KR101684381B1 - Electrode Assembly with Safety Membrane and Secondary Battery Having the Same - Google Patents

Abstract

The present invention relates to an electrode assembly having a structure in which two or more unit cells are sequentially stacked or folded by a long sheet-
Wherein the unit cells include bi-cells including a positive electrode, a negative electrode, and a separation membrane, and at least one of the bi-cells includes a cross-sectional electrode coated with an electrode active material on one surface of the current collector, And a safety separation membrane having a thickness of 110% to 220% of the thickness of the separation membrane is interposed between the cross-sectional electrode and the double-sided electrode.

Description

Technical Field [0001] The present invention relates to an electrode assembly having a safety separator and a secondary battery including the electrode assembly.

The present invention relates to an electrode assembly having a safety separator and a secondary battery including the electrode assembly.

2. Description of the Related Art As technology development and demand for mobile devices have increased, the demand for secondary batteries as energy sources has been rapidly increasing, and a lot of research has been conducted on secondary batteries that can meet various demands.

Such a secondary battery includes a cylindrical battery and a prismatic battery in which an electrode assembly is embedded in a cylindrical or rectangular metal can according to the shape of the battery case, and a pouch-type battery in which an electrode assembly is embedded in a pouch-shaped case of an aluminum laminate sheet .

Also, the secondary battery is classified according to the structure of the electrode assembly composed of the positive electrode, the negative electrode, and the separation membrane. Representatively, the secondary battery is composed of long-sheet type anodes and cathodes, A stacked (stacked) electrode assembly in which a plurality of positive electrodes and negative electrodes cut in units of a predetermined size are sequentially stacked with a separator interposed therebetween, a stacked (stacked) electrode assembly in which a predetermined unit of positive and negative electrodes are stacked, A bicell or full cell, which is a stacked unit cell, is placed on a separation film, and then a stacked / folded electrode assembly having a wound structure or a bicell or full cell ) Are stacked with a separator interposed therebetween.

In recent years, a secondary battery including an electrode assembly including a bi-cell or a pull cell having a high structural applicability has been attracting attention in recent years in response to various types of devices as well as a simple manufacturing process and a low manufacturing cost.

On the other hand, when the electrode assembly is penetrated by a sharp needle-like conductor having electrical conductivity such as a nail, the anode and the cathode are electrically connected by the needle-shaped conductor, and the current flows to the needle-shaped conductor having low resistance. At this time, deformation of the penetrating electrode occurs, and a high resistance heat is generated by the electric current passing through the contact resistance portion between the positive electrode active material and the negative electrode active material. If the temperature of the electrode assembly rises above a critical value due to the above heat, the oxide structure of the cathode active material is collapsed and thermal runaway occurs, which may be a major cause of ignition or explosion of the electrode assembly and the secondary battery.

In addition, when the electrode active material or the collector bent by the needle-shaped conductor comes in contact with the opposite electrode facing each other, heat generation higher than the resistance heat is generated, which can further accelerate the above-described thermal runaway phenomenon. May occur more seriously in a bi-cell including electrodes and an electrode assembly containing the same.

Accordingly, there is a high need for an electrode assembly having a structure that prevents short circuit, ignition, explosion, etc., and thereby improves safety, and a secondary battery including the electrode assembly.

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 conducted intensive research and various experiments and have confirmed that the conventional problems can be solved fundamentally when a safety separator having an excellent elongation and a thick thickness is used, and thus the present invention has been accomplished.

Therefore, the electrode assembly according to the present invention is an electrode assembly having a structure in which two or more unit cells are sequentially stacked or folded by a long sheet-like separation film,

Wherein the unit cells include bi-cells including a positive electrode, a negative electrode, and a separation membrane, and at least one of the bi-cells includes a cross-sectional electrode coated with an electrode active material on one surface of the current collector, And a safety separation membrane having a thickness of 110% to 220% with respect to a thickness of the separation membrane is interposed between the cross-sectional electrode and the double-sided electrode.

That is, when the needle-shaped conductor passes through the electrode assembly, the safety separator included in the bicell is extended by frictional force with the needle-shaped conductor, so that the contact portion between the needle-shaped conductor and the anode and the cathode is minimized And as a result, excessive current can be prevented from flowing to the needle-shaped conductor.

Thus, the cross-sectional electrode may be disposed at an outermost edge of the electrode assembly that is vulnerable to penetration of the needle-like conductor, and the outermost electrode may be at the top and / or bottom of the electrode assembly.

At this time, the safety separation membrane may have a thickness of 15 micrometers to 30 micrometers, and more specifically 20 micrometers. Considering the elongation of the safety separator and the volume of the electrode assembly, when the thickness of the safety separator is less than 15 micrometers, when the needle-shaped conductor penetrates the electrode assembly, it can not be sufficiently drawn, and when it exceeds 30 micrometers, The volume may increase, which is not preferable.

The separator may be thinner than the safety separator to reduce the volume of the electrode assembly, and more specifically, may have a thickness of 10 to 14 micrometers. When the thickness of the separator is less than 10 micrometers, the mechanical rigidity of the separator is low, and there is a possibility that the electrode assembly ruptures when the electrode assembly shrinks and expands. When the thickness exceeds 14 micrometers, the volume of the electrode assembly may increase, not.

In one specific example, the bi-cells may include a first bi-cell disposed at an outermost portion of the electrode assembly and a second bi-cell disposed at a remaining portion except an outermost portion of the electrode assembly, And the second bi-cell may have the same structure and / or different structures.

Specifically, the first bi-cell may have a structure in which a cross-sectional electrode, a separation membrane, a double-sided electrode, a separation membrane, and a double-sided electrode are sequentially stacked.

The second bi-cell may have a structure in which a double-sided electrode, a separation membrane, a double-sided electrode, a separation membrane, and a double-sided electrode are sequentially stacked in a structure different from that of the first bi-cell.

In the present specification, the term " electrode " refers to both a positive electrode coated with a positive electrode active material on a current collector and a negative electrode coated with a negative electrode active material on the current collector, and the double-sided electrode includes an electrode active material such as an anode active material It may be an electrode coated with a cathode active material.

That is, the first bi-cell may have a structure in which a cross-sectional electrode, an anode, a separator, a double-sided cathode, a separator, and a double-sided anode are sequentially stacked on the anode. On the contrary, It may be a laminated structure.

Alternatively, the second bi-cell may have a structure in which a double-sided anode, a separator, a double-sided cathode, a separator, and a double-sided anode are sequentially stacked. Of course.

On the other hand, the first bi-cell and the second bi-cell are unit cells capable of generating electric power, and they can be combined in various ways to constitute an electrode assembly.

As a first example of such an electrode assembly, the electrode assembly includes a first bi-cell and a second bi-cell arranged on a long sheet-like separation film, / RTI > may be a stacked / folded structure stacked over the separation film. The stack / folding structure has an advantage of facilitating automation of the process.

As another example of the electrode assembly, the electrode assembly may be a stack / lamination structure in which a separator having an adhesive such as PVDF is interposed between the first bi-cell and the second bi-cell, have. This structure has an advantage that the volume of the electrode assembly does not increase according to the thickness of the separation film.

In one specific example, the outermost first bi-cell may be a structure in which the cross-sectional electrode of the first bi-cell is located at the outermost portion of the electrode assembly.

The structure described above is disposed at the outermost portion of the electrode assembly, which is the point where the end-face electrode first penetrates the needle-shaped conductor, so that the metal current collector of the end-face electrode contacts the needle- The electrode can be prevented from coming into contact with the double-sided electrode having the opposite polarity to the single-sided electrode or from contacting the needle-like conductor with the electrodes of the electrode assembly.

Specifically, when the needle-shaped conductor passes through the electrode assembly, the safety separation membrane is bent in the penetrating direction by the downward force of the needle-shaped conductor, and is increased by the frictional force with the needle-shaped conductor. As a result, the safety separator wraps around the penetrating end faces of the remaining electrodes except for the end face electrode, thereby preventing a short circuit due to contact between the needle-like conductor and the electrode.

Meanwhile, in one specific example, the separation membrane and the safety separation membrane may be safety / Reinforcing Separators (SRS) membranes of organic / inorganic complex porous.

Such an SRS separator does not cause high-temperature heat shrinkage due to the heat resistance of the inorganic particles. Even if the electrode assembly penetrates through the needle-like conductor, the elongation of the safety separator can be maintained.

The SRS separation membrane may have a structure in which inorganic particles and a binder polymer are coated on the polyolefin-based membrane substrate.

The SRS separation membrane may have a uniform pore structure formed by the interstitial volume between the inorganic particles, which is the active layer component, together with the pore structure included in the separation membrane substrate itself, The impact can be considerably alleviated, the lithium ion can smoothly move through the pores, a large amount of electrolyte can be filled, and a high impregnation rate can be exhibited, so that the performance of the battery can be improved at the same time.

The separator substrate and the active layer exist as anchoring between the pores on the surface of the polyolefin-based separator substrate and the active layer, so that the separator substrate and the active layer can physically and firmly bond to each other. Considering the bonding force and the pore structure existing on the separation membrane, it can have a thickness ratio of 9: 1 to 1: 9, and more specifically, a thickness ratio of 5: 5.

In the SRS separator, one of the active layer components formed on the surface of the polyolefin-based separator substrate and / or the pores of the substrate is an inorganic particle conventionally used in the art.

The inorganic particles enable the formation of voids between the inorganic particles to form micropores and serve as a kind of spacer capable of maintaining the physical shape. In addition, since the inorganic particles generally have a property that their physical properties do not change even at a high temperature of 200 DEG C or more, the formed organic / inorganic composite porous film has excellent heat resistance.

The inorganic particles are not particularly limited as long as they are electrochemically stable. That is, the inorganic particles usable in the present invention are not particularly limited as long as the oxidation and / or reduction reaction does not occur in the operating voltage range of the applied battery (for example, 0 to 5 V based on Li / Li +). Particularly, when inorganic particles having an ion-transporting ability are used, the ion conductivity in the electrochemical device can be increased and the performance can be improved. Therefore, it is preferable that the ionic conductivity is as high as possible. In addition, when the inorganic particles have a high density, it is difficult to disperse the particles at the time of coating, and there is a problem of an increase in weight during the production of the battery. In the case of an inorganic substance having a high dielectric constant, dissociation of an electrolyte salt, for example, a lithium salt, in the liquid electrolyte also contributes to increase ionic conductivity of the electrolyte.

For the reasons stated above, the inorganic particles may be at least one selected from the group consisting of (a) inorganic particles having piezoelectricity and (b) inorganic particles having lithium ion transferring ability.

The piezoelectricity inorganic particle means a non-conductive material at normal pressure or a material having electrical conductivity due to a change in internal structure when a certain pressure is applied, and exhibits a high permittivity with a dielectric constant of 100 or more, The charge is generated in the case of applying tensile or compressive force, so that one side is charged positively and the other side is negatively charged, thereby generating a potential difference between both sides.

When inorganic particles having the above-described characteristics are used as a porous active layer component, if an internal short-circuit of both electrodes occurs due to an external impact such as a needle-like conductor, the anode and the cathode are directly Not only does not contact but also the potential difference in the particle occurs due to the piezoelectricity of the inorganic particles. As a result, the electrons move between the two electrodes, that is, the minute current flows, so that the voltage of the cell is reduced and the safety is improved .

Examples of the inorganic particles having piezoelectricity include BaTiO ₃ , Pb (Zr, Ti) O ₃ (PZT), Pb _{1 -x} La _x Zr _{1 -y} Ti _y O ₃ (PLZT), PB (Mg ₃ Nb _2/3 ) O ₃ -PbTiO ₃ (PMN-PT) and hafnia (HfO ₂ ), but the present invention is not limited thereto.

The inorganic particles having the lithium ion transferring ability refer to inorganic particles that contain a lithium element but do not store lithium but have a function of transferring lithium ions. The inorganic particles having lithium ion transferring ability exist in the particle structure Since lithium ions can be transferred and transferred due to a kind of defect, the lithium ion conductivity in the battery can be improved and the battery performance can be improved.

Examples of the inorganic particles having lithium ion transferring ability include lithium phosphate (Li ₃ PO ₄ ), lithium titanium phosphate (Li _x Ti _y (PO ₄ ) ₃ , 0 <x <2, 0 <y < titanium phosphate _{(Li x Al y Ti z (} PO 4) 3, 0 <x <2, 0 <y <1, 0 <z <3), (LiAlTiP) x O y series glass (0 <x <4, 0 <y <13), lithium lanthanum titanate _{(Li x La y TiO 3,} 0 <x <2, 0 <y <3), lithium germanium Mani help thiophosphate _{(Li x Ge y P z S} w, 0 <x (Li _x N _y , 0 <x <4, 0 <y <2), SiS ₂ (Li _x Si (0 <y <1, 0 <z < _{y S z, 0 <x <} 3, 0 <y <2, 0 <z <4) based glass, and _{P 2 S 5 (Li x P} y S z, 0 <x <3, 0 <y <3, 0 < z < 7) series glass, but the present invention is not limited thereto.

The composition ratio of the inorganic particles and the binder polymer as the active layer component is not particularly limited, but can be adjusted within a range of 10:90 to 99: 1 wt.%, And is preferably in a range of 80:20 to 99: 1 wt. When the ratio is less than 10: 90% by weight, the content of the polymer is excessively increased, resulting in a decrease in the pore size and porosity due to the reduction of the void space formed between the inorganic particles, , The mechanical properties of the final organic / inorganic composite porous membrane may be deteriorated due to the weakening of the adhesion between the inorganic materials because the polymer content is too small.

The active layer of the organic / inorganic composite porous separator may further include other commonly known additives in addition to the inorganic particles and polymers described above.

In the organic / inorganic composite porous separator, a substrate coated with a mixture of inorganic particles and a binder polymer as the active layer constituent may be a polyolefin-based separator commonly used in the art. Examples of the polyolefin-based separation membrane component include high-density polyethylene, linear low-density polyethylene, low-density polyethylene, ultra-high molecular weight polyethylene, polypropylene or derivatives thereof.

Other components of the electrode assembly according to the present invention will be described below.

The positive electrode is prepared, for example, by coating a mixture of the positive electrode active material, the conductive material and the binder on the positive electrode current collector, and drying the mixture. Optionally, a filler may be further added to the mixture.

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 cathode current collector generally has a thickness of 3 micrometers to 500 micrometers.

Such a positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. Examples of the positive electrode current collector include stainless steel, aluminum, nickel, titanium, sintered carbon, aluminum or stainless steel A surface treated with carbon, nickel, titanium, silver, or the like may be used, but may be aluminum in detail. 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 material is usually added in an amount of 1 to 50% 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 that 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 50 wt% based on the total weight of the mixture containing the cathode active material. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene , Polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butylene rubber, fluorine rubber, various copolymers and the like.

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

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

The negative electrode 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 &lt; x &lt; Lithium metal; Lithium alloy; Silicon-based alloys; Tin alloy; _{SnO, SnO 2, PbO, PbO} 2, Pb 2 O 3, Pb 3 O 4, Sb 2 O 3, Sb 2 O 4, Sb 2 O 5, GeO, GeO 2, Bi 2 O 3, Bi 2 O 4, and Bi ₂ O ₅ ; Conductive polymers such as polyacetylene; Li-Co-Ni-based materials and the like can be used.

The negative electrode current collector is generally made to have a thickness of 3 micrometers to 500 micrometers.

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

The present invention also provides a secondary battery in which the electrode assembly is embedded in a battery case.

The battery case may be a pouch type case or a metal can type case of an aluminum laminate sheet, but is not limited thereto.

The lithium secondary battery includes the electrode assembly and a lithium salt-containing nonaqueous electrolyte.

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

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

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

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

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

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

In 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 non-aqueous electrolyte.

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

Such a device type may be, for example, but not limited to, a cell phone, a portable computer, a smart phone, a smart pad, a tablet PC, or a netbook.

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, in the electrode assembly according to the present invention, the safety separator having a thickness of 110% to 220% of the thickness of the separation membrane is interposed between the two-sided electrodes, The safety separating membrane having a large thickness can be stretched by the frictional force with the needle-shaped conductor, so that the contact portion between the needle-shaped conductor and the electrode can be minimized, and consequently, the overcurrent can be prevented from flowing to the needle-shaped conductor.

1 is a vertical sectional view of a first bicycle according to the present invention;
2 is a vertical cross-sectional view of a second bi-cell according to the present invention;
3 is a schematic diagram of an electrode assembly according to one embodiment of the present invention;
4 is a schematic diagram of an electrode assembly according to another embodiment of the present invention;
5 is a schematic view showing a form in which a first bi-cell is penetrated through a needle-shaped conductor in the electrode assembly of the present invention.

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.

FIG. 1 and FIG. 2 schematically show vertical sections of a first bi-cell and a second bi-cell according to the present invention.

Hereinafter, for convenience of explanation, the unit cell having the cross-sectional electrode set as the anode and the first bi-cell as the unit electrode / separator / cathode / separator / anode is described as a unit cell, but the present invention is not limited to the above- .

1, the first bi-cell 100 includes a cross-sectional electrode 110, a safety separator 120, a double-sided cathode 130, a separator 140, and a double-sided anode 150 in this order.

The positive electrode active material layer 112 is coated on only one side of the metal current collector 114 with respect to the direction in which the end face electrode 110 faces the double-sided negative electrode 130. The double-sided anode 150 is coated with the cathode active material layers 151 and 151a on both sides of the current collector 152 and the anode active material is coated on both sides of the current collector.

The safety separator 120 is interposed between the end face electrode 110 and the both face cathode 130 and the separator 140 is interposed between the both face face anode 130 and the both face anodes 150. The separation membrane (140) and the safety separation membrane (120) are composed of an organic / inorganic composite porous SRS separation membrane.

The second bi-cell 200 shown in FIG. 2 has the unit structure of the anode / separator / cathode / separator / anode and the unit structure of the cathode / separator / anode / separator / cathode, Branch structure. In this specification, a cell in which a cathode is located at the center of a bi-cell is referred to as an A-type bi-cell 200a, and a cell in which an anode is located at a center is referred to as a C-type bi-

In the case of the A-type bi-cell 200a, the structure of the second bi-cell 200 includes a double-sided anode 202a, a separation membrane 204a, a double-sided cathode 203a, a separation membrane 204a ', and a double-sided anode 202a' And a structure in which the double-sided cathode 203c, the separation membrane 204c, the double-sided anode 202c, the separation membrane 204c ', and the double-sided cathode 203c' are stacked in this order in the case of the C- consist of.

That is, the second bi-cell 200 differs from the first bi-cell 100 in that the safety separator 120 and the end-face electrode 110 are not included, and the thin SRS separator is used, Which minimizes the volume of the gas.

FIG. 3 schematically shows a stack / folding type electrode assembly including first and second bi-cells of FIGS. 1 and 2. FIG. 4 is a cross- And stacks / lamination electrode assemblies composed of second bi-cells are schematically illustrated.

Referring to FIG. 3 together with FIGS. 1 and 2, the electrode assembly 300 includes first bi-cells 100 and 100 'and second bi-cells 200c and 200c arranged on the separation film 310, 200c and 200a are folded so that the first bi-cells 100 and 100 'and the second bi-cells 200c, 200c' and 200a are stacked and folded.

The first bi-cells 100 and 100 'are disposed at the upper and lower ends of the electrode assembly 300 and the outermost portions of the first bi-cells 100 and 100' At the outer periphery, cross-sectional electrodes 110 and 110 'are located together with safety separators 120 and 120'.

The first bi-cell 100 has a structure in which the cross-sectional electrode 110, the safety separator 120, the double-sided cathode 130, the separator 140, and the double-sided anode 150 are sequentially stacked. A plurality of C-type bi-cells 200c (200c, 200c, 200c) are stacked in this order on the cell 110, 110 ', where a double-sided cathode 203c, a separator 204c, a separator 204c' And 200c 'are disposed in the vicinity of the C-type bi-cell 200c, and the A-type bi-cell 200a is disposed between the C-type bi-cells 200c and 200c'.

At the end of the folding, an insulating tape 360 is added to stably maintain the stacking and folding structure.

The electrode assembly 400 of FIG. 4 has a structure in which the first bi-cells 100 and 100 'and the second bi-cells 200c, 200a and 200c' are stacked, The first bi-cells 100 and 100 'are disposed at the upper and lower ends of the first bi-cells 100 and 100', and the outermost portions of the first bi-cells 100 and 100 ' Sectional electrodes 110 and 110 'are positioned together with the electrodes 120 and 120'.

The C-type bi-cells 200c and 200c 'of the second bi-cells 200c, 200a and 200c' are disposed adjacent to the first bi-cells 100 and 100 '. The A-type bi-cell 200a is disposed at the center of the electrode assembly 400.

The heat-sealable separation film 410 is interposed at the interface between each first bi-cell and the second bi-cells 100, 200c, 200a, 200c ', and 100' When the first bi-cell and the second bi-cells 100, 200c, 200a, 200c ', and 100' are stacked by thermal fusion, &Quot;). &Lt; / RTI &gt;

As described above, the electrode assemblies 300 and 400 of the present invention are improved in the safety of penetration of the needle-shaped conductors by the cross-sectional electrodes of the electrode assemblies 300 and 400 and the safety separator. Referring to FIG. 5, a first biocell located at the outermost periphery of the electrode assembly 300 or 400 according to the present invention is vertically penetrated by a needle-like conductor.

5, the needle-shaped conductor 590 includes a cross-sectional electrode 510 of the first bi-cell 501 located at the outermost of the electrode assembly, a safety separator 520, a double-sided cathode 530, a separator 540 ), And a double-sided anode 550 in this order. At this time, the metal current collector 511 penetrates the surface of the metal current collector 511 by the penetrating force and the frictional force of the needle-like conductor 590, and is simultaneously stretched in the direction of movement of the needle-shaped conductor 590, And comes into contact with the conductor 590. Likewise, the safety separator 520 between the end surface electrode 510 and the double-sided cathode 530 is also penetrated by the penetration force of the needle-shaped conductor 590 and is stretched together in the direction of movement of the needle-shaped conductor 590, Separating the current collector 511 and the double-sided cathode 530 from each other. Therefore, the safety separator 520 blocks the chance of direct contact between the end surface electrode 510 and the both surface side electrode 530, thereby preventing a short circuit due to mutual opposite electrode contact. Also, the safety separator 520 blocks direct contact of the needle-shaped conductor 590 with the double-sided cathode 530 and the double-sided anode 550, thereby preventing the risk of short circuit.

While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments.

Claims (21)

An electrode assembly having a structure in which two or more unit cells are sequentially stacked or folded by a long sheet-like separation film,
Wherein the unit cells include bi-cells including a positive electrode, a negative electrode, and a separation membrane, and at least one of the bi-cells includes a cross-sectional electrode coated with an electrode active material on one surface of the current collector, Wherein a safety separation membrane having a thickness of 110% to 220% of the thickness of the separation membrane is interposed between the end face electrode and the both face side electrode. The electrode assembly according to claim 1, wherein the bi-cells include a first bi-cell disposed at an outermost portion of the electrode assembly and a second bi-cell disposed at a remaining portion except the outermost portion of the electrode assembly. The electrode assembly according to claim 2, wherein the first bi-cell is a structure in which a cross-sectional electrode, a separation membrane, a double-sided electrode, a separation membrane, and a double-sided electrode are sequentially stacked. The electrode assembly according to claim 2, wherein the second bi-cell has the same structure as the first bi-cell, or a structure in which a double-sided electrode, a separator, a double-sided electrode, a separator, and a double-sided electrode are sequentially stacked. The electrode assembly according to claim 3 or 4, wherein the double-sided electrode is coated with an electrode active material on both sides of the current collector. 4. The electrode assembly of claim 3, wherein the cross-section electrode is located at an outermost portion of the electrode assembly. The electrode assembly according to claim 1, wherein the separation membrane and the safety separation membrane are SRS (Safety-Reinforcing Separators) separators of organic / inorganic complex porous. The electrode assembly of claim 1, wherein the separator has a thickness of 10 micrometers to 14 micrometers. 2. The electrode assembly of claim 1, wherein the safety isolation layer has a thickness of about 15 micrometers to about 30 micrometers. 10. The electrode assembly of claim 9, wherein the thickness of the safety isolation layer is 20 micrometers. The electrode assembly according to claim 7, wherein the SRS separator comprises an active layer made of inorganic particles and a binder polymer on the polyolefin-based separator. The electrode assembly according to claim 11, wherein the separator substrate and the active layer have a thickness ratio of 9: 1 to 1: 9. 13. The electrode assembly of claim 12, wherein the thickness ratio is 5: 5. The electrode assembly according to claim 11, wherein the inorganic particles are at least one selected from the group consisting of (a) inorganic particles having piezoelectricity and (b) inorganic particles having lithium ion transferring ability. The method of claim 14, wherein the inorganic particles having the piezoelectricity is _{BaTiO 3, Pb (Zr, Ti} ) O 3 (PZT), Pb 1-x La x Zr 1-y Ti y O 3 (PLZT), PB (Mg 3 Nb _2/3 ) O ₃ -PbTiO ₃ (PMN-PT) and hafnia (HfO ₂ ). The lithium secondary battery according to claim 14, wherein the inorganic particles having lithium ion transferring capability are lithium phosphate (Li ₃ PO ₄ ), lithium titanium phosphate (Li _x Ti _y (PO ₄ ) ₃ , 0 <x <2, 3), lithium aluminum titanium phosphate _{(Li x Al y Ti z (} PO 4) 3, 0 <x <2, 0 <y <1, 0 <z <3), (LiAlTiP) x O y series glass (0 < x <4, 0 <y < 13), lithium lanthanum titanate _{(Li x La y TiO 3,} 0 <x <2, 0 <y <3), lithium germanium Mani help thiophosphate (Li _x Ge _y P _z S _{w, 0 <x <4,} 0 <y <1, 0 <z <1, 0 <w <5), lithium nitrides _{(Li x N y, 0 <} x <4, 0 <y <2), SiS _{2 (Li x Si y S z} , 0 <x <3, 0 <y <2, 0 <z <4) based glass, and _{P 2 S 5 (Li x P} y S z, 0 <x <3, 0 < y <3, 0 <z <7) series glass. The secondary battery according to claim 1, wherein the electrode assembly is embedded in a battery case. The secondary battery according to claim 17, wherein the battery case is an aluminum laminate sheet pouch type case or a metal can case. A battery pack comprising the secondary battery according to claim 17 as a unit battery. A device as claimed in claim 19 comprising a battery pack as a power source. 21. The device of claim 20, wherein the device is selected from a cell phone, a portable computer, a smart phone, a smart pad, a tablet PC, a netbook.

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