metastable phase, the orthorhombic phase is easier to synthesize.

[0007] In view of the above, various studies have been made on the synthesis of orthorhombic phase LiMnO ₂ , especially among lithium manganese oxides, as a positive electrode material for a high capacity lithium ion secondary battery. For example, Reference 1 (RJ
Gummow, DCLies, and MMThackeray, Material Rese
arch Bulletin, 28, (1993), pp. 1249-56.)
MnO ₂ and LiOH are used as starting materials, and calcined in an argon stream in the presence of carbon (reducing agent) to produce orthorhombic LiMnO ₂
Is described.

However, this method is not suitable for mass production on an industrial scale because the firing atmosphere needs to be reduced by using a reducing agent as described above.

[0009] For example, in Japanese Patent Application Laid-Open No. 6-349494, MnOOH or Mn (O
It is disclosed that low-crystalline orthorhombic LiMnO ₂ can be produced by subjecting H) ₂ to ion exchange and heat reaction in a solvent containing lithium ions at a temperature of 350 ° C. or lower.

[0010] However, this method requires a two-step process of an ion exchange process and a heating process. In particular, during the heating process, it is necessary to use a vacuum and an inert atmosphere in order to prevent the sample from being oxidized and to prevent the orthorhombic structure from being decomposed. It is a barrier. Therefore,
It is necessary to develop a synthesis process that does not require such atmosphere control, and the hydrothermal method has attracted attention as one of the synthesis processes.

[0011]

Regarding the hydrothermal method, the present inventors have already shown that orthorhombic LiMnO ₂ can be easily produced from MnOOH and LiOH at a temperature of 300 ° C. or less using the hydrothermal method. (Reference 2: M.Tabu
chi, K. Ado, C. Masquelier, I. Matsubara, H. Sakaebe,
H.Kageyama, H.Kobayashi, R.Kanno and O.Nakamura, S
olid State Ionics, 89, (1996), pp.53-63). Furthermore, the present inventors have already found a technique for producing orthorhombic LiMnO ₂ by using manganese oxide, manganese hydroxide, manganese carbonate, or the like as a starting material, and performing a hydrothermal treatment together with lithium hydroxide (Japanese Unexamined Patent Publication (Kokai) No. Heisei 9 (1994) -207). 11-13
No. 0438).

[0012] However, in these hydrothermal methods, although atmosphere control is not required, when different metals are contained in order to improve the characteristics of orthorhombic LiMnO ₂ (especially the charge / discharge characteristics as an electrode material), The manufacturing process becomes complicated. Therefore, the orthorhombic LiMnO containing the dissimilar metal
_It is considered difficult to reduce the manufacturing cost of ( ₂ ).

As described above, the orthorhombic LiMn containing the dissimilar metal is used.
A technique for producing O ₂ , that is, a material for a positive electrode of a lithium ion battery having excellent charge / discharge characteristics on an industrial scale has not yet been developed.

Accordingly, it is a main object of the present invention to provide a method for producing a novel lithium ion battery cathode material which provides battery characteristics equal to or better than conventional orthorhombic phase LiMnO ₂ on an industrial scale. is there.

[0015]

Means for Solving the Problems The present inventor has made intensive studies in view of the above-mentioned problems of the prior art, and as a result, it has been found that the above object can be achieved by producing iron-containing orthorhombic LiMnO ₂ by a specific method. And completed the present invention.

That is, the present invention relates to the following positive electrode material for a lithium ion secondary battery and a method for producing the same.

1. Composition formula LiMn _1-y Fe _y O ₂ (however,
0 <y <0.5) A positive electrode material for a lithium ion secondary battery, which is a lithium-containing composite oxide substantially composed of an orthorhombic phase.

2. After adding a lithium compound, an oxidizing agent and an alkali to a solution containing manganese ions (II) and iron ions (III), the resulting mixed solution is subjected to hydrothermal treatment at 400 ° C. or lower to obtain a composition formula LiMn _1-y Fe _y O ₂
(However, a method for producing a positive electrode material for a lithium ion secondary battery, characterized by obtaining a lithium-containing composite oxide represented by 0 <y <0.5).

[0019]

DETAILED DESCRIPTION OF THE INVENTION 1. Lithium ion secondary battery positive electrode
Material for Lithium Ion Secondary Battery The material for a positive electrode of a lithium ion secondary battery of the present invention is a lithium-containing composite oxide represented by the composition formula LiMn _1-y Fe _y O ₂ (where 0 <y <0.5), and substantially Is composed of an orthorhombic phase. That is, the composite oxide is obtained by substituting a part of Mn of LiMnO ₂ with Fe. By substituting with Fe, the charge / discharge characteristics as a positive electrode material can be improved and the cost of the material can be reduced.

The value of y is generally 0 <y <0.5, preferably 0.01 ≦ y ≦ 0.2. y is 0.
It can be set appropriately within a range of less than 5 according to desired electrical characteristics and the like. When the value of y is 0.5 or more, the LiFeO ₂ phase having no electrochemical activity becomes the main generated phase, which is not preferable.

The crystal form of the above-mentioned composite oxide is usually substantially composed of an orthorhombic phase. However, other crystalline phases or amorphous portions may be included as long as the effects of the present invention are not impaired.

The material of the present invention can be suitably used for a positive electrode of a lithium ion secondary battery. In addition to using the positive electrode material of the present invention as a positive electrode material (positive electrode active material), a lithium ion secondary battery can be manufactured by adopting known components of a lithium ion secondary battery as they are. For example, a material in which the material for a positive electrode of the present invention is fixed to a current collector is used as a positive electrode, metallic lithium is used as a negative electrode, and a lithium compound such as lithium perchlorate is used as an electrolytic solution in an organic solvent (ethylene carbonate, dimethyl carbonate, etc.). The lithium ion secondary battery can be assembled by using a material which has been dissolved in a lithium ion battery and using a known separator or the like. 2. Method for producing positive electrode material for lithium ion secondary battery The method for producing the positive electrode material for lithium ion secondary battery according to the present invention comprises manganese ion (II) and iron ion (III).
After adding a lithium compound, an oxidizing agent and an alkali to the solution containing, the resulting mixed solution is subjected to hydrothermal treatment at 400 ° C. or lower to obtain a composition formula of LiMn _1-y Fe _y O ₂ (however,
It is characterized by obtaining a lithium-containing composite oxide represented by 0 <y <0.5).

Manganese ion (II) and iron ion (II
As the solution containing I), an aqueous solution containing both ions can be suitably used. Such an aqueous solution can be prepared, for example, by dissolving a manganese compound and an iron compound in water.

The manganese compound and the iron compound are not particularly limited as long as they can serve as sources of manganese ions (II) and iron ions (III), respectively.

Examples of the manganese compound include water-soluble salts such as manganese nitrate, manganese chloride and manganese sulfate; hydroxides such as manganese hydroxide; oxides such as manganese oxide; and ammonium salts containing manganese (sulfuric acid). Manganese ammonium salt) and the like. These can be used alone or in combination of two or more.

Examples of the iron compound include water-soluble salts of iron such as iron nitrate, iron chloride and iron sulfate (nitrates, sulfates and chlorides), hydroxides such as iron hydroxide and oxides such as iron oxide. And ammonium salts containing iron (ammonium iron sulfate). These can be used alone or in combination of two or more.

These manganese compounds and iron compounds may be hydrates or anhydrides. In addition,
When a compound that is hardly soluble in water such as iron oxide and manganese oxide is used, an aqueous solution may be prepared by dissolving in water using a suitable acid such as hydrochloric acid or nitric acid.

The concentration of manganese ion and iron ion in the solution may be appropriately set according to the desired composition and the like, but is usually 0.01 to 2 mol / mol in terms of the total concentration of both (in terms of anhydride).
It may be about liter, more preferably 0.1 to 0.5 mol / liter. The proportions of manganese ions and iron ions may be appropriately set according to the substitution ratio of iron in the obtained composite oxide.

Next, a lithium compound, an oxidizing agent and an alkali are added to the above solution. The order in which these are added is not particularly limited, and they may be added in any order, or may be added simultaneously.

The lithium compound is not particularly limited, and examples thereof include lithium hydroxide (which may be either anhydrous or hydrate), lithium chloride, lithium nitrate, lithium carbonate and the like. These can be used alone or in combination of two or more. Among these lithium compounds, lithium hydroxide is preferable.

The amount of the lithium compound to be used is not particularly limited.
The concentration may be about 5 mol / l, more preferably 0.5 to 2 mol / l.

As the oxidizing agent, those known as known oxidizing agents can be used. For example, potassium chlorate,
Examples include sodium chlorate, hydrogen peroxide and the like. These can be used alone or in combination of two or more. Of these oxidants, potassium chlorate is preferred.

The amount of the oxidizing agent can be appropriately changed depending on the kind of the oxidizing agent to be used and the like, but is usually about 0.1 to 5 mol / l, preferably 0.5 to 2 mol / l.

As the alkali, known ones can be used. For example, sodium hydroxide, potassium hydroxide, ammonia and the like can be mentioned. These can be used alone or in combination of two or more. Of these alkalis, potassium hydroxide is preferred.

The amount of alkali used may be such that the above solution becomes completely alkaline, and is usually 0.5 to 50.
It may be about mol / l, preferably 1 to 20 mol / l.

After adding a lithium compound, an oxidizing agent and an alkali to the above solution, the solution is subjected to hydrothermal treatment at 400 ° C. or lower to obtain a composition formula LiMn _1-y Fe _y O ₂ (where 0 <y <
0.5) is obtained.

The temperature of the hydrothermal treatment may be usually 400 ° C. or lower, preferably about 100 to 400 ° C., more preferably 100 to 300 ° C., and most preferably 150 to 25 ° C.
The temperature may be set to 0 ° C. The duration of the hydrothermal treatment may be appropriately set according to the hydrothermal treatment temperature or the like. For example, when the hydrothermal treatment temperature is 100 to 300 ° C., it is usually about 0.1 to 72 hours, and when the hydrothermal treatment temperature is 150 to 250 ° C., it is usually about 1 to 60 hours. The pressure of the hydrothermal treatment may be performed under a saturated steam pressure.

The method of hydrothermal treatment may be such that a known hydrothermal reactor (for example, a commercially available autoclave or the like) is used, and the above solution is loaded into the apparatus together with the container.

After the completion of the hydrothermal reaction, the reaction product may be washed with water if necessary, and the reaction product may be recovered by a known solid-liquid separation method such as filtration. After the collection, drying may be performed as needed. Drying may be either natural drying or heat drying, and in the case of heat drying, the drying temperature is usually 60 to 1
The temperature may be set to about 00 ° C.

[0040]

The positive electrode material according to the present invention has a structure in which a part of Mn of LiMnO ₂ is replaced by inexpensive Fe, and at the same time, has the same or better battery characteristics as the case where conventional orthorhombic LiMnO ₂ is used. Therefore, it is possible to contribute to the cost reduction of the positive electrode material and eventually the lithium ion secondary battery.

The production method of the present invention does not require atmosphere control as in the conventional method, and can easily synthesize iron-containing LiMnO ₂ by a hydrothermal method at a relatively low temperature of 400 ° C. or less, so that the production method is low in cost. Thus, a positive electrode material can be provided.

[0042]

The following examples are provided to further clarify the features of the present invention. The scope of the present invention is not limited to the contents of these examples.

The crystal phases of the samples obtained in the examples were identified by X-ray diffraction analysis. Valence state analysis of iron was measured by ⁵⁷ Fe Mossbauer spectroscopy. Valence state analysis of manganese was measured by an X-ray absorption spectrum at the MnK absorption edge. Composition analysis was performed by inductively coupled plasma (ICP) and atomic absorption spectrometry.

Example 1 Synthesis of LiMnO ₂ containing 1% iron (LiFe _0.01 Mn _0.99 O ₂ ) Iron nitrate (II) was placed in a polytetrafluoroethylene beaker.
I) 0.101 g of 9-hydrate and 7.104 g of manganese (II) nitrate hexahydrate (Fe: Mn molar ratio 1:99) were added,
100 ml of distilled water was added and stirred, and completely dissolved. To this mixed aqueous solution, 10 g of potassium chlorate, 20 g of lithium hydroxide and 70 g of potassium hydroxide were added, and a precipitate was obtained by sufficiently stirring. The beaker was placed in a hydrothermal reactor (autoclave) at 220 ° C. for 1 hour.
Hydrothermal treatment for hours. After the completion of the hydrothermal treatment, the hydrothermal reactor is cooled to around room temperature, the container is taken out of the furnace, and the generated precipitate is washed with distilled water to remove excess lithium hydroxide and other salts. After removal, the mixture was filtered and dried to obtain a powdery product.

Next, X-ray diffraction analysis of this powdery product was performed. The result is shown in FIG. FIG. 1A shows an X-ray diffraction pattern of an undoped LiMnO ₂ sample synthesized in the above method without adding iron nitrate (that is, the sample obtained in Comparative Example 1). All peaks are in reference 4 (R. Hoppe, G. Brachtel, and M. Jansen, Z. Ano
rg. Allg. Chem., 417, (1975), 1-10.), a unit cell (space group: Pmn) of orthorhombic LiMnO _2.
m, a = 2.805 °, b = 5.757 °, c = 4.
572 °). Table 1 shows the results of the chemical analysis.

[0046]

[Table 1]

The lattice constant calculated from each peak in the powdery product (a = 2.80822 (13) Å, b =
5.7457 (3) Å, c = 4.56991 (17)
Å) is different from the original one (see FIG. 2), 1.1% iron is contained as charged (chemical analysis in Table 1), L
Since the i / (Fe + Mn) value is approximately 1, the powder product is LiMnO ₂ containing 1% iron (LiFe _0.01 Mn _0.99
O ₂ ).

Example 2 Synthesis of LiMnO ₂ containing 3% iron (LiFe _0.03 Mn _0.97 O ₂ ) In a polytetrafluoroethylene beaker, 0.303 g of iron (III) nitrate 9 hydrate and manganese (II) nitrate 6 were added.
6.960 g of hydrate (Fe: Mn molar ratio of 3:97) was added, 100 ml of distilled water was added, and the mixture was stirred and completely dissolved. To this mixed aqueous solution, 10 g of potassium chlorate, 20 g of lithium hydroxide and 70 g of potassium hydroxide were added, and a precipitate was obtained by sufficiently stirring. This beaker was left in a hydrothermal reactor (autoclave) and subjected to hydrothermal treatment at 220 ° C. for 1 hour. After the completion of the hydrothermal treatment, the reactor was cooled to around room temperature, the container was taken out of the furnace, and the generated precipitate was washed with distilled water to remove excess lithium hydroxide and other salts. Thereafter, the resultant was filtered and dried to obtain a powdery product. The X-ray diffraction pattern of this powdery product is shown in FIG. All peaks are listed in reference 4 (R. Hoppe, G. Brachtel, and M. Jansen,
Z. Anorg. Allg. Chem., 417, (1975), 1-10.), An orthorhombic LiMnO ₂ unit cell (space group:
Pmnm, a = 2.805 °, b = 5.757 °,
c = 4.572 °). Table 1 shows the results of the chemical analysis.

A lattice constant calculated from each peak of the powdery product (a = 2.8133 (15) Å, b = 5.743)
8 (12) Å, c = 4.5696 (8) Å) is different from the original one (LiMnO ₂ ) (see FIG. 2), and iron is contained 2.8% substantially as charged (see Table ₂ ). 1), and the Li / (Fe + Mn) value is approximately 1, so that the powdery product is LiMnO ₂ containing 3% iron (LiFe
_0.03 Mn _0.97 O ₂ ).

Example 3 Synthesis of LiMnO ₂ containing 5% iron (LiFe _0.05 Mn _0.95 O ₂ ) Iron nitrate (II) was placed in a polytetrafluoroethylene beaker.
I) 0.505 g of 9-hydrate and 6.820 g of manganese (II) nitrate hexahydrate (Fe: Mn molar ratio of 5:95) were added,
100 ml of distilled water was added, and the mixture was stirred and completely dissolved. To this mixed aqueous solution, 10 g of potassium chlorate, 20 g of lithium hydroxide and 70 g of potassium hydroxide were added, and a precipitate was obtained by sufficiently stirring. The beaker was placed in a hydrothermal reactor (autoclave) at 220 ° C. for 1 hour.
Hydrothermal treatment for hours. After the completion of the hydrothermal treatment, the reactor was cooled to around room temperature, the vessel was taken out of the furnace, and the generated precipitate was washed with distilled water to remove excess lithium hydroxide and other salts. Thereafter, the resultant was filtered and dried to obtain a powdery product. X of this powdery product
The line diffraction pattern is shown in FIG. Table 1 shows the results of the chemical analysis.

All peaks are in reference 4 (R. Hoppe,
G. Brachtel, and M. Jansen, Z. Anorg. Allg. Chem., 4
17, (1975), 1-10.)
Unit cell of MnO 2 (space group: Pmnm, a = 2.80
5 °, b = 5.757 °, c = 4.572 °) and could be indexed. Lattice constant calculated from each peak of the powdery product (a = 2.8158 (6) Å, b =
5.7423 (12) Å, c = 4.5589 (9) Å)
Is different from the original one (LiMnO ₂ ) (see FIG. 2), that iron is contained at 5.1% according to the charged amount (chemical analysis in Table 1), and the Li / (Fe + Mn) value is almost 1
Therefore, the powdery product is LiMnO containing 5% iron.
₂ (LiFe _0.05 Mn _0.95 O ₂ ).

Example 4 LiMnO ₂ containing 10% iron (LiFe _0.10 Mn _0.90 O ₂ )
Synthesis of iron nitrate (II) in a polytetrafluoroethylene beaker
I) 1.01 g of 9-hydrate and 6.46 g of manganese (II) nitrate hexahydrate (10:90 molar ratio of Fe: Mn) were added, and 100 ml of distilled water was added, followed by stirring to completely dissolve. .
To this mixed aqueous solution, 10 g of potassium chlorate, 20 g of lithium hydroxide, and 70 g of potassium hydroxide were added, and sufficiently stirred to obtain a precipitate. This beaker was left in a hydrothermal reactor (autoclave) and subjected to hydrothermal treatment at 220 ° C. for 1 hour. After the completion of the hydrothermal treatment, the reactor was cooled to around room temperature, the container was taken out of the furnace, and the generated precipitate was washed with distilled water to remove excess lithium hydroxide and other salts. Thereafter, the resultant was filtered and dried to obtain a powdery product. The X-ray diffraction pattern of this powdery product is shown in FIG. Table 1 shows the results of the chemical analysis.

All peaks are in reference 4 (R. Hoppe,
G. Brachtel, and M. Jansen, Z. Anorg. Allg. Chem., 4
17, (1975), 1-10.)
MnO _TwoUnit cell (space group: Pmnm, a = 2.805)
Å, b = 5.757Å, c = 4.572Å) with index
I was able to kill. Calculated from each peak of powdered product
Lattice constant (a = 2.8285 (6)}, b = 5.
7577 (13) Å, c = 4.5426 (8) Å)
(LiMnO_Two) (See Figure 2), iron
Is contained as 10.1% almost according to the charged amount (Table 1
Chemical analysis), Li / (Fe + Mn) value is almost 1.
From the above, the powder product is LiMnO containing 10% iron._Two(L
ife_0.10Mn_0.90O_Two).

Comparative Example 1 Synthesis of undoped LiMnO _{2 In} a polytetrafluoroethylene beaker, 7.18 g of manganese (II) nitrate hexahydrate was placed, and 100 ml of distilled water was added.
The mixture was added and stirred to dissolve completely. To this mixed aqueous solution, 10 g of potassium chlorate, 20 g of lithium hydroxide and 70 g of potassium hydroxide were added, and sufficiently stirred to obtain a precipitate. This beaker was left in a hydrothermal reactor (autoclave) and subjected to hydrothermal treatment at 220 ° C. for 1 hour. After the completion of the hydrothermal treatment, the reactor was cooled to around room temperature, the container was taken out of the furnace, and the generated precipitate was washed with distilled water to remove excess lithium hydroxide and other salts. Thereafter, the resultant was filtered and dried to obtain a powdery product. The X-ray diffraction pattern of this powdery product is shown in FIG.
Shown in Table 1 shows the results of the chemical analysis.

All peaks are in reference 4 (R. Hoppe,
G. Brachtel, and M. Jansen, Z. Anorg. Allg. Chem., 4
17, (1975), 1-10.)
MnO _TwoUnit cell (space group: Pmnm, a = 2.80)
5Å, b = 5.757Å, c = 4.572Å)
Could be numbered. From each peak of powdered product
Calculated lattice constant (a = 2.80346 (6)), b
= 5.734304 (14) Å, c = 4.56889
(8) ②) was close to the above reported value. Chemical analysis (Table 1)
The Li / Mn value is approximately 1
The product is undoped LiMnO_TwoWas confirmed.

Test Example 1 In order to confirm the valence state of iron in the sample, 3% and 10%
To% Fe-LiMnO ₂ samples, ⁵⁷ Fe at room temperature
The Mössbauer spectroscopy was measured. The result is shown in FIG.
Shown in The obtained spectrum is a doublet roughly split into two, indicating that this sample is a paramagnetic substance at room temperature. Further, since the doublet was asymmetric, fitting using two or three doublet components revealed that the isotope shift (IS) value and the quadrupole splitting (QS) value of each component were different. Table 2 shows the parameters of these components.

[0057]

[Table 2]

The IS value of both components is +0.3 to 0.4 mm /
s, and a high spin iron trivalent compound (L
iFeO ₂ , α-NaFeO ₂ , 5% iron-containing LiCoO ₂
(Reference 5: M. Tabuchi, K. Ado, H. Kobayashi, H. Saka
ebe, H. Kageyama, C. Masquelier, M. Yonemura, A. Hiran
o and R. Kanno, J. Mater. Chem., 9, (1999), 199-20
It is close to the IS value of 4.)). From this, it was found that the iron in this sample maintained a high spin trivalent state, which agrees with the expectation from the composition formula (LiFe _x Mn _{1 -x} O ₂ ).

Test Example 2 To examine the valence state of manganese in the sample, 10%
X-ray absorption spectrum measurement at the MnK absorption edge was performed on the iron-containing LiMnO ₂ sample. FIG. 4 shows the results. The orthorhombic LiMn used in Comparative Example 1 as a standard sample
O ₂ (high spin trivalent manganese compound) and monoclinic Li ₂
MnO ₃ (tetravalent manganese compound) was used. Since the resulting spectrum substantially overlapping the spectra of orthorhombic LiMnO _2, Mn is orthorhombic in the iron-containing LiMnO ₂ LiM
Like nO _2, it can be interpreted as maintaining a high spin trivalent state. This means that the iron-containing LiMnO ₂ sample
It is consistent with that has a composition of _{Fe x Mn 1-x O 2} .

Test Example 3 Each of the samples obtained in Examples and Comparative Examples was used as a positive electrode, metallic lithium was used as a negative electrode, and lithium perchlorate was used as an electrolytic solution in a mixed solvent of ethylene carbonate and dimethyl carbonate (volume ratio 1: 1). Lithium ion secondary battery (coin type) using a 1 mol / liter solution
Was prepared. Porous polypropylene was used as a separator.

The charge / discharge characteristics of each battery were determined as (2.3 to 4.3).
V, current 0.15 mA). The results are shown in Table 3 and FIGS. 5 (a) to 5 (e).

[0062]

[Table 3]

As is clear from the results of Table 3 or FIGS. 5B to 5E, the iron-containing LiMnO ₂ has a flat potential of about 3.5 V, and an initial charge capacity of 124 to 176 mAh / g. It can be seen that it has an initial discharge capacity of 59 to 112 mAh / g (corresponding to 47 to 64% of the initial charge capacity (see Table 3)).

The iron-containing LiMnO ₂ is the same as the initial charge / discharge capacity of the orthorhombic LiMnO ₂ containing no iron (FIG. 5A,
It can be seen that the capacity and reversibility can be improved by adding iron (1 to 10%) as compared to 134 mAh / g during charging and 43 mAh / g during discharging, which corresponds to 32% during charging.

As described above, according to the present invention, it is possible to provide an iron-containing lithium manganese oxide for a positive electrode material of a lithium ion secondary battery.

[Brief description of the drawings]

FIG. 1 is a diagram showing an X-ray diffraction pattern of orthorhombic LiMnO ₂ and iron-containing LiMnO ₂ obtained in the present invention.

FIG. 2 is a graph showing the iron content dependence of the lattice constant of orthorhombic unit cells obtained from an XRD pattern.

FIG. 3 LiMnO ₂ containing 3% iron and Li containing 10% iron
Is a diagram showing the ⁵⁷ Fe Mesubauwa spectrum of MnO _2. Each point indicates an actually measured value, a solid line indicates a calculated value, and a broken line indicates each doublet component.

FIG. 4 shows an X-ray absorption spectrum (black square) at the MnK absorption edge of LiMnO ₂ containing 10% iron and orthorhombic Li
MnO _2, a diagram illustrating a comparison between the monoclinic Li ₂ MnO ₃ (both solid line).

FIG. 5 is a diagram showing initial charge / discharge characteristics of a coin-type lithium battery in which undoped LiMnO ₂ and iron-containing LiMnO ₂ are used as a positive electrode and lithium metal is used as a negative electrode. The upward curve corresponds to the charge curve, and the downward curve corresponds to the discharge curve.
The potential range is 2.3 to 4.3 V and the current is 0.15 mA.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Sakabe Hikasato 1-3-131 Midorioka, Ikeda-shi, Osaka Inside the Industrial Technology Research Institute Osaka Industrial Research Institute (72) Inventor Hiroyuki Kageyama 1 Midorioka, Ikeda-shi, Osaka No.8-31 F-term in Osaka Institute of Technology (reference) 4G002 AA06 AB02 AE05 5H050 AA19 BA17 CA09 FA19 GA02 GA10 GA15 GA27 HA02 HA14

Claims (5)

[Claims] A composition formula LiMn _1-y Fe _y O ₂ (where 0 <
a lithium-containing composite oxide represented by the formula y <0.5), which is substantially composed of an orthorhombic phase; 2. Manganese ion (II) and iron ion (II)
After adding and mixing a lithium compound, an oxidizing agent and an alkali to the solution containing I), the resulting mixed solution is subjected to hydrothermal treatment at 400 ° C. or lower to obtain a composition formula LiMn _1-y Fe _y O
_{2 A} method for producing a positive electrode material for a lithium ion secondary battery, comprising obtaining a lithium-containing composite oxide represented by the following formula (where 0 <y <0.5). 3. The method according to claim 2, wherein the hydrothermal treatment is performed in a temperature range of 100 to 400 ° C. 4. The method according to claim 2, wherein the oxidizing agent is potassium chlorate.
Or the production method according to 3. 5. The method according to claim 2, wherein the alkali is potassium hydroxide.