KR20160059948A - Positive active material for rechargeable lithium battery, and positive active material layer and rechargeable lithium battery including the same - Google Patents

Abstract

Provided are a positive electrode active material for a lithium secondary battery, a positive electrode active material layer comprising the same, and a lithium secondary battery. The positive electrode active material for a lithium secondary battery comprises: core particles; and a coating layer surrounding the core particles, wherein the core particles comprise lithium nickel-based oxide particles including a nickel-contained metal and lithium. The lithium nickel-based oxide particles comprise nickel of 80 atom% or more with respect to the total atomic weight of the nickel-contained metal, the coating layer comprises metal sulfide mixed to a surface of the core particles, and the metal sulfide has a layer structure.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a positive electrode active material for a lithium secondary battery, a positive electrode active material layer containing the same, a lithium secondary battery having the positive active material layer,

A cathode active material layer for a lithium secondary battery, a cathode active material layer containing the same, and a lithium secondary battery.

BACKGROUND ART [0002] Lithium transition metal complex oxides (hereinafter referred to as "high nickel complex oxides") containing nickel (Ni) as a main component are attracting much attention due to their being a cathode active material having relatively high potential and high capacity.

Accordingly, various cathode active materials using a high nickel complex oxide have been proposed.

However, a lithium ion secondary battery including a high-nickel-based composite oxide as a cathode active material has a problem in that the thermal stability at the time of charging deteriorates. Specifically, there has been a problem that the amount of heat generated during charging becomes very large. This is presumably because the stability of trivalent nickel is deteriorated at the time of charging and nickel dioxide (NiO ₂ ) releases oxygen to become stable nickel oxide (NiO).

One embodiment is to provide a positive electrode active material for a lithium secondary battery which improves the thermal stability at the time of charging while ensuring the discharge capacity of the battery.

Another embodiment is to provide a cathode active material layer comprising the cathode active material.

Another embodiment is to provide a lithium secondary battery comprising the cathode active material layer.

One embodiment includes core particles; And a coating layer surrounding the core particle, wherein the core particle comprises a lithium-nickel-based oxide particle including a nickel-containing metal and lithium, and the lithium-nickel-based oxide particle comprises nickel At least 80 atomic%, and the coating layer comprises a metal sulfide compounded on the surface of the core particle, and the metal sulfide has a layered structure.

The core particle may include a lithium nickel oxide particle represented by the following formula (1).

[Chemical Formula 1]

Li _a Ni _x Co _y M _z O ₂

(In the formula 1,

M is at least one element selected from the group consisting of Al, Mn, Cr, Fe, V, Mg, Ti, At least one metal selected from tungsten (W), copper (Cu), zinc (Zn), gallium (Ga), indium (In), tin (Sn), lanthanum (La), and cerium (Ce)

0.2? A? 1.2, 0.8? X <1, 0 <y? 0.2, 0? Z? 0.1, x + y + z =

The metal sulfide may have a structure in which unit structures are stacked, and the unit structure may include a plurality of sulfur atoms and a metal atom layer disposed between the sulfur atoms.

The metal sulfide may include at least one selected from molybdenum sulfide, tungsten sulfide, and titanium sulfide.

The metal sulfide may be crystalline.

The metal sulfide may be contained in an amount of 1 wt% to 5 wt% based on 100 wt% of the core particles.

Another embodiment provides a cathode active material layer for a lithium secondary battery comprising the cathode active material.

Another embodiment provides a lithium secondary battery comprising the cathode active material layer.

The details of other embodiments are included in the detailed description below.

The thermal stability at the time of charging can be improved while securing the discharge capacity of the lithium secondary battery using the high-nickel-based composite oxide.

1 is a cross-sectional view showing a schematic configuration of a lithium secondary battery according to one embodiment.
2 is a schematic view showing a configuration of a cathode active material for a lithium secondary battery according to one embodiment.
3 is a schematic view showing a structure of a metal sulfide constituting a part of a cathode active material according to an embodiment.
4 is a differential scanning calorimetry (DSC) graph of Example 2 and Comparative Example 1. Fig.
5 is a scanning electron microscope (SEM) photograph of the cathode active material according to Example 1. Fig.
6 is an energy dispersive X-ray analysis (EDS) image of Ni atoms in the cathode active material according to Example 1. FIG.
7 is an energy dispersive X-ray analysis (EDS) image of the S atom in the cathode active material according to Example 1. FIG.
FIG. 8 is an energy dispersive X-ray analysis (EDS) image of Mo atoms in the cathode active material according to Example 1. FIG.

Hereinafter, embodiments of the present invention will be described in detail. However, it should be understood that the present invention is not limited thereto, and the present invention is only defined by the scope of the following claims.

It is to be understood that where a layer, film, region, plate, or the like is referred to as being "on" another portion, unless stated otherwise in this specification, .

Hereinafter, a lithium secondary battery according to one embodiment will be described with reference to FIG.

1 is a cross-sectional view showing a schematic configuration of a lithium secondary battery according to one embodiment.

1, the lithium secondary battery 10 includes an anode 20, a cathode 30, and a separator layer 40. The shape of the lithium secondary battery 10 is not particularly limited and may be, for example, a cylindrical shape, a square shape, a laminate shape, a button shape, or the like.

The anode 20 includes a current collector 21 and a cathode active material layer 22 formed on the current collector 21.

The current collector 21 may include, but is not limited to, aluminum.

The cathode active material layer 22 includes a cathode active material, and may further include at least one of a conductive material and a binder.

Hereinafter, the positive electrode active material will be described with reference to FIG. 2. However, the positive electrode active material is not limited to the structure of FIG.

2 is a schematic view showing a configuration of a cathode active material for a lithium secondary battery according to one embodiment.

2, the cathode active material 22a may include core particles 22b and a coating layer 22c surrounding the core particles 22b.

The core particles 22b are not particularly limited as long as they can be used as a cathode active material for a lithium secondary battery. For example, lithium nickel oxide particles can be used.

The lithium nickel-based oxide particles include a nickel-containing metal and lithium, and may contain, for example, 80 at% or more of nickel relative to the total atomic weight of the nickel-containing metal. In other words, the lithium nickel oxide particles may be a high nickel composite oxide.

The core particle may be, for example, a lithium nickel oxide particle represented by the following formula (1).

[Chemical Formula 1]

Li _a Ni _x Co _y M _z O ₂

Wherein M is at least one element selected from the group consisting of Al, Mn, Cr, Fe, V, Mg, Ti, Zr, Nb, Mo, W, Cu, Zn, Ga, In, Sn, La, and Ce. At least one metal and 0.2 = a? 1.2, 0.8? X <1, 0 <y? 0.2, 0? Z? 0.1, x + y + z =

The coating layer 22c is a layer surrounding the core particles 22b and may include a metal sulfide compounded on the surface of the core particles 22b.

The metal sulfide may have a layer structure. When the positive electrode active material formed by compounding the metal sulfide having such a layer structure on the surface of the core particles is used for the lithium secondary battery, in contrast to the case where the metal sulfide is simply included in the core 22b without forming a layer structure, Can be greatly improved.

The layer structure of the metal sulfide will be described with reference to FIG.

3 is a schematic view showing a structure of a metal sulfide constituting a part of a cathode active material according to an embodiment.

Referring to FIG. 3, the metal sulfide may have a structure in which a plurality of unit structures 24 are stacked. Each of the unit structures 24 may include a plurality of sulfur atoms 25 and a metal atom layer 26 located between the sulfur atoms 25. The sulfur atom layer 25 may be composed of a sulfur atom 25a. The metal atom layer 26 may be composed of metal atoms 26a. Each metal atom 26a may be combined with the sulfur atom 25a.

The metal sulfide having the above structure may have a structure similar to graphite.

These metal sulfides are thermally very stable. For example, the melting point of the metal sulfide may be 1000 ° C or higher. As an example of the metal sulfide, the melting point of molybdenum sulfide may be 1185 캜, and the melting point of tungsten sulfide may be 1250 캜.

The interaction between the unit structures 24 is weak and slippery. Since the metal sulfide unit structure having such a layer structure is easily slipped, when the positive electrode active material formed by compounding on the surface of the core particles is used for the lithium secondary battery, the density of the electrode can be improved.

The metal sulfide may also have a semiconductor level of conductivity.

By compounding the metal sulfide having such structural characteristics on the surface of the core particles 22b, the thermal stability at the time of filling the lithium secondary battery 10 can be improved.

Examples of the metal sulfide include at least one selected from molybdenum sulfide (MoS ₂ ), tungsten sulfide (WS ₂ ) and titanium sulfide (TiS ₂ ). The molybdenum sulfide, tungsten sulfide and titanium sulfide may all have the same structure as shown in Fig. Of these, molybdenum sulfide and tungsten sulfide, which are easier to handle, can be used.

The metal sulfide may be crystalline. When the crystalline metal sulfide is used, the thermal stability upon filling of the core particles 22b can be further improved.

In the complexation of the metal sulfide on the surface of the core particles, the method of the complexation is not particularly limited. For example, the metal sulfide may be compounded on the surface of the core particles 22b by dry-compounding, or may be compounded on the surface of the core particles 22b by wet-compounding such as spray coating or the like.

The metal sulfide may be compounded on the surface of the core particle at 1 wt% to 5 wt% with respect to 100 wt% of the core particles, for example, 2 wt% to 5 wt%. When the metal sulfide is compounded within the above content range, sufficient thermal stability and discharge capacity of the lithium secondary battery can be secured at the same time.

Hereinafter, a method for producing the positive electrode active material will be described.

First, a method for producing a lithium nickel oxide particle corresponding to one example of the core particle will be described. The method for producing the lithium nickel oxide particles is not particularly limited, and for example, coprecipitation may be used.

Hereinafter, a method for producing lithium nickel oxide particles using the coprecipitation method is described, and only one example of the production method is described. However, the mixing amount, raw materials and the like are not limited thereto.

First, a mixed aqueous solution is prepared by dissolving nickel sulfate hexahydrate (NiSO ₄ .6H ₂ O), cobalt sulfate pentahydrate (CoSO ₄ .5H ₂ O), and metal (M) containing compound in ion exchange water. At this time, the total weight of the nickel sulfate hexahydrate, the cobalt sulfate tetrahydrate and the metal (M) -containing compound may be, for example, about 20% by weight based on the total weight of the mixed aqueous solution. Further, the nickel sulfate hexahydrate, the cobalt sulfate hydrate and the metal (M) -containing compound may be mixed so that the molar ratio of each element of Ni, Co and M is a desired value. On the other hand, the molar ratio of each element is determined according to the composition of the lithium nickel-based oxide to be produced, for example, LiNi _{0 . 85} Co _{0 . 1} Al _{0 . 05} O ₂ , the molar ratio of the elements Ni: Co: Al is 85: 10: 5.

The metal element M in the metal (M) -containing compound is at least one element selected from the group consisting of aluminum (Al), manganese (Mn), chromium (Cr), iron (Fe), vanadium (V), magnesium (Mg), titanium ), Niobium (Nb), molybdenum (Mo), tungsten (W), copper (Cu), zinc, gallium, indium, tin, lanthanum and cerium ). &Lt; / RTI &gt; Examples of the metal (M) -containing compound include various salts, oxides and hydroxides of the metal element M such as sulfate and nitrate.

Further, a predetermined amount, for example, 500 ml of ion-exchanged water is added to the reaction layer, and the temperature is maintained at 50 占 폚. Hereinafter, the aqueous solution in the reaction layer is referred to as a reaction layer aqueous solution. Subsequently, the ion-exchange water is bubbled by an inert gas such as nitrogen to remove dissolved oxygen. Subsequently, the ion-exchanged water in the reaction layer is stirred, and while the temperature of the ion-exchanged water is maintained at 50 캜, the above-mentioned mixed aqueous solution is added dropwise to the ion-exchanged water. In addition, saturated NaCO ₃ aqueous solution is added to ion-exchanged water in an excess amount to Ni, Co and Al of the aqueous mixed solution. On the other hand, during the dropwise addition, the pH of the reaction layer aqueous solution is maintained at 11.5 and the temperature is maintained at 50 ° C. The dropping rate of the mixed aqueous solution and the saturated aqueous NaCO ₃ solution is not particularly limited, but may be, for example, about 3 ml / min, and the dropping time is, for example, about 10 hours. As a result, the hydroxide salt of each metal element coprecipitates.

Subsequently, the solid-liquid separation, for example, suction filtration is carried out, the coprecipitation hydroxide salt is taken out from the reaction layer aqueous solution, and the coprecipitated hydroxide salt taken out is washed with ion exchange water. Then, the coprecipitation hydroxide salt is vacuum-dried at about 100 DEG C for about 10 hours, for example.

Then, the coprecipitate salt after drying is pulverized with a mortar for several minutes to obtain a dry powder, and then the dry powder and lithium hydroxide (LiOH) are mixed to produce a mixed powder. At this time, the molar ratio of Li to Ni, Co and M (Ni + Co + M = Me) is determined according to the composition of the lithium nickel oxide. For example, LiNi _{0 . 85} Co _{0 . 1} Al _{0 . 05} O ₂ , the molar ratio of Li: Me to Li and Me is 1: 1.

Then, the lithium nickel-based oxide particles can be produced by firing the mixed powder. Since nickel atoms in the mixed powder are liable to be reduced, firing can be performed in an oxidizing atmosphere. The oxidizing atmosphere may be, for example, an oxygen atmosphere. The firing time and firing temperature can be arbitrarily controlled, and can be performed, for example, at about 700 ° C. to 800 ° C. for about 10 hours.

Next, the surface of the prepared core particles is compounded with a metal sulfide to form a coating layer.

The method of the compounding is not particularly limited. For example, the metal sulfide may be compounded on the surface of the core particle by dry-compounding, or may be compounded on the surface of the core particle by wet-compounding such as spray coating or the like.

The dry complexation can be carried out, for example, by the following process. The core particles and the metal sulfide are added to a powder particle treatment apparatus NOBILTA MINI (NOB-MINI) manufactured by a dry particle hybridization apparatus such as Hosokawa Micron Corporation at a weight ratio of 1: 0.01 to 1: 0.05 , At a peripheral speed of 1000 rpm to 4000 rpm, and for a drive time of 5 minutes to 15 minutes, whereby the metal sulfide can be compounded on the surface of the core particles.

The wet-compounding may be performed, for example, by the following process. First, a slurry for spray coating is prepared. As the dispersion medium of the slurry, other than water, for example, alcohol, ketone, toluene and the like can be mentioned. The metal sulfide is added to the dispersion medium, and the metal sulfide is dispersed in the dispersion medium by stirring the dispersion medium or irradiating ultrasonic waves to the dispersion medium. Then, the slurry and the core particles are put into a spray coating apparatus, for example, a tumbling fluidized bed granulating-coating machine (MP-01) manufactured by Powrex Corporation. At this time, the weight ratio of the core particles to the metal sulfides in the slurry may be in a weight ratio of 1: 0.01 to 1: 0.05. Subsequently, by driving the spray coating apparatus, the metal sulfide can be compounded on the surface of the core particles.

The cathode active material can be produced by the above process.

The content of the positive electrode active material in the positive electrode active material layer is not particularly limited and may be any value as long as it is applied to the positive electrode active material layer of the lithium secondary battery.

The conductive material may include carbon black such as ketjen black and acetylene black, natural graphite, and artificial graphite. However, the conductive material is not particularly limited as long as it enhances the conductivity of the anode.

The content of the conductive material is not particularly limited, and any content can be used as long as it is applied to the positive electrode active material layer of the lithium secondary battery.

Examples of the binder include polyvinylidene fluoride, ethylene-propylene-diene terpolymer, styrene-butadiene rubber, acrylonitrile-butadiene rubber, fluororubber, polyvinylacetate, polymethylmethacrylate, polyethylene, Nitrocellulose, and the like, but is not particularly limited as long as it can bind the positive electrode active material and the conductive material on the current collector.

The content of the binder is not particularly limited, and any content can be used as long as the content is applied to the positive electrode active material layer of the lithium secondary battery.

The anode (20) can be manufactured as follows. First, the above-mentioned mixture of the cathode active material, the conductive material and the binder in a desired ratio is dispersed in an organic solvent such as N-methyl-2-pyrrolidone to form a slurry. Then, the slurry is coated on the current collector 21 and dried to form the positive electrode active material layer 22. At this time, the coating method is not particularly limited, and for example, a knife coater method, a gravure coater method, or the like can be used. Subsequently, the positive electrode 20 can be manufactured by compressing the positive electrode active material layer 22 to a desired thickness by a compressor. The thickness of the positive electrode active material layer 22 is not particularly limited and may be a thickness of the positive electrode active material layer of the lithium secondary battery.

The step of applying the positive electrode active material 22a on the current collector may be performed under a drying environment of a dew point temperature of -40 DEG C or less with a low moisture content. If water or the like adheres to the cathode active material particles, LiOH and Li ₂ CO _{3 on the} surface of the cathode active material may react with moisture or the like during the high-temperature storage, thereby possibly generating gas.

The cathode 30 includes a current collector 31 and a negative electrode active material layer 32 formed on the current collector 31.

The current collector 31 may include, for example, copper (Cu), nickel (Ni), or the like.

The negative electrode active material layer 32 may be any material as long as it is used as a negative electrode active material layer of a lithium secondary battery. For example, the negative electrode active material layer 32 includes a negative electrode active material, and may further include a binder.

The negative electrode active material may be a carbon-based material, a silicon-based material, a tin-based material, a lithium metal oxide, a metal lithium, or the like, or a mixture of two or more thereof. The carbon-based material may be, for example, graphite based materials such as artificial graphite, natural graphite, a mixture of artificial graphite and natural graphite, and natural graphite coated with artificial graphite. The silicon-based material may be, for example, silicon, a silicon oxide, a silicon-containing alloy, or a mixture of these with a graphite-based material. The silicon oxide may be represented by SiOx (0 < x? 2). The silicon-containing alloy is an alloy in which the content of silicon is the greatest among all the metal elements with respect to the total amount of the alloy, and examples thereof include Si-Al-Fe alloys. The tin-based material may be, for example, tin, tin oxide, a tin-containing alloy, a mixture thereof with a graphite-based material, or the like. The lithium metal oxide includes, for example, a titanium oxide-based compound such as Li ₄ Ti ₅ O ₁₂ . According to one embodiment, when the graphite is used, the cycle life characteristics of the lithium secondary battery can be further improved.

The binder is not particularly limited, and the same binder as that used in the positive electrode may be used.

The weight ratio of the negative electrode active material to the binder is not particularly limited and may be used in a weight ratio used in a conventional lithium secondary battery.

The cathode 30 may be manufactured as follows. The negative electrode active material and the binder are mixed in a desired ratio and dispersed in an organic solvent such as N-methyl-2-pyrrolidone to prepare a slurry. Then, the slurry is coated on the current collector 31 and dried to form the negative electrode active material layer 32. Next, Subsequently, the negative electrode active material layer 32 is compressed to a desired thickness by a compressor, whereby the negative electrode 30 can be manufactured. The thickness of the negative electrode active material layer 32 is not particularly limited and may be the thickness of the negative electrode active material layer of the lithium secondary battery. When metal lithium is used as the negative electrode active material layer 32, a metal lithium foil can be overlapped on the current collector 31. [

The separator layer 40 may include a separator and an electrolytic solution.

The separator is not particularly limited, and any separator may be used as long as it is used as a separator of a lithium secondary battery. For example, a porous film or nonwoven fabric exhibiting excellent high rate discharge performance can be used singly or in combination.

For example, the substrate constituting the raw material of the separator may be, for example, a polyolefin resin, a polyester resin, a polyvinylidene difluoride (PVDF), a vinylidene difluoride-hexafluoropropylene copolymer, Vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene difluoride-trifluoroethylene copolymer, vinylidene difluoride-fluoroethylene copolymer, vinylidene difluoride-fluoroethylene copolymer, vinylidene difluoride- Vinylidene fluoride-vinylidene difluoride-trifluoroethylene copolymer, vinylidene difluoride-hexafluoroacetone copolymer, vinylidene difluoride-ethylene copolymer, vinylidene difluoride-propylene copolymer, vinylidene difluoride-trifluoropropylene copolymer, Rye-tetrafluoroethylene-hexafluoropropylene copolymer, vinylidene difluoride-ethylene -Tetrafluoroethylene copolymer, and the like. Examples of the polyolefin-based resin include polyethylene and polypropylene. Examples of the polyester-based resin include polyethylene terephthalate and polybutylene terephthalate.

The porosity of the separator is not particularly limited, and the porosity of the separator of the lithium secondary battery can be arbitrarily applied.

The separator may include a coating layer formed on at least one side of the substrate and including an inorganic filler. The inorganic filler may include Al ₂ O ₃ , Mg (OH) ₂ , SiO ₂ , and the like. The coating layer containing the inorganic filler may prevent direct contact between the positive electrode and the separator base material, prevent oxidation and decomposition of the electrolyte generated on the surface of the positive electrode when stored at high temperature, and inhibit generation of gas which is a decomposition product of the electrolyte solution.

 The coating layer containing the inorganic filler may be formed on only one side of the base material of the separator, or on both sides of the base material of the separator. When the coating layer is formed on at least the anode-side substrate, direct contact between the anode and the electrolyte can be prevented.

On the other hand, the coating layer containing the inorganic filler is not limited to be formed in the separator but may be formed on the anode. When a coating layer containing an inorganic filler is formed on both surfaces of the anode, direct contact between the anode and the separator can be prevented.

In addition, the coating layer containing the inorganic filler may be formed on both the substrate of the separator and the anode.

The coating layer containing the inorganic filler may further include a binder such as polyvinylidene fluoride or the like.

The electrolytic solution may have a composition containing an electrolytic salt in a non-aqueous solvent.

Examples of the non-aqueous solvent include cyclic carbonates such as propylene carbonate, ethylene carbonate, butylene carbonate, chloroethylene carbonate and vinylene carbonate; Chain carbonates such as dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate; cyclic esters such as? -butyrolactone and? -valerolactone; Chain esters such as methyl formate, methyl acetate and butyric acid methyl; Tetrahydrofuran or a derivative thereof; Ethers such as 1,3-dioxane, 1,4-dioxane, 1,2-dimethoxyethane, 1,4-dibutoxyethane and methyl diglyme; Nitriles such as acetonitrile and benzonitrile; Dioxolane or derivatives thereof; Ethylene sulfide, sulfolane, sultone or a derivative thereof may be used alone or as a mixture of two or more thereof, but is not limited thereto.

The electrolyte salt may be, for _{example, LiClO 4, LiBF 4, LiAsF} 6, LiPF 6, LiPF 6 - x (CnF 2n + 1) x (1 <x <6, n = 1 or 2), LiSCN, LiBr, LiI, Li ₂ SO _4, Li ₂ B ₁₀ Cl _10, NaClO _4, NaI, NaSCN, NaBr, KClO _4, an inorganic ion salt containing lithium, sodium or potassium, such as one type of KSCN; _{LiCF 3 SO 3, LiN (CF} 3 SO 2) 2, LiN (C 2 F 5 SO 2) 2, LiN (CF 3 SO 2) (C 4 F 9 SO 2), LiC (CF 3 SO 2) 3, _{LiC (C 2 F 5 SO 2} ) 3, (CH 3) 4 NBF 4, (CH 3) 4 NBr, (C 2 H 5) 4 NClO 4, (C 2 H 5) 4 NI, (C 3 H 7 _{) 4 NBr, (nC 4 H} 9) 4 NClO 4, (nC 4 H 9) 4 NI, (C 2 H 5) 4 N- _{maleate, (C 2 H 5) 4} N- benzoate, (C ₂ H ₅ ) ₄ N-phthalate, lithium stearylsulfonate, lithium octylsulfonate, and lithium dodecylbenzenesulfonate. These ionic compounds may be used singly or in combination of two or more.

The concentration of the electrolyte salt is not particularly limited, and may be used in a concentration of, for example, 0.5 to 2.0 mol / L.

Hereinafter, a method of manufacturing the lithium secondary battery 10 will be described.

The separator is disposed between the anode 20 and the cathode 30 to prepare an electrode structure and then the electrode structure is processed into a desired shape such as a cylindrical shape, a square shape, a laminate shape, a button shape, Lt; / RTI &gt; Subsequently, the non-aqueous electrolyte is injected into the container to impregnate each of the pores in the separator with an electrolytic solution, whereby a lithium secondary battery can be manufactured.

Hereinafter, specific embodiments of the present invention will be described. However, the embodiments described below are only intended to illustrate or explain the present invention, and thus the present invention should not be limited thereto. In addition, contents not described here can be inferred sufficiently technically if they are skilled in the art, and a description thereof will be omitted.

(Production of Lithium Nickel-Based Oxide Particles)

Manufacturing example  One

Nickel sulfate hexahydrate (NiSO ₄ 6H ₂ O), cobalt sulfate 5 hydrate (CoSO ₄ 5H ₂ O) and aluminum nitrate (Al (NO ₃ ) ₃ ) are dissolved in ion-exchanged water to prepare a mixed aqueous solution. At this time, the total weight of the nickel sulfate hexahydrate, the cobalt sulfate pentahydrate, and the aluminum nitrate may be determined to be 20% by weight based on the total weight of the mixed aqueous solution. Further, the mixing ratio of nickel sulfate hexahydrate, cobalt sulfate hydrate and aluminum nitrate can be determined so that the molar ratio of Ni, Co and Al is Ni: Co: Al = 85: 10: 5.

Further, 500 ml of ion-exchanged water was added to the reaction layer, and the temperature was maintained at 50 占 폚. Subsequently, dissolved oxygen is removed by bubbling ion-exchange water with nitrogen gas. Subsequently, the ion-exchanged water in the reaction layer is stirred, and while the temperature of the ion-exchanged water is maintained at 50 캜, the above-mentioned mixed aqueous solution is added dropwise to the ion-exchanged water. In addition, saturated NaCO ₃ aqueous solution is added to ion-exchanged water in an excess amount to Ni, Co and Al of the aqueous mixed solution. During the dropwise addition, the pH of the reaction layer aqueous solution is maintained at 11.5 and the temperature is maintained at 50 ° C. The dropping rate of the mixed aqueous solution and the saturated aqueous NaCO ₃ solution was 3 ml / min, and the dropping time was about 10 hours. The stirring speed was 4 to 5 m / s as the peripheral speed. Accordingly, the hydroxide salt of each metal element can coprecipitate.

 Subsequently, the solid-liquid separation, for example, suction filtration is carried out, the coprecipitation hydroxide salt is taken out from the reaction layer aqueous solution, and the coprecipitated hydroxide salt taken out is washed with ion exchange water. Then, the coprecipitation hydroxide salt is vacuum-dried at about 100 DEG C for about 10 hours, for example.

Then, the coprecipitate salt after drying is pulverized with a mortar for several minutes to obtain a dry powder, and then the dry powder and lithium hydroxide (LiOH) are mixed to produce a mixed powder. At this time, the molar ratio of Li to Ni, Co and Al (Ni + Co + Al = Me), that is, the molar ratio of Li to Me to Li: Me can be set to 1: 1.

Then, the mixed powder was calcined at 700 ° C to 800 ° C for 10 hours to obtain a lithium nickel oxide, that is, LiNi _{0 . 85} Co _{0 . 1} Al _{0 . 05} O ₂ can be produced.

The average particle size (D50) of the lithium nickel oxide was measured with a laser diffraction scattering particle size distribution meter (Nikkiso Co., Ltd., Microtrac MT3000), and it could be 7 m. The average particle diameter (D50) at this time means the particle diameter at which the integrated value becomes 50% in the diameter distribution of the diameter when the secondary particles of the lithium nickel oxide are regarded as spheres.

(Coin half cell production)

Example  One

Crystalline molybdenum sulfide was compounded on the surface of the lithium nickel oxide particles produced in Production Example 1 by spray coating.

For example, molybdenum sulfide is added to ethanol as a dispersion medium, and ethanol is stirred to prepare a slurry. Then, the slurry and the lithium-nickel-based oxide particles are put into a tumbling fluidized bed granulating-coating machine (MP-01) manufactured by Powrex Corporation. At this time, the content of molybdenum sulfide is 1 wt% based on 100 wt% of the lithium nickel oxide particles. Subsequently, MP-01 is driven to complex molybdenum sulfide on the surface of the lithium nickel oxide particles, thereby preparing a positive electrode active material.

The above-prepared cathode active material, acetylene black and polyvinylidene fluoride were mixed in a weight ratio of 95: 2: 3, and the mixture was dispersed in N-methyl-2-pyrrolidone to prepare a slurry. The slurry may be coated on an aluminum foil under a drying environment at a dew point temperature of -40 占 폚 or less and dried to form a cathode active material layer. Rolled so that the thickness of the positive electrode active material layer becomes 50 占 퐉 to prepare a positive electrode.

The negative electrode can be produced by coating a metal lithium foil on a copper foil.

A porous polypropylene film having a thickness of 12 탆 was prepared as a separator, and a separator was disposed between the positive electrode and the negative electrode to form an electrode structure.

Next, the electrode structure is processed into a size of a coin half cell and stored in a container of a coin half cell. Subsequently, lithium hexafluorophosphate was dissolved in a nonaqueous solvent prepared by mixing ethylene carbonate and dimethyl carbonate at a volume ratio of 3: 7 at a concentration of 1.3 mol / L to prepare an electrolytic solution. Subsequently, the electrolytic solution is injected into the coin half cell, and the electrolytic solution is impregnated into the separator to manufacture the half cell according to the first embodiment.

Example  2

A half cell was fabricated in the same manner as in Example 1 except that molybdenum sulfide was added in an amount of 2% by weight based on 100% by weight of lithium nickel oxide particles to prepare a cathode active material.

Example  3

A half cell was fabricated in the same manner as in Example 1 except that molybdenum sulfide was added in an amount of 5% by weight based on 100% by weight of lithium nickel oxide particles to prepare a cathode active material.

Example  4

A half cell was fabricated in the same manner as in Example 1, except that the cathode active material was produced by the following dry type hybridization.

Lithium nickel oxide particles and a metal sulfide were charged into a NOBILTA MINI (NOB-MINI) powder processing apparatus manufactured by Hosokawa Micron Co., Ltd. at a weight ratio of 1: 0.02, Drive the tammini. In this case, the molybdenum sulfide is agitated inside the device by mechanical force, so that it sticks to the surface of the lithium nickel-based oxide particles. Accordingly, the cathode active material can be produced by complexing molybdenum sulfide on the surface of the lithium nickel oxide particles.

Example  5

A half cell was fabricated in the same manner as in Example 1, except that the positive electrode active material was prepared by changing the metal sulfide complexing to the lithium nickel oxide particles to crystalline tungsten sulfide.

Comparative Example  One

A half cell was fabricated in the same manner as in Example 1 except that non-complexed lithium nickel oxide particles were used as a cathode active material.

Comparative Example  2

A half cell was fabricated in the same manner as in Example 1 except that molybdenum sulfide was added in an amount of 0.5% by weight based on 100% by weight of lithium nickel oxide particles to prepare a cathode active material.

Comparative Example  3

A half cell was fabricated in the same manner as in Example 1, except that molybdenum sulfide was added in an amount of 10% by weight based on 100% by weight of lithium nickel oxide particles to prepare a positive electrode active material.

Comparative Example  4

A half cell was fabricated in the same manner as in Example 1, except that lithium-nickel-based oxide particles were compounded with graphite to prepare a positive electrode active material.

Comparative Example  5

Acetylene black, polyvinylidene fluoride and molybdenum sulfide were dispersed in N-methyl-2-pyrrolidone to prepare a slurry. Then, the lithium nickel oxide particles prepared in Preparation Example 1 were added to the slurry and dispersed. At this time, the weight ratio of lithium nickel oxide particles, acetylene black, and polyvinylidene fluoride may be 95: 2: 3, and molybdenum sulfide may be mixed in an amount of 2% by weight based on 100% by weight of the lithium nickel oxide particles . In other words, molybdenum sulfide and lithium nickel oxide particles are simply mixed. A half cell was fabricated in the same manner as in Example 1, except that the positive electrode was prepared in the same manner as in Example 1 using the dispersion.

Evaluation 1: SEM -EDS analysis

In order to confirm that the surface of the lithium nickel oxide particles was complexed with molybdenum sulfide, the positive electrode active material was analyzed by SEM-EDS, and the results are shown in FIGS. 5 to 8.

FIG. 5 is a scanning electron microscope (SEM) photograph of the cathode active material according to Example 1, FIG. 6 is an energy dispersive X-ray analysis (EDS) image of Ni atoms in the cathode active material according to Example 1, FIG. 8 is a graph showing energy dispersive X-ray analysis (EDS) of a Mo atom in a cathode active material according to Example 1, ) It is a photograph.

Figs. 6 to 8 are obtained by analyzing the same object as the observation object obtained when the SEM image of Fig. 5 is obtained, and the magnifications of Figs. 5 to 8 are the same. 6 to 8, the white luminescent spot represents an element to be observed.

5 to 8, it is confirmed that molybdenum sulfide is complexed on the surface of the lithium nickel oxide particles.

Evaluation 2: Rate (rate) characteristic measurement

Charge / discharge of the half cell is performed at the charge / discharge rate and cut off voltage shown in Table 1 below. Charging and discharging are carried out at room temperature (25 ° C). The third cycle ends with charging. CC-CV means constant current constant voltage, and CC means constant current. Then, the discharge capacity at the second cycle was measured, and this value was determined as the initial capacity. The results are shown in Table 2 below.

Test cycle Charging rate Discharge rate Cutoff voltage (V) One 0.1C CC-CV 0.1C CC 4.3 - 3.0 2 (defined as initial capacity) 0.2C CC-CV 0.2C CC 4.3 - 3.0 3 0.2C CC-CV
(Terminated by charge) - 4.3 - 3.0

Evaluation 3: Thermal stability

The half-cell in the charged state is disassembled, the positive electrode is taken out, and the positive electrode mixture is scraped off from the positive electrode. Subsequently, 2 mg of the positive electrode mixture and 2 mg of the electrolytic solution used for the half-cell fabrication were mixed, and the mixture was introduced into a differential scanning calorimeter (X-DSC7000 manufactured by Seiko Instruments Inc.) to obtain a differential scanning calorimetry (DSC) . At this time, the temperature rise rate is 5 ° C / min.

The total calorific value and the peak height at the time of maximum heat generation were measured according to the obtained DSC curve. The total calorific value was calculated according to the area surrounded by the DSC curve and the baseline, and the results are shown in Table 2 below.

4 is a differential scanning calorimetry (DSC) graph of Example 2 and Comparative Example 1. Fig. In Fig. 4, the horizontal axis represents the sample temperature (占 폚) and the vertical axis represents DSC (占 W / mg).

Additive material Compounding method Addition amount
(weight%) Initial discharge capacity
(mAh / g) Total calorific value
(J / g) Maximum heat
Peak height
(Ratio to Comparative Example 1) Comparative Example 1 none - 0 200 2000 100 Comparative Example 2 MoS ₂ Spray coating 0.5 199 1950 90 Example 1 MoS ₂ Spray coating One 198 1830 70 Example 2 MoS ₂ Spray coating 2 196 1800 50 Example 3 MoS ₂ Spray coating 5 190 1780 40 Comparative Example 3 MoS ₂ Spray coating 10 160 1500 35 Example 4 MoS ₂ Mechanical stirring 2 195 1830 50 Example 5 WS ₂ Spray coating 2 199 1850 75 Comparative Example 4 black smoke Spray coating 2 199 2100 110 Comparative Example 5 MoS ₂ Simple mixing 2 165 1800 60

In Table 2, the additive material represents a material to be compounded with lithium nickel-based oxide particles or a material to be simply mixed with lithium nickel-based oxide particles. The addition amount represents the weight percentage of the material which is compounded or simply mixed with respect to 100 wt% of the lithium nickel oxide particles. The maximum exothermic peak height represents the ratio of the peak height at the time of maximum heat generation to that of Comparative Example 1. Here, the peak height at the time of maximum heat generation in Comparative Example 1 is assumed to be 100.

Referring to Table 2 and FIG. 4, it can be seen that the total calorific value and the maximum exothermic peak height are lower than those of Comparative Examples 1 to 5 in Examples 1 to 5.

The initial discharge capacities of Examples 1 to 5 are equivalent to those of Comparative Example 1. Accordingly, the positive electrode active material according to one embodiment has excellent thermal stability at the time of charging. Also, the discharge capacity is maintained at substantially the same value as in Comparative Example 1. [

In particular, referring to Examples 1 to 3 and Comparative Examples 2 and 3, it can be seen that excellent effects are obtained when the amount of the metal sulfide added is within a range of 1 to 5 wt%.

Also, referring to Examples 1 to 3 and Comparative Example 4, it can be seen that the maximum exothermic peak height of Comparative Example 4 is higher than that of Comparative Example 1. Thus, it can be seen that when the metal sulfide is compounded on the surface of the lithium nickel oxide particles, the thermal stability at the time of charging is improved.

In addition, referring to Examples 1 to 3 and Comparative Example 5, it can be understood that sufficient discharge capacity can not be obtained simply by mixing the metal sulfide with the lithium nickel oxide particles, and by compounding on the surface of the lithium nickel oxide particles, Can be obtained.

Also, referring to Examples 1 to 3 and Example 4, it can be seen that excellent effects can be obtained regardless of the method of compounding.

Also, referring to Examples 1 to 3 and Example 5, it can be seen that excellent effects can be obtained even when tungsten sulfide is used as the metal sulfide.

 As described above, the positive electrode active material according to one embodiment can improve the thermal stability at the time of charging while securing the discharge capacity of the lithium secondary battery.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, And falls within the scope of the invention.

10 lithium secondary battery
20 anode
21 Home
22 cathode active material layer
22a cathode active material
22b core particle
22c coating layer
30 cathode
31 Home Full
32 Anode active material layer
40 Separator layer

Claims (8)

Core particles; And
And a coating layer surrounding the core particles,
Wherein the core particle comprises lithium nickel-based oxide particles including a nickel-containing metal and lithium,
Wherein the lithium nickel oxide particles contain at least 80 atomic% of nickel based on the total atomic weight of the nickel-containing metal,
Wherein the coating layer comprises a metal sulfide compounded on the surface of the core particle,
Wherein the metal sulfide has a layered structure. The method of claim 1,
Wherein the core particle comprises a lithium nickel oxide particle represented by the following formula (1).
[Chemical Formula 1]
Li _a Ni _x Co _y M _z O ₂
(In the formula 1,
M is at least one element selected from the group consisting of Al, Mn, Cr, Fe, V, Mg, Ti, At least one metal selected from tungsten (W), copper (Cu), zinc (Zn), gallium (Ga), indium (In), tin (Sn), lanthanum (La), and cerium (Ce)
0.2? A? 1.2, 0.8? X <1, 0 <y? 0.2, 0? Z? 0.1, x + y + z = The method of claim 1,
The metal sulfide has a structure in which unit structures are laminated,
Wherein the unit structure includes a plurality of sulfur atoms and a metal atom layer disposed between the sulfur atoms. The method of claim 1,
Wherein the metal sulfide includes at least one selected from molybdenum sulfide, tungsten sulfide, and titanium sulfide. The method of claim 1,
Wherein the metal sulfide is crystalline. The method of claim 1,
Wherein the metal sulfide is contained in an amount of 1 wt% to 5 wt% based on 100 wt% of the core particles. A cathode active material layer for a lithium secondary battery, comprising the cathode active material of any one of claims 1 to 6. A lithium secondary battery comprising the cathode active material layer of claim 7.

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