KR101064729B1 - Cathode active material for lithium secondary battery and lithium secondary battery comprising same - Google Patents

Abstract

The present invention relates to a positive electrode active material for a lithium secondary battery and a lithium secondary battery comprising the same, wherein the positive electrode active material is a retardable intercalation / de-intercalation of lithium and a metal compound layer formed on a surface thereof. It includes an additive compound represented by the formula (1).

[Formula 1]

Li _x Ni _y M _1-y O ₂

(Wherein, 2.01 ≦ x ≦ 2.1, 0.95 ≦ y ≦ 1,

M is selected from the group consisting of Al, Co, Ni, Mn, Fe and mixtures thereof)

As the positive electrode active material of the present invention includes an additive compound having a metal compound layer formed on the surface thereof, the charge capacity may be increased, the irreversible capacity of the battery may be reduced, and the safety may be increased.

Cathode active material, metal oxide layer, irreversible capacity, explosion

Description

A positive electrode active material for a lithium secondary battery and a lithium secondary battery including the same {POSITIVE ACTIVE MATERIAL FOR RECHARGEABLE LITHIUM BATTERY AND RECHARGEABLE LITHIUM BATTERY COMPRISING SAME}

The present invention relates to a cathode active material for a lithium secondary battery and a lithium secondary battery including the same, and more particularly, to a cathode active material for a lithium secondary battery having excellent safety and a lithium secondary battery including the same.

Cells generate electricity by using materials that can electrochemically react to the positive and negative electrodes. A typical example of such a battery is a lithium secondary battery that generates electric energy by a change in chemical potential when lithium ions are intercalated / deintercalated at a positive electrode and a negative electrode.

The lithium secondary battery is manufactured by using a material capable of reversible intercalation / deintercalation of lithium ions as a positive electrode and a negative electrode active material, and filling an organic electrolyte or a polymer electrolyte between the positive electrode and the negative electrode.

LiCoO ₂ , LiN _1-x M _x O ₂ (x is 0.95 to 1, M is Al, Co, Ni, Mn, or Fe) or LiMn ₂ O ₄ may be used as the cathode active material. _It is mainly used because of its high _divalent volumetric energy density, high temperature characteristics, in particular, cycle life characteristics at 60 ° C and swelling characteristics at 90 ° C.

However, as the capacity of lithium secondary batteries increases, studies on safety are still required.

The main problem that occurs during operation of the lithium secondary battery is related to overcharge (12V) due to a defect or failure in the battery protection device. The LiCoO ₂ positive electrode causes a rapid exothermic reaction with the electrolyte during the overcharge process, causing short circuit of the battery, and also the temperature increase and internal short circuit of the cell eventually cause the battery to explode.

In order to improve such 12V overcharge safety, a method of coating LiCoO ₂ or LiNi _0.8 Co _0.1 Mn _0.1 O ₂ surface with AlPO ₄ nanoparticles has been attempted. In addition, methods have been attempted to add electrolyte additives such as 3-chloroanisole, biphenyl and cyclohexyl benzene. However, the coating method increases costs, and the use of electrolyte additives causes a problem of lowering electrochemical properties.

Recently, a LiCoO ₂ and orthorhombic Immm (orthorhombic Immm) study, the over-discharge inhibition 1.5V from lithium-ion battery by mixing Li ₂ NiO ₂ physically reported. However, this method has an excessive distribution of Ni ²⁺ on the surface of LiNiO ₂ , which is one of the problems of using Ni-rich compounds, and reacts with moisture in the air to form impurities of LiOH and Li ₂ CO ₃ . These impurities cause a problem of lowering the capacity. Also, The presence of these impurities causes gas generation during the chemical conversion process during the manufacturing of lithium ion batteries and when stored at temperatures higher than 60 ° C. in the charged state, resulting in excessive battery swelling.

An object of the present invention is to provide a positive electrode active material for a lithium secondary battery excellent in safety.

Another object of the present invention to provide a lithium secondary battery including the positive electrode active material.

Technical problems to be achieved by the present invention are not limited to the technical problems mentioned above, and other technical problems not mentioned will be clearly understood by those skilled in the art from the following description.

A first embodiment of the present invention for achieving the above object comprises a lythiated compound capable of reversible intercalation / deintercalation of lithium and an additive compound represented by the formula (1) in which a metal compound layer is formed on the surface It provides a positive electrode active material for a lithium secondary battery.

[Formula 1]

Li _x Ni _y M _1-y O ₂

(Wherein, 2.01 ≦ x ≦ 2.1, 0.95 ≦ y ≦ 1,

M is selected from the group consisting of Al, Co, Ni, Mn, Fe and mixtures thereof)

A second embodiment of the present invention is to provide a lithium secondary battery including a positive electrode including the positive electrode active material, a negative electrode including the negative electrode active material and an electrolyte.

As the positive electrode active material of the present invention includes an additive compound having a metal compound layer formed on the surface thereof, the charge capacity may be increased, the irreversible capacity of the battery may be reduced, and the safety may be increased.

Hereinafter, embodiments of the present invention will be described in detail. However, this is presented as an example, by which the present invention is not limited and the present invention is defined only by the scope of the claims to be described later.

The positive electrode active material according to the first embodiment of the present invention is a lithium including a lithium compound capable of reversible intercalation / deintercalation of lithium and an additive compound represented by the following Chemical Formula 1 in which a metal compound layer is formed on the surface: Provided is a cathode active material for a secondary battery.

[Formula 1]

Li _x Ni _y M _1-y O ₂

In the above formula, 2.01 ≦ x ≦ 2.1 and 0.95 ≦ y ≦ 1 are preferred. In the case of using the compound of the formula (I) having an x value of less than 2.01, the capacity of the final positive electrode active material is lowered, which is not preferable. If it exceeds 2.1, unreacted LiOH is formed and the capacity is lowered. It is not desirable because there is a problem of danger.

In the above formula, M is selected from the group consisting of Al, Co, Ni, Mn, Fe, and mixtures thereof.

In the metal compound constituting the metal compound layer, the metal is preferably Al, Mg, transition metal or a combination thereof, and Al, Mg, Zn, Ti or a combination thereof is preferable.

The metal compound may be an oxide or hydroxide containing a metal.

The metal compound layer may be formed on the surface of the compound represented by Chemical Formula 1, thereby solving the problem of reacting with moisture by exposing the compound of Chemical Formula 1 to air.

The thickness of the metal compound layer is preferably 10 nm to 2 μm. If the thickness of the metal compound layer is thinner than 10 nm, there is a problem of reacting with moisture.

The additive compound preferably contains 0.5 to 2 parts by weight of a metal compound per 100 parts by weight of the compound represented by Formula 1, and more preferably 0.5 to 1 part by weight. When the amount of the metal compound is less than 0.5 parts by weight per 100 parts by weight of the compound represented by Formula 1, there is a problem that the metal compound does not uniformly coat the compound represented by Formula 1, and when the amount exceeds 2 parts by weight, the coating layer It is not preferable because there is a problem that the thickness is so thick that the implementation capacity does not come out.

The additive compound is preferably prepared using the compound represented by Formula 1 having a high purity of 99.5 to 99.9%. When the purity of the compound represented by the formula (1) is included in the high purity of 99.5% -99.9%, it is preferable because there is little impurities such as LiOH to obtain a pure Li ₂ NiO ₂ phase.

The compound represented by Chemical Formula 1 having such a high purity is a lithium compound prepared by heat-treating Li ₂ CO ₃ having a high purity of 99.5 to 99% at 600 to 700 ° C. under an oxygen atmosphere, a nickel compound is mixed, and the mixture is It may be prepared by using a heat treatment at 600 to 700 ℃, but may be used in addition to any prepared in any process. NiO may be used as the nickel compound. The mixing ratio of the lithium compound and the nickel compound may be mixed in an appropriate molar ratio so that the compound of Formula 1 is obtained.

Since the additive compound has a metal compound layer formed on the surface thereof, the additive compound has little reactivity with moisture in the air, and thus, when the compound is used for the positive electrode, the irreversible capacity can be significantly reduced without causing swelling of the battery. . In addition, the additive compound plays a role as a surplus current consumer, thereby improving thermal safety during battery charging, thereby suppressing explosion of the battery during 12V overcharging.

The mixing ratio of the lythiated compound and the additive compound is preferably 90:10 to 97: 3 by weight, more preferably 96: 4 to 97: 3 by weight. When the additive compound is used in a smaller amount or in excess of the mixing ratio, the irreversible capacity cannot be controlled, which is not preferable.

The lythiated compound capable of reversible intercalation / deintercalation of lithium may be any compound generally used in a lithium secondary battery, and examples thereof include a compound of Chemical Formulas 2 to 6 below. .

[Formula 2]

Li _x Co _1-y M ' _y D ₂

(3)

Li _x Co _1-y M ' _y O _2-z X _z

[Formula 4]

Li _x Co _1-y Ni _y O _2-z X _z

[Chemical Formula 5]

Li _x Co _1-yz Ni _y M ' _z D _α

[Formula 6]

Li _x Co _1-yz Ni _y M ' _z O _2-α X _α

Wherein 0.9 ≦ x ≦ 1.1, 0 ≦ y ≦ 0.5, 0 ≦ z ≦ 0.5, 0 ≦ α ≦ 2, and M ′ is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V and At least one element selected from the group consisting of rare earth elements, D is at least one element selected from the group consisting of O, F, S and P, and X is at least one selected from the group consisting of F, S and P Is an element of.)

The positive electrode active material of the present invention is prepared by mixing a lythiated compound and an additive compound. In this case, the mixing ratio of the lythiated compound and the additive compound is preferably 90:10 to 97: 3 by weight, more preferably 96: 4 to 97: 3 by weight.

The additive compound may be prepared by mixing the compound of Formula 1 with a metal salt solution and heat treating it.

[Formula 1]

Li _x Ni _y M _1-y O ₂

(Wherein, 2.01 ≦ x ≦ 2.1, 0.95 ≦ y ≦ 1,

M is selected from the group consisting of Al, Co, Ni, Mn, Fe and mixtures thereof)

The metal salt solution may be prepared by dissolving an alkoxide, oxide, nitrate salt, and acetate salt containing a metal in a solvent. As the metal, Al, Mg, transition metal or a combination thereof is preferable, and Al, Mg, Zn, Ti or a combination thereof is preferable. As the solvent, alcohols such as ethanol and propanol or acetone may be used. In addition, the concentration of the metal salt solution is preferably 1 to 4% by weight. If the concentration of the metal salt solution is less than 1% by weight, the compound represented by Chemical Formula 1 cannot be uniformly coated with the metal compound, which is not preferable. If the concentration of the metal salt solution exceeds 4% by weight, the coating layer formed is thickened. There is a problem with capacity implementation, which is undesirable.

The heat treatment step is preferably carried out at 100 to 600 ℃, wherein the heat treatment time is appropriate 5 to 10 hours.

According to the heat treatment process, the metal salt is converted into a metal oxide or a metal hydroxide according to the type of the metal salt solution in the metal salt solution, and is present as a layer on the surface of the compound of Formula 1. In addition, as the metal compound is converted, some may react with the compound of Formula 1 to generate a solid solution such as Li—O—metal—Ni—O, and may be included in the additive compound.

The positive electrode active material of the present invention can be usefully used for the positive electrode of an electrochemical cell such as a lithium secondary battery. The lithium secondary battery includes a negative electrode and an electrolyte including a negative electrode active material together with a positive electrode.

The positive electrode is prepared by mixing a positive electrode active material according to the present invention, a conductive material, a binder and a solvent to prepare a positive electrode active material composition, and then coating and drying the aluminum active material directly. Alternatively, the cathode active material composition may be cast on a separate support, and then the film obtained by peeling from the support may be manufactured by laminating on an aluminum current collector.

The conductive material is carbon black, graphite, metal powder, the binder is vinylidene fluoride / hexafluoropropylene copolymer, polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polytetrafluoroethylene And mixtures thereof. In addition, N-methylpyrrolidone, acetone, tetrahydrofuran, decane, etc. are used as a solvent. In this case, the contents of the positive electrode active material, the conductive material, the binder, and the solvent are used at levels commonly used in lithium secondary batteries.

Like the positive electrode, the negative electrode is mixed with a negative electrode active material, a binder, and a solvent to prepare an anode active material composition, and the negative electrode active material film coated on the copper current collector or cast on a separate support and peeled from the support is coated on the copper current collector. It is prepared by lamination. At this time, the negative electrode active material composition may further contain a conductive material if necessary.

As the negative electrode active material, a material capable of intercalating / deintercalating lithium is used, and for example, lithium metal, lithium alloy, coke, artificial graphite, natural graphite, organic polymer compound combustor, carbon fiber, or the like is used. . In addition, a conductive material, a binder, and a solvent are used similarly to the case of the positive electrode mentioned above.

The separator may be used as long as it is commonly used in lithium secondary batteries. For example, polyethylene, polypropylene, polyvinylidene fluoride or two or more multilayer films thereof may be used, and a polyethylene / polypropylene two-layer separator, It goes without saying that a mixed multilayer film such as polyethylene / polypropylene / polyethylene three-layer separator, polypropylene / polyethylene / polypropylene three-layer separator and the like can be used.

As the electrolyte to be charged in the lithium secondary battery, a non-aqueous electrolyte or a known solid electrolyte may be used, and a lithium salt is used.

Although the solvent of the said non-aqueous electrolyte is not specifically limited, Cyclic carbonate, such as ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate; Chain carbonates such as dimethyl carbonate, methyl ethyl carbonate and diethyl carbonate; Esters such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate and γ-butyrolactone; Ethers such as 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 1,2-dioxane and 2-methyltetrahydrofuran; Nitriles such as acetonitrile; Or amides such as dimethylformamide can be used. These can be used individually or in combination of two or more. In particular, a mixed solvent of a cyclic carbonate and a linear carbonate can be preferably used.

As the electrolyte, a gel polymer electrolyte in which an electrolyte solution is impregnated with a polymer electrolyte such as polyethylene oxide or polyacrylonitrile, or an inorganic solid electrolyte such as LiI or Li ₃ N can be used.

The lithium salt is LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , LiSbF ₆ , LiAlO ₄ , LiAlCl ₄ , One selected from the group consisting of LiCl and LiI is possible.

Hereinafter, preferred examples and comparative examples of the present invention are described. However, the following examples are only preferred examples of the present invention and the present invention is not limited to the following examples.

(Example 1)

Li ₂ CO ₃ having a purity of 99.9% was calcined and pyrolyzed at 700 ° C. under an oxygen atmosphere to prepare Li ₂ O having a purity of 99.9%.

37 g of NiO (average particle size: 10 mu m) and the prepared Li ₂ O were uniformly mixed using an automatic mixing machine under an N ₂ stream in a 50: 20.5 weight ratio. The mixture was calcined at 600 ° C. for 10 hours under pure N ₂ atmosphere to prepare Li _2.05 NiO ₂ having a purity of 99%.

1.5 g of Al isopropoxide was dissolved in 50 g of ethanol. 50 g of Li _2.05 NiO ₂ having a purity of 99.99% prepared according to the above process was added to the solution, and mixed for 20 minutes. The mixture was dried at 120 ° C. for 12 hours to prepare Li _2.05 NiO ₂ (additive compound) in which an Al ₂ O ₃ layer was formed on the surface. At this time, the thickness of the Al ₂ O ₃ layer was 20nm, the content of Al ₂ O ₃ was 0.5 parts by weight based on 100 parts by weight of Li _2.05 NiO ₂ .

A positive electrode active material was prepared by mixing LiCoO ₂ having an average particle diameter of 18 μm and the additive compound prepared in a 96: 4 weight ratio.

After dissolving the polyvinylidene fluoride binder (Quera Corporation) in a N-methyl-2-pyrrolidone solvent, the positive electrode active material and the super P carbon black conductive material were added to this solution to prepare a positive electrode active material slurry. At this time, the mixing ratio of the positive electrode active material, the conductive material and the binder was 96: 2: 2 by weight. The slurry was coated on Al foil, and a positive electrode was prepared by a conventional method of drying at 130 ° C. for 20 minutes.

A natural graphite negative electrode active material and a polyvinylidene fluoride binder were mixed in N-methyl-2-pyrrolidone in a 94: 6 weight ratio to prepare a negative electrode active material slurry. The negative electrode was manufactured by the conventional method of coating this negative electrode active material slurry on Cu foil.

Size 463450 using the positive electrode and the negative electrode, and a liquid electrolyte containing less than 20 ppm of HF (ethylene carbonate / dimethyl carbonate / diethyl carbonate dissolved in 1M LiPF ₆ , 1/1 / 1 volume ratio) (Cheil Industries, Korea) A rectangular battery of was prepared. In this case, the dimensional ratio of the positive electrode and the negative electrode was 1.08: 1, and the theoretical charging capacity of the lithium ion battery was 940 mAh.

(Example 2)

Li ₂ CO ₃ having a purity of 99.9% was calcined and pyrolyzed at 700 ° C. under an oxygen atmosphere to prepare Li ₂ O having a purity of 99.9%.

50 g of NiO (average particle diameter: 10 mu m) and the prepared Li ₂ O were uniformly mixed using an automatic mixing machine under an N ₂ stream in a 50: 20.1 weight ratio. The mixture was calcined at 600 ° C. for 10 hours under pure N ₂ atmosphere to prepare Li _2.01 NiO ₂ having a purity of 99%.

1.5 g of Al isopropoxide was dissolved in 50 g of ethanol. 50 g of Li _2.01 NiO ₂ having a purity of 99.99% prepared according to the above process was added to the solution, and mixed for 20 minutes. The mixture was dried at 120 ° C. for 12 hours to prepare Li _2.01 NiO ₂ (additive compound) in which an Al ₂ O ₃ layer was formed on the surface. At this time, the thickness of the Al ₂ O ₃ layer was 20nm, the content of Al ₂ O ₃ was 0.5 parts by weight based on 100 parts by weight of Li _2.01 NiO ₂ .

A positive electrode active material was prepared by mixing LiCoO ₂ having an average particle diameter of 18 μm and the additive compound prepared at a weight ratio of 96: 4.

A lithium ion battery was manufactured in the same manner as in Example 1, except that the positive electrode active material was used.

(Example 3)

Li ₂ CO ₃ having a purity of 99.9% was calcined and pyrolyzed at 700 ° C. under an oxygen atmosphere to prepare Li ₂ O having a purity of 99.9%.

48 g of NiO (average particle diameter: 10 mu m) and the above prepared Li ₂ O were uniformly mixed using an automatic mixing machine under an N ₂ stream in a 50:21 weight ratio. The mixture was calcined at 600 ° C. for 10 hours under pure N ₂ atmosphere to prepare Li _2.1 NiO ₂ having a purity of 99%.

1.5 g of Al isopropoxide was dissolved in 50 g of ethanol. 50 g of Li _2.1 NiO ₂ having a purity of 99.99% prepared according to the above process was added to the solution and mixed for 20 minutes. The mixture was dried at 120 ° C. for 12 hours to prepare Li _2.1 NiO ₂ (additive compound) in which an Al ₂ O ₃ layer was formed on the surface. At this time, the thickness of the Al ₂ O ₃ layer was 20nm, the content of Al ₂ O ₃ was 0.5 parts by weight based on 100 parts by weight of Li _2.1 NiO ₂ .

A positive electrode active material was prepared by mixing LiCoO ₂ having an average particle diameter of 18 μm and the additive compound prepared at a weight ratio of 96: 4.

A lithium ion battery was manufactured in the same manner as in Example 1, except that the positive electrode active material was used.

(Example 4)

A lithium ion battery was manufactured in the same manner as in Example 1, except that LiCoO ₂ having an average particle diameter of 18 μm and the positive electrode active material prepared by mixing the additive compound in a 90:10 weight ratio were used.

(Example 5)

A lithium ion battery was manufactured in the same manner as in Example 1, except that LiCoO ₂ having an average particle diameter of 18 μm and a cathode active material prepared by mixing an additive compound in a 97: 3 weight ratio were used.

(Example 6)

6 g Al isopropoxide was dissolved in 50 g ethanol. 100 g of Li _2.05 NiO ₂ having a purity of 99.99% prepared according to the process of Example 1 was added to the solution, and mixed for 20 minutes. The mixture was dried at 120 ° C. for 12 hours to prepare Li _2.05 NiO ₂ (additive compound) in which an Al ₂ O ₃ layer was formed on the surface. At this time, the thickness of the Al ₂ O ₃ layer was 150nm, the content of Al ₂ O ₃ was 2 parts by weight based on 100 parts by weight of Li _2.05 NiO ₂ .

A positive electrode active material was prepared by mixing LiCoO ₂ having an average particle diameter of 18 μm and the additive compound prepared at a weight ratio of 96: 4.

A lithium ion battery was manufactured in the same manner as in Example 1, except that the positive electrode active material was used.

(Comparative Example 1)

A lithium ion battery was manufactured in the same manner as in Example 1, except that only LiCoO ₂ having an average particle diameter of 18 μm was used as the cathode active material.

(Comparative Example 2)

Li ₂ CO ₃ having a purity of 99.9% was calcined and pyrolyzed at 700 ° C. under an oxygen atmosphere to prepare Li ₂ O having a purity of 99.9%.

37 g of NiO (average particle size: 10 mu m) and the prepared Li ₂ O were uniformly mixed using an automatic mixing machine under an N ₂ stream in a 50: 20.5 weight ratio. The mixture was calcined at 600 ° C. for 10 hours under pure N ₂ atmosphere to prepare Li _2.05 NiO ₂ (additive compound) having a purity of 99%.

A positive electrode active material was prepared by mixing LiCoO ₂ having an average particle diameter of 18 μm with the prepared additive compound at a weight ratio of 96: 4.

After dissolving the polyvinylidene fluoride binder (Quera Corporation) in a N-methyl-2-pyrrolidone solvent, the positive electrode active material and the super P carbon black conductive material were added to this solution to prepare a positive electrode active material slurry. At this time, the mixing ratio of the positive electrode active material, the conductive material and the binder was 96: 2: 2 by weight. The slurry was coated on Al foil and dried at 130 ° C. for 20 minutes to prepare a positive electrode.

A natural graphite negative electrode active material and a polyvinylidene fluoride binder were mixed in N-methyl-2-pyrrolidone in a 94: 6 weight ratio to prepare a negative electrode active material slurry. The negative electrode was manufactured by the conventional method of coating this negative electrode active material slurry on Cu foil.

Size 463450 using the positive electrode and the negative electrode, and a liquid electrolyte containing less than 20 ppm of HF (ethylene carbonate / dimethyl carbonate / diethyl carbonate dissolved in 1M LiPF ₆ , 1/1 / 1 volume ratio) (Cheil Industries, Korea) A rectangular battery of was prepared. At this time, the area ratio of the positive electrode and the negative electrode was 1.08: 1, and the theoretical charging capacity of the lithium ion battery was 940 mAh.

(Comparative Example 3)

Li ₂ CO ₃ having a purity of 99.9% was calcined and pyrolyzed at 700 ° C. under an oxygen atmosphere to prepare Li ₂ O having a purity of 99.9%.

48 g of NiO (average particle diameter: 10 mu m) and the prepared Li ₂ O were uniformly mixed using an automatic mixing machine under an N ₂ stream in a 50: 20 weight ratio. The mixture was calcined at 600 ° C. for 10 hours under pure N ₂ atmosphere to prepare Li ₂ NiO ₂ having a purity of 99%.

1.5 g of Al isopropoxide was dissolved in 50 g of ethanol. 50 g of Li ₂ NiO ₂ having a purity of 99.99% prepared according to the above process was added to the solution, and mixed for 20 minutes. The mixture was dried at 120 ° C. for 12 hours to prepare Li ₂ NiO ₂ (additive compound) in which an Al ₂ O ₃ layer was formed on the surface. At this time, the thickness of the Al ₂ O ₃ layer was 20nm, the content of Al ₂ O ₃ was 0.5 parts by weight based on 100 parts by weight of Li ₂ NiO ₂ .

A positive electrode active material was prepared by mixing LiCoO ₂ having an average particle diameter of 18 μm and an additive compound in a weight ratio of 96: 4.

A lithium ion battery was manufactured in the same manner as in Example 1, except that the positive electrode active material was used.

(Comparative Example 4)

Li ₂ CO ₃ having a purity of 99.9% was calcined and pyrolyzed at 700 ° C. under an oxygen atmosphere to prepare Li ₂ O having a purity of 99.9%.

47 g of NiO (average particle diameter: 10 mu m) and the prepared Li ₂ O were uniformly mixed using an automatic mixing machine under an N ₂ stream in a 50:22 weight ratio. The mixture was calcined at 600 ° C. for 10 hours under pure N ₂ atmosphere to prepare Li _2.2 NiO ₂ having a purity of 99%.

1.5 g of Al isopropoxide was dissolved in 50 g of ethanol. 50 g of Li _2.2 NiO ₂ having a purity of 99.99% prepared according to the above process was added to the solution, and mixed for 20 minutes. The mixture was dried at 120 ° C. for 12 hours to prepare Li _2.2 NiO ₂ (additive compound) in which an Al ₂ O ₃ layer was formed on the surface. At this time, the thickness of the Al ₂ O ₃ layer was 20nm, the content of Al ₂ O ₃ was 0.5 parts by weight based on 100 parts by weight of Li _2.2 NiO ₂ .

A positive electrode active material was prepared by mixing LiCoO ₂ having an average particle diameter of 18 μm and an additive compound in a weight ratio of 96: 4.

A lithium ion battery was manufactured in the same manner as in Example 1, except that the positive electrode active material was used.

(Reference Example 1)

Lithium ion was carried out in the same manner as in Example 1 except for using a positive electrode active material prepared by mixing LiCoO ₂ having an average particle diameter of 18 μm and Li _2.05 NiO ₂ having an Al ₂ O ₃ layer at a weight ratio of 98: 2. The battery was prepared.

(Reference Example 2)

Lithium ion was carried out in the same manner as in Example 1 except that LiCoO ₂ having an average particle diameter of 18 μm and a cathode active material prepared by mixing Li _2.05 NiO ₂ having an Al ₂ O ₃ layer in a _88:12 weight ratio were used. The battery was prepared.

* SEM photo

1,000 magnification SEM photographs of Li _2.05 NiO ₂ on the surface of the Al ₂ O ₃ layer prepared in Example 1 are shown in FIG. 1A, 10,000 magnification SEM images in FIG. 2A, and 100,000 magnification SEM images in FIG. 3A, respectively. . In addition, the 1000 magnification SEM photograph of Li _2.05 NiO ₂ prepared in Comparative Example 2 is shown in FIG. 1B, the 10,000 magnification SEM photograph is shown in FIG. 2B, and the 100,000 magnification SEM photograph is shown in FIG. 3B, respectively.

As shown in FIGS. 1B, 2B and 3B, Li _2.05 NiO ₂ without Al ₂ O ₃ layer prepared in Comparative Example 2 was agglomerated caterpillar-like having a length of about 0.5 μm and a diameter of about 80 nm. It can be seen that caterpillar-like particles exist on the surface. However, Li _2.05 NiO ₂ in which the Al ₂ O ₃ layer was formed on the surface, as shown in FIGS. 1A, 2A, and 3A, the caterpillar-like particles disappeared, and the surface became uniform. In addition, although FIG. 3A shows a magnification of FIG. 2A 10 times, some of the caterpillar-like particles are present, but the surface _{morphology of} Li _2.05 NiO ₂ (FIG. 3B) without the Al ₂ O ₃ layer of Comparative Example 2 is shown. It can be seen that the remarkably different. As a result, an Al ₂ O ₃ layer was formed on the surface, and Al ₂ O ₃ was formed, whereby Al ₂ O ₃ reacted with bulk Li _2.05 NiO ₂ to form a Li—O—Al—Ni—O solid solution. It can be seen that.

* XRD measurement

The XRD patterns of Li _2.0 NiO ₂ and Li _2.05 NiO ₂ without Al ₂ O ₃ layer formed on the surface of the Al ₂ O ₃ layer prepared according to Example 1 and Comparative Example 2 were measured and the results are shown in FIG. 4. It was. As shown in FIG. 4, although a small peak of the NiO phase appears, it can be seen that Example 1 and Comparative Example 2 can be classified into an orthorhombic phase having a space group of Immm . In addition, both Example 1 and Comparative Example 2 showed a = 3.744 ms, b = 2.780 ms, c = 9.026 ms similarly to each other regardless of the presence or absence of an Al ₂ O ₃ layer.

* Evaluation of capacity and voltage characteristics with and without Al ₂ O ₃ layer

Using the Comparative Example 2, the Li _2.05 NiO ₂ as in Example 1 Li _2.05 NiO ₂ having a Al ₂ O ₃ layer on the prepared surface in the production in a positive electrode active material and using a lithium foil as a counter electrode, and vacuum sealed in an aluminum pouch To prepare a half cell. At this time, the vacuum sealing process was carried out in a glove box filled with an inert gas to prevent oxidation and contamination of the battery. Charge and discharge of the prepared battery at 4.3 to 1.5V at 0.5C, the initial charge and discharge characteristics results are shown in FIG. As shown in FIG. 5 and Comparative Example ₂ Li 2 NiO 2 of the charge capacity is 337mAh / g, the discharge capacity was as 250mAh / g. On the other hand, Li _2.05 NiO ₂ formed on the surface of the Al ₂ O ₃ layer of Example 1 has a charge capacity of 420mAh / g and discharge capacity of 310mAh / g, showing an improved initial capacity compared to Comparative Example 2. These results are in accordance with the Li _2.05 NiO ₂ Al ₂ O ₃ layer is formed on the surface, side reactions are less occurs than the Li _2.05 NiO ₂ Al ₂ O ₃ layer is not formed on the surface, the structure is stabilized lithium ions are It seems to be because more can be inserted.

As shown in FIG. 5, the irreversible capacity ratio between 4.3V and 2.85V was 71% (between 4.2V and 2.75V vs. graphite).

* Water absorption evaluation with and without Al ₂ O ₃ layer

Comparative Example 2 after 30 minutes exposure in a Li _2.05 NiO ₂ having a Al ₂ O ₃ layer air on the surface manufactured by the manufactured Li _2.05 NiO ₂ as in Example 1 in to measure the water content. As a result, Li ₂ NiO ₂ prepared in Comparative Example 2 had a sharp increase in moisture content of 260ppmm to 3000ppm before exposure to air. On the other hand, Li _2.05 NiO _2, the surface of which was prepared in Example 1 and coated with an Al ₂ O ₃ layer, increased its moisture content from 250 ppm to 300 ppm after 30 minutes of exposure before exposure to air.

In addition, the FT-IR spectrum after exposing Li _2.05 NiO ₂ having Al ₂ O ₃ layer formed on the surface of Example 1 to air for 7 hours was measured, and the results are shown in FIG. 6. Further, by measuring FT-IR spectrum after exposing to air for 7 hours and compared to before exposure to the example 2 of the Li _2.05 NiO ₂ in air, and the results are shown together in Fig. As shown in FIG. 6, Example 1 showed no spectral change even after 7 hours of exposure in air. On the other hand, Comparative Example 2, the surface of the Al ₂ O ₃ layer if the non-coated Li _2.05 NiO ₂ was increased by about 3500cm ^-1 and a peak of water and CO ₂ is significantly from 2500cm ^-1 of. As with the compound of Comparative Example 2, when absorbing moisture, non-conductive Li ₂ CO ₃ and LiOH phases form on the particle surface, which leads to a decrease in capacity. Thus, the additive of Comparative Example 2 exposed for 7 hours rapidly reduced the charge capacity to 120 mAh / g, the additive of Example 1 did not show a decrease in capacity.

* Evaluation of charge and discharge characteristics of lithium ion battery

The lithium ion batteries prepared according to Comparative Examples 1 to 4 and Examples 1 to 6 were aged at 21 ° C. for 2 days, and then subjected to chemical formation at 2.75 V to 4.2 V at 0.2 C, followed by coulomb. The efficiency was measured. Results of Example 1 and Comparative Example 1 among the measured coulomb efficiencies are shown in FIGS. 7A and 7B, respectively. In Figures 7a and 7b Qirre. Represents the irreversible capacity%.

As shown in FIG. 7B, in the lithium ion battery of Comparative Example 1 without using an additive, the coulombic efficiency was 92%, that is, the irreversible capacity was 8%. In addition, the coulombic efficiency of the lithium secondary battery of Comparative Example 2 was 94%, that is, the irreversible capacity was 6%, the Coulomb efficiency of Comparative Example 3 was 95% (nonreversible capacity: 5%), and the Coulomb efficiency of Comparative Example 4 was 93% ( Irreversible capacity: 7%). In addition, the coulombic efficiency of Reference Example 1 was 96% (nonreversible capacity: 4%), and the coulombic efficiency of Reference Example 2 was 95% (nonreversible capacity: 5%). In contrast, as shown in FIG. 7A, in the case of Example 1 using the additive, the same charge / discharge capacity of 945 mAh was obtained without a coulombic efficiency of 100%, that is, without irreversible capacity. In addition, in Example 2, the coulombic efficiency is 98%, in the case of Example 3, the coulombic efficiency is 99%, in Example 4, the coulombic efficiency is 97%, in Example 5, the coulombic efficiency is 97%, Example In the case of 6, the coulombic efficiency was 96%.

This result indicates that the Li _2.05 NiO ₂ additive has a high irreversible capacity, that is, lithium ions intercalated on the graphite layer during charge and discharge are not completely deintercalated but remain between the graphite layers, and thus remain between the graphite layers. This means that lithium ions compensate for the irreversible capacity generated at the cathode. Moreover, even if an additive compound is used, such an irreversible capacity compensation effect is excellent when the composition of the additive is in the range of Li _x NiO ₂ and x is in the range of 2.01-2.1 (result of Example 1-4). When x is 2 (Comparative Example 3) or x is 2.2 (Comparative Example 4), it can be seen that there is almost no irreversible capacity compensation effect.

In order to find out the irreversible capacity of the positive electrode and the negative electrode, a coin-type half cell using a LiCoO ₂ positive electrode, a lithium counter electrode, and a natural graphite negative electrode and a lithium counter electrode was manufactured, and charged and discharged once to 0.2 V at 4.3 V. The results of measuring the coulombic efficiency are shown in FIG. 8. In Fig. 8, Qirre. Represents the irreversible capacity%. As shown in FIG. 8, LiCoO ₂ has no irreversible capacity, but in the case of natural graphite, 9% of irreversible capacity was generated.

* High rate characteristics

The lithium ion batteries prepared according to Examples 1 to 6 and Reference Example 2 were charged with a 4.2V constant current method, and maintained at 4.2V for 5 hours in a constant voltage method (CV). The filling rate was carried out while increasing to 0.5C, 1C and 2C.

The results are shown in FIG. As shown in FIG. 9, the dose retention rate of Example 1 was 96%, the dose retention rate of Example 2 was 96%, the dose retention rate of Example 3 was 96%, the dose retention rate of Example 4 was 93%, and performed at 2C. The capacity retention rate of Example 5 was 95%, and the capacity retention rate of Example 6 was 96%. The result was similar to that of a battery using only a LiCoO ₂ positive electrode active material without an additive. From this result, it can be seen that even if the Li _2.05 NiO ₂ additive compound coated with an Al ₂ O ₃ layer is used for the positive electrode, the rate characteristic does not decrease.

On the contrary, when the amount of the additive used was excessively large (Reference Example 2), a result was obtained in which the rate characteristic was lowered as 86%.

* Cycle life characteristics

The lithium ion battery prepared according to Example 1 was charged with a 4.2V constant current method, and maintained at 4.2V for 5 hours in a constant voltage method (CV). The charging rate was 0.2C, the discharge rate was 1C, and charging and discharging was performed 250 times.

The dose retention rate was measured, and the result is shown in FIG. As a result, the capacity retention rate was 87% (from 934 mAh to 810 mAh). This result is similar to a battery using only LiCoO ₂ without an additive compound. Therefore, it can be seen from this result that even if the Li _2.05 NiO ₂ additive having the Al ₂ O ₃ layer formed on the surface is used for the positive electrode, the cycle life characteristics of the battery are not deteriorated.

* Energy density

As a result of measuring the energy density of the lithium ion battery prepared according to Example 1, 3.6 g / cc was obtained, which was similar to the battery without the additive.

From the above experimental results, it can be seen that when the Al ₂ O ₃ layer-coated Li ₂ NiO ₂ additive is used for the anode, the initial capacity reduction problem can be solved without deteriorating cycle life characteristics, rate characteristics and energy density. .

* Thermal stability and overcharge evaluation

After overcharging the lithium ion batteries prepared according to Example 1 and Comparative Example 1 at 1A constant current while increasing the voltage to 12V, the surface temperature thereof was measured, and the results are shown in FIG. 11. The cell surface temperature was observed using a K-type thermometer located at the center of the largest side of the cell can and tightly bonded with insulating tape.

As shown in FIG. 11, after the battery of Comparative Example 1 rapidly increased to 12V while 6V was exceeded, the voltage rapidly decreased to 0V, and the maximum temperature thereof was increased to 300 ° C. In addition, as a result of performing the same experiment using five batteries prepared according to Comparative Example 1, four were obtained as described above, and one of them exploded.

The result is that the internal temperature can increase above the polymer separator's melting point (Tm = 120-160 ° C), causing separator shutdown and rapidly increasing cell resistance. Also, as shown in FIG. 11, it can be expected that further increase in internal temperature may melt lithium metal (Tm = 180 ° C.) deposited on the separator and the cathode, resulting in an internal short circuit. These results were similarly obtained in Reference Example 1 in which the additive compound was used in a small amount. That is, it can be seen that the overcharge characteristics deteriorate when the additive compound is used in a small amount.

In contrast, the battery of Example 1 gradually increased in voltage, had a maximum voltage of 5.3V for about 80 minutes, and maintained about 35 minutes at this voltage. As these results as digested with NiO during the charge and discharge as the Li _2.05 NiO ₂ having a Al ₂ O ₃ layer used as an additive unstable structurally, consume excess current when the overcharge, Li _2.05 NiO ₂ is completely decomposed to NiO The voltage does not increase until

Moreover, when the battery of Example 1 reached 12V, the battery surface temperature reached the maximum of 100 degreeC. These symptoms may be Li _2.05 NiO ₂ decomposition while suppressing the increase in voltage and, Li _2.05 NiO ₂ is during the decomposition, heat becomes a, disperse rapidly out of the battery than to accumulate in the cell because it decreases the cell surface temperature, and cell Can suppress explosion.

After the overcharge experiment, except for the swelling generated as a result of gas generation due to electrolyte decomposition, the battery morphology was the same as the morphology existing before charging, as shown in FIG. 13, but in the case of Comparative Example 1 As shown in FIG. 12, it can be seen that the battery is crushed. It can be seen from this result that the Li _2.05 NiO ₂ additive serves as a surplus current consumer, and consequently increases the rate of heat release to the outside of the cell.

* Capacity measurement

After dissolving polyvinylidene fluoride binder (Querasa) in N-methyl-2-pyrrolidone solvent, the additive compound prepared in Examples 1 to 4 and Comparative Examples 2 to 4 as a positive electrode active material in this solution Super P carbon black was added as a conductive material to prepare a positive electrode active material slurry. At this time, the mixing ratio of the positive electrode active material, the conductive material and the binder was 96: 2: 2 by weight. The positive electrode active material slurry was coated on Al foil, and a positive electrode was manufactured by a conventional method of drying at 130 ° C. for 20 minutes. Using this positive electrode and lithium metal counter electrode, the half cell was produced by the conventional method. After charging and discharging the battery at 0.2C, the charge capacity thereof was measured and shown in Table 1 below.

In addition, after charging and discharging the lithium secondary battery (full cell) prepared according to Examples 1 to 4 and Comparative Examples 2 to 4 at 0.2C, the discharge capacity thereof was measured and shown in Table 1 below. .

Charge capacity, mAh / g (half cell) Discharge Capacity, mAh / g (On Battery) Example 1 420 155 Example 2 400 154 Example 3 380 155 Example 4 350 149 Comparative Example 2 337 150 Comparative Example 3 345 151 Comparative Example 4 320 148

As shown in Table 1, Al ₂ O ₃ coating layer is Examples 1 to 4 with an additive compound that is, Al ₂ O ₃ coating layer is not the comparative example 2, and Al ₂ O ₃ coating layer is, the x value of 2, although It can be seen that the charge capacity and the discharge capacity are superior to Comparative Example 3 using the phosphorus additive compound and Comparative Example 4 using the additive compound having an x value of 2.2.

All simple modifications or changes of the present invention can be easily carried out by those skilled in the art, and all such modifications or changes can be seen to be included in the scope of the present invention.

FIG. 1A is a SEM photograph of 1,000 magnification of Li _2.05 NiO ₂ having an Al ₂ O ₃ layer formed on a surface prepared in Example 1 of the present invention. FIG.

FIG. 1B is a SEM photograph of a 1000 × magnification of Li _2.05 NiO ₂ on which the Al ₂ O ₃ layer was not formed on the surface prepared in Comparative Example 2.

Figure 2a is a 10,000 magnification SEM photograph of Li _2.05 NiO ₂ Al ₂ O ₃ layer is formed on the surface prepared according to Example 1 of the present invention.

2B is a 10,000 magnification SEM photograph of Li _2.05 NiO ₂ in which no Al ₂ O ₃ layer was formed on the surface prepared in Comparative Example 2. FIG.

3A is a 100,000 magnification SEM photograph of Li _2.05 NiO ₂ having an Al ₂ O ₃ layer formed on a surface prepared according to Example 1 of the present invention.

Figure 3b is a 100,000 magnification SEM photograph of Li _2.05 NiO ₂ without Al ₂ O ₃ layer formed on the surface prepared in Comparative Example 2.

4 Al ₂ O ₃ layer is formed Li _2.05 NiO ₂ and the comparative example to the surface prepared in 2 Al ₂ O ₃ layer XRD pattern of a Li _2.05 NiO ₂ is not formed on the surface prepared in Example 1 of the present invention; Graph showing the measurement.

Figure 5 is the initial charge of Li _2.05 NiO ₂ are not the Al ₂ O ₃ layer on the prepared surface in comparison with the Li _2.05 NiO ₂ having a Al ₂ O ₃ layer on the prepared surface of Example 2 formed in the first embodiment of the present invention Graph showing discharge characteristics.

6 is a graph showing the FT-IR spectrum after exposure to air for 7 hours Li _2.05 NiO ₂ in which the Al ₂ O ₃ layer was formed on the surface prepared in Example 1 of the present invention and the surface prepared in Comparative Example 2 Graph showing FT-IR spectra before and after Li _2.05 NiO ₂ without Al ₂ O ₃ layer exposed to air.

Figure 7a is a graph showing the initial charge and discharge characteristics of the battery prepared according to Example 1 of the present invention.

Figure 7b is a graph showing the initial charge and discharge characteristics of the battery prepared according to Comparative Example 1.

Fig. 8 is a graph showing the coulombic efficiency after one time charge and discharge of the LiCoO ₂ positive electrode half cell and the natural negative electrode half cell.

9 is a graph showing the high rate characteristics of the battery prepared according to Example 1 of the present invention.

10 is a graph showing the cycle life characteristics of the battery prepared according to Example 1 of the present invention.

11 is a graph showing the voltage and the battery temperature after performing the overcharge experiment of the lithium ion battery prepared according to Example 1 and Comparative Example 1 of the present invention.

12 is a photograph showing the battery morphology after the overcharge experiment of the lithium ion battery prepared according to Example 1 of the present invention.

Figure 13 is a photograph showing the battery morphology after the overcharge experiment of the lithium ion battery prepared according to Comparative Example 1.

Claims (9)

Lithiated compounds capable of reversible intercalation / deintercalation of lithium; And A metal compound layer comprises an additive compound represented by the following formula (1) formed on the surface, The mixing ratio of the lythiated compound and the additive compound is 96: 4 to 97: 3 by weight, The additive compound is a positive electrode active material for a lithium secondary battery containing 0.5 to 2 parts by weight of the metal compound with respect to 100 parts by weight of the compound represented by the formula (1). [Formula 1] Li _x Ni _y M _1-y O ₂ (Wherein, 2.01 ≦ x ≦ 2.1, 0.95 ≦ y ≦ 1, M is selected from the group consisting of Al, Co, Ni, Mn, Fe and mixtures thereof) The method of claim 1, The metal of the metal compound layer is selected from the group consisting of Al, Mg, transition metals, and combinations thereof. The method of claim 2, The metal is selected from the group consisting of Al, Mg, Zn, Ti, and combinations thereof. delete delete The method of claim 1, The metal compound layer has a thickness of 10 nm to 2 μm. delete The method of claim 1, The additive compound is a positive electrode active material for a lithium secondary battery is prepared by forming a metal compound layer on the compound represented by the formula (1) having a purity of 99.5 to 99.9%. A positive electrode including a positive electrode active material; A negative electrode including a negative electrode active material; And Contains an electrolyte, A lithium secondary battery, wherein the cathode active material is the cathode active material according to any one of claims 1 to 3, 6, and 8.

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