KR100551886B1 - Pouch type Lithium secondary battery - Google Patents

Abstract

A pouch-type lithium secondary battery is disclosed.

The present invention provides a pouch type lithium secondary battery comprising an electrode assembly including a positive electrode, a separator, and a negative electrode, a pouch for sealing an electrode assembly, and a hard case containing a pouch, wherein the metal of the pouch is in a state where the hard case is coupled. A pouch terminal electrically connected to the foil is formed to be electrically connected to the outside of the hard case.

In bare cell conditions as well as in hard case battery products, the short circuit between positive / negative and pouch metal foils can be easily identified.

Description

Pouch type lithium secondary battery {Pouch type Lithium secondary battery}

1 is a perspective view showing a state before a pouch is sealed in an example of a pouch-type lithium secondary battery.

2 is a perspective view illustrating a battery in a bare cell state in which pouch sealing is performed according to an embodiment of the present invention.

3 is a partially exploded perspective view illustrating a form in which terminals are formed in a battery in a bare cell state according to another exemplary embodiment of the present invention.

Figure 4 shows the surface exposed the electrode in the hard pack state of the pouch-type lithium secondary battery formed in accordance with an embodiment of the present invention.

* Explanation of symbols for the main parts of the drawings

10: upper pouch 11: inner polymer film

12: metal foil 20: lower pouch

21: groove 23: edge portion

30: electrode assembly

31: anode 33: separator

35: negative electrode 37: positive electrode tab

38: negative electrode tab 39: tape

41: internal terminal 43: electrode

51: hard case 57: positive terminal

58: negative electrode terminal 59: pouch terminal

The present invention relates to a lithium secondary battery using lithium ions, and more particularly, to a pouch type lithium secondary battery having a form in which an electrode assembly including a positive electrode, a negative electrode, and a separator is accommodated in a pouch.

As wireless and portable devices such as video cameras, portable telephones, notebook computers, portable personal digital assistants (PDAs), and electric bicycles, electric vehicles, and electric tools are becoming lighter and more functional, batteries are used as driving power for these products. Increasing the importance of, and a lot of research on the battery has been done.

In particular, lithium secondary batteries capable of charging and discharging have a higher energy density per unit weight and rapid charge than conventional lead storage batteries, nickel-cadmium batteries, nickel-hydrogen batteries, and nickel-zinc batteries due to the light atomic characteristics of lithium. Since this is possible, research and development on this is being actively conducted.

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.

A lithium ion polymer battery is a lithium ion polymer battery using a fully solid lithium ion polymer battery containing no organic electrolyte at all according to the type of polymer solid electrolyte and a gel polymer electrolyte containing an organic electrolyte solution. Can be divided.

In the case of the lithium ion polymer battery, the leakage problem of the electrolyte may be prevented in a simpler form in the case of the lithium ion polymer battery as compared with the lithium ion battery using the liquid electrolyte. 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.

The use of a multilayer film pouch has the advantage of significantly reducing the weight of the battery than 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 surface 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.

1 is a perspective view showing a state before a pouch is sealed in an example of a pouch-type lithium secondary battery.

An example of a method of forming a conventional pouch will be described with reference to FIG. 1. First, the upper part 10 and the lower part 20 of the pouch are formed by folding the middle in the longitudinal direction of one side of the rectangular pouch film which is usually formed integrally. The lower part 20 is provided with a groove 21 in which the electrode assembly 30 can be accommodated by pressing. The conventional electrode assembly 30 is formed in a jelly roll form by winding a multilayer film on which the anode 31, the separator 33, and the cathode 35 are stacked in a spiral shape. When winding up the jelly roll, a separator is added to the positive or negative side to prevent short circuit between the positive and negative electrodes.

The formed jelly roll is placed in the lower groove 21 of the pouch film. The pouch is sealed by heating and pressing the closely contacted portion while the edge portion 23 around the lower groove 21 and the edge portion of the upper portion of the pouch film corresponding thereto are in close contact with each other.

Meanwhile, electrode tabs 37 and 39 or electrode leads are formed at one side of the anode 31 and the cathode 35 to electrically connect the anode 31 and the cathode 35 of the electrode assembly 30 to the outside of the pouch. do. In the electrode assembly in a wound jelly roll state, the positive electrode tab 37 and the negative electrode tab 38 are arranged side by side at regular intervals. These electrode tabs 37 and 38 are formed to protrude from the jelly roll in a direction perpendicular to the direction in which the jelly roll is wound, and pass through the pouch through one sealed side of the pouch film.

The electrode tabs generally take the form of tabs of metal, usually aluminum, copper or nickel. They must have sufficient thickness and dimensions to be the passage of current without significant voltage drop. In the pouch sealing process, a specific tape is contained on the surface of the polymer film to strengthen the bond between the polymer film 11 on the inner surface of the pouch and the metal forming the electrode tabs 37 and 38, or a separate tape having these components before sealing. 39 may be attached to the portion where the electrode tabs 37 and 38 adhere to the pouch.

Nevertheless, an increase in the thickness of the electrode tabs causes a problem in sealing the pouch in the area where the electrode tab passes through the pouch. For example, metal tabs quickly remove heat during heat sealing, making it difficult to control the sealing temperature. In addition, electrode tabs formed of metal result in uneven pressure due to their thickness, which also leads to a decrease in sealing reliability.

As a result, when the upper edge portion and the lower edge portion of the pouch are contacted and fused, the polymer film 11 on the inner surface of the pouch is damaged due to an excessively high temperature and pressure or a long time for fusion. Short circuits between (37,38) and the metal foil 13 of the pouch may occur. In addition, the sealing of the pouch is incomplete, the electrolyte may leak when there is an electrolyte.

If a short circuit occurs between the electrode tabs 37 and 38 and the metal foil 13 of the pouch in both the positive and negative electrodes, there is a high possibility that discharge occurs between the tabs through the metal foil 13, resulting in overheating and swelling. Resulting in lower product yield.

In addition, in the event of a short circuit between the anode tab (copper) and the aluminum forming the metal foil of the pouch, the aluminum foil acting as a barrier continues to corrode and remove, especially in the presence of electrolytes. The diffusion of water and oxygen molecules through the metal is extremely low, but the diffusion of water and oxygen molecules through the polymer membrane can affect the function of the cell. Therefore, the battery's ability to cut off the pouch causes evaporation of the organic electrolyte of the separator or inflow of external moisture or oxygen, resulting in a swelling phenomenon that increases the pressure due to gas generation. do.

By the way, as a case where minute short circuit occurs between copper forming the negative electrode tab of the electrode assembly and the aluminum foil of the pouch, the corrosion of the aluminum foil is often slow but continuous. In this case, in a bare cell where the pouch is completely exposed to the outside, it is possible to measure the potential (OCV) or the internal resistance (IR) between the aluminum foil and the cathode or anode exposed through the cut surface of the pouch. Short circuits can be detected and defective products excluded.

However, a short circuit between the negative electrode tab and the metal foil of the pouch may lead to a protective circuit structure such as a protective circuit board (PCM) or positive temperature coefficient (PTC) in a bare cell where the pouch is once formed. It can also occur when attached to form a core pack. Alternatively, when forming a hard pack in which a core pack is bonded to a hard case, a short circuit may occur between the negative electrode tab and the metal foil of the pouch due to the conducting wire or the accessory circuit portion inside the hard case.

In these cases, the cut surfaces of the pouches in the hard pack state are all covered by a structure such as a hard case when viewed from the outside. Therefore, in the finished battery having a hard case, since only the positive electrode terminal and the negative electrode terminal are exposed, there is no suitable method for detecting a short circuit between the negative electrode tab and the pouch aluminum foil by measuring the potential or the internal resistance.

Eventually, the corrosion of the aluminum inside the battery case in the hard case forms a malfunction, and the short-circuit problem between the negative electrode tab and the aluminum foil may be surfaced at the customer's use stage, which may increase the loss and significantly impair the product reliability. A problem arises.

The present invention is to eliminate the above-mentioned conventional problems, pouch-type lithium that can detect corrosion due to short circuit between the electrode tab of the lithium secondary battery and the metal foil of the pouch even before shipping the product in the hard case state of the finished product It is an object to provide a secondary battery.

It is an object of the present invention to provide a pouch-type lithium secondary battery having a pouch capable of detecting a short circuit between the metal foil of the pouch and the electrode tab immediately after the pouch seal is made.

The present invention for achieving the above object,

A pouch type lithium secondary battery comprising an electrode assembly including a positive electrode, a separator, and a negative electrode, a pouch for sealing the electrode assembly, and a hard case containing the pouch,

The pouch terminal electrically connected to the metal foil of the pouch in a state in which the hard case is coupled is formed to be electrically connected to the outside of the hard case.

In the present invention, a portion of the outer pouch polymer film may be removed from the pouch for the electrical connection with the pouch terminal so that the exposed portion of the metal foil serves as the inner terminal. At this time, it is preferable that the inner terminal is formed at the outer edge of the edge portion fused for sealing the pouch with a portion between the positive and negative electrode tabs.

In the present invention, the inner terminal formed to be connected to the pouch terminal may be formed in a hook or pin shape. In this case, the hook or pin may be formed to be in electrical connection with the pouch metal foil while passing through the fused edge at a portion of the fused edge in the sealed pouch or in electrical connection with the pouch metal foil exposed at the end of the pouch.

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

2 is a perspective view illustrating a battery in a bare cell state in which pouch sealing is performed according to an embodiment of the present invention.

Referring to FIG. 2, the inside of the pouch exposing a part of the pouch metal foil at the edge located at the side where the negative electrode tab 37 and the positive electrode tab 38 are drawn out of the edge 23 fused in the bare cell 1. The terminal 41 is formed. The inner terminal 41 may be formed by exposing a metal foil by partially removing the outer polymer layer among the multilayers when forming the pouch layer. Alternatively, the pouch may be formed by removing a portion of the outer polymer layer after the pouch is formed. However, since the metal foil is thin in this area, it may not be suitable to weld the structure to be connected to the pouch terminal of the hard case.

3 is a partially exploded perspective view illustrating a form in which terminals are formed in a battery in a bare cell state according to another exemplary embodiment of the present invention.

Referring to FIG. 3, an edge portion located at a position where a pouch inner terminal of FIG. 2 is formed, that is, a side at which the negative electrode tab 37 and the positive electrode tab 38 are drawn out of the edges fused in the bare cell 1 ( 23, a tip-shaped electrode 43 is formed. The electrode 43 is coupled to the female part 431 and the male part 432 through the pouch at the fusion edge 23 of the pouch. As the male accessory 432 penetrates the pouch, the metal foil of the pouch is electrically connected to the electrode 43 naturally. It is preferable to use an electrode such as a material of metal foil (usually aluminum) because it prevents electrochemical action.

On the other hand, if the tip button electrode 43 is too thick, the pouch sealing surface may be damaged by damaging the pouch sealing surface, so that the hole is formed thin, and the head of the electrode is formed thin so as not to make unnecessary space. In addition, the portion of the pouch is preferably formed at the edge of the center of the sealed edge 23 of the pouch.

In the present invention, as a means for connecting the metal foil of the pouch and the pouch terminal exposed to the hard case, first, a method such as connecting the positive and negative tabs in the bare cell state to the positive and negative terminals of the hard case is used. You can think of it. For example, a third connection plate is formed on the protection circuit structure together with the positive connection plate and the negative connection plate. And when forming a core pack in a bare cell state, the inner terminal by which a part of outer pouch outer polymer film was removed is connected to the 3rd connection plate. The third connection plate is connected to the pouch terminal when the electrode connection plates are connected to the external electrode terminals in the hard case mounting step.

Figure 4 shows the surface exposed the electrode in the hard pack state of the pouch-type lithium secondary battery formed in accordance with an embodiment of the present invention.

Referring to FIG. 4, two positive terminals 57 are disposed on the lower left side of the back of the hard case 51, two negative terminals 58 are disposed on the lower right side, one between the positive terminal 57 and the negative terminal 58. The pouch terminal 59 is formed.

In the finished battery having a hard case, not only the positive terminal and the negative terminal but also the pouch terminal 59 connected to the metal foil of the pouch are exposed so that the potential (OCV) or internal resistance (IR) between the negative terminal and the pouch terminal is measured. In this way, a short circuit between the negative electrode tab and the pouch aluminum foil can be easily and immediately detected.

According to the present invention, the short circuit between the electrode and the pouch metal foil can be easily confirmed not only in the bare cell state but also in the battery case in the hard case form.

Therefore, even if there is a fine short circuit in the prior art, if it is not detected in the bare cell state, it cannot be detected in the hard pack state, and the metal foil corrosion of the pouch proceeds inside the battery, thereby preventing most of the problems that surface defects and increase losses in the battery use stage. can do.

Claims (4)

An electrode assembly including an anode, a separator, and a cathode, A pouch for sealing the electrode assembly, In the pouch type lithium secondary battery comprising a hard case containing the pouch, A pouch type lithium secondary battery, wherein a pouch terminal electrically connected to a metal foil of the pouch in a state in which the hard case is coupled is formed to be connected to the outside of the hard case together with a positive electrode terminal and a negative electrode terminal. The method of claim 1, A pouch type lithium secondary battery having an inner terminal formed by removing an outer polymer film on the surface of the pouch for electrical connection with the pouch terminal. The method of claim 1, The inner terminal on the pouch formed to be connected to the pouch terminal is a pouch type lithium secondary battery, characterized in that formed in the form of a tick button penetrating through the pouch film. The method of claim 1, A pouch type lithium secondary battery, characterized in that a connecting plate is provided in the protective circuit structure as a means for connecting the metal foil of the pouch and the pouch terminal therein.

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