KR20150028537A - Stack and Folding-Typed Electrode Assembly Having Improved Electrolyte Wetting Property and Method of Preparation of the Same - Google Patents

Abstract

The present invention relates to a stack-folding type electrode assembly, and a manufacturing method thereof, wherein the stack-folding type electrode assembly has a structure wound in the state of positioning unit cells, which include an anode, a cathode and a separation membrane, on a separation film, and the separation film and the unit cells are formed to have partial lamination in the mutual interface to be partially attached. According to the present invention, the stack-folding type electrode assembly has an electrolyte fluid path for flowing the electrolyte, thereby remarkably improving the electrolyte wettability.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a stack-folding type electrode assembly having improved electrolyte impregnability, and a stack-

The present invention relates to an electrode assembly having improved electrolyte impregnability and a method of manufacturing the same. More particularly, the present invention relates to a stack-folding type electrode assembly having a structure in which unit cells including an anode, a cathode, Wherein the separation film and the unit cell are in the form of a partial lamination of a structure in which the interface between the separation film and the unit cell is partially in close contact with each other, and a method of manufacturing the same.

As technology development and demand for mobile devices have increased, the demand for secondary batteries as energy sources is rapidly increasing. In recent years, the use of secondary batteries as a power source for electric vehicles (EV) and hybrid electric vehicles (HEV) Among such secondary batteries, there is a high demand for lithium secondary batteries having high energy density, high discharge voltage and output stability.

The secondary battery may be classified according to how the electrode assembly having the anode / separator / cathode structure is formed. Typically, the jelly-roll (cathode) structure is a structure in which the anode and the cathode of the long sheet type are wound with the separator interposed therebetween (Stacked) electrode assembly in which a plurality of positive electrodes and negative electrodes cut in units of a predetermined size are sequentially stacked with a separator interposed therebetween, a stacked (stacked) electrode assembly in which a predetermined unit of positive and negative electrodes are stacked A stack-folding type electrode assembly in which stacked unit cells, for example, Bi-cells or full cells are wound, can be mentioned.

Since the conventional jelly-roll type electrode assembly in the electrode assembly body is formed into a cylindrical or elliptical structure by winding a long sheet-like anode and a cathode in a densified state, the stress caused by the expansion and contraction of the electrode during charging / When the stress accumulation exceeds a certain limit, deformation of the electrode assembly occurs. As a result of the deformation of the electrode assembly, the intervals between the electrodes become uneven, so that the performance of the battery drastically deteriorates. As a result, Resulting in a safety threat.

Further, since the long sheet-like positive electrode and the negative electrode are required to be wound, it is difficult to rapidly wind the positive electrode and the negative electrode while maintaining a constant distance between the positive electrode and the negative electrode.

On the other hand, since the stacked electrode assembly requires a plurality of anode and cathode unit members to be sequentially stacked, a process of transferring the electrode plate for manufacturing the unit pieces is separately required, and a time and effort are required for the sequential stacking process, I have.

In order to solve these problems, an electrode assembly having a progressive structure of a jelly roll type and a stack type is proposed. The bipolar cell or the full cell, which are laminated with a predetermined unit of anode and cathode through a separator, A stack-folding type electrode assembly having a structure in which a sheet is wound up has been developed.

Figs. 1-4 disclose a schematic diagram of one exemplary bi-cell and pull-cell that can be used as a unit cell in such a stack-folding electrode assembly.

Meanwhile, in order for the secondary battery including the above-mentioned electrode assemblies to have a high capacity and a high energy density and to maintain a long lifetime, the electrode assembly disposed inside the battery is completely impregnated with the electrolyte solution so that the electrode reaction between the electrodes can be actively performed When the electrode assembly is imperfectly impregnated with the electrolyte solution, the reaction between the electrodes is not smooth, resulting in an increase in resistance and an abrupt drop in the output characteristics and the capacity of the battery. As a result, The battery is exposed to the risk of deterioration or explosion of the battery.

Therefore, in order to improve the performance of the secondary battery and improve the safety, various methods for improving the electrolyte impregnability of the electrode assembly have been continuously carried out, and the causes of improvement in the electrolyte impregnability have been investigated Attempts are continuing.

Particularly, the stack-folding type electrode assembly as described above can solve the disadvantages of the jelly-roll type or stacked type electrode assembly as described above. However, when the impregnation property of the electrolytic solution relative to the inner pull cell or the bi- Has a disadvantage that the impregnation speed is slow. Further, when the electrolyte is vaporized in an emergency such as high temperature or overcharge, or gas is generated inside the electrode assembly, it is difficult for the vaporized electrolyte or gas to be easily discharged to the outside due to the separation membrane sheet The expansion phenomenon is relatively high.

In this regard. FIG. 5 schematically shows a lamination process 100 of a unit cell and a separation film of a conventional stack-folding type electrode assembly.

Referring to FIG. 5, the unit cells 110 placed on the separation film 111 are heated by the heater 120, and then laminated by a cylindrical pressing roll 130 as a whole. However, if the separating film 111 and the unit cells 110 are laminated as a whole, the adhesion between the electrodes and between the electrodes and the separator increases, so that it becomes more difficult for the electrolytic solution to permeate or the gas to be released when the gas is generated. As a result, It is difficult to realize a high capacity, high output and high energy density of the secondary battery including the secondary battery, and also there is a problem in safety of the battery in terms of safety.

In recent years, as a device or a device becomes larger, a battery which is larger in capacity and size of a battery becomes a continuous requirement. However, in this case, the problem of electrolyte impregnability becomes even greater. That is, as the volume to be infiltrated by the electrolyte decreases and the area becomes wider, the possibility that the electrolyte does not reach the inside of the battery and exists only locally on the outside becomes high. The battery thus produced has a disadvantage in that the amount of the electrolytic solution partially becomes insufficient in the inside of the battery, so that the capacity and performance of the battery are greatly reduced

In order to solve this problem, an electrolyte solution is injected at a high temperature or an electrolyte solution is injected under a pressure or a reduced pressure in order to improve the impregnability of the electrolyte solution. However, the membrane is shrunk by heat to cause an internal short circuit The problem continued to arise.

Therefore, there is a high need for a technique for improving the performance of the battery by increasing the impregnation property of the electrolyte in the stack-folding type secondary battery.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-described problems of the prior art and the technical problems required from the past.

The inventors of the present application have conducted intensive research and various experiments and have found that when the electrode assembly of the stacked-folding type electrode assembly is partially manufactured by partially laminating the interface between the separation film and the unit cell, It was confirmed that the electrolyte impregnation performance of the assembly was improved and the gas was smoothly discharged at the time of the generation of the internal gas, thereby completing the present invention.

Accordingly, the stack-folding type electrode assembly according to the present invention is a stack-folding type electrode assembly having a structure in which unit cells including an anode, a cathode, and a separator are placed on a separation film, The cells are characterized in that they are in the form of a partial lamination of a structure in which the interfaces between the cells are partially in close contact with each other.

The inventors of the present application have recognized that the adhesion force between the unit cells and the separating film is a problem as one of the causes of low electrolyte impregnability of the stack-folding type electrode assembly, and after intensive research, they have been separated by partial lamination It has been found that when the electrolyte flow path for electrolyte flow is formed by forming a portion that is not in close contact with the interface between the film and the unit cell, the electrolyte impregnability is greatly improved.

Therefore, according to the stack-folding type electrode assembly of the present invention, since the separation film and the unit cell are partially laminated, an electrolyte flow path for electrolyte flow can be formed at the interface between the separation film and the unit cell, have.

For example, the electrolyte flow path may be formed by a strip having one side end or both side ends communicating with the outside of the interface between the separating film and the unit cell so as to facilitate the discharge of the gas to the outside when the electrolyte is easily permeated, ) Shape.

The shape of the electrolytic solution flow path is not particularly limited as long as it is a shape that can easily be impregnated with the electrolytic solution. In one specific example, two or more electrolyte flow paths are formed parallel to each other, Or may be formed in a radial shape.

Partial lamination for forming the electrolyte flow path may be performed using unit pressure cells, for example, a pressure roll or a pressure jig, placed on the separation film. In this case, the partial lamination is carried out in consideration of the shape of the desired electrolyte flow path, and the shape of the electrolyte flow path is not limited as long as the shape of the electrolyte flow path may be varied. For example, the shape may be circular or polygonal Lt; / RTI >

On the other hand, as described above, even when the partial lamination is performed in order to improve the impregnability of the electrolyte solution and smooth the discharge of the internal gas, the increase of the internal resistance between the separation film and the unit cell is suppressed, An adhesion force of a predetermined strength or more is required.

Thus, in one specific example, the interface between the separation film and the unit cell that is not contacted by the partial lamination may be between 10 and 90% of the total system area of the separator and the unit cell, more specifically between 30 and 80% Lt; / RTI >

When the separation film and the unit cell are not in close contact with each other, the separation film and the unit cell are separated from each other during the repeated charging and discharging of the secondary battery, so that the internal resistance can be increased. Is less than 10%, it is difficult to exhibit the effects of the present invention, such as improvement in electrolyte impregnability and easiness in releasing internal gas, which is not preferable.

When the stack-folding type electrode assembly according to the present invention is used as described above, the impregnability of the electrolyte solution is improved, so that it is possible to use an electrode assembly having a large capacity and a large area, (Mm ² ) of the upper and lower surfaces of the electrode assembly with respect to the thickness (mm) of the electrode assembly may be 5 or more, and more specifically 10 or more and 50 or less.

In this case, in the three-axis direction constituting the stack-folding type electrode assembly, the length in the stacking direction including the bi-cell and / or the pull cells is the thickness (mm) of the electrode assembly, (Mm < ² >) of the upper surface and the lower surface of the electrode assembly.

Generally, when a large-capacity, large-area battery is manufactured as described above, as the volume of the electrolyte to be infiltrated decreases and the area becomes wider, the possibility that the electrolyte does not reach the inside of the battery, There is a problem in that the capacity and performance of the battery are greatly reduced because the amount of the electrolyte partially becomes insufficient in the interior of the electrode assembly. However, when the stack-folding type electrode assembly according to the present invention is used, Assembly is possible.

The present invention further provides a method of manufacturing the stack-folding type electrode assembly, and a method of manufacturing the stack-folding type electrode assembly according to the present invention will be described in detail below.

The method of fabricating the stack-folding type electrode assembly includes:

A process of manufacturing unit cells including an anode, a cathode, and a separator;

Positioning the unit cells on a separation film;

Partially laminating the unit cells positioned on the separation film continuously using a pressure roll, or partially laminating unit cells positioned on the separation film using a pressing jig; And

Winding the partially laminated separation film and the unit cells;

And a control unit.

At this time, the pressing roll or the pressing jig may have grooves for partial lamination formed on the outer surface in contact with the unit cell.

In some cases, the unit cells may be heated by a heater after the unit cells are positioned on the separation film.

FIGS. 6 and 7 schematically show lamination processes 200 and 300 of a unit cell and a separation film of a stack-folding type electrode assembly according to an embodiment of the present invention.

6, the unit cells 210 placed on the separation film 211 are heated by the heater 220, and then partially laminated by the pressure roll 230. As shown in FIG.

The laminated unit cells 210 'have grooves for partial lamination formed on the outer surface of the pressing roll 230 contacting the unit cells. The laminated unit cells 210' are separated from each other by a protruding portion of the pressing roll 230, (210'-1) and the interface 210'-2 that is not closely contacted by the depressed portion. For convenience of explanation, FIG. 6 shows the interface 210'-1 and the interface 210'-2 so that they can be seen from the outside. At this time, the shape of the partial lamination is formed in parallel by the shape of the pressing roll 230, and a plurality of strip-shaped electrolyte flow paths in which both end portions are communicated to the outside of the interface between the separation film and the unit cell are formed parallel to each other Structure is created.

Referring to Fig. 7, the unit cells 310 placed on the separation film 311 are heated by the heater 320 and then partially laminated by the pressing jig 330. Fig.

In the pressing jig 330, grooves for partial lamination are formed on the outer surface in contact with the unit cells in a circular shape. The laminated unit cells 310 'are separated from the separation film by the protruding portions of the pressing jig 330 And includes the interface 310'-2 that is not in contact with the adhered interface 310'-1 and the depressed portion. For convenience of description, the interface 310'-1 and the interface 310'-2 can be seen from the outside as in FIG. 7 as described above.

At this time, the shape of the partial lamination is formed into a circular shape by the shape of the pressing jig 330.

Although the present invention has been described with reference to the drawings for the purpose of facilitating the understanding of the present invention, the partial lamination shape and the like are not limited thereto but may vary and the scope of the present invention is not limited thereto.

When the separation film and the unit cells are partially laminated, the electrolyte flow path is formed at the non-adhered interface so that the electrolyte can easily permeate to the center of the electrode assembly. Therefore, the lithium ions move smoothly between the anode and the cathode of the unit cells Thus, battery performance such as lifetime characteristics, room temperature, and low temperature output characteristics of the secondary battery can be improved. In addition, the discharge of the gas generated during the charging / discharging process of the battery through the electrolyte flow path can be smoothly discharged, so that the safety of the battery can be improved.

The unit cells may be a bi-cell or a full cell, and a bi-cell and a full cell may be used together. As described in the above-mentioned prior art, the bi-cell has a stacked structure in which cells of the same kind are located on both sides, for example, a positive electrode-separator-negative electrode-separator-positive electrode or a negative electrode- - a cell made up of cathodes. A pull cell is a stacked structure in which different kinds of electrodes are located on both sides of the cell, and is, for example, a cell made of a cathode-separator-cathode.

In order to construct an electrode assembly using a pull cell, a plurality of pull cells must be stacked so that the anode and the cathode face each other with the separation film interposed therebetween. In order to construct the electrode assembly using the bi- A plurality of bi-cells must be stacked such that the bi-cells of the anode / separator / cathode / separator / anode structure and the bi-cells of the cathode / separator / anode / separator / cathode structure face each other.

At this time, the stack including the anode, the cathode, and the separator, that is, the unit cells, can be laminated as a whole. Unlike the partial lamination of the unit cell and the separation film, the unit cells each have a limited outer circumferential surface, so that the electrolyte is entirely laminated in order to facilitate impregnation and gas discharge of the electrolyte, increase in internal resistance, desirable.

The separation film has a unit length that can cover a plurality of unit cells included therein. The separation film is bent inward for each unit length, and starts from the center unit cell to surround each unit cell continuously from the center to the outermost unit cell.

Here, the end sealing of the separation film may be sealed by heat sealing or an adhesive film. As the separation film used for winding the unit cell, an insulating thin film having high ion permeability and mechanical strength is used. The pore diameter of the separation film is generally 0.01 to 10 micrometers, and the thickness is generally 5 to 300 micrometers.

Such separation films include, for example, olefin-based polymers such as polypropylene, which is chemically resistant and hydrophobic; A sheet or nonwoven fabric made of glass fiber, polyethylene or the like; Kraft paper and the like are used. Representative examples currently on the market include Celgard TM 2400, 2300 (from Hoechest Celanese Corp.), polypropylene separator (from Ube Industries Ltd. or Pall RAI), and polyethylene series (from Tonen or Entek).

In some cases, a gel polymer electrolyte may be coated on the separation film to improve the stability of the cell. Representative examples of such a gel polymer include polyethylene oxide, polyvinylidene fluoride, and polyacrylonitrile.

The anode is prepared by applying a mixture of a cathode active material, a conductive material and a binder on a cathode current collector, followed by drying and pressing. If necessary, a filler may be further added to the mixture.

The cathode current collector generally has a thickness of 3 to 500 mu m. Such a positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. Examples of the positive electrode current collector include stainless steel, aluminum, nickel, titanium, sintered carbon, aluminum or stainless steel A surface treated with carbon, nickel, titanium, silver or the like may be used. The current collector may have fine irregularities on the surface thereof to increase the adhesive force of the cathode active material, and various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric are possible.

The cathode active material may be a layered compound such as lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), or a compound substituted with one or more transition metals; The formula Li _{1 + x} Mn _{2 - x} O ₄ (Where x is 0 to 0.33), lithium manganese oxides such as LiMnO ₃ , LiMn ₂ O ₃ and LiMnO ₂ ; Lithium copper oxide (Li ₂ CuO ₂ ); Vanadium oxides such as LiV ₃ O ₈ , LiFe ₃ O ₄ , V ₂ O ₅ and Cu ₂ V ₂ O ₇ ; A Ni-site type lithium nickel oxide expressed by the formula LiNi _1-x M _x O ₂ (where M = Co, Mn, Al, Cu, Fe, Mg, B or Ga and x = 0.01 to 0.3); Formula _{LiMn 2-x M x O 2} ( where, M = Co, Ni, Fe , Cr, and Zn, or Ta, x = 0.01 ~ 0.1 Im) or Li ₂ Mn ₃ MO ₈ (where, M = Fe, Co, Ni, Cu, or Zn); A lithium manganese composite oxide having a spinel structure represented by LiNi _x Mn _2-x O ₄ ; LiMn ₂ O _{4 in} which a part of Li in the formula is substituted with an alkaline earth metal ion; Disulfide compounds; Fe ₂ (MoO ₄ ) ₃ , and the like. However, the present invention is not limited to these.

The conductive material is usually added in an amount of 1 to 30% by weight based on the total weight of the mixture including the cathode active material. Such a conductive material is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery, for example, graphite such as natural graphite or artificial graphite; Carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskey such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used.

The binder is a component which assists in bonding of the active material and the conductive material and bonding to the current collector, and is usually added in an amount of 1 to 30% by weight based on the total weight of the mixture containing the cathode active material. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene , Polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butylene rubber, fluorine rubber, various copolymers and the like.

The filler is optionally used as a component for suppressing the expansion of the anode, and is not particularly limited as long as it is a fibrous material without causing a chemical change in the battery. Examples of the filler include olefin polymers such as polyethylene and polypropylene; Fibrous materials such as glass fibers and carbon fibers are used.

The negative electrode is prepared by coating, drying and pressing the negative electrode active material on the negative electrode current collector, and may optionally further include a conductive material, a binder, a filler, and the like as described above.

The negative electrode current collector is generally made to have a thickness of 3 to 500 mu m. Such an anode current collector is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery, and examples of the anode current collector include copper, stainless steel, aluminum, nickel, titanium, sintered carbon, a surface of copper or stainless steel A surface treated with carbon, nickel, titanium, silver or the like, an aluminum-cadmium alloy, or the like can be used. In addition, like the positive electrode collector, fine unevenness can be formed on the surface to enhance the bonding force of the negative electrode active material, and it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams and nonwoven fabrics.

The negative electrode active material may include, for example, carbon such as non-graphitized carbon or graphite carbon; _{Li x Fe 2 O 3 (0≤x≤1} ), Li x WO 2 (0≤x≤1), Sn x Me 1 - x Me 'y O z (Me: Mn, Fe, Pb, Ge; Me' : Metal complex oxides such as Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, Halogen, 0 < x &lt; Lithium metal; Lithium alloy; Silicon-based alloys; Tin alloy; _{SnO, SnO 2, PbO, PbO} 2, Pb 2 O 3, Pb 3 O 4, Sb 2 O 3, Sb 2 O 4, Sb 2 O 5, GeO, GeO 2, Bi 2 O 3, Bi 2 O 4, and Bi ₂ O ₅ ; Conductive polymers such as polyacetylene; Li-Co-Ni-based materials and the like can be used.

The separation membrane is interposed between the anode and the cathode, and an insulating thin film having high ion permeability and mechanical strength is used. The pore diameter of the separator is generally 0.01 to 10 mu m and the thickness is generally 5 to 300 mu m. Such separation membranes include, for example, olefinic polymers such as polypropylene, which are chemically resistant and hydrophobic; A sheet or nonwoven fabric made of glass fiber, polyethylene or the like is used. When a solid electrolyte such as a polymer is used as an electrolyte, the solid electrolyte may also serve as a separation membrane.

The present invention also provides a secondary battery including the stack-folding type electrode assembly.

The secondary battery may be a lithium secondary battery, and the lithium secondary battery may have a structure in which the nonaqueous electrolyte solution containing a lithium salt is impregnated in the electrode assembly.

The nonaqueous electrolytic solution containing a lithium salt is composed of a nonaqueous electrolyte and a lithium salt. Nonaqueous organic solvents, organic solid electrolytes, inorganic solid electrolytes, and the like are used as the nonaqueous electrolytic solution, but the present invention is not limited thereto.

Examples of the non-aqueous organic solvent include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma -Butyrolactone, 1,2-dimethoxyethane, tetrahydroxyfuran, 2-methyltetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane , Acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate Nonionic organic solvents such as tetrahydrofuran derivatives, ethers, methyl pyrophosphate, ethyl propionate and the like can be used.

Examples of the organic solid electrolyte include a polymer electrolyte such as a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphate ester polymer, an agitation lysine, a polyester sulfide, a polyvinyl alcohol, a polyvinylidene fluoride, A polymer containing an ionic dissociation group and the like may be used.

Examples of the inorganic solid electrolyte include Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, LiSiO ₄ , LiSiO ₄ -LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Nitrides, halides and sulfates of Li such as Li ₄ SiO ₄ -LiI-LiOH and Li ₃ PO ₄ -Li ₂ S-SiS ₂ can be used.

The lithium salt is a material that is readily soluble in the non-aqueous electrolyte, for example, LiCl, LiBr, LiI, LiClO 4, LiBF 4, LiB 10 Cl 10, LiPF 6, LiCF 3 SO 3, LiCF 3 CO 2, LiAsF _{6, LiSbF 6, LiAlCl 4,} CH 3 SO 3 Li, (CF 3 SO 2) 2 NLi, chloroborane lithium, lower aliphatic carboxylic acid lithium, lithium tetraphenyl borate and imide.

For the purpose of improving the charge / discharge characteristics and the flame retardancy, the electrolytic solution is preferably mixed with an organic solvent such as pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, glyme, Benzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N, N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, . In some cases, halogen-containing solvents such as carbon tetrachloride and ethylene trifluoride may be further added to impart nonflammability. In order to improve the high-temperature storage characteristics, carbon dioxide gas may be further added. FEC (Fluoro-Ethylene Carbonate, PRS (Propene sultone), and the like.

In one specific _{example, LiPF 6, LiClO 4, LiBF} 4, LiN (SO 2 CF 3) 2 , such as a lithium salt, a highly dielectric solvent of DEC, DMC or EMC Fig solvent cyclic carbonate and a low viscosity of the EC or PC of To a mixed solvent of linear carbonate to prepare a nonaqueous electrolyte solution containing a lithium salt.

The present invention also provides a battery module including the secondary battery as a unit cell, and provides the device including the battery module.

Specific examples of the device include a power tool which is powered by an electric motor and moves; An electric vehicle including an electric vehicle (EV), a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), and the like; An electric motorcycle including an electric bike (E-bike) and an electric scooter (E-scooter); An electric golf cart; And a power storage system, but the present invention is not limited thereto.

As described above, the stack-folding type electrode assembly according to the present invention has a structure in which the separation film and the unit cell are partially laminated and the interface between the separation film and the unit cell is partially abutted, thereby providing an electrolyte flow path for circulating the electrolyte The impregnating property and the impregnation speed for the electrolytic solution are remarkably improved, thereby improving the cell performance such as lifetime characteristics, output characteristics and capacity.

In addition, there is an effect that the safety of the battery is improved by smoothly discharging gas such as electrolytic solution and gas vaporized by high temperature and overcharge.

Figures 1 and 2 are schematic diagrams of one exemplary pull cell that may be used as a unit cell of a stack-folding electrode assembly;
Figures 3 and 4 are schematic diagrams of one exemplary bi-cell that can be used as a unit cell of a stack-folding type electrode assembly;
5 is a schematic view showing a process of laminating a unit cell and a separation film of a stack-folding type electrode assembly according to the prior art;
6 is a schematic view showing a process of laminating a unit cell and a separation film of a stack-folding type electrode assembly according to one embodiment of the present invention;
7 is a schematic view showing a process of laminating a unit cell and a separation film of a stack-folding type electrode assembly according to another embodiment of the present invention;

Hereinafter, the present invention will be described with reference to Examples. However, the following Examples are intended to illustrate the present invention, and the scope of the present invention is not limited thereto.

&Lt; Example 1 >

Negative electrode active material (Graphite), conductive material (Denka black) and binder (PVdF) were mixed in NMP at a weight ratio of 90: 5: 5 and mixed to prepare a negative electrode material mixture. The negative electrode material mixture was coated on a 20 탆 thick copper foil Rolled and dried to prepare a negative electrode.

The anode in the LiMn ₂ O ₄ and _{Li 1/3 Ni 1/3} Mn 1/3 Co 1/3 O 2 using a positive electrode active material, and 90 a conductive material (Denka black), a binder (PVdF), respectively: 5 : 5, and the mixture was mixed. Then, the positive electrode mixture was coated on an aluminum foil having a thickness of 20 탆, rolled and dried to prepare a positive electrode.

A plurality of bi-cells (FIG. 3) having a stacked structure of a positive electrode / separator / negative electrode / separator / positive electrode and a negative electrode / separator / positive electrode / separator / negative electrode (Fig. 4) having a stacked structure of a plurality of bi-cells.

A pressing roll having grooves arranged in such a manner that the positive electrode and the negative electrode face each other in the lamination interface on the continuous long separation film and the interface between the separation film and the bi- Partially laminated. At this time, the interface between the separation film and the unit cell which were not closely adhered by the partial lamination was about 40 to 60% of the total system area of the separation membrane and the unit cell.

A stack-folding type electrode assembly was manufactured by winding it, and the stack was housed in a pouch-shaped battery case. Then, ethyl carbonate, dimethyl carbonate, and ethyl methyl carbonate were mixed at a ratio of 1: 1: 1 based on the volume ratio, A lithium nonaqueous electrolyte solution containing 1 M of LiPF ₆ was injected and sealed to assemble the lithium secondary battery.

&Lt; Example 2 >

As a cathode active material, LiNi _{0 .6} Mn _{0 .2} was assembled, and the lithium secondary battery in the same manner as in Example 1 except for using Co _{0 .2} O _2.

&Lt; Comparative Example 1 &

A lithium secondary battery was produced in the same manner as in Example 1, except that the separating film and the bi-cells were entirely laminated using a cylindrical press roll having no grooved portion.

<Experimental Example 1>

Evaluation of life characteristics of secondary battery

The secondary batteries of Example 1 and Comparative Example 1 were charged and discharged in the range of 2.5 to 4.15 V at 1 C and 31 mA. The battery was repeatedly cycled at room temperature for 50 cycles, and the change in the charging capacity of the battery was measured. The results are shown in Table 1 below.

Initial capacity (mAh) Capacity after 50 cycles (mAh) Capacity retention rate (%) Example 1 31.7 29.2 92 Example 2 31.87 39.38 92.2 Comparative Example 1 31.1 24.9 80

Referring to Table 1, the batteries of Examples 1 and 2 according to the present invention had an initial capacity of about 31.7 mAh or more and a capacity maintenance rate of 92% or more, while the battery of Comparative Example 1 had an initial capacity of 31.1 mAh, 80%, and the cells of Examples 1 and 2 had a higher capacity than the battery of Comparative Example 1, and showed a smaller capacity reduction even after repeated charging and discharging.

<Experimental Example 2>

In order to measure the output at SOC 50 after forming the secondary batteries of Example 1 and Comparative Example 1 up to about 3.8 V, the time required for fixing the output value at 0.8 W and reaching the lower limit voltage of 2.5 V is shown in Table 2 Respectively. At this time, it can be seen that as the output time increases, the cell has a higher output value.

Output time (seconds) Output rate (%) Example 1 40 100 (standard) Example 2 42 105 Comparative Example 1 34 85

Referring to Table 2, it can be seen that the secondary batteries of Examples 1 and 2 according to the present invention have an SOC 50 output of at least 25% at room temperature, as compared with the secondary battery of Comparative Example 1. [ On the other hand, since the output increases at a similar rate over the SOC change, it can be predicted that the secondary batteries of Examples 1 and 2 have superior output characteristics over the entire SOC period as compared with the secondary battery of Comparative Example 1.

Those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims (21)

A stack-folding type electrode assembly having a structure in which unit cells including an anode, a cathode, and a separator are placed on a separation film,
Wherein the separation film and the unit cell are in the form of a partial lamination of a structure in which the interface between the separation film and the unit cell is partially in close contact with each other. The stack-folding type electrode assembly according to claim 1, wherein an electrolyte flow path for electrolyte flow is formed at an interface between the separation film and the unit cell which are not adhered by the partial lamination. [3] The electrode assembly of claim 2, wherein the electrolyte flow path has a strip shape in which one end portion or both end portions of the electrolyte flow path communicate with the outside of the interface between the separation film and the unit cell. The electrode assembly according to claim 2, wherein two or more electrolyte flow paths are formed parallel to each other. The electrode assembly according to claim 2, wherein two or more electrolyte flow paths are formed to cross each other. The electrode assembly according to claim 2, wherein at least two electrolyte flow paths are formed in a radial shape. The stack-folding electrode assembly of claim 1, wherein the partial lamination has a circular or polygonal shape in plan view. The stack-folding type electrode assembly according to claim 1, wherein the interface between the separation film and the unit cell which are not adhered by the partial lamination is 10 to 90% of the total system area of the unit cell and the separator. 9. The stack-folding type electrode assembly according to claim 8, wherein the interface between the separation film and the unit cell which are not adhered by the partial lamination is 30 to 80% of the total system area of the unit cell and the separator. The stack-folding type electrode assembly according to claim 1, wherein the stack-folding type electrode assembly is a large area electrode assembly in which a ratio of an area (mm ² ) of a top surface and a bottom surface of the electrode assembly to a thickness (mm ² ) Stack-folding electrode assembly. The stack-folding type electrode assembly according to claim 1, wherein the partial lamination is performed by a pressure roll or a pressing jig. The stack-folding type electrode assembly according to claim 1, wherein the unit cell is a laminated body including an anode, a cathode, and a separator. A method of manufacturing a stack-folding type electrode assembly according to claim 1,
A process of manufacturing unit cells including an anode, a cathode, and a separator;
Positioning the unit cells on a separation film;
Continuously laminating the unit cells located on the separation film using a pressure roll; And
Winding the partially laminated separation film and the unit cells;
&Lt; / RTI &gt; A method of manufacturing a stack-folding type electrode assembly according to claim 1,
A process of manufacturing unit cells including an anode, a cathode, and a separator;
Positioning the unit cells on a separation film;
Partially laminating the unit cells positioned on the separation film using a pressing jig; And
Winding the partially laminated separation film and the unit cells;
&Lt; / RTI &gt; 15. The manufacturing method according to claim 13 or 14, wherein the pressing roll or the pressing jig is formed with grooves for partial lamination on the outer surface in contact with the unit cell. 15. The method of claim 13 or 14, further comprising heating the unit cells with a heater after placing the unit cells on the separation film. A secondary battery comprising a stack-folding type electrode assembly according to any one of claims 1 to 12. The secondary battery according to claim 17, wherein the secondary battery is a lithium secondary battery. A battery module comprising a secondary battery according to claim 17 as a unit cell. A device comprising a battery module according to claim 19. 21. The device of claim 20, wherein the device is an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, or a system for power storage.

Images