KR20130093815A - Electrochemical capacitor, method for preparing the same - Google Patents

Abstract

PURPOSE: An electrochemical capacitor and a manufacturing method thereof are provided to lower cathode potential so as to be close to OV in comparison to lithium, thereby increasing voltage. CONSTITUTION: A cathode includes a LiC6 layer (120) on a cathode current collector (110). The cathode includes an active material layer (130) on the cathode current collector. The electric potential of the cathode is maintained within the range of 0 to 0.2V. The thickness of the LiC6 layer is about 10 μm or less. An anode includes an active material layer on an anode current collector.

Description

Electrochemical Capacitor, and Method for Preparing the Same {Electrochemical capacitor, method for preparing the same}

The present invention relates to an electrochemical capacitor and a method of manufacturing the same.

Supercapacitors are capacitors with very high capacitance, also called ultracapacitors or ultracapacitors. In academic terms, the electrochemical capacitor is distinguished from the conventional electrostatic or electrolytic method.

Supercapacitors have Electric Double Layer Capacitors that accumulate electricity through electrostatic adsorption and desorption of ions, Pseudocapacitors that accumulate electricity through redox reactions, and Asymmetric electrodes. It can be divided into hybrid capacitors.

Batteries, the most common energy storage device, are used in many applications because they can store a great deal of energy in a relatively small volume and weight, and can provide adequate output in many applications. However, batteries have a common problem of low storage characteristics and cycle life regardless of the type. This is due to the deterioration of the natural or use of chemicals contained in the battery, and there is no alternative to this, so there is no choice but to accept the disadvantage of the battery.

Supercapacitors, on the other hand, differ from batteries that use chemical reactions. 　 Charge phenomenon by transfer or surface chemical reaction is used. Accordingly, it is rapidly becoming a next-generation energy storage device that can be used as a secondary battery or a battery replacement due to its fast charge and discharge, high charge and discharge efficiency and semi-permanent cycle life characteristics.

Despite these advantages, however, supercapacitors are more limited in their utility due to their lower capacity than batteries. Therefore, the effort to improve the capacity of the cell while maintaining high output characteristics is the most important problem of the current supercapacitor.

Lithium ion secondary batteries have been studied as high-capacity and potent power sources, and some of them have already been commercialized, but electric double layer capacitors (EDLC) have attracted attention recently because they are still problematic for safety, cycle life, and high output characteristics.

Since the EDLC has polarized electrodes using active carbon as the active material for both the positive electrode and the negative electrode, the energy density is smaller than that of the secondary battery, but the instantaneous output is very excellent and the long life characteristics of up to 500,000 cycles are achieved. It is currently used for power supply for memory backup and heavy equipment requiring high power.

Here, in order to solve the high capacity of the capacitor, the most important point is to charge a large amount of active material in the cell or to increase the specific surface area of the active material, but the specific surface area with high specific gravity of micropores that does not contribute significantly to the capacity In the case of the dose is not well expressed, there is a limit to the high capacity by optimizing the pore structure of the active material.

As another high capacity method, it is conceivable to set the charging voltage high. In general, EDLC is charged in the 2.5 to 2.7V range, but if it can be charged at higher voltages, it can significantly improve the energy density (E = 1 / 2CV ² ).

However, when the charge voltage of the capacitor is increased, the charge potential of the anode is increased, resulting in decomposition of the electrolyte, resulting in gas generation or electrode deterioration, resulting in an increase in internal resistance and ultimately, a decrease in cell life. .

Meanwhile, the lithium ion capacitor (LIC) developed by JM energy and ACT in Japan achieved an increase in energy density due to the voltage increase without significantly reducing the EDLC output reduction compared to the conventional pseudo capacitor. (See FIG. 1, FIG. 2). In other words, using activated carbon with a large specific surface area at the positive electrode and using a carbon material capable of reversibly intercalating and deintercalating lithium ions at the negative electrode, it can be used in a wide voltage range of 2.0 to 4.0V. And products with high energy density and excellent charge / discharge cycle reliability began to be produced.

However, in the case of such LIC, the cathode capacitance per unit volume is about 3 to 4 times larger than that of the anode (it may vary depending on the characteristics of the cathode or anode material, but considering the theoretical capacity of general activated carbon and graphite) In order to achieve maximum capacity, the thickness of the anode should be 3-4 times larger than the thickness of the cathode. In this case, the relatively thick anode causes an increase in resistance, which leads to a sharp decrease in cell output characteristics.

Accordingly, an object of the present invention is to increase the voltage by lowering the cathode potential close to 0V compared to lithium, while maintaining the high output characteristics of EDLC using the active activated carbon as an active material in the production of supercapacitor electrode, thereby maximizing energy density It is an object of the present invention to provide an electrochemical capacitor including an electrode, and a method of manufacturing the same.

An electrochemical capacitor according to an exemplary embodiment of the present invention is characterized by using a LiC ₆ layer on a negative electrode current collector, a negative electrode including an active material layer, and a positive electrode including an active material layer on the positive electrode current collector.

According to one embodiment of the invention, the thickness of the LiC ₆ layer is preferably formed to 10㎛ or less.

According to one embodiment of the invention, the active material of the positive electrode and the negative electrode may be the same or different, respectively, activated carbon, carbon nanotubes (CNT), graphite, carbon aerogels, polyacrylonitrile (PAN), carbon nanofibers ( CNF), activated carbon nanofibers (ACNF), vapor-grown carbon fibres (VGCF), and graphene.

According to one embodiment of the present invention, the active material of the positive electrode and the negative electrode may be most preferably used activated carbon having a specific surface area of 1,500 ~ 3,000 ㎡ / g.

It is preferable that the active material layer of the negative electrode is formed 10 to 20% thinner than the active material layer of the positive electrode.

The potential of the negative electrode may be maintained at 0 ~ 0.2V.

The electrochemical capacitor according to an embodiment of the present invention is a negative electrode current collector comprising: whole form a LiC ₆ layer to the negative electrode producing method comprising a step of forming an active material layer on the LiC ₆ layer, and a cathode current collector onto the active material to the A cathode manufacturing step comprising a layer may be included.

The thickness of the LiC ₆ layer is preferably formed to 10㎛ or less.

According to an embodiment of the present invention, while maintaining the high output characteristics of the EDLC using the existing activated carbon as an active material, by lowering the negative electrode potential close to 0V compared to lithium, by increasing the voltage, to provide an electrochemical capacitor that can maximize the energy density can do.

1 is a conceptual diagram of a lithium ion capacitor LIC,
2 is a graph of a voltage and potential relationship of a lithium ion capacitor LIC,
3 is an electrode structure according to an embodiment of the present invention.

Hereinafter, the present invention will be described in more detail.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms "a,""an," and "the" include singular forms unless the context clearly dictates otherwise. Also, " comprise "and / or" comprising "when used herein should be interpreted as specifying the presence of stated shapes, numbers, steps, operations, elements, elements, and / And does not preclude the presence or addition of one or more other features, integers, operations, elements, elements, and / or groups.

In the electrochemical capacitor of the present invention, when manufacturing a cathode, a thin LiC6 layer is first formed on a current collector, and an active material layer is formed thereon, thereby lowering a cathode potential close to 0 V compared to lithium, increasing voltage, and maximizing energy density. will be.

As shown in FIG. 3, the electrochemical capacitor according to the present invention includes a negative electrode 100 including a LiC ₆ layer 120, and an active material layer 130 on the negative electrode current collector 110, and a positive electrode current collector. A positive electrode 200 including an active material layer 230 is formed on the 210.

That is, the cathode 200 is manufactured by applying the active material layer 230 to the cathode current collector 210 as in the conventional EDLC (a), and in the case of the anode 100, the LiC ₆ layer on the anode current collector 110. After applying (120), the active material layer 130 is applied on the LiC ₆ layer 120 is prepared (b).

When manufacturing a negative electrode as in the present invention, the potential of the negative electrode can be dropped to near 0V compared to lithium by applying the LiC ₆ layer 120 in advance before forming the active material layer.

The closer to the stoichiometry ratio in the LiC ₆ layer, the higher the probability that this voltage will remain converging to 0V. For example, at LixC ₆ (x can range from 0 to 1, the voltage can remain at 0V as close to 1), and the doping level of Li is staged if the value of x is 0.5 to 1.0 In stages 1 and 2, the Li / Li + potential is below 0.1V. In addition, when x is 0.34 to 0.5, the doping amount is increased and the potential increases to 0.15V as it goes to stage 3. If the actual x value drops to 0.2 or less, and the Li doping amount is greatly reduced, the potential rapidly increases to 0.2V or more, which may cause a decrease in the voltage of the cell, which may cause energy density to decrease.

According to one embodiment of the present invention, the thickness of the LiC ₆ layer is preferably 10 μm or less, preferably 1 to 2 μm, so that the thickness of the cathode is not too large, and the thickness of the LiC ₆ layer is increased. If it exceeds 10 μm it is not preferable because it is too different from the output characteristics of the EDLC level.

When the LiC ₆ layer is formed, an active material layer is formed on the LiC ₆ layer. The active material of the negative electrode is activated carbon, carbon nanotubes (CNT), graphite, carbon aerogels, polyacrylonitrile (PAN), carbon nanofibers (CNF), activated carbon nanofibers (ACNF), vapor-grown carbon fibers (VGCF), and It may be one or more selected from the group consisting of graphene, and among these, activated carbon having a specific surface area of 1,500 to 3,000 m 2 / g may be most preferably used.

The active material layer needs to be cell balanced so that the thickness of the activated carbon electrode applied to the anode later is thin, so that the theoretical capacity between the two electrodes is not significantly different. Therefore, the active material layer of the negative electrode is preferably formed 10 to 20% thinner than the active material layer of the positive electrode.

By adopting the electrode of this structure, the cell can have both the existing EDLC high power characteristics and the high energy density characteristics of the existing LiC, which enables the manufacture of high capacity and high power cells, and when modularized, it is advantageous in terms of volume and weight. I can take it.

The electrochemical capacitor according to an embodiment of the present invention is a negative electrode current collector comprising: whole form a LiC ₆ layer to the negative electrode producing method comprising a step of forming an active material layer on the LiC ₆ layer, and a cathode current collector onto the active material to the It can be prepared through an anode manufacturing step comprising a layer.

As the negative electrode current collector, all materials conventionally used in an electric double layer capacitor or a lithium ion battery may be used. For example, stainless steel, copper, nickel, and alloys thereof may be used, and copper is preferable. Moreover, it is preferable that the thickness is about 10-300 micrometers. The current collector may include not only the foil of the metal but also an etched metal foil or an opening metal such as expanded metal, punching metal, net, foam or the like through the front and back surfaces.

The LiC ₆ layer is thinned to a thickness of about 10 μm or less on the negative electrode current collector so that the negative electrode is not too thick. The method of forming the LiC ₆ layer includes wet direct doping, wet short doping, and Li deposited dry doping. The method is not particularly limited.

An active material layer is formed on the LiC ₆ layer, and the active material layer may be prepared by coating an active material slurry including a conductive material, a binder, a solvent, and the like. In addition, in the present invention, the mixture of the electrode active material, the conductive material, and the solvent may be molded into a sheet shape using the binder resin, or the extruded molded sheet may be bonded to the LiC ₆ layer using a conductive adhesive. have.

The conductive material included in the active material slurry may use at least one conductive carbon selected from the group consisting of super-P, graphite, acetylene black, carbon black, and Ketjen black.

Further, examples of the binder of the present invention 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 carboxymethylcellulose (CMC); One or more selected from rubber-based resins such as styrene-butadiene rubber (SBR) and mixtures thereof may be used, but is not particularly limited thereto. Any binder resin used in a conventional electrochemical capacitor may be used.

The active material layer of the negative electrode is preferably 10 to 20% thinner than the active material layer of the positive electrode to control cell balancing.

In addition, the positive electrode according to the present invention may be prepared by coating an active material layer on a positive electrode current collector.

As the positive electrode current collector according to the present invention, an article of a material conventionally used as an electric double layer capacitor or a lithium ion battery can be used, and for example, at least one member selected from the group consisting of aluminum, stainless steel, titanium, tantalum, and niobium. Of these, aluminum is preferred.

The thickness of the positive electrode collector is preferably about 10 to 300 mu m. The current collector may include not only the foil of the metal but also an etched metal foil or an opening metal such as expanded metal, punching metal, net, foam or the like through the front and back surfaces.

The positive electrode active material layer may be prepared by applying an active material slurry containing a conductive material, a binder, a solvent, and the like. In the present invention, a mixture of the electrode active material, the conductive material, and the solvent may be molded into a sheet shape using the binder resin, or a molded sheet extruded by an extrusion method may be bonded to the current collector using a conductive adhesive.

The electrode active material, the conductive material, the binder, and the solvent included in the positive electrode active material slurry may be the same as those used when preparing the negative electrode active material slurry.

The electrochemical capacitor according to the present invention may be manufactured by insulating the positive electrode and the negative electrode with a separator, impregnating the electrolyte, and storing the same in an exterior material.

The separator according to the present invention may use materials of any material conventionally used in an electric double layer capacitor or a lithium ion battery. 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) And microporous films prepared from one or more polymers selected from the group consisting of polyimide (PI), polyethylene oxide (PEO), polypropylene oxide (PPO), cellulose polymers, and polyacrylic polymers. A multilayer film obtained by polymerizing the porous film may also be used, and among them, a cellulose-based polymer may be preferably used.

The thickness of the separator is preferably about 10 ~ 40㎛, but is not limited thereto.

Electrolyte solution of the present invention comprises a non-lithium salt such as a spiro salt, TEABF4, TEMABF4, LiPF ₆ , LiBF ₄ , LiCLO ₄ , LiN (CF ₃ SO ₂ ) ₂ , CF ₃ SO ₃ Li, LiC (SO ₂ CF _{3) 3,} LiAsF _6, and an organic electrolyte solution containing a lithium salt such as LiSbF ₆ or a mixture thereof can be used for both. The solvent may be one or more selected from the group consisting of an acrylonitrile solvent, ethylene carbonate, propylene carbonate, dimethyl carbonate, ethylmethyl carbonate, sulfolane and dimethoxyethane, but is not limited thereto. The electrolyte solution combining these solutes and solvents has high withstand voltage and high electrical conductivity. The concentration of the electrolyte in the electrolyte is preferably 0.1 to 2.5 mol / L and 0.5 to 2 mol / L.

As the case (exterior material) of the electrochemical capacitor of the present invention, it is preferable to use a laminate film or a rectangular aluminum case containing aluminum commonly used in a secondary battery and an electric double layer capacitor, but is not particularly limited thereto.

Hereinafter, preferred embodiments of the present invention will be described in detail. The following examples are intended to illustrate the present invention, but the scope of the present invention should not be construed as being limited by these examples. In the following examples, specific compounds are exemplified. However, it is apparent to those skilled in the art that equivalents of these compounds can be used in similar amounts.

Example  One

1) cathode manufacturing

The LiC ₆ layer was applied to a thickness of about 2 μm through a doping process after applying Li intercalated graphite using a comma coater on an aluminum etching foil having a thickness of 20 μm.

A negative electrode active material slurry was prepared by mixing and stirring 85 g of activated carbon (specific surface area 2150 m ² / g), 12 g of acetylene black as a conductive material, and 11.5 g of PVDF as a binder to 210 g of NMP. The active material slurry was coated on the LiC ₆ layer by using a comma coater (comma coater) of about 54㎛ thickness (10% compared to the positive electrode active material layer).

Prior to assembly of the cell, it was dried for 24 hours in a vacuum at 120 ℃.

2) anode manufacturing

85 g of activated carbon (specific surface area 2150 m ² / g), 12 g of acetylene black as a conductive material, 3.5 g of CMC as a binder, 12.0 g of SBR, and 5.5 g of PTFE were mixed and stirred in 225 g of water to prepare a positive electrode active material slurry.

The positive electrode active material slurry was applied on a 20-micrometer-thick aluminum etching foil using a comma coater, and after temporary drying, it cut | disconnected so that an electrode size might be 50 mm x 100 mm. The thickness of the cross section of the electrode is 60㎛ . Prior to assembly of the cell, it was dried for 48 hours in a vacuum at 120 ℃.

2) cell manufacturing

A separator (TF4035, NKK, cellulose separator) was inserted between the prepared anode and cathode, and 1.6 mol / liter of electrolyte (TEABF ₄ + LiBF ₄ salt (1: 1 ratio) in an acrylonitrile solvent) was added. Density | concentration), and it put into the laminated film case and sealed.

Comparative Example  One

1) electrode manufacturing

An electrode active material slurry was prepared by mixing and stirring 85 g of general activated carbon (specific surface area 2150 m ² / g), 12 g of acetylene black as a single conductive material, 3.5 g of CMC, 12.0 g of SBR, and 5.5 g of PTFE as a binder in 225 g of water.

The electrode active material slurry was applied using a comma coater on an aluminum etching foil having a thickness of 20 μm, and temporarily dried, and then cut to have an electrode size of 50 mm × 100 mm. The cross-sectional thickness of the electrode was 60 µm. Prior to assembly of the cell, it was dried for 48 hours in a vacuum at 120 ℃.

2) cell manufacturing

Using the electrode as a positive electrode and a negative electrode, a separator (TF4035, NKK, cellulose separator) was inserted between the positive electrode and the negative electrode, and an electrolyte solution (concentration of 1.6 mol / liter of TEABF ₄ salt in acrylonitrile solvent) was added. It was made to impregnate, and it put in the laminated film case and sealed.

Experimental Example  Electrochemistry Capacitor  Capacity evaluation of the cell

At constant temperature and constant temperature of 25 ° C., a current density of 1 mA / cm 2 at a constant current-constant voltage was charged to 2.5 V for Comparative Example 1 and 3.0 V for Example 1, held for 30 minutes, and then again maintained at 1 mA / cm 2. Capacity of the last cycle was measured by discharging three times with constant current, and the results are shown in Table 1 below. In addition, the resistance characteristics of each cell were measured by ampere-ohm meter and impedance spectroscopy, and the results are shown in Table 1 below.

division Initial capacity characteristic (F) Resistance characteristic (AC ESR, mΩ) Comparative Example 1 11.57 19.12 Example 1 20.66 20.21

In the case of Example 1, the voltage of the entire cell actually increased to 4V or more due to the reduction of the cathode potential due to the formation of the LiC ₆ layer, but in spite of measuring only up to 3V in consideration of long-term reliability and stability, It can be seen that the initial capacity characteristics are nearly twice that of the superior.

100: cathode
110: negative electrode current collector
120: LiC ₆ Layer
130: negative electrode active material layer
200: anode
210: positive electrode current collector
230: positive electrode active material layer

Claims (8)

A negative electrode including a LiC ₆ layer and an active material layer on a negative electrode current collector, and
An electrochemical capacitor using a positive electrode comprising an active material layer on a positive electrode current collector.
The method of claim 1,
The thickness of the LiC ₆ layer is formed to less than 10㎛ electrochemical capacitor.
The method of claim 1,
Active materials of the positive electrode and the negative electrode may be the same or different, respectively, activated carbon, carbon nanotubes (CNT), graphite, carbon aerogels, polyacrylonitrile (PAN), carbon nanofibers (CNF), activated carbon nanofibers (ACNF) ), At least one carbon material selected from the group consisting of vapor-grown carbon fiber (VGCF), and graphene.
The method of claim 1,
The active material of the positive electrode and the negative electrode is an electrochemical capacitor of activated carbon having a specific surface area of 1,500 ~ 3,000 m 2 / g.
The method of claim 1,
The active material layer of the negative electrode is an electrochemical capacitor is formed 10 to 20% thinner than the active material layer of the positive electrode.
The method of claim 1,
The potential of the cathode is maintained at 0 ~ 0.2V electrochemical capacitor.
Forming a LiC ₆ layer on the negative electrode current collector,
A negative electrode manufacturing step comprising forming an active material layer on the LiC ₆ layer, And
A method of manufacturing an electrochemical capacitor comprising a cathode manufacturing step including an active material layer on a cathode current collector.
The method of claim 7, wherein
The thickness of the LiC ₆ layer is 10㎛ or less manufacturing method of the electrochemical capacitor.

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