KR20200069820A - Electrochemical device - Google Patents

Abstract

An electrochemical device according to one embodiment of the present invention includes an anode comprising coke-based activated carbon, a cathode comprising palm tree-based activated carbon, and a separator interposed between the anode and the cathode. The mass of the coke-based activated carbon in the anode and the mass of palm tree-based activated carbon in the cathode satisfies inequality 1, wherein the inequality 1 is ¦([Mc]-[Mp])¦ / ([Mc]+[Mp]) <= 0.05. In the inequality 1, [Mc] represents the mass of coke-based activated carbon in the anode, and [Mp] represents the mass of palm-based activated carbon in the cathode.

Description

Electrochemical device {ELECTROCHEMICAL DEVICE}

It relates to an electrochemical device. More specifically, the present invention relates to an electrochemical device having excellent capacity and lifespan characteristics, even though the thicknesses of the positive and negative active materials are different.

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

Among the electrochemical devices, an electric double layer capacitor (EDLC) is a pair having a positive electrode and a negative electrode disposed between two electrodes facing each other with a separator (separator, separator or separator) interposed therebetween. It is an energy storage medium using the generated charge layer (electric double layer), which is a device capable of continuous charging/discharging.

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

In the method of adjusting the electrode potential of the conventional electric double layer capacitor, the weight of the cell is increased by differentiating the weight of the positive electrode and the negative electrode, and by placing a difference in resistance between the positive electrode and the negative electrode. That is, it is a method of increasing the voltage of the cell by controlling the thickness of the positive electrode active material and the negative electrode active material by making the thickness of the positive electrode active material thicker and increasing the difference in resistance between the positive electrode and the negative electrode.

Alternatively, the electrode potential may be controlled by controlling the mass of the active material applied to the positive electrode and the negative electrode.

However, since the above-described method cannot effectively control the potential difference between the positive electrode and the negative electrode, there is a limit in improving the voltage or energy density.

It provides an electrochemical device. More specifically, by applying different types of active materials of the positive electrode and the negative electrode, even if the thickness is the same, it provides an electrochemical device having excellent capacity and life characteristics.

The electrochemical device according to an embodiment of the present invention includes a positive electrode comprising coke-based activated carbon, a negative electrode and a positive electrode comprising palm-based activated carbon, and a separator interposed between the negative electrode, and the mass and negative electrode of coke-based activated carbon in the positive electrode. The mass of the palm tree-based activated carbon in the body satisfies the following equation 1.

[Equation 1]

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

0.05

(In formula 1, [Mc] represents the mass of coke-based activated carbon in the anode, and [Mp] represents the mass of palm-based activated carbon in the cathode.)

Coke-based activated carbon includes mesopores having a diameter of 2 to 50 nm and micropores having a diameter of less than 2 nm, and the ratio of the volume of the micropores to the sum of the volumes of the mesopores and the micropores is 70 to 90% Can be

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

Palm tree-based activated carbon includes mesopores having a diameter of 2 to 50 nm and micropores having 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 Less than 80%.

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

The difference between the thickness of coke-based activated carbon in the anode and the thickness of palm-based activated carbon in the cathode may be 15 μm or less.

In one embodiment of the present invention, different kinds of active materials of the positive electrode and the negative electrode are applied differently, and even if the thickness is the same, an electrochemical device having excellent capacity and life characteristics can be obtained.

1 is a result of pore structure analysis and surface area analysis of the active material in the preparation example.
2 is a graph measuring the capacitance of the charge-discharge rate in Experimental Example 1.
3 is a graph measuring capacitance for each cycle in Experimental Example 1.
4 is a result of bulk resistance analysis of EIS components before and after the cycle in Experimental Example 1.
5 is a result of the analysis of the interface resistance of the EIS component before and after the cycle in Experimental Example 1.
6 is a graph measuring the capacitance of the charge-discharge rate in Experimental Example 2.

In the present specification, when a part “includes” a certain component, it means that the component may further include other components, not to exclude other components, unless specifically stated otherwise. The terms "about", "substantially", and the like, as used throughout this specification, are used in or at a value close to that value when manufacturing and material tolerances specific to the stated meaning are given, and are understood herein. To aid, accurate or absolute figures are used to prevent unscrupulous use of the disclosed disclosure by unscrupulous infringers. The term “~(step)” or “step of” as used in the present specification does not mean “step for”.

In this specification, the term "combination of these" included in the expression of the marki form means one or more mixtures or combinations selected from the group consisting of the elements described in the expression of the marki form, the components It means to include 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 the present invention is not limited thereby, and the present invention is only defined by the scope of 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.

The electrochemical device according to an embodiment of the present invention includes an anode comprising coke-based activated carbon, a cathode comprising palm-based activated carbon, and a separator interposed between the anode and the cathode.

The positive electrode may be formed by applying or attaching a positive electrode active material to the positive electrode current collector. Similarly, the negative electrode may be formed by applying or attaching a negative electrode active material to the negative electrode current collector. In more detail, the active material, the conductive material, the binder and the solvent are mixed in a mixer to slurry. The slurryed mixture may be formed by applying an active material (electrode layer) to the current collector by applying convection drying and evaporating the solvent on the current collector such as aluminum foil.

As the positive electrode current collector and the negative electrode current collector, a current collector material of an 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 not only a metal foil, but also an etched metal foil, or a shape having a hole penetrating the front and back surfaces such as expanded metal, punching metal, net, and foam.

The conductive material may include conductive powders such as super-P, super-P, ketjen black, acetylene black, carbon black, and graphite, but is not limited thereto and may include all kinds of conductive materials used in conventional electrochemical devices. have.

Examples of the binder include fluorine-based resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF); Thermoplastic resins such as polyimide, polyamideimide, polyedylene (PE), and polypropylene (PP); Cellulose-based resins such as carboxymethyl cellulose (CMC); Rubber-based resins such as styrene-butadiene rubber (SBR) and one or more selected from mixtures thereof may be used, but are not particularly limited thereto, and all binder resins used in general electrochemical devices may be used.

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

Alternatively, an electrolyte may be included as a separator, and the electrolytic solvent is used for dissolving or dissociating the electrolyte salt, and is not particularly limited as long as it is used as an electrolytic solvent for a conventional electrolyte. Cyclic carbonate, linear carbonate, lactone, ether , Esters, sulfoxides, acetonitrile, lactams, ketones, and halogen derivatives thereof, respectively, or may be used by mixing two or more. Examples of cyclic carbonates include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), fluorethylene carbonate (FEC), and examples of linear carbonates include diethyl carbonate (DEC) and dimethyl carbonate (DMC). ), dipropyl carbonate (DPC), ethyl methyl carbonate (EMC), and methyl propyl carbonate (MPC). Examples of lactones are gamma-butyrolactone (GBL), and examples of ethers are dibutyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, 1, 2-diethoxy ethane. Examples of such esters 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, etc., the lactam includes N-methyl-2-pyrrolidone (NMP), and the ketone includes polymethylvinyl ketone. In addition, these halogen derivatives can also be used, and are not limited to the above-described exemplified electrolyte electrolytic solvents. In addition, these electrolytic solvents may be used alone or in combination of two or more.

The electrolyte solution may further include an electrolyte salt. The electrolyte salt dissociates in the electrolytic solvent to act as a component of ion conduction in the electrochemical device, and may serve to promote the movement of cations between the anode and the cathode. For example, SBPBF ₄ (spirobipyrrolidinium tetrafluoroborate), TEABF ₄ , EMIBF4, TEMABF ₄ , or a combination thereof. The content of the electrolyte salt in the gel polymer electrolyte is the number of moles (mol) with respect to the electrolytic solvent (L) in the electrolyte, and may be 0.5 to 3.0 M. In this case, the gel polymer electrolyte may have an appropriate viscosity as a gel form, and the electrolyte salt may be dissolved in an electrolytic solvent, contributing to the effective migration of cations.

In one embodiment of the present invention, different kinds of active materials of the positive electrode and the negative electrode are applied differently, and even if the thickness is the same, an electrochemical device having excellent capacity and life can be obtained.

Specifically, as the positive electrode active material, coke-based activated carbon may be used. In addition, as the negative electrode active material, palm tree-based activated carbon may be used. By applying different kinds of active materials of the positive electrode and the negative electrode as described above, it is possible to obtain an electrochemical device having excellent capacity and life.

Coke-based activated carbon applied to the positive electrode active material contributes to improving the capacity of the electrochemical device. Coke-based activated carbon means activated carbon using coke as a raw material.

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

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

When the palm tree-based activated carbon is used as the negative electrode active material, the aforementioned deterioration of the active material occurs relatively little. Palm tree-based activated carbon means activated carbon using coke as a raw material.

Palm tree-based activated carbon, palm tree-based activated carbon includes mesopores having a diameter of 2 to 50 nm and micropores having 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 More than 60% and less than 80%. In addition, palm tree-based activated carbon may have a total specific surface area (BET) of 1700 to 2100 m ² /g. As such, it is possible to improve the service life through proper pore characteristics. More specifically, palm tree-based activated carbon may have a volume ratio of micropores to 75% to 79% of the sum of the volumes of mesopores and the micropores. 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 coke-based activated carbon in the positive electrode and the mass of palm-based activated carbon in the negative electrode satisfy Equation 1 below.

[Equation 1]

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

0.05

(In formula 1, [Mc] represents the mass of coke-based activated carbon in the anode, and [Mp] represents the mass of palm-based activated carbon in the cathode.)

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

The difference between the thickness of coke-based activated carbon in the anode and the thickness of palm-based activated carbon in the cathode may be 15 μm or less. By reducing 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, the capacity can be further improved.

Hereinafter, preferred embodiments of the present invention will be described. However, the following examples are only preferred examples of the present invention, and the present invention is not limited to the following examples.

Manufacturing example

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

Porous structure analysis and surface area analysis of the active materials of Preparation Example 1 and Preparation Example 2 were summarized in FIGS. 1 and 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 ) Preparation Example 1 (coke-based activated carbon) 2138 347.7 2486 0.97 0.21 1.18 Production Example 2 (palm water activated carbon) 1712.8 305.8 2019 0.76 0.22 0.98

Experimental Example 1: Evaluation according to positive and negative electrode active material types

Example 1

Coke-based activated carbon of Preparation Example 1 as a positive electrode active material and palm-based activated carbon of Production Example 2 as a negative electrode active material were used.

m 으로 동일하였다.An electrode was prepared by coating on an aluminum current collector using an active material. The amount of the active material was the same as the positive electrode and the negative electrode, respectively, at 0.0545 g, and the thickness was 163

It was the same as m.

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

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

Comparative Example 1

It was carried out in the same manner as in Example 1, except that the coke-based activated carbon of Preparation Example 1 and the coke-based activated carbon of Preparation Example 1 were used as the cathode active material.

Comparative Example 2

It was carried out in the same manner as in Example 1, except that the palm tree-based activated carbon of Preparation Example 2 and the palm tree-based activated carbon of Preparation Example 2 were used as the cathode active material.

Comparative Example 3

It was carried out in the same manner as in Example 1, except that the palm tree-based activated carbon of Preparation Example 2 and the coke-based activated carbon of Preparation Example 1 were used as the cathode active material.

Charge/discharge performance measurement

The cells prepared in Example 1 and Comparative Examples 1 to 3 were charged at a rate of 0.1, 0.2, 0.4, 0.8, 1.6, and 3.2 A/g for each rate at 20°C. CC (constant current; galvanostatic) charge, CC discharge, 0 to 3.0 V charge/discharge was performed. After performing the cycle experiment five times for each rate, the fifth 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 shows 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, Comparative Example 3 using palm trees as the positive electrode shows a higher capacitance at the overall charge and discharge rate than Example 1. . In the case of Example 1, it can be seen that it shows improved capacity characteristics than Comparative Example 2.

Cycle life evaluation

The cells prepared in Example 1 and Comparative Examples 1 to 3 were subjected to cycles of 0 to 3.0 V charging and discharging at a temperature of 20°C at a rate of 3.2 A g-1 for 5000 cycles with CC-charge and CC-discharge. The charge/discharge cycle capacity was measured and shown in FIG. 3.

3, it can be seen that Comparative Examples 1 and 3 show the lowest lifespan characteristics. In both Comparative Example 1 and Comparative Example 3, when coke activated carbon was used as the negative electrode, it was confirmed that the initial capacity was high but the lifespan was continuously decreased. Comparative Examples 2 and 1 have the best life characteristics, but it can be seen that Example 1, which has a high initial capacity, maintains a high capacitance during a cycle than Comparative Example 2.

EIS resistance evaluation

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

4 and 5, it can be seen that, as a whole, each resistance component increases after the cycle compared to before the cycle, but the interface resistance increases more than the bulk resistance at an increase rate. In the case of Comparative Example 1 and Comparative Example 3 in which the deterioration of the life characteristics was observed, it was confirmed that the interface resistance was greatly increased, which is used for a larger overvoltage and a negative electrode at a negative electrode that may be generated when the same amount of active material is coated It is because of the coke-based activated carbon.

On the other hand, in the case of Comparative Examples 2 and 1, it can be confirmed that such deterioration of the active material occurred relatively little, and it can be confirmed that the use of palm tree-based activated carbon as the negative electrode can suppress the deterioration of the active material.

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

Comparative Example 4

The amount of the positive electrode active material was 0.0491 g, and the amount of the negative electrode active material was applied to 0.0545 g.

Comparative Example 5

The amount of the positive electrode active material was 0.0545 g, and the amount of the negative electrode active material was applied to 0.0491 g.

Charge/discharge performance measurement

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

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

The present invention is not limited to the above embodiments, but may be manufactured in various different forms, and those skilled in the art to which the present invention pertains have other specific forms without changing the technical spirit or essential features of the present invention. It will be understood that can be carried out. Therefore, it should be understood that the embodiments described above are illustrative in all respects and not restrictive.

Claims (6)

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

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