KR100261120B1 - Lithium manganese oxide, method for manufacturing the same and secondary lithiumion ion battery having same - Google Patents

Abstract

PURPOSE: Provided are lithium manganese oxide fine powder and process for producing the same, which are excellent in capacity properties, and electric charge and discharge properties. CONSTITUTION: The process comprises the steps of: i) dissolving lithium acetate and manganese acetate in a solvent; ii) adding gelatin to the solution and removing the solvent to form gel; iii) calcining the gel at 300-500deg.C to form lithium manganese oxide powder; iv) crushing the powder and sintering it at 750-850deg.C for 6-12hrs; and then v) cooling the sintered article. The lithium manganese oxide(LixMn2O4, wherein, x is 1-1.05) fine powder is characterized by having powder particle of octahedron, particle diameter of 0.3-1micrometer and powder particle of 3-4m¬2/g.

Description

Lithium manganese oxide fine powder, a method for manufacturing the same, and a lithium ion secondary battery employing a positive electrode having the same as an active material {Lithium manganese oxide, method for manufacturing the same and secondary lithiumion ion battery having same}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium secondary battery, and relates to a lithium manganese oxide fine powder, a manufacturing method thereof, and a lithium ion secondary battery employing a positive electrode containing the lithium manganese oxide as an active material.

In lithium ion secondary batteries, the charge and discharge capacity of the positive electrode varies depending on the particle size and particle structure of the active material. In other words, the smaller the particle size of the active material, the faster the diffusion of lithium ions can increase the charge / discharge capacity of the positive electrode, and the charge / discharge capacity of the positive electrode itself can be increased even when the particle structure is easily diffused. Can be increased.

Lithium manganese oxide is mainly used as a positive electrode active material in lithium ion secondary batteries, such as lithium nickel oxide, lithium cobalt oxide, etc., it is preferred because of the low cost, pollution-free and high energy density compared to other active materials.

There are various methods of manufacturing the positive electrode active material, and only two methods will be described herein.

First, according to the solid solution synthesis method, the lithium manganese oxide may be prepared by uniformly mixing the lithium salt and manganese oxide using a device such as a ball mill, and then heat-treating the lithium salt in the heat treatment process Li ions decomposed and decomposed by ions are dissolved into the lattice of manganese oxide to form lithium manganese oxide. At this time, since the particles become larger as the heat treatment temperature is higher and the heat treatment time is longer, it is very important to properly control the heat treatment time and temperature.

As another method, the sol-gel method is widely used in the synthesis of ceramics, and is also used as a method for producing lithium metal oxides used as positive electrode active materials for lithium secondary batteries in that an oxide having a relatively stabilized structure can be synthesized. Has been. This sol-gel method produces a sol solution containing a raw material and a chelate compound, allows lithium and metal cations to bind to the chelate compound under appropriate conditions, and then decomposes the chelate by heat treatment to remove it. As a result, a lithium metal oxide having a stable structure is formed. Although the sol-gel method can obtain a powder having a finer particle size than the solid solution synthesis method described above, the additives (particularly, chelating compounds) used are expensive and the process itself is hydrolyzed-condensed and aggregated. I still had to be cumbersome to repeat.

The technical problem to be achieved by the present invention is to provide a lithium manganese oxide that can increase the capacity of the positive electrode when used as a positive electrode active material of a lithium ion secondary battery to solve the above problems by uniform and fine particle size and structure.

Another technical problem to be achieved by the present invention is to provide a method for simply manufacturing the lithium manganese oxide.

Another technical problem to be achieved by the present invention is to provide a lithium secondary battery having improved capacity by employing a positive electrode using the lithium manganese oxide as an active material.

1 is a graph illustrating a change in the active material capacity of a lithium secondary battery employing a lithium manganese oxide sintered at 800 ° C. for 6 hours in accordance with one embodiment of the present invention. Discharge rate: 0.3C).

2 is a graph for explaining the high-rate charge and discharge characteristics (1C) of a lithium secondary battery employing a lithium manganese oxide sintered for 6 hours at 800 ℃ according to an embodiment of the present invention.

3 is a scanning electron micrograph of lithium manganese oxide sintered for 12 hours at 800 ℃ according to an embodiment of the present invention.

4 is a graph illustrating a change in the active material capacity of the lithium secondary battery employing a lithium manganese oxide sintered at 800 ° C. for 12 hours according to one embodiment of the present disclosure according to repeated charging and discharging cycles (0.3) C).

5 is a graph illustrating a change in active material capacity of a lithium secondary battery employing lithium manganese oxide sintered at 800 ° C. for 12 hours according to another embodiment of the present invention.

In order to achieve the first object of the present invention, in the present invention, lithium manganese oxide (Li _x Mn ₂ O ₄ (x is 1-1.05)) is provided as a fine powder lithium manganese oxide powder of the octahedral form.

In the lithium manganese oxide according to the present invention, the particle size is 0.3-1 탆, and the specific surface area is 3-4.5 m 2 / g.

Another object of the present invention, a) dissolving lithium acetate and manganese acetate in a solvent; b) adding gelatin to the solution obtained in the step and removing the solvent to form a gel; c) calcining the gel at 300 to 500 ° C. to form lithium manganese oxide powder; d) pulverizing the powder and then sintering at 750 to 850 ° C .; And e) cooling the sintered product. A method of preparing a lithium manganese oxide (Li _x Mn ₂ O ₄ (x is 1-1.05)) fine powder is achieved.

The lithium manganese oxide fine powder produced by the method of the present invention has an octahedral particle shape, a particle size of 0.3-1 μm, and a specific surface area of 3-4.5 m 2 / g.

In addition, another technical problem of the present invention is a lithium ion secondary battery comprising a positive electrode, a carbon-based negative electrode, and a non-aqueous electrolyte containing a lithium metal oxide as an active material, wherein the lithium metal oxide of the positive electrode is octahedral in the form of powder particles. It can be achieved by a lithium ion secondary battery characterized in that the lithium manganese oxide (Li _x Mn ₂ O ₄ (x is 1-1.05)).

The lithium manganese oxide has a particle size of 0.3-1 μm and a specific surface area of 3-4.5 m 2 / g.

Hereinafter, the present invention will be described in more detail.

In the present invention, it is characterized in that the gelatin is used in the manufacturing process of the lithium manganese oxide fine powder. Gelatin has amino and carbonyl groups as proteins, and these functional groups serve as reactive sites that chelate cations. Compared to the citric acid used as a chelate compound in the conventional sol-gel method, gelatin has about 550 times the number of reactive sites per molecule, which is more functional and thus lowers the manufacturing cost of the positive electrode active material. In the preparation of the positive electrode active material by the sol-gel method, gelatin is used to chelate lithium and manganese cations used as the main components of the positive electrode active material, thereby stabilizing the structure of the finally formed lithium manganese oxide. By changing inorganic cations into gels in the "frogen" state, even in small amounts, the aggregation and hydrolysis-condensation processes, which have been a problem in the conventional case, can be minimized, greatly reducing the time required for the entire synthesis process. Can be. The structure determined by the gelatin is maintained even after the gelatin is removed during the subsequent calcination and sintering, so that most of the lithium manganese oxide particles produced are octahedral and the specific surface area is increased.

In more detail, the method for producing a lithium manganese oxide according to the present invention, first dissolving lithium acetate and manganese acetate in a solvent, and then gelatin is added thereto. At this time, the lithium acetate and manganese acetate are mixed in a molar ratio of 1: 2-1.05: 2, which is a mixing ratio similar to that generally applied to lithium manganese oxide used as a cathode active material of a lithium ion secondary battery. Gelatin is added as much as 5-15% by weight based on the total amount of lithium acetate and manganese acetate, the present invention is not significantly affected by the mixing ratio of gelatin, to obtain a proper solubility when gelatin is used in the above range Because it can. In addition, alcohol or distilled water is used as the solvent, among which methanol and ethanol are preferable.

Then, the temperature is raised to 90 to 150 ℃ to completely dissolve the gelatin in this process, the solvent is naturally evaporated, removed to make a viscous material, and cooled to room temperature to form a transparent gel. When the gel is calcined while increasing the temperature to 300-500 ° C., the gel initially dissolves slowly and begins to foam and then the polymer begins to degrade. In this process, carbon dioxide and water vapor are generated to form lithium manganese oxide powder. The powder is pulverized and heated at about 750 to 850 ° C., preferably about 800 ° C., at a heating rate of about 1-3 ° C. per minute, and maintained for about 6-12 hours. At this time, in the case of sintering at about 800 ℃, if the sintering time is shorter than 6 hours, the sintering time is not sufficiently sintered, on the contrary, if it exceeds 12 hours, the powder particles grow to form large particles, and the capacity decreases as the specific surface area decreases. It is undesirable because it happens. Then, when cooled again at a cooling rate of 0.1-2 ℃ per minute to obtain the octahedral form lithium manganese oxide powder of the cathode active material of the present invention. Since the particles of the lithium manganese oxide powder have an octahedral shape, insertion / deintercalation of lithium ions can be made more easily and effectively, thereby increasing the capacity of the battery.

Since the method for producing the positive electrode from the positive electrode active material is not particularly limited, a method commonly used may be applied as it is. In addition, also in manufacturing a lithium secondary battery using the positive electrode thus prepared, the conductive agent and the binder commonly used in the field of the present invention is used. Examples of such conductive agents include acetylene black or carbon black, and examples of the binder include polyvinylidene fluoride.

Hereinafter, the present invention will be described in more detail with reference to the following examples.

Example 1

0.1 mol of lithium acetate (CH ₃ CO ₂ Li.2H ₂ O) and 0.2 mol of manganese acetate ((CH ₃ CO ₂ ) ₂ Mn.4H ₂ O) were added to 50 ml of methanol and dissolved completely under stirring. . 4 g of gelatin was then added to the solution, which was then heated at 120 ° C. to remove the solvent and form a gel. The gel was calcined at 400 ° C. to form lithium manganese oxide (LiMn ₂ O ₄ ) powder, which was then ground in a mortar and ground. Subsequently, the pulverized lithium manganese oxide powder was heated to about 800 ° C. at a temperature increase rate of 1 ° C./min, sintered for 6 hours, and then cooled to room temperature at a rate of 0.5 ° C./min per minute to form lithium manganese oxide (LiMn ₂ O). ₄ ) A fine powder was formed. The specific surface area of the lithium manganese oxide fine powder thus prepared was 4.5 m 2 / g.

To 5 g of a mixture (88: 5: 7 wt%) of the lithium manganese oxide fine powder prepared in this way, carbon black and polyvinylidene fluoride, 6 ml of NMP (N-methylpyrrolidone) was added until a paste was obtained. Mix thoroughly. The paste was placed in a vacuum oven to remove bubbles, and then coated on aluminum foil with a thickness of 200 μm using a doctor blade. This was put in a vacuum oven at 150 ℃ dried for 2 hours and then pressurized to prepare a pole plate. The pole plate was cut into a circle having a diameter of 2 cm, and then welded to a can of a coin battery to form a positive electrode. The negative electrode was then cut into lithium foils of the same size as the positive electrode to determine the capacity of the positive electrode and then pressed with nickel foil and welded into a glove box in the cap of a coin cell. Finally, a separator (trade name: 3M) and an electrolyte (EC / DMC (ethylene carbonate / dimethylene carbonate) + LiPF ₆ ) were installed to complete a coin battery.

The result of charging and discharging the coin battery thus produced at 0.3C is shown in the graph of FIG. Referring to FIG. 1, the initial capacity of the active material was 129 mAh / g, and the capacity of the active material in the case of 30 charge / discharge cycles was not much lower than the capacity of the active material in the case of 20 charge / discharge cycles.

On the other hand, the coin battery was subjected to high rate charge and discharge at 1 C up to 100 times, and the change in active material capacity was measured.

As can be seen from the graph of Figure 2, after 80 charge and discharge not only did not decrease the capacity of the active material but also showed a slightly increased aspect, the active material capacity at 100 charge / discharge at a high rate of 75% of the initial active material capacity To a degree. From this, it can be seen that when the lithium manganese oxide according to the present invention is employed as a positive electrode active material of a lithium ion secondary battery, a battery excellent in high rate charge / discharge characteristics can be obtained.

Example 2

4 g of gelatin was completely dissolved in 50 ml of distilled water, followed by 1 mol of lithium acetate (CH ₃ CO ₂ Li.2H ₂ O) and 2 mol of manganese acetate ((CH ₃ CO ₂ ) ₂ Mn.4H ₂ O. ) Was added and dissolved completely under stirring to prepare a solution, and then heated to 90 ° C. to remove the solvent to form a gel by the same method as in Example 1 except that lithium manganese oxide (LiMn ₂ O ₄ ) fine Powder was prepared and a lithium coin battery was prepared using this as a positive electrode active material.

As a result of performing a charge / discharge test on this lithium coin battery, the active material capacity characteristics and high rate charge / discharge characteristics were generally excellent as in the result of Example 1.

Example 3

A lithium manganese oxide fine powder was formed in the same manner as in Example 1 except that the pulverized lithium manganese oxide powder was sintered at 800 ° C. for 12 hours. The specific surface area of the lithium manganese oxide fine powder thus produced was 3.7 m 2 / g. A scanning electron microscope (SEM) photograph of the fine powder is shown in FIG. 3, which shows that the shape of the particles is almost octahedral, and the particle size is 1 μm or less.

Using this oxide as an active material, a coin battery was produced in the same manner as in Example 1, and a charge and discharge test was conducted. The result is shown as a graph of FIG.

4, the initial capacity of the active material is 123 mAh / g, which is lower than the result of Example 1, but very good level, the reduction of the active material capacity due to the repeated charge and discharge cycle is also large, but the acceptable range compared to Example 1 The level does not escape. The initial capacity of the active material is lower than that of Example 1 because it is believed that the specific surface area of the powder particles is reduced as the powder particles grow as the sintering time is longer.

Example 4

A lithium manganese oxide (Li _1.05 Mn ₂ O ₄ ) fine powder was prepared in the same manner as in Example 3 except for using lithium acetate and manganese acetate in a molar ratio of 1.05: 2, and using lithium coin as the cathode active material. The battery was prepared. A charge and discharge test was conducted on this lithium coin battery, and the results are shown as a graph in FIG. 5.

5, the initial capacity of the active material is very good as 117mAh / g, it can be seen that even if the charge and discharge cycle is repeated, the reduction in the capacity of the active material is not very large.

The lithium manganese oxide fine powder particles according to the present invention may have an octahedral shape and have a fine particle size, thereby increasing capacity when used as a cathode active material of a lithium ion secondary battery. In addition, such a lithium manganese oxide can be manufactured easily and at a low cost compared to the prior art, and thus, a lithium ion secondary battery employing a positive electrode using the active material thereof has excellent capacity characteristics and high rate charge / discharge characteristics, thereby expanding its application range. Can be.

Claims (7)

Li-manganese oxide (Li _x Mn ₂ O ₄ (x is 1-1.05)) fine powder, characterized in that the particle shape of the powder is octahedron, the particle size is 0.3-1㎛ and specific surface area is 3-4.5㎡ / g Lithium manganese oxide fine powder. a) dissolving lithium acetate and manganese acetate in a solvent; b) adding gelatin to the solution obtained in the step and removing the solvent to form a gel; c) calcining the gel at 300 to 500 ° C. to form lithium manganese oxide powder; d) pulverizing the powder and then sintering at 750 to 850 ° C. for 6 to 12 hours; And e) manufacturing a lithium manganese oxide (Li _x Mn ₂ O ₄ (x is 1-1.05)) fine powder comprising the step of cooling the sintered product. The method of claim 2, wherein the lithium manganese oxide fine powder particles have an octahedral form. The method of claim 3, wherein the lithium manganese oxide fine powder has a particle size of 0.3-1 탆 and a specific surface area of 3-4.5 m 2 / g. The method of claim 2 wherein the solvent in step a) is alcohol or distilled water. The method of claim 2, wherein the gelatin content in step b) is 5-15% by weight based on the total amount of lithium acetate and manganese acetate. In a lithium ion secondary battery comprising a positive electrode having a lithium metal oxide as an active material, a carbon-based negative electrode, and a non-aqueous electrolyte, the lithium metal oxide of the positive electrode has an octahedron of the powder particles, a particle size of 0.3-1 μm, and a specific ratio. Lithium manganese oxide Li _x Mn ₂ O ₄ (x is 1-1.05) having a surface area of 3-4.5 m 2 / g Li-ion secondary battery.

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