KR20080006103A - Pouch type rechargeable battery - Google Patents

Abstract

A pouch type rechargeable battery is provided to inhibit leakage of liquid or inflow of external air by forming even sealing in a portion in which an electrode tap is drawn out, and to prevent the risk of a short circuit caused by electrode taps. A pouch type rechargeable battery includes: an electrode assembly comprising two kinds of electrode plates having each electrode tap(30,40) and a separator interposed between the electrode plates; and a pouch type case which has a sealing part(15) in at least a partial peripheral region, and covers the electrode assembly to seal the electrode assembly from the outside while the electrode taps are drawn out through the sealing part. A tape(20) wider than the electrode tap is placed between the electrode tap and the pouch type case in the sealing part region in which the electrode tap and the pouch type case overlap with each other. A stepped portion(151) narrower than the tape and wider than the electrode tap is formed in the overlapping sealing region.

Description

Pouch type rechargeable battery {Pouch type rechargeable battery}

1A and 1B are cross-sectional views before and after sealing of a sealing part of a pouch-type secondary battery in which electrode tabs are drawn out in an embodiment according to the present invention.

FIG. 2 is a plan view of the pouch type secondary battery after the sealing is performed as shown in FIG.

* Explanation of symbols for the main parts of the drawings

10: pouch membrane 20: tape

30, 40: electrode tab 101, 102: mold

17: space region 15: sealing portion

151: stepped portion

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pouch type secondary battery, and more particularly, to a configuration of an electrode tab lead-out portion of a pouch type secondary battery used in a small electronic device.

Many electronic devices used while moving are developed and accordingly, the use of batteries as a power source for these devices increases. Secondary batteries, unlike disposable batteries, can be charged and discharged, and thus can be reused, which has advantages in terms of economy. Lead batteries, nickel-acid batteries, nickel-metal hydride batteries and the like are used as secondary batteries. In recent years, the use of lithium secondary batteries as a power source for notebook computers and mobile phones has increased significantly.

Lithium secondary batteries use nonaqueous electrolytes because of their reactivity with lithium. This electrolyte may be a solid polymer containing lithium salts, or may be a liquid phase in which lithium salts dissociate in an organic solvent. When the lithium secondary battery is classified according to the type of electrolyte, the lithium secondary battery may be classified into a lithium metal battery using a liquid electrolyte, a lithium ion battery, and a lithium ion polymer battery using a polymer solid electrolyte.

In the case of a fully solid lithium ion polymer battery, there is no leakage problem of the organic electrolyte, and in the case of a gel type lithium ion polymer battery containing the organic electrolyte, the leakage problem of the electrolyte is simple compared with the lithium ion battery using the liquid electrolyte. Can be prevented. For example, a lithium ion polymer battery may use a multilayer film pouch consisting of a metal foil and one or more polymer films covering the foil in place of a metal can of a lithium ion battery.

When using a multilayer film pouch, the weight of the battery can be significantly reduced than when using a metal can. Aluminum is usually used as a metal forming a foil in a multilayer film pouch. The polymer film forming the inner layer of the pouch film protects the metal foil from the electrolyte and prevents short circuit between the positive electrode, the negative electrode, and the electrode tabs.

In order to form a pouch-type lithium secondary battery, first, an electrode assembly formed by stacking or winding a cathode, a separator, and an anode is placed in a pouch in a sealed state. The bare cell battery is formed by heat-sealing the upper and lower pouch films at the open edges of the pouches.

A core pack is formed by attaching an accessory or structure, such as a protective circuit module (PCM) or a positive temperature coefficient (PTC), to a bare cell formed by pouch sealing.

The pack battery may be formed by combining the core pack battery into a hard case or by using a separate exterior plate and resin molding.

However, as small devices such as MP3 are newly introduced among mobile electronic devices, batteries used in such small devices should be smaller due to the size limitations of the devices. However, if the existing battery is simply reduced, there is a problem such that the risk of short circuit between the electrode tabs drawn out of the case increases, and thus, a new process method and battery structure development for a small battery is required.

On the other hand, when looking at the configuration of the tab lead-out portion in the conventional pouch battery, one side of the pouch forming a substantially rectangular shape when folded in front of the wide side is folded, the other three sides are sealed by a method such as heat fusion. The electrode tabs are pulled out side by side with one sealed side. The pouch is formed by laminating a polymer on both sides of a metal foil such as aluminum. At this time, the stretched polypropylene (CPP: Casted Polyprophylen) suitable for thermal fusion is laminated on the inner surface that is fused while facing each other.

When the CPP layer is melted and pushed away from the sealing portion from which the electrode tabs are drawn out, a short circuit occurs when the metal foil forming the pouch substrate and the two electrode tabs are connected to each other. Even when only one electrode is connected to the metal foil, or the metal foil exposed at the end is directly connected to the outer conductor, galvanic corrosion occurs, and the pouch cannot act as a shield of moisture or outside air.

In addition, due to heterogeneity between the CPP layer and the electrode tab, sealing may not be performed well, and leakage may occur at a portion where they meet each other, and even in the case of a polymer battery, external moisture or air may be introduced to cause a battery defect.

To avoid these problems, a strip tape is attached to the overlapping portion of the electrode tab with the pouch. However, the portion where the electrode tab or the strip tape overlaps on the sealing surface of the pouch has a step with other portions. And, due to this step, the sealing may not be even.

The present invention is a sealing of the electrode tab lead-out portion in order to solve the problem that the sealing is not even due to the thickness difference in the portion where the electrode tab is drawn out in the above-described conventional pouch type secondary battery, leakage, moisture inflow, etc. It is an object of the present invention to provide a pouch type secondary battery having a configuration that enables to evenly.

An object of the present invention is to provide a pouch type secondary battery having a configuration capable of preventing the risk of short circuit caused by electrode tabs that are simultaneously drawn out.

In order to achieve the above object, the present invention provides an electrode assembly comprising two kinds of electrode plates having respective electrode tabs and a separator interposed between the electrode plates, and a sealing portion is formed in at least a portion of the peripheral region, and the electrode tabs are formed. In the pouch-type secondary battery having a pouch-type case surrounding the electrode assembly and sealed from the outside while being drawn out to the outside through the sealing portion

A tape having a width wider than that of the electrode tab is disposed between the electrode tab and the pouch-type case in the sealing portion region where the electrode tab and the pouch-type case overlap, and the sealing portion region is smaller than the width of the tape and the electrode tab. It is characterized in that it is formed to have a wider stepped portion.

In the present invention, the stepped portion, when the distance between the two electrode tabs of the polarity of the pouch-type secondary battery is L1, the ratio L1 / L2 between the two values in the range of 0.2 to 1.5 when the stepped portion width is L2, more preferably Is preferably in the range of 0.5 to 1.5.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings.

1A and 1B are cross-sectional views before and after sealing of a sealing part of a pouch-type secondary battery in which electrode tabs are drawn out in an embodiment according to the present invention.

FIG. 1A shows the positional relationship between the pouch film 10, the electrode tab 30, and the strip tape 20 forming the pouch type secondary battery case before sealing of the sealing portion. At this time, it can be seen that the jig of the sealing apparatus for forming the stepped sealing area or the molds 101 and 102 itself are formed to be stepped with other parts. The boundary of the stepped sealing region is located between the edge of the electrode tab 30 and the edge of the tape 20. In this case, when the sealing is made, a part of the strip tape 20 is placed on the stepped portion 103 of the mold 102 so that the pressure is low even when melting occurs, so that the thickness becomes thick. In the strip tape 20, the outer side may be pressed by the unstepped portion of the mold 102 to join a thick portion while being driven toward the stepped portion 103 by the pressure while being melted. Therefore, after sealing, the molten strip tape 20 ′ is maintained in close contact with the electrode tab 30 by a uniform pressure as a whole.

If the boundary of the stepped sealing area is formed on the electrode tab, when sealing is made, it is impossible to achieve the purpose of stable sealing by dividing the thick area and the thin area of the sealing part. May be exposed.

On the contrary, when the boundary is located outside the edge of the strip tape 20, even when the boundary is a thin area from the boundary to the strip tape edge, a space is formed between the mold surfaces when sealing, and pressure may not be sufficiently transmitted, and leakage may occur after the sealing.

FIG. 2 is a plan view of the pouch type secondary battery after the sealing is performed as shown in FIG.

Referring to FIG. 2, the pouch membrane is divided into two largely facing portions, folded at the middle boundary, and formed by sealing at three sides except the folded boundary. In the lower portion of the two facing portions, a groove-shaped space region 17 in which the electrode assembly is to be accommodated is formed in a region other than the periphery by pressing or the like. The upper part is a cover which covers the space of the groove shape of the lower part. The upper side and the lower side make the sealing part 15 through the three-side sealing to seal the space of the groove shape from the outside.

The electrode assembly is accommodated in the space formed by the pouch. The electrode assembly is formed by stacking and winding a positive electrode plate, a separator, and a negative electrode plate to form a jelly roll. Withdrawn side by side.

Each electrode tab 30, 40 is covered with a strip tape 20 in the sealing portion 15, the strip tape 20 protruding a little upward from the boundary of the pouch. In the entire sealing portion 15, a stepped portion 151 smaller than the width of the strip tape 20 and wider than the electrode tabs 30 and 40 is formed. The step 151 boundary is inside the boundary formed by the strip tape 20 and outside the boundary formed by the electrode tabs 30 and 40.

An interval or a separation distance between the electrode tabs 30 and 40 of two polarities of the pouch type secondary battery is indicated by L1, and the width of the stepped portion 151 is represented by L2.

In the embodiment of the present invention, L1 and L2 are defined such that L1 / L2 is greater than or equal to 0.2 and less than or equal to 1.5. This value may not be a problem in a battery having a wider electrode assembly than the electrode tab. However, the width of the electrode assembly or the length of the side where the electrode tab is drawn out of the pouch is 30 mm or less, particularly in a small battery of 20 mm or less, usually the width of the electrode assembly or pouch is less than four times the width of the tape which is integral with the electrode tab. L1 / L2 value is important.

In the battery, electrode tabs are often used with a nickel plate having a thickness of about 100 micrometers, and even in a small battery, the width thereof is limited to 2 mm or more or 3 mm or more, so it is difficult to become smaller. This is because when the thickness of the electrode tab is smaller than that, sufficient current cannot flow, or an internal resistance increases or workability is poor. Thus, the strip tape also has a width of at least 3 mm, usually 5-6 mm for workability.

As the above-described limiting conditions increase, in the small battery, the electrode tabs may not be sufficiently spaced apart due to the limitation of their width. If the separation distance L1 of the electrode tab is narrowed, the possibility of a short circuit between the electrode tabs increases in a battery forming process or the like, and the defective rate rapidly increases. In a small cell, when the width of the step portion is L2, the width of the electrode tab increases, L2 increases, and the separation distance L1 between the electrode tabs generally decreases, so that the L1 / L2 value decreases more rapidly. In addition, when the value of L1 / L2 is less than 0.2, it is impossible to produce a practical process, and it is found that the value of L1 / L2 should be at least 0.5 or more in order to perform a stable process from short-circuit between electrodes in consideration of other process deviations. .

On the other hand, increasing the L1 value by separating the two electrode tabs away from each other to avoid a short circuit between the electrodes in a small cell results in a relatively low value of L2 and more precisely, a smaller width of the electrode tab. The reduction of the width of the electrode tab requires deterioration of workability, such as welding, accuracy of a process or a part, and an increase in internal resistance, resulting in a reduction in battery capacity.

In addition, this problem was found to cause serious defects when the L1 / L2 value exceeds 1.5. In other words, it is not necessary to directly reduce the width of the electrode tab or the tape by widening the gap between the electrode tabs at smaller values, but at larger values, the size of the electrode tabs decreases as the separation distance between the two electrode tabs increases. As listed below, the problems listed will become important.

In addition, when the L1 / L2 value is more than 1.5 it increases very rapidly, it can be seen that these problems are exposed synergistically. On the other hand, even if the L1 / L2 value exceeds 1.5, it may be considered to reduce the size of the stepped portion without reducing the size of the tab in order to prevent this problem from seriously occurring. Therefore, it can be seen that external moisture or air enters the pouch and causes a problem.

According to the present invention, the sealing is even in spite of the difference in thickness at the portion where the electrode tab is drawn out in the pouch type secondary battery, thereby preventing leakage or inflow of air.

The present invention can prevent the risk of a short circuit caused by the electrode tab which is simultaneously drawn out, and at the same time can prevent problems such as an increase in internal resistance or a decrease in process workability.

Claims (6)

An electrode assembly comprising two kinds of electrode plates having respective electrode tabs and a separator interposed between the electrode plates, and a sealing portion is formed in at least a portion of the peripheral region, and the electrode tab is drawn out through the sealing portion. In the pouch type secondary battery having a pouch type case surrounding the electrode assembly and sealed from the outside A tape having a wider width than that of the electrode tab is provided between the electrode tab and the pouch-type case in an area of the sealing portion where the electrode tab and the pouch-type case overlap. A pouch type secondary battery, wherein a stepped portion having a width smaller than the width of the tape and wider than the electrode tab is formed in an area of the overlapping sealing portion. The method of claim 1, When the separation distance between the two electrode tabs of the two polarity is called L1, and the width of the stepped portion L2, the ratio between the two values L1 / L2 is formed to be greater than or equal to 0.2 and less than or equal to 1.5 in the range Pouch type secondary battery to be made. The method of claim 2, The pouch type secondary battery of claim 1, wherein L1 / L2 is formed to be greater than or equal to 0.5 and less than or equal to 1.5. The method according to any one of claims 1 to 3, Pouch-type secondary battery, characterized in that the width of the electrode assembly is formed to 30mm or less. The method of claim 4, wherein Pouch type secondary battery, characterized in that the width of the electrode assembly is formed to less than 20mm. The method of claim 4, wherein The width of the electrode assembly is a pouch type secondary battery, characterized in that less than four times the width of the tape.

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