KR20080027502A - Secondary battery improved safety for external-impact and internal-short - Google Patents

Abstract

A secondary battery is provided to improve safety and lifespan by preventing an internal short and inhibiting the reduction in battery capacity, and effectively emit heat generated during charge and discharge or operation thereof. A secondary battery(100) has an electrode assembly(jelly roll) within a battery case, wherein the electrode assembly(110) is manufactured by winding a positive electrode/a separator/a negative electrode into a roll. The secondary battery has a spiral structure in horizontal section and is obtained by inserting a center pin(200) made of an insulating material into a core of the jelly roll. The center pin is formed of synthetic resin, synthetic rubber, or a composite thereof.

Description

Secondary Battery Improved Safety for External-Impact and Internal-Short}

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 a vertical sectional perspective view of a cylindrical secondary battery according to one embodiment of the present invention;

4 is a horizontal cross-sectional view of the center pin along the straight line B-B in the battery of FIG. 3.

The present invention relates to a secondary battery having improved safety against external shock and internal short circuit, and more particularly, to a secondary battery in which an electrode assembly (jelly roll) manufactured by winding a cathode / separator / cathode is embedded in a battery case. The present invention provides a secondary battery having a spiral structure wound in a horizontal cross section and having a center pin made of an insulating material inserted into a core of a jelly roll.

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, secondary batteries are classified into cylindrical batteries and rectangular batteries in which the electrode assembly is embedded in a cylindrical or rectangular metal can, and pouch-type batteries in which the electrode assembly is embedded in a pouch type case of an aluminum laminate sheet. .

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 And a plurality of positive and negative electrodes of a predetermined size are classified into a stack type in which a plurality of positive and negative electrodes 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.

The jelly-roll type electrode assembly is mainly used for cylindrical cells and rectangular cells, and FIG. 1 schematically shows a vertical cross-sectional perspective view of a cylindrical cell including a jelly-roll type electrode assembly.

Referring to FIG. 1, the cylindrical secondary battery 10 accommodates a jelly-roll type (wound) electrode assembly 20 in a cylindrical case 30 and injects an electrolyte solution into the cylindrical case 30, and then the case 30. ) Is manufactured by combining a top cap 40 having an electrode terminal (for example, a positive electrode terminal; not shown) formed at an open upper end of the panel.

The electrode assembly 20 has a structure in which a cathode 21, a cathode 22, and a separator 23 are sequentially stacked and wound in a jelly-roll shape, and at its core (center of the jelly-roll), a cylindrical center pin is formed. 50 is inserted. The center pin 50 is a structure in which the plate is rounded, and as shown in FIG. 2, the center pin 50 has a hollow cylindrical structure in which the end portion 51 is not in contact with the horizontal cross section. The center pin prevents the winding form of the electrode assembly from being deformed by an external impact, serves to release heat generated during charging and discharging and operation, and is generally made of a metal material to impart a predetermined strength.

However, the center pin is easily deformed by the hollow internal structure when an external shock such as dropping or crimping of the battery is applied, and the inner end of the center pin is opened by contacting the electrode through the separator through the non-contacted end of the center pin. It may cause. In addition, during charging and discharging of the battery, the jelly-roll tends to deform while undergoing repeated expansion and contraction, and in this process, stress is concentrated to the center, and the electrode penetrates the separator and contacts the metal center pin, causing an internal short circuit. In some cases. The deformation of the jelly-roll also causes a change in the distance between the electrodes, resulting in problems such as increased internal resistance, reduced capacity, and shorter lifespan.

Therefore, there is a high need for a technology capable of effectively preventing internal short circuits due to deformation of the center pin and improving battery safety and extending battery life.

In this regard, Japanese Patent Application Laid-Open Nos. Hei 08-273697, Hei 09-270251, Hei 11-204130 and 2003-092148, and Korean Patent Application Laid-Open No. 2003-043745 have some modifications of the above structure. Center pins are shown. However, these center pins have their advantages, but they do not solve all of the problems described above.

Accordingly, an object of the present invention is to solve the problems of the prior art as described above and the technical problems that have been requested from the past.

After repeated studies and various experiments, the inventors have a spiral structure wound in a horizontal cross-section and when the center pin made of an insulating material is inserted into the core of the jelly-roll, the center is caused by external shock and repeated charging and discharging. By suppressing the deformation of the pins, it is possible to prevent internal short circuits and to reduce battery capacity, thereby improving battery safety and lifespan, and effectively dissipating heat generated during charging and discharging or operation. It was confirmed that the present invention was completed.

A secondary battery according to the present invention for achieving the above object is a secondary battery in which an electrode assembly (jelly-roll) manufactured by winding a cathode / separator / cathode is embedded in a battery case, and has a spiral structure wound in a horizontal cross section. And a center pin made of an insulating material inserted into the core of the jelly-roll.

As described above, in the secondary battery according to the present invention, since the center pin has a structure in which the center pin is empty and spirally wound, the electrode assembly (jelly roll) repeatedly contracts and expands due to continuous charging and discharging of the battery. When the strain force is absorbed, stress accumulation can be prevented, and heat generated during charging and discharging and operation can be effectively released into the empty space in the center, thereby ultimately improving the safety and life of the battery.

In one preferred embodiment, the center pin is not particularly limited as long as it is an insulating material, for example, synthetic resin such as polypropylene, polyethylene, polyimide, synthetic rubber such as polybutadiene, or a complex thereof. However, it is not limited only to these.

The center pin is preferably wound in two to ten winding structures based on a horizontal cross section. The number of windings of the center pin affects the mechanical stiffness and elastic force of the center pin along with the kind of material and the thickness of the winding surface thereof, and also affects the discharge of generated heat or the battery capacity depending on the size of the outer diameter. For example, when the outer diameter of the center pin is kept constant and the number of windings is increased, the center pin is extended in its inner direction so that the center empty space is narrowed, so that the generated heat may not be effectively discharged. have. On the other hand, if the number of windings is increased regardless of the outer diameter of the center pin, the center pin may have a larger space in the battery case, thereby reducing the capacity of the battery. Therefore, the center pin may have a higher mechanical rigidity as the number of winding times increases, but the above problems may occur. Therefore, an appropriate number of winding may be determined in consideration of these points.

In addition, the center pin is preferably an outer diameter of 2 to 5 mm. Since the outer diameter itself means the total size of the center pin, it is not preferable because the capacity of the battery is small when the outer diameter is too large, whereas the mechanical rigidity of the center pin is small when the outer diameter is too small. Therefore, it is more preferable to manufacture the center pin to have the outer diameter of the said range in addition to the number of windings of the said range.

Exemplary structures of such center pins can be easily seen in the following drawings.

3 schematically illustrates a vertical cross-sectional perspective view of a cylindrical secondary battery according to one embodiment of the present invention, and FIG. 4 schematically illustrates a horizontal cross-sectional view along a straight line B-B of FIG. 3. Hereinafter, the present invention will be described in more detail with reference to the drawings, but the scope of the present invention is not limited thereto.

Referring to these drawings, the secondary battery 100 is composed of a jelly-roll type electrode assembly 110 in which the center pin 200 is inserted into the core, and has a diameter R _B of 18 mm as an 18650 standard. , The length L is 65 mm. The center pin 200 included in the secondary battery 100 has a structure wound three times on a horizontal cross section based on an outer diameter R _C of 4 mm, and the winding structure is wound as closely as possible without being spaced apart. It is therefore compact and can provide excellent mechanical rigidity.

In the present invention, the secondary battery is preferably a cylindrical secondary battery in shape, and a lithium-based secondary battery having high energy density, discharge voltage, and output stability in terms of materials. More preferably, it may be a cylindrical lithium secondary battery in which a jelly-roll type electrode assembly is embedded in a battery case of a cylindrical metal can.

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

In general, a lithium secondary battery is composed of a positive electrode, a negative electrode, a separator, a lithium salt-containing nonaqueous electrolyte, and the like.

The positive electrode is produced by, for example, applying a mixture of a positive electrode active material, a conductive agent, and a binder onto a positive electrode current collector, followed by drying, and optionally, a filler is further added.

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 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; Li _{1 + x} Mn _{2 - x} O ₄ (Where x is 0 to 0.33), lithium manganese oxides such as 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 conductive agent is typically added in an amount of 1 to 50 wt% based on the total weight of the mixture including the positive electrode active material. Such a conductive agent is not particularly limited as long as it has conductivity without causing chemical change in the battery. Examples of the conductive agent 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 oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used. In some cases, since the conductive second coating layer is added to the positive electrode active material, the addition of the conductive agent may be omitted.

The binder is a component that assists in bonding the active material and the conductive agent 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 is manufactured by applying and drying a negative electrode material on the negative electrode current collector, and if necessary, the components 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': Al, B, P, Si, Group 1, 2, 3 of the periodic table) Metal composite oxides such as a group element, 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 oxides such as Bi ₂ O ₅ ; Conductive polymers such as polyacetylene; Li-Co-Ni-based materials and the like can be used.

The separator is interposed between the cathode and the anode, and an insulating thin film having high ion permeability and mechanical strength is used. The pore diameter of the 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 non-woven fabrics made of glass fibers or polyethylene are used. When a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte may also serve as a separator.

A lithium salt containing non-aqueous electrolyte solution consists of a nonaqueous electrolyte solution and a lithium salt. As the nonaqueous electrolyte, a liquid nonaqueous electrolyte, a solid electrolyte, an inorganic solid electrolyte, and the like are used.

As said liquid nonaqueous electrolyte, N-methyl- 2-pyrrolidinone, a propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma- Butyl lactone, 1,2-dimethoxy ethane, tetrahydroxy franc, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxorone, formamide, dimethylformamide, dioxorone , Acetonitrile, nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxy methane, dioxorone derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbo Aprotic organic solvents such as nate derivatives, tetrahydrofuran derivatives, ethers, methyl pyroionate and ethyl propionate can be used.

Examples of the organic solid electrolytes include polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate ester polymers, polyedgetion lysine, polyester sulfides, polyvinyl alcohols, polyvinylidene fluorides, Polymers containing ionic dissociating groups and the like can 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, sulfates and the like of Li, such as Li ₄ SiO ₄ -LiI-LiOH, Li ₃ PO ₄ -Li ₂ S-SiS ₂ , and the like, may 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, the lithium salt-containing non-aqueous electrolyte contains pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, and hexa for the purpose of improving charge and discharge characteristics and flame retardancy. Phosphate triamide, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N, N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxy ethanol, aluminum trichloride And the like may be added. 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.

The lithium secondary battery according to the present invention can be produced by conventional methods known in the art. That is, it may be prepared by inserting a porous separator between the anode and the cathode and injecting the electrolyte therein.

The positive electrode may be manufactured by, for example, applying a slurry containing the lithium transition metal oxide active material, the conductive material, and the binder described above onto a current collector and then drying. Similarly, the negative electrode can be prepared by, for example, applying a slurry containing the above-described carbon active material, a conductive material and a binder onto a thin current collector and then drying it.

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

The polypropylene sheet was wound three times on a horizontal cross section, as shown in FIG. 4, to produce a center pin having an outer diameter of 4 mm, and the center pin was inserted into the core of the electrode assembly to be 18650 (diameter 18 mm, length 65). mm) cylindrical secondary batteries were fabricated.

Comparative Example 1

A cylindrical secondary battery was fabricated in the same manner as in Example 1, except that a center pin having a hollow circular structure was manufactured, as shown in FIG. Was prepared.

Experimental Example 1

Ten batteries prepared in Example 1 and ten batteries prepared in Comparative Example 1 were subjected to an impact test at a voltage of 4.2 V. The impact test was performed by dropping a rod-shaped object having a diameter of 15.8 mm and a weight of 9.1 kg at a height of 61 cm to check whether a short circuit occurred.

As a result, all the batteries according to Example 1 did not have a short circuit, whereas short circuits were observed in three of the batteries according to Comparative Example 1. As a result of disassembling and inspecting the batteries of Comparative Example 1 in which a short circuit was induced, it was confirmed that a short circuit was caused by connecting the end of the center pin to the electrode of the jelly-roll through the separator.

Experimental Example 2

After repeatedly charging and discharging 10 batteries manufactured in Example 1 and 10 batteries prepared in Comparative Example 1 under 1C-1C conditions, the discharge capacity at the time of final charging and discharging was measured, and the battery was disassembled to change internally. Was observed.

As a result, the batteries of Example 1 exhibited a high discharge capacity of about 10% compared to those of Comparative Example 1. In addition, the batteries of Comparative Example 1 were found to have a severe degree of twist of the jelly-roll compared to the batteries of Example 1. This is because the continuous expansion and contraction of the jelly-roll in the cell of Example 1 was buffered by the elastic center pin, whereby accumulation of stress was prevented.

As described above, the secondary battery according to the present invention can suppress the deformation of the center pin by the external shock and repeated charging and discharging to prevent the internal short circuit and suppress the decrease in battery capacity, thereby the safety and life of the battery It can improve the, and has the effect of releasing heat generated during charging or discharging or operation.

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.

Claims (6)

A secondary battery in which an electrode assembly (jelly-roll) manufactured by winding an anode / separation membrane / cathode is built in a battery case, and has a spiral structure wound in a horizontal cross section, and a center pin made of an insulating material is placed at the center of the jelly-roll. A secondary battery, characterized in that inserted. The secondary battery of claim 1, wherein the center pin is made of synthetic resin, synthetic rubber, or a composite thereof. The secondary battery of claim 1, wherein the center pin has a winding structure of 2 to 10 times. The secondary battery of claim 1, wherein the center pin has an outer diameter of 2 to 5 mm. The secondary battery as claimed in claim 1, wherein the battery case is a cylindrical metal can. The secondary battery of claim 1, wherein the battery is a lithium secondary battery.

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