WO2019059655A2 - Positive electrode for secondary battery and secondary battery comprising same - Google Patents

Abstract

Provided are a positive electrode for a secondary battery, comprising a first positive electrode mixture layer formed on a positive electrode current collector; and a second positive electrode mixture layer formed on the first positive electrode mixture layer, wherein the first positive electrode mixture layer has a working voltage of 4.25 to 6.0V and includes an overcharging active material that generates lithium and gas during the charging, and a lithium secondary battery comprising the positive electrode.

Description

Secondary battery anode and secondary battery comprising same

Mutual citation with related application

This application claims the benefit of priority based on Korean Patent Application No. 10-2017-0120694 filed on September 19, 2017, and Korean Patent Application No. 10-2018-0111643 filed on September 18, 2018, The entire contents of which are incorporated herein by reference.

Technical field

The present invention relates to a positive electrode for a secondary battery and a secondary battery including the same.

As technology development and demand for mobile devices increase, the demand for secondary batteries as energy sources is rapidly increasing. Among such secondary batteries, lithium secondary batteries having a high energy density and voltage, a long cycle life, and a low self-discharge rate are commercially available and widely used.

However, in the case of a lithium secondary battery, it can be overcharged beyond a normal charging region, and this phenomenon is referred to as overcharge phenomenon. When the lithium secondary battery is overcharged at a normal operating voltage or higher, heat is generated due to electrical resistance in the battery, and the temperature gradually rises. At this time, excessive lithium is discharged from the anode in the normal charging state, More lithium than is possible to enter, excess lithium is deposited on the cathode surface in the form of lithium metal. Also, when overcharging occurs, the structure collapses at the anode to provide not only thermal energy but also oxygen. When the separator is melted by the heat rapidly generated at the anode and the cathode, the anode and the cathode may develop into an inter short state have. When this condition is reached, the battery becomes extremely dangerous and can even explode.

Therefore, in order to solve the above-mentioned problems, studies on a method including an additive such as an overcharge inhibitor in the electrolytic solution and the development of related materials have been actively studied. However, even if the electrolyte contains an inhibitor, there is a problem that it is difficult to prevent the heat generation of the anode or the cathode in advance.

On the other hand, an overshooting phenomenon occurs in which the voltage increases as the resistance increases during overcharging. However, there is a problem that the stability or safety of the battery is deteriorated because the battery is heated or exploded before overshooting occurs.

An object of the present invention is to provide a positive electrode for a secondary battery that can prevent a battery from being exploded or heated by heat accumulated in the battery before reaching an overcharge reference voltage (about 8V to 10V).

The present invention provides a positive electrode current collector comprising: a first positive electrode mixture layer formed on a positive electrode collector; And a second positive electrode material mixture layer formed on the first positive electrode material mixture layer, wherein the first positive electrode material mixture layer has an operating voltage of 4.25 to 6.0 V, and includes an overcharging active material which generates lithium and gas upon charging A positive electrode for a secondary battery is provided.

According to another aspect of the present invention, there is provided a method of manufacturing a positive electrode collector, comprising: forming a first positive electrode mixture layer on a positive electrode collector; And forming a second positive electrode material mixture layer on the first positive electrode material mixture layer, wherein the first positive electrode material mixture layer has an operating voltage of 4.25 to 6.0 V, A method for manufacturing a positive electrode for a secondary battery including an active material is provided.

The present invention also provides a secondary battery comprising the positive electrode for the secondary battery.

The positive electrode for a secondary battery according to the present invention includes a mixed layer including an overcharge active material which generates lithium and gas when the battery is driven and charged at an overcharge voltage level higher than an operating voltage of a general lithium secondary battery. Therefore, the resistance and the voltage of the battery rapidly increase before the battery is damaged or exploded due to the residual heat accumulated in the battery during the overcharge of the secondary battery and the explosion of the battery, so that the life characteristics and safety of the battery can be improved.

Hereinafter, the present invention will be described in detail in order to facilitate understanding of the present invention. Herein, terms and words used in the present specification and claims should not be construed to be limited to ordinary or dictionary meanings, and the inventor may appropriately define the concept of the term to describe its own invention in the best way. It should be construed as meaning and concept consistent with the technical idea of the present invention.

When the secondary battery is overcharged, there is a problem that the secondary battery is exploded or ignited due to the heat generated by the oxidative decomposition reaction of the electrolyte and the heat accumulated in the battery. Generally, whether or not the secondary battery is overcharged is evaluated based on whether the voltage of the secondary battery reaches a high level of about 8 to 10 V. However, due to the heat generated by the decomposition of the electrolyte before the voltage abruptly increases, Or ignited and the stability of the battery is deteriorated.

Therefore, the present inventors have found that an overcharging active material layer capable of generating lithium and gas in a range lower than a voltage at which a battery is driven and a range in which an electrolyte undergo oxidative decomposition at the time of overcharging can be lowered is stacked on one surface of a positive electrode Respectively. Accordingly, when the battery is charged in the voltage range, gas is generated, and the resistance rapidly increases, and the voltage can be rapidly increased so as to be proportional thereto.

In the case of using the positive electrode having the layer formed of the positive electrode active material for overcharge according to the present invention, the resistance of the positive electrode active material is increased due to the reaction of the positive electrode active material before the exothermic reaction occurs, A positive electrode for a secondary battery capable of preventing a heat generation or an explosion due to an oxidative decomposition reaction of an electrolyte to reach a voltage range corresponding to a voltage of a termination condition due to a sudden rise in the voltage of the positive electrode, Thereby providing a secondary battery.

Anode for secondary battery

Hereinafter, a cathode for a secondary battery according to the present invention will be described.

A positive electrode for a secondary battery according to the present invention comprises: a first positive electrode material mixture layer formed on a positive electrode current collector; And a second positive electrode material mixture layer formed on the first positive electrode material mixture layer, wherein the first positive electrode material mixture layer has an operating voltage of 4.25 to 6.0 V, and includes an overcharging active material which generates lithium and gas upon charging do.

In the present invention, the cathode current collector is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery, and for example, a cathode may be formed on the surface of stainless steel, aluminum, nickel, titanium, , Nickel, titanium, silver, or the like may be used. In addition, the cathode current collector may have a thickness of 3 to 500 탆, and fine unevenness may be formed on the surface of the current collector to increase the adhesive force of the cathode active material. For example, it can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric.

Meanwhile, the first positive electrode material mixture layer formed on the positive electrode collector may include an overcharging active material having an operating voltage of 4.25 to 6.0 V and generating lithium and gas upon charging.

In the present invention, the operating voltage means a voltage range in which the overcharge-generating active material generates lithium and gas when the voltage reaches the above-mentioned range. The operating voltage is not necessarily limited to the above range, But it can be regarded as the operating voltage range of the first positive electrode mixture layer if the voltage is lower than the voltage at which the reaction heat generated by oxidative decomposition of the electrolyte is generated.

In the present invention, the supercharging active material may include at least one element selected from the group consisting of a carbon element and a nitrogen element. When the overcharging active material contains the carbon element and / or the nitrogen element, it generates carbon dioxide (CO) and / or carbon monoxide (CO ₂ ) within the operating voltage range and is vaporized. The overchargeable active material contained in the first positive electrode material mixture layer generates gas and is vaporized, and at the same time, a part of the positive electrode is lost, so that the positive electrode resistance rapidly increases. Accordingly, the voltage of the anode also rises in proportion to the anode resistance, so that the supply of the voltage is stopped before the electrolyte is oxidized and decomposed to generate heat in the secondary battery.

In one embodiment of the present invention, the overcharging active material is selected from the group consisting of Li ₂ C ₂ O ₄ , Li ₂ C ₄ O ₄ , Li ₂ C ₃ O ₅ , Li ₂ C ₄ O _6, and LiN ₃ In particular, the material which is highly sensitive to the reaction within the specific operating voltage range, more preferably, the overcharging active material may be Li ₂ C ₂ O ₄ .

In the present invention, the overcharging active material may be contained in an amount of 60 to 99.9% by weight, preferably 65 to 99.8% by weight, and more preferably 70 to 99.8% by weight based on the total weight of the first cathode mix layer. When the overchargeable active material is included within the above range, when a voltage within the operating voltage range is applied to the battery, lithium and gas are sufficiently generated and the resistance and voltage may rise to a certain level or more. In addition, when the overcharge-capable active material is included in the above range, the capacity of the battery can be relatively increased. Therefore, it is preferable that the overcharging active material is contained within the above range.

Meanwhile, in the present invention, the thickness of the first positive electrode material mixture layer is 0.1 to 30 탆, more preferably 0.2 to 10 탆. When the thickness of the first anodic coalescing layer is thinner than the above range, even if the voltage supplied to the battery reaches the voltage of the operating range and lithium and gas are generated, the amount of generated gas is small and the resistance rises accordingly The voltage of the anode is not likely to rise sharply. On the other hand, when the first positive electrode material mixture layer is formed to a thickness exceeding the above range, the charge / discharge performance of the electrode may be deteriorated. Even after the voltage supplied to the battery reaches the voltage of the operating range, 1 part of the positive electrode mixture layer is present on the positive electrode, the resistance of the positive electrode is not increased rapidly, and the electrolyte oxidative decomposition reaction can be continuously induced, so that the stability of the battery may be lowered by the exothermic reaction.

In the present invention, the first positive electrode material mixture layer may further include a binder and a conductive material together with the above-described overchargeable active material.

The binder serves to improve the adhesion between the positive electrode active material particles and the adhesion between the positive electrode active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose ), Starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, and various copolymers thereof. One kind or a mixture of two or more kinds of them may be used.

The binder may be contained in an amount of 0.1 to 40% by weight, preferably 0.1 to 35% by weight, more preferably 0.1 to 30% by weight based on the total weight of the first cathode mix layer. When the binder is contained in the range below the above range, the adhesion between the first positive electrode mixture layer and the positive electrode collector is weak and the life characteristics of the battery may be deteriorated. When the binder is contained in the range exceeding the above range, The materials constituting the first positive electrode mixture layer may be aggregated and the first positive electrode material mixture layer may not be uniformly formed and the lifetime characteristics of the battery may be deteriorated, Is preferably included within the above range.

The conductive material is used for imparting conductivity to the electrode. The conductive material is not particularly limited as long as it has electron conductivity without causing chemical change. Specific examples thereof include graphite such as natural graphite and artificial graphite; Carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, summer black and carbon fiber; Metal powder or metal fibers such as copper, nickel, aluminum and silver; Conductive whiskey such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; And polyphenylene derivatives. These may be used alone or in admixture of two or more.

The conductive material may be included in an amount of 0.1 to 40% by weight, preferably 0.1 to 35% by weight, and more preferably 0.1 to 30% by weight based on the total weight of the cathode active material layer. When the conductive material is included within the above range, a conductivity of a certain level or higher can be given to the electrode. However, when it is contained in the range below the above range, it is difficult to impart a certain level of conductivity to the electrode. If it exceeds the above range, coagulation phenomenon occurs between the conductive materials and the first positive electrode material mixture layer is not uniformly formed, It is preferable that the conductive material is contained within the above range.

In the present invention, the second positive electrode material mixture layer is a layer formed on the first positive electrode material mixture layer and contains lithium transition metal oxide as the positive electrode active material.

More specifically, the lithium-transition as the metal _{oxide, Li x1 CoO 2 (0.5 <} x 1 <1.3), Li x2 NiO 2 (0.5 <x 2 <1.3), Li x3 MnO 2 (0.5 <x 3 <1.3), _{Li x4 Mn 2 O 4 (0.5} <x 4 <1.3), Li x5 (Ni a1 Co b1 Mn c1) O 2 (0.5 <x 5 <1.3, 0 <a 1 <1, 0 <b 1 <1, 0 _{<c 1 <1, a 1} + b 1 + c 1 = 1), Li x6 Ni 1 -y1 Co y1 O 2 (0.5 <x 6 <1.3, 0 <y 1 <1), Li x7 Co 1 - y2 _{Mn y2 O 2 (0.5 <x} 7 <1.3, 0≤y 2 <1), Li x8 Ni 1 -y3 Mn y3 O 2 (0.5 <x 8 <1.3, O≤y3 <1), Li x9 (Ni a2 _{Co b2 Mn c2) O 4 (} 0.5 <x 9 <1.3, 0 <a 2 <2, 0 <b 2 <2, 0 <c 2 <2, a 2 + b 2 + c 2 = 2), Li x10 _{Mn 2 - z1 Ni z1 O 4} (0.5 <x 10 <1.3, 0 <z 1 <2), Li x11 Mn 2 -z Co z O 4 (0.5 <x 11 <1.3, 0 <z <2), Li _{x12 CoPO 4 (0.5 <x 12} <1.3), Li x13 FePO 4 (0.5 <x 13 <1.3) and _{Li 1 + a3 [Ni x14 Mn} y3 Co z2 M v1] O (2-c) A c3 (M is A is at least one element selected from the group consisting of Al, Zr, Zn, Ti, Mg, Ga and In, or two or more elements selected from the group consisting of P, F, S and N, 0? X _14? 1.0, 0? Y ₃ <0.6, 0? Z ₂ <0.6 _{, 0≤v 1 ≤0.1, 0≤a 3 <} 0.3, 0≤c 3 ≤0.2, a 3 + x 14 + y 3 + z 2 + v 1 = 1) using at least one selected from the group consisting of .

In the present invention, the second positive electrode material mixture layer may further include a binder and a conductive material, and the binder and the conductive material used for the second positive electrode material mixture layer may include a binder and a conductive material used for the first positive electrode material mixture layer And the types of the binder and the conductive material are the same as those described above.

Meanwhile, in the case of the second positive electrode material mixture layer, when the lithium-transition metal oxide, the binder and the conductive material are included, the lithium-transition metal oxide is 80 to 99.9% by weight based on the total weight of the second positive electrode material mixture layer, 85 to 99.8% by weight, and more preferably 90 to 99.8% by weight.

The binder may contain 0.1 to 20% by weight, preferably 0.1 to 15% by weight, more preferably 0.1 to 10% by weight based on the total weight of the second positive electrode material mixture layer.

The conductive material may include 0.1 to 20% by weight, preferably 0.1 to 15% by weight, more preferably 0.1 to 10% by weight based on the total weight of the second cathode mix layer.

If the lithium transition metal oxide is contained in the range below the range, lithium ions may not be sufficiently supplied to the cathode. If the lithium transition metal oxide is contained in the range exceeding the above range, the performance of the battery may deteriorate due to the conductivity and adhesion of the electrode. Therefore, it is more preferable that the lithium transition metal oxide is included within the above range in consideration of the capacity and life performance of the battery. In the case of the second positive electrode material mixture layer, when the binder and the conductive material are contained within the above range, the adhesion between the first positive electrode material mixture layer and the second positive electrode material mixture layer can be improved and the conductivity can be maintained to a certain level or more. However, when the binder is included in the range below the above range, the adhesion between the second positive electrode material mixture layer and the first positive electrode material mixture layer may be deteriorated, and when the conductive material is contained in the range below the second positive electrode material mixture layer, Can also be lowered. When the binder and the conductive material are included in the amount exceeding the above range, aggregation phenomenon occurs between the materials forming the second positive electrode material mixture layer, resulting in deterioration in adhesion to the first positive electrode material mixture layer, and battery life characteristics are deteriorated . Therefore, it is more preferable that the binder and the conductive material are included within the above range.

In the present invention, the thickness of the second positive electrode material mixture layer is 20 to 500 mu m, more preferably 50 to 300 mu m. When the thickness of the second positive electrode material mixture layer is less than the above range, lithium ions may not be sufficiently supplied into the battery. When the thickness exceeds the above range, the total thickness of the positive electrode increases, It is more preferable that the thickness of the second positive electrode material mixture layer is within the above range.

In the present invention, the thickness ratio of the first positive electrode material mixture layer and the second positive electrode material mixture layer is 1: 1 to 1: 300, more preferably 1:50 to 1: 200. When the thickness ratio of the first positive electrode material mixture layer and the second positive electrode material mixture layer is within the above range, the first positive electrode material mixture layer may be formed so as to abruptly increase the resistance and the voltage, so that the lifetime performance and stability of the battery may be improved , Lithium ions are sufficiently supplied and the battery capacity can be improved.

When the lithium secondary battery including the positive electrode according to an embodiment of the present invention is in an overcharged state, the electrical contact between the positive electrode collector and the second positive electrode mixture layer by the breakage of the first positive electrode mixture layer Can be blocked.

Method for manufacturing positive electrode for secondary battery

Hereinafter, a method of manufacturing a positive electrode for a secondary battery according to the present invention will be described.

In the present invention, there is provided a method for producing a battery pack, comprising the steps of (1) forming a first positive electrode mixture layer on a positive electrode collector, and (2) forming a second positive electrode mixture layer on the first positive electrode mixture layer, The positive electrode material mixture layer has an operating voltage of 4.25 to 6.0 V and includes an overcharging active material which generates lithium and gas upon charging.

(1) First positive electrode mixture layer formation step

The method of forming the first positive electrode material mixture layer containing the overcharge-capable active material is not particularly limited. Preferably, the step of forming the first anode mixture layer comprises: mixing the overcharging active material with a conductive material and a binder to form a first anode formation composition; And applying the composition for forming an anode on the positive electrode current collector.

The overcharge-capable active material, the conductive material and the binder may be dissolved or dispersed in a solvent to prepare a composition for forming a first anode. The types and contents of the overcharging active material, the conductive material and the binder are as described above.

Meanwhile, the solvent for forming the first anode forming composition may be a solvent commonly used in the art, and examples thereof include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpiperazine (NMP), acetone, or water, and either one of them alone or a mixture of two or more of them may be used. The amount of the solvent used is sufficient to dissolve or disperse the overchargeable active material, the conductive material and the binder in consideration of the application thickness of the slurry and the yield of the slurry, and then to have a viscosity capable of exhibiting excellent thickness uniformity Do.

Next, the first positive electrode composition composition may be coated on the positive electrode collector, followed by drying and rolling to form the first positive electrode mixture layer.

Alternatively, the anode may be produced by casting the first composition for forming an anode on a separate support, then peeling the support from the support, and laminating the film on the cathode current collector.

(2) Second positive electrode material mixture layer forming step

In the present invention, the second positive electrode material mixture layer is formed on the first positive electrode material mixture layer, and the method of forming the second positive electrode material mixture layer is not particularly limited.

However, the second positive electrode mixture layer may be formed by mixing the lithium transition metal oxide with a conductive material and a binder to form a second positive electrode composition; And applying the second composition for forming an anode on the first positive electrode material mixture layer.

Applying the second positive electrode material mixture composition comprising the lithium transition metal oxide and, optionally, a binder and a conductive material, onto the first positive electrode material mixture layer formed on the positive electrode current collector, followed by drying and rolling have.

At this time, the type and content of the lithium transition metal oxide, the binder, the conductive material, and the solvent for forming the second positive electrode material mixture composition are as described above.

Lithium secondary battery

Hereinafter, a lithium secondary battery according to the present invention will be described.

The lithium secondary battery according to the present invention includes a positive electrode, a negative electrode disposed opposite to the positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte.

The anode is as described above. The lithium secondary battery may further include a battery container for storing the positive electrode, the negative electrode and the electrode assembly of the separator, and a sealing member for sealing the battery container.

The negative electrode includes a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector. The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. For example, the negative electrode current collector may be formed on the surface of copper, stainless steel, aluminum, nickel, titanium, sintered carbon, Carbon, nickel, titanium, silver or the like, aluminum-cadmium alloy, or the like may be used. In addition, the negative electrode collector may have a thickness of 3 to 500 탆, and similarly to the positive electrode collector, fine unevenness may be formed on the surface of the collector to enhance the binding force of the negative electrode active material. For example, it can 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 anode active material layer optionally includes a binder and a conductive material together with the anode active material. The negative electrode active material layer may be formed by applying and drying a composition for forming a negative electrode including a negative electrode active material on the negative electrode collector and, optionally, a binder and a conductive material, or by casting the composition for forming a negative electrode on a separate support , And a film obtained by peeling from the support may be laminated on the negative electrode collector.

As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples thereof include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber and amorphous carbon; Metal compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys or Al alloys; Metal oxides such as SiOx (0 < x < 2), SnO2, vanadium oxide, lithium vanadium oxide and the like capable of doping and dedoping lithium; Or a composite containing the metallic compound and the carbonaceous material such as Si-C composite or Sn-C composite, and any one or a mixture of two or more thereof may be used. Also, a metal lithium thin film may be used as the negative electrode active material. The carbon material may be both low-crystalline carbon and high-crystallinity carbon. Examples of the low-crystalline carbon include soft carbon and hard carbon. Examples of the highly crystalline carbon include natural graphite, artificial graphite, artificial graphite or artificial graphite, Kish graphite graphite, pyrolytic carbon, mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches and petroleum or coal tar coke derived cokes).

The binder and the conductive material are the same as those described above for the anode.

Meanwhile, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a moving path of lithium ions. The separator can be used without limitation, as long as it is used as a separator in a lithium secondary battery. Particularly, It is preferable to have a low resistance and an excellent ability to impregnate the electrolyte. Specifically, porous polymer films such as porous polymer films made of polyolefin-based polymers such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers and ethylene / methacrylate copolymers, May be used. Further, a nonwoven fabric made of a conventional porous nonwoven fabric, for example, glass fiber of high melting point, polyethylene terephthalate fiber, or the like may be used. In order to secure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymer material may be used, and may be optionally used as a single layer or a multilayer structure.

Examples of the electrolyte used in the present invention include an organic-based liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, and a molten inorganic electrolyte that can be used in the production of a lithium secondary battery. It is not.

Specifically, the electrolyte may include an organic solvent and a lithium salt.

The organic solvent may be used without limitation as long as it can act as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, examples of the organic solvent include ester solvents such as methyl acetate, ethyl acetate,? -Butyrolactone and? -Caprolactone; Ether solvents such as dibutyl ether or tetrahydrofuran; Ketone solvents such as cyclohexanone; Aromatic hydrocarbon solvents such as benzene and fluorobenzene; Dimethyl carbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), propylene carbonate PC) and the like; Alcohol solvents such as ethyl alcohol and isopropyl alcohol; R-CN (R is a straight, branched or cyclic hydrocarbon group of C2 to C20, which may contain a double bond aromatic ring or an ether bond); Amides such as dimethylformamide; Dioxolanes such as 1,3-dioxolane; Or sulfolane may be used. Of these, a carbonate-based solvent is more preferable, and a cyclic carbonate (for example, ethylene carbonate or propylene carbonate) having a high ionic conductivity and a high dielectric constant, such as ethylene carbonate or propylene carbonate, which can increase the charge- (For example, ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate, etc.). In this case, when the cyclic carbonate and the chain carbonate are mixed in a volume ratio of about 1: 1 to about 1: 9, the performance of the electrolytic solution may be excellent.

The lithium salt can be used without particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the lithium _{salt, LiPF 6, LiClO 4, LiAsF} 6, LiBF 4, LiSbF 6, LiAl0 4, LiAlCl 4, LiCF 3 SO 3, LiC 4 F 9 SO 3, LiN (C 2 F 5 SO 3) 2 _{, LiN (C 2 F 5 SO} 2) 2, LiN (CF 3 SO 2) 2. LiCl, LiI, or LiB (C ₂ O ₄ ) ₂ may be used. The concentration of the lithium salt is preferably in the range of 0.1 to 2.0 M. When the concentration of the lithium salt is within the above range, the electrolyte has an appropriate conductivity and viscosity, so that it can exhibit excellent electrolyte performance and the lithium ion can effectively move.

In addition to the electrolyte components, the electrolyte may contain, for example, a haloalkylene carbonate-based compound such as difluoroethylene carbonate or the like, pyridine, triethanolamine, or the like for the purpose of improving lifetime characteristics of the battery, Ethyl phosphite, triethanol amine, cyclic ether, ethylenediamine, glyme, hexametriamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N, At least one additive such as benzyl alcohol, benzyl alcohol, benzyl alcohol, benzyl alcohol, benzyl alcohol, benzyl alcohol, benzyl alcohol, benzyl alcohol, benzyl alcohol, The additive may be included in an amount of 0.1 to 5% by weight based on the total weight of the electrolyte.

As described above, the lithium secondary battery including the positive electrode according to the present invention stably exhibits excellent discharge capacity, output characteristics, and capacity retention ratio, and thus can be applied to portable devices such as mobile phones, notebook computers, digital cameras, and hybrid electric vehicles electric vehicle (HEV), and the like.

Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily carry out the present invention. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

Example

Example  One

< The first anode Compound layer  Formation>

Li ₂ C ₂ O ₄ , a conductive material (denka black KF1100), and a PVDF binder were mixed in a weight ratio of 90: 5: 5 and NMP as a solvent. The resultant mixture was subjected to dispersion treatment for 30 minutes using a disperser (Paste mixer or homo disperse) to prepare a composition for forming a first positive electrode material mixture layer (solid content: about 70% by weight).

The composition for forming the first positive electrode material mixture layer was coated on the aluminum current collector, dried at 120 ° C, and rolled to form a first positive electrode material mixture layer on the aluminum current collector.

&Lt; Preparation of positive electrode &

Then, LiNi _{0 . 6} Co _{0 . 2} Mn _{0 . 2} O ₂ , a conductive material (denka black KF1100) and a PVDF binder in a weight ratio of 96: 2: 2, and mixed using NMP as a solvent. The resultant mixture was subjected to dispersion treatment for 30 minutes using a disperser (Paste mixer or homo disperse) to prepare a composition for forming a second positive electrode material mixture layer (solid content: about 75% by weight) The composition for forming the positive electrode material mixture layer was coated on the first positive electrode material mixture layer, dried at 120 캜 and rolled to prepare a positive electrode.

Example  2

A positive electrode in Example 1 in the preparation of the first positive electrode material mixture layer composition, Li ₂ C ₂ O ₄ instead of Li ₂ in the same manner except that the C ₄ O ₄ was prepared.

Example  3

A positive electrode was prepared in the same manner as in Example 1 except that LiN ₃ was used instead of Li ₂ C ₂ O ₄ in the preparation of the first positive electrode material mixture composition.

Comparative Example

Comparative Example  One

Except that the first positive electrode material mixture layer was not formed in Example 1 and the composition for forming the second positive electrode material mixture layer was immediately applied to the aluminum current collector and dried at 120 캜 and then rolled, .

Comparative Example  2

A positive electrode in Example 1 when producing the first positive electrode material mixture layer composition in, Li ₂ C ₂ O ₄ instead of Li ₂ in the same manner except that the CO ₃ was prepared.

Comparative Example  3

LiNi _{0 . 6} Co _{0 . 2} Mn _{0 . 2} O ₂ , a conductive material (denka black KF1100) and a PVDF binder in a weight ratio of 96: 2: 2, and mixed using NMP as a solvent. Further, 3 wt% of Li ₂ C ₂ O ₄ was added and mixed. The resultant mixture was subjected to dispersion treatment for 30 minutes using a disperser (Paste mixer or homo disperse) to prepare a composition for forming a positive electrode material mixture layer (solid content: about 70% by weight) The composition for forming a layer was applied to an aluminum current collector, dried at 120 캜, and rolled to form a positive electrode mixture layer on the aluminum current collector.

Manufacturing example

A lithium secondary battery was prepared using the positive electrodes prepared in Examples 1 to 3 and Comparative Examples 1 to 3, respectively. More specifically, it is as follows.

&Lt; Preparation of negative electrode &

The negative electrode active material slurry was prepared by mixing natural graphite, a carbon black conductive material, carboxymethyl cellulose (CMC) and a styrene butadiene rubber (SBR) binder in a weight ratio of 96: 1: 1: 2 and using H ₂ O as a solvent . The negative electrode active material slurry was applied to a copper current collector, followed by drying and rolling to prepare a negative electrode.

< Lithium secondary battery  Manufacturing>

An electrode assembly was manufactured through a separator made of porous polyethylene between each of the positive electrodes and the negative electrodes prepared in Examples 1 to 3 and Comparative Examples 1 to 3, the electrode assembly was placed inside the case, An electrolyte was injected to prepare a lithium secondary battery. The electrolyte solution was prepared by dissolving 1.0 M lithium hexafluorophosphate (LiPF ₆ ) in an organic solvent composed of ethylene carbonate / dimethyl carbonate / ethyl methyl carbonate (mixed volume ratio of EC / DMC / EMC = 3/4/3) Respectively.

Experimental Example  : Overcharge Battery Safety Test

Experimental Example  One

The lithium secondary batteries produced using the positive electrodes of Examples 1 to 3 and Comparative Examples 1 to 3 were charged under the charging conditions shown in Table 1 below to determine the voltage at the time of generation of the gas (the operating voltage of the first positive electrode material mixture layer (V)) was measured. The operating voltages measured at this time are shown in Table 1 below.

	Charging conditions	The operating voltage (V) of the first positive-
Example 1	0.1 C @ 25 C	5.0 to 5.2V
Example 2	0.1 C @ 25 C	4.25-6V
	1.0 C @ 25 C	4.5 ~ 6V
	1.0 C @ 60 C	4.25 to 5.4 V
Example 3	1.0 C @ 25 C	5.0 to 5.8V
Comparative Example 1	0.1 C @ 25 C	No operation
Comparative Example 2	0.1 C @ 25 C	No operation
Comparative Example 3	0.1 C @ 25 C	No operation

Experimental Example  2

The lithium secondary battery prepared using the positive electrodes of Examples 1 to 3 and Comparative Examples 1 to 3 was subjected to stability test while being charged at 1.0 C in SOC 100 for one hour. At this time, when the voltage of the lithium secondary battery reaches 8.4 V without heat or explosion, it is evaluated as Pass. When the secondary battery fails to reach the voltage and the secondary battery is heated or exploded, it is evaluated as Fail. The experimental results are shown in Table 2 below.

	Stability Passability (1.0C @ 25 ℃ Evaluation)
Example 1	Pass
Example 2	Pass
Example 3	Pass
Comparative Example 1	Fail
Comparative Example 2	Fail
Comparative Example 3	Fail

Referring to Table 2, in Examples 1 to 3, the secondary battery reached 8.4 V without exothermic or explosion, and passed the stability test. In Comparative Examples 1 to 3, the secondary battery was heated or exploded before 8.4 V, Respectively. In the case of Comparative Example 2, although the oxidation reaction of Li ₂ CO ₃ proceeded during overcharging, Li ₂ CO ₃ itself was not consumed or extinguished, so that the degree of resistance increase was slight. In Comparative Example 3, Li ₂ C ₂ O ₄ , even if Li ₂ C ₂ O ₄ is consumed or extinguished, the resistance is lower than those of Examples 1 to 3 formed of the positive electrode mixture layer of two layers, I think.

Claims (19)

1. A first positive electrode mixture layer formed on the positive electrode collector; And

   And a second positive electrode material mixture layer formed on the first positive electrode material mixture layer,

   Wherein the first positive electrode material mixture layer has an operating voltage of 4.25 to 6.0 V and includes an overcharging active material which generates lithium and gas upon charging.
2. The method according to claim 1,

   Wherein the overcharging active material comprises at least one element selected from the group consisting of a carbon element and a nitrogen element.
3. 3. The method of claim 2,

   Wherein the overcharging active material is at least one or more selected from the group consisting of Li ₂ C ₂ O ₄ , Li ₂ C ₄ O ₄ , Li ₂ C ₃ O ₅ , Li ₂ C ₄ O ₆ and LiN ₃ .
4. The method of claim 3,

   The overcharging active material is Li ₂ C ₂ O ₄ Lt; RTI ID = 0.0 &gt; a &lt; / RTI &gt;
5. The method according to claim 1,

   Wherein the first positive electrode material mixture layer has a thickness of 0.1 to 30 占 퐉.
6. The method according to claim 1,

   Wherein the thickness of the second positive electrode material mixture layer is 20 to 500 m.
7. The method according to claim 1,

   Wherein the thickness ratio of the first positive electrode material mixture layer and the second positive electrode material mixture layer is from 1: 1 to 1: 300.
8. The method according to claim 1,

   Wherein the first positive electrode material mixture layer further comprises a binder and a conductive material.
9. The method according to claim 1,

   Wherein the second positive electrode material mixture layer comprises a lithium transition metal oxide.
10. 10. The method of claim 9,

    The lithium transition metal _{oxide, Li x1 CoO 2 (0.5 <} x 1 <1.3), Li x2 NiO 2 (0.5 <x 2 <1.3), Li x3 MnO 2 (0.5 <x 3 <1.3), Li x4 Mn 2 _{O 4 (0.5 <x 4 <} 1.3), Li x5 (Ni a1 Co b1 Mn c1) O 2 (0.5 <x 5 <1.3, 0 <a 1 <1, 0 <b 1 <1, 0 <c 1 < _{1, a 1 + b 1 +} c 1 = 1), Li x6 Ni 1 - y1 Co y1 O 2 (0.5 <x 6 <1.3, 0 <y 1 <1), Li x7 Co 1 -y2 Mn y2 O 2 _{(0.5 <x 7 <1.3,} 0≤y 2 <1), Li x8 Ni 1 - y3 Mn y3 O 2 (0.5 <x 8 <1.3, O≤y3 <1), Li x9 (Ni a2 Co b2 Mn c2 _{) O 4 (0.5 <x 9} <1.3, 0 <a 2 <2, 0 <b 2 <2, 0 <c 2 <2, a 2 + b 2 + c 2 = 2), Li x10 Mn 2 -z1 _{Ni z1 O 4 (0.5 <x} 10 <1.3, 0 <z 1 <2), Li x11 Mn 2 - z Co z O 4 (0.5 <x 11 <1.3, 0 <z <2), Li x12 CoPO 4 ( _{0.5 <x 12 <1.3),} Li x13 FePO 4 (0.5 <x 13 <1.3) and _{Li 1 + a3 [Ni x14 Mn} y3 Co z2 M v1] O (2-c) A c3 (M is Al, Zr, Zn, Ti, Mg, Ga, and any one or two or more of these elements is selected from the group consisting of in, and; a is at least one member selected from the group consisting of P, F, S and N, 0≤x _{14 ≤1.0, 0≤y 3 <0.6, 0≤z} 2 <0.6, 0≤v 1 ≤0.1, 0≤a _{3 <0.3, 0≤c 3 ≤0.2,} a 3 + x 14 + y 3 + z 2 + v 1 = 1) the positive electrode of a secondary battery is at least at least one selected from the group consisting of.
11. Forming a first positive electrode mixture layer on the positive electrode collector; And

    And forming a second positive electrode material mixture layer on the first positive electrode material mixture layer,

    Wherein the first positive electrode material mixture layer has an operating voltage of 4.25 to 6.0 V and includes an overcharging active material which generates lithium and gas upon charging.
12. 12. The method of claim 11,

    Wherein the overcharging active material comprises at least one element selected from the group consisting of a carbon element and a nitrogen element.
13. 13. The method of claim 12,

    The overcharging active material may be Li ₂ C ₂ O ₄ , Li ₂ C ₄ O ₄ , Li ₂ C ₃ O ₅ , Li ₂ C ₄ O _6, and LiN ₃ Wherein the positive electrode active material is at least one selected from the group consisting of a positive electrode active material and a negative electrode active material.
14. 14. The method of claim 13,

    Wherein the overcharging active material is Li ₂ C ₄ O ₄ .
15. 12. The method of claim 11,

    Wherein the first positive electrode material mixture layer is formed to a thickness of 0.1 to 30 占 퐉.
16. 12. The method of claim 11,

    Wherein the second positive electrode material mixture layer has a thickness of 20 to 500 mu m.
17. 12. The method of claim 11,

    Wherein the thickness ratio of the first positive electrode material mixture layer and the second positive electrode material mixture layer is from 1: 1 to 1: 300.
18. 11. A lithium secondary battery comprising a positive electrode for a secondary battery according to any one of claims 1 to 10.
19. 19. The method of claim 18,

    Wherein when the lithium secondary battery is in an overcharged state, electrical contact between the positive electrode collector and the second positive electrode mixture layer is blocked by breakage of the structure of the first positive electrode mixture layer.