KR101156955B1 - Electrode Assembly of Improved Stability and Secondary Battery Comprising the Same - Google Patents

Abstract

The present invention includes a stack type or a stack type / foldable type electrode assembly having a cathode / membrane / cathode structure and a cathode having a larger structure than a cathode in the electrode assembly, the electrode active material being protruded to one side of a cathode current collector. A plurality of uncoated uncoated portions ("anode tabs") are bonded to one anode lead, and the width of the anode tab at the joining site is smaller than the width of the anode lead or a predetermined width from the top of the cathode. Provided is an electrode assembly having a structure in which slits are formed at a spaced apart position and a secondary battery including the same.

Description

Electrode assembly with improved safety and secondary battery comprising same {Electrode Assembly of Improved Stability and Secondary Battery Comprising the Same}

1 is a perspective view of a general pouch type secondary battery including a stacked electrode assembly;

FIG. 2 is a partially enlarged view of a top inside a battery case in which the positive electrode tabs are densely coupled in the secondary battery of FIG. 1 and connected to the positive electrode lead;

3 is a schematic diagram of an electrode assembly included in a general pouch-type battery;

4 is a schematic diagram of an electrode assembly according to one embodiment of the present invention;

5 is a schematic view of an electrode assembly according to another embodiment of the present invention.

The present invention relates to a secondary battery, and more particularly, a secondary battery having a stack type or a stack type / fold type electrode assembly having a cathode / separation membrane / cathode structure and having a cathode larger than the anode in the electrode assembly. A plurality of plain portions ("anode tabs"), which are not coated with the electrode active material while protruding to one side of the whole, are bonded to one positive electrode lead, and the width of the positive electrode tab at the bonding site is smaller than that of the positive electrode lead. The present invention relates to an electrode assembly having a structure in which a slit is formed at a position separated by a predetermined width from an upper end of a structure or a negative electrode, and a secondary battery including the same.

As technology development and demand for mobile devices increase, the demand for secondary batteries as an energy source is rapidly increasing, and accordingly, a lot of researches on batteries that can meet various demands have been conducted.

Typically, there is a high demand for square and pouch type batteries that can be applied to products such as mobile phones with a thin thickness in terms of shape of the battery, and lithium cobalt polymer batteries with high energy density, discharge voltage and output stability in terms of materials. The demand for lithium secondary batteries is high.

One of the major research tasks in such secondary batteries is to improve safety. In general, lithium secondary batteries are subject to high temperature and high pressure inside the battery, which may be caused by abnormal operating conditions of the battery, such as internal short circuits, overcharge conditions exceeding the allowed currents and voltages, exposure to high temperatures, and impact from falling. This may cause an explosion of the battery. In one such case, there is a possibility that the secondary battery may generate an internal short circuit upon impact such as a drop or an action of an external force.

According to the shape of the battery case, secondary batteries are classified into cylindrical batteries and rectangular batteries in which the electrode assembly is embedded in a cylindrical or rectangular metal can, and pouch-type batteries in which the electrode assembly is embedded in a pouch type case of an aluminum laminate sheet. .

1 is a perspective view schematically illustrating a pouch-type battery including a stacked electrode assembly.

Referring to FIG. 1, the pouch-type battery cell 10 has a structure in which two electrode leads 11 and 12 protrude from each other to protrude from an upper end and a lower end of the battery main body 13. The battery case 14 is composed of two upper and lower units, and both side surfaces 14b and upper and lower ends 14a, which are mutually contacting portions, with electrode assemblies (not shown) mounted on an accommodating portion formed on an inner surface thereof. The battery cells 10 are made by attaching 14c). The battery case 14 has a laminate structure of a resin layer / metal foil layer / resin layer, and can be attached by mutually fusion bonding the resin layer by applying heat and pressure to both side surfaces 14b and the upper and lower ends 14a and 14c which are in contact with each other. In some cases, the adhesive may be attached using an adhesive.

FIG. 2 is a partially enlarged view of an upper portion of the inside of the battery case in which the positive electrode tabs are coupled in a dense form and connected to the positive lead in the pouch-type battery of FIG. 1.

Referring to FIG. 2, a plurality of positive electrode tabs 22 extending and protruding from the positive electrode current collector 21 of the electrode assembly 20 may be, for example, a positive electrode lead in the form of a weld portion integrally joined by welding. Connected to (11). The positive lead 11 is sealed by the battery case 14 with the opposite end to which the positive electrode tab weld is connected is exposed. Since the plurality of positive electrode tabs 22 are integrally coupled to form a welded portion, the inner upper end of the battery case 140 is spaced apart from the upper surface of the electrode assembly 20 by a predetermined distance, and the positive electrode tabs 22 of the welded portion are formed. Is bent in a substantially V shape.

However, although the mechanical rigidity of the battery case itself is not excellent, and the electrode assembly 20 included in the battery is embedded in the form of being wrapped in the battery case 14, it is not fixed by it, so that external force is not applied to the battery. When the electrode assembly is deformed while being applied or repeating expansion and contraction during charging and discharging, a short circuit occurs when the positive electrode tab 23 ruptures. That is, the positive electrode tab 23 is ruptured by external shocks such as expansion and contraction, vibration, and drop due to repeated charging and discharging, such that the positive electrode tab 23 or the positive electrode lead 11 of the electrode assembly 30 contacts the negative electrode. This may cause an internal short circuit, which greatly reduces the safety of the battery.

Accordingly, there is a high demand for a technology capable of ensuring safety of a battery in a more efficient manner in a secondary battery having a stacked type or a stacked / folded electrode assembly.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-described problems of the prior art and the technical problems required from the past.

After in-depth research and various experiments on the secondary battery, the inventors of the present application make the width of the positive electrode tab to which the active material protruding from the positive electrode current collector is less than that of the positive electrode lead, or the slits on the positive electrode tab. When formed, it was confirmed that the internal short circuit caused by the bursting of the positive electrode tab can be prevented and the safety of the battery can be greatly improved, and the present invention has been completed.

Therefore, the secondary battery according to the present invention includes a stack type or a stack type / fold type electrode assembly having a cathode / separation membrane / cathode structure and a cathode having a structure in which an anode is larger than a cathode in the electrode assembly. A plurality of plain portions ("anode tabs"), which are not coated with the electrode active material in a protruding state, are bonded to one anode lead, and the width of the cathode tab at the bonding site is smaller than that of the anode lead. have.

The electrode tabs of the stacked or stacked / foldable secondary battery are arranged substantially parallel to the direction of the electrode plate, and in order to connect the tabs to one electrode lead, the plurality of tabs are collected and aligned, and then welded. The process is necessary. In this way, when the plurality of tabs are integrated in one direction, the thickness of the battery is changed according to the length to the welded portion and the number of stacked electrode plates, and naturally, curved portions of the electrode tabs are formed. The curved portion is a portion of the current collector (uncoated portion) to which the active material extending from each current collector is not coated, and is a portion that causes a short circuit of the battery when contact is made with an opposite current collector or the active material of the electrode assembly. .

In addition, in the lithium secondary battery, the size of the negative electrode plate is made larger than the size of the positive electrode plate in consideration of the problem that lithium ions in the electrolyte precipitate from the negative electrode to the lithium metal during the charge and discharge process. Therefore, in such a structure, when a drop, an external impact, or the like is applied, the positive electrode tab is ruptured, and the negative electrode (current collector or active material) of the electrode assembly is likely to come into contact with the internal short circuit.

In this structure, as described above, the width of the positive electrode tab of the current collector is formed to be smaller than the width of the positive electrode lead, so that when the electrode assembly is deformed while repeating expansion and contraction during dropping, application of external force, and charging and discharging, the positive electrode Minimizing the deformation of the tab prevents its rupture, ultimately ensuring safety against internal short circuits.

In the present invention, the positive electrode tabs can be connected to the positive lead in a variety of ways, preferably more stably by welding. Such welding may be performed by, for example, ultrasonic welding, laser welding, resistance welding, or the like.

The width of the positive electrode tab connected to the positive lead is preferably about 80 to 95% based on the width of the positive lead. If the width of the positive electrode tab is too narrow, it is easy to rupture even at a small external force, and the internal resistance may increase, resulting in deterioration of the battery performance. On the contrary, if the width of the positive electrode tab is too wide, the positive electrode tab may be damaged due to external force application or abnormal operation. When ruptured it may cause a short circuit as described above.

According to another preferred embodiment of the present invention, a secondary battery having a stack type or a stack type / fold type electrode assembly having a cathode / separation membrane / cathode structure and having a cathode larger than the anode in the electrode assembly, A plurality of plain portions ("anode tabs"), which are not coated with the electrode active material while protruding to one side of the whole, are bonded to one positive electrode lead, and the positive electrode tabs are positioned at a predetermined distance from the end of the negative electrode tab. The slits may be formed in a shape parallel to the ends of the cathode.

That is, when the electrode assembly is deformed due to battery drop, external impact, or repeated expansion and contraction during charging and discharging, the anode plain portion ruptures, and thus the slit portion is separated from the upper portion of the cathode at a predetermined width. By forming the structure, it is possible to ensure the safety of the battery by guiding the rupture portion of the positive electrode non-coating portion to a range where no short circuit is caused, that is, a position spaced apart from the upper end of the negative electrode by a predetermined width.

The width of this slit is preferably formed to a length of approximately 5 to 30% based on the width of the positive electrode tab. If the width of the slit is too narrow, the above effect of inducing the short circuit is not induced by the slit structure, and on the contrary, if the width thereof is too wide, the slit may be easily ruptured even by small external force or deformation of the electrode assembly. It is not desirable because it can.

In addition, the formation position of the slit is spaced by a length of 0.5 to 3 mm relative to the end of the cathode, taking into account the possibility that the ruptured anode tab is in contact with the cathode end and the size of the site for bonding the anode tab to the electrode lead. It is preferred that it is a position.

In one preferred embodiment, the slit is preferably formed on both sides of the positive electrode tab, it is possible to induce preferential rupture of the slit site even in the external force or deformation in various directions with respect to the electrode assembly.

The slit-formed positive electrode tabs may be connected to the positive electrode lead in various ways, and may be more stably connected by welding. Such welding may be performed by, for example, ultrasonic welding, laser welding, resistance welding, or the like.

The width of the positive electrode tab may vary depending on the size, output, etc. of the battery, and may be appropriately determined within a range that is not easily ruptured by the application of an external force and abnormal operation and is less affected by the deformation of the electrode assembly.

The stack type electrode assembly may be manufactured by sequentially cutting the positive electrode and the negative electrode in units of a predetermined size and interposing the separators sequentially.

The stack / foldable electrode assembly may be manufactured by forming a bicell or a full cell as a unit cell of a small unit in a stacked manner, placing a plurality of them on a long separation film (separation sheet), and winding them sequentially. Further details of the electrode assembly of the stack / foldable structure are disclosed in Korean Patent Application Publication Nos. 2001-0082058, 2001-0082059, and 2001-0082060 to the present applicants. Is incorporated by reference.

The secondary battery according to the present invention can be preferably used in a medium-large battery module of high output large capacity, in which safety is a problem. Since the medium-large battery module includes a plurality of secondary batteries as unit cells, safety may be greatly threatened by a chain reaction when an abnormality occurs in some unit cells.

Accordingly, the present invention also relates to a medium-large battery module including the secondary battery as a unit cell.

The medium-large battery module is not particularly limited as long as it is a battery module electrically connecting two or more secondary batteries. For example, the medium-large battery module is used for a power source of a notebook computer, an e-bike, an electric vehicle, a hybrid electric vehicle, and the like. It may be a battery module.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings, but the present invention is not limited by the scope of the present invention.

3 schematically shows an electrode assembly included in a general pouch-type battery.

Referring to FIG. 3, in the stacked electrode assembly stacked between the anode 21 and the cathode 31 with the separator 50 interposed therebetween, the anode tab 23 and the cathode tab 33 face each other and have an upper end portion of the electrode assembly. It consists of a structure that protrudes at the bottom and respectively. The positive electrode tab 23 and the negative electrode tab 33 are connected to the positive electrode lead 11 and the negative electrode lead 12, respectively, and collect and align a plurality of tabs to connect the tabs and the electrode leads by ultrasonic welding 25. .

However, when the electrode assembly is deformed due to the drop of the battery, the application of external force, repeated charge and discharge, and the predetermined portion A of the positive electrode tab 23 is ruptured, the positive electrode tab 23 extends beyond the separator 50. In contact with the cathode 31 has a problem causing an internal short circuit.

4 schematically shows an electrode assembly according to one embodiment of the present invention.

Referring to FIG. 4, the electrode assembly of the secondary battery is stacked between the positive electrode 100 and the negative electrode 200 with a separator 300 interposed therebetween, and the positive electrode tab 110 protruding from the positive electrode 100 and the negative electrode 200. ) And the negative electrode tab 210 is configured to be connected to the positive lead 120 and the negative lead 220, respectively.

The positive electrode tab 110 is coupled to the positive lead 120 by ultrasonic welding, and the width of the positive electrode tab 110 is smaller than the width of the positive lead 120 at the coupling portion 130. This structure minimizes the phenomenon in which the positive electrode tab 110 protruding from the electrode assembly is deformed when the electrode assembly is deformed by torsion, rupture, etc. while repeating expansion and contraction during battery drop, external force application, and charge / discharge. , Can prevent its rupture.

5 schematically shows an electrode assembly according to another embodiment of the present invention.

Referring to FIG. 5, the electrode assembly has a structure in which a slit 142 is formed in the positive electrode tab 140 at a position spaced apart from the upper end of the negative electrode 200 by a predetermined width h. Therefore, when the electrode assembly is deformed due to various causes, stress is concentrated on the slit 142 of the positive electrode tab 140 to induce a rupture. Even if the slit 142 is ruptured, the ruptured end of the positive electrode tab 140 does not contact the cathode 200 beyond the separator 300.

Slits 142 are formed on both sides of the positive electrode tab 140, and even if the deformation is caused in various directions of the electrode assembly, the slit 142 more easily induces a rupture in a range that does not cause a short circuit, thereby preventing the internal short circuit It can prevent.

Those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

As described above, in the secondary battery according to the present invention, the width of the positive electrode tab to which the active material protruding from the positive electrode current collector is not smaller than the width of the positive electrode lead or the slits are formed in the positive electrode tab, thereby It is effective in preventing the internal short circuit caused by the rupture or inducing the rupture of the positive electrode tab in a range where a short circuit does not occur, thereby greatly improving the safety of the battery.

Claims (10)

A secondary battery having a stack type or a stack type / foldable type electrode assembly having a cathode / separation membrane / cathode structure and having a cathode larger than the anode in the electrode assembly, wherein the electrode active material is coated while protruding toward one side of the cathode current collector. And a plurality of uncoated portions ("anode tabs"), which are not present, are bonded to one positive electrode lead, and the width of the positive electrode tab at the coupling site is smaller than the width of the positive electrode lead. The secondary battery of claim 1, wherein the positive electrode tabs are coupled to the positive electrode lead by welding. The secondary battery of claim 1, wherein the width of the positive electrode tab is 80 to 95% based on the width of the positive electrode lead. A secondary battery having a stack type or a stack type / foldable type electrode assembly having a cathode / separation membrane / cathode structure and having a cathode larger than the anode in the electrode assembly, wherein the electrode active material is coated while protruding toward one side of the cathode current collector. A plurality of unsupported plain portions ("anode tabs") are joined to one anode lead, and the anode tabs have slits formed in a shape parallel to the ends of the cathode on a predetermined distance from the end of the cathode. Secondary battery, characterized in that. The secondary battery of claim 4, wherein the slits are formed at positions spaced apart from each other by 0.5 to 3 mm in length with respect to the end of the negative electrode. The secondary battery of claim 5, wherein the slit has a width of about 5 to 30% based on the width of the positive electrode tab. The secondary battery of claim 6, wherein the slits are formed at both sides of the positive electrode tab, respectively. The secondary battery of claim 4, wherein the positive electrode tabs are coupled to the positive electrode lead by welding. A medium-large battery module comprising the secondary battery according to claim 1 or 8 as a unit cell. The medium and large battery module of claim 9, wherein the battery module is used as a power source for an electric vehicle or a hybrid electric vehicle.

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