HYBRID CAPACITOR

Abstract

Embodiments of the invention provide a hybrid capacitor that includes a cathode, an anode, a separator and an electrolyte solution. The hybrid capacitor includes a first structure including a cathode containing activated carbon and an anode containing lithium, and a second structure including activated carbon layers formed on both surfaces of a current collector.

Description

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional application of and claims the benefit of and priority to U.S. patent application Ser. No. 13/448,236, entitled, “HYBRID CAPACITOR,” filed on Apr. 16, 2012, which claims priority under 35 U.S.C. §119 to Korean Patent Application No. KR 10-2011-0045737, entitled, “HYBRID CAPACITOR,” filed on May 16, 2011, which are all hereby incorporated by reference in their entirety into this application.

BACKGROUND

1. Field of the Invention

The present invention relates to a hybrid capacitor, and more particularly, to a hybrid capacitor in which a complex structure of a lithium ion capacitor and an electric double layer capacitor is implemented in a single cell to thereby improve a manufacturing efficiency thereof and increase energy density and power density characteristics thereof.

2. Description of the Related Art

A secondary battery, such as a lithium ion battery, which is a representative energy storage device having high energy density, has recently become prominent and has been used as an important energy storage device for various mobile electronic devices.

Among next generation energy storage devices, a device called an ultracapacitor or a supercapacitor has been prominent as a next generation energy storage device due to rapid charging and discharging speed, high stability, and environment-friendly characteristics.

The secondary battery has an advantage in that it has high energy density; however, it has a disadvantage in that it has limited output characteristics. The supercapacitor has an advantage in that it has output characteristics significantly higher than those of the secondary battery; however, it has a disadvantage in that it has low energy density.

In the case of the supercapacitor, a lithium pre-doping technology has been proposed in order overcome the above-mentioned disadvantage. A lithium ion capacitor (LIC) having three to four times more energy density as compared to the energy density of the electric double layer capacitor according to the conventional art by using the above-mentioned technology has started to be commercialized.

A kind of supercapacitors will be simply described. A general supercapacitor is configured of an electrode structure, a separator, an electrolyte solution, and the like. The supercapacitor is driven based on an electrochemical reaction mechanism that carrier ions in the electrolyte solution are selectively adsorbed to the electrode by applying power to the electrode structure. As representative, supercapacitors, a lithium ion capacitor (LIC), an electric double layer capacitor (EDLC), a pseudocapacitor, a hybrid capacitor, as non-limiting example, are currently used.

The lithium ion capacitor is a supercapacitor that uses a cathode made of activated carbon and an anode made of graphite, and uses lithium ions as carrier ions. The electric double layer capacitor is a supercapacitor that uses an electrode made of activated carbon and uses an electric double layer charging as a reaction mechanism. The pseudocapacitor is a supercapacitor which uses a transition metal oxide or a conductive polymer as an electrode and uses a pseudo capacitance as a reaction mechanism. The hybrid capacitor is a supercapacitor having intermediate characteristics between the electric double layer capacitor and the pseudocapacitor.

However, the energy storage devices as described above have a relatively lower capacitance than a secondary battery. This is the reason that most of the supercapacitors as described above are driven by a charging and discharging mechanism using the movement of carrier ions on the interface between the electrode and the electrolyte solution and a chemical reaction on the surface of the electrode. Therefore, in an energy storage device such as a supercapacitor, a need currently exists for developing a technology that improves a relatively low capacitance.

Meanwhile, in both of the lithium ion secondary battery (LIB) and the lithium ion capacitor (LIC) as described above, graphite, which is a carbon material, has been mainly used as a material of an anode. Particularly, in the case of the LIC, in order to increase energy density, the anode lithiated, so that it has a potential of 0.1 V or less has been used. Here, as a method of lithiating the anode, several methods may be used. However, a method of immersing the anode in an ethylene carbonate (EC) based electrolyte solution containing lithium salts has been mainly used. In this case, a solid electrolyte interface (SEI) film is formed on a surface of the graphite. This SEI film passes lithium ions therethrough and is cointercalated with solvent molecules to thereby suppress a side effect that graphite layers are peeled off. Therefore, it has been known that the SEI film is a factor having an important effect on characteristics of the LIC and the LIB.

However, since the SEI film is formed at an initial stage, an initial charging and discharging efficiency and a capacitance of the graphite having a large irreversible capacitance are inevitably reduced. In addition, in a propylene carbonate (PC) based electrolyte solution having excellent low temperature characteristics, the SEI film is not formed; rather, as is generated. Therefore, it has been known that low temperature characteristics of the LIC become poorer than those of the EDLC. Further, in a process of doping the anode with lithium, it is difficult to perform uniform doping, a long time is required, and a performance is unstable, such that there is a limitation in commercialization. Furthermore, the LIC cannot but basically have deteriorated power characteristics due to non-polarization characteristics of the anode, as compared to the EDLC.

Meanwhile, in order to overcome the disadvantages of the secondary battery, research into and development for a technology of systematically combining the EDLC with the existing lithium ion polymer battery have been conducted. As a result of the research and development, a complex battery capable of increasing an instantaneous output arid having increased energy density has been proposed. However, the complex battery has a complicated structure in view of a circuit or a manufacturing process thereof and has an increased mounting space, such that it runs counter to the trend toward miniaturization of the battery.

A need for a technology capable of basically solving the above-mentioned problems gradually increases.

SUMMARY

Accordingly, embodiments of the invention have been made to provide a hybrid capacitor having an increased output and capacitance.

Further, embodiments of the invention have been made to provide a hybrid capacitor in which one cell includes an electrode structure implementing a relative high capacitance and an electrode structure implementing a relative high output, such that only advantages of the existing LIC and EDLC are combined with each other using a complex reaction mechanism through the electrode structures.

According to various embodiments of the invention, there is provided a hybrid capacitor that includes a cathode, an anode, a separator and an electrolyte solution. The hybrid capacitor, includes a first structure including a cathode containing activated carbon and an anode containing lithium, and a second structure including activated carbon layers formed on both surfaces of a current collector.

According to another embodiment of the invention, there is provided a hybrid capacitor including a first structure including a cathode containing activated carbon and an anode containing lithium, and second structures each disposed on both sides of the first structure, the second structure including activated carbon layers formed on both surfaces of a current collector.

According to an embodiment, the cathode and the anode include a separator provided therebetween.

According to an embodiment, the first and second structures include a separator provided therebetween.

According to an embodiment, the cathode is formed by attaching a conductive material, activated carbon, and a binder to both surfaces of a current collector.

According to an embodiment, the current collector is an aluminum foil.

According to an embodiment, the anode includes lithium metal layers formed on both surfaces of a current collector.

According to an embodiment, the current collector is a copper foil.

According to an embodiment, the lithium metal layers further include lithium nitride (Li₃N) layers formed on outer surfaces thereof.

According to an embodiment, the second structure is formed by attaching a material containing 5 to 10 wt % of conductive material, 80˜90 wt % of activated carbon, and 5˜10 wt % of binder to both surfaces of the current collector.

According to an embodiment, the electrolyte solution is a mixture of a lithium salt and a non-lithium salt.

According to another embodiment of the invention, there is provided a hybrid capacitor including a first electrode including lithium layers formed on both surfaces of a current collector, a second electrode including activated carbon layers formed on both surfaces of an aluminum foil, and a third electrode including activated carbon layers formed on both surfaces of a current collector. The electrodes are disposed in the order of the third electrode, the first electrode, the second electrode, and the third electrode.

According to an embodiment, at least two combinations of the first and second electrodes are disposed between the two third electrodes disposed at an outermost portion of the hybrid capacitor.

According to an embodiment, the electrodes include separators provided thereamong.

According to an embodiment, the first electrode includes lithium metal layers formed on both surfaces of a current collector.

According to an embodiment, the current collector is a copper foil.

According to an embodiment, the lithium metal layers further include lithium nitride (Li₃N) layers formed on outer surfaces thereof.

According to an embodiment, the second electrode is formed by attaching a conductive material, activated carbon, and a binder to both surfaces of an aluminum foil.

According to an embodiment, the third electrode is formed by attaching a material containing 5 to 10 wt % of conductive material, 80˜90 wt % of activated carbon, and 5˜10 % of binder to both surfaces of the current collector.

According to an embodiment, the electrolyte solution is a mixture of a lithium salt and a non-lithium salt.

According to an embodiment, the lithium salt is at least one selected from a group consisting of LiPF₆, LiBF₄, LiSbF₆, LiAsF₆, LiClO₄, LiN(C₂F₅SO2)₂, LiN(CF₃SO₂)₂, and CF₃SO₃Li, LiC(CF₃SO₂)₃.

According to at embodiment, the non-lithium salt is at least one selected from a group consisting of TEABF₄, TEMABF₄, SBPBF₄, EMIBF₄, DEMEBF₄.

Various objects, advantages and features of the invention will become apparent from the following description of embodiments with reference to the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

These and other features, aspects, and advantages of the invention are better understood with regard to the following Detailed Description, appended Claims, and accompanying Figures. It is to be noted, however, that the Figures illustrate only various embodiments of the invention and are therefore not to be considered limiting of the invention's scope as it may include other effective embodiments as well.

FIG. 1 is a view schematically showing a hybrid capacitor according to an embodiment of the invention.

FIG. 2 is a view schematically showing a hybrid capacitor according to an embodiment of the invention.

FIG. 3 is a view schematically showing a hybrid capacitor according to an embodiment of the invention.

DETAILED DESCRIPTION

Advantages and features of the present invention and methods of accomplishing the same will be apparent by referring to embodiments described below in detail in connection with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below and may be implemented in various different forms. The embodiments are provided only for completing the disclosure of the present invention and for fully representing the scope of the present invention to those skilled in the art.

For simplicity and clarity of illustration, the drawing figures illustrate the general manner of construction, and descriptions and details of well-known features and techniques may be omitted to avoid unnecessarily obscuring the discussion of the described embodiments of the invention. Additionally, elements in the drawing figures are not necessarily drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help improve understanding of embodiments of the present invention. Like reference numerals refer to like elements throughout the specification.

Hereinafter, an energy storage device according to various embodiments of the invention will he described in detail with reference to the accompanying drawings.

FIG. 1 is a view schematically showing a hybrid capacitor according to an embodiment of the invention.

Referring to FIG. 1, a hybrid capacitor according to an embodiment of the invention is configured to include a first structure 100 including a cathode 20 containing activated carbon 21 and an anode 10 containing lithium; and a second structure 200 including activated carbon layers formed on both surfaces of a current collector.

When the hybrid capacitor is configured as shown in FIG. 1 a charging and discharging process is performed between the anode 10 and the cathode 20 and between the anode 10 and the second structure 200 by the same mechanism as that of a lithium ion capacitor (LIC).

FIG. 3 is a view schematically showing a hybrid capacitor according to an embodiment of the invention. Referring to the FIG. 3 each of the second structures 200 including the activated carbon layers formed on both surfaces of the current collector is disposed on both sides of the first structure 100 including the cathode 20 containing the activated carbons and the anode 10 containing the lithium. In this configuration, a charging and discharging process is performed between the anode 10 and the cathode 20 and between the anode 10 and the second structure 200 by the same mechanism as that of the LIC and he performed between the cathode 20 and the second structure 200 by the same mechanism as that of an electric double layer capacitor (EDLC).

In this configuration, the cathode 20 and the anode 30 and/or the first structure 100 and the second structure 200 include a separator 30 provided therebetween.

According to an embodiment, the cathode 20 is formed by attaching a conductive material, activated carbon, and a binder to both surfaces of a current collector. Particularly, the current collector 22 is an aluminum foil.

According to an embodiment, the anode 10 is mainly made of graphite, similar to the general LIC according to the conventional art, and is pre-doped with lithium and then used.

However, according to another embodiment of the invention, lithium metal layers 12, 14 are included in the anode 10 in order to reduce the possibility of short circuit generation due to the growth of a lithium electrode in the LIC according to the conventional art. In this configuration, as the current collector 13, a copper foil is used.

According to an embodiment, the lithium metal layers 12, 14 further include lithium nitride (Li₃N) layers 11, 15 formed on outer surfaces thereof.

According to an embodiment, the lithium nitride is also called transition metal doped lithium nitride. A technology capable of controlling the number of lithium ion vacancies and the degree of transition metal substitution has been developed, such that applicability has increased. The lithium nitride is an excellent anode material for a rechargeable battery. Since electron conductivity and ion conductivity of the lithium nitride are determined by the number of vacancies existing in an internal structure thereof, the technology capable of controlling the number of lithium ion vacancies and the degree of transition metal substitution has been developed, thereby making it possible to expect a considerable ripple effect.

Since atomic lithium theoretically has a high capacitance and an excellent oxidation-reduction property, it has been recognized as an optimal anode material. However, the atomic lithium easily decomposes, such that it has low structural stability. In order to supplement this problem, lithium doped graphite has been developed.

Since the lithium nitride has high structural stability and capacitance, it is regarded as the most prominent material capable of replacing the lithium doped graphite. Pure lithium nitride has excellent ion conductivity; however, it has lower electric conductivity. Therefore, it is preferable to increase electric conductivity by doping the pure lithium nitride with a specific transition metal.

The lithium nitride has a special laminar structure in which a lithium-only layer is interposed between layers in which lithium and nitrogen coexist. It was found that transition metal substitution is selectively generated only in the lithium-only layer. When lithium ions composing the lithium-only layer are substituted with the transition metal, lithium ions composing the lithium-nitrogen layer are removed, such that vacancies occur.

Since ionic conduction of the lithium nitride is created in a process in which the lithium ions move to the vacancies, as the number of vacancies increases, conductivity increases. A temperature and a time of a synthesis reaction of the transition metal doped lithium nitride are controlled, thereby making it possible to control the number of lithium ion vacancies and a substituted area. When the amount of transition metal is fixed and a reaction temperature is increased, the lithium ion vacancies are increased. It means that electric conductivity and ion conductivity of the doped lithium nitride are controlled by controlling a reaction temperature or a reaction time in a synthesis process.

Since the lithium nitride has the characteristics as described above, it may be used as an anode material of the hybrid capacitor, instead of the lithium doped graphite according to the conventional art. According to an embodiment of the invention, the lithium nitride is used, thereby making it possible to solve a short circuit problem due to the growth of the lithium electrode according to the related art. Furthermore, it is possible to solve problems, such as an inefficiency and a limitation in reliability due to the lithium pre-doping process that has been necessarily performed in order to implement the lithium doped graphite according to the related art.

According to an embodiment, the second structure 200 is funned by attaching a material containing 5 to 10 wt % of conductive material, 80˜90 wt % of activated carbon, and 5˜10 wt % of binder to both surfaces of the current collector.

According to an embodiment, the second structure 200 serves to increase energy density and improve of output characteristics within a cell. However, in the case of the hybrid capacitor according to an embodiment of the invention, the increase in energy density is accomplished by the lithium metal layer or the lithium nitride and improvement in output characteristics is accomplished by the electrode containing the activated carbon. Meanwhile, the second structure 200 is introduced, thereby making it possible to reduce the entire resistance of the cell and allow a process of storing and discharging an electrical energy generated by a physicochemical mechanism between electrodes to be efficiently performed.

Therefore, according to an embodiment, the second structure 200 is formed to have a higher content of conductive material and a thinner thickness than those of the general electrode made of the activated carbon, thereby making it possible to accomplish an object of reducing the entire resistance of the cell.

According to an embodiment, a mixture of lithium salts and non-lithium salts is used as an electrolyte solution.

According to an embodiment, more specifically, at least one of lithium salts, such as LiPF₆, LiBF₄, LiSbF₆, LiAsF₆, LiClO₄, LiN(C₂F₅SO2)₂, LiN(CF₃SO₂)₂, CF₃SO₃Li, LiC(CF₃SO₂)₃, as non-limiting examples, and at least one of non-lithium salts for the EDLC, such as TEABF₄, TEMABF₄, SBPBF₄, EMIBF₄, DEMEBF₄, as non-limiting examples, are mixed with each other in a non-aqueous solvent for a supercapacitor or a secondary battery, making it possible to maximize a capacitance increase effect due to adsorption and desorption of other element ions in addition to intercalation and deintercalation effects of the lithium ions. In addition, a generation amount of a hydrogen fluoride (HF) by hydrolysis is smaller as compared to the existing single lithium salt electrolyte solution, thereby making it possible to increase a lifespan of the supercapacitor.

In a preparatory experiment, since the lithium salt has the highest ion conductivity, the LiPF6 currently used most as the lithium salt was mixed with each of the three non-lithium salts for the EDLC and capacitances thereof were measured. As a result of the measurement, it was shown that all of three mixtures have a higher capacitance as compared to a single salt.

FIG. 2 is a view schematically showing a hybrid capacitor according to another embodiment of the invention.

A hybrid capacitor according to another embodiment of the invention includes a first electrode 10 including lithium layers formed on both surfaces of a current collector 13, a second electrode 20 including activated carbon layers 21 formed on both surfaces of an aluminum foil 22, and a third electrode 200 including activated carbon layers formed on both surfaces of a current collector. According to an embodiment, the electrodes are disposed in the order of the third electrode 200, the first electrode 10, the second electrode 20, and the third electrode 200.

According to an embodiment, in this configuration, at least two combinations of the first and second electrodes 10, 20 are disposed between the two third electrodes 200 disposed at an outermost portion of the hybrid capacitor, thereby making it possible to increase energy density of a cell. As a result, the energy density of the cell may be simply controlled by the number of first and second electrodes 10, 20. In addition, in this configuration, the electrodes include separators 30 provided thereamong.

Further, according to an embodiment, the first electrode 10 includes lithium metal layers 12, 14 formed on both surfaces of a current collector 13. According to an embodiment, the current collector 13 is a copper foil.

In addition, according to an embodiment, the lithium metal layers 12, 14 further include lithium nitride (Li₃N) layers 11, 15 formed on outer surfaces thereof. Since the reason has been described above, an overlapped description will be omitted.

In the hybrid capacitor according to the various embodiments of the invention configured as described above, a charging and discharging process is performed between the first and second electrodes 10, 20 and between the first and third electrodes 10, 200 by the same mechanism as that of the LIC, and is performed between the second and third electrodes 20, 200 by the same mechanism as that of an electric double layer capacitor (EDLC) according to the conventional art. Reaction mechanisms of the LIC and the EDLC are already known technologies. Therefore, a detailed description thereof will be omitted.

According to an embodiment, the anode 10 of the first structure 100 described above corresponds to the first electrode 10, the cathode 20 thereof corresponds to the second electrode 20, and the second structure 200 corresponds to the third electrode 200.

With the above-mentioned configuration and operating principle, it is possible to implement a novel hybrid capacitor in which only advantages of the LIC and the EDLC are combined with each other.

With the hybrid capacitor according to an embodiment of the invention, characteristics of an LIC and characteristics of an EDLC are implemented in a single cell, thereby making it possible to increase energy density and improve output characteristics.

In addition, it is possible to solve a short circuit problem due to the gradual growth of the lithium ions in the anode as well as problems such as a reduction in process efficiency, an increase in cost, and a limitation in securing reliability due to lithium pre-doping that has existed in the LIC according to the conventional art.

Further, the hybrid capacitor, according to various embodiments, includes the electrode having a high content of conductive material and a thin thickness, thereby making it possible to improve the output characteristics simultaneously with reducing the entire resistance of the cell. Furthermore, the number of the electrodes within the hybrid capacitor are increased or decreased as needed, thereby making it possible to easily set required energy density.

Terms used herein are provided to explain embodiments, not limiting the present invention. Throughout this specification, the singular form includes the plural form unless the context clearly indicates otherwise. When terms “comprises” and/or “comprising” used herein do not preclude existence and addition of another component, step, operation and/or device, in addition to the above-mentioned component, step, operation and/or device.

Embodiments of the present invention may suitably comprise, consist or consist essentially of the elements disclosed and may be practiced in the absence of an element not disclosed. For example, it can be recognized by those skilled in the art that certain steps can be combined into a single step.

The terms and words used in the present specification and claims should not be interpreted as being limited to typical meanings or dictionary definitions, but should be interpreted as having meanings and concepts relevant to the technical scope of the present invention based on the rule according to which an inventor can appropriately define the concept of the term to describe the best method he or she knows for carrying out the invention.

The terms “first,” “second,” “third,” “fourth,” and the like in the description and in the claims, if any, are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the invention described herein are, for example, capable of operation sequences other than those illustrated or otherwise described herein. Similarly, if a method is described herein as comprising a series of steps, the order of such steps as presented herein is not necessarily the only order in which such steps may be performed, and certain of the stated steps may possibly be omitted and/or certain other steps not described herein may possibly be added to the method.

The singular forms “a,” “an,” and “the” include plural referents, unless the context clearly dictates otherwise.

As used herein and in the appended claims, the words “comprise,” “has,” and “include” and all grammatical variations thereof are each intended to have an open, non-limiting meaning that does not exclude additional elements or steps.

As used herein, the terms “left,” “right,” “front,” “back,” “top,” “bottom,” “over,” “under,” and the like in the description and in the claims, if any, are used for descriptive purposes and not necessarily for describing permanent relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the invention described herein are, for example, capable of operation in other orientations than those illustrated or otherwise described herein. The term “coupled,” as used herein, is defined as directly or indirectly connected in an electrical or non-electrical manner. Objects described herein as being “adjacent to” each other may be in physical contact with each other, in close proximity to each other, or in the same general region or area as each other, as appropriate for the context in which the phrase is used, Occurrences of the phrase “according to an embodiment” herein do not necessarily all refer to the same embodiment.

Ranges may be expressed herein as from about one particular value, and/or to about another particular value. When such a range is expressed, it is to be understood that another embodiment is from the one particular value and/or to the other particular value, along with all combinations within said range.

Although the present invention has been described in detail, it should be understood that various changes, substitutions, and alterations can be made hereupon without departing from the principle and scope of the invention. Accordingly, the scope of the present invention should be determined by the following claims and their appropriate legal equivalents.

Claims

1. A hybrid capacitor that includes a cathode, an anode, a separator and an electrolyte solution, the hybrid capacitor comprising:

a first structure including a cathode containing activated carbon and an anode containing lithium; and

a second structure including activated carbon layers formed on both surfaces of a current collector.

2. A hybrid capacitor that includes a cathode, an anode, a separator and an electrolyte solution, the hybrid capacitor comprising:

a first structure including a cathode containing activated carbon and an anode Containing lithium; and

second structures each disposed on both sides of the first structure, the second structure including activated carbon layers formed on both surfaces of a current collector.

3. The hybrid capacitor according to claim 1, wherein the cathode and the anode include a separator provided therebetween.

4. The hybrid capacitor according to claim 1, wherein the first and second structures include a separator provided therebetween.

5. The hybrid capacitor according to claim 1, wherein the cathode is formed by attaching a conductive material, activated carbon, and a binder to both surfaces of a current collector.

6. The hybrid capacitor according to claim 5, wherein the current collector is an aluminum foil.

7. The hybrid capacitor according to claim 1, wherein the anode includes lithium metal layers formed on both surfaces of a current collector.

8. The hybrid capacitor according to claim 7, wherein the current collector is copper foil.

9. The hybrid capacitor according to claim 7, wherein lithium metal layers further include lithium nitride (Li3N) layers formed on outer surfaces thereof.

10. The hybrid capacitor according to claim 1, wherein the second structure is formed by attaching a material containing 5 to 10 wt % of conductive material, 80˜90 wt % of activated carbon, and 5˜10 wt % of binder to both surfaces of the current collector.

11. The hybrid capacitor according to claim 1, wherein the electrolyte solution is a mixture of a lithium salt and a non-lithium salt.