CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a national phase entry under 35 U.S.C. § 371 of International Application No. PCT/KR2017/015179, filed Dec. 21, 2017, which claims priority to Korean Patent Application No. 10-2017-0008355, filed Jan. 18, 2017 in the Republic of Korea, the disclosures of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a battery cell including an electrode lead located so as to face the outer surface of an electrode assembly.

BACKGROUND ART

The rapid increase in the use of fossil fuels has accelerated the demand for alternative energy sources or clean energy sources, and research has been actively carried out into power generation and power storage using electrochemistry.

A typical example of an electrochemical device using such electrochemical energy is a secondary battery, which has been increasingly used in various fields.

As portable devices, such as portable computers, portable phones, and cameras, have been increasingly developed and the demand for such mobile devices has increased in recent years, the demand for secondary batteries as energy sources for such mobile devices has also sharply increased. Among such secondary batteries is a lithium secondary battery that exhibits high charge and discharge characteristics, exhibits long lifespan characteristics, and is environmentally friendly, into which much research has been carried out and which is now commercialized and widely used.

An electrode assembly, which is mounted in a battery case, is a power-generating element that has a structure in which a positive electrode, a separator, and a negative electrode are stacked and that can be charged and discharged. The electrode assembly is classified as a jelly-roll type electrode assembly, which is configured to have a structure in which a long sheet type positive electrode and a long sheet type negative electrode, to which active materials are applied, are wound in the state in which a separator is disposed between the positive electrode and the negative electrode, or a stacked type electrode assembly, which is configured to have a structure in which a plurality of positive electrodes having a predetermined size and a plurality of negative electrodes having a predetermined size are sequentially stacked in the state in which separators are disposed respectively between the positive electrodes and the negative electrodes.

There has been developed a stacked/folded type electrode assembly having an improved structure, which is a combination of the jelly-roll type electrode assembly and the stacked type electrode assembly. The stacked/folded type electrode assembly is configured to have a structure in which a plurality of full cells, each of which has a positive electrode/separator/negative electrode structure and has a predetermined unit size, are arranged, or a plurality of bi-cells, each of which has a positive electrode (or negative electrode)/separator/negative electrode (or positive electrode)/separator/positive electrode (or negative electrode) structure and has a predetermined unit size, are arranged, is folded using a long continuous separation film.

Meanwhile, the lithium secondary battery, which is one of the secondary batteries, has lower weight and higher energy density than other secondary batteries, and thus the demand for the lithium secondary battery is on an increasing trend. In particular, for a prismatic battery, the volume of electrode tabs that protrude outwards from an electrode assembly, in which a plurality of electrode plates and a plurality of separators are stacked, and the volume of an electrode lead that protrudes outwards in the state of being connected to the electrode tabs excessively increase the volume of a secondary battery, whereby the energy density of the secondary battery is reduced. Furthermore, unnecessary dead space is formed in a device in which the secondary battery mounted.

FIG. 1is an exploded perspective view schematically showing a conventional general pouch-shaped battery cell including a stacked type electrode assembly.

Referring toFIG. 1, the pouch-shaped battery cell, which is denoted by reference numeral10, is configured to have a structure in which an electrode assembly30is mounted in a pouch-shaped battery case20, in which electrode tabs31and32of the electrode assembly are welded to two electrode leads40and41, respectively, and in which the battery case20is sealed in the state in which the electrode leads are exposed outwards from the battery case. The electrode leads are located in the direction in which the electrode tabs protrude. The capacity of the battery cell is reduced by the tab-lead coupling portions and the electrode leads, whereby the total energy capacity of the battery cell is reduced.

In order to solve these problems, batteries having various novel structures have been introduced in recent years. However, the introduced batteries still do not satisfactorily solve the above problems. For this reason, the demand for a battery suitable for miniaturization of a device while having improved energy density is being continued.

Therefore, there is an urgent necessity for technology that is capable of fundamentally solving the above problems.

DISCLOSURE

Technical Problem

The present invention has been made to solve the above problems and other technical problems that have yet to be resolved.

As a result of a variety of extensive and intensive studies and experiments to solve the problems described above, the inventors of the present application have found that, in the case in which one end of an electrode lead is coupled to electrode tabs and in which a lead body of an electrode lead is located so as to face the outermost surface of an electrode assembly in the state of being parallel to a plurality of electrode plates such that an opposite end of the electrode lead is located on the outer surface of a cell case, as will be described below, the electrode lead does not protrude outwards from the electrode assembly. It is possible to reduce the size of unnecessary dead space of the battery cell that is occupied by a tab-lead coupling portion and the electrode lead and to improve the utilization of the inner space of a device in which the battery cell is mounted. The present invention has been completed based on these findings.

Technical Solution

In accordance with an aspect of the present invention, the above and other objects can be accomplished by the provision of a battery cell configured such that an electrode assembly, including a positive electrode and a negative electrode stacked in the state in which a separator is interposed between the positive electrode and the negative electrode, is mounted in a pouch-shaped cell case, wherein electrode tabs protruding outwards from a plurality of electrode plates are coupled to a first lead end of an electrode lead, a second lead end of the electrode lead, which is an opposite end to the first lead end, is located on the outer surface of the cell case in the state of being parallel to the electrode plates, and a lead body provided between the first lead end and the second lead end is located so as to face the outermost surface of the electrode assembly in the state of being maintained parallel to the electrode plates.

In a conventional electrode assembly, the electrode tabs and a tab-lead coupling portion protrude to occupy a predetermined volume of the battery cell, whereby space that does not contribute to the improvement in the capacity of a secondary battery is formed in the battery cell.

In contrast, in the electrode assembly according to the present invention, the size of the space that is occupied by the electrode tabs and the tab-lead coupling portion, which do not contribute to the improvement in the capacity of the secondary battery, is reduced, whereby it is possible to considerably improve the energy density of the secondary battery.

In a concrete example, the electrode lead may be configured such that, in the state in which the second lead end, the lead body, and the first lead end are arranged so as to be sequentially located in the state of being parallel to the direction in which the electrode tabs protrude outwards, the first lead end is coupled to the electrode tabs, and a portion of the lead body is bent at an angle of 180 degrees with respect to a remaining portion of the lead body such that the second lead end is located on the outer surface of the cell case.

In addition, the electrode lead may be configured such that, in the state in which the lead body and the first lead end are arranged so as to be sequentially located in the state of being parallel to the direction in which the electrode tabs protrude outwards, the first lead end is coupled to the electrode tabs, and an auxiliary lead, which forms the second lead end, is further coupled to the lead body.

Specifically, the auxiliary lead may be connected to the lead body by welding, and may be made of a metal material so as to function as a lead.

Meanwhile, a coupling portion of the electrode tabs and the first lead end may be bent at an angle of 90 degrees with respect to the lead body so as to face the side surface of the electrode assembly.

Since the coupling portion of the electrode tabs and the first lead end is bent so as to face the side surface of the electrode assembly, the size of an unnecessary space formed in a structure in which the electrode tabs and the electrode lead protrude outwards from the electrode assembly may be effectively reduced. The coupling portion of the electrode tabs and the first lead end is not necessarily bent at an angle of 90 degrees. The coupling portion of the electrode tabs and the first lead end may be bent at an angle of 75 to 105 degrees toward the side surface of the electrode assembly on the basis of the direction in which the electrode tabs protrude. In the case in which the coupling portion of the electrode tabs and the first lead end is excessively bent toward the side surface of the electrode assembly, however, the electrode tabs may come into contact with the side surfaces of the electrode plates, whereby a short circuit may occur and thus the safety of the battery cell may be reduced. For this reason, it is sufficient for the electrode lead to exhibit enough strength to remain bent even when external impact is applied thereto. A protective member may be disposed between the bent electrode tabs and the side surface of the electrode assembly.

Meanwhile, the electrode lead according to the present invention may be manufactured by bending a single flat lead or by welding two separate leads. In addition, the electrode lead according to the present invention may be manufactured using a mold having a shape corresponding to the shape of the electrode lead.

Since the electrode lead is located on the surface of the electrode assembly so as to face the outermost surface of the electrode assembly in the state of being maintained parallel to the electrode plates, as described above, the electrode assembly according to the present invention does not have a structure in which the electrode lead protrudes outwards from the electrode assembly, whereby the size of unnecessary dead space may be reduced. In addition, the portion of the electrode lead that is connected to the electrode tabs is bent toward the side surface of the electrode assembly, whereby it is possible to considerably reduce the volume of the battery cell while maintaining the same capacity. Furthermore, in the case in which a battery module is manufactured using battery cells according to the present invention, as will be described below, it is not necessary to perform a welding process for interconnecting the battery cells, and therefore it is possible to simply manufacture the battery module. Consequently, the present invention is advantageous in terms of the manufacturing cost and the manufacturing process.

Specifically, the size of the second lead end may be equivalent to 10% to 95% of the planar size of the outer surface of the cell case, on which the second lead end is located.

The second lead end is substantially a portion for electrical connection with an external device. As the size of the second lead end that is exposed to the outside is increased within the above range, the resistance of the battery cell is decreased.

Meanwhile, the cell case may be made of a laminate sheet including a metal layer and a resin layer, and the outer edge of the cell case may be sealed by thermal fusion. Specifically, one end of the laminate sheet is interposed and fixed between distal portions of the electrode assembly and the lead body that face each other, and the opposite end of the laminate sheet is interposed and fixed between the second lead end and the lead body, whereby the laminate sheet wraps the electrode assembly. The remaining ends of the laminate sheet, which are not fixed by the electrode lead, are sealed by thermal fusion to form the cell case.

In the battery cell according to the present invention, the separator may be interposed between the lead body and the outermost surface of the electrode assembly. Specifically, a stacked/folded type electrode assembly may be configured such that a separator sheet for winding the electrodes is interposed between the lead body and the outermost surface of the electrode assembly, and a stacked type electrode assembly may be configured such that a separator is further disposed on the outermost electrode plate.

According to the present invention, the electrode tabs and the electrode lead may be used for a positive electrode or a negative electrode. In a concrete example, positive electrode tabs of the electrode assembly may protrude outwards in a first direction while negative electrode tabs of the electrode assembly may protrude outwards in a second direction, which is opposite the first direction, a second lead end of a positive electrode lead coupled to the positive electrode tabs may be located on a first outer surface of the cell case, and a second lead end of a negative electrode lead coupled to the negative electrode tabs may be located on a second outer surface of the cell case, which is opposite the first outer surface. Consequently, the positive electrode lead end and the negative electrode lead end are located on different outer surfaces of the electrode assembly.

In accordance with another aspect of the present invention, there is provided a battery module including two or more battery cells according to the present invention. The size of the dead space that is occupied by the electrode tabs and the electrode lead may be reduced, whereby the energy density of the battery cell may be increased. Consequently, the energy density of the battery module including the battery cells may also be increased.

Meanwhile, in the battery module, the battery cells may be arranged in a stacked state so as to have a structure in which the outer surfaces of adjacent cell cases, on which the respective electrode leads of the battery cells are located, face each other. In the structure in which the battery cells are arranged in the stacked state, the electrode leads face each other, whereby the battery cells are electrically connected to each other.

Specifically, in the battery module, the battery cells, which are arranged in the stacked state, may physically contact each other in a non-welding fashion. Since the battery cells are stacked without an additional welding process in order to manufacture the battery module, it is possible to simplify the process of manufacturing the battery module and to reduce the cost of manufacturing the battery module.

