Patent Publication Number: US-2012033346-A1

Title: Energy storage device

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the benefit under 35 U.S.C. Section [120, 119, 119(e)] of Korean Patent Application Serial No. 10-2010-0075636, entitled “Energy Storage Device”, filed on Aug. 5, 2010″, which is hereby incorporated by reference in its entirety into this application. 
     BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention relates to an energy storage device, and more particularly, to an energy storage device with improved capacitance and output. 
     2. Description of the Related Art 
     Among next energy storage devices, a device called an ultra capacitor or a super capacitor has been in the limelight due to a rapid charging/discharging rate, high stability, and environmentally friendly characteristics. A general super capacitor is configured of an electrode structure, a separator, an electrolyte solution, and the like. The super capacitor 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 super capacitors, a lithium ion capacitor (LIC), an electric double layer capacitor (EDLC), a pseudocapacitor, a hybrid capacitor, and the like are currently used. 
     The lithium ion capacitor is a super capacitor which uses a positive electrode made of activated carbon and a negative electrode made of graphite, and uses lithium ions as carrier ions. The electric double layer capacitor is a super capacitor which uses an electrode made of activated carbon and uses an electric double layer charging as a reaction mechanism. The pseudocapacitor is a super capacitor which uses a transition metal oxide or a conductive polymer as an electrode and uses pseudo-capacitance as a reaction mechanism. The hybrid capacitor is a super capacitor which has 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 reason is that most of the super capacitors as described above are driven by a charging/discharging mechanism using the movement of carrier ions on the interface between the electrode and the electrolyte and a chemical reaction on the surface of the electrode. At present, in an energy storage device such as a super capacitor, a need exists for a technology development for improving a relatively low capacitance. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide an energy storage device with improved output and capacitance. 
     Another object of the present invention is to provide a hybrid type energy storage device in which an electrode structure implementing relatively high capacitance and an electrode structure implementing relatively high output are provided in a single cell. 
     Another object of the present invention is to provide a hybrid type energy storage device in which an energy storage structure using a reaction mechanism implementing relatively high capacitance and an energy storage structure using a reaction mechanism implementing relatively high output are provided in a single cell. 
     According to an exemplary embodiment of the present invention, there is provided an energy storage device, including: a case providing an internal space with a first space and a second space; an electrolyte solution filled in the internal space of the case; a positive electrode structure disposed on an interface between the first space and the second space and having a cathode active material layer including activated carbon; a first negative electrode disposed in the first space and having a first anode active material layer including graphite; and a second negative electrode disposed in the second space and having a second cathode active material layer including activated carbon. 
     The positive electrode structure may further include a positive electrode collector of which surface is coated with the cathode active material layer, wherein the positive electrode collector is used as a partition wall partitioning the first space from the second space. 
     The positive electrode collector may include an aluminum foil. 
     The first negative electrode may further include a first negative electrode collector of which surface is coated with the first anode active material layer and the second negative electrode may further include a second negative electrode collector of which surface is coated with the second anode active material layer. 
     The first negative electrode collector may include a copper foil, and the second negative electrode collector may include an aluminum foil. 
     The electrolyte solution may include a first electrolyte solution filled in the first space, wherein the first electrolyte solution may include at least any one of LiPF6, LiBF4, LiSbF6, LiAsF5, LiClO4, LiN, CF3S03, LiC, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiC(SO2CF3)2, LiPF4(CF3)2, LiPF3(C2F5)3, LiPF3(CF3)3, LiPF5(iso-C3F7)3, LiPF5(iso-C3F7), (CF2)2(SO2)2NLi, and (CF2)3(SO2)2NLi. 
     The electrolyte solution may include a second electrolyte solution filled in the second space, wherein the second electrolyte solution may include at least any one of tetraethyl ammonium tetrafluoroborate (TEABF4), tetraethylmethyl ammonium tetrafluoroborate (TEMABF4), ethylmethyl ammonium tetrafluoro (EMBF4), and diethylmethyl ammonium tetrafluoroborate (DEMEBF4), and spirobipyrrolidinium tetrafluoroborate (SBPBF4). 
     The energy storage device may further include a first separator disposed between the positive electrode structure and the first negative electrode; and a second separator disposed between the positive electrode structure and the second negative electrode. 
     According to another exemplary embodiment of the present invention, there is provided an energy storage device, including: a case providing an internal space with a first space and a second space; a first electrolyte solution filled in the first space and a second electrolyte solution filled in the second space; a positive electrode structure disposed on an interface between the first space and the second space and having a cathode active material layer; a first negative electrode disposed in the first space and having a first anode active material layer; and a second negative electrode disposed in the second space and having a second anode active material layer, wherein the first electrolyte solution includes first positive ions having a charging reaction mechanism that they are stored to the inside of the first anode active material layer, and the second electrolyte solution includes second positive ions having a charging reaction mechanism that they are absorbed to the surface of the second anode active material layer. 
     The first positive ions may include lithium (Li + ) ions. The second positive ions may include ammonium (NH 4   + ) ions. The cathode active material layer may include activated carbon, the first anode active material layer may include graphite, and the second anode active material layer may include activated carbon. 
     The positive electrode structure may further include a positive electrode collector of which surface is coated with the cathode active material layer, wherein the positive electrode collector is used as a partition wall partitioning the first space from the second space. 
     The positive electrode structure and the first negative electrode may form an electrode structure of a lithium ion capacitor (LIC), and the positive electrode structure and the second negative electrode may form an electrode structure of an electric double layer capacitor (EDLC). 
     The positive electrode structure may further include a positive electrode collector of which surface is coated with the cathode active material layer, the first negative electrode may further include a first negative electrode collector of which surface is coated with the first anode active material layer, and the second negative electrode may further include a second negative electrode collector of which surface is coated with the second anode active material layer, wherein the positive electrode collector may include an aluminum foil, the first negative electrode collector may include a copper foil, and the second negative electrode collector may include an aluminum foil. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram showing an energy storage device according to an exemplary embodiment of the present invention; 
         FIG. 2  is a diagram for explaining a reaction mechanism when charging the energy storage device of  FIG. 1 ; and 
         FIG. 3  is a diagram for explaining a reaction mechanism when discharging the energy storage device of  FIG. 1 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Various advantages and features of the present invention and methods accomplishing thereof will become apparent from the following description of embodiments with reference to the accompanying drawings. However, the present invention may be modified in many different forms and it should not be limited to the embodiments set forth herein. These embodiments may be provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like reference numerals in the drawings denote like elements. 
     Terms used in the present specification are for explaining the embodiments rather than limiting the present invention. Unless explicitly described to the contrary, a singular form includes a plural form in the present specification. The word “comprise” and variations such as “comprises” or “comprising,” will be understood to imply the inclusion of stated constituents, steps, operations and/or elements but not the exclusion of any other constituents, steps, operations and/or elements. 
     Hereinafter, an energy storage device according to the present invention will be described in detail with reference to the accompanying drawings. 
       FIG. 1  is a diagram showing an energy storage device according to an exemplary embodiment of the present invention. Referring to  FIG. 1 , an energy storage device  100  according to an exemplary embodiment of the present invention may include an electrode structure, a separator  130 , and an electrolyte solution  140 . 
     The electrode structure may include a positive electrode structure  110  and a negative electrode structure  120 . The positive electrode and negative electrode structures  110  and  120  may be disposed in a case (not shown). Portions of the positive electrode and negative electrode structures  110  and  120  may be selectively exposed to the outside of the case. The positive electrode structure  110  and the negative electrode structure  120  may exchange carrier ions, which are electrochemical reaction mediators, through the electrolyte solution  140 . 
     The positive electrode structure  110  may be disposed to be opposite to the negative electrode structure  120 , while having the separator  130  therebetween. The positive electrode structure  110  may include a positive electrode collector  112  and a cathode active material layer  114  covering the surface of the positive electrode collector  112 . As the positive electrode collector  112 , any one of various kinds of metal foils may be used. The cathode active material layer  114  may be formed by coating the surface of the metal foil with a cathode active material. As an example, the positive electrode collector  112  may be an aluminum foil and the cathode active material layer  114  may be a coating layer made of active carbon. 
     Meanwhile, the positive electrode structure  110  may be used as a partition wall partitioning inner space of the energy storage device  100 . For example, the positive electrode collector  112  may partition the case so that the inner space of the case is divided into two spaces. To this end, the positive electrode collector  112  may be provided to have a metal foil disposed so as to vertically cross the case. Therefore, the inner space of the case may be divided into a first space  101  and a second space  102 , partitioned from each other, and the positive electrode collector  112  may be substantially disposed on the interface between the first space  101  and the second space  102 . 
     The negative electrode structure  120  may include a first negative electrode  122  disposed on one side of the positive electrode structure  110  and a second negative electrode  124  disposed on the other side of the positive electrode structure  110  based on the positive electrode structure  110 . 
     The first negative electrode  122  may be disposed in the first space  101 . The first negative electrode  122  may include a first negative electrode collector  122   a  and a first anode active material layer  122   b  formed on the surface of the first negative electrode collector  122   a . As the first negative electrode collector  122   a , various kinds of metal foils may be used and the first anode active material layer  122   b  may be formed by coating the surface of the metal foil with a first anode active material. As an example, as the first negative electrode collector  122   a , a copper foil may be used and as the first anode active material layer  122   b , a thin film made of graphite may be used. 
     The second negative electrode  124  may be disposed in the second space  102 . The second negative electrode  124  may include a second negative electrode collector  124   a  and a second anode active material layer  124   b  formed on the surface of the second negative electrode collector  124   a . As the second negative electrode collector  124   a , various kinds of metal foils may be used and the second anode active material layer  124   b  may be formed by coating the surface of the metal foil with a second anode active material. As an example, as the second negative electrode collector  124   a , an aluminum foil may be used and as the second anode active material layer  124   b , a thin film made of active carbon may be used. 
     The separator  130  may be selectively disposed between the positive electrode structure  110  and the negative electrode structure  120 . As an example, the separator  130  may include a first separator  132  disposed in the first space  101  and a second separator  134  disposed in the second space  102 . The first separator  132  may be disposed between the positive electrode structure  110  and the first negative electrode  122 , thereby making it possible to partition the positive electrode structure  110  from the first negative electrode  122 . Similarly, the second separator  134  may be disposed between the positive electrode structure  110  and the second negative electrode  124 , thereby making it possible to partition the positive electrode structure  110  from the second negative electrode  124 . As the separator  130 , at least any one of nonwoven fabric, polytetrafluorethylene (PTFE), a porous film, a craft fiber, a cellulosic electrolytic paper, rayon fiber, and other various kinds of sheets may be used. 
     The electrolyte solution  140  may be filled in the case. The electrolyte solution  140  may include positive ions and negative ions, which are moving mediators between the positive electrode structure  110  and the negative electrode structure  120 . The electrolyte solution  140  may be a composition prepared by melting electrolyte salt in a predetermined solvent. For example, the electrolyte solution  140  may include a first electrolyte solution  142  filled in the first space  101  and a second electrolyte solution  144  filled in the second space  102 . 
     The first electrolyte solution  142  may be a composition prepared by melting first electrolyte salt in the solvent. The first electrolyte salt may have first positive ions  142   a  having a charging reaction mechanism that they are stored to the inside of the first anode active material layer  122   b  of the first negative electrode  122 . As the first electrolyte salt, lithium-based electrolyte salt may be used. The lithium-based electrolyte salt may be salt including lithium (Li + ) ions as carrier ions between the positive electrode structure  110  and the first negative electrode  122  at the time of charging and discharging operations of the energy storage device  100 . For example, the lithium-based electrolyte salt may include at least any one of LiPF6, LiBF4, LiSbF6, LiAsF5, LiClO4, LiN, CF3SO3, and LiC. Alternatively, the lithium-based electrolyte salt may include at least any one of LiN(SO2CF3)2, LiN(SO2C2F5)2, LiC(SO2CF3)2, LiPF4(CF3)2, LiPF3(C2F5)3, LiPF3(CF3)3, LiPF5(iso-C3F7)3, LiPF5(iso-C3F7), (CF2)2(SO2)2NLi, and (CF2)3(SO2)2NLi. 
     The second electrolyte solution  144  may be a composition prepared by melting second electrolyte salt in the solvent. The second electrolyte salt may have second positive ions  144   a  having a charging reaction mechanism that they are absorbed and detached to and from the surface of the second anode active material layer  124   b  of the second negative electrode  124 . As the second electrolyte salt, nonlithium-based electrolyte salt may be used. The nonlithium-based electrolyte salt may be salt including nonlithium ions used as carrier ions between the positive electrode structure  110  and the second negative electrode  124  at the time of charging and discharging operations of the energy storage device  100 . For example, the nonlithium-base electrolyte salt may include ammonium (NH 4   + ) ions. More specifically, the nonlithium-based electrolyte salt may include at least any one of tetraethyl ammonium tetrafluoroborate (TEABF4), tetraethylmethyl ammonium tetrafluoroborate (TEMABF4), ethylmethyl ammonium tetrafluoro (EMBF4), and diethylmethyl ammonium tetrafluoroborate (DEMEBF4). Alternatively, the nonlithium-based electrolyte salt may include spirobipyrrolidinium tetrafluoroborate (SBPBF4). 
     The solvent of the first and second electrolyte solution may include at least any one of annular carbonate and linear carbonate. For example, as the annular carbonate, at least any one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), and vinyl ethylene carbonate (VEC). As the linear carbonate, at least any one of dimethyl carbonate (DMC), methyl ethyl carbonate (MEC), diethyl carbonate (DEC), methyl propyl carbonate (MPC), dipropyl carbonate (DPC), metylbutyl carbonate (MBC), and dibutyl carbonate (DBC). 
     Various kinds of ether, ester, and amide-based solvent may also be used. 
     As described above, the energy storage device  100  according to the exemplary embodiment of the present invention may have a structure of a hybrid type super capacitor in which a single positive electrode structure  110  and two first and second negative electrodes  122  and  124  are provided in a single cell to be operated in each different reaction mechanism. For example, an electrode structure configured of the positive electrode structure  110  and the first negative electrode  122 , that is, an electrode structure of a lithium ion capacitor (LIC), may be provided in the first space  101  of the energy storage device  100  and an electrode structure configured of the positive electrode structure  110  and the second negative electrode  124 , that is, an electrode structure of an electric double layer capacitor (EDLC), may be provided in the second space  102  of the energy storage device  100 . Herein, the electrode structure of the lithium ion capacitor is similar to an electrode structure of a battery using activated carbon and graphite, thereby making it possible to implement higher capacitance as compared to the electrode structure of the electric double layer capacitor. On the other hand, the charging and discharging of the electrode structure of the electric double layer capacitor are driven by the electric double layer charging that uses activated carbon as a reaction mechanism, thereby making it possible to implement higher output as compared to the electrode structure of the lithium ion capacitor. Therefore, the energy storage device  100  according to the present invention has a single cell in which the electrode structure implementing relatively higher capacitance and the electrode structure implementing relatively higher output are provided, thereby making it possible to have a structure of a hybrid type super capacitor with improved output and capacitance. 
     Continuously, charging and discharging mechanisms of the energy storage device according to the exemplary embodiment of the present invention will be described in detail. Herein, a description overlapping with the energy storage device  100  described above may be omitted or simplified. 
       FIG. 2  is a diagram for explaining a reaction mechanism when charging the energy storage device of  FIG. 1  and  FIG. 3  is a diagram for explaining a reaction mechanism when discharging the energy storage device of  FIG. 1 . 
     Referring to  FIGS. 2 and 3 , when a charging operation of the energy storage device  100  according to the present invention starts, the charging thereof may be simultaneously performed from a first electrode structure configured of the positive electrode structure  110  and the first negative electrode  122  and a second electrode structure configured of the positive electrode structure  110  and the second negative electrode  124 . More specifically, positive power may be applied to a positive electrode collector  112  of the positive electrode structure  110  and negative power may be applied to a first negative electrode collector  122   a  of the first negative electrode  122 . Therefore, positive ions  142   a  in the first electrolyte solution  142  may be stored to the inside of a first anode active material layer  122   b  of the first negative electrode  122 , and negative ions  142   b  therein may be absorbed to the surface of a cathode active material layer  114  of the positive electrode structure  110 . That is, a charging reaction mechanism that the positive ions  142   a  in the first electrolyte solution  142  are stored to the inside of the first anode active material layer  122   b  may be implemented in a first space  101  of the energy storage device  100 . At the same time, positive ions  144   a  in the second electrolyte solution  144  may be absorbed to the surface of a second anode active material layer  124   b  of the second negative electrode  124 , and negative ions  144   b  therein may be absorbed to the surface of a cathode active material layer  114  of the positive electrode structure  110 . That is, a charging reaction mechanism that the positive ions  144   a  in the second electrolyte solution  144  are absorbed to the surface of the second anode active material layer  124   b  may be implemented in a second space  102  of the energy storage device  100 . 
     Herein, the first electrode structure forms the electrode structure of the lithium ion capacitor (LIC), thereby making it possible to implement relatively higher capacitance as compared to the second electrode structure forming the electrode structure of the electric double layer capacitor (EDLC). Therefore, the energy storage device  100  supplements the second electrode structure having relatively low capacitance, thereby making it possible to further improve capacitance by the first electrode structure. 
     When the charging operation is completed, power applied to the positive electrode structure  110  and the negative electrode structure  120  of the energy storage device  100  may be stopped. Then, the energy storage device  100  is used. Herein, the output of the energy storage device  100  may be simultaneously performed from the first electrode structure and the second electrode structure. At this time, the second electrode structure may implement higher output as compared to the first electrode structure. Therefore, the energy storage device  100  supplements the first electrode structure having relatively low output, thereby making it possible to further improve output by the second electrode structure. 
     As described above, the energy storage device  100  according to the present invention may operate in the first space  101  by the lithium ion capacitor (LIC) reaction mechanism that lithium (Li + ) ions between the cathode active material layer  114  and the first anode active material layer  122   b  are used as carrier ions, and may operate in the second space  102  by the electric double layer charging reaction mechanism that nonlithium ions (for example, ammonium (NH 4   + ) ions) between the cathode active material layer  114  and the second anode active layer  124   b  are used as carrier ions. Therefore, in the energy storage device  100  according to the present invention, the charging/discharging mechanism implementing relatively high capacitance and the charging/discharging mechanism implementing relatively high output are mutually supplemented to be driven in a single cell, thereby making it possible to have a structure with improved capacitance and output. 
     In the energy storage device according to the present invention, a single positive electrode structure and two negative electrodes are provided in a single cell, thereby making it possible to have a structure of a hybrid type super capacitor in which they operate using different charging and discharging reaction mechanisms. Therefore, the energy storage device according to the present invention may have the structure of the hybrid type super capacitor in which different electrode structures of the super capacitor are provided in a single cell. 
     The energy storage device according to the present invention may include a single common positive electrode structure, a first negative electrode forming an electrode structure of a lithium ion capacitor (LIC) together with the common positive electrode structure, and a second negative electrode forming an electrode structure of an electric double layer capacitor (EDLC) together with the common positive electrode structure. Therefore, the energy storage device according to the present invention has the electrode structure of the lithium ion capacitor implementing relatively high capacitance and the electrode structure of the electric double layer capacitor implementing relatively high output, thereby making it possible to have a structure with improved capacitance and output. 
     The energy storage device according to the present invention may include a single common positive electrode structure, a first negative electrode, and a second negative electrode provided in a single cell, wherein the first negative electrode has a reaction mechanism capable of implementing relatively high capacitance together with the positive electrode structure, and the second negative electrode has a reaction mechanism capable of implementing relatively high output together with the positive electrode structure. Therefore, in the energy storage device according to the present invention, the reaction mechanism implementing relatively high capacitance and the reaction mechanism implementing relatively high output are supplemented and driven in a single cell, thereby making it possible to have a structure with improved capacitance and output. 
     The present invention has been described in connection with what is presently considered to be practical exemplary embodiments. Although the exemplary embodiments of the present invention have been described, the present invention may be also used in various other combinations, modifications and environments. In other words, the present invention may be changed or modified within the range of concept of the invention disclosed in the specification, the range equivalent to the disclosure and/or the range of the technology or knowledge in the field to which the present invention pertains. The exemplary embodiments described above have been provided to explain the best state in carrying out the present invention. Therefore, they may be carried out in other states known to the field to which the present invention pertains in using other inventions such as the present invention and also be modified in various forms required in specific application fields and usages of the invention. Therefore, it is to be understood that the invention is not limited to the disclosed embodiments. It is to be understood that other embodiments are also included within the spirit and scope of the appended claims.