KR102570628B1 - Electrochemical device - Google Patents

Abstract

An electrochemical device according to an embodiment of the present invention includes a positive electrode containing coke-based activated carbon, a negative electrode containing palm tree-based activated carbon, and a separator interposed between the positive electrode and the negative electrode, and the mass of the coke-based activated carbon in the positive electrode and the The mass of the palm tree-based activated carbon in the negative electrode satisfies Equation 1 below.
[Equation 1]
|([M _C ] - [M _P ])|/([Mc]+[Mp]) ≤ 0.05
(In Equation 1, [M _C ] represents the mass of coke-based activated carbon in the positive electrode, and [M _P ] represents the mass of palm tree-based activated carbon in the negative electrode.)

Description

Electrochemical device {ELECTROCHEMICAL DEVICE}

It relates to electrochemical devices. More specifically, it relates to an electrochemical device having excellent capacity and lifespan characteristics even when different types of active materials are applied to the positive electrode and the negative electrode so as to have the same thickness.

Recently, as interest in energy storage and conversion technologies has increased, interest in various types of electrochemical devices has been focused.

Among the electrochemical devices, the Electric Double Layer Capacitor (EDLC) is a pair of two electrodes with a different sign on the opposite side by arranging two electrodes, an anode and a cathode, facing each other with a separator (separator) in between. As an energy storage medium using the electric charge layer (electric double layer) of

In the case of an electric double layer capacitor, it is known that the potential of the positive electrode and the negative electrode are the same during charging/discharging, and it is known that a high voltage can be obtained by adjusting the potential of the positive electrode.

In the conventional method for adjusting the electrode potential of the electric double layer capacitor, the voltage of the cell is increased by varying the weight of the positive electrode and the negative electrode, and by setting a difference in resistance between the positive electrode and the negative electrode. That is, in adjusting the thickness of the positive electrode active material and the negative electrode active material, the thickness of the positive electrode active material is increased to increase the voltage of the cell due to the difference in resistance between the positive electrode and the negative electrode.

Alternatively, the electrode potential is controlled by adjusting the mass of the active material applied to the positive electrode and the negative electrode.

However, since the above method cannot effectively control the potential difference between the anode and the cathode, there is a limit to improving voltage or energy density.

An electrochemical device is provided. More specifically, an electrochemical device having excellent capacity and lifespan characteristics is provided even when different types of active materials are applied to the positive electrode and the negative electrode so as to have the same thickness.

An electrochemical device according to an embodiment of the present invention includes a positive electrode including coke-based activated carbon, a negative electrode including palm tree-based activated carbon, and a separator interposed between the positive electrode and the negative electrode, and the mass and negative electrode of the coke-based activated carbon in the positive electrode. The mass of the palm tree-based activated carbon within satisfies Equation 1 below.

[Equation 1]

|([Mc]-[Mp])|/([Mc]+[Mp]) 0.05

(In Equation 1, [Mc] represents the mass of coke-based activated carbon in the positive electrode, and [Mp] represents the mass of palm tree-based activated carbon in the negative electrode.)

The coke-based activated carbon includes mesopores with a diameter of 2 to 50 nm and micropores with a diameter of less than 2 nm, and the volume ratio of the micropores to the sum of the volumes of the mesopores and the micropores is 70 to 90%. can be

The coke-based activated carbon may have a total specific surface area (BET) of 2100 to 2500 m ² /g.

The palm tree-based activated carbon includes mesopores with a diameter of 2 to 50 nm and micropores with a diameter of less than 2 nm, and the volume ratio of the micropores to the sum of the volumes of the mesopores and the micropores is 60% or more, and may be less than 80%.

The palm tree-based activated carbon may have a total specific surface area (BET) of 1700 to 2100 m ² /g.

A difference between the thickness of the coke-based activated carbon in the positive electrode and the thickness of the palm tree-based activated carbon in the negative electrode may be 15 μm or less.

In one embodiment of the present invention, an electrochemical device having excellent capacity and lifespan characteristics may be obtained by applying different types of active materials to the cathode and anode, even if the thickness is the same.

1 is a result of pore structure analysis and surface area analysis of an active material in Preparation Example.
2 is a graph measuring capacitance versus charge/discharge rate in Experimental Example 1;
3 is a graph of measuring capacitance per cycle in Experimental Example 1;
4 is a bulk resistance analysis result of EIS components before and after cycles in Experimental Example 1.
5 is an analysis result of interfacial resistance among EIS components before and after cycles in Experimental Example 1.
6 is a graph measuring capacitance versus charge/discharge rate in Experimental Example 2.

In the present specification, when a certain component is said to "include", it means that it may further include other components without excluding other components unless otherwise stated. As used throughout this specification, the terms "about," "substantially," and the like are used at or approximating that value when manufacturing and material tolerances inherent in the stated meaning are given, and do not convey the understanding of this application. Accurate or absolute figures are used to help prevent exploitation by unscrupulous infringers of the disclosed disclosure. The term "step of (doing)" or "step of" as used throughout the present specification does not mean "step for".

In this specification, the term "combination of these" included in the expression of the Markush form means a mixture or combination of one or more selected from the group consisting of the components described in the expression of the Markush form, It means including one or more selected from the group consisting of.

Based on the above definition, embodiments of the present invention will be described in detail. However, these are presented as examples, and thereby the present invention is not limited and the present invention is only defined by the scope of the claims to be described later.

In one embodiment of the present invention, the electrochemical device may be an electrostatic double-layer capacitor.

Hereinafter, each configuration of the electrochemical device will be described in detail.

An electrochemical device according to an embodiment of the present invention includes a positive electrode containing coke-based activated carbon, a negative electrode containing palm tree-based activated carbon, and a separator interposed between the positive electrode and the negative electrode.

The positive electrode may be formed by applying or attaching a positive electrode active material to a positive electrode current collector. Similarly, the negative electrode may be formed by applying or attaching an anode active material to the negative electrode current collector. More specifically, the slurry is formed by mixing the active material, the conductive material, the binder, and the solvent in a mixer. The slurried mixture may be formed by applying it on a current collector such as aluminum foil and then drying it by convection to evaporate the solvent to attach the active material (electrode layer) to the current collector.

As the positive electrode current collector and the negative electrode current collector, the material of the current collector of the electrochemical device may be used without limitation. For example, one or more selected from the group consisting of aluminum, stainless steel, titanium, tantalum, or niobium may be used. The shape of the positive electrode current collector may be a shape having holes penetrating the front and back surfaces, such as an etched metal foil, an expanded metal, a punched metal, a net, or a foam, as well as a metal foil.

Conductive materials may include conductive powders such as Super-P, Ketjen Black, acetylene black, carbon black, and graphite, but are not limited thereto, and may include all types of conductive materials used in general electrochemical devices. there is.

Examples of the binder include fluorine-based resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF); thermoplastic resins such as polyimide, polyamideimide, polyethylene (PE), and polypropylene (PP); cellulosic resins such as carboxymethylcellulose (CMC); At least one selected from rubber-based resins such as styrene-butadiene rubber (SBR) and mixtures thereof may be used, but is not particularly limited thereto, and all binder resins used in conventional electrochemical devices may be used.

The separator according to the present invention can use all materials used in conventional electrochemical devices without limitation. For example, polyethylene (PE), polypropylene (PP), polyvinylidene fluoride (PVDF), polyvinylidene chloride, polyacrylonitrile (PAN), polyacrylamide (PAAm), polytetrafluoroethylene ( PTFE), polysulfone, polyethersulfone (PES), polycarbonate (PC), polyamide (PA), polyimide (PI), polyethylene oxide (PEO), polypropylene oxide (PPO), cellulosic polymers, and poly and a microporous film made of one or more polymers selected from the group consisting of acrylic polymers. In addition, a multilayer film obtained by polymerizing the porous film may be used, and among these, a cellulose-based polymer may be preferably used.

Alternatively, it may include an electrolyte solution as a separator, and the electrolyte solvent is used to dissolve or dissociate electrolyte salts, and is not particularly limited as long as it is used as an electrolyte solvent for conventional electrolytes, and cyclic carbonates, linear carbonates, lactones, ethers , esters, sulfoxides, acetonitrile, lactams, ketones, and halogen derivatives thereof, etc. may be used alone or in combination of two or more. Examples of cyclic carbonates include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), fluoroethylene carbonate (FEC), and the like, and examples of linear carbonates include diethyl carbonate (DEC), dimethyl carbonate (DMC), ), dipropyl carbonate (DPC), ethyl methyl carbonate (EMC), and methyl propyl carbonate (MPC). Examples of lactones include gamma butyrolactone (GBL), examples of ethers include dibutyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, 1, 2-diethoxyethane and the like. Examples of the ester include methyl formate, ethyl formate, propyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, butyl propionate, methyl pivalate, and the like. In addition, the sulfoxide includes dimethyl sulfoxide and the like, the lactam includes N-methyl-2-pyrrolidone (NMP) and the like, and the ketone includes polymethylvinyl ketone. In addition, these halogen derivatives can also be used, and are not limited to the above-exemplified electrolyte solution electrolytic solvents. In addition, these electrolysis solvents can be used individually or in mixture of 2 or more types.

The electrolyte solution may further include an electrolyte salt. The electrolyte salt is dissociated in an electrolytic solvent and acts as a component of ion conduction in an electrochemical device, and may serve to promote the movement of cations between an anode and a cathode. For example, it may be SBPBF ₄ (spirobipyrrolidinium tetrafluoroborate), TEABF ₄ , EMIBF 4 , TEMABF ₄ , or a combination thereof. The amount of the electrolyte salt in the gel polymer electrolyte may be 0.5 to 3.0 M in moles (mol) based on the electrolyte solvent (L) in the electrolyte. In this case, the gel polymer electrolyte may have an appropriate viscosity in the form of a gel, and the electrolyte salt may be dissolved in an electrolyte solvent to contribute to the effective movement of cations.

In one embodiment of the present invention, an electrochemical device having excellent capacity and lifespan can be obtained even if the thickness is the same by applying different types of active materials for the positive electrode and the negative electrode.

Specifically, coke-based activated carbon may be used as the cathode active material. In addition, palm tree-based activated carbon may be used as the anode active material. As such, by applying different types of active materials for the positive electrode and the negative electrode, an electrochemical device having excellent capacity and lifespan can be obtained.

Coke-based activated carbon applied to the cathode active material contributes to improving the capacity of an electrochemical device. Coke-based activated carbon means activated carbon that is activated by using coke as a raw material.

The coke-based activated carbon includes mesopores with a diameter of 2 to 50 nm and micropores with a diameter of less than 2 nm, and the volume ratio of the micropores to the sum of the volumes of the mesopores and the micropores is 70 to 90%. can In addition, the coke-based activated carbon may have a total specific surface area (BET) of 2100 to 2500 m ² /g. Thus, the capacity can be improved through appropriate pore characteristics. More specifically, the volume ratio of micropores to the sum of the volumes of mesopores and micropores in the coke-based activated carbon may be 80 to 85%. In addition, the coke-based activated carbon may have a specific surface area (BET) of 2400 to 2500 m ² /g.

Palm tree-based activated carbon applied to the negative electrode active material contributes to improving the lifespan of the electrochemical device. When the same amount of active material is coated on the positive electrode and the negative electrode, a larger overvoltage is generated at the negative electrode, which adversely affects the pores of the active material due to the repulsive force between electrons and ions. In severe cases, cracks and detachment between active materials may also occur, and furthermore, detachment from the aluminum current collector may also occur.

When palm tree-based activated carbon is used as an anode active material, the above-described active material deterioration phenomenon occurs relatively little. Palm tree-based activated carbon refers to activated carbon that is activated using coke as a raw material.

Palm-based activated carbon includes mesopores with a diameter of 2 to 50 nm and micropores with a diameter of less than 2 nm, and the volume ratio of the micropores to the sum of the volumes of the mesopores and the micropores is It may be greater than 60% and less than 80%. In addition, the palm tree-based activated carbon may have a total specific surface area (BET) of 1700 to 2100 m ² /g. As such, the lifespan can be improved through proper pore characteristics. More specifically, in the palm tree-based activated carbon, the ratio of the volume of the micropores to the sum of the volumes of the mesopores and the micropores may be 75% to 79%. In addition, the palm tree-based activated carbon may have a specific surface area (BET) of 2000 to 2100 m ² /g.

The mass of the coke-based activated carbon in the positive electrode and the mass of the palm tree-based activated carbon in the negative electrode satisfy Equation 1 below.

[Equation 1]

|([Mc]-[Mp])|/([Mc]+[Mp]) 0.05

(In Equation 1, [Mc] represents the mass of coke-based activated carbon in the positive electrode, and [Mp] represents the mass of palm tree-based activated carbon in the negative electrode.)

When Equation 1 is satisfied, it is advantageous in that the maximum capacity can be realized because the maximum amount of the active material can be used. More specifically, the value of Equation 1 may be 0 to 0.01.

A difference between the thickness of the coke-based activated carbon in the positive electrode and the thickness of the palm tree-based activated carbon in the negative electrode may be 15 μm or less. The capacity can be further improved by reducing the difference between the thickness of the coke-based activated carbon in the positive electrode and the thickness of the palm tree-based activated carbon in the negative electrode.

Hereinafter, preferred embodiments of the present invention are described. However, the following example is only a preferred embodiment of the present invention, but the present invention is not limited to the following example.

manufacturing example

Coke-based activated carbon was prepared as an active material (Preparation Example 1). In addition, palm tree-based activated carbon was prepared as an active material (Preparation Example 2).

Pore structures and surface areas of the active materials of Preparation Examples 1 and 2 were analyzed and summarized in FIG. 1 and Table 1.

S _micro
(m ² /g, t-plot) S _meso
(m ² /g, BJH) S _total
(m ² /g, S _micro + S _meso ) V _micro
(cm ³ /g, t-plot) V _meso
(cm ³ /g, BJH) V _total
(cm ³ /g, V _micro + V _meso ) Production Example 1 (coke-based activated carbon) 2138 347.7 2486 0.97 0.21 1.18 Production Example 2 (palm-based activated carbon) 1712.8 305.8 2019 0.76 0.22 0.98

Experimental Example 1: Evaluation according to the type of cathode and anode active materials

Example 1

The coke-based activated carbon of Preparation Example 1 was used as the positive electrode active material and the palm tree-based activated carbon of Preparation Example 2 was used as the negative electrode active material.

An electrode was prepared by coating an aluminum current collector using an active material. The amount of active material was the same at 0.0545 g each for the positive and negative electrodes, and the thickness was 163 equal to m.

A cellulose separator was interposed between the electrodes, and assembled into a pouch cell.

As an electrolyte, an electrolyte in which 1M SBPBF ₄ salt was dissolved in acetonitrile (ACN) was used.

Comparative Example 1

The same procedure as in Example 1 was performed except that the coke-based activated carbon of Preparation Example 1 was used as the positive electrode active material and the coke-based activated carbon of Preparation Example 1 was used as the negative electrode active material.

Comparative Example 2

The same procedure as in Example 1 was performed except that the palm tree-based activated carbon of Preparation Example 2 was used as the positive electrode active material and the palm tree-based activated carbon of Preparation Example 2 was used as the negative electrode active material.

Comparative Example 3

The same procedure as in Example 1 was performed except that the palm tree-based activated carbon of Preparation Example 2 was used as the positive electrode active material and the coke-based activated carbon of Preparation Example 1 was used as the negative electrode active material.

Charge/discharge performance measurement

Cells prepared in Example 1 and Comparative Examples 1 to 3 were tested at 20 ° C. at rates of 0.1, 0.2, 0.4, 0.8, 1.6, 3.2 A / g, CC (constant current; galvanostatic) charge, CC discharge, 0 ~ 3.0 V charge/discharge was performed. After conducting the cycle experiment 5 times for each rate, the 5th cycle capacity for each rate was measured and shown in FIG. 2 .

As shown in FIG. 2 , it can be confirmed that Comparative Example 1 exhibits the highest capacitance at the overall charge/discharge rate. In the case of Comparative Example 2, it shows the lowest capacitance. On the other hand, in the case of Comparative Example 3 and Example 1, which are asymmetric systems in which the active materials of the positive electrode and the negative electrode are different from each other, it can be confirmed that Comparative Example 3 using palm trees as the positive electrode has higher capacitance at the overall charge and discharge rate than Example 1. . In the case of Example 1, it can be seen that improved capacity characteristics are shown compared to Comparative Example 2.

Cycle life evaluation

Cells prepared in Example 1 and Comparative Examples 1 to 3 were charged and discharged 5000 times with CC-charge and CC-discharge at 0 to 3.0 V at a rate of 3.2 A g-1 at room temperature of 20 ° C. The charge/discharge cycle capacity was measured and shown in FIG. 3 .

As shown in Figure 3, in the case of Comparative Example 1 and Comparative Example 3 it can be seen that the lowest life characteristics. Comparative Example 1 and Comparative Example 3 both use coke activated carbon for the negative electrode, and it can be seen that the initial capacity is high, but the lifespan is continuously reduced. Comparative Example 2 and Example 1 have the best lifespan characteristics, but it can be seen that Example 1, which has a higher initial capacitance, maintains higher capacitance during cycles than Comparative Example 2.

EIS resistance evaluation

EIS was measured in the frequency range between 30 mHz and 200 kHz with an amplitude of 10 mV while the cells prepared in Example 1 and Comparative Examples 1 to 3 were charged at 3.0 V before and after cycle life evaluation at 20 ° C. .

As shown in FIGS. 4 and 5, it can be seen that each resistance component increases after the cycle as a whole compared to before the cycle, but the interface resistance increases at a greater rate than the bulk resistance. In the case of Comparative Example 1 and Comparative Example 3, in which life characteristics were deteriorated, it was confirmed that the interface resistance increased very significantly, which is greater overvoltage at the negative electrode that can be generated when the same amount of active material is coated and used for the negative electrode This is because of the coke-based activated carbon.

On the other hand, in Comparative Example 2 and Example 1, it can be confirmed that such active material degradation has occurred relatively little, and it can be confirmed that using palm tree-based activated carbon for the negative electrode can suppress active material degradation.

Experimental Example 2: Evaluation according to the amount of positive and negative active materials

Comparative Example 4

The same procedure as in Example 1 was performed except that the amount of the negative active material was increased by applying 0.0491 g of the positive electrode active material and 0.0545 g of the negative electrode active material.

Comparative Example 5

The same procedure as in Example 1 was performed except that the amount of the positive electrode active material was increased by coating the amount of the positive electrode active material at 0.0545 g and the amount of the negative electrode active material at 0.0491 g.

Charge/discharge performance measurement

Cells prepared in Example 1, Comparative Example 4, and Comparative Example 5 were tested at 20 ° C. at rates of 0.1, 0.2, 0.4, 0.8, 1.6, and 3.2 A / g, CC (constant current; galvanostatic) charge, CC discharge, 0 ~ 3.0 V charge/discharge was performed. After conducting the cycle experiment 5 times for each rate, the 5th cycle capacity for each rate was measured and shown in FIG. 6 .

As can be seen in FIG. 6 , it can be seen that the case of Example 1 exhibits the best capacitance.

The present invention is not limited to the above embodiments, but can be manufactured in a variety of different forms, and those skilled in the art to which the present invention pertains may take other specific forms without changing the technical spirit or essential features of the present invention. It will be understood that it can be implemented as. Therefore, the embodiments described above should be understood as illustrative in all respects and not limiting.

Claims (6)

A positive electrode containing coke-based activated carbon;
A negative electrode containing palm tree-based activated carbon and
A separator interposed between the positive electrode and the negative electrode,
The mass of the coke-based activated carbon in the positive electrode and the mass of the palm tree-based activated carbon in the negative electrode satisfy Equation 1 below,
The coke-based activated carbon includes mesopores with a diameter of 2 to 50 nm and micropores with a diameter of less than 2 nm, and the volume ratio of the micropores to the sum of the volumes of the mesopores and the micropores is 70 to 50 nm. is 90%,
The coke-based activated carbon has a total specific surface area (BET) of 2100 to 2500 m ² /g,
The palm tree-based activated carbon includes mesopores with a diameter of 2 to 50 nm and micropores with a diameter of less than 2 nm, and the volume ratio of the micropores to the sum of the volumes of the mesopores and the micropores is 60%. greater than and less than 80%;
The palm tree-based activated carbon has a total specific surface area (BET) of 1700 to 2100 m ² /g,
The electrochemical device wherein the difference between the thickness of the coke-based activated carbon in the anode and the thickness of the palm tree-based activated carbon in the cathode is 15 μm or less.
[Equation 1]
|([Mc]-[Mp])|/([Mc]+[Mp]) ≤ 0.05
(In Equation 1, [Mc] represents the mass of coke-based activated carbon in the positive electrode, and [Mp] represents the mass of palm tree-based activated carbon in the negative electrode.) delete delete delete delete delete