KR101744120B1 - Pouch-typed Secondary Battery of Improved Safety of Nail Penetration Test - Google Patents

Abstract

The present invention relates to an electrode assembly and a lithium secondary battery including the same, wherein an anode located at an outermost portion of a unit cell laminate structure is thicker than an electrode located inside the electrode assembly, in order to improve safety in the needle penetration test of the battery cell And more particularly, to an electrode assembly comprising a plurality of unit cells and a separation film for continuously winding up the unit cells, wherein the electrode assembly has n unit cells arranged on a long length separating film And the first unit cell is located at the center of the electrode assembly with respect to the stacking direction of the unit cells and the n-1 unit cell and the n unit cell are located at the outermost of the electrode assembly, n unit cell, and at least one unit cell of the n-th unit cell and the (n-1) th unit cell in the unit cell laminate structure is formed of It characterized in that it comprises a thick anode, or positive electrode and the negative electrode than in the sub-electrode assembly and to a lithium secondary battery comprising the same.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a pouch-typed secondary battery,

The present invention relates to an electrode assembly including a unit cell having improved safety and a capacity per unit volume, and a lithium secondary battery including the electrode assembly.

As technology development and demand for mobile devices have increased, there has been a rapid increase in demand for secondary batteries as energy sources. Among such secondary batteries, lithium secondary batteries, which exhibit high energy density and operational potential, long cycle life, Batteries have been commercialized and widely used.

However, since such a lithium secondary battery has a problem in safety, attempts have been made to solve it.

Specifically, when the lithium secondary battery is overcharged, excess lithium comes out from the anode and excess lithium is inserted into the cathode, so that lithium metal having a very high reactivity is deposited on the surface of the cathode, and the anode also becomes thermally unstable. The explosion reaction of the battery causes a sudden exothermic reaction, resulting in safety problems such as ignition and explosion of the battery.

 In addition, when a material having electrical conductivity such as a nail penetrates the battery, electrochemical energy inside the battery is converted into thermal energy, and rapid heat generation occurs. As a result, the positive or negative electrode material chemically reacts with heat, Causing a safety problem such as ignition or explosion of the battery.

In the case of nail penetration, compression, impact, high temperature exposure, etc., the anode and the cathode inside the battery are internally short-circuited. At this time, an excessive current flows locally and a heat is generated by this current. Since the magnitude of the short-circuit current due to local short circuit is inversely proportional to the resistance, the short-circuit current flows through the metal foil mainly used as a current collector, and the current flows through the metal foil used as the current collector. A very high heat is locally generated around the portion.

If a heat is generated in the battery, the separator shrinks and short-circuits the positive and negative electrodes again, and repeated heat generation and shrinkage of the separator shrinks the short-circuit section, resulting in thermal runaway, And the electrolytic solution react with each other or burn, which is a very large exothermic reaction, which eventually causes the battery to ignite or explode. This risk is particularly important as the energy density increases as the capacity of the lithium secondary battery increases.

In order to overcome such a problem and to improve the safety during overcharging, a material having high thermal conductivity or a bulletproof material is attached to the pouch so as to pass the other material before the nail penetrates, However, such a method has a problem in that additional process and cost are required in manufacturing the secondary battery, the volume increases, and the capacity per unit volume is reduced.

Therefore, there is a high need for a secondary battery which can effectively improve the safety of the battery without additional process and material, and can increase the cycle characteristic and capacity per unit volume.

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

The inventors of the present application have carried out intensive research and various experiments and, as will be described later, in an electrode assembly comprising a plurality of unit cells and a separation film for continuously winding up the unit cells, It has been confirmed that a desired effect can be achieved when at least one unit cell in the outermost unit cell includes a positive electrode or a positive electrode and a negative electrode which are thicker than the electrodes located in the inside, .

Accordingly, an electrode assembly according to the present invention includes an electrode assembly including a plurality of unit cells and a separation film for continuously winding the unit cells,

The electrode assembly includes a first unit cell, a second unit cell, and a second unit cell. The first unit cell is located at the center of the electrode assembly with respect to the stacking direction of the unit cells, And the n-th unit cell is sequentially wound from the first unit cell to the n-th unit cell so as to be positioned at the outermost portion of the electrode assembly;

In the unit cell laminated structure, at least one unit cell of the n-th unit cell and the (n-1) th unit cell includes a positive electrode or a positive electrode and a negative electrode which are thicker than the electrodes located inside. The n is a natural number of 3 to 20, and may be an odd number or an even number.

In one specific example, at least one unit cell of the n-2 th unit cell and the n-3 th unit cell of the unit cell laminated structure has a thicker anode than the electrodes located in the first unit cell to the (n-4) Or at least one of the n-4 th unit cell and the (n-5) th unit cell may include a positive electrode that is thicker than the electrodes located in the 1 st to (n-6) th unit cells, or And may include an anode and a cathode. (Where n is a natural number from 8 to 20)

That is, for example, when the electrode assembly includes nine unit cells, the ninth unit cell and the eighth unit cell, which are positioned at the outermost positions in the unit cell stack structure, A thicker anode, or an anode and a cathode, wherein the ninth unit cell to the sixth unit cell are thicker than the first unit cell to the fifth unit cell, or an anode and a cathode, To the fourth unit cell may include a positive electrode or a positive electrode and a cathode that are thicker than the first unit cell to the third unit cell.

At this time, considering the problem that the impregnability of the electrolyte solution is decreased due to the increase of the thickness of the electrodes, the rate characteristic is decreased, the battery is disadvantageous for winding, and the volume of the battery is increased. As long as the safety of the needle- It is most preferable that only the n-th unit cell and / or the (n-1) th unit cell are thicker than the unit cells located inside, or the anode and the cathode.

Here, the thickness of the electrode means the thickness of the electrode assembly comprising the electrode active material and the current collector, and when the electrode mixture is prepared in the form of a slurry by mixing a predetermined solvent, the thickness of the solid material excluding the solvent in the slurry .

In other words, the thickness of the current collector constituting the anode located at the outermost of the n-th unit cell and the (n-1) th unit cell is the same as the thickness of the current collector of the anode or the cathodes located inside, The thickness of the positive electrode mixture constituting the anode located at the outermost periphery is thicker than the electrode mixture of the electrode located in the inside so that the short circuit current is blocked by the high anode mixture to prevent the continuous heat generation and reduce the risk of ignition. .

Specifically, the outermost electrode may be 5% to 50% thicker than the electrodes located inside. If the outermost electrodes are thicker than 50% in comparison with the electrodes inside, it is difficult to predict the capacity of the battery and there is a problem that the outermost electrodes are out of the stretching / There is a problem that it is difficult to achieve a desired effect when the difference is less than 5%. It is more preferable that the difference in thickness is 5% to 50%.

In the present invention, the average thickness of the electrodes is not less than 80 micrometers and not more than 200 micrometers. Specifically, the thickness of the electrode located in the inner portion is not less than 80 micrometers and not more than 150 micrometers in a condition range smaller than the thickness of the electrode located at the outermost portion, and the thickness of the electrode located at the outermost portion is not less than 100 micrometers and not more than 180 micrometers have.

In the case of an electrode located in the inside, an electrode having a thickness of less than 80 micrometers outside the above-mentioned range is difficult to obtain a desired capacity because the application amount of the electrode mixture is too small. When the electrode has a thickness exceeding 150 micrometers, There is a problem that the rate characteristic decreases.

In the case of the electrode located at the outermost part, if it is out of the above range and has a thickness of less than 100 micrometers, it is difficult to achieve the intended effect because the thickness is different from that of the electrode located inside, If the thickness of the electrode located inside is more than 150 micrometers, the total impregnation property is likewise deteriorated, which is disadvantageous for winding, and the volume of the battery becomes large, making it difficult to apply to small-sized apparatuses.

In one specific example, the unit cells include a bicell having electrodes of the same polarity located at both ends of the unit cell and a full cell having electrodes of different polarity located at both ends of the unit cell, or a structure including only a full cell.

Specifically, a pull cell as a unit cell is a cell having a unit structure of a cathode / separator / cathode, and is a cell in which an anode and a cathode are disposed on both sides of the cell. Such a pull cell may include a cathode / separator / cathode cell and an anode / separator / cathode / separator / anode / separator / cathode cell having the most basic structure. In order to construct an electrochemical cell including the secondary cell by using such a pull cell, a plurality of pull cells should be stacked such that the anode and the cathode face each other with the separation film interposed therebetween.

Also, the bi-cell as a unit cell may have a structure such as a unit structure (A-type bi-cell) of a cathode / separator / cathode / separator / anode and a unit structure (C-type bi-cell) of a cathode / separator / anode / In which the same electrode is located. In order to construct an electrochemical cell including a secondary cell using such a bi-cell, a bi-cell and a cathode / separator / anode / separator / cathode structure of a cathode / separator / cathode / separator / A plurality of bi-cells must be stacked so that the bi-cells face each other.

In the unit cell laminated structure, the first unit cell is positioned at the center of the electrode assembly with respect to the stacking direction of the unit cells, and the n-1 th unit cell and the n th unit cell are located at the outermost positions of the electrode assembly, The unit cells are sequentially wound from the first unit cell to the n-th unit cell, and each unit cell may consist of only an A-type bi-cell or a C-type bi-cell.

When the n is an odd number, the n-th unit cell and the (n-1) th unit cell located at the outermost unit are arranged such that the polarity of the electrode facing each other with the separation film after winding is different, The n-th unit cell and the (n-1) th unit cell have the same structure so as to maintain the series connection. That is, when each unit cell is composed of bi-cells and n is an odd number, if the n-1 unit cell is an A-type bi-cell, the n-th unit cell is also an A-type bi- If it is a C-type bi-cell, the n-th unit cell is also a C-type bi-cell.

The n-unit cell or n-1 unit cell may be an A-type bi-cell or a C-type bi-cell, but it is preferably an A-type bi-cell so that the polarity of the outermost electrode is an anode.

For example, when the electrode assembly includes unit cells composed of only seven bi-cells, the first unit cell is positioned at the center of the electrode assembly with respect to the stacking direction of the unit cells, And the seventh unit cells are respectively located. Here, when the sixth unit cell is the A-type bi-cell, the seventh unit cell is also the A-type bi-cell, and when the sixth unit cell is the C-type bi-cell, the seventh unit cell is also the C-type bi- cell. The sixth unit cell and the seventh unit cell are preferably an A-type bipolar cell and preferably include a positive electrode that is thicker than the first unit cell to the fifth unit cell so as to improve safety in the needle penetration test.

The anodes located at the outermost peripheries according to the present invention may also have a structure in which the thicknesses of the positive electrode material mixture layers are equal to each other so as to ensure the normal efficiency of the manufacturing process. Specifically, when the n-1 th unit cell and the n th unit cell are A-type bi-cells, the anode is located at the outermost portion of the wound electrode assembly, and the anode located at the outermost portion is thicker than the anode Structure, and may have the same thickness.

In one specific example, the positive electrode constituting the bi-cell or pull-cell is composed of a structure in which a positive electrode mixture layer containing a positive electrode active material is applied to the current collector, and the negative electrode is formed by applying a negative electrode mixture layer containing a negative electrode active material Structure. In addition, in order to exhibit excellent capacity, the positive electrode or negative electrode may have a structure in which the positive electrode or negative electrode mixture layer containing an active material is applied on both sides of the current collector.

At this time, in order to reduce the normal time and cost of the manufacturing process, the thicknesses of the collectors of the positive electrode are the same and the thicknesses of the collectors of the negative electrode are the same.

The present invention also provides a lithium secondary battery comprising a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte containing a lithium salt.

In one specific example, the cathode active material constituting the positive electrode mixture may include at least one compound selected from the following formula (1)

Li _x M _y M ' _(2-y) O _z A _4-z (1)

0.85? X? 1.15

0.5? Y? 2.0

1.5? Z? 4.0

M is at least one member selected from the group consisting of Ni, Mn, Co, Ru, Mo, Cu, Nb, Te, Re, Ir, Pt, Cr, S, W, Os and Po;

M 'is one selected from the group consisting of Al, Ti, Mg, Fe, Cr, V, Cu, B, Ca, Zn, Zr, Nb, Mo, Sr, Sb, W, Bi, Or more;

A is a monovalent or divalent anion.

The cathode active material includes a layered crystal structure or a spinel crystal structure lithium-containing metal oxide and a lithium-containing nickel oxide. Spinel Crystal Structure The lithium-containing metal oxide has a composition of LiM ₂ O ₄ , (M = Mn, Ni), and the spinel oxide having a cubic crystal structure has a voltage behavior of 4 V. Due to the three- Which is superior to an anode material of a layered structure. LiMn ₂ O ₄ , which is a representative manganese-based spinel material, is superior in terms of cost due to the use of low-cost Mn, but has a life-span problem of a rapid capacity decrease due to the release of Mn, which is a transition metal, at an elevated temperature. It is preferred that it comprises at least one compound selected from formula (1a)

_{Li a M (1-b)} M 'b O c A 2-c (1a)

0.85? A?

0.5? B? 1

1.8? C? 2.0

M comprises Co and optionally comprises at least one selected from Ni and Mn;

M 'is at least one selected from the group consisting of Al, Ti, Mg, Fe, Cr, V, Cu, B, Ca, Zn, Zr, Nb, Mo, Sr, Sb, W and Bi;

A is a monovalent or divalent anion.

The compound represented by the general formula (Ia) generally has a structure of a-NaFeO ₂ of hexagonal symmetry, and has excellent lifetime characteristics and charge / discharge efficiency. (LiCoO ₂ ), LiNiO ₂ , two kinds of transition metals (LiNi _x Co _y O ₂ ), or LiNi _x Co _y Mn _z O ₂ in which three kinds of transition metals are mixed, Li [Ni _1/3 Co _1/3 Mn _1/3 ] O _{2 in which} three kinds of transition metals are uniformly distributed, and the like.

In addition to the compound of formula (1a), general lithium transition metal oxides which do not satisfy the above conditions may be further included. These general lithium transition metal oxides include oxides composed of only one kind of Ni, Co, and Mn, and oxides containing two or more kinds, and examples thereof include lithium transition metal oxides known in the art. In this case, the compound of formula (I) may be contained in an amount of at least 30% by weight, more specifically 50% by weight or more, based on the total weight of the active material.

The positive electrode or the negative electrode according to the present invention may be prepared by mixing a positive electrode or a negative electrode mixture containing a conductive agent and a binder with a predetermined solvent such as water or NMP to form a slurry, Applying the slurry to the positive electrode current collector, followed by drying and rolling.

If necessary, the positive electrode or negative electrode mixture may further contain at least one substance selected from the group consisting of a viscosity adjusting agent and a filler.

The cathode current collector is generally made to have a thickness of 3 to 500 mu m. Such a positive electrode collector is not particularly limited as long as it has conductivity without causing chemical change to the battery, and may be formed on the surface of stainless steel, aluminum, nickel, titanium, sintered carbon or aluminum or stainless steel 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 conductive agent is a component for further improving the conductivity of the electrode active material and may be added in an amount of 0.01 to 30% by weight based on the total weight of the electrode mixture. Such a conductive agent is not particularly limited as long as it has electrical conductivity without causing a chemical change in the battery, and examples thereof include graphite such as natural graphite and 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 added to the binder in an amount of 1 to 30% by weight, based on the total weight of the mixture containing the cathode active material, as a component that assists in bonding between the active material and the conductive agent and bonding to the current collector. 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, and various copolymers.

The viscosity adjusting agent may be added up to 30% by weight based on the total weight of the electrode mixture, so as to control the viscosity of the electrode mixture so that the mixing process of the electrode mixture and the coating process on the collector may be easy. Examples of such viscosity modifiers include carboxymethylcellulose, polyvinylidene fluoride and the like, but are not limited thereto. In some cases, the above-described solvent may play a role as a viscosity adjusting agent.

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

The negative electrode may be prepared by applying a negative electrode mixture containing a negative electrode active material on a negative electrode collector, followed by drying. The negative electrode mixture may further contain a conductive agent, a binder, and the like as described above .

The negative electrode 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 high conductivity without causing chemical changes in the battery, and examples thereof include copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless steel Surface-treated with carbon, nickel, titanium, silver or the like, 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.

Examples of the negative electrode active material include carbon and graphite materials such as natural graphite, artificial graphite, expanded graphite, carbon fiber, non-graphitizable carbon, carbon black, carbon nanotube, fullerene and activated carbon; Metals such as Al, Si, Sn, Ag, Bi, Mg, Zn, In, Ge, Pb, Pt, and Ti that can be alloyed with lithium and compounds containing these elements; Complexes of metals and their compounds and carbon and graphite materials; Lithium-containing nitrides, and the like. Among them, a carbon-based active material, a tin-based active material, a silicon-based active material, or a silicon-carbon based active material is more preferable, and these may be used singly or in combination of two or more.

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 lithium salt-containing non-aqueous electrolyte solution is composed of an electrolytic solution and a lithium salt. As the electrolyte, a non-aqueous organic solvent, an organic solid electrolyte, and an inorganic solid electrolyte may be used.

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 3 Li, (CF 3 SO 2) 2 NLi, chloroborane lithium, lower aliphatic carboxylic acid lithium, lithium tetraphenyl borate and imide have.

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), FEC (fluoro-ethylene carbonate), and the like.

The present invention also provides a lithium secondary battery in which an electrode assembly is embedded in a battery case together with a non-aqueous electrolyte.

Specifically, the battery case may include a laminate sheet including a resin layer and a metal layer. Specifically, it may be a pouch-shaped battery case made of a laminate sheet comprising an outer coating layer made of a weather resistant polymer, an inner sealant layer made of a heat-sealable polymer, and a barrier layer interposed between the outer coating layer and the inner sealant layer, A pouch-shaped battery case made of an aluminum laminate sheet having a barrier layer made of Al.

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

Specific examples of such a device include a small device such as a computer, a mobile phone, a power tool, a power tool powered by an electric 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.

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.

As described above, the electrode assembly according to the present invention includes a plurality of unit cells and a separation film for continuously winding up the unit cells. In the electrode assembly, at least one of the unit cells located at the outermost of the unit cell stack structure The unit cell of the unit cell includes a positive electrode or a positive electrode and a negative electrode which are thicker than the electrodes positioned inside, thereby effectively improving the safety of the cell while preventing the thickness of the entire electrode from rising.

1 is a schematic view of a typical prior art stack / folding type electrode assembly before winding;
Figure 2 is a schematic representation after winding of a conventional representative stack / folding type electrode assembly;
3 is a schematic view of an electrode assembly according to one embodiment of the present invention before winding;
4 is a schematic view after winding of an electrode assembly according to one embodiment of the present invention;
5 is a schematic view showing an A-type bi-cell and a C-type bi-cell which are the internal unit cells of FIG. 4;
6 is a schematic diagram of an A-type bi-cell which is the outermost unit cell of FIG. 4; And
FIG. 7 is a schematic view of the needle-shaped conductor passing through the outermost unit cell of FIG. 2 and the outermost unit cell of FIG. 4;

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings, but the present invention is not limited by the scope of the present invention.

1 and 2 schematically show a general structure of a typical stack / folding type electrode assembly of the related art.

1, the electrode assembly 10 includes a cathode-separator-anode-separator-cathode unit C-type bi-cells 20, 50 and 60 and a cathode-separator- 2, 3, 4, 5, and 6 on the separation film 90. The electrode assembly 10 is formed of a combination of the A type bi-cells 30, 40, 70, 6 and 7 are arranged and the separation films 90 are sequentially wound in the first unit cell 20 to the seventh unit cell 80 direction 91 to produce the electrode assembly 10 as shown in FIG.

2, the separation film 90 interposed between the unit cells 20, 30, 40, 50, 60, 70, and 80 of the electrode assembly 10 has electrode terminals 30, 40, 50, 60, 70, 80 of the unit cells 20, The lower anode 71 and the upper anode 81 located in the outermost unit cells 70 and 80 of the electrode assembly 10 constitute the unit cells 20, And have the same thickness as the electrodes.

3 and 4 are schematic views of an electrode assembly according to one embodiment of the present invention.

4, the electrode assembly 100 includes a cathode-separator-anode-separator-cathode unit C-type bi-cells 200, 500 and 600 and a cathode-separator-cathode- And the first unit cell 200 is a C-type bi-cell. When the first unit cell 200 is disposed in such a manner that the facing electrodes have opposite polarities, The sixth unit cell 700 and the seventh unit cell 800 located at the outermost are the A type bicells. In the electrode assembly 100, the unit cells 200, 300, 400, 500, 600, 700, and 800 are arranged on the separation film 900 and the seventh unit cells 800 ) Direction 901, and the electrode assembly 100 as shown in FIG. 4 is manufactured.

Accordingly, the anodes 701 and 801 are located at the outermost portions of the electrode assembly after winding, and the outermost anodes 701 and 801 are formed in the inner unit cells 701 and 801, unlike the outermost anodes 71 and 81 of FIGS. The electrodes 200, 300, 400, 500, 600, 700, and 800 are thicker than the electrodes.

FIG. 5 is a schematic diagram of a first unit cell 200 and a second unit cell 300 among the C-type bi-cells, which are internal unit cells of FIG.

The C-type bicells 200, 500 and 600 of FIG. 4 have the same structure as the first unit cell 200 and the A-type bicells 300 and 400 have the same structure as the second unit cell 300 . The first unit cell 200 has a structure of a cathode 201, a separation membrane 204, an anode 202, a separation membrane 204, and a cathode 203. The negative electrode 201 facing the separator has a structure in which positive electrode mixture layers 201a and 201c including a positive electrode active material are coated on both sides of the current collector 201b. The second unit cell 300 has a structure of an anode 301 / a separator 304 / a cathode 302 / a separator 304 / an anode 303. The anode 301 facing the separator has a structure in which the cathode mixture layers 301a and 301c including the cathode active material are coated on both sides of the current collector 301b.

The current collector 201b included in the cathode 201 of the first unit cell 200 has the same thickness as the current collector included in the anode 202 and the cathode 203 constituting the first unit cell, The current collector 301b included in the anode 301 of the unit cell 300 and the cathode 302 constituting the second unit cell 300 and the current collector included in the anode 303 have the same thickness.

FIG. 6 is a schematic diagram of a sixth unit cell 700, which is one of the outermost unit cells of FIG. 4. FIG. 7 is a cross-sectional view of the unit cell 70 located at the lowermost end of FIG. 700) through the needle-shaped conductor. Referring to FIG. 6, the sixth unit cell 700 has a structure in which the outermost electrode is thicker than the other electrodes. The sixth unit cell 700 may have the same structure as the unit cell 710 and / or the unit cell 720.

The unit cell 710 has an A-type bi-cell structure of an anode 711, a separation membrane 714, a cathode 712, a separation membrane 714, and an anode 713, And the electrodes 712 and 713 located at the same position.

Likewise, the unit cell 720 includes an A-type bi-cell structure of an anode 721, a separation membrane 724, a cathode 722, a separation membrane 724, and a cathode 723, The electrodes 722 and 723 are thicker than the electrodes 722 and 723 located inside.

When the unit cell 710 and the unit cell 720 are compared with each other, the anode 711 located at the outermost portion of the unit cell 710 is coated with the cathode mixture 711a applied on one surface of the current collector 711b, And the anode 721 located at the outermost periphery of the unit cell 720 has the same structure as the cathode mixture 721a and 721c on both sides of the current collector 721b.

Referring to FIG. 7, in the case of the unit cell 700, in the needle penetration test, the outermost cathode composite 711a has a thick structure, and the area where the needle-shaped conductor A touches the cathode mixture 711a having a high resistance The unit cell 70 has a small contact area with the positive electrode mixture 71a while passing through the positive electrode 71 located at the outermost periphery of the unit cell 70, The unit cell 700 can prevent heat generation and fire more effectively than the unit cell 70 and improve the safety.

Hereinafter, the present invention will be described in further detail with reference to the following examples. However, the following examples are for illustrative purposes only and are not intended to limit the scope of the present invention.

≪ Example 1 >

Manufacture of anode

LiCoO ₂ was used as a positive electrode active material, and N-methyl-2-pyrrolidone (NMP) as a solvent was added to 96% by weight of LiCoO ₂ and 2.0% by weight of Super-P The anode mixture slurry was prepared, coated on aluminum foil, dried and pressed to prepare a cathode.

Cathode manufacturing

Artificial graphite was used as the negative electrode active material. An anode mixture slurry was prepared by adding 96.3% by weight of artificial graphite, 1.0% by weight of Super-P (conductive agent) and 2.7% by weight of PVdF (binder) The negative electrode was prepared by coating, drying and pressing on copper foil.

Manufacture of Secondary Battery

Three C-type bi-cells such as 200 in FIG. 5 and two A-type bi-cells such as 300 in FIG. 5 were fabricated to have an electrode thickness of 100 micrometers using the anode and the cathode, Two A-type bi-cells are fabricated, one with an anode and a cathode each having a thickness of 100 micrometers, and one with a thickness of 130 micrometers. The bi-cells having the structure as shown in FIG. 5 become the first unit cell and the fifth unit cell, and the A-type bi-cell including the outermost electrode having the structure of FIG. 6, 3 and the seventh bi-cells were sequentially wound using a polypropylene separation film to produce an electrode assembly as shown in FIG. 4, and the electrode assembly was placed in a pouch Shaped battery case, and then a 1M LiPF ₆ carbonate-based solution electrolyte was injected to complete the secondary battery.

≪ Comparative Example 1 &

A secondary battery was manufactured in the same manner as in Example 1, except that the outermost electrodes of the sixth unit cell and the seventh unit cell were formed to have a thickness of 100 micrometers in the same manner as the internal electrodes.

<Experimental Example 1>

Twenty secondary batteries prepared in Example 1 and Comparative Example 1 were prepared in a fully charged state of 4.35V. Using a nail penetration tester, a 2.5 mm diameter nail made of iron was pierced through the center of the cell, and the ignition was measured.

The penetration speed of the nail was constant at 12 m / min. The results are summarized in Table 1 below.

Whether ignited Unknown Sample Maximum Temperature (℃) Example 1 No ignition 85.5 Comparative Example 1 Ignition 105.5

As shown in Table 1, the secondary batteries according to the present invention were not short-circuited and ignited, while the secondary batteries of Comparative Example 1 were short-circuited and ignited in a plurality of batteries.

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 (21)

An electrode assembly comprising a plurality of unit cells and a separation film for continuously winding up the unit cells,
The electrode assembly includes a first unit cell, a second unit cell, and a second unit cell. The first unit cell is located at the center of the electrode assembly with respect to the stacking direction of the unit cells, And the n-th unit cell is sequentially wound from the first unit cell to the n-th unit cell so as to be positioned at the outermost portion of the electrode assembly,
In the unit cell laminated structure, at least one unit cell of the n-th unit cell and the (n-1) th unit cell includes a positive electrode or a positive electrode and a negative electrode which are thicker than the electrodes located inside,
The electrodes are formed as a positive electrode or a negative electrode. The positive electrode has a structure in which a positive electrode mixture layer containing a positive electrode active material is applied to the current collector. The negative electrode has a structure in which a negative electrode mixture layer containing a negative electrode active material is coated on the current collector However,
And at least one of the n-th unit cell and the (n-1) th unit cell is a bi-cell. The method of claim 1, wherein at least one unit cell of the n-2 th unit cell and the n-3 th unit cell of the unit cell laminated structure has a thickness larger than that of the electrodes located in the first unit cell to the n- , Or an anode and a cathode. The method of claim 2, wherein at least one unit cell of the n-4th unit cell and the n-5th unit cell of the unit cell laminated structure has a thickness larger than that of the first unit cell to the n- , Or an anode and a cathode. [3] The apparatus of claim 1, wherein the unit cells are bicells having electrodes of the same polarity positioned at both ends of the unit cells, and / or full-cell electrodes having different polarities are disposed at both ends of the unit cell. . delete The electrode assembly according to claim 1, wherein the current collectors of the positive electrode have the same thickness and the collectors of the negative electrode have the same thickness. The electrode assembly according to claim 1, wherein the cathode active material comprises at least one compound selected from the group consisting of:
Li _x M _y M ' _(2-y) O _z A _4-z (1)
0.85? X? 1.15
0.5? Y? 2.0
1.5? Z? 4.0
M is at least one member selected from the group consisting of Ni, Mn, Co, Ru, Mo, Cu, Nb, Te, Re, Ir, Pt, Cr, S, W, Os and Po;
M 'is one selected from the group consisting of Al, Ti, Mg, Fe, Cr, V, Cu, B, Ca, Zn, Zr, Nb, Mo, Sr, Sb, W, Bi, Or more;
A is a monovalent or divalent anion. The electrode assembly according to claim 1, wherein the cathode active material comprises at least one compound selected from the group consisting of:
_{Li a M (1-b)} M 'b O c A 2-c (1a)
0.85? A?
0.5? B? 1
1.8? C? 2.0
M comprises Co and optionally comprises at least one selected from Ni and Mn;
M 'is at least one selected from the group consisting of Al, Ti, Mg, Fe, Cr, V, Cu, B, Ca, Zn, Zr, Nb, Mo, Sr, Sb, W and Bi;
A is a monovalent or divalent anion. delete The electrode assembly of claim 1, wherein the bi-cell is positioned at both ends of the unit cell with an anode. The biosensor according to claim 10, wherein the thickness of the anode mixture layer located at the outermost side of the bi-cell is thicker than the thickness of the cathode mixture layer of the bi-cell or pull-cell located in the first unit cell to the n- Assembly. The method of claim 1, wherein the n-th unit cell and the (n-1) th unit cell are bi-
Wherein the thickness of the positive electrode mixture layer is the same at the outermost positive electrode of the bi-cell as the n-th unit cell and the positive electrode of the bi-cell as the n-1-th unit cell. The electrode assembly of claim 1, wherein the outermost electrode is 5% to 50% thicker than the internally disposed electrodes. The electrode assembly according to claim 1, wherein a thickness of the outermost electrode is 100 micrometers or more to 180 micrometers or less. The electrode assembly according to claim 1, wherein the thickness of the electrode located inside the electrode assembly is in a range of 80 micrometers to 150 micrometers below a thickness of the outermost electrode. The electrode assembly according to claim 1, wherein a thickness of the outermost electrode is 100 micrometers or more and 180 micrometers or less, and a thickness of the electrode is 80 to 150 micrometers. The lithium secondary battery according to claim 1, wherein the electrode assembly is embedded in the battery case together with the nonaqueous electrolyte solution. The lithium secondary battery according to claim 17, wherein the battery case is a battery case of a laminate sheet including a resin layer and a metal layer. A battery pack comprising the lithium secondary battery according to claim 17. A device comprising a battery pack according to claim 19. 21. The device of claim 20, wherein the device is a computer, a mobile phone, a wearable electronic device, a power tool, an electric vehicle (EV), a hybrid electric vehicle, a plug- , Or a system for power storage.

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