JP5515063B2 - Lithium manganese composite oxide, method for producing the same, and lithium battery - Google Patents

Description

  The present invention relates to a lithium manganese composite oxide, a method for producing the same, and a lithium battery using the lithium manganese composite oxide as a positive electrode active material.

  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 during charging and discharging. For example, lithium manganese composite oxide (LiMn ₂ O ₄ ) having a cubic spinel structure applied to a lithium ion secondary battery is less expensive than other electrode materials (lithium cobalt composite oxide, etc.) It is well known that the main component is a stable manganese and the safety in a charged state is remarkably excellent.

  However, the lithium manganese composite oxide having this spinel structure is caused by the unstable crystal structure, and the capacity rapidly decreases when the discharge end voltage is lowered to about 2 V and the charge / discharge cycle is repeated. End up. Further, when the temperature is 50 ° C. or higher, there is a problem that the characteristics are remarkably deteriorated due to the dissolution of manganese in the electrolytic solution. For this reason, the use of this material has not progressed as expected.

On the other hand, as a feature of the crystal structure, an alkali manganese composite oxide (NaMn ₂ O ₄ , LiMn ₂ O ₄ ) having an orthorhombic calcium ferrite (CaFe ₂ O ₄ ) type structure can be produced by a high-temperature and high-pressure synthesis method. It has already been reported (see Patent Document 1, Non-Patent Documents 1 and 2)

  Since this lithium manganese composite oxide having a calcium ferrite structure has a one-dimensional tunnel structure occupied by lithium ions, a good conduction path in the crystal structure of lithium ions is secured, and a skeletal structure It was thought that lithium ion desorption / insertion reaction was possible by the trivalent to tetravalent oxidation-reduction reaction of manganese that forms. Furthermore, since it is predicted that the skeletal structure has high stability against the lithium ion desorption / insertion reaction, the lithium manganese composite oxide having this crystal structure is a promising material from the viewpoint of application to a lithium battery. It was thought that.

  However, the lithium manganese composite oxide having the calcium ferrite type structure of Patent Document 1 and Non-Patent Documents 1 and 2 hardly causes a lithium insertion reaction, and the amount of lithium that can be inserted is 0.1 or less per chemical formula. It was revealed that it is not suitable for use as an electrode material (see Non-Patent Document 2).

Therefore, recently, Li _x Mn ₂ O ₄ (0.5 ≦ x ≦ 0.9) is represented by a lithium-deficient composition formula, which has a calcium ferrite structure as a crystal structure and is long in the a-axis direction. A lithium manganese composite oxide having periodicity has been proposed (see Patent Document 2). A lithium battery using this lithium manganese composite oxide as a positive electrode active material has a high capacity and is capable of reversible lithium insertion / extraction reaction.

  However, a lithium battery using this lithium manganese composite oxide as a positive electrode active material has a problem of having a low average discharge potential while having a high capacity. For this reason, a lithium manganese composite oxide having a calcium ferrite type structure with an improved average discharge potential has been desired for practical use.

JP 2007-112673 A JP 2008-198553 A

J. et al. Akimoto, J. et al. Awaka, N.A. Kijima, Y. et al. Takahashi, Y. et al. Maruta, K.M. Tokiwa, T .; Watanabe, J.A. Solid State Chem. , 179, 169-174 (2006) K. Yamaura, Q. Huang, L.H. Zhang, K.K. Takada, Y .; Baba, T.A. Nagai, Y .; Matsui, K .; Kosuda, E .; Takayama-Muromachi, J. et al. Am. Chem. Soc. , 128, 9448-9456 (2006)

  Therefore, in order to solve such a conventional problem, the present invention provides a lithium manganese composite oxide having a calcium ferrite structure and an improved average discharge potential, a method for producing the same, and the lithium manganese composite oxide. An object is to provide a lithium battery used as a positive electrode active material.

The inventors of the present invention have made extensive studies to solve the above problems. As a result, it was found that the above problems can be solved by substituting part or all of manganese sites of LiMn ₂ O ₄ having a calcium ferrite type structure with a transition metal element such as Ti and Ni, and the present invention has been completed. It was. More specifically, the present invention is as follows.

(1) the composition formula _{Li x M z Mn 2-z} O 4 (M is, Ti, V, Cr, Fe , Co, Ni, Cu, Zn, Al, and at least one selected from the group consisting of Mg Element, 0.3 ≦ x ≦ 1.1, and 0 <z ≦ 2.0.) And having a calcium ferrite structure as a crystal structure.

  (2) The lithium manganese composite oxide according to (1), wherein M is at least one element selected from the group consisting of Ti and Ni.

  (3) At least one metal selected from the group consisting of sodium or a sodium compound, manganese or a manganese compound, and Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Al, and Mg, or oxidation thereof The lithium containing the product is heated at 800 to 1500 ° C. under high pressure conditions of 10,000 to 100,000 atm, and sodium contained in the obtained compound is replaced with lithium by ion exchange treatment. Manufacturing method of manganese composite oxide.

  (4) A lithium battery using the lithium manganese composite oxide according to (1) or (2) as a positive electrode active material.

  According to the present invention, a lithium manganese composite oxide having a calcium ferrite structure and an improved average discharge potential, a method for producing the same, and a lithium battery using the lithium manganese composite oxide as a positive electrode active material are provided. can do.

It is a schematic diagram which shows an example (coin-type secondary battery) of a lithium battery. It is a figure which shows the charging / discharging characteristic of the lithium battery which used the lithium manganese complex oxide of Example 1 as a positive electrode active material. It is a figure which shows the charging / discharging characteristic of the lithium battery which used the lithium manganese complex oxide of Example 2 as a positive electrode active material. It is a figure which shows the charging / discharging characteristic of the lithium battery which used the lithium manganese complex oxide of Example 3 as a positive electrode active material. It is a figure which shows the charging / discharging characteristic of the lithium battery which used the lithium manganese complex oxide of Example 4 as a positive electrode active material.

<Lithium manganese composite oxide and method for producing the same>
Lithium-manganese composite oxide according to the present invention, the composition formula _{Li x M z Mn 2-z} O 4 (M is, Ti, V, Cr, Fe , Co, Ni, Cu, Zn, a group consisting of Al, and Mg At least one element selected from the group consisting of 0.3 ≦ x ≦ 1.1 and 0 <z ≦ 2.0.) And having a calcium ferrite structure as a crystal structure To do.
This lithium manganese composite oxide is obtained by substituting part or all of the manganese site of LiMn ₂ O ₄ having a conventionally known calcium ferrite type structure with a transition metal element. Thus, by replacing part or all of the manganese site of LiMn ₂ O ₄ with a transition metal element, the average discharge potential when the lithium manganese composite oxide is used as a positive electrode active material of a lithium battery can be improved. it can.

The lithium manganese composite oxide according to the present invention is selected from the group consisting of, for example, sodium or sodium compound, manganese or manganese compound, Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Al, and Mg A mixture containing at least one kind of metal (hereinafter referred to as “transition metal”) or an oxide thereof (hereinafter referred to as “transition metal oxide”) under high pressure conditions of 10,000 to 100,000 atm. It can be manufactured by heating at 800 to 1500 ° C. and replacing sodium contained in the obtained compound with lithium by ion exchange treatment (ion exchange synthesis method).
Further, by heating a mixture containing lithium or a lithium compound, manganese or a manganese compound, and a transition metal or a transition metal oxide at 800 to 1500 ° C. under a high pressure condition of 10,000 to 100,000 atmospheres, The lithium manganese composite oxide according to the present invention can be produced (high pressure synthesis method).

  Hereinafter, the method for producing a lithium manganese composite oxide according to the present invention will be described in more detail.

(Synthesis of lithium manganese composite oxide by ion exchange synthesis method)
In the ion exchange synthesis method, first, sodium or a sodium compound, manganese or a manganese compound, and a transition metal or a transition metal oxide are mixed.

The sodium compound is not particularly limited, and examples thereof include oxides such as Na ₂ O and Na ₂ O ₂ , salts such as Na ₂ CO ₃ and NaNO ₃ , and hydroxides such as NaOH. Among these, Na ₂ O _{2 and the} like are particularly preferable.

The manganese compound is not particularly _{limited, Mn 3 O 4, Mn 2} O 3, MnO oxides such _2, etc. MnCO 3, MnCl ₂ salts, Mn _(OH) hydroxide ₂ or the like, such as MnOOH An oxide hydroxide etc. are mentioned. Among these, Mn ₂ O ₃ , Mn ₃ O ₄ , MnO _{2 and the} like are particularly preferable.

The transition metal oxide is not particularly _{limited, Ti 2 O 3, TiO 2} , V 2 O 3, VO 2, Cr 2 O 3, Fe 2 O 3, Co 3 O 4, NiO, CuO, ZnO, Al ₂ O ₃ , MgO and the like.

The mixing ratio of sodium or a sodium compound, manganese or a manganese compound, and a transition metal or a transition metal oxide should just be a ratio from which a calcium ferrite type structure is obtained. _{Specifically, Na x M z Mn 2-} z O 4 (M is, Ti, V, Cr, Fe , Co, Ni, Cu, Zn, Al, and at least one selected from the group consisting of Mg It is sufficient to mix so as to satisfy the composition formula of (element).

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

Next, the mixture is baked under high temperature and high pressure conditions to obtain a compound represented by the composition formula Na _x M _z Mn _{2 -z} O ₄ .
Although a calcination temperature can be suitably set according to the composition of a mixture, etc., it is about 800-1500 degreeC normally, Preferably it is 1000-1400 degreeC. In particular, when M is Ti, 1000 to 1300 ° C is preferable, and when M is Ni, 1000 to 1100 ° C is preferable.
The firing pressure is 10,000 to 100,000 atm, preferably 30,000 to 80,000 atm, and more preferably 40,000 to 50,000 atm. The firing time can be appropriately changed according to the firing temperature and the like. For example, when the firing temperature is 1000 to 1100 ° C., it is preferably 1 to 3 hours. The cooling method is not particularly limited, but is usually natural cooling (rapid cooling) or slow cooling.
After firing, the fired product may be pulverized by a known method as necessary.

Then, the compound represented by the composition formula _{Na x M z Mn 2-z} O 4, by performing the ion exchange process in a molten salt containing a lithium compound, having a crystal structure of the calcium ferrite type, and sodium There compound represented by the composition formula _{Li x M z Mn 2-z} O 4 substituted lithium is obtained.

At this time, it is preferable to perform the ion exchange treatment while dispersing the pulverized Na _x M _z Mn _{2 -z} O ₄ in the molten salt containing the lithium compound. As the molten salt, one containing at least one salt that melts at a low temperature such as lithium nitrate, lithium chloride, lithium bromide, or lithium iodide can be used. The lithium compound and the Na _x M _z Mn _{2 -z} O ₄ powder are preferably mixed well. The mixing ratio is usually 2 to 40 at a molar ratio of Na in _{Li / Na x M z Mn 2} -z O 4 in the molten salt, it is preferably 10 to 30.

  The ion exchange temperature is 250 to 450 ° C, preferably 270 to 360 ° C. When the ion exchange temperature is lower than 250 ° C., it is difficult to sufficiently substitute lithium. On the other hand, when the ion exchange temperature is higher than 450 ° 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 1 to 30 hours, preferably 5 to 15 hours.

In addition, 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 can also be used. In this case, an organic solvent obtained by dissolving lithium compound, a _{Na x M z Mn 2-z} O 4 , which is ground up, is at a temperature below 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 ion exchange temperature is usually 100 to 200 ° C, preferably 140 to 180 ° C. 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 low temperatures.

  As the lithium compound, 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. As the organic solvent, higher alcohols such as hexanol and ethoxyethanol, ethers such as diethylene glycol monoethyl ether, and organic solvents having a boiling point of 140 ° C. or higher are preferable in terms of good workability. These may be used alone or in combination of two or more as required.

The density | concentration of the lithium compound in an organic solvent or aqueous solution is 3-10 mol% normally, Preferably it is 4-6 mol%. Dispersion concentration of _{Na x M z Mn 2-z} O 4 in an organic solvent or aqueous solution is not particularly limited, is preferably 1 to 20 wt% from the viewpoint of operability and economy.

After the ion exchange treatment, the resulting product is thoroughly washed with distilled water, then washed with methanol, ethanol, etc., and dried to obtain the target composition formula Li _x M _z Mn _2-z O ₄ . Is obtained. 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.

  Depending on the conditions of the ion exchange treatment, the lithium may not be completely replaced and a trace amount of sodium may remain.

(Synthesis of lithium manganese composite oxide by high pressure synthesis method)
In the high-pressure synthesis method, lithium or a lithium compound, manganese or a manganese compound, and a transition metal or a transition metal oxide are first mixed.

The lithium compound is not particularly limited, and examples thereof include oxides such as Li ₂ O and Li ₂ O ₂ , salts such as Li ₂ CO ₃ and LiNO ₃ , and hydroxides such as LiOH. Among these, Li ₂ O and the like are particularly preferable.

  Examples of the manganese compound and the transition metal oxide include the same compounds as those used in the ion exchange synthesis method.

The mixing ratio of lithium or a lithium compound, manganese or a manganese compound, and a transition metal or a transition metal oxide may be a ratio at which a calcium ferrite structure is obtained. _{Specifically, Li x M z Mn 2-} z O 4 (M is, Ti, V, Cr, Fe , Co, Ni, Cu, Zn, Al, and at least one selected from the group consisting of Mg It is sufficient to mix so as to satisfy the composition formula of (element).

  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.

Next, the mixture is baked under high temperature and high pressure conditions to obtain a compound represented by the composition formula Li _x M _z Mn _{2 -z} O ₄ .
Although a calcination temperature can be suitably set according to the composition of a mixture, etc., it is about 800-1500 degreeC normally, Preferably it is 1000-1400 degreeC. The firing pressure is 10,000 to 100,000 atm, preferably 30,000 to 80,000 atm, and more preferably 40,000 to 50,000 atm. The firing time can be appropriately changed according to the firing temperature and the like. For example, when the firing temperature is 1050 to 1300 ° C., it is preferably 1 to 3 hours. The cooling method is not particularly limited, but is usually natural cooling (rapid cooling) or slow cooling.
After firing, the fired product may be pulverized by a known method as necessary.

<Lithium battery>
The lithium battery according to the present invention uses the lithium manganese composite oxide according to the present invention as a positive electrode active material. Except for using the lithium manganese composite oxide according to the present invention as the positive electrode active material, battery elements of known lithium batteries (coin type, button type, cylindrical type, all solid type, etc.) can be employed as they are.

  As an example, FIG. 1 shows a schematic diagram when the lithium battery according to the present invention is applied to a coin-type secondary battery. As shown in FIG. 1, the coin-type secondary battery 1 includes a positive electrode 2, a negative electrode 3, a separator 4, a negative electrode terminal 5, an insulating packing 6, and a positive electrode can 7.

  The positive electrode 2 is prepared by blending a lithium manganese composite oxide according to the present invention with a conductive agent, a binder or the like as necessary to prepare an electrode mixture, and pressure bonding this to a current collector. . As the current collector, stainless steel mesh, aluminum mesh, aluminum foil or the like can be used. As the conductive agent, acetylene black, ketjen black, or the like can be used. As the binder, tetrafluoroethylene, polyvinylidene fluoride, or the like can be used.

  The composition of the lithium manganese composite oxide, the conductive agent, the binder, etc. in the electrode mixture is not particularly limited. Usually, the conductive agent is about 1-30% by mass (preferably 5-25% by mass), and the binder is used. The content may be 0 to 30% by mass (preferably 3 to 10% by mass), and the balance may be a lithium manganese composite oxide.

  As the negative electrode 3, a known material that occludes lithium, such as lithium metal or lithium alloy, can be used.

As the separator 4, the negative electrode terminal 5, the insulating packing 6, and the positive electrode can 7, known ones can be employed.
Moreover, a well-known thing can be employ | adopted also as electrolyte solution. For example, an electrolyte such as lithium perchlorate or lithium hexafluorophosphate dissolved in a solvent such as ethylene carbonate (EC), dimethyl carbonate (DMC), propylene carbonate (PC), or diethyl carbonate (DEC) Can be adopted.

  Examples of the present invention will be described below, but the scope of the present invention is not limited to these examples.

<Preparation of lithium manganese composite oxide>
[Example 1]
Purity of 97% or more of _Na 2 _{O 2} powder, 99.9% purity or more _MnO 2, _Mn 2 _{O 3} powder, and the _Ti 2 _{O 3} powder having a purity of 99.9% at a molar ratio of 1: 1.8 The mixture was uniformly mixed in a glove box purged with argon gas at a ratio of 0.2. By filling the mixture in a gold capsule and holding it at 45,000 atm and 1200 ° C. for 5 hours using a cubic anvil type high pressure synthesizer, NaTi _0.2 Mn _1.8 O ₄ is obtained. Obtained.

Next, the NaTi _0.2 Mn _1.8 O ₄ powder sample is mixed with LiNO ₃ (purity 99% or more) of about 60 times the sample by mass ratio, placed in an alumina crucible, and 360 ° C. in air. The ion exchange treatment was performed by performing the heat treatment for 10 hours. After the ion exchange treatment, it was washed with pure water and dried.

When the chemical composition of the obtained compound was analyzed by ICP emission analysis (trade name Optima 3000, manufactured by PerkinElmer Japan), it was confirmed that it was a composition formula of Li _0.94 Ti _0.18 Mn _1.82 O _4. It was done. Further, when the crystal structure was analyzed by a powder X-ray diffractometer (trade name RINT-Ultima III, manufactured by Rigaku), it became clear that the crystal structure of the orthorhombic system and space group Pnma had good crystallinity. It was. As a result of the crystal structure analysis, the lattice constant was as follows.
a = 0.872953 nm
b = 0.283829 nm
c = 1.053373 nm

[Example 2]
Purity of 97% or more of _Na 2 _{O 2} powder, 99.9% purity or more _MnO 2, _Mn 2 _{O 3} powder, and the _Ti 2 _{O 3} powder having a purity of 99.9% at a molar ratio of 1: 1.6 The mixture was uniformly mixed in a glove box purged with argon gas at a ratio of 0.4. By filling the mixture in a gold capsule and holding it at 45,000 atm and 1200 ° C. for 5 hours using a cubic anvil type high pressure synthesizer, NaTi _0.4 Mn _1.6 O ₄ is obtained. Obtained.

Next, the NaTi _0.4 Mn _1.6 O ₄ powder sample was mixed with about 60 times the amount of LiNO ₃ (purity 99% or more) by mass ratio, placed in an alumina crucible, and 360 ° C. in air. The ion exchange treatment was performed by performing the heat treatment for 10 hours. After the ion exchange treatment, LiTi _0.4 Mn _1.6 O ₄ was obtained by washing with pure water and drying.

The obtained compound was analyzed by a powder X-ray diffractometer (trade name RINT-UtimaIII, manufactured by Rigaku Corporation). As a result, the crystal structure of the orthorhombic system and the space group Pnma had good crystallinity. Became clear. As a result of the crystal structure analysis, the lattice constant was as follows.
a = 0.869015 nm
b = 0.284224 nm
c = 1.030214 nm
[Example 3]
Purity of 97% or more of _Na 2 _{O 2} powder, 99.9% purity or more _MnO 2, _Mn 2 _{O 3} powder, and the _Ti 2 _{O 3} powder having a purity of 99.9% at a molar ratio of 1: 1: 1 The mixture was uniformly mixed in a glove box purged with argon gas. NaTiMnO ₄ was obtained by filling the mixture in a gold capsule and holding it at 45,000 atm and 1200 ° C. for 5 hours using a cubic anvil type high pressure synthesizer.

Next, the NaTiMnO ₄ powder sample is mixed with LiNO ₃ (purity 99% or more) of about 60 times the sample by mass ratio, placed in an alumina crucible, and heated in air at 360 ° C. for 10 hours. Thus, ion exchange treatment was performed. After the ion exchange treatment, it was washed with pure water and dried.

When the chemical composition of the obtained compound was analyzed by ICP emission analysis (trade name Optima 3000, manufactured by PerkinElmer Japan), it was confirmed that it was a composition formula of Li _1.06 Ti _0.96 Mn _1.04 O _4. It was done. Further, when the crystal structure was analyzed by a powder X-ray diffractometer (trade name RINT-Ultima III, manufactured by Rigaku), it became clear that the crystal structure of the orthorhombic system and space group Pnma had good crystallinity. It was. As a result of the crystal structure analysis, the lattice constant was as follows.
a = 0.8828nm
b = 0.289941 nm
c = 1.0771 nm

[Example 4]
Purity of 97% or more of _Na 2 _{O 2} powder, powder of a purity of 99.9% or more of _MnO 2, _Mn 2 _{O 3,} and a purity of 99.9% or higher NiO powder in a molar ratio of 1: 1.8: 0. The mixture was uniformly mixed in a glove box purged with argon gas at a ratio of 2. By filling the mixture in a gold capsule and holding it at 45,000 atm and 1200 ° C. for 5 hours using a cubic anvil type high pressure synthesizer, NaNi _0.2 Mn _1.8 O ₄ is obtained. Obtained.

Next, the NaNi _0.2 Mn _1.8 O ₄ powder sample was mixed with about 60 times the amount of LiNO ₃ (purity 99% or more) by mass ratio, placed in an alumina crucible, and 360 ° C. in air. The ion exchange treatment was performed by performing the heat treatment for 10 hours. After the ion exchange treatment, LiNi _0.2 Mn _1.8 O ₄ was obtained by washing with pure water and drying.

The obtained compound was analyzed by a powder X-ray diffractometer (trade name RINT-UtimaIII, manufactured by Rigaku Corporation). As a result, the crystal structure of the orthorhombic system and the space group Pnma had good crystallinity. Became clear. As a result of the crystal structure analysis, the lattice constant was as follows.
a = 0.86922 nm
b = 0.283405 nm
c = 1.456568 nm

[Comparative Example 1]
Purity of 97% or more of _Na 2 _{O 2} powder, and the powder having a purity of 99.9% or more of _MnO 2, _Mn 2 _{O 3} in a molar ratio of 1: 2 ratio, uniformly in a glove box that argon gas replacement Mixed. NaMn ₂ O ₄ was obtained by filling the mixture in a gold capsule and holding it under a temperature and pressure condition of 45,000 atm and 1200 ° C. for 5 hours using a cubic anvil type high pressure synthesizer.

Next, the NaMn ₂ O ₄ powder sample is mixed with approximately 60 times the amount of LiNO ₃ (purity 99% or more) by mass ratio, placed in an alumina crucible, and heated in air at 360 ° C. for 10 hours. By performing, ion exchange was performed. After ion exchange, it was washed with pure water and dried.

When the chemical composition of the obtained compound was analyzed by ICP emission analysis (trade name Optima 3000, manufactured by PerkinElmer Japan), it was confirmed to be a composition formula of Li _0.81 Mn ₂ O ₄ . Further, when the crystal structure was analyzed by a powder X-ray diffractometer (trade name RINT-Ultima III, manufactured by Rigaku), it became clear that the crystal structure of the orthorhombic system and space group Pnma had good crystallinity. It was. Moreover, the lattice constant refined from the crystal structure analysis was the following value.
a = 0.87276 nm (error ± 0.00003 nm)
b = 0.28333 nm (error ± 0.00001 nm)
c = 1.05392 nm (error ± 0.00004 nm)

<Production and evaluation of lithium batteries>
Using the lithium manganese composite oxides of Examples 1 to 4 and Comparative Example 1 thus obtained as the positive electrode active material, lithium batteries (coin type secondary batteries) having the structure shown in FIG. 1 were produced.
The positive electrode is prepared by blending lithium manganese composite oxide, acetylene black as a conductive agent, and tetrafluoroethylene as a binder so as to have a mass ratio of 10: 5: 1, This was produced by pressure bonding to an aluminum mesh as a current collector. Lithium metal was used as the negative electrode. As the electrolytic solution, a 1M solution in which lithium hexafluorophosphate was dissolved in a mixed solvent (volume ratio 1: 1) of ethylene carbonate (EC) and diethyl carbonate (DEC) was used.
The battery was produced according to a known cell configuration / assembly method.

About each produced lithium battery, 10 cycles of charging / discharging tests were performed by the current density of 10 mA / g and the cut-off potential of 4.8-1.0V on 25 degreeC temperature conditions.
The charge / discharge curves of the lithium batteries using the lithium manganese composite oxides of Examples 1 to 4 are shown in FIGS. For comparison, FIGS. 2 to 5 also show initial charge / discharge curves of a lithium battery using the lithium manganese composite oxide of Comparative Example 1. FIG.
Table 1 below shows the initial discharge capacity, average discharge potential, and energy density of lithium batteries using the lithium manganese composite oxides of Examples 1 to 4 and Comparative Example 1.

As can be seen from FIGS. 2 to 5, by replacing a part of the manganese site of LiMn ₂ O ₄ with Ti and Ni, the flat portion observed at 2.7 V or less during the discharge of LiMn ₂ O ₄ disappears, Smooth charge / discharge characteristics are shown. This suggests that the phase change associated with the insertion / extraction reaction of lithium in the low voltage portion and the high voltage portion is suppressed.
Moreover, as can be seen from FIGS. 2 to 5 and Table 1, the average discharge potential of the lithium battery was improved by substituting some of the manganese sites of LiMn ₂ O ₄ with Ti and Ni. In particular, in the case of Ti, the effect was higher as the substitution ratio was lower.

  1 coin-type secondary battery, 2 positive electrode, 3 negative electrode, 4 separator, 5 negative electrode terminal, 6 insulating packing, 7 positive electrode can

Claims (4)

Composition formula _{Li x M z Mn 2-z} O 4 (M is, Ti, V, Cr, Fe , Co, Ni, Cu, Zn, is at least one element selected from the group consisting of Al, and Mg 0.3 ≦ x ≦ 1.1 and 0 <z ≦ 2.0.), And having a calcium ferrite structure as a crystal structure.   The lithium manganese composite oxide according to claim 1, wherein M is at least one element selected from the group consisting of Ti and Ni.   Sodium or a sodium compound, manganese or a manganese compound, and at least one metal selected from the group consisting of Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Al, and Mg, or an oxide thereof. Lithium manganese composite oxidation characterized by heating a mixture containing the mixture at 800 to 1500 ° C. under high pressure conditions of 10,000 to 100,000 atm and replacing sodium contained in the obtained compound with lithium by ion exchange treatment Manufacturing method.   A lithium battery comprising the lithium manganese composite oxide according to claim 1 or 2 as a positive electrode active material.

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