KR100406793B1 - secondary battery - Google Patents

Abstract

Disclosed is a secondary battery. The present invention provides an outer container, a polymer electrolyte injected into the outer container, installed in the outer container, at least one of an anode and a cathode having a first through hole formed therein so that the polymer electrolyte can be introduced to the center portion; It characterized in that it comprises a separator interposed between the anode and the cathode.

Description

Secondary battery

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to secondary batteries, and more particularly, to secondary batteries with improved electrode assemblies consisting of anodes, cathodes, and separators.

Secondary battery refers to a battery that can be charged and discharged. Recently, as the electric, electronic, communication, and computer industries develop rapidly, the demand for high performance and high safety lithium secondary batteries is gradually increasing, and in particular, the miniaturization of electronic devices Increasingly, the demand for miniaturization and thinning is increasing day by day. In order to meet these demands, a lithium ion polymer battery has been most interested in recent years.

Lithium-ion polymer battery is a high-tech battery that can control the size and shape as desired, high energy density per unit weight, high voltage and large capacity by lamination.

However, the commercialization of such lithium ion polymer batteries is still sluggish because the manufacturing cost is too high compared to the lithium ion batteries, which are conventional lithium secondary batteries, and the development of suitable polymer electrolyte materials applicable to lithium polymer batteries is sluggish. to be.

In the conventional manufacturing process of the lithium ion polymer battery, an anode, a cathode, and a polymer electrolyte are prepared and laminated, or a polymer electrolyte is directly coated and laminated on the cathode or the anode, and then a battery assembly is prepared. After the plasticizer is extracted to form pores, an organic solvent (ie, electrolyte) containing lithium salt is injected. However, this manufacturing process has a problem in that the manufacturing cost of the lithium ion polymer battery is high because all the processes must be carried out under dry conditions.

In order to solve this problem, a recently developed process is to prepare a gel polymer electrolyte by injecting an electrolyte solution in which a lithium salt and an organic solvent are mixed with a monomer or a prepolymer, instead of using a conventional lithium ion battery manufacturing process. It is a process consisting of steps. Such a process is called a "in-cell polymerization process", and in order to commercialize such a process, a polymer electrolyte formed by polymerization satisfies basic characteristics such as excellent ion conducting properties and electrochemical stability, and also includes an electrolyte solution containing a monomer or a prepolymer. It should satisfy the property that the viscosity should be low so as to be easily injected into this battery.

The lithium secondary battery generally uses a cylindrical case or a rectangular case as an outer container for sealing the electrode assembly. Recently, however, a method of using a pouch has been in the spotlight. This is because the use of the pouch not only increases the energy density per unit weight and volume, makes the battery thinner and lighter, but also lowers the material cost of the outer container.

In a conventional lithium secondary battery, anode and cathode swell due to side reactions in a battery as charging and discharging are repeated, thereby increasing the thickness of the battery. As a result, adhesion between the anode and the separator, between the cathode and the separator, and between the current collector of the anode and the cathode and the electrode active material layer may be weakened, resulting in a gap, thereby increasing the interface resistance.

The present invention has been made to solve the above problems, the technical problem to be achieved by the present invention is to improve the adhesion in the electrode assembly consisting of the anode, the cathode and the separator, the performance that can prevent the increase of the interface resistance is improved It is to provide a secondary battery.

1 is an exploded perspective view showing an embodiment of a secondary battery according to the present invention in which the electrode assembly is a wound type and uses a pouch as an outer container.

Figure 2 is an exploded perspective view showing an embodiment of a secondary battery according to the present invention in which the electrode assembly is stacked and uses a pouch as an outer container.

3 is a partial cross-sectional view schematically showing an embodiment of an electrode assembly installed in the secondary battery of the present invention.

Figure 4 is a partial cross-sectional view schematically showing another embodiment of the electrode assembly installed in the secondary battery of the present invention

<Explanation of symbols for the main parts of the drawings>

10,21 ... electrode assembly 11,22 ... pouch

16,17,25,26 ... electrode terminals 31,41 ... cathode

34,44 ... Anode 37,47 ... Separator

In order to achieve the above technical problem, the present invention provides an outer container, a polymer electrolyte injected into the outer container, and installed in the outer container so that the first through hole may be introduced to the center of the outer container. And a separator formed between the anode and the cathode and a second through hole formed between the anode and the cathode, wherein the first through hole and the second through hole are positioned on the same axis.

The present invention is characterized in that the laminated anode, the separator and the cathode is wound in a roll, or the separator, the anode, the separator, and the cathode are additionally laminated on the stack and installed in the outer container.

The present invention is that the anode and the cathode is configured to include a current collector consisting of expanded metal (punched metal), punched metal (punched metal) or foil (foil), and an active material coated on the surface of the current collector It features.

The present invention is characterized in that the polymer electrolyte is formed by thermally polymerizing a composition consisting of an organic solvent comprising a prepolymer and a lithium salt which is a copolymer of vinylidene fluoride and hexafluoropropylene.

The present invention is that the polymer electrolyte is formed from the thermal polymerization of a composition in which any one selected from the group consisting of fluorinated monomers, ether monomers, acrylate monomers and prepolymers thereof is added to an organic solvent containing a lithium salt and mixed. It features one.

Hereinafter, the secondary battery according to the present invention will be described in detail with reference to the accompanying drawings.

1 is an exploded perspective view showing an embodiment of a secondary battery of the present invention in which the electrode assembly is a wound type and uses a pouch as an outer container.

The secondary battery of FIG. 1 is an electrode assembly 10 including a cathode 11, an anode 12, and a separator 13 as a lithium secondary battery, a pouch 11 and a pouch that wrap and seal the electrode assembly 10. And a polymer electrolyte (not shown) to be filled in the internal space of (11). The electrode assembly 10 is formed by inserting the separator 13 between the cathode 11 and the anode 12 and winding the separator 13 in a roll shape to the center of the electrode assembly 10. The through hole 18 is formed to be easily injected. The cathode tab 14 and the anode tab 15, which serve as an electrical path between the electrode assembly 10 and the outside, are drawn out of the cathode 11 and the anode 12 to form electrode terminals 16 and 17.

Figure 2 is an exploded perspective view showing an embodiment of a secondary battery of the present invention in which the electrode assembly is stacked and uses a pouch as an outer container.

The secondary battery of FIG. 2 is also a lithium secondary battery of an electrode assembly 21 formed by alternately stacking a cathode, an anode, and a separator, and a pouch 22 and a pouch 22 that wrap and seal the electrode assembly 21. It comprises a polymer electrolyte (not shown) to be filled in the inner space. The electrode assembly 21 has a through hole 27 so that the polymer electrolyte (not shown) can be easily introduced to the center of the electrode assembly 21. A current formed in the electrode assembly 21 is formed. The electrode terminals (or lead wires) 25 and 26, which serve as electrical passages for guiding the outside thereof, are connected to the cathode tabs and the anode tabs 23 and 24 provided on the cathode and the anode and exposed to a predetermined length out of the pouch 22. Located.

In the case of the lithium secondary battery of FIG. 1 or 2, the electrode assemblies 10 and 21 are placed in the pouches 11 and 22 while only part of the electrode terminals 16 and 17 and 25 and 26 are exposed. After injecting the composition, the heat-adhesive material between the edge portion of the upper pouch and the edge portion of the lower pouch is adhered and sealed to form a polymer electrolyte in a gel state by the above-described in-cell polymerization process.

3 is a partial cross-sectional view schematically showing an embodiment of an electrode assembly portion of the secondary battery of the present invention, which corresponds to a portion of a cross section of the electrode assembly 10 or 21 of FIG. 1 or 2.

Referring to the drawings, an electrode assembly consisting of a cathode 31, an anode 34 and a separator 37 is embedded in the pouches 11 and 22 of FIG. 1 or 2 and between the pouches 11 and 22 and the electrode assembly. The space is filled with a polymer electrolyte (not shown). The polymer electrolyte is formed by an in-cell polymerization step of thermally polymerizing in a pouch using an organic solvent containing a polymer matrix and a lithium salt as a composition. The polymer matrix may be made of a prepolymer which is a copolymer of vinylidene fluoride and hexafluoropropylene. In addition, the polymer matrix may be made of any one selected from the group consisting of fluorine monomers, ether monomers, acrylate monomers, and prepolymers thereof. The lithium salt and the organic solvent may be used without particular limitation as long as it is widely known in the art, but the lithium salt may include lithium perchlorate (LiClO ₄ ), lithium tetrafluoroborate (LiBF ₄ ), and lithium hexafluorophosphate ( LiPF ₆ ), lithium trimethane sulfonate (LiCF ₃ SO ₃ ) and lithium bistrifluoromethanesulfonylamide (LiN (CF ₃ SO ₂ ) ₂ ) are preferably one or more selected from the group consisting of: Examples of the organic solvent include propylene carbonate, ethylene carbonate, dimethyl carbonate, methylethyl carbonate, diethyl carbonate, tetrahydrofuran, 2-methyltetrahydrofuran, diethoxyethane, methylformate, ethylformate and γ-butyrolactone It is preferably at least one selected from the group consisting of. The composition is injected into a pouch in which the electrode assembly is embedded, the pouch is sealed, and then left in an oven controlled at a predetermined temperature for a predetermined time to thermally polymerize the polymer matrix to form a polymer electrolyte in a gel state.

The cathode 31 and the anode 34 are respectively coated on the current collectors 32 and 35 and the films obtained by being directly coated or dried on a separate support and then peeled from the support, onto the current collectors 32 and 35. And the electrode active material layers 33 and 36 formed. As the current collector 32 of the cathode 31, an expanded metal, a punched metal, or a foil made of aluminum is used, and the current collector 35 of the anode 34 is made of copper. Expanded metal, punched metal, or foil is used. The electrode active material layers 33 and 36 include an electrode active material, a binder, a conductive agent, and a solvent. As the electrode active material of the cathode 31, a lithium composite oxide such as LiCoO 2 is used as the electrode active material of the anode 34. Carbon, graphite, etc. are used. In addition, carbon black is used as the conductive agent, and at least one selected from fluorine-based polymers such as polyvinyl alcohol, methyl cellulose, carboxymethyl cellulose, polyethylene glycol and polyvinylidene fluoride is used as the binder, and N-methyl is used as the solvent. 2-pyrrolidone, acetone or mixtures thereof are used.

The through holes 38a and 38b are formed by punching the cathode 31 and the anode 34 formed by stacking the electrode active material layers 33 and 36 on the current collectors 32 and 35. According to the drawings, the through holes 38a and 38b are formed in both the cathode 31 and the anode 34, but may be formed in only one of them. The unit electrode assembly 30 is formed by stacking the separator 37 between the cathode 31 and the anode 34 on which the through holes 38a and 38b are formed. The separator 37 is not particularly limited, but in the case of using a polyethylene separator or the like, the separator 37 is preferably wound in a roll shape.

The unit electrode assembly 30 is shown to omit on the drawing the same extending from side to side. In the case of the winding type as shown in FIG. 1, the unit electrode assembly 30 is rolled up into a pouch to manufacture a battery. In the case of the stacked type as illustrated in FIG. 2, the separator 37 and the electrode 31 are formed in the unit assembly 30. 34) are alternately added, stacked, and placed in a pouch to fabricate a battery.

When the battery is configured with the unit electrode assembly 30, the polymer electrolyte in a gel state formed by thermal polymerization penetrates between the through holes 38a and 38b, so that the unit electrode assembly 30 may be firmly tightened. In the drawing, the through hole 38a of the cathode 31 and the through hole 38b of the anode 34 are formed to correspond to the same vertical line, but they are not formed on the same line. You will know.

4 is a partial cross-sectional view schematically showing another embodiment of the electrode assembly portion of the secondary battery of the present invention, which also corresponds to a portion of the cross section of the electrode assembly 10, 21 of FIG.

Referring to the drawings, the embodiment of FIG. 4 is composed of the components as shown in FIG. 3, but the through holes 48a, 48b, and 48c formed in the cathode 41, the anode 44, and the separator 47, respectively, are the same. When the cathode 41, the anode 44, and the separator 47 are sequentially stacked on the vertical axis, the unit electrode assembly 40 itself also has a hole. When the above holes are formed at once by stacking the cathode 41, the anode 44, and the separator 47, a notch is formed at the edge of the punched hole, and a short may occur. Since it becomes large, it is preferable to form a through hole separately, and to arrange by lamination | stacking. When the battery is configured with the unit electrode assembly 40, the polymer electrolyte in a gel state formed by thermal polymerization may be connected to each other through the through hole, and thus the unit electrode assembly 40 may be more firmly tightened.

Although the above embodiment has been mentioned based on the lithium secondary battery, it will be appreciated that the present invention can be applied to all secondary batteries in which a polymer electrolyte is used.

As described above, the secondary battery according to the present invention has the following effects.

First, due to the gel polymer electrolyte filled in the through-holes, the current collector of the cathode and the anode and the electrode active material layer are tightly tightened, thereby enhancing adhesion.

Second, even if the volume of the cathode and the anode is expanded due to side reactions due to the repeated charging and discharging of the battery can be compensated in a way that the diameter of the through hole is reduced to prevent the increase in the thickness of the battery.

Third, despite the repeated use of the battery as described above, it is possible to prevent the increase of the interfacial resistance by maintaining a strong contact between the layers in the electrode assembly.

Fourth, since the through-hole is formed on the plane during the formation of the cathode and the anode, the surface area is increased to shorten the drying time.

Although the present invention has been described with reference to the embodiments illustrated in the drawings, this is merely exemplary, and it will be understood by those skilled in the art that various modifications and equivalent other embodiments are possible. Therefore, the true scope of protection of the present invention should be defined only by the appended claims.

Claims (7)

With an outer container, A gel polymer electrolyte injected into the outer container; An anode and a cathode installed in the outer container, the first through-holes of which are formed so that the polymer electrolyte can be injected to the center; A separator interposed between the anode and the cathode and having a second through hole formed therein; And the first through hole and the second through hole are positioned on the same axis. delete delete The method of claim 1, The laminated anode, separator, and cathode may be wound in a roll, or may be additionally stacked in the order of separator, anode, separator, and cathode on the stack and installed in the outer container. The method of claim 1, The anode and the cathode are secondary, characterized in that comprises a current collector made of expanded metal, punched metal (foil) or foil and an active material coated on the surface of the current collector battery. The method of claim 1, The polymer electrolyte is a secondary battery, characterized in that formed by thermal polymerization of a composition consisting of an organic solvent comprising a prepolymer and a lithium salt which is a copolymer of vinylidene fluoride and hexafluoropropylene. The method of claim 1, The polymer electrolyte is formed from thermal polymerization of a composition in which any one selected from the group consisting of fluorinated monomers, ether monomers, acrylate monomers, and prepolymers thereof is added to an organic solvent containing a lithium salt and mixed. Rechargeable battery