WO2006126854A1

WO2006126854A1 - Processes of preparing manganese oxides and processes of preparing spinel type cathode active material using the same

Info

Publication number: WO2006126854A1
Application number: PCT/KR2006/002014
Authority: WO
Inventors: Yang Kook Sun; Woo Seong Kim; Ki Soo Lee
Original assignee: Dae-Jung Chemicals & Metals Co., Ltd.
Priority date: 2005-05-27
Filing date: 2006-05-26
Publication date: 2006-11-30

Abstract

The present invention provides a process for preparing a manganese oxide Li1+α[MxMn2-α-x] O4 (wherein 0 ≤ α ≤ 0.15, 0 ≤ x ≤ 0.2) in a spherical particulate form having a high tap density, and a process for preparing a spinel type cathode active material Li1+α[MxMn2-α-x] O4-ZFZ (wherein 0 ≤ a ≤ 0.15, 0 ≤ x < 0.2, 0.01 < z ≤ 0.15, M = at least one metal selected from Al, Mg, Ni, Co, Cr, Mo and W), which has a high tap density and a small specific surface area, using the manganese oxide. A spinel type cathode active material in a spherical particulate form, which has high structural stability at high temperatures and a high volume energy density due to increased tap density, can be obtained according to the present invention.

Description

[DESCRIPTION]

[invention Title]

PROCESSES OF PREPARING MANGANESE OXIDES AND PROCESSES OF PREPARING SPINEL TYPE CATHODE ACTIVE MATERIAL USING THE SAME

[Technical Field]

The present invention relates to a process for preparing manganese oxide and a process for preparing a spinel type cathode active material using the prepared manganese oxide, and in particular, to a process for preparing manganese oxide in a spherical particulate form which has a uniform particle size distribution, a high tap density and excellent life span characteristics, using a co- immersion method, and a process for preparing a spinel type cathode active material for lithium secondary battery, which has excellent life span characteristics and a high volume energy density, using the prepared manganese oxide. [Background Art]

Lithium secondary batteries have high energy densities, which may be as high as 1.5 to 2 times the energy density of Ni/Cd batteries for the same unit volume, and thus are widely used as a power supply device for mobile phones, notebook computers and the like. Further, although the lithium secondary batteries have low irreversible capacities (mh/g) compared with conventional LiCoO₂, 4V-class spinel type LiMn₂O₄, which is of low price, low toxicity and high thermal stability, is currently being developed as a cathode active material for hybrid electric vehicles (HEV) of the next generation.

In the case of synthesizing LiMn₂O₄ by an existing solid phase reaction process, when lithium and manganese oxide are mixed and fired, 4V-class spinel type LiMn₂O₄ composed of secondary particles having a size of 5 to 30 μm, which are formed by aggregation of primary particles having a size of 0.5 to 5 μm, can be obtained. However, in the case of synthesizing by the solid phase reaction process, it is difficult to control the size of the powder particles to be uniform, and thus, it is difficult to obtain uniform particles with a narrow particle size distribution. Also, aggregation of non-uniform primary particles leads to disadvantages such as low packing density, high specific surface area, difficulties in the synthesis of a powder composed of single particles, and particles being readily breakable even at low pressures.

In order to complement such disadvantages, LiMnO₄ is being synthesized by a wet process, in which an aqueous solution of a manganese salt and an aqueous solution of a lithium salt are mixed, the solvent is evaporated to obtain a lithium-manganese complex oxide as a manganese oxide, and then the resulting lithium-manganese complex oxide is thermally treated to synthesize LiMn₂O₄ particles having a size of a few μm (Solid State Ionics, 100, 115 (1997)). A LiMn₂O₄ having a size of a few micrometers and a large specific surface area exhibits a large discharge capacity. However, the high reactivity with an electrolyte due to the large specific area induces an increase in the amount of manganese elution into the electrolyte, and in particular, the amount of manganese dissolution increases at high temperatures of 60⁰C or higher, thus causing a problem of a rapid decrease in the capacity {Electrochemical and Solid- State Letters, 8(3), A171 (2005)).

In order to address such decrease in the capacity due to manganese dissolution at high temperatures, there have been conducted researches on substitution of oxygen atoms with fluorine atoms, but the problem of manganese dissolution has not been completely solved {Journal of Power Sources, 81-82, 458-462 (1999)). In addition, a technique of preparing manganese oxide

(Mn₃O₄) by a wet synthesis process for synthesizing a manganese oxide precursor in the form of manganese hydroxide

(Mn(OH₂)) in an aqueous solution, and then subjecting the manganese hydroxide to an oxidation step (JP-A No. 2004- 292264). However, this synthetic process is disadvantageous in that the process for preparation consists of three steps, including conducting a first reaction to provide a suspension of the manganese hydroxide, heating this suspension in a nitrogen atmosphere at 90⁰C, and conducting an oxidation reaction again at 6O⁰C. Thus, the preparation processes are complicated, and the particles of the powder thus produced have angular shapes such as triangular, rectangular and polygonal, and also a non-uniform size distribution. A cathode active material having such polyhedral shape results in that the current is concentrated on single spots in the powder particle during high throughput charging and discharging, thereby inducing localized heat generation and stability problem in the battery.

Therefore, the existing solid phase reaction process and wet reaction process for the synthesis of spinel type LiMn₂O₄ are disadvantageous in that control of the size and shape of the particles is not easy, and it is difficult to synthesize a powder with a uniform particle size distribution. Thus, it is necessary to develop a new process for synthesizing a spinel type cathode active material having a small specific surface area and a high volume energy density, while suppressing a manganese dissolution reaction. [Disclosure] [Technical Problem]

An object of the present invention is to satisfy such necessity, and to provide a manganese oxide in the form of spherical single particles with a uniform particle size distribution, having a high tap density, excellent life span characteristics and a high volume energy density, and a process for preparing a spinel type cathode active material using the manganese oxide. Thus, the inventors of the invention found that it is possible to provide a manganese oxide in a spherical form by a simple process for preparation involving continuous formation of manganese hydroxide and manganese oxide, and a continuous particle growth reaction, thus completing the invention.

[Technical Solution]

According to a first aspect of the present invention to achieve the object described above, there is provided a process for preparing manganese oxide, comprising the steps of: (a) introducing an aqueous solution of a manganese salt, an aqueous solution of ammonia as a complexing agent, and an aqueous alkali solution providing hydroxyl groups as a pH adjusting agent, into a co-immersion reactor and mixing the components; (b) further introducing an aqueous solution of a manganese salt and an aqueous solution of ammonia that have been prepared separately, into the co-immersion reactor to obtain manganese hydroxide; and (c) introducing air into the co-immersion reactor to oxidize the manganese hydroxide in an acidic atmosphere to obtain manganese oxide.

According to a second aspect of the present invention, there is provided a process for preparing a spinel type cathode active material for lithium secondary battery, comprising the steps of (a) introducing an aqueous solution of a manganese salt, an aqueous solution of ammonia as a complexing agent, and an aqueous alkali solution providing hydroxyl groups as a pH adjusting agent, into a co-immersion reactor and mixing the components; (b) further introducing an aqueous solution of a manganese salt and an aqueous solution of ammonia that have been prepared separately, into the co-immersion reactor to obtain manganese hydroxide; (c) introducing air into the co-immersion reactor to oxidize the manganese hydroxide in an acidic atmosphere to obtain manganese oxide; and (d) mixing the obtained manganese oxide with a lithium compound, and firing the mixture.

[Advantageous Effects]

As described above, the process for preparing manganese oxide of the present invention allows preparation of manganese oxide in the form of spherical particles with a uniform particle size distribution, which has a high tap density of 2.5 g/ml or greater, and the process for preparing a spinel type cathode active material through a synthesis using the manganese oxide allows preparation of a spinel type cathode active material in the form of particles having excellent crystallinity and a low specific surface area, thus significantly improving the manganese dissolution problem, and resulting in excellent battery characteristics such as charging-discharging cycle characteristics and capacity preservation characteristics, at high temperatures.

[Description of Drawings]

Fig. 1 is a scanning electron microscopic (SEM) photograph of the manganese oxide synthesized by the process of Example 1 of the present invention. Fig. 2 is a SEM photograph of the cathode active material particles synthesized by the process of Example 1.

Fig. 3 shows X-ray diffraction patterns of the manganese oxide synthesized in Example 1, and of trimanganese tetra oxide, a commercially available manganese oxide.

Fig. 4 shows X-ray diffraction patterns of LiM^O₄ synthesized in Examples 1, 3 and 4, and Comparative Example 1.

Fig. 5 is a SEM photograph of the manganese oxide synthesized by the process of Example 2.

Fig. 6 is a SEM photograph of the manganese oxide synthesized by the process of Example 3.

Fig. 7 is a SEM photograph of the manganese oxide synthesized by the process of Example 4.

Fig. 8 is a graph showing the life span characteristics according to the charging/discharging cycle of LiMn₂O₄ synthesized in Example 1, Example 3, Example 4 and Comparative Example 1. Fig. 9 is a SEM photograph of the Lii.₀₅Mn_I195O₃.₉₅F₀.₀₅ synthesized by the process of Example 6.

Fig. 10 is a SEM photograph of the Li₁.₀5Mn1.₉₅O₃.₉₅F0.₀₅ synthesized by the process of Example 7.

Fig. 11 is a SEM photograph of the Li1.05Mn1.95O3.95F0.05 synthesized by the process of Example 8.

Fig. 12 is a graph showing the life span characteristics according to the charging/discharging cycle, of Li1.05Mn1.95O3.95F0.05 synthesized at 750⁰C, 900⁰C and 950°C, respectively, in Examples 5 to 7. Fig. 13 is a SEM photograph of the manganese oxide synthesized by the process of Comparative Example 1.

Fig. 14 is a SEM photograph of the LiMn₂O₄ powder fired by the process of Comparative Example 1.

Fig. 15 is a SEM photograph of the manganese oxide synthesized by the process of Comparative Example 2.

Fig. 16 is a SEM photograph of the manganese oxide synthesized by the process of Comparative Example 3.

Fig. 17 is a SEM photograph of the manganese oxide synthesized by the process of Comparative Example 4.

Fig. 18 is a SEM photograph of the manganese oxide (Nio.025Mno.9-75) 3O4 obtained according to the present invention.

Fig. 19 is a SEM photograph of the manganese oxide (Nio.₀2₅Mno.₉-7₅) ₃O₄ obtained according to the present invention. Fig. 20 is an X-ray diffraction pattern of the manganese oxide (Ni₀.025Mn₀.₉-7₅) 3O4 obtained according to the present invention.

Fig. 21 is a SEM photograph of the cathode active material Lii.05 (Nio.o25Mno.97₅) 1.95O4 obtained according to the present invention.

Fig. 22 is a SEM photograph of the cathode active material Lii.05 (Nio.o25Mno.975) 1.95O4 obtained according to the present invention.

Fig. 23 is an X-ray diffraction pattern of the cathode active material Lii.₀₅ (Nio.o₂₅Mno.97₅) 1.₉5O4 obtained according to the present invention.

Fig. 24 is an X-ray diffraction pattern of the cathode active material Liχ.05 (Alo.iMni.βs) O3.95F0.05 obtained according to the present invention. Fig. 25 is an X-ray diffraction pattern of the cathode active material Lii.os (Mgo.iMni.βs) O3.95F0.05 obtained according to the present invention.

Fig. 26 is an X-ray diffraction pattern of the cathode active material Lii.os (Al₀.₀₅ Mg_0-OsMnI_-8S)O_3-95F_0-Os obtained according to the present invention.

Fig. 27 is a graph showing the life span characteristics according to the charging/discharging cycle, of the cathode active material synthesized in Examples 10 to 12 of the present invention.

Fig. 28 is a SEM photograph of the manganese complex oxide Li1.05Nio.1Mn1.85O3.95Fc1.₀₅ powder synthesized by the conventional solid phase process.

Fig. 29 and Fig. 30 are SEM photographs of the manganese complex oxide intermediate synthesized using oxygen as the gas supplied to the reactor.

Fig. 31 and Fig. 32 are SEM photographs of the manganese complex oxide intermediate synthesized by adjusting the concentration of the ammonia supplied to the reactor to 7.14 M.

[Best Mode]

Hereinafter, preferred Examples of the present invention will be described in detail with reference to the attached drawings. The manganese oxide provided by the present invention is prepared using a co-immersion process, and is a material which can be prepared as a spinel type cathode active material for secondary lithium batteries when mixed with a lithium compound. The manganese oxide provided by the present invention is characterized by being a spherical particle having a composition of Mn₃C^ and a uniform particle size distribution.

Further, the manganese oxide is also characterized in that the particle size is 5 to 15 μm, and the tap density is 2.5 g/ml. When the particle size is within the above- mentioned range, the particles have a greater hardness and a greater mass than nano-sized particles, and thus, the particles can be easily produced into electrodes without breakage or deformation during the production of electrode. The specific surface area is also decreased, thus giving an effect of further reducing side reactions with the electrolyte solution. Furthermore, when the tap density is high, the amount of the manganese oxide that can be packed per unit volume is increased, thus attaining a good property to increase the capacity per unit volume.

The manganese oxide is in a pure crystalline form without any impurities, and has superior crystallinity compared with commercialized manganese oxides. The manganese oxide can be prepared as a cathode active material for lithium secondary batteries when mixed with a lithium manganate compound as follows.

According to the present invention, a spinel type cathode active material for lithium secondary battery having the formula of Lii_+α[Mn₂-_α] O₄ (0 < α < 0.15) using the manganese oxide can be provided. Furthermore, a spinel type cathode active material for lithium secondary battery having the formula of Lii_+α [Mn₂-_α] O₄__ZF_Z (0 < α < 0.15, and 0.01 < z < 0.15) can be provided.

As the process for preparing the spinel type cathode active material of the invention, there is provided a process for preparing manganese oxide, comprising the steps of mixing an aqueous solution of at least one manganese salt selected from manganese sulfate, manganese nitrate, manganese chloride and manganese fluoride, an aqueous solution of ammonia as a complexing agent, and an aqueous alkali solution providing hydroxyl groups as a pH adjusting agent, to form manganese hydroxide; and blowing air as an oxidizing agent into the solution mixture to convert the previously formed manganese hydroxide into manganese oxide.

The process for preparation can be divided into two major steps, such as a first step of simultaneously mixing an aqueous solution of at least one manganese salt selected from manganese sulfate, manganese nitrate, manganese chloride and manganese fluoride, an aqueous solution of ammonia, and an aqueous alkali solution in a 4-L co- immersion reactor, and allowing the components to react for a certain length of time (12 to 24 hr) to obtain manganese hydroxide in a spherical particulate form; and a second step of blowing air as an oxidizing agent to the manganese hydroxide to convert the manganese hydroxide to manganese oxide . It is preferable to carry out the first step by using an aqueous solution of a manganese salt, that is, an aqueous solution of at least one manganese salt selected from manganese sulfate, manganese nitrate, manganese chloride and manganese fluoride, and conducting the reaction for a certain length of time (12 to 24 hr) , with the pH of the solution in the reactor being adjusted to 9.0 to 11.5. This is because when the pH value is less than 9.0, the surfaces of the prepared manganese oxide particles become sharp and angular, and the tap density is decreased, while when the pH value is greater than 11.5, the tap density is decreased.

The aqueous solution of a manganese salt that can be used does not include any metal salts other than manganese salts. The concentration of ammonia is set initially to 0.07 to 0.1 M inside the reactor, while the concentration of ammonia introduced from the outside of the reactor is 2.85 to 5.7 M. The concentration of ammonia in the aqueous ammonia solution introduced to the reactor is preferably 30% to 60% of the concentration of manganese in the aqueous solution of manganese salt.

This is because, when the amount of the aqueous solution of ammonia as a complexing agent is small, it is difficult to obtain manganese oxide in a spherical form, and particle formation is unsatisfactorily achieved. On the other hand, when the amount of the aqueous solution of ammonia is large, particle formation is achieved; however, it is again difficult to obtain manganese oxide in a spherical particulate form, and to obtain a uniform particle size distribution, thus the specific surface area being increased and the tap density being decreased.

In addition, the residence time for the aqueous solution of a manganese salt in the co-immersion reactor is preferably set to 12 to 24 hours. It is because, when the residence time is shorter than 12 hours, formation of manganese oxide particles is difficult, and the tap density is decreased, with the particle surfaces becoming rough. On the other hand, when the residence time is longer than 24 hours, fine dust-like particles are formed on the surface of growing particles, which is not favorable. Meanwhile, to the manganese hydroxide prepared in the first step after undergoing the above-described procedure, air is blown in as an oxidizing agent to convert the manganese hydroxide to manganese oxide, which is then washed with double-distilled water, and dried at 110⁰C for 24 hours to completely remove impurities.

Here, the manganese oxide according to the present invention is obtained by introducing air as an oxidizing agent, because during the synthesis of manganese oxide of a spinel structure, when a reductive atmosphere or a high oxygen concentration such as pure oxygen is used, it is difficult to obtain manganese oxide in a spherical particulate form having a good tap density.

On the other hand, the present invention provides a process for preparing a spinel type cathode active material for lithium secondary battery, further comprising the steps of mixing the manganese oxide with a lithium compound and maintaining the mixture at 450 to 600⁰C for 5 to 10 hours for preliminary calcination; firing the mixture at 750 to 1000⁰C for 10 to 20 hours; and annealing the resulting product at 600⁰C for 10 to 20 hours. The lithium compound being used is preferably a mixture of at least one selected from the group consisting of lithium hydroxide, lithium fluoride, lithium nitrate and lithium carbonate. Furthermore, according to the present invention, as the calcination temperature is lower, the initial capacity increases, but the material has a problem of poor life span characteristics. However, as the calcination temperature is higher, there occurs a decrease in the initial capacity due to a reduction in the amount of manganese elution caused by a decrease in the specific surface area, but there is an advantage of increased life span characteristics.

It is believed that such excellent life span characteristics are attributable to the stability of the crystalline structure due to fluorine substitution and improved surface characteristics, and since lithium compounds consist of single particles, the amount of manganese dissolution is decreased in correspondence to a decrease in the specific surface area. [EXAMPLE 1]

4 L of distilled water and 10 g of an aqueous solution of ammonia (30 wt%) were introduced into a co-immersion reactor (capacity: 4 L, output of rotating motor: 80 W or greater) , and then air was supplied into the reactor at a rate of 1 L/min. While maintaining the temperature in the reactor at 50⁰C, the content in the reactor was stirred at a rate of 1100 rpm.

Then, an aqueous solution of manganese sulfate at a concentration of 2 M, and an aqueous solution of ammonia at a concentration of 4.5 wt% were continuously introduced to the reactor at flow rates of 0.3 L/hr and 0.03 L/hr, respectively, using metering pumps. A solution of sodium hydroxide at a concentration of 4 M, which had a role of adjusting pH, was automatically supplied according to the determined pH. Here, the pH value was adjusted to 10.0, and the average residence time for the solution was controlled to be about 6 hours by adjusting the flow rate. Air was blown into the reactor to achieve an acidic atmosphere, and when the reaction reached a steady state, manganese oxide in a spherical particulate form was continuously obtained through an overflow pipe. The obtained manganese oxide was dried at 110⁰C for 24 hours to remove moisture in the oxide. Fig. 1 shows a scanning electron microscopic (SEM) (trade name: JSM 6400, manufactured by JEOL Inc., Japan) photograph of a manganese oxide intermediate synthesized by the process described above.

The manganese oxide and lithium hydroxide (LiOH) were mixed at a molar ratio of 1: 1.05, and then the mixture was heated at a heating rate of 2°C/min. Subsequently, after maintaining the mixture at 500⁰C for 10 hours, the mixture was thoroughly mixed and fired at 750⁰C for 12 hours to obtain a LiM^O₄ cathode active material powder having a spinel structure. Fig. 2 and Fig. 3 respectively show the SEM photograph and X-ray diffraction pattern of the obtained powder.

In order to evaluate the properties of the LiMn₂O₄ cathode active material prepared by the above-described process, a charging/discharging test was performed using a charger/discharger (Model No.: Toscat 3000U, manufactured by Toyo System Co., Ltd., Japan), which is an electrochemical analyzer, at ambient temperature (3O⁰C) and at a high temperature (60⁰C) in a potential region of 3.4 to 4.3 V at a current density of 0.4 mA/cm².

Meanwhile, for the production of electrodes, the above cathode active material, acetylene black as a binding agent, and polyvinylidene fluoride (PVdF) were mixed at a weight ratio of 80:10:10 to produce a slurry. This slurry was uniformly coated on an aluminum foil having a thickness 20 μm, and dried in a vacuum at 12O⁰C to produce a cathode. Together with the produced cathode, lithium foil was used as a counter electrode, a porous polyethylene membrane (Celgard 2300, manufactured by Celgard LLC, thickness: 25 μm) was used as a separator, and a liquid electrolyte having LiPF₆ dissolved in a solvent mixture of ethylene carbonate and diethyl carbonate at a volume ratio of 1:1 at a concentration of 1 M was used, to produce a coin cell according to a conventionally known production process. The characteristics of the cathode active material were evaluated.

Fig. 4 shows X-ray diffraction patterns of the manganese oxide synthesized in Example 1 and of a commercially available manganese oxide powder. The manganese oxide powder synthesized by the process of Example 1 was composed of pure crystals containing no impurities, and showed excellent crystallinity compared with the commercially available manganese oxide. [EXAMPLE 2]

A manganese oxide was synthesized in the same manner as in Example 1, except that the concentration of the aqueous solution of ammonia supplied to the co-immersion reactor was adjusted to 6 wt%, and the product was evaluated for the battery characteristics. Fig. 5 shows a SEM (trade name: JSM 6400, manufactured by JEOL, Inc., Japan) photograph of the synthesized manganese oxide intermediate.

[EXAMPLE 3] A manganese oxide was synthesized in the same manner as in Example 1, except that the calcination temperature was set to 850⁰C, and the product was evaluated for the battery characteristics. Fig. 3 and Fig. 6 show an X-ray diffraction pattern and a SEM photograph, respectively, of the synthesized spinel type LiMn₂O₄. [Example 4]

A manganese oxide was synthesized in the same manner as in Example 1, except that the calcination temperature was set to 900⁰C, and the product was evaluated for the battery characteristics. Fig. 3 and Fig. 7 show an X-ray diffraction pattern and a SEM photograph, respectively, of the synthesized spinel type LiMn₂O₄.

The X-ray diffraction patterns of the LiMn₂O₄ synthesized at 750⁰C in Example 1, at 850°C in Example 3, at

900⁰C in Example 4, and at 75O⁰C in Comparative Example 1, respectively, are shown in Fig. 3. It can be seen that synthesis was well achieved in all of the cases, to result in single-phase spinel type compounds without impurities, regardless of the calcination temperature and the type of manganese oxide.

Fig. 2 shows a SEM photograph of LiMn₂O₄ prepared in Example 1, Fig. 6 shows a SEM photograph of LiMn₂O₄ prepared in Example 3, and Fig. 7 shows a SEM photograph of LiMn₂O₄ prepared in Example 4. In the case of Example 1, the LiMn₂O₄ was composed of secondary particles formed from aggregates of primary particles having a size of 2 to 4 μm, but as the calcination temperature increased, the size of the primary particles increased. In the case of the LiMn₂O₄ powder of Example 4, the primary particles underwent complete growth to single particles having a size of about 8 μm.

The specific surface areas and tap densities of the

LiMn₂CU synthesized by Example 1, Example 3, Comparative Example 1 and Comparative Example 4 are shown in Table 2.

The LiMn₂O₄ synthesized in Comparative Example 1 showed a higher specific surface area and a lower tap density, compared with the powders synthesized by the process of the present invention. The samples synthesized according to the present invention had smaller specific surface areas and higher tap densities, as the calcination temperature increased.

Fig. 8 shows the discharging capacities according to the charging/discharging cycle of the LiMn₂O₄ fired at 75O⁰C in Example 1, at 85O⁰C in Example 3, and at 900⁰C in Example

4, respectively. The powder synthesized in Comparative

Example 1 showed poor life span characteristics compared with the powders synthesized according to the present invention. As the calcination temperature increased, the amount of manganese elution decreased, due to a reduction in the specific surface area, thus resulting in excellent life span characteristics.

[EXAMPLE 5]

A mixture of the manganese oxide synthesized in the same manner as in Example 1 and lithium manganese oxide (lithium hydroxide : lithium fluoride = 1:0.05 by mole) were thoroughly mixed at a molar ratio of 1.95:1.08, maintained at 450 to 55O⁰C for 10 hours, then mixed again, and subsequently fired at 750⁰C for 12 hours to synthesize Li1.05Mn1.95O3.95F0.05 • The evaluation of battery characteristics was carried out in the same manner as in Example 1.

[EXAMPLE 6] A mixture of the manganese oxide synthesized by the same process as that of Example 1 and lithium manganese oxide (lithium hydroxide : lithium fluoride = 1:0.05 by mole) were thoroughly mixed at a molar ratio of 1.95:1.08, maintained at 450 to 550⁰C for 10 hours, then mixed again, and subsequently fired at 900⁰C for 12 hours to synthesize Li1.05Mn1.95O3.95F0.05- The evaluation of battery characteristics was carried out in the same manner as in Example 1.

[EXAMPLE 7] A mixture of the manganese oxide synthesized by the same process as that of Example 1 and lithium manganese oxide (lithium hydroxide: lithium fluoride = 1:0.05 by mole) were thoroughly mixed at a molar ratio of 1.95:1.08, maintained at 450 to 55O⁰C for 10 hours, then mixed again, and subsequently fired at 95O⁰C for 12 hours to synthesize Li1.05Mn1.95O3.95F0.05- The evaluation of battery characteristics was carried out in the same manner as in Example 1. [EXAMPLE 8]

A mixture of the manganese oxide synthesized by the same process as that of Example 1 and lithium manganese oxide (lithium hydroxide: lithium fluoride = 1:0.05 by mole) were thoroughly mixed at a molar ratio of 1.95:1.08, maintained at 450 to 550⁰C for 10 hours, then mixed again, and subsequently fired at 1000⁰C for 12 hours to synthesize Li1.05Mn1.95O3.95F0.05- The evaluation of battery characteristics was carried out in the same manner as in Example 1. Here, as described in the above, SEM photographs of the Li1.05Mn1.95O3.95F0.05 obtained from Example 6 to Example 8 are shown in Fig. 9 to Fig. 11, respectively. In the case of the manganese oxide powder fired at 900⁰C in Example 6, the primary particles and the secondary particles composed of primary particles underwent complete growth to single particles. In the case of firing at a temperature of 95O⁰C or higher, primary particles underwent complete growth, and the powder consisted only of single particles.

Fig. 12 shows the life span characteristics according to the charging/discharging cycle at 60⁰C of the Li1.05Mn1.95O3.95F0.05 synthesized in Example 5 to Example 7.

Referring to Fig. 12, as the calcination temperature was lower, the initial capacity increased, but the life span characteristics were poor. On the other hand, as the calcination temperature was higher, the initial capacity increased, but the life span characteristics increased. In the case of Example 5 where calcination was performed at 75O⁰C, the sample showed a capacity preservation rate of 89% with respect to the initial capacity after 100 cycles, but in the case of Example 7 where calcination was performed at 95O⁰C, the sample showed excellent life span characteristics with a capacity preservation rate of 97%.

Such excellent life span characteristics were obtained because the fluorine substitution led to stability in the crystal structure and improvement in the surface properties, and the sample composed of single particles had a reduced specific surface area, and thus a reduced amount of manganese dissolution. [COMPARATIVE EXAMPLE 1]

The manganese oxide synthesized by a solid phase process was used, and this was mixed thoroughly with lithium hydroxide in a crucible at a molar ratio of 1:1.05, and then firing the mixture in the same manner as in Example 1. The battery characteristics were evaluated. Fig. 13 shows a SEM photograph of the manganese oxide, while Fig. 14 shows a SEM photograph of the fired LiMn₂O₄ powder. The X-ray diffraction pattern of the fired LiM^O₄ powder is shown in Fig. 3. Commercially available manganese oxide was composed of nano-sized particles, and had a low tap density of 1.02 g/ml .

[COMPARATIVE EXAMPLE 2]

A manganese oxide was synthesized in the same manner as in Example 1, except that oxygen was used as the gas supplied to the reactor, and the product was evaluated for battery characteristics. Fig. 15 shows a SEM (trade name: JSM 6400, manufactured by JEOL, Inc. Japan) photograph of the synthesized manganese oxide intermediate. [COMPARATIVE EXAMPLE 3]

A manganese oxide was synthesized in the same manner as in Example 1, except that oxygen was used as the gas supplied to the reactor, and the pH in the reactor was adjusted to 7.0. The product was evaluated for battery characteristics. Fig. 16 shows a SEM (trade name: JSM 6400, manufactured by JEOL, Inc. Japan) photograph of the synthesized manganese oxide intermediate. [COMPARATIVE EXAMPLE 4] A manganese oxide was synthesized in the same manner as in Example 1, except that nitrogen was used as the gas supplied to the reactor, and the product was evaluated for battery characteristics. Fig. 17 shows a SEM (trade name: JSM 6400, manufactured by JEOL, Inc. Japan) photograph of the synthesized manganese oxide intermediate.

The conditions for the manganese oxide syntheses performed in Examples 1 and 2, and Comparative Examples 2 to 4 are shown in Table 1. In the cases pf Example 1, Example 2, Comparative Example 2 and Comparative Example 3, the prepared manganese hydroxide was converted to manganese oxide by an oxidation reaction; however, in the case of Comparative Example 4, the prepared manganese hydroxide maintained the manganese hydroxide form during the reaction in a nitrogen atmosphere. Specifically, in the case of the powder synthesized in Comparative Example 4 (reacted in a nitrogen atmosphere) , the manganese hydroxide form and a porous structure were maintained so that the resulting product had the lowest tap density of 1.12 g/ml as shown in Table 1. On the other hand, in the cases of changing the atmosphere in the reactor with oxygen to oxidize the prepared manganese hydroxide during a reaction (Comparative Examples 2 and 3), manganese oxides were obtained, but the particle size was reduced to 3 to 5 μm, while the tap density slightly increased to 1.8 g/ml in the case of Comparative Example 2, and to 1.57 g/ml in the case of Comparative Example 3, compared with the tap density of the manganese hydroxide.

However, when air was used for the atmosphere in the reactor (Examples 1 and 2), the rate of oxidation reaction was decreased during the generation of manganese oxide, and thus the particle size of the powder was about 7 to 10 μm, similar in size to the starting manganese hydroxide. The tap density was as high as about 2.5 to 2.6 g/ml, regardless of the amount of ammonia water supplied to the outside. [Table 1]

[Table 2]

Hereinafter, a metal-containing manganese complex oxide and a process for preparing a cathode active material for lithium secondary battery using the material will be described in detail.

The manganese complex oxide provided according to the present invention is a material that can be produced into a cathode active material for lithium secondary battery by mixing with a lithium compound. The manganese complex oxide provided according to the present invention is characterized in that the material has a composition represented by the formula: [Mni-_XM_X] ₃O₄, wherein M is at least one metal selected from aluminum (Al), magnesium (Mg), nickel (Ni), cobalt (Co) , chromium (Cr) , molybdenum (Mo) and tungsten (W) , and x is such that 0.01 ≤ x ≤ 0.2, and is in a spherical particulate form with a uniform particle size distribution, formula: [Mni__xM_x] ₃O₄, wherein M is at least one metal selected from aluminum (Al) , magnesium (Mg) , nickel (Ni) , cobalt (Co) , chromium (Cr) , molybdenum (Mo) and tungsten (W) , and x is such that 0.01 ≤ x ≤ 0.2, and is in a spherical particulate form with a uniform particle size distribution.

The manganese complex oxide is also characterized in that it has a particle size of 5 to 15 μm and a tap density of 2.5 g/ml or greater. Here, when the particle size reaches the value mentioned above, the particles have a greater hardness and a greater mass compared with nano-sized particles, and thus can be easily produced into electrodes without breakage or deformation during the production of electrode. Also, the specific surface area is reduced, thus resulting in an effect of further reducing any side reactions with the electrolyte solution. When the tap density is large, the amount of the material that can be introduced to the reaction per unit volume increases, and thus, the capacity per unit volume is also favorably increased.

The manganese complex oxide is a pure crystalline material having no impurities, and has superior crystallinity compared with commercially available manganese complex oxides. The manganese complex oxide can be mixed with a lithium-manganese oxide mixture and can be produced into a cathode active material for lithium secondary battery as follows.

According to the present invention, a spinel type cathode active material for lithium secondary battery, having a composition represented by the formula: Lii_+α [M_xMn2-_α- _x]0₄ (0 < α < 0.15, 0.01 < x < 0.2, M = at least one metal selected from Al, Mg, Ni, Co, Cr, Mo and W) , can be provided by using the manganese complex oxide. Furthermore, a spinel type cathode active material for lithium secondary battery, having a composition represented by the formula: Lii_+α [M_xMn₂-_Oi- χ]0₄-_zF_z (0 < α < 0.15, 0.01 ≤ x < 0.2, 0.01 < z < 0.15, M = at least one metal selected from Al, Mg, Ni, Co, Cr, Mo and W) , can be provided. As the process for preparing the cathode active material according to the present invention, a process for preparing manganese complex oxide comprising the steps of mixing an aqueous solution of a manganese oxide, an aqueous solution of ammonia as a complexing agent, and an aqueous alkali solution providing hydroxyl groups as a pH adjusting agent, to form manganese complex hydroxide; and blowing air as an oxidizing agent to the solution mixture to convert the previously formed manganese complex hydroxide to a manganese complex oxide. The process for preparation can be divided into two major steps, such as a first step of simultaneously mixing an aqueous solution of a manganese oxide, an aqueous solution of ammonia and an aqueous alkali solution in a 4-L co-immersion reactor, and allowing the components to react for a certain length of time (12 to 24 hours) to obtain a manganese complex hydroxide in a spherical particulate form; and a second step of blowing air as an oxidizing agent to the manganese complex hydroxide to convert the manganese complex hydroxide to manganese complex oxide.

It is preferable to carry out the first step by using an aqueous solution of a manganese complex oxide containing at least one metal salt selected from the salts of Al, Mg, Ni, Co, Cr, Mo and W, and allowing the reaction to proceed after adjusting the pH of the solution mixture in the reactor to 9.0 to 11.5, for a certain length of time (12 to 24 hours) .

The aqueous solution of manganese complex oxide being used may not contain a metal salt. The concentration of the ammonia is set initially to 0.07 to 0.1 M inside the reactor, while the concentration of ammonia introduced from the outside of the reactor is 2.85 to 5.7 M. The concentration of ammonia in the aqueous ammonia solution introduced to the reactor is preferably 30% to 60% of the concentration of manganese in the aqueous solution of manganese compound.

To the manganese complex hydroxide containing transition metal prepared in the first step, air is blown into the reactor as an oxidizing agent to convert the manganese complex hydroxide to manganese complex oxide, then washed with double-distilled water, and dried at 110⁰C for 24 hours to completely remove any impurities.

According to the present invention, a process for preparing a spinel type cathode active material for lithium secondary battery, further comprising the steps of mixing the manganese complex oxide with a lithium compound, and subjecting the mixture to primary calcination by maintaining the mixture at 450 to 600⁰C for 5 to 10 hours; subjecting the resulting calcination product to secondary calcination at 750 to 1000⁰C for 10 to 20 hours; and annealing the calcination product at 600⁰C for 10 to 20 hours. It is preferable to use at least one compound selected from lithium hydroxide, lithium fluoride, lithium nitrate and lithium carbonate, as the lithium compound. Here, according to the present invention, as the calcination temperature is lower, the initial capacity increases, but the life span characteristics become poorer. On the other hand, as the calcination temperature is higher, the initial capacity is decreased due to a reduction in the amount of manganese elution caused by a decrease in the specific surface area, but the life span characteristics are advantageously enhanced. It is believed that such excellent life span characteristics are attributable to the stability of the crystalline structure due to fluorine substitution and improved surface characteristics, and since lithium compounds consist of primary single particles, the amount of manganese dissolution is decreased in correspondence to a reduction in the specific surface area. [EXAMPLE 9]

4 L of distilled water and 10 g of an aqueous solution of ammonia (30 wt%) were introduced into a co-immersion reactor (capacity: 4 L, output of the rotating motor: 80 W or greater) , and then air was supplied into the reactor at a rate of 1 L/min. While maintaining the temperature inside the reactor at 5O⁰C, the content of the reactor was stirred at a rate of 1100 rpm.

Subsequently, an aqueous solution of manganese sulfate at a concentration of 1.95 M and of nickel sulfide at a concentration of 0.05 M, and an aqueous solution of ammonia at a concentration of 4.5 wt% were continuously introduced to the reactor at the rates of 0.3 L/hr and 0.03 L/hr, respectively, using metering pumps. A solution of sodium hydroxide at a concentration of 4 M, which had a role of adjusting pH, was automatically supplied according to the determined pH. Here, the pH value was adjusted to 10.0, and the average residence time of the solution was controlled to be about 6 hours by adjusting the flow rate. Air was blown into the reactor to achieve an acidic atmosphere, and when the reaction reached a steady state, (Ni₀.02₅Mn₀.₉-7₅) 3O4 in a spherical particulate form was continuously obtained through an overflow pipe.

The obtained (Ni₀.₀₂₅Mn₀.₉-₇₅) ₃O₄ was dried at 110⁰C for 24 hours to remove the moisture in the oxide. Fig. 18 and Fig. 19 show SEM (trade name: JSM 6400, manufactured by JEOL Inc., Japan) photographs of the (Ni₀.025Mn₀.9-75) 3O4 intermediate synthesized by the process described above.

The manganese complex oxide (Nio.o2₅Mno.₉75) ₃O4 and lithium hydroxide (LiOH) were mixed at a molar ratio of 1: 1.05, and then the mixture was heated at a heating rate of 2°C/min. Subsequently, after maintaining the mixture at 500⁰C for 10 hours, the mixture was thoroughly mixed and fired at 750⁰C for 12 hours to obtain a Lii.₀₅ (Nio.o₂₅Mrio.₉7₅) ₁.₉₅O4 cathode active material powder having a spinel structure. Fig. 21 and Fig. 22 show SEM photographs of the obtained powder, while Fig. 23 shows an X-ray diffraction pattern of the powder.

In order to evaluate the properties of the Lii.o5 (Nio.025Mn₀.9-75) 1.95O4 cathode active material prepared by the above-described process, a charging/discharging test was performed using a charger/discharger (Model No.: Toscat

3000U, manufactured by Toyo System Co., Ltd., Japan), which is an electrochemical analyzer, at ambient temperature

(30⁰C) and at a high temperature (6O⁰C) in a potential region of 3.4 to 4.3 V at a current density of 0.4 mA/cm².

Meanwhile, for the production of electrode, the above- mentioned cathode active material, acetylene black as a binding agent, and polyvinylidene fluoride (PVdF) were mixed at a weight ratio of 80:10:10 to produce a slurry. This slurry was uniformly coated on an aluminum foil having a thickness 20 μm, and dried in a vacuum at 12O⁰C to produce a cathode. Together with the produced cathode, lithium foil was used as a counter electrode, a porous polyethylene membrane (Celgard 2300, manufactured by Celgard LLC, thickness: 25 μm) was used as a separator, and a liquid electrolyte having LiPFβ dissolved at a concentration of 1 M in a solvent mixture of ethylene carbonate and diethyl carbonate at a volume ratio of 1:1 was used, to produce a coin cell according to a conventionally known production process. The characteristics of the cathode active material were evaluated.

The (Ni₀.Q₂₅M11₀.₉-₇₅) ₃O₄ powder synthesized by the method of Example 9 was a pure crystal having no impurities, and had superior crystallinity compared with commercially available manganese complex oxide.

[EXAMPLE 10] The manganese complex oxide synthesized in the same manner as in Example 9 except that the synthesis was performed with Ni being replaced by Al, a lithium manganese oxide mixture (lithium hydroxide: lithium fluoride = 1:0.05 by moles) , and aluminum hydroxide were thoroughly mixed at a molar ratio of 1.85:1.08:0.1, and the mixture was maintained at 450 to 550⁰C for 10 hours, then thoroughly mixed, and fired at 850⁰C for 12 hours to synthesize Lii.o5 (Alo.1Mn1.85) O3.95F0.05- The X-ray diffraction pattern of the obtained cathode active material is shown in Fig. 24. [EXAMPLE 11]

The manganese complex oxide synthesized in the same manner as in Example 9 except that the synthesis was performed with Ni being replaced by Mg, a lithium manganese oxide mixture (lithium hydroxide: lithium fluoride = 1:0.05 by moles), and aluminum hydroxide were thoroughly mixed at a molar ratio of 1.85:1.08:0.1, and the mixture was maintained at 450 to 550⁰C for 10 hours, then thoroughly mixed, and fired at 850⁰C for 12 hours to synthesize Lii.o5 (Mgo.1Mn1.85) O3.95F0.05- The X-ray diffraction pattern of the obtained cathode active material is shown in Fig. 25. [EXAMPLE 12]

The manganese complex oxide synthesized in the same manner as in Example 9 except that the synthesis was performed with Ni being replaced by Al and Mg, a lithium manganese oxide mixture (lithium hydroxide: lithium fluoride

= 1:0.05 by moles), and aluminum hydroxide were thoroughly mixed at a molar ratio of 1.85:1.08:0.1, and the mixture was maintained at 450 to 550⁰C for 10 hours, then thoroughly, and fired at 850⁰C for 12 hours to synthesize

Lii.o5 (Alo.o5Mgo.θ5Mni.85)θ3.9₅F₀.o5. Evaluation of the battery characteristics was conducted in the same manner as in

Example 1. The X-ray diffraction pattern of the obtained

Lii.o5 (Alo.05Mgo.05Mn1.85) O3.95F0.O5 cathode active material is shown in Fig. 26.

[COMPARATIVE EXAMPLE 5]

The manganese complex oxide synthesized by the solid phase method was used as the manganese oxide, and this was thoroughly mixed with lithium hydroxide at a molar ratio of 1:1.05 using a crucible. The mixture was fired in the same manner as in Example 1. Fig. 28 shows a SEM photograph of the Li1.05Ni0.1Mn1.35O3.95F0.05 powder obtained by firing the mixture of manganese oxide and lithium manganese oxide. The above-mentioned manganese complex oxide was composed of nano-sized particles, and had a low tap density of 1.00 g/ml. [COMPARATIVE EXAMPLE 6]

A manganese complex oxide intermediate was synthesized in the same manner as in Example 9, except that oxygen was used as the gas supplied into the reactor, and SEM (trade name: JSM 6400, manufactured by JEOL, Inc., Japan) photographs of the resulting compound are shown in Fig. 29 and Fig. 30. When the atmosphere for the reaction was filled with oxygen, the produced particles were not uniform and did not have regular spherical surfaces. The tap density was also confirmed to be lower than that of conventional products.

[COMPARATIVE EXAMPLE 7]

A manganese complex oxide intermediate was synthesized in the same manner as in Example 9, except that the concentration of the ammonia supplied into the reactor was adjusted to 7.14 M, and SEM (trade name: JSM 6400, manufactured by JEOL, Inc., Japan) photographs of the resulting compound are shown in Fig. 31 and Fig. 32. It was obvious that the amount of ammonia was so large that there was a problem in the particle formation, [industrial Applicability]

As examined above, the process for preparing manganese oxide and the process for preparing a spinel type cathode active material using the manganese oxide according to the present invention are applied to the manufacture of the manganese oxide or the spinel type cathode active material utilized in lithium secondary batteries. As shown above, the present invention was described with reference to a limited number of Examples and Drawings, but the present invention is not intended to be limited thereby, and it will be clear to those having ordinary skill in the art that various modifications and alterations are possible within the spirit of the present invention and the scope of the attached claims.

Claims

[CLAIMS]

[Claim l]

A process for preparing manganese oxide, comprising the steps of: (a) Introducing an aqueous solution of a manganese salt, an aqueous solution of ammonia as a complexing agent, and an aqueous alkali solution providing hydroxyl groups as a pH- adjusting agent into a co-immersion reactor, and mixing the components; (b) further introducing an aqueous solution of a manganese salt and an aqueous solution of ammonia that have been prepared separately, into the co-immersion reactor to obtain manganese hydroxide; and

(c) introducing air into the co-immersion reactor to oxidize the manganese hydroxide in an oxidizing atmosphere to obtain manganese oxide. [Claim 2]

The process for preparing manganese oxide according to claim 1, the concentration of ammonia in the aqueous solution of ammonia added in step (b) is 30% to 60% of the concentration of manganese in the aqueous solution of a manganese salt. [Claim 3]

The process for preparing manganese oxide according to claim 1, wherein the residence time taken by the aqueous solution of a manganese salt in the co-immersion reactor is 12 to 24 hours.

[Claim 4] The process for preparing manganese oxide according to claim 1, wherein the aqueous alkali solution is introduced into the co-immersion reactor such that the pH in the reactor reaches 9.0 to 11.5.

[Claim 5] The process for preparing manganese oxide according to claim 1, wherein the manganese oxide has a composition represented by the formula: Mn₃O₄.

[Claim β]

The process for preparing manganese oxide according to claim 1 or 2, wherein the aqueous solution of a manganese salt in step (b) further contains at least one metal selected from aluminum, magnesium, nickel, cobalt, chromium, molybdenum and tungsten, and the manganese oxide in step (c) is a manganese complex oxide further containing at least one metal selected from aluminum, magnesium, nickel, cobalt, chromium, molybdenum and tungsten. [Claim 7]

The process for preparing manganese oxide according to claim 1 or 6, wherein the manganese oxide or the manganese complex oxide has a particle size of 5 to 15 μm, and a tap density of 2.5 g/ml or greater.

[Claim 8]

A process for preparing a spinel type cathode active material, comprising the steps of:

(a) Introducing an aqueous solution of a manganese salt, an aqueous solution of ammonia as a complexing agent, and an aqueous alkali solution providing hydroxyl groups as a pH- adjusting agent into a co-immersion reactor, and mixing the components;

(b) further introducing an aqueous solution of manganese and an aqueous solution of ammonia that have been prepared separately, into the co-immersion reactor to obtain manganese hydroxide; (c) introducing air into the co-immersion reactor to oxidize the manganese oxide in an oxidizing atmosphere to obtain manganese oxide; and

(d) mixing the manganese oxide with a lithium compound, and firing the mixture.