KR0158281B1 - Proecss for preparing li-co oxide powder - Google Patents

Abstract

The present invention relates to a method for producing lithium cobalt oxide powder, and to an electrode and a lithium secondary battery manufactured using the same, which can lower the heat treatment temperature during the preparation of lithium cobalt oxide powder used as a negative electrode active material, and stoichiometrically It is possible to produce a uniform powder, and also to produce a powder with small particles, thereby providing an excellent battery having high charge and discharge efficiency, long battery life, and high energy density per unit weight.

Description

Method for producing lithium cobalt oxide (LiCoO2) powder, electrode and lithium secondary battery manufactured using the same

1 is a schematic flowchart of a method of manufacturing lithium cobalt oxide powder and an electrode using the same according to the present invention.

2 is a diagram showing a thermogravimetric analysis (TG) / differential thermal analysis (DTA) curve of a powder synthesized to prepare a lithium cobalt oxide powder of the present invention.

3 is a view showing an X-ray diffraction pattern (XRD pattern) of the lithium cobalt oxide powder Preparation Example 1 (OA-7 LiCoO ₂ ) and 2 (OA-9 LiCoO ₂ ) of the present invention.

4a and 4b is a magnification of the electron microscope (SEM) photograph of the surface of the lithium cobalt oxide powder prepared in Example 1 (OA-7 LiCoO ₂ ) of lithium cobalt oxide powder of the present invention magnified 1,000 times and 2,000 times.

5a and 5b is a magnification of 1,000 times and 2,000 times the electron micrograph of the surface of the lithium cobalt oxide powder prepared in Example 2 (OA-9 LiCoO ₂ ) of the lithium cobalt oxide powder of the present invention.

6a and 6b are enlarged 1,000 times and 2,000 times, respectively, of electron micrographs of the electrode surface of the electrode manufacturing example 1 of the present invention.

7A and 7B are enlarged 1,000 times and 2,000 times, respectively, of electron micrographs of the electrode surface manufactured by the electrode preparation example 2 of the present invention.

8 is a diagram showing a cyclic voltage current curve of an electrode made of the powder of lithium cobalt oxide powder Preparation Example 1 when the scanning speed is 0.01 mA / sec.

9 is a diagram showing a cyclic voltage current curve of an electrode made of the powder of lithium cobalt oxide powder Preparation Example 1 when the scanning speed is 2 mA / sec.

10 is a diagram showing a cyclic voltage current curve of an electrode made of the powder of lithium cobalt oxide powder Preparation Example 2 when the scanning speed is 2 mA / sec.

FIG. 11 is a view showing a first constant current charge / discharge characteristic curve when a test battery is configured with an electrode made of the powder of lithium cobalt oxide powder Preparation Example 1 according to lithium content. FIG.

12 is a diagram showing a first constant current charge / discharge characteristic curve when a test battery is configured with an electrode made of the powder of lithium cobalt oxide powder Preparation Example 2 according to lithium content.

FIG. 13 is a graph showing charge and discharge curves of a lithium cobalt oxide powder preparation example 1 electrode during constant current charge and discharge. FIG.

14 is a view showing a charge and discharge curve of a lithium cobalt oxide powder Preparation Example 2 electrode during constant current charge and discharge.

FIG. 15 is a diagram showing the charge / discharge capacity change of the constant current charge / discharge LiCoO ₂ / Li secondary battery.

The present invention relates to a method for producing lithium cobalt oxide (LiCoO ₂ ) powder, and to an electrode (cathode) and a lithium secondary battery prepared using the same, in particular lithium cobalt oxide powder used as a negative electrode active material of a lithium secondary battery The present invention relates to an electrode prepared by mixing a conductive material and a binder with a lithium cobalt oxide powder prepared by the method, and a lithium secondary battery using the electrode as a negative electrode.

In general, in order to be used as an anode active material of a lithium secondary battery, it must have the following characteristics. First, the reaction must be reversible when reacting with lithium. That is, the charging and discharging efficiency should be nearly 100%. Second, the intercalation / deintercalation of Li ⁺ ions should not destroy the structure of the negative electrode active material. As a negative electrode active material for a lithium secondary battery having such characteristics, various transition metal oxides (LiCoO ₂ , LiNiO ₂ , LiCo _X Ni ₁ -other than titanium (TiS ₂ ), vanadium (VO _X ), molybdenum (MoS _X ), etc. XO ₂ and LiMn ₂ O ₄ ) and the like are a lot of research is in progress. Lithium cobalt oxide (LiCoO ₂ ) is one of a series of compounds having a layered rock salt structure, which forms a basic skeleton of a close packed network of oxygen, and cubic Li ⁺ and Co ³⁺ ions present on (111) of the rock salt structure are alternately arranged in each layer. At this time, the lattice is deformed by Li ⁺ and Co ³⁺ ions present on the (111) plane to have hexagonal symmetry. Therefore, it has an α-NaFeO ₂ structure and is a space group The crystal structure of 3 m (three triple axis) is shown.

In addition, in order to use lithium cobalt oxide (LiCoO ₂ ) as a negative electrode active material, there should be no change in structure as charging and discharging proceeds in a battery reaction proceeding as in the following Formula (1).

The lithium ions deintercalated in the charging process of Equation (1) move to the positive electrode active material, and are intercalated into lithium cobalt oxide when the discharge process proceeds.

Lithium cobalt oxide has the advantages of high discharge voltage and high theoretical energy density. However, lithium cobalt oxide has electrochemically different characteristics depending on the type of starting material, atmosphere, heat treatment time, and temperature setting conditions.

Lithium cobalt oxide powder currently developed and the electrode of a lithium secondary battery manufactured using the same are described, for example, in US Patent No. 5,160,716 filed by MMThackeray Group (November 3, 1992). (anhydrous Li ₂ CO ₃ ) and anhydrous cobalt carbonate (anyhydrous CoCO ₃ ) are mixed in a solid state, heat treatment temperature 200 ~ 600 ℃, heat treatment time 12-168 hours, atmosphere is oxygen, air or mixed heat treatment in a mixed state lithium Cobalt oxide powder is manufactured. The electrode is manufactured using polytetrafluoroethy lene as a binder and acetylene black as a conductive material. However, the present invention has the advantage of being synthesized at low temperatures, but due to the structural stability problem that is believed to be due to the heat treatment temperature, if the redox continues as a result of the measurement of cyclic voltammetry, the redox wave is rapidly reduced and thus for secondary batteries. There is a problem that it is not suitable as an active substance.

In addition, European Patent No. 462,575 (June 18, 1991), filed by Miyal and Seiihi, contains lithium anhydrous lithium carbonate (Li ₂ CO ₃ ) and cobalt carbonate (CoCO ₃ ) as a starting material for synthesis. Cobalt oxide powder is manufactured. This lithium tinate (Li ₂ CO ₃ ) was not left in the lithium cobalt oxide powder.

The electrode is mixed using polyvinylidene fluoride dissolved in N-methyl-2-pyrrolidone solvent as a binder and the dough is applied on an aluminum foil. And dried at 60 deg. However, this invention has the advantage of low self-discharge, but has a disadvantage that the discharge capacity is as small as 105mAh / g.

In addition, European Patent No. 243,926 (April 28, 1987), filed by Nagaura, has a 1: 1 atomic ratio of lithium carbonate (Li ₂ CO ₃ ) and cobalt carbonate (CoCO ₃ ) as starting materials for synthesis. In a solid state, and heat treated at 900 ° C. for 5 hours in air to produce lithium cobalt oxide. The electrode is made of pellets by mixing Teflon powder (3% by weight or 2% by weight) as a binder and graphite (graphite, 27% by weight or 9.3% by weight) as a conductive material. However, since the present invention uses Teflon powder as a binder, since the electrode thickness cannot be made thin in actual cylindrical battery manufacturing, the powder density is low and the energy density per cell is limited. In addition, there is a disadvantage that the voltage flatness during discharge is not good.

In Japanese Unexamined Patent Application Publication No. Hei 1-304664, 1 mol of lithium carbonate (Li ₂ CO ₃ ) and 1 mol of cobalt carbonate (CoCO ₃ ) are mixed in solid state as a starting material for synthesis, and then 900 ° C. in air for 5 hours. Heat treatment to produce lithium cobalt oxide powder. According to the result of the particle size, the capacity is about 100mAh / g among the particles of 10-150㎛ size, which shows almost similar value but the capacity is not high.

Accordingly, the present invention is to solve the above problems, an object of the present invention is to prepare a lithium cobalt oxide powder used as a negative electrode active material for lithium secondary batteries using a liquid phase reaction (coprecipitation method) of the lithium cobalt oxide powder It is to provide a manufacturing method.

Another object of the present invention is to provide a lithium secondary battery electrode (cathode) prepared by mixing a conductive material and a binder with lithium cobalt oxide powder.

Still another object of the present invention is to provide a lithium secondary battery using an electrode prepared using lithium cobalt oxide powder as a negative electrode.

According to a feature of the present invention, a liquid complex (coprecipitation method) is used to synthesize a complex in a liquid state, and then subjected to appropriate heat treatment to synthesize at a low temperature, and to obtain a lithium cobalt oxide powder having a small particle size and well grown crystals. Manufacture. In addition, heat treatment is performed once more to reduce the stable crystal structure and unreacted material.

According to another feature of the present invention, a lithium cobalt oxide powder having a stable structure is prepared even when the intercalation / deintercalation reaction of lithium is continued, and a lithium 2 powder is mixed by mixing a conductive material and a binder with the lithium cobalt oxide powder. The battery electrode (cathode) is manufactured.

According to another feature of the present invention, a lithium secondary battery is manufactured from a negative electrode, a positive electrode, and an electrolyte prepared using lithium cobalt oxide powder.

Hereinafter, with reference to the accompanying drawings will be described in detail the present invention.

Referring to Figure 1 will be described in detail a method for producing lithium cobalt oxide powder.

First, polybasic organic acid (Humic acid) is dissolved in water. Lithium hydroxide (LiOH.H ₂ O) aqueous solution is slowly added to the organic acid solution and stirred while heating to form an organic acid complex (metal complex) in a gel state (liquid reaction step). The gelled organic acid complex is dried on a hot plate and combusted to synthesize a precursor of lithium cobalt oxide (synthesis step). The synthesized precursor was placed in an alumina crucible and calcined for 12 hours at 450 ° C. for 6 hours at 350 ° C. to form primary lithium cobalt oxide powder (first heat treatment step). The primary lithium cobalt oxide powder is pulverized, heat treated again at 700 ° C. or 900 ° C. for 24 hours, and then gradually cooled at room temperature to sinter the secondary lithium cobalt oxide powder (second heat treatment step). After finely pulverizing this secondary lithium cobalt powder, a lithium cobalt oxide powder having a size of 45 μm or less is obtained using a sieve (filtering step). This lithium cobalt oxide is stable in air even after the synthesis is completed.

FIG. 2 shows a thermogravimetric analysis (TG) / differential thermal analysis (DTA) curve of the lithium cobalt oxide powder to determine the heat treatment temperature of the lithium cobalt oxide powder synthesized by the liquid phase reaction (coprecipitation method). After 600 ° C., there is almost no weight loss and the reaction is completed.

Next, the manufacturing example of the electrode using lithium cobalt oxide powder is demonstrated.

85% by weight of the lithium cobalt oxide powder prepared as the negative electrode active material, 10% by weight of acetylene black conductive material and N-methyl-pyrrolidone (NMP) solvent polyvinylidene fluoride (Polyvinilidenefluoride 5% by weight of binder (PVDF) was uniformly mixed, and then uniformly coated on both sides of SUS 316 exmet (or Al foil) collector electrode of 1 cm × 1 cm (area 1 cm 2). Vacuum drying for 24 hours at to prepare an electrode (cathode). In preparing the electrode (cathode), the negative electrode active material can be used up to 90% by weight, and the conductive material is 12 to 5% by weight.

Next, a lithium secondary battery constructed using an electrode manufactured using the lithium cobalt oxide powder will be described.

An electrode manufactured by using the synthesized lithium cobalt oxide powder, a conductive material, and a binder as a cathode, an electrode manufactured by using lithium, lithium aluminum alloy, carbon, or graphite-based material as a cathode, and lithium cobalt oxide (LiClO ₄ ) Is dissolved in propylene carbonate to form a lithium secondary battery using an electrolyte. The electrolyte may be LiAsF ₆ , LiPF ₆ , LiBF ₄ , LiClO ₄ , and the solvent may be propylene carbonate, ethylene carbonate, diethyl carbonate, 1,2-dimethoxyethane ( Mixed solvents such as 1,2-dimethoxyethane) and dimethyl carbonate may also be used.

The lithium cobalt oxide powder prepared by the present invention should have a low moisture content and maintain the best charge and discharge characteristics when the particle size is 45 μm or less.

Lithium Cobalt Oxide Powder Preparation Example 1

Humic acid is dissolved in water. Lithium hydroxide (LiOH.H ₂ O) aqueous solution was slowly added to the organic acid solution and stirred, and a cobalt nitrate (Co (NO ₃ ) ₂ .6H ₂ O) aqueous solution was stirred to form a metal complex. The precursors are synthesized by drying and burning on a plate. The precursor was calcined for 6 hours at 350 ° C. and 12 hours at 450 ° C., heat-treated at 700 ° C. for 24 hours, and then pulverized once more at 700 ° C. for 24 hours to form lithium cobalt oxide powder. Manufacture.

(A) of FIG. 3 shows an X-ray diffraction pattern (XRD pattern) of the prepared lithium cobalt oxide powder (OA-7 LiCoO ₂ ). The X-rays used were CuK _α1 lines monochromated with a nickel filter, and a voltage of 30 mA was used. When the pattern index (peak indexing) with hexagonal system, each pattern (peak) from the left is (003), (101), (006), (102), (104), (105), (107), ( Corresponds to the crystal planes 108, 110, and 113. It can be seen that the peak of the (003) plane near 18 ° was so large that a well-developed oxide was synthesized.

The lattice constants were 2.089 a and 13.972Å for the a and c axes, respectively. 1 (003) / 1 (104) was 6.70 and c / a was 4.98.

4A and 4B show electron microscope (SEM) photographs of the surface shape of the lithium cobalt oxide powder Preparation Example 1 (OA-7 LiCoO ₂ ). It can be seen that particles smaller than 10 μm are agglomerated, the surface of the particles is smooth and crystal growth is good.

Lithium Cobalt Oxide Powder Preparation Example 2

Precursors were synthesized in the same manner as in Preparation Example 1 of lithium cobalt oxide powder, and the final heat treatment temperature was heat-treated and pulverized at 900 ° C. for 24 hours, and then heat treated once more at 900 ° C. for 24 hours to prepare lithium cobalt oxide.

FIG. 3 (b) shows the X-ray diffraction pattern of the prepared lithium cobalt oxide powder (OA-9 LiCoO ₂ ). As in Example 1 of powder preparation, it can be seen that the peak of the (003) plane is large and crystals are well developed. When the lattice constants were obtained, a and c were 2.818 ms and 14.075 ms, respectively. 1 (003) / 1 (104) was 8.09 and c / a was 4.99.

5A and 5B show electron micrographs of the surface shape of lithium cobalt oxide powder Preparation Example 2 (OA-9 LiCoO ₂ ). It can be seen that small particles are mixed with particles of about 30 μm in size.

Electrode Preparation Example 1

The electrode (negative electrode) is a 5% weight of polyvinylidene fluoride (PVDF) dissolved in 85% by weight of lithium cobalt oxide powder negative electrode active material, 10% by weight of acetylene black conductive material and N-methylpyrrolidone (NMP) solvent. % Binder was uniformly mixed, and then uniformly applied to both sides of the SUS 316exmet (or Al foil) collector electrode of 1 cm × 1 cm (cross section, area 1 cm 2), followed by vacuum drying at 150 ° C. for 24 hours. An electrode (cathode) is produced. Electron micrographs of the electrode thus prepared are shown in FIGS. 6a and 6b. Small particles of acetylene black as a conductive material and lithium cobalt oxide as a negative electrode active material are well mixed.

Electrode Preparation Example 2

The electrode (cathode) is a negative electrode active material of 88% by weight of lithium cobalt oxide powder, 3% of polyvinyl fluoride (PVDF) dissolved in 9% by weight of acetylene black conductive material and N-methylpyrrolidone (NMP) solvent. % Binder was uniformly mixed and then uniformly applied to both sides of SUS 316exmet (or Al foil) collector electrode of 1 cm × 1 cm (cross section, area 1 cm 2), followed by vacuum drying at 150 ° C. for 24 hours. Manufacture. Electron micrographs of the electrode thus prepared are shown in FIGS. 7a and 7b. As shown in FIG. 6, it can be seen that acetylene black and lithium cobalt oxide are well mixed.

[Battery Configuration Example]

A cathode prepared by mixing lithium cobalt oxide powder as a negative electrode active material, acetylene black as a conductive material and polyvinyl fluoride as a binder, a cathode made of lithium foil, and 1M lithium oxide / propylene carbonate (LiClO ₄ / propylene carbonate) A test cell is constructed using the electrolyte solution of. The electrode area was 1 cm × 1 cm (cross section basis, 1 cm 2), and the reference electrode and the counter electrode used for electrochemical measurement were pure lithium metal foil.

In addition, the electrochemical characteristics were tested using a cell composed of electrodes prepared using the lithium cobalt oxide powder Preparation Example 1. A cyclic voltammogram at a scanning speed of 0.01 mV / sec is shown in FIG. Redox waves appeared at 4.0V and 3.85V. Fig. 9 shows a cyclic voltage current curve when the scanning speed is 2 mV / sec and the potential region is cycled 85 times at 4.3V to 3.0V.

Lithium cobalt oxide (LiCoO ₂ ) / lithium batteries have an open circuit voltage of 3.05V to 3.15V. As shown in FIG. 8, oxidation (charging and de-insertion in battery reaction) starts from 3.85V, and reduction (discharging and insertion in battery reaction) starts at 4.15V. In the case of the electrode made of lithium cobalt oxide powder preparation example 1, the oxidation / reduction capacity is almost constant even if it is about 85 times gentle. In addition, FIG. 10 is a diagram illustrating a case where a scanning speed of 2 mV / sec and a potential region were circulated 80 times at 4.3 V to 3.0 V using an electrode made of lithium cobalt oxide powder Preparation Example 2, and lithium cobalt oxide powder Preparation Example 1 Unlike the electrode made of a gradual decrease until 17 times, after which the redox capacity was almost constant.

FIG. 11 shows the first constant current charge / discharge characteristic curve when the test battery is composed of the electrode made of the electrode preparation example 1 using the powder of lithium cobalt oxide powder preparation example 1, and has a current density of 0.2 mA / cm 2 (34 hours). Rate), the charge upper limit voltage 4.35V, and the first charge / discharge curve when the Li / Li ⁺ reference electrode was charged are expressed as a change in voltage according to x of Li ₁ -xCoO ₂ . As shown in FIG. 11, the voltage gradually decreased to 3.7V during discharge, and thus the voltage flatness was excellent. After 3.7V, the voltage rapidly decreased. The charging capacity is 152.7mAh / g, the discharge capacity is 142.6mAh / g, and the charging and discharging efficiency is 93.4%.

FIG. 12 shows the first constant current charge / discharge characteristic curve when the test battery is composed of the electrode prepared in Electrode Preparation Example 2 using the powder of Lithium Cobalt Oxide Powder Preparation Example 2, and the charge capacity is 155.5 mAh / g, The discharge capacity is 141.9 mAh / g, and the charge and discharge efficiency is 90.7%.

FIG. 13 shows the charge and discharge upper and lower voltages of the test battery of the low electrode manufacturing example 1 at 4.2 V and 3.6 V for the Li / Li ⁺ reference electrode, respectively, and the current density is 1 mA / cm 2 at four charge and discharge times. The charge and discharge curves are shown. As a result, the charging capacity was 112.5 mAh / g in the first charge, and almost constant from 92.3 mAh / g to 91.6 mAh / g after the fourth charge and discharge, and the discharge capacity was 99.5 mAh / g at the first discharge. After the discharge, it was constant at 92.3 mAh / g. The charging and discharging efficiency was initially 88.5%, but after the fourth charging and discharging, the excellent characteristic was maintained at about 100%.

On the other hand, Figure 14 shows the charge and discharge curves when the charge and discharge upper and lower voltages of the test battery of the electrode preparation example 2 were 4.2V and 3.6V for the Li / Li ⁺ reference electrodes, respectively, and were charged and discharged six times. . As a result, the charging capacity was sharply decreased from 100.7 mAh / g of the first charge after the fifth charge to 60.1 mAh / g, and the discharge capacity was 72.9 mAh / g at the first discharge and after the fifth discharge. Reduced to 58.6 mAh / g. The charging and discharging efficiency was initially 72.4%, but after the second charge and discharge, it was about 95%.

15 shows charge and discharge capacities (a, b) of electrode preparation example 1, charge and discharge capacities (c, d) of electrode preparation example 2, and charge and discharge capacities (e, f) of electrodes made of CFM lithium cobalt oxide powder. The change was shown.

Lithium cobalt oxide (LiCoO ₂ ) (0≤X≤1.1) synthesized in the present invention may be prepared by firstly using a liquid phase reaction (coprecipitation method) to lower the heat treatment temperature, and secondly, to obtain a stoichiometrically uniform powder. Production is possible, and third, the production of powder with small particles is possible. In addition, when the lithium cobalt oxide powder of the present invention is used as a negative electrode active material of a lithium secondary battery (ion battery), it not only has excellent voltage flatness, but also has high charge and discharge efficiency, long battery life, and high energy density per unit weight. Excellent batteries can be produced. In addition, it can be used as a power source for small high-performance electronic devices, and can also be used as a negative electrode active material of a large capacity battery.

Claims (1)

Polybasic organic acid (Humic acid) was dissolved in water, lithium hydroxide (LiOH. H ₂ O) dropping gradually dropped an aqueous solution, and cobalt nitrate _{(Co (NO 3) 2.} 6H 2 O) by dropping an aqueous solution sufficient reaction Stirring and heating to form an organic acid complex (metal complex) in a gel state, and drying and burning the organic acid complex formed in the liquid phase reaction on a hot plate to burn the precursor of lithium cobalt oxide. primary heat treatment to prepare primary lithium cobalt oxide powder by calcining the precursor prepared in the synthesis process and the precursor synthesized in the synthesis process in an alumina crucible for 6 hours at 350 ° C. and 12 hours at 450 ° C. The primary lithium cobalt oxide powder obtained in the step and the primary heat treatment step is pulverized, heat treated at 700 ° C. or 900 ° C. for 24 hours, and then gradually cooled to room temperature to obtain secondary lithium cobalt. Secondary heat treatment step of sintering the oxide powder, and finely pulverized secondary lithium cobalt powder obtained in the second heat treatment step, and then using a sieve (sieve) to obtain a powder having a diameter smaller than 45㎛ Method for producing lithium cobalt oxide powder.