KR20070025687A - Lithium rechargeable battery - Google Patents

Abstract

Provided is a lithium secondary battery, whose casing for housing an electrode assembly shows high space utilization efficiency so that the battery has an improved capacity. The lithium secondary battery(100) comprises: an electrode assembly including a cathode plate and an anode plate disposed opposite to each other and a separator interposed between the cathode plate and the anode plate; and a casing(300) for housing the electrode assembly, wherein the casing has a larger thickness at the upper part thereof than that of the lower part thereof. Accordingly, the electrode assembly has a larger thickness at the upper part thereof than that of the lower part thereof.

Description

Lithium rechargeable battery

1 is a perspective view of a lithium secondary battery according to an embodiment of the present invention.

2A-2B are right side views of FIG. 1

3A is a perspective view of an electrode assembly according to an embodiment of the present invention

3B is a right side view of FIG. 3A

4 is a perspective view of an electrode plate according to a first embodiment of the present invention;

5 is a perspective view of an electrode plate according to a second embodiment of the present invention;

<Description of Symbols for Main Parts of Drawings>

100-lithium secondary battery 200-electrode assembly

210-Positive Tab 220-Negative Tab

230, 230 '-Bipolar Plate 240-Separator

250-Negative Plate 300-Case

400-Cap Assembly 410-Electrode Terminal

420-Electrolytic solution inlet 540, 540 '-Positive electrode current collector

545, 545 '-Anode Plain 550, 550'-Anode Active Material Layer

The present invention relates to a lithium secondary battery, and more particularly, the upper thickness of the square or pouch type lithium secondary battery case is formed to be thicker than the lower thickness to manufacture a structure that fits the cell phone battery case, and thus the upper thickness of the electrode assembly By forming a thicker than the lower thickness relates to a lithium secondary battery for reducing the waste of space and improve the capacity of the battery.

Lithium secondary batteries include lithium metal secondary batteries and lithium ion secondary batteries. In particular, lithium-ion secondary batteries are extremely lightweight and have a higher energy density per weight than conventional batteries, and are characterized by high output voltage and low self-discharge rate, and heavy metals such as cadmium (Cd) and mercury (Hg) that pollute the environment. It is environmentally friendly because it does not use. Therefore, it is widely used in small electronic products such as laptops, camcorders and mobile phones.

Lithium ion secondary batteries are divided into cylindrical, rectangular, and pouch types according to their shape. In addition, depending on the type of electrolyte used, it is divided into a lithium ion secondary battery using a liquid electrolyte and a lithium ion polymer battery using a solid polymer electrolyte. Lithium ion polymer batteries are divided into solid and gel types.

The lithium ion secondary battery is typically formed by including an electrode assembly in which a positive electrode plate, a negative electrode plate, and a separator are wound, a case accommodating the electrode assembly, and a cap assembly sealing the case in the case of a cylindrical or rectangular shape. The pouch type is sealed by applying high temperature and high pressure to one side of the pouch instead of the cap assembly. After forming the bare cell, a battery pack is formed by mounting a protection circuit and sealing the bare cell and the protection circuit with a resin or the like.

On the other hand, in the case of a square or pouch type is often used for power of the mobile phone. In the cell phone battery case, there is a structure in which the thickness of the upper part is thicker than the thickness of the lower part in consideration of the external appearance of the cell phone. Here, the upper part is defined as the cap assembly direction in the case of a square, and the opposite direction of the folded side without sealing the case in the case of a pouch type. In this case, the bare cell of the conventional rectangular or pouch type battery has the same thickness of upper and lower parts, and when the bare cell is inserted into the cell phone battery case, a predetermined space of the upper part of the battery case becomes empty. This is not desirable for miniaturization because of the wasted space inside the battery case, and there is also a problem that the capacity of the battery is inefficient.

The present invention is to solve the problems of the conventional lithium secondary battery described above, by adjusting the thickness of the upper and lower parts of the bare cell to fit exactly inside the mobile phone battery case so that there is no wasted space inside the battery case, accordingly An object of the present invention is to provide a lithium secondary battery having an increased capacity by increasing an upper thickness of an electrode assembly inserted into a bare cell.

A lithium secondary battery of the present invention for achieving the above object is a lithium secondary battery comprising an electrode assembly having a positive electrode plate and a negative electrode plate facing each other, a separator interposed between the positive electrode plate and the negative electrode plate, a case accommodating the electrode assembly. In the case, the thickness of the upper portion is characterized in that formed thicker than the thickness of the lower portion. At this time, the electrode assembly may be formed thicker than the thickness of the upper portion.

In addition, the positive electrode active material layer formed on the positive electrode plate and the negative electrode active material layer formed on the negative electrode plate may be formed so that the thickness of the upper portion than the thickness of the lower portion. In addition, the horizontal length of the sides forming the positive electrode and the negative electrode plate perpendicular to the winding axis may be formed longer than the length of the lower portion. In addition, the longitudinal length, which is a side parallel to the winding axis of the sides constituting the positive electrode plate and the negative electrode plate may be formed such that the outer side of the electrode assembly is less than or equal to the inner side.

In addition, the case may have a thickness of 0.1 to 0.4 mm thicker than the thickness of the upper portion. In addition, the lithium secondary battery may be a square or pouch type.

In addition, the shape of the side of the case may be trapezoidal.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, here, for convenience of description, description will be made with respect to the square lithium secondary battery. Therefore, the present invention is not limited to the case of the rectangular lithium secondary battery, and may be applied to other types of lithium secondary batteries. In addition, the electrode plate according to the embodiment of the present invention will be described based on the positive electrode plate. Therefore, of course, the present invention can be applied to the negative electrode plate as well.

1 is a perspective view of a lithium secondary battery according to an embodiment of the present invention. 2A to 2A are right side views of FIG. 1. 3A is a perspective view of an electrode assembly according to an embodiment of the present invention. 3B is a right side view of FIG. 3A. 4 is a perspective view of an electrode plate according to a first embodiment of the present invention. 5 is a perspective view of an electrode plate according to a second embodiment of the present invention.

Lithium secondary battery 100 according to an embodiment of the present invention, the electrode assembly 200, the case 300 for accommodating the electrode assembly 200, the cap assembly 400 for sealing the case 300; Pouch type does not exist).

Referring to FIG. 3A, the electrode assembly 200 includes a positive electrode plate 230 and a negative electrode plate 250 facing each other, and a separator 240 interposed between the positive electrode plate 230 and the negative electrode plate 250. . Referring to FIG. 3B, the electrode assembly 200 is formed to have a thickness greater than that of the lower portion. The reason is detailed below.

Referring to FIG. 4, the positive electrode plate 230 includes a positive electrode current collector 540 and a positive electrode active material layer 550 formed on the positive electrode current collector 540. At the end of the cathode current collector 540, a cathode non-coating portion 545, which is a portion where the cathode active material layer 550 is not formed, is formed. The positive electrode non-coating portion 545 is formed with a positive electrode tab 210 electrically connected to the external circuit so that electrons collected in the positive electrode current collector 540 flow into the external circuit. The positive electrode current collector 540 is formed of aluminum (Al) having excellent electrical conductivity, and the positive electrode tab 210 is also formed of aluminum (Al). The positive electrode tab 210 is typically welded to the positive electrode non-coating portion 545 by ultrasonic welding. The cathode active material layer 550 is formed by mixing a conductive material and a binder with a lithium metal oxide such as lithium cobalt (LiCoO 2) so that lithium ions may be occluded or desorbed. In addition, after the positive electrode tab 210 is welded to the positive electrode plain portion 545, a tape (not shown) is attached to prevent the positive electrode tab 210 from being separated.

According to the first exemplary embodiment of the present invention (see FIG. 4), the positive electrode plate 230 is formed such that the thickness of the cathode active material layer 550 is thicker than the thickness of the lower portion. As described above, an upper portion of the positive electrode plate 230 is a direction in which the cap assembly 400 is located, and a lower portion of the positive electrode plate 230 is a direction in which a lower surface of the case 300 is located. The thickness of the upper portion of the cathode active material layer 550 is formed to be thicker so that the thickness of the upper portion of the electrode assembly 200 is thicker than the thickness of the lower portion when the anode plate 230 is wound. Since the upper portion of the cathode active material layer 550 is formed thick, the space for occluding and desorbing lithium ions also increases, resulting in an increase in battery capacity.

According to the second embodiment of the present invention (see FIG. 5), the positive electrode plate 230 ′ is formed to have a longer horizontal length than the lower horizontal length. Here, the horizontal length refers to a side perpendicular to the winding axis of the sides constituting the bipolar plate 230 ′. In addition, the longitudinal length of the positive electrode plate 230 ′ is formed to decrease toward the outermost side from the core side of the electrode assembly 200. Here, the vertical length refers to the side parallel to the winding axis of the sides constituting the positive plate. As the upper horizontal length is formed to be long, the horizontal length of the upper part of the positive electrode active material layer 550 'coated on the positive electrode current collector 540' is also formed to be long. As a result, the longitudinal length of the positive electrode plate 230 ′ decreases toward the outermost portion of the electrode assembly 200. As such, the horizontal length of the positive electrode plate 230 ′ is long, so that the thickness of the upper portion of the electrode assembly 200 is thicker than the lower thickness when the positive electrode plate 230 ′ is wound. Since the upper portion of the positive electrode active material layer 550 ′ is formed to be thick, the space in which lithium ions can be occluded and desorbed also increases, resulting in an increase in battery capacity.

 The negative electrode plate 250 includes a negative electrode current collector for collecting electrons generated by a chemical reaction, and a negative electrode active material layer formed on the negative electrode current collector. An anode non-coating portion in which the anode active material layer is not formed is formed at an end of the anode current collector. The negative electrode non-coating portion has a negative electrode tab 220 electrically connected to an external circuit so that electrons collected in the negative electrode current collector may flow to an external circuit. A tape is attached on the negative electrode tab 220 so that the negative electrode tab 220 does not leave the negative electrode non-coating portion. The negative electrode current collector is usually formed of copper (Cu) or nickel (Ni) having excellent electrical conductivity, and the negative electrode tab is usually formed of nickel (Ni). The negative electrode active material layer is formed by mixing a conductive material and a binder in a carbon material so that lithium ions can be occluded and desorbed.

According to the first embodiment of the present invention, the negative electrode plate 250, as in the positive electrode plate 230, is formed such that the thickness of the negative electrode active material layer is thicker than the thickness of the lower portion. Since the upper portion of the negative electrode active material layer is formed to be thick, the space for occluding and desorbing lithium ions is also increased, resulting in an increase in battery capacity.

According to the second embodiment of the present invention, the negative electrode plate 250 is formed to have a longer horizontal length than the lower horizontal length similarly to the positive electrode plate 230 ′. In this way, the horizontal length of the negative electrode plate is formed to be longer, the thickness of the upper electrode assembly 200 is formed thicker than the lower thickness when the negative electrode plate is wound. Since the upper portion of the anode active material layer is formed thick, the space for lithium ions to occlude and desorb is also increased, resulting in an increase in battery capacity.

The separator 240 is interposed between the positive electrode plate 230 and the negative electrode plate 250 to prevent shorts that may occur between the positive electrode plate 230 and the negative electrode plate 250. The separator 240 is usually formed of thermoplastic resin such as polyethylene (PE), polypropylene (PP), and the surface thereof has a porous membrane structure. The porous membrane structure becomes an insulating film when the separator 240 melts when the temperature rises inside the battery and becomes close to the melting point of the thermoplastic resin. This phenomenon is called sealing or shutting down the separator. By switching to the insulating film as described above, the movement of lithium ions between the positive electrode plate 230 and the negative electrode plate 250 is blocked, and no further current flows, thereby stopping the temperature increase in the battery.

The case 300 is formed of a metal can in the case of a rectangular lithium secondary battery and a multilayered film pouch in the case of a pouch-type lithium secondary battery.

First, the case 300 of a rectangular lithium secondary battery will be described. Referring to FIG. 1, the case 300 includes a front surface and a rear surface of a substantially rectangular shape, a side surface of a substantially trapezoidal shape, and a bottom surface of a substantially rectangular shape, and an upper portion thereof is opened. The electrode assembly 200 is inserted into the opened upper portion. In addition, an electrolyte solution is impregnated between the electrode assemblies 200 to enable the movement of lithium ions. The material of the case 300 is mainly light aluminum (Al). The upper portion of the case 300 is sealed by the cap assembly 400, the leakage of the electrolyte is prevented. The case 300 has a thickness of an upper portion formed thicker than a thickness of a lower portion. Preferably, the case 300 has a thickness of about 0.1 mm to about 0.4 mm thicker than the thickness of the lower portion. This is because the case size of the mobile phone battery is approximately 0.1 to 0.4 mm thicker than the thickness of the lower side. However, in the present invention, the numerical value is not limited to such a thickness difference, and of course, it may be formed in various thickness differences according to the specifications of the battery case. Therefore, the shape of the side of the surface forming the thickness of the case 300 becomes a substantially trapezoidal shape. Depending on the shape of the cell phone battery case may be a general trapezoidal shape (see Fig. 2a), or may be a rectangular trapezoidal shape (see Fig. 2b).

Next, the case of the pouch type lithium secondary battery is demonstrated. In the case of a pouch type, a multilayer film pouch composed of a foil and at least one polymer film covering the foil is used instead 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 the metal forming the foil in the multilayer film pouch. The polymer film forming the inner layer of the pouch film protects the metal foil from the electrolyte and prevents a short circuit between the positive electrode plate, the negative electrode plate, and the electrode tabs. In the case of the pouch type, the thickness of the upper part of the case is formed thicker than that of the lower part as in the case of the square type.

The cap assembly 400 includes a cap plate, an insulation plate, a terminal plate, and an electrode terminal 410. The cap assembly 400 is combined with a separate insulating case is coupled to the upper opening of the case 300 to seal the case 300. However, the cap assembly 400 does not exist in the pouch type lithium secondary battery. In the pouch type, the edges of the three sides except for one side formed by the folded portion of the pouch film form a top and a bottom of the pouch by folding the middle in the longitudinal direction of one side of the rectangular pouch film which is usually formed integrally. The lower portion is formed with a groove that can accommodate the battery cell through a press (press) process or the like. The upper and lower portions of the pouch film are sealed by heating and pressing in a state where the upper and lower portions of the four sides around the lower groove are in close contact.

As described above, the present invention is not limited to the specific preferred embodiments described above, and any person having ordinary skill in the art to which the present invention pertains without departing from the gist of the present invention claimed in the claims. Various modifications are possible, of course, and such changes are within the scope of the claims.

According to the lithium secondary battery according to the present invention, the upper thickness of the square or pouch type lithium secondary battery case is formed thicker than the lower thickness to manufacture a structure to fit the cell phone battery case, accordingly the upper thickness of the electrode assembly than the lower thickness By forming a thick, there is an effect that can reduce the wasted space in the battery case when the existing bare cell is inserted, and can also improve the capacity of the battery by the thickened electrode assembly.

Claims (8)

In a lithium secondary battery comprising an electrode assembly having a positive electrode plate and a negative electrode plate facing each other, a separator interposed between the positive electrode plate and the negative electrode plate, a case for accommodating the electrode assembly, The case is a lithium secondary battery, characterized in that the thickness of the upper portion is formed thicker than the thickness of the lower portion. The method of claim 1, The electrode assembly is a lithium secondary battery, characterized in that the thickness of the upper is formed thicker than the thickness of the lower. The method of claim 2, The positive electrode active material layer formed on the positive electrode plate and the negative electrode active material layer formed on the negative electrode plate is a lithium secondary battery, characterized in that the thickness of the upper portion is formed thicker than the thickness of the lower portion. The method of claim 2, Lithium secondary battery, characterized in that the horizontal length of the sides forming the positive axis and the negative electrode plate of the sides forming the vertical axis is longer than the length of the lower portion. The method of claim 4, wherein The vertical length of the sides of the positive electrode plate and the negative electrode plate parallel to the winding axis is formed so that the outer side of the electrode assembly is less than or equal to the inner side portion. The method of claim 1, The case is a lithium secondary battery, characterized in that the thickness of the upper portion formed by 0.1 ~ 0.4mm thicker than the thickness of the lower. The method of claim 1, The lithium secondary battery is a lithium secondary battery, characterized in that the square or pouch type. The method of claim 1, Side shape of the case is a lithium secondary battery, characterized in that the trapezoid.

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