KR100912787B1 - Hybrid-typed Electrode Assembly - Google Patents

Abstract

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 in the state where the separator is interposed, at least one of the electrode group (A) The present invention provides an electrode assembly composed of an electrode active material having excellent rate characteristics compared to other electrode groups.

Accordingly, the electrode assembly according to the present invention may improve the excellent pulse discharge characteristics without lowering the capacity by configuring the electrode active material of some electrode groups (anode / separation membrane / cathode electrode unit) with a material having excellent rate characteristics. Since the manufacture of the assembly can be achieved by a simple process, there is an effect that the manufacturing cost of the battery cell can be lowered.

Description

Hybrid-typed Electrode Assembly

1 and 2 are perspective views showing a process of assembling and assembling the electrode assembly according to an embodiment of the present invention.

The present invention is a hybrid electrode assembly having excellent pulse discharge characteristics composed of a plurality of electrode groups capable of charging and discharging, and more particularly, among the electrode groups having a structure in which the anode and the cathode face each other with the separator interposed therebetween. The present invention relates to an electrode assembly comprising an electrode active material having excellent rate characteristics compared to other electrode groups so that at least one or more electrode groups can exhibit excellent high rate discharge characteristics.

With the development of technology and increasing demand for mobile devices, the demand for secondary batteries is also rapidly increasing. Among them, lithium secondary batteries with high energy density, high operating voltage, and excellent storage and life characteristics are used for various mobile devices as well as various electronic products. It is widely used for energy support.

A lithium secondary battery uses a metal oxide such as LiCoO ₂ as a positive electrode active material and a carbon material such as graphite as a negative electrode active material, and a porous polymer separator is placed between the negative electrode and the positive electrode, and contains a non-aqueous electrolyte containing lithium salt such as LiPF ₆ . It will be prepared by putting. During charging, lithium ions of the positive electrode active material are released and inserted into the carbon layer of the negative electrode. On discharge, lithium ions of the carbon layer are released and inserted into the positive electrode active material. This serves as a moving medium. Such a lithium secondary battery should basically be stable in the operating voltage range of the battery, have high charging and discharging efficiency, and have an ability to transfer ions at a sufficiently high speed. However, the lithium secondary battery has a disadvantage in that the charge and discharge performance due to instantaneous high current is lower than the high energy density.

On the other hand, due to trends such as multifunction, high performance, and miniaturization of mobile devices, the demand for secondary batteries having small and large capacities is increasing. Therefore, in recent years, research and product development for increasing energy density by increasing the loading amount of the electrode and reducing the porosity in the conventional lithium secondary battery (LIPB) have been conducted. However, electrodes with high loading and low porosity have to limit the diffusion of lithium ions into the electrodes, that is, the kinetics of lithium ions, which leads to a big problem in capacity reduction during high rate charge and discharge. have. Particularly, in the case of pulse discharge, a high current must be output in a short time, thereby causing a significant reduction in capacity.

For example, the Global System for Mobile communication (GSM) scheme, which is widely used by European cell phone manufacturers, must provide high current for a short period of time during the discharge cycle. It is known that capacity deterioration is serious at high rate discharge, and it is urgent to compensate for this.

Therefore, there is a high need for a technology for a secondary battery capable of exhibiting excellent pulse discharge characteristics as described above.

The present invention aims to solve the problems of the prior art as described above and the technical problems that have been requested from the past.

The inventors of the present application, after in-depth study and various experiments, maintain a high capacity when some of the electrode groups of the electrode assembly are composed of an electrode active material having excellent rate characteristics compared to other electrode groups. It confirmed that excellent pulse discharge characteristic was exhibited, and came to complete this invention.

Therefore, the electrode assembly according to the present invention is 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 them. The above electrode groups are characterized in that the electrode active material having a rate characteristic of 30% or more than other electrode groups to exhibit excellent high rate discharge characteristics.

That is, the electrode assembly according to the present invention is a combination of the electrode group consisting of an electrode active material having excellent rate characteristics having a relatively high rate of charge and discharge characteristics between a plurality of electrode groups having a high energy density and charge and discharge characteristics between the two Characterized in that configured to complement the battery characteristics.

In the present invention, the "high rate characteristic of a specific electrode group" means that the rate characteristic is higher than other electrode groups. Here, the 'rate characteristic' is a criterion for knowing the relative magnitude of the current regardless of the size of the battery, and the discharge of the current of the battery at 1 hour for 1 C discharge at 0.1 hour is referred to as 10 C discharge.

The electrode group having a high rate characteristic is preferably 30% or more higher than the rate characteristic of other electrode groups. If the difference in rate characteristics is smaller than the above range, it may be difficult to exhibit the desired level of pulse discharge characteristics, which is not preferable.

The rate characteristics of the electrode group can be determined by various causes, but mainly depends on the loading state of the electrode active material on the current collector, such as the type, porosity, density, and the like of the electrode active material.

Therefore, the rate characteristic of the specific electrode group which contributes to the improvement of the pulse discharge characteristic can be achieved by using the electrode active material which is at least 30% higher than the electrode active material of other electrode groups. In this case, the electrode active material having excellent rate characteristics may be a positive electrode active material, a negative electrode active material, or both.

In the case of the positive electrode active material, the positive electrode active material of the specific electrode group preferably comprises spinel-based LiMn ₂ O ₄ , LiMn _{1 - x} Ni _x O ₂ (0 <X <1), or a mixture thereof as a main component. Can be. In general lithium secondary batteries, lithium cobalt oxide is widely used as a cathode active material. However, lithium cobalt oxide in the specific electrode group according to the present invention has a capacity reduction rate due to a change in crystal structure during high rate charge / discharge compared to the above active materials. It is not preferable because it is large. On the other hand, the positive electrode active material in the other electrode groups except for the specific electrode group is used a material having a relatively low rate characteristics, such a material may include a conventional lithium cobalt oxide as a main component.

In the case of the negative electrode active material, the negative electrode active material of the specific electrode group may preferably be configured to contain amorphous graphite as a main component. In general lithium secondary batteries, crystalline graphite and the like are frequently used as a negative electrode active material. However, in the specific electrode group according to the present invention, crystalline graphite is not preferable due to low rate characteristics and a large volume change during charge and discharge. On the other hand, as the negative electrode active material in the other electrode groups except for the specific electrode group, a material having a relatively low rate property is used. Such a material may include crystalline graphite as a main component, as a matter of course.

In the above, the inclusion of a specific substance as a main component of the electrode active material means that the resulting rate characteristics of the specific electrode group are included in an amount capable of exhibiting a desired pulse discharge characteristic as compared with the rate characteristic of the other electrode groups. . Therefore, the range of the main component may mean preferably 50% by weight or more, more preferably 70% by weight or more based on the total weight of the electrode active material.

In order to further enhance the rate characteristic of the specific electrode group, in one preferred example, the electrodes of the specific electrode group may be configured to have a porosity of at least 30% or more. That is, when a large amount of pores are included in order to increase the porosity, the specific surface area of the electrode active material layer in contact with the electrolyte is widened and the degree of connection of the pores is increased. As a result, the impregnation ratio of the electrolyte may be increased, resulting in rapid charge and discharge characteristics. . As such, when a material having excellent rate characteristics is used as an electrode active material of a specific electrode group and the electrode of the specific electrode group is formed in a highly porous structure, the rate characteristic of the electrode group may be further increased.

On the other hand, the electrode assembly capable of charging and discharging is largely classified into a cylindrical shape and a plate shape according to the form (outer structure) embedded in the case, and also a jelly-roll type and a stack according to the stacking shape (internal structure) of the electrode assembly. Classified as a type.

The jelly-roll type electrode assembly may be formed by stacking a long sheet-shaped anode and a cathode with a separator interposed therebetween and winding them round to form a cross-sectional circular structure, or after winding in such a circular structure, compresses in one direction to roughly cross-section. It can be made into a 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.

Such a jelly-roll type and stacked type composite structure, which is a bi-cell or full cell as a unit cell of a small unit by a stacking method, placed a plurality of them on a long separation film (membrane sheet), and then wound sequentially There are also stack / foldable electrode assemblies made of roughly plate-like structures.

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.

In the present invention, the electrode assembly is preferably composed of a stack or a stack / folding structure, more preferably comprises a stack / folding structure containing a unit cell of a full cell or bicell as the electrode group.

In this case, at least one of the unit cells may be a unit cell composed of an electrode active material having excellent rate characteristics, or a unit cell composed of an electrode active material having excellent rate characteristics and composed of an electrode having a high porosity.

In one preferred example, at least one of the unit cells is composed of unit cells having relatively high rate characteristics, and sequentially wound in a state where a plurality of unit cells are positioned on an elongated separator sheet to manufacture an electrode assembly. Can be. In this case, in order to facilitate the manufacturing process of the electrode assembly and to minimize the interference with other unit cells in the charging and discharging process, it is necessary to configure the uppermost unit cell and the lowermost unit cell as unit cells each having a high rate characteristic. More preferred.

The number of unit cells having relatively high rate characteristics is not particularly limited. However, if the number of the unit cells is too large, the capacity of the entire electrode assembly may be reduced, and therefore, preferably 40% or less, based on the total number of unit cells. More preferably, it may be necessary to determine at a level of 20% or less.

In the electrode assembly of the present invention, the high rate characteristic unit cell (s) and the remaining low rate characteristic unit cells do not have to be particularly different in other cell configurations except for the rate characteristic. In addition, the electrode assembly according to the present invention can be made of a variety of electrode active material configuration depending on the use thereof.

The present invention also provides an electrochemical cell comprising the electrode assembly, and representative examples of such an electrochemical cell include secondary batteries and capacitors.

The secondary battery has a structure in which the electrode assembly capable of charging and discharging is impregnated with an ion-containing electrolyte solution and built 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 applied to 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 secondary battery according to the present invention can be preferably used in a device in which the discharge is performed by the pulse discharge method, and more particularly in the device using the GSM discharge method.

As described above, the GSM method is discharged by a high current within a short time, it is a cause of capacity deterioration in the case of the conventional lithium-ion or lithium-ion polymer battery, the secondary battery of the present invention is excellent electrode By using a part of the group, the output energy used when discharging a high current in a short time can be compensated, and capacity degradation of the battery can be prevented during pulse discharge.

Hereinafter, although described with reference to the drawings according to an embodiment of the present invention, this is for easier understanding of the present invention, the scope of the present invention is not limited thereto.

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 on the basis of the winding direction are composed of unit cells 21 and 22 having high rate characteristics.

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, the unit cells 21 and 22 having two high rate characteristics positioned at the end of the winding based on the winding direction are respectively positioned at the top and bottom of the electrode assembly during the final winding. Therefore, the assembly process of the electrode assembly itself is facilitated, and the interference phenomenon to the unit cells having the remaining low rate characteristics in the charging and discharging process can be minimized.

Although the drawings according to the embodiments of the present invention have been described by way of example, those of ordinary skill in the art to which the present invention pertains will be able to perform various applications and modifications within the scope of the present invention.

As described above, the electrode assembly according to the present invention can improve the pulse discharge characteristics while minimizing the capacity reduction by including a portion of the electrode group having a high rate characteristics, the production of such an electrode assembly can be achieved by a simple process As a result, the manufacturing cost can be lowered compared to the existing hybrid cell.

Claims (16)

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 A is a different electrode. It is composed of an electrode active material having a rate characteristic of more than 30% compared to the group, The positive electrode active material of the electrode group (A) is composed of a structure containing a spinel-based LiMn ₂ O ₄ , LiMn _1-x Ni _x O ₂ (0 <x <1), or a mixture thereof as a main component, The negative electrode active material of the electrode group (A) is composed of a composition containing amorphous graphite as a main component, The electrode assembly is an electrode assembly, characterized in that consisting of a stack / folding type structure containing a unit cell of a full cell or bicell as the electrode group. delete delete delete delete delete The electrode assembly of claim 1, wherein the electrode of the electrode group (A) has a porosity of 30% or more. delete delete delete delete 2. The electrode assembly of claim 1, wherein the electrode assembly is formed by sequentially winding and stacking a plurality of unit cells on a long separator sheet, wherein each of the uppermost unit cell and the lowermost unit cell is a unit. An electrode assembly, characterized in that the cell (A). The electrode assembly of claim 1, wherein the number of unit cells (A) is determined at a level of 40% or less based on the total number of unit cells. An electrochemical cell comprising the electrode assembly according to claim 1. 15. The electrochemical cell of claim 14, wherein said cell is a lithium secondary battery. 16. The electrochemical cell of claim 15, wherein said battery is charged and discharged in a pulsed discharge manner.

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