WO2018066633A1

WO2018066633A1 - Titanium- and/or germanium-substituted lithium manganese composite oxide and method for producing same

Info

Publication number: WO2018066633A1
Application number: PCT/JP2017/036223
Authority: WO
Inventors: 田渕　光春; 京介堂前; 英香渋谷; 田村　宜之; 亮太弓削; 直樹河野
Original assignee: 国立研究開発法人産業技術総合研究所; 株式会社田中化学研究所; 日本電気株式会社
Priority date: 2016-10-07
Filing date: 2017-10-05
Publication date: 2018-04-12
Also published as: JPWO2018066633A1; JP7048944B2

Abstract

A lithium manganese composite oxide which is represented by general formula (1) Li_1+x(M¹ _yM² _zMn_1-y-z)_1-xO₂ (wherein M¹ represents Fe and/or Ni; M² represents Ti and/or Ge; and x, y and Z satisfy 0 < x < 1/3, 0 ≤ y ≤ 0.4 and 0 < z ≤ 0.3) and contains a crystal phase having a monoclinic layered rock salt structure or a hexagonal layered rock salt structure is a novel material that has few resource constraints and uses low-cost elements, while achieving high capacity and high discharge voltage and exhibiting excellent long-term cycle characteristics for maintaining the similarity of the shapes of charge/discharge curves during charge/discharge cycles if used for a positive electrode material for lithium ion secondary batteries.

Description

Titanium and / or germanium-substituted lithium manganese composite oxide and method for producing the same

The present invention relates to a titanium and / or germanium substituted lithium manganese composite oxide and a method for producing the same.

Currently, most of the secondary batteries installed in portable devices such as mobile phones, smartphones, notebook computers, and tablet computers in Japan are lithium ion secondary batteries. In the future, lithium ion secondary batteries are being put into practical use as large batteries for electric vehicles, power load leveling systems, and the like, and their importance is increasing.

Currently, in lithium ion secondary batteries, a lithium-containing transition metal oxide is used as the positive electrode material, and a carbon material such as graphite is used as the negative electrode material. In particular, the amount of lithium ions reversibly desorbed (equivalent to charging) and inserted (equivalent to discharging) in the positive electrode material determines the capacity of the battery, and the voltage at the time of desorption and insertion determines the operating voltage of the battery. Battery capacity and operating voltage are determined by the positive electrode. Furthermore, the cost of the constituent members of the battery is highest for the positive electrode active material, and the selection of the positive electrode material is most important in the development of a lithium ion secondary battery.

For this reason, further increase in demand for the positive electrode material is expected as the use of the lithium ion secondary battery is expanded and the size thereof is increased. However, lithium cobaltate, which is usually used as a positive electrode material, contains a large amount of cobalt, which is a rare metal, and is one of the factors that increase the material cost of lithium ion secondary batteries. Furthermore, considering that about 20% of cobalt resources are currently used in the battery industry, it is considered difficult to meet future demand growth with only the positive electrode material made of LiCoO ₂ . For this reason, especially in order to use for large sized lithium ion secondary batteries, such as a use for motor vehicles, the oxide positive electrode material using an element rich in resources is calculated | required.

At present, as a cathode material that is less expensive and less resource-constrained, the present inventors have developed a layered rock-salt-type solid solution (Li _{1 + x} (Fe ₁ ) consisting of lithium manganese oxide (Li ₂ MnO ₃ ) and lithium ferrite. _y Mn _1-y ) _1-x O ₂ (0 <x <1/3, 0 <y <1), sometimes referred to as “iron-containing Li ₂ MnO ₃ ”) Has an average discharge voltage close to 4 V, comparable to that of lithium cobalt oxide (see, for example, Patent Document 1).

In addition, the present inventors have found that lithium manganese oxide (such as iron and nickel-containing Li ₂ MnO ₃ ) containing abundant nickel together with iron can remarkably improve cycle deterioration in the 4 V region ( For example, see Patent Document 2).

Furthermore, the present inventors have shown that lithium manganese oxides (such as titanium-containing Li ₂ MnO ₃ , iron and titanium-containing Li ₂ MnO ₃ ) containing titanium that is resource-rich and inexpensive together with iron exhibit high capacity, In particular, it has been found that a specific chemical composition and transition metal ion distribution are excellent in discharge characteristics under a high current density at room temperature and discharge characteristics at a low temperature (see, for example, Patent Document 3).

As described above, various reports have been made on lithium manganese-based positive electrode materials that can replace lithium cobalt-based positive electrode materials, but further improvement in charge / discharge characteristics is desired.

JP 2002-068748 A JP 2003-048718 A JP 2008-063211 A

However, when the lithium manganese composite oxides of Patent Documents 1 and 2 are used, by repeating charge and discharge, the crystal phase of the layered rock salt structure is gradually changed to the crystal phase of the spinel structure or the lithium excess crystal phase. Due to the change, a sudden drop in potential is observed around 3.5V during discharge, and additional capacity appears around 2.2V during discharge. Industrially, it is preferable that the charge / discharge curve shape can be maintained even after 100 cycles or 1000 cycles, but this method shows a decrease in charge / discharge characteristics before that. For this reason, the lithium manganese composite oxides of Patent Documents 1 and 2 change the charge / discharge curve shape remarkably due to these two types of crystal structure transitions, and the similarity of the charge / discharge curve during the charge / discharge cycle cannot be maintained. It is not preferable for practical use.

Moreover, the lithium manganese composite oxide of Patent Document 3 has a low discharge voltage and a large charge / discharge curve hysteresis.

The present invention has been made in view of the current state of the prior art described above, and uses a low-cost element with less resource restrictions and has a high capacity when used as a positive electrode material for a lithium ion secondary battery. The main object of the present invention is to provide a novel material that has a high discharge voltage and is excellent in cycle characteristics over a long period of time because the similarity of the charge / discharge curve shape during the charge / discharge cycle can be maintained.

The inventors of the present invention have intensively studied to achieve the above-described object. As a result, a composite oxide in which a specific amount of titanium and / or germanium is further dissolved in a Li ₂ MnO ₃ type composite oxide containing a specific amount of iron and / or nickel is less expensive and less expensive. In addition, when used as a positive electrode material for lithium ion secondary batteries, it has a high capacity, a high discharge voltage, and the similarity of the charge / discharge curve shape during the charge / discharge cycle It was found that long-term cycle characteristics are excellent. Based on such knowledge, the present inventors have further studied and completed the present invention. That is, the present invention includes the following configurations.
Item 1. General formula (1):
Li _{1 + x} (M ¹ _y M ² _z Mn _1-yz ) _1-x O ₂ (1)
[Wherein M ¹ represents Fe and / or Ni. M ² represents Ti and / or Ge. x, y, and z represent 0 <x <1/3, 0 ≦ y ≦ 0.4, and 0 <z ≦ 0.3. ]
And
A lithium manganese composite oxide containing a crystal phase of a monoclinic layered rock salt type structure or a hexagonal layered rock salt type structure.
Item 2. Item 2. The lithium manganese composite oxide according to Item 1, wherein M ¹ in the general formula (1) contains Ni.
Item 3. Item 3. The lithium manganese composite oxide according to Item 1 or 2, comprising only a crystal phase having a monoclinic layered rock salt structure.
Item 4. Item 4. The method for producing a lithium manganese composite oxide according to any one of Items 1 to 3,
(1) a step of forming a precipitate by making a mixture containing a manganese compound and at least one compound selected from the group consisting of an iron compound and a nickel compound alkaline,
(2) A step of subjecting the precipitate obtained in step 1 to wet oxidation and aging,
(3) A production method comprising a step of heating the aged product obtained in step 2 in the order of coexistence of a raw material compound containing a lithium compound.
Item 5. Item 5. The method according to Item 4, wherein the mixture in Step 1 further contains a titanium compound.
Item 6. Item 6. The production method according to

Item

4 or 5, wherein the raw material compound in Step 3 further contains a germanium compound.
Item 7. Item 7. The production method according to any one of Items 4 to 6, wherein Step 3 is a step of heating after mixing the aged product obtained in Step 2 and the raw material compound.
Item 8. Item 8. The manufacturing method according to any one of Items 4 to 7, wherein the heating in Step 3 is a step of heating again in the air or in an inert atmosphere after heating in the air.
Item 9. Item 4. A positive electrode material for a lithium ion secondary battery comprising the lithium manganese composite oxide according to any one of Items 1 to 3.
Item 10. Item 10. A lithium ion secondary battery comprising the positive electrode material for a lithium ion secondary battery according to Item 9.

According to the present invention, when used as a positive electrode material for a lithium ion secondary battery while using an inexpensive element with few resource restrictions, it has a high capacity, a high discharge voltage, and a charge. Since the similarity of the charge / discharge curve shape during the discharge cycle can be maintained, a novel material excellent in long-term cycle characteristics can be provided.

In particular, the lithium manganese composite oxide of the present invention is chemically stable even when charged to a high potential, and therefore can exhibit excellent charge / discharge characteristics even during long-term cycles.

The measured (+) and calculated (solid line) X-ray diffraction patterns of the sample obtained in Example 1 are shown. 2 shows a charge / discharge curve of a lithium secondary battery in which the sample obtained in Example 1 is a positive electrode material and metal lithium is a negative electrode material. The measured (+) and calculated (solid line) X-ray diffraction patterns of the sample obtained in Comparative Example 1 are shown. 2 shows a charge / discharge curve of a lithium secondary battery using the sample obtained in Comparative Example 1 as a positive electrode material and metallic lithium as a negative electrode material. The measured (+) and calculated (solid line) X-ray diffraction patterns of the sample obtained in Example 2 are shown. 2 shows a charge / discharge curve of a lithium secondary battery using the sample obtained in Example 2 as a positive electrode material and metallic lithium as a negative electrode material. The measured (+) and calculated (solid line) X-ray diffraction patterns of the sample obtained in Comparative Example 2 are shown. 2 shows a charge / discharge curve of a lithium secondary battery in which the sample obtained in Comparative Example 2 was used as a positive electrode material and metallic lithium was used as a negative electrode material. The measured (+) and calculated (solid line) X-ray diffraction patterns of the sample obtained in Example 3 are shown. 2 shows a charge / discharge curve of a lithium secondary battery in which the sample obtained in Example 3 was used as a positive electrode material and metal lithium was used as a negative electrode material. The measured (+) and calculated (solid line) X-ray diffraction patterns of the sample obtained in Comparative Example 3 are shown. 2 shows a charge / discharge curve of a lithium secondary battery using the sample obtained in Comparative Example 3 as a positive electrode material and metallic lithium as a negative electrode material. The measured (+) and calculated (solid line) X-ray diffraction patterns of the sample obtained in Example 4 are shown. 2 shows a charge / discharge curve of a lithium secondary battery in which the sample obtained in Example 4 was used as a positive electrode material and metallic lithium was used as a negative electrode material. The measured (+) and calculated (solid line) X-ray diffraction patterns of the sample obtained in Comparative Example 4 are shown. 2 shows a charge / discharge curve of a lithium secondary battery in which the sample obtained in Comparative Example 4 is a positive electrode material and metallic lithium is a negative electrode material. The measured (+) and calculated (solid line) X-ray diffraction patterns of the sample obtained in Example 5 are shown. The charging / discharging curve of the lithium secondary battery which used the sample obtained in Example 5 as a positive electrode material and used metallic lithium as a negative electrode material is shown.

1. Lithium manganese complex oxide The lithium manganese complex oxide of the present invention has the general formula (1):
Li _{1 + x} (M ¹ _y M ² _z Mn _1-yz ) _1-x O ₂ (1)
[Wherein M ¹ represents Fe and / or Ni. M ² represents Ti and / or Ge. x, y, and z represent 0 <x <1/3, 0 ≦ y ≦ 0.4, and 0 <z ≦ 0.3. ]
And includes a crystal phase of a monoclinic layered rock salt type structure or a hexagonal layered rock salt type structure based on a rock salt type structure.

Monoclinic layered rock salt structure is a space group:

In a crystalline phase that can be attributed, in particular, capacity and in terms of cycle characteristics, Li ₂ MnO ₃ type monoclinic layered rock salt consisting only crystal phase with a unit cell similar to Li ₂ MnO ₃ A crystal phase with a mold structure is preferred.

On the other hand, the hexagonal layered rock-salt structure is a space group:

In a crystalline phase that can be attributed, in particular, capacity and in terms of the cycle characteristics, the crystalline phase of LiNiO ₂ type hexagonal layered rock-salt structure comprising only crystalline phase with a unit cell similar to LiNiO ₂ It is preferable that

The lithium manganese composite oxide of the present invention may have only one or both of the crystal phases of the above monoclinic layered rock salt structure and hexagonal layered rock salt structure. Also good. In any case, the lithium manganese composite oxide of the present invention has a high capacity, a high discharge voltage, and a charge / discharge cycle when used as a positive electrode material for a lithium ion secondary battery. This material is excellent in cycle characteristics over a long period of time because the similarity of the charge / discharge curve shape can be maintained.

When the lithium manganese based composite oxide of the present invention has both the monoclinic layered rock salt structure and the crystal phase of the hexagonal layered rock salt structure, the proportion of each crystal phase is not particularly limited, and is usually layered. The total crystal phase of the rock salt type structure is 100% by weight, the crystal phase of the monoclinic layered rock salt type structure is 1 to 99% by weight (especially 5 to 95% by weight, and further 10 to 90% by weight), hexagonal layered rock salt The crystal phase of the mold structure is preferably 1 to 99% by weight (particularly 5 to 95% by weight, more preferably 10 to 90% by weight).

On the other hand, the lithium manganese composite oxide of the present invention only needs to contain the crystal phase of the above monoclinic layered rock salt structure or hexagonal layered rock salt structure, and other rock salt structures with different cation distributions ( For example, a mixed phase including a crystal phase of a cubic rock salt structure or the like may be used. Further, the lithium manganese composite oxide of the present invention may be a material composed only of the crystal phase of the above monoclinic layered rock salt structure and / or hexagonal layered rock salt structure.

According to the production method of the present invention to be described later, the resulting lithium manganese composite oxide is likely to form a material consisting only of the crystal phase of the above monoclinic layered rock salt structure and / or hexagonal layered rock salt structure. However, when synthesizing at a low temperature of 600 ° C. or lower, for example, a crystal phase having a cubic rock salt structure may be included. Since the crystal phase of this cubic rock salt structure is also a crystal structure that exhibits excellent charge / discharge characteristics, it does not matter if it has this crystal structure.

However, in the present invention, having a monoclinic layered rock salt type structure and a hexagonal layered rock salt type crystal phase, when used in a positive electrode material for a lithium ion secondary battery, has a high capacity and high Monoclinic layered rock salt structure and hexagonal layered rock salt because it has a discharge voltage and is excellent in long-term cycle characteristics because it can maintain the similarity of the charge / discharge curve shape during the charge / discharge cycle The proportion of the crystal phase of the mold structure is preferably high. From such a viewpoint, when the lithium manganese composite oxide of the present invention has other rock salt type structures (cubic rock salt type structures, etc.) having different cation distributions, the ratio of the layered rock salt type structure to the crystal phase is Usually, the total amount of the lithium manganese composite oxide of the present invention is 100% by weight, the crystal phase of the layered rock salt structure is 1 to 99% by weight (especially 10 to 95% by weight, more preferably 50 to 90% by weight), etc. The crystal phase of the rock salt type structure (such as cubic rock salt type structure) is preferably 1 to 99% by weight (especially 5 to 90% by weight, more preferably 10 to 50% by weight).

The lithium manganese based composite oxide of the present invention contains Li, Mn and M ² as essential elements as represented by the above general formula (1), and further, M ¹ is dissolved as required. I am letting.

When the lithium manganese-based composite oxide contains an M ¹ (if a solid solution of M ^{^1),} M ¹ ion amount to solid solution of the present invention (y ^{^{value; M 1 / (M 1 +}} M 2 + Mn)) is 40% or less of the total amount of metal ions other than Li ions (0 <y ≦ 0.4), preferably 5 to 35% (0.05 ≦ y ≦ 0.35), more preferably 10 to 30% (0.1 ≦ y ≦ 0.3). When the amount of solid solution (y value) of M ¹ ions is excessive, the amount of Mn is relatively reduced, so that the lithium content per composition formula is lowered, so that the charge / discharge capacity is significantly lowered. On the other hand, by setting the lower limit of the solid solution amount (y value) of M ¹ ions within the above range, the discharge potential can be further increased and the hysteresis can be further reduced.

(If a solid solution of M ¹⁾ the lithium-manganese-based composite oxide of the present invention may contain M ^1, Li, in the form of replacing Mn or the like, when present in the layered rock-salt structure It seems that only one of Fe and Ni may be included, or both Fe and Ni may be included. More specifically, although Fe is cheaper than Ni, Ni has a higher oxidation-reduction potential, so it is easier to increase the discharge voltage, so applications where high potential is required (such as large lithium ion secondary for automotive applications) Suitable for batteries. For this reason, about the usage-amount of Fe and Ni, it is preferable to set suitably according to a use. For example, when both Fe and Ni are included, the total amount of M ¹ element is 100% by weight, and Fe is preferably 10 to 90% by weight (particularly 30 to 70% by weight, more preferably 40 to 60% by weight). The amount of Ni used is set so that the total amount with the amount of Fe used is 100% by weight.

The amount of M ² ions (z value; M ² / (M ¹ + M ² + Mn)) dissolved in the lithium manganese composite oxide of the present invention is 30% or less of the total amount of metal ions other than Li ions ( 0 <z ≦ 0.3), preferably 1 to 25% (0.01 ≦ z ≦ 0.25). When using Ti as M ² is, M ² ion amount is preferably 10 ~ 25% (0.10 ≦ z ≦ 0.25), when using the Ge is, M ² ion amount is 1 ~ 10% (0.01 ≦ z ≦ 0.10) is preferred. When using both the Ti and Ge as M ² is preferably set as appropriate depending on the ratio. When the solid solution amount (z value) of M ² ions is excessive, the charge / discharge capacity is remarkably lowered due to the low electrochemical activity of M ² ions. On the other hand, when the solid solution amount (z value) of the M ² ion is too small, it is difficult to maintain the similarity of the charge / discharge curve shape during the charge / discharge cycle, so that the cycle characteristics when the charge / discharge cycle is performed for a long time are inferior.

M ² in the lithium manganese composite oxide of the present invention is also considered to be present in the layered rock-salt structure in the form of substituting Li, Mn, etc. like M ¹ , but only one of Ti and Ge May be included, and both Ti and Ge may be included. More specifically, although Ti is cheaper than Ge, Ge can exhibit an excellent effect with a small amount of elements, and therefore, when Ge is used, the amount of raw material used can be reduced. For this reason, about the usage-amount of Ti and Ge, it is preferable to set suitably according to a use. For example, when both Ti and Ge are included, the total amount of M ² elements is 100% by weight, and Ti is preferably 10 to 90% by weight (particularly 30 to 70% by weight, more preferably 40 to 60% by weight). The amount of Ge used is set so that the total amount with the amount of Ti used is 100% by weight.

The total amount (y + z) of M ¹ and M ² to be dissolved in the lithium manganese composite oxide of the present invention is preferably 70% or less (0 <y + z ≦ 0.7) in the general formula (1), 10 to 60% (0.1 ≦ y + z ≦ 0.6) is more preferable, 20 to 50% (0.2 ≦ y + z ≦ 0.5) is further preferable, and 25 to 45% (0.25 ≦ y + z ≦ 0.45) is particularly preferable. . As a result, when used as a positive electrode material for a lithium ion secondary battery, the capacity is increased, the discharge voltage is increased, and it is easy to maintain the similarity of the charge / discharge curve shape during the charge / discharge cycle. The cycle characteristics of the period can be made more excellent.

In the lithium manganese composite oxide of the present invention, the amount of Li ions (x) is the average valence of the transition metal as long as the crystal phase of the monoclinic layered rock salt structure or the hexagonal layered rock salt structure can be maintained. It can take values between 0 and 1/3 depending on the number. Usually, 0.100 to 0.300 is preferable, 0.200 to 0.280 is more preferable, and 0.230 to 0.270 is further preferable.

Further, the lithium manganese based composite oxide of the present invention includes lithium hydroxide, lithium carbonate, iron compound, nickel compound, titanium compound, germanium compound, manganese compound, and compounds that do not significantly affect the charge / discharge characteristics. A hydrate of: an impurity phase such as a composite metal compound containing two or more of lithium, iron, nickel, titanium, and germanium. For the amount of impurity phase other than the crystal phase of monoclinic layered rock salt structure, hexagonal layered rock salt structure and other rock salt structures with different cation distribution (cubic rock salt structure, etc.) For example, 0 to 10% by weight is preferable in the lithium manganese composite oxide of the present invention, and 0 to 5% by weight is more preferable.

The lithium manganese composite oxide of the present invention that satisfies the above conditions can maintain the similarity of the charge / discharge curve shape even during a long charge / discharge cycle, and the spinel from the crystal phase of the layered rock salt structure. Abrupt potential drop around 3.5 放電 V during discharge based on the phase transition to the crystalline phase of the type structure, and addition around 2.2 V during discharge based on the phase transition from the crystal phase of the layered rock salt type structure to the lithium-rich crystal phase Therefore, the lithium manganese composite oxide of the present invention not only has a high capacity and a high discharge voltage, but also has excellent cycle characteristics even during a long charge / discharge cycle. Have. For this reason, the lithium manganese composite oxide of the present invention is extremely useful as a positive electrode material for large-sized lithium ion secondary batteries for in-vehicle use as well as small-sized consumer lithium ion secondary batteries.

2. Method for Producing Lithium Manganese Composite Oxide The lithium manganese composite oxide of the present invention can be synthesized by using an ordinary composite oxide synthesis method. Specifically, it can be synthesized by a coprecipitation-firing method, a coprecipitation-hydrothermal-firing method, a solid phase reaction method, or the like. From the viewpoint of easily producing a complex oxide having particularly excellent charge / discharge characteristics, it is preferable to employ a coprecipitation-firing method.

For example, when the coprecipitation-firing method is adopted, for example,
(1) A step of forming a precipitate by making a mixture containing a manganese compound, at least one compound selected from the group consisting of an iron compound and a nickel compound, and a titanium compound as necessary, alkaline (hereinafter referred to as step 1 and step 1) Sometimes)
(2) A step of subjecting the precipitate obtained in step 1 to wet oxidation treatment and aging (hereinafter sometimes referred to as step 2),
(3) Manufacture comprising a step of heating the aged product obtained in step 2 in the presence of a lithium compound and, if necessary, a raw material compound containing a germanium compound (hereinafter also referred to as step 3) in this order. By the method, the lithium manganese composite oxide of the present invention can be obtained.

(2-1) Process 1
In step 1, a mixture containing a manganese compound and at least one compound selected from the group consisting of an iron compound and a nickel compound is made alkaline to form a precipitate. Specifically, it is convenient to form a precipitate as alkaline from a solution of a mixture containing a manganese compound and at least one compound selected from the group consisting of an iron compound and a nickel compound.

In addition, in the lithium manganese composite oxide of the present invention to be finally obtained, when it contains a Ti element, at least one compound selected from the group consisting of a manganese compound and an iron compound and a nickel compound, It is preferable that the mixture containing the titanium compound is made alkaline to form a precipitate. Specifically, it is convenient to form a precipitate by adding a solution of a mixture containing a manganese compound, at least one compound selected from the group consisting of an iron compound and a nickel compound, and a titanium compound to an alkali. .

As the manganese compound, iron compound, nickel compound and titanium compound, a component capable of forming a mixed aqueous solution containing these compounds is preferable. It is preferable to use a water-soluble compound. Specific examples of such water-soluble compounds include water-soluble salts such as manganese, iron, nickel or titanium chlorides, nitrates, sulfates, oxalates and acetates; hydroxides and the like. it can. Moreover, the compound containing several metal seed | species, such as manganese titanate, nickel titanate, nickel manganate, iron manganate, can also be used. As a manganese compound, permanganates such as potassium permanganate can also achieve uniform distribution of metals other than lithium ions, and charge / discharge characteristics can be further improved. These water-soluble compounds can employ both anhydrides and hydrates. Further, even water-insoluble compounds such as manganese, iron, nickel or titanium oxides and metals can be dissolved in an acid such as sulfuric acid and hydrochloric acid and used as an aqueous solution. Each of these raw material compounds can be used individually for each metal source, or can be used in combination of two or more.

The mixing ratio of the manganese compound, iron compound, nickel compound and titanium compound can be the same element ratio as the element ratio in the target lithium manganese composite oxide of the present invention.

The concentration of each compound in the case of a mixed aqueous solution is not particularly limited, and can be appropriately determined so that a uniform mixed aqueous solution can be formed and a coprecipitate can be smoothly formed. Usually, the total concentration of the manganese compound, iron compound, nickel compound and titanium compound is preferably 0.01 to 5 mol / L, particularly preferably 0.1 to 2 mol / L.

As a solvent in the case of a mixed aqueous solution, water can be used alone, or a water-alcohol mixed solvent containing a water-soluble alcohol such as methanol or ethanol can be used. By using a water-alcohol mixed solvent, the alcohol acts as an antifreeze and precipitates can be formed at temperatures below 0 ° C. By performing precipitate formation at low temperatures, prone lithium ferrite during precipitation when containing Fe as M ¹ element suppresses more the formation of impurities such as manganese ferrite, i.e. uniform co more transition metal distribution You can get a deposit. In addition, since a manganese source such as potassium permanganate, which is difficult to form a precipitate only with water, can be used, the range of raw material selection is further expanded. The amount of alcohol used can be determined appropriately according to the target precipitation temperature, etc., and is usually 50 parts by weight or less (for example, 10 to 50 parts by weight) with respect to 100 parts by weight of water. Is appropriate.

A precipitate (coprecipitate) can be generated by making the mixture (particularly the mixed aqueous solution) alkaline. Conditions for forming a good precipitate cannot be defined unconditionally because they vary depending on the type, concentration, etc. of each compound contained in the mixture (particularly the mixed aqueous solution), but usually a pH of 8 or more (for example, pH 8 to 14) is preferable. More preferably, the pH is 11 or more (for example, pH 11 to 14).

There is no particular limitation on the method of making the mixture (especially the mixed aqueous solution) alkaline. Usually, the mixture (particularly the mixed aqueous solution) is added to an aqueous solution containing alkali in order to form a uniform precipitate. A precipitate (coprecipitate) can also be formed by the method. The precipitate can also be obtained by adding an alkali or an aqueous solution containing an alkali to the mixed aqueous solution.

As the alkali used to make the mixture (in particular, the mixed aqueous solution) alkaline, for example, alkali metal hydroxides such as potassium hydroxide, sodium hydroxide, and lithium hydroxide, ammonia, and the like can be used. When these alkalis are used as an aqueous solution, for example, they can be used as an aqueous solution having a concentration of 0.1 to 20 mol / L, particularly 0.3 to 10 mol / L. In addition, the alkali can be dissolved in a water-alcohol mixed solvent containing a water-soluble alcohol, similarly to the mixed aqueous solution of the metal compound described above.

During precipitation, the temperature of the mixture (particularly the mixed aqueous solution) is usually -50 to 50 ° C, particularly -20 to 30 ° C, so that when M ¹ contains Fe, The generation of spinel ferrite due to the generation of sum heat is further suppressed, and fine and homogeneous precipitates (coprecipitates) are easily formed. It becomes easy to synthesize manganese-based composite oxides. Moreover, in order to form a precipitate (coprecipitate) satisfactorily in this step, the mixture (particularly the mixed aqueous solution) is required to take at least several hours against alkali in order to further suppress the generation of heat of neutralization. The method of gradually dripping is preferable. In this case, the longer the reaction time, the better. However, in practice, 1 hour to 1 day, particularly 2 to 12 hours are preferable.

(2-2) Step 2
After the precipitate (coprecipitate) is formed in the above step 1, the precipitate (coprecipitate) is aged by wet oxidation. Specifically, in step 2, the precipitate (coprecipitate) obtained in step 1 is subjected to wet oxidation treatment and aged. More specifically, it can be aged by bubbling by bubbling oxygen-containing gas into the alkaline aqueous solution containing the precipitate (coprecipitate) obtained in the above step 1 with a compressor, an oxygen gas generator or the like. it can.

The gas to be blown preferably contains a certain amount of oxygen. Specifically, it is preferable to contain 10 to 100% by volume of oxygen of the gas to be blown. Examples of such a gas to be blown include air and oxygen, and oxygen is preferable.

The aging temperature is not particularly limited, and a temperature at which wet oxidation treatment of the precipitate (coprecipitate) can be performed is preferable. Usually, 0 to 150 ° C. is preferable, and 10 to 100 ° C. is more preferable. Further, the aging time is not particularly limited, and a time during which the wet oxidation treatment of the precipitate (coprecipitate) can be performed is preferable. The longer the aging time is, the better. In practice, however, 0.5 to 7 days is preferable, and 2 to 4 days is more preferable.

It is also possible to purify the precipitate by washing the resulting precipitate with distilled water or the like as necessary to remove excess alkali components, residual raw materials, etc., and filtering.

(2-3) Step 3
Next, in step 3, the aged product obtained in step 2 is heated in the presence of a raw material compound containing a lithium compound. Specifically, the aged product obtained in step 2 and an aqueous solution containing a raw material compound containing a lithium compound may be heated (particularly calcined) after forming a slurry and drying and grinding as required. preferable.

In the aqueous solution to be used, the content of the aged product obtained in the above step 2 is usually preferably 100 to 3000 g, more preferably 500 to 2000 g per 1 L of water.

Examples of the lithium compound include water-soluble lithium salts such as lithium chloride, lithium iodide, lithium nitrate, lithium acetate, and lithium hydroxide; lithium carbonate and the like. These lithium compounds can be used alone or in combination of two or more. Moreover, as a lithium compound, both an anhydride and a hydrate can be employ | adopted. In particular, when the lithium manganese composite oxide of the present invention contains Ge, it is preferable to use lithium hydroxide as the lithium compound because the water-insoluble germanium compound can be easily dissolved.

The amount of the lithium compound used is preferably Li / (M ¹ + M ² ) = 1 to 5, preferably 1.5 to 3, based on the total amount of the aged product obtained in the above step 2 and the germanium compound described later. More preferred.

Further, the concentration of the lithium compound in the aqueous solution is usually preferably 0.1 to 10 mol / L, more preferably 1 to 8 mol / L.

Further, when the lithium manganese composite oxide of the present invention contains Ge, it is preferable to use a germanium compound as a raw material compound.

Examples of germanium compounds include water-soluble germanium compounds such as germanium chloride and germanium iodide; water-insoluble germanium compounds such as germanium oxide and metal germanium. When using a water-insoluble germanium compound, taking advantage of the fact that germanium is an amphoteric element, the germanium compound is dissolved with an acid or alkali as described above to improve the reactivity with the aged product obtained in step 2. It is preferable. In addition, when using lithium hydroxide as a lithium compound, it is possible to dissolve a water-insoluble germanium compound without using an acid or an alkali separately.

When washing is performed after heating, the amount of germanium that is washed away is large, and therefore the amount of germanium compound added (the amount charged) is preferably greater than the content in the composite oxide to be obtained. From such a viewpoint, the amount of the germanium compound used is preferably Ge / (M ¹ + M ² ) = 0.01 to 0.5, based on the total amount of the matured product obtained in the above step 2 and the germanium compound. 0.1 to 0.4 is more preferable.

Further, the concentration of the germanium compound in the aqueous solution is usually preferably from 0.05 to 1.0 mol / L, more preferably from 0.1 to 0.7 mol / L.

The mixing method of the aged product obtained in step 2, the lithium compound and, if necessary, the zirconium compound is not particularly limited. For example, after adding the aged product obtained in Step 2 to an aqueous solution of a water-soluble lithium compound and stirring and dispersing it, an aqueous solution of a water-soluble germanium compound or an alkali solution of a water-insoluble germanium compound that is separately prepared is added. After stirring well, it is preferable to dry and pulverize as necessary.

Stirring can be carried out by a usual method, for example, it is preferable to stir with a known mixer such as a mixer, a V-type mixer, a W-type mixer, or a ribbon mixer.

When drying, the drying conditions are not particularly limited. For example, the drying temperature is preferably 20 to 100 ° C., more preferably 30 to 80 ° C. The drying time is preferably, for example, 1 hour to 5 days, and more preferably 12 hours to 3 days.

In order to improve the reactivity during the subsequent heat treatment, it is preferable to grind. Regarding the degree of pulverization, it is preferable that coarse particles are not included and the mixture has a uniform color tone. When pulverizing, a normal method can be adopted, and for example, pulverization can be performed by a vibration mill, a ball mill, a jet mill or the like. Further, the grinding can be repeated twice or more. In addition, the heat treatment can be performed by gradually increasing the heating temperature.

The heat treatment is usually preferably performed in a closed container (such as an electric furnace).

The heating conditions are not particularly limited, but the final heating temperature is preferably 750 ° C. or higher in order to further stabilize the charge / discharge cycle characteristics. The heating temperature is preferably 1000 ° C. or lower so that lithium is less likely to volatilize. The final heating temperature is particularly preferably 800 to 950 ° C. By heating (especially firing) in this range, lithium manganese not only has a high capacity and a high discharge voltage, but also has excellent cycle characteristics even during a long charge / discharge cycle. It is easy to obtain a composite oxide.

The heating atmosphere (particularly the firing atmosphere) is not particularly limited. When the final heating atmosphere is an inert atmosphere such as nitrogen or argon or a reducing atmosphere, in order to suppress the decomposition of the sample, heat it beforehand in the air at a low temperature of 500 to 750 ° C (especially 550 to 700 ° C) ( It is preferable to perform final heating (particularly final baking) in an inert atmosphere or a reducing atmosphere after firing. Even when the final heating atmosphere is air, two-stage heating (especially firing) can be performed in order to more precisely control the Li content, powder characteristics, and the like. When the final heating atmosphere is a reducing atmosphere, for example, by baking in an inert atmosphere in the presence of organic matter, carbon powder, etc., heat treatment (particularly baking) in a reducing atmosphere is possible. is there.

The organic substance is not particularly limited, and a carbon-containing compound that can be decomposed into a reducing atmosphere at the heating temperature (particularly the firing temperature) is preferable. In particular, when a water-soluble organic substance is used, it is advantageous because it can be dispersed and mixed with the lithium manganese composite oxide powder in an aqueous solution state. Specific examples of such organic substances include sucrose, glucose, starch, acetic acid, citric acid, oxalic acid, benzoic acid, aminoacetic acid and the like.

As the carbon powder, for example, carbon powder obtained by thermal decomposition of an organic substance, for example, graphite, acetylene black, or the like can be used.

The above-mentioned organic substances and carbon powder can be used alone or in combination of two or more.

The amount of at least one component selected from the group consisting of organic matter and carbon powder is preferably 0.001 to 5 times mol, and 0.01 to 1 times mol in terms of the molar amount of carbon with respect to the lithium manganese composite oxide. More preferred. When used as an aqueous solution, the concentration of the organic substance or the like can be appropriately determined so as to be within the above-mentioned range of use amount.

The heating time is not particularly limited. More specifically, the holding time at the final heating temperature is preferably 10 minutes to 24 hours, more preferably 30 minutes to 12 hours. In addition, when performing two-stage heat treatment, the holding time at the first stage heating temperature is preferably 10 minutes to 24 hours (particularly 30 minutes to 12 hours), and the holding time at the second stage final heating temperature is 10 minutes. ~ 24 hours (especially 30 minutes to 12 hours) is preferred.

After obtaining the lithium manganese composite oxide of the present invention by the above-described method, the obtained fired product may be subjected to a water washing treatment, a solvent washing treatment, etc., in order to remove an excess lithium compound, if necessary. it can. Thereafter, filtration is performed, and for example, heat drying can be performed at 80 ° C. or higher, preferably 100 ° C. or higher.

Further, if necessary, the heat-dried material is pulverized, and a lithium compound and an organic material are added and heated (particularly calcined), washed, and dried to repeatedly perform a series of operations, whereby the lithium manganese composite oxide It is also possible to further improve the excellent characteristics.

3. Lithium Ion Secondary Battery A lithium ion secondary battery using the lithium manganese composite oxide of the present invention can be produced by a known method. For example, the lithium manganese composite oxide of the present invention is used as a positive electrode material, and known metal lithium, carbon-based materials (activated carbon, graphite, etc.), silicon, silicon oxide, Si—SiO based materials, lithium as negative electrode materials A solution in which lithium salt such as lithium perchlorate or LiPF ₆ is dissolved in a solvent composed of one or more of known ethylene carbonate, dimethyl carbonate, diethyl carbonate, etc. Solution), inorganic solid electrolyte (Li ₂ S-P ₂ S ₅ series, Li ₂ S-GeS ₂ -P ₂ S ₅ series, etc.) and other known battery components, Thus, a lithium ion secondary battery can be assembled. In the present invention, the “lithium ion secondary battery” is a concept including a “lithium secondary battery” using metallic lithium as a negative electrode material. In the present invention, the term “lithium ion secondary battery” refers to both a “nonaqueous lithium ion secondary battery” using a nonaqueous electrolyte and an “all solid lithium ion secondary battery” using a solid electrolyte. It is a concept to include.

Hereinafter, examples and comparative examples will be shown to further clarify the features of the present invention, but the present invention is not limited to the following examples.

[Example 1]
Sample synthesis, structure and composition evaluation 10.10 g of iron (III) nitrate nonahydrate, 7.27 g of nickel (II) nitrate hexahydrate, 40.00 g of 30% titanium sulfate (IV) aqueous solution, manganese (II) chloride 4 water 29.69 g of Japanese product (total amount 0.25 mol, Fe: Ni: Ti: Mn molar ratio 1: 1: 2: 6) was added to 500 mL of distilled water and completely dissolved. In another beaker, 50 g of sodium hydroxide was weighed, 500 mL of distilled water was added and dissolved while stirring to prepare an aqueous sodium hydroxide solution. This aqueous sodium hydroxide solution was placed in a titanium beaker and allowed to stand in a thermostat kept at 20 ° C. Next, the metal salt aqueous solution was gradually dropped into the sodium hydroxide solution over about 3 hours to form an Fe—Ni—Ti—Mn precipitate (coprecipitate). After confirming that the reaction solution was completely alkaline, oxygen was blown into the reaction solution containing the coprecipitate with stirring at room temperature for 2 days to ripen the precipitate.

The obtained precipitate was washed with distilled water, filtered, and mixed with 18.47 g of 0.25 mol lithium carbonate dispersed in distilled water to form a uniform slurry. The slurry was transferred to a tetrafluoroethylene petri dish, dried at 50 ° C. for 2 days, and then pulverized to prepare a firing raw material.

Next, the obtained powder was heated to 650 ° C. over 1 hour, held at that temperature for 5 hours, and then cooled in the furnace to near room temperature. After pulverization, the temperature was raised again to 850 ° C. over 1 hour in a nitrogen stream using an electric furnace, held at that temperature for 5 hours, and then cooled to near room temperature in the furnace. In other words, the sample was prepared by firing in air in the first stage and in a nitrogen atmosphere in the second stage. In order to remove the fired product from the electric furnace and remove the excess lithium salt, the fired product is washed with distilled water, filtered, and dried to powder the target iron, nickel and titanium substituted Li ₂ MnO ₃ Obtained as a product.

Evaluation by X-ray diffraction The actual measurement (+) and calculation (solid line) X-ray diffraction patterns of this final product are shown in FIG. From the analysis results by Rietveld analysis program RIETAN-FP, all peaks can be indexed with the lattice constants listed in Table 1 below, and only the crystalline phase with monoclinic Li ₂ MnO ₃ unit cells (C2 / m) I understood that it consists of. Also, when the transition metal ion distribution in the structure shown in Table 2 was confirmed, the sample of Example 1 had a smaller amount of transition metal in the Li-Mn layer than the sample of Comparative Example 1 not containing Ti described later, and the Li single layer. It can be seen that the amount of inner transition metal is large, and that transition metal ions tend to be irregularly arranged by introducing Ti. In addition, it can be seen that the sample of Example 1 has a higher degree of hexagonal network alignment than the sample of Comparative Example 1 that does not contain Ti described later.

Evaluation by chemical analysis Based on chemical analysis, the Fe, Ni, and Ti contents with respect to the total amount of metals other than lithium are 10 mol%, 10 mol% (y value equivalent to 0.20), and 20 mol% (z value equivalent to 0.20), respectively. Since the Li / (M ¹ + M ² + Mn) ratio is 1.68 (x value conversion 0.254), the target composition formula Li _{1 + x} (M ¹ _y M ² _z Mn _1-yz ) ₁ It is clear that a lithium manganese composite oxide having _-x O ₂ was obtained.

The details of the charge / discharge characteristic evaluation are described in the charge / discharge characteristic evaluation described later. A lithium secondary battery using the obtained sample as the positive electrode material and metallic lithium as the negative electrode material was prepared, and an activation treatment and a cycle test were performed. It was.

From the results of FIG. 2 and Table 4, the sample of Example 1 not only shows a charge / discharge capacity of approximately 240 mAh / g after activation, but also contains a M ² element described later, and is a comparative example obtained under the same production conditions. Compared with the sample No. 1, not only the charge / discharge characteristics at the first cycle after the activation treatment are almost the same, but also the charge / discharge curves similar to those at the 20th cycle after the activation treatment up to 50 cycles after the activation treatment. Show. In other words, a sudden drop in potential from around 3.7 V accompanying the structural transition from the layered rock salt structure to the spinel phase during 50-cycle discharge after activation treatment, and the Li ₂ (Ni, Mn) O ₂ phase from the layered rock salt structure From the fact that no additional capacity appears at 2.2 V or less accompanying the structural transition to, it is clear that the positive electrode material is excellent in high capacity and long-term cycle characteristics.

[Comparative Example 1]
Starting materials: iron nitrate (III) nonahydrate 10.10 g, nickel nitrate (II) hexahydrate 7.27 g, manganese chloride tetrahydrate 39.58 g (total 0.25 mol, Fe: Ni: Mn mol) The ratio 1: 1: 8) was added to 500 mL of distilled water and completely dissolved. Thereafter, the positive electrode material was produced in the same manner as in Example 1.

The actual measurement (+) and calculation (solid line) X-ray diffraction patterns of this final product are shown in FIG. From the analysis results of the Rietveld analysis program RIETAN-FP, all peaks can be indexed with the lattice constants shown in Table 1 below, and only from the crystalline phase with monoclinic Li ₂ MnO ₃ unit cells (C2 / m) I found out that

Also, from chemical analysis, the Fe and Ni contents with respect to the total amount of metals other than lithium are maintained at 10 mol% and 10 mol% (y value equivalent to 0.20), respectively, and the Li / (M ¹ + Mn) ratio Was 1.71 (x value conversion 0.262), and a lithium manganese composite oxide having a composition formula Li _{1 + x} (M ¹ _y Mn _1-y ) _1-x O ₂ not containing M ² was obtained. Is clear.

Furthermore, the lithium secondary battery which made the obtained sample the positive electrode material and made metal lithium into the negative electrode material was produced in the procedure as described in the charge / discharge characteristic evaluation mentioned later for details, and the activation process and the cycle test were done. The evaluation results of the charge / discharge characteristics are shown in FIG. 4 and Table 3, the sample of Comparative Example 1 shows a charge / discharge capacity of approximately 250 mAh / g after activation, but 3.7 times due to the structural transition from the layered rock salt structure to the spinel phase during 50 cycles of discharge after the activation treatment. Implemented because of the sudden drop in potential from around V and the appearance of additional capacity below 2.2 V due to the structural transition from the layered rock salt structure to the Li ₂ (Ni, Mn) O ₂ phase Compared to the lithium manganese composite oxide of Example 1, it is clear that the cathode material is inferior in long-term cycle characteristics.

[Example 2]
A sample was prepared in the same manner as in Example 1 except that the final firing atmosphere was air. In other words, the sample was prepared by firing twice in the air. FIG. 5 shows the measured (+) and calculated (solid line) X-ray diffraction patterns of this final product. From the analysis results of the Rietveld analysis program RIETAN-FP, all peaks can be indexed with the lattice constants shown in Table 1 below, and only from the crystalline phase with monoclinic Li ₂ MnO ₃ unit cells (C2 / m) I found out that

Further, when the transition metal ion distribution in the structure of Table 2 described later is confirmed, the sample of Example 2 has a smaller amount of transition metal in the Li-Mn layer than the sample of Comparative Example 2 that does not contain Ti described later. It can be seen that the amount of transition metal in the single layer is large, and that transition metal ions tend to be irregularly arranged by introducing Ti. In addition, it can be seen that the sample of Example 2 has a higher degree of hexagonal network alignment than the sample of Comparative Example 2 that does not contain Ti described later.

Also, according to chemical analysis, the Fe, Ni, and Ti contents with respect to the total amount of metals other than lithium were maintained at 10 mol%, 10 mol% (y value equivalent to 0.20), and 20 mol% (z value equivalent to 0.20), respectively. Since the Li / (M ¹ + M ² + Mn) ratio is also 1.72 (x value conversion 0.265), the target composition formula Li _{1 + x} (M ¹ _y M ² _z Mn _1-yz ) _1-x O It is clear that a lithium manganese composite oxide having ₂ was obtained.

Furthermore, the lithium secondary battery which made the obtained sample the positive electrode material and made metal lithium into the negative electrode material was produced in the procedure as described in the charge / discharge characteristic evaluation mentioned later for details, and the activation process and the cycle test were done. The evaluation results of the charge / discharge characteristics are shown in FIG. 6 and Table 3, the sample of Example 2 not only shows a charge / discharge capacity close to 240 mAh / g after activation, but also does not contain the M ² element described later, and the sample of Comparative Example 2 obtained under the same production conditions. Compared to the sample, not only the charge / discharge characteristics at the first cycle after the activation treatment are almost equivalent, but also a charge / discharge curve similar to that at the 20th cycle after the activation treatment is shown up to 50 cycles after the activation treatment. Yes. In other words, a sudden drop in potential from around 3.7 V accompanying the structural transition from the layered rock-salt structure to the spinel phase during 50-cycle discharge after activation treatment, and the Li ₂ (Ni, Mn) O ₂ phase from the layered rock-salt structure From the fact that no additional capacity appears at 2.2 V or less due to the structural transition, it is clear that the positive electrode material is excellent in high capacity and long-term cycle characteristics.

[Comparative Example 2]
Starting materials: iron nitrate (III) nonahydrate 10.10 g, nickel nitrate (II) hexahydrate 7.27 g, manganese chloride tetrahydrate 39.58 g (total 0.25 mol, Fe: Ni: Mn mol) The ratio 1: 1: 8) was added to 500 mL of distilled water and completely dissolved. Thereafter, the cathode material was produced in the same manner as in Example 2.

FIG. 7 shows the measured (+) and calculated (solid line) X-ray diffraction patterns of this final product. From the analysis results of the Rietveld analysis program RIETAN-FP, all peaks can be indexed with the lattice constants shown in Table 1 below, and only from the crystalline phase with monoclinic Li ₂ MnO ₃ unit cells (C2 / m) I found out that

Also, from chemical analysis, the Fe and Ni contents with respect to the total amount of metals other than lithium are maintained at 10 mol% and 10 mol% (y value equivalent to 0.20), respectively, and the Li / (M ¹ + Mn) ratio 1.73 (x value conversion 0.267), a lithium manganese composite oxide having a composition formula Li _{1 + x} (M ¹ _y Mn _1-y ) _1-x O ₂ not containing M ² was obtained. Is clear.

Furthermore, the lithium secondary battery which made the obtained sample the positive electrode material and made metal lithium into the negative electrode material was produced in the procedure as described in the charge / discharge characteristic evaluation mentioned later for details, and the activation process and the cycle test were done. The evaluation results of the charge / discharge characteristics are shown in FIG. 8 and Table 3, the sample of Comparative Example 2 shows a charge / discharge capacity of approximately 250 mAh / g after activation, but 3.7 cycles accompanying the structural transition from the layered rock-salt structure to the spinel phase during 50 cycles of discharge after activation. Implemented because of the sudden drop in potential from around V and the appearance of additional capacity below 2.2 V due to the structural transition from the layered rock salt structure to the Li ₂ (Ni, Mn) O ₂ phase Compared with the lithium manganese composite oxide of Example 2, it is clear that the cathode material is inferior in long-term cycle characteristics.

[Example 3]
A sample was prepared in the same manner as in Example 1 except that the final firing conditions were 900 ° C. and 5 hours in the air. In other words, the sample was prepared by firing twice in the air. The actual measurement (+) and calculation (solid line) X-ray diffraction patterns of this final product are shown in FIG. From the analysis results of the Rietveld analysis program RIETAN-FP, all peaks can be indexed with the lattice constants shown in Table 1 below, and only from the crystalline phase with monoclinic Li ₂ MnO ₃ unit cells (C2 / m) I found out that

Further, when the transition metal ion distribution in the structure of Table 2 described later is confirmed, the sample of Example 3 has a smaller amount of transition metal in the Li-Mn layer than the sample of Comparative Example 3 not containing Ti described later, and Li It can be seen that the amount of transition metal in the single layer is large, and that transition metal ions tend to be irregularly arranged by introducing Ti. In addition, it can be seen that the sample of Example 3 has a higher degree of hexagonal network alignment than the sample of Comparative Example 3 that does not contain Ti described later.

Also, according to chemical analysis, the Fe, Ni, and Ti contents with respect to the total amount of metals other than lithium were maintained at 10 mol%, 10 mol% (y value equivalent to 0.20), and 20 mol% (z value equivalent to 0.20), respectively. Since the Li / (M ¹ + M ² + Mn) ratio is 1.74 (x value conversion 0.270), the target composition formula Li _{1 + x} (M ¹ _y M ² _z Mn _1-yz ) _1-x O It is clear that a lithium manganese composite oxide having ₂ was obtained.

Furthermore, the lithium secondary battery which made the obtained sample the positive electrode material and made metal lithium into the negative electrode material was produced in the procedure as described in the charge / discharge characteristic evaluation mentioned later for details, and the activation process and the cycle test were done. The evaluation results of the charge / discharge characteristics are shown in FIG. 10 and Table 3, the sample of Example 3 not only shows a charge / discharge capacity close to 200 mAh / g after activation, but also contains the M ² element described later and is a sample of Comparative Example 3 obtained under the same production conditions. Compared with, the charge / discharge characteristics at the first cycle after the activation treatment are almost equal, and the charge / discharge curve is similar to that at the 20th cycle after the activation treatment up to 50 cycles after the activation treatment. . In other words, a sudden drop in potential from around 3.7 V accompanying the structural transition from the layered rock salt structure to the spinel phase during 50-cycle discharge after activation treatment, and the Li ₂ (Ni, Mn) O ₂ phase from the layered rock salt structure From the fact that no additional capacity appears at 2.2 V or less accompanying the structural transition to, it is clear that the positive electrode material is excellent in high capacity and long-term cycle characteristics.

[Comparative Example 3]
Starting materials: iron nitrate (III) nonahydrate 10.10 g, nickel nitrate (II) hexahydrate 7.27 g, manganese chloride tetrahydrate 39.58 g (total 0.25 mol, Fe: Ni: Mn mol) The ratio 1: 1: 8) was added to 500 mL of distilled water and completely dissolved. Thereafter, the positive electrode material was produced in the same manner as in Example 3.

The measured (+) and calculated (solid line) X-ray diffraction patterns of this final product are shown in FIG. From the analysis results of the Rietveld analysis program RIETAN-FP, all peaks can be indexed with the lattice constants shown in Table 1 below, and only from the crystalline phase with monoclinic Li ₂ MnO ₃ unit cells (C2 / m) I found out that

Furthermore, the lithium secondary battery which made the obtained sample the positive electrode material and made metal lithium into the negative electrode material was produced in the procedure as described in the charge / discharge characteristic evaluation mentioned later for details, and the activation process and the cycle test were done. The evaluation results of the charge / discharge characteristics are shown in FIG. 12 and Table 3, the sample of Comparative Example 3 shows a charge / discharge capacity close to 230 mAh / g after activation, but during the 50-cycle discharge after the activation treatment, 3.7 is associated with the structural transition from the layered rock salt structure to the spinel phase. Implemented because of the sudden drop in potential from around V and the appearance of additional capacity below 2.2 V due to the structural transition from the layered rock salt structure to the Li ₂ (Ni, Mn) O ₂ phase Compared with the lithium manganese composite oxide of Example 3, it is clear that the cathode material is inferior in long-term cycle characteristics.

[Example 4]
A sample was prepared in the same manner as in Example 1 except that the final firing conditions were 900 ° C. and 5 hours in a nitrogen stream. The actual measurement (+) and calculation (solid line) X-ray diffraction patterns of this final product are shown in FIG. From the analysis results of the Rietveld analysis program RIETAN-FP, all peaks can be indexed with the lattice constants shown in Table 1 below, and only from the crystalline phase with monoclinic Li ₂ MnO ₃ unit cells (C2 / m) I found out that

Further, when the transition metal ion distribution in the structure of Table 2 described later is confirmed, the sample of Example 4 has a smaller amount of transition metal in the Li-Mn layer than the sample of Comparative Example 4 which does not contain Ti described later. It can be seen that the amount of transition metal in the single layer is large, and that transition metal ions tend to be irregularly arranged by introducing Ti. Further, it can be seen that the sample of Example 4 has a higher degree of hexagonal network regular arrangement than the sample of Comparative Example 4 which does not contain Ti described later.

Also, according to chemical analysis, the Fe, Ni, and Ti contents with respect to the total amount of metals other than lithium were maintained at 10 mol%, 10 mol% (y value equivalent to 0.20), and 20 mol% (z value equivalent to 0.20), respectively. The Li / (M ¹ + M ² + Mn) ratio is also 1.64 (x value conversion 0.242), so the target composition formula Li _{1 + x} (M ¹ _y M ² _z Mn _1-yz ) _1-x O It is clear that a lithium manganese composite oxide having ₂ was obtained.

Furthermore, the lithium secondary battery which made the obtained sample the positive electrode material and made metal lithium into the negative electrode material was produced in the procedure as described in the charge / discharge characteristic evaluation mentioned later for details, and the activation process and the cycle test were done. The evaluation results of the charge / discharge characteristics are shown in FIG. 14 and Table 3, the sample of Example 4 not only shows a charge / discharge capacity close to 200 mAh / g after activation, but also contains the M ² element described later, and the sample of Comparative Example 4 obtained under the same production conditions. Compared with, the charge / discharge characteristics at the first cycle after the activation treatment are almost equal, and the charge / discharge curve is similar to that at the 20th cycle after the activation treatment up to 50 cycles after the activation treatment. . In other words, a sudden drop in potential from around 3.7 V accompanying the structural transition from the layered rock salt structure to the spinel phase during 50-cycle discharge after activation treatment, and the Li ₂ (Ni, Mn) O ₂ phase from the layered rock salt structure From the fact that no additional capacity appears at 2.2 V or less accompanying the structural transition to, it is clear that the positive electrode material is excellent in high capacity and long-term cycle characteristics.

[Comparative Example 4]
Starting materials: iron nitrate (III) nonahydrate 10.10 g, nickel nitrate (II) hexahydrate 7.27 g, manganese chloride tetrahydrate 39.58 g (total 0.25 mol, Fe: Ni: Mn mol) The ratio 1: 1: 8) was added to 500 mL of distilled water and completely dissolved. Thereafter, the positive electrode material was produced in the same manner as in Example 4.

Also, from chemical analysis, the Fe and Ni contents with respect to the total amount of metals other than lithium are maintained at 10 mol% and 10 mol% (y value equivalent to 0.20), respectively, and the Li / (M ¹ + Mn) ratio Was 1.72 (x value conversion 0.265), and a lithium manganese composite oxide having a composition formula Li _{1 + x} (M ¹ _y Mn _1-y ) _1-x O ₂ not containing M ² was obtained. Is clear.

Furthermore, the lithium secondary battery which made the obtained sample the positive electrode material and made metal lithium into the negative electrode material was produced in the procedure as described in the charge / discharge characteristic evaluation mentioned later for details, and the activation process and the cycle test were done. The evaluation results of the charge / discharge characteristics are shown in FIG. 16 and Table 3, the sample of Comparative Example 4 shows a charge / discharge capacity close to 200 mAh / g after activation, but it is 3.7 with the structural transition from the layered rock salt structure to the spinel phase after 50 cycles of discharge after the activation treatment. Implemented because of the sudden drop in potential from around V and the appearance of additional capacity below 2.2 V due to the structural transition from the layered rock salt structure to the Li ₂ (Ni, Mn) O ₂ phase As compared with the lithium manganese composite oxide of Example 4, it is clear that the cathode material is inferior in long-term cycle characteristics.

[Example 5]
Sample synthesis, structure and composition evaluation 10.10 g of iron (III) nitrate nonahydrate, 7.27 g of nickel (II) nitrate hexahydrate, 29.69 g of manganese (II) chloride tetrahydrate (total amount 0.25 mol, Fe: Ni: Mn molar ratio 1: 1: 6) was added to 500 mL of distilled water and completely dissolved. In another beaker, 50 g of sodium hydroxide was weighed, 500 mL of distilled water was added and dissolved while stirring to prepare an aqueous sodium hydroxide solution. This aqueous sodium hydroxide solution was placed in a titanium beaker and allowed to stand in a thermostat kept at 20 ° C. Next, the metal salt aqueous solution was gradually dropped into the sodium hydroxide solution over about 3 hours to form an Fe—Ni—Mn precipitate (coprecipitate). After confirming that the reaction solution was completely alkaline, oxygen was blown into the reaction solution containing the coprecipitate with stirring at room temperature for 2 days to ripen the precipitate.

The obtained precipitate was washed with distilled water, filtered, dispersed with distilled water and completely dissolved in lithium hydroxide monohydrate 20.98 g (0.5 mol) and GeO ₂ 5.23 g (0.05 mol) and a mixer Mix to form a uniform slurry. The slurry was transferred to a tetrafluoroethylene petri dish, dried at 50 ° C. for 2 days, and then pulverized to prepare a firing raw material.

Next, the obtained powder was heated to 650 ° C. over 1 hour, held at that temperature for 5 hours, and then cooled in the furnace to near room temperature. After pulverization, the temperature was raised again to 900 ° C. over 1 hour in a nitrogen stream using an electric furnace, held at that temperature for 5 hours, and then cooled to near room temperature in the furnace. In order to remove the fired product from the electric furnace and remove the excess lithium salt, the fired product is washed with distilled water, filtered and dried to powder the target product, iron, nickel and germanium substituted Li ₂ MnO ₃ Obtained as a product.

Evaluation by X-ray diffraction The actual measurement (+) and calculation (solid line) X-ray diffraction patterns of this final product are shown in FIG. From the analysis results by Rietveld analysis program RIETAN-FP, all peaks can be indexed with the lattice constants listed in Table 1 below, and only the crystalline phase with monoclinic Li ₂ MnO ₃ unit cells (C2 / m) I understood that it consists of. Also, when the transition metal ion distribution in the structure shown in Table 2 was confirmed, the sample of Example 5 had a smaller amount of transition metal in the Li-Mn layer than the sample of Comparative Example 4 containing no Ge, and the Li single layer. It can be seen that the amount of the transition metal is large, and that the transition metal ions tend to be irregularly arranged by introducing Ge. In addition, it can be seen that the sample of Example 5 has a higher degree of hexagonal network alignment than the sample of Comparative Example 4 that does not contain Ge described above.

Evaluation by chemical analysis Based on chemical analysis, the Fe, Ni, and Ge contents with respect to the total amount of metals other than lithium differ from the charged amounts, but 12 mol% and 12 mol% (equivalent to y value 0.24) and 4 mol% (z value), respectively. 0.04) and the Li / (M ¹ + M ² + Mn) ratio is 1.65 (x value conversion 0.245), so the target composition formula Li _{1 + x} (M ¹ _y M ² _z Mn _1-yz ) It is clear that a lithium manganese composite oxide having _1-x O ₂ was obtained. The reason why the content deviated from the charged amount is presumably because Ge was partially eluted during washing with water after firing because of the amphoteric metal. However, since it is not completely eliminated, it is possible to increase the Ge content by increasing the amount charged.

The details of the charge / discharge characteristic evaluation are described in the charge / discharge characteristic evaluation described later. A lithium secondary battery using the obtained sample as the positive electrode material and metallic lithium as the negative electrode material was prepared, and an activation treatment and a cycle test were performed. It was. From the results shown in FIG. 18 and Table 4, the sample of Example 5 not only shows a charge / discharge capacity of nearly 250 mAh / g after activation, but also contains the aforementioned M ² element and is a comparative example obtained under the same production conditions. Compared with the sample of 4, the charge / discharge characteristics at the 1st cycle after the activation treatment are improved, and the charge / discharge curve similar to that at the 20th cycle after the activation treatment is shown up to 50 cycles after the activation treatment. Show. In other words, a sudden drop in potential from around 3.7 V accompanying the structural transition from the layered rock-salt structure to the spinel phase during 50-cycle discharge after activation treatment, and the Li ₂ (Ni, Mn) O ₂ phase from the layered rock-salt structure From the fact that no additional capacity appears at 2.2 V or less due to the structural transition, it is clear that the positive electrode material is excellent in high capacity and long-term cycle characteristics.

[Test results]
Evaluation by X-ray diffraction From the X-ray diffraction patterns of the samples obtained in Examples 1 to 5 and Comparative Examples 1 to 4, the Rietveld analysis program RIETAN-FP (F. Izumi, K. Momma, "Three-Dimensional Visualization in Powder Diffraction ", Solid State Phenomena, Vol. 130, pp. 15-20, 2007), the lattice constant and lattice volume of each sample were evaluated. The results are shown in Table 1. In Table 1, a, b, and c indicate the lengths of the respective axes, and β indicates an angle between the edges c and a. V represents the lattice volume.

Next, from the X-ray diffraction patterns of the samples obtained in Examples 1 to 5 and Comparative Examples 1 to 4, the calculation pattern obtained from the structural model in which the amount of transition metal at each lattice position is variable is matched with the actual measurement pattern. Thus, the transition metal ion distribution in the structure was evaluated. The results are shown in Table 2.

In the case of Li ₂ MnO ₃ which is a known substance, when Mn ions are regularly arranged, Mn occupies 100% of the hexagonal mesh configuration position (4g) position, and the hexagonal network center position (2b Mn ions are not present at other positions such as), but in reality, 100% of Mn ions are not present at the 4g position, and some Mn ions are arranged at three Li positions. In Table 2, g _4g indicates the Mn occupancy at the hexagonal mesh position (4g) position, g _2b indicates the Mn occupancy at the 2b position, g _2c indicates the Mn occupancy at the 2c position, and g _4h indicates The Mn occupancy at 4h position is shown. The difference in Mn occupancy between the 4g position and the 2b position (g _4g -g _2b ) is defined as hexagonal network regularity, and the larger the value, the more ideal the Li ₂ MnO ₃ type monoclinic layered rock salt structure To do. The average value 1 indicates the average occupancy (element ratio (%)) of the transition metal element at the lattice positions (4g and 2b positions) in the Li-Mn layer, and the average value 2 indicates the lattice in the Li single layer. The average occupancy (element ratio (%)) of the transition metal element at the position (positions 4h and 2c) is shown. In addition, the total amount of transition metals is based on the occupancy of the transition metal elements (element ratio (%)) at the lattice positions (4g and 2b) in the Li-Mn layer using the monoclinic layered rock salt structure model. The sum of the occupation ratio (element ratio (%)) of the transition metal element at the lattice position (4h and 2c) in the single layer is shown. A smaller average value 1 and a larger average value 2 mean that the transition metal ions are irregularly arranged.

Evaluation by Chemical Analysis etc. The samples obtained in Examples 1 to 5 and Comparative Examples 1 to 4 were subjected to chemical analysis by ICP emission analysis. The results are shown in Table 3. The results are shown in Table 3.

Charge / Discharge Characteristic Evaluation Charge / discharge tests were conducted using the samples obtained in Examples 1 to 5 and Comparative Examples 1 to 4 as positive electrode materials. Specifically, 5 mg of the samples obtained in Examples 1 to 5 and Comparative Examples 1 to 4 were mixed well with 5 mg of acetylene black, and then 0.5 mg of polytetrafluoroethylene powder was added and bonded, and crimped onto an Al mesh. Thus, a positive electrode was produced. The obtained positive electrode was vacuum-dried at 120 ° C. overnight, and then a lithium secondary battery was produced in the glove box. As the electrolytic solution, a solution in which LiPF ₆ was dissolved in a mixed solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC) (volume ratio 3: 7) was used, and metallic lithium was used as the negative electrode.

The charge / discharge test was shifted to a cycle deterioration test after the stage charge process for obtaining an activated sample. The test is performed at the start of charging, and is cycled by increasing the charging capacity in the order of 80, 120, 160, and 200 mAh / g at a potential range of 2.0 to 4.8 V, a test temperature of 30 ° C., and a current density of 40 mA / g. Activation processing was performed by constant current-constant voltage charging up to 4.8 V (current termination at 4.8 V was 10 mA / g). The stage charge activation treatment is essential for evaluating the charge / discharge characteristics of the lithium manganese composite oxide of the present invention. In particular, it is an essential process when Fe is contained as the M ¹ element. After the activation process, the charge / discharge curve changes as the cycle progresses (especially the deviation from the similar shape seen after the 20th cycle) by evaluating up to 50 cycles with constant current charge / discharge at 2.0-4.8V. ) Was evaluated. In particular, as described above, in the discharge curve at 50 cycle discharge after activation (54 cycle discharge: 54d), (1) abruptly around 3.7V accompanying the structural transition from the layered rock salt structure to the spinel phase The presence or absence of additional capacitance at 2.2 V or lower due to (2) structural transition to the Li ₂ (Mn, Ni) O ₂ phase was evaluated. The results are shown in FIGS. 2, 4, 6, 8, 10, 12, 14, 16 and 18 and Table 4. 2, 4, 6, 8, 10, 12, 14, 16, and 18, a charging curve (5c) at the time of 1 cycle charging after the activation process, and a charging curve at the time of 20 cycles charging after the activation process ( 24c), charge curve at the time of 50 cycles after activation treatment (54c), discharge curve after 1 cycle discharge after activation treatment (5d), discharge curve after 20 cycles after activation treatment (24d), and activity The discharge curve (54d) at the time of 50-cycle discharge after the oxidization treatment is shown, with a curve rising to the right corresponding to charging and a curve falling to the right corresponding to discharging. In Table 4, Q _5c is the capacity at one cycle after activation, Q _5d is the capacity at one cycle after activation, Q _54d is the capacity at 50 cycles after activation, (Q _1d sum of ~ Q _5d) / (sum of Q _1c ~ Q _5c) is one in which the sum of the discharge capacity of each cycle in step charge activated during processing, divided by the sum of the charge capacity of each cycle. V _{5d · ave} represents the initial average discharge voltage during one cycle discharge after the activation treatment.

As is clear from the above Examples and Comparative Examples, the lithium manganese composite oxide of the present invention not only exhibits a large charge / discharge capacity of 200 mAh / g or more for the first time, but also includes two side reactions that occur after the cycle has elapsed. It was confirmed that the substance has excellent long-term cycle characteristics and suppresses the change in crystal structure due to.

Claims

General formula (1):
Li 1 + x (M 1 y M 2 z Mn 1-yz ) 1-x O 2 (1)
[Wherein M 1 represents Fe and / or Ni. M 2 represents Ti and / or Ge. x, y, and z represent 0 <x <1/3, 0 ≦ y ≦ 0.4, and 0 <z ≦ 0.3. ]
And
A lithium manganese composite oxide containing a crystal phase of a monoclinic layered rock salt type structure or a hexagonal layered rock salt type structure.
The lithium manganese composite oxide according to claim 1 , wherein M 1 in the general formula (1) contains Ni.
The lithium manganese composite oxide according to claim 1 or 2, comprising only a crystal phase having a monoclinic layered rock salt structure.
A method for producing a lithium manganese composite oxide according to any one of claims 1 to 3,
(1) a step of forming a precipitate by making a mixture containing a manganese compound and at least one compound selected from the group consisting of an iron compound and a nickel compound alkaline,
(2) A step of subjecting the precipitate obtained in step 1 to wet oxidation and aging,
(3) A production method comprising a step of heating the aged product obtained in step 2 in the order of coexistence of a raw material compound containing a lithium compound.
The manufacturing method of Claim 4 with which the mixture in the said process 1 contains a titanium compound further.
The manufacturing method of Claim 4 or 5 with which the raw material compound in the said process 3 contains a germanium compound further.
The production method according to any one of claims 4 to 6, wherein the step 3 is a step of heating after mixing the aged product obtained in the step 2 and the raw material compound.
The production method according to any one of claims 4 to 7, wherein the heating in the step 3 is a step of heating again in the air or in an inert atmosphere after heating in the air.
A positive electrode material for a lithium ion secondary battery comprising the lithium manganese composite oxide according to any one of claims 1 to 3.
The lithium ion secondary battery which uses the positive electrode material for lithium ion secondary batteries of Claim 9 as a component.