KR102448301B1 - Cobalt oxide for lithium secondary battery, preparing method thereof, lithium cobalt oxide formed therefrom, and lithium secondary battery including positive electrode comprising the lithium cobalt oxide - Google Patents

Abstract

In the X-ray diffraction analysis, the intensity ratio of the second peak having 2θ of 31.3±1° to the first peak of 2θ of 19±1° is 0.8 to 1.2, and cobalt oxide for lithium secondary batteries having a tap density of 2.8 to 3.0 g/cc (Co ₃ O ₄ ), a manufacturing method thereof, a lithium cobalt oxide for a lithium secondary battery obtained from the cobalt oxide, and a lithium secondary battery having a positive electrode including the same are provided.

Description

Cobalt oxide for lithium secondary battery, manufacturing method thereof, lithium cobalt oxide formed therefrom, and lithium secondary battery having a positive electrode including the same electrode comprising the lithium cobalt oxide}

It relates to a lithium secondary battery having cobalt oxide for a lithium secondary battery, a manufacturing method thereof, a lithium cobalt oxide formed therefrom, and a positive electrode including the same.

Lithium secondary batteries have a high voltage and high energy density, and thus are used for various purposes. For example, in the field of electric vehicles (HEV, PHEV), etc., a lithium secondary battery having excellent discharge capacity is required because it can operate at a high temperature and has to charge or discharge a large amount of electricity.

Lithium cobalt oxide is widely used as a cathode active material because of its excellent energy density per volume. In order to further improve the capacity of such lithium cobalt oxide, it is required to increase the density of this material.

One aspect is to provide a cobalt oxide for a lithium secondary battery having an improved density and a method for manufacturing the same.

Another aspect is to provide a lithium secondary battery with improved cell performance by employing a lithium cobalt oxide formed from the above-described cobalt oxide and a positive electrode including the same.

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According to one aspect,

In the X-ray diffraction analysis, the intensity ratio of the second peak having 2θ of 31.3±1° to the first peak of 2θ of 19±1° is 0.8 to 1.2, and cobalt oxide for lithium secondary batteries having a tap density of 2.8 to 3.0 g/cc (Co ₃ O ₄ ) is provided.

Conducting a precipitation reaction of a mixture containing a cobalt precursor and a precipitating agent according to another aspect, wherein the precipitation reaction reacts in an oxidizing gas atmosphere to prepare the above-described cobalt oxide (Co ₃ O ₄ ) For lithium secondary batteries comprising the steps of: A method for producing cobalt oxide is provided.

According to another aspect, it is represented by Formula 1 below, has a spherical particle shape, has a pellet density of 3.98 to 4.2 g/cc, an average particle diameter (D50) of 23 to 28 μm, and a particle diameter (D90) of 35 to 45 μm, and , the particle diameter (D10) is provided with a lithium cobalt oxide for a lithium secondary battery of 10 to 13㎛.

[Formula 1]

Li _a Co _b O _c

In Formula 1, 0.9≤a≤1.1, 0.98≤b≤1.00, and 1.9≤c≤2.1.

According to another aspect, there is provided a lithium secondary battery having a positive electrode containing the above-described lithium cobalt oxide.

When cobalt oxide according to an embodiment is used, lithium cobalt oxide having an improved density can be prepared. An electrode containing such lithium cobalt oxide has improved density characteristics, and by employing it, a lithium secondary battery having excellent lifespan characteristics and rate-limiting characteristics can be manufactured.

1A is a schematic diagram of a lithium secondary battery according to an embodiment.
1B is a view for explaining a manufacturing process of lithium cobalt oxide according to an embodiment.
1C is a view for explaining a general manufacturing process of lithium cobalt oxide.
2a and 2b show the results of X-ray diffraction analysis for cobalt oxide (Co ₃ O ₄ ) prepared according to Example 1 and Comparative Example 1, respectively.
3 is a graph showing the results of measuring the density of the positive electrode according to the press gap in the positive electrode prepared according to Preparation Example 1 and Comparative Preparation Example 1.
4 shows a change in capacity retention rate for a coin cell manufactured according to Preparation Example 1. FIG.
5A and 5B are scanning electron microscope (SEM) pictures of cobalt oxide prepared according to Example 1. FIG.
6a and 6b are SEM images of cobalt oxide prepared according to Comparative Example 1.

Hereinafter, a lithium secondary battery having a positive electrode including a lithium cobalt oxide for a lithium secondary battery according to exemplary embodiments, a method for manufacturing the same, and a lithium cobalt oxide formed therefrom will be described in more detail.

In X-ray diffraction analysis, the intensity ratio of the second peak having 2θ of 31.3±1° to the first peak of 2θ of 19±1° is 0.8 to 1.2, and the tap density is 2.8 to 3.0 g/cc of cobalt oxide for lithium secondary batteries. (Co ₃ O ₄ ) is provided.

The first peak is for the (111) crystal plane of cobalt oxide, and the second peak is for the (220) crystal plane of cobalt oxide.

The intensity ratio of the second peak to the first peak is, for example, 1.0.

Cobalt oxide, a precursor of conventional lithium cobalt oxide, has an average particle diameter of 5 to 7 μm. In the case of producing lithium cobalt oxide having a large particle size using such cobalt oxide, lithium precursors such as lithium carbonate and lithium hydroxide are added in an excess of 1.04 to 1.05 based on 1 mole of cobalt oxide. As such, when an excess lithium precursor is used, a process of removing excess lithium must be performed, thereby increasing the manufacturing cost of lithium cobalt oxide.

Lithium cobalt oxide can be obtained according to a general manufacturing method as shown in FIG. 1C. First, CoOOH obtained by the co-precipitation reaction is heat-treated to prepare cobalt oxide (Co ₃ O ₄ ). A lithium precursor is added to the prepared cobalt oxide and heat-treated to obtain lithium cobalt oxide. Then, the lithium cobalt oxide is pulverized and subjected to a post-treatment process and a sieving process to remove residual lithium.

According to the manufacturing method of lithium cobalt oxide according to one embodiment, as shown in FIG. 1B, a precipitation reaction of a cobalt precursor is performed, and oxygen is injected to accelerate oxidation during the precipitation reaction to prepare cobalt oxide. A lithium precursor is added to the thus prepared cobalt oxide and heat-treated to prepare lithium cobalt oxide. Cobalt oxide according to an embodiment is prepared by an oxidative precipitation method. Unlike the conventional method for producing cobalt oxide shown in FIG. 1C, cobalt oxide according to an embodiment does not need to go through a heat treatment step, so that the manufacturing cost of cobalt oxide is very reduced. And by not going through the heat treatment step, it is possible to obtain high-density cobalt oxide without pores. By using such a high-density cobalt oxide, it becomes possible to manufacture an electrode having an improved electrode density.

Then, a lithium precursor is mixed with cobalt oxide and heat-treated to obtain a desired lithium cobalt oxide. The content of the cobalt oxide and the lithium precursor is stoichiometrically adjusted to obtain the compound of Formula 1, and the lithium precursor is added only as stoichiometrically necessary to prepare the target, and is not used in excess. For example, the compound of Formula 1 is LiCoO2, and when preparing such a compound, cobalt oxide and a lithium precursor are used, for example, in a molar ratio of about 1:1. After that, the lithium cobalt oxide is pulverized and sieved.

The average particle diameter (D50) of the cobalt oxide according to an embodiment is 15 to 18 μm, for example, 16 to 17 μm. As described above, since the average particle diameter of the cobalt oxide according to the embodiment has a large size as described above, it is possible to easily prepare a large particle diameter lithium cobalt oxide without using an excessive amount of a lithium precursor as in the conventional lithium cobalt oxide.

The intensity ratio of the second peak with 2θ of 31.3±1° to the first peak with 2θ of 19±1 in X-ray diffraction analysis gives information ^on the ratio of Co ^{3+ and} Co ²⁺ in Co ₃ O ₄ . In cobalt oxide (Co ₃ O ₄ ) according to an embodiment, Co ^{2 +} (tet) and The atomic ratio of Co ^{3 +} (oct) is 1:2.1 to 1:2.25.

The lithium cobalt oxide formed from the cobalt oxide has a pellet density of 3.98 to 4.2 g/cc. The tap density of cobalt oxide is excellent, for example, 2.8 to 3.0 g/cc. When the pellet density and tap density of cobalt oxide are within the above ranges, an electrode having excellent density characteristics can be manufactured.

The density of the positive electrode formed using lithium cobalt oxide according to an embodiment is excellent in 4.05 to 4.15 g/cc. By using the electrode having improved electrode density as described above, a lithium secondary battery having excellent lifespan characteristics and rate-rate characteristics can be manufactured. If only the electrode plate density is increased through excessive pressing in a state where the pellet density of cobalt oxide and lithium cobalt oxide formed therefrom is not improved, problems such as breaking of the electrode plate or impregnation of the electrolyte become disadvantageous, and lithium secondary battery lifespan and electrochemical properties may be reduced. However, since the tap density of cobalt oxide and the pellet density of lithium cobalt oxide according to an embodiment are improved, it is possible to prevent the above-mentioned problems from occurring in advance when pressing using them, and the electrochemical properties of lithium cobalt oxide are also excellent.

In addition, since the lithium precursor is not used in excess during the production of lithium cobalt oxide, the content of residual lithium resulting from the excess lithium precursor is small. The content of residual lithium is, for example, 500 ppm or less. Here, the content of residual lithium is determined by a titration method.

The lithium cobalt oxide according to an embodiment has an average particle diameter (D50) of 23 to 28 μm, a particle diameter (D90) of 35 to 45 μm, and a particle diameter (D10) of 10 to 13 μm.

In the present specification, "D50", "D90", and "D10" are the particle diameters of points reaching 50%, 90%, and 10% of the volume percentage in the cumulative curve when the cumulative curve of the particle size distribution is obtained with the total volume being 100%, respectively. As , it means the particle size where the volume becomes 50%, 90%, and 10% by accumulating from the smaller particle size.

Lithium cobalt oxide according to an embodiment is a compound having a spherical particle shape represented by the following Chemical Formula 1, a pellet density of 3.98 to 4.2 g/cc, an average particle diameter (D50) of 23 to 28 μm, and D90 of 35 to 45 μm, and D10 is 10 to 13 μm.

[Formula 1]

Li _a Co _b O _c

In Formula 1, 0.9≤a≤1.1, 0.98≤b≤1.00, and 1.9≤c≤2.1.

Lithium cobalt oxide according to an embodiment has a high pellet density, a spherical particle shape, and a good sphericity, so that a specific surface area can be minimized. When such lithium cobalt oxide is used, a positive electrode having excellent chemical stability even under high-temperature charging and discharging conditions and a lithium secondary battery having improved capacity and rate-rate characteristics can be manufactured by employing such a positive electrode.

When the pellet density of the lithium cobalt oxide is out of the above range, the rate and capacity characteristics of the lithium secondary battery including the positive electrode may be deteriorated.

The lithium cobalt oxide represented by Formula 1 is, for example, LiCoO ₂ .

The lithium cobalt oxide is one or more elements selected from magnesium (Mg), calcium (Ca), strontium (Sr), titanium (Ti), zirconium (Zr), boron (B), aluminum (Al) and fluorine (F). may include more. If the positive electrode is manufactured using lithium cobalt oxide containing more of these elements, the electrochemical properties of the lithium secondary battery may be further improved.

Hereinafter, a method of manufacturing cobalt oxide for a lithium secondary battery according to an embodiment will be described in more detail.

A precipitation reaction of a mixture containing cobalt sulfate, a cobalt precursor, a precipitating agent, and a solvent is performed, and an oxidizing gas such as oxygen is injected to accelerate oxidation during the precipitation reaction in an oxidizing gas atmosphere.

During the precipitation reaction, a chelating agent may be optionally added to the mixture. As the chelating agent, any one commonly used in the art may be used. Chelating agents are used, for example, ammonia, ammonia sulfate, and the like.

The precipitation reaction proceeds at 60 to 80°C. The precipitation reaction is carried out in the above-mentioned temperature range.

During the process, cobalt oxide having excellent density characteristics can be obtained.

The pH of the mixture is adjusted in the range of 11 to 12. When the pH of the mixture is in the range of 11 to 12, cobalt oxide having a desired particle state can be obtained.

As a precipitating agent, a sodium hydroxide solution, sodium carbonate solution, etc. are used as a pH adjusting agent of a mixture.

As the solvent, water or the like is used. The content of the solvent is 100 to 3000 parts by weight based on 100 parts by weight of the cobalt precursor. When the content of the solvent is within the above range, a mixture in which each component is uniformly mixed can be obtained.

The cobalt oxide obtained according to the above-described process has improved pellet density compared to the cobalt oxide obtained by the conventional manufacturing method. When such cobalt oxide is used, a high-density lithium cobalt oxide having a large particle size can be obtained. By using such lithium cobalt oxide, a positive electrode having an improved electrode density can be manufactured.

A method for preparing lithium cobalt oxide from cobalt oxide obtained according to the above process is as follows.

A lithium precursor is mixed with the cobalt oxide, and heat treatment of the mixture is performed.

As the lithium precursor, lithium hydroxide, lithium fluoride, lithium carbonate, or a mixture thereof is used. The content of the lithium precursor is stoichiometrically controlled to obtain the lithium cobalt oxide of Formula 1 above. For example, when preparing lithium cobalt oxide (LiCoO ₂ ), the content of the lithium precursor is about 1.0 mole based on 1 mole of cobalt oxide.

The heat treatment is performed at a temperature of 1000 to 1200 °C. When the heat treatment temperature is in the above range, the pellet density of lithium cobalt oxide is excellent.

Lithium cobalt oxide having a desired average particle diameter and pellet density can be obtained by pulverizing the resultant obtained by performing heat treatment and then performing sieving.

According to an embodiment, the average particle diameter (D50) of the cobalt oxide is 15 to 18 μm, the particle diameter (D90) is 23 to 25 μm, and the particle diameter (D10) is 5 to 7 μm.

Hereinafter, a process for manufacturing a lithium secondary battery using the above-described lithium cobalt oxide as a positive electrode active material for a lithium secondary battery will be described, but a method for manufacturing a lithium secondary battery having a positive electrode, a negative electrode, a lithium salt-containing nonaqueous electrolyte, and a separator is described. decide to do

The positive electrode and the negative electrode are prepared by respectively coating and drying a composition for forming a positive electrode active material layer and a composition for forming a negative electrode active material layer on a current collector.

The composition for forming the cathode active material is prepared by mixing a cathode active material, a conductive agent, a binder and a solvent, and the above-described lithium cobalt oxide is used as the cathode active material.

The binder is a component that assists in bonding the active material and the conductive agent and bonding to the current collector, and is added in an amount of 1 to 50 parts by weight based on 100 parts by weight of the total weight of the positive electrode active material. Non-limiting examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoro ethylene, polyethylene, polypropylene, ethylene-propylene-diene ter polymer (EPDM), sulfonated EPDM, styrene butyrene rubber, fluororubber, various copolymers, and the like. The content is used in an amount of 1 to 5 parts by weight based on 100 parts by weight of the total weight of the positive electrode active material. When the content of the binder is within the above range, the binding force of the active material layer to the current collector is good.

The conductive agent is not particularly limited as long as it has conductivity without causing a chemical change in the battery. For example, graphite such as natural graphite or artificial graphite; carbon-based substances such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black; conductive fibers such as carbon fibers and metal fibers; metal powders such as carbon fluoride, aluminum, and nickel powder; conductive whiskeys such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives may be used.

The amount of the conductive agent is 1 to 5 parts by weight based on 100 parts by weight of the total weight of the positive electrode active material. When the content of the conductive agent is within the above range, the conductivity characteristics of the finally obtained electrode are excellent.

As a non-limiting example of the solvent, N-methylpyrrolidone and the like are used.

The amount of the solvent is 10 to 200 parts by weight based on 100 parts by weight of the positive electrode active material. When the content of the solvent is within the above range, the operation for forming the active material layer is easy.

The positive electrode current collector has a thickness of 3 to 500 μm, and is not particularly limited as long as it has high conductivity without causing chemical change in the battery, for example, stainless steel, aluminum, nickel, titanium, heat-treated carbon, Alternatively, a surface treated with carbon, nickel, titanium, silver, etc. on the surface of aluminum or stainless steel may be used. The current collector may increase the adhesive force of the positive electrode active material by forming fine irregularities on its surface, and various forms such as a film, a sheet, a foil, a net, a porous body, a foam body, and a nonwoven body are possible.

Separately, a composition for forming a negative electrode active material layer is prepared by mixing a negative electrode active material, a binder, a conductive agent, and a solvent.

As the negative active material, a material capable of occluding and releasing lithium ions is used. Non-limiting examples of the negative active material include graphite, carbon-based materials such as carbon, lithium metal, alloys thereof, silicon oxide-based materials, and the like. According to an embodiment of the present invention, silicon oxide is used.

The binder is added in an amount of 1 to 50 parts by weight based on 100 parts by weight of the total weight of the negative active material. As a non-limiting example of such a binder, the same kind as the positive electrode may be used.

The conductive agent is used in an amount of 1 to 5 parts by weight based on 100 parts by weight of the total weight of the negative active material. When the content of the conductive agent is within the above range, the conductivity characteristics of the finally obtained electrode are excellent.

The amount of the solvent is 10 to 200 parts by weight based on 100 parts by weight of the total weight of the negative active material. When the content of the solvent is within the above range, the operation for forming the anode active material layer is easy.

The conductive agent and the solvent may be the same type of material as that of the positive electrode.

As the negative electrode current collector, it is generally made to have a thickness of 3 to 500 μm. Such a negative current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, heat-treated carbon, or a surface of copper or stainless steel. Carbon, nickel, titanium, silver, etc. surface-treated, aluminum-cadmium alloy, etc. may be used. In addition, like the positive electrode current collector, the bonding strength of the negative electrode active material may be strengthened by forming fine irregularities on the surface, and may be used in various forms such as a film, sheet, foil, net, porous body, foam, non-woven body, and the like.

A separator is interposed between the positive electrode and the negative electrode manufactured according to the above process.

The separator has a pore diameter of 0.01 to 10 μm and a thickness of generally 5 to 300 μm. Specific examples include olefin-based polymers such as polypropylene and polyethylene; Alternatively, a sheet or non-woven fabric made of glass fiber is used. When a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte may also serve as a separator.

The lithium salt-containing non-aqueous electrolyte consists of a non-aqueous electrolyte and lithium. As the non-aqueous electrolyte, a non-aqueous electrolyte, an organic solid electrolyte, an inorganic solid electrolyte, and the like are used.

Examples of the non-aqueous electrolyte include, but are not limited to, N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1, 2-dimethoxyethane, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, N,N-formamide, N,N-dimethylformamide, acetonitrile, nitromethane, methyl formate, acetic acid Methyl, phosphoric acid triester, trimethoxy methane, dioxolane derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether, pyro An aprotic organic solvent such as methyl pionate or ethyl propionate may be used.

Examples of the organic solid electrolyte include, but are not limited to, polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphoric acid ester polymers, polyvinyl alcohol, polyvinylidene fluoride, and the like.

Examples of the inorganic solid electrolyte include, but are not limited to, Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Li ₄ SiO ₄ -LiI- LiOH, Li ₃ PO ₄ -Li ₂ S-SiS ₂ and the like may be used.

The lithium salt is a material readily soluble in the non-aqueous electrolyte, and includes, but is not limited to, LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF ₆ , LiSbF ₆ , LiAlCl ₄ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, (CF ₃ SO ₂ ) ₂ NLi, (FSO ₂ ) ₂ NLi, lithium chloroborate, lithium lower aliphatic carboxylate, lithium tetraphenyl borate and the like can be used.

1 is a cross-sectional view schematically showing a representative structure of a lithium secondary battery 10 according to an embodiment.

Referring to FIG. 1 , the lithium secondary battery 10 includes a positive electrode 13 , a negative electrode 12 , and a separator 14 disposed between the positive electrode 13 and the negative electrode 12 , the positive electrode 13 , and the negative electrode (12) and an electrolyte (not shown) impregnated in the separator 14, a battery case 15, and a cap assembly 16 for enclosing the battery case 15 as main parts. The lithium secondary battery 10 may be configured by sequentially stacking the positive electrode 13 , the negative electrode 12 , and the separator 14 , and then storing the positive electrode 13 , the negative electrode 12 , and the separator 14 in the battery case 15 in a spirally wound state. The battery case 15 is sealed together with the cap assembly 16 to complete the lithium secondary battery 10 .

The present invention will be described in more detail through the following examples and comparative examples. However, the examples are provided to illustrate the present invention, and the scope of the present invention is not limited thereto.

Example 1: cobalt oxide and lithium cobalt oxide Produce

About 1.5M of cobalt sulfate aqueous solution and 3.0M of NaOH solution as a precipitating agent were prepared, respectively, and these solutions were simultaneously introduced into the reactor, and then the pH of the reaction mixture was adjusted to about 11.5, and the precipitation reaction was carried out at about 70°C.

Oxygen was injected to accelerate oxidation during the precipitation reaction, and the reaction method was performed in a continuous flow stirred-tank reactor (CSTR) type. The average particle diameter (D50) of the spherical Co ₃ O ₄ obtained through this process was about 15 μm. This was repeatedly performed through a washing process using deionized water in a centrifuge until the SO ₄ content became 100 ppm or less.

A sieving operation was performed through a sieve of about 270 mesh to obtain high-density cobalt oxide (Co ₃ O ₄ ).

The cobalt oxide and lithium carbonate were dry mixed at a 1:1 mixing molar ratio for 5 minutes in a mixer, and heat treatment was performed at about 1100° C. for 10 hours to obtain lithium cobalt oxide (LiCoO ₂ ).

After heat treatment, the jet mill was operated at 2000 rpm, and then sieving was performed with a 325 mesh.

Example 2

Cobalt oxide (Co ₃ O ₄ ) and lithium cobalt oxide (LiCoO ₂ ) were obtained in the same manner as in Example 1, except that the reaction temperature was changed to about 80° C. during the precipitation reaction for preparing cobalt oxide.

comparative example One

About 1.5M aqueous cobalt sulfate solution, 3.0M NH ₄ HCO ₃ solution as a precipitating agent, and NH ₄ OH aqueous solution as a chelating agent were prepared, respectively, and these three solutions were simultaneously introduced into the reactor, and then the pH of the reaction mixture was adjusted to about 11.2. The precipitation reaction was carried out at about 40° C. to form a precipitate CoOOH.

After the obtained precipitate was filtered, washed and dried overnight at 120° C., it was subjected to primary heat treatment at about 800° C. to obtain cobalt oxide (Co ₃ O ₄ ). The average particle diameter of the cobalt oxide was about 5.4 μm.

The cobalt oxide and lithium carbonate were dry-mixed at a molar ratio of 1:1.04 in a mixer for 5 minutes, and secondary heat treatment was performed at about 1100° C. for 10 hours. After the secondary heat treatment, pulverization was carried out at 2000 rpm with a jet mill. Subsequently, residual lithium post-treatment was performed and sieving was performed to obtain lithium cobalt oxide (LiCoO ₂ ).

Production example One

A coin cell was manufactured using the lithium cobalt oxide (LiCoO ₂ ) prepared according to Example 1 as follows.

A cathode active material layer uniformly dispersed by mixing 96 g of lithium cobalt oxide (LiCoO ₂ ) obtained according to Example 1, 2 g of polyvinylidene fluoride, 47 g of N-methylpyrrolidone as a solvent, and 2 g of carbon black as a conductive agent A forming slurry was prepared,

The slurry prepared according to the above process was coated on an aluminum foil using a doctor blade to form a thin electrode plate, dried at 135° C. for 3 hours or more, and then a positive electrode was manufactured by rolling and vacuum drying.

A 2032 type coin cell was manufactured using the positive electrode and the lithium metal counter electrode. A separator (thickness: about 16 μm) made of a porous polyethylene (PE) film was interposed between the positive electrode and the lithium metal counter electrode, and electrolyte was injected to fabricate a coin cell.

At this time, as the electrolyte, a solution containing 1.1M LiPF ₆ dissolved in a solvent in which ethylene carbonate (EC) and ethylmethyl carbonate (EMC) were mixed in a volume ratio of 3:5 was used.

Production example 2

A coin cell was manufactured in the same manner as in Preparation Example 1, except that lithium cobalt oxide (LiCoO ₂ ) obtained according to Example 2 was used instead of lithium cobalt oxide (LiCoO ₂ ) obtained according to Example 1 .

Comparative production example One

A coin cell was manufactured in the same manner as in Preparation Example 1, except that lithium cobalt oxide (LiCoO ₂ ) obtained according to Comparative Example 1 was used instead of lithium cobalt oxide (LiCoO ₂ ) obtained according to Example 1 .

evaluation example One: XRD analysis

X-ray diffraction analysis was performed on cobalt oxide (Co ₃ O ₄ ) prepared according to Example 1 and Comparative Example 1.

The analysis results are shown in FIGS. 2A and 2B, respectively.

In the cobalt oxide prepared according to Example 1, as shown in FIG. 2a, the intensity ratio of the second peak having 2θ of 31.3° to the first peak having 2θ of about 19° in X-ray diffraction analysis was about 1. In contrast, as shown in FIG. 2b , in the cobalt oxide prepared according to Comparative Example 1, the intensity ratio of the second peak having 2θ of 31.3° to the first peak having 2θ of about 19° was about 2. As such, it was found that the cobalt oxide of Example 1 was different from the case of Comparative Example 1 in that the intensity ratio of the second peak to the first peak was different. And each parameter obtained through X-ray diffraction analysis was investigated, and it is shown in Table 1 below.

Sample a(Å) x(O)=y(O)=z(O) Co ²⁺ (tet) Co ³⁺ (oct) R _B Example 1 8.0821 0.2617 0.480 1.072 8.8 Comparative Example 1 8.0811 0.2613 0.510 1.023 7.8

R _B represents the accuracy of fitting to the actual XRD pattern, a is the a-axis in the structure, and x(O) = y(O) = z(O) is the amount of oxygen in the structure. Indicates position coordinates. And oct is an abbreviation for Octahedral, and tet is an abbreviation for tetrahedral.

Referring to Table 1, in the cobalt oxide of Example 1, Co ^{3 +} (oct) was observed relatively more than Co ^{2 +} (tet), so that Co ^{2 +} (tet) and Co ^{3 +} (oct) was almost 1:2.23 atomic ratio. In contrast, in Comparative Example 1, Co ^{2 +} (tet) and Co ^{3 +} (oct) had an atomic ratio of about 1:2.

Evaluation Example 2: Pellet density and electrode density

The pellet density of lithium cobalt oxide obtained according to Example 1 and Comparative Example 1 was measured and shown in Table 2 below. Here, the pellet density is measured using a pellet density tester, and 3 g of a positive active material in a circular mode with a diameter of 1.273 Cm is added and 1500 kgf/cm ² obtained by applying pressure.

division Pellet density (g/cc) Example 1 3.98 Comparative Example 1 3.87

As shown in Table 2, the lithium cobalt oxide prepared according to Example 1 had an increased pellet density compared to the lithium cobalt oxide prepared according to Comparative Example 1.

In addition, the density of the positive electrode prepared according to Preparation Example 1 and Comparative Preparation Example 1 was measured, and the results are shown in Table 3 and FIG. 3 below. The density of the anode is calculated by dividing the weight of the anode by the volume of the anode.

division Anode Density (g/cc) Production example 1 4.09 Comparative Production Example 1 4.00

As shown in Table 3 and FIG. 3, the positive electrode prepared according to Preparation Example 1 had improved anode density compared to the electrode prepared according to Comparative Preparation Example 1.

Evaluation Example 3: Charge/discharge experiment (initial charge/discharge efficiency and capacity retention rate)

In the coin cells manufactured according to Preparation Example 1 and Comparative Preparation Example 1, the charging/discharging characteristics were evaluated under the following conditions with a charger/discharger.

The coin cells prepared in Example 1 and Comparative Preparation Example 1 were charged with a constant current at a current of 25 to 0.1C rate until the voltage reached 4.55V (vs. Li), and then maintained at 4.55V in the constant voltage mode. A cut-off was performed at a current of 0.05C rate. Then, it was discharged at a constant current of 0.1C rate until the voltage reached 3.0V (vs. Li) during discharge (Hwaseong phase, 1 ^st cycle).

The lithium battery that has undergone the 1st cycle of the formation step is charged with a constant current from 25 to a current of 0.2C rate until the voltage reaches ^4.55V (vs. Li), and then, while maintaining 4.55V in the constant voltage mode, at a rate of 0.05C A cut-off was made in current. Then, it was discharged at a constant current of 0.2C rate until the voltage reached 3.0V (vs. Li) during discharge (Hwaseong stage, 2nd cycle).

The lithium battery that had undergone the formation step was charged with a constant current at 25°C at a rate of 1.0C until the voltage reached 4.55V (vs. Li). Then, while maintaining 4.35V in the constant voltage mode, a cut-off was performed at a current of 0.05C rate. Then, a cycle of discharging at a constant current of 1.0C rate until the voltage reached 3.0V (vs. Li) during discharging was repeated until ^50th cycle.

Initial charge efficiency (I.C.E) was calculated according to Equation 1 below, and the results are shown in Table 4 below.

[Equation 1]

Initial charge/discharge efficiency [%] = [1 ^st cycle discharge capacity/1 ^st cycle charge capacity] × 100

In addition, the capacity retention ratio of the coin cell manufactured according to Preparation Example 1 is as shown in FIG. 5 .

division Charging capacity (mAh/g) Discharge capacity (mAh/g) I.C.E (%) Production Example 1 223 219 98 Comparative Production Example 1 220 216 98

As shown in Table 4, the coin cell manufactured according to Preparation Example 1 exhibited almost the same initial efficiency characteristics as that of Comparative Preparation Example 1.

In addition, as shown in FIG. 4 , it was found that the coin cell manufactured according to Preparation Example 1 had excellent capacity retention.

evaluation example 4: rate characteristic

Each coin cell prepared according to Preparation Example 1-2 and Comparative Preparation Example 1 was charged with a constant current to 4.5V at a rate of 0.1C in the 1st cycle, and discharged with a constant current to 3.0V at a rate of 0.1C.

In the ^2nd cycle, constant current charging was performed to 4.5V at a rate of 0.5C, followed by constant voltage charging until the current reached 0.05C while maintaining 4.6V, followed by constant current discharge to 3.0V at a rate of 0.2C.

In the ^3rd cycle, constant current charging was performed at a rate of 0.5C to 4.5V, followed by constant voltage charging until the current reached 0.05C while maintaining 4.6V, followed by constant current discharge at a rate of 1.0C to 3.0V.

4th The cycle was followed by constant current charging to 4.5V at a rate of 0.5C, constant voltage charging until the current reached 0.05C while maintaining 4.6V, and constant current discharging to 3.0V at a rate of 2.0C.

The rate-rate characteristics of the coin cells prepared according to Preparation Example 1 and Comparative Preparation Example 1 are respectively shown in Table 5 below.

In Table 5 below, the rate characteristic can be calculated by Equations 2 and 3 below.

[Equation 2]

Rate characteristic (1C/0.1C)(%) = (discharge capacity in 3rd cycle)/(discharge capacity in 1st cycle)X100

[Equation 3]

Rate characteristic (2C/0.2C)(%) = (discharge capacity at 4th cycle)/(discharge capacity at ^2nd cycle) X100

division Rate characteristic (1C/0.1C)(%) Rate characteristic (2C/0.2C)(%) Production Example 1 88 85 Comparative Production Example 1 86 83

As shown in Table 5, the coin cell prepared according to Preparation Example 1 had improved rate-rate characteristics compared to Comparative Preparation Example 1.

evaluation example 5: Scanning electron microscope ( SEM )

A scanning electron microscope analysis was performed on the cobalt oxide obtained according to Example 1 and Comparative Example 1. The scanning electron micrograph of the cobalt oxide of Example 1 is as shown in FIGS. 5A to 5C, and the scanning electron micrograph of the cobalt oxide of Comparative Example 1 is as shown in FIGS. 6A and 6B.

Referring to this, it was confirmed that the shape of the cobalt oxide of Example 1 was different from that of the cobalt oxide obtained according to Comparative Example 1. The shape of the primary particles of the cobalt oxide of Example 1 was needle-like, and at the same time it included spots, and the shape of the secondary particles was spherical, and it was found that the particle diameter was in the range of 15 to 17 μm.

evaluation example 6: Particle size distribution test

1) Cobalt oxide

The particle size distribution of the cobalt oxide obtained according to Example 1 and Comparative Example 1 was analyzed.

The particle size distribution analysis was measured using the dynamic light scattering method, and was used to evaluate the particle size distribution.

Thus, D10, D90, and D50 were calculated based on the particle volume by dry laser diffraction particle size analysis.

The particle size distribution is shown in Table 6 below.

division D10
(μm) D90
(μm) D50
(μm) Tap density (g/cc) Example 1 6.73 23.3 16.2 2.9 Comparative Example 1 2.6 8.8 5.4 1.7

As shown in Table 6, it was found that the cobalt oxide prepared according to Example 1 had a larger average particle diameter and a larger tap density compared to the cobalt oxide obtained according to Comparative Example 1.

2) Lithium cobalt oxide

The particle size distribution of lithium cobalt oxide obtained according to Example 1 and Comparative Example 1 was analyzed. The particle size distribution analysis was measured using the dynamic light scattering method, and D10, D90, and D50 were calculated based on the particle volume by dry laser diffraction particle size analysis to evaluate the particle size distribution.

The particle size distribution is shown in Table 7 below.

division D10
(μm) D90
(μm) D50
(μm) Example 1 12.1 37.6 23 Comparative Example 1 8.5 34.18 17.93

As shown in Table 7, it was found that the lithium cobalt oxide prepared according to Example 1 had a larger average particle diameter compared to the lithium cobalt oxide obtained according to Comparative Example 1.

Although it has been described with reference to the embodiments above, it will be understood by those skilled in the art that various modifications and changes can be made without departing from the spirit and scope of the following claims.

10: lithium secondary battery 12: negative electrode
13: positive electrode 14: separator
15: battery case 16: cap assembly

Claims (10)

The intensity ratio of the second peak having 2θ of 31.3±1° to the first peak having 2θ of 19±1° in X-ray diffraction analysis is 0.8 to 1.2, the tap density is 2.8 to 3.0 g/cc, and the average of cobalt oxide The particle diameter (D50) is 15 to 18㎛, the particle diameter (D90) is 23 to 25㎛, the particle diameter (D10) is 5 to 7㎛, cobalt oxide for a lithium secondary battery (Co ₃ O ₄ ). delete Conducting a precipitation reaction of a mixture containing a cobalt precursor and a precipitating agent, wherein the precipitation reaction is reacted under an oxidizing gas atmosphere to prepare the cobalt oxide (Co ₃ O ₄ ) of claim 1, wherein the pH of the mixture is 11.0 to 12.0, a method for producing cobalt oxide for a lithium secondary battery carried out at a temperature of 60 to 80 ℃. 4. The method of claim 3,
After carrying out the step of reacting in the oxidizing gas atmosphere,
washing the reaction product; and a sieving step. delete 4. The method of claim 3,
A method for producing cobalt oxide for a lithium secondary battery, wherein the cobalt precursor is cobalt sulfate. It is represented by the following Chemical Formula 1, has a spherical particle shape, has a pellet density of 3.98 to 4.2 g/cc, an average particle diameter (D50) is 23 to 28 μm, and a particle diameter (D90) is 35 to 45 μm, and a particle diameter (D10) is a lithium cobalt oxide for lithium secondary batteries of 10 to 13 μm,
Lithium cobalt oxide for lithium secondary batteries, wherein the lithium cobalt oxide is obtained by heat-treating a mixture of the cobalt oxide and lithium precursor of claim 1 :
[Formula 1]
Li _a Co _b O _c
In Formula 1, 0.9≤a≤1.1, 0.98≤b≤1.00, and 1.9≤c≤2.1. 8. The method of claim 7,
The lithium cobalt oxide further comprises one or more selected from magnesium (Mg), calcium (Ca), strontium (Sr), titanium (Ti), zirconium (Zr), boron (B), aluminum (Al) and fluorine (F). Lithium cobalt oxide for lithium secondary batteries, including. A lithium secondary battery having a positive electrode containing the lithium cobalt oxide of claim 7 or 8. The lithium secondary battery according to claim 9, wherein the positive electrode has a density of 4.05 to 4.15 g/cc.

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