KR100733391B1 - Electric energy storage device - Google Patents

Abstract

An electrical energy storage device having high capacity, high output and high voltage stability is an electrode having active carbon having an average pore size of a first size as an active material and an electrolyte having an average ion diameter of a second size corresponding to 25% or less of the first size. An electrolyte solution containing a salt and propylene carbonate is provided. The electric energy storage device can be easily displaced in the pores of activated carbon having a large specific surface area by dissolving electrolyte salts such as quaternary ammonium salts and imidazolium-based compounds in environmentally friendly solvents such as propylene carbonate, thereby maintaining high capacity and High voltage stability can be achieved.

Description

ELECTRIC ENERGY STORAGE DEVICES {ELECTRIC ENERGY STORAGE DEVICE}

1 is a cross-sectional view of a unit cell of an electrical energy storage device according to a preferred embodiment of the present invention.

2 is a perspective view schematically showing an electric energy storage device according to a preferred embodiment of the present invention.

3 is a graph showing a change in capacity ratio of low current and high current after a cycle test for an electric energy storage device having different types of electrolyte salts.

4A is a graph showing changes in electric capacity after a cycle test for an electric energy storage device having different types of electrolyte salts.

4B is a graph showing a change in internal resistance after a cycle test for an electric energy storage device having different types of electrolyte salts.

5A is a graph showing a change in electric capacity after a high temperature application test for an electric energy storage device having different types of electrolyte salts.

5B is a graph showing a change in internal resistance after a high temperature application test for an electric energy storage device having different types of electrolyte salts.

The present invention relates to an electrical energy storage device, and more particularly to an electrical energy storage device having a high capacity, high power and high voltage stability.

Electrical energy storage devices such as batteries, electrolytic capacitors, and electric double layer capacitors are composed of an active material layer, a current collector, a separator, an electrolyte, and the like. The active material layer is a part for storing electrical energy, and different active materials are used depending on the type. The current collector serves to discharge electrical energy stored in the active material layer to the outside or to transfer electrical energy applied from the outside to the active material, and a metal film is mainly used.

Meanwhile, the separator serves to prevent electrical conduction between the anode and the cathode and to enable only ion conduction, and a porous polypropylene or paper is commonly used. Electrolytes are ions dissolved in a solvent to store electrical energy. Various electrolytes are used depending on the type of active material.

Electrical energy storage devices that use acetonitrile as an electrolyte have high voltage stability, a wide operating temperature range, and low internal resistance, resulting in excellent high power characteristics and long life over 500,000 cycles. have. However, acetonitrile is very harmful as 2730-3800 mg / kg of LD 50 (oral rat), which is the result of toxicity test for rodents. In addition, the boiling point and flash point (flash point) is low, there is a risk of explosion and ignition. Furthermore, the presence of acids or water vapors upon ignition may lead to the generation of very toxic gases such as cyanide, cyanogens (CN ₂ ) or nitrogen monoxide (NO _x ). For this reason, development of environment-friendly electric energy storage devices including non-toxic electrolytes is required in applications such as hybrid electric vehicles, toys, and solar cell energy sources.

US Pat. No. 6,535,373 (issued to Smith et al.) Discloses an ionic liquid electrolyte and an electrolyte in which ammonium salts are mixed with derivatives thereof. The ionic liquid electrolyte in the liquid state at room temperature has the advantage of high electrical conductivity and solubility, and low precipitation temperature of the solute at a freezing point of minus 30 ° C or lower. On the other hand, salts such as tetraethylammonium have a relatively better electrochemical stability than ionic liquid electrolytes, but begin to freeze below -30 ° C, resulting in a sharp drop in low temperature properties. In this way, electrolytes having different properties are mixed with each other to secure the electrical conductivity and electrochemical stability of the electrolyte. However, since nitrile solvents such as acetonitrile, propionitrile, glutaronitrile, etc. are used, there is a possibility of explosion and ignition and harm to humans. Holding

 Recently, propylene carbonate has been considered as an alternative electrolyte for acetonitrile. Propylene carbonate has 29 g / kg of Eldy 50, which is relatively harmful compared to acetonitrile, has a high flash point and no harmful gas upon ignition. However, propylene carbonate has a relatively high viscosity and low electrical conductivity than acetonitrile, and has a problem in that the cell resistance of the electrolyte is high and the high output characteristics are deteriorated. In addition, there is a limit that the operating temperature range is narrowed because the solubility of the solute is significantly decreased due to a significant decrease in the solubility of ions below minus 25 ° C. Therefore, the development of an electrolyte having high electrical conductivity and ionic solubility at the acetonitrile electrolyte level while using propylene carbonate as the electrolyte is required.

U.S. Patent No. 6,487,066 discloses imidazolium, an ionic liquid electrolyte, as an electrolyte of an electric double layer capacitor. The electric double layer capacitor is composed of graphite-like microcystalline carbon and an organic electrolyte including imidazolium and its derivatives, and has a specific surface area of several tens of m ² / g. A method of realizing high voltage and high capacity by inserting solute ions between microcystalline carbon layers is disclosed. However, graphite, which is the anode material of secondary batteries, increases the lattice spacing when lithium ions (0.076 nm) are inserted between crystal layers (d002 = 0.335 nm), thereby expanding the electrode volume and causing cycles. The service life is reduced. Likewise, when the electrolyte ions (0.343 to 0.303 nm) are inserted between the graphite microcrystalline carbon layers (d002 = 0.365 nm), the electrode volume rapidly expands and the active material is peeled off. In addition, since the rate of insertion or desorption of electrolyte ions between the graphite-like microcrystalline carbon layers is slow, the high output characteristics of the electrical energy storage device are deteriorated.

In order to improve low temperature characteristics and high output characteristics in an electrical energy storage device using a propylene carbonate electrolyte, activated carbon having large pores may be considered as an active material of the electrical energy storage device so that electrolyte ions can be easily moved. However, the electrical capacity of an electrical energy storage device depends on the amount of charge electrically adsorbed on the surface of the activated carbon, and the larger the specific surface area of the activated carbon, the higher the electrical capacity generally. As the porosity of activated carbon increases, the specific surface area decreases, thereby reducing the amount of energy that can be stored in the activated carbon. Therefore, it is required to develop an electrode active material and an electrolyte that can easily move the electrolyte ions and at the same time ensure a sufficient electric capacity.

Accordingly, it is an object of the present invention to provide an electrical energy storage device having high capacity, high power and high voltage stability while using environmentally friendly electrolyte.

In order to achieve the above object of the present invention, the present invention provides an electric power comprising an electrode including an activated carbon having an average pore size of the first size and an electrolyte solution containing an electrolyte salt having an average ion diameter of the second size as an active material. Provide an energy storage device. According to a preferred embodiment of the present invention, the second size is 25% or less of the first size and the electrolyte solution includes propylene carbonate.

According to a preferred embodiment of the present invention, the first size is preferably 10 to 20 mm 3, more preferably 13 to 15 mm 3. In addition, the activated carbon preferably has a specific surface area of 1000 m ² / g or more, and more preferably, the activated carbon has a specific surface area of 2000 m ² / g or more. In addition, the electrolyte may further include ethylene carbonate, dimethyl carbonate, diethyl carbonate, and the like together with propylene carbonate.

According to a preferred embodiment of the present invention, the electrolyte salt having an average ion diameter of the second size includes a quaternary ammonium salt, an imidazolium-based compound and the like. Examples of the quaternary ammonium salt include tetraethylammonium salt, triethylmethylammonium salt, diethyldimethylammonium salt, ethyltrimethylammonium salt, and the like. Examples of salts of quaternary ammonium salts include tetrafluoroborate (BF ₄ ), hexafluorophosphate (PF ₆ ), perchlorate (ClO ₄ ), and the like. The imidazolium-based compound is represented by the following formula (1).

(In Formula 1, R1 and R2 represent an alkyl group having 1 to 5 carbon atoms and X represents a tetrafluoroborate group (BF ₄ ), a hexafluorophosphate group (PF ₆ ) or a triflate group (CF ₃ SO ₃ ). Indicates.)

In order to achieve the above object of the present invention, the present invention provides an electrode comprising activated carbon having an average pore size of the first size as an active material and (i) a first average ion diameter of a second size smaller than the first size; An imidazolium compound having a tetraethylammonium salt having (ii) a quaternary ammonium salt having a second average ion diameter smaller than the first average ion diameter and (iii) a third average ion diameter smaller than the second average ion diameter It provides an electrical energy storage device having an electrolyte salt comprising an electrolyte salt and a propylene carbonate (propylene carbonate). Here, the quaternary ammonium salt includes triethylmethylammonium salt, diethyldimethylammonium salt, ethyltrimethylammonium salt, and the like. According to a preferred embodiment of the present invention, the weight ratio of the tetraethylammonium salt, the quaternary ammonium salt and the imidazolium compound based on the total weight of the electrolyte salt is 3 to 5: 2 to 4: 2 to 4 It is preferable.

According to the present invention, the electrical energy storage device as described above can easily move in the pores of activated carbon having a large specific surface area such as quaternary ammonium salt and imidazolium compound dissolved in an environmentally friendly electrolyte such as propylene carbonate. This enables high output and high voltage stability while maintaining high capacity.

Hereinafter, an electrical energy storage device according to exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a cross-sectional view of a unit cell of an electrical energy storage device according to a preferred embodiment of the present invention, Figure 2 is a perspective view schematically showing the electrical energy storage device according to a preferred embodiment of the present invention.

1 and 2, a unit cell of the electrical energy storage device has a positive electrode 10 and a negative electrode 12 separated by a separator 14, and the positive electrode 10 and the negative electrode ( The space between 12 has a structure in which the electrolyte solution 16 is filled. The unit cells are separated by a separator, and a large number of layers are sequentially stacked, and they are embedded in a case made of a rectangular parallelepiped or cylindrical aluminum or a molding resin together with an organic electrolyte to form a rectangular parallelepiped stacked cell or a cylindrical wound cell. Form. The positive lead 10 and the negative lead 22 are formed to protrude from the positive electrode 10 and the negative electrode 12 in the same direction, and the positive electrode terminal is formed in the direction from which the positive lead 20 and the negative lead 22 extend. Two through holes are formed in which the 24 and the negative electrode terminal 26 are assembled. The positive electrode terminal 24 and the negative electrode terminal 26 installed through the through hole have a bolt shape having a head, and a nut 28 is fastened to the protruding end and fixed to the case 30. Head portions of the positive electrode terminal 24 and the negative electrode terminal 26 are connected to the positive electrode lead wire 20 and the negative electrode lead wire 22 of the winding body 32, respectively.

The electrical energy storage device according to the present invention includes activated carbon as an active material of the electrode. The activated carbon may be used for the positive electrode or the negative electrode, but is preferably used for both the positive electrode and the negative electrode. In an electric energy storage device using activated carbon as an active material of an electrode, the electric double layer capacitance is proportional to the size of the specific surface area of the activated carbon. The specific surface area of the activated carbon is mostly due to micropores having a size of 20 kPa or less, and when the size is 10 kPa or less, it is difficult to form an electric double layer in a system using propylene carbonate as an electrolyte, and thus high capacity cannot be realized. Thus, the more micropores of the minimum size at which the electric double layer can be formed, the greater the amount of energy that can be stored in the electrical energy storage device. Therefore, the preferred pore size of activated carbon according to the present invention is 10 to 20 kPa, more preferably 13 to 15 kPa. Here, the mean pore size means an average size of micropores in activated carbon in a range of 500 kPa or less of mesopores. In addition, in the electrical energy storage device according to the present invention, in order to ensure a high capacity, the size of the specific surface area of the activated carbon is preferably 1000 m ² / g or more, and more preferably 2000 m ² / g or more.

On the other hand, the high power characteristics of the electrical energy storage device depends on whether the electrolyte ions easily move into the micropores of the activated carbon to maintain a constant concentration. When the electrical energy storage device including the same electrolyte salt is charged and discharged at a slow rate, there is no difference in capacitance according to electrolytes such as acetonitrile and propylene carbonate. However, since the viscosity of propylene carbonate is higher than that of acetonitrile, the faster the charge / discharge rate, the slower the response rate of ions in the propylene carbonate electrolyte.

The electric double layer capacitance of the electrical energy storage device depends on the concentration of the electrolyte forming the electric double layer in addition to the size of the specific surface area of the activated carbon. When high viscosity propylene carbonate is used as the electrolyte, electrolyte ions are difficult to enter into the micropores of the activated carbon rapidly and the electrolyte concentration in the activated carbon micropores gradually decreases. As the high-speed charging and discharging continues, the number of effective ions for forming an electric double layer in the micropores of activated carbon gradually decreases, so the capacity of the electric double layer decreases rapidly. Therefore, when high viscosity propylene carbonate is used as the electrolyte, it is possible to overcome the lowering of the capacitance due to the decrease in the response speed of ions in the electrolyte by applying an electrolyte salt having a smaller ion diameter than the average pore size of activated carbon.

The electrical energy storage device according to the present invention includes propylene carbonate as the electrolyte. According to a preferred embodiment of the present invention, the electrolyte further includes ethylene carbonate, dimethyl carbonate, diethyl carbonate, and the like together with propylene carbonate.

In the electrical energy storage device according to the present invention, the average ion diameter of the electrolyte salt is preferably 25% or less of the average pore size of the activated carbon. Examples of the electrolyte salt include quaternary ammonium salts, imidazolium compounds, and the like. These can be used individually or in mixture.

According to a preferred embodiment of the present invention, examples of the quaternary ammonium salt include tetraethylammonium salt, triethylmethylammonium salt, diethyldimethylammonium salt, ethyltrimethylammonium salt, and the like. Can be mentioned. These can be used individually or in mixture. Here, examples of the material used as the salt of the quaternary ammonium salt include tetrafluoroborate group (BF ₄ ), hexafluorophosphate group (PF ₆ ), perchlorate (ClO ₄ ), and the like.

According to a preferred embodiment of the present invention, the imidazolium compound is represented by the following formula (1). These can be used individually or in mixture.

[Formula 1]

(In Formula 1, R1 and R2 represent an alkyl group having 1 to 5 carbon atoms and X represents a tetrafluoroborate group (BF ₄ ), a hexafluorophosphate group (PF ₆ ) or a triflate group (CF ₃ SO ₃ ). Indicates.)

In the electrical energy storage device according to an embodiment of the present invention, tetraethylammonium salt, quaternary ammonium salt having an average ion diameter of 5% or more smaller than tetraethylammonium salt, and an average ion diameter of 10% or more than the tetraethylammonium salt as electrolyte salts. Small imidazolium-based compounds. Based on the total weight of the electrolyte salt, the weight ratio of the tetraethylammonium salt, the quaternary ammonium salt having an average ionic diameter of 5% or more than that of the tetraethylammonium salt, and the imidazolium compound is 3 to 5: 2 to 4: 2 to It is preferable that it is four. Here, examples of quaternary ammonium salts having an average ion diameter of 5% or more than the tetraethylammonium salt include triethylmethylammonium salt, diethyldimethylammonium salt, ethyltrimethylammonium salt, and the like. . These can be used individually or in mixture. Examples of the material used as the salt of the quaternary ammonium salt include tetrafluoroborate group (BF ₄ ), hexafluorophosphate group (PF ₆ ), perchlorate (ClO ₄ ), and the like.

According to the present invention, the electrical energy storage device as described above can easily move in the pores of activated carbon having a large specific surface area such as quaternary ammonium salt and imidazolium compound dissolved in an environmentally friendly electrolyte such as propylene carbonate. This enables high output and high voltage stability while maintaining high capacity.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. However, it will be appreciated that the following examples are intended to illustrate the invention and the invention is not limited to the following examples and can be modified and modified in various ways.

Capacitance evaluation according to solvent type of electrolyte

Example 1

Activated carbon having an average surface area of 2120 m ² / g and a mesopore of 500 kPa or less and an average size of micropore of 13.9 kPa was used as an active material for the electrode, and 1 mol of tetraethylammonium tetrafluoroborate was added to propylene carbonate. An electric energy storage device was manufactured using the dissolved electrolyte solution.

Comparative Example 1

Activated carbon having an average surface area of 2120 m ² / g and a mesopore of 500 µm or less and having an average size of fine pores of 13.9 µm is used as an active material for the electrode, and 1 mol of tetraethylammonium tetrafluoroborate is acetonitrile. An electric energy storage device was manufactured using the electrolyte solution dissolved in the.

Specific gravimetric capacitances based on the weight of activated carbon were measured for the electrical energy storage devices according to Example 1 and Comparative Example 1. The measurement results of the capacitance are as shown in Table 1 below.

Electrolyte Activated carbon Electric capacity (F / g) Specific surface area (m ² / g) Average pore size Example 1 Propylene carbonate 2120 13.9 37.8 Comparative Example 1 Acetonitrile 2120 13.9 37.3

 Referring to Table 1, the electrical capacity of the electrical energy storage device according to Example 1 was found to be slightly larger than the electrical capacity of the electrical energy storage device according to Comparative Example 1. According to an embodiment of the present invention, it can be seen that the electrical energy storage device using propylene carbonate as the solvent of the electrolyte has a similar or better electrical capacity than the electrical energy storage device using acetonitrile as the solvent of the electrolyte.

Performance Evaluation of Electrical Energy Storage Device According to Electrolytes Salts

Example 2

Activated carbon with a specific surface area of 2120 m ² / g and an average size of fine pores in the range of 500 microns or less of mesopore is used as an electrode active material, Tetraethylammonium tetrafluoroborate, triethylmethylammonium tetrafluoroborate, and ethylmethylimidazolium tetrafluoroborate are dissolved in propylene carbonate in an electrolyte salt in a weight ratio of 4: 3: 3 based on the total weight of the electrolyte salt. The electrolytic storage device was manufactured using the prepared electrolyte solution.

Comparative Example 2

Activated carbon with a specific surface area of 2120 m ² / g and a mesopore of 500 kPa or less and an average size of micropore of 13.9 kW is used as an active material for the electrode, and an electrolyte solution in which a conventional electrolyte salt is dissolved in propylene carbonate is used. An electrical energy storage device was manufactured.

For the electrical energy storage device according to Example 2 and Comparative Example 2, the change of the capacitance ratio of low current and high current after the cycle test was measured according to the ultracapacitor test conditions of the US Department of Energy. At this time, the charge and discharge time of one cycle was 1 minute.

3 is a graph showing a change in capacity ratio of low current and high current after a cycle test for an electric energy storage device having different types of electrolyte salts.

Referring to FIG. 3, the electrical energy storage device according to Comparative Example 2 using a conventional electrolyte salt rapidly increases in capacity ratio between low current and high current as the cycle progresses, but uses an electrolyte salt according to an embodiment of the present invention. In the electrical energy storage device according to Example 2, it can be seen that the capacity ratio of the low current and the high current maintains a ratio almost similar to the initial period even after a long cycle.

4A is a graph showing a change in electric capacity after a cycle test for an electric energy storage device having different types of electrolyte salts, and FIG. 4B is a graph showing a change in internal resistance after a cycle test for an electric energy storage device having different types of electrolyte salts. to be.

4A and 4B, the electrical energy storage device according to Comparative Example 2 decreases linearly with the passage of the cycle, and maintains only about 60% of the initial capacitance after 50,000 cycles. Electrical energy storage devices have been shown to maintain more than 85% of their initial capacity after 250,000 cycles. Therefore, it can be seen that the electric energy storage device according to the present invention has a lifespan improved by five times or more compared with the existing electric energy storage device.

FIG. 5A is a graph showing a change in electric capacity after a high temperature application test for an electric energy storage device having different types of electrolyte salts, and FIG. 5B is a change in internal resistance after a high temperature application test for an electric energy storage device having different types of electrolyte salts. It is a graph showing.

5A and 5B, the electric energy storage device according to 2 compared with Example 2 has a tendency that the electric capacity decreases and the internal resistance gradually increases with the application of high temperature. However, it can be seen that the electric energy storage device according to Example 2 has a smaller reduction in electric capacity and an increase in internal resistance than the electric energy storage device according to Comparative Example 2. Therefore, it can be seen that the electrical energy storage device according to the present invention exhibits electrochemically stable behavior.

As described above, according to the present invention, electrolyte salts such as quaternary ammonium salts and imidazolium compounds can be dissolved in environmentally friendly electrolytes such as propylene carbonate and can easily move in pores of activated carbon having a large specific surface area, thereby maintaining high capacity. An electric energy storage device having high output and high voltage stability can be implemented.

While the above has been described with reference to preferred embodiments of the present invention, those skilled in the art will be able to variously modify and change the present invention without departing from the spirit and scope of the present invention as set forth in the claims below. It will be appreciated.

Claims (20)

delete delete delete delete delete delete delete delete delete delete delete delete An electrode comprising activated carbon having an average pore size of a first size as an active material; And (i) a tetraethylammonium salt having an average ion diameter of a second size smaller than the first size, (ii) a quaternary ammonium salt having an average ion diameter less than the average ion diameter of the tetraethylammonium salt, and (iii) the quaternary An imidazolium compound having an average ion diameter smaller than the average ion diameter of the ammonium salt, wherein the weight ratio of the tetraethylammonium salt, the quaternary ammonium salt and the imidazolium compound is 3 to 5: 2 to 4: 2 to An electrical energy storage device comprising an electrolyte solution comprising an electrolyte salt of 4 and propylene carbonate. The electrical energy storage device according to claim 13, wherein the first size is 10 to 20 kW. 15. The electrical energy storage device of claim 14, wherein said first size is between 13 and 15 microns. The electrical energy storage device of claim 13, wherein the electrolyte further comprises at least one selected from the group consisting of ethylene carbonate, dimethyl carbonate, and diethyl carbonate. delete The quaternary ammonium salt of claim 13, wherein the quaternary ammonium salt comprises at least one selected from the group consisting of triethylmethylammonium salt, diethyldimethylammonium salt, and ethyltrimethylammonium salt. Electrical energy storage devices. 20. The method of claim 18, wherein the salt of the quaternary ammonium salt is characterized in that it comprises at least one selected from the group consisting of tetrafluoroborate (BF ₄ ), hexafluorophosphate (PF ₆ ) and perchlorate (ClO ₄ ) Electric energy storage device. The electrical energy storage device according to claim 13, wherein the imidazolium-based compound is represented by the following formula (1).

(One) (In the above formula, R1 and R2 represents an alkyl group having 1 to 5 carbon atoms, X represents a tetrafluoroborate group (BF ₄ ), hexafluorophosphate group (PF ₆ ) or triflate group (CF ₃ SO ₃ ) .)

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