KR101475426B1 - Cylindrical Secondary Battery Containing Center Pin of Novel Structure - Google Patents

Abstract

The present invention relates to an electrode assembly (jelly-roll) manufactured by winding a separator interposed between an anode and a cathode, and a cap assembly mounted on an upper end of the battery case, And a center pin having a length longer than the length of the jelly-roll is inserted in the core of the jelly-roll in a longitudinal cross section of the battery.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a cylindrical secondary battery including a center pin having a novel structure,

More particularly, the present invention relates to a cylindrical secondary battery including a center pin having a novel structure, and more particularly, to a cylindrical secondary battery including a cylindrical battery cell including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, A secondary battery having a structure in which a cap assembly is mounted on the upper end of the battery case and a center pin having a length longer than the length of the jelly-roll is inserted into the core of the jelly- will be.

As technology development and demand for mobile devices have increased, the demand for secondary batteries as energy sources has been rapidly increasing. Many researches have been conducted on lithium secondary batteries with high energy density and discharge voltage among such secondary batteries. .

The secondary battery is classified into a cylindrical battery and a prismatic battery in which the electrode assembly is housed in a cylindrical or rectangular metal can according to the shape of the battery case, and a pouch-shaped battery in which the electrode assembly is housed in a pouch-shaped case of an aluminum laminate sheet .

The electrode assembly incorporated in the battery case is a chargeable and dischargeable power generation device composed of a positive electrode, a negative electrode, and a separator layer interposed between the positive electrode and the negative electrode. The electrode assembly includes a separator between the positive electrode and the negative electrode coated with the active material A stack type unit cell in which a plurality of positive and negative electrodes of a predetermined size are stacked in a state in which a separation membrane is interposed and stacked unit cells such as a bi-cell or pull cell are stacked in a long length separator sheet And stacked / folded type. Among them, the jelly-roll type electrode assembly has an advantage of being easy to manufacture and having a high energy density per weight.

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

Referring to FIG. 1, a cylindrical secondary battery 10 includes a jelly-roll type (wound type) electrode assembly 20 accommodated in a cylindrical case 30, an electrolyte is injected into the cylindrical case 30, And a top cap 40 having an electrode terminal (for example, a positive electrode terminal;

The electrode assembly 20 has a structure in which an anode 21 and a cathode 22 are sequentially laminated and wound in a round shape and a cylindrical center pin 50 is formed on the core (jelly- Is inserted. The center pin 50 is generally made of a metal material in order to impart a predetermined strength and has a structure in which the plate material is bent in a round shape. As shown in FIG. 2, the center pin 50 has a hollow cylindrical shape Structure. The center pin 50 functions as a channel for fixing and supporting the electrode assembly and a gas for discharging gas generated by an internal reaction during charging, discharging and operation.

However, since the length l of the center pin 50 is shorter than the length L of the electrode assembly, deformation of the hollow internal structure of the center pin is liable to occur when an external impact such as dropping and pressing of the battery is applied, By such a deformation, it is deformed into a sharp shape, and it is possible to penetrate the separation membrane and contact the electrode, thereby causing an internal short circuit.

Therefore, a structure in which both side ends 51 are bent toward the center of the center pin 50 is also used. However, in spite of such a modification of the structure, when the center pin 50 applies a large pressure, its shape is deformed flatly, thereby pressing the separation membrane, resulting in a short circuit.

The short circuit at the central portion of the electrode assembly 20 is more serious in terms of the safety of the battery as compared with the short circuit caused at the outside or adjacent portions thereof. That is, the heat generated during the internal short circuit of the central region tends to accumulate without being easily conducted to the outside, which further increases the risk of ignition or explosion of the battery.

In addition, as the recent incidences of the firing of the notebook PCs have become more conspicuous, the importance of the safety of the battery is more emphasized.

Therefore, there is a high need for a technique capable of effectively preventing internal short-circuiting due to deformation of the center pin and thus igniting the battery, thereby improving the safety of the battery.

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

The inventors of the present application have conducted intensive research and various experiments and have found that when a center pin having a length longer than the length of the jelly-roll is inserted into the jelly-roll in the longitudinal cross section of the battery, Even when the center pin is deformed due to the impact, the end of the center pin can be prevented from being in contact with the electrode assembly, thereby preventing the internal short circuit. Thus, it is confirmed that the safety of the battery can be greatly improved. I have come to completion.

According to an aspect of the present invention, there is provided a secondary battery comprising: a cylindrical battery case having an anode assembly, a cathode assembly, and an electrode assembly (jelly-roll) manufactured by winding a separator interposed between the anode assembly and the cathode assembly, A cap assembly is mounted on the top of the battery case, and a center pin having a length longer than the length of the jelly-roll is inserted into the core of the jelly-roll in the longitudinal cross section of the battery.

As described above, in the secondary battery according to the present invention, since the center pin has a length longer than the length of the jelly-roll, contact between the center pin and the electrode assembly due to deformation of the center pin does not occur during an external impact, The safety of the battery can ultimately be greatly improved.

The center pin according to the present invention may be formed of an insulating material, a conductive material, or the like if it is manufactured with the above structure. Examples of the insulating material include one or two or more polymer materials selected from the group consisting of polypropylene, polyimide, polyamide, polycarbonate, and polymethyl methacrylate, and a complex material including the polymer and filler Etc., but is not limited to these. In terms of imparting excellent mechanical rigidity, a metal material may be preferably used.

In some cases, the center pin may have three to eight winding structures with respect to the horizontal cross section. The number of turns of the center pin affects the mechanical stiffness and elasticity of the center pin as well as the type of material and the winding surface of the center pin, and may affect the discharge of gas or the capacity of the battery 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 times of winding is increased, the space inside the center pin is narrowed, so that the gas can not be effectively discharged. On the other hand, if the number of times of winding is increased irrespective of the outer diameter of the center pin, the space occupied by the center pin in the battery case may be widened and the capacity of the battery may be reduced. Therefore, as the number of turns of the center pin increases, mechanical stiffness can be exhibited. However, since the above problems may occur, it is possible to determine the appropriate number of times of winding by taking these points into consideration.

In one preferred example, the center pin may be longer in the range of 1-15%, based on the length of the jelly-roll. In other words, since the length of the center pin is longer than the length of the jelly-roll, it is possible to fundamentally prevent a local short-circuit due to contact with the electrode assembly when the center pin is deformed, .

The total length of the center pin may preferably be 55 mm to 65 mm, and more preferably 59.5 mm to 61 mm.

The length of the center pin protruded from the upper end of the jelly-roll may be in a range of 0.1 mm to 1 mm. Length, and more preferably 0.1 mm to 0.5 mm. If the length is too small, internal short-circuiting may occur due to contact between the jelly-roll and the center pin at the time of deformation of the center pin. On the contrary, if too large, the volume of the cylindrical battery becomes large.

It is preferable that the center pin has an outer diameter of 2 to 5 mm. Since the outer diameter itself refers to the total size of the center pin, if the outer diameter is too large, the capacity of the battery becomes small. On the contrary, if the outer diameter is too small, the mechanical rigidity of the center pin becomes small. Therefore, it is more preferable to manufacture the center pin so as to have the outside diameter in the above range in addition to the number of times of winding in the above range.

The secondary battery of the present invention is preferably a cylindrical secondary battery in terms of shape, and in terms of material, a lithium-based secondary battery having high energy density, discharge voltage, and output stability is preferable. More preferably, it is 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.

Generally, a lithium secondary battery is composed of a positive electrode, a negative electrode, a separator, a non-aqueous electrolyte containing a lithium salt, and the like.

The positive electrode is prepared, for example, by applying a mixture of a positive electrode active material, a conductive material and a binder on a positive electrode current collector, followed by drying, and if necessary, a filler is further added.

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 change in the battery, and may be formed of a material such as stainless steel, aluminum, nickel, titanium, sintered carbon, or a surface of aluminum or stainless steel Treated with carbon, nickel, titanium, silver or the like may be used. The current collector may have fine irregularities on the surface thereof to increase the adhesive force of the cathode active material, and various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric are possible.

The cathode 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 and Cu ₂ V ₂ O ₇ ; Formula _{LiNi 1 - x M x O 2} ( where, the M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, x = 0.01 ~ 0.3 Im) Ni site type lithium nickel oxide which is represented by; Formula _{LiMn 2 - x M x O 2} ( where, M = Co, Ni, Fe , Cr, and Zn, or Ta, x = 0.01 ~ 0.1 Im) or Li ₂ Mn ₃ MO ₈ (where, M = Fe, Co, Ni, Cu, or Zn); LiMn ₂ O _{4 in} which a part of Li in the formula is substituted with an alkaline earth metal ion; Disulfide compounds; Fe ₂ (MoO ₄ ) ₃ , and the like. However, the present invention is not limited to these.

The conductive material is usually added in an amount of 1 to 30% 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 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 material may be omitted.

The binder is a component which 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 30% by weight 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 manufactured by applying a negative electrode material on the negative electrode collector and drying the same, and if necessary, the above-described components may further be included.

The negative electrode collector is generally made to have a thickness of 3 to 500 mu m. Such an anode current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery, and may be formed of a material such as copper, stainless steel, aluminum, nickel, titanium, fired carbon, 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 negative electrode material may be, for example, carbon such as non-graphitized carbon or graphite carbon; _{Li x Fe 2 O 3 (0≤x≤1} ), Li x WO 2 (0≤x≤1), Sn x Me 1-x Me 'y O z (Me: Mn, Fe, Pb, Ge; Me' : Metal complex oxides such as Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, Halogen, 0 < x &lt; Lithium metal; Lithium alloy; Silicon-based alloys; Tin alloy; _{SnO, SnO 2, PbO, PbO} 2, Pb 2 O 3, Pb 3 O 4, Sb 2 O 3, Sb 2 O 4, Sb 2 O 5, GeO, GeO 2, Bi 2 O 3, Bi 2 O 4, and Bi ₂ O ₅ ; Conductive polymers such as polyacetylene; Li-Co-Ni-based materials and the like can be used.

The separation membrane 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 0.01 to 10 mu m and the thickness is generally 5 to 300 mu m. Such separation membranes include, for example, olefinic polymers such as polypropylene, which are chemically resistant and hydrophobic; A sheet or nonwoven fabric made of glass fiber, polyethylene or the like is used. When a solid electrolyte such as a polymer is used as an electrolyte, the solid electrolyte may also serve as a separation membrane.

The non-aqueous electrolyte solution containing a lithium salt is composed of a non-aqueous electrolyte and a lithium salt. As the non-aqueous electrolyte, a liquid non-aqueous electrolyte, a solid electrolyte, and an inorganic solid electrolyte are used.

Examples of the liquid nonaqueous electrolytic solution include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butylolactone, Ethane, tetrahydroxyfuran, 2-methyltetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, Methyl, triethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ether, pyrophosphoric acid Methyl propionate, and ethyl propionate may 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, Polymers containing ionic dissociation 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 and sulfates of Li such as Li ₄ SiO ₄ -LiI-LiOH and Li ₃ PO ₄ -Li ₂ S-SiS ₂ can be used.

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

For the purpose of improving charge / discharge characteristics, flame retardancy, etc., the nonaqueous electrolyte containing a lithium salt is preferably used in an amount of 0.1 to 5 wt% based on the total weight of the electrolyte salt, such as pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, N, N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, aluminum trichloride, etc. May be added. In some cases, a halogen-containing solvent such as carbon tetrachloride or ethylene trifluoride may be further added to impart nonflammability, or carbon dioxide gas may be further added to improve high-temperature storage characteristics.

The lithium secondary battery according to the present invention can be manufactured by a conventional method known in the art. That is, a porous separator may be inserted between the anode and the cathode, and an electrolyte may be injected into the separator.

The anode can be produced, for example, by applying a slurry containing the above-described lithium transition metal oxide active material, a conductive material and a binder on a current collector, followed by drying. Likewise, the negative electrode can be produced, for example, by 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.

The secondary battery according to the present invention can be preferably used for a medium-sized or large-sized battery module of high power, large capacity, which is particularly problematic in safety. Since the middle- or large-sized battery module includes a plurality of secondary cells as a unit cell, safety may be seriously threatened by a chain reaction when an abnormality occurs in some unit cells.

Accordingly, the present invention also relates to a middle- to large-sized battery module including the secondary battery as a unit cell.

The battery module is not particularly limited as long as it is a battery module in which two or more secondary batteries are electrically connected to each other. For example, the battery module is used for a power source for a notebook computer, an e-bike, an electric vehicle, Battery module.

1 is a vertical cross-sectional perspective view of a prior art cylindrical battery incorporating a jelly-roll type electrode assembly;
2 is a horizontal cross-sectional view of the center pin along line AA in the battery of FIG. 1;
3 is a vertical cross-sectional view of a cylindrical rechargeable battery according to an embodiment of the present invention.
4 is a photograph showing that a conventional cylindrical battery is short-circuited and ignited.

Hereinafter, the contents of the present invention will be described in detail with reference to the drawings, but the scope of the present invention is not limited thereto.

3 is a vertical cross-sectional view of a cylindrical secondary battery according to an embodiment of the present invention.

Referring to FIG. 3, the secondary battery 100 includes a jelly-roll type electrode assembly 110 having a center pin 200 inserted therein. The 18650 standard has a diameter R of about 18 mm , And the length (L) is about 65 mm.

The center pin 200 included in the secondary battery 100 has a structure in which the center pin 200 is wound three times in a horizontal section on the basis of the outer diameter r of 4 mm. The length of the center pin 200 is about 60 mm, and the length of the center pin protruding from the top of the jelly-roll 110 is about 0.3 mm. In this case, the contact between the center pin and the jelly-roll can be prevented in advance by deformation of the center pin, so that the occurrence of an internal short-circuit can be fundamentally prevented.

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

[Example 1]

A center pin having an outer diameter of 4 mm and a height of 59.8 mm was manufactured by winding a sheet of polypropylene having a thickness of 0.45 mm three times and thermally fixing the center pin. The center pin was inserted into the core of the electrode assembly, A diameter of 18 mm, and a length of 65 mm). The length of the center pin projecting from the top of the electrode assembly is about 0.1 mm.

[Example 2]

A cylindrical secondary battery was manufactured in the same manner as in Example 1 except that a stainless steel plate was used to manufacture a center pin of 60 mm.

[Comparative Example 1]

A cylindrical secondary battery was manufactured in the same manner as in Example 1 except that a stainless steel plate was used to manufacture a center pin of 57.5 mm.

[Experimental Example 1]

Twenty batteries prepared in Examples 1 and 2 and 20 batteries prepared in Comparative Example 1 were subjected to a short-circuit test at a voltage of 4.2 V. The shot test was carried out by measuring a battery charged at 4.2 V and measuring a distance of 610 25 mm from a rod-shaped object having a diameter of 15.8 mm and a weight of 9.1 kg to check whether a short circuit occurred.

As a result, as shown in Table 1, all the batteries according to Examples 1 and 2 did not undergo a short circuit, while short and ignition were confirmed in two of the batteries according to Comparative Example 1. As a result of examining the batteries of Comparative Example 1 in which short-circuit was induced, it was confirmed that the end of the center pin was connected to the electrode of the jelly-roll through the separator to cause a short circuit. (See Fig. 4)

[Table 1]

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.

Claims (12)

An electrode assembly (jelly-roll) manufactured by winding a positive electrode / separator / negative electrode is embedded in a cylindrical battery case, and a cap assembly is mounted on the upper end of the battery case. The length of the jelly- A long-length center pin is inserted into the core of the jelly-roll,
The top of the center pin is positioned between the top of the jelly-roll and the bottom of the cap assembly,
Wherein the length of the center pin projecting from the upper end of the jelly-roll is 0.1 mm to 1 mm. [2] The method of claim 1, wherein the center pin comprises one or more polymer materials selected from the group consisting of polypropylene, polyimide, polyamide, polycarbonate, and polymethylmethacrylate, a composite material comprising the polymer and a filler &Lt; / RTI &gt; The secondary battery according to claim 1, wherein the center pin is made of a metal material. The secondary battery according to claim 1, wherein the center pin is wound three to eight times. The secondary battery according to claim 1, wherein the center pin is longer in a range of 1 to 15% based on the length of the jelly-roll. The secondary battery according to claim 1, wherein an entire length of the center pin is 55 mm to 65 mm. delete delete The secondary battery according to claim 1, wherein the center pin has an outer diameter of 2 to 5 mm. The secondary battery according to claim 1, wherein the battery is a lithium secondary battery. A middle- or large-sized battery module including the secondary battery according to claim 1 as a unit cell. 12. The middle- or large-sized battery module according to claim 11, wherein the battery module is used for powering a notebook computer, an e-bike, an electric vehicle, or a hybrid electric vehicle.

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