KR20120070851A - Secondary battery having electrode lead comprising conducting polymer - Google Patents

Abstract

PURPOSE: A secondary battery comprising a conductive polymer is provided to prevent the leakage of ignitable materials such as electrolyte, to stop the operation of a battery by shorting an electrode lead, thereby improving stability. CONSTITUTION: A secondary battery comprises an electrode assembly with structure of positive electrode/separator/negative electrode, electrolyte impregnated in the electrode assembly, a battery case sealing the electrode assembly and the electrolyte, and electrode leads as input/output terminals for electrically connecting the positive electrode and the negative electrode in the electrode assembly to an external device. The electrode lead is projected to an external battery through the battery case, and comprises a conductive polymer capable of disconnecting electrical connection by raising resistance or melting when the temperature of a battery increases.

Description

Secondary Battery Using Electrode Lead Conductive Polymer {Secondary Battery Having Electrode Lead Comprising Conducting Polymer}

The present invention relates to a secondary battery using an electrode lead that provides improved battery safety, and more particularly, to an electrode assembly having an anode / separation membrane / cathode structure, an electrolyte solution impregnated in the electrode assembly, the electrode assembly, and an electrolyte solution. A battery case that is sealed, and an input / output terminal for electrically connecting the positive electrode and the negative electrode of the electrode assembly to an external device. The battery case protrudes out of the battery via the battery case and melts or increases resistance when the temperature of the battery increases. It relates to a secondary battery comprising a configuration including an electrode lead containing a conductive polymer that can block the electrical connection.

As technology development and demand for mobile devices increase, the demand for secondary batteries as an energy source is rapidly increasing, and accordingly, a lot of researches on secondary batteries that can meet various needs have been conducted.

Rechargeable batteries are not only mobile phones, digital electronics such as mobile phones, digital cameras, PDAs, notebooks, etc., but also energy sources for power devices such as electric bicycles (EVs), electric vehicles (EVs), and hybrid electric vehicles (HEVs). It is attracting a lot of attention.

Small battery packs with one battery cell are used for small devices such as mobile phones and cameras, while two or more battery cells (hereinafter, sometimes referred to as multi-cells) are used for medium and large devices such as notebooks and electric vehicles. Medium or large battery packs in which battery packs are connected in parallel and / or in series are used.

Lithium secondary batteries have a problem of low safety while having excellent electrical characteristics. For example, lithium secondary batteries cause decomposition reactions of battery components, such as active materials and electrolytes, under abnormal operating conditions such as overcharge, overdischarge, exposure to high temperatures, and electrical short circuits to generate heat and gas, resulting in high temperature and high pressure. The condition of may further accelerate the decomposition reaction, resulting in an air ignition or explosion.

Therefore, the lithium secondary battery includes a protection circuit that blocks current during overcharge, over discharge, and overcurrent, a PTC element (Positive Temperature Coefficient Element) that blocks current by increasing resistance when temperature rises, and a current when pressure rises due to gas generation. Safety systems are provided, such as safety vents to shut off or vent the gases. For example, in a cylindrical small secondary battery, a PTC element and a safety vent are usually installed on an electrode assembly (power generation element) of a cathode / separator / cathode embedded in a cylindrical can. Protection circuit modules and PTC elements are generally mounted on top of a rectangular can or pouch case in which the generator is sealed.

The safety problem of the lithium secondary battery is more serious in the medium-large battery pack of the multi-cell structure. In the battery pack of the multi-cell structure, due to the use of a large number of battery cells, the abnormal operation in some battery cells may cause a chain reaction to other battery cells, the resulting ignition and explosion can lead to large accidents to be. Accordingly, the medium and large battery packs are provided with safety systems such as fuses, bimetals, and battery management systems (BMSs) for protecting the battery cells from overdischarge, overcharge, overcurrent, and the like.

However, lithium secondary batteries are deteriorated gradually during continuous use, that is, during continuous charging and discharging, such as power generators, electrical connection members, and the like. This causes the battery cells (cans, pouch cases) to expand slowly. In addition, in general, BMS, a safety system, detects overdischarge, overcharge, and overcurrent, and controls / protects the battery pack. However, when the BMS is inoperative in an abnormal situation, it becomes difficult to control the battery pack for risk and safety. .

Since medium and large battery packs generally have a structure in which a plurality of battery cells are fixedly mounted in a predetermined case, each expanded battery cell is further pressurized in a limited case, and there is a risk of fire and explosion under abnormal operating conditions. This greatly increases.

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

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.

After extensive research and various experiments, the inventors of the present application have developed an electrode lead having a structure containing a predetermined conductive polymer material, and the secondary battery using the electrode lead reacts directly with temperature to cut off the electrical connection. By operating in such a way, there is a problem with the existing technology of breaking the cell lead by using the pressure when the battery cell expands due to abnormal operation of the battery pack or deterioration due to prolonged charging and discharging. Entering the step has already been found to be able to fundamentally solve the electrical and thermochemical risks), and came to complete the present invention.

Therefore, the secondary battery according to the present invention,

An electrode assembly having an anode / separation membrane / cathode structure and an electrolyte solution impregnated in the electrode assembly;

A battery case sealing the electrode assembly and the electrolyte solution; And

An input / output terminal for electrically connecting the positive electrode and the negative electrode of the electrode assembly to an external device, protruding out of the battery via a battery case, and capable of blocking electrical connection by melting or increasing resistance when the temperature of the battery increases. An electrode lead containing a polymer;

It is configured to include.

In the secondary battery according to the present invention, a conductive polymer is included in the electrode lead, and under normal operating conditions, the battery may be operated under abnormal operating conditions, for example, overcurrent, without disturbing its original function, that is, conduction function. Due to the high temperature of the electrode leads, the conductive polymer material may be melted or the resistance may be increased while the resistance of the electrode leads is blocked, thereby blocking the electrical connection.

As one preferred embodiment, the conductive polymer material may be at least one compound selected from the group consisting of polyaniline, polyacetylene, polyphenylene, polythiophene, and polypyrrole. These polymer materials have a property of melting or increasing resistance when reaching a predetermined temperature with increasing temperature. In particular, it may be preferably polyaniline. Polyaniline has an electrical conductivity comparable to that of metals, and has a relatively low melting point compared to metals, so that the polyaniline may be melted when reaching a high temperature that threatens the safety of the battery, thereby achieving desired disconnection.

The molecular weight of such polyaniline is preferably 50,000 to 1,000,000. Too low a molecular weight polymer may be difficult to exhibit the desired electrical conductivity, on the contrary, too high a molecular weight is undesirable because side reactions occur in the synthesis process may adversely affect the physical properties of the polymer.

The conductive polymer may be included in the electrode lead in various forms. As an example, the electrode lead may be made of the conductive polymer itself.

As another example, the electrode lead may be made of a conductive polymer composite in which a filler of metal powder and / or carbon powder is included in the matrix of the conductive polymer. The electrode lead of such a composite structure can further improve the electrical conductivity by the filler of the metal powder and / or carbon powder, and has the advantage of increasing the mechanical rigidity.

In this case, the metal powder is not particularly limited, and for example, silver powder, aluminum powder, copper powder, iron powder, nickel powder, or the like may be used.

In one preferred embodiment, the melting point of the conductive polymer is preferably 80 ℃ to 150 ℃, more preferably 90 to 140 ℃ range can be. If the melting point is too high, there is a problem that the battery case sealing portion first melts before the conductive polymer is melted in the temperature rise process, and the electrolyte, which is sealed inside the battery case, begins to leak. It is not preferable because the electrode leads may be disconnected even under operating conditions.

The above temperature condition may be applied as it is to the temperature condition in which the resistance increases. That is, by setting the resistance to rise in the above temperature conditions, it is possible to perform the function of the current blocking for the security security.

The electrode lead is preferably 3 to 8 mm in width and 0.1 to 0.5 mm in thickness.

The secondary battery according to the present invention is not particularly limited as long as it has the above characteristics, and may be preferably applied to the lithium secondary battery as described above.

In particular, the secondary battery of the present invention may be used as a unit battery of a battery pack which is a power source of a device requiring high temperature safety and the like.

Preferably, the device may be a mobile electronic device, an electric vehicle (EV), a hybrid electric vehicle (HEV) or a plug-in hybrid electric vehicle (HEV) or a power storage device.

As described above, the secondary battery of the present invention includes an electrode lead containing a conductive polymer, and thus, the electrode lead is a battery under abnormal operating conditions in which the temperature rises excessively while the electrode lead performs an inherently energizing function under normal operating conditions. By reacting sensitively to the temperature change of, achieving the disadvantage can provide high safety.

In the following, the present invention will be described in more detail in order to practice the present invention in detail, which is intended to facilitate understanding of the present invention, and the scope of the present invention is not limited thereto.

The secondary battery according to the present invention may have a structure in which a lithium salt-containing non-aqueous electrolyte solution is impregnated in an electrode assembly having a separator interposed between a positive electrode and a negative electrode.

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

The positive electrode is prepared by, for example, applying a positive electrode mixture containing a mixture of a positive electrode active material, a conductive material, and a binder to the remaining portions of the positive electrode current collector except for the portion where the tab is formed. Therefore, further fillers may be added to the mixture.

The cathode current collector generally has a thickness of 3 to 500 mu m. Such a positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. 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 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 + y} Mn _2-y O ₄ (where y 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-y M _y O ₂ , wherein M = Co, Mn, Al, Cu, Fe, Mg, B, or Ga, and y = 0.01 to 0.3; Formula LiMn _2-y M _y O ₂ , wherein M = Co, Ni, Fe, Cr, Zn or Ta and y = 0.01 to 0.1, or Li ₂ Mn ₃ MO ₈ , where 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. However, the present invention is not limited to these.

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 electrical conductivity without causing chemical changes in the battery, for example, graphite such as natural graphite or 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 fiber and metal fiber; 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 butadiene 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.

On the other hand, the negative electrode is manufactured by applying, drying, and pressing the negative electrode active material to the remaining portions except for the portion where the tab is to be formed on the negative electrode current collector sheet, and optionally, the conductive material, binder, filler, etc. may be selectively It may be further included.

The negative electrode current collector is generally made to have a thickness of 3 to 500 mu m. 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 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 active 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-Co-Ni-based materials and the like can be used.

The separation membrane 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 0.01 to 10 mu m and the thickness is generally 5 to 300 mu m. 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 an electrolyte, the solid electrolyte may also serve as a separation membrane.

The lithium salt-containing nonaqueous electrolyte solution is composed of an electrolyte solution and a lithium salt. As the electrolyte solution, a nonaqueous organic solvent, an organic solid electrolyte, and an inorganic solid electrolyte may be used.

As the non-aqueous organic solvent, for example, N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butylo lactone, 1,2-dime Methoxy ethane, tetrahydroxy franc, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolon, formamide, dimethylformamide, dioxoron, acetonitrile, nitromethane, methyl formate, Methyl acetate, phosphate triester, trimethoxy methane, dioxorone derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether, Aprotic organic solvents such as methyl pyroionate, ethyl propionate, and the like can be used.

Examples of the organic solid electrolyte include a polymer electrolyte such as a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphate ester polymer, an agitation lysine, a polyester sulfide, a polyvinyl alcohol, a polyvinylidene fluoride, A polymer containing an ionic dissociation group and the like may be used.

As the inorganic solid electrolyte, for example, 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 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 the charge / discharge characteristics and the flame retardancy, the electrolytic solution is preferably mixed with an organic solvent such as pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, glyme, Benzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N, N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, . In some cases, a halogen-containing solvent such as carbon tetrachloride or ethylene trifluoride may be further added to impart nonflammability, or a carbon dioxide gas may be further added to improve high-temperature storage characteristics.

The secondary battery of the present invention is an electrode assembly manufactured by the above method, and has a structure that is embedded in a battery case impregnated with an ion-containing electrolyte solution, and an input / output terminal for electrically connecting the positive electrode and the negative electrode of the electrode assembly to an external device. The present invention provides a configuration including an electrode lead protruding out of a cell and including a conductive polymer so as to block electrical connection by melting or increasing resistance when the temperature of the cell rises.

 The electrode lead causes a relatively large heat generation in an abnormal operating state of the battery, for example, an external short through which overcurrent flows, and as a result, when the overcurrent occurs, the electrode lead is automatically destroyed or the resistance increases to prevent further energization. Can act as a battery safety element.

This principle is described in detail as follows.

In general, the relationship between the resistance and the current and the calorific value is expressed by the following equation.

R = R ₀ (1 + aT) (1)

W = I ² x R (2)

In the above formula, T is a temperature and a is a constant that varies depending on the type of conductor. W is a calorific value, I is a current, and R is a resistance.

In the secondary battery according to the present invention, since the electrode lead includes a conductive polymer, when a high temperature is generated during energization of overcurrent, as the resistance increases as in Equation 1 above, the calorific value of the electrode lead is as in Equation 2 above. When the polymer material reaches a melting point or more rapidly, the polymer lead melts and the electrode lead itself breaks, thereby blocking the electrical connection.

The range of overcurrent that causes an increase in resistance such that the electrode lead breaks or shorts out may be determined by various factors related to the unit cell and the battery pack configuration, such as the structure, size, number, and operating voltage of the unit cell. have. For example, in a medium-large battery pack as a power source of an electric vehicle and a hybrid electric vehicle, a current of 50 to 100 A flows and a maximum of 150 to 250 A flows under normal operating conditions. When a current of about 500 A or more flows through the unit cell of the battery pack, a swelling phenomenon occurs. When a current of about 1600 A or more flows, a part of the battery case adjacent to the electrode lead is separated, and a current of about 1800 to 2000 A or more is applied. When flowing, the electrolyte component and the like are ejected in the form of a spray along with the separation of the seal, causing ignition by the overheated electrode lead.

Therefore, in the present invention, the magnitude of the overcurrent that causes breakage or increase in resistance of the electrode lead means a magnitude of current that does not cause separation of the seal or at least does not cause leakage of volatile components.

The present invention also provides a medium-large battery pack consisting of one or more secondary batteries as described above.

In general, a medium-large battery pack is configured by electrically connecting a plurality of unit cells. In the case of high output as well as a large capacity, since at least some or all of the unit cells are connected in series, at least one or two or more of the unit cells of the series connection is configured as the secondary battery. In the series connection, even if some unit electricity is interrupted, the operation of the battery pack system is stopped, thereby ensuring the desired safety in the present invention.

Specifically, when an overcurrent flows momentarily due to abnormal operation of the medium-large battery pack, the heat of the overheated electrode terminal is conducted to the seal of the battery case, and the electrode lead is broken or disconnected by an increase in resistance before the seal is separated. By preventing the outflow of flammable substances such as electrolyte and stopping the operation of the battery, safety can be ensured. In addition, as described above, the secondary battery has an effect of securing the safety of the battery by breaking the electrode lead or increasing its resistance under an overcurrent that is relatively smaller than the amount of current at which the seal is separated.

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 (15)

An electrode assembly having an anode / separation membrane / cathode structure and an electrolyte solution impregnated in the electrode assembly;
A battery case sealing the electrode assembly and the electrolyte solution; And
An input / output terminal for electrically connecting the positive electrode and the negative electrode of the electrode assembly to an external device, protruding out of the battery via a battery case, and capable of blocking electrical connection by melting or increasing resistance when the temperature of the battery increases. An electrode lead containing a polymer;
Secondary battery, characterized in that consisting of a configuration comprising a. The secondary battery of claim 1, wherein the conductive polymer material is at least one selected from the group consisting of polyaniline, polyacetylene, polyphenylene, polythiophene, and polypyrrole. The secondary battery of claim 1, wherein the conductive polymer material is polyaniline. The secondary battery of claim 3, wherein the polyaniline has a molecular weight of 50,000 to 1,000,000. The secondary battery of claim 1, wherein the electrode lead is made of a conductive polymer. The secondary battery of claim 1, wherein the electrode lead is made of a conductive polymer composite including a metal powder and / or a carbon powder filler in a matrix of the conductive polymer. The secondary battery of claim 6, wherein the metal powder is silver or aluminum. The secondary battery of claim 1, wherein a melting point of the conductive polymer is 80 ° C. to 150 ° C. 6. The secondary battery of claim 1, wherein a melting point of the conductive polymer is 90 ° C. to 140 ° C. 7. The secondary battery of claim 1, wherein the electrode lead has a width of 3 to 8 mm. The secondary battery of claim 1, wherein the electrode lead has a thickness of 0.1 to 0.5 mm. The secondary battery of claim 1, wherein the secondary battery is a lithium secondary battery. A battery pack comprising the lithium secondary battery according to claim 12 as a unit cell. A device comprising the battery pack according to claim 13 as a power source. 15. The device of claim 14, wherein the device is a mobile electronic device, an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, or a power storage device.