JP5120919B2 - Active material for lithium battery, method for producing the same, and lithium battery using the active material - Google Patents

Description

  The present invention relates to an active material for a lithium battery, a method for producing the same, and a lithium battery using the active material as a constituent member of an electrode.

  Currently, in Japan, many manganese oxides are used as electrode materials in portable game machines, alkaline batteries for cameras, lithium batteries, or lithium ion batteries mounted on portable electronic devices such as mobile phones and laptop computers. It is used as In the future, in addition to the demand for portable electronic devices so far, the importance of batteries as an emergency backup power source and distributed power source is increasing.

An important point in application to such a battery is the safety of the battery at the time of discharging or charging. For example, spinel type lithium manganese oxide (LiMn ₂ O ₄ ) applied to a lithium ion secondary battery. It is well known that, as compared with other electrode materials (for example, lithium cobalt oxide), the main component is inexpensive manganese and the safety in the charged state is remarkably excellent.

  However, due to the unstable crystal structure, when the end-of-discharge voltage is lowered to about 2 V and the charge / discharge cycle is repeated, the capacity decreases rapidly, and the manganese electrolyte at 50 ° C. or higher The use of this material has not progressed as expected as it also has the problem of significant property degradation due to dissolution.

Up to now, substance development has been developed for alkali manganese oxide systems assuming application to such battery materials. For example, for sodium manganese oxides, Na _0.20 MnO ₂ , Na _0.40 MnO ₂ , Na _0.44 MnO ₂ , Na _0.70 MnO ₂ , NaMnO ₂ are known (eg, non- Neither is used as an electrode material.
J. et al. P. Parant, R.A. Olazcuaga, M .; Devalette, C.I. Fouassier, P.A. Hagenmuller, J. et al. Solid State Chem. , 3, 1-11 (1971)

On the other hand, it has already been proposed that alkali manganese composite oxides NaMn ₂ O ₄ and LiMn ₂ O ₄ having a calcium ferrite CaFe ₂ O ₄ type structure can be produced by a high-temperature high-pressure synthesis method as a feature of the crystal structure. Yes. (See Patent Document 1, Non-Patent Documents 2 and 3)
Japanese Patent Application No. 2005-307387 J. et al. Akimoto, J. et al. Awaka, N .; Kijima, Y. et al. Takahashi, Y .; Maruta, K.M. Tokiwa, T .; Watanabe, J. et al. Solid State Chem. , 179, 169-174 (2006) K. Yamaura, Q .; Huang, L.H. Zhang, K .; Takada, Y .; Baba, T.A. Nagai, Y .; Matsui, K .; Kosuda, E .; Takayama-Muromachi, J. et al. Am. Chem. Soc. , 128, 9448-9456 (2006)

Since LiMn ₂ O ₄ having this calcium ferrite CaFe ₂ O ₄ type structure has a one-dimensional tunnel structure occupied by lithium ions as shown in FIG. 1, it has a good conduction path in the crystal structure of lithium ions. In addition, it was considered that the elimination and insertion reaction of lithium ions was possible by the trivalent to tetravalent oxidation-reduction reaction of manganese forming the skeleton structure. Further, since it is predicted that the skeletal structure has high stability against the lithium ion desorption / insertion reaction, a manganese oxide having this crystal structure is promising from the viewpoint of application to the lithium battery. Material.

However, since the known calcium ferrite type LiMn ₂ O ₄ hardly causes a lithium insertion reaction and the amount of lithium that can be inserted is 0.1 or less per chemical formula, it is not suitable for use as a battery material. (See Non-Patent Document 3)

  Therefore, the present invention solves the above-mentioned problems as described above, and has a safer and superior battery characteristic, which has an inexpensive manganese oxide as a main component and a calcium ferrite structure as a basic structure. An object is to provide an active material, a method for producing the same, and a lithium battery using the active material as a constituent member of an electrode.

As a result of intensive studies, the present inventor has obtained a Li _x Mn ₂ O ₄ (0) that has a calcium ferrite type basic structure, has a long periodicity in the a-axis direction, and introduces lithium site defects that facilitate lithium diffusion. .5 ≦ x ≦ 0.9) has been found to have good charge / discharge characteristics as an active material for lithium batteries, and the present invention has been completed.

That is, the present invention employs the configurations 1 to 5 shown below.
1. Li _x Mn ₂ O ₄ (composition range: 0.5 ≦ x ≦ 0.9) is expressed by a lithium-deficient chemical composition formula, and has an orthorhombic calcium ferrite structure as a crystal structure and is long in the a-axis direction. An active material for a lithium battery, comprising a polycrystal having periodicity.
2. Of the crystal lattice of the orthorhombic calcium ferrite type structure, which is expressed by the chemical composition formula of lithium deficiency type Li _x Mn ₂ O ₄ (composition range: 0.5 ≦ x ≦ 0.9), a An active material for a lithium battery, characterized by comprising a polycrystalline body having an axial length in the range of 0.871 nm to 0.882 nm and having a long periodicity in the a-axis direction.
3. 3. The method for producing an active material for a lithium battery according to 1 or 2, wherein a mixture containing a lithium compound and a manganese compound is heated under a high temperature of 1150 to 1250 ° C. and a high pressure of 10,000 to 100,000 atm. .
4). A mixture containing a sodium compound and a manganese compound is heated under a high temperature of 1150 to 1250 ° C. and a high pressure of 10,000 to 100,000 atmospheres, and the resulting sodium compound is subjected to an ion exchange treatment, whereby sodium is converted into lithium. The method for producing an active material for a lithium battery according to claim 1, wherein the material is exchanged.
5). A lithium battery comprising two electrodes used as a positive electrode and a negative electrode and an electrolyte, wherein the lithium battery active material according to claim 1 or 2 is used as a material constituting the electrode.
In the present invention, “having long periodicity in the a-axis direction” means a characteristic of a crystal structure in which a large crystal structure unit of the basic structure is required due to disorder of atomic arrangement or the like. This feature is observed in a reciprocal lattice photograph such as electron beam diffraction as a weak superlattice reflection in which the basic a-axis length should be tripled or quadrupled, or a streak line indicating a lattice mismatch structure.

According to the present invention, there is provided a lithium-deficient Li _x Mn ₂ O ₄ lithium battery active material having a calcium ferrite type structure as a basic structure and having a long periodicity in the a-axis direction and having high safety and excellent charge / discharge characteristics. Manufacturable. And it became possible to implement | achieve the lithium battery which has the outstanding characteristic by using this active material as an electrode material.

The active material for a lithium battery of the present invention has a calcium ferrite type basic structure, and Li _x Mn ₂ O ₄ (0.5 ≦ x ≦ 0.9) into which lithium site defects that facilitate lithium diffusion are introduced. It is the material characterized by having a chemical composition.
The preferred crystal structure of Li _x Mn ₂ O ₄ is characterized in that, among the orthorhombic lattice constants, the a-axis length is in the range of 0.871 nm to 0.882 nm and has a long periodicity. And
The Li _x Mn ₂ O ₄ active material of the present invention is a mixture containing a lithium compound and a manganese compound mixed so as to be lithium deficient under a high temperature of 800 to 1400 ° C. and a high pressure of 10,000 to 100,000 atmospheres. It can be manufactured by heating. In addition, a mixture containing a sodium compound and a manganese compound is heated under a high temperature of 800 to 1400 ° C. and a high pressure of 10,000 to 100,000 atmospheres, and the produced sodium compound NaMn ₂ O ₄ is subjected to an ion exchange treatment. Can also be produced by exchanging sodium for lithium.
In particular, as a condition for synthesizing a material having a lithium periodic defect and having a long period, the synthesis temperature is preferably a high temperature of 1150 to 1250 ° C. When the synthesis temperature is lower than 1150 ° C., lithium deficiency is difficult to be introduced, and in this case, a known LiMn ₂ O ₄ having no long periodicity is synthesized.

  A lithium battery using an electrode containing an active material for a lithium battery of the present invention as a constituent member is a battery that has a high capacity and is capable of a reversible lithium insertion / extraction reaction and can be expected to have high reliability. .

Hereafter, the manufacturing method of the active material for lithium batteries of this invention is demonstrated in more detail.
(Synthesis of Li _x Mn ₂ O ₄ active material by high-pressure synthesis method)
Of the present invention, the Li _x Mn ₂ O ₄ active material is produced by firing a mixture of at least one of lithium and a lithium compound and at least one of manganese and a manganese compound under high temperature and high pressure conditions. Can do.

As the lithium raw material, at least one of lithium (metallic lithium) and a lithium compound is used. The lithium compound is not particularly limited as long as it contains lithium. For example, oxides such as Li ₂ O and Li ₂ O ₂ , salts such as Li ₂ CO ₃ and LiNO ₃ , hydroxides such as LiOH, and the like Is mentioned. Among these, the oxide Li ₂ O is particularly preferable.

As the manganese raw material, at least one of manganese (metallic manganese) and a manganese compound is used. The manganese compound is not particularly limited as long as it contains manganese. For example, oxides such as Mn ₃ O ₄ , Mn ₂ O ₃ and MnO ₂ , salts such as MnCO ₃ and MnCl ₂ , Mn (OH) ₂ And hydroxides such as MnOOH and the like. Among these, Mn ₂ O ₃ , Mn ₃ O ₄ , MnO _{2 and the} like are particularly preferable.

First, a mixture containing these is prepared. The mixing ratio of the lithium raw material and the manganese raw material is preferably such that the calcium ferrite type structure is generated and the lithium site is lost. Specifically, the chemical composition formula of Li _x Mn ₂ O ₄ may be such that x is 0.9 or less. For example, mixing may be performed so that the lithium amount x is about 0.5 to 0.9, preferably 0.6 to 0.8.

  The mixing method is not particularly limited as long as they can be mixed uniformly, and may be mixed using a known mixer such as a mixer.

  The mixture is then fired under high temperature and high pressure conditions. The firing temperature can be appropriately set according to the composition of the mixture, but is usually about 800 to 1400 ° C, preferably 1150 to 1250 ° C. The firing pressure may be 10,000 to 100,000 atmospheres, preferably 30,000 to 80,000 atmospheres, more preferably 40,000 to 50,000 atmospheres. The firing time can be appropriately changed according to the firing temperature and the like. For example, when the firing temperature is 1150 to 1250 ° C., it is preferably 1 to 10 hours. Although the cooling method is not particularly limited, it may be naturally cooled (rapid cooling) or gradually cooled.

  After firing, the fired product may be pulverized by a known method as necessary.

(Synthesis of Li _x Mn ₂ O ₄ active material by ion exchange synthesis method)
Of the present invention, the Li _x Mn ₂ O ₄ active material can also be produced by a method in which sodium is ion-exchanged with lithium using NaMn ₂ O ₄ produced by a high-pressure synthesis method as a starting material. In general, in such an ion exchange synthesis method, it is known that sodium remains depending on the conditions of the exchange reaction. That is, the exact chemical composition of the Li _x Mn ₂ O ₄ active material produced by this production method is Li _x Na _y Mn ₂ O ₄ (0.5 ≦ x ≦ 0.9, 0 ≦ y ≦ 0.4, x + y ≦ 0.9).

NaMn ₂ O _{4 as a} starting material can be produced by firing a mixture of at least one of sodium and a sodium compound and at least one of manganese and a manganese compound under high temperature and high pressure conditions.

As the sodium raw material, at least one of sodium (metallic sodium) and a sodium compound is used. The sodium compound is not particularly limited as long as it contains sodium. For example, oxides such as Na ₂ O and Na ₂ O ₂ , salts such as Na ₂ CO ₃ and NaNO ₃ , hydroxides such as NaOH, etc. Is mentioned. Among these, peroxide Na ₂ O _{2 and the} like are particularly preferable.

As the manganese raw material, at least one of manganese (metallic manganese) and a manganese compound is used. The manganese compound is not particularly limited as long as it contains manganese. For example, oxides such as Mn ₃ O ₄ , Mn ₂ O ₃ and MnO ₂ , salts such as MnCO ₃ and MnCl ₂ , Mn (OH) ₂ And hydroxides such as MnOOH and the like. Among these, Mn ₂ O ₃ , Mn ₃ O ₄ , MnO _{2 and the} like are particularly preferable.

First, a mixture containing these is prepared. It is preferable to mix the sodium raw material and the manganese raw material in such a ratio that the calcium ferrite type structure is formed. Specifically, the chemical composition may be Na _x Mn ₂ O ₄ (x = 1). For example, mixing may be performed so that the amount of sodium x is about 0.5 to 2, preferably 0.8 to 1.5.

  The mixing method is not particularly limited as long as they can be mixed uniformly, and may be mixed using a known mixer such as a mixer.

  The mixture is then fired under high temperature and high pressure conditions. The firing temperature can be appropriately set according to the composition of the mixture, but is usually about 800 to 1400 ° C, preferably 1150 to 1250 ° C. The firing pressure may be 10,000 to 100,000 atmospheres, preferably 30,000 to 80,000 atmospheres, more preferably 40,000 to 50,000 atmospheres. The firing time can be appropriately changed according to the firing temperature and the like. For example, when the firing temperature is 1150 to 1250 ° C., it is preferably 1 to 10 hours. Although the cooling method is not particularly limited, it may be naturally cooled (rapid cooling) or gradually cooled.

  After firing, the fired product may be pulverized by a known method as necessary.

Next, the calcined NaMn ₂ O ₄ is subjected to an ion exchange treatment in a molten salt containing a lithium compound, or in an organic solvent or an aqueous solution, so that it has a calcium ferrite type crystal structure, and sodium is exchanged for lithium. And a compound represented by the chemical composition formula Li _x Mn ₂ O ₄ partially lacking lithium is obtained.

In this case, it is preferable to perform the ion exchange treatment while dispersing the pulverized NaMn ₂ O ₄ in the molten salt containing the lithium-containing compound. As the molten salt, a molten salt containing any one or more of salts that melt at a low temperature such as lithium nitrate, lithium chloride, lithium bromide, and lithium iodide can be used. As a preferred method, a lithium compound and NaMn ₂ O ₄ fired powder are mixed well. The mixing ratio is usually ₂ to 40, preferably 10 to 30, in terms of the molar ratio of Na in Li / NaMn ₂ O ₄ in the molten salt.

  The temperature of ion exchange is 200 ° C to 400 ° C, preferably 330 to 380 ° C. When the ion exchange temperature is lower than 330 ° C., it is difficult to introduce lithium site defects. On the other hand, when the ion exchange temperature is higher than 380 ° C., a part of the ion exchange temperature changes to a spinel structure, so that a uniform crystal structure cannot be obtained. The treatment time is usually 2 to 20 hours, preferably 5 to 15 hours.

Furthermore, as a method of ion exchange treatment, a method of treating in an organic solvent or an aqueous solution in which a lithium compound is dissolved is also suitable. In this case, crushed NaMn ₂ O ₄ is put into an organic solvent in which a lithium-containing compound is dissolved, and the treatment is performed at a temperature equal to or lower than the boiling point of the organic solvent. In order to increase the ion exchange rate, it is preferable to perform ion exchange while refluxing the solvent near the boiling point of the organic solvent. The treatment temperature is usually 100 ° C to 200 ° C, preferably 140 ° C to 180 ° C. Further, the treatment time is not particularly limited, but it is usually 5 to 50 hours, preferably 10 to 20 hours, because a reaction time is required at a low temperature.

  As the lithium-containing compound used in the present invention, carbonates, acetates, nitrates, oxalates, halides, butyllithium and the like are preferable, and these may be used alone or in combination of two or more as required. Further, as the organic solvent used in the present invention, higher alcohols such as hexanol and ethoxyethanol, ethers such as diethylene glycol monoethyl ether, or organic solvents having a boiling point of 140 ° C. or higher are good in workability. preferable. These may be used alone or in combination of two or more as required.

The density | concentration of the lithium containing compound in an organic solvent or aqueous solution is 3-10 mol% normally, Preferably it is 4-6 mol%. The dispersion concentration of NaMn ₂ O _{4 in} the organic solvent or aqueous solution is not particularly limited, but is preferably 1 to 20% by weight from the viewpoints of operability and economy.

After the ion exchange treatment, the obtained product is thoroughly washed with distilled water, then washed with methanol and ethanol, and dried to obtain the intended Li _x Mn ₂ O ₄ . The washing method and the drying method are not particularly limited, and a normal method may be used, or natural drying in a desiccator may be used.

(Lithium battery)
The lithium secondary battery of the present invention uses an electrode containing the Li _x Mn ₂ O ₄ active material as a constituent member. That is, a battery element of a known lithium battery (coin type, button type, cylindrical type, all solid type, etc.) is employed as it is except that the Li _x Mn ₂ O ₄ active material of the present invention is used as one of electrode materials. Can do.
FIG. 2 is a schematic view showing an example in which the lithium battery of the present invention is applied to a coin-type secondary battery. The coin-type secondary battery 1 includes a negative electrode terminal 2, a negative electrode 3, a (separator + electrolyte) 4, an insulating packing 5, a positive electrode 6, and a positive electrode can 7.

In the present invention, the Li _x Mn ₂ O ₄ active material of the present invention is mixed with a conductive agent, a binder or the like as necessary to prepare an electrode mixture, and this is crimped to a current collector. An electrode can be produced. As the current collector, a stainless mesh, aluminum foil or the like can be preferably used. As the conductive agent, acetylene black, ketjen black or the like can be preferably used. As the binder, tetrafluoroethylene, polyvinylidene fluoride, or the like can be preferably used.

The composition of the Li _x Mn ₂ O ₄ active material, the conductive agent, the binder and the like in the electrode mixture is not particularly limited, but usually the conductive agent is about 1 to 30% by weight (preferably 5 to 25% by weight). The binder may be 0 to 30% by weight (preferably 3 to 10% by weight), and the remainder may be a Li _x Mn ₂ O ₄ active material.

  In the lithium battery of the present invention, as the counter electrode with respect to the electrode, for example, a known lithium-occlusion material such as metal lithium or lithium alloy can be employed.

  In the lithium battery of the present invention, a known battery element may be adopted for the separator, the battery container, and the like.

  Furthermore, known electrolyte solutions, solid electrolytes, and the like can be applied as the electrolyte. For example, as an electrolytic solution, an electrolyte such as lithium perchlorate or lithium hexafluorophosphate is used in a solvent such as ethylene carbonate (EC), dimethyl carbonate (DMC), propylene carbonate (PC), or diethyl carbonate (DEC). What was dissolved can be used.

  EXAMPLES Examples will be shown below to clarify the features of the present invention, but the present invention is not limited to these examples.

[Example 1]
(Production of Li _x Mn ₂ O ₄ active material by high-pressure synthesis method)
Lithium oxide (Li ₂ O) powder having a purity of 97% or more and manganese oxide (mixture of MnO ₂ and Mn ₂ O ₃ ) powder having a purity of 99.9% or more in a molar ratio of 0.75: 2. Mix uniformly in a gas-substituted glove box. The mixture was packed in a gold capsule and synthesized by holding it for 5 hours under a temperature and pressure condition of 45,000 atm and 1200 ° C. using a cubic anvil type high pressure synthesizer, and Li _x Mn ₂ O ₄ was obtained. I was able to get it.

When the chemical composition of the obtained black polycrystalline sample was analyzed by ICP emission analysis (trade name Optima 3000, manufactured by PerkinElmer Japan), it was confirmed that the chemical formula was Li _0.69 Mn ₂ O ₄ . . Furthermore, the X-ray powder X-ray diffractometer (trade name RINT-Ultima III, manufactured by Rigaku) clearly shows that the crystal structure of the orthorhombic system and the space group Pnma is almost single phase with good crystallinity. became. The powder X-ray diffraction _{pattern of} this Li _0.69 Mn ₂ O ₄ is shown in FIG. In addition, the refined lattice constant from the crystal structure analysis is as follows, and the a-axis length is clearly shorter than the known LiMn ₂ O ₄ value (0.883336 nm), and the difference due to the presence or absence of lithium deficiency. Conceivable.
a = 0.80875 nm (error ± 0.00009 nm)
b = 0.28359 nm (error ± 0.00003 nm)
c = 1.06526 nm (error ± 0.00011 nm)

The field emission electron microscope (JEOL Ltd., trade name JEM-2010F) by, at an acceleration voltage 200 kV, it was taken the _Li 0.69 _Mn 2 _{O 4} electron diffraction image of the sample, in FIG. 4 As shown, a weak superlattice reflection having a long periodicity of 3 times in the a-axis direction was observed.

(Lithium battery)
Thus the Li _x Mn ₂ O ₄ active material obtained, acetylene black as a conductive agent, a tetrafluoroethylene as a binder, the weight ratio 80: 15: was blended so that 5 the electrode prepared 1M solution in which lithium hexafluorophosphate was dissolved in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) (volume ratio 1: 1) using lithium metal as a counter electrode was used as an electrolytic solution. A lithium battery (coin-type secondary battery) having the structure shown in FIG. 2 was produced and its charge / discharge characteristics were tested. The battery was produced according to a known cell configuration / assembly method.

The manufactured lithium battery was subjected to a charge / discharge test at a current density of 10 mA / g and a cut-off potential of 4.8-1.0 V under a temperature condition of 25 ° C., and an initial discharge capacity of about 144 mAh / g was 2 It has been found that a flat discharge portion is provided in the vicinity of .8 V and that charge and discharge can be performed reversibly. The voltage change accompanying charging / discharging is shown in FIG. From this, it was revealed that calcium ferrite type Li _x Mn ₂ O ₄ into which lithium deficiency was introduced was excellent as a battery material.

[Example 2]
(Production of Li _x Mn ₂ O ₄ Active Material by Ion Exchange Synthesis Method)
Sodium peroxide (Na ₂ O ₂ ) powder having a purity of 97% or more and manganese oxide (mixture of MnO ₂ and Mn ₂ O ₃ ) powder having a purity of 99.9% or more in a molar ratio of 1: 2 Mix uniformly in a gas-substituted glove box. The mixture was filled in a gold capsule and synthesized using a cubic anvil type high pressure synthesizer by holding it at 45,000 atm and 1200 ° C. for 5 hours under the conditions of NaMn ₂ O as a starting material. ₄ could be obtained.

When the chemical composition of the obtained black polycrystalline sample was analyzed by ICP emission analysis (manufactured by PerkinElmer Japan, trade name Optima 3000), it was confirmed that the chemical formula was NaMn ₂ O ₄ . Furthermore, the X-ray powder X-ray diffractometer (trade name RINT-Ultima III, manufactured by Rigaku) clearly shows that the crystal structure of the orthorhombic system and the space group Pnma is almost single phase with good crystallinity. became. In addition, the lattice constant refined from the crystal structure analysis was the following value, which was in good agreement with the known NaMn ₂ O ₄ value.
a = 0.88714 nm (error ± 0.00004 nm)
b = 0.28436 nm (error ± 0.00002 nm)
c = 1.12382 nm (error ± 0.00008 nm)

Next, a NaMn ₂ O ₄ powder sample is mixed with lithium nitrate (purity 99% or more) of about 60 times the weight ratio of the sample, placed in an alumina crucible, and heat-treated at 360 ° C. for 10 hours in air. By performing, ion exchange was performed.

After ion exchange, washing with pure water and drying were performed, and the target Li _x Mn ₂ O ₄ could be obtained.

When the chemical composition of the obtained black polycrystalline sample was analyzed by ICP emission analysis (trade name Optima 3000, manufactured by PerkinElmer Japan), it was confirmed that the chemical formula was Li _0.81 Mn ₂ O ₄ . . The amount of sodium remaining was 0.02 wt% or less. Furthermore, the X-ray powder X-ray diffractometer (trade name RINT-Ultima III, manufactured by Rigaku) clearly shows that the crystal structure of the orthorhombic system and the space group Pnma is almost single phase with good crystallinity. became. The powder X-ray diffraction _{pattern of} this Li _0.81 Mn ₂ O ₄ is shown in FIG. In addition, the refined lattice constant from the crystal structure analysis is as follows, and the a-axis length is clearly shorter than the known LiMn ₂ O ₄ value (0.883336 nm), and the difference due to the presence or absence of lithium deficiency. Conceivable.
a = 0.87276 nm (error ± 0.00003 nm)
b = 0.28333 nm (error ± 0.00001 nm)
c = 1.05392 nm (error ± 0.00004 nm)

The field emission electron microscope (JEOL Ltd., trade name JEM-2010F) by, at an acceleration voltage 200 kV, the present _Li 0.81 _Mn 2 _{O 4} electron diffraction image of the sample was taken, in Figure 7 As shown, a weak superlattice reflection having a long periodicity of four times in the a-axis direction and a streak line in the a-axis direction corresponding to the mismatched structure of the crystal lattice were observed.

(Lithium battery)
For the Li _x Mn ₂ O ₄ active material thus obtained, an electrode was produced in the same manner as in Example 1, and a lithium battery (coin-type secondary battery) similar to that in Example 1 was produced. When this lithium battery was subjected to a charge / discharge test under the same conditions as in Example 1, it was found that it had an initial discharge capacity of about 331 mAh / g, a discharge potential of about 3 V, and could be reversibly charged and discharged. did. The voltage change accompanying charging / discharging is shown in FIG. From this, it became clear that calcium ferrite type Li _x Mn ₂ O ₄ into which lithium deficiency was introduced is useful as a battery material with a high capacity.

The calcium ferrite type Li _x Mn ₂ O ₄ active material having a lithium deficiency of the present invention is excellent in that a good conduction path of lithium ions is ensured and a high capacity from the characteristics of the crystal structure. It is a material having battery characteristics. Therefore, it has a high practical value as an active material for a lithium battery.

In addition, the production method is a useful technique capable of suppressing the generation of compounds such as spinel type LiMn ₂ O ₄ which is a low-pressure phase degradation problem and Li ₂ MnO ₃ which is not battery active.

Furthermore, the lithium battery using the calcium ferrite type Li _x Mn ₂ O ₄ active material having a lithium deficiency of the present invention as an electrode material can have a 3V-class discharge potential and can be used as a secondary battery. It is a battery that can be expected to have a high capacity.

Is a schematic diagram for explaining the crystal structure of Li _x Mn ₂ O ₄ active material having a calcium ferrite structure of the present invention. Represents lithium ions partially lacking white spheres. It is a schematic diagram which shows an example (coin-type secondary battery) of a lithium battery. _{2 is} a powder X-ray diffraction pattern of the calcium ferrite type Li _0.69 Mn ₂ O ₄ active material of the present invention obtained in Example 1. FIG. _{2 is} an electron diffraction pattern of the calcium ferrite type Li _0.69 Mn ₂ O ₄ active material of the present invention obtained in Example 1. FIG. It is a figure which shows the charging / discharging characteristic of the battery of this invention obtained in Example 1. FIG. _{4 is} a powder X-ray diffraction pattern of the calcium ferrite type Li _0.81 Mn ₂ O ₄ active material of the present invention obtained in Example 2. FIG. _{4 is} an electron diffraction pattern of the calcium ferrite type Li _0.81 Mn ₂ O ₄ active material of the present invention obtained in Example 2. FIG. It is a figure which shows the charging / discharging characteristic of the battery of this invention obtained in Example 2. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Coin type lithium secondary battery 2 Negative electrode terminal 3 Negative electrode 4 Separator + Electrolyte 5 Insulation packing 6 Positive electrode 7 Positive electrode can

Claims (5)

Li _x Mn ₂ O ₄ (composition range: 0.5 ≦ x ≦ 0.9) is expressed by a lithium-deficient chemical composition formula, and has an orthorhombic calcium ferrite structure as a crystal structure and is long in the a-axis direction. An active material for a lithium battery, comprising a polycrystal having periodicity. Of the crystal lattice of the orthorhombic calcium ferrite type structure, which is expressed by the chemical composition formula of lithium deficiency type Li _x Mn ₂ O ₄ (composition range: 0.5 ≦ x ≦ 0.9), a An active material for a lithium battery, characterized by comprising a polycrystalline body having an axial length in the range of 0.871 nm to 0.882 nm and having a long periodicity in the a-axis direction. 3. The lithium battery active material according to claim 1, wherein the mixture containing the lithium compound and the manganese compound is heated under a high temperature of 1150 to 1250 ° C. and a high pressure of 10,000 to 100,000 atmospheres. Production method. A mixture containing a sodium compound and a manganese compound is heated under a high temperature of 1150 to 1250 ° C. and a high pressure of 10,000 to 100,000 atmospheres, and the resulting sodium compound is subjected to an ion exchange treatment, whereby sodium is converted into lithium. The method for producing an active material for a lithium battery according to claim 1, wherein the material is exchanged.   A lithium battery comprising two electrodes used as a positive electrode and a negative electrode and an electrolyte, wherein the lithium battery active material according to claim 1 or 2 is used as a material constituting the electrode.