KR100871345B1 - Secondary Battery of Improved Safety and Capacity - Google Patents

Abstract

The present invention relates to a secondary battery in which an electrode assembly having a structure in which a plurality of electrode plates are stacked and interconnecting electrode tabs with a separator interposed therebetween is embedded in a battery case, and interconnections of the electrode tabs are formed on an inner surface of the battery case. The electrode assembly is inverted and installed so as to be positioned at the lower end, and is electrically connected to the electrode lead on the top of the battery case through the upper electrode tab formed on one or more electrode plates while the electrode assembly is inverted. It provides a secondary battery.

Therefore, the secondary battery according to the present invention can further improve safety by preventing an internal short circuit caused by movement of the electrode assembly when a drop or external shock is applied, and utilizes the internal space of the battery case to maximize the capacity of the same standard. There are advantages you can have.

Description

Secondary Battery of Improved Safety and Capacity

1 is an exploded perspective view of a general structure of a conventional pouch type secondary battery;

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 front perspective view of a state in which the secondary battery of FIG. 1 is assembled;

4 is an exploded perspective view of a secondary battery according to one embodiment of the present invention;

5 is an exploded perspective view of a state before assembly of an electrode assembly in the secondary battery of FIG. 4;

6 is a front perspective view of a state in which the secondary battery of FIG. 4 is assembled.

The present invention relates to a secondary battery capable of improving safety and capacity, and more particularly, an electrode assembly having a structure in which a plurality of electrode plates are stacked and interconnected electrode tabs are interposed with a separator interposed therebetween. An embedded secondary battery, wherein an electrode assembly is inverted so that interconnections of the electrode tabs are located at a lower inner surface of a battery case, and an upper electrode formed on one or more electrode plates while the electrode assembly is inverted. It relates to a secondary battery characterized in that it is electrically connected to the electrode lead on the top of the battery case through the tab.

As technology development and demand for mobile devices increase, the demand for batteries as energy sources is rapidly increasing, and accordingly, many studies on batteries that can meet various demands have been conducted.

Representatively, there is a high demand for rectangular secondary batteries and pouch secondary batteries, which can be applied to products such as mobile phones with a thin thickness in terms of shape of batteries, and lithium ion batteries with high energy density, discharge voltage, and output stability in terms of materials. There is a high demand for lithium secondary batteries such as lithium ion polymer batteries.

In addition, secondary batteries are classified according to the structure of the electrode assembly having a cathode / separation membrane / cathode structure. Representatively, a jelly having a structure in which long sheet-shaped anodes and cathodes are wound with a separator interposed therebetween -Roll (electrode) electrode assembly, a stack (stacked type) electrode assembly in which a plurality of positive and negative electrodes cut in units of a predetermined size are sequentially stacked with a separator, and the positive and negative electrodes of a predetermined unit are interposed through a separator And a stacked / folding electrode assembly having a structure in which a bi-cell or full cells stacked in a state are wound.

Recently, a pouch type battery having a structure in which a stack type or a stack / fold type electrode assembly is incorporated in a pouch type battery case of an aluminum laminate sheet has attracted much attention due to its low manufacturing cost, low weight, and easy shape deformation. And its usage is gradually increasing.

FIG. 1 is a schematic exploded perspective view of a general structure of a conventional representative pouch type secondary battery.

Referring to FIG. 1, the pouch type secondary battery 10 may include an electrode assembly 30, electrode tabs 40 and 50 extending from the electrode assembly 30, and electrodes welded to the electrode tabs 40 and 50. And a battery case 20 accommodating the leads 60 and 70 and the electrode assembly 30.

The electrode assembly 30 is a power generator in which a positive electrode and a negative electrode are sequentially stacked in a state where a separator is interposed therebetween, and has a stack type or a stack / fold type structure. The electrode tabs 40, 50 extend from each electrode plate of the electrode assembly 30, and the electrode leads 60, 70 may include a plurality of electrode tabs 40, 50 extending from each electrode plate, for example. , Respectively, are electrically connected by welding, and are exposed to the outside of the battery case 20. In addition, an insulating film 80 is attached to a portion of the upper and lower surfaces of the electrode leads 60 and 70 in order to increase the sealing degree with the battery case 20 and to secure an electrical insulating state.

The battery case 20 is made of an aluminum laminate sheet, provides a space for accommodating the electrode assembly 30, and has a pouch shape as a whole. In the case of the stacked electrode assembly 30 as shown in FIG. 1, the battery case 20 so that the plurality of positive electrode tabs 40 and the plurality of negative electrode tabs 50 may be coupled together to the electrode leads 60 and 70. The inner top is spaced apart from the electrode assembly 30.

FIG. 2 is a partially enlarged view of an upper portion of a battery case connected to a cathode lead by combining positively connected tabs of the secondary battery of FIG. 1, and FIG. 3 is a front view of the assembled secondary battery of FIG. 1. Perspective view is shown.

Referring to these drawings, the plurality of positive electrode tabs 40 extending from the positive electrode current collector 41 of the electrode assembly 30 protrude from the positive electrode lead, for example, in the form of a welded portion integrally joined by welding. Connected to 60. The positive lead 60 is sealed by the battery case 20 with the opposite end 61 to which the positive electrode tab welding part is connected is exposed. Since the plurality of positive electrode tabs 40 are integrally coupled to form a welded portion, the inner upper end of the battery case 20 is spaced apart from the upper surface of the electrode assembly 30 by a predetermined distance, and the positive electrode tabs 40 of the welded portion are formed. Is bent in a substantially V shape. Therefore, the coupling region between the electrode tabs and the electrode lead is also referred to as a V-forming region.

However, such V-forming sites have a number of problems in terms of battery capacity and safety. First, since the capacity of the battery is substantially determined by the size of the electrode assembly 30, the presence of the V-forming portion limits the size of the electrode assembly 30 embedded in the battery case 20, and thus the capacity of the battery. Results in a decrease. That is, as shown in Figure 3, the distance (L ₁ ) between the top surface of the electrode assembly 30 and the insulating film 80 is very large, it is inevitable to reduce the size of the electrode assembly 30 by such a distance.

In addition, when the battery falls to its upper end, i.e., the positive lead 60, or when a physical external force is applied to the upper end of the battery, the electrode assembly 30 moves to the upper end of the inner surface of the battery case 20, or Since the negative electrode of the electrode assembly 30 may be crushed to contact the positive electrode tab 42 or the positive electrode lead 61 and cause an internal short circuit, the safety of the battery is greatly reduced.

Therefore, there is a high need for a technology that can solve the capacity and safety problems of the battery according to the V-forming site.

The present invention aims to solve the problems of the prior art as described above and the technical problems that have been requested from the past.

Specifically, it is an object of the present invention to provide a secondary battery that can further improve safety by preventing an internal short circuit caused by the movement of the electrode assembly when a drop or external shock is applied.

Still another object of the present invention is to provide a secondary battery having a higher capacity than the same standard by utilizing the internal space of the battery case to the maximum.

A secondary battery according to the present invention for achieving this purpose is a secondary battery in which an electrode assembly having a structure in which a plurality of electrode plates are stacked and interconnecting electrode tabs thereof with a separator interposed therebetween is embedded in a battery case. The electrode assembly is inverted and installed so that the interconnections of the electrode tabs are located at the bottom of the inner surface of the battery case. It is comprised by being electrically connected to the electrode lead.

Therefore, in the secondary battery according to the present invention, the connection parts between the electrode tabs are placed in close contact with the bottom of the inner surface of the battery case, and the connection parts between the upper electrode tabs and the electrode leads are located in close contact with the top of the inner surface of the battery case. By minimizing the space for the formation of the battery case, the capacity of the battery case can be made larger than that of the same standard, and the connection parts are separated from each other so as to be in close contact with the upper and lower ends of the inner surface of the battery case, thereby suppressing the movement of the electrode assembly. When applying an external force such as an impact, it is possible to ensure more excellent safety.

The electrode assembly is not particularly limited as long as it is a structure that connects a plurality of electrode tabs to form an anode and a cathode, and preferably includes a stack type structure and a stack / fold type structure. 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, which are described in the context of the present invention. Incorporated by reference.

In one preferred embodiment, the upper electrode tab may be formed on at least one positive electrode plate and at least one negative electrode plate among the electrode plates constituting the electrode assembly, more preferably one positive electrode plate and the negative electrode plate. Only may be formed respectively. If the upper electrode tabs are formed on at least one of the positive electrode plate and the negative electrode plate, a separate process for connecting the upper electrode tabs should be added, and the volume increases when the upper electrode tabs are in close contact with each other. This is because the space occupied by becomes wider. Therefore, it is particularly preferable that the electrode assembly includes one anode plate and one cathode plate each having two electrode tabs formed thereon.

In addition, in the present invention, the upper electrode tab may be configured to be somewhat larger than other electrode tabs so that the upper electrode tab may serve as an electrode lead by itself without being connected to a separate electrode lead. In this case, a separate process for electrical connection between the upper electrode tab and the electrode lead can be omitted, and many problems due to the weakness of the connection portion can be solved.

Hereinafter, for convenience of description, the electrode tabs other than the upper electrode tab connected to the electrode lead, that is, the electrode tabs for electrically connecting the electrode plates are referred to as lower electrode tabs.

The lower electrode tabs may be interconnected in various ways, and may be more stably connected by ultrasonic welding.

In general, since the electrode assembly uses a separator having a larger size than the anode and the cathode in order to prevent a short circuit, the outer circumferential surface of the electrode assembly is substantially surrounded by separators extending longer than the anode and the cathode. Therefore, even if the portions where the electrode tabs are interconnected are bent and adhered to the bottom surface of the electrode assembly, a short circuit is not caused.

In the present invention, in order to further reduce the possibility of a short circuit due to such bending and close contact at the connection portions of the lower electrode tabs, the separator size of the electrode assembly is larger than that of a conventional electrode assembly, or the lower end is made of an insulating member such as an insulating film. The connection portion of the electrode tab may be applied in advance and then bent to be in close contact with the bottom surface of the electrode assembly.

As described above, since the connecting portion between the lower electrode tabs and the connecting portion between the upper electrode tab and the electrode lead are positioned in close contact with the lower and upper ends of the electrode assembly, respectively, the dead space does not exist or at least the dead space as a whole. By minimizing the size, a battery having a compact structure can be completed, and the upper and lower ends of the electrode assembly are in close contact with the inner surface of the battery case, respectively, to prevent the electrode assembly from moving even when an external force is applied.

The battery according to the present invention can be preferably used in a so-called lithium ion polymer battery in which the lithium electrolyte is impregnated in the electrode assembly in the form of a gel.

In addition, the battery according to the present invention can be preferably applied to a pouch type battery in which an electrode assembly is built in a pouch type case of a laminate sheet, specifically, an aluminum laminate sheet, including a metal layer and a resin layer.

Hereinafter, although described with reference to the drawings according to an embodiment of the present invention, this is for easier understanding of the present invention, the scope of the present invention is not limited thereto.

4 is an exploded perspective view schematically showing a secondary battery according to an embodiment of the present invention.

Referring to FIG. 4, the secondary battery 100 includes lower positive electrode tabs 330, 331, 332... And lower negative electrode tabs 340, 341, 342. 301 and the upper negative electrode tab 302 are welded to the positive electrode lead 400 and the negative electrode lead 401, respectively, and the battery case 200 that can accommodate the electrode assembly 300 consist of.

The electrode assembly 300 includes a positive electrode plate 310 having a top positive electrode tab 301 and a bottom positive electrode tab 330 protruding from the top layer thereof, and a top negative electrode tab 302 and a bottom negative electrode tab 340 protruding from each other. Each one of the negative electrode plate 320 is included. The specific structure of the electrode assembly can be more easily confirmed in FIG. 5 in which an exploded perspective view thereof is schematically shown.

Referring to FIG. 5, the electrode assembly 300 includes one positive electrode plate 310 and a top negative electrode tab 302 and a bottom negative electrode tab 340 protruding from the upper positive electrode tab 301 and the lower positive electrode tab 330. One protruding cathode plate 320, and a plurality of anode plates 311, 312... Which protrude only the lower anode tabs 331, 332..., And the lower cathode tabs 341, 342. A plurality of negative electrode plates 321 and 322 are manufactured by sequentially stacking using the separator 350.

Referring back to FIG. 4, the lower positive electrode tabs 331, 332... And the lower negative electrode tabs 341, 342... Are in close contact with the bottom surface 360 of the electrode assembly 300 in an ultrasonically fused state. In this case, the lower positive electrode tabs 331, 332... And the lower negative electrode tabs 341, 342... Are connected to the lower surface 360 of the electrode assembly 300 to prevent short circuits. , 332... And the lower negative electrode tabs 341, 342..., And the lower negative electrode tabs 341, 342.

While the electrode assembly 300 is mounted on the accommodating portion 210 of the battery case 200, the upper positive electrode tab 301 and the upper negative electrode tab 302 are in close contact with the upper end of the battery case 200 without undergoing a bending process. The anode plate 310 and the cathode plate 320, on which two electrode tabs 301, 330; 302, 340 are formed, are positioned on the uppermost layer of the electrode assembly 300 so as to be immediately located at the site.

In addition, although not shown in the drawing, the upper positive electrode tab 301 and the upper negative electrode tab 302 are not connected to the positive lead 400 and the negative lead 401, which partially protrude outwards, respectively, and are the battery case itself. It may also protrude directly to the outside of the 200.

FIG. 6 schematically illustrates a front perspective view of the assembled state of the secondary battery of FIG. 4.

Referring to FIG. 6, the secondary battery 100 greatly reduces the distance L ₂ between the top surface of the electrode assembly 300 and the insulating film 420, thereby comparing the electrode assembly with the same standard of the battery case 200. The size of the battery can be increased by making the size 300 larger. In addition, since the secondary battery 100 does not have a space in which the electrode assembly 300 can move inside the battery case 200, the secondary battery 100 may further secure safety against short circuits during dropping and external impact.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the following Examples are provided to illustrate the present invention, and the scope of the present invention is not limited thereto.

Example 1

95% by weight of LiCoO ₂ , 2.5% by weight of Super-P (conductor) and 2.5% by weight of PVdF (binder) were added to NMP (N-methyl-2-pyrrolidone) as a cathode active material to prepare a cathode mixture slurry. 95% by weight of artificial graphite, 1% by weight of Super-P (conductive agent) and 4% by weight of PVdF (binder) were added to NMP as a solvent to prepare a negative electrode mixture slurry, which was applied to aluminum foil and copper foil, respectively. .

The aluminum foil and the copper foil were cut into a plurality of plates each having electrode tabs formed on only one side and one plate having electrode tabs formed on both sides thereof, as shown in FIG. . Then, using Celgard ^TM (TONEN) as a separator, an electrode assembly was manufactured by sequentially stacking the positive electrode plate and the negative electrode plate having electrode tabs formed on both sides thereof, and sequentially stacking the remaining positive electrode plate and the negative electrode plate. . After mounting the electrode assembly in the pouch type battery case in an inverted state, as shown in Figure 4, the electrolyte was injected to complete the battery.

Comparative Example 1

Except for fabricating an electrode assembly using a positive electrode plate and a negative electrode plate with an electrode tab formed on one side and the same as in FIG. To complete.

Experimental Example 1

In each of the 20 prepared batteries in Example 1 and Comparative Example 1, the battery drop experiment was repeated 50 times in the direction of the electrode lead protruding direction of the battery at a height of 1.5 m, and then confirmed whether the short circuit. The results are shown in Table 1 below.

TABLE 1

As shown in Table 1, the cells of Example 1 according to the present invention did not cause a short circuit in all 20 cells in the front drop experiment. That is, since no empty space exists between the upper end of the inner surface of the battery case and the electrode assembly, a short circuit due to the movement of the electrode assembly does not occur when the battery falls. On the other hand, the batteries of Comparative Example 1 were short-circuited in many batteries.

In addition, in terms of the capacity of the battery, when the battery case of the same size is used, the battery of Example 1 can increase the size of the electrode plate to which the active material is applied by about 10% compared to the battery of Comparative Example 1 Confirmed. Therefore, the capacity of the battery can be increased by that amount.

As described above, the secondary battery according to the present invention can further improve safety by preventing an internal short circuit caused by the movement of the electrode assembly when a drop or external shock is applied, thereby making the same use by making the most of the internal space of the battery case. It has the advantage of having a high capacity compared to the standard.

Those skilled in the art to which the present invention pertains will be able to perform various applications and modifications within the scope of the present invention based on the above contents.

Claims (8)

A secondary battery in which a stack type or a stack / fold type electrode assembly, which is a structure for stacking a plurality of electrode plates and interconnecting electrode tabs with a separator interposed therebetween, is embedded in a battery case. The electrode assembly is inverted and installed so as to be positioned at the lower end of the inner surface of the battery case, and the upper electrode tab is formed on only one of the positive electrode plate and the negative electrode plate of the plurality of electrode plates constituting the electrode assembly while the electrode assembly is inverted. Secondary battery, characterized in that is electrically connected to the electrode lead on the top of the battery case. delete delete The method of claim 1, wherein in the inverted state, the lower electrode tabs of the electrode assembly are electrically connected by ultrasonic welding and the electrode tab connection portion is coated with an insulating member, and then bending is performed to be in close contact with the lower surface of the electrode assembly. A secondary battery characterized by. The secondary battery according to claim 4, wherein an electrode film connection portion is wrapped with an insulating film as the insulating member. The secondary battery of claim 1, wherein the secondary battery is a lithium ion polymer battery. The secondary battery according to claim 1, wherein the battery case is a pouch type case of a laminate sheet including a metal layer and a resin layer. The secondary battery of claim 7, wherein the sheet is an aluminum sheet.

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