Electrode assembly and lithium ion secondary battery using the same

An electrode assembly and a lithium ion secondary battery using the same capable of preventing a short circuit from being created in an outer peripheral portion of the electrode assembly. Uncoated areas of positive and negative electrode plates and an active material layer in the inner and outer peripheral portions of the electrode assembly are optimally aligned such that the thickness of the electrode assembly is uniformly formed widthwise along the electrode assembly.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korea Patent Application No. 2004-0048994 filed on Jun. 28, 2004, in the Korean Intellectual Property Office, the entire content of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electrode assembly and a lithium ion secondary battery using the same, and more particularly, to an electrode assembly and a lithium ion secondary battery capable of preventing a short circuit from being created in an outer peripheral portion of the electrode assembly.

2. Description of the Prior Art

As is generally known in the art, secondary batteries are different from primary batteries in that secondary batteries can charge and discharge electric power. Secondary batteries have been extensively used in advanced electronic technology fields for portable electronic appliances, such as portable phones, notebook computers and camcorders.

Particularly, lithium ion secondary batteries represent an operational voltage of about 3.7V, which is three times higher than that of Ni—Cd batteries or Ni-MH batteries used as power sources for portable electronic appliances. In addition, the lithium ion secondary batteries have high energy density per unit weight, so the lithium secondary batteries are extensively used in the advanced electronic technology fields.

In general, lithium ion secondary batteries include lithium-based oxides as positive electrode active materials and carbon materials as negative electrode active materials. In addition, secondary batteries are classified into liquid electrolyte batteries and high polymer electrolyte batteries according to the electrolytes used for the secondary batteries. The secondary batteries using the liquid electrolyte are called “lithium ion secondary batteries” and the secondary batteries using the high polymer electrolyte are called “lithium polymer secondary batteries”. In addition, the lithium ion secondary batteries can be formed with various shapes, such as cylinder type lithium ion secondary batteries, can type lithium ion secondary batteries and pouch type lithium ion secondary batteries.

As shown inFIGS. 1 and 2, the typical can type lithium ion secondary battery includes a can10, an electrode assembly20accommodated in the can10, and a cap assembly70for sealing an upper opening section of the can10.

The can10is made from a metal having a hexahedral shape and acts as a terminal. The can10includes an upper opening section10athrough which the electrode assembly20is accommodated in the can10.

Referring toFIG. 2, the electrode assembly20includes a positive electrode plate30, a negative electrode plate40, and a separator50. The positive electrode plate30and the negative electrode plate40are wound in the form of a jelly-roll while interposing the separator50therebetween.

The positive electrode plate30includes a positive electrode collector32made from a laminated aluminum foil and a positive electrode active material layer34including lithium-based oxides coated on inner and outer surfaces of the positive electrode collector32. The positive electrode collector32is formed with a positive electrode uncoated area32a, in which the positive electrode active material layer34is not coated, corresponding to both ends of the positive electrode plate30. A positive electrode tap36is fixed to the positive electrode uncoated area32aby means of ultrasonic welding in such a manner that an end of the positive electrode tap36can upwardly protrude beyond an upper end of the positive electrode collector32. The positive electrode tap36is generally made from Ni or a Ni-alloy. However, it is also possible to fabricate the positive electrode tap36by using other metallic materials.

The negative electrode plate40includes a negative electrode collector42made from a laminated aluminum foil and a negative electrode active material layer44including carbon materials coated on inner and outer surfaces of the negative electrode collector42. The negative electrode collector42is formed with a negative electrode uncoated area42a, in which the negative electrode active material layer44is not coated, corresponding to both ends of the negative electrode plate40. A negative electrode tap46is fixed to the negative electrode uncoated area42aby means of ultrasonic welding in such a manner that an end of the negative electrode tap46can upwardly protrude beyond an upper end of the negative electrode collector42. The negative electrode tap46is generally made from Ni or a Ni-alloy. However, it is also possible to fabricate the negative electrode tap46by using other metallic materials.

The separator50is interposed between the positive electrode plate30and the negative electrode plate40so as to insulate the positive electrode plate30from the negative electrode plate40. The separator50is made from polyethylene, polypropylene, or composition of polyethylene and polypropylene. In one exemplary embodiment, the separator50has a width larger than that of the positive electrode plate30and the negative electrode plate40in order to effectively prevent a short circuit between the positive electrode plate30and the negative electrode plate40.

The cap assembly70includes a cap plate71, an insulative plate72, a terminal plate73and a negative electrode terminal74. The cap assembly70is accommodated in a separate insulative case79and is coupled with the upper opening section10aof the can10so as to seal the can10.

However, referring toFIG. 2, the positive electrode tap36of the electrode assembly20is overlapped with the positive and negative electrode active material layers34and44of the positive and negative electrode plates30and40in a widthwise direction of the electrode assembly20, so the thickness of the electrode assembly20becomes uneven widthwise along the electrode assembly20. That is, as can be understood from a graph shown inFIG. 3, thickness variation may significantly occur in the widthwise direction of the electrode assembly20. In particular, a left part of the graph shows a great increase of the thickness of the electrode assembly20relative to other parts thereof. This is because the positive electrode tap36may be in the left part together with the positive and negative electrode active material layers34and44of the positive and negative electrode plates30and40. In this case, it is difficult to uniformly wind the electrode assembly20in a compact size so that the electrode assembly20accommodated in the can10cannot possess optimum volume. Accordingly, it is difficult to increase energy density of the secondary battery.

In addition, as energy density of the lithium ion secondary battery increases, heat is increasingly generated from the can during the overcharge/over-discharge or the short circuit between electrodes. Particularly, welding sections of the negative electrode plate40and the positive electrode plate30for the negative electrode tap46and the positive electrode tap36may be bonded with hetero-metal, internal resistance is increased in the welding sections of the negative electrode plate40and the positive electrode plate30so that the welding section generates a large amount of heat. If heat is generated in the vicinity of the electrode tap, the separator for insulating the positive electrode plate from the negative electrode plate may melt and shrink. In particular, a part making contact with the positive electrode tap shown inFIG. 2generates a great amount of heat so an end portion of the separator positioned adjacent to the positive electrode plate may be significantly shrunk. In an extreme case, the separator aligned between the negative electrode plate and the positive electrode plate disappears. In this case, a short circuit could result between the positive electrode plate and the negative electrode plate.

SUMMARY OF THE INVENTION

In accordance with the present invention an electrode assembly and a lithium ion secondary battery using the same is provided capable of preventing a short circuit from being created in an outer peripheral portion of the electrode assembly by optimally aligning uncoated areas of positive and negative electrode plates and an active material layer in the inner and outer peripheral portions of the electrode assembly such that the thickness of the electrode assembly is uniformly formed widthwise along the electrode assembly.

According to one aspect of the present invention, there is provided an electrode assembly comprising: a positive electrode plate including a positive electrode collector and a positive electrode active material layer and formed at both sides thereof with a positive electrode uncoated area; a negative electrode plate including a negative electrode collector and a negative electrode active material layer and formed at both sides thereof with a negative electrode uncoated areas; a separator for insulating the positive electrode plate from the negative electrode plate; a positive electrode tap fixed to the positive electrode uncoated area; and a negative electrode tap fixed to the negative electrode uncoated area. When the positive electrode plate and the negative electrode plate are wound from an inner peripheral portion to an outer peripheral portion of the electrode assembly, an end portion of the negative electrode active material layer of the negative electrode plate formed in the outer peripheral portion of the electrode assembly is positioned in the positive electrode uncoated area of the positive electrode plate formed in the inner peripheral portion of the electrode assembly when viewed in a widthwise direction of the electrode assembly.

According to an exemplary embodiment of the present invention, an end portion of the positive electrode uncoated area of the positive electrode plate formed in the inner peripheral portion of the electrode assembly is aligned in an approximately same position as an end portion of the negative electrode active material layer of the negative electrode plate formed in the outer peripheral portion of the electrode assembly when viewed in the widthwise direction of the electrode assembly.

According to an exemplary embodiment of the present invention, an end portion of the positive electrode uncoated area formed on inner and outer surfaces of the positive electrode plate positioned in the outer peripheral portion of the electrode assembly is aligned within the negative electrode uncoated area formed on an outer surface of the negative collector positioned in the inner peripheral portion of the electrode assembly when viewed in the widthwise direction of the electrode assembly.

According to an exemplary embodiment of the present invention, an end portion of the negative electrode uncoated area formed on an outer surface of the negative electrode plate positioned in the inner peripheral portion of the electrode assembly is aligned in a approximately same position as the end portion of the positive electrode active material layer formed on an outer surface of the positive electrode plate positioned in the outer peripheral portion of the electrode assembly when viewed in the widthwise direction of the electrode assembly.

According to an exemplary embodiment of the present invention, the end portion of the negative electrode uncoated area formed on an outer surface of the negative electrode collector positioned in the inner peripheral portion of the electrode assembly is aligned in a approximately same position as the end portion of the positive electrode active material layer formed on an inner surface of the positive electrode collector positioned in the outer peripheral portion of the electrode assembly when viewed in the widthwise direction of the electrode assembly.

According to an exemplary embodiment of the present invention, an end portion of the positive electrode uncoated area of the positive electrode plate positioned in the inner peripheral portion of the electrode assembly is spaced from an end portion of the negative electrode uncoated area formed on inner and outer surfaces of the negative electrode plate by a predetermined distance in the widthwise direction of the electrode assembly within the negative electrode active material layer formed on inner and outer surfaces of the negative electrode plate positioned in the inner peripheral portion of the electrode assembly.

According to an exemplary embodiment of the present invention, the end portion of the positive electrode uncoated area of the positive electrode plate is spaced from the end portion of the negative electrode uncoated area formed on the inner and outer surfaces of the negative electrode plate by 2 to 4 mm.

According to an exemplary embodiment of the present invention, the end portion of the negative electrode active material layer of the negative electrode plate positioned in the outer peripheral portion of the electrode assembly is spaced from an end portion of the positive electrode active material layer formed on inner and outer surfaces of the positive electrode plate by a predetermined distance within the positive electrode uncoated area formed on the inner and outer surfaces of the positive electrode plate positioned in the outer peripheral portion of the electrode assembly.

According to an exemplary embodiment of the present invention, the end portion of the negative electrode active material layer of the negative electrode plate is spaced from the end portion of the positive electrode active material layer formed on the inner and outer surfaces of the positive electrode plate by 2 to 4 mm.

According to an exemplary embodiment of the present invention, the positive electrode tap is formed on the positive electrode uncoated area of the positive electrode plate positioned in the outer peripheral portion of the electrode assembly and is spaced from an end portion of the positive electrode uncoated area of the positive electrode plate positioned in the inner peripheral portion of the electrode assembly by a predetermined distance in a direction of the positive electrode active material layer of the positive electrode plate.

According to an exemplary embodiment of the present invention, the positive electrode tap is formed on an inner surface or an outer surface of the positive electrode uncoated area.

According to an exemplary embodiment of the present invention, the positive electrode tap is formed in opposition to the positive electrode uncoated area of the positive electrode plate positioned in the inner peripheral portion of the electrode assembly in the widthwise direction of the electrode assembly.

According to an exemplary embodiment of the present invention, the negative electrode uncoated area of the negative electrode plate positioned in the outer peripheral portion of the electrode assembly extends by a predetermined width from the end portion of the negative electrode active material layer of the negative electrode plate.

According to an exemplary embodiment of the present invention, an end portion of the negative electrode uncoated area is formed on a predetermined region in which the outer peripheral portion of the electrode assembly is linearly formed.

According to an exemplary embodiment of the present invention, the negative electrode uncoated area of the negative electrode plate has a width of about 2 mm to 4 mm.

According to another aspect of the present invention, there is provided a lithium ion secondary battery comprising: an electrode assembly including a negative electrode plate, a positive electrode plate, and a separator for insulating the negative electrode plate from the positive electrode plate; a can for receiving the electrode assembly; and a cap assembly including cap plate for sealing an upper opening section of the can and an electrode terminal inserted into a terminal hole formed in the cap plate while being insulated therefrom. When the positive electrode plate and the negative electrode plate are wound from an inner peripheral portion to an outer peripheral portion of the electrode assembly, an end portion of the negative electrode active material layer of the negative electrode plate formed in the outer peripheral portion of the electrode assembly is positioned in the positive electrode uncoated area of the positive electrode plate formed in the inner peripheral portion of the electrode assembly when viewed in a widthwise direction of the electrode assembly.

DETAILED DESCRIPTION

Referring toFIGS. 1 and 4, the lithium ion secondary battery according to the present invention includes a can10, an electrode assembly100(in place of electrode assembly20of the prior art) accommodated in the can10, and a cap assembly70for sealing an upper opening section of the can10. Herein, the same reference numerals are used to designate the same or similar components of the conventional secondary battery.

Referring toFIG. 1, the can10is made from a metal having a hexahedral shape and acts as a terminal. The can10includes an upper opening section10athrough which the electrode assembly100is accommodated in the can10.

The cap assembly70includes a cap plate71, an insulative plate72, a terminal plate23and a negative electrode terminal74. The negative electrode terminal74is fixedly inserted into a terminal hole formed in the cap plate71while being insulated therefrom. The cap assembly70is accommodated in a separate insulative case79and is coupled with the upper opening section10aof the can10so as to seal the can10.

Referring toFIG. 4, the electrode assembly100includes a positive electrode plate130, a negative electrode plate140, and a separator150. The positive electrode plate130and the negative electrode plate140are wound in a jelly-roll configuration while interposing the separator150therebetween.

In the following description, when the electrode assembly has been wound, a central portion of the electrode assembly is called an “inner peripheral potion” and an outer portion of the electrode assembly is called an “outer peripheral portion”. Accordingly, the inner peripheral portion is opposite to the outer peripheral portion.

The electrode assembly100is provided at the inner peripheral portion thereof with a negative electrode tap146which is welded to a negative electrode uncoated area of the negative electrode plate140and upwardly protrudes beyond the upper portion of the electrode assembly100. In addition, the electrode assembly100is provided at the outer peripheral portion thereof with a positive electrode tap136, which is welded to a positive electrode uncoated area of the positive electrode plate130and upwardly protrudes beyond the upper portion of the electrode assembly100. The position of the positive electrode tap136may be replaced with the position of the negative electrode tap146.

The positive electrode plate130includes a positive electrode collector132, a positive electrode active material layer134, and the positive electrode tap136.

The positive electrode collector132is made from laminated aluminum foil with a thickness in a range of between about 10 to 30 μm. The positive electrode collector132is formed at inner and outer surfaces thereof with the positive electrode active material layer134, which is mainly composed of lithium-based oxides. In addition, positive electrode uncoated areas133aand133b, in which the positive electrode active material layer134is not coated, are formed on inner and outer surfaces of the positive electrode collector132. However, in a predetermined outer peripheral region of the electrode assembly100, the positive electrode active material layer134is formed only one surface of the positive electrode collector132and the positive electrode uncoated area133bis formed on the other surface of the positive electrode collector132. The positive electrode active material layer134is coated on inner and outer surfaces of the positive electrode collector132with a thickness in a range of about 60 to 100 μm.

The positive electrode tab136is fixed to the positive electrode uncoated area formed on one end of the positive electrode plate130through laser welding or resistance welding. The positive electrode tab136is made from Ni and an upper end of the positive electrode tab136upwardly protrudes beyond the upper end of the positive electrode collector132. In one exemplary embodiment, the positive electrode tap136has a thickness of about 80 to 120 μm.

The negative electrode plate140includes a negative electrode collector142, a negative electrode active material layer144, a negative electrode tap146, and a negative electrode insulative plate148.

The negative electrode collector142is made from laminated aluminum foil with a thickness in a range of about 10 to 30 μm. The negative electrode collector142is formed at inner and outer surfaces thereof with the negative electrode active material layer144, which is mainly composed of carbon materials. In addition, negative electrode uncoated areas143aand143b, in which the negative electrode active material layer144is absent, are formed on inner and outer surfaces of the negative electrode collector142. However, in a predetermined inner peripheral region of the electrode assembly100, the negative electrode active material layer144is formed only one surface of the negative electrode collector142and the negative electrode uncoated area143ais formed on the other surface of the negative electrode collector142. The negative electrode active material layer144is coated on inner and outer surfaces of the negative electrode collector142with a thickness in a range of between about 80 to 100 μm.

The negative electrode tab146is made from Ni and fixed to the negative electrode uncoated area of the negative electrode plate140positioned at the inner peripheral portion of the electrode assembly100through laser welding or resistance welding. An upper end of the negative electrode tab146upwardly protrudes beyond the upper end of the negative electrode collector142. In one exemplary embodiment, the negative electrode tap146has a thickness of about 80 to 120 μm.

Referring toFIG. 4, the separator150is interposed between the positive electrode plate130and the negative electrode plate140so as to insulate the positive electrode plate130from the negative electrode plate140when they are wound in order to form the electrode assembly100.

Hereinafter, the position of the active material layers134and144in the positive electrode plate130and the negative electrode plate140, respectively, of the electrode assembly100will be described in more detail. It should be noted that the electrode assembly100is wound from the inner peripheral portion to the outer peripheral portion thereof.

Predetermined reference lines “a” and “b” are formed vertically to the widthwise direction of the electrode assembly100. Reference lines “a” and “b” are adopted to precisely explain the relationship between the uncoated areas and the active material layers which are formed in the inner peripheral portion and the outer peripheral portion of the electrode assembly100, respectively, after the electrode assembly100has been formed.

In addition, surfaces of the positive and negative electrode plates130and140facing a central portion of the electrode assembly100will be referred to as “inner surfaces” and surfaces of the positive and negative electrode plates130and140opposite to the inner surfaces will be referred to as “outer surfaces”.

First, the description will be made in relation to positions of the positive electrode uncoated area133aof the positive electrode plate130formed in the inner peripheral portion of the electrode assembly100and the end portion of the negative electrode active material layer144of the negative electrode plate140formed in the outer peripheral portion of the electrode assembly100.

The positive electrode plate130positioned in the inner peripheral portion of the electrode assembly100includes the positive electrode uncoated area133a, which is formed between the positive electrode plate130and the negative electrode plate140and provided on inner and outer surfaces of the positive electrode collector132with a predetermined width. In one exemplary embodiment, the width of the positive electrode uncoated area133aof the positive electrode plate130is at least 2 mm. If the width of the positive electrode uncoated area133ais less than 2 mm, the positive electrode active layer134may be excessively formed beyond the positive electrode collector132when forming the positive electrode active layer134on the positive electrode collector132of the positive electrode plate130, thereby causing waste of the active materials.

The end portion of the negative electrode active material layer144of the negative electrode plate140positioned in the outer peripheral portion of the electrode assembly100is formed within the positive electrode uncoated area133aof the positive electrode plate130positioned in the inner peripheral portion of the electrode assembly100when the positive electrode plate130and the negative electrode plate140have been wound from the inner peripheral portion to the outer peripheral portion of the electrode assembly100. More specifically, the end portion of the negative electrode active material layer144of the negative electrode plate140is positioned between an end portion (reference line “a”) of the positive electrode uncoated area133aof the positive electrode plate130positioned in the inner peripheral portion of the electrode assembly100and an end portion of the positive electrode plate130. In one exemplary embodiment, the end portion of the negative electrode active material layer144of the negative electrode plate140and the end portion of the positive electrode uncoated area133aof the positive electrode plate130are positioned in line with reference line “a”. In this case, thickness variation of the electrode assembly100can be minimized while maximizing areas of the positive electrode active layer134and the negative electrode active material layer144.

The positions of the end portion of the negative electrode uncoated area143aof the negative electrode plate140formed in the inner peripheral portion of the electrode assembly100and the end portion of the positive electrode active layer134of the positive electrode plate130formed in the outer peripheral portion of the electrode assembly100will now be described.

The negative electrode plate140positioned in the inner peripheral portion of the electrode assembly100extends from a predetermined inner peripheral portion of the electrode assembly100, and the negative electrode uncoated area143ais formed on inner and outer surfaces of the negative electrode collector142of the negative electrode plate140. Since the negative electrode tap146is installed on the negative electrode uncoated area143a, the negative electrode uncoated area143amust have a sufficient width for installing the negative electrode tap146thereon. The negative electrode uncoated area143aextends from the end portion of the negative electrode plate140by a predetermined distance. Referring toFIG. 4, the negative electrode uncoated area143ais formed on inner and outer surfaces of the negative electrode collector142in a region between the end portion of the negative electrode collector142and reference line “b.” At reference line “b,” the negative electrode active material layer144is formed on the outer surface of the negative electrode collector142, and the negative electrode uncoated area143ais formed on the inner surface of the negative electrode collector142. When the negative electrode plate140has been wound once, the negative electrode uncoated area143ais not provided in the inner surface of the negative electrode collector142and the negative electrode active material layer144is formed on the inner and outer surfaces of the negative electrode collector142from reference line “b.” Therefore, the end portion of the negative electrode uncoated area143aformed in the inner surface of the negative electrode plate140and the end portion of the negative electrode uncoated area143aformed in the outer surface of the negative electrode plate140may simultaneously end at reference line “b” when viewed in the widthwise direction of the electrode assembly100.

When the positive electrode plate130is positioned in the outer peripheral portion of the electrode assembly100, at the outer surface of the positive electrode collector132positioned before an outermost portion of the electrode assembly100the end portion of the positive electrode active material layer134is positioned within the negative electrode uncoated area143aformed on the outer surface of the negative electrode plate140positioned in the inner peripheral portion of the electrode assembly100when viewed in the widthwise direction of the electrode assembly100. In addition, at the inner surface of the positive electrode collector132positioned at the outermost portion of the electrode assembly100, the end portion of the positive electrode active material layer134is positioned within the negative electrode uncoated area143aformed on the outer surface or the inner surface of the negative electrode plate140positioned in the inner peripheral portion of the electrode assembly100when viewed in the widthwise direction of the electrode assembly100.

Therefore, a start portion of the positive electrode uncoated area133bformed on the inner and outer surfaces of the positive electrode plate130positioned in the outer peripheral portion of the electrode assembly100, that is, the end portion of the positive electrode active material layer134of the positive electrode plate130is formed within the negative electrode uncoated area143aformed on the outer surface of the negative electrode plate140positioned in the inner peripheral portion of the electrode assembly100. In one exemplary embodiment, the end portion of the positive electrode active material layer134formed on the outer surface of the positive electrode connector132positioned in the outer peripheral portion of the electrode assembly100and the end portion of the positive electrode active material layer134formed on the inner surface of the positive electrode connector132are provided in the same position as the end portion of the negative electrode uncoated area143aformed on the outer surface of the negative electrode plate140positioned in the inner peripheral portion of the electrode assembly100when viewed in the widthwise direction of the electrode assembly100. In other words, the end portion of the positive electrode active material layer134formed on the outer surface of the positive electrode connector132, the end portion of the positive electrode active material layer134formed on the inner surface of the positive electrode connector132, and the end portion of the negative electrode uncoated area143aformed on the outer surface of the negative electrode plate140positioned in the inner peripheral portion of the electrode assembly100are positioned in reference line “b.” In this case, thickness variation of the electrode assembly100can be minimized while maximizing areas of the positive electrode active layer134and the negative electrode active material layer144.

In addition, reference line “b” is spaced from reference line “a” by a predetermined distance. Thus, the end portion of the positive electrode uncoated area133aof the positive electrode plate130positioned in the inner peripheral portion of the electrode assembly100is spaced from the end portion of the negative electrode uncoated area formed on the inner and outer surfaces of the negative electrode collector142positioned in the inner peripheral portion of the electrode assembly100. In one exemplary embodiment, the end portion of the positive electrode uncoated area133ais spaced from the end portion of the negative electrode uncoated area143aby a predetermined distance of about 2 to 4 mm. If the distance between the end portion of the positive electrode uncoated area133aand the end portion of the negative electrode uncoated area143ais less than 2 mm, the positive electrode active material layer134may make direct contact with the negative electrode uncoated area143aof the negative electrode plate140when the positive electrode plate130and the negative electrode plate140are wound together. In addition, if the distance between the end portion of the positive electrode uncoated area133aand the end portion of the negative electrode uncoated area143ais larger than 4 mm, the size of the positive electrode active material layer134is reduced, thereby lowering capacity of the secondary battery.

In addition, the end portion of the negative electrode active material layer144positioned in the outer peripheral portion of the electrode assembly100is positioned within the positive electrode uncoated area133bformed on the inner and outer surfaces of the positive electrode plate130positioned in the outer peripheral portion of the electrode assembly while being spaced from the end portion of the positive electrode active material layer134formed on the inner and outer surfaces of the positive electrode plate130by a predetermined distance. In one exemplary embodiment, the end portion of the negative electrode active material layer144of the negative electrode plate140is spaced from the end portion of the positive electrode active material layer134of the positive electrode plate130by a predetermined distance of about 2 to 4 mm. If the distance between the end portion of the negative electrode active material layer144and the end portion of the positive electrode active material layer134is less than 2 mm, the positive electrode active material layer134may make direct contact with the negative electrode uncoated area143aof the negative electrode plate140when the positive electrode plate130and the negative electrode plate140are wound together. In addition, if the distance between the end portion of the negative electrode active material layer144and the end portion of the positive electrode active material layer134is larger than 4 mm, the size of the positive electrode active material layer134is reduced, thereby lowering capacity of the secondary battery.

The positive electrode uncoated area133bof the positive electrode plate130may be formed by further winding the positive electrode plate130halfway around the electrode assembly100.

The positive electrode tap136is installed on the positive electrode uncoated area133bof the positive electrode plate130positioned in the outer peripheral portion of the electrode assembly100while being spaced from the end portion of the positive electrode uncoated area133aof the positive electrode plate130positioned in the inner peripheral portion of the electrode assembly100by a predetermined distance in the direction of the positive electrode active material layer134of the positive electrode plate130. At this time, the positive electrode cap136may be formed on the inner surface of the outer surface of the positive electrode uncoated area133b. In one exemplary embodiment, the positive electrode cap136is aligned in opposition to the positive electrode uncoated area133aof the positive electrode plate130positioned in the inner peripheral portion of the electrode assembly100when viewed in the widthwise direction of the electrode assembly100. The positive electrode uncoated area133bof the positive electrode plate130may discharge heat generated from the inner portion of the electrode assembly100to an exterior so the positive electrode uncoated area133bhas a predetermined length sufficient for discharging heat to the exterior.

The negative electrode cap146may be formed on the inner surface of the outer surface of the negative electrode uncoated area143bformed on the outer surface of the negative electrode plate140positioned in the inner peripheral portion of the electrode assembly100.

According to the electrode assembly100having the above structure, start portions of the uncoated areas of the positive and negative electrode plates130and140are identical to the end portion of the active material layers134and144of the positive and negative electrode plates130and140, so the thickness of the electrode assembly100may be uniformly formed.

AlthoughFIG. 4shows reference lines “a” and “b” aligned in the center portion of the electrode assembly100, reference lines “a” and “b” may be shifted from the center portion of the electrode assembly100by a predetermined distance. At this time, the positions of the uncoated areas of the positive and negative electrode plates130,140relative to the positions of the active material layers134,144of the positive and negative electrode plates130,140, respectively, are not changed.

FIG. 5shows an electrode assembly according to another exemplary embodiment of the present invention. Hereinafter, the electrode assembly shown inFIG. 5will be described on the basis of differences thereof with regard to the electrode assembly shown inFIG. 4.

Referring toFIG. 5, the electrode assembly100′ includes a negative electrode plate140′ positioned in the outer peripheral portion of the electrode assembly100′ and formed with a negative electrode uncoated area143b′ having a relatively short width. In one exemplary embodiment, the width of the negative electrode uncoated area143b′ of the negative electrode plate140′ is about 2 to 4 mm from an end portion of the negative electrode active material layer144′ of the negative electrode plate140′. If the width of the negative electrode uncoated area143b′ of the negative electrode plate140′ is less than 2 mm, the negative electrode active material layer144′ may be excessively formed beyond a negative electrode collector142′ when forming the negative electrode active material layer144′ on the negative electrode collector142′. In addition, if the width of the negative electrode uncoated area143b′ of the negative electrode plate140′ is larger than 4 mm, the length of the negative electrode uncoated area143b′ is unnecessarily lengthened.

A separator150′ may extend to the end portion of a positive electrode plate130′ from the inner peripheral portion of the electrode assembly100′.

Therefore, an increase of the thickness of the electrode assembly100′ caused by the positive electrode tap136′ can be minimized. In addition, even if the separator150′ shrinks due to heat generated from the secondary battery, the negative electrode uncoated area143b′ of the negative electrode plate140′ may not be exposed.

Hereinafter, an operation of the electrode assembly according to exemplary embodiments of the present invention will be described.

Referring toFIG. 6, unlike the conventional electrode assembly (see,FIG. 3), the thickness of the exemplary electrode assembly100of the present invention may not vary significantly. That is, the thickness of the electrode assembly100may be evenly formed in the widthwise direction of the electrode assembly100without creating significant thickness variation.

In addition, since the thickness of the lithium ion secondary battery employing the electrode assembly100may be evenly formed in the widthwise direction thereof, an outer appearance of the lithium ion secondary battery, particularly, the thickness of the lithium ion secondary battery may be easily managed.

Although embodiments of the present invention has been described in relation to the can type electrode assembly having a jelly roll type electrode assembly, the embodiments described are applicable not only for a square type secondary battery, but also for a pouch type secondary battery using a jelly roll type electrode assembly.

According to exemplary embodiments of the present invention, the thickness of the electrode assembly may be uniformly formed in the widthwise direction thereof by optimally aligning the uncoated areas and active material layers in the inner and outer peripheral portions of the electrode assembly used for the secondary battery.

In addition, according to exemplary embodiments of the present invention, the length of the negative electrode uncoated area of the negative electrode plate formed in the outer peripheral portion of the electrode assembly may be minimized so that a short circuit can be prevented between the negative electrode plate and the positive electrode plate even if the separator has shrunk due to heat generated in the vicinity of the positive electrode tap, thereby improving stability of the secondary battery.