JP7206808B2 - Cobalt-manganese composite oxide, production method thereof, and use thereof - Google Patents

Description

The present invention relates to a cobalt-manganese composite oxide, a method for producing the same, and applications thereof. The present invention relates to a method for producing a lithium-cobalt-manganese composite oxide using the cobalt-manganese composite oxide, and a lithium secondary battery using the lithium-cobalt-manganese composite oxide as a positive electrode.

Lithium-cobalt-manganese composite oxides are attracting attention as positive electrode active materials for 5V class lithium secondary batteries. Examples of the method for producing the lithium-cobalt-manganese composite oxide (so-called active material) include a solid phase reaction method in which a lithium source, a cobalt source, and a manganese source are mixed and fired, and a cobalt-manganese composite compound. (so-called precursor) and a lithium source are reacted.

A spinel-type lithium-cobalt-manganese-containing composite oxide having a space group of Fd-3m is known (Patent Document 1). The spinel-type lithium-cobalt-manganese-containing composite oxide is prepared by mixing a lithium source, a manganese source, and a cobalt source, wet granulating the mixture by a spray heat drying method, and is produced by a so-called solid phase reaction method. .

Japanese Patent No. 5813277

Regarding the spinel-type lithium-cobalt-manganese-containing composite oxide obtained by the solid-phase reaction method of Patent Document 1, it is difficult to say that cobalt and manganese are sufficiently dispersed at the atomic level, and there is a problem that the homogeneity is poor. .

An object of the present invention is to provide a lithium-cobalt-manganese-containing composite oxide with excellent homogeneity. To this end, a spinel-type cobalt-manganese composite oxide (precursor) in which cobalt and manganese are dispersed at the atomic level is prepared. to provide.

As a result of intensive studies on cobalt-manganese-based composite oxides, the present inventors have found a spinel-type composite oxide having a Co:Mn composition (molar ratio) of about 1:1, which has never existed before, and have completed the present invention. rice field. _That is _, the present invention has a _cubic The present invention relates to a cobalt-manganese composite oxide characterized by a crystal spinel structure, a method for producing the same, and uses thereof.

The cobalt-manganese-based composite oxide (precursor) of the present invention is extremely close to a single crystal phase. active material) can be provided.

In addition, the cobalt-manganese composite oxide of the present invention has the effect of being excellent in storage stability.

In addition, the lithium-cobalt-manganese composite oxide obtained by using the cobalt-manganese composite oxide of the present invention as a precursor has a higher lithium-dioxide content than the conventional solid-phase reaction method lithium-cobalt-manganese composite oxide. It is effective in improving the performance of the secondary battery.

The present invention will be described in detail below.

The cobalt-manganese composite oxide of the present invention has a chemical composition formula of Co _(1.5+x) Mn _(1.5−x) O ₄ (where −0.15≦x≦0.15). be done.

Regarding the above x, −0.15≦x≦0.15, but if x is within this range, the content of cobalt involved in oxidation-reduction can be secured, and around 5 V (Li metal negative electrode standard) more battery capacity. The x is preferably −0.10≦x≦0.10, more preferably −0.05≦x≦0.05.

The cobalt-manganese composite oxide of the present invention has a cubic spinel crystal structure. The cubic spinel type has the advantage that the element distribution of Co and Mn is made uniform and a regular Co—Mn arrangement is easily realized. Further, since both the raw material and the lithium-cobalt-manganese-based composite oxide as the final product have a spinel structure, there is an advantage that the reaction between the raw material and the lithium compound tends to proceed smoothly. Here, the cubic spinel type means that the crystal lattice is classified as a cubic system, the crystal structure is a spinel type, and the space group is preferably Fd-3m. In addition, since the content of the cubic spinel-type oxide is high and becomes the main phase, the lattice constant a is preferably 8.15 to 8.35 Å, more preferably 8.20 to 8.30 Å, and 8.22. ~8.30 Å is more preferred, and 8.25-8.30 Å is particularly preferred. When the lattice constant a is 8.25-8.30 Å, a crystal phase very close to a single crystal phase is obtained. The cubic spinel type crystal structure is not only the single crystal phase of the cubic spinel type structure, but also the cubic spinel type structure as the main phase, oxyhydroxide, hydrotalcite type hydroxide Either or both of may be produced in a trace amount to form a subphase.

The cobalt-manganese composite oxide of the present invention preferably has a Na content of 3000 ppm or less. When the Na content is 3000 ppm or less, the lithium-cobalt-manganese composite oxide obtained by using the cobalt-manganese composite oxide does not hinder the movement of lithium, and the discharge capacity tends to increase. The Na content is more preferably 2000 ppm or less, still more preferably 1700 ppm or less, even more preferably 1500 ppm or less, particularly preferably 1200 ppm or less, and most preferably 1000 ppm or less, in terms of excellent discharge capacity.

The cobalt-manganese composite oxide of the present invention preferably has an SO ₄ content of 1% by weight or less. When the SO ₄ content is 1% by weight or less, when the lithium-cobalt-manganese composite oxide is produced using the cobalt-manganese composite oxide, a compound is formed with Li metal to form Li ₂ SO ₄ etc. is suppressed locally, and the battery capacity tends to increase. Therefore, the SO ₄ content is more preferably 0.6% by weight or less, and even more preferably 0.3% by weight or less.

The average particle size of the cobalt-manganese composite oxide of the present invention is not particularly limited. 15 μm is more preferred. The average particle size means the average particle size of secondary particles obtained by aggregating primary particles, and represents a so-called agglomerated particle size.

The particle size distribution of the cobalt-manganese composite oxide of the present invention is not particularly limited, and examples thereof include monodisperse particle size distribution and bimodal particle size distribution. When the particle size distribution is monodisperse, that is, monomodal, the particle size is uniform even when used as a positive electrode, so that the charging/discharging reaction becomes more uniform.

The BET specific surface area of the cobalt-manganese composite oxide of the present invention is not particularly limited, but it is preferably 100 m ² /g or less, and 75 m ² /g, in terms of easily obtaining high filling properties. It is more preferably 50 m ² /g or less, particularly preferably 25 m ² /g or less, and most preferably 15 m ² /g or less. Generally, since there is a correlation between the fillability and the BET specific surface area, a powder with a low specific surface area can be easily obtained with a high fillability.

Next, the method for producing the cobalt-manganese composite oxide of the present invention will be described.

The cobalt-manganese-based composite oxide of the present invention is obtained by adding an aqueous solution containing a cobalt salt compound and a manganese salt compound and an oxidizing agent at a redox potential of -0.2 to 0.3 V under pH 8.0 to 12.0 conditions. It can be produced by mixing, and the desired cobalt-manganese composite oxide can be precipitated in the mixed aqueous solution by this operation.

Examples of the cobalt salt compound include, but are not limited to, cobalt sulfate, cobalt chloride, cobalt nitrate, and cobalt acetate. The aqueous solution containing a cobalt salt compound is not particularly limited, but examples include aqueous solutions in which cobalt sulfate, cobalt chloride, cobalt nitrate, cobalt acetate, etc. are dissolved, and inorganic acids such as sulfuric acid, hydrochloric acid, and nitric acid. , an aqueous solution in which cobalt is dissolved in an acid such as acetic acid, and the like. Cobalt sulfate is preferable as the cobalt salt compound.

Examples of the manganese salt compound include, but are not limited to, manganese sulfate, manganese chloride, manganese nitrate, and manganese acetate. The aqueous solution containing a manganese salt compound is not particularly limited. , an aqueous solution in which manganese is dissolved in an acid such as acetic acid, and the like. Manganese sulfate is preferable as the manganese salt compound.

Further, in the production method of the present invention, the ratio of cobalt and manganese is preferably adjusted to the ratio of cobalt:manganese of the target cobalt-manganese composite oxide. Therefore, the molar ratio of cobalt and manganese is preferably Co:Mn=1.50+x:1.50−x (where −0.15≦x≦0.15).

The total concentration of cobalt and manganese (metal concentration) in the aqueous metal salt solution is arbitrary, but is preferably 1.0 mol/L or more, more preferably 2.0 mol/L or more, in terms of excellent productivity.

In order to maintain the reaction conditions of pH 8.0 to 12.0, it is preferable to appropriately add and mix an acid or a base. Examples of the acid include, but are not limited to, sulfuric acid, hydrochloric acid, nitric acid, and acetic acid. The base is not particularly limited, but examples include caustic soda, caustic potash, lithium hydroxide, calcium hydroxide, barium hydroxide, sodium carbonate, sodium bicarbonate and the like.

When adding the acid or base, the acid or base may be added directly or may be added as an aqueous solution. When added as an aqueous solution, the concentration is not particularly limited, but for example, 1 mol/L or more can be exemplified.

In the present invention, in order to maintain the reaction conditions of pH 8.0 to 12.0, it is preferable to add an aqueous solution of caustic soda. It is possible to use an aqueous solution of sodium hydroxide produced from the above with adjusted concentration.

In the production method of the present invention, the method of adding and mixing an acid or a base to control the pH is not particularly limited. For example, it may be carried out continuously or intermittently.

Examples of the oxidizing agent include, but are not limited to, aerobic gas and hydrogen peroxide water. Examples of the aerobic gas include, but are not limited to, air, oxygen, and the like. Air is most preferred economically. A gas such as air or oxygen is added by bubbling using a bubbler or the like. On the other hand, the hydrogen peroxide solution can be mixed in the same manner as the metal salt solution and the caustic soda solution. As the concentration of the hydrogen peroxide solution, 3 to 30% by weight can be exemplified.

The production method of the present invention is carried out under conditions of pH 8.0 to 12.0. If the pH is less than 8.0, the difference in solubility between cobalt and manganese becomes significant, causing a shift in the desired composition ratio between cobalt and manganese. become The pH is preferably 8.0 to 11.0, more preferably 8.0 to 9.5, in that the production ratio of the cubic spinel-type oxide can be increased. Furthermore, pH 8.25 to 9.25 is particularly preferable in terms of enabling production with high production efficiency.

In the production method of the present invention, an aqueous solution containing a cobalt salt compound and a manganese salt compound and an oxidizing agent are mixed at an oxidation-reduction potential of -0.2 to 0.3V. The oxidation-reduction potential also affects the crystal structure to be produced. If the oxidation-reduction potential exceeds 0.3 V, it deviates from the deposition potential of manganese, causing a deviation in the composition ratio of cobalt and manganese. On the other hand, if the oxidation-reduction potential is less than -0.2 V, the crystallinity is lowered and the film becomes amorphous. A range of -0.1 to 0.2 V is preferred to approximate a single crystal phase. The redox potential can be controlled by the amount of oxidizing agent supplied.

Although the temperature at which the oxidizing agent is added to the aqueous solution containing the cobalt salt compound and the manganese salt compound is not particularly limited, it is usually preferably 40° C. or higher. The temperature is more preferably 50° C. or higher, still more preferably 60° C. or higher, and particularly preferably 60 to 80° C., in that the oxidation reaction of the aqueous metal salt solution proceeds easily and the cobalt-manganese composite oxide is more likely to precipitate. .

The method for producing a cobalt-manganese composite oxide according to the present invention does not require any special atmosphere control, and can be carried out in a normal atmospheric atmosphere.

The method for producing the cobalt-manganese composite oxide of the present invention can be either a batch system or a continuous system. Mixing time is arbitrary in the case of batch type. Examples include 3 to 48 hours, and further 6 to 24 hours. On the other hand, in the case of the continuous type, the average residence time of the cobalt-manganese composite oxide particles in the reaction vessel is preferably 1 to 30 hours, more preferably 3 to 20 hours.

The cobalt-manganese composite oxide precipitated by the method for producing a cobalt-manganese composite oxide of the present invention can be isolated by an operation such as filtration, and further washed and dried for handling. preferably.

Impurities adhering to and adsorbed on the cobalt-manganese composite oxide can be removed by washing. The washing method is not particularly limited, but for example, a method of adding a cobalt-manganese composite oxide to water (for example, pure water, tap water, river water, etc.) and dissolving impurities in the water is exemplified. can.

Moisture in the cobalt-manganese composite oxide can be removed by drying. Although the drying method is not particularly limited, for example, the cobalt-manganese composite oxide is dried by heating at 110 to 150° C. for 2 to 15 hours.

In the production method of the present invention, pulverization may be performed after washing and drying.

In pulverization, a powder having an average particle size suitable for the application is obtained. Pulverization conditions are arbitrary as long as the desired average particle size is obtained. For example, wet pulverization, dry pulverization, or the like can be used.

The cobalt-manganese composite oxide of the present invention can be used for producing a lithium-cobalt-manganese composite oxide.

When producing a lithium-cobalt-manganese composite oxide using the cobalt-manganese composite oxide of the present invention as a raw material, the production method includes a mixing step of mixing the cobalt-manganese composite oxide and the lithium compound. , a firing process and an annealing process.

Any lithium compound can be used in the mixing step. Examples of lithium compounds include one or more selected from the group consisting of lithium hydroxide, lithium oxide, lithium carbonate, lithium iodide, lithium nitrate, lithium oxalate, and alkyllithium. As a preferable lithium compound, any one or more selected from the group consisting of lithium hydroxide, lithium oxide and lithium carbonate can be exemplified.

In the firing step, a lithium-cobalt-manganese composite oxide can be produced by firing the mixture obtained in the mixing step. Firing is not particularly limited, but can usually be carried out in the temperature range of 500 to 1000°C. The firing can be performed in various atmospheres such as air and oxygen.

In the annealing step, a temperature range of 500 to 800° C. is preferable, and a temperature range of 600 to 750° C. is more preferable. is preferred. If the annealing step is not performed, the amount of oxygen deficiency increases and the charge/discharge capacity decreases.

The lithium-cobalt-manganese composite oxide thus obtained is used as a positive electrode active material for lithium secondary batteries.

As the negative electrode active material used in the lithium secondary battery of the present invention, metallic lithium and materials capable of intercalating and deintercalating lithium or lithium ions can be used. Examples include metallic lithium, lithium/aluminum alloy, lithium/tin alloy, lithium/lead alloy, and carbon materials capable of electrochemically intercalating/deintercalating lithium ions. A carbon material that can be desorbed is particularly preferred from the standpoint of safety and battery characteristics.

The electrolyte used in the lithium secondary battery of the present invention is not particularly limited. Electrolytes can be used.

The separator used in the lithium secondary battery of the present invention is not particularly limited, but for example, a microporous film made of polyethylene or polypropylene can be used.

As an example of the configuration of the lithium secondary battery as described above, for example, after molding a mixture with a conductive agent into a pellet shape, the molded product obtained by drying under reduced pressure at 100 to 200 ° C. is used as a battery positive electrode, and metallic lithium Examples include those using a negative electrode made of foil, and an electrolytic solution obtained by dissolving lithium hexafluorophosphate in a mixed solvent of ethylene carbonate and diethyl carbonate.

1 is an XRD pattern of the cobalt-manganese composite oxide of Example 1. FIG. 2 is a particle size distribution curve of the cobalt-manganese composite oxide of Example 1. FIG. 1 is a scanning electron micrograph of a cobalt-manganese composite oxide of Example 1. FIG. 4 is a particle size distribution curve of the cobalt-manganese composite oxide of Example 2. FIG. 4 is a particle size distribution curve of the cobalt-manganese composite oxide of Example 3. FIG. 4 is a particle size distribution curve of the cobalt-manganese composite oxide of Example 4. FIG. 4 is a scanning electron micrograph of the cobalt-manganese composite oxide of Example 4. FIG. 10 is an XRD pattern of the cobalt-manganese composite oxide of Example 5. FIG. 4 is a particle size distribution curve of the cobalt-manganese composite oxide of Example 5. FIG. 4 is a scanning electron micrograph of the cobalt-manganese composite oxide of Example 5. FIG. 4 is an elemental mapping of the cobalt-manganese composite oxide of Example 5. FIG. 10 is an XRD pattern of the cobalt-manganese composite oxide of Example 6. FIG. 10 is an XRD pattern of the cobalt-manganese composite oxide of Example 9. FIG. 10 is a scanning electron micrograph of the cobalt-manganese composite oxide of Example 9. FIG. 10 is an XRD pattern of the lithium-cobalt-manganese composite oxide of Example 10. FIG.

EXAMPLES The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

<Powder X-ray diffraction measurement>
Using an X-ray diffractometer (trade name: Ultima4, manufactured by Rigaku), the obtained sample was subjected to powder X-ray diffraction measurement. CuKα rays (λ = 1.5405 Å) are used as the radiation source, the measurement mode is step scan, the scan conditions are sampling width 2θ = 0.04°, measurement time is 4 seconds, and the measurement range is 10° to 90° as 2θ. measured in the range of

<Analysis of crystal structure and measurement of lattice constant>
In the XRD pattern obtained by the XRD measurement under the above conditions, structural refinement of the cubic spinel crystal phase was performed by the Rietveld method. The lattice constant a was obtained by pattern fitting using the analysis software PDXL-2 attached to the X-ray diffractometer. 2θ=19.2°±0.5° and 2θ=66.0°±0.5° for the oxyhydroxide type structure, which is a byproduct phase, and 2θ=11.0° for the hydrotalcite type oxide structure. Their formation was confirmed by observing diffraction peaks that could not be attributed to the cubic spinel structure at 7°±1.0°. In addition, the oxyhydroxide structure has the strongest diffraction peak at 2θ = 19.2° ± 0.5°, but the crystal phase of the cubic spinel structure has a 2θ = 18.5° ± 0.5°. When overlapped with the diffraction peak of , it may appear as a single synthetic peak. In this case, the presence or absence of the oxyhydroxide structure was confirmed by comparing the intensity ratio with other diffraction peaks.

<Measurement of chemical composition>
Composition analysis of the obtained sample was performed by inductively coupled plasma emission spectrometry (ICP method). That is, the measurement solution was prepared by heating and acid-dissolving the sample powder, the hydrogen peroxide solution, and the hydrochloric acid aqueous solution. The chemical composition of the obtained sample was analyzed by measuring the obtained measurement solution using a general inductively coupled plasma emission spectrometer (trade name: OPTIMA3000DV, manufactured by PERKIN ELMER).

<Measurement of average particle size>
The average particle size of the obtained sample was measured in HRA mode using a laser diffraction particle size distribution analyzer (trade name: Microtrac MT3300EXII, manufactured by Microtrac Bell).

<Measurement of specific surface area>
1.0 g of the obtained composite oxide was pretreated in a nitrogen stream at 150° C. for 1 hour using an automatic flow-type specific surface area measuring device (trade name: Flowsorb 3-2305, manufactured by Micrometrics), and then subjected to the BET 1-point method. The specific surface area (m ² /g) was obtained by dividing the adsorption/desorption area by the weight.

<Measurement of elemental mapping>
Using a field emission electron microscope (FE-SEM, trade name: JSM-7600F, manufactured by JEOL Ltd.)/energy dispersive spectrometer (EDS, trade name: NSS312E+UltraDry 30 mm ² , manufactured by Thermo Fisher Scientific), ion milling was performed. The distribution of Co element and Mn element in the cross section of the sample was measured at an acceleration voltage of 10 kV.

<Battery performance evaluation>
A battery characteristic test was performed on the positive electrode of the lithium-cobalt-manganese composite oxide.

The resulting lithium-cobalt-manganese composite oxide powder (positive electrode active material), acetylene black as a conductive aid, and PVDF as a binder were mixed at a mass ratio of 88:6:6, and NMP was added. Adjusted to a paste. This paste was applied to an Al foil current collector having a thickness of 10.7 μm and dried at 150° C. under reduced pressure. After that, it was cut into a size of φ13 mm and pressed at 2 t/m ² to obtain a positive electrode. The positive electrode for battery thus obtained, the negative electrode made of metallic lithium foil (thickness: 0.2 mm), and the electrolytic solution obtained by dissolving lithium hexafluorophosphate in a mixed solvent of ethylene carbonate and diethyl carbonate at a concentration of ¹ mol/dm3. A battery was constructed using the liquid. The battery was charged and discharged at a constant current at a battery voltage between 5.4 V and 3.0 V at room temperature. It was charged and discharged at a current density of 10 mA/g, and each specific capacity (mAh/g) was measured.

Example 1
Cobalt sulfate and manganese sulfate were dissolved in pure water to obtain an aqueous solution (metal salt aqueous solution) containing 1.0 mol/L (liter) of cobalt sulfate and 1.0 mol/L of manganese sulfate. The total concentration of all metals in the metal salt aqueous solution was 2.0 mol/L.

Further, after putting 300 g of pure water into a reaction vessel having an inner volume of 1 L, the temperature was raised to 60° C. and maintained.

The obtained metal salt aqueous solution was continuously supplied to the reactor at a supply rate of 0.35 g/min. As an oxidant, air was bubbled into the reactor at a supply rate of 1 L/min. Furthermore, when supplying the metal salt aqueous solution and air, the reaction was allowed to proceed continuously while intermittently adding a 2.5 mol/L sodium hydroxide aqueous solution (caustic soda aqueous solution) so that the pH was 8.25. (The oxidation-reduction potential during the reaction was 0.13 V). Due to the above reaction, a cobalt-manganese composite compound was precipitated in the reaction vessel to obtain a slurry. A wet cake was obtained by filtering the slurry in the reaction vessel and washing with pure water. By drying the wet cake at 110° C. for 15 hours, a cobalt-manganese composite oxide was obtained.

FIG. 1 shows the XRD pattern of the obtained cobalt-manganese composite oxide. From FIG. 1, although a faint diffraction peak is seen near 2θ=12°, it can be said to be a single crystal phase with a substantially cubic spinel structure.

FIG. 2 shows the particle size distribution curve of the obtained cobalt-manganese composite oxide. From FIG. 2, it can be said that a wide range of particle sizes is normally distributed.

A scanning electron micrograph of the obtained cobalt-manganese composite oxide is shown in FIG.

Table 1 shows the measurement results of the obtained cobalt-manganese composite oxide (chemical composition formula: Co _1.493 Mn _1.507 O ₄ ).

Example 2
A slurry was obtained in the same manner as in Example 1, except that the reaction was allowed to proceed continuously while intermittently adding a 2.5 mol/L aqueous sodium hydroxide solution so that the pH was 8.75 ( The oxidation-reduction potential during the reaction was 0.09 V). The resulting slurry was filtered, washed and dried in the same manner as in Example 1 to obtain a cobalt-manganese composite oxide.

The XRD pattern of the obtained cobalt-manganese composite oxide is almost the same as that shown in FIG. rice field.

FIG. 4 shows the particle size distribution curve of the obtained cobalt-manganese composite oxide. From FIG. 4, it can be said that uniform particle diameters are monodisperse.

Table 1 shows the measurement results of the obtained cobalt-manganese composite oxide (chemical composition formula: Co _1.514 Mn _1.486 O ₄ ).

Example 3
A slurry was obtained in the same manner as in Example 1, except that the reaction was allowed to proceed continuously while intermittently adding a 2.5 mol/L aqueous sodium hydroxide solution so that the pH was 9.00 ( The oxidation-reduction potential during the reaction was 0.10 V). The resulting slurry was filtered, washed and dried in the same manner as in Example 1 to obtain a cobalt-manganese composite oxide.

The XRD pattern of the obtained cobalt-manganese composite oxide is almost the same as that shown in FIG. rice field.

FIG. 5 shows the particle size distribution curve of the obtained cobalt-manganese composite oxide. From FIG. 5, it can be said that uniform particle diameters are monodisperse.

Table 1 shows the measurement results of the obtained cobalt-manganese composite oxide (chemical composition formula: Co _1.510 Mn _1.490 O ₄ ).

Example 4
A slurry was obtained in the same manner as in Example 1, except that the reaction was allowed to proceed continuously while intermittently adding a 2.5 mol/L aqueous sodium hydroxide solution so that the pH was 9.25 ( The oxidation-reduction potential during the reaction was 0.08 V). The resulting slurry was filtered, washed and dried in the same manner as in Example 1 to obtain a cobalt-manganese composite oxide.

The XRD pattern of the obtained cobalt-manganese composite oxide was almost the same as that shown in FIG.

FIG. 6 shows the particle size distribution curve of the obtained cobalt-manganese composite oxide. From FIG. 6, it can be said that the uniform particle size is monodispersed.

A scanning electron micrograph of the obtained cobalt-manganese composite oxide is shown in FIG.

Table 1 shows the measurement results of the obtained cobalt-manganese composite oxide (chemical composition formula: Co _1.490 Mn _1.510 O ₄ ).

Example 5
The reaction was allowed to proceed continuously while intermittently adding 2.5 mol/L aqueous sodium hydroxide solution so that the pH was 8.5 (the oxidation-reduction potential during the reaction was 0.09 V), A slurry was obtained in the same manner as in Example 1, except that the slurry was obtained by continuously extruding from the reactor outlet. The resulting slurry was filtered, washed and dried in the same manner as in Example 1 to obtain a cobalt-manganese composite oxide.

FIG. 8 shows the XRD pattern of the obtained cobalt-manganese composite oxide. From FIG. 8, it could be said that it was a single crystal phase with a cubic spinel structure.

FIG. 9 shows the particle size distribution curve of the obtained cobalt-manganese composite oxide. From FIG. 9, it can be said that the uniform particle size is monodispersed.

A scanning electron micrograph of the obtained cobalt-manganese composite oxide is shown in FIG.

Element mapping of the obtained cobalt-manganese composite oxide is shown in FIG. From FIG. 11, no segregation of Co element and Mn element was observed, indicating high homogeneity.

Table 1 shows the measurement results of the obtained cobalt-manganese composite oxide (chemical composition formula: Co _1.515 Mn _1.485 O ₄ ).

Example 6
A slurry was obtained in the same manner as in Example 1, except that the reaction was allowed to proceed continuously while intermittently adding a 2.5 mol/L aqueous sodium hydroxide solution so that the pH was 9.5 ( The oxidation-reduction potential during the reaction was 0.08 V). The resulting slurry was filtered, washed and dried in the same manner as in Example 1 to obtain a cobalt-manganese composite oxide.

FIG. 12 shows the XRD pattern of the obtained cobalt-manganese composite oxide. From FIG. 12, weak diffraction peaks corresponding to oxyhydroxide were observed near 2θ = 34° and 2θ = 66°. It can be said that it is a phase. In addition, the existence of the oxyhydroxide phase could be confirmed from the fact that the intensity of the diffraction peak at 2θ=18.5°±1.0° was clearly stronger than those of Examples 1 to 5.

It was clear that the crystalline phase fraction of the cubic spinel-type structure was higher than other subphases.

Table 1 shows the measurement results of the obtained cobalt-manganese composite oxide (chemical composition formula: Co _1.508 Mn _1.492 O ₄ ).

Example 7
A slurry was obtained in the same manner as in Example 1, except that the reaction was allowed to proceed continuously while intermittently adding a 2.5 mol/L aqueous sodium hydroxide solution so that the pH was 9.75 ( The oxidation-reduction potential during the reaction was 0.09 V). The resulting slurry was filtered, washed and dried in the same manner as in Example 1 to obtain a cobalt-manganese composite oxide.

The XRD pattern of the obtained cobalt-manganese composite oxide was almost the same as that shown in FIG. It can be said that the crystalline spinel type structure is the main phase and the oxyhydroxide type structure is the secondary phase. It was clear that the crystalline phase fraction of the cubic spinel-type structure was higher than other subphases.

Table 1 shows the measurement results of the obtained cobalt-manganese composite oxide (chemical composition formula: Co _1.518 Mn _1.482 O ₄ ).

Example 8
A slurry was obtained in the same manner as in Example 1, except that the reaction was allowed to proceed continuously while intermittently adding a 2.5 mol/L aqueous sodium hydroxide solution so that the pH was 10.25 ( The oxidation-reduction potential during the reaction was 0.05 V). The resulting slurry was filtered, washed and dried in the same manner as in Example 1 to obtain a cobalt-manganese composite oxide.

The XRD pattern of the obtained cobalt-manganese composite oxide was almost the same as that shown in FIG. It can be said that the crystalline spinel type structure is the main phase and the oxyhydroxide type structure is the secondary phase. It was clear that the crystalline phase fraction of the cubic spinel-type structure was higher than other subphases.

Table 1 shows the measurement results of the obtained cobalt-manganese composite oxide (chemical composition formula: Co _1.496 Mn _1.504 O ₄ ).

Example 9
A slurry was obtained in the same manner as in Example 1, except that the reaction was allowed to proceed continuously while intermittently adding a 2.5 mol/L aqueous sodium hydroxide solution so that the pH was 11.25 ( The oxidation-reduction potential during the reaction was -0.01 V). The resulting slurry was filtered, washed and dried in the same manner as in Example 1 to obtain a cobalt-manganese composite oxide.

FIG. 13 shows the XRD pattern of the obtained cobalt-manganese composite oxide. From FIG. 13, it can be said that the cubic spinel type structure is the main phase, and the oxyhydroxide type structure and hydrotalcite type oxide structure are the secondary phases.

A scanning electron micrograph of the obtained cobalt-manganese composite oxide is shown in FIG.

Table 1 shows the measurement results of the obtained cobalt-manganese composite oxide (chemical composition formula: Co _1.479 Mn _1.521 O ₄ ).

Example 10
The cobalt-manganese-based composite oxide obtained in Example 5 and lithium carbonate were mixed and fired in an air stream at 900°C for 12 hours. A lithium-cobalt-manganese composite oxide was obtained by annealing for a period of time. From the results of the chemical composition analysis, it was possible to represent the composition formula: LiCoMnO ₄ .

FIG. 15 shows the XRD pattern of the obtained lithium-cobalt-manganese composite oxide. From FIG. 15, it can be said that the crystal has a cubic spinel structure belonging to the space group Fd-3m.

Table 2 shows the battery performance evaluation results of the obtained lithium-cobalt-manganese composite oxide. Table 2 shows that the battery has a large discharge capacity at 4.7 V or higher and a high energy density.

The cobalt-manganese composite oxide of the present invention can be used as a precursor of a lithium-cobalt-manganese composite oxide used as a positive electrode active material for lithium secondary batteries. It is possible to construct a high-performance lithium secondary battery using the composite oxide as a battery positive electrode.

Claims (9)

The chemical composition formula is represented by Co _(1.5+x) Mn _(1.5−x) O ₄ (where −0.15≦x≦0.15), and the crystal structure is a cubic spinel structure . A cobalt-manganese composite oxide characterized by having a single crystal phase and having an average particle size of 2 to 15 μm . 2. The cobalt-manganese composite oxide according to claim 1, wherein the space group is Fd-3m and the lattice constant a is 8.15 to 8.35 Å. 3. The cobalt-manganese composite oxide according to claim 1, wherein the Na content is 3000 ppm or less. 4. The cobalt-manganese composite oxide according to any one of claims 1 to 3, characterized in that the SO ₄ content is 1% by weight or less. 5. The cobalt-manganese composite oxide according to any one of claims 1 to 4, which has a monomodal particle size distribution. 6. The cobalt-manganese composite oxide according to any one of claims 1 to 5, which has a BET specific surface area of 100 m ² /g or less. Claims 1 to 1, characterized in that the aqueous solution containing cobalt sulfate and manganese sulfate and the oxidizing agent are mixed at a redox potential of -0.2 to 0.3 V under pH conditions of 8.0 to 12.0. 7. A method for producing a cobalt-manganese composite oxide according to any one of items 6. Production of a lithium-cobalt-manganese composite oxide characterized by mixing the cobalt-manganese composite oxide according to any one of claims 1 to 6 and a lithium compound, firing and annealing. Method. A lithium secondary battery, wherein the lithium-cobalt-manganese composite oxide obtained by the method for producing a lithium-cobalt-manganese composite oxide according to claim 8 is used as a positive electrode active material.

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