KR20150043721A - Hybrid Stack ＆ Folding Typed Electrode Assembly and Secondary Battery Comprising the Same - Google Patents

Abstract

The present invention relates to a stack-folding type electrode assembly of a structure in which unit cells including a positive electrode, where a positive electrode compound including a positive electrode active material, a conductive material, and a binder is spread on a current collector, are wound by a separation film, and to a secondary battery comprising the same. The loading amount of the positive electrode active material in unit cells located on the outermost layer of the stack-folding type assembly is relatively larger than the loading amount of the positive electrode active material in unit cells located inside the outermost layer.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a hybrid stack-folding type electrode assembly and a secondary battery including the hybrid stack-folding type electrode assembly.

The present invention relates to a hybrid stack-folding type electrode assembly having improved safety and energy density, and a secondary battery including the same.

Due to the depletion of fossil fuels, the price of energy sources has risen and the interest in environmental pollution has been amplified, so the demand for environmentally friendly alternative energy sources has become an indispensable factor for future life. Especially, And miniaturization, the demand for a secondary battery having a small size and a high capacity is increasing.

Typically, in view of the shape of the battery, there is a high demand for a prismatic secondary battery and a pouch-type secondary battery that can be applied to products such as mobile phones with a small thickness. In terms of materials, lithium ion batteries having high energy density, discharge voltage, There is a high demand for a lithium secondary battery such as a lithium ion polymer battery.

The electrode assembly of the anode / separator / cathode structure constituting the secondary battery is largely classified into a jelly-roll type (winding type) and a stack type (laminate type) depending on its structure. In the jelly-roll type electrode assembly, an electrode active material or the like is coated on a metal foil used as a current collector, dried and pressed, cut into a band shape having a desired width and length, and a cathode and an anode are diaphragm- . Although the jelly-roll type electrode assembly is suitable for a cylindrical battery, when it is applied to a square or pouch type battery, it has disadvantages such as separation of electrode active material and low space utilization. On the other hand, the stacked electrode assembly has a structure in which a plurality of anode and cathode unit members are sequentially laminated, and it is easy to obtain a rectangular shape. However, when the manufacturing process is troublesome and impact is applied, .

In order to solve such a problem, an electrode assembly of advanced structure which is a mixed type of jelly-roll type and stack type has been proposed in which a full cell or a positive electrode (cathode) / separator / A stack / folding type electrode assembly having a structure in which a bicell having a (bipolar) / separator / anode (cathode) structure is folded by using a long continuous membrane is developed and disclosed in Korean Patent Application Publication 2001-82058, 2001-82059, 2001-82060, and the like.

On the other hand, a lithium secondary battery used in an electric automobile must be able to be used for more than 10 years under severe conditions in which charging / discharging due to a large current repeats in a short time, in addition to high energy density and characteristics capable of exhibiting large output in a short time, It is inevitably required to have safety and long-term life characteristics far superior to those of a small lithium secondary battery.

In order to produce a battery having a high energy density, the thickness of the electrode must be increased, and more specifically, the thickness of the mixture layer including the electrode active material applied to the collector of the electrode must be increased. However, when the thickness of the electrode mixture layer is increased collectively, various problems arise.

One of the biggest problems is that the electrode is not sufficiently wetted with electrolyte. In general, the electrolyte does not have a high affinity for the electrode material mixture components, and when the volume of the electrode mixture layer is increased, the flow path of the electrolyte solution becomes long, so that the electrolyte solution is not easily permeated, It is difficult to do. If the electrolyte does not sufficiently penetrate into the electrode, the movement of the ions is slowed down and the electrode reaction can not be smoothly performed, resulting in a deterioration of the efficiency of the battery.

For this reason, while conventional stack / folding type electrode assemblies have been proposed, for example, to increase the number of stacks while reducing the loading amount of the electrodes constituting the bi-cells, conventionally, 2n +1 (where n is an integer of 2 to a) bi-cells are stacked to increase the number of stacks in units of 2n + 1 in order to increase the energy density as described above, stacking / folding Type electrode assembly has a lower capacity than a stack / folding type electrode assembly having a smaller stack number. That is, there is a problem that the energy density is low relative to the volume.

Therefore, in order to prevent an increase in the volume of the battery due to an increase in the thickness of the electrode, a technology for further increasing the energy density of the final battery while maintaining a proper stack number is required. In particular, a plurality of battery modules The need for such a high-capacity large capacity battery pack is further demanded.

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 the loading amount of the cathode active material in the unit cells located in the outermost layers of the stack- It is possible to exhibit excellent safety and an energy density higher than that of a volume, thereby exhibiting excellent capacity and life characteristics, so that the desired effect can be achieved And the present invention has been accomplished.

Accordingly, the present invention is a stack-folding type electrode assembly having a structure in which unit cells including a positive electrode coated with a positive electrode mixture containing a positive electrode active material, a conductive material and a binder are wound by a separator film, Characterized in that the loading amount of the cathode active material in the unit cells located in the outermost layers of the folding electrode assembly is relatively larger than the loading amount of the cathode active material in the unit cells located inside the outermost layers, Type electrode assembly.

Specifically, the loading amounts of the cathode active materials of the unit cells located in the uppermost layer and the lower layer, which are the outermost layers of the stack-folding type electrode assembly, may be the same or may be different from each other.

Therefore, in the unit cells located in the inner side in the present invention, the amount of loading of the cathode active material may be 40 to 95% of the amount of the cathode active material loading of the unit cells located in the outermost layers, and may be 50 to 80% .

Specifically, the amount of loading of the positive electrode active material in the inner unit cells may be the same or may be different from each other.

The unit cell may be a bi-cell or a full cell.

The bi-cell may have a structure in which an anode or a cathode is positioned at both ends of the unit cell.

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

The battery pack may be used as a power source for devices requiring high temperature stability, long cycle characteristics, and high rate characteristics. The device may be a computer, a mobile phone, a power tool, an electric vehicle (EV) An electric vehicle, a plug-in hybrid electric vehicle, a motorcycle, an electric golf cart, or a system for power storage.

As described above, the stack-folding type electrode assembly according to the present invention is characterized in that the loading amount of the cathode active material in the unit cells located in the outermost layers of the stack-folding type electrode assembly is smaller than that of the unit cells located inside the outermost layers Since it is relatively larger than the amount of loading of the cathode active material in the cells, it exhibits appropriate rate characteristics and exhibits excellent safety even in an external impact, and includes unit cells all of the same type as the unit cells located inside the outermost layers Can have a higher energy density than a stack-folding type electrode assembly, and exhibit excellent capacity and life characteristics.

1 is a schematic view showing the shape of a unit cell of the present invention.

Accordingly, the present invention is a stack-folding type electrode assembly having a structure in which unit cells including a positive electrode coated with a positive electrode mixture containing a positive electrode active material, a conductive material and a binder are wound by a separator film, Characterized in that the loading amount of the cathode active material in the unit cells located in the outermost layers of the folding electrode assembly is relatively larger than the loading amount of the cathode active material in the unit cells located inside the outermost layers, Type electrode assembly.

The nail test and the impact test were conducted to investigate the safety of a battery against an external impact. In general, nail tests were carried out when the loading amount of the cathode active material in the unit cells of the stack- The test and impact test characteristics are excellent, and the energy density of the battery can be increased. However, when the loading amount of the positive electrode active material is excessively high, the rate of impregnation of the electrolyte solution having a low affinity for the positive electrode active material into the positive electrode active material layer is low, and the diffusion travel distance of lithium ions is increased. Lt; / RTI >

In the stack-folding type electrode assembly according to the present invention, the loading amount of the positive electrode active material in the unit cells located in the outermost layers is different from the loading amount of the positive electrode active material in the unit cells located inside the outermost layers, Particularly, since the loading amount of the cathode active material in the unit cells located in the outermost layers is relatively large, it is possible to exhibit excellent safety against external impact while maintaining proper rate characteristics, and exhibit excellent capacity and life characteristics.

Specifically, the amount of loading of the positive electrode active material in the unit cells located in the uppermost layer and the lowermost layer, which are the outermost layers of the stack-folding type electrode assembly, depends on the loading amount of the positive electrode active material in the unit cells located inside the outermost layers May be mutually the same within a relatively larger range, and may be different from one another.

When the loading amounts of the positive electrode active materials of the unit cells located in the upper and lower layers, which are the outermost layers of the stack-folding type electrode assembly, are different from each other, the loading amount of the positive electrode active material May be greater than the loading amount of the cathode active material of the unit cells located in the lower layer, and conversely, the loading amount of the cathode active material of the unit cells located in the lower layer may be larger than the loading amount of the cathode active material of the unit cells located in the upper layer .

On the other hand, when the amount of the cathode active material loaded in the unit cells located on the inner side is excessively small, there is a fear that the capacity is reduced and the lifetime characteristics of the battery are deteriorated. When the amount of loading of the cathode active material is excessively large, wetting is not sufficiently achieved and the rate characteristics of the battery may be deteriorated.

Therefore, in the unit cells located in the inner side in the present invention, the amount of loading of the cathode active material may be 40 to 95% of the amount of the cathode active material loading of the unit cells located in the outermost layers, and may be 50 to 80% .

Specifically, the amount of loading of the positive electrode active material in the inner unit cells may be the same or may be different from each other.

If the loading amount of the cathode active material in the unit cells located inside the stack-folding type electrode assembly is different from each other, the unit cells located in the outermost layers may have various values within a range smaller than the loading amount of the cathode active material.

The unit cell may be a bi-cell or a full cell.

The bi-cell may have a structure in which an anode or a cathode is positioned at both ends of the unit cell. Specifically, the 'bicell' is a unit in which the same electrode is disposed on both sides of a cell, such as a unit structure of a cathode / separator / cathode / separator / anode and a unit structure of a cathode / separator / anode / separator / Cell is formed by stacking a plurality of bi-cells such that the bi-cell of the anode / separator / cathode / separator / anode structure and the bi-cell of the cathode / separator / anode / separator / cathode structure face each other with the separation film interposed therebetween.

The full cell is a unit cell having a unit structure of a cathode / separator / cathode, in which an anode and a cathode are positioned on both sides of the cell. Such a full cell includes a positive electrode / separator / negative electrode cell and a positive electrode / separator / negative electrode / separator / positive electrode / separator / negative electrode cell having the most basic structure. Are stacked.

In one example, the unit cells can be arranged as shown in Fig. 1, where A and B are unit cells of the same kind and are wound in the direction of the arrow. Here, the loading amount of the cathode active material in the unit cells located in the outermost layers may be relatively larger than the loading amount of the cathode active material in the unit cells located inside the outermost layers.

The positive electrode is prepared, for example, by applying a mixture of a positive electrode active material, a conductive material and a binder to both surfaces of a positive electrode current collector, followed by drying and pressing, and if necessary, a filler may be further added to the mixture.

The positive electrode current collector is not particularly limited as long as the positive electrode current collector has high conductivity without causing chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, and aluminum or stainless steel A surface of which is surface treated with carbon, nickel, titanium or silver can be used, and in detail, aluminum can 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, for example, a layered compound such as lithium cobalt oxide (LiCoO ₂ ) or lithium nickel oxide (LiNiO ₂ ) or a compound substituted with one or more transition metals; Lithium manganese oxides such as Li _{1 + x} Mn _{2 -x} O ₄ (where x is 0 to 0.33), LiMnO ₃ , LiMn ₂ O ₃ , LiMnO ₂ and the like; 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); 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.

On the other hand, the negative electrode is manufactured by applying, drying and pressing an anode active material on an anode 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 not particularly limited as long as it has conductivity without causing a chemical change in the battery. For example, the negative electrode current collector may have a surface of copper, stainless steel, aluminum, nickel, titanium, sintered carbon, 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.

In the present invention, the thickness of the anode current collector may be the same within a range of 6 micrometers to 30 micrometers, but they may have different values in some cases.

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 < 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 membrane is generally 0.01 to 10 micrometers, and the thickness is generally 5 to 300 micrometers. 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.

On the other hand, the separation film in which such unit cells are arranged and wound may or may not be the same material as the separation membrane.

The present invention also provides a secondary battery comprising the stack-folding type electrode assembly, wherein the secondary battery is formed by impregnating a stacked-folding type electrode assembly according to the present invention with a non-aqueous electrolyte containing a lithium salt .

The lithium salt-containing nonaqueous electrolyte is composed of a nonaqueous electrolyte and a lithium salt. Examples of the nonaqueous electrolyte include nonaqueous organic solvents, organic solid electrolytes, inorganic solid electrolytes, and the like.

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 derivatives, Tetrahydrofuran derivatives, ether, 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 substance that is soluble in the nonaqueous electrolyte and includes, 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 carboxylate lithium, lithium tetraphenylborate, and imide.

The nonaqueous electrolyte may contain, for the purpose of improving charge / discharge characteristics, flame retardancy, etc., for example, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, glyme, N, N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, aluminum trichloride and the like may be added have. 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 a preferred _{embodiment, 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 And then adding it to a mixed solvent of linear carbonate to prepare a lithium salt-containing nonaqueous electrolyte.

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

The battery pack may be used as a power source for devices requiring high temperature stability, long cycle characteristics, and high rate characteristics. Examples of the battery pack include small devices such as a computer, a mobile phone, and a power tool, A power tool powered by the motor; 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; Power storage systems, and the like, but are not limited thereto.

Such a lithium secondary battery, a middle- or large-sized battery module including the same as a unit battery, and a structure and a manufacturing method of the battery pack are well known in the art, and a detailed description thereof will be omitted herein.

It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

Claims (14)

A stack-folding type electrode assembly having a structure in which unit cells including a positive electrode active material, a conductive material, and a positive electrode material mixture containing a binder are wound on a current collector are wound by a separation film,
Wherein the loading amount of the cathode active material in the unit cells located in the outermost layers of the stack-folding type electrode assembly is relatively larger than the loading amount of the cathode active material in the unit cells located inside the outermost layers. A folding type electrode assembly. The stack-folding type electrode assembly according to claim 1, wherein the unit cells located in the uppermost layer and the lowermost layer, which are the outermost layers of the stack-folding type electrode assembly, have the same amount of loading of the cathode active material. The stack-folding type electrode assembly according to claim 1, wherein the loading amounts of the cathode active material in the unit cells located at the top layer and the bottom layer, respectively, of the outermost layers of the stack-folding type electrode assembly are different from each other. The stack-folding type electrode assembly according to claim 1, wherein the amount of the cathode active material loaded in the unit cells located at the inner side is about 40 to 95% of the amount of the cathode active material loaded in the unit cells located in the outermost layers. The stack-folding type electrode assembly according to claim 1, wherein the anode active material loading amount in the inwardly positioned unit cells is 50 to 80% of the cathode active material loading amount of the unit cells located in the outermost layers. The stack-folding type electrode assembly according to claim 1, wherein the inwardly positioned unit cells have the same amount of cathode active material loading. The stack-folding type electrode assembly according to claim 1, wherein the inwardly positioned unit cells have different amounts of cathode active material loading. The stack-folding type electrode assembly according to claim 1, wherein the unit cell is a bi-cell or a pull-cell. The stack-folding type electrode assembly according to claim 8, wherein the bi-cell is a structure in which an anode or a cathode is positioned at both ends of the unit cell. A secondary battery comprising a stack-folding type electrode assembly according to any one of claims 1 to 9. A battery module comprising a secondary battery according to claim 10 as a unit cell. A battery pack comprising the battery module according to claim 11. A device comprising a battery pack according to claim 12. 14. The device of claim 13, wherein the device is a computer, a mobile phone, a power tool, an electric vehicle (EV), a hybrid electric vehicle, a plug- Lt; / RTI > system.

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