Secondary battery

Disclosed is a secondary battery which can improve safety by forming a carbon coating layer and an electrode active material layer on an electrode plate such that ends of the carbon coating layer and the electrode active material layer are in different positions. As an example, the disclosed secondary battery comprises: an electrode assembly including a first electrode plate, a second electrode plate, and a separator interposed therebetween; and a case for receiving the electrode assembly, wherein the first electrode plate comprises: a first electrode collector; a carbon coating layer formed on at least one surface of the first electrode collector; and a first electrode active material layer covering at least a portion of the carbon coating layer, wherein the carbon coating layer and the electrode active material layer are formed such that the end of the carbon coating layer and the end of the first electrode active material layer are in different positions, and a protrusion is formed on at least one of the end of the carbon coating layer and the end of the first electrode active material layer.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a National Phase Patent Application of International Patent Application Number PCT/KR2017/007666, filed on Jul. 17, 2017, which claims priority of Korean Patent Application No. 10-2016-0097948, filed Aug. 1, 2016. The entire contents of both of which are incorporated herein by reference.

TECHNICAL FIELD

Embodiments of the present invention relate to a secondary battery.

BACKGROUND ART

Unlike a primary battery that cannot be charged, a secondary battery may be recharged. A low-capacity secondary battery comprised of one single battery cell is used as the power source for various portable small-sized electronic devices, such as cellular phones, and camcorders. A high-capacity secondary battery in which several tens of battery cells are connected in a battery pack is widely used as the power source for motor drives, such as those in hybrid electric vehicles.

The secondary battery is manufactured in various shapes, and representative shapes thereof include a cylindrical shape, a prismatic shape and a pouch shape. The secondary battery is configured such that an electrode assembly formed by positive and negative electrode plates with a separator as an insulator interposed therebetween, and an electrolyte, are received in a case, and a cap plate is coupled to the case. Of course, positive and negative electrode terminals are connected to the electrode assembly and then exposed or protruded to the outside of the case.

Technical Problems to be Solved

Embodiments of the present invention provide a secondary battery which can improve safety by forming a carbon coating layer and an electrode active material layer on an electrode plate such that ends of the carbon coating layer and the electrode active material layer are in different positions.

Technical Solutions

In accordance with an embodiment of the present invention, there is provided a secondary battery comprising an electrode assembly including a first electrode plate, a second electrode plate, and a separator interposed therebetween, and a case for receiving the electrode assembly, wherein the first electrode plate comprises: a first electrode collector; a carbon coating layer formed on at least one surface of the first electrode collector; and a first electrode active material layer covering at least a portion of the carbon coating layer, wherein the carbon coating layer and the electrode active material layer are formed such that the end of the carbon coating layer and the end of the first electrode active material layer are in different positions, and a protrusion is formed on at least one of the end of the carbon coating layer and the end of the first electrode active material layer.

Here, the first electrode active material layer may be formed to cover at least a portion of the first electrode collector.

In addition, the protrusion may include a first protrusion protruded from the end of the carbon coating layer in a thickness direction, and a second protrusion protruded from the end of the first electrode active material layer in a thickness direction.

In addition, the first electrode active material layer may be formed such that its end is extended longer than the end of the carbon coating layer.

In addition, the second protrusion may be positioned between the end the carbon coating layer and the end of the first electrode active material layer.

In addition, the carbon coating layer may be formed such that its end is extended longer than the end of the first electrode active material layer.

In addition, the first protrusion may be positioned between the end of the first electrode active material layer and the end of the carbon coating layer.

In addition, the end of the carbon coating layer and the end of the first electrode active material layer may be spaced a preset distance apart from each other.

In addition, the distance may be set to be in the range from 1 mm to 10 mm.

Advantageous Effects

As described above, in the secondary battery according to the embodiment of the present invention, the end of the carbon coating layer coated on an electrode plate and the end of the electrode active material layer are in different positions to prevent protrusions of the carbon coating layer and the electrode active material layer from overlapping each other, thereby suppressing defects of the secondary battery and improving the safety of the secondary battery. That is to say, the carbon coating layer and the electrode active material layer may be coated by, for example, but not limited to, slot die coating. Here, the protrusions formed on a coating start portion and/or a coating end portion in a thickness direction may be relatively thick. Therefore, if the ends of the carbon coating layer and the electrode active material layer respectively having the protrusions are in the same position, they may become thicker than prescribed thickness levels, so that the active material may be delaminated during a pressing step and/or lithium ions may be precipitated through the protrusions during a battery operation (charging or discharging). In the secondary battery according to the embodiment of the present invention, however, since the ends of the carbon coating layer and the electrode active material layer having the protrusions are in different positions, as described above, the delamination of the electrode active material and/or precipitation of lithium ions can be prevented.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, a preferred embodiment of the present invention will be described in detail.

Various embodiments of the present invention may be embodied in many different forms and should not be construed as being limited to the example embodiments set forth herein. Rather, these example embodiments of the disclosure are provided so that this disclosure will be thorough and complete and will convey inventive concepts of the disclosure to those skilled in the art.

In the accompanying drawings, sizes or thicknesses of various components are exaggerated for brevity and clarity. Like numbers refer to like elements throughout. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprise” and/or “comprising,” when used in this specification, specify the presence of stated features, numbers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, numbers, steps, operations, elements, components, and/or groups thereof.

It will be understood that, although the terms first, second, etc. may be used herein to describe various members, elements, regions, layers and/or sections, these members, elements, regions, layers and/or sections should not be limited by these terms. These terms are only used to distinguish one member, element, region, layer and/or section from another.

Hereinafter, a secondary battery according to an embodiment of the present invention will be described.

FIG. 1is a perspective view of a secondary battery according to an embodiment of the present invention.FIG. 2is an exploded perspective view of an electrode assembly in the secondary battery according to an embodiment of the present invention.

Referring toFIGS. 1 and 2, the secondary battery10according to an embodiment of the present invention may include an electrode assembly100and a case200for receiving the electrode assembly100.

The electrode assembly100is formed by stacking or winding a first electrode plate110, a second electrode plate120and a separator130interposed therebetween. That is to say, the electrode assembly110may be formed by stacking the first and second electrode plates110and120and the separator130, as illustrated inFIG. 2, and winding the stacked structure. The wound electrode assembly110is received in the case200. Meanwhile, the first electrode plate110may be a negative electrode and the second electrode plate120may be a positive electrode, or vice versa.

The first electrode plate110includes a first electrode collector111, a coating region112formed on at least one surface of the first electrode collector111, and a first electrode non-coating portion115where the coating region112is not formed. Here, the coating region112may include a carbon coating layer113and a first electrode active material layer114, which will later be described. The carbon coating layer113may be interposed between the first electrode collector111and the first electrode active material layer114to reduce interfacial resistance therebetween and to increase conductivity. Therefore, the carbon coating layer113may reduce internal resistance of the secondary battery and may increase charging/discharging cycle life.

When the first electrode plate110is a negative electrode, the first electrode collector111may include a conductive metal thin plate made of, for example, but not limited to, copper (Cu) or nickel (Ni) foil. The carbon coating layer113may include one or more carbon-based material selected from the group consisting of, for example, but not limited to, graphite, carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, carbon fiber and fluorocarbon. In addition, the first electrode active material layer114may be formed using, for example, but not limited to, carbon-based material, Si, Sn, tin oxide, tin alloy complex, transition metal oxide, lithium metal nitride or metal oxide. However, the present invention does not limit the material of the first electrode plate110to those disclosed herein, as described above.

A configuration of the coating region112will later be described in more detail.

A first electrode tab140is formed in the first electrode non-coating portion115of the first electrode plate110, where the coating region112is not formed. One end of the first electrode tab140is electrically connected to the first electrode non-coating portion115, and the other end thereof is drawn to the outside of the case200. Meanwhile, an insulation film160for insulation is attached to a region of the first electrode tab140, which contacts the case200.

The second electrode plate120includes a second electrode collector121, a second electrode active material layer122formed on at least one surface of the second electrode collector121, and a second electrode non-coating portion125where the second electrode active material layer122is not formed.

When the second electrode plate120is a positive electrode, the second electrode collector121may include a highly conductive metal thin plate made of, for example, but not limited to, aluminum foil. In addition, the second electrode active material layer122may include, for example, but not limited to, a chalcogenide compound including, for example, a composite metal oxide, such as LiCoO2, LiMn2O4, LiNiO2, or LiNiMnO2. However, the present invention does not limit the material of the second electrode plate120to those disclosed herein, as described above.

A second electrode tab150is formed in the second electrode non-coating portion125of the second electrode plate120, where the second electrode active material layer122is not formed. One end of the second electrode tab150is electrically connected to the second electrode non-coating portion125, and the other end thereof is drawn to the outside of the case200. Meanwhile, the insulation film160for insulation is attached to a region of the second electrode tab150, which contacts the case200of the first electrode tab140.

The separator130is interposed between the first electrode plate110and the second electrode plate120to prevent electrical short circuits from occurring therebetween. In addition, the separator130may be formed of a porous layer to allow lithium ions to move between the first electrode plate110and the second electrode plate120. The separator130may be made, for example, of polyethylene, polypropylene, or a copolymer of polypropylene and polyethylene, but the present invention does not limit the material of the separator130to those disclosed herein. To prevent electrical short circuits from occurring between the first electrode plate110and the second electrode plate120, the separator130may have a larger width than the first and second electrode plates110and120. In some cases, the separator130may be an organic and/or inorganic solid electrolyte itself.

The insulation film160electrically insulates each of the first and second electrode tabs140and150and the case200from each other. The insulation film160may be made of, for example, polyphenylene sulfide (PPS), polyimide (PI) or polypropylene (PP), but the present invention does not limit the material of the insulation film160to those disclosed herein.

An electrolyte solution (not illustrated) with the electrode assembly100may be received in the case200. The electrolyte solution may serve as a movement medium of lithium ions generated by an electrochemical reaction taking place between the positive and negative electrodes of the secondary battery100during charging/discharging, and may include a non-aqueous organic solution that is a mixture of lithium salt and high-purity organic solvent. In addition, the electrolyte solution may be a polymer based on a polymeric electrolyte. As described above, when the organic and/or inorganic solid electrolyte is used, the electrolyte solution may not be provided.

The case200consists of an upper case210and a lower case220, which are formed by bending a rectangular pouch layer formed in a single body at its center in a lengthwise direction. A groove221, which is formed to receive the electrode assembly100and the electrolyte solution by, for example, a pressing step, and a sealing part222for being sealed with the upper case210, are formed in the lower case220.

Meanwhile, the embodiment of the present invention discloses that the secondary battery10is configured such that the electrode assembly100is received in the pouch-type case200, but aspects of the present invention are not limited thereto. That is to say, the secondary battery10may be a prismatic battery or a cylindrical battery, rather than the pouch-type battery.

FIG. 3is a cross-sectional view of the electrode assembly illustrated inFIG. 2.FIG. 4is an enlarged cross-sectional view of a portion A ofFIG. 3. For brevity and clarity, thicknesses and lengths in the electrode assembly illustrated inFIGS. 3 and 4may be exaggerated or reduced.

Referring toFIGS. 3 and 4, the coating region112is formed on both surfaces of the first electrode collector111. The coating region112includes the carbon coating layer113and the first electrode active material layer114. As illustrated, the coating region112may be formed on both surfaces of the first electrode collector111. In some cases, the coating region112may be formed on only one selected from both surfaces of the first electrode collector111.

The carbon coating layer113is formed to cover at least a portion of the first electrode collector111. A first protrusion113athat is relatively thick in a thickness direction exists at opposite ends of the carbon coating layer113. That is to say, the first protrusion113aexists at a leading edge part and a trailing edge part, which are coated with the carbon coating layer113, to protrude more thickly than other coating regions, except for the leading edge part and the trailing edge part.

The first protrusion113ais inevitably formed in the course of forming the carbon coating layer113. That is to say, when slurry for forming the carbon coating layer113is coated on the first electrode collector111, rising of the slurry may occur to the leading edge part (i.e., a coating start portion) and the trailing edge part (i.e., a coating end portion) due to characteristics of coating process. That is to say, the reason for the rising of the slurry is that the coating process is nonuniformly performed at the leading edge part and the trailing edge part of the carbon coating layer113, which is attributed to characteristics of the slurry and coating machine employed. As such, the first protrusion113aexists at the leading edge part and the trailing edge part of the carbon coating layer113due to the rising of the slurry.

The first electrode active material layer114is formed to cover at least a portion of the first electrode collector111. In addition, the first electrode active material layer114is formed to cover at least a portion of the carbon coating layer113as well. A second protrusion114aexists at opposite ends of the first electrode active material layer114. That is to say, the second protrusion114ais formed at a leading edge part and a trailing edge part, which are coated with the first electrode active material layer114, the second protrusion114aprotruded more thickly than other coating regions, except for the leading edge part and the trailing edge part.

The second protrusion114ais inevitably formed in the coating process of the first electrode active material layer114. That is to say, like the first protrusion113a, the second protrusion114ais also formed because slurry coating is nonuniformly performed at the leading edge part and the trailing edge part due to characteristics of coating process.

Meanwhile, the end of the carbon coating layer113and the end of the first electrode active material layer114may be in different positions. That is to say, in an embodiment of the present invention, the end of the first electrode active material layer114is extended longer than the end of the carbon coating layer113. In other words, the first electrode active material layer114is formed longer than the carbon coating layer113. Therefore, the first electrode active material layer114may be formed to entirely cover the carbon coating layer113. In addition, the carbon coating layer113is not exposed to the outside by the first electrode active material layer114.

Specifically, as illustrated inFIG. 4, the end of the first electrode active material layer114is spaced a preset distance D apart from the end of the carbon coating layer113. In addition, the distance D is set to prevent the first protrusion113aand the second protrusion114afrom overlapping each other. Therefore, the second protrusion114ais positioned between an extension line L1of the end of the carbon coating layer113and an extension line L2of the end of the first electrode active material layer114. In addition, the second protrusion114ais preferably positioned at a region spaced apart from the extension line L1of the end of the carbon coating layer113.

Meanwhile, the distance D is preferably set to be in the range from 1 mm to 10 mm. Here, since the end of the carbon coating layer113and the end of the first electrode active material layer114may be in different positions, the distance D will not be zero (0). More preferably, the distance D may be set to be in the range from 2.5 mm to 5 mm. If the distance D is less than 2.5 mm, the first and second protrusions113aand114amay overlap each other, which is not desirable. If the distance D is greater than 5 mm, a difference between lengths of the carbon coating layer113and the first electrode active material layer114may become unnecessarily increased, which is not desirable, either.

In the embodiment of the present invention, the end of the carbon coating layer113and the end of the first electrode active material layer114are made to be in different positions, thereby preventing the first protrusion113aand the second protrusion114afrom overlapping each other. Therefore, it is possible to prevent the safety of the secondary battery from being impaired due to overlapping of the first and second protrusions113aand114a.

That is to say, when the end of the carbon coating layer113and the end of the first electrode active material layer114are positioned on the same line, the first and second protrusions113aand114amay overlap each other, making the secondary battery vulnerable to damages or defects. For example, during the pressing step of the first electrode plate110, active material delamination may occur to the relatively thick overlapping area of the first and second protrusions113aand114a. In addition, during charging/discharging of the secondary battery10, movement of lithium ions may not be facilitated at the relatively thick overlapping area of the first and second protrusions113aand114a, resulting in precipitation of the lithium ions. In particular, the precipitation of the lithium ions may cause the lithium ions to pass through neighboring first and second electrode plates110and120or a neighboring separator130, resulting in ignition of the secondary battery10.

In the embodiment of the present invention, the coating region112is more uniformly formed by forming the first and second protrusions113aand114aso as not to overlap each other, thereby. Therefore, active material delamination due to overlapping of the first and second protrusions113aand114acan be suppressed, thereby improving the processing reliability. In addition, precipitation of lithium ion can be eliminated, thereby reducing defects of the secondary battery10and improving the safety of the secondary battery10.

While the embodiment of the present invention illustrates that the carbon coating layer113is formed only on the first electrode plate110, the carbon coating layer113may also be formed on the second electrode plate120as well. That is to say, the carbon coating layer113may be interposed between the second electrode collector121and the second electrode active material layer122of the second electrode plate120.

Hereinafter, a secondary battery according to another embodiment of the present invention will be described.

FIG. 5is a cross-sectional view of a region corresponding toFIG. 4in a secondary battery according to another embodiment of the present invention. Since the secondary battery according to another embodiment of the present invention is substantially the same with the secondary battery10according to the previous embodiment, except for a configuration of a coating region312, repeated explanation will not be given.

Referring toFIG. 5, a coating region312is formed on at least one surface of the first electrode collector (111ofFIG. 3). Here, the coating region312includes a carbon coating layer313and a first electrode active material layer314. In addition, the carbon coating layer313and the first electrode active material layer314include a first protrusion313aand a second protrusion314aformed at their ends, respectively.

The carbon coating layer313and the first electrode active material layer314may be formed such that the end of the carbon coating layer313and the end of the first electrode active material layer314are in different positions. That is to say, in another embodiment of the present invention, the carbon coating layer313is formed such that its end is extended longer than the end of the first electrode active material layer314. In other words, the carbon coating layer313is formed longer than the first electrode active material layer314. Therefore, the first electrode active material layer314covers at least a portion of the carbon coating layer313. In addition, the end of the carbon coating layer313is exposed to the outside by the first electrode active material layer314.

Specifically, the end of the carbon coating layer313and the end of the first electrode active material layer314are spaced a preset distance D apart from each other. In addition, the distance D is set such that the first protrusion313aand the second protrusion314ado not overlap each other. Therefore, the first protrusion313ais positioned between an extension line L3of the end of the first electrode active material layer314and an extension line L4of the end of the carbon coating layer313. In addition, the first protrusion313ais preferably positioned at a region spaced apart from the extension line L3of the end of the first electrode active material layer314.

Meanwhile, the distance D may be set to be in the range from 1 mm to 10 mm. Of course, since the end of the first electrode active material layer314and the end of the carbon coating layer313are in different positions, the distance D may not be zero (0). Preferably, the distance D may be set to be in the range from 2.5 mm to 5 mm. If the distance D is less than 2.5 mm, the first and second protrusions313aand314amay overlap each other, which is not desirable. In addition, if the distance D is greater than 5 mm, a difference between lengths of the carbon coating layer313and the first electrode active material layer314may become unnecessarily increased, which is not desirable, either.

In another embodiment of the present invention, the carbon coating layer313and the first electrode active material layer314may be formed such that the end of the carbon coating layer313and the end of the first electrode active material layer314are in different positions, thereby preventing the first protrusion313aand the second protrusion314afrom overlapping each other. Therefore, the delamination of the electrode active material and/or precipitation of lithium ions can be prevented, thereby suppressing defects of the secondary battery and improving the safety of the secondary battery.

Meanwhile, the configuration of the coating region312according to the current embodiment and the configuration of the coating region112according to the previous embodiment can be both applied in combination. That is to say, a combination of different configurations can be applied to coating regions formed at both ends of the first electrode plate110such that the configuration of the coating region112according to the previous embodiment is applied to one end coating region and the configuration of the coating region312according to the current embodiment is applied to the other end coating region.

In addition, although not illustrated, the carbon coating layer may also be formed on a second electrode plate. Here, the carbon coating layer and a second electrode active material layer formed on the second electrode plate may be configured by applying the configuration of the coating region112according to the previous embodiment of the present invention alone, by applying the configuration of the coating region312according to the current embodiment of the present invention alone, or by applying the configurations of the coating regions212and312according to both embodiments in combination.

FIGS. 6 and 7are photographs for comparison of a secondary battery in which ends of two coating layers formed on electrode plates are on the same line and a secondary battery in which ends of two coating layers are in different positions.

Table 1 shows observation results of active material delamination and lithium precipitation depending on the distance D between the end of the carbon coating layer and the end of the first electrode active material layer. Here, assuming that the origin O is the end of the carbon coating layer, the distance D indicates a position of the end of the first electrode active material layer spaced apart from the origin O. In addition, the (+) sign means that the end of the first electrode active material layer is extended longer than the end of the carbon coating layer, and the (−) sign means that the end of the first electrode active material layer is extended to be shorter than the end of the carbon coating layer. That is to say, the configuration of the coating region112disclosed in the previous embodiment is applied in Examples 1 and 2, and the configuration of the coating region312disclosed in the current embodiment is applied in Examples 3 and 4.

As to the active material delamination in Table 1, the observation results are obtained by determining whether the amount of the delaminated active material stuck on a press roll during a pressing step performed after forming a coating region on a first electrode plate exceeds a predetermined level.

As to the lithium precipitation in Table 1, the observation results are obtained by determining whether lithium is precipitated at a boundary region between the coating region and the first electrode non-coating portion after performing charging and discharging operations on an electrode assembly at a predetermined level and then disassembling the electrode assembly. Here, the observation result of Comparative Example 1 is illustrated inFIG. 6, and the observation result of Example 1 is illustrated inFIG. 7.

In Comparative Example 1, when the end of the carbon coating layer and the end of the first electrode active material layer are positioned on the same line (D=0 mm), occurrences of active material delamination and lithium precipitation were observed. Specifically, referring toFIG. 6, it was confirmed that a precipitation region existed at a boundary between the coating region (C) and the non-coating portion (N). That is to say, it is understood that the protrusion of the carbon coating layer and the protrusion of the first electrode active material layer overlap each other, a rising phenomenon occurring at the end of the coating region is maximized, consequently resulting in active material delamination and lithium precipitation.

However, when the end of the carbon coating layer and the end of the first electrode active material layer are spaced the distance D apart from each other (D=+5 mm) (Example 1), occurrences of active material delamination and lithium precipitation were not observed. Specifically, referring toFIG. 7, it was confirmed that only a boundary portion between the coating region (C) and the non-coating portion (N) was observed but lithium precipitation was not observed. That is to say, it is understood that the protrusion of the carbon coating layer and the protrusion of the first electrode active material layer did not overlap each other, and the coating region C was more uniformly formed, consequently preventing the active material delamination and lithium precipitation from occurring due to overlapping of the protrusions of the carbon coating layer and the first electrode active material layer.

In addition, when the distances D between the end of the carbon coating layer and the end of the first electrode active material layer are +3 mm, −3 mm and −5 mm, respectively (Examples 2, 3 and 4), it was confirmed that occurrences of active material delamination and lithium precipitation were not observed, as indicated in Table 1.

That is to say, in the secondary battery according to the present invention, the end of the carbon coating layer and the end of the first electrode active material layer are in different positions in the first electrode plate and the respective protrusions do not overlap each other, thereby improving the safety of the secondary battery.

Although the foregoing embodiments have been described to practice the secondary battery of the present invention, these embodiments are set forth for illustrative purposes and do not serve to limit the invention. Those skilled in the art will readily appreciate that many modifications and variations can be made, without departing from the spirit and scope of the invention as defined in the appended claims, and such modifications and variations are encompassed within the scope and spirit of the present invention.

EXPLANATION OF REFERENCE NUMERALS