WO2014069887A1 - Electrochemical cell - Google Patents

Abstract

The present invention relates to an electrochemical cell, comprising: an anode electrode including a porous material such as activated carbon; and a cathode electrode using a lithium intercalation material such as carbon, graphite, and a lithium titanium oxide (LTO; Li₄Ti₅O₁₂), wherein a lithium solution having lithium dissolved in a solvent such as ethyl amine is injected into an electrode in order to dope lithium into the cathode electrode through lithium intercalation, the solvent is removed from the lithium solution so as to disperse lithium in the electrode and to supply lithium to the electrode, and an electrolyte is injected into the electrode so as to dope lithium into the cathode electrode, thereby simplifying the structure of the electrochemical cell and facilitating the manufacture thereof.

Description

Electrochemical cell

The present invention relates to an electrochemical cell, which is easy to manufacture and to an electrochemical cell having improved power characteristics.

An electric double layer capacitor representing an ultracapacitor has a cathode electrode and an anode electrode having an active material containing porous carbon such as activated carbon, carbon nanotubes, carbon nanofibers, and graphene whose specific surface area exceeds 1000 m ² / g.

 Electric double layer capacitors have been commercially successful because of their excellent power characteristics and long life, but in order to further expand their application, they need to be improved in terms of price and performance.

In particular, in terms of performance, the energy density of the electric double layer capacitor is only about 6 Wh / kg, which is very low compared to about 150 Wh / kg of lithium ion batteries. Increasing the energy density makes it lighter and smaller and less expensive.

However, in order to improve energy density in an electric double layer capacitor, the capacitance of the activated carbon must be increased or the operating voltage must be increased. However, the symmetric type electric double layer capacitor used for the anode electrode and the cathode electrode having a large specific surface area is used on the surface of the activated carbon. Due to the reaction between the adsorbed impurities and the electrolyte, it is currently difficult to realize an operating voltage of more than 2.7V. Nevertheless, electric double layer capacitors have excellent power characteristics and long life. In contrast, secondary batteries such as lithium-ion batteries have very high energy densities but have limited power characteristics and lifetimes.

Among the electrochemical cells, the combination of the advantages of these two types of energy storage devices is also referred to as asymmetric capacitors (Asymmetry Capacitor) or hybrid capacitor (Hybrid Capacitor).

Such an electrochemical cell uses a porous material such as activated carbon as the active material in one electrode from the anode electrode or cathode electrode, and has the form of using the electrode of the secondary battery on the other electrode the intermediate characteristics of the electric double layer capacitor and a secondary battery.

One representative of such an electrochemical cell is a lithium ion capacitor.

Lithium-ion capacitors use an electrolyte containing lithium salt and use graphite as a lithium intercalation material for the negative electrode, such as a lithium ion battery, use activated carbon for the positive electrode, and a negative electrode By doping lithium to graphite to use the low redox potential of lithium, the operating voltage of the capacitor reaches 4.2V and the energy density can be increased to about 20 Wh / kg.

However, in the case of a lithium ion battery, lithium oxide such as lithium cobalt oxide or lithium iron phosphate is used for the positive electrode , and thus , lithium doped through intercalation to the graphite of the negative electrode is positive. Lithium ion capacitors can be provided at the electrode, but since activated carbon is used at the positive electrode, other means are needed to provide lithium doped with graphite. Of course, it is also possible to include a compound containing lithium in the positive electrode, but has the disadvantage of reducing the capacity of the lithium ion capacitor with a decrease in the amount of activated carbon. In addition, since the amount of lithium ions contained in the electrolyte is limited, another method for supplying lithium necessary for doping is needed.

For this reason, in lithium ion capacitors, it is necessary to additionally provide internally or externally lithium doped to the negative electrode.

Conventional methods of doping lithium include the potential difference between lithium foil and graphite by arranging a negative electrode including graphite and a lithium foil so as to face each other and electrically connecting the same, and then inserting the same into an electrolyte containing lithium salt. Lithium of the lithium foil in an electrochemical method by using a method of intercalating the lithium of the lithium foil with graphite or by placing a separator between the anode electrode and the lithium foil containing graphite and applying a potential A method of intercalating with this graphite was used.

However, this method has a complicated process and takes a long time, and there is a problem that lithium doping is difficult when the number of stacked layers increases.

In particular, a large amount of stacking or cylindrical winding (electrode assembly) is required for the electrode assembly, so various doping methods have been developed.

U.S. Patent No. 6,461,769 discloses a method of forming a hole in a positive electrode and a negative electrode current collector in a laminated structure and a cylindrical structure to allow lithium ions to move and disposing lithium metal at the outermost to electrochemically dope lithium. However, in this method, lithium can be doped in the laminated structure and the cylindrical structure, but the doping process takes a long time and the electrical resistance of the current collector is increased by the hole, so the resistance of the capacitor increases and the tensile strength of the current collector decreases. It has the disadvantage of being difficult to manufacture.

The patent document 6,558,846 discloses a positive electrode using a transition metal oxide containing activated carbon and lithium for the positive electrode, a carbon material capable of lithium doping and undoping for the negative electrode, and an electrolyte containing lithium salt. A method of electrochemically doping lithium contained in a transition metal oxide containing lithium to a carbon material of a cathode electrode has been developed. In this way, lithium doping is possible in a high-capacity laminated structure and a cylindrical structure. However, this method has the disadvantage that the capacity of the capacitor is reduced by reducing the active carbon content in the positive electrode.

U.S. Patent Document 8,034,642 describes a lithium film formed on a substrate by a liquid phase method or a vapor phase method, and then transfers a lithium film to a cathode electrode to form a lithium film on a cathode electrode, followed by an electrolyte containing a lithium salt. Was developed to inject lithium into the cathode electrode from the lithium layer formed on the cathode electrode. In addition, U.S. Patent Publication No. 2012-0050953 discloses forming a lithium film on a surface of a separator and assembling the lithium film to contact a cathode electrode, and then injecting an electrolyte containing lithium salt to inject lithium into the cathode electrode from a lithium film electrically connected to the cathode electrode. A method was developed to allow doping.

These methods enable lithium doping through lithium intercalation in high-capacity laminated and cylindrical structures, but most processes have to be carried out in a dry room because of lithium, which requires high process costs such as expensive facility maintenance costs and low melting point of lithium. And because of the high reactivity has a disadvantage that a lot of restrictions in the overall process, such as drying process.

In addition, a method of vapor deposition of lithium into a cathode electrode including graphite in a vacuum has been attempted, but suffers from the electrode damage caused by heat during deposition and the same problem mentioned above.

Lithium ion capacitors are commercially available in pouch type products that use a stacked structure mainly due to the high difficulty of the lithium doping process. However, the pouch type is very vulnerable to an increase in internal pressure, so a low operating voltage is used to mitigate gas generation.

In addition, for a large capacity lithium ion capacitor, a cylindrical structure is preferable to the stacked type. Cylindrical lithium ion capacitors using a metal case can prevent deformation of the case even if the internal pressure increases, so that the operating voltage can be increased and it is also advantageous to increase the capacity. To this end, it is necessary to develop a structure and method for facilitating injection of electrolyte into the electrode and facilitating gas discharge generated in the lithium doping process.

In addition, in order to improve the power characteristics of lithium ion capacitors, structures and methods for lowering the resistance need to be developed.

The present invention is to solve the above problems, the positive electrode and the carbon, graphite, lithium titanium oxide (LTO: Li ₄ Ti ₅ O ₁₂ , Lithium, including a porous material such as activated carbon, carbon nanotubes, carbon nanofibers) Simplify the structure, assembly process, and lithium doping process of an electrochemical cell using a cathode electrode containing a lithium intercalation material such as Titanium Oxide, and improve the compatibility of the electrochemical cell and the electric double layer capacitor manufacturing equipment and It is to provide an electrochemical cell that reduces manufacturing costs, facilitates the manufacture of large-capacity electrochemical cells, increases operating voltage, and improves power characteristics by minimizing the required infrastructure costs.

In order to achieve the above object, an electrochemical cell according to the present invention includes a cathode electrode including a porous electrode and a cathode doped with lithium, and at least one of the anode electrode and the cathode electrode. Injecting a lithium solution (Lithium solution) in which lithium is dissolved in the electrode and removing the solvent of the injected lithium solution, characterized in that lithium is supplied to at least one of the positive electrode and the negative electrode.

An electrochemical cell according to the present invention includes an electrolyte including a lithium salt, a positive electrode including a current collector and a porous material, a negative electrode including a current collector and a material doped with lithium, the electrode and the electrolyte. A case used as a terminal for receiving and covering the case and a lid used as a terminal opposite to the case,

The material of the case is characterized by using the same series of materials as the current collector of the positive electrode and the material of the lid is characterized by using the same series of material as the current collector of the negative electrode.

The electrochemical cell according to the present invention has a simple lithium doping process and can be easily applied to a laminated and cylindrical structure, thereby facilitating the preparation of a large-capacity electrochemical cell.

In addition, the electrochemical cell according to the present invention does not include an additional structure for supplying lithium, and has the same structure as a conventional electric double layer capacitor and a lithium ion battery, and thus may share manufacturing facilities, and include lithium in an assembly process. Since there is no need to use a dry room, manufacturing costs, including infrastructure costs, can be reduced.

In addition, the electrochemical cell according to the present invention can escape the limitations of the assembly and drying process due to lithium by supplying lithium to the electrode before the injection of electrolyte after assembly and drying, thereby reducing the manufacturing cost and improving the performance and reliability of the electrochemical cell. You can.

In addition, the electrochemical cell according to the present invention has improved power characteristics.

1 is a cross-sectional view schematically showing the configuration of an electrochemical cell according to the present invention.

2 is a perspective view of an electrode in which grooves are formed in an electrode surface according to the present invention.

3 is a perspective view of an electrochemical cell with reduced internal resistance and simple structure in accordance with the present invention.

4 is a perspective view of an electrode having a current collector extension portion in which an active material layer is not formed on one side of the electrode according to the present invention.

5 is a perspective view showing an example of an arrangement structure of a positive electrode and a negative electrode constituting an electrode assembly according to the present invention.

Hereinafter, with reference to the accompanying drawings will be described in detail a preferred embodiment of the present invention.

1 is a cross-sectional view schematically showing the configuration of an electrochemical cell according to the present invention.

Referring to FIG. 1, the electrochemical cell 100 includes a positive electrode 112, a negative electrode 114, a separator 116, an electrolyte 118, a case 120, and a terminal 122.

The anode electrode 112 is a porous material used as an active material, and a porous carbon powder such as activated carbon, carbon nanotubes, carbon nanofibers, or a fine powder, such as acetylene black, which is used to improve conductivity of the electrode and the electrode, and a binder. After mixing, the coating is made on an aluminum sheet used as a current collector.

The negative electrode 114 is made by mixing graphite powder, a conductive agent, and a binder, which are mainly used among lithium intercalation materials for lithium doping as an active material, and then coating the copper sheet used as a current collector.

The separator 116 transmits ions contained in the electrolyte but electrically insulates the anode electrode and the cathode electrode, and porous pulp or fiber is used.

The electrolyte 118 contains a lithium salt like a lithium ion battery, mainly EC (Ethylene Carbonate) as a solvent, dimethyl carbonate (DMC) as a co-solvent, and LiPF ₆ as a solute. do.

In order to operate the electrochemical cell 100 as illustrated in FIG. 1, lithium is doped into the graphite of the negative electrode to reach the redox potential of the lithium. In the lithium ion battery for lithium doping, lithium is intercalated from the lithium oxide contained in the positive electrode to the graphite of the negative electrode in the formation process.

However, in the electrochemical cell according to the present invention, since the active material of the positive electrode is porous carbon, another method is used as a lithium supply method for lithium doping.

Conventional methods are intercalated from lithium to graphite due to the potential difference between graphite and lithium when the electrolyte is injected when the lithium film is superimposed on the cathode electrode or the lithium film is transferred to the cathode as described in US Patent Document 8,034,642.

Lithium is well soluble in aliphatic amines such as ethyl amine. Therefore, when lithium is dissolved in a solvent in which lithium is well dissolved, such as ethylamine, the lithium solution is evaporated, and then the lithium is precipitated again. In accordance with the present invention, a lithium solution is injected into an electrode by dipping a positive electrode or a negative electrode into a lithium solution in which lithium is dissolved or spraying a lithium solution on the electrode, and then the solvent of the lithium solution is evaporated from the electrode. If it is removed, lithium remains in the surface of the electrode and in the pores of the electrode.

After assembling an electrochemical cell as shown in FIG. 1 using such a positive electrode or a negative electrode, an electrolyte containing lithium salt is injected into the electrochemical cell, and lithium present in the electrode may be carbon or graphite due to a potential difference with carbon or graphite. Intercalation occurs with lithium doped.

If lithium is supplied to the negative electrode, after electrochemical cell assembly, an electrolyte containing lithium salt is supplied, and lithium is doped by intercalation with graphite due to a potential difference between lithium and graphite.

However, if lithium is supplied to the anode electrode and then the electrolyte containing lithium salt is supplied after electrochemical cell assembly, if the lithium intercalation material such as activated carbon is used for the anode electrode, intercalation occurs at the anode electrode, Lithium is doped into the lithium electrode so that the lithium present in the positive electrode is intercalated at the negative electrode to be doped in the negative electrode. When an electrolyte is injected, a potential is applied to the electrochemical cell to transfer the lithium present in the positive electrode to the negative electrode. You can.

A more preferred embodiment of the present invention is to assemble the electrochemical cell as shown in Figure 1 and then to dry the electrochemical cell and to supply lithium to the electrode before injecting the electrolyte.

After assembling and drying the electrochemical cell, the lithium solution containing lithium is injected into the electrochemical cell. Each electrode is wetted by the lithium solution injected into the positive electrode and the negative electrode of the electrochemical cell. Is filled. Subsequently, when the solvent is evaporated and removed from the injected lithium solution by using a method such as reduced pressure, lithium is distributed on the place where the lithium solution in the electrode is filled and on each electrode surface.

When an electrolyte containing a lithium salt is injected into an electrochemical cell, lithium distributed in the electrode is intercalated into carbon by a potential difference, thereby performing doping of lithium.

Meanwhile, the electrochemical cell according to the present invention contains carbon not only in the cathode electrode but also in the anode electrode, so that intercalation of lithium is generated only at the cathode electrode. As lithium is supplied from the positive electrode of the lithium ion battery to the negative electrode, lithium distributed in the positive electrode moves to the negative electrode and intercalates with graphite of the negative electrode.

Supplying lithium to the electrochemical cell before the electrolyte injection and doping the lithium after the electrolyte injection as in the present invention can facilitate the process and reduce the manufacturing cost by eliminating lithium in the electrochemical cell assembly and drying process.

Porous carbon used in the anode electrode of the electrochemical cell easily adsorbs moisture and needs to be dried for a long time at a high temperature to remove moisture from the electrode, which adversely affects the performance and reliability of the electrochemical cell. However, lithium is not only highly reactive but also has a melting point of only 180 ^° C. If lithium is included before drying, it limits the drying of the electrochemical cell. Lowering the drying temperature of the electrochemical cell adversely affects the reliability.To assemble the electrochemical cell after drying the electrode in advance, the electrochemical cell assembly equipment must be installed in the dry room. As the dry room also contains approximately 2% moisture, longer stays in the dry room adversely affect reliability.

Therefore, in this respect, the method of supplying lithium to the electrode before the electrolyte injection after the electrochemical cell assembly and drying as in the present invention is effective in improving the reliability as well as reducing the manufacturing cost.

On the other hand, unlike the stacked type, the cylindrical shape in which the electrode is wound takes longer time than the stacked type in that the electrode is compressed and the electrolyte is injected and the gas is discharged.

In particular, in the present invention, since the solvent must be evaporated again after injecting the lithium solution into the electrode before injecting the electrolyte, a solvent having a low viscosity and a low breaking point as a solvent of the lithium solution is more effective, and the electrode also has a groove on the electrode surface as shown in FIG. 2. Formation of 30 makes it possible to smoothly inject the electrolyte and the lithium solution and to discharge the gas and the vapor.

Furthermore, when the groove 30 is formed in a direction inclined with respect to the length direction of the electrode, the electrochemical cell can smoothly discharge the gas regardless of the installation direction in the vertical direction or the horizontal direction.

Meanwhile, when the outer side of the electrode assembly of the electrochemical cell is the negative electrode, lithium supplied to the electrode by lithium solution injection and solvent drying spontaneously doped into the graphite of the negative electrode after the electrolyte injection, thereby remaining lithium without dope. Can be prevented.

In addition, it is advantageous to use a metal material instead of a pouch in which aluminum is deposited on the film as the case of the electrochemical cell according to the present invention. Even when the operating voltage of the electrochemical cell according to the present invention is increased, the voltage of the cathode electrode is hardly changed and the voltage of the anode electrode is increased. As the voltage of the positive electrode rises, gas is generated as a by-product due to an electrochemical reaction between the electrolyte and the impurities adsorbed on the surface of the activated carbon used as the active material. In the case of using the pouch as a case of the electrochemical cell, as the gas is generated inside the electrochemical cell, as the internal pressure increases, it is difficult to maintain the shape of the electrochemical cell because the pouch swells, thereby reducing the operating voltage. However, if a metal material is used instead of a pouch as a cell case, the shape of the cell can be maintained even if the internal pressure is increased by the gas, thereby increasing the operating voltage of the electrochemical cell.

In the case of using a metal case for an electrochemical cell, when the metal case is charged with a positive electrode, lithium distributed on the surface of the case by the lithium solution is doped with a negative electrode, thereby minimizing lithium remaining on the inner surface of the case. In this case, the case material is preferably aluminum or an aluminum alloy, or the same element or alloy having the same series as the current collector of the positive electrode.

This structure is also advantageous in weight reduction of the electrochemical cell. Even if lithium is supplied in the same manner as in the prior art, an electrochemical cell including an electrolyte including lithium, a positive electrode including porous carbon, and a negative electrode including lithium intercalation material regardless of the lithium supply method In the case of using a metal case as a terminal, the case is used as an anode and the case material is aluminum or aluminum alloy than the case is used as a cathode and the case material is copper used as a current collector of a cathode electrode. It is more preferable in terms of weight and price. In order for an electrochemical cell to be used for a large output, the internal resistance of the electrochemical cell must be reduced. In particular, in order to reduce the internal resistance of the large-capacity electrochemical cell made of a cylindrical shape and simplify the assembly process, a structure as shown in FIG. 3 is preferable.

The current collector extension 111 in which the positive electrode and the negative electrode included in the electrode assembly of the electrochemical cell having the cylindrical structure as shown in FIG. 3 is not formed with the active material layer 115 on one side of the electrode as shown in FIG. 4. 5, the separator 116 is interposed therebetween, and the current collector extension 111 of the positive electrode 112 and the negative electrode 114 is arranged to face outward, and then the electrode assembly 310 is manufactured. After inserting the electrode assembly 310 into the case 300 in which the grooves 312 (groove) for laser welding are formed, the lid 314 in which the grooves 312 for laser welding are formed is insulated from the case 300. After covering with a gasket or a rubber ring, a laser beam is irradiated to each groove 312 from the outside to weld the current collector extension 111 of each electrode to the case 300 and the lid 314. In this structure, the case 300 and the lid 314 serve as terminals. This structure can minimize the current transfer path between the electrode and the terminal, which is effective in reducing the internal resistance of the electrochemical cell.

As described above, since the case 300 is preferably used as the positive electrode in the structure as shown in FIG. 3, the lid is preferably used as the negative electrode. Using the case 300 as an anode is advantageous in terms of minimizing lithium residual as described above, and in case of using the case 300 as an anode, aluminum may be used as the case material, which is advantageous in terms of weight and price.

Further, in consideration of weldability and soldering, it is advantageous that the case 300 uses the same material as the current collector material of the positive electrode and the lid uses the same material as the current collector material of the negative electrode.

In an electrochemical cell, an aluminum sheet is mainly used as a current collector of a positive electrode, and a copper sheet is mainly used as a current collector of a negative electrode. Therefore, the case material is preferably aluminum or an aluminum alloy, and the material of the lid 314 is preferably copper or a copper alloy or included in the connection portion.

Although the structure, operation, and manufacturing method of the present invention have been disclosed in various embodiments in the description of the present invention, those skilled in the art or skilled in the art may be modified in various forms within the scope of the present invention.

The above description is merely illustrative of the technical idea of the present invention, and those skilled in the art to which the present invention pertains may make various modifications and changes without departing from the essential characteristics of the present invention. Therefore, the embodiments disclosed in the present invention are not intended to limit the technical idea of the present invention but to describe the present invention, and the scope of the technical idea of the present invention is not limited by these embodiments. The protection scope of the present invention should be interpreted by the following claims, and all technical ideas within the equivalent scope should be interpreted as being included in the scope of the present invention.

Claims (15)

In an electrochemical cell that stores electrical energy, Porous anode electrodes; And A negative electrode comprising a material doped with lithium; Including, Injecting a lithium solution in which lithium is dissolved in at least one of the positive electrode and the negative electrode, removes the solvent of the injected lithium solution to supply lithium to at least one of the positive electrode and the negative electrode Electrochemical cell, characterized in that. The method of claim 1, Injecting an electrolyte into the electrochemical cell and applying an electric potential to the electrochemical cell to dope the lithium present in the positive electrode with the negative electrode. The method of claim 1, The anode electrode is an electrochemical cell comprising activated carbon. The method of claim 1, The lithium doped material of the negative electrode is an electrochemical cell, characterized in that the graphite. The method of claim 1, The electrochemical cell further comprises a case and a lid for receiving the electrode, the case is an anode, the cap is an electrochemical cell, characterized in that the charge to the cathode. The method of claim 5, The material of the case is an electrochemical cell, characterized in that the aluminum or aluminum alloy. The method of claim 5, The material of the lid is an electrochemical cell comprising copper or copper alloy. The method according to claim 6 or 7, Wherein each electrode includes a current collector, and the case and the lid are at least one of welding and soldering in connection with the current collector of each electrode. The method of claim 1, And an outer polarity of the electrode assembly including the anode electrode and the cathode electrode is a cathode. The method of claim 1, Electrochemical cell, characterized in that the groove is formed on the surface of at least one of the anode electrode and the cathode electrode. The method of claim 10, The groove is an electrochemical cell, characterized in that formed in the direction inclined with respect to the longitudinal direction of the electrode. The method of claim 1, After assembling the electrochemical cell, the lithium solution is injected into the positive electrode and the negative electrode, and the lithium solution is supplied to the positive electrode and the negative electrode by removing the solvent of the injected lithium solution. . In an electrochemical cell that stores electrical energy, An electrolyte comprising a lithium salt; A positive electrode including a current collector and a porous material; A negative electrode including a current collector and a material doped with lithium; A case accommodating the positive electrode, the negative electrode and the electrolyte and used as a terminal; And A lid covering the case and used as a terminal opposite to the case; Including, The material of the case is the material of the same series as the current collector of the positive electrode and the material of the lid is characterized in that the material of the same series as the current collector of the negative electrode. The method of claim 13, And the current collector of the case, the positive electrode, and the current collector of the lid and the negative electrode are connected by at least one of welding and soldering. The method of claim 13, The material of the case is aluminum or aluminum alloy, the material of the lid is electrochemical cell, characterized in that it comprises copper or copper alloy.

Images