KR100778998B1 - Lithium rechargeable battery - Google Patents

Abstract

The present invention relates to a lithium secondary battery, and more particularly, to a surface of an insulating plate having a shape that blocks almost the entire upper and lower parts of a battery due to its geometric structure, or a surfactant for coating a surface of the electrolyte with a polymer material or reducing the surface tension of the electrolyte. By lowering the exclusive tendency of the surface of the insulating plate to the electrolyte solution, the electrolyte flowability inside the battery increases, so that the impregnation rate of the electrolyte solution can be improved and the impregnation rate of the electrolyte solution is improved. The present invention relates to a lithium secondary battery capable of improving productivity by reducing an impregnation process time taking up a portion.

Lithium Secondary Battery, Insulation Plate, Impregnation, Surfactant

Description

Lithium rechargeable battery

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

2 is a cross-sectional view taken along the line A-A of FIG.

3A is a plan view of a phase insulating plate according to an embodiment of the present invention.

FIG. 3B is a cross-sectional view taken along the line B-B in FIG. 3A

Figure 4a is a plan view of a lower insulating plate according to an embodiment of the present invention

4B is a cross-sectional view taken along the line C-C in FIG. 4A

<Description of Symbols for Main Parts of Drawings>

100-cylindrical lithium secondary battery 200-electrode assembly

210-Positive Plate 215-Positive Tab

220-Negative Plate 225-Negative Tab

230-Separator 241-Phase Insulation Plate

242-Hole 243-Hole for Positive Tab

244-Hollow 245-Lower Insulation Plate

246-Holes for Cathode Tab 249-Coating Layer

300-Can 400-Cap Assembly

The present invention relates to a lithium secondary battery, and more particularly, to a lithium secondary battery which improves the impregnation of an electrolyte by coating a surface of the insulating plate with a material familiar with the electrolyte while using an existing insulation plate made of a material that is not familiar with the electrolyte. It relates to a battery.

In general, as the light weight and high functionality of portable wireless devices such as a video camera, a portable telephone, a portable computer, and the like progress, a lot of researches have been conducted on secondary batteries used as driving power. Such secondary batteries include, for example, nickel cadmium batteries, nickel hydrogen batteries, nickel zinc batteries, and lithium secondary batteries. Among them, lithium secondary batteries are rechargeable, compact, and large-capacity, and are widely used in advanced electronic devices because of their high operating voltage and high energy density per unit weight. These portable electric / electronic devices have a battery pack that can be operated in a place where no separate power source is provided. The built-in battery pack includes at least one battery therein for outputting a predetermined level of voltage for driving the portable electric / electronic device for a period of time.

In view of economical aspects, the battery pack employs a secondary battery capable of charging and discharging. Representative secondary batteries include lithium secondary batteries such as nickel-cadmium batteries, nickel-hydrogen batteries, lithium batteries and lithium ion batteries.

In particular, the lithium secondary battery has an operating voltage of 3.6 V, which is three times higher than that of a nickel-cadmium battery or a nickel-hydrogen battery, which is widely used as a power source for portable electronic equipment, and is rapidly expanding in terms of high energy density per unit weight. It is a trend.

Such lithium secondary batteries mainly use lithium-based oxides as positive electrode active materials and carbon materials as negative electrode active materials. In general, the battery is classified into a liquid electrolyte battery and a polymer electrolyte battery according to the type of electrolyte. A battery using a liquid electrolyte is called a lithium ion battery, and a battery using a polymer electrolyte is called a lithium polymer battery. In addition, the lithium secondary battery is manufactured in various shapes, and typical shapes include cylindrical, square, and pouch types.

Typically, the cylindrical lithium secondary battery is positioned between a positive electrode plate coated with a positive electrode active material, a negative electrode plate coated with a negative electrode active material, and between the positive electrode plate and the negative electrode plate to prevent a short and to allow only movement of lithium ion. An electrode assembly in which the separator is wound in a substantially cylindrical shape, a cylindrical case accommodating the electrode assembly, and an electrolyte solution injected into the cylindrical case to allow lithium ions to move.

This cylindrical lithium secondary battery is manufactured as follows.

First, a cathode electrode plate coated with the cathode active material and a cathode electrode plate connected with a cathode active material, an anode electrode plate coated with a cathode active material, an anode tab connected with a separator, and a separator are stacked, and then wound in a substantially cylindrical shape to prepare an electrode assembly. Then, the substantially cylindrical electrode assembly is accommodated in the cylindrical case to prevent the electrode assembly from being separated, the electrolyte is injected into the cylindrical case, and then sealed to complete the cylindrical lithium secondary battery.

Meanwhile, before inserting the electrode assembly into the cylindrical case, a lower insulating plate is inserted to insulate the electrode assembly from the cylindrical case. In addition, after the electrode assembly is inserted, a phase insulating plate is inserted to insulate the electrode assembly from the cap assembly before sealing.

In addition, in the case of the rectangular lithium secondary battery, an insulating case for supporting the cap assembly and insulating between the terminal plate and the electrode assembly and a lower insulating plate for insulating between the rectangular case and the electrode assembly are inserted.

Since these insulating plates are usually made of polyethylene (PE) or polypropylene (PP), they are not familiar with the electrolyte solution. Therefore, the electrolyte solution is an obstacle to sufficient impregnation of the electrode assembly. In addition, as the capacity of the battery increases, the electrode assembly also increases in density, resulting in an increase in the outer diameter of the electrode assembly. When the outer diameter of the electrode assembly is increased, the space between the cylindrical case and the electrode assembly is reduced, which makes the structure more difficult to impregnate the electrolyte.

The present invention is to solve the problems of the conventional lithium secondary battery described above, by coating a material of a material easy to impregnate the electrolyte on the surface of the upper insulating plate or insulating case and the lower insulating plate of the lithium secondary battery, In the case of the electrode assembly, an object of the present invention is to provide a lithium secondary battery with improved electrolyte impregnation.

Lithium secondary battery of the present invention for achieving the above object, an electrode assembly, a case for accommodating the electrode assembly, a cap assembly for sealing the case, located between the electrode assembly and the case or between the electrode assembly and the cap assembly. In the lithium secondary battery comprising an insulating plate, at least one surface of the insulating plate is characterized in that the wettability and spreadability to the electrolyte solution is coated with a material friendly to the electrolyte solution. In this case, the material friendly to the electrolyte may be a polymer material. In this case, the polymer material may be polyvinyl difluoride (PVdF). In this case, the polyvinyl difluoride (PVdF) is preferably any one of PVdF 761, PVdF 2801, a mixture of PVdF 761 and PVdF 2801.

In addition, the polymer material may include any one of an ester group and a carboxylic group.

In addition, the material familiar with the electrolyte may be a surfactant. At this time, the surfactant may be BRIJ®.

In addition, the insulating plate may be made of polyethylene (PE) or polypropylene (PP). In addition, the lithium secondary battery may have a cylindrical shape having a phase insulating plate. In this case, the phase insulation plate may have a plurality of holes formed on its surface.

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

1 is a perspective view of a cylindrical lithium secondary battery according to an exemplary embodiment of the present invention, and FIG. 2 is a sectional view taken along the line A-A of FIG. However, here, the description has been developed as a cylindrical lithium secondary battery for convenience, but the present invention may be applied to the case of a rectangular lithium secondary battery.

1 and 2, the cylindrical lithium secondary battery 100 includes an electrode assembly 200, a cylindrical can 300 containing the electrode assembly 200 and an electrolyte, and an upper portion of the cylindrical can 300. It is formed to include a cap assembly 400 for sealing the cylindrical can 300 to flow the current generated in the electrode assembly 200 to an external device.

Referring to FIG. 2, the electrode assembly 200 includes a positive electrode plate 210 coated with a positive electrode active material layer on a surface of a positive electrode current collector, a negative electrode plate 220 coated with a negative electrode active material layer on a surface of a negative electrode current collector, and the positive electrode plate. A separator 230 positioned between the 210 and the negative electrode plate 220 to electrically insulate the positive electrode plate 210 and the negative electrode plate 220 is wound and formed in a jelly-roll shape.

Although not shown in detail in the drawing, the positive electrode plate 210 includes a positive electrode current collector made of a thin metal plate having excellent conductivity, for example, aluminum (Al) foil, and a positive electrode active material layer coated on both surfaces thereof. have. Both ends of the positive electrode plate 210 are provided with a positive electrode current collector region, that is, a positive electrode non-coating portion, in which a positive electrode active material layer is not formed. One end of the positive electrode non-coating portion is generally formed of aluminum (Al), and the positive electrode tab 215 protruding a predetermined length to the upper portion of the electrode assembly 200 is bonded.

In addition, the negative electrode plate 220 includes a negative electrode current collector made of a conductive metal thin plate, for example, copper (Cu) or nickel (Ni) foil, and a negative electrode active material layer coated on both surfaces thereof. Both ends of the negative electrode plate 220 are provided with a negative electrode current collector region, that is, a negative electrode non-coating portion, in which a negative electrode active material layer is not formed. One end of the negative electrode non-coating portion is generally formed of nickel (Ni), and the negative electrode tab 225 protruding a predetermined length to the lower portion of the electrode assembly 200 is bonded. In addition, the upper and lower portions of the electrode assembly 200 may further include insulating plates 241 and 245 for preventing contact with the cap assembly 400 or the cylindrical can 300, respectively.

2 and 3A, an upper insulation plate 241 is positioned between the cap assembly 400, in particular the safety vent 410 and the top of the electrode assembly 200. The phase insulation plate 241 prevents a short circuit that may occur between the electrode assembly 200 and the cap assembly 400 including the safety tab 410 electrically connected to the electrode tab, for example, the positive electrode tab 215. do. Referring to FIG. 3A, the phase insulating plate 241 includes a hole 242 serving as a passage through which the injected electrolyte is settled and a hole for positive electrode tab serving as a passage through which the electrode tab, for example, the positive electrode tab 215, exits. 243 and a hollow 244 in contact with one end of the center pin are formed. In addition, referring to FIG. 3B, the phase insulating plate 241 is formed with a coating layer 249 coated with a thin polymer material or a surfactant.

2 and 4A, the lower insulating plate 245 is positioned between the bottom plate 320 of the can and the lower portion of the electrode assembly 200. The lower insulating plate 245 prevents a short circuit that may occur between the electrode 300 and the can 300 including the lower plate 320 electrically connected to the electrode tab, for example, the negative electrode tab 225. . Referring to FIG. 4A ′, the lower insulating plate 245 includes a hole 246 for a negative electrode tab serving as a passage through which an electrode tab, for example, a negative electrode tab 225 exits, and a hollow 247 in contact with one end of a center pin. ) Is formed. In addition, referring to FIG. 4B, the lower insulating plate 245 is formed with a coating layer 249 coated with a thin polymer material or a surfactant.

When the negative electrode tab 225 is formed at the outermost portion of the electrode assembly 200, the negative electrode tab hole 246 may not be formed. In this case, the lower insulating plate 245 is positioned under the electrode assembly 200, the negative electrode tab 225 is bent at approximately right angles, and then the negative electrode tab 225 is welded to the bottom surface 320 of the can. .

The material of the upper insulating plate 241 and the lower insulating plate 245 is typically a polyolefin resin such as polyethylene (PE), polypropylene (PP), polyimide (PI), or the like. Polyethylene is light due to its low density, soft and stretchy due to insufficient molecular arrangement, and has a small tensile strength but high impact resistance. Therefore, it is easy to process and easy to use. In addition, since it is composed of only CH2, electrical insulation is excellent, and as shown in the structural formula, it is also excellent as a high frequency insulation material because of its symmetry around the carbon (C) chain.

Polypropylene occurs with ethylene when decomposing naphtha. It has an isotatic structure, and thus the methyl groups are arranged in the same direction as the structural formula. The crystallinity is large before molding, but falls after molding. The electrical properties of polypropylene and polyimide are similar to polyethylene.

However, these polyethylene (PE), polypropylene (PP) and the like have poor affinity with the non-aqueous electrolyte. This is because the surface energy difference between the molecules of the non-aqueous electrolyte and the molecules on the surface of the polyethylene (PE) or polypropylene (PP) material is large, so that the bonding between the molecules is not easy. Therefore, when the electrolyte solution is deposited on an insulating plate made of polyethylene (PE) or polypropylene (PP), the electrolyte is roughly spherical due to surface tension, so that wettability and spreadability are remarkably inferior.

According to the embodiment of the present invention, the impregnating property of the electrolyte is improved by coating a material familiar with the electrolyte on the surface of the existing insulating plate having a poor affinity with the electrolyte. As a material familiar with the electrolyte, polyvinyl difluoride (hereinafter referred to as PVdF) is a high molecular material. PVdF is a structure in which -CH2-CF2- is repeated and is a kind of fluorine (F) resin used as a binder when coating an electrode active material on a current collector. The main chain of the fluorine (F) resin is a bond such as a polyolefin composed of C-C bonds, and is a synthetic resin having a structure in which part or all of hydrogen of the polyolefin is replaced by a fluorine atom (F).

As a result of experiments on the impregnation of the electrolyte, it is PVdF 761 and PVdF 2801 which have good spreadability and wettability among non-aqueous electrolytes. Therefore, the PVdF as a coating material of the insulating plate is preferably one of the mixture of PVdF 761, PVdF 2801, PVdF 761 and PVdF 2801.

As described above, in order to improve the wettability and spreadability of the electrolyte, the coating material of the insulating plate may be PVdF, and an ester group or a carboxylic group, which is a hydrophilic atomic group instead of PVdF, may be included. The polymeric material may be used as a coating material for the insulating plate.

An ester group is an atomic group constituting an aliphatic compound represented by RCOOR ', and ester refers to a compound obtained by condensation of an alcohol or phenol with an organic or inorganic acid to lose water (H 2 O). In particular, inorganic acid esters such as sulfate ester and nitrate ester are used as organic solvents. The carboxy group is an atomic group constituting an aliphatic compound represented by RCOOH, and carboxylic acid includes acetic acid (CH 3 COOH), benzoic acid (C 6 H 5 COOH), and the like.

Since the polymer material containing the ester group or the carboxy group has good affinity with the non-aqueous electrolyte, when the ester group or the carboxyl group-containing sulfate ester, acetic acid or the like is used, the wettability and spreadability of the electrolyte are improved. As a result, the impregnation of the electrolyte solution is improved.

In this case, however, the surface of the coated insulating plate should not be swelled. Swelling is one of the characteristics of polymers. Polymers have crystalline and amorphous portions, and solvent molecules penetrate into amorphous portions, increasing their volume. This phenomenon can occur over a long period of time even in the crystalline part, but due to the close distance between the polymer chains, it is more difficult to occur than the amorphous part.

When the polymer material including an ester group or a carboxy group absorbs the non-aqueous electrolyte solution and swelling occurs due to overcharging or the like, the surface of the insulating plate is swollen to deform the electrode assembly. Therefore, when coating the material familiar with the electrolyte on the surface of the insulating plate, it is necessary to form a thin coating layer so that swelling does not occur.

The surface of the insulating plate may be coated with a surfactant.

Surfactant is a substance that has a hydrophilic group and a lipophilic group at the same time, which lowers the surface tension of water and acts as a penetrating, dispersing, emulsifying, and foaming material among the materials. It makes water penetrate well and mixes well with the oil attached to the fiber to remove the laundry. Surfactants can be broadly classified into anionic surfactants, cationic surfactants, nonionic surfactants, and amphoteric surfactants. Anionic surfactants are mainly used in synthetic detergents.

When the surfactant is dissolved in water, the lipophilic part is ion-dissociated with negative charge (-), and the lipophilic part is ion-dissociated with positive charge (+). In addition, it is an amphoteric surfactant that dissociates with a positive charge (+) or a negative charge (-) according to the hydrogen ion concentration of water, and a nonionic surfactant does not dissociate ion.

BRIJ® is a nonionic surfactant that does not have a group that dissociates into ions in aqueous solution and has a -OH group. Although the hydrophilicity is relatively small, the hydrophilicity is excellent because it has ester (ether) and ether (ether) bond in the molecule. However, the BRIJ® is an example of a surfactant applicable to the present invention, and the type of the surfactant is not limited thereto.

When the surfactant comes into contact with the non-aqueous electrolyte, lipophilic groups of the constituent molecules of the surfactant adhere to the surfaces of the non-aqueous electrolyte molecules. Therefore, the interface area between the surfactant and the non-aqueous electrolyte is increased and the surface tension of the electrolyte is reduced. As a result, the wettability and spreadability of the electrolyte solution are improved.

As described above, when the surface of the insulating plate is coated with a polymer material friendly to the electrolyte or coated with a surfactant, the surface of the insulating plate is not exclusive to the electrolyte, so that the settling rate of the electrolyte and the impregnation rate of the electrolyte can be increased. Such a coating layer for surface modification exhibits a sufficient effect even in a thickness of less than 1㎛, almost monolayer (monolayer) about enough effect can be seen.

Referring to FIG. 2, the cylindrical can 300 may include a cylindrical side plate 310 having a predetermined diameter and a cylindrical side plate 310 to form a predetermined space in which the cylindrical electrode assembly 200 may be accommodated. When the lower surface plate 320 is formed to seal the lower portion, the upper portion of the cylindrical side plate 310 is opened to insert the electrode assembly 200. As the negative electrode tab 225 of the electrode assembly 200 is bonded to the center of the bottom plate 320 of the cylindrical can 300, the cylindrical can 300 itself serves as a negative electrode. In addition, the cylindrical can 300 is generally formed of nickel (Ni), iron (Fe) or an alloy thereof. In addition, the cylindrical can 300 is formed with a crimping portion 330 that is bent from the top to the top to press the upper portion of the cap assembly 400 coupled to the upper opening. In addition, the cylindrical can 300 is recessed inward to press the lower portion of the cap assembly 400 at a position spaced apart from the crimping portion 330 by a distance corresponding to the thickness of the cap assembly 400. Fine beading portion 340 is further formed.

2, the cap assembly 400 includes a safety vent 410, a current blocking means 420, a secondary protection element 480, and a cap up 490. The safety vent 410 has a plate-shaped protrusion projecting downward in the center thereof is located at the bottom of the cap assembly 400, the protrusion is deformed in the upper direction by the pressure generated inside the secondary battery. The positive electrode tab 215 drawn from the positive electrode plate 210 and the negative electrode plate 220 of the electrode assembly 200, for example, the positive electrode plate 210, is welded to a predetermined surface of the lower surface of the safety vent 410. The safety vent 410 and the positive electrode plate 210 of the electrode assembly 200 are electrically connected. Here, the other electrode plate, for example, the cathode, of the positive electrode plate 210 and the negative electrode plate 220 is electrically connected to the can 300 by a tab or direct contact method.

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 surface of the insulating plate having a geometrical shape covering the entire upper and lower parts of the battery is coated with a polymer material familiar with the electrolyte, or coated with a surfactant that reduces the surface tension of the electrolyte. By lowering the exclusive propensity of the surface of the insulating plate to increase the electrolyte flowability inside the battery, it is possible to improve the impregnation rate of the electrolyte solution with evenly impregnated, and impregnation that takes up a large part of the overall process time as the impregnation of the electrolyte is improved Process time can be shortened to improve productivity.

Claims (10)

A lithium secondary battery comprising an electrode assembly, a case accommodating the electrode assembly, a cap assembly sealing the case, and an insulating plate positioned between the electrode assembly and the case or between the electrode assembly and the cap assembly. At least one surface of the insulating plate is a lithium secondary battery, characterized in that the polymer material having wettability and spreadability to the electrolyte. delete The method of claim 1, The polymer material is a lithium secondary battery, characterized in that the polyvinyl difluoride (PVdF). The method of claim 3, wherein The polyvinyl difluoride (PVdF) is a lithium secondary battery, characterized in that any one of PVdF 761, PVdF 2801, a mixture of the PVdF 761 and PVdF 2801. The method of claim 1, The polymer material is a lithium secondary battery comprising any one of an ester group or a carboxylic group. The method of claim 1, The polymer material is a lithium secondary battery, characterized in that the surfactant. The method of claim 6, The surfactant is a lithium secondary battery, characterized in that the BRIJ®. The method of claim 1, The material of the insulating plate is a lithium secondary battery, characterized in that the polyethylene (PE) or polypropylene (PP). The method of claim 1, The lithium secondary battery is a lithium secondary battery, characterized in that the cylindrical having a phase insulating plate. The method of claim 9, The phase insulating plate is a lithium secondary battery, characterized in that a plurality of holes are formed on the surface.

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