KR101769589B1 - Synthesis of electrochemical active multiphase cobalt oxides for electrode materials - Google Patents

Abstract

The present invention relates to a manufacturing method of an electrode active material for a lithium secondary battery, and the electrode active material manufactured by the method. The manufacturing method of an electrode active material for a lithium secondary battery according to the present invention is capable of manufacturing an electrode active material containing multiphase cobalt metal oxide using a heterocyclic compound having five rings. Accordingly, it is possible to manufacture an electrode active material having excellent electrochemical characteristics as compared with an electrode active material containing single phase cobalt metal oxide or being manufactured by using a hexagonal ring heterocyclic compound.

Description

TECHNICAL FIELD [0001] The present invention relates to a composite compound type cobalt metal oxide having high electrochemical activity,

The present invention relates to a method for producing an electrode active material for a lithium secondary battery and an electrode active material produced thereby.

Recently, with the development of high-tech electronics industry, it has become possible to reduce the size and weight of electronic equipment, so that the use of portable electronic devices is increasing. One example of the power source of such portable electronic devices is lithium secondary battery. Accordingly, various studies for increasing the lifetime of the lithium secondary battery are underway, and in particular, the transition metal oxide is attracting attention as an electrode active material or a catalyst of a lithium secondary battery.

The transition metal oxide generally has a higher theoretical capacity than graphite used as an anode active material. When such a transition metal oxide is formed into nanoparticles, the migration path of lithium ions and electrons is shortened and the reaction surface area And the volume expansion during charging and discharging is minimized, so that the lifetime of the lithium secondary battery can be increased. Accordingly, studies are underway to produce various nanoparticle shapes and to have certain electrochemical properties.

In other words, lithium secondary battery is a device that converts chemical energy into electric energy. The double anode material should have a wide surface area and therefore a good reaction surface area and easy movement of lithium or electrons in the active material. Methods for inducing nanoparticles of an active material to satisfy such physical properties are generally known, and attempts have been made to variously change nanoparticle shapes to increase the surface area of the active material.

In the case of cobalt oxide, the possibility of utilizing each composition as a cathode material for a lithium ion battery anode or a metal air battery cathode has been studied. The theoretical capacity of cathode material of cobalt tetroxide (CO ₃ O ₄ ) can be as high as 890 mAhg ^-1 and cobalt monoxide (CoO) can increase the lifetime of lithium secondary battery due to excellent electrochemical reversible reaction Lt; / RTI >

In addition to these single materials, various composite materials have been studied as electrode materials for lithium secondary batteries in order to fully exploit the merits of different materials. For example, Non-Patent Document 1 discloses a porous MnCo ₂ O ₄ To produce both conductive layers of uniform surface with microspheres and to confirm its electrochemical performance.

However, it has been generally known that a composite material method requiring a large amount of time and processing, such as mechanical mixing and complicated multi-step synthesis method, is generally known after synthesizing individual materials through different artificial synthesis methods.

Accordingly, the present inventors prepared a nanoparticle shape of metal oxide by selecting a compound capable of forming a particle shape of cobalt oxide having a unique shape among heterocyclic compounds, and in particular, a method of producing a cobalt oxide oxide And an electrode material using the same.

Dalton Transactions (2016) 45, 5064-5070

An object of the present invention is to provide a method for producing an electrode active material for a lithium secondary battery comprising a cobalt oxide oxide of a composite phase.

Another object of the present invention is to provide an electrode active material for a lithium secondary battery, which is produced by the above production method.

Still another object of the present invention is to provide a negative electrode and a positive electrode for a lithium secondary battery comprising the electrode active material and a catalyst.

Another object of the present invention is to provide a lithium secondary battery including a cathode for a lithium secondary battery comprising an electrode active material or a catalyst, and a metal air battery including a cathode for a metal air battery.

In order to achieve the above object,

The present invention relates to a process for preparing a mixed solution (step 1) by mixing a metal oxide precursor and an unsubstituted or substituted 5-membered heterocyclic compound containing at least one nitrogen atom in a solvent;

A step (step 2) of preparing an electrode active material precursor by heating the mixed solution prepared in the step 1; And

(3) drying the electrode active material precursor prepared in the step 2 and then heat treating the electrode active material precursor,

Wherein the substituted 5-membered heterocyclic compound is a 5-membered heterocyclic compound substituted with at least one C _1-10 straight-chain or branched alkyl.

In addition, the present invention provides an electrode active material for a lithium secondary battery, which is produced by the above production method.

Further, the present invention provides a negative electrode and a positive electrode for a lithium secondary battery comprising the electrode active material produced by the above-described production method.

The present invention also provides a lithium secondary battery including a negative electrode for a lithium secondary battery and a positive electrode for a metal air battery including an electrode active material produced by the above manufacturing method.

The method for preparing an electrode active material for a lithium secondary battery according to the present invention can produce an electrode active material containing a multiphase cobalt metal oxide by using a pentacyclic heterocycle compound, Or an electrode active material having excellent electrochemical characteristics as compared with an electrode active material prepared by using a heterocyclic compound having six rings.

1 shows X-ray diffraction analysis results of an electrode material prepared by artificially mixing the CO ₃ O ₄ -CoO 2 composite electrode material prepared in Example 1-3 of the present invention and the commercial cobalt oxide of Comparative Example 3 Graph.
FIGS. 2-5 show the CO ₃ O ₄ -CoO composite electrode material prepared in Example 1 of the present invention, the CO ₃ O ₄ (SEM) of the electrode material and the electrode material prepared by artificially mixing the cobalt oxide of Comparative Example 3 before and after the heat treatment.
FIGS. 6 to 9 show the CO ₃ O ₄ -CoO 2 composite electrode material prepared in Example 1 of the present invention, the CO ₃ O ₄ The electrochemical characteristics of the electrode material prepared by artificially mixing the electrode material and the cobalt oxide of Comparative Example 3 with charging and discharging capacity.
10-11 are graphs showing the relationship between the CO ₃ O ₄ -CoO composite electrode material prepared in Example 1 of the present invention and the CO ₃ O ₄ The electrode material is analyzed by cyclic voltammetry and is shown as a voltage and a current.

Hereinafter, the present invention will be described in detail.

The present invention relates to a process for preparing a mixed solution (step 1) by mixing a metal oxide precursor and an unsubstituted or substituted 5-membered heterocyclic compound containing at least one nitrogen atom in a solvent;

A step (step 2) of preparing an electrode active material precursor by heating the mixed solution prepared in the step 1; And

And drying the electrode active material precursor prepared in the step 2 and then heat treating the electrode active material precursor (step 3). The present invention also provides a method for producing an electrode active material for a lithium secondary battery.

Hereinafter, a method of manufacturing an electrode active material for a lithium secondary battery according to the present invention will be described in detail.

In the method for producing an electrode active material for a lithium secondary battery according to the present invention, the step 1 is a step of preparing a mixed solution by mixing a metal oxide precursor and an unsubstituted or substituted 5-membered heterocyclic compound containing at least one nitrogen, to be.

The substituted 5-membered heterocyclic compound may be a 5-membered heterocyclic compound substituted with at least one C _1-10 straight-chain or branched alkyl. Preferably, the compound represented by the formula (1) Most preferably, 3,5-dimethylpyrazole can be used.

[Chemical Formula 1]

(In the formula 1,

R ¹ and R ² are independently C _1-6 straight or branched chain alkyl.

The metal oxide precursor of step 1 is preferably cobalt nitrate hexahydrate (Co (NO ₃ ) ₂ .6H ₂ O).

Further, at least one solvent selected from the group consisting of distilled water and C ₁ to C ₃ alcohols can be used as the solvent of step 1 above.

In the method for producing an electrode active material for a lithium secondary battery according to the present invention, the step 2 is a step of preparing an electrode active material precursor by heating the mixed solution prepared in the step 1.

At this time, the heating is preferably performed by irradiating microwaves at a temperature of 100 ° C to 200 ° C for 10 minutes to 120 minutes, and irradiating the microwaves at a temperature of 140 ° C to 180 ° C for 20 minutes to 60 minutes , And it is most preferable to conduct microwave irradiation at a temperature of 160 DEG C for 30 minutes.

When the heating temperature is lower than 100 ° C., a sufficient heat source is not transferred to the mixed solution, which leads to a problem that the precursor of the electrode active material is not smoothly produced. When the heating temperature is higher than 200 ° C., There is a problem that an excessive heat source is transferred compared to a heat source required for manufacturing, thereby forming a by-product.

In the method for producing an electrode active material for a lithium secondary battery according to the present invention, the step 3 is a step of drying the electrode active material precursor prepared in the step 2 and then performing a heat treatment.

At this time, the drying is preferably performed in an oven at 90 ° C to 150 ° C, more preferably at a temperature of 110 ° C to 130 ° C, and most preferably at a temperature of 120 ° C.

If the drying temperature is lower than 90 ° C., sufficient drying may not be performed. Thus, there is a problem that the electrical characteristics of the electrode active material to be produced are reduced. If the drying temperature is more than 150 ° C., by-products are formed.

In addition, the heat treatment is preferably performed at a temperature of 400 ° C to 1000 ° C for 30 minutes to 300 minutes, more preferably at a temperature of 500 ° C to 900 ° C for 60 minutes.

When the heat treatment temperature is lower than 400 ° C., there is a problem that sufficient electric heat source required for the production of the electrode active material is not transferred, so that the electrical characteristics of the electrode active material may be reduced. When the heat treatment is performed at a temperature exceeding 1000 ° C. There is a problem that by-products are formed.

The method for preparing an electrode active material for a lithium secondary battery according to the present invention can produce an electrode active material containing a multiphase cobalt metal oxide by using a heterocyclic compound having five rings,

Accordingly, it is possible to produce an electrode active material having excellent electrochemical characteristics as compared with an electrode active material containing a single phase cobalt metal oxide or a hexagonal ring heterocyclic compound.

In addition, the present invention provides an electrode active material for a lithium secondary battery, which is produced by the above production method.

Further, the present invention provides a positive electrode for a lithium secondary battery comprising an electrode active material produced by the above-described production method.

In addition, the present invention provides a lithium secondary battery including a positive electrode for a lithium secondary battery including an electrode active material produced by the above-described method.

Hereinafter, the present invention will be described in detail with reference to Examples and Experimental Examples. However, the present invention is not limited by Examples and Experimental Examples.

< Example  1> Co ₃ O ₄ - CoO Composite phase  Electrode material manufacturing 1

873.09 mg of cobalt precursor Co (NO ₃ ) ₂ .6H ₂ O was added to 30 mL of methanol and stirred at room temperature for 10 minutes. To the solution was added a mixed solution prepared by dissolving 1153.56 mg of 3,5-dimethylpyrazole serving as an additive in 10 mL of methanol, and the mixture was stirred for 30 minutes. Microwave irradiation was carried out at 160 DEG C for 30 minutes, followed by drying and grinding treatment at 120 DEG C in an oven.

Then, the mixture was added to an alumina boat and heat-treated in an atmosphere of nitrogen at 500 ° C. for 30 minutes using an electric furnace for 30 minutes to prepare a cobalt oxide Co ₃ O ₄ -CoO composite electrode material.

< Example  2> Co ₃ O ₄ - CoO Composite phase  Electrode material manufacturing 2

The cobalt oxide Co ₃ O ₄ -CoO composite electrode material was prepared in the same manner as in Example 1, except that the heat treatment temperature was 700 ° C.

< Example  3> Co ₃ O ₄ - CoO Composite phase  Electrode material manufacturing 3

The cobalt oxide Co ₃ O ₄ -CoO composite electrode material was prepared in the same manner as in Example 1, except that the heat treatment temperature was 900 ° C.

< Comparative Example  1> DABCO  With additives Co ₃ O ₄  Electrode material manufacturing

The cobalt oxide Co ₃ O ₄ electrode material was prepared in the same manner as in <Embodiment 1> except that 3,5-dimethylpyrazole in Example 1 was changed to DABCO and weighed 1346.16 g.

< Comparative Example  2> Pyrazine  With additives Co ₃ O ₄  Electrode material manufacturing

The cobalt oxide Co ₃ O ₄ electrode material was prepared in the same manner as in <Embodiment 1> except that 3,5-dimethylpyrazole of Example 1 was changed to pyrazine and weighed 961.08 g.

< Comparative Example  3> Manufacture of cobalt oxide electrode material using commercial reagent

The cobalt oxide electrode material having a Co ₃ O ₄ -CoO 2 composite phase was prepared by mixing a molar ratio of Co ₃ O ₄ : CoO = 1.3: 4 using a commercially available reagent.

The commercially available reagent used was Sigma Aldrich model 221643 for Co ₃ O ₄ and Sigma Aldrich model 343163 for CoO.

< Experimental Example  1> X-ray diffraction analysis

In order to analyze the crystal structure of the electrode material produced by the manufacturing method according to the present invention, X-ray diffraction analysis was performed and the results are shown in FIG.

1 shows X-ray diffraction analysis results of an electrode material prepared by artificially mixing the CO ₃ O ₄ -CoO 2 composite electrode material prepared in Example 1-3 of the present invention and the commercial cobalt oxide of Comparative Example 3 Graph.

As shown in FIG. 1, the electrode material produced by the manufacturing method according to the present invention exists as a CO ₃ O ₄ -CoO 2 composite phase.

< Experimental Example  2> Evaluation of particle shape

In order to confirm the microstructure of the electrode material produced by the manufacturing method according to the present invention, the electrode materials before and after the heat treatment in Example 1 and Comparative Example 1-3 were observed under a scanning electron microscope (SEM, Tescan Mira 3 LMU FEG, Voltage 10 kV, Coater was observed with Quorum Q150T ES / 10 mA, 120s Pt coating). The results are shown in Figs. 2-5.

FIGS. 2-5 show the CO ₃ O ₄ -CoO composite electrode material prepared in Example 1 of the present invention, the CO ₃ O ₄ (SEM) of the electrode material and the electrode material prepared by artificially mixing the cobalt oxide of Comparative Example 3 before and after the heat treatment.

As shown in FIG. 2-5, the electrode material of Example 1 in which 3,5-dimethylpyrazole was used as the heterocyclic compound and the heat treatment was performed at a temperature of 500 ° C, which is the heat treatment temperature range of the present invention, It can be confirmed that spherical particles having a very uniform shape are mixed.

On the other hand, in Comparative Example 1 using DABCO as the heterocyclic compound, Comparative Example 2 using the pyrazine, and Comparative Example 3 using the commercial reagent, it was found that extremely heterogeneous particles were mixed.

Therefore, it is understood that 3,5-dimethylpyrazole is preferably used as the heterocyclic compound when the electrode material is produced by the production method of the present invention.

< Experimental Example  3> Electrochemical Characterization

In order to evaluate the electrochemical characteristics of the electrode material produced by the manufacturing method according to the present invention, the following experiment was performed using the electrode material prepared in Example 1 and Comparative Example 1-3.

An electrode was fabricated using the electrode material prepared in Example 1 and Comparative Example 1-3 to form a half cell. The manufacturing process of the electrode is as follows.

PTFE (Polytetrafluoroethylene) used as a binder was dissolved in a mixed solution of distilled water and isopropanol in a volume ratio of 1: 1, and then mixed with the electrode material prepared in Example 1 or Comparative Example 1-3. At this time, the weight ratio of the electrode material and the binder was 8: 2. The slurry thus prepared was coated on a SUS (Steel Use Stainless) net having a circular shape and then dried in an oven controlled at a temperature of 120 ° C for 15 minutes.

The half-cell was fabricated using a 2032-type coin cell with a bipolar half-cell. Lithium metal foil was used as a reference electrode, and a celgard was used as a separation membrane. N, N-dimethylacetamide (N, NDimethylacetamide, DMAc) in which 1.0 M of LiNO ₃ was dissolved was used as an electrolyte. Half cells were fabricated in a dry box in an inert argon (Ar) atmosphere.

Charging and discharging tests were carried out at a constant current (CC) at a temperature of 25 ° C and a constant current of 15 mA / g was applied. At this time, the discharge cut-off voltage was set to ^{4.2V (vs Li / Li +.} ) - off (cut-off) voltage of 2.0 V (vs.Li/Li ^+), the charge cut. The results are shown in Table 6-9 and Table 1 below.

FIGS. 6 to 9 show the CO ₃ O ₄ -CoO 2 composite electrode material prepared in Example 1 of the present invention, the CO ₃ O ₄ The results of the electrochemical characterization of the electrode material and the electrode material prepared by artificially mixing the cobalt oxide of Comparative Example 3 are shown in terms of charge and discharge capacities. The 1st, 2nd, 5th, and 10th are the number of charge / .

Example 1 Comparative Example 1 Comparative Example 2 Comparative Example 3 Negative active material
First discharge capacity
(mAhg ^-1 ) 821 1117 1140 1086 Negative active material
10th discharge capacity
(mAhg ^-1 ) 560 413 700 429

As shown in FIGS. 6-9 and Table 1, when the negative electrode active material was prepared by adding 3,5-dimethylpyrazole, the initial discharge capacity was found to be 821 mAhg ^-1 . When this was compared with the results shown in Comparative Example 1-3, It can be seen that the retention rate of the capacity of the electrode material is remarkably high.

< Experimental Example  4> Cyclic voltammetric method (cyclic voltammetry ) analysis

The cyclic voltammetry was measured using BioLogic's VMP3 and the instrument was controlled using the EC-LAB program. Experiments were performed on the finished battery at a temperature of 25 ° C with a scan rate fixed at 0.1 mVs ^-1 . The voltage was scanned from 0.1V to 3V and repeated four times in total. The electrochemical reaction corresponding to each reaction potential can be predicted by measuring the change in the amount of current according to the voltage condition applied through the cyclic voltammetry. The results are shown in Figs. 10 and 11.

10 is a result of analysis of the Co ₃ O ₄ -CoO composite electrode material prepared in Example 1 of the present invention by a cyclic voltammetry.

More specifically, in the anodic scan, the oxidation peak near 2.0 V is an oxidation peak in which Co is oxidized to Co ²⁺ . In the case of a cathodic scan, the reduction peak near 1.3 V after the second cycle is a reduction peak in which Co ^{2 +} is reduced to Co. The reduction peak near 0.5 V in the first cycle is a reduction peak due to the formation of a solid electrolyte interphase (SEI) layer between the electrode and the electrolyte. In particular, the amount of change during the reduction reaction due to cyclic repetition can be predicted to be progressively progressed according to the complex phase.

11 is a result of analysis of the Co ₃ O ₄ single phase electrode material prepared in Comparative Example 1 of the present invention by a cyclic voltammetry.

More specifically, the two peaks in the vicinity of 2.0V and 2.6V in the vicinity of the positive electrode scan (Anodic scan) corresponds to the peak Co Co ^{2 + 3} is oxidized to Co ^{+ 2} to Co ⁺ respectively. A peak of 1.0 V in a cathodic scan corresponds to a peak where Co ^{3 +} is reduced to Co ^{2 +} and Co ^{2 +} is reduced to Co. The huge reduction peak of 0.8 V in the first cycle is the reduction peak due to SEI layer formation between the electrode and electrolyte.

Claims (10)

Preparing a mixed solution by mixing a cobalt oxide precursor and a compound represented by the following formula (1) in a solvent (step 1);
A step (step 2) of preparing an electrode active material precursor by heating the mixed solution prepared in the step 1; And
(3) drying the electrode active material precursor prepared in the step (2) and then heat treating the electrode active material precursor prepared in the step (2)
[Chemical Formula 1]

(In the formula 1,
R ¹ and R ² are independently C _1-6 straight or branched chain alkyl.
The method according to claim 1,
Wherein the cobalt oxide precursor of step 1 is cobalt nitrate hexahydrate (Co (NO ₃ ) ₂ .6H ₂ O).
delete The method according to claim 1,
Wherein the solvent of step 1 comprises at least one selected from the group consisting of distilled water and C ₁ to C ₃ alcohols.
The method according to claim 1,
Wherein the heating in step 2 is performed by irradiating the microwave at a temperature of 100 ° C to 200 ° C for 10 minutes to 120 minutes.
The method according to claim 1,
Wherein drying in step 3 is carried out in an oven at 90 to 150 캜.
The method according to claim 1,
Wherein the heat treatment in step 3 is performed at a temperature of 400 to 1000 占 폚 for 30 minutes to 300 minutes.
An electrode active material for a lithium secondary battery, which is produced by the production method of claim 1.
A positive electrode for a lithium secondary battery comprising an electrode active material produced by the manufacturing method of claim 1.
A lithium secondary battery comprising a positive electrode for a lithium secondary battery comprising an electrode active material produced by the manufacturing method of claim 1.

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