KR20150033395A - 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 negative electrode where a negative electrode compound is spread on a negative electrode current collector are wound by a separation film, and more specifically, to a stack-folding type electrode assembly comprising two or more first type unit cells and two or more second type unit cells, wherein the thickness of a negative electrode current collector of the first type unit cell and the thickness of a negative electrode current collector of the second type unit cell are different; and the thickness of the negative electrode current collector in the first type unit cells or the second type unit cells located at the outermost layer (n floor; a natural number greater than or equal to 2) of the stack-folding type electrode assembly is relatively smaller than the thickness of the negative electrode current collector in the second type unit cells or the first type unit cells located at an internal layer (n-1 floor; a natural number greater than or equal to 2) facing the outermost layer, and to a secondary battery comprising the same.

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 / anode structure constituting the secondary battery is largely classified into a jelly-roll type (wound type) and a stacked type (laminated 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, dielectrically separated from the positive electrode and the negative electrode using a separator, . 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 cathode and anode unit bodies are sequentially stacked, 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, and has a structure of a full cell or a negative electrode (anode) / separator / A stack / folding type electrode assembly having a structure in which a bicell having a negative electrode / separator / negative electrode structure is folded by using a continuous long separator film has been developed and disclosed in Korean Patent Application Laid- 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 assembly layer is increased, 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, the conventional stack / folding type electrode assemblies are required to have a high energy density characteristic and a high output capacity in such a manner as to increase the number of stacks while reducing the loading amount of the electrodes constituting the bi- To improve the characteristics.

In this case, conventionally, 2n + 1 (where n is an integer of 2 to a) bi-cells are overlapped. However, when the number of stacks is increased by 2n + 1 in order to increase the energy density as described above, , The stack / folding type electrode assembly having a large number of stacks had a lower capacity than the stack / folding type electrode assembly having a small 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, as will be described later, in a stack-folding type electrode assembly including two types of unit cells of different cathode current collectors, the stack- When the thickness of the negative electrode collector in the unit cell located in the outermost layer of the assembly is relatively smaller than the thickness of the negative electrode collector in the unit cell located in the inner layer facing the outermost layer, And have completed the present invention.

Accordingly, the present invention provides a stack-folding type electrode assembly having a structure in which unit cells including a negative electrode coated with a negative electrode mixture on a negative electrode collector are wound by a separation film, Wherein the thickness of the negative electrode collector of the first type unit cell and the thickness of the negative electrode collector of the second type unit cell are different from each other; The thickness of the negative electrode current collector in the first type unit cell or the second type unit cell located in the outermost layer (n layer (n is a natural number of 2 or more) of the stack-folding type electrode assembly is the thickness of the inner layer facing the outermost layer folded electrode assembly is characterized in that the thickness of the negative electrode collector is relatively smaller in the second type unit cell or the first type unit cell located in the n-type layer (n-1 layer; n is a natural number of 2 or more).

In the present invention, the first type unit cell and the second type unit cell may be bicells having structures in which electrodes of the same polarity are located at both ends of the unit cell. Specifically, the first type unit cell may be a bi-cell having a structure in which the cathode is located at both ends of the unit cell, and the second type unit cell may be a bi-cell having a structure in which an anode is located at both ends of the unit cell.

In this case, the thickness of the negative electrode collector of the first type unit cell may be not less than 6 micrometers and less than 15 micrometers, the thickness of the negative electrode collector of the second type unit cell may be not less than 15 micrometers and not more than 30 micrometers, On the contrary, the thickness of the negative electrode collector of the second type unit cell may be not less than 6 micrometers and less than 15 micrometers, and the thickness of the negative electrode collector of the first type unit cell may be not less than 15 micrometers and not more than 30 micrometers.

More specifically, the thickness of the negative electrode collector of the first type unit cell is 8 to 12 micrometers, and the thickness of the negative electrode collector of the second type unit cell is 15 to 20 micrometers And the thickness of the negative electrode collector of the first type unit cell may be not less than 15 micrometers and not more than 20 micrometers, and conversely, the thickness of the negative electrode collector of the second type unit cell may be not less than 8 micrometers and not more than 12 micrometers, have.

3, when the first type unit cell exists in the outermost layer, the total number of the first type unit cells is larger than the total number of the first type unit cells located in the inner layer facing the outermost layer, Lt; / RTI > On the contrary, when the second type unit cell exists in the outermost layer, the total number of the second type unit cells may be larger than the total number of first type unit cells located in the inner layer facing the outermost layer Of course.

In some cases, in addition to the first type unit cell and the second type unit cell, the third type unit cell may further include one or more third type unit cells. In this case, As shown in FIG.

The thickness of the negative electrode collector of the third type unit cell may be not less than 6 micrometers and not more than 30 micrometers, and may be appropriately selected in accordance with a desired battery characteristic.

The anode current collector is not particularly limited as long as it has high conductivity without causing a chemical change in the battery. For example, the anode current collector may be made of copper, stainless steel, aluminum, nickel, titanium, sintered carbon, A surface treated with carbon, nickel, titanium, silver, or the like, and an aluminum-cadmium alloy may be used. In particular, copper may be used.

The present invention also provides a secondary battery including the stack-folding type electrode assembly, which provides the battery module including the secondary battery as a unit battery, and provides the 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.

As described above, in the stack-folding type electrode assembly according to the present invention, the cathode current collectors of the first type unit cell and the second type unit cell have different thicknesses, and the outermost layer (n layer; n is 2 or more (N-1) layer (n is a natural number of 2 or more) facing the outermost layer, the thickness of the negative electrode collector in the first type unit cell or the second type unit cell located in the second type Unit cell or the first type unit cell includes unit cells relatively smaller than the thickness of the negative electrode current collector so as to prevent ignition and explosion of the battery from penetration of the sucking body to thereby exhibit improved safety, The electrode assembly can have a higher energy density than the stack-folding type electrode assembly including the unit cells of the same type, as compared with the stack-folding type electrode assembly, thereby exhibiting excellent capacity and life characteristics.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view showing a configuration of a first type unit cell of the present invention; FIG.
2 is a schematic view showing a configuration of a second type unit cell of the present invention;
3 is a schematic diagram of a manner of arranging first type unit cells and second type unit cells on a separation film according to one embodiment of the present invention; And
Fig. 4 is a schematic view showing the shape of a third type unit cell of the present invention. Fig.

Accordingly, the present invention provides a stack-folding type electrode assembly having a structure in which unit cells including a negative electrode coated with a negative electrode mixture on a negative electrode collector are wound by a separation film, Wherein the thickness of the negative electrode collector of the first type unit cell and the thickness of the negative electrode collector of the second type unit cell are different from each other; The thickness of the negative electrode current collector in the first type unit cell or the second type unit cell located in the outermost layer (n layer (n is a natural number of 2 or more) of the stack-folding type electrode assembly is the thickness of the inner layer facing the outermost layer folded electrode assembly is characterized in that the thickness of the negative electrode collector is relatively smaller in the second type unit cell or the first type unit cell located in the n-type layer (n-1 layer; n is a natural number of 2 or more).

The electrode assembly according to the present invention has a higher energy density than the stack-folding type electrode assembly in which the unit cell located in the inner layer facing the outermost layer and the unit cell having the same thickness of the anode current collector have the same thickness It is possible not only to exhibit a high energy density characteristic with respect to the same thickness, but also to prevent the ignition and explosion of the battery from penetrating the needle body, thereby exhibiting improved safety.

In the present invention, the first type unit cell and the second type unit cell may be bicells having structures in which electrodes of the same polarity are located at both ends of the unit cell. Specifically, the first type unit cell may be a bi-cell having a structure in which the cathode is located at both ends of the unit cell, and the second type unit cell may be a bi-cell having a structure in which an anode is located at both ends of the unit cell.

1 and 2 illustrate the two types of bi-cell structures. Referring to FIG. 1, a cell including a cathode-separator-anode-separator-cathode is illustrated as a bi-cell having a structure in which the cathode is located at both ends of the unit cell. Referring to FIG. 2, A cell composed of a cathode-separator-cathode-separator-cathode is shown as a bi-cell having a structure located at a position shown in FIG.

The bi-cells are an example, and more bi-cells of a stack number are possible.

On the other hand, FIG. 3 shows a schematic view in which these two types of unit cells are arranged on a separation film. However, the arrangement of FIG. 3 is only one example, and the negative electrode and the positive electrode may be alternately arranged in the wound electrode assembly, so the present invention is not limited thereto.

In this case, the thickness of the negative electrode collector of the first type unit cell may be not less than 6 micrometers and less than 15 micrometers, the thickness of the negative electrode collector of the second type unit cell may be not less than 15 micrometers and not more than 30 micrometers, On the contrary, the thickness of the negative electrode collector of the second type unit cell may be not less than 6 micrometers and less than 15 micrometers, and the thickness of the negative electrode collector of the first type unit cell may be not less than 15 micrometers and not more than 30 micrometers.

More specifically, the thickness of the negative electrode collector of the first type unit cell is 8 to 12 micrometers, and the thickness of the negative electrode collector of the second type unit cell is 15 to 20 micrometers And the thickness of the negative electrode collector of the first type unit cell may be not less than 15 micrometers and not more than 20 micrometers, and conversely, the thickness of the negative electrode collector of the second type unit cell may be not less than 8 micrometers and not more than 12 micrometers, have.

If the thickness of the negative electrode current collector is excessively large, the number of unit cells in the electrode assembly of the same thickness is relatively small, so that the amount of loading may be reduced. When the thickness of the negative electrode collector is excessively thin, It is not preferable because a problem may arise.

The stack-folding type electrode assembly according to the present invention is constructed by overlapping unit cells of 2m + 1 (where m is a natural number equal to or greater than 1) unit cells.

3, when the first type unit cell exists in the outermost layer, the total number of the first type unit cells is larger than the total number of the first type unit cells located in the inner layer facing the outermost layer, Lt; / RTI > On the contrary, when the second type unit cell exists in the outermost layer, the total number of the second type unit cells may be larger than the total number of first type unit cells located in the inner layer facing the outermost layer Of course.

Accordingly, in the stack-folding type electrode assembly, the thickness of the negative electrode collector is larger than the number of unit cells having a relatively large thickness of the negative electrode collector, so that the unit cell having the same thickness of the negative electrode collector is included It is possible to exhibit high energy density characteristics in comparison with the same thickness as the electrode assembly, and to prevent the ignition and explosion of the battery from penetrating the needle body, thereby exhibiting improved safety.

In some cases, in addition to the first type unit cell and the second type unit cell, the third type unit cell may further include one or more third type unit cells. In this case, As shown in FIG.

As shown in FIG. 4, for example, the pull cells can have a negative electrode-separator-positive electrode structure, a negative electrode-separator-positive electrode-separator-negative electrode-separator-positive electrode structure, Of course.

The thickness of the negative electrode collector of the third type unit cell may be not less than 6 micrometers and not more than 30 micrometers, and may be appropriately selected in accordance with a desired battery characteristic.

The position of the third type unit cell is not limited and may be located between the first type unit cell and the second type unit cells and may be located at the outermost position of the electrode assembly.

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

The anode current collector is not particularly limited as long as it has high conductivity without causing a chemical change in the battery. For example, the anode current collector may be made of copper, stainless steel, aluminum, nickel, titanium, sintered carbon, A surface treated with carbon, nickel, titanium, silver, or the like, and an aluminum-cadmium alloy may be used. In particular, copper may be used. The current collector may have fine irregularities on the surface thereof to increase the adhesive force of the negative electrode 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 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, but the present invention is not limited thereto.

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 anode 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 that assists in binding of the active material to the conductive material and bonding to the current collector, and is usually added in an amount of 1 to 30 wt% based on the total weight of the mixture containing the negative 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 negative electrode, and is not particularly limited as long as it is a fibrous material without causing 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 positive electrode is prepared by applying, drying and pressing the positive electrode active material on the positive electrode current collector, and may optionally further include a conductive material, a binder, a filler, and the like as described above.

The positive electrode current collector is not particularly limited as long as the positive electrode current collector has conductivity without causing chemical change in the battery. For example, the negative electrode current collector is made of stainless steel, aluminum, nickel, The surface of stainless steel may be surface treated with carbon, nickel, titanium or silver, or the like. In addition, like the negative electrode collector, fine unevenness can be formed on the surface to enhance the bonding force of the positive electrode active material, and it can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric.

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

The cathode active material may be, for example, 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; 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 separation membrane is interposed between the cathode and the anode, 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 (18)

A stack-folding type electrode assembly having a structure in which unit cells including a negative electrode coated with a negative electrode mixture on a negative electrode collector are wound by a separating film,
Wherein the thickness of the negative collector of the first type unit cell and the thickness of the negative collector of the second type unit cell are different from each other;
The thickness of the negative electrode current collector in the first type unit cell or the second type unit cell located in the outermost layer (n layer (n is a natural number of 2 or more) of the stack-folding type electrode assembly is the thickness of the inner layer facing the outermost layer wherein the thickness of the negative electrode collector is smaller than the thickness of the negative electrode collector in the second type unit cell or the first type unit cell located in the n-type layer (n-1 layer; n is a natural number of 2 or more). The stack-folding type electrode assembly according to claim 1, wherein the first type unit cell and the second type unit cell are bi-cells having electrodes of the same polarity positioned at both ends of the unit cell. The method of claim 2, wherein the first type unit cell is a bi-cell having a structure in which a cathode is positioned at both ends of the unit cell, and the second type unit cell is a bi- cell having a structure in which an anode is positioned at both ends of the unit cell Wherein the stacked electrode assembly is a stacked-type electrode assembly. The method according to claim 3, wherein the thickness of the negative electrode collector of the first type unit cell is from 6 micrometers or more to less than 15 micrometers, and the thickness of the negative electrode collector of the second type unit cell is from 15 micrometers to 30 micrometers Wherein the stacked-folded electrode assembly comprises: The method according to claim 3, wherein the thickness of the negative electrode collector of the second type unit cell is from 6 micrometers or more to less than 15 micrometers, and the thickness of the negative electrode collector of the first type unit cell is 15 micrometers or more to 30 micrometers or less Wherein the stacked-folded electrode assembly comprises: The method according to claim 3, wherein the thickness of the negative electrode collector of the first type unit cell is 8 to 12 micrometers and the thickness of the negative electrode collector of the second type unit cell is 15 to 20 micrometers Wherein the stacked-folded electrode assembly comprises: The method according to claim 3, wherein the thickness of the negative collector of the second type unit cell is 8 to 12 micrometers, and the thickness of the negative collector of the first type unit cell is 15 to 20 micrometers Wherein the stacked-folded electrode assembly comprises: The negative electrode collector according to claim 1, wherein the negative electrode current collector is one obtained by surface-treating a surface of copper, stainless steel, aluminum, nickel, titanium, fired carbon, copper or stainless steel with carbon, nickel, titanium, silver, Alloy. ≪ RTI ID = 0.0 > 11. < / RTI > The stack-folding type electrode assembly according to claim 1, wherein the negative electrode collector is copper. The stack-folding type electrode assembly according to claim 3, wherein the total number of the first type unit cells is greater than the total number of the second type unit cells. The stack-folding type electrode assembly of claim 1, further comprising at least one third type unit cell in addition to the first type unit cell and the second type unit cell. 12. The stack-folding type electrode assembly according to claim 11, wherein the third type unit cell is a pull cell having a structure in which electrodes having different polarities are located at both ends of the unit cell. 12. The stack-folding type electrode assembly according to claim 11, wherein the thickness of the negative electrode collector of the third type unit cell is not less than 6 micrometers and not more than 30 micrometers. A secondary battery comprising a stack-folding type electrode assembly according to any one of claims 1 to 13. 15. A battery module comprising a secondary battery according to claim 14 as a unit cell. A battery pack comprising the battery module according to claim 15. A device comprising a battery pack according to claim 16. 18. The system of claim 17, 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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