KR20190047203A - Positive electrode active material for lithium secondary battery, preparing method of the same, positive electrode and lithium secondary battery including the same - Google Patents

Abstract

The present invention relates to an anode for a lithium secondary battery, a manufacturing method for the anode for a lithium secondary battery, and a lithium secondary battery including the same. The anode for a lithium secondary battery comprises: an anode collector; and an overcharge prevention layer which is formed on the anode collector and includes at least one between compounds represented by formula 1, Li_2MnO_3, and formula 2, Li_x1Ni_aCo_bMn_cO_2; and an anode active material layer which is formed on the overcharge prevention layer. In formula 2, 1.10 <= x1 <= 1.30, 0.45 <= a <= 0.55, 0.05 <= b <= 0.2, and 0.30 <= c <= 0.50. The anode for a lithium secondary battery of the present invention can secure stability of a battery.

Description

FIELD OF THE INVENTION The present invention relates to a positive electrode active material for a lithium secondary battery, a method for producing the same, a positive electrode for a lithium secondary battery, and a lithium secondary battery including the same. BACKGROUND ART [0002]

The present invention relates to a positive electrode active material for a lithium secondary battery, a method for producing the positive electrode active material, a positive electrode for a lithium secondary battery including the positive electrode active material, and a lithium secondary battery.

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 high energy density and operating potential, long cycle life and low self discharge rate are commercialized and widely used.

In recent years, lithium secondary batteries have been used as power sources for medium- and large-sized devices such as electric vehicles. Therefore, a high capacity, high energy density, and low cost of lithium secondary batteries have been demanded. Fe and the like are being actively studied.

One of the major research tasks of such a lithium secondary battery is to improve the safety of a battery using the same while realizing a high capacity and high output electrode active material.

Currently, lithium secondary batteries are designed for use in specific voltage ranges (typically 4.4 V or less) to ensure durability and safety. However, unexpectedly, the cell potential may rise above that (up to ~ 12V). If the overcharged state exceeds the allowable current or voltage, it may cause serious safety problems such as explosion or ignition of the lithium secondary battery. have. Particularly, a lithium secondary battery used in a middle- or large-sized battery pack using an electric power source such as an electric vehicle or a hybrid vehicle requires a long service life, and at the same time, it is more important to ensure safety because of the density of a plurality of battery cells.

Therefore, there is a demand for development of a battery in which the overcharging phenomenon of the lithium secondary battery is prevented in advance, and the safety is improved from the risk of ignition or explosion.

Korea Patent Publication No. 2006-0062005

In order to solve the above-mentioned problems, a first technical object of the present invention is to provide a positive electrode for a lithium secondary battery capable of securing the safety of a battery by blocking a charging current by increasing resistance during overcharging.

A second aspect of the present invention is to provide a lithium secondary battery including the positive electrode for the lithium secondary battery.

The present invention relates to a positive electrode collector, An overcharge preventing layer formed on the positive electrode current collector and containing at least one of the following compounds represented by the following Chemical Formulas 1 and 2; And a positive electrode active material layer formed on the over-charge preventing layer,

[Chemical Formula 1]

Li ₂ MnO ₃

(2)

Li _{x 1} Ni _a Co _b Mn _c O ₂

1.10? X1? 1.30, 0.45? A? 0.55, 0.05? B? 0.2, 0.30? C? 0.50).

Also, the anode according to the present invention; cathode; And a separator interposed between the anode and the cathode; And an electrolyte. &Lt; IMAGE &gt;

The positive electrode according to the present invention is characterized in that an overcharge preventing layer containing at least one of Li ₂ MnO ₃ and Li _{x 1} Ni _a Co _b Mn _c O ₂ is formed on the positive electrode collector, And overcharging is terminated by shutting off the charging current, so that the safety of the battery can be improved.

1 is a graph showing the oxygen gas content according to the voltage of the overcharge preventing layer prepared in Example 1 and Example 2 of the present invention.
FIG. 2 is a graph showing voltage behavior of lithium secondary batteries according to Example 1 and Comparative Example 1 according to capacity during overcharging. FIG.
3 is a graph showing voltage behavior of lithium secondary batteries manufactured in Comparative Example 2 of the present invention over time in overcharging.

Hereinafter, the present invention will be described in more detail.

The terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms and the inventor may appropriately define the concept of the term in order to best describe its invention It should be construed as meaning and concept consistent with the technical idea of the present invention.

A positive electrode for a lithium secondary battery according to an embodiment of the present invention includes a positive electrode collector; An overcharge preventing layer formed on the positive electrode current collector and comprising at least one or more compounds represented by the following general formulas (1) and (2); And a positive electrode active material layer formed on the overcharge preventing layer:

[Chemical Formula 1]

Li ₂ MnO ₃

(2)

Li _{x 1} Ni _a Co _b Mn _c O ₂

1.10? X1? 1.30, 0.45? A? 0.55, 0.05? B? 0.2, 0.30? C? 0.50).

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

First, the positive electrode includes an overcharge preventing layer formed on the positive electrode collector and a positive electrode active material layer formed on the overcharge preventing layer.

The positive electrode according to the present invention can improve the stability of the positive electrode without lowering the energy density by forming the two-layer structure including the overcharge preventing layer and the positive active material layer on the positive electrode current collector as described above.

Specifically, the present invention provides a two-layer structure in which an overcharge preventing layer is formed on a positive electrode collector and at least one of the compounds represented by the general formulas (1) and (2) is formed and a positive electrode active material layer is formed on the overcharge preventing layer By using this, gas is generated at a high voltage of 4.4 V or higher and the charging current is interrupted to terminate the overcharging, so that the safety of the battery can be improved while minimizing the decrease in the energy density.

The positive electrode current collector is not particularly limited as long as it has conductivity without causing chemical changes in the battery. For example, carbon, 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 overcharge prevention layer includes at least one of the compounds represented by Chemical Formulas 1 and 2, and dissociates the compound at a high voltage of 4.4 V or higher to generate a gas. At this time, the high voltage may be, for example, 4.4V or more, preferably 4.4V to 12V.

With the above overcharge prevention decomposition when comprise Li ₂ MnO ₃ represented by the formula (1), at least the high voltage 4.4V through the reaction described in Scheme to which the Li ₂ MnO _3, O ₂ gas is generated, and the O ₂ A gap is generated between the positive electrode current collector and the positive electrode active material layer by the gas.

Li (Li _1/3 Mn _2/3 ) O ₂ → (Li _1/3 Mn _2/3 ) O _3/2 + 1/4 O ₂

On the other hand, the Li _x Ni _a Co _b Mn _c O ₂ compound represented by the formula (2) has a molar ratio of Li / metal (including Ni, Co and Mn), that is, x1 / (a + b + c) At the same time, the molar ratio of Ni: Mn, that is, a: c is 1: (0.9-1.9). Thus, the compound of Formula 2, which contains Li, Mn and Ni so as to satisfy a specific molar ratio, is partially converted to Li ₂ MnO ₃ , and Li ₂ MnO ₃ produced by the conversion is converted into a Oxygen gas is generated when dissociated.

A gap is generated between the cathode current collector and the cathode active material layer due to dissociated oxygen gas in the compound, thereby reducing the adhesive force between the cathode current collector and the cathode active material layer, The conductive path is also blocked and current flow is interrupted. Accordingly, the voltage of the secondary battery can be rapidly increased to reach the end voltage, and the overcharge can be quickly terminated, thereby preventing ignition or explosion of the battery.

The compound represented by Formula 1 and / or Formula 2 may be contained in an amount of 80 to 100 parts by weight based on 100 parts by weight of the overcharge preventing layer. If the amount of the compound is less than 80 parts by weight based on 100 parts by weight of the overcharge preventing layer, the effect of generating gas at a high voltage of 4.4 V or higher due to the formation of the overcharge preventing layer is insignificant, .

On the other hand, the over-discharge preventing layer may further include a conductive material or a binder optionally.

When the over-current protection layer further includes a conductive material, the conductive material may be, for example, graphite such as natural graphite or 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 conductive polymers such as polyphenylene derivatives, and the like, and may include at least one of these.

The conductive material may further include 0.1 to 10 parts by weight, preferably 5 to 10 parts by weight, based on 100 parts by weight of the overcharge preventing layer.

If the over-charge protection layer further comprises a binder, the binder may be, for example, polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, Polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene - diene polymer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluorine rubber, or various copolymers thereof, and may include at least one of these. The binder may further comprise 0.1 to 10 parts by weight, preferably 5 to 10 parts by weight, based on 100 parts by weight of the overcharge preventing layer.

The thickness of the overcharge preventing layer may be 0.1 탆 to 10 탆, preferably 0.1 탆 to 3 탆. For example, when the thickness of the overcharge preventing layer satisfies the above range, it is possible to uniformly form the overcharge preventing layer while minimizing loss of the energy density of the electrode.

Further, the positive electrode according to the present invention includes a positive electrode active material layer formed on the overcharge preventing layer. The cathode active material layer may further include a conductive material and a binder optionally together with the cathode active material.

As the cathode active material, compounds capable of reversible intercalation and deintercalation of lithium may be used. The cathode active material may be a layered compound such as lithium cobalt oxide [Li _{x 1} CoO ₂ (0.5 <x 1 <1.3)], lithium nickel oxide [Li _{x 2} NiO ₂ (0.5 <x 2 <1.3)] or an additional transition metal &Lt; / RTI &gt; Lithium manganese oxides such as Li _{1 + x 3} Mn _{2 - x 3} O ₄ (where 0? X _3? 0.33), LiMnO ₃ , LiMn ₂ O ₃ , or Li _{x 4} MnO ₂ (0.5 <x4 <1.3); Lithium copper oxide (Li ₂ CuO ₂ ); Vanadium oxides such as LiV ₃ O ₈ , V ₂ O ₅ , or Cu ₂ V ₂ O ₇ ; In formula ^{_{LiNi 1-x5 M 1 x5 O}} 2 ( where, M ¹ is being Co, Mn, Al, Cu, Fe, Mg, B and is at least one or more selected from the group consisting of Ga, 0.01≤x5≤0.5) A lithium nickel complex oxide represented by; Formula ₂ LiMn _{- x6 x6} M ² O ₂ (wherein, M ² is Co, Ni, and Fe, Cr, at least one or more selected from the group consisting of Zn and Ta, 0.01≤x6≤0.1 Im) or Li ₂ Mn ₃ M ³ O ₈ (wherein M ³ is at least one selected from the group consisting of Fe, Co, Ni, Cu and Zn); Formula ^{_{LiFe 1 - x7 M 4 x7 PO}} 4 ( where, M ⁴ is selected from the group consisting of Al, Mg, Ni, Co, Mn, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn , and Y And 0? X7? 0.5); LiMn ₂ O _{4 in} which a part of Li in the formula is substituted with an alkaline earth metal ion; Disulfide compounds; Fe ₂ (MoO ₄ ) ₃ . The cathode active material may preferably be a lithium nickel complex oxide, more preferably lithium nickel cobalt manganese oxide. For example, when a lithium nickel cobalt manganese oxide is used, a positive electrode having a high capacity characteristic can be produced.

For example, the positive electrode active material may be contained in an amount of 40 to 99.9 parts by weight, preferably 60 to 99.8 parts by weight based on 100 parts by weight of the positive electrode active material layer.

The conductive material contained in the positive electrode active material layer can be used without particular limitation as far as it does not cause chemical change and has electronic conductivity. For example, graphite such as natural graphite or 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 conductive polymers such as polyphenylene derivatives, and the like, and may include at least one of these.

The conductive material may be added in an amount of 0.1 to 30 parts by weight, preferably 1 to 20 parts by weight, more preferably 1 to 10 parts by weight based on 100 parts by weight of the cathode active material layer. When the conductive material is included in the positive electrode active material layer in an amount of 0.1 to 30 parts by weight, the resistance reduction effect of the secondary battery including the conductive material can be achieved.

The binder serves to improve adhesion between the positive electrode active material particles and adhesion of the overcharge preventing layer and the positive electrode active material layer. 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, or various copolymers thereof, and the like, and may include at least one of these. The binder may be included in an amount of 1 to 30% by weight based on the total weight of the cathode active material layer.

The thickness of the cathode active material layer may be 50 탆 to 150 탆, preferably 100 탆 to 125 탆. For example, when the thickness of the cathode active material layer satisfies the above range, the packing density of the electrode can be ensured and the cathode active material layer can be formed without loss of energy density.

The positive electrode may be manufactured according to a conventional positive electrode manufacturing method, except that the positive electrode active material described above is used. Specifically, the cathode active material and optionally the binder and the conductive material may be dissolved or dispersed in a solvent to prepare a composition for forming a cathode active material layer, which is then applied onto the cathode current collector, followed by drying and rolling.

Examples of the solvent include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, and the like. Water and the like, and at least one or more of them may be used. The amount of the solvent to be used is sufficient to dissolve or disperse the cathode active material, the conductive material and the binder in consideration of the coating thickness of the slurry and the yield of the slurry, and then to have a viscosity capable of exhibiting excellent thickness uniformity Do.

Alternatively, the positive electrode may be produced by casting the composition for forming the positive electrode active material layer on a separate support, and then laminating a film obtained by peeling from the support onto the positive electrode collector.

In addition, the present invention can produce an electrochemical device including the positive electrode. The electrochemical device may be specifically a battery, a capacitor, or the like, and more specifically, it may be a lithium secondary battery.

Specifically, the lithium secondary battery includes a positive electrode, a negative electrode disposed opposite to the positive electrode, and a separation membrane and an electrolyte interposed between the positive electrode and the negative electrode. The positive electrode is the same as that described above, Only the remaining configuration will be described in detail below.

The lithium secondary battery may further include a battery container for housing the electrode assembly of the anode, the cathode, and the separator, and a sealing member for sealing the battery container.

In the lithium secondary battery, 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.

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 capable of doping and dedoping lithium such as SiO? (0 <? <2), SnO ₂ , vanadium oxide, and lithium vanadium oxide; 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 negative electrode active material may include 80% by weight to 99% by weight based on the total weight of the negative electrode active material layer.

The binder is a component for assisting the bonding between the conductive material, the active material and the current collector, and is usually added in an amount of 0.1% by weight to 10% by weight based on the total weight of the negative electrode active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene Examples thereof include ethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluorine rubber and various copolymers thereof.

The conductive material may be added in an amount of 10 wt% or less, preferably 5 wt% or less, based on the total weight of the negative electrode active material layer, as a component for further improving the conductivity of the negative 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 black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskey such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used.

For example, the negative electrode active material layer is prepared by applying and drying a composition for forming a negative electrode active material layer, which is prepared by dissolving or dispersing a negative electrode active material on a negative electrode current collector, and optionally a binder and a conductive material in a solvent, Casting a composition for forming an active material layer on a separate support, and then laminating a film obtained by peeling from the support onto a negative electrode current collector.

The negative electrode active material layer may be formed by applying and drying a composition for forming a negative electrode active material layer prepared by dissolving or dispersing a negative electrode active material on a negative electrode collector and optionally a binder and a conductive material in a solvent, Casting the composition on a separate support, and then peeling the support from the support to laminate a film on the negative electrode current collector.

Meanwhile, in the lithium secondary battery, the separation membrane separates the cathode and the anode and provides a passage for lithium ion. The separation membrane can be used without any particular limitation as long as it is used as a separation membrane 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 the separator may be selectively used as a single layer or a multilayer structure.

Examples of the electrolyte used in the present invention include an organic 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 linear, branched or cyclic hydrocarbon group having 2 to 20 carbon atoms, 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. Among these, a carbonate-based solvent is preferable, and a cyclic carbonate (for example, ethylene carbonate or propylene carbonate) having a high ionic conductivity and a high dielectric constant, for example, such as ethylene carbonate or propylene carbonate, For example, ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate) is more preferable. 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, since the lithium secondary battery including the cathode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics and life characteristics, it can be used in portable devices such as mobile phones, notebook computers, digital cameras, and hybrid electric vehicles hybrid electric vehicle (HEV)).

According to another embodiment of the present invention, there is provided a battery module including the lithium secondary battery as a unit cell and a battery pack including the same.

The battery module or the battery pack may include a power tool; An electric vehicle including an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); Or a power storage system, as shown in FIG.

The external shape of the lithium secondary battery of the present invention is not particularly limited, but may be a cylindrical shape, a square shape, a pouch shape, a coin shape, or the like using a can.

The lithium secondary battery according to the present invention can be used not only in a battery cell used as a power source of a small device but also as a unit cell in a middle- or large-sized battery module including a plurality of battery cells.

Hereinafter, the present invention will be described in detail by way of examples with reference to the following examples. However, the embodiments according to the present invention can be modified into various other forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. The embodiments of the present invention are provided to enable those skilled in the art to more fully understand the present invention.

Example

Example 1

Li ₂ MnO ₃ , a Denka Black conductive material, and a PVdF binder in a weight ratio of 8: 1: 1 in N-methyl pyrrolidone (NMP) solvent to prepare a slurry for an overcharge preventing layer.

Separately, LiNi _{0 . 6} Mn _{0 . 2} Co _{0 . 2} O ₂ cathode active material, Denka Black conductive material, and polyvinylidene fluoride (PVdF) binder were mixed in a NMP solvent at a weight ratio of 92.5: 3.5: 4 to prepare a cathode active material slurry.

The slurry for anti-overcharge protection layer prepared above was coated on an aluminum foil having a thickness of 20 mu m and dried to form a 3 mu m-thick positive electrode overcharge preventing layer. Next, the above-prepared slurry of the positive electrode active material was coated on the over-charge preventing layer, dried, and rolled to produce a positive electrode having a positive electrode active material layer having a thickness of 125 mu m on the over-charge preventing layer.

On the other hand, a graphite negative electrode active material, an acetylene black conductive material, and a polyvinylidene fluoride binder were mixed at a weight ratio of 96.5: 0.5: 3 and added to distilled water as a solvent to prepare an anode slurry. The negative electrode slurry was applied to a copper foil having a thickness of 8 占 퐉, dried and then rolled to produce a negative electrode.

The prepared positive electrode and negative electrode were laminated together with a polyethylene separator to prepare an electrode assembly. The electrode assembly was placed in a battery case, and a mixed solvent of ethylene carbonate: ethyl methyl carbonate: dimethyl carbonate in a weight ratio of 3: 3: of injecting a liquid electrolyte was LiPF ₆ was dissolved, to thereby prepare a lithium secondary battery.

Example 2

Instead of Li ₂ MnO ₃ used in Example _{1 . 1} Ni _{0 . 45} Co _{0 . 20} Mn _{0 . 35} O ₂ was used as a positive electrode, and a lithium secondary battery including the positive electrode was prepared in the same manner as in Example 1 above.

Comparative Example 1

A lithium secondary battery was produced in the same manner as in Example 1, except that the anode active material slurry prepared in Example 1 was applied on an aluminum foil having a thickness of 20 탆, dried, and then rolled to produce a positive electrode. .

Comparative Example 2

LiNi _{0 . 6} Mn _{0 . 2} Co _{0 . 2} O ₂ cathode active material, an acetylene black conductive material, a polyvinyl fluoride binder, and Li ₂ MnO ₃ in a weight ratio of 90: 3.5: 4: 2.5 in N-methylpyrrolidone solvent to prepare a cathode active material slurry.

A lithium secondary battery was prepared in the same manner as in Example 1, except that the cathode active material slurry prepared above was coated on an aluminum foil having a thickness of 20 탆, dried, and roll-pressed to prepare a positive electrode.

Experimental Example 1: Disintegration test of the overcharge preventing layer

Using the lithium secondary batteries prepared in Examples 1 and 2, it was confirmed whether or not the overcharge preventing layer was decomposed at a high voltage. Specifically, the lithium secondary batteries prepared in Examples 1 and 2 were charged to 4.25 V and 4.45 V under 0.1 C and 0.05 C cut off conditions, respectively, and then subjected to XRD analysis and gas chromatograph-mass spectrometer GC-MS) were used to calculate the oxygen content of the overcharge preventing layer of the lithium secondary battery charged at 4.25 V and 4.45 V, respectively.

In this connection, FIG. 1 shows the ratio of the three-component content of the overcharge preventing layer of the lithium secondary battery packed at 4.45 V when the oxygen content of the overcharge preventing layer of the rechargeable lithium secondary battery is set to 100% at 4.25 V.

As shown in FIG. 1, the oxygen content of the overcharge preventing layer in the lithium secondary battery charged at 4.45 V was lower than that of the lithium secondary battery charged at 4.25 V, And that it has occurred.

Experimental Example 2: Overcharge Test

An overcharging test was conducted using the lithium secondary batteries prepared in Example 1 and Comparative Examples 1 and 2.

Specifically, the lithium secondary battery manufactured in Example 1 and Comparative Example 1 was charged and discharged once with 0.1 C to 4.25 V at 0.05 C cut off, and then allowed to stand for 0.5 hour to stabilize the voltage. After the cell voltage was stabilized, the voltage change according to capacity was measured while overcharging to 5V at 1C. The measurement results are shown in Fig.

Referring to FIG. 2, when the charging voltage of the lithium secondary battery is 4.4 V or more, it can be seen that the voltage rises sharply, indicating that the resistance has increased sharply. The voltage rise of the lithium secondary battery of Example 1 and the lithium secondary battery of Comparative Example 1 occurred at a voltage of 4.4 V or more, but the voltage rise of the lithium secondary battery of Example 1 was steeper than that of the lithium secondary battery of Comparative Example 1 It can be seen that the lithium secondary battery of Example 1 reaches the overcharge end voltage more quickly than the lithium secondary battery of Comparative Example 1. [

On the other hand, the lithium secondary battery manufactured in Comparative Example 2 was charged and discharged once at 0.1 C to 4.25 V at 0.05 C cut off, and then allowed to stand for 0.5 hour to stabilize the voltage. After the cell voltage was stabilized, the voltage change over time was measured while overcharging to 5V at 1C. The measurement results are shown in Fig.

As shown in FIG. 3, the lithium secondary battery manufactured in Comparative Example 2 showed a sharp rise in voltage at a high voltage of 4.4 V or higher, and a gradual increase in voltage when it was close to 5 V. As a result, it was confirmed that the lithium secondary battery manufactured in Comparative Example 2 did not reach the overcharge end voltage, and there is a possibility that the charge / discharge is additionally performed in the vicinity of 5V.

Claims (8)

Anode collector;
An overcharge preventing layer formed on the positive electrode current collector and containing at least one of the following compounds represented by the following Chemical Formulas 1 and 2; And
And a positive electrode active material layer formed on the overcharge preventing layer,
[Chemical Formula 1]
Li ₂ MnO ₃
(2)
Li _{x 1} Ni _a Co _b Mn _c O ₂
1.10? X1? 1.30, 0.45? A? 0.55, 0.05? B? 0.2, 0.30? C? 0.50).
The method according to claim 1,
Wherein the compound represented by Chemical Formula 1 and Chemical Formula 2 is dissociated at a high voltage of 4.4 V or higher to generate a gas.
3. The method of claim 2,
Wherein the high voltage is 4.4V to 12V.
The method according to claim 1,
Wherein in the formula (2), x1 / (a + b + c) ≥1.1 and a: c is 1: (0.9-1.9).
The method according to claim 1,
Wherein the overcharge preventing layer further comprises a conductive material or a binder.
The method according to claim 1,
Wherein the thickness of the overcharge preventing layer is 0.1 占 퐉 to 10 占 퐉.
The method according to claim 1,
Wherein the thickness of the cathode active material layer is 50 占 퐉 to 150 占 퐉.
A cathode according to any one of claims 1 to 7; cathode; And a separator interposed between the anode and the cathode; And an electrolyte.

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