JP7192397B2 - Lithium-cobalt-manganese composite oxide and lithium secondary battery containing the same - Google Patents

Description

The present invention relates to a lithium-cobalt-manganese composite oxide and a lithium secondary battery containing the same.

Lithium ion secondary batteries (LIB) are used as power sources for mobile phones, notebook computers, AV equipment, electric vehicles, and the like. LiCoO ₂ is mainly used for the positive electrode material of the secondary battery.

In recent years, with the increase in power demand for mobile devices and the shift to LIBs such as hybrid electric vehicles, lithium ion secondary batteries with higher energy density and higher safety are in demand. Therefore, as a new positive electrode material, cubic spinel-type lithium that operates at 4.5 V or higher, in which part of the Mn sites in LiMn ₂ O ₄ is replaced with other transition metals (Cr, Co, Ni, Fe, Cu) Development of transition metal oxides has been actively carried out.

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 lithium, cobalt, and manganese are sufficiently dispersed at the atomic level, and the homogeneity is poor. There was a problem that the capacity of 0.5 V or more was not sufficiently produced.

An object of the present invention is to provide a lithium-cobalt-manganese composite oxide having a high energy density and a lithium secondary battery containing the same.

As a result of intensive studies on lithium-cobalt-manganese composite oxides with high energy density and safety, the inventors of the present invention found that a battery using a specific lithium-cobalt-manganese composite oxide for the positive electrode has a voltage of 4.5V. The inventors have found that a large charge/discharge capacity is exhibited in the above voltage range, and have completed the present invention. That is, in the present invention, the chemical composition formula is Li _(1.0+a) Co _x Mn _(2.0-xa) O _(4-δ) (where -0.15 ≤ a ≤ 0.15, 0.00). 9 ≤ x ≤ 1.1, 0 ≤ δ ≤ 0.5), the crystal structure is a cubic spinel structure, the crystallite size is 50 to 100 nm, and the lattice strain is 0.5%. A lithium-cobalt-manganese composite oxide and a lithium secondary battery containing the same characterized by:

The lithium-cobalt-manganese composite oxide of the present invention has a specified crystallite size while maintaining a constant average particle size, so that it efficiently exhibits capacity at an operating potential of 4.5 V or more, and furthermore Excellent structural stability and high energy density could be achieved. Therefore, the lithium-cobalt-manganese composite oxide proposed by the present invention can provide excellent performance when used as a positive electrode active material for various lithium secondary batteries.

The present invention will be described in detail below.

The lithium-cobalt-manganese composite oxide of the present invention has a chemical composition formula of Li _{(1.0+a) CoxMn (2.0-xa) O4} (where -0.15≤a≤0. 15, where 0.9≤x≤1.1).

Regarding the above a, −0.15≦a≦0.15, and if a is within this range, it becomes easy to synthesize a cubic spinel structure. The a is preferably −0.10≦a≦0.10, more preferably −0.05≦a≦0.08.

Regarding the above x, 0.9 ≤ x ≤ 1.1, but if x is within this range, the content of cobalt involved in the oxidation-reduction reaction can be secured, and around 5 V (Li metal negative electrode standard) more battery capacity. Note that x preferably satisfies 0.95≦x≦1.1.

Since the spinel structure generally contains oxygen deficiency, O ₄ in the above chemical composition formula is actually O _(4-δ) (0 ≤ δ ≤ 0.5), and a part of oxygen is It may be missing or substituted with another element such as fluorine.

The lithium-cobalt-manganese composite oxide of the present invention has a crystallite size of 50 to 100 nm. When the crystallite size is less than 50 nm, structural irregularity occurs and diffusion of lithium ions is inhibited. It affects the diffusion path of lithium ions during charging and discharging, and the capacity is more likely to be expressed in the region of 4.5 V or higher. It is more preferably ~100 nm, and even more preferably 55 to 85 nm.

Here, "crystallite size" means the largest collection that can be regarded as a single crystal, and can be obtained from the full width at half maximum of the diffraction peak observed by XRD measurement. It should be noted that the parameter is essentially the same as the crystallite size determined by the fundamental method described in Patent Document 1, and it is considered that there is no difference in numerical values depending on the determination method.

The lithium-cobalt-manganese composite oxide of the present invention has a lattice strain of 0.5% or less. If the lattice strain exceeds 0.5%, the distortion of the crystal structure becomes large, and the crystal structure becomes unstable because it does not expand or contract isotropically during lithium ion insertion/extraction. The distortion of the crystal structure is small, and the crystal structure is more stable because it expands and contracts isotropically when lithium ions are inserted and extracted. more preferred.

The lattice strain is obtained from the diffraction peaks of the obtained XRD pattern by using the Williamson-Hall equation. Note that the distortion obtained by the fundamental method described in Patent Document 1 is essentially the same parameter, and it is considered that there is no difference in numerical values depending on the method of obtaining.

The average particle size of the lithium-cobalt-manganese-based composite oxide of the present invention is preferably 1 to 20 μm because it affects the diffusion distance of lithium ions and allows more efficient utilization of the entire charge-discharge capacity. ~20 μm is more preferable, and 2 to 15 μm is even more preferable. Further, within the above range, there is also the advantage that the electrodes can be easily formed and the packing density is high. 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 lithium-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 lithium-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. In addition, since the transition metal is arranged three-dimensionally, it also has the advantage of having a strong crystal structure and excellent stability. Here, the cubic spinel-type structure refers to a crystal lattice classified as a cubic crystal, a spinel-type crystal structure, and preferably having a space group of Fd-3m. Further, since the cubic spinel type oxide has a high content and becomes the main phase, the lattice constant a is preferably 8.03 to 8.07 Å, more preferably 8.03 to 8.06 Å. In the case of 8.03-8.06 Å, a crystal phase very close to a single crystal phase is obtained. In addition, other crystal phases may be contained as subphases as long as they are 0.5% by mass or less. This is because it is believed that this level does not affect the performance of the lithium-cobalt-manganese composite oxide of the present invention.

The BET specific surface area of the lithium-cobalt-manganese-based composite oxide of the present invention is not particularly limited, but is preferably 0.05 to 5 m ² /g from the viewpoint that higher filling properties can be easily obtained. It is preferably 0.05 to 1 m ² /g or less, and even more preferably 0.05 to 0.5 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 lithium-cobalt-manganese composite oxide of the present invention will be described.

The lithium-cobalt-manganese-based composite oxide of the present invention can be obtained, for example, by mixing a manganese compound, a cobalt compound, and a lithium compound, firing, and annealing (heat treatment).

Any manganese compound can be used. Examples of manganese compounds include manganese carbonate, manganese nitrate, manganese chloride, manganese dioxide, and trimanganese tetraoxide.

Any cobalt compound can be used. Examples include basic cobalt carbonate, cobalt nitrate, cobalt chloride, cobalt oxyhydroxide, cobalt hydroxide, cobalt oxide, and hydrous cobalt oxide.

The form and state of the manganese compound and cobalt compound are not limited, and by using a composite compound (cobalt-manganese composite compound) obtained by a coprecipitation method or the like as a raw material, the homogeneity of the metal elements can be improved. An excellent lithium-cobalt-manganese composite oxide can be obtained.

A cobalt-manganese composite compound can be produced by mixing an aqueous solution containing a cobalt salt compound and a manganese salt compound with an oxidizing agent under pH conditions of 8.0 to 12.0.

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.

In the production of the cobalt-manganese composite compound, the ratio of cobalt and manganese is preferably adjusted to the cobalt:manganese ratio of the desired cobalt-manganese composite compound.

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 order to maintain the reaction conditions of pH 8.0 to 12.0, it is preferable to add an aqueous solution of caustic soda. A concentration-adjusted sodium oxide aqueous solution can be used.

In the production of the cobalt-manganese composite compound, the method of adding and mixing an acid or a base to control the pH is not particularly limited. For example, it may be performed continuously or intermittently. good.

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.

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 method for producing the cobalt-manganese composite compound 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 compound 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.

The cobalt-manganese composite compound precipitated by the method for producing a cobalt-manganese composite compound can be isolated by an operation such as filtration, and it is preferable to further wash and dry it in terms of handling.

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

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

In the production of the cobalt-manganese composite compound, it may be washed, dried and then pulverized.

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 compound obtained by the above method can be used for producing a lithium-cobalt-manganese composite oxide.

When producing the lithium-cobalt-manganese-based composite oxide of the present invention using a cobalt-manganese-based composite oxide as a raw material, the manufacturing method includes a mixing step of mixing the cobalt-manganese-based 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 at a temperature range of 500 to 1000° C., preferably at a temperature range of 700 to 1000° C. in order to promote crystal growth. 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.

In the production of the lithium-cobalt-manganese composite oxide, it may be washed, dried and then pulverized. 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 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 lithium-cobalt-manganese composite oxide of Example 1. FIG. 1 is a scanning electron micrograph of the lithium-cobalt-manganese composite oxide of Example 1. FIG. 4 is an XRD pattern of the lithium-cobalt-manganese composite oxide of Example 2. FIG. 4 is an XRD pattern of the lithium-cobalt-manganese composite oxide of Example 3. FIG. 4 is an XRD pattern of the lithium-cobalt-manganese composite oxide of Example 4. FIG. 4 is an XRD pattern of the lithium-nickel-manganese composite oxide of Comparative Example 1. FIG. 4 is a scanning electron micrograph of the lithium-nickel-manganese composite oxide of Comparative Example 1. FIG. 4 is an XRD pattern of the lithium-cobalt-manganese composite oxide of Comparative Example 2. FIG. 4 is a scanning electron micrograph of the lithium-cobalt-manganese composite oxide of Comparative Example 2. 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.

<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.

<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 resulting battery positive electrode, negative electrode made of metallic lithium foil (thickness: 0.2 mm), and electrolytic solution in which lithium hexafluorophosphate was dissolved 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 0.46 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 8.5. (The oxidation-reduction potential during the reaction was 0.08 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. The wet cake was dried at 110° C. for 15 hours to obtain a cobalt-manganese composite compound.

The resulting cobalt-manganese composite compound and lithium carbonate were mixed, baked in an air stream at 900° C. for 12 hours, and then annealed at 700° C. for 24 hours, 650° C. for 24 hours, and 600° C. for 150 hours. , a lithium-cobalt-manganese composite oxide was obtained. Table 1 shows the manufacturing conditions.

From the results of the chemical composition analysis, it was possible to express the chemical composition formula as Li _1.01 Co _1.01 Mn _0.99 O ₄ .

FIG. 1 shows the XRD pattern of the obtained lithium-cobalt-manganese composite oxide. From FIG. 1, it can be said that the crystal has a cubic spinel structure belonging to the space group Fd-3m.

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

Table 2 shows the measurement results of the obtained lithium-cobalt-manganese composite oxide.

Table 3 shows the battery performance evaluation results of the obtained lithium-cobalt-manganese composite oxide. From Table 3, it was shown that the discharge capacity of 4.7 V or higher is large and the battery has a high energy density.

Example 2
A cobalt-manganese composite compound obtained in the same manner as in Example 1 was mixed with lithium carbonate, fired at 900°C for 12 hours, then annealed at 700°C for 24 hours, 650°C for 24 hours, and 600°C for 24 hours. A lithium-cobalt-manganese composite oxide was obtained in the same manner as in Example 1, except that Table 1 shows the manufacturing conditions.

From the results of the chemical composition analysis, it could be represented as a chemical composition formula Li _0.97 Co _1.01 Mn _0.99 O ₄ .

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

Table 2 shows the measurement results of the obtained lithium-cobalt-manganese composite oxide.

Table 3 shows the battery performance evaluation results of the obtained lithium-cobalt-manganese composite oxide.

Example 3
A cobalt-manganese composite compound obtained in the same manner as in Example 1 and lithium carbonate were mixed, fired at 900° C. for 12 hours, and then annealed at 700° C. for 12 hours. - A cobalt-manganese composite oxide was obtained. Table 1 shows the manufacturing conditions.

From the results of the chemical composition analysis, it was possible to express the chemical composition formula as Li _0.94 Co _1.02 Mn _0.98 O ₄ .

FIG. 4 shows the XRD pattern of the obtained lithium-cobalt-manganese composite oxide. From FIG. 4, it can be said that the crystal has a cubic spinel structure belonging to the space group Fd-3m.

Table 2 shows the measurement results of the obtained lithium-cobalt-manganese composite oxide.

Table 3 shows the battery performance evaluation results of the obtained lithium-cobalt-manganese composite oxide.

Example 4
A cobalt-manganese composite compound obtained in the same manner as in Example 1 was mixed with lithium carbonate, fired at 850°C for 12 hours, then annealed at 700°C for 24 hours, 650°C for 24 hours, and 600°C for 24 hours. A lithium-cobalt-manganese composite oxide was obtained in the same manner as in Example 1, except that Table 1 shows the manufacturing conditions.

From the results of the chemical composition analysis, it could be expressed as the chemical composition formula Li _0.94 Co _1.01 Mn _0.99 O ₄ .

FIG. 5 shows the XRD pattern of the obtained lithium-cobalt-manganese composite oxide. From FIG. 5, it can be said that the crystal has a cubic spinel structure belonging to the space group Fd-3m.

Table 2 shows the measurement results of the obtained lithium-cobalt-manganese composite oxide.

Table 3 shows the battery performance evaluation results of the obtained lithium-cobalt-manganese composite oxide.

Comparative example 1
Nickel sulfate and manganese sulfate were dissolved in pure water to obtain an aqueous solution (metal salt aqueous solution) containing 0.5 mol/L (liter) of nickel sulfate and 1.5 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 80° C. and maintained.

The obtained metal salt aqueous solution was continuously supplied to the reactor at a supply rate of 0.46 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 9.25. (The oxidation-reduction potential during the reaction was 0.08 V). As a result of the reaction, a nickel-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. The wet cake was dried at 110° C. for 15 hours to obtain a nickel-manganese composite compound.

The resulting nickel-manganese composite compound and lithium carbonate were mixed, sintered in an air stream at 900° C. for 12 hours, and then annealed at 700° C. for 48 hours to obtain a lithium-nickel-manganese composite oxide. . Table 1 shows the manufacturing conditions.

From the results of the chemical composition analysis, it was possible to express the chemical composition formula as Li _0.91 Ni _0.50 Mn _1.50 O ₄ .

FIG. 6 shows the XRD pattern of the obtained lithium-nickel-manganese composite oxide. From FIG. 6, it can be said that the crystal has a cubic spinel structure belonging to the space group Fd-3m.

A scanning electron micrograph of the resulting lithium-nickel-manganese composite oxide is shown in FIG.

Table 2 shows the measurement results of the obtained lithium-nickel-manganese composite oxide.

Table 3 shows the battery performance evaluation results of the obtained lithium-nickel-manganese composite oxide.

Comparative example 2
A cobalt-manganese composite compound obtained in the same manner as in Example 1 and lithium carbonate were mixed and fired at 900° C. for 12 hours to obtain a lithium-cobalt-manganese composite oxide without annealing. Table 1 shows the manufacturing conditions.

From the results of the chemical composition analysis, it was possible to express the chemical composition formula Li _1.00 Co _1.01 Mn _0.99 O ₄ .

FIG. 8 shows the XRD pattern of the obtained lithium-cobalt-manganese composite oxide. From FIG. 8, in addition to the cubic spinel structure attributed to the space group Fd-3m, multiple peaks can be confirmed in the vicinity of 2θ = 20 to 23°, so it is understood that Li ₂ MnO ₃ is phase split. rice field.

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

Table 2 shows the measurement results of the obtained lithium-cobalt-manganese composite oxide.

Table 3 shows the battery performance evaluation results of the obtained lithium-cobalt-manganese composite oxide.

The lithium-cobalt-manganese composite oxide of the present invention can be used as a positive electrode active material for lithium secondary batteries, and the lithium-cobalt-manganese composite oxide can be used as a positive electrode for batteries with a high energy density. It becomes possible to configure a high-performance lithium secondary battery.

Claims (5)

The chemical composition formula is represented by Li(1.0+a)CoxMn(2.0-xa)O4 (where -0.15 ≤ a ≤ 0.15 and 0.9 ≤ x ≤ 1.1) A lithium-cobalt-manganese composite oxide characterized by having a cubic spinel crystal structure, a crystallite size of 50 to 85 nm, and a lattice strain of 0.5% or less. 2. The lithium-cobalt-manganese composite oxide according to claim 1, which has an average particle size of 1 to 20 μm. 3. The lithium-cobalt-manganese composite oxide according to claim 1, wherein the space group is Fd-3m and the lattice constant a is 8.03 to 8.07 Å. The lithium-cobalt-manganese composite oxide according to any one of claims 1 to 3, which has a BET specific surface area of 0.05 to 5 m ² /g. A lithium secondary battery comprising the lithium-cobalt-manganese composite oxide according to any one of claims 1 to 4.

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