KR20090006565A - Secondary battery having separator coated with solid phase particle at core region - Google Patents

Abstract

A secondary battery is provided to prevent firing and explosion due to internal short or overcharging caused by the transformation of a center pin due to external shock, thereby improving the safety of a battery. A secondary battery has a structure inserted with a center pin inside the center of the electrode assembly(500) winding a positive electrode sheet and negative electrode sheet in a state where a separation film is interposed. The solid particle coating layer(510) including solid phase particles is formed on the separation film adjacent to the winding center.

Description

Secondary Battery Coated with Solid Particles on Separation Membrane {Secondary Battery Having Separator Coated with Solid Phase Particle at Core Region}

The present invention relates to a secondary battery in which solid particles are coated on a separator in a center portion, and more particularly, to an electrode assembly ('jelly-roll') in which a cathode sheet and a cathode sheet are wound in a round state with a separator interposed therebetween. A secondary battery having a structure in which a center pin is inserted into a winding center, and a secondary battery characterized in that a coating layer containing a solid particle ('solid particle coating layer') is formed on a separator adjacent to a winding center.

As the development and demand for mobile devices increases, the demand for secondary batteries as energy sources is increasing rapidly. Among them, many researches have been conducted and commercialized and widely used for lithium secondary batteries with high energy density and discharge voltage. It is used.

According to the shape of the battery case, the secondary battery is classified into a cylindrical battery and a rectangular battery in which the electrode assembly is embedded in a cylindrical or rectangular metal can, and a pouch type battery in which the electrode assembly is embedded in a pouch type case of an aluminum laminate sheet. do.

In addition, the electrode assembly embedded in the battery case is a power generator capable of charging and discharging composed of a laminated structure of the anode / separator / cathode, a jelly-roll type wound through a separator between the long sheet-type anode and cathode coated with the active material The structure is classified into a stacked structure in which a plurality of positive and negative electrodes of a predetermined size are sequentially stacked in a state where a separator is interposed therebetween. Among them, the jelly-roll type electrode assembly has advantages of easy manufacturing and high energy density per weight.

Jelly-roll type electrode assembly is mainly used in cylindrical cells and rectangular cells, Figure 1 is a vertical cross-sectional perspective view of a cylindrical cell including a jelly-roll type electrode assembly is schematically shown, Figure 2 according to the prior art A horizontal cross-sectional perspective view of the center pin is schematically shown.

Referring to these drawings, the cylindrical secondary battery 10 accommodates the jelly-roll type (wound) electrode assembly 20 in the cylindrical case 30 and injects the electrolyte solution into the cylindrical case 30, and then the case 30. ) Is manufactured by combining the top cap 40 having the electrode terminal (for example, a positive electrode terminal) formed at the open upper end.

The electrode assembly 20 has a structure in which a cathode 21, a cathode 22, and a separator 23 are sequentially stacked to be wound in the form of a jelly roll, and generally has a cylindrical shape at its winding center (the center of the jelly roll). The center pin 50 is inserted.

The center pin 50 is generally made of a metal material to impart a predetermined strength, and has a structure in which a plate is rounded. As shown in FIG. 2, the center pin 50 has a hollow cross section in which the end portions 51 are not in contact with each other. It consists of a cylindrical structure in the form of a pipe that the end portion 51 in contact with the cylindrical structure or the horizontal cross section. In some cases, a deformed structure in which an end portion 51 in a horizontal cross section is bent into a hollow inside is also used.

The center pin 50 serves to fix and support the electrode assembly, and serves as a passage for discharging and discharging the gas generated during charging and discharging or operation. However, the center pin 50 of such a structure tends to be deformed to the hollow or pipe-type internal structure when an external shock such as dropping or crimping of the battery is applied, and the non-contacting end of the center pin ( 51) or bent corners, etc., may penetrate the separator and contact the electrode or press the jelly roll to cause an internal short circuit.

In particular, due to the deformation of the center pin, the separator in the core portion is torn or ruptured, whereby the short-circuit current is concentrated in the local area, and the resistance of the current is increased and the heat generation amount is increased when heat dissipation to the outside is not easy. This causes a problem that the battery ignites and explodes.

On the other hand, the inflow of foreign matter from the outside into the battery, or the step between the components of the jelly-roll causes a sliding phenomenon due to the difference in the degree of volume expansion of the jelly-roll due to repeated charge and discharge, such a jelly- The slippage of the roll mainly causes internal short circuits in the core area.

Therefore, when an external shock that is likely to cause an internal short circuit is applied, it prevents the battery from igniting and exploding due to deformation of the center pin and overcharging, and suppresses the sliding of the jelly roll due to the inflow of foreign substances or the step difference. There is a need for technology that improves safety.

In this regard, Korean Patent No. 0535734 discloses a lithium secondary battery including an electrode in which a ceramic layer is uniformly formed on an electrode plate having a step between a plain portion and an application portion. However, since the entire ceramic layer is formed on the electrode plate, an additional process such as uniformly controlling the thickness of the separator film is required to increase the manufacturing cost, and the ceramic film formed on the electrode plate surface increases the travel time and distance of the lithium ions. As a result, there is a problem of lowering the rate characteristic of the secondary battery. Furthermore, the film coated on the non-coated portion of the metal current collector has a disadvantage in that the jelly-roll type electrode assembly is easily detached when the jelly-roll type electrode assembly is repeatedly expanded and contracted in a large number of charge and discharge processes due to the low interfacial properties of the metal. The occurrence of a short circuit at the center of the winding is particularly serious in terms of safety because it is not easy to dissipate heat due to the structural characteristics of the jelly-roll type electrode assembly, and thus, when the coating film is detached from the plain part, the desired safety cannot be secured.

In addition, Japanese Patent Application Laid-Open No. 2005-063680 discloses an inner short circuit due to volume change during charging and discharging by wrapping an insulating tape between an electrode tab of an anode and a cathode and an active material coating part in a central portion of a jelly-roll type electrode assembly. Disclosed is a battery capable of preventing the same. However, the insulating tape attached to the ends of the positive electrode and the negative electrode increases the volume or thickness of the jelly-roll type electrode assembly compared to the same size, and may be caused by the inflow of foreign matter from the outside into the cell or the step between the components of the jelly-roll. There is a limit to prevent the internal short circuit (short circuit caused by the sliding phenomenon) and the like.

Therefore, there is a high need for a technology that can fundamentally solve these problems.

The present invention aims to solve the problems of the prior art as described above and the technical problems that have been requested from the past.

After extensive research and various experiments, the inventors of the present application have a coating layer including solid particles on a separator adjacent to a winding center in a jelly-roll type electrode assembly in which a cathode sheet and a cathode sheet are wound roundly with a separator interposed therebetween. In the case of forming the center pin, the center pin inserted in the center of the core is prevented from being ignited and exploded by an internal short circuit or overcharge caused by deformation or slipping due to an external impact, thereby improving the safety of the secondary battery. The present invention has been completed.

Therefore, the secondary battery according to the present invention is a secondary battery having a structure in which a center pin is inserted into a winding center of an electrode assembly ('jelly-roll') in which a positive electrode sheet and a negative electrode sheet are roundly wound while a separator is interposed therebetween. The coating layer containing the solid particles ('solid particle coating layer') is formed on the separator adjacent to the membrane.

According to the present invention, by forming a coating layer containing solid particles on the separator of the jelly-roll located in the center of the winding, the heat dissipation is not easy when the internal short circuit occurs, so the center of the jelly-roll is most likely to ignite and explode By applying a high strength to the membrane of the membrane, it prevents the membrane from penetrating by the end or corner of the deformed center pin when the external impact is applied, and minimizes the pressure of the jelly-roll to ignite and explode due to internal short circuit You can prevent it.

In addition, when heat is generated inside the battery due to an internal short circuit, the jelly-roll is not easily dissipated to the outside due to its structural characteristics, so that decomposition of the electrolyte is promoted, and a large amount of gas is released, and fine sparks are generated. In addition, it causes serious problems in terms of safety, such as the possibility of ignition and explosion being increased. The coating layer containing the solid particles absorbs high heat inside the battery and at the same time suppresses shrinkage of the separator due to high heat. Ultimately, the safety of the battery can be secured.

Furthermore, the coating layer including the solid particles may contribute to improving the safety of the battery by suppressing the slippage of the jelly-roll caused by the inflow of foreign matter or the step between the components of the jelly-roll at the central portion of the jelly-roll. Can be.

These various effects are achieved by coating the solid particle coating layer on the separator adjacent to the winding center.

In one preferred example, the solid particle coating layer may be a structure formed on one side or both sides of the separator from the winding start point to the position corresponding to the starting point of the active material coating in the positive electrode or negative electrode foil which is the current collector.

In the laminated structure of the anode / separation membrane / cathode / separation membrane in the developed state prior to the winding of the jelly-roll type electrode assembly, the position corresponding to the starting point of application of the active material of the electrode foil from the end of the separation membrane at the starting point of winding the two separators, namely Forming the solid particle coating layer on the separator that reaches the boundary between the uncoated portion of the electrode foil and the active material applying portion is a method of forming the solid particle coating layer with little effect on the total thickness or volume of the finished electrode assembly. desirable. However, the fact that the end of the solid particle coating layer reaches the boundary portion does not mean that the application portion must coincide with the boundary portion, but should be interpreted as a meaning encompassing the case where it is applied to a portion including the surroundings. do.

The solid particle coating layer may be formed on one side or both sides of the separator, but it is more preferable to form on both sides in terms of imparting high strength to the separator.

In addition, when the solid particle coating layer is too thick, it can increase the overall thickness or volume of the finished electrode assembly, and if the coating layer is too thin, gives the separator a desired strength and absorbs high heat inside the battery; At the same time, it may be difficult to expect the effect of forming the solid particle coating layer, such as suppressing the shrinkage of the separator due to high heat, it is preferable to have a thickness of 3 to 15 ㎛, more preferably 4 to 9 ㎛ thickness. Do.

The separator 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 from 0.01 to 10 ㎛ ㎛, thickness is generally 5 ~ 300 ㎛. As such a separator, for example, olefin polymers such as chemical resistance and hydrophobic polypropylene; Sheets or nonwovens made of glass fibers or polyethylene may be used, and among these, olefin polymers are more preferred.

The solid particles are not particularly limited as long as the particles are made of materials capable of exerting a predetermined effect according to the present invention without affecting the physical and chemical properties of the separator, for example, inorganic powder, polymer resin powder, And it may be one or more selected from the group consisting of microcapsules containing a security collateral material.

As said inorganic powder, ceramic powders, such as lead titanate powder, a barium titanate powder, a titanate powder, an alumina silicate, a silica, a mullite, an alumina, are preferable, for example, As said polymer resin powder, Preference is given to porous beads made of polymer resins such as crosslinked copolymer beads such as styrene, alkylstyrene, divinylbenzene and trivinylbenzene.

In addition, the microcapsules having the built-in safety collateral material, for example, has a built-in safety collateral material such as powdered extinguishing agent, inert gas discharged at a dangerous temperature of approximately 100 to 150 degrees at the time of heat generation due to internal short circuit or overcharge, etc. In this case, the shell of the microcapsules containing such a security collateral material may be melted or ruptured at the above temperature.

The particle size of the solid particles is preferably 1 to 10 μm, and more preferably 2 to 4 μm, and when the particle size of the solid particles is too large, it may be difficult to uniformly coat the separator and provide a predetermined strength to the separator. In addition, it is not preferable in terms of imparting. On the contrary, when the particle size is too small, it is not preferable because there may be a limit in absorbing high heat when generating high heat inside the battery and suppressing shrinkage of the separator due to high heat.

In one preferred example, the solid particles may be included in the coating layer of the binder substrate.

The method for forming the coating layer including the solid particles is not particularly limited, and may be selected from known methods or performed by a new suitable method. For example, a solvent in which a binder such as polyvinylidene fluoride or polyvinyl alcohol is dissolved. After uniformly dispersing the solid particles in the mixture, the mixed coating liquid may be formed by applying the mixed coating liquid to both sides of the separator adjacent to the winding center and then drying the mixed particles.

The binder substrate is a material capable of providing a predetermined bonding force without affecting the physical and chemical properties of the battery internal environment such as a separator, an electrolyte, and the like, and is generally used in the manufacture of electrodes, as described later in the electrode configuration. A binder material, such as PVdF (polyvinylidene fluoride), can be preferably used.

In particular, the secondary battery according to the present invention may be preferably applied to a lithium secondary battery prepared by impregnating a lithium-containing electrolyte in a state in which an electrode assembly is embedded in a battery case.

Other components of the lithium secondary battery according to the present invention will be described below.

The positive electrode for a lithium secondary battery is manufactured by, for example, applying a mixture of a positive electrode active material, a conductive material, and a binder in the form of a slurry on a positive electrode current collector, followed by drying and compressing the filler. It may be added further.

The positive electrode active material may be a layered compound such as lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), or a compound substituted with one or more transition metals; Lithium manganese oxides such as Li _{1 + x} Mn _2-x O ₄ (where x is 0 to 0.33), LiMnO ₃ , LiMn ₂ O ₃ , LiMnO _2, and the like; Lithium copper oxide (Li ₂ CuO ₂ ); Vanadium oxides such as LiV ₃ O ₈ , LiFe ₃ O ₄ , V ₂ O ₅ , Cu ₂ V ₂ O ₇ and the like; Ni-site type lithium nickel oxide represented by the formula LiNi _{1 - x} M _x O ₂ , wherein 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 (wherein M = Co, Ni, Fe, Cr, Zn or Ta and x = 0.01 to 0.1) or Li ₂ Mn ₃ MO ₈ (wherein M = Fe, Co, Lithium manganese composite oxide represented by Ni, Cu, or Zn); LiMn ₂ O _{4 in} which a part of Li in the formula is substituted with alkaline earth metal ions; Disulfide compounds; Fe ₂ (MoO ₄ ) ₃ and the like, but are not limited to these.

The positive electrode current collector is generally made to a thickness of 3 to 500 μm. Such a positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. For example, the surface of stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel Surface treated with carbon, nickel, titanium, silver or the like can be used. The current collector may form fine irregularities on its surface to increase the adhesion of the positive electrode active material, and may be in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric.

The conductive material is typically added in an amount of 1 to 50% by weight based on the total weight of the mixture including the positive electrode active material. Such a conductive material is not particularly limited as long as it has conductivity without causing chemical change in the battery, and examples thereof include graphite such as natural graphite and artificial graphite; Carbon blacks such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and summer black; Conductive fibers such as carbon fibers and metal fibers; Metal powders such as carbon fluoride powder, aluminum powder and nickel powder; Conductive whiskeys 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 the active material and the conductive material to the current collector, and is generally added in an amount of 1 to 50 wt% based on the total weight of the mixture including the positive electrode active material. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, 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 inhibiting expansion of the positive electrode, and is not particularly limited as long as it is a fibrous material without causing chemical change in the battery. Examples of the filler include olefinic polymers such as polyethylene and polypropylene; Fibrous materials, such as glass fiber and carbon fiber, are used.

The negative electrode for a lithium secondary battery is manufactured by coating, drying, and compressing a negative electrode material on a negative electrode current collector, and if necessary, components of the positive electrode (binder, conductive material, filler, etc.) as described above may be further included.

The negative electrode current collector is generally made to a thickness of 3 to 500 ㎛. Such a negative electrode current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery. For example, the surface of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel Surface-treated with carbon, nickel, titanium, silver, and the like, aluminum-cadmium alloy, and the like can be used. In addition, like the positive electrode current collector, fine concavities and convexities may be formed on the surface to enhance the bonding strength of the negative electrode active material, and may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric.

The negative electrode material may be, for example, carbon such as hardly graphitized carbon or graphite carbon; Li _x Fe ₂ O ₃ (0 ≦ _x ≦ 1), Li _x WO ₂ (0 ≦ _x ≦ 1), Sn _x Me _{1- x} Me ' _y O _z (Me: Mn, Fe, Pb, Ge; Me' Metal complex oxides such as Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, halogen, 0 <x ≦ 1; 1 ≦ y ≦ 3; 1 ≦ z ≦ 8); Lithium metal; Lithium alloys; Silicon-based alloys; Tin-based alloys; 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 metal oxides such as Bi ₂ O ₅ ; Conductive polymers such as polyacetylene; Li-C-oNi-based materials and the like can be used.

The nonaqueous electrolyte for lithium secondary batteries consists of a nonaqueous electrolyte and a lithium salt.

Examples of the nonaqueous electrolyte include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butylo lactone, and 1,2-dimethoxy ethane. , Tetrahydroxy franc, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolon, formamide, dimethylformamide, dioxolon, acetonitrile, nitromethane, methyl formate, methyl acetate , Phosphoric acid triester, trimethoxy methane, dioxolon derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether, methyl pyroionate Aprotic organic solvents, such as ethyl propionate, can be used.

The lithium salt is a good material to be dissolved 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.

In addition, for the purpose of improving charge / discharge characteristics, flame retardancy, etc., for example, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphate triamide, etc. , Nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N, N-imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxy ethanol, aluminum trichloride, etc. may be added. have. In some cases, in order to impart nonflammability, halogen-containing solvents such as carbon tetrachloride and ethylene trifluoride may be further included, and carbon dioxide gas may be further included to improve high temperature storage characteristics.

As described above, the secondary battery according to the present invention is a secondary battery having a structure in which a center pin is inserted into a winding center of an electrode assembly ('jelly-roll') in which a positive electrode sheet and a negative electrode sheet are roundly wound while a separator is interposed therebetween. As the coating layer containing the solid particles ('solid particle coating layer') is formed on the separator adjacent to the winding center, an internal short circuit caused by deformation of the center pin inserted in the center of the core of the jelly-roll may be deformed by an external impact. By preventing ignition and explosion due to overcharging, the safety of the battery can be improved.

Hereinafter, although described with reference to the drawings according to an embodiment of the present invention, this is for easier understanding of the present invention, the scope of the present invention is not limited thereto.

FIG. 3 is a schematic view of a development before a winding process of an electrode assembly according to an exemplary embodiment of the present disclosure.

Referring to FIG. 3, in the laminate structure of the anode / separation membrane / cathode / separation membrane, a position corresponding to the active material application starting point region 310 of the positive electrode 300 beyond the active material application starting point region 410 of the negative electrode 400. Until, solid particle coating layers 110 and 210 are formed on both surfaces of each separator 100 and 200.

When the laminate structure of the anode / separation membrane / cathode / separation membrane is wound in the direction of an arrow to manufacture a jelly-roll type electrode assembly, the corresponding portions of the separation membranes 100 and 200 on which the solid particle coating layers 110 and 210 are formed are shown in FIG. 4. As will be described, it is located approximately at the center of the winding to ensure the safety of the battery.

4 is a horizontal cross-sectional view of a jelly-roll electrode assembly in which a coating layer including solid particles is formed on a separator adjacent to a winding center according to one embodiment of the present invention.

Referring to FIG. 4, a coating layer 510 including solid particles is formed on the separator of the core portion of the jelly-roll 500. Since the coating layer 510 is mainly applied on the separator corresponding to the uncoated portion of the current collector, it does not affect the operation of the battery. In addition, the coating layer 510 improves the strength of the separator, and prevents the separator from being penetrated by an end portion or a corner portion of the deformed center pin (not shown) upon application of an external impact, and the jelly-roll 500 By minimizing pressure, it is possible to prevent fire and explosion due to internal short circuit.

In addition, the coating layer 510 formed on the separator of the core portion where heat dissipation is not easy due to the occurrence of internal short circuits and is highly likely to ignite and explode is absorbed by the solid particles contained therein and at the same time absorbs high heat inside the battery. Shrinkage of the separator due to high heat can ultimately ensure the safety of the battery.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the following Examples are provided to illustrate the present invention, and the scope of the present invention is not limited thereto.

Example 1

1-1. Manufacture of anode

LiCoO ₂ was used as the positive electrode active material, 94% by weight of LiCoO ₂ , 3.5% by weight of Super-P (conductive material) and 2.5% by weight of PVdF (binder) were added to N-methyl-2-pyrrolidone (NMP) as a solvent. After preparing the positive electrode mixture slurry, the positive electrode was prepared by coating, drying and pressing on aluminum foil.

1-2. Preparation of Cathode

Artificial negative electrode was used as the negative electrode active material, 94% by weight of artificial graphite, 1% by weight of Super-P (conductive material), and 5% by weight of PVdF (binder) were added to NMP as a solvent to prepare a negative electrode mixture slurry. The negative electrode was prepared by coating, drying and pressing on copper foil.

1-3. Preparation of Coating Solution Containing Solid Particles

Alumina powder was uniformly dispersed and mixed in a mixed solution of propylene carbonate solvent and PVdF to prepare a coating solution containing solid particles.

1-4. Preparation of Membrane

As shown in FIG. 3, a coating solution of 1-3 is applied on both sides from one end of the porous separator (Celgard ^TM ) to a position from the positive electrode tab portion of the positive electrode foil to a position corresponding to the positive electrode active material application starting point region. And drying to prepare a separation membrane containing solid particles in a portion adjacent to the winding center.

1-5. Manufacture of batteries

Interposed between the anode and the cathode prepared in 1-1 and 1-2, respectively, the separator 1-4 and the solid particle coating layer and the positive electrode tab is formed in the positive position, and then in this state The positive electrode was wound round so as to be positioned inside, built in a cylindrical battery case, and impregnated with a carbonate electrolyte of 1M LiPF ₆ to mount a CID on the top to prepare a cylindrical battery of 18650 (diameter 18 mm, length 65 mm). .

Example 2

A battery was manufactured in the same manner as in Example 1, except that the coating solution of 1-3 was applied to only one surface of the separator when preparing the separator of Example 1-4.

Comparative Example 1

An electrode and a battery were manufactured in the same manner as in Example 1, except that the coating layer including the solid particles was not formed in the separator.

Experimental Example 1

For each of the five full-charged cylindrical batteries prepared in Example 1, Example 2 and Comparative Example 1 in the vertical direction of the battery, a rod weighing 9.1 kg and a diameter of 15.8 mm by dropping at a height of 61 cm After inducing a short circuit at the electrode facing area, it was confirmed whether to ignite / explode.

As a result, all of the batteries of Example 1 were safe without ignition / explosion, but the batteries of Comparative Example 1 ignited / exploded in five batteries, and high heat occurred in all five batteries. On the other hand, the batteries of Example 2 only generated high heat in all five. Therefore, the battery of Example 1 according to the present invention forms a coating layer including solid particles on the separator adjacent to the winding center, thereby minimizing the damage of the membrane or the compression of the jelly roll due to the deformation of the center pin when an external impact is applied. It can be seen that the increase in the internal temperature is suppressed and ultimately the safety of the battery is improved.

Those skilled in the art to which the present invention pertains will be able to perform various applications and modifications within the scope of the present invention based on the above contents.

1 is a vertical cross-sectional perspective view of a cylindrical battery of the prior art incorporating a jelly-roll electrode assembly;

2 is a horizontal cross-sectional view of the center pin along straight line A-A in the cell of FIG. 1;

3 is an exploded view before a winding process of an electrode assembly according to one embodiment of the present invention;

4 is a horizontal cross-sectional view of a jelly-roll in which a coating layer including solid particles is formed on a separator adjacent to a winding center.

Claims (9)

A secondary battery having a center pin inserted into a winding center of an electrode assembly ('jelly-roll') in which a positive electrode sheet and a negative electrode sheet are roundly wound with a separator interposed therebetween, and including solid particles on a separator adjacent to the winding center. ('Solid particle coating layer') is a secondary battery characterized by the above-mentioned. The secondary solid particle coating layer of claim 1, wherein the solid particle coating layer is formed on one side or both sides of the separation membrane from a starting point of winding to a position corresponding to the starting point of the active material application in the anode foil or the cathode foil as the current collector. battery. The secondary battery of claim 1, wherein the solid particle coating layer has a thickness of 3 to 15 μm. The secondary battery of claim 1, wherein the solid particles are one or more selected from the group consisting of an inorganic powder, a polymer resin powder, and a microcapsule containing a safety collateral material. The secondary battery of claim 4, wherein the inorganic powder is a ceramic powder, and the polymer resin powder is a porous bead made of a polymer resin. The secondary battery of claim 1, wherein a particle diameter of the solid particles is 1 μm to 10 μm. The secondary battery of claim 1, wherein the solid particles are included in a coating layer of a binder substrate. The secondary battery of claim 7, wherein the binder substrate is PVdF. The secondary battery of claim 1, wherein the battery is a lithium secondary battery.

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