KR20130123492A - Lithium secondary battery having excellent stability against overcharge - Google Patents

Abstract

The present invention relates to an electrode for a lithium secondary battery including an electrode active material formed on both or either of a current collector, comprising an interface layer inserted between the current collector and the electrode active material so as to flexibly control electric current between the current collector and the electrode active material depending on the inner temperature of the battery. The interface layer has nonconductive second polymer particles dispersed in a conductive first polymer coating layer. The present invention provides the electrode for a lithium secondary battery and a lithium secondary battery including the electrode. The present invention can secure stability by blocking electric current when the temperature inside the battery rises due to factors such as overcharge.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a lithium secondary battery,

The present invention provides an excellent safety by providing an interfacial layer for interrupting the current flow between the current collector and the electrode active material layer when the internal temperature of the battery abnormally rises due to overcurrent, An electrode for a lithium secondary battery and a lithium secondary battery having the electrode and ensuring safety.

Due to the rapid increase in the use of fossil fuels, the demand for the use of alternative energy or clean energy is increasing. As a part of this, the most active field of research is electric power generation and storage. At present, a typical example of an electrochemical device utilizing such electrochemical energy is a secondary battery. Many studies have been made on a lithium secondary battery which exhibits high energy density and operating potential, long cycle life and low self-discharge rate among such secondary batteries , And it has been commercialized and widely used.

On the other hand, the high energy density means that the high energy density can be exposed to the high risk at the same time, so that the higher the energy density, the higher the risk of ignition and explosion. In fact, the lithium secondary battery, which is currently the mainstream of secondary batteries, has a disadvantage that safety is low. For example, when the battery is overcharged to about 4.5 V or more, decomposition reaction of the cathode active material occurs, dendrite growth of lithium metal at the cathode, and decomposition reaction of the electrolyte occur. As a result, a thermal runaway phenomenon occurs in which the temperature of the battery rises sharply. When the temperature rises to a predetermined temperature or more due to the heat involved in this process, a large number of decomposition reactions and side reactions rapidly progress. . Such a risk of ignition / explosion is the most fatal disadvantage of the lithium secondary battery.

Therefore, there is a high need for a technique that can effectively prevent the ignition of the battery due to thermal runaway due to continuous energization of the electrode assembly, thereby improving the safety of the battery.

SUMMARY OF THE INVENTION The present invention has been conceived to solve the above-mentioned problems of the prior art, and it is an object of the present invention to provide a method of operating a battery in which the current between the current collector and the electrode active material layer is energized under normal operating conditions of the battery and the internal temperature of the battery rises abnormally The present invention has been completed based on the fact that an interfacial layer that automatically cuts off the current flow between the current collector and the electrode active material layer can be secured.

Accordingly, it is an object of the present invention to provide an electrode having an interfacial layer interposed between a current collector and an electrode active material layer, the interfacial layer being capable of variably controlling energization between the current collector and the electrode active material layer, And a lithium secondary battery capable of simultaneously exhibiting a lithium secondary battery.

The present invention relates to an electrode for a lithium secondary battery comprising an electrode active material layer formed on one surface or both surfaces of a current collector, wherein the electrode is interposed between the current collector and the electrode active material layer, Wherein the interface layer is formed by dispersing and arranging nonconductive second polymer particles in the conductive first polymer coating layer. The present invention also provides an electrode for a lithium secondary battery.

According to an embodiment of the present invention, the glass transition temperature (T _m ) or the melting temperature (T _g ) of the nonconductive second polymer may be in the range of 80 to 100 ° C. The nonconductive second polymer may be selected from the group consisting of polyethylene, polypropylene, and polystyrene.

In addition, the nonconductive second polymer particles may be bead-shaped or core-shell-structured particles.

The composite particle of the core-shell structure comprises: (i) a core portion containing a substance that undergoes phase change at a temperature higher than a predetermined temperature and thereby expands in volume; And (ii) a nonconductive second polymer shell portion surrounding the core portion while accommodating the material.

Here, the substance contained in the core portion may be a substance which is vaporized, sublimed or pyrolyzed to a gaseous state in a temperature range of a certain temperature or higher, or a compound containing the substance.

According to an embodiment of the present invention, the conductive first polymer may be at least one selected from the group consisting of polyacetylene, polyaniline, polypyrrole, polythiophene, poly sulfur nitride, PEDOT poly (ethylenedioxy) thiophene, poly (p-phenylene), poly (thienylene vinylene), and polyphenylene.

According to an embodiment of the present invention, the content of the nonconductive second polymer may be in the range of 20 to 50 parts by weight based on 100 parts by weight of the conductive first polymer.

In the present invention, the electrode is characterized in that the flow of current between the current collector and the electrode active material layer is blocked by the volume expansion of the non-conductive second polymer particles disposed inside the interface layer at a temperature of 80 to 100 ° C inside the battery .

In addition, the present invention provides a lithium secondary battery including a cathode, a cathode, a separator, and an electrolyte, wherein the anode, cathode, or both electrodes may be the above-described electrode.

Further, the present invention provides a method of manufacturing a semiconductor device, And a conductive first polymer coating layer formed on one or both surfaces of the current collector, wherein nonconductive second polymer particles are dispersed and disposed in the conductive first polymer coating layer.

In the present invention, the interfacial layer capable of varying the energization between the current collector and the electrode active material layer in accordance with the internal temperature of the battery is provided, so that the safety can be improved without deteriorating the performance of the battery.

1 is a side sectional view showing the structure of a conventional electrode.
2 is a side sectional view showing the structure of an electrode according to an embodiment of the present invention.
FIG. 3 is a schematic view showing a safety action mechanism of overcharge of an electrode according to the present invention.
4 is a graph showing an overcharge evaluation using the battery of Comparative Example 1. Fig.

Hereinafter, the present invention will be described in detail.

An object of the present invention is to prevent thermal runaway due to continuous energization of the electrode assembly and ignition of the battery when the internal temperature of the battery abnormally rises due to overcharging or the like.

To this end, in the present invention, And securing the safety of the battery by interposing an interface layer between the electrode active material layer applied on the current collector and the electrode active material layer capable of varying the energization between them according to the internal temperature of the battery.

<Home>

A current collector according to the present invention comprises a current collector (10); And a conductive first polymer coating layer (31) formed on one side or both sides of the current collector, wherein the nonconductive second polymer particles (32) are dispersedly disposed in the conductive first polymer coating layer have.

The current collector is not particularly limited as long as it is an electron conductive material that does not cause a chemical change and does not cause a chemical change at an operating voltage of a battery electrode constituted by a conventional metal foil having electron conductivity. Non-limiting examples of usable metal foils include aluminum, copper, tin, bismuth, silicon, antimony, nickel, titanium, vanadium, chromium, manganese, iron, cobalt, zinc, molybdenum, tungsten, silver, copper, lanthanum, ruthenium , At least one metal selected from the group consisting of platinum and iridium, or an alloy thereof. The metal foil may have a surface roughness in a predetermined range.

The conductive first polymer coating layer formed on the current collector may use any conventional conductive polymer known in the art without limitation.

A conductive polymer is a polymer having a π-conjugated system formed from organic monomers and formed by carbon-carbon bonds in which carbon Pz orbital overlaps and alternates. In the present invention, polymers having an extended? -Cooled group which is intended to form a charge transporting complex will be referred to.

Non-limiting examples of conductive first polymers that can be used include polyacetylene, polyaniline, polypyrrole, polythiophene, poly sulfur nitride, PEDOT (poly ethylenedioxy thiophene, poly (p-phenylene), poly (thienylene vinylene), polyphenylene, and mixtures thereof.

The nonconductive second polymer dispersed in the conductive first polymer coating layer may be a conventional insulating polymer known in the art.

In this case, the nonconductive second polymer may have a glass transition temperature (T _g ) and / or a melting point (T _m ) at which the internal temperature of the battery expands in a predetermined temperature range. For example, it may have a glass transition temperature or melting point in the range of 80 to 100 占 폚. Non-limiting examples of the nonconductive second polymer that can be used include polyethylene, polypropylene, polystyrene, or a mixture of one or more of these.

The nonconductive second polymer particles dispersed and disposed in the conductive first polymer coating layer of the present invention may be bead-shaped or core-shell-structured particles.

Here, the composite particle of the core-shell structure includes (i) a core portion containing a substance that undergoes a phase change at a temperature above a certain temperature to be expanded in volume; And (ii) a nonconductive second polymer shell portion surrounding the core portion, while accommodating the material.

The substance contained in the core portion may be a substance which is vaporized, sublimed or pyrolyzed at a temperature in a range of not lower than a certain temperature to become a gaseous state or a compound containing the substance. Non-limiting examples of usable core-containing materials include azo (-N = N-) based compounds, hydrazide based compounds, carbazarded based compounds, carbonate based compounds and the like.

The content of the nonconductive second polymer may be appropriately controlled within a range of exhibiting a safety effect of the battery, and may be 20 to 50 parts by weight per 100 parts by weight of the conductive first polymer.

The current collector according to the present invention can be manufactured by coating a mixture of a conductive first polymer and a nonconductive second polymer on one surface or both surfaces of an electric current collector having electron conductivity. Alternatively, the conductive first polymer-containing solution may be first applied on one side or both sides of the current collector to disperse the nonconductive second polymer particles, and then the conductive first polymer-containing solution may be coated again.

Here, the mixture of the conductive first polymer and the nonconductive second polymer may be a non-conductive second polymer particle dispersed in a solution in which the conductive first polymer is dissolved.

The method of applying the mixture on the current collector is not particularly limited, and for example, a method such as doctor blade, immersion, and brushing may be used. Also, the amount of coating is not particularly limited, but may be, for example, one in which the thickness of the conductive first polymer coating layer formed after removal of solvent or dispersion medium is in the range of 5 to 10 mu m. And then, if necessary, roll-pressing and processing.

<Electrode>

2, the electrode according to the present invention includes an electrode active material layer 20 formed on one surface or both surfaces of a current collector 10, and is interposed between the current collector and the electrode active material layer, And an interface layer (30) capable of variably controlling energization between them according to an internal temperature of the conductive polymer coating layer (31), wherein the interface layer is formed by disposing nonconductive second polymer particles (32) in the conductive first polymer coating layer Lt; / RTI &gt;

In the interfacial layer 30, the non-conductive second polymer particles may be uniformly dispersed in the conductive first polymer coating layer, or may be distributed in the conductive first polymer coating layer. In this case, in order to block the current flow between the collector and the electrode active material layer when the internal temperature of the battery rises abnormally, it is preferable that the nonconductive second polymer particles are arranged in a predetermined pattern in a part of the conductive first polymer coating layer .

3A, the current collector 10 and the electrode active material layer 20 are covered with the conductive first polymer coating layer 31 (see FIG. 3A) interposed therebetween, , The performance of the battery due to the introduction of the interface layer 30 is not caused. On the other hand, when the internal temperature of the battery rises by 80 to 100 ° C or more due to overcharging or the like, as shown in FIG. 3B, the nonconductive second polymer particles 32 disposed inside the interface layer 30 are significantly And the flow of current between the current collector 10 and the electrode active material layer 20 is blocked by the thus expanded nonconductive second polymer particles. Thus, continuous energization of the electrode assembly is suppressed, Can be effectively prevented.

The method for producing the electrode according to the present invention is not particularly limited, and may be carried out by, for example, (a) mixing an electrode material such as an electrode active material, if necessary, with a conductive material, a binder, etc. to prepare an electrode slurry, Applying; And (b) drying the electrode.

The solvent or dispersion medium used to prepare the binder solution may be any conventional solvent used in the art, including, but not limited to, N-methylpyrrolidone, acetone, dimethylacetamide, An organic solvent such as aldehyde, an inorganic solvent such as water, or a mixture thereof. The amount of the solvent used is sufficient to dissolve and disperse the active material, the conductive material, the electrode binder, the filler, and the adhesion additive in consideration of the coating thickness and the production yield of the electrode slurry. The solvents are removed by drying after coating the electrode slurry on a current collector.

The electrode active material and, if necessary, the conductive material are added to and mixed with the prepared binder solution to prepare an electrode slurry, which is then applied on the collector according to the present invention and dried to complete the electrode fabrication. The electrode drying process may also be carried out according to conventional methods known in the art, and one example may be hot air drying.

The conductive material is usually added in an amount of 1 to 50 parts 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; Conductive fibers such as carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black and summer black, carbon fibers and metal fibers; Metal powders such as carbon fluoride, aluminum, 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.

The binder is a component that assists in bonding between the active material and the conductive material and bonding to the current collector, and is usually added in an amount of 1 to 50 parts by weight based on the total weight of the mixture containing the 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 butyrene rubber, fluorine rubber, various copolymers, and the like.

The filler is not particularly limited as long as it is a fibrous material without causing any chemical change in the cell, and is used selectively as a component for suppressing the expansion of the electrode. Examples thereof include an olefin polymer such as polyethylene and polypropylene; Fiber-like materials such as glass fiber, carbon fiber and the like can be used.

The electrode active material layer 20 may be a positive electrode active material layer or a negative electrode active material layer, each of which includes a positive electrode active material and a negative electrode active material.

The cathode active material can be a conventional cathode active material that can be used for the anode of a conventional lithium secondary battery. Nonlimiting examples of usable cathode active materials include lithium transition metal complex oxides such as LiM _x O _y (M = Co, Ni, Mn, Co _a Ni _b Mn _c ) (for example, lithium manganese such as LiMn ₂ O ₄ Complex oxides, lithium nickel oxides such as LiNiO ₂ , lithium cobalt oxides such as LiCoO ₂ , and vanadium oxide containing lithium in which manganese, nickel, and cobalt are partially substituted with other transition metals or the like), or chalcogen Compounds (for example, manganese dioxide, titanium disulfide, molybdenum disulfide, etc.), and the like. More specifically, LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , Li (Ni _a Co _b Mn _c ) O ₂ (0 <a <1, 0 <b <1, 0 <c < _{+ c = 1), LiNi 1} - Y Co Y O 2, LiCo 1 -Y Mn Y O 2, LiNi 1 - Y Mn Y O 2 ( here, 0≤Y <1), Li ( Ni a Co b Mn _{c) O 4 (0 <a} <2, 0 <b <2, 0 <c <2, a + b + c = 2), LiMn 2 - z Ni z O 4, LiMn 2 -z Co z O 4 ( here, the 0 <Z <2), LiCoPO 4, LiFePO 4 or a mixture thereof.

The negative electrode active material may be a conventional negative electrode active material that can be used for a negative electrode of a conventional lithium secondary battery. Non-limiting examples of usable negative electrode active materials include lithium metal or lithium alloys, lithium adsorbent materials such as carbon, petroleum coke, activated carbon, graphite, silicon, tin, , An active material used as a cathode, and the like.

In the present invention, an electrode is manufactured using a current collector in which a conductive first polymer coating layer in which nonconductive second polymer particles are dispersed is already formed. However, it is not limited to the above-mentioned production method, but it is also within the scope of the present invention to form an electrode active material layer on the conductive first polymer coating layer on which the nonconductive second polymer particles are dispersed on the current collector .

<Lithium secondary battery>

The present invention provides a lithium secondary battery comprising the positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte containing a lithium salt. In this case, the anode, the cathode, or both electrodes may be an electrode according to the present invention.

Generally, a lithium secondary battery is composed of a positive electrode composed of a positive electrode material and a current collector, a negative electrode composed of a negative electrode material and a current collector, and a separator capable of blocking electron conduction and conducting lithium ions between the positive electrode and the negative electrode, The void of the membrane material contains an electrolyte solution for the conduction of lithium ions.

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 may generally be in the range of 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 said lithium salt containing non-aqueous electrolyte solution consists of a nonaqueous electrolyte solution and a lithium salt. As the nonaqueous electrolyte, a non-aqueous organic solvent, an organic solid electrolyte, an inorganic solid electrolyte, and the like are used.

Examples of the non-aqueous organic solvent include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butylo lactone, and 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, dioxoron derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate Aprotic organic solvents, such as ethyl propionate, 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, 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 the charge-discharge characteristics and the flame retardancy, the non-aqueous liquid electrolyte may contain, for example, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, glyme, N, N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, aluminum trichloride and the like are added It is possible. 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.

10: whole house
20: electrode active material layer
30: Interface layer
31: conductive first polymer
32: nonconductive second polymer

Claims (11)

1. An electrode for a lithium secondary battery comprising an electrode active material layer formed on one surface or both surfaces of a current collector,
Wherein the electrode includes an interface layer interposed between the current collector and the electrode active material layer and capable of variably controlling the current flow between the current collector and the electrode active material layer according to an internal temperature of the battery,
Wherein the interface layer is formed by dispersing and arranging nonconductive second polymer particles inside the conductive first polymer coating layer. The electrode for a lithium secondary battery according to claim 1, wherein the non-conductive second polymer has a glass transition temperature (T _m ) or a melting temperature (T _g ) of 80 to 100 ° C. The electrode for a lithium secondary battery according to claim 1, wherein the nonconductive second polymer is selected from the group consisting of polyethylene, polypropylene, and polystyrene. The electrode for a lithium secondary battery according to claim 1, wherein the nonconductive second polymer particles are bead-shaped or core-shell-structured particles. The composite particle of claim 4, wherein the composite particle of the core-
(i) a core portion containing a substance which is phase-changed at a temperature higher than a predetermined temperature and expanded in volume; And
(ii) a nonconductive second polymer shell portion surrounding the core portion while accommodating the material. The electrode for a lithium secondary battery according to claim 5, wherein the substance contained in the core part is a substance which is vaporized, sublimed or pyrolyzed to a gaseous state in a temperature range of not lower than a certain temperature or a compound containing the substance. The conductive polymer of claim 1, wherein the conductive first polymer is selected from the group consisting of polyacetylene, polyaniline, polypyrrole, polythiophene, poly sulfur nitride, poly (ethylenedioxy wherein the polymer is selected from the group consisting of polythiophene, poly (p-phenylene), poly (thienylene vinylene), and polyphenylene. The electrode for a lithium secondary battery according to claim 1, wherein the content of the nonconductive second polymer ranges from 20 to 50 parts by weight based on 100 parts by weight of the conductive first polymer. The electrode according to claim 1, wherein the electrode is configured such that the current flow between the current collector and the electrode active material layer is blocked by the volume expansion of the nonconductive second polymer particles disposed inside the interface layer at a temperature of 80 to 100 ° C inside the battery Wherein the electrode is a lithium secondary battery. A lithium secondary battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the positive electrode, the negative electrode, or both electrodes are the electrodes according to any one of claims 1 to 9. Collecting house; And
And a conductive first polymer coating layer formed on one surface or both surfaces of the current collector, wherein nonconductive second polymer particles are dispersed and disposed in the conductive first polymer coating layer.

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