KR100551397B1 - Pouch type lithium secondary battery - Google Patents

Abstract

A pouch-type lithium secondary battery is disclosed.

In the lithium secondary battery according to the present invention, a positive electrode plate, a separator, and a negative electrode plate are stacked, and a positive electrode plate and a negative electrode plate are provided with an electrode assembly having electrode tabs formed thereon, and a pouch wrapped around the electrode assembly and penetrated by the electrode tab. At least one side of is characterized in that it is covered with a continuous tape in the portion overlapping the sealing portion of the pouch and in the portion overlapping the positive or negative plates.

Thus, the process time and cost of the protective and sealing taping operations can be halved, and the tape is not stuck in place according to the process variation, thereby fundamentally preventing defects from occurring in the unprotected portion.

Description

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 plan view showing a state in which an electrode tab is attached to an electrode plate 310 such as a positive electrode plate or a negative electrode plate as an example of the prior art;

3 is a plan view showing a state in which a tape is attached to the electrode tab according to an embodiment of the present invention;

4 is a cross-sectional view illustrating a cross section taken along line AA of FIG. 3.

5 is a cross-sectional view showing a state in which the electrode tab and the front and rear tapes are attached to the electrode plate in another embodiment of the present invention.

* Explanation of symbols for the main parts of the drawings

10: upper pouch 11: polymer film

13: metal foil 20: lower pouch

21: groove 23: edge portion

30 electrode assembly 31 anode

33: separator 35: negative electrode

37: negative electrode tab 38: positive electrode tab

39,319,423: sealing tape 310: electrode plate

317: electrode tab 321: protective tape

420,421 tape

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 structure including a positive electrode, a negative electrode, and a separator is accommodated in a pouch.

Lithium secondary batteries that can be charged and discharged have higher energy density per unit weight and can be charged faster than conventional lead-acid batteries, nickel-cadmium batteries, nickel-hydrogen batteries, and nickel-zinc batteries due to the light atomic characteristics of lithium. Because of this, research and development on this is actively progressing.

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. Lithium ion polymer battery is a lithium ion polymer battery that uses a fully solid lithium ion polymer battery that does not contain any organic electrolyte depending on the type of polymer solid electrolyte, and a gel polymer electrolyte containing organic electrolyte. Can be divided.

In the case of a fully solid lithium ion polymer battery, there is no problem of leakage of the organic electrolyte. In the case of a gel-type lithium ion polymer battery containing an organic electrolyte, a problem of leakage of the organic electrolyte may occur. However, the problem of leakage of the electrolyte may be prevented in a simpler form compared to a lithium ion battery using a liquid electrolyte. For example, a lithium ion polymer battery may use a multilayer membrane pouch 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. The polymer film forming the inner layer of the pouch film protects the metal foil of the intermediate layer 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.

Referring to FIG. 1, a general forming method of a pouch-type lithium secondary battery is first formed by folding a rectangular pouch film in the middle to form an upper portion 10 and a lower portion 20 of the pouch. The lower part 20 is provided with a groove 21 in which the electrode assembly can be accommodated by pressing.

The ordinary electrode assembly 30 is wound into a multi-layer film laminated in the order of the anode 31, the separator 33, and the cathode 35 in a spiral shape to form a jelly roll. When winding up the jelly roll, a separator is added to the electrode surface exposed to the outside of the roll to prevent a short circuit between the positive electrode and the negative electrode. The formed jelly roll is placed in the lower groove 21 of the pouch film and heated and pressurized in a state in which the edge portion is in close contact with each other to perform pouch sealing.

In order to electrically connect the positive electrode 31 and the negative electrode 35 of the electrode assembly 30 to the outside of the pouch, electrode tabs 37 and 38 or electrode leads are formed at one side of the positive electrode 31 and the negative electrode 35. These electrode tabs 37 and 38 are formed to protrude from the jelly roll in the direction perpendicular to the direction in which the jelly roll is wound, and are drawn out through the pouch through a sealed side of the pouch film.

A sealing tape 39 may be attached to the electrode tab to help seal the pouch, and the pouch film has a form in which the polymer film 11 is laminated on the inside and outside of the metal foil 13.

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

Then, the core pack is built into the hard case and combined to form a completed hard pack battery. The hard case may be formed using a polypropylene resin or the like without a separate circuit or metal part inside, but there may be a separate circuit or conductor part inside the hard case depending on the characteristics of the device in which the battery is used.

2 is a plan view illustrating a state in which an electrode tab is attached to an electrode plate 310 such as a positive electrode plate or a negative electrode plate, as an example of the related art.

Referring to the drawings, the electrode tab 317 is generally formed of metal, usually aluminum, copper or nickel. They must have sufficient thickness and dimensions to be the passage of current without significant resistance. In order to enhance the adhesion between the polymer film on the inner surface of the pouch and the metal forming the electrode tab 317 in the pouch sealing process, a specific sealing material may be contained on the surface of the polymer film or the components may be easily adhered before the pouch sealing. The tape 319 may be attached to a portion where the electrode tab 317 contacts the pouch.

Meanwhile, the sealing tape 319 attached to the electrode tab 317 increases the adhesiveness between the electrode tab 317 and the pouch sealing surface, and also increases the sealing reliability of the pouch at the portion where the electrode tab 317 passes. Do it. The sealing tape 319 also serves to prevent electrical connection between the aluminum foil of the pouch film and the electrode tab 317.

In more detail, when the thickness of the electrode tabs 317 is increased, the electrode tab 317 quickly removes heat during heat sealing in the region where the electrode tabs 317 pass through the pouch, thereby making it difficult to control the sealing temperature. Electrode tab 317 causes non-uniform pressure due to its thickness, which also leads to poor sealing reliability.

As a result, when the upper edge portion and the lower edge portion of the pouch are contacted and fused, the polymer tab on the inner side of the pouch is pushed or damaged due to excessively high temperature and pressure or a long time for fusion. Short circuits between 317 and the metal foil of the pouch may occur. Therefore, the metal foil of the pouch is corroded and moisture and oxygen flow into the pouch, causing abnormalities such as swelling and deterioration of the battery.

At this time, if the sealing tape 319 is attached to the electrode tab 317, even if the polymer layer of the inner surface of the pouch is damaged, the electrode tab 317 and the aluminum foil of the pouch may be prevented from directly contacting. In addition, the sealing tape 319 attached to the electrode tab 317 serves to cushion the pressure difference between where the electrode tab 317 is and where it is not, thereby improving the sealing state.

On the other hand, to form the electrode assembly in the lower portion of the electrode tab 317, in particular the corner of the electrode tab 317 overlapping the electrode tab 310 and the electrode tab 317, such as an aluminum plate or a copper plate of each electrode constituting the current collector In order for the electrode plate 310 to be wound and press-molded or in another process, pressure may be intensively applied. For example, when a pressure of about 300 kg / cm ² is applied to the electrode assembly in order to form a jelly roll in a flat shape after winding the electrode assembly, more pressure is concentrated in the corner portion.

 In this case, damage such as scratches or tears may occur in the current collector metal foil, the electrode active material, or the separator that overlaps the electrode tab 317. If scratches or other breakages occur, particles separated from the active material or foil may cause internal short circuits, and even short circuits between the electrodes may cause short circuits and other battery failures.

Accordingly, the lower portion of the electrode tab, the portion where the electrode tab and the electrode plate are attached, attach a separate protective tape 321 on the electrode tab to disperse the pressure, wrap the sharp edges, and then overlap the electrode tab 317 in the operation of press molding after winding. Prevent scratches or breakage at the losing part.

However, the sealing tape 319 operation for protecting the overlapping portion of the electrode tab 317 and the pouch sealing surface, and the protective tape 321 operation for protecting the overlapping portion over the electrode tab 317 serve their respective purposes. Is done separately. And since the purpose of each tape operation | work differs, the tape used also differs. For example, the protective tape 321 is mainly made of a material having strong mechanical strength, such as PET and ETC, and the sealing tape 319 is a poly having a melting point of about 180 ° C. so as not to withstand and remove heat applied in a pouch sealing operation. Propylene resin is used. Therefore, each of these processes requires time and effort individually.

In addition, when the protective tape 321 and the sealing tape 319 overlap, the overlapping portion becomes even a little thick, so that the pressure of this portion is not uniform during pouch sealing, and between the protective tape 321 and the sealing tape 319. If there is a portion where the electrode tab 317 is exposed, this may cause problems such as scratches, breakage, and pouch sealing problems mentioned above.

Disclosure of Invention The present invention aims to provide a pouch type lithium secondary battery having a configuration capable of improving process efficiency and reducing the possibility of defects. do.

Pouch-type lithium secondary battery of the present invention for achieving the above object,

A positive electrode plate, a separator, and a negative electrode plate are laminated, and an electrode assembly having electrode tabs formed on each of the positive electrode plate and the negative electrode plate,

In the lithium secondary battery wrapped around the electrode assembly and provided with a pouch penetrated by the electrode tab,

At least one surface of the electrode tab, characterized in that the sealing tape covering the portion overlapping with the sealing portion of the pouch and a protective tape covering the portion overlapping with the positive electrode plate or the negative electrode plate is characterized in that one tape is integrally connected.

In the present invention, the tape covering the electrode tab may be a polypropylene resin that can withstand high pressure heating at the time of sealing the pouch or a film made by mixing a certain ratio of polypropylene with polypropylene. The thickness of the film is preferably 10 to 50 micrometers (micrometers) in consideration of the fact that the film must be able to withstand mechanical pressure without being damaged.

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

3 is a plan view showing a state in which a tape is attached to the electrode tab according to an embodiment of the present invention, Figure 4 is a cross-sectional view showing a cross section taken along the line AA of FIG.

3 and 4, in order to form the illustrated state, first, the electrode tab 317 is attached to the electrode plate 310. The electrode plate 310 to which the electrode tab 317 is attached is coated with an active material on a rectangular current collector made of metal foil. The positive electrode plate of the electrode plate 310 is usually formed by coating a positive electrode active material such as lithium cobalt or lithium manganate on an aluminum current collector, and the negative electrode plate is usually formed by coating carbon with a negative electrode active material on a copper current collector. However, a portion of the current collector surface including a portion to which the electrode tab 317 is attached is not coated with the active material in order to prevent easy attachment of the electrode tab and defects due to separation of the active material during winding processing.

The tape 420 is attached on the electrode tab 317 to cover all of the electrode tabs 317 below the portion overlapping the pouch sealing surface of the electrode tab 317. The tapes 420 are attached to positions corresponding to each other such that the tapes 420 overlap not only the front side but also the rear side of the electrode tab 420 with the same length when viewed from above. Taping operations of the front and rear surfaces may be performed sequentially or simultaneously.

The tape 420 attached to the front surface of the electrode tab 317 and the tape 420 attached to the rear surface are usually made of the same material, and 20 μm thick so as not to be melted out or broken in a pouch sealing operation in which heat and pressure are applied. Polypropylene film is used. The thickness of the film can be added or subtracted according to the external pressure on the electrode assembly.

5 is a cross-sectional view showing a state in which the electrode tab and the front and rear tapes are attached to the electrode plate in another embodiment of the present invention.

As shown in FIG. 4, a tape 421 is provided on the front of the electrode tab 317 so as to protect both the portion where the electrode tab 317 overlaps the pouch sealing portion and the portion that overlaps the electrode plate 310. The long side is attached, and a short sealing tape 423 is attached to the rear side so that the electrode tab can protect only the portion overlapping the pouch sealing portion.

According to the present invention, by attaching the protective tape and the sealing tape to the electrode tab separately in one step, the process time and cost of taping can be reduced by half, thereby improving the efficiency of the battery manufacturing process. .

Further, according to the present invention, it is possible to fundamentally prevent the occurrence of a defect in a portion that is not protected by the two tapes because the sealing tape and the protective tape are not attached in place according to the process variation.

Although the present invention has been described with reference to the illustrated embodiments, it is merely exemplary, and it is to be understood that the present invention may cover various modifications and equivalent other embodiments that can be made by those skilled in the art. Will understand.

Claims (4)

A positive electrode plate, a separator, and a negative electrode plate are laminated, and an electrode assembly having electrode tabs formed on each of the positive electrode plate and the negative electrode plate, In the pouch-type lithium secondary battery wrapped around the electrode assembly and provided with a pouch penetrated by the electrode tab, A pouch type comprising a sealing tape covering at least one side of the electrode tab and a portion overlapping the sealing portion of the pouch and a protective tape covering the portion overlapping the positive electrode plate or the negative electrode plate. Lithium secondary battery. The method of claim 1, The tape is a pouch type lithium secondary battery, characterized in that formed of a polypropylene resin or a resin in which polypropylene and polypropylene are mixed at a predetermined ratio. The method of claim 2, The tape is a pouch type lithium secondary battery, characterized in that consisting of a film of 10 to 50 μm thick. The method of claim 1, The tape is a pouch type lithium secondary battery, characterized in that attached to the position overlapping each other with the same length on the front and rear of the electrode tab in the state attached to the positive electrode plate or the negative electrode plate.

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