KR20080009354A - Cylindrical secondary battery having high safety by radiant heat - Google Patents

Abstract

A cylindrical lithium secondary battery is provided to reduce weight, to lower a manufacturing cost and to improve safety by excellent heat radiation without the deterioration of battery characteristics. A cylindrical lithium secondary battery comprises a jelly roll type electrode assembly and a lithium electrolyte solution which are accommodated inside a metal can of a battery case, wherein the battery case is connected with the negative electrode of the jelly roll type electrode assembly, and the inner surface in contact with the lithium electrolyte solution is plated with the copper having a high thermal conductivity. Preferably the main body of the metal can is made of stainless steel.

Description

Cylindrical secondary battery having improved safety by heat dissipation {Cylindrical Secondary Battery Having High Safety by Radiant Heat}

The present invention relates to a cylindrical secondary battery having improved safety by heat dissipation, and more particularly, when overheating occurs due to abnormal operation of the battery, it can be quickly conducted to the outside to be cooled to room temperature, jelly-roll type electrode A secondary battery in which an assembly is embedded in a metal can as a battery case together with a lithium electrolyte, wherein the battery case is connected to a negative electrode of a jelly-roll, and is related to a cylindrical secondary battery made of heat conductive copper having a high inner surface in contact with the lithium electrolyte. will be.

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 on lithium secondary batteries with high energy density and high discharge voltage. It is widely used.

Recently, secondary batteries capable of charging and discharging have been widely used as energy sources of wireless mobile devices. In addition, the secondary battery has attracted attention as a power source for electric vehicles (EVs) and hybrid electric vehicles (HEVs), which are proposed as a way to solve air pollution of conventional gasoline and diesel vehicles that use fossil fuels. have.

When a lithium secondary battery is used as a power source for a mobile phone or a notebook, a secondary battery that provides a stable output is required, while when used as a power source of a power tool such as an electric drill, it provides instantaneous high output. There is a need for a secondary battery that can be stable against external physical shocks such as vibration and dropping. As described above, although lithium secondary batteries have some differences in physical properties required according to the field of use, they are basically based on charge and discharge characteristics due to the movement of lithium ions.

Such lithium secondary batteries are roughly classified into cylindrical secondary batteries, rectangular secondary batteries, and pouch secondary batteries according to their shape. The square and pouch type secondary batteries are frequently used as small mobile devices such as mobile phones due to their thin thicknesses, or unit cells of medium and large battery packs due to their ease of lamination. On the other hand, the cylindrical battery has a relatively large capacity and has the advantage of being structurally stable, it is widely used in medium devices such as notebooks.

The rectangular secondary battery and the cylindrical secondary battery using the metal can as the battery case are different in appearance as well as internal configuration due to their use, electrochemical properties, and the like.

First, as described above, since the rectangular secondary battery is mainly used as a power source for a small mobile device, it is more essential that the weight is lighter than the cost. In that aspect, a small weight aluminum can is mainly used as a battery case. On the other hand, since cylindrical secondary batteries are mainly used in medium-sized devices such as notebooks, which require a large capacity rather than light weight, stainless steel cans, which are about twice as heavy as aluminum but much cheaper, are mainly used as battery cases.

In this way, as the material of the battery case is changed, the configurations of the electrodes of the rectangular secondary battery and the cylindrical secondary battery also vary.

In the rectangular secondary battery, a positive electrode is directly connected to a battery case (aluminum can) of an electrode assembly of a positive electrode, a separator, and a negative electrode, and a negative electrode is connected to an external input / output terminal insulated from the battery case. On the other hand, in the cylindrical secondary battery, the negative electrode of the electrode assembly is directly connected to the battery case (stainless steel), and the positive electrode is connected to an external input / output terminal while being insulated from the battery case.

The reason for having another electrode structure in this way is as follows. When an anode of an electrode assembly is connected to an aluminum can (that is, when aluminum is used as a cathode) in a rectangular secondary battery, there is a tendency to react with lithium of an electrolyte at a charge and discharge potential to form an irreversible AL-LI alloy. On the other hand, when copper is used as the anode, it tends to dissolve in the electrolyte at the charge and discharge potential. Therefore, the positive electrode current collector of the electrode assembly is made of aluminum, the negative electrode current collector is made of copper, and the positive electrode of the electrode assembly is connected to the aluminum can in the rectangular secondary battery.

Meanwhile, lithium secondary batteries have many problems in terms of safety. In other words, the cathode active material and the anode active material are thermally unstable in the charged state, and not only generate heat more than a certain temperature, but also lead to thermal runaway when excessive current is energized by a momentary external and internal short circuit in the charged state. .

Problems related to the safety of lithium secondary batteries tend to be caused by overheating due to various causes or worsened by overheating. Therefore, when overheating is caused, by effectively dissipating it, the problem caused by overheating can be alleviated to some extent.

As described above, one of methods for effectively removing the overheat caused by the inside of the battery may be to increase the heat dissipation efficiency by making the battery case a high thermal conductive material.

Since aluminum, which is a case material of the rectangular secondary battery, has a very high thermal conductivity, at least the heat dissipation through the battery case in the rectangular secondary battery may be realized to some extent.

On the other hand, the stainless steel used as the case material of the cylindrical secondary battery has a heat conductivity of only about 1/4 to 1/5 of the aluminum, there is a problem in heat dissipation through the battery case. Although the case of the cylindrical secondary battery may be considered to be made of a high thermal conductive material such as aluminum, the problems described above may cause high irreversible reaction and an increase in battery manufacturing cost. have.

Accordingly, the present invention proposes a technique for manufacturing a cylindrical secondary battery using a battery case in which copper is plated on an inner surface of a can body such as stainless steel as described in detail below.

Although it is not a technique for a cylindrical secondary battery, as examples of using copper as a material of a battery case, Korean Patent Application Publication Nos. 2006-0028171, 2006-0028170, and 2006-0028169 describe specific cap plate coupling structures. The use of copper or a copper alloy as one of several metal materials of the battery case in a rectangular secondary battery including, US Patent Application Publication No. 2004-0258986 is a clamp case for wrapping a laminated electrode assembly in a rectangular secondary battery One of several metal materials illustrates the use of copper.

However, since copper generally exhibits high thermal conductivity but is very heavy in weight and low in mechanical stiffness, it is difficult to apply it directly to the material of a real battery case, and the above techniques only exemplify copper as one of several metal materials. It is only to do.

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.

Specifically, an object of the present invention is a battery of a new configuration that is relatively light, inexpensive, has a certain mechanical rigidity, and can greatly improve safety by excellent heat dissipation characteristics without impairing operating characteristics of the battery. It is to provide a cylindrical lithium secondary battery including a case.

Cylindrical lithium secondary battery according to the present invention for achieving this object is a jelly-roll type electrode assembly is embedded in a metal can as a battery case with a lithium electrolyte, the battery case is connected to the negative electrode of the jelly-roll type electrode assembly The inner surface in contact with the lithium electrolyte is composed of copper plated with high thermal conductivity.

Therefore, in the cylindrical lithium secondary battery according to the present invention, since the battery case is connected to the negative electrode of the electrode assembly and copper is plated on the inner surface thereof, deterioration of the battery performance due to the irreversible reaction as described above does not occur, and the battery When overheating occurs in the interior of the high heat dissipation characteristics by the copper in contact with the electrolyte can improve the safety.

Most of the overheating in the battery is caused by abnormal exothermic reaction and thermal runaway of the electrode assembly and the electrolyte. In this case, the heat conduction from the electrolyte to the battery case is a bottleneck in the heat dissipation mechanism of the battery. . Moreover, when the battery case itself is made of a metal having low thermal conductivity, the heat dissipation process does not proceed effectively.

On the other hand, in the present invention, since copper is plated on the inner surface of the battery case, the heat dissipation bottleneck from the electrolyte solution as described above to the battery case can be largely solved. In addition, since the copper is formed of a thin film plating layer, the weight increase problem when the entire battery case is made of copper can be solved.

The body of the battery case in which copper is plated on the inner surface, that is, the body of the metal can, various metals may be used, and preferably, stainless steel having excellent mechanical strength and low cost may be used. In some cases, aluminum may be used when a low-weight cylindrical secondary battery is required. In the case of using the aluminum itself as a battery case in a cylindrical secondary battery, the problem of high irreversible reaction as described above is caused, but the above problems can be solved by plating copper on the inner surface as in the present invention.

In the cylindrical secondary battery according to the present invention, the thickness of the battery case body and the copper plating layer may be appropriately determined in consideration of the use of the battery, the weight, and the like. In one preferred embodiment, the can body of the stainless steel may have a thickness of 50 to 500 μm. It has a copper layer to be plated on its inner surface can be configured to have a thickness of 1 to 100 ㎛ in a range smaller than the thickness of the can body.

The shape of the copper plating layer is not particularly limited, and for example, a shape in which the entire surface of the inner surface of the can body is plated, a shape in which a plurality of strips are plated at regular intervals, a shape in which a plaid is plated, and an island-sea ( It may be a shape that is plated in the shape of an island-in-sea).

The plating of copper may be used methods known in the art, for example, electroplating, vacuum deposition, and the like may be used.

The jelly-roll type electrode assembly is manufactured by winding roundly in a state in which a separator is interposed between a long sheet-type anode and a cathode.

The lithium secondary battery including the jelly-roll type electrode assembly has a structure in which a jelly-roll type electrode assembly of a cathode / separation membrane / cathode and a lithium salt-containing nonaqueous electrolyte are embedded in the metal can.

The positive electrode is prepared 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 may be further added to the mixture.

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 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 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 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 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 the 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, for example, olefinic polymers such as polyethylene, 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 metal 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 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 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.

The lithium salt-containing non-aqueous electrolyte solution consists of an organic solvent and a lithium salt.

As said organic solvent, for example, N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyl Low lactone, 1,2-dimethoxy ethane, tetrahydroxy franc, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolon, formamide, dimethylformamide, dioxolon, aceto Nitrile, nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxy methane, dioxorone derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative Aprotic organic solvents such as tetrahydrofuran derivatives, ethers, methyl pyroionate and ethyl propionate can be used.

The lithium salt is a material dissolving and dissociating in the organic solvent, 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., the non-aqueous electrolyte solution includes, for example, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, and hexaphosphate triamide. Nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N, N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrroles, 2-methoxy ethanol, aluminum trichloride, etc. It may be. 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.

Hereinafter, the present invention will be described in detail by way of examples, but the scope of the present invention is not limited thereto.

Comparative Example 1

Carbon powder and fluorine resin compound (PVdF) were mixed in a weight ratio of 90:10, and 100 parts by weight of the mixture was kneaded in 70 parts by weight of N-methyl pyrrolidene (NMP) to prepare a slurry, and then coated on both sides of a copper current collector substrate. And then dried. Then, pressure rolling was performed to prepare a negative electrode having a thickness of 200 μm, a length of 510 mm, and a width of 56 mm. At one end of the cathode, a copper tab connected to an outer conductor was welded with a spot welder.

In addition, an acetylene black and a fluorine resin compound (PVdF) were mixed in a weight ratio of 90: 5: 5 with an active material and a conductive current collector powder having a LiCoO ₂ composition, and 100 parts by weight of the mixture was kneaded in 40 parts by weight of NMP to prepare a slurry. Then, after coating and drying on both sides of the aluminum current collector, the other side was also applied as above and dried. Then, pressure rolling was performed to prepare a positive electrode having a thickness of 200 μm, a length of 450 mm, and a width of 54 mm. At one end of the anode, an aluminum tab to be connected to an outer conductor was fused with a spot welder.

The anode and the cathode prepared as described above were rolled up several times using a winder (winding device) in the state of interposing a porous polyethylene film to prepare a jelly roll.

An aluminum pressure release valve mounted on the battery cover by inserting the jelly-roll into a stainless steel can having a thickness of 200 μm, an outer diameter of 18 mm, and a height of 65 mm, welding the negative lead to the battery can, and extracting the positive lead from the positive electrode current collector. Welded on. Then, a cylindrical lithium secondary battery was prepared by injecting EC and EMC in a solvent of 1: 2 mixed with an electrolyte solution using LiPF ₆ .

The battery prepared above was charged to a constant current of 0.2 C to 4.2 V, and then charged to a limit current of 50 mA at 4.2 V by the constant voltage method. After that, the time taken to ignite was put in an oven maintained at 150 ℃.

Example 1

A cylindrical lithium secondary battery was manufactured in the same manner as in Comparative Example 1, except that a metal can coated with 10 μm thick copper was used as a battery case by using an electroplating method on an inner surface of a stainless steel can having a thickness of 190 μm. And test experiments were performed.

[Examples 2 to 5]

A cylindrical lithium secondary battery was manufactured in the same manner as in Comparative Example 1 except for using a metal can coated with a copper thickness as shown in Table 1 on the inner surface of the stainless steel can using an electrolytic plating method. And test experiments were performed. However, in order to maintain the same thickness as the metal can of Comparative Example 1, the thickness of the stainless steel can was changed corresponding to the thickness of the copper plating layer.

TABLE 1

As shown in Table 1, the cylindrical lithium secondary battery of Examples 1 to 5 according to the present invention has a longer time to ignite than the battery of Comparative Example 1, so that the safety of the battery increases. It can be seen. This is because the thermal conductivity of copper is 7 times higher than that of stainless steel, which is a material of a conventional can, thereby efficiently dissipating heat generated during self-heating of a lithium secondary battery, thereby suppressing battery temperature rise.

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.

As described above, the cylindrical lithium secondary battery according to the present invention is relatively light, inexpensive, has a certain mechanical rigidity, and impairs the operation characteristics of the battery by plating copper of high thermal conductivity on the inner surface of the metal can. It is possible to greatly improve the safety by excellent heat dissipation characteristics without making it.

Claims (5)

A jelly-roll type electrode assembly is embedded in a metal can as a battery case together with a lithium electrolyte solution, and the battery case is plated with copper having high thermal conductivity connected to the negative electrode of the jelly-roll type electrode assembly and in contact with the lithium electrolyte solution. Cylindrical lithium secondary battery characterized in that. The cylindrical lithium secondary battery of claim 1, wherein the body of the metal can is made of stainless steel. The can body of stainless steel has a thickness of 50 to 500 μm, and the copper layer plated on the inner surface thereof has a thickness of 1 to 100 μm in a range smaller than the thickness of the can body. Cylindrical lithium secondary battery. The method of claim 1, wherein the copper plating layer has a shape that is plated on the entire inner surface of the can body, a shape where a plurality of strips are plated at regular intervals, a shape plated with a checkered shape, or an island-sea. Cylindrical lithium secondary battery, characterized in that the plated in the shape of in-sea). The cylindrical lithium secondary battery according to claim 1, wherein the copper plating is formed by an electroplating method or a vacuum deposition method.