JPWO2018066633A1 - Titanium and / or germanium substituted lithium manganese based composite oxide and method for producing the same - Google Patents

Abstract

General formula (1): Li1 + x (M1yM2zMn1-y-z) 1-xO2 (1) [wherein M1 represents Fe and / or Ni. M2 represents Ti and / or Ge. x, y, and z represent 0 <x <1/3, 0 ≦ y ≦ 0.4, and 0 <z ≦ 0.3. The lithium manganese-based composite oxide including a crystal phase of a monoclinic layered rock salt type structure or a hexagonal layered rock salt type structure uses an inexpensive element with less resource restrictions and lithium ions. When used as a positive electrode material for a secondary battery, it has a high capacity, a high discharge voltage, and maintains the similarity of the charge / discharge curve shape during the charge / discharge cycle. It is an excellent new material.

Description

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

  At present, most of secondary batteries installed in portable devices such as mobile phones, smartphones, notebook computers, tablet computers, etc. in Japan are lithium ion secondary batteries. Lithium ion secondary batteries are being put to practical use as large batteries such as electric vehicles and power load leveling systems in the future, and their importance is increasing more and more.

  At present, in lithium ion secondary batteries, a lithium-containing transition metal oxide is used as a positive electrode material, and a carbon material such as graphite is used as a negative electrode material. In particular, in the positive electrode material, the amount of lithium ions reversibly desorbed (corresponding to charge) and inserted (corresponded to discharge) 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 component parts of the battery is the highest in the positive electrode active material, and the selection of the positive electrode material is the most important in the development of a lithium ion secondary battery.

For this reason, with the application expansion and enlargement of a lithium ion secondary battery, the further increase in demand of positive electrode material is anticipated. However, since lithium cobaltate usually used as a positive electrode material contains a large amount of cobalt which is a rare metal, it is one of the factors that increase the material cost of the lithium ion secondary battery. Furthermore, considering that about 20% of cobalt resources are currently used in the battery industry, it is considered difficult to meet future demand expansion with only the positive electrode material composed of LiCoO ₂ . For this reason, in particular, in order to be used for a large-sized lithium ion secondary battery for automotive applications and the like, an oxide positive electrode material using an element abundant in resources is required.

At present, as a cheaper and less resource-constrained positive electrode material, the present inventors have found that a solid solution (Li _{1 + x} (Fe _{1 + x 2} Fe) of a layered rock salt type structure comprising 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) (hereinafter sometimes referred to as "iron-containing Li ₂ MnO ₃ "), the charge-discharge test at room temperature Have found that they have an average discharge voltage close to 4 V, similar to lithium cobalt oxide (see, for example, Patent Document 1).

In addition, the present inventors have found that lithium manganese oxides (iron and nickel-containing Li ₂ MnO _3, etc.) containing iron as well as resources rich in resources can significantly improve cycle deterioration in the 4 V region ( See, for example, Patent Document 2).

Furthermore, the present inventors show high capacity of lithium manganese oxide (titanium-containing Li ₂ MnO ₃ , iron and titanium-containing Li ₂ MnO _3, etc.) containing iron as well as resource-rich and inexpensive titanium. In particular, it has been found that discharge characteristics at high current density at room temperature and discharge characteristics at low temperature are excellent in specific chemical composition and transition metal ion distribution (see, for example, Patent Document 3).

  As mentioned above, although various reports are made about lithium manganese system positive electrode material which can be substituted to lithium cobalt system positive electrode material, further improvement in charge and discharge characteristics is desired.

Japanese Patent Application Laid-Open No. 2002-068748 Japanese Patent Application Laid-Open No. 2003-048718 JP, 2008-063211, A

  However, when the lithium manganese-based composite oxides of Patent Documents 1 and 2 are used, 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 by repeating charging and discharging. Due to the change, a rapid potential drop is observed around 3.5 V during discharge, and an additional capacity is observed around 2.2 V during discharge. Industrially, it is preferable that the charge / discharge curve shape can be maintained even after 100 cycles or 1000 cycles have elapsed, but in this method, the charge / discharge characteristics are degraded before that. For this reason, in the lithium manganese-based composite oxides of Patent Documents 1 and 2, the charge / discharge curve shape is significantly changed by these two types of crystal structure transition, and the similarity between the charge / discharge curves during charge / discharge cycles can not be maintained. Unpreferable for practical use.

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

  The present invention has been made in view of the above-mentioned current state of the prior art, and uses an inexpensive element with few resource restrictions, and has a high capacity when used as a positive electrode material for lithium ion secondary batteries. A main object of the present invention is to provide a novel material which has a high discharge voltage and can maintain the similarity between charge and discharge curve shapes during charge and discharge cycles and is excellent in long-term cycle characteristics.

The present inventors have intensively researched to achieve the above-mentioned purpose. As a result, complex oxides in which a specific amount of titanium and / or germanium is solid-solved in a Li ₂ MnO ₃ type complex oxide containing a specific amount of iron and / or nickel are less resource-constrained and inexpensive Elements, and when used as a positive electrode material for lithium ion secondary batteries, have high capacity, high discharge voltage, and similarity of charge and discharge curve shape during charge and discharge cycle It has been found that the long-term cycle characteristics are excellent for maintaining the Based on such findings, 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 indicate 0 <x <1/3, 0 ≦ y ≦ 0.4, and 0 <z ≦ 0.3. ]
Represented by, and
Lithium manganese-based composite oxide containing a crystal phase of monoclinic layered rock salt type structure or hexagonal layered rock salt type structure.
Item 2. The lithium manganese-based composite oxide according to Item 1, wherein M ¹ in the general formula (1) contains Ni.
Item 3. Item 3. The lithium manganese-based composite oxide according to Item 1 or 2, which comprises only a crystal phase of a monoclinic layered rock salt type structure.
Item 4. It is a manufacturing method of lithium manganese system complex oxide in any one of claim 1 to 3,
(1) 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 treatment and aging it;
(3) A manufacturing method comprising the steps of heating the matured product obtained in step 2 in the coexistence of a raw material compound containing a lithium compound in this order.
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 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 the step 3 is a step of heating after mixing the matured product obtained in the step 2 and the raw material compound.
Item 8. Item 8. The method according to any one of Items 4 to 7, wherein the heating in the step 3 is a step of heating again in the atmosphere and then in the atmosphere or in an inert atmosphere.
Item 9. The positive electrode material for lithium ion secondary batteries which consists of lithium manganese type complex oxide in any one of claim | item 1-3.
Item 10. 10. A lithium ion secondary battery comprising the positive electrode material for a lithium ion secondary battery according to item 9 as a component.

  According to the present invention, when used as a positive electrode material for a lithium ion secondary battery while using inexpensive elements with few resource restrictions, it has a high capacity and a high discharge voltage. It is possible to provide a novel material having excellent long-term cycle characteristics because it is possible to maintain the similarity between the charge and discharge curve shapes during the discharge cycle.

  In particular, the lithium manganese-based composite oxide of the present invention is chemically stable even at the time of charging up to a high potential, so that excellent charge / discharge characteristics can be exhibited even in long-term cycles.

The measurement (+) and calculation (solid line) X-ray-diffraction pattern of the sample obtained in Example 1 are shown. The charge / discharge curve of the lithium secondary battery which used the sample obtained in Example 1 as positive electrode material, and used metal lithium as negative electrode material is shown. The measurement (+) and calculation (solid line) X-ray-diffraction pattern of the sample obtained by the comparative example 1 are shown. The charge / discharge curve of the lithium secondary battery which used the sample obtained by the comparative example 1 as positive electrode material, and used metal lithium as negative electrode material is shown. The measurement (+) and calculation (solid line) X-ray-diffraction pattern of the sample obtained in Example 2 are shown. The charge / discharge curve of the lithium secondary battery which used the sample obtained in Example 2 as positive electrode material, and used metal lithium as negative electrode material is shown. The measurement (+) and calculation (solid line) X-ray-diffraction pattern of the sample obtained by the comparative example 2 are shown. The charge / discharge curve of the lithium secondary battery which used the sample obtained by the comparative example 2 as positive electrode material, and used metal lithium as negative electrode material is shown. The measurement (+) and calculation (solid line) X-ray-diffraction pattern of the sample obtained in Example 3 are shown. The charge-and-discharge curve of the lithium secondary battery which used the sample obtained in Example 3 as positive electrode material, and used metal lithium as negative electrode material is shown. The measurement (+) and calculation (solid line) X-ray-diffraction pattern of the sample obtained by the comparative example 3 are shown. The charge / discharge curve of the lithium secondary battery which used the sample obtained by the comparative example 3 as positive electrode material, and used metal lithium as negative electrode material is shown. The measurement (+) and calculation (solid line) X-ray-diffraction pattern of the sample obtained in Example 4 are shown. The charge / discharge curve of the lithium secondary battery which made the sample obtained in Example 4 the positive electrode material, and made metal lithium the negative electrode material is shown. The measurement (+) and calculation (solid line) X-ray-diffraction pattern of the sample obtained by the comparative example 4 are shown. The charge / discharge curve of the lithium secondary battery which used the sample obtained by the comparative example 4 as positive electrode material, and used metal lithium as negative electrode material is shown. The measurement (+) and calculation (solid line) X-ray-diffraction pattern of the sample obtained in Example 5 are shown. The charge / discharge curve of the lithium secondary battery which used the sample obtained in Example 5 as positive electrode material, and used metal lithium as negative electrode material is shown.

1. Lithium-manganese-based composite oxide The lithium-manganese-based composite oxide of the present invention has a 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 indicate 0 <x <1/3, 0 ≦ y ≦ 0.4, and 0 <z ≦ 0.3. ]
And a crystal phase of a monoclinic layered rock salt type structure or a hexagonal layered rock salt type structure based on the rock salt type structure.

  Monoclinic layered rock salt type structure is a space group:

Li ₂ MnO ₃ type monoclinic layered rock salt consisting only of a crystal phase having a unit cell similar to Li ₂ MnO ₃ from the viewpoint of capacity and cycle characteristics. It is preferable that it is a crystalline phase of type structure.

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

The crystal phase of the LiNiO ₂ type hexagonal layered rock salt type structure consisting only of the crystal phase having unit cells similar to LiNiO ₂ from the viewpoint of capacity and cycle characteristics. Is preferred.

  The lithium manganese-based composite oxide of the present invention may have only one or both of the crystal phases of the monoclinic layered rock salt type structure and the hexagonal layered rock salt type structure described above. It is also good. In any case, the lithium manganese-based composite oxide of the present invention has a high capacity and a high discharge voltage when used as a positive electrode material for lithium ion secondary batteries, and at the time of charge and discharge cycles. The material is excellent in long-term cycle characteristics because it can maintain the similarity between the charge and discharge curve shapes.

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

  On the other hand, the lithium manganese-based composite oxide of the present invention only needs to contain the crystal phase of the monoclinic layered rock salt type structure or hexagonal layered rock salt type structure described above, and other rock salt type structures different in cation distribution ( For example, it may be a mixed phase containing a crystal phase of cubic rock salt type structure etc.). In addition, the lithium manganese-based composite oxide of the present invention may be a material comprising only the crystal phase of the monoclinic layered rock salt type structure and / or the hexagonal layered rock salt type structure described above.

  According to the manufacturing method of the present invention to be described later, a lithium manganese-based composite oxide to be obtained is likely to form a material consisting only of the crystal phase of the monoclinic layered rock salt type structure and / or hexagonal layered rock salt type structure described above. However, when synthesized at a low temperature of, for example, 600 ° C. or less, a crystal phase of cubic rock salt type structure may be included. Since the crystal phase of this cubic rock salt type structure is also a crystal structure that exhibits excellent charge and discharge characteristics, even if it has this crystal structure, there is no problem at all.

  However, in the present invention, having a crystal phase of a monoclinic layered rock salt type structure and a hexagonal layered rock salt type structure, when used as a positive electrode material for a lithium ion secondary battery, has a high capacity and is high A monoclinic layered rock salt type structure and a hexagonal layered rock salt because it is a material that has a discharge voltage and is excellent in long-term cycle characteristics because it can maintain the similarity between charge and discharge curve shapes during charge and discharge cycles. It is preferable that the proportion of the crystal phase of the type structure is high. From this point of view, when the lithium manganese-based composite oxide of the present invention has another rock salt type structure (cubic rock salt type structure, etc.) having a different cation distribution, the ratio of the layered rock salt type structure to the crystal phase is Usually, assuming that 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 type structure is 1 to 99% by weight (especially 10 to 95% by weight, further 50 to 90% by weight) The crystal phase of the rock salt type structure (cubic rock salt type structure etc.) is preferably 1 to 99% by weight (especially 5 to 90% by weight, further 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-mentioned general formula (1), and further, M ¹ is dissolved if necessary. I am doing it.

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 (0 <y ≦ 0.4), preferably 5 to 35% (0.05 ≦ y ≦ 0.35), more preferably 10 to 30% (0.1 ≦ y) of the total amount of metal ions other than Li ions ≦ 0.3). When the amount of solid solution (y value) of M ¹ ions becomes excessive, the amount of Mn relatively decreases, and the lithium content per composition formula decreases, so the charge / discharge capacity significantly decreases. On the other hand, by setting the lower limit value of the solid solution amount (y value) of M ¹ ion to the above range, the discharge potential can be further raised 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 As it seems, only one of Fe and Ni may be contained, or both of Fe and Ni may be contained. More specifically, although Fe is cheaper than Ni, Ni has a higher oxidation-reduction potential and the discharge voltage can be easily increased. Therefore, applications requiring high potential (large lithium ion secondary such as automotive applications etc.) Batteries etc.). Therefore, it is preferable to appropriately set the amounts of Fe and Ni used according to the application. For example, when containing both Fe and Ni, as 100% by weight of the total amount of M ¹ element, Fe is 10 to 90 wt% (in particular 30 to 70 wt%, further 40 to 60% by weight) is preferred. The amount of Ni used is set such 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)) to be dissolved in the lithium manganese-based 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 to 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 of M ² ions (z value) becomes excessive, the charge-discharge capacity from low electrochemical activity of the M ² ion is significantly lowered. On the other hand, if the amount (z value) of the solid solution of M ² ions is too small, it is difficult to maintain the similarity of the charge-discharge curve shape during charge-discharge cycles, so the cycle characteristics in the case of long charge / discharge cycles are inferior.

Like M ¹ in the lithium manganese-based composite oxide of the present invention, M ² is considered to be present in the layered rock salt type structure in the form of substituting Li, Mn, etc., but only one of Ti and Ge May be contained, or both Ti and Ge may be contained. More specifically, although Ti is cheaper than Ge, Ge can exert excellent effects with a small amount of elements, and therefore, when Ge is used, the amount of raw materials used can also be reduced. Therefore, it is preferable to appropriately set the amounts of Ti and Ge used according to the application. For example, when containing both Ti and Ge, as 100% by weight of the total amount of M ² element, Ti is 10 to 90 wt% (in particular 30 to 70 wt%, further 40 to 60% by weight) is preferred. The amount of Ge used is set such that the total amount with the amount of Ti used is 100% by weight.

In the general formula (1), the total amount (y + z) of M ¹ and M ² dissolved in the lithium manganese composite oxide of the present invention is preferably 70% or less (0 <y + z ≦ 0.7), 10 to 60% (0.1 ≦ y + z ≦ 0.6) is more preferable, 20 to 50% (0.2 ≦ y + z ≦ 0.5) is more 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 lithium ion secondary batteries, the capacity can be further increased, the discharge voltage can be further increased, and the similarity between the charge and discharge curve shapes during charge and discharge cycles can be easily maintained. The cycle characteristics of the period can be made better.

  Further, in the lithium manganese-based composite oxide of the present invention, the Li ion content (x) is an 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. Depending on the number, it can take values between 0 and 1/3. Usually, 0.100 to 0.300 is preferable, 0.200 to 0.280 is more preferable, and 0.230 to 0.270 is more preferable.

  Furthermore, the lithium manganese-based composite oxide of the present invention is a lithium hydroxide, lithium carbonate, iron compound, nickel compound, titanium compound, germanium compound, manganese compound, and these compounds in a range that does not significantly affect charge and discharge characteristics. The hydrate of the present invention may contain an impurity phase such as a composite metal compound containing two or more of lithium, iron, nickel, titanium and germanium. Regarding the amount of impurity phase other than crystal phase of monoclinic layered rock salt type structure, hexagonal layered rock salt type structure and other rock salt type structures (cubic rock salt type structure etc.) different in cation distribution, the effect of the present invention It can be in a range that does not damage, for example, 0 to 10% by weight is preferable, and 0 to 5% by weight is more preferable in the lithium manganese-based composite oxide of the present invention.

  The lithium manganese-based composite oxide of the present invention satisfying 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 crystalline phase of the layered rock salt type structure Potential drop around 3.5 V during discharge based on the phase transition to the crystal phase of type structure and addition around 2.2 V during discharge based on the phase transition from the crystal phase of layered rock salt structure to the lithium excess crystal phase Since the lithium manganese composite oxide of the present invention not only has a high capacity and a high discharge voltage, it also has excellent cycle characteristics even during long-term charge and discharge cycles. Have. For this reason, the lithium manganese-based composite oxide of the present invention is extremely useful as a positive electrode material not only for small consumer lithium ion secondary batteries but also for large lithium ion secondary batteries for vehicles and the like.

2. Method of producing lithium manganese-based composite oxide The lithium manganese-based composite oxide of the present invention can be synthesized using a conventional composite oxide synthesis method. Specifically, it is possible to synthesize by the coprecipitation-calcination method, the coprecipitation-hydrothermal-calcination method, the solid phase reaction method and the like. From the viewpoint of easily producing a composite oxide having particularly excellent charge and discharge characteristics, it is preferable to adopt a coprecipitation-calcination method.

For example, in the case of employing the coprecipitation-baking method, 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 optionally a titanium compound alkaline I may say),
(2) A step of subjecting the precipitate obtained in step 1 to wet oxidation treatment and aging (hereinafter also referred to as step 2),
(3) A process comprising heating steps (hereinafter also referred to as step 3) of heating the matured product obtained in step 2 in the coexistence of a lithium compound and, if necessary, a raw material compound containing a germanium compound The lithium manganese-based composite oxide of the present invention can be obtained by the method.

(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.

  When the lithium manganese-based composite oxide of the present invention to be finally obtained contains a Ti element, the manganese compound and at least one compound selected from the group consisting of an iron compound and a nickel compound Preferably, the mixture containing the titanium compound and the titanium compound is made alkaline to form a precipitate. Specifically, it is convenient to add 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 to form a precipitate. .

  As a manganese compound, an iron compound, a nickel compound, and a titanium compound, the component which can form the mixed aqueous solution containing these compounds is preferable. It is preferred to use a water soluble compound. Specific examples of such water-soluble compounds include, for example, water-soluble salts such as chlorides, nitrates, sulfates, oxalates and acetates of manganese, iron, nickel or titanium; hydroxides, etc. it can. In addition, compounds containing a plurality of metal species such as manganese titanate, nickel titanate, nickel manganate, iron manganate and the like can also be used. As a manganese compound, permanganate salts such as potassium permanganate can also make the metal distribution other than lithium ion uniform, and charge / discharge characteristics can be further improved. As these water soluble compounds, any of anhydrides and hydrates can be adopted. Further, even non-water-soluble compounds such as oxides of manganese, iron, nickel or titanium, metals and the like can be used as an aqueous solution by dissolving them using an acid such as sulfuric acid or hydrochloric acid. Each of these raw material compounds can be used alone for each metal source, or two or more of them can be used in combination.

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

  The concentration of each compound in the case of the mixed aqueous solution is not particularly limited, and can be appropriately determined so as to be able to form a uniform mixed aqueous solution and to form a coprecipitate smoothly. Usually, the total concentration of the manganese compound, the iron compound, the nickel compound and the 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 using a mixed aqueous solution, water can be used alone, or a water-alcohol mixed solvent containing a water-soluble alcohol such as methanol and ethanol can be used. By using a water-alcohol mixed solvent, the alcohol acts as an antifreeze liquid, and precipitation can be performed at a temperature below 0 ° C. The formation of precipitates at a low temperature further suppresses the formation of impurities such as lithium ferrite and manganese ferrite which are easily generated during the formation of precipitates when Fe is contained as an M ¹ element, that is, a more uniform codistribution of transition metal distribution. You can get a deposit. In addition, since a manganese source such as potassium permanganate which is difficult to form precipitates by water alone can also be adopted, the range of selection of raw materials is further expanded. The amount of alcohol used can be appropriately determined according to the target precipitation temperature and the like, and is usually 50 parts by weight or less (e.g. 10 to 50 parts by weight) with respect to 100 parts by weight of water. Is appropriate.

  By making the mixture (particularly, the mixed aqueous solution) alkaline, a precipitate (coprecipitate) can be generated. The conditions for forming a good precipitate are different depending on the type and concentration of each compound contained in the mixture (particularly the mixed aqueous solution), and thus can not be generally defined, but usually pH 8 or more (eg pH 8 to 14) is preferable , PH 11 or more (for example, pH 11 to 14) is more preferable.

  There is no particular limitation on the method of making the mixture (particularly the mixed aqueous solution) alkaline, and usually, the mixture (particularly the mixed aqueous solution) is added to an aqueous solution containing alkali for the formation of a uniform precipitate. A precipitate (co-precipitate) can also be formed by the method. A precipitate can also be obtained by adding an alkali or an aqueous solution containing an alkali to the mixed aqueous solution.

  Examples of the alkali used to make the mixture (particularly the mixed aqueous solution) alkaline include alkali metal hydroxides such as potassium hydroxide, sodium hydroxide and lithium hydroxide, and ammonia. 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. The alkali can also be dissolved in a water-alcohol mixed solvent containing a water-soluble alcohol, as in the case of the mixed aqueous solution of the metal compound described above.

In the case of containing Fe as M ¹ by setting the temperature of the mixture (particularly the mixed aqueous solution) to usually −50 to 50 ° C., particularly −20 to 30 ° C. during precipitation. Since the formation of spinel ferrite accompanying the heat generation is further suppressed and fine and homogeneous precipitates (coprecipitates) are easily formed, the reactivity with the lithium compound described later is further enhanced, and the lithium of the present invention It becomes easy to synthesize a manganese-based composite oxide. Also, in order to form precipitates (coprecipitates) well in this step, it is necessary to apply the mixture (particularly the mixed aqueous solution) to the alkali for at least several hours in order to further suppress the generation of heat of neutralization. The method of dropping gradually is preferable. The longer the reaction time, the better, but in practice it is preferably 1 hour to 1 day, especially 2 to 12 hours.

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

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

  The ripening 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 in which the wet oxidation treatment of the precipitate (coprecipitate) can be performed is preferable. The longer the ripening time, the better, but in practice, 0.5 to 7 days are preferable, and 2 to 4 days are more preferable.

  It is also possible to refine the precipitate by washing the obtained precipitate with distilled water or the like as necessary to remove excess alkali components, residual raw materials and the like, and filtering it off.

(2-3) Process 3
Next, in step 3, the matured product obtained in step 2 is heated in the coexistence of a raw material compound containing a lithium compound. Specifically, an aqueous solution containing the matured product obtained in step 2 and a raw material compound containing a lithium compound may be heated as needed, after forming a slurry, drying and crushing, and then heating (particularly baking). preferable.

  Usually, 100-3000 g is preferable per 1 L of water, and, as for content of the ripening thing obtained at the said process 2 in the aqueous solution to be used, 500-2000 g is more preferable.

  Examples of lithium compounds that can be used 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, in the case where the lithium manganese-based 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 based on the total amount of the matured product obtained in the above step 2 and the germanium compound described later, and 1.5 to 3 is preferable. More preferable.

  Moreover, normally 0.1-10 mol / L is preferable, and, as for the density | concentration of the lithium compound in aqueous solution, 1-8 mol / L is more preferable.

  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 the germanium compound include water-soluble germanium compounds such as germanium chloride and germanium iodide; and water-insoluble germanium compounds such as germanium oxide and metallic germanium. In the case of using a water-insoluble germanium compound, the reactivity with the aged product obtained in step 2 is improved by dissolving the germanium compound with an acid or the above-mentioned alkali or the like, taking advantage of the fact that germanium is an amphoteric element. Is preferred. When lithium hydroxide is used as the lithium compound, it is possible to dissolve the water-insoluble germanium compound without separately using an acid or an alkali.

When the cleaning treatment is performed after heating, the amount of germanium to be washed away is large, so the addition amount (feed amount) of the germanium compound is preferably larger 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 aged product obtained in the above step 2 and the germanium compound, 0.1 to 0.4 is more preferable.

  Moreover, 0.05-1.0 mol / L is preferable normally, and, as for the density | concentration of the germanium compound in aqueous solution, 0.1-0.7 mol / L is more preferable.

  The method of mixing the matured product obtained in step 2 with the lithium compound and, if necessary, the zirconium compound is not particularly limited. For example, the matured product obtained in step 2 is added to an aqueous solution of a water-soluble lithium compound, stirred and dispersed, and then an aqueous solution of a water-soluble germanium compound or an alkaline solution of a non-water-soluble germanium compound prepared separately is added. After well stirring, it is preferable to dry and grind as necessary.

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

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

  It is preferable to grind | pulverize in order to improve the reactivity in the case of the later heat processing. With regard to the degree of grinding, it is preferable that the mixture has a uniform color tone without containing coarse particles. In the case of pulverizing, a usual method can be adopted, and for example, it can be pulverized by a vibration mill, a ball mill, a jet mill or the like. The grinding can also be repeated two or more times. The heat treatment can also be carried out by gradually raising the heating temperature.

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

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

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

  There is no particular limitation on the organic substance, and a carbon-containing compound that can be decomposed at the above heating temperature (in particular, the baking temperature) to make a reducing atmosphere is preferable. In particular, when using a water-soluble organic substance, it is advantageous because it can be dispersed and mixed with the lithium manganese-based 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 carbon powder, for example, carbon powder obtained by thermal decomposition of an organic substance, for example, graphite, acetylene black and the like can be used.

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

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

  The heating time is also not particularly limited. More specifically, the holding time at the final heating temperature is preferably 10 minutes to 24 hours, and more preferably 30 minutes to 12 hours. When two-step heat treatment is performed, the holding time at the first heating temperature is preferably 10 minutes to 24 hours (particularly 30 minutes to 12 hours), and the holding time at the second heating temperature is 10 minutes. -24 hours (especially 30 minutes-12 hours) are preferable.

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

  Furthermore, if necessary, this heat-dried product is pulverized, a lithium compound and an organic substance are added, heating (in particular firing) is performed, and a series of operations of washing and drying are repeated to repeat the lithium manganese-based composite oxide It is also possible to further improve the excellent properties of

3. Lithium Ion Secondary Battery A lithium ion secondary battery using the lithium manganese composite oxide of the present invention can be manufactured by a known method. For example, the lithium manganese-based composite oxide of the present invention is used as the positive electrode material, and known metal lithium, carbon-based material (activated carbon, graphite etc.), silicon, silicon oxide, Si-SiO-based material, lithium as the negative electrode material A solution in which a lithium oxide such as lithium perchlorate or LiPF ₆ is dissolved in a solvent comprising one or more of known ethylene carbonate, dimethyl carbonate, diethyl carbonate and the like as an electrolytic solution using a titanium oxide etc. (organic electrolysis Solution), inorganic solid electrolytes (Li ₂ S-P ₂ S ₅ system, Li ₂ S-GeS _2- P ₂ S ₅ system, etc.), and further using other known battery components According to the above, the lithium ion secondary battery can be assembled. In the present invention, “lithium ion secondary battery” is a concept including “lithium secondary battery” using metallic lithium as an anode material. In the present invention, the term "lithium ion secondary battery" refers to both "nonaqueous lithium ion secondary battery" using a non-aqueous electrolyte and "all solid lithium ion secondary battery" using a solid electrolyte. It is an included concept.

  Examples and Comparative Examples will be shown below to make the features of the present invention clearer, but the present invention is not limited to the following examples.

Example 1
Sample synthesis, and structure and composition evaluation 10.10 g of iron (III) nitrate 9 hydrate, 7.27 g of nickel (II) nitrate hexahydrate, 40.00 g of 30% aqueous solution of titanium (IV) sulfate, manganese (II) chloride 4 water 29.69 g of the hydrate (total 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 a separate beaker, 50 g of sodium hydroxide was weighed, and 500 mL of distilled water was added and dissolved with stirring to prepare an aqueous sodium hydroxide solution. The aqueous sodium hydroxide solution was placed in a titanium beaker and allowed to stand in a thermostat kept at 20 ° C. Next, the above metal salt aqueous solution was gradually added dropwise to the sodium hydroxide solution over about 3 hours to form Fe-Ni-Ti-Mn precipitate (coprecipitate). It was confirmed that the reaction solution was completely alkaline, and oxygen was blown into the reaction solution containing the coprecipitate under stirring for 2 days at room temperature to carry out a wet oxidation treatment to age the precipitate.

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

The powder obtained was then heated to 650 ° C. over 1 hour, held at that temperature for 5 hours, and cooled to around room temperature in a furnace. After crushing, the temperature was raised again to 850 ° C. in a nitrogen stream for 1 hour using an electric furnace, and after holding for 5 hours at that temperature, it was cooled to around room temperature in the furnace. That is, the sample preparation was performed by baking in the air in the first stage and in a nitrogen atmosphere in the second stage. The fired product is taken out of the electric furnace, and the fired product is washed with distilled water, filtered and dried to remove the excess lithium salt, and the desired product, iron, nickel and titanium-substituted Li ₂ MnO ₃ powder are obtained. It was obtained as a round product.

Evaluation by X-Ray Diffraction The actual (+) and calculated (solid line) X-ray diffraction pattern of this final product is shown in FIG. According to the analysis result by Rietveld analysis program RIETAN-FP, all peaks can be indexed by the lattice constants described in Table 1 below, and only the crystal phase having unit cells (C2 / m) of monoclinic Li ₂ MnO ₃ It turned out that it consists of. In addition, when the distribution of transition metal ions in the structure in Table 2 is confirmed, the sample of Example 1 has a smaller amount of transition metal in the Li-Mn layer compared to the sample of Comparative Example 1 not including Ti described later, and a single Li layer. It can be seen that the amount of internal transition metal is large, and it is understood that transition metal ions tend to be irregularly arranged due to the introduction of Ti. Further, it is understood that the sample of Example 1 has a higher degree of hexagonal mesh arrangement, as compared to the sample of Comparative Example 1 which does not contain Ti described later.

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

The charge / discharge characteristic evaluation details are the procedure described in charge / discharge characteristic evaluation which will be described later. A lithium secondary battery is prepared using the obtained sample as a positive electrode material and metal lithium as a negative electrode material, and the activation treatment and cycle test are performed. The

From the results of FIG. 2 and Table 4, the sample of Example 1 not only exhibits a charge / discharge capacity close to 240 mAh / g after activation but also contains the M ² element described later, and is a comparative example obtained under the same preparation conditions Compared to the sample 1, not only the charge-discharge characteristics at 1 cycle after activation treatment are almost equal, but the charge-discharge curve similar to that at 20 cycles after activation treatment up to 50 cycles after activation treatment It shows. In other words, during 50 cycles after activation treatment, a rapid potential drop from around 3.7 V accompanied by a structural transition from a layered rock salt structure to a spinel phase during 50 cycles of discharge, or a layered rock salt structure causes a Li ₂ (Ni, Mn) O ₂ phase It is clear that it is a positive electrode material excellent in high capacity and long-term cycle characteristics, since no appearance of additional capacity at 2.2 V or less accompanying structural transition is observed.

Comparative Example 1
Starting materials: 10.10 g of iron (III) nitrate 9 hydrate, 7.27 g of nickel (II) nitrate hexahydrate, 39.58 g of manganese (II) chloride tetrahydrate (total amount of 0.25 mol, Fe: Ni: Mn mol The ratio 1: 1: 8) was added to 500 mL of distilled water and completely dissolved. After that, the positive electrode material was manufactured in the same manner as in Example 1.

The measured (+) and calculated (solid line) X-ray diffraction patterns of this final product are shown in FIG. According to the analysis result by Rietveld analysis program RIETAN-FP, all peaks can be indexed by the lattice constant in Table 1 described later, and only from the crystal phase having unit cells (C2 / m) of monoclinic Li ₂ MnO ₃ It turned out that it became.

Also, according to chemical analysis, Fe and Ni contents with respect to the total metal amount other than lithium maintain 10 mol% and 10 mol% (equivalent to y value 0.20) which are preparation amounts, respectively, and Li / (M ¹ + Mn) ratio Since it is also 1.71 (x value conversion 0.262), the lithium manganese-based 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, according to the procedure described in charge and discharge characteristic evaluation to be described later, a lithium secondary battery was prepared using the obtained sample as a positive electrode material and metal lithium as a negative electrode material, and subjected to activation treatment and cycle test. The evaluation results of the charge and discharge characteristics are shown in FIG. 4 and Table 3. From FIG. 4 and Table 3, the sample of Comparative Example 1 shows charge / discharge capacity close to 250 mAh / g after activation, but at 50 cycles after activation treatment, 3.7 accompanied by structural transition from layered rock salt type structure to spinel phase It is possible to observe an abrupt potential drop from around V and the appearance of additional capacity below 2.2 V due to the structural transition from a layered rock salt type structure to a Li ₂ (Ni, Mn) O ₂ phase. It is apparent that the cathode material is inferior in long-term cycle characteristics as compared to the lithium manganese composite oxide of Example 1.

Example 2
A sample was prepared in the same manner as in Example 1 except that the final firing atmosphere was in the air. That is, the sample preparation was performed by baking twice in the air. The measured (+) and calculated (solid line) X-ray diffraction patterns of this final product are shown in FIG. According to the analysis result by Rietveld analysis program RIETAN-FP, all peaks can be indexed by the lattice constant in Table 1 described later, and only from the crystal phase having unit cells (C2 / m) of monoclinic Li ₂ MnO ₃ It turned out that it became.

  In addition, when the distribution of transition metal ions in the structure in Table 2 described later is confirmed, the amount of transition metal in the Li-Mn layer in the sample of Example 2 is smaller than that in the sample of Comparative Example 2 not including Ti described later. It can be seen that the amount of transition metal in a single layer is large, and it is understood that transition metal ions tend to be irregularly arranged due to the introduction of Ti. In addition, it can be seen that the sample of Example 2 has a higher degree of hexagonal mesh arrangement, as compared to the sample of Comparative Example 2 which does not contain Ti described later.

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

Furthermore, according to the procedure described in charge and discharge characteristic evaluation to be described later, a lithium secondary battery was prepared using the obtained sample as a positive electrode material and metal lithium as a negative electrode material, and subjected to activation treatment and cycle test. The evaluation results of the charge and discharge characteristics are shown in FIG. 6 and Table 3. From FIG. 6 and Table 3, the sample of Example 2 not only exhibits a charge-discharge capacity close to 240 mAh / g after activation but also contains the M ² element described later, and is obtained under the same preparation conditions as Comparative Example 2 Not only the charge and discharge characteristics at 1 cycle after activation treatment are almost equal to those of the sample, but the charge and discharge curve similar to that at 20 cycles after activation treatment is shown up to 50 cycles after activation treatment. There is. That is, during 50 cycles of activation treatment, a rapid potential drop from around 3.7 V accompanying the structural transition from the layered rock salt structure to the spinel phase during the 50 cycle discharge, and from the layered rock salt structure, the Li ₂ (Ni, Mn) O ₂ phase It is clear that the positive electrode material is excellent in high capacity and long-term cycle characteristics, since no appearance of additional capacity at 2.2 V or less is observed with the structural transition to.

Comparative Example 2
Starting materials: 10.10 g of iron (III) nitrate 9 hydrate, 7.27 g of nickel (II) nitrate hexahydrate, 39.58 g of manganese (II) chloride tetrahydrate (total amount of 0.25 mol, Fe: Ni: Mn mol The ratio 1: 1: 8) was added to 500 mL of distilled water and completely dissolved. After that, the positive electrode material was manufactured in the same manner as in Example 2.

The measured (+) and calculated (solid line) X-ray diffraction patterns of this final product are shown in FIG. According to the analysis result by Rietveld analysis program RIETAN-FP, all peaks can be indexed by the lattice constant in Table 1 described later, and only from the crystal phase having unit cells (C2 / m) of monoclinic Li ₂ MnO ₃ It turned out that it became.

Also, according to chemical analysis, Fe and Ni contents with respect to the total metal amount other than lithium maintain 10 mol% and 10 mol% (equivalent to y value 0.20) which are preparation amounts, respectively, and Li / (M ¹ + Mn) ratio Also, lithium manganese-based 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 since it is also 1.73 (0.267 in terms of x value) Is clear.

Furthermore, according to the procedure described in charge and discharge characteristic evaluation to be described later, a lithium secondary battery was prepared using the obtained sample as a positive electrode material and metal lithium as a negative electrode material, and subjected to activation treatment and cycle test. The evaluation results of the charge and discharge characteristics are shown in FIG. 8 and Table 3. According to FIG. 8 and Table 3, the sample of Comparative Example 2 exhibits a charge-discharge capacity close to 250 mAh / g after activation, but at 50 cycles of discharge after activation treatment, 3.7 associated with structural transition from layered rock salt type structure to spinel phase It is possible to observe an abrupt potential drop from around V and the appearance of additional capacity below 2.2 V due to the structural transition from a layered rock salt type structure to a Li ₂ (Ni, Mn) O ₂ phase. It is apparent that the cathode material is inferior in long-term cycle characteristics as compared to the lithium manganese-based composite oxide of Example 2.

[Example 3]
A sample was prepared in the same manner as in Example 1 except that the final firing conditions were set to 900 ° C., 5 hours, and in the air. That is, the sample preparation was performed by baking twice in the air. The measured (+) and calculated (solid line) X-ray diffraction patterns of this final product are shown in FIG. According to the analysis result by Rietveld analysis program RIETAN-FP, all peaks can be indexed by the lattice constant in Table 1 described later, and only from the crystal phase having unit cells (C2 / m) of monoclinic Li ₂ MnO ₃ It turned out that it became.

  In addition, when the distribution of transition metal ions in the structure in Table 2 to be described later is confirmed, the amount of transition metal in the Li-Mn layer in the sample of Example 3 is smaller than that in the sample of Comparative Example 3 which does not contain Ti described later It can be seen that the amount of transition metal in a single layer is large, and it is understood that transition metal ions tend to be irregularly arranged due to the introduction of Ti. In addition, it is understood that the sample of Example 3 has a higher degree of hexagonal mesh arrangement, as compared to the sample of Comparative Example 3 which does not contain Ti described later.

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

Furthermore, according to the procedure described in charge and discharge characteristic evaluation to be described later, a lithium secondary battery was prepared using the obtained sample as a positive electrode material and metal lithium as a negative electrode material, and subjected to activation treatment and cycle test. The evaluation results of the charge and discharge characteristics are shown in FIG. 10 and Table 3. From FIG. 10 and Table 3, the sample of Example 3 shows not only charge / discharge capacity close to 200 mAh / g after activation but also the sample of Comparative Example 3 obtained under the same preparation conditions without containing the element M ² described later. Not only the charge and discharge characteristics at 1 cycle after activation processing are almost equal to that of, but the charge and discharge curves similar to those at 20 cycles after activation treatment are shown up to 50 cycles after activation treatment. . In other words, during 50 cycles after activation treatment, a rapid potential drop from around 3.7 V accompanied by a structural transition from a layered rock salt structure to a spinel phase during 50 cycles of discharge, or a layered rock salt structure causes a Li ₂ (Ni, Mn) O ₂ phase It is clear that it is a positive electrode material excellent in high capacity and long-term cycle characteristics, since no appearance of additional capacity at 2.2 V or less accompanying structural transition is observed.

Comparative Example 3
Starting materials: 10.10 g of iron (III) nitrate 9 hydrate, 7.27 g of nickel (II) nitrate hexahydrate, 39.58 g of manganese (II) chloride tetrahydrate (total amount of 0.25 mol, Fe: Ni: Mn mol The ratio 1: 1: 8) was added to 500 mL of distilled water and completely dissolved. After that, the positive electrode material was manufactured 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. According to the analysis result by Rietveld analysis program RIETAN-FP, all peaks can be indexed by the lattice constant in Table 1 described later, and only from the crystal phase having unit cells (C2 / m) of monoclinic Li ₂ MnO ₃ It turned out that it became.

Also, according to chemical analysis, Fe and Ni contents with respect to the total metal amount other than lithium maintain 10 mol% and 10 mol% (equivalent to y value 0.20) which are preparation amounts, respectively, and Li / (M ¹ + Mn) ratio Since it is also 1.71 (x value conversion 0.262), the lithium manganese-based 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, according to the procedure described in charge and discharge characteristic evaluation to be described later, a lithium secondary battery was prepared using the obtained sample as a positive electrode material and metal lithium as a negative electrode material, and subjected to activation treatment and cycle test. The evaluation results of the charge and discharge characteristics are shown in FIG. 12 and Table 3. According to FIG. 12 and Table 3, the sample of Comparative Example 3 exhibits a charge-discharge capacity close to 230 mAh / g after activation, but during 50 cycles of discharge after activation treatment, 3.7 associated with structural transition from layered rock salt type structure to spinel phase It is possible to observe an abrupt potential drop from around V and the appearance of additional capacity below 2.2 V due to the structural transition from a layered rock salt type structure to a Li ₂ (Ni, Mn) O ₂ phase. It is apparent that the cathode material is inferior in long-term cycle characteristics as compared to the lithium manganese composite oxide of Example 3.

Example 4
A sample was prepared in the same manner as in Example 1 except that the final firing conditions were 900 ° C., 5 hours, and a nitrogen stream. The measured (+) and calculated (solid line) X-ray diffraction patterns of this final product are shown in FIG. According to the analysis result by Rietveld analysis program RIETAN-FP, all peaks can be indexed by the lattice constant in Table 1 described later, and only from the crystal phase having unit cells (C2 / m) of monoclinic Li ₂ MnO ₃ It turned out that it became.

  In addition, when the distribution of transition metal ions in the structure in Table 2 described later is confirmed, the amount of transition metal in the Li—Mn layer is smaller in the sample of Example 4 as compared with the sample of Comparative Example 4 not including Ti described later. It can be seen that the amount of transition metal in a single layer is large, and it is understood that transition metal ions tend to be irregularly arranged due to the introduction of Ti. In addition, it is understood that the sample of Example 4 has a higher degree of hexagonal mesh arrangement, as compared to the sample of Comparative Example 4 which does not contain Ti described later.

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

Furthermore, according to the procedure described in charge and discharge characteristic evaluation to be described later, a lithium secondary battery was prepared using the obtained sample as a positive electrode material and metal lithium as a negative electrode material, and subjected to activation treatment and cycle test. The evaluation results of the charge and discharge characteristics are shown in FIG. 14 and Table 3. From FIG. 14 and Table 3, the sample of Example 4 not only shows charge / discharge capacity close to 200 mAh / g after activation but also the sample of Comparative Example 4 obtained under the same preparation conditions without containing the element M ² described later. Not only the charge and discharge characteristics at 1 cycle after activation processing are almost equal to that of, but the charge and discharge curves similar to those at 20 cycles after activation treatment are shown up to 50 cycles after activation treatment. . In other words, during 50 cycles after activation treatment, a rapid potential drop from around 3.7 V accompanied by a structural transition from a layered rock salt structure to a spinel phase during 50 cycles of discharge, or a layered rock salt structure causes a Li ₂ (Ni, Mn) O ₂ phase It is clear that it is a positive electrode material excellent in high capacity and long-term cycle characteristics, since no appearance of additional capacity at 2.2 V or less accompanying structural transition is observed.

Comparative Example 4
Starting materials: 10.10 g of iron (III) nitrate 9 hydrate, 7.27 g of nickel (II) nitrate hexahydrate, 39.58 g of manganese (II) chloride tetrahydrate (total amount of 0.25 mol, Fe: Ni: Mn mol The ratio 1: 1: 8) was added to 500 mL of distilled water and completely dissolved. After that, the positive electrode material was manufactured in the same manner as in Example 4.

The measured (+) and calculated (solid line) X-ray diffraction patterns of this final product are shown in FIG. According to the analysis result by Rietveld analysis program RIETAN-FP, all peaks can be indexed by the lattice constant in Table 1 described later, and only from the crystal phase having unit cells (C2 / m) of monoclinic Li ₂ MnO ₃ It turned out that it became.

Also, according to chemical analysis, Fe and Ni contents with respect to the total metal amount other than lithium maintain 10 mol% and 10 mol% (equivalent to y value 0.20) which are preparation amounts, respectively, and Li / (M ¹ + Mn) ratio Lithium manganese-based composite oxide having a composition formula Li _{1 + x} (M ¹ _y Mn _1-y ) _1-x O ₂ not containing M ² because it is also 1.72 (0.265 in terms of x value) Is clear.

Furthermore, according to the procedure described in charge and discharge characteristic evaluation to be described later, a lithium secondary battery was prepared using the obtained sample as a positive electrode material and metal lithium as a negative electrode material, and subjected to activation treatment and cycle test. The evaluation results of the charge and discharge characteristics are shown in FIG. 16 and Table 3. From FIG. 16 and Table 3, the sample of Comparative Example 4 shows charge / discharge capacity close to 200 mAh / g after activation, but at 50 cycles after activation treatment, 3.7 accompanied with structural transition from layered rock salt type structure to spinel phase It is possible to observe an abrupt potential drop from around V and the appearance of additional capacity below 2.2 V due to the structural transition from a layered rock salt type structure to a Li ₂ (Ni, Mn) O ₂ phase. It is apparent that the positive electrode material is inferior in long-term cycle characteristics as compared to the lithium manganese composite oxide of Example 4.

[Example 5]
Sample synthesis, and structure and composition evaluation 10.10 g of iron (III) nitrate 9 hydrate, 7.27 g of nickel (II) nitrate hexahydrate, 29.69 g of manganese (II) chloride tetrahydrate (total 0.25 mol, Fe: Ni: Mn molar ratio 1: 1: 6) was added to 500 mL of distilled water and completely dissolved. In a separate beaker, 50 g of sodium hydroxide was weighed, and 500 mL of distilled water was added and dissolved with stirring to prepare an aqueous sodium hydroxide solution. The aqueous sodium hydroxide solution was placed in a titanium beaker and allowed to stand in a thermostat kept at 20 ° C. Then, to the sodium hydroxide solution, the above metal salt aqueous solution was gradually dropped over about 3 hours to form Fe-Ni-Mn precipitate (coprecipitate). It was confirmed that the reaction solution was completely alkaline, and oxygen was blown into the reaction solution containing the coprecipitate under stirring for 2 days at room temperature to carry out a wet oxidation treatment to age the precipitate.

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

The powder obtained was then heated to 650 ° C. over 1 hour, held at that temperature for 5 hours, and cooled to around room temperature in a furnace. After crushing, the temperature was raised again to 900 ° C. in a nitrogen stream for 1 hour using an electric furnace, and after holding for 5 hours at that temperature, it was cooled to around room temperature in the furnace. The baked product is taken out of the electric furnace, and the baked product is washed with distilled water, filtered and dried to remove the excess lithium salt, and the desired product, iron, nickel and germanium substituted Li ₂ MnO ₃ powder is obtained. It was obtained as a round product.

Evaluation by X-ray Diffraction The measured (+) and calculated (solid line) X-ray diffraction pattern of this final product is shown in FIG. According to the analysis result by Rietveld analysis program RIETAN-FP, all peaks can be indexed by the lattice constants described in Table 1 below, and only the crystal phase having unit cells (C2 / m) of monoclinic Li ₂ MnO ₃ It turned out that it consists of. In addition, when the distribution of transition metal ions in the structure in Table 2 is confirmed, the amount of transition metal in the Li-Mn layer in the sample of Example 5 is smaller than that of the sample of Comparative Example 4 not containing Ge described above. It can be seen that the amount of internal transition metal is large, and it is understood that transition metal ions tend to be irregularly arranged due to the introduction of Ge. Further, it is understood that the sample of Example 5 has a higher hexagonal network regularity as compared with the sample of Comparative Example 4 which does not contain Ge described above.

Evaluation based on chemical analysis etc. Based on the chemical analysis, although the contents of Fe, Ni and Ge relative to the total amount of metals other than lithium are different from the preparation amounts, 12 mol% and 12 mol% (y value 0.24 equivalent) and 4 mol% (z value respectively) (Equivalent to 0.04), and the Li / (M ¹ + M ² + Mn) ratio is also 1.65 (0.245 in terms of x value), so that the target composition formula Li _{1 + x} (M ¹ _y M ² _z Mn _1-yz ) It is apparent that a lithium manganese-based composite oxide having _1-x O ₂ was obtained. The reason why the content deviates from the preparation amount is considered to be that Ge was partly eluted at the time of washing with water after firing due to the amphoteric metal. However, since it is not completely eliminated, it can be dealt with by increasing the preparation amount etc. in order to increase the Ge content.

The charge / discharge characteristic evaluation details are the procedure described in charge / discharge characteristic evaluation which will be described later. A lithium secondary battery is prepared using the obtained sample as a positive electrode material and metal lithium as a negative electrode material, and the activation treatment and cycle test are performed. The From the results of FIG. 18 and Table 4, the sample of Example 5 not only exhibits a charge / discharge capacity close to 250 mAh / g after activation, but also contains the above-mentioned M ² element, and is a comparative example obtained under the same preparation conditions Not only the charge and discharge characteristics in one cycle after activation processing are improved as compared with the sample 4 but also the charge and discharge curves similar to those in 20 cycles after activation processing up to 50 cycles after activation processing It shows. That is, during 50 cycles of activation treatment, a rapid potential drop from around 3.7 V accompanying the structural transition from the layered rock salt structure to the spinel phase during the 50 cycle discharge, and from the layered rock salt structure, the Li ₂ (Ni, Mn) O ₂ phase It is clear that the positive electrode material is excellent in high capacity and long-term cycle characteristics, since no appearance of additional capacity at 2.2 V or less is observed with the structural transition to.

[Test results]
Evaluation by X-ray Diffraction Based on 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" The lattice constant and lattice volume of each sample were evaluated from the analysis results by Diffraction ", Solid State Phenomena, Vol. 130, pp. 15-20, 2007). The results are shown in Table 1. In Table 1, a, b and c indicate the lengths of the respective axes, and β indicates the angle between 稜 c and a. Also, V represents a lattice volume.

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

In addition, in Li ₂ MnO ₃ which is a known substance, when the Mn ions are in a regular arrangement state, 100% of Mn is occupied at the hexagonal network lattice constitution position (4 g) position, and the hexagonal mesh center position (2 b) which is Li position. Etc., but in practice, there is no 100% Mn ion at the 4 g position, and some of the Mn ions are arranged at three Li positions. In Table 2, g ₄ g indicates the Mn occupancy at the hexagonal mesh position (4 g), g 2 _b indicates the Mn occupancy at 2 b, g ₂ c indicates the Mn occupancy at ₂ c, and g 4 _h The Mn occupancy rate at the 4 h position is shown. The difference in Mn occupancy (g _4g- g _2b ) between the 4g position and the 2b position is defined as the degree of hexagonal network order, and the larger the value, the more ideal is the Li ₂ MnO ₃ type monoclinic layered rock salt type structure. Do. The average value 1 indicates the average occupancy (element ratio (%)) of transition metal elements at lattice positions (4 g and 2 b positions) in the Li-Mn layer, and the average value 2 indicates lattices in the Li single layer The average occupancy (element ratio (%)) of transition metal elements at positions (4h and 2c positions) is shown. In addition, the total transition metal content is determined by the ratio (element ratio (%)) of the transition metal element at the lattice position (4 g and 2 b) in the Li-Mn layer when using the monoclinic layered rock salt type structural model and Li The sum of the occupancy (element ratio (%)) of the transition metal element at lattice positions (4 h and 2 c) in a single layer is shown. The smaller the average value 1 and the larger the average value 2, the more irregular the transition metal ions.

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 Characteristics Evaluation Using the samples obtained in Examples 1 to 5 and Comparative Examples 1 to 4 as a positive electrode material, a charge / discharge test was performed. Specifically, after 5 mg of the samples obtained in Examples 1 to 5 and Comparative Examples 1 to 4 are well mixed with 5 mg of acetylene black, 0.5 mg of polytetrafluoroethylene powder is added thereto for binding, and pressure bonding is performed on Al mesh. The positive electrode was prepared. The obtained positive electrode was vacuum dried overnight at 120 ° C., and then a lithium secondary battery was produced in a glove box. Electrolyte LiPF ₆ mixed solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC) (volume ratio of 3: 7) solution dissolved in using, the negative electrode using metallic lithium.

The charge and discharge test was transferred to a cycle deterioration test after a step charge process for obtaining an activated sample. The test is performed at the start of charging, and cycling is performed by increasing the charge capacity in the order of 80, 120, 160 and 200 mAh / g at a potential range of 2.0-4.8 V, a test temperature of 30 ° C., and a current density of 40 mA / g. The activation treatment was performed by constant current-constant voltage charging (current termination at 4.8 V is 10 mA / g) to 4.8 V. The step charge activation treatment is essential for the evaluation of the charge and discharge characteristics of the lithium manganese composite oxide of the present invention. In particular, when Fe is contained as the M ¹ element, this is an essential process. After activation treatment, evaluation is made up to 50 cycles with constant current charge and discharge at 2.0-4.8 V, and charge / discharge curve changes with cycle progress (especially deviation from conformal shape seen after 20 cycles) Was evaluated. In particular, as described above, in the discharge curve at 50 cycles after activation (during 54 cycles: 54 d), (1) the abrupt change around 3.7 V due to the structural transition from the layered rock salt structure to the spinel phase The potential drop and (2) the presence or absence of the appearance of additional capacity at 2.2 V or less accompanying the 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 in Table 4. In FIGS. 2, 4, 6, 8, 10, 12, 14, 16 and 18, the charge curve (5c) at 1 cycle charge after activation, the charge curve at 20 cycles charge after activation ((c) 24c), charge curve (54c) at 50 cycles charge after activation treatment, discharge curve (5d) at 1 cycle discharge after activation treatment, discharge curve (24d) at 20 cycles discharge after activation treatment, and activation The discharge curve (54d) at 50 cycles of discharge after the chemical treatment is shown, and the curve rising to the right corresponds to charging, and the curve falling to the right corresponds to discharging. Also, in Table 4, Q _5c is the capacity during one cycle charge after activation, Q _{5 d} is the capacity during one cycle discharge after activation, Q _{54 d} is the capacity during 50 cycles discharge after activation, (Q _1d sum to Q _5d) / (sum of Q _1c to 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 _{5 d · ave} indicates the initial average discharge voltage during one cycle discharge after activation treatment.

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

Claims (10)

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 indicate 0 <x <1/3, 0 ≦ y ≦ 0.4, and 0 <z ≦ 0.3. ]
Represented by, and
Lithium manganese-based composite oxide containing a crystal phase of monoclinic layered rock salt type structure or hexagonal layered rock salt type structure. The lithium manganese-based composite oxide according to claim ¹ , wherein M ¹ in the general formula (1) contains Ni. The lithium manganese-based composite oxide according to claim 1 or 2, which comprises only a crystal phase of a monoclinic layered rock salt type structure. It is a manufacturing method of lithium manganese system complex oxide in any one of Claims 1-3,
(1) 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 treatment and aging it;
(3) A manufacturing method comprising the steps of heating the matured product obtained in step 2 in the coexistence of a raw material compound containing a lithium compound in this order. The method according to claim 4, wherein the mixture in step 1 further contains a titanium compound. The manufacturing method according to claim 4 or 5, wherein the raw material compound in the step 3 further contains a germanium compound. The method according to any one of claims 4 to 6, wherein the step 3 is a step of heating after mixing the matured product obtained in the step 2 and the raw material compound. The 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 atmosphere and then again in the atmosphere or in an inert atmosphere. The positive electrode material for lithium ion secondary batteries which consists of a lithium manganese type complex oxide in any one of Claims 1-3. A lithium ion secondary battery comprising the positive electrode material for a lithium ion secondary battery according to claim 9 as a component.

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