KR101675976B1 - Electrode Assembly with Membrane of High Elongation Property and Secondary Battery Having the Same - Google Patents

Abstract

The present invention relates to a stack / folding type electrode assembly having a structure in which two or more unit cells each having a separator interposed between a positive electrode and a negative electrode coated with an electrode mixture containing an electrode active material on a current collector are wound in a long sheet- , The positive electrode is a structure in which a positive electrode mixture is coated on an aluminum foil as a current collector, the negative electrode is a structure in which a negative electrode mixture is coated on a metal foil other than aluminum as a current collector, wherein the unit cells located at the outermost outermost unit cells of the unit cells include a full-cell or a bi-cell, wherein the outermost electrode is a cross-sectional electrode, and the electrode mixture in the cross- Wherein the stretching ratio of the separating film is higher than that of the separating film It relates to an electrode assembly of the large features.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to an electrode assembly having a separator for high elongation characteristics,

The present invention relates to an electrode assembly having a highly stretched 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.

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

Also, the secondary battery is classified according to how the electrode assembly having the anode / separator / cathode structure is formed. Typically, the long battery-shaped anodes and cathodes are jelly- 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 stack / folding type electrode assembly having a structure in which a bi-cell or a full cell stacked in a single state is wound around a separator sheet.

The electrode assembly composed of the anode / separator / cathode may have a laminated structure, but a plurality of electrodes (anode and cathode) may be laminated in a state that the separator is interposed therebetween and then bonded to each other by heating / It is possible. In this case, the bonding of the electrode and the separator is achieved by heating / pressing the electrode and the adhesive layer applied on the separator in face-to-face relationship. Therefore, the separator is generally coated with a binder material in order to improve the adhesion with the electrode.

However, when the separator coated with the binder material is used in an electrochemical cell such as a battery, if the binder powder has weak adhesion to the separator substrate, the binder is removed from the separator substrate in the electrolyte injection and degassing process Flow phenomenon may occur, resulting in poor battery cell appearance and deterioration of performance.

One of the major research tasks in such secondary batteries is to improve safety. Generally, a lithium secondary battery is a battery having a high temperature and a high pressure inside a battery which can be caused by an abnormal operating state of the battery such as an internal short, an overcharged state exceeding an allowable current and a voltage, a shock caused by exposure to a high temperature, Thereby causing explosion of the battery.

Generally, a method of forming an anode active material in an amount larger than the amount of a cathode active material is widely used in the battery as a whole, so that a positive electrode current collector, which faces the anode active material coating layer via a separator, (So-called " non-coated portion ") in which the active material is not applied.

However, 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-like 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.

 Therefore, there is a high need for a technique for securing the safety of a secondary battery in a safer and more efficient manner.

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. In the stack / folding type secondary battery, when a binder in which an inorganic binder coating layer is formed on a surface is used as a separation film for winding up a stacked electrode assembly, Since the thickness of the separation film is equal to or more than a certain range, it is possible to suppress the occurrence of sparks during the needle piercing, and it is confirmed that the stability of the battery can be greatly improved and the reduction in the charging capacity can be reduced. It came.

Therefore, the electrode assembly according to the present invention is characterized in that a stack of a structure in which two or more unit cells having a separator interposed between a positive electrode and a negative electrode coated with an electrode mixture containing an electrode active material in a current collector are wound in a long sheet- / Folding type electrode assembly, wherein the positive electrode is a structure in which a positive electrode mixture is coated on an aluminum foil as a current collector, and the negative electrode is a structure in which a negative electrode mixture is coated on a metal foil other than aluminum as a current collector, The cells include one or more full-cells or bi-cells. Out of the unit cells, the unit cells located at the outermost of the electrode assembly have the outermost electrode as a cross-section electrode, In the electrode, the electrode mixture is applied to only one surface of the current collector facing the separator, The elongation is characterized by being relatively larger than the separator.

In a safety evaluation test of a battery such as needle-shaped conductor penetration, the main cause of the explosion or ignition of the battery is a high resistance heat due to the electric current passing through the contact resistance portion between the positive electrode active material and the negative electrode active material due to the deformation of the electrode when passing through the conductor. If the internal temperature of the battery rises above a critical value due to the resistance heat, the oxide structure of the cathode active material is collapsed to cause thermal runaway, thereby causing ignition or explosion of the battery.

In general, since the cathode active material is an oxide, the electrical conductivity is low and the resistance is higher than that of the anode active material. The needle conductive body is a metal, and thus the resistance is very low as compared with the anode or the cathode active material. Therefore, in order to improve the safety of the battery by lowering the resistance of the penetrating portion generated when the needle-shaped conductor penetrates, lowering the resistance of the cathode active material is the most important factor.

The electrode assembly may be manufactured by placing each unit cell in a stacked state on a long sheet-like separation film at a predetermined distance, winding the same, inserting it into a battery case, and sealing the electrode assembly. In one specific example, The unit cells include bi-cells, and 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.

A bi-cell is a cell in which the same electrode is located in the outermost electrode such as a unit cell of a cathode / separator / cathode / separator / anode, and a unit cell of a cathode / separator / anode / separator / cathode. In this specification, the unit cell of the anode / separator / cathode / separator / anode structure is defined as "A-type bi-cell" and the unit cell of the cathode / separator / anode / separator / cathode structure is defined as "C- . That is, a cell in which the electrode located at the center of the bi-cell is a cathode is called an A-type bi-cell, and a cell that is an anode is called a C-type bi-cell.

In one specific example, the first bi-cell has a structure in which a first anode of a cross-section anode, a separator, a first anode of a double-sided cathode, a second anode of a separator and a double- , A second anode of a double-sided anode, a separator, and a second cathode of a double-sided cathode are stacked in this order, and the second bi-cell has a structure in which a second cathode, a second anode and a second cathode are stacked , Or a structure in which a second anode, a second cathode, and a second anode are sequentially stacked with a separator interposed therebetween.

The first bi-cell is a bi-cell disposed at the outermost portion of the electrode assembly. The first bi-cell has a first surface coated with a cathode active material and disposed to face the separation membrane, and a first surface coated with the cathode active material And a second surface disposed so as to face the outside of the electrode assembly. The first negative electrode of the first bi-cell may correspond to the first positive electrode and the negative active material may correspond to the positive active material. The first negative electrode may be coated with the negative electrode active material, And a second surface disposed so that the negative electrode active material is not coated and is directed to the outside of the electrode assembly.

If the electrodes on both sides of the cell have the same structure, the number of the positive electrode and the negative electrode and the number of the safety separator or separator is not limited to such a first bi-cell or the second bi-cell.

The unit cells may include a first pull cell disposed at an outermost portion of the electrode assembly and a second pull cell disposed at a remaining portion except the outermost portion.

A full cell is a cell in which different electrodes are located on both sides of a cell, such as a unit cell of a cathode / separator / cathode and a unit cell of a cathode / separator / anode. Since the electrodes existing in the outermost cell of the pull cell are different from each other, the pull cells may be positioned and aligned by aligning the electrode directions of the pull cells.

In one specific example, the first pull cell has a structure in which a first anode of a cross-section anode, a second cathode of a separator and a double-sided cathode are stacked in order, or a first anode of a cross- The second pull cell has a structure in which a second anode of a double-sided cathode, a separator and a second anode of a double-sided anode are stacked in order, or a structure in which a second anode of a double- Lt; / RTI >

The first pull cell is a first pull cell disposed on the outermost side of the electrode assembly. The first positive electrode of the first pull cell is coated with a cathode active material and is disposed facing the separator. The first pull cell is coated with a cathode active material, As shown in Fig. On the other hand, the first negative electrode of the first pull cell is composed of a first surface coated with a negative electrode active material and arranged so as to face the separator, and a second surface coated with the negative electrode active material and facing the outside of the electrode assembly .

If the first pull cell or the second pull cell has a structure in which electrodes on both sides of the cell are different from each other, the number of the anode, the cathode, and the separator constituting the first pull cell or the second pull cell is not particularly limited.

In one example according to the present invention, the separation film of the present invention may be composed of a separation membrane having a higher elongation percentage by using a thicker material than that of the separation membrane. Specifically, the separation film may have an elongation of 105% to 500% And more specifically, an elongation of 120% to 300%.

When the elongation percentage of the separator film is less than 120%, it is difficult to exhibit the effect of preventing the electrode active material or the current collector from contacting each other as the number of pull cells or bi-cells stacked on the electrode assembly increases, , The thickness of the separator film becomes thicker in order to exhibit the above effect, so that the capacity of the battery is reduced, which is not preferable.

The present invention is also directed to a structure for preventing a reduction in the capacity of a battery and improving the safety of a battery. In one specific example, the separation film and the separation membrane are formed by using an organic / inorganic composite porous SRS (Safety-Reinforcing Separator) .

The SRS separation membrane is manufactured by applying an active layer component composed of inorganic particles and a binder polymer on a polyolefin-based separation membrane substrate. At this time, in addition to the pore structure contained in the separation membrane substrate itself, the SRS separation membrane is formed by interstitial volume between inorganic particles And has a uniform pore structure.

The SRS separator composed of the inorganic particles and the binder polymer does not generate high temperature thermal shrinkage due to the heat resistance of the inorganic particles. Therefore, in the electrochemical device using the organic / inorganic composite porous film as a separator, even if the separator ruptures in the cell due to internal or external factors such as high temperature, overcharging, external impact, etc., The electrodes are hardly short-circuited completely, and even if a short circuit occurs, the short-circuited area is prevented from being greatly enlarged, thereby improving the safety of the battery.

In the organic / inorganic composite porous 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 ordinarily 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 properties in which the 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 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 1/3 Nb 2 _{/ 3} ) O ₃ -PbTiO ₃ (PMN-PT), hafnia (HfO ₂ ), SrTiO ₃ , SnO ₂ , CeO ₂ , MgO, NiO, CaO, ZnO, ZrO ₂ , Y ₂ O ₃ , Al ₂ O ₃ , TiO ₂ , SiC, or a mixture thereof, but 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 < (Li _x Al _y Ti _z (PO ₄ ) ₃ , 0 <x <2, 0 <y <1, 0 <z <3), 14Li ₂ O-9Al ₂ O ₃ -38TiO ₂ -39P ₂ O ₅ (0 <x <4, 0 <y <13), lithium lanthanum titanate (Li _x La _y TiO ₃ , 0 <x <2, 0 <y <3), Li (LiAlTiP) _x O _y series glass (Li _x Ge _y P _z S _w , 0 <x <4, 0 <y <1, 0 <z <1, 0 <w <5) such as _3.25 Ge _0.25 P _0.75 S ₄ , lithium nitride such as _{Li 3 N (Li x N y} , 0 <x <4, 0 <y <2), Li 3 PO 4 -Li 2 S-SiS 2 SiS 2 based glass (Li _x Si _y S, such as _{z, 0 <x <3,} 0 <y <2, 0 <z <4), LiI-Li 2 SP 2 S 5 as P ₂ S ₅ based _{glass (Li x P y S z} , 0 <x <3 , such , 0 <y <3, 0 <z <7), or a mixture thereof, but 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.

In one specific example, the separator may have a thickness of 10 micrometers to 14 micrometers, and the separation film may have a thickness of 15 micrometers to 30 micrometers.

More specifically, the thickness of the separation film may be 20 micrometers. When the thickness of the separation film is less than 15 micrometers, safety can not be ensured because the needle-like conductor can not be sufficiently drawn when the needle-shaped conductor penetrates the electrode assembly, and when the needle- If it exceeds the meter, the separation membrane volume may increase and the charging capacity is lowered, which is not preferable.

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 current collector generally has a thickness of 3 to 500 mu m.

Such a positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. Examples of the positive electrode current collector include stainless steel, aluminum, nickel, titanium, sintered carbon, aluminum or stainless steel A surface treated with carbon, nickel, titanium, silver, or the like may be used, 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 current collector is generally made to have a thickness of 3 to 500 mu m.

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

The 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.

The types of such devices may be, for example, but not limited to, mobile phones, portable computers, smart phones, smart pads, tablet PCs, and netbooks.

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.

It is an object of the present invention to provide a separator for a stack / folding type secondary battery, which comprises an inorganic binder coating layer and has a thickness of a certain range or more, This is to fundamentally solve the problem of a sudden decrease in safety due to impact.

It is a further object of the present invention to provide a separator inserted in an electrode assembly that uses a thinner separator to maintain electrical performance such as a high capacity, a rate characteristic, and an electric capacity, exhibits a high capacity relative to the volume of the electrode assembly, The separation film surrounding the assembly is relatively thicker than the separation membrane to increase elongation so as to suppress the occurrence of sparks during needle penetration and improve the safety of the battery.

Figure 1 is a schematic view of a configuration before winding to form an electrode assembly;
2 is a schematic diagram of a wound stack / folding type electrode assembly according to one embodiment of the present invention;
3 is a schematic view of a unit cell of an electrode assembly according to one embodiment of the present invention;
4 is a schematic view of a unit cell of an electrode assembly according to one embodiment of the present invention;
5 is a schematic view of a unit cell of an electrode assembly according to an embodiment of the present invention;
6 is a partial schematic view of an outermost portion of a needle-like conductor passing through the electrode assembly according to 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 is a schematic view showing a state before the electrode assembly is formed and before the unit cells are placed on the separation film 110 and wound. Referring to FIG. 1, a structure of the separating film 110 is shown before the bi-cells and / or pull cells 101, 102, 103, 104, and 105 are wound on the separating film 110.

The separation membrane 110 and the separating film 110 located inside the unit cells 101, 102, 103, 104, and 105 are formed by applying an active layer made of inorganic particles and a binder polymer on a polyolefin- It has a structure that is less affected by impacts.

The separation film surrounding the unit cell of the electrode assembly of the present invention uses a SRS separation membrane that is thicker than the separation membrane interposed between the unit cells so that the charging capacity is not reduced while suppressing the volume increase. By increasing the thickness of the SRS separator used as the separating film to be contacted and improving the elongation, safety from external impact can also be improved.

2, a stack / folding type electrode assembly 200 including first bi-cells 210 and second bi-cells 221 and 222 is schematically illustrated. Referring to FIG. 2, the electrode assembly 200 is formed by winding first bi-cells 210 and second bi-cells 221 and 222 at regular intervals on a separation film 240. In addition, some or all of the second bi-cells 221 and 222 may be replaced with a pull cell, and the second bi-cells 221 and 222 may be additionally formed together with the pull cell.

In addition, the separation film 240 uses a thicker material than the separation membrane 230 interposed between the bi-cells 210. Specifically, since the separation film 240 is formed to have a thickness of 15 micrometers to 30 micrometers and the separation membrane 230 uses a thickness of 10 micrometers to 14 micrometers, (240) has an elongation of 105% to 500% with respect to the separator (230).

The first bi-cells 210 are disposed at the uppermost and lowermost ends of the electrode assembly 200 and the second bi-cells 221 and 222 are disposed at portions except where the first bi- . In addition, the second bi-cells may be located at the locations of the pull cells, and an insulating tape 250 may be added to the folding structure to stably maintain the stacking and folding structure.

FIG. 3 is a vertical cross-sectional schematic diagram of a first bicycle according to the present invention, and FIG. 4 is a schematic vertical cross-sectional view of a second bicycle.

3, the first bi-cell 300a is an A-type bi-cell having a center electrode as a cathode. The first bi-cell 300a includes a first anode 331, a separation membrane 305, a second cathode 320, a separation membrane 305, Two positive electrodes 330 are stacked in this order.

The first anode 331 is coated with a cathode active material 301 on only one side of the cathode current collector 303 with respect to a direction facing the separator 305 and the second cathode 320 is coated on the cathode current collector 304, And a double-sided electrode coated with a negative electrode active material 302 on both sides.

The separator 305 is interposed between the first anode 331 and the second cathode 320 or between the second anode 330 and the second cathode 320. The separation membrane is an SRS separation membrane and can be formed to have a proper thickness in consideration of safety improvement and prevention of reduction in charge / discharge capacity of the secondary battery.

As the first bi-cell 300b, the C-type bi-cell in which the middle electrode is an anode is reversed in the order of the positive electrode and the negative electrode as compared with the first bi-cell 300a, The cathode active material 301 may correspond to the anode current collector 304 and the anode active material 302, respectively.

 4, the second bi-cell 400a is formed by stacking a second anode 420, a separation membrane 405, a second cathode 410, a separation membrane 405, and a second anode 420 in this order. And the second bi-cell 400b is formed by sequentially stacking a second cathode 410, a separation membrane 405, a second anode 420, a separation membrane 405, and a second cathode 410 in this order.

The second anode 420 constituting the second bi-cell 400a is a double-sided electrode coated with a cathode active material 401 on both sides of the cathode current collector 403 and the second cathode 410 is a double- 404 are coated with a negative electrode active material 402 on both sides thereof.

The thicknesses b of the separators 305 and 405 interposed between the first bi-cells 300a and 300b and the second bi-cells 400a and 400b are equal to each other, ) (B < a).

5 illustrates a pull cell constituting an electrode assembly according to an embodiment of the present invention. More specifically, the pull cells 500a and 500b are arranged such that the second anode 520 and the second cathode 510 sandwich the separator 505 therebetween. Specifically, the pull cell 500a includes a second anode 520, a separator 505, and a second electrode 520 on both surfaces of the cathode current collector 503, on which the cathode active material 501 is applied. And the second cathode 510 on which the anode active material 502 is coated on both sides of the anode current collector 504 are stacked in this order or the pull cell 500b of another form is formed of a second cathode 510, the separator 505, and the second anode 520 in this order.

As described above, the above-described unit cells 300a, 300b, 400a, and 400b have improved safety for penetration of the needle-like conductor by the separation film. As described above, The electrode assemblies 101, 102, 103, 104, and 105, in which the cells 300a, 300b, 400a, and 400b are stacked and wound on the separation film 110, Will be described in detail below with reference to FIG.

Referring to FIG. 6, a separation film 610 having electrode assemblies formed by winding and stacking unit cells is an SRS separator coated with an inorganic particle and a binder polymer active layer 602 on a separation membrane substrate 601, The separation film 610 is formed to have a relatively large thickness (a > b) as compared with the separator 620 interposed between the anode 611 and the cathode 612 constituting the bipolar cell or the pull cell.

When the needle-like conductor 640 penetrates the electrode assembly in the vertical direction, the anode 611, the separator 620, the cathode 612, and the separator 620 are sequentially arranged starting from the outermost separator film 610 Through. At this time, the surface of the separation film 610 is penetrated by the penetrating force and the frictional force of the needle-like conductor 640, and is simultaneously brought into contact with the needle-like conductor 640 in the direction of movement of the needle-shaped conductor 640, It is possible to prevent direct contact between the needle-shaped conductor 640 and the electrodes 611 and 612 or between the anode 611 and the cathode 612 because the separation film 610 passes through the anode 611 and the cathode 612. [ do.

Therefore, the safety of the electrode assembly can be significantly improved by preventing ignition by heating the electrode assembly by the needle-shaped conductor 640. [

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 (19)

A stack / folding type electrode assembly having a structure in which two or more unit cells each having a separator interposed between a positive electrode and a negative electrode coated with an electrode mixture containing an electrode active material on a current collector are wound in a sheet-
The positive electrode is a structure in which a positive electrode mixture is coated on an aluminum foil as a current collector, and the negative electrode has a structure in which a negative electrode mixture is coated on a metal foil other than aluminum as a current collector;
The unit cells include a first bi-cell disposed at the outermost portion of the electrode assembly and a second bi-cell disposed at the remaining portion;
The first bi-cell has a structure in which a first anode of a single-sided anode, a second anode of a double-sided anode, and a second anode of a double-sided anode are stacked in this order with a separator interposed therebetween, or a structure in which a first cathode of a single- A structure in which a positive electrode and a second negative electrode of a double-sided negative electrode are sequentially stacked with a separator interposed therebetween;
The second bi-cell may have a structure in which a second cathode, a second anode, and a second cathode are sequentially stacked with a separator interposed therebetween, or a structure in which a second anode, a second anode, and a second anode are stacked ;
Among the unit cells, the first bi-cells positioned at the outermost part of the electrode assembly are composed of a single-sided electrode at the outermost electrode, and the electrode mixture is applied to only one surface of the current collector facing the separator;
Wherein the separation film has an elongation of 105% to 500% with respect to the separation membrane,
Wherein the separation membrane has a thickness of 10 micrometers to 14 micrometers and the separation film has a thickness of 15 micrometers to 30 micrometers. delete delete A stack / folding type electrode assembly having a structure in which two or more unit cells each having a separator interposed between a positive electrode and a negative electrode coated with an electrode mixture containing an electrode active material on a current collector are wound in a sheet-
The positive electrode is a structure in which a positive electrode mixture is coated on an aluminum foil as a current collector, and the negative electrode has a structure in which a negative electrode mixture is coated on a metal foil other than aluminum as a current collector;
The unit cells include a first pull cell disposed at the outermost portion of the electrode assembly and a second pull cell disposed at the remaining portion;
Wherein the first pull cell has a structure in which a first anode of a cross section anode, a separator and a second cathode of a double-sided cathode are stacked in order, or a first anode of a cross-section cathode, a separator, and a second anode of a double-
The second pull cell has a structure in which a second anode of a double-sided cathode, a separator, and a second anode of a double-sided anode are stacked in order, or a second anode of the double-sided anode, a separator and a second cathode of the double-
Among the unit cells, the first pull cells located at the outermost part of the electrode assembly are composed of one end electrode and the electrode assembly in the end electrode is applied to only one surface of the collector facing the separator;
Wherein the separation film has an elongation of 105% to 500% with respect to the separation membrane,
Wherein the separation membrane has a thickness of 10 micrometers to 14 micrometers and the separation film has a thickness of 15 micrometers to 30 micrometers. delete delete The electrode assembly according to claim 1 or 4, wherein the separation film has an elongation of 120% to 300% with respect to the separation membrane. The electrode assembly according to claim 1 or 4, wherein the separation film and the separation membrane are safety / Reinforcing Separators (SRS) separators of organic / inorganic complex porous. The electrode assembly according to claim 8, 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 9, 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 10, 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 1 _{/ 3} Nb _2/3 ) O ₃ -PbTiO ₃ (PMN-PT), hafnia (HfO ₂ ), SrTiO ₃ , SnO ₂ , CeO ₂ , MgO, NiO, CaO, ZnO, ZrO ₂ , Y ₂ O ₃ , Al ₂ O ₃ , TiO ₂ , SiC, or a mixture thereof. The lithium secondary battery according to claim 10, 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, 0 < ), 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 (Li _x La _y Ti _z O ₃ , 0 <x <2, 0 <y <3), lithium germanium 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 series _{glass (Li x Si y S z} , 0 <x <3, 0 <y <2, 0 <z <4), P 2 S 5 based _{glass (Li x P y S z} , 0 <x <3, 0 <y <3, 0 <z <7), or a mixture thereof. delete The electrode assembly according to claim 1 or 4, wherein the separation film has a thickness of 20 micrometers. A secondary battery in which the electrode assembly according to claim 1 or 2 is embedded in a battery case. The secondary battery according to claim 15, wherein the battery case is a pouch-type case or a metal can case of an aluminum laminate sheet. A battery pack comprising the secondary battery according to claim 16 as a unit battery. A device as claimed in claim 17 comprising a battery pack as a power source. 19. The device of claim 18, wherein the device is selected from a cell phone, a portable computer, a smart phone, a smart pad, a tablet PC, and a netbook.

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