Pouch-type lithium secondary battery

Abstract

The present invention relates to a lithium secondary battery, and more particularly, to a pouch-type lithium secondary battery in which a positive electrode lead tab and a negative electrode lead tab are formed at one end of a positive electrode and a negative electrode, respectively, in which a length of a separator located between a positive electrode and a negative electrode is controlled to protrude from an end of the positive electrode, and the length of the protruding portion of the separator is controlled to a maximum length up to a sealing portion located along an edge of the pouch, thereby preventing a gap between the positive electrode and the negative electrode, and improving safety and life characteristics.

Description

Technical Field

[0001] This application claims the benefit of priority based on Korean Patent Application No. 2021-0160923, filed on November 22, 2021, and Korean Patent Application No. 2022-0153613, filed on November 16, 2022, and all the contents disclosed in the documents of the corresponding Korean patent applications are incorporated herein by reference in their entirety.

[0002] The present invention relates to a pouch-type lithium secondary battery.

Background Art

[0003] Generally, types of secondary batteries include nickel-cadmium batteries, nickel-metal hydride batteries, lithium-ion batteries, and lithium-ion polymer batteries. Such secondary batteries are used not only in small products such as digital cameras, P-DVDs, MP3Ps, mobile phones, PDAs, Portable Game Devices, Power Tools, and E-bikes, but also in large products that require high power such as electric vehicles and hybrid vehicles, power storage devices for storing excess generated power and new renewable energy, and backup power storage devices.

[0004] The lithium secondary battery generally consists of a positive electrode, a separator, and a negative electrode, and these materials are selected considering factors such as the battery life, charge-discharge capacity, temperature characteristics, and stability. In the lithium secondary battery, the charge-discharge process proceeds while repeating the process of lithium ions being intercalated into and deintercalated from the graphite electrode of the negative electrode from the lithium metal oxide of the positive electrode. Generally, the lithium secondary battery has a three-layer structure of positive electrode / separator / negative electrode, or has been designed with a five-layer structure of positive electrode / separator / negative electrode / separator / positive-negative electrode, or negative electrode / separator / positive electrode / separator / negative electrode. Also, in the above structure, each layer of the negative electrode or positive electrode is coated and laminated with the same amount of electrode active material, and each negative electrode and positive electrode have the same thickness. The unit cells are assembled to form one electrode assembly or secondary battery.

[0005] In such a secondary battery, for the unidirectional form of the electrode terminal, after the electrode taps of the positive and negative electrodes of the electrode assembly are formed in the same direction, an electrode lead is connected to the electrode tap to form the electrode terminal. In the case of a unidirectional cell, there are disadvantages to the battery life due to non-uniform use of the cell's active material during heat generation, charging, and discharging of the electrode lead.

[0006] For the bidirectional form of the electrode terminal, after the positive and negative electrode taps of the electrode assembly are formed on the opposing surfaces of the electrode assembly, an electrode lead is connected to the electrode tap to form the electrode terminal. In the case of constructing a battery pack with a bidirectional cell, there is a disadvantage that it occupies more space than a unidirectional cell, resulting in a decrease in energy density.

[0007] In particular, in the case of the unidirectional form of the electrode terminal, the electrode taps of the positive and negative electrodes are formed in the same direction, and as the charge-discharge of the battery proceeds, there may occur a problem that lithium dendrites deposited on the negative electrode are grounded to the electrode tap of the positive electrode, resulting in a short circuit.

[0008] Therefore, in a lithium secondary battery having a unidirectional electrode terminal, research and development of a lithium secondary battery structure capable of preventing a short circuit between the positive electrode and the negative electrode even when lithium dendrites grow from the negative electrode has been continuously demanded.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0010] As a result of extensive research by the present inventors to solve the above problems, in a pouch-type lithium secondary battery in which a positive electrode lead tap and a negative electrode lead tap are formed at one end of the positive electrode and the negative electrode, respectively, the length of the separator located between the positive electrode and the negative electrode is controlled so that the separator protrudes compared to the end of the positive electrode, and the length of the protruding portion of the separator is controlled up to the sealing portion located along the edge of the pouch at most, it was confirmed that a short circuit between the positive electrode and the negative electrode can be prevented, and thereby the safety and life characteristics of the battery can be improved.

[0011] Therefore, an object of the present invention is to provide a pouch-type lithium secondary battery having a structure capable of preventing a short circuit between a positive electrode and a negative electrode.

Means for Solving the Problems

[0012] To achieve the above object, the present invention provides an electrode assembly including a positive electrode, a separator, and a negative electrode; a pouch for housing the electrode assembly; and a secondary battery including an electrode lead tap electrically connected to the electrode assembly, wherein the electrode lead tap has a positive electrode lead tap and a negative electrode lead tap, The pouch has a sealing portion at the edge and a bonding portion that seals a portion where the positive electrode lead tap and the negative electrode lead tap protrude outside the pouch through the sealing portion. Provided is a pouch-type lithium secondary battery, wherein the separator is in a form protruding more than one end of the positive electrode, and the length of the protruding portion is equal to or less than the length from one end of the positive electrode to the sealing portion.

[0013] The positive electrode has a positive electrode lead tap electrically connected to one end, the negative electrode has a negative electrode lead tap electrically connected to one end, and the positive electrode lead tap and the negative electrode lead tap may be electrically connected to the positive electrode and the negative electrode in the same direction or in opposite directions.

[0014] The pouch may be an aluminum pouch.

[0015] The bonding portion may contain a thermoplastic resin.

[0016] A part of the protruding portion of the separator may have an insulating layer.

[0017] The insulating layer may be formed on one or both surfaces of the separator.

[0018] The insulating layer may contain one or more selected from the group consisting of polyethylene (PE), polypropylene (PP), and polyethylene terephthalate (PET).

[0019] One end of the separator may be partially protruded so as to overlap with the positive electrode lead tap, or may be in a form that wraps the positive electrode lead tap.

[0020] The negative electrode may be a lithium negative electrode.

[0021] The lithium secondary battery may be a lithium-sulfur secondary battery.

Advantages of the Invention

[0022] According to the present invention, in a pouch-type lithium secondary battery in which a positive electrode lead tap and a negative electrode lead tap are formed at one end of a positive electrode and a negative electrode, respectively, by making a separator protrude more than one end of the positive electrode, even when lithium dendrites grow at the negative electrode during battery operation, the contact between the lithium dendrites and the positive electrode is minimized structurally to prevent a short circuit between the positive electrode and the negative electrode, and the stability and life characteristics of the battery can be improved.

Brief Description of the Drawings

[0023]

Figure 1

Figure 2

Figure 3

Figure 4

Modes for Carrying Out the Invention

[0024] Hereinafter, in order to facilitate the understanding of the present invention, the present invention will be described in more detail.

[0025] Terms and words used in this specification and claims should not be construed in a limited sense in accordance with ordinary or dictionary meanings, and should be construed in a meaning and concept that conforms to the technical idea of the present invention in accordance with the principle that the inventor can appropriately define the concept of the terms in order to explain his invention in the best way.

[0026] Pouch-type lithium secondary battery The present invention relates to a pouch-type lithium secondary battery, and by controlling the length of a separator in a pouch-type lithium secondary battery including an electrode assembly in which a positive electrode, a separator, and a negative electrode are sequentially laminated, it relates to a lithium secondary battery having a structure that prevents a short circuit between the positive electrode and the negative electrode due to lithium dendrites growing from the negative electrode during charge and discharge.

[0027] Hereinafter, the present invention will be described in more detail with reference to the drawings.

[0028] FIG. 1 is a schematic diagram showing a cross-section of an electrode assembly included in a pouch-type lithium secondary battery according to a preferred embodiment of the present invention.

[0029] Referring to FIG. 1, the electrode assembly 10 included in the pouch-type lithium secondary battery 1 of the present invention has a form in which a positive electrode 100, a separator 300, and a negative electrode 200 are sequentially laminated, and is characterized in that the length of the separator 300 is longer than the length of the positive electrode 100. Further, the length of the separator 300 may be longer than the length of the negative electrode 200.

[0030] Since the separator 300 is longer in length than the positive electrode 100, it is in a form protruding with one end of the positive electrode 100 as a reference. Further, since the separator 300 may also be longer in length than the negative electrode 200, it may be in a form protruding with one end of the negative electrode 200 as a reference.

[0031] At this time, only one end of the positive electrode has a positive electrode lead tap electrically connected thereto, and only one end of the negative electrode has a negative electrode lead tap electrically connected thereto. In the electrode assembly, the directions in which the positive electrode lead tap and the negative electrode lead tap are connected to the positive electrode and the negative electrode may be the same direction or opposite directions.

[0032] FIG. 2 is a partial schematic diagram showing a portion where a positive electrode lead tap and a negative electrode lead tap protrude in a pouch-type lithium secondary battery according to a preferred embodiment of the present invention, and may be a cross-sectional view of the pouch-type lithium secondary battery. FIG. 3 shows an exploded view of an electrode assembly included in a pouch-type lithium secondary battery according to a preferred embodiment of the present invention.

[0033] Referring to FIG. 2, in the pouch-type lithium secondary battery 1, an electrode assembly 10 in which a positive electrode 100, a separator 300, and a negative electrode 200 are laminated is housed in a pouch 300.

[0034] Referring to FIG. 3, the separator 300 included in the electrode assembly 10 included in the pouch-type lithium secondary battery 1 is longer in length than the positive electrode 100. Specifically, it protrudes by a length d, which is the length of the protruding portion of the separator 300, with one end of the positive electrode 100 as a reference.

[0035] In the electrode assembly 10, the separator 300 may be in a form protruding compared to one end of the positive electrode 100 (not shown). The length of the protruding portion of the separator 300 may be equal to or less than the length from one end of the positive electrode to the sealing portion 310. In other words, the length (d) of the protruding portion of the separator 300 may be equal to or less than the length (H) from one end of the positive electrode 100 to the sealing portion 310, specifically, the inner surface of the sealing portion 310 (d≦H). More specifically, d≦H, d≦0.9*H, d≦0.7*H, d≦0.5*H, or d≦0.5*H may be acceptable. The lower limit value of d is not particularly limited as long as it exceeds 0. For example, it may be 0.1*H or more (d≧0.1*H). If d exceeds H (d>H), a part of the separator, for example, the end, will be included inside the sealing portion, and sealing cannot be properly performed. When injecting the electrolyte into the pouch, the electrolyte may flow into the sealing portion or flow out to the outside along the separator.

[0036] Also, the electrode assembly 10 is electrically connected to an electrode lead tap, and the electrode lead tap includes a positive electrode lead tap 110 and a negative electrode lead tap 210.

[0037] The positive electrode 100 has a positive electrode lead tap 110 electrically connected to one end, and the negative electrode 200 has a negative electrode lead tap 120 electrically connected to one end. The positive electrode lead tap 110 and the negative electrode lead tap 120 are electrically connected to the positive electrode 100 and the negative electrode 200 in the same direction.

[0038] Inside the pouch 300, the electrode assembly 10 is housed. The pouch 300 has a sealing portion 310 formed along the edge of the pouch 300 and a joining portion 320 that seals the portions where the positive electrode lead tap 110 and the negative electrode lead tap 210 protrude outside the pouch 300 through the sealing portion 310.

[0039] The joining portion 320 can seal the pouch 300 and at the same time serve as a buffer for the sealing portion 310. If too high a pressure and / or temperature is applied to the joining portion 320, the joining portion 320 will be damaged, and current conduction will occur between the aluminum pouch and the electrode lead taps, thereby The joining portion 320 can serve as a buffer for the sealing portion 310. If too high a pressure and / or temperature is applied to the joining portion 320, damage will occur, and current conduction will occur between the aluminum pouch 300 and the positive electrode lead tap and / or the negative electrode lead tap, thereby possibly reducing the safety of the battery.

[0040] Considering such functionality of the joining portion 320, the joining portion 320 may be formed of a thermoplastic resin.

[0041] The thermoplastic resin is not particularly limited as long as it can seal the pouch 300 and serve as a buffer for the sealing portion 310. For example, the thermoplastic resin may be one or more selected from the group consisting of polyvinyl chloride (PVC), polystyrene (PS), polycarbonate (PC), polymethyl methacrylate (PMMA), acrylonitrile butadiene styrene (ABS), polyurethane (PU), polyamide (PA), polyacetal (POM), polyphenylene sulfide (PPS), polybutylene terephthalate (PBT), polyimide (PI), liquid crystal polymer (LCP), polyether ether ketone (PEEK), polyether ketone (PEK), ethylene propylene diene methylene rubber (EPDM), and acrylic rubber (ACM).

[0042] In the present invention, the protruding portion of the separation membrane may be formed with an insulating layer. The insulating layer may be partially formed at the end of the protruding portion of the separation membrane. For example, the insulating layer may be formed from one end of the edge of the protruding portion of the separation membrane to a length of d / 5, 4 / d, or 3 / d.

[0043] The insulating layer may be formed on one or both sides of the separation membrane. When the insulating layer is formed on one side of the separation membrane, if it is formed on the surface facing the negative electrode, it is effective in preventing a short-circuit phenomenon due to the growth of lithium dendrites from the negative electrode.

[0044] The insulating layer contains an insulating substance, and the insulating substance is not particularly limited as long as it is a material having insulating properties. For example, it may be any one of polyethylene (PE), polypropylene (PP), and polyethylene terephthalate (PET), or a derivative of any one of these, or a copolymer containing any one or more of these.

[0045] Further, the insulating substance may further contain PVDF (Polyvinylidene fluoride) which is excellent in high strength, processability, and chemical resistance.

[0046] The insulating layer may have a structure in which the above-described insulating substance is coated, or a structure in which an insulating tape is attached to the corresponding portion. The insulating tape can be formed with a structure containing any one of PE, PP, and PET, or a derivative of any one of these, or a copolymer containing any one or more of these.

[0047] Further, the separation membrane can also be formed so that only the portion overlapping the positive electrode lead tap protrudes.

[0048] FIG. 4 shows an exploded view of an electrode assembly included in a pouch-type lithium secondary battery according to another preferred embodiment of the present invention. One end of the separator 300 may protrude so as to overlap with the positive electrode lead tap 110. More specifically, one end of the separator 300 may protrude to wrap the positive electrode lead tap 110.

[0049] Since the negative electrode lead tap 210 is itself a negative electrode active material, the separator 300 may protrude so as to overlap with the negative electrode lead tap 210 portion or wrap the negative electrode lead tap 210, and lithium dendrites can grow by reaction with the electrolyte. On the other hand, since there is no positive electrode active material on the positive electrode lead tap 110, if one end of the separator 300 protrudes so as to overlap with the positive electrode lead tap 110 portion or wraps the positive electrode lead tap 110 portion, side reactions do not proceed and contact with lithium dendrites may be prevented.

[0050] The lithium secondary battery as described above is intended to prevent lithium dendrites grown at the negative electrode from contacting the positive electrode, so it is effective when a lithium negative electrode is used as the negative electrode.

[0051] Further, the lithium secondary battery may be a lithium-sulfur secondary battery containing sulfur as a positive electrode active material.

[0052] The positive electrode, separator, and electrolyte included in the lithium-sulfur secondary battery can be prepared by ordinary components and manufacturing methods, respectively. The outer shape of the lithium-sulfur secondary battery is not particularly limited, and may be a cylindrical shape, a rectangular shape, a pouch type, a coin type, etc. using a can.

[0053] As described above, although the present invention has been described by way of limited embodiments and drawings, the present invention is not limited thereby, and various modifications and variations are possible within the equivalent scope of the technical idea of the present invention and the claims described below by those having ordinary knowledge in the technical field to which the present invention pertains.

Description of Reference Numerals

[0054] 1: Pouch-type lithium secondary battery 10: Electrode assembly 100: Positive electrode 110: Positive electrode lead tap 200: Negative electrode 210: Negative electrode lead tap 300: Pouch 310: Sealing part 320: Joint part d: Length of the portion where the separator protrudes from one end of the positive electrode H: Length from one end of the positive electrode to the sealing part

Claims

1. An electrode assembly comprising a positive electrode, a separator, and a negative electrode; A pouch for housing the electrode assembly; and A secondary battery including an electrode lead tap electrically connected to the electrode assembly, The electrode lead tap includes a positive electrode lead tap and a negative electrode lead tap, The pouch has a sealing portion at the edge and a joining portion that seals a portion where the positive electrode lead tap and the negative electrode lead tap protrude outside the pouch through the sealing portion, The separator is in a form protruding more than one end of the positive electrode, and the length of the protruding portion is equal to or less than the length from one end of the positive electrode to the sealing portion, A pouch-type lithium secondary battery in which a part of the protruding portion of the separator has an insulating layer.

2. The positive electrode has a positive electrode lead tap electrically connected to one end, The negative electrode has a negative electrode lead tap electrically connected to one end, The pouch-type lithium secondary battery according to claim 1, wherein the positive electrode lead tap and the negative electrode lead tap are electrically connected to the positive electrode and the negative electrode in the same direction or in opposite directions.

3. The pouch-type lithium secondary battery according to claim 1, wherein the pouch is an aluminum pouch.

4. The pouch-type lithium secondary battery according to claim 1, wherein the joining portion contains a thermoplastic resin.

5. The pouch-type lithium secondary battery according to claim 1, wherein the insulating layer is formed on one or both surfaces of the separator.

6. The pouch-type lithium secondary battery according to claim 1, wherein the insulating layer contains one or more selected from the group consisting of polyethylene (PE), polypropylene (PP), and polyethylene terephthalate (PET).

7. One end of the separation membrane is partially protruded so as to overlap with the positive electrode lead tap or is in a form that wraps the positive electrode lead tap. The pouch-type lithium secondary battery according to claim 1.

8. The negative electrode is a lithium negative electrode. The pouch-type lithium secondary battery according to claim 1.

9. The lithium secondary battery is a lithium-sulfur secondary battery. The pouch-type lithium secondary battery according to any one of claims 1 to 8.

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