KR20070104689A - Secondary battery of improved safety employing electrode assembly covered with separator film - Google Patents

Abstract

A lithium ion polymer secondary battery including an electrode assembly surrounded with a separator film is provided to prevent an internal short when the electrode assembly moves upon dropping of the battery while not adversely affecting the electrolyte used in the battery. A lithium ion polymer secondary battery comprises an electrode assembly(300) including a separator having an adhesive layer coated on both surfaces thereof, a cathode and an anode attached to both surfaces of the separator with the adhesive layer, and a lithium electrolyte, wherein the outer surface of the electrode assembly is surrounded with a film(600) coated with an adhesive layer formed of the same fluoropolymer as the separator along the direction toward the electrode terminals(400,410) of the electrode assembly.

Description

Secondary Battery of Improved Safety Employing Electrode Assembly Covered with Separator Film}

1 is a schematic diagram of a general structure of a conventional LiPB including a stacked electrode assembly;

2 to 5 are schematic views of a series of processes for applying a film to the outer surface of the electrode assembly according to one embodiment of the present invention;

6 is a schematic diagram of an electrode assembly in which a film surrounds an outer surface between electrode terminals according to another embodiment of the present invention.

The present invention relates to a secondary battery having improved safety including an electrode assembly wrapped by a separator film, and more particularly, in a state in which a cathode and an anode are attached to both sides thereof by an adhesive layer coated on both sides of the separator. A lithium ion polymer battery comprising an electrode assembly impregnated with a lithium electrolyte, wherein a film coated with an adhesive layer of a fluorine-based polymer as the same material as the separator in the electrode assembly wraps the outer surface toward the electrode terminal of the electrode assembly. A secondary battery having a structure attached in a state.

As the development and demand for mobile devices increases, the demand for secondary batteries as a source of energy is increasing rapidly. Among them, many researches have been conducted and commercialized and widely used for lithium secondary batteries with high energy density and high discharge voltage. It is used.

Representatively, 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 batteries, and lithium ion batteries with high energy density, discharge voltage and output stability in terms of materials, and lithium ions. There is a high demand for secondary batteries such as polymer batteries and lithium polymer batteries.

Lithium ion polymer battery (LiPB) refers to a battery having a structure in which leakage of electrolyte is minimized by bonding them after interposing a separator between a positive electrode and a negative electrode and impregnating a lithium electrolyte. In general, it is prepared by coating the adhesive layer on both sides of the separator and heat-sealing the positive electrode and the negative electrode to which the active material is applied.

In general, LiPB has a structure in which the stacked electrode assembly of the electrode structure as described above is embedded in a pouch type case of an aluminum laminate sheet and sealed.

1 schematically illustrates a general structure of a representative LiPB including a stacked electrode assembly.

Referring to FIG. 1, in the LiPB 100, an electrode assembly 300 including a cathode, an anode, and a separator disposed therebetween is formed inside a pouch-type battery case 200. Two electrode leads 400 and 410 electrically connected to 304 are sealed to be exposed to the outside.

The battery case 200 is formed of a soft packaging material such as an aluminum laminate sheet, and includes a case body 210 and a body 210 including a recess 230 having a concave shape in which the electrode assembly 300 can be seated. It consists of a lid 220 connected as one body.

The electrode assembly 300 used in the LiPB 100 may have a jellyroll-type structure in addition to the stacked structure as shown in FIG. 1. In the stacked electrode assembly 300, a plurality of positive electrode tabs 302 and a plurality of negative electrode tabs 304 are welded to the electrode leads 400 and 410, and the electrode leads 400 and 410 are connected to the battery case 200. Insulation film 500 is attached to the upper and lower surfaces to ensure the electrical insulation and sealing properties.

Lithium secondary batteries such as LiPB may ignite and explode when exposed to high temperatures. In addition, even when a large current flows within a short time due to overcharging, an external short circuit, nail penetration, local crush, or the like, there is a risk of fire / explosion while the battery is heated by IR heating. As the temperature of the battery rises, the reaction between the electrolyte and the electrode is accelerated. As a result, heat of reaction is generated to further increase the temperature of the battery, which in turn accelerates the reaction between the electrolyte and the electrode. Thus, the temperature of the battery rises rapidly, which in turn accelerates the reaction between the electrolyte and the electrode. By this circulation, a thermal runaway phenomenon in which the temperature of the battery rises rapidly occurs, and when the temperature rises to a certain level or more, the battery may ignite. In addition, as a result of the reaction between the electrolyte and the electrode, gas is generated to increase the battery internal pressure, and the lithium secondary battery explodes above a certain pressure. The risk of ignition and explosion can be said to be the most fatal disadvantage of lithium secondary batteries.

In particular, LiPB as shown in FIG. 1 is easily deformed by dropping, external impact, etc., because the battery case is made of a soft packaging material of weak strength, and further, an internal short circuit may be caused by the movement of the electrode assembly inside the battery case. . That is, a short circuit may occur as the electrode tab or the electrode lead contacts the upper end of the electrode assembly. Since the fall of the battery occurs frequently during the use of the battery, there is a high need for a technology capable of ensuring the safety of the battery in a more efficient manner.

Some prior art proposes a method of attaching an adhesive tape to a part of the electrode assembly or inserting a foreign material into the upper space of the electrode assembly in order to prevent an internal short circuit caused by the movement of the electrode assembly. There is a problem of reducing the performance of the battery by causing an undesired chemical reaction.

Therefore, an object of the present invention is to solve the problems of the prior art as described above and the technical problem that has been requested from the past.

That is, it is an object of the present invention to provide a lithium ion polymer battery which greatly reduces the possibility of internal short circuiting when the electrode assembly moves due to the drop of the battery.

It is still another object of the present invention to provide a lithium ion polymer battery in which the material used for suppressing such internal short circuit does not affect the electrolyte solution or the like, thereby reducing the performance of the battery.

The lithium ion polymer battery according to the present invention for achieving the above object comprises an electrode assembly impregnated with lithium electrolyte in a state where the positive electrode and the negative electrode are attached to both sides thereof by an adhesive layer coated on both sides of the separator. The secondary battery has a structure in which a film coated with an adhesive layer of a fluorine-based polymer as the same material as the separator in the electrode assembly is attached to the electrode terminal of the electrode assembly with its outer surface wrapped.

Accordingly, the lithium ion polymer battery of the present invention is attached to the outer surface of the electrode assembly while the film of the polymer material is attached to the electrode terminal in the direction of the electrode assembly. Since it is wrapped with an insulating film, even when the battery falls, the risk of internal short circuit can be greatly reduced. In addition, since the separator used in the construction of the electrode assembly is generally composed of an olefin-based polymer which is inert to an electrode active material, an electrolyte, and the like, in the battery of the present invention, a separate film is added to cover the outer surface of the electrode assembly. Does not adversely affect performance.

The shape of the electrode assembly in the present invention may be varied, for example, by placing a separator between the positive electrode and the negative electrode to which the active material is applied on the current collector, respectively, and wound it into a cylindrical structure and then compressed in the thickness direction It may be a plate-shaped electrode assembly such as a jelly-roll electrode assembly, or a stacked electrode assembly in which the anode / separator / cathode is sequentially stacked. In particular, since the stacked electrode assembly as shown in FIG. 1 has a high risk of an internal short circuit when the battery falls, the present invention may be preferably applied to a battery including the stacked electrode assembly.

As described above, the film is made of the same material as the separator for a lithium ion polymer battery. For example, the film is formed of a fluorine-based polymer on the surface of a polyethylene substrate, a polypropylene substrate, or a polypropylene / polyethylene / polypropylene multilayer substrate. The adhesive layer is coated. However, the adhesive layer on the surface of the film substrate does not necessarily have to be coated on the entire surface of the substrate, and for example, the adhesive layer may be coated only at a portion where the film intersects with the film surrounding the electrode assembly.

Examples of the fluorine-based polymer of the adhesive layer may include PVdF, which may be bonded to the active material layer or to each other by a thermal fusion method. Therefore, mutual adhesion occurs while applying heat and pressure to the intersections of the film in a state in which the electrode assembly is wrapped.

The thickness of the film is not particularly limited, and preferably 10 to 50 um thick film can be used.

The film may cover a range of covering the outer surface of the electrode assembly, for example, the structure surrounding the entire upper surface of the electrode assembly except the electrode terminal, the structure surrounding the outer surface of the electrode assembly with only the space between the electrode terminals, and the like. It may be possible.

When the film surrounds the entire outer surface of the electrode assembly, an opening is formed at a position corresponding to the electrode terminals of the electrode assembly, so that the electrode terminals may protrude even if the film surrounds the top surface of the electrode assembly.

Hereinafter, the content of the present invention will be described with reference to the drawings according to some embodiments of the present invention, but the scope of the present invention is not limited thereto.

2 to 5 schematically show a series of processes for applying a film to the outer surface of the electrode assembly according to one embodiment of the present invention.

Referring to these drawings, the electrode assembly 300 has a plurality of positive and negative electrodes are stacked in a state where a separator is interposed, and the positive electrode terminal 400 and the negative electrode terminal 410 protrude from the top. The positive electrode and the negative electrode are thermally fused to the separator and impregnated with a lithium electrolyte.

The film 600 to be applied to the outer surface of the electrode assembly 300 has openings 620 and 622 formed in the folding part 610 at a position corresponding to the electrode terminals 400 and 410 of the electrode assembly 300. The folding unit 610 is applied to surround the electrode assembly 300 such that the folding unit 610 is positioned on the top surface of the electrode assembly 300. Accordingly, the electrode terminals 400 and 410 protrude from the openings 620 and 622 in the state in which the film 600 surrounds the electrode assembly 300.

The length of the film 600 is a length in which portions of the film 600 may overlap each other while completely surrounding the outer surface of the electrode assembly 300. Preferably, the overlapping portion 630 may be formed such that the length of one side of the folding unit 610 is relatively long such that the overlapping portion 630 is positioned on the upper or lower surface of the electrode assembly 300.

In a state in which the outer surface of the electrode assembly 300 is wrapped, heat and pressure are applied to the overlapping portion 630 to be fused. Accordingly, the film 600 may stably maintain its shape by elastically wrapping the outer surface of the electrode assembly 300 to prevent some electrodes from protruding when mounted in the battery case (not shown). In addition, since the upper end of the electrode assembly 300 is applied by the film 600, when the battery falls, the electrode terminals 400 and 410 may not be in contact with the upper end of the electrode assembly 300 to prevent short circuits.

6 is a schematic diagram of an electrode assembly in which a film surrounds an outer surface between electrode terminals according to another embodiment of the present invention.

Referring to FIG. 6, there is a difference in that the film 601 is narrower than the film 600 of FIG. 3. Accordingly, the film 601 surrounds the outer surface of the electrode assembly 301 with a space between the electrode terminals 400 and 410, and the openings 620 and 622 as shown in FIG. 3 are not perforated. However, it is the same as the film 600 of FIG. 3 in that the overlapping portion 631 is thermally fused to be attached in a state in which the outer surface of the electrode assembly 301 is wrapped.

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.

As described above, in the secondary battery according to the present invention, since the film of the same material as the separator constituting the electrode assembly surrounds the outer surface of the electrode assembly, internal short circuits can be greatly suppressed when the battery falls without affecting the performance of the battery. It works.

Claims (10)

A secondary battery comprising an electrode assembly impregnated with a lithium electrolyte in a state in which a positive electrode and a negative electrode are attached to both surfaces thereof by an adhesive layer coated on both surfaces of a separator, and the same material as that of the separator in the electrode assembly. A lithium ion polymer battery having a structure in which a film coated with an adhesive layer is attached to the electrode terminal of the electrode assembly with its outer surface wrapped. The lithium ion polymer battery according to claim 1, wherein the film is coated with an adhesive layer of a fluorine-based polymer on a surface of a polyethylene substrate, a polypropylene substrate, or a polypropylene / polyethylene / polypropylene multilayer substrate. The lithium ion polymer battery according to claim 1, wherein the adhesive layer is made of PVdF. The lithium ion polymer battery of claim 1, wherein the film has a thickness of about 10 μm to about 50 μm. The lithium ion polymer battery of claim 1, wherein the film surrounds an entire upper surface of the electrode assembly except for the electrode terminal. The lithium ion polymer battery of claim 5, wherein an opening is formed at a position corresponding to the electrode terminals of the electrode assembly. The lithium ion polymer battery of claim 1, wherein the film surrounds the electrode assembly only with a space between the electrode terminals. The lithium ion polymer battery of claim 1, wherein the adhesive layer is coated on the entire surface of the film. The lithium ion polymer battery of claim 1, wherein an adhesive layer is coated only at a portion where the film intersects the electrode assembly. The lithium ion polymer battery of claim 1, wherein the film is attached by thermal fusion.

Images