KR20200077177A - Lithium cobalt oxide-carbon composite for positive active material for lithium ion capacitor, positive active material comprising the same, lithium ion capacitor comprising the same, and preparation method thereof - Google Patents

Abstract

The present invention relates to a lithium cobalt oxide-carbon composite for lithium ion capacitors, a positive electrode active material containing the same, a lithium ion capacitor containing the same, and a manufacturing method thereof. The lithium cobalt oxide-carbon composite for lithium ion capacitors according to an embodiment of the present invention contains a lithium metal compound and carbon, and is represented by the following formula: Li_(6-x)CoO_4·C, 0<=x<=4. Therefore, the present invention can improve doping efficiency and safety.

Description

Lithium Cobalt Oxide-Carbon Composite for Lithium Ion Capacitor, Cathode Active Material Containing It, Lithium Ion Capacitor Containing The Same, and Method for Producing The Same TECHNICAL , LITHIUM ION CAPACITOR COMPRISING THE SAME, AND PREPARATION METHOD THEREOF}

The present invention relates to a lithium cobalt oxide-carbon composite for a lithium ion capacitor, a positive electrode active material comprising the same, a lithium ion capacitor comprising the same, and a method of manufacturing the same.

2. Description of the Related Art As the spread of mobile electronic devices such as smartphones spreads, development of secondary batteries such as nickel-metal hydride batteries, lithium secondary batteries, supercapacitors, and lithium ion capacitors is actively progressing. The lithium ion capacitor (LIC) is a new concept having both the advantages of high power and long life of the existing electric double layer capacitor (EDLC) and the high energy density of the lithium ion battery. It is spotlighted as a secondary battery system.

Electric double layer capacitors have limited application in various applications due to low energy density despite excellent output characteristics and life characteristics. As a means for solving the problem of the electric double layer capacitor, a hybrid capacitor having improved energy density by applying a material capable of inserting and deintercalating lithium ions into a positive electrode active material or a negative electrode active material has been proposed. In particular, a positive electrode active material applied in an existing electric double layer capacitor is used as a positive electrode, and a lithium ion capacitor using a carbon-based material capable of intercalating and deintercalating lithium ions as a negative electrode active material has been proposed.

Since the lithium ion capacitor uses a material capable of inserting and deintercalating lithium ions at a low reaction potential as a negative electrode active material, the degree of improvement in energy density is greater than that of other hybrid capacitors. In particular, the lithium ion capacitor can significantly lower the potential of the negative electrode by pre-doping lithium ions having a high ionization tendency to the negative electrode, and the cell voltage can also be improved compared to a conventional electric double layer capacitor, thereby enabling high voltage and high energy density. Can be implemented.

However, such lithium ion capacitors require a lithium doping process for the insertion and desorption reactions of lithium as well as the electrochemical adsorption and desorption reactions. Conventional lithium doping process technology, there is a method in which the metal lithium laminated by the potential difference between the negative electrode and the metallic lithium is melted into the negative electrode by simply shorting the negative electrode and the metallic lithium by putting an electrolyte solution after laminating the metallic lithium to the electrode. However, this method is difficult to control the amount of lithium doped to the negative electrode, it is difficult to secure the safety of the lithium metal generated in the doping process, and thus there is a problem that it is difficult to apply to mass production.

Korea Patent Publication No. 2012-0035131

An object of the present invention is to provide a lithium cobalt oxide-carbon composite for a lithium ion capacitor capable of stably doping electrochemically lithium on a negative electrode, a positive electrode active material comprising the same, a lithium ion capacitor comprising the same, and a method of manufacturing the same. . In addition, it is possible to provide a lithium cobalt oxide-carbon composite for lithium ion capacitors that can be stably processed in a moisture environment.

In addition, it is possible to improve the doping efficiency and safety, and to provide a manufacturing method suitable for mass production.

In addition, it is possible to provide a lithium ion capacitor having high energy density, excellent output characteristics and life characteristics.

The lithium cobalt oxide-carbon composite for a lithium ion capacitor according to an embodiment of the present invention includes a lithium metal compound and carbon, and is represented by the following formula.

[Formula]

Li _6-x CoO ₄ · C

In the above formula, 0≤x≤4.

The content of the carbon may be 5 wt% or less with respect to the entire composition.

The carbon may be derived from sucrose.

The positive electrode active material for a lithium ion capacitor according to an embodiment of the present invention includes a lithium metal compound and carbon, and includes a lithium cobalt oxide-carbon composite represented by the following formula.

[Formula]

Li _6-x CoO ₄ · C

In the above formula, 0≤x≤4.

A lithium ion capacitor according to an embodiment of the present invention includes a lithium metal compound and carbon, and includes a positive electrode active material for a lithium ion capacitor represented by the following formula.

[Formula]

Li _6-x CoO ₄ · C

In the above formula, 0≤x≤4.

A method of manufacturing a positive electrode active material additive for a lithium ion capacitor according to an embodiment of the present invention comprises the steps of mixing a lithium precursor, cobalt oxide and a reducing agent to form a mixture; Heat treating the mixture; And obtaining a lithium cobalt oxide-carbon composite for lithium ion capacitors from the heat-treated mixture.

The lithium precursor may be lithium hydroxide.

The reducing agent may be sucrose.

In the step of forming the mixture, the content of the lithium precursor may be 65 to 78 wt% with respect to the entire mixture, and the content of the cobalt oxide may be 17 to 30 wt% with respect to the entire mixture.

In the step of forming the mixture, the content of the reducing agent may be 4 to 6 wt% based on the entire mixture.

The heat treatment may be performed at a temperature of 750 to 950°C for 5 to 20 hours.

The lithium cobalt oxide-carbon composite for a lithium ion capacitor according to an embodiment of the present invention can stably doping lithium on the negative electrode electrochemically. In addition, it is possible to provide a lithium cobalt oxide-carbon composite for lithium ion capacitors that can be stably processed in a moisture environment.

In addition, it is possible to improve the doping efficiency and safety, and to provide a manufacturing method suitable for mass production.

In addition, it is possible to provide a lithium ion capacitor having high energy density, excellent output characteristics and life characteristics.

1 shows a lithium ion capacitor according to an embodiment of the present invention.
Figure 2 shows a method of manufacturing a lithium cobalt oxide-carbon composite for lithium ion capacitors according to an embodiment of the present invention.
3 is an EDS analysis result of the embodiment.
4 shows the XRD analysis results of the examples, and FIGS. 5 to 11 show the XRD analysis results of Comparative Examples 1 to 7.
12 is an electrical characteristic analysis graph of an embodiment, and FIGS. 13 and 14 are electrical characteristic analysis graphs of Comparative Examples 6 and 7, respectively.
15 is an XRD graph for evaluation of moisture stability in Examples.
16 is an XRD graph of moisture stability evaluation of Comparative Example 1.
17 is a graph showing a voltage change according to a capacity during pre-doping.
18 is a graph showing a voltage change according to the capacity of a lithium ion capacitor during charging and discharging.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. However, the embodiments of the present invention may be modified in various other forms, and the scope of the present invention is not limited to the embodiments described below. In addition, embodiments of the present invention are provided to more fully describe the present invention to those skilled in the art.

Lithium cobalt oxide-carbon composite for lithium ion capacitors

The lithium cobalt oxide-carbon composite for a lithium ion capacitor according to an embodiment of the present invention includes a lithium metal compound and carbon and is represented by the following formula.

[Formula]

Li _6-x CoO ₄ · C

In the above formula, 0≤x≤4.

The lithium metal compound may be present in a crystalline or amorphous phase, and carbon may be disposed as an atom, a crystalline phase, or an amorphous phase in the grain or amorphous phase of the lithium metal compound phase. The chemical formula of the lithium metal compound is represented by Li _6-x CoO ₄ , and 0≤x≤4 in the above formula.

The content of carbon in the total lithium cobalt oxide-carbon composite may be 10 wt% or less, preferably 5 wt% or less. Carbon is derived from a reducing agent during the process of preparing a lithium cobalt oxide-carbon composite, and the content in the final product lithium cobalt oxide-carbon composite can be determined by controlling the total amount of reducing agent added. Specifically, the carbon may be derived from sucrose.

The lithium cobalt oxide-carbon composite for lithium ion capacitors may have an average particle size of 10 μm or less. Lithium ion capacitors using the average particle diameter range may have high capacity and high efficiency characteristics.

Positive electrode active material for lithium ion capacitors

The positive electrode active material for a lithium ion capacitor according to an embodiment of the present invention includes a lithium metal compound and carbon, and includes a lithium cobalt oxide-carbon composite represented by the following formula.

[Formula]

Li _6-x CoO ₄ · C

In the above formula, 0≤x≤4.

In addition, a binder and a conductive material may be further included, and the lithium cobalt oxide-carbon composite for lithium ion capacitor, a binder, or a conductive material may be in a liquid or gel form mixed with a solvent.

The lithium cobalt oxide-carbon composite is described above.

The content of each component in the positive electrode active material for a lithium ion capacitor may be 20 to 50 wt% of a lithium cobalt oxide-carbon composite, 1 to 60 wt% of a binder, and 1 to 10 wt% of a conductive agent with respect to the entire positive electrode active material, and a solvent therein It may further include 1 to 20wt%.

The binder is not particularly limited as long as it is generally used in the art, for example, polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, Polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene butylene rubber and fluorine rubber.

The conductive agent is not particularly limited as long as it is a conductive material generally used in the art, for example graphite; Carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, metal powder and metal oxide.

The solvent may be an organic solvent or water.

Lithium ion capacitor

1 shows a lithium ion capacitor 100 according to an embodiment of the present invention.

The lithium ion capacitor 100 according to an embodiment of the present invention includes a lithium metal compound and carbon, and includes a positive electrode active material for a lithium ion capacitor represented by the following formula.

[Formula]

Li _6-x CoO ₄ · C

In the above formula, 0≤x≤4.

Referring to FIG. 1, the lithium ion capacitor 100 includes a positive electrode current collector 120, a positive electrode active material 110 disposed on the positive electrode current collector 120, a negative electrode current collector 140, and the negative electrode current collector 140. ) The negative electrode active material 130 disposed on, the positive electrode active material 110 and the negative electrode active material 130 disposed between the separation membrane 150 and the positive electrode active material 110 and negative electrode active material 130 in the movement path of lithium ions It may be configured to include an electrolyte 160 to provide.

The positive electrode active material for a lithium ion capacitor is described above.

The positive electrode current collector and the negative electrode current collector function as a support for supporting the positive electrode active material and the negative electrode active material, respectively, and are connected to external electrodes to provide a current passage. The positive electrode current collector and the negative electrode current collector may be in the form of a film, porous body, foam, or mesh, and may be made of a conductive material such as stainless steel or aluminum.

The negative electrode active material may be a carbon-based material capable of intercalating and deintercalating lithium ions, and is not particularly limited.

The electrolyte solution serves as a medium capable of transferring lithium ions, and includes an electrolyte and a solvent. The electrolyte may include any one of LiPF ₆ , LiBF ₄ and LiCIO ₄ lithium salts, and is not particularly limited.

The separator may include a hole through which lithium ions can pass, and may be made of a polymer material such as a polypropylene film.

Method for manufacturing lithium cobalt oxide-carbon composite for lithium ion capacitor

Figure 2 shows a method of manufacturing a lithium cobalt oxide-carbon composite for lithium ion capacitors according to an embodiment of the present invention.

A method of manufacturing a lithium cobalt oxide-carbon composite for a lithium ion capacitor according to an embodiment of the present invention comprises: mixing a lithium precursor, cobalt oxide and a reducing agent to form a mixture; Heat treating the mixture; And obtaining a lithium cobalt oxide-carbon composite for lithium ion capacitors from the heat-treated mixture.

In the step of forming the mixture, lithium precursor, cobalt oxide, and a reducing agent may be mixed using a stirrer or a mixer.

The cobalt oxide may be mixed in a powder state, in which case the average particle diameter of the cobalt oxide powder may be 10 to 100 μm. The cobalt oxide may have a formula of CoO or Co ₃ O ₄ .

The lithium precursor may be lithium hydroxide, lithium carbonate, lithium fluoride, and mixtures thereof, preferably lithium hydroxide. The lithium precursor may be mixed in a powder state, in which case the average particle diameter of the lithium precursor may be 10 to 50 μm.

The reducing agent may be a material containing carbon, preferably sucrose. Li _6-x CoO ₄ ·C can be stably produced by using sucrose as the reducing agent.

In this step, in the step of forming the mixture, the content of the lithium precursor may be 65 to 78 wt%, preferably 70 to 75 wt% with respect to the entire mixture. The content of the cobalt oxide may be 17 to 30 wt%, preferably 20 to 25 wt% with respect to the entire mixture. In the step of forming the mixture, the content of the reducing agent may be 4 to 6 wt% based on the entire mixture. By controlling the content of each component in this way, the formation of unreacted substances or impurities in the finally produced lithium cobalt oxide-carbon composite can be minimized, thereby maximizing the efficiency of the prepared positive electrode active material.

The heat treatment may be performed at a temperature of 750 to 950°C for 5 to 20 hours. When the heat treatment temperature is less than 750°C, the lithium precursor, cobalt oxide, and reducing agent do not react sufficiently, so there is a problem that unreacted lithium precursor and cobalt oxide remain, and when it exceeds 950°C, the produced lithium cobalt oxide- A problem that the sphericity and density of the carbon composite are lowered may occur, and a problem that cobalt oxide remains may occur.

Next, a lithium cobalt oxide-carbon composite for a lithium ion capacitor is obtained from the heat-treated mixture. In this step, it may further include a step of washing and drying the heat-treated mixture as necessary.

Method for manufacturing a positive electrode for a lithium ion capacitor

The positive electrode includes a positive electrode current collector and a positive electrode active material disposed on the positive electrode current collector. A method of manufacturing a positive electrode according to an embodiment of the present invention includes: forming a mixture by mixing a lithium cobalt oxide-carbon composite for a lithium ion capacitor, a conductive agent, a binder, and a solvent prepared by the method described above; Applying the mixture to a positive electrode current collector; And drying the mixture applied to the positive electrode current collector.

In the step of forming a mixture by mixing the lithium cobalt oxide-carbon composite for a lithium ion capacitor, a conductive agent, a binder, and a solvent, the content of each component is 1 to 60 wt% of the binder, 1 to 10 wt% of the conductive agent to the entire mixture , A solvent of 1 to 20 wt% and the balance lithium cobalt oxide-carbon composite. In addition, the content of the lithium cobalt oxide-carbon composite may be 20 to 50 wt% with respect to the entire mixture.

The binder is not particularly limited as long as it is generally used in the art, for example, polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, Polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene butylene rubber and fluorine rubber.

The conductive agent is not particularly limited as long as it is a conductive material generally used in the art, for example graphite; Carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, metal powder and metal oxide.

The solvent may be an organic solvent or water.

In the step of applying the mixture to the positive electrode current collector, the positive electrode current collector functions as a support for supporting the positive electrode active material, and is connected to an external electrode to provide a current passage. The positive electrode current collector may be a film, a porous body, a foam, a mesh shape, or the like, and may be made of a conductive material such as stainless steel or aluminum.

Examples and comparative examples

Example

As a lithium precursor, L&F's lithium hydroxide (LiOH.H ₂ O) 0.7583g, L&F's cobalt oxide (Co ₃ O ₄ ) 0.2417g, and Sigma Aldrich's Sucrose 0.0556g as a reducing agent were mixed and dry mixed. Run for 30 minutes. The content of sucrose in the whole mixture was 5.3 wt%.

Next, the mixture was heat treated in an Ar atmosphere. The heat treatment was performed by heating at 800° C. at a heating rate of 5° C./min, and maintaining at 800° C. for 10 hours.

Next, the heated mixture was gradually cooled to room temperature to obtain a lithium cobalt oxide-carbon composite for lithium ion capacitors.

Comparative Example 1

It was prepared in the same manner as in Example, except that only lithium hydroxide and cobalt oxide were mixed without a reducing agent.

Comparative Example 2

It was prepared in the same manner as in Example, except that 0.0556 g of stearic acid was used instead of sucrose as a reducing agent.

Comparative Example 3

It was prepared in the same manner as in Example, except that 0.0556 g of Super P was mixed instead of sucrose as a reducing agent.

Comparative Example 4

It was prepared in the same manner as in Example, except that the heat treatment temperature was set to 700 ℃.

Comparative Example 5

It was prepared in the same manner as in Example, except that the heat treatment temperature was set to 900 ℃.

Comparative Example 6

It was prepared in the same manner as in Example, except that the content of sucrose was mixed to 0.0252g. The content of sucrose in the whole mixture was 2.4 wt%.

Comparative Example 7

It was prepared in the same manner as in Example, except that the content of sucrose was mixed to 0.0923g. The content of sucrose in the total mixture was 8.8 wt%.

Experimental example

EDS analysis

3 is an EDS analysis result of the embodiment. According to the EDS analysis, the contents of C, O, and Co included in Examples are shown in Table 1.

element Wt% C 3.24 O 58.11 Co 38.66 total 100.00

XRD analysis

XRD analysis was performed for Examples and Comparative Examples 1 to 7 using Cu-Kα1 radiation. 4 shows the XRD analysis results of the examples, and FIGS. 5 to 11 show the XRD analysis results of Comparative Examples 1 to 7.

4 to 7, it can be seen that when sucrose is added as a reducing agent, the final product is produced in a stable form as compared to a case where a reducing agent is not added or another carbon source is added. When no reducing agent is added or another type of carbon source is added, materials such as α-Co and β-Co are generated, and when this is used as a positive electrode active material, pre-doping of the negative electrode may not be efficiently performed.

4, 8 and 9, it can be seen that when the heat treatment temperature is 800°C, the final product is produced in a stable form. When the heat treatment temperature is 700°C and 900°C, a material such as CoO is generated, and when it is used as a positive electrode active material, pre-doping of the negative electrode may not be efficiently performed.

4, 10 and 11, when the content of the reducing agent is 5.3wt%, it can be seen that the final product is produced in a stable form. When the content of the reducing agent is 2.4wt% and 8.8wt, substances such as α-Co, β-Co, and CoO are generated, and when this is used as a positive electrode active material, pre-doping of the negative electrode may not be efficiently performed.

Electrical characteristic analysis

To analyze the electrical characteristics, a coin cell was prepared and a coin cell test was conducted. The positive electrode was prepared by mixing the composites, Super P and PVdF obtained in Examples and Comparative Examples in a weight ratio of 90:5:5, respectively, and a negative electrode was used for lithium metal. As the electrolyte, 1.3M LiPF ₆ in EC:DMC=3:7 (v/v) was used. Charge and discharge conditions were applied CC, cut-off 2.0 to 4.3V, and 3 cycles were performed with 0.1C charge/discharge.

12 is an electrical characteristic analysis graph of an embodiment, and FIGS. 13 and 14 are electrical characteristic analysis graphs of Comparative Examples 6 and 7, respectively. Table 2 describes the electrical properties analysis results of Examples and Comparative Examples 6 and 7.

Number of cycles Example Comparative Example 6 Comparative Example 7 Charging capacity
(mAh/g) Discharge capacity
(mAh/g) Charging capacity
(mAh/g) Discharge capacity
(mAh/g) Charging capacity
(mAh/g) Discharge capacity
(mAh/g) 1 time 606.37 7.58 390.27 9.35 412.29 11.58 Episode 2 6.22 4.71 22.30 7.05 14.49 8.44 3rd time 3.38 3.78 14.68 5.76 9.37 5.92

Referring to Table 2 and FIGS. 12 to 14, it can be seen that the charging and discharging characteristics are improved in the case of the embodiment.

Moisture stability evaluation

Example and Comparative Example 1 was left for 30 minutes at a temperature of 30°C and a relative humidity of 25%, and then XRD was measured using Cu-Kα1 radiation. 15 is an XRD graph for evaluating moisture stability in Examples, and FIG. 16 is an XRD graph for evaluating moisture stability in Comparative Example 1.

In the case of the example, when comparing FIGS. 4 and 15, it can be seen that there is no change in the peak on the XRD graph. On the other hand, in Comparative Example 1, when comparing FIGS. 5 and 16, it can be seen that the peak height on the XRD graph is changed. Through this, it can be seen that the embodiment has higher water stability than the comparative example.

Analysis of electrical properties of lithium ion capacitors

To analyze the electrical properties of the lithium ion capacitor, a Beaker cell test was performed. The positive electrode was prepared by mixing the composites obtained in Examples and Comparative Examples, activated carbon (AC), Super P and PVdF in a ratio of 18:72:5:5 by weight, respectively, and the negative electrode was natural graphite (Natural graphite). ), CMC and SBR were prepared by mixing in a ratio of 96:2:2 by weight, respectively. As the electrolyte, 1.3M LiPF ₆ in EC:DMC=3:7 (v/v) was used.

17 is a graph showing a voltage change according to a capacity during pre-doping. Pre-doping was performed by charging up to 4.2V under 0.1C conditions.

18 is a graph showing a voltage change according to the capacity of a lithium ion capacitor during charging and discharging. For the charge/discharge conditions, cut-off 1.5-3.9V was applied, and two cycles were performed with 0.1C charge/discharge.

The present invention is not limited by the above-described embodiments and the accompanying drawings, but is intended to be limited by the appended claims. Accordingly, various forms of substitution, modification, and modification will be possible by those skilled in the art without departing from the technical spirit of the present invention as set forth in the claims, and this also belongs to the scope of the present invention. something to do.

100: lithium ion capacitor
110: positive electrode active material
120: anode current collector
130: negative electrode active material
140: cathode current collector
150: separator
160: electrolyte

Claims (13)

Containing lithium metal compounds and carbon,
Represented by the following formula,
Lithium cobalt oxide-carbon composite for lithium ion capacitors:
[Formula]
Li _6-x CoO ₄ · C
In the above formula, 0≤x≤4.
According to claim 1,
The content of the carbon is 5wt% or less with respect to the entire composition,
Lithium cobalt oxide-carbon composite for lithium ion capacitors.
According to claim 1,
The carbon is derived from sucrose (sucrose),
Lithium cobalt oxide-carbon composite for lithium ion capacitors.
A lithium metal compound and a carbon containing a lithium cobalt oxide-carbon composite represented by the following formula,
Positive active material for lithium ion capacitors:
[Formula]
Li _6-x CoO ₄ · C
In the above formula, 0≤x≤4.
It includes a lithium metal compound and carbon and includes a positive electrode active material for a lithium ion capacitor represented by the following formula,
Lithium ion capacitor.
[Formula]
Li _6-x CoO ₄ · C
In the above formula, 0≤x≤4.
Mixing a lithium precursor, cobalt oxide, and a reducing agent to form a mixture;
Heat treating the mixture; And
Including the step of obtaining a lithium cobalt oxide-carbon composite for a lithium ion capacitor from the heat-treated mixture;
Method for manufacturing lithium cobalt oxide-carbon composite for lithium ion capacitors.
The method of claim 6,
The lithium precursor is lithium hydroxide,
Method for manufacturing lithium cobalt oxide-carbon composite for lithium ion capacitors.
The method of claim 7,
The reducing agent is sucrose (sucrose),
Method for manufacturing lithium cobalt oxide-carbon composite for lithium ion capacitors.
The method of claim 7,
In the step of forming the mixture,
The content of the lithium precursor is 65 to 78 wt% with respect to the entire mixture
Method for manufacturing lithium cobalt oxide-carbon composite for lithium ion capacitors.
The method of claim 7,
In the step of forming the mixture,
The content of the cobalt oxide is 17 to 30 wt% based on the total mixture
Method for manufacturing lithium cobalt oxide-carbon composite for lithium ion capacitors.
The method of claim 7,
In the step of forming the mixture,
The content of the reducing agent is 4 to 6wt% relative to the entire mixture,
Method for manufacturing lithium cobalt oxide-carbon composite for lithium ion capacitors.
The method of claim 7,
The heat treatment step,
Carried out at a temperature of 750 to 950°C,
Method for manufacturing lithium cobalt oxide-carbon composite for lithium ion capacitors.
The method of claim 7,
The heat treatment step,
Performed for 5 to 20 hours,
Method for manufacturing lithium cobalt oxide-carbon composite for lithium ion capacitors.

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