KR20110037998A - Electrode assembly of improved power property and secondary battery comprising the same - Google Patents

Abstract

PURPOSE: An electrode assembly is provided to embody a combined system of a capacitor and a secondary battery within one cell through a simple assembling process and to improve output characteristics without the degeneration of capacity. CONSTITUTION: An electrode assembly is composed of a plurality of electrode groups capable of charging/discharging. The electrode groups have a structure where a positive electrode and a negative electrode are faced in the state that a separation film is interposed, wherein at least one electrode group comprises a capacitor type electrode group. The negative electrode of the capacitor type electrode group is faced with a unit cell for a secondary battery.

Description

Electrode assembly with improved output characteristics and secondary battery comprising the same {Electrode Assembly of Improved Power Property and Secondary Battery Comprising the Same}

The present invention is an electrode assembly composed of a plurality of electrode groups capable of charging and discharging, the electrode group is composed of a structure in which the positive electrode and the negative electrode facing the separator interposed, at least one of the electrode group is a capacitor-type electrode The present invention relates to a composite electrode assembly having a structure in which a negative electrode of a capacitor-type electrode group faces a unit cell for a secondary battery, and a secondary battery including the same.

As technology development and demand for mobile devices have increased, the demand for secondary batteries as energy sources has been rapidly increasing. Many researches have been conducted on lithium secondary batteries with high energy density and discharge voltage among such secondary batteries. .

However, the secondary battery has a disadvantage in that the charge / discharge performance due to instantaneous high current is inferior to the high energy density, and in order to compensate for this, an electric double layer capacitor (EDLC) has been systematically incorporated into a conventional lithium ion polymer battery (LIPB). Research and development on combining technology is being done.

In general, capacitors are devices that accumulate charge when voltage is applied, and exhibit high output characteristics. Representative electrochemical capacitors are classified into electric double-layer capacitors (EDLC) and pseudo-capacitors (Pseudo-capacitors). Can be. An electric double layer capacitor is a device for storing charge by charging ions on an electrolyte and electrons on an electrode in an electric double-layer formed at an interface between an electrode and an electrolyte, and a similar capacitor uses a Faraday reaction to It is a device that stores electrons near the surface.

Among them, the electric double layer capacitor is composed of an equivalent circuit in which a double-layer capacitance and an equivalent series resistance (ESR) are connected in series, wherein the double-layer capacitance is proportional to the surface area of the electrode. ESR is the sum of the resistance of the electrode, the resistance of the electrolyte solution and the resistance of the electrolyte in the electrode pores. The double layer capacitor has excellent instantaneous high output characteristics, but has a disadvantage in that energy density and storage characteristics are inferior to conventional secondary batteries.

The composite battery combined with the secondary battery using the characteristics of the capacitor has the advantage that the instantaneous output can be increased and the energy density is high. However, composite batteries known to date have related devices that interconnect independent structures of secondary batteries and capacitors to manufacture related devices, and thus have a problem in that the manufacturing process is complicated and the installation space increases, thereby counteracting the miniaturization of batteries. have.

In addition, carbon material is often used as an electrode material of an electric double layer capacitor, and in order to exhibit excellent characteristics of an electric double layer capacitor, the carbon material must have (i) a large amount of pores and thus have a large specific surface area. The electrode resistance should be low when fabricating the electrode because it is excellent. It should be possible to charge and discharge quickly.

In order to satisfy these conditions, existing capacitors use activated carbon as an electrode material. However, since activated carbon is relatively expensive, the production cost is increased, and it is difficult to apply to actual mass production.

Therefore, there is a high need for a technology that can fundamentally solve many of the above problems.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-described problems of the prior art and the technical problems required from the past.

Specifically, it is an object of the present invention to provide a complex electrode assembly of a more compact structure by a simple manufacturing process by implementing a coupling system of a capacitor and a secondary battery in a single cell.

It is still another object of the present invention to provide a composite electrode assembly having a desired level of battery characteristics while lowering manufacturing costs by extending the range of electrode materials usable for capacitors.

It is another object of the present invention to provide a secondary battery having the desired level of high power, high energy density, and continuous charge / discharge characteristics, including the composite electrode assembly.

The composite electrode assembly according to the present invention for achieving the above object is an electrode assembly composed of a plurality of electrode groups capable of charging and discharging, the electrode group is composed of a structure in which the anode and the cathode face in the state where the separator is interposed. At least one of the electrode groups includes a capacitor-type electrode group, and the cathode of the capacitor-type electrode group is configured to face the unit cell for a secondary battery.

That is, the composite electrode assembly according to the present invention complements the battery characteristics by combining a capacitor type electrode group having a relatively high rate discharge characteristics among a plurality of electrode groups having a high energy density and charge and discharge characteristics. I could do it. Further, in the capacitor type electrode group, the capacitor electrode facing the unit cells for the secondary battery is constituted by the negative electrode, so that the negative electrode and the capacitor of the unit cell for the secondary battery in which ions such as lithium ions share the electrolyte in one battery cell By occluding and / or releasing the negative electrode together, the complementary relationship between the battery characteristics between the two is further improved. In particular, when the electrode of the unit cell for secondary batteries facing the capacitor type electrode group is a positive electrode, since it can exhibit high interaction with the negative electrode of the capacitor type electrode group, it is more preferable.

The electrode assemblies capable of charging and discharging are largely classified into cylindrical and plate shapes according to the form (outer structure) built into the case, and are also jelly-roll type and stack type according to the stack type (internal structure) of the electrode assembly. Are classified.

The jelly-roll type electrode assembly is formed by stacking a long sheet-shaped anode and a cathode with a separator interposed therebetween, then winding in a circular cross-section to make a cylindrical structure, or winding in such a cylindrical structure and compressing in one direction to cross-section. It can be made into a roughly plate-like structure. On the other hand, the stacked electrode assembly may be formed in a plate-like structure by cutting the positive electrode and the negative electrode in units of a predetermined size and sequentially stacking them through a separator.

Preferably, as a composite structure (stack / folding structure), a bicell or full cell is formed as a unit cell of small units in a stacked manner, and a plurality of them are placed on a long separation film (separation sheet) and sequentially wound. It can be taken and made into a generally plate-shaped structure as a whole.

The 'full cell' is a unit cell composed of a unit structure of an anode, a separator, and a cathode, and is a cell in which an anode and a cathode are located at both sides of the cell, respectively. Such a full cell may include an anode / separator / cathode cell and an anode / separator / cathode / separator / anode / separator / cathode cell having the most basic structure. In order to configure an electrochemical cell such as a secondary battery using such a full cell, a plurality of full cells should be stacked such that the positive electrode and the negative electrode face each other with the separation film interposed therebetween.

The 'bicell' is a unit cell in which the same electrode is positioned at both sides of the cell, such as a unit structure of an anode / separator / cathode / separator / anode and a unit structure of a cathode / separator / anode / separator / cathode. In order to construct an electrochemical cell including a secondary battery using such a bicell, a bicell and a cathode, a separator, an anode, a separator, and a cathode structure of the anode / separator / cathode / separator / anode structure with the separator film interposed therebetween. A plurality of bicells should be stacked so that the bicells face each other.

Further details of the electrode assembly of the stack / foldable structure are disclosed in Korean Patent Application Publication Nos. 2001-0082058, 2001-0082059, and 2001-0082060 to the present applicants. Is incorporated by reference.

The electrode assembly of the present invention preferably has a stack / folding structure including the full cell or bicell unit cell as described above as the electrode group. Such a stack / foldable electrode assembly uses a capacitor type electrode group as a unit cell, such as a full cell or a bicell, so that the electrode assembly is easy to handle in an assembly process and has excellent structural stability of the manufactured electrode assembly. Has an advantage.

Therefore, by combining at least one or more of the unit cells (electrode groups) of the electrode assembly as a capacitor-type unit cell (electrode group) it is possible to implement a combination system of a capacitor and a secondary battery in a single cell.

Such a capacitor-type unit cell may have a structure in which a separator is interposed between an anode and a cathode on which a carbon-based material is coated on a metal sheet, respectively. Depending on the configuration, the capacitor-type unit cell may have a bicell structure, or may have a full cell structure.

As a representative example of the capacitor type unit cell, a unit cell having an electric double layer capacitor structure may be used. When a pair of solid electrodes were placed in an electrolyte ion solution and applied a DC voltage, (-) ions were positively induced at the positively polarized electrode and (+) ions were electrostatically induced at the (-) polarized electrode. An electric double layer is formed at the electrolyte interface. The charge stored in this way is calculated by Equation 1 below.

(1)

(One)

In Equation 1, ε: permittivity, σ: electrolyte ion radius, and S: specific surface area.

In determining the capacity of the electric double layer capacitor, as shown in Equation 1, it can be seen that the larger the specific surface area, the higher the dielectric constant of the electrolyte, and the smaller the radius of ions in the formation of the double layer, the larger the capacity can be obtained. Can be. In addition, the capacity is determined by the internal resistance (ESR) of the electrode, the relationship between the pore distribution of the electrode and the electrolyte ions, the breakdown voltage, and the like.

The electric double layer capacitor is composed of an electrode, a separator, an electrolyte, a current collector, and the like. Among them, the core of the capacitor is the selection of the material used for the electrode. The electrode material should be large in electrical conductivity, high in specific surface area, electrochemically stable and inexpensive. Therefore, the capacitor-type unit cell may have a structure in which a separator is interposed between the anode and the cathode on which the carbon-based material is coated on the metal sheet, respectively.

Preferably, in the capacitor type unit cell, the carbon-based material applied to the surface of the capacitor anode or cathode may be made of a structure of graphite and / or activated carbon.

Activated carbon may be generally used as the carbon-based material, and graphite may also be used. In the case of activated carbon, many pores are distributed to form an electric double layer having a high charge capacity. In addition, graphite may be pointed out as a problem due to its low charge capacity due to its relatively small specific surface area, but it may be used as one of the preferable electrode materials which can lower the manufacturing cost of the capacitor due to the low price. Therefore, as one preferred embodiment of the present invention, by applying activated carbon to the positive electrode and graphite to the negative electrode, it is possible to implement a capacitor-type unit cell having a relatively high charge capacity in spite of a low manufacturing cost.

Among the unit cells of the stack / foldable electrode assembly, the remaining unit cells except for the capacitor type unit cell (secondary cell unit cells) may include a transition metal oxide as a positive electrode active material and a carbon-based material as a negative electrode active material. Can be. Preferred examples thereof include a structure in which aluminum (Al) and copper (Cu) foils are used as positive electrode plates and negative electrode plates, respectively, and LiCoO ₂ and graphite are respectively coated on the surfaces thereof as active materials.

The stack / foldable electrode assembly has a structure in which a plurality of unit cells are sequentially wound and stacked on a long separation film. Therefore, in such a laminated structure, when the unit cell which shows relatively high penetration resistance is located in the outermost part, there exists an effect which can suppress to some extent the battery short-circuited by a needle-like body. According to the experiments performed by the inventors of the present application, it was confirmed that the carbon-based material constituting the negative electrode active material exhibits relatively high penetration resistance compared to the lithium transition metal oxide constituting the positive electrode active material in a general lithium secondary battery. In view of this point, a capacitor type unit cell in which both the anode and the cathode are made of a carbon-based material can exhibit relatively excellent penetration resistance.

Therefore, in one preferred example, the uppermost unit cell and the lowermost unit cell each have a structure of capacitor type unit cells.

The present invention also provides a secondary battery comprising the electrode assembly.

The secondary battery has a structure in which the electrode assembly capable of charging and discharging is impregnated with an ion-containing electrolyte solution is embedded in the battery case, and in particular, the mechanical rigidity of the battery case is small so that deformation may easily occur when dropping or external impact is applied. The electrode assembly according to the present invention may be preferably used in a secondary battery using a plate-shaped battery case.

The secondary battery is preferably a lithium secondary battery having a high energy density, a discharge voltage, and an output stability, and among these, a lithium ion polymer which is less likely to leak electrolyte, has a low weight and manufacturing cost, and is easily manufactured in various forms. Secondary batteries are more preferred. Other components and a manufacturing method of the lithium secondary battery are well known in the art, and a detailed description thereof will be omitted herein.

The present invention also provides a high output large-capacity battery pack configured by connecting a plurality of secondary batteries as unit cells.

The medium-large battery pack according to the present invention may be manufactured by combining unit cells according to a desired output and capacity, and have a limited mounting space and require high output characteristics, such as an electric vehicle, a hybrid electric vehicle, an electric motorcycle, an electric bicycle, and the like. It can be preferably used as a power source, and in particular, can be preferably used as a power source of an electric vehicle or a hybrid electric vehicle.

As described above, the composite electrode assembly according to the present invention may implement a coupling system of a capacitor and a secondary battery in a single cell by a simple assembly process, and not only reduce the manufacturing cost of the battery cell. There is an effect that can significantly improve the output characteristics without deterioration of the capacity.

1 and 2 are perspective views showing the assembly process and the assembly process of the electrode assembly according to an embodiment of the present invention;
3 is an exploded perspective view of a capacitor-type unit cell according to one embodiment of the present invention;
4 and 5 are partial cross-sectional views of an electrode assembly according to one embodiment of the present invention, respectively.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings, but the present invention is not limited by the scope of the present invention.

1 and 2 are perspective views showing before and during the assembly of the electrode assembly according to an embodiment of the present invention, respectively.

Referring to FIG. 1, first, a plurality of bicells 10 having a stacked structure of an anode (cathode) / separator / cathode (anode) / separator / anode (cathode) are formed in a continuous separation film 30 having a long length. Position on. The bicells 10 properly arrange the positive electrode and the negative electrode bicells in the winding process so that the positive electrode and the negative electrode face each other at their lamination interface during winding. At this time, the two unit cells of the winding end are constituted by the capacitor type unit cells 21 and 22 on the basis of the winding direction.

In FIG. 2, an electrode assembly in a state in which a winding process is almost finished is illustrated. In the wound state, the positive electrode terminal 11 and the negative electrode terminal 12 are stacked in the same one direction. Meanwhile, as shown in FIG. 1, two capacitor-type unit cells 21 and 22 positioned at the winding end with respect to the winding direction are positioned at the top and bottom of the electrode assembly at the end of the winding. As a result, the electrode assembly is improved in performance while increasing durability against needle passage.

3 is an exploded view schematically showing a capacitor-type unit cell according to an embodiment of the present invention.

Referring to FIG. 3, the capacitor-type unit cell 100 has a structure in which the anode 130, the separator 140, the cathode 150, the separator 140, and the anode 130, which are cut to a predetermined size, are sequentially stacked. Consists of On one side of the positive electrode plate 130 and the negative electrode plate 150, the electrode tabs 110 and 120 are attached to each other in a protruding state, and the separator 140 is interposed therebetween. In the positive electrode plate 130, activated carbon is coated on an aluminum (Al) foil as an active material. The negative electrode plate 150 uses copper (Cu) foil and graphite is coated as an active material.

As shown in FIG. 3, unit cells each having a positive electrode at both sides may be referred to as a capacitor type positive electrode unit cell. In contrast to FIG. 3, unit cells each having a negative electrode at both sides may be referred to as a capacitor type negative electrode unit cell. The capacitor type positive electrode unit cell and the capacitor type negative electrode unit cell may be used in the same manner as in FIG. 1, when the stack / folding electrode assembly is configured, similarly to the positive electrode and negative electrode bicells for general secondary batteries.

4 and 5 show partial cross-sectional views of an electrode assembly according to one embodiment of the present invention, respectively.

Referring to FIG. 4, the capacitor type unit cell 200, the separator 300, and the secondary cell unit cell 400 have a stacked structure, in which the capacitor type unit cell 200 is again an anode 210 / separator. It is laminated | stacked in the structure of (220) / cathode 230. The negative electrode 230 of the capacitor-type unit cell 200 is a structure that faces the secondary cell unit cell 400 and the separator 300 therebetween, and among them, faces the positive electrode 410 of the secondary cell unit cell 400. It is a structure.

In addition, the anode 210 of the capacitor-type unit cell 200 is coated with activated carbon 211 on both sides of the aluminum metal plate, and the cathode 230 is coated with graphite 231 on the copper metal plate, and the anode 210. ) And the cathode 230 is a structure in which the separator 220 is interposed.

Referring to FIG. 5, the electrode assembly of the secondary cell unit cell 400 facing the capacitor-type unit cell 200 is the same as the electrode assembly of FIG. 4 except that the electrode 420 is a negative electrode 420.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the following Examples are provided to illustrate the present invention, and the scope of the present invention is not limited thereto.

Example 1

1-1. Manufacture of unit cell for secondary battery

The positive electrode sheet is composed of 95% by weight of lithium cobalt oxide (LiCoO ₂ ), 2.5% by weight of Super-P (conductive agent) and 2.5% by weight of PVdF (binder) as a positive electrode active material to N-methyl-2-pyrrolidone (NMP). A positive electrode mixture slurry was prepared by addition, and coated, dried, and pressed on one surface of the aluminum foil, respectively.

In the negative electrode sheet, 93% by weight of artificial graphite, 2.5% by weight of Super-P (conductor) and 4.5% by weight of PVdF (binder) were added to NMP to prepare a negative electrode mixture slurry as a negative electrode active material.

As the separator, Celgard ^TM , which is an insulating thin film having high ion permeability and mechanical strength, was used.

1-2. Fabrication of unit cell for capacitor

The positive electrode sheet was prepared by preparing a positive electrode mixture slurry using activated carbon and then applying it to an aluminum foil, and the negative electrode sheet was prepared by preparing a negative electrode mixture slurry using artificial graphite and then coating the copper foil. In addition, the separator used was the same product as the separator of the unit cell for secondary batteries of Example 1-1.

1-3. Assembly of composite electrode assembly

A plurality of bicells having a laminated structure of anode (cathode) / membrane / cathode (anode) / separator / anode (cathode) were placed on a long continuous separator film, and the bicells had their lamination interfaces when wound up. In order to align the positive and negative electrodes bipolar and negative electrodes to face each other. At this time, two capacitor-type unit cells were positioned at the winding end with respect to the winding direction.

Based on the winding direction, two capacitor-type unit cells were positioned at the winding end, and the electrode assembly was wound to be positioned at the top and bottom of the electrode assembly at the end of the winding, and a seal tape was placed on one side of the outer surface of the wound electrode assembly. Attached to complete the assembly.

Comparative Example 1

An electrode assembly was manufactured in the same manner as in Example 1, except that no capacitor type unit cell was used.

Comparative Example 2

An electrode assembly was manufactured in the same manner as in Example 1, except that an active material was not applied to one surface of the capacitor unit cell in a direction facing the secondary cell unit cell.

Experimental Example 1

In order to confirm the charge and discharge characteristics of the electrode assemblies prepared according to Example 1, Comparative Examples 1 and 2, the output values of the respective electrode assemblies were measured at -30 ° C and room temperature. The results are shown in Table 1 below.

TABLE 1

Looking at the Table 1, it can be seen that the electrode assembly of Example 1 has a relatively excellent output characteristics at both minus 30 ℃ and room temperature. Through this, it can be seen that the increased battery characteristics, in particular, the output characteristics are significantly increased compared to the electrode assembly of Comparative Example 1 that does not use the capacitor-type unit cell.

In addition, even when a capacitor type unit cell is used, when the active material is not coated on the surface facing the unit cell for secondary batteries as in Comparative Example 2, it can be seen that the increase in output characteristics is relatively large. Through this, the active material is also applied to the surface of the capacitor-type unit cell facing the secondary cell unit cell, it can be seen that the interaction between the two more active during charging and discharging to further improve the overall output characteristics of the battery cell.

Those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims (10)

An electrode assembly composed of a plurality of electrode groups capable of charging and discharging, wherein the electrode groups have a structure in which an anode and a cathode face each other with a separator interposed therebetween, and at least one of the electrode groups includes a capacitor type electrode group. And an anode of the capacitor-type electrode group facing the secondary cell unit cell, and having an stacked structure. The electrode assembly according to claim 1, wherein the electrode of the unit cell for secondary batteries facing the capacitor-type electrode group is a positive electrode. The electrode assembly of claim 1, wherein the capacitor-type electrode group has a structure in which a separator is interposed between an anode and a cathode on which a carbon-based material is coated on a metal sheet, respectively. 4. The electrode assembly of claim 3, wherein the carbonaceous material is (i) graphite, or (ii) activated carbon, or (iii) graphite and activated carbon. The electrode assembly of claim 1, wherein the top and bottom ends of the electrode assembly stacked structure are each formed of a capacitor type electrode group. The electrode assembly of claim 1, wherein the secondary cell unit cell comprises a transition metal oxide as a positive electrode active material and a carbon-based material as a negative electrode active material. A secondary battery comprising the electrode assembly according to any one of claims 1 to 6. 8. The secondary battery of claim 7, wherein the battery is a lithium ion polymer battery. A medium-large battery pack comprising the secondary battery according to claim 8 as a unit cell. The medium and large battery pack of claim 9, wherein the battery pack is used as a power source of an electric vehicle or a hybrid electric vehicle.

Images