KR101049543B1 - Cathode active material for lithium secondary battery, preparation method thereof, and lithium secondary battery comprising same - Google Patents

Abstract

The present invention provides any one compound selected from the group consisting of a first lithium transition metal composite oxide comprising a compound represented by the formula (1), and a compound represented by the formula (2), a compound represented by the formula (3), and combinations thereof It provides a cathode active material for a lithium secondary battery comprising a second lithium transition metal composite oxide.

Definitions for the compounds represented by Formulas 1 to 3 are as described in the detailed description of the specification. The positive electrode active material for a lithium secondary battery has excellent tap density, and improves the life characteristics, charge and discharge characteristics, and rate characteristics of a lithium secondary battery using the positive electrode active material.

Lithium Secondary Battery, Cathode Active Material, Mixing Ratio, Layered Structure, Coprecipitation Method, Layered Cathode Active Material, Tap Density, High Rate Properties, Coating, Metal Fluoride

Description

A cathode active material for a lithium secondary battery, a method of manufacturing the same, and a lithium secondary battery comprising the same.

The present invention relates to a positive electrode active material for a lithium secondary battery, a method of manufacturing the same, and a lithium secondary battery including the same, and more particularly, has an excellent tap density and improves life characteristics, charge and discharge characteristics, and rate characteristics of a lithium secondary battery. It relates to a positive electrode active material for a lithium secondary battery, a manufacturing method thereof, and a lithium secondary battery including the same.

Recently, thanks to the rapid development of the electronics, telecommunications, and computer industries, the use of portable electronic products such as camcorders, mobile phones, notebook PCs, and the like, has increased the demand for light, long-lasting and reliable batteries. In particular, the lithium secondary battery has an operating voltage of 3.7 V or more, and has a higher energy density per unit weight than a nickel-cadmium battery or a nickel-hydrogen battery. It is increasing day by day.

Recently, research on power sources for electric vehicles by hybridizing an internal combustion engine and a lithium secondary battery has been actively conducted in the US, Japan, and Europe. Recently, the development of plug-in hybrid (P-HEV) batteries for automobiles with a mileage of less than 60 miles per day is actively underway in the United States. The P-HEV battery is a battery having almost the characteristics of an electric vehicle, the development of a high capacity battery is the biggest problem. In particular, the development of a positive electrode material having a high tap density of 2.0 g / cc or more and high capacity of 230 mAh / g or more is a major challenge.

Anode materials currently commercialized or under development include LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , Li _{1 + X} [Mn _2-x M _x ] O ₄ , and LiFePO ₄ .

Commercially available small lithium ion secondary batteries mainly use LiCoO ₂ as a positive electrode active material. LiCoO ₂ is an excellent material having stable charge and discharge characteristics, excellent electronic conductivity, high battery voltage, high stability, and flat discharge voltage characteristics. However, Co has low reserves, is expensive, and toxic to humans. Therefore, development of other anode materials is desired.

LiNiO ₂ is a promising positive electrode material for P-HEV battery because it shows high capacity of 200 mAh / g or more at 4.3 V charging, but this positive electrode active material has unstable crystal structure due to de-lithium during charging. This has a very poor disadvantage. That is, when a battery in an overcharged state is heated to 200 to 270 ° C, a drastic structural change occurs, and an oxygen release reaction in the lattice due to such a structural change proceeds (JRDahn et al ., Solid State Ionics , 69, 265). (1994)). In order to improve this, many attempts have been made to substitute a portion of nickel with a transition metal element to shift the exotherm starting temperature to the high temperature side or to broaden the exothermic peak to prevent the rapid exotherm (T.Ohzuku et al ., J. Electrochem . Soc., 142, 4033 (1995), Japanese Patent Laid-Open No. 237631). But still no satisfactory results are obtained.

Part of the LiMn ₂ O ₄ is commercialized in low-cost products, but LiMn ₂ O ₄ having a spinel structure has a theoretical capacity of 148 mAh / g, which is smaller than other materials, and has a three-dimensional tunnel structure, thereby inserting lithium ions. In addition, the diffusion coefficient is large compared to LiCoO ₂ and LiNiO ₂ having a two-dimensional structure due to the large diffusion resistance during desorption and poor cycle characteristics due to the Jahn-Teller effect. In particular, the high temperature property at 55 ° C or higher is inferior to LiCoO ₂ and is not widely used in actual batteries.

Recently, research on a cathode active material for a lithium ion secondary battery has been progressing toward finding a material having both high energy density and excellent lifespan, which is stable at a high charge voltage of 4.2 V or more in place of LiCoO ₂ .

An object of the present invention is to provide a positive electrode active material for a lithium secondary battery having an excellent tap density and improving the life characteristics, charge and discharge characteristics, and rate characteristics of the lithium secondary battery.

Another object of the present invention is to provide a method for producing the positive electrode active material for a lithium secondary battery.

Still another object of the present invention is to provide a lithium secondary battery including the cathode active material.

According to one embodiment of the present invention, a group consisting of a first lithium transition metal complex oxide including a compound represented by the following Chemical Formula 1, a compound represented by the following Chemical Formula 2, a compound represented by the following Chemical Formula 3, and a combination thereof It provides a cathode active material for a lithium secondary battery comprising a second lithium transition metal composite oxide containing any one compound selected from.

[Formula 1]

Li _a Ni _x Co _y Mn _z M _1-xyz O _2-δ Q _δ

(In the formula 1,

M is Mg, Al, B, Ca, Na, K, Sr, Cr, V, Ti, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W, and combinations thereof Q is a halogen element or S, 0.95≤a≤1.2, 0.05≤x≤0.9, 0.01≤y≤0.5, 0.005≤z≤0.5, 0.8≤x + y + z≤ 1.05, 0≤δ≤0.1)

[Formula 2]

Li [Li _{(1-2x) / 3} Ni _x Mn _{(2-x) / 3} ] O _2-δ Q _δ

(In Formula 2,

Q is a halogen element or S and 0 <x <1/3, 0≤δ≤0.1)

(3)

Li [Li _x Ni _y Co _1-3x-2y Mn _{2x + y} ] O _2-δ Q _δ

(In Chemical Formula 3,

Q is a halogen element or S and 0 <x <1/3, 0 <y <(1-3x) / 2, 0≤δ≤0.1)

According to another embodiment of the present invention, a method of preparing a coprecipitation compound by coprecipitation of an aqueous metal salt solution, a chelating agent, and a basic aqueous solution; Preparing an active material precursor by drying or heat treating the co-precipitation compound; Mixing the active material precursor with a lithium salt and then baking to prepare a compound represented by Chemical Formulas 1 to 3; And mixing any one compound selected from the group consisting of a compound represented by Formula 2, a compound represented by Formula 3, and a combination thereof with a compound represented by Formula 1 It provides a method for producing.

According to another embodiment of the present invention, a lithium secondary battery including the cathode active material is provided.

The positive electrode active material for a lithium secondary battery of the present invention has an excellent tap density and improves the life characteristics, charge and discharge characteristics, and rate characteristics of the lithium secondary battery.

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

According to one embodiment of the present invention, a group consisting of a first lithium transition metal complex oxide including a compound represented by the following Chemical Formula 1, a compound represented by the following Chemical Formula 2, a compound represented by the following Chemical Formula 3, and a combination thereof It provides a cathode active material for a lithium secondary battery comprising a second lithium transition metal composite oxide containing any one compound selected from.

[Formula 1]

Li _a Ni _x Co _y Mn _z M _1-xyz O _2-δ Q _δ

(In the formula 1,

M is Mg, Al, B, Ca, Na, K, Sr, Cr, V, Ti, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W, and combinations thereof Q is a halogen element or S, and 0.95≤a≤1.2, 0.05≤x≤0.9, 0.01≤y≤0.5, 0.005≤z≤0.5, 0.8≤x + y + z≤ 1.05, 0≤δ≤0.1)

[Formula 2]

Li [Li _{(1-2x) / 3} Ni _x Mn _{(2-x) / 3} ] O _2-δ Q _δ

(In Formula 2,

Q is a halogen element or S and 0 <x <1/3, 0≤δ≤0.1)

(3)

Li [Li _x Ni _y Co _1-3x-2y Mn _{2x + y} ] O _2-δ Q _δ

(In Chemical Formula 3,

Q is a halogen element or S and 0 <x <1/3, 0 <y <(1-3x) / 2, 0≤δ≤0.1)

The positive electrode active material according to the embodiment of the present invention increases the mixture density of the electrode, and improves the capacity per volume and the capacity per weight of the positive electrode, and has excellent high rate characteristics and lifetime characteristics in a high potential region of 4.6 V or more. .

The compound represented by the formula (1) is a lithium transition metal complex oxide containing Mn, Ni, and Co, the compound having the same composition of Mn and Ni shows high thermal stability even in the state of charge (high oxidation state). In a battery containing Mn, Ni, and Co, and having a layered lithium transition metal composite oxide as the positive electrode active material, even when the charge end voltage of the battery is increased to deepen the depth of charge of the positive electrode, It can be expected that the reliability of the battery will be remarkably improved from the high thermal stability.

Lithium transition metal composite oxides containing Mn, Ni, and Co show excellent life characteristics during 4.3 V charging, but their life characteristics are significantly reduced due to the change in crystal structure when charging and discharging in the high potential region of 4.5 V or higher. This is because, when the charge end voltage is increased, the structure of the positive electrode active material deteriorates, and the decomposition of the electrolyte is likely to occur on the surface of the positive electrode.

However, as in the compound represented by Chemical Formula 1, M (where M is Mg, Al, B, Ca, Na, K, Sr, Cr, V, Ti, Fe, Zr, Zn, Si, Y, Nb, Ga, Is any element selected from the group consisting of Sn, Mo, W, and combinations thereof) or Q (where Q is a halogen element or S), thereby significantly improving the cycle characteristics in the high potential region. have.

In addition, the compound represented by Formula 2 or the compound represented by Formula 3 exhibits a high capacity of 240 mAh / g or more at 4.6 V charge. In addition, the compound represented by the formula (2) or the compound represented by the formula (3) has a high tap density, high electrode density, thereby excellent energy density. In addition, due to the high electron conductivity, not only the rate characteristic is excellent, but also the discharge potential does not drop according to the charge / discharge cycle, so that it can be used in actual batteries.

The second lithium-transition metal composite oxide is more preferable that the preferable and 2.2 to 2.5 g / cm ³ greater than the tap density is 2.2 g / cm ^3. When the tap density of the second lithium transition metal composite oxide is less than 2.2 g / cm ³ , the second lithium transition metal composite oxide has a low tap density and low energy density, despite having high capacity characteristics. In addition, due to low electronic conductivity, not only the rate characteristics are poor, but also the discharge potential is lowered according to charge and discharge cycles, making it difficult to use in actual batteries. In addition, if the tap density is too high, the energy density increases, but the rate characteristics may be poor due to the slow diffusion of lithium ions during charge and discharge, and may be difficult to use in actual batteries due to the low discharge potential according to the charge and discharge cycle. have.

The lithium transition metal complex oxide selected from the group consisting of the compound represented by Formula 1, the compound represented by Formula 2, the compound represented by Formula 3, and combinations thereof is preferably coated with metal fluoride. .

By coating the lithium transition metal composite oxide with a metal fluoride, it is possible to further improve high rate characteristics and cycle characteristics of the battery. The metal fluoride coating layer can prevent direct contact between the electrolyte and the positive electrode active material, thereby inhibiting decomposition of the positive electrode due to the oxidation reaction of the electrolyte, thereby reducing the increase in interfacial resistance according to the charge and discharge cycle, and thus the life characteristics of the lithium secondary battery, and High temperature discharge characteristics can be significantly improved. In addition, by improving the mobility of lithium ions to improve the discharge potential, the charge and discharge characteristics, the life characteristics, the rate characteristics, and the like of the lithium secondary battery are greatly improved.

In addition, the compound represented by the formula (2) or the compound represented by the formula (3) having a high capacity characteristics shows a high discharge capacity of 240 mAh / g or more, but the capacity decreases while the discharge curve decreases according to the charge and discharge cycle, Due to its low electronic conductivity, the rate characteristic drops off with increasing current. In addition, due to the large amount of Mn, the powder has a lower tap density, which significantly reduces the weight and volumetric energy density of the battery and thus cannot be used in a real cell. According to one embodiment of the present invention, the compound represented by the formula (2) or the compound represented by the formula (3) is also coated with a metal fluoride to suppress the increase in the interface resistance between the electrolyte and the positive electrode active material to improve the high rate characteristics Can be.

The metal fluoride preferably forms a coating layer that evenly surrounds the surface of the compound represented by Formulas 1 to 3, wherein the fluorine atoms of the metal fluoride have a predetermined depth inside the particles of the compound represented by Formulas 1 to 3. More preferably, it penetrates to and is present.

The metal fluoride is LiF, NaF, KF, MgF ₂ , CaF ₂ , CuF ₂ , CdF ₂ , FeF ₂ , MnF ₂ , NiF ₂ , PbF ₂ , SnF ₂ , SrF ₂ , XeF ₂ , ZnF ₂ , AlF ₃ , _{BF 3, BiF 3, CeF 3} , CrF 3, FeF 3, InF 3, LaF 3, MnF 3, NdF 3, VOF 3, YF 3, CeF 4, GeF 4, HfF 4, SiF 4, SnF 4, TiF 4 , VF ₄ , ZrF ₄ , VF ₅ , NbF ₅ , SbF ₅ , TaF ₅ , BiF ₅ , MoF ₆ , ReF ₆ , SF ₆ , WF ₆ , and mixtures thereof. In particular, it is more preferable to use AlF ₃ .

In this case, the coating amount of the metal fluoride is preferably 0.1 to 5 mol%, more preferably 0.2 to 3 mol% with respect to the lithium transition metal composite oxide. If the coating amount of the metal fluoride is less than 0.1 mol%, the coating effect does not appear, and if it exceeds 5 mol%, the ratio of the inert coating layer is increased to reduce the initial discharge capacity, and the high rate characteristic is reduced due to the thick coating layer. do.

The cathode active material may include 95 to 5 parts by weight of the first lithium transition metal complex oxide, and 5 to 95 parts by weight of the second lithium transition metal complex oxide, and 70 to 30 weight of the first lithium transition metal complex oxide. More preferably, and 30 to 70 parts by weight of the second lithium transition metal composite oxide. When the content ratio of the first lithium transition metal composite oxide and the second lithium transition metal composite oxide is within the above range, a battery having excellent cycle characteristics, high rate characteristics, and energy density even in a high potential region having a charge termination voltage of 4.6 V is obtained. Can be.

Compounds represented by Chemical Formulas 1 to 3 are prepared by coprecipitation of a metal salt aqueous solution, a chelating agent, and a basic aqueous solution to prepare a coprecipitation compound, and a dry or heat treatment of the coprecipitation compound to prepare an active material precursor. It may be prepared by mixing and firing.

First, an aqueous metal salt solution, a chelating agent, and a basic aqueous solution are injected into a reactor to obtain a coprecipitation compound through a coprecipitation reaction.

When preparing a compound represented by Formula 1, the aqueous metal salt solution is nickel, cobalt, manganese, and optionally metal M (where M is Mg, Al, B, Ca, Na, K, Sr, Cr, V, Ti, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W, and any one element selected from the group consisting of a combination thereof) containing a metal salt, When preparing the compound to be represented, the aqueous metal salt solution contains a metal salt containing nickel, and manganese, and when preparing the compound represented by the formula (3), the aqueous metal salt solution is a metal salt containing nickel, manganese, and cobalt It contains.

The nickel, cobalt, manganese, and the like in the aqueous metal salt solution are mixed to satisfy the stoichiometric ratios described in the compounds represented by Chemical Formulas 1 to 3. The concentration of the aqueous metal salt solution is preferably 1M to 3M, since a positive electrode active material having high capacity characteristics can be produced.

The metal salt is not particularly limited as long as it can be dissolved in water, and sulfates, nitrates, acetates, halides, hydroxides and the like can be preferably used.

As the chelating agent, any one selected from the group consisting of ammonia aqueous solution, ammonium sulfate aqueous solution, and mixtures thereof may be preferably used.

It is preferable that it is 0.2-0.5: 1, and, as for the molar ratio of the said chelating agent and the said metal salt aqueous solution, it is more preferable that it is 0.2-0.4: 1. In this case, the molar ratio of the chelating agent is 0.2 to 0.5 moles with respect to 1 mole of the aqueous metal solution, but the chelating agent reacts with the metal at least 1 to 1 to form a complex, but the chelating agent can be recovered and used again. This is because the ratio is an optimal condition for increasing and stabilizing the crystallinity of the positive electrode active material.

The basic aqueous solution is preferably any one selected from the group consisting of NaOH, KOH, and combinations thereof, and the concentration of the basic aqueous solution is preferably 2M to 10M, more preferably 2M to 5M. When the concentration of the basic aqueous solution is too low, the particle formation time may be long, the tap density may decrease, and the yield of the coprecipitation reactant may decrease. On the other hand, if the concentration is too high, the rapid growth of the particles by the rapid reaction it is difficult to form a uniform particle and the tap density may also drop.

The coprecipitation reaction is a reaction in which two or more elements are simultaneously precipitated in an aqueous solution to obtain a composite hydroxide. Here the average time the aqueous solution stays in the reactor is adjusted to 4 to 12 hours, the pH is adjusted to 9.5 to 12.5, preferably 10 to 11.5, the temperature of the reactor is maintained at 50 to 80 ℃, 500 It is preferable to stir at a stirring speed of from 2000 rpm.

The reason for adjusting the pH and the temperature in the reactor as described above is that it is difficult to obtain a high density composite hydroxide because the produced composite hydroxide precipitates in complex salt form at a low temperature.

The reactor in which such co-precipitation reaction is carried out can use a conventional reactor used in this field, it is not particularly limited in the present invention. However, one or more baffles, preferably one to four baffles, are provided inside the reactor, and a cylinder is provided to uniformly mix the upper and lower portions of the reactor core, and the stirring blade has a reverse wing type rotary blade. It is preferred that the reactor is equipped with a device.

The baffle is to control the intensity and direction of the material when mixing the reaction materials, and to solve the local nonuniformity of the reaction solution by increasing the turbulent effect, which is located 2 to 3 cm from the inside of the reactor It is preferable. By using such a reactor, the tap density of the coprecipitation compound obtained after the coprecipitation reaction can be improved by about 10% or more. As a result, the tap density of the prepared coprecipitation compound is 1.05 g / cm 3 or more, preferably 1.25 g / cm 3 or more, and more preferably 1.45 g / cm 3 or more.

Next, the obtained coprecipitation compound is dried or heat treated to prepare an active material precursor. At this time, when only drying is performed, the active material precursor maintains the complex hydroxide form, and when the heat treatment is performed, the active material precursor is converted into the complex oxide form.

The drying process is performed for 15 to 30 hours at 110 to 200 ℃, through this drying to prepare an active material precursor in the form of a composite hydroxide. In addition, the heat treatment process is carried out at 400 to 550 ℃ for 4 to 10 hours, through the heat treatment is prepared as an active material precursor in the form of transition metal complex oxide.

In this case, the active material precursor has a form of secondary particles in which the primary particles are agglomerated with each other by drying or heat-treating primary particles, which are the coprecipitation compound.

Next, the active material precursor is mixed with a lithium salt and then fired to prepare a cathode active material for a lithium secondary battery.

In this case, the lithium salt may be any one selected from the group consisting of lithium nitrate, lithium acetate, lithium carbonate, lithium hydroxide, and combinations thereof.

The lithium salt is mixed so as to satisfy the stoichiometric ratio described in the active material precursor and the compound represented by Formulas 1 to 3, wherein the mixing is not particularly limited in the present invention, both conventional wet mixing or dry mixing are possible.

It is preferable to perform the said baking process at 700-1100 degreeC. The baking atmosphere is preferably an oxidizing atmosphere of air or oxygen, and the baking time is preferably 10 to 30 hours.

At this time, the preliminary firing may be carried out by maintaining at 250 to 650 ° C. for 5 to 20 hours before the firing step, and, if necessary, the annealing process may be performed at 600 to 750 ° C. for 10 to 20 hours after the firing step.

In addition, it is preferable to further include the step of adding a sintering additive when mixing the active material precursor and the lithium salt. The sintering additive may preferably be any one selected from the group consisting of compounds containing ammonium ions, metal oxides, metal halides, and combinations thereof.

The compound containing the ammonium ion is preferably any one selected from the group consisting of NH ₄ F, NH ₄ NO ₃ , (NH ₄ ) ₂ SO ₄ , and combinations thereof, wherein the metal oxide is B ₂ O ₃ , Bi ₂ O ₃ , and any one selected from the group consisting of a combination thereof, the metal halide is preferably any one selected from the group consisting of NiCl ₂ , CaCl ₂ , and combinations thereof. .

The sintering additive is preferably used in an amount of 0.01 to 0.2 mole with respect to 1 mole of the active material precursor. When the content of the sintering additive is too low, the effect of improving the sintering characteristics of the active material precursor may be insignificant. If the content of the sintering additive is higher than the above range, the initial capacity may be decreased during charging and discharging, or the performance as the positive electrode active material may be deteriorated.

In addition, the method of manufacturing a cathode active material according to an embodiment of the present invention is selected from the group consisting of the compound represented by Formula 1, the compound represented by Formula 2, the compound represented by Formula 3, and combinations thereof It is preferable to further include coating any one lithium transition metal composite oxide with a metal fluoride. The method of coating the lithium transition metal composite oxide with the metal fluoride is not particularly limited, and any conventionally used method may be used.

The metal fluoride is LiF, NaF, KF, MgF ₂ , CaF ₂ , CuF ₂ , CdF ₂ , FeF ₂ , MnF ₂ , NiF ₂ , PbF ₂ , SnF ₂ , SrF ₂ , XeF ₂ , ZnF ₂ , AlF ₃ , _{BF 3, BiF 3, CeF 3} , CrF 3, FeF 3, InF 3, LaF 3, MnF 3, NdF 3, VOF 3, YF 3, CeF 4, GeF 4, HfF 4, SiF 4, SnF 4, TiF 4 , VF ₄ , ZrF ₄ , VF ₅ , NbF ₅ , SbF ₅ , TaF ₅ , BiF ₅ , MoF ₆ , ReF ₆ , SF ₆ , WF ₆ , and mixtures thereof. Can be.

The coated metal fluoride is placed on the surface of the lithium transition metal composite oxide by van der Waals forces. The coating layer thus formed suppresses the structural change of the lithium transition metal composite oxide and the reaction with the electrolyte, thereby improving cycle characteristics, and increasing the mobility of lithium ions present in the electrolyte, thereby improving rate characteristics.

In addition, the method of manufacturing a cathode active material according to an embodiment of the present invention is selected from the group consisting of the compound represented by Formula 1, the compound represented by Formula 2, the compound represented by Formula 3, and combinations thereof The method may further include improving cycle characteristics and high rate characteristics by replacing oxygen, which is an anion of any one of the lithium transition metal complex oxides, with fluorine.

The substituted fluorine atom exists as a chemical bond having strong covalent bonds on the surface of the lithium composite metal oxide particle. In addition, the fluorine atom is mainly present on the particle surface, but exists with a certain concentration distribution up to the inside of the particle. For this reason, the fluorine atoms on the surface of the particles stabilize the surface of the lithium composite metal oxide crystals, inhibit decomposition of the contacting electrolyte solution, and protect the surface of the positive electrode active material from hydrofluoric acid (HF) to prevent dissolution of transition metals, thereby preventing the dissolution of transition metals. Improve chemical properties.

The cathode active material for a rechargeable lithium battery according to one embodiment of the present invention may be any one compound selected from the group consisting of a compound represented by Formula 2, a compound represented by Formula 3, and a combination thereof. The compound represented by 1 can be mixed and manufactured. The method of mixing is not particularly limited, and any method can be used as long as it is a conventionally used method.

According to another embodiment of the present invention, there is provided a lithium secondary battery including a positive electrode including the positive electrode active material, a negative electrode including a negative electrode active material, and an electrolyte present between the positive electrode and the negative electrode.

DETAILED DESCRIPTION Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention.

The lithium secondary battery may be a lithium ion battery, a lithium ion polymer battery, or a lithium polymer battery according to the type of separator and electrolyte used, and may be cylindrical, square, coin type, or pouch type depending on the form.

1 is a schematic cross-sectional view of a rechargeable lithium battery according to one embodiment of the present invention. Referring to FIG. 1, the lithium secondary battery 4 includes an electrode assembly 44 including a positive electrode 42, a negative electrode 41, and a separator 43 existing between the positive electrode 42 and the negative electrode 41. To the case 45, the electrolyte (not shown) is injected into the upper portion of the case 45 and sealed with a cap plate 46 and a gasket 47, and then assembled.

The cathode 42 includes a cathode active material according to an embodiment of the present invention. The positive electrode 42 may be prepared by mixing the positive electrode active material, the conductive agent, and the binder to prepare a composition for forming a positive electrode active material layer, and then coating the composition on a positive electrode current collector such as aluminum foil and rolling the same. . Metal fluoride may optionally be further added when preparing the composition for forming the cathode active material layer.

As the binder, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropylene cellulose, diacetylene cellulose, polyvinyl chloride, polyvinylpyrrolidone, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene or polypropylene may be used. It may be, but is not limited thereto.

In addition, any conductive material may be used as long as the conductive material is used in the battery. Examples thereof include natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, copper, nickel, aluminum, silver, and the like. Metal powders, metal fibers and the like can be used.

The negative electrode 41 includes a negative electrode active material. As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples of the negative electrode active material include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fibers, and amorphous carbon, lithium, lithium alloys, alloys, intermetallic compounds, organic compounds, inorganic compounds, metal complexes, and lithium polymers such as organic polymer compounds. Use compounds that can intestine and release ions. Each of the above compounds can be used alone or in any combination within a range that does not impair the effects of the present invention.

More specifically, carbonaceous materials include coke, pyrolytic carbon, natural graphite, artificial graphite, meso carbon micro beads, graphitized meso face spheres, vapor grown carbon, glassy carbons, and polyacrylonitrile. Any one selected from the group consisting of carbon fiber based on nitrile (poly acrylonitrile), pitch-based, cellulose-based, vapor-grown carbon, amorphous carbon, carbon the organic material is fired and mixtures thereof, It can be used in arbitrary combination in the range which does not impair the effect of this invention.

As the lithium alloy, a Li-Al alloy, a Li-Al-Mn alloy, a Li-Al-Mg alloy, a Li-Al-Sn alloy, a Li-Al-In alloy, or a Li-Al-Cd alloy , Li-Al-Te based alloy, Li-Ga based alloy, Li-Cd based alloy, Li-In based alloy, Li-Pb based alloy, Li-Bi based alloy, Li-Mg based alloy and the like can be used. As an alloy and an intermetallic compound, the compound of a transition metal and silicon, the compound of a transition metal, and tin, etc. can be used, Especially a compound of nickel and silicon is preferable.

Like the positive electrode 42, the negative electrode 41 is also prepared by mixing the negative electrode active material, a binder, and optionally a conductive material to prepare a composition for forming a negative electrode active material layer, and then applying the same to a negative electrode current collector such as copper foil. Can be.

As the electrolyte (not shown), a non-aqueous electrolyte or a known solid electrolyte may be used, and a lithium salt is used.

The lithium salt is not particularly limited as a lithium salt commonly used, and for example, the lithium salt is LiClO ₄ , LiBF ₄ , LiPF ₆ , LiAlCl ₄ , LiSbF ₆ , LiSCN, LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , Li (CF ₃ SO ₂ ) ₂ , LiAsF ₆ , LiN (CF ₃ SO ₂ ) ₂ , LiB ₁₀ Cl ₁₀ , LiBOB (lithium Bis (oxalato) borate), lower aliphatic lithium carbonate, lithium chloroborane, tetraphenylboric acid Lithium, and LiN (CF ₃ SO ₂ ), LiN (C ₂ F ₅ SO ₂ ), 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₎ are already available such as the dE (imide), such as acids.

The lithium salts may be used alone or in any combination within the range not impairing the effects of the present invention, and it is particularly preferable to use LiPF ₆ .

In addition, carbon tetrachloride, ethylene trifluorochloride, or phosphate containing phosphorus may be included in the electrolyte to render the electrolyte nonflammable.

In addition to the electrolyte, any one solid electrolyte selected from the group consisting of inorganic solid electrolytes, organic solid electrolytes, and mixtures thereof may be used.

Examples of the inorganic solid electrolyte include Li ₄ SiO ₄ , Li ₄ SiO ₄ -LiI-LiOH, Li ₃ PO ₄ -Li ₄ SiO ₄ , Li ₂ SiS ₃ , Li ₃ PO ₄ -Li ₂ S-SiS ₂ , and phosphorus sulfide compounds And any one selected from the group consisting of a mixture thereof can be used.

The organic solid electrolyte may be polyethylene oxide, polypropylene oxide, polyvinyl alcohol, polyvinylidene fluoride, fluoropropylene, or the like, derivatives, mixtures, or copolymers thereof.

The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move. As the non-aqueous organic solvent, any one selected from the group consisting of cyclic carbonates, chain carbonates, chain carboxylic acid esters, lactone compounds, and mixtures thereof can be used.

The cyclic fluoride includes ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), and a mixture thereof. Any one selected from can be used.

The chain carbonate is selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC) dipropyl carbonate (DPC), and mixtures thereof. You can use either one.

The chain carboxylic acid ester may be any one selected from the group consisting of methyl formate, methyl acetate, methyl propionate, ethyl propionate, and mixtures thereof. .

As the lactone compound, γ-butyrolactone (γ-butyrolactone, GBL) may be used.

Meanwhile, the separator 43 may exist between the positive electrode 42 and the negative electrode 41 according to the type of the lithium secondary battery. As the separator 43, polyethylene, polypropylene, polyvinylidene fluoride or two or more multilayer films thereof may be used, and polyethylene / polypropylene two-layer separator, polyethylene / polypropylene / polyethylene three-layer separator, polypropylene / polyethylene Of course, a mixed multilayer film such as a polypropylene three-layer separator can be used.

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

(Production of battery)

(Manufacture example 1: LiNi _0.4 Co _0.3 Mn _0.28 Mg _0.02 O ₂ Manufacture)

4 liters of distilled water was added to the coprecipitation reactor (capacity 4L, the output of the rotary motor 80W) and nitrogen gas was supplied to the reactor at a rate of 0.5 liters / minute to remove dissolved oxygen and maintain the reactor temperature at 50 ° C at 1000 rpm. Stirred.

Here, a 2.4 M aqueous metal solution containing nickel sulfate, cobalt sulfate, manganese sulfate, and magnesium sulfate in a 40: 30: 28: 2 molar ratio was 0.3 liters / hour, and a 0.03 liter / s of ammonia solution of 3.6 M concentration was added. The reactor was continuously fed in time. In addition, an aqueous NaOH solution at a concentration of 4.8 M was supplied for pH adjustment so that the pH in the reactor was maintained at 11.

Then, the co-precipitation reaction was performed by adjusting the impeller speed of the reactor to 1000 rpm. At this time, the flow rate was adjusted so that the average residence time of the solution in the reactor was about 6 hours, and after the reaction reached a steady state, a steady state duration was given to the reactant to obtain a more dense coprecipitation compound.

The obtained coprecipitation compound was filtered, washed with water, and then dried in a warm air dryer at 110 ° C. for 15 hours to obtain an active material precursor (Ni _0.4 Co _0.3 Mn _0.28 Mg _0.02 (OH) ₂ ).

After mixing the obtained active material precursor and lithium hydroxide (LiOH) was heated at a temperature increase rate of 1 ℃ / min, and then maintained at 500 ℃ for 5 hours to perform pre-firing, followed by firing at 930 ℃ 20 hours LiNi _0.4 Co _0.3 Mn _0.28 Mg _0.02 O ₂ was obtained.

(Production Example 2: Li [Li _0.2 Ni _0.133 Co ₀ . ₁₃₄ Mn _0.533 ] O ₂ Manufacture)

4 liters of distilled water was added to the coprecipitation reactor (capacity 4L, the output of the rotary motor 80W) and nitrogen gas was supplied to the reactor at a rate of 0.5 liters / minute to remove dissolved oxygen and maintain the reactor temperature at 50 ° C at 1000 rpm. Stirred.

Here, a 2.4 M aqueous metal salt solution containing nickel sulfate, cobalt sulfate, and manganese sulfate in a 16.6: 16.6: 66.8 molar ratio was continuously added to the reactor at 0.3 liter / hour, and a 3.6 M ammonia solution at 0.03 liter / hour in the reactor. Was added. In addition, 4.8 M NaOH aqueous solution was supplied for pH adjustment so that the pH in the reactor was maintained at 10.

Subsequently, co-precipitation reaction was performed by adjusting the impeller speed of the reactor to 1000 rpm. At this time, the flow rate was adjusted so that the average residence time of the solution in the reactor was about 6 hours, and after the reaction reached a steady state, a steady state duration was given to the reactant to form a more dense coprecipitation compound.

The obtained coprecipitation compound was filtered, washed with water, and then dried in a warm air dryer at 110 ° C. for 15 hours to obtain an active material precursor (Ni _0.166 Co _0.166 Mn _0.668 (OH) ₂ ).

After mixing the obtained active material precursor and lithium hydroxide (LiOH) was heated at a temperature increase rate of 1 ℃ / min, and then maintained at 500 ℃ for 5 hours to perform pre-firing, followed by firing at 900 ℃ 24 hours Li [Li _0.2 Ni _0.133 Co _0.134 Mn _0.533 ] O ₂ was obtained.

(Manufacture example 3: LiNi _0.8 Co _0.1 Mn _0.08 Mg _0.02 O ₂ Manufacture)

The active material precursor [Ni _0.8 Co _0.1 Mn _0.08 Mg _0.02 ] (OH) _{2 in the} same manner as in Example 1, except that nickel sulfate, cobalt sulfate, manganese sulfate, and magnesium sulfate were used in a molar ratio of 80: 10: 10: 8: _2. Got. In addition, after mixing the obtained active material precursor and lithium hydroxide (LiOH) was heated at a heating rate of 2 ℃ / min, and then maintained at 500 ℃ for 5 hours to perform pre-firing, followed by firing at 780 ℃ 20 hours LiNi _0.8 Co _0.1 Mn _0.08 Mg _0.02 O ₂ was obtained.

(Manufacture example 4: LiNi _0.4 Co _0.3 Mn _0.28 Mg _0.02 O _1.99 F _0.01 Manufacture)

1 ° C / min after mixing the active material precursor (Ni _0.4 Co _0.3 Mn _0.28 Mg _0.02 (OH) ₂ ), lithium hydroxide (LiOH), and lithium fluorine (LiF) obtained in Preparation Example 1 in a 1.00: 0.99: 0.01 molar ratio. After preheating was carried out by heating at a rate of temperature increase of 500 ℃ for 5 hours, followed by firing at 900 ℃ 20 hours to obtain LiNi _0.4 Co _0.3 Mn _0.28 Mg _0.02 O _1.99 F _0.01 .

(Production example 5: AlF ₃  Coated with Li [Li _0.2 Ni _0.133 Co ₀ . ₁₃₄ Mn _0.533 ] O ₂ Manufacture)

1) Preparation of AlF ₃ Coating Liquid

A 50 ml aqueous solution of 0.05 M Al (NO ₃ ) ₃ 9H ₂ O was made in a 500 ml glass beaker. At this time, while maintaining the temperature of the aqueous solution at 20 ℃, while stirring at a stirring speed of 600rpm, 50ml of 0.35M NH ₄ F aqueous solution was continuously added to the beaker at a rate of 5ml / min. At this time, pH was 10.00 when NH ₄ F aqueous solution was added.

Subsequently, 2 ml of NH ₄ OH was added to the beaker and stirred for 1 hour to precipitate all unreacted materials to obtain a coating compound. At this time, the amount of NH ₄ OH was 0.35M. The obtained precipitated coating compound precipitated, that is, the viscosity of the coating solution was about 2.5cP pH was maintained at 10.00, it was white. The composition of the prepared coating compound was AlF ₃ , the average size of the particles was about 50 to 200 nm, the specific surface area was 70m ² / g.

2) Manufacture of Coated Cathode Active Material

100 g of Li [Li _0.2 Ni _0.133 Co _0. Prepared in Preparation Example 2 in 100 ml of the coating solution in which AlF ₃ was dispersed in 0.05M. ₁₃₄ Mn _0.533 ] O ₂ was slowly impregnated and then stirred at a stirring speed of 1000 rpm while maintaining the temperature at 20 ° C. At this time, the pH was maintained at 10.00 and the viscosity was about 10 cP.

The reaction was dried in a thermostat at 110 ° C. for 24 hours and then heat treated at 400 ° C. to give AlF ₃ coated Li [Li _0.2 Ni _0.133 Co ₀ . ₁₃₄ Mn _0.533 ] O ₂ was prepared.

Example 1: LiNi _0.4 Co _0.3 Mn _0.28 Mg _0.02 O ₂ And Li [Li _0.2 Ni _0.133 Co ₀ . ₁₃₄ Mn _0.533 ] O ₂ 50: 50 positive electrode active material mixed in a weight ratio)

LiNi _0.4 Co _0.3 Mn _0.28 Mg _0.02 O ₂ prepared in Preparation Example 1 and Li [Li _0.2 Ni _0.133 Co ₀ . ₁₃₄ Mn _0.533] O ₂ to 50: a mixture of from Ishihara how the expression grinding mortar so that a weight ratio of 50, to obtain a positive electrode active material. Subsequently, polyvinylidene fluoride was dissolved in N-methyl-2-pyrrolidone as a dispersion medium as a binder, and carbon was used as the conductive agent so that the weight ratio of the positive electrode active material, the conductive agent, and the binder was 85: 7.5: 7.5. After addition and mixing, a positive electrode slurry was prepared. The prepared positive electrode slurry was uniformly applied to an aluminum foil having a thickness of 20 μm, and vacuum dried at 120 ° C. to prepare a positive electrode for a lithium secondary battery.

LiPF ₆ was dissolved in a solvent in which ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 3: 7 so as to have a concentration of 1 mol / L to prepare an electrolyte solution.

 The anode prepared above, a lithium foil as a counter electrode, a porous polyethylene membrane (manufactured by Celgard ELC, Celgard 2300, thickness: 25 μm) as a separator, and a commonly known preparation using the prepared electrolyte solution The coin cell of the C2032 standard was manufactured according to the process.

Example 2: Li [Ni _0.4 Co _0.3 Mn _0.28 Mg _0.02 ] O ₂ And Li [Li _0.2 Ni _0.133 Co ₀ . ₁₃₄ Mn _0.533 ] O ₂ end 70: 30 weight ratio positive electrode active material)

Example, except that the weight ratio of Li [Ni _0.4 Co _0.3 Mn _0.28 Mg _0.02 ] O ₂ and Li [Li _0.2 Ni _0.133 Co _0.134 Mn _0.533 ] O ₂ is 70:30 The battery was manufactured by the same method as 1.

Example 3: LiNi _0.8 Co _0.1 Mn _0.08 Mg _0.02 O ₂ And Li [Li _0.2 Ni _0.133 Co ₀ . ₁₃₄ Mn _0.533 ] O ₂ 50: 50 positive electrode active material mixed in a weight ratio)

A battery was manufactured in the same manner as in Example 1, except that LiNi _0.8 Co _0.1 Mn _0.08 Mg _0.02 O ₂ prepared in Preparation Example 3 was used instead of LiNi _0.4 Co _0.3 Mn _0.28 Mg _0.02 O ₂ .

Example 4: LiNi _0.4 Co _0.3 Mn _0.28 Mg _0.02 O _1.99 F _0.01 And Li [Li _0.2 Ni _0.133 Co ₀ . ₁₃₄ Mn _0.533 ] O ₂ Is a positive electrode active material mixed at a weight ratio of 50 to 50)

A battery was manufactured in the same manner as in Example 1, except that LiNi _0.4 Co _0.3 Mn _0.28 Mg _0.02 O _1.99 F _0.01 was used in Preparation Example 4 instead of LiNi _0.4 Co _0.3 Mn _0.28 Mg _0.02 O ₂ .

Example 5: LiNi _0.4 Co _0.3 Mn _0.28 Mg _0.02 O ₂ And AlF ₃ Coated with Li [Li _0.2 Ni _0.133 Co ₀ . ₁₃₄ Mn _0.533 ] O ₂ 50: 50 positive electrode active material mixed in a weight ratio)

Li [Li _0.2 Ni _0.133 Co ₀ . Li [Li _0.2 Ni _0.133 Co _0. Coated with AlF ₃ prepared in Preparation Example 5 instead of ₁₃₄ Mn _0.533 ] O ₂ . Example, except using ₁₃₄ Mn _0.533 ] O ₂ The battery was manufactured by the same method as 1.

(Comparative Example 1: Li [Li _0.2 Ni _0.133 Co _0.134 Mn _0.555 ] O ₂  Cathode active material)

A battery was manufactured in the same manner as in Example 1, except that Li [Li _0.2 Ni _0.133 Co _0.134 Mn _0.555 ] O ₂ prepared in Preparation Example 2 was used alone.

Comparative Example 2: LiNi _0.4 Co _0.3 Mn _0.28 Mg _0.02 O ₂  Cathode active material)

A battery was manufactured in the same manner as in Example 1, except that LiNi _0.4 Co _0.3 Mn _0.28 Mg _0.02 O ₂ prepared in Preparation Example 1 was used alone.

Comparative Example 3: LiNi _0.8 Co _0.1 Mn _0.08 Mg _0.02 O ₂  Cathode active material)

A battery was manufactured in the same manner as in Example 1, except that LiNi _0.8 Co _0.1 Mn _0.08 Mg _0.02 O ₂ prepared in Preparation Example 3 was used alone.

Comparative Example 4: LiNi _0.4 Co _0.3 Mn _0.28 Mg _0.02 O _1.99 F _0.01  Cathode active material)

A battery was manufactured in the same manner as in Example 1, except that LiNi _0.4 Co _0.3 Mn _0.28 Mg _0.02 O _1.99 F _0.01 prepared in Preparation Example 4 was used alone.

(Comparative Example 5: AlF ₃  Coated Li [Li _0.2 Ni _0.133 Co _0.134 Mn _0.555 ] O ₂  Cathode active material)

A battery was manufactured in the same manner as in Example 1, except that Li [Li _0.2 Ni _0.133 Co _0.134 Mn _0.555 ] O ₂ prepared in Preparation Example 5 was used alone.

Experimental Example 1 Tap Density Measurement

The tap density (g / cm 3) of the positive electrode active materials used in Examples 1 to 5 and Comparative Examples 1 to 5 was measured.

After putting 10 g of the positive electrode active material into a 10 ml glass beaker, a glass beaker is placed in an ultrasonic generator, and ultrasonic waves are applied for 30 minutes to vibrate. Thereafter, the volume of the positive electrode active material was measured in a glass beaker to measure the tap density (g / cm 3). After repeating this ten times, the tap density (g / cm 3) of the positive electrode active material was measured, and its average value was determined as the tap density of the positive electrode active material.

The measured tap densities of the positive electrode active materials used in Examples 1 to 4 and Comparative Example 4 are shown in Table 1 below.

TABLE 1

Example 1 Example 2 Example 3 Example 4 Comparative Example 4 Tap density
(g / cm3) 1.89 1.78 1.93 1.95 1.65

Referring to Table 1, it can be seen that the tap density of the positive electrode active material used in Examples 1 to 4 increased compared to the positive electrode active material used in Comparative Example 1. The tap density of the second lithium transition metal composite oxide used in Examples 1 to 4 was 2.2 g / cm 3. This is because it has a high value. The increased tap density improves the capacity per volume and capacity per weight of the positive electrode so that it can exhibit excellent properties in terms of energy density.

In addition, through Examples 1 and 2, it can be seen that as the content of the first lithium transition metal composite oxide increases, the amount of increase in tap density decreases. Therefore, it can be seen that the larger the content ratio of the first lithium transition metal composite oxide is, the more disadvantageous in terms of energy density.

Experimental Example 2: Evaluation of Capacity Characteristics of a Battery

The discharge capacity of the batteries of Examples 1 to 5 was charged and discharged for 3 cycles by applying a current of 20 mAg ^-1 (0.08 C) in the range of 2.0 to 4.6 V, and then 50 mAg ^-1 (0.2 C) was measured. Charging and discharging were performed by applying a current of a) to measure the discharge capacity. The discharge capacity of the first cycle obtained at the applied current of 20 mAg ^-1 (0.08 C) and 50 mAg ^-1 (0.2 C) is shown in Table 2 below.

TABLE 2

Example 1 Example 2 Example 3 Example 4 Example 5 20 mAg ^-1 discharge capacity 220mAhg ^-1 224mAhg ^-1 234mAhg ^-1 218 mAhg ^-1 220mAhg ^-1 50 mAg ^-1 discharge capacity 210mAhg ^-1 211mAhg ^-1 223mAhg ^-1 209 mAhg ^-1 210mAhg ^-1

Referring to Table 2, the discharge capacity of the battery including the positive electrode active material of Examples 1 to 5 at 20 mAg ^-1 applied current shows a high energy capacity per weight of about 220 mAhg ^-1 or more. In addition, it can be seen that even at 50 mAg ⁻¹ applied current, a high energy-per-weight capacity of about 210 mAhg ⁻¹ or more is maintained. In particular, the discharge capacity in Example 3 is 20 mAg ^-1 is shown the discharge capacity at a current of 234 mAhg ^-1 shows the excellent energy capacity per weight.

Experimental Example 3: Evaluation of Discharge Curve of Battery

3-1) Comparison of Example 1, Example # 2, and Comparative Example 1

Using the coin cells of Example 1, Example 2, and Comparative Example 1 charge and discharge test was performed while applying an applied current of 50 mAg ^-1 (0.2 C) in the range of 2.0 V to 4.6 V. At this time, the charge and discharge test compared the discharge curve of 5 cycles to compare the respective discharge potential.

2 is a charge / discharge curve showing the five cycle discharge potentials of the coin cells of Example 1, Example 2, and Comparative Example 1. FIG.

Referring to FIG. 2, in Example 1, the discharge potential is increased compared to Comparative Example 1 to show excellent characteristics in terms of energy density, and Example 2 also has excellent characteristics in terms of energy density due to an increase in discharge potential. It was confirmed that there is. However, as the weight ratio of the first lithium transition metal composite oxide increases, the increase in discharge potential decreases, which is disadvantageous in terms of energy density.

3-2) Comparison of Example 1, Example 3, and Comparative Example 1

Charge and discharge tests were performed by applying an applied current of 50 mAg ⁻¹ (0.2 C) in the range of 2.0 V to 4.6 V using the coin cells of Example 1, Example 3, and Comparative Example 1. At this time, the charge and discharge test compared the discharge curve of 5 cycles to compare the respective discharge potential.

3 is a charge / discharge curve showing five cycle discharge potentials of the coin cells of Example 1, Example 3, and Comparative Example 1. FIG.

Referring to FIG. 3, in Example 1, the discharge potential was increased in comparison with Comparative Example 1 to show excellent characteristics in terms of energy density, and Example 3 also had excellent characteristics in terms of energy density due to an increase in discharge potential. It was confirmed that there is. Particularly, in the case of Example 3, it can be seen that the discharge potential is increased while maintaining a high capacity at an energy capacity per weight of 220 mAh / g or more, thereby showing an excellent energy density characteristic.

Experimental Example 4: Evaluation of Cycle Life Characteristics of a Battery

4-1) Comparison of Example 1, Example 2, and Comparative Example 2

Charge and discharge tests were performed by applying 50 mAg ⁻¹ (0.2 C) applied current in the range of 2.0 V to 4.6 V using the coin cells of Example 1, Example 2, and Comparative Example 2. At this time, the charge and discharge test was evaluated as the capacity retention rate relative to the initial capacity during the 70 cycles and the results are shown in Table 3.

[Table 3]

Example 1 Example 2 Comparative Example 2  Capacity retention rate (%) 93.3%
(194 mAh / g) 93.4%
(197 mAh / g) 87.2%
(169 mAh / g)

Referring to Table 3, in the case of Examples 1 and 2, even if the cycle characteristics of the high voltage of 4.6V, the capacity retention rate of 93% or more compared to the initial capacity. However, in the case of Comparative Example 2, it can be seen that the cycle characteristics are somewhat low, 87.2%.

4-2) Comparison of Example 1, Example 3, and Comparative Example 3

Using the coin cells of Example 1, Example 3, and Comparative Example 3, the charge and discharge test was performed while applying an applied current of 50 mAg ^-1 (0.2 C) in the range of 2.0 V to 4.6 V. At this time, the charge and discharge test was evaluated as the capacity retention rate relative to the initial capacity during the 70 cycles and the results are shown in Table 4 below.

[Table 4]

Example 1 Example 3 Comparative Example 3  Capacity retention rate (%) 93.3%
(194 mAh / g) 93.1%
(207 mAh / g) 86.0%
(178 mAh / g)

Referring to Table 4, in the case of Examples 1 and 3, the cycle characteristics show a capacity retention ratio of 93% or more compared to the initial capacity even at a high voltage of 4.6 V, and shows very excellent life characteristics. In particular, in the case of Example 3, even after maintaining 70 cycles, while maintaining a high energy-per-weight capacity of 200 mAh / g, excellent life characteristics are exhibited.

However, in the case of Comparative Example 3, it can be seen that the cycle characteristics are somewhat low, 86.0%.

4-3) Comparison of Example 4, Comparative Example 2, and Comparative Example 4

Using the coin cells of Example 4, Comparative Example 2, and Comparative Example 4, the charge and discharge test was performed while applying a 50 mAg ^-1 (0.2 C) applied current in the range of 2.0 V to 4.6 V. At this time, the charge and discharge test was evaluated as the capacity retention rate relative to the initial capacity during the 70 cycles, the results are shown in Table 5 below.

TABLE 5

Example 4 Comparative Example 2 Comparative Example 4  Capacity retention rate (%) 92.9%
(204 mAh / g) 87.2%
(168 mAh / g) 88.8%
(170 mAh / g)

Referring to Table 5, in the case of Example 4, the cycle characteristic shows a capacity retention of about 93% compared to the initial capacity even at a high voltage of 4.6 V and shows very excellent life characteristics. This is because fluorine particles substituted with oxygen mainly exist as covalently bonded chemical bonds on the surface of the particles to stabilize the surface of the lithium transition metal composite oxide crystals and to suppress decomposition of the contacted electrolyte solution, and at the same time, the anode from the hydrofluoric acid (HF) This is because the electrochemical properties are improved by protecting the surface of the active material to prevent dissolution of the transition metal.

This can be confirmed from the result that the comparative example 4 substituted with the fluorine slightly improved the lifetime characteristics compared with the comparative example 2. However, in the case of Comparative Example 4, the cycle characteristics were 88.8%, which is slightly lower than that of Example 4.

4-4) Comparison of Example 5 and Comparative Example 2

Using the coin battery of Example 5 and Comparative Example 2, the charge and discharge test was performed while applying an applied current of 50 mAg ^-1 (0.2 C) in the range of 2.0 V to 4.6 V. At this time, the charge and discharge test was evaluated by the capacity retention rate relative to the initial capacity during the 70 cycles, the results are shown in Table 6.

TABLE 6

Example 5 Comparative Example 2  Capacity retention rate (%) 91.1%
(190mAh / g) 87.2%
(169 mAh / g)

Referring to Table 6, in the case of Example 4, the cycle characteristic shows a capacity retention of about 91% compared to the initial capacity even at a high voltage of 4.6 V, and shows a very good lifespan characteristic and a high energy capacity per weight of 190 mAh / g. It can be seen that it is maintained. This is because the coating layer made of AlF ₃ nanoparticles suppressed the structural change of the cathode active material and the reaction with the electrolyte.

However, in the case of Comparative Example 2, it can be seen that the cycle characteristics are somewhat low, 87.2%.

Experimental Example 5: Evaluation of Rate Characteristics of a Battery

5-1) Comparison of Example 1, Example 3, and Comparative Example 1

The coin batteries of Example 1, Example 3, and Comparative Example 1 were used to charge at a constant current of 0.2 C at room temperature until the voltage reached 4.6 V, and 0.2 C, 0.5 C, 1 C, 3 C The discharge capacity (mAhg ⁻¹ ) of the battery was measured at each constant current by discharging in a sequence until the voltage reached 2.0 V in constant current at three cycles. At this time, the rate characteristic test changed the average value of the discharge capacity measured at 3 C constant current every 3 cycles to the capacity retention ratio compared to the average value of the discharge capacity measured at 0.2 C constant current, and evaluated the characteristics thereof. The results are shown in Table 7 below. It was.

TABLE 7

Example 1 Example 3 Comparative Example 1  Capacity retention rate (%) 85.6% 82.2% 68.8%

Referring to Table 7, it can be seen that in the case of Examples 1 and 3, the rate characteristic shows a capacity retention ratio of 80% or more compared to 0.2 C discharge capacity even at a high applied current of 3 C, and shows a very excellent rate characteristic.

However, in the case of Comparative Example 1 it can be seen that due to the low electron conductivity of the positive electrode active material, the rate characteristic is slightly lower than 70%.

5-2) Comparison of Example 4 and Comparative Example 1

Using the coin battery of Example 4 and Comparative Example 1, the battery was charged at a constant current of 0.2 C at room temperature until the voltage reached 4.6 V, and then at a constant current in the order of 0.2 C, 0.5 C, 1 C, and 3 C. The discharge capacity (mAhg ⁻¹ ) of the battery was measured at each constant current by discharging until the voltage reached 2.0 V every three cycles. In this case, the rate characteristic test changed the average value of the discharge capacity measured at the constant current of 3 C every 3 cycles to the capacity retention ratio compared to the average value of the discharge capacity measured at the constant current of 0.2 C, and evaluated the characteristics thereof. Indicated.

[Table 8]

Example 4 Comparative Example 1 Capacity retention rate (%) 80.0% 68.8%

Referring to Table 8, it can be seen that in the case of Example 4, the rate characteristic shows a capacity retention rate of 80% compared to 0.2 C discharge capacity even at a high applied current of 3 C and shows a very excellent rate characteristic. This is because fluorine particles substituted with oxygen mainly exist as covalently bonded chemical bonds on the surface of the particles to stabilize the surface of the lithium transition metal composite oxide crystals and to suppress decomposition of the contacted electrolyte solution, and at the same time, the anode from the hydrofluoric acid (HF) This is because the surface of the active material is protected to prevent dissolution of the transition metal to improve electrochemical properties.

However, in the case of Comparative Example 1 it can be seen that due to the low conductivity of this material, the rate characteristic appears to be somewhat lower than 70%.

5-3) Comparison of Example 5, Comparative Example 1, and Comparative Example 5

Using the coin batteries of Example 5, Comparative Example 1, and Comparative Example 5, the battery was charged at a constant current of 0.2 C at room temperature until the voltage reached 4.6 V, followed by the order of 0.2 C, 0.5 C, 1 C, 3 C. As described above, the discharge capacity (mAhg ⁻¹ ) of the battery was measured at each constant current by discharging at a constant current until the voltage reached 2.0 V every three cycles. At this time, the rate characteristic test changed the average value of the discharge capacity measured at 3 C constant current every 3 cycles to the capacity retention ratio compared to the average value of the discharge capacity measured at 0.2 C constant current, and evaluated the characteristics thereof. Indicated.

TABLE 9

Example 5 Comparative Example 1 Comparative Example 5 Capacity retention rate (%) 80.0% 68.8% 70.0%

Referring to Table 9, it can be seen that in the case of Example 5, the rate characteristic shows a capacity retention ratio of 80% or more compared to the 0.2 C discharge capacity even at a high applied current of 3 C, and shows a very excellent rate characteristic. This is because the coating layer made of AlF ₃ nanoparticles improved the rate characteristic by increasing the mobility of lithium ions present in the electrolyte.

This can be confirmed also from the result that the comparative example 5 has a somewhat increased rate characteristic compared with the comparative example 1. However, in the case of Comparative Example 5, it can be seen that the rate characteristic is somewhat lower than 70% compared to Example 5.

1 is a schematic cross-sectional view of a lithium secondary battery according to an embodiment of the present invention.

FIG. 2 is a charge and discharge curve showing five cycle discharge potentials of the coin cells of Example 1, Example 2, and Comparative Example 1. FIG.

Figure 3 is a charge and discharge curve showing the five cycle discharge potential of the coin cell of Example 1, Example 3, and Comparative Example 1.

<Explanation of symbols for the main parts of the drawings>

4: lithium secondary battery 41: negative electrode

42: anode 43: separator

44 electrode assembly 45 case

46: cap plate 47: gasket

Claims (27)

A first lithium transition metal composite oxide comprising a compound represented by Formula 1, and A second lithium transition metal composite oxide comprising a compound represented by Formula 2 or a compound represented by Formula 3 A cathode active material for a lithium secondary battery comprising a. [Formula 1] Li _a Ni _x Co _y Mn _z M _1-xyz O _2-δ Q _δ (In the formula 1, M is Mg, Al, B, Ca, Na, K, Sr, Cr, V, Ti, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W, and combinations thereof Q is a halogen element or S, and 0.95≤a≤1.2, 0.05≤x≤0.9, 0.01≤y≤0.5, 0.005≤z≤0.5, 0.8≤x + y + z≤ 1.05, 0≤δ≤0.1) [Formula 2] Li [Li _{(1-2x) / 3} Ni _x Mn _{(2-x) / 3} ] O _2-δ Q _δ (In Formula 2, Q is a halogen element or S and 0 <x <1/3, 0≤δ≤0.1) (3) Li [Li _x Ni _y Co _1-3x-2y Mn _{2x + y} ] O _2-δ Q _δ (In Chemical Formula 3, Q is a halogen element or S and 0 <x <1/3, 0 <y <(1-3x) / 2, 0≤δ≤0.1) The method of claim 1, The second lithium transition metal composite oxide has a tap density of 2.2 g / cm ³ or more. The method of claim 1, The lithium transition metal composite oxide selected from the group consisting of the compound represented by Formula 1, the compound represented by Formula 2, the compound represented by Formula 3, and combinations thereof is coated with metal fluoride Positive electrode active material for secondary batteries. The method of claim 3, The metal fluoride is LiF, NaF, KF, MgF ₂ , CaF ₂ , CuF ₂ , CdF ₂ , FeF ₂ , MnF ₂ , NiF ₂ , PbF ₂ , SnF ₂ , SrF ₂ , XeF ₂ , ZnF ₂ , AlF ₃ , _{BF 3, BiF 3, CeF 3} , CrF 3, FeF 3, InF 3, LaF 3, MnF 3, NdF 3, VOF 3, YF 3, CeF 4, GeF 4, HfF 4, SiF 4, SnF 4, TiF 4 , VF ₄ , ZrF ₄ , VF ₅ , NbF ₅ , SbF ₅ , TaF ₅ , BiF ₅ , MoF ₆ , ReF ₆ , SF ₆ , WF ₆ , and any one selected from the group consisting of a mixture thereof Positive electrode active material for secondary batteries. The method of claim 3, The metal fluoride is to form a coating layer surrounding the surface of the lithium transition metal composite oxide positive electrode active material for a lithium secondary battery. The method of claim 3, The positive electrode active material for lithium secondary batteries, wherein the fluorine atom of the metal fluoride is also present inside the particles of the lithium transition metal composite oxide. The method of claim 3, The coating amount of the metal fluoride is 0.1-5 mol% based on the lithium transition metal composite oxide. The method of claim 1, The cathode active material includes 95 to 5 parts by weight of the first lithium transition metal composite oxide, and 5 to 95 parts by weight of the second lithium transition metal composite oxide. Coprecipitation of an aqueous metal salt solution, a chelating agent, and a basic aqueous solution to prepare a coprecipitation compound; Preparing an active material precursor by drying or heat treating the co-precipitation compound; Mixing the active material precursor with a lithium salt and then baking to prepare a compound represented by Chemical Formulas 1 to 3; And Mixing the compound represented by Formula 2 or the compound represented by Formula 3 with the compound represented by Formula 1 Method for producing a positive electrode active material for a lithium secondary battery comprising a. [Formula 1] Li _a Ni _x Co _y Mn _z M _1-xyz O _2-δ Q _δ (In the formula 1, M is Mg, Al, B, Ca, Na, K, Sr, Cr, V, Ti, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W, and combinations thereof Q is a halogen element or S, and 0.95≤a≤1.2, 0.05≤x≤0.9, 0.01≤y≤0.5, 0.005≤z≤0.5, 0.8≤x + y + z≤ 1.05, 0≤δ≤0.1) [Formula 2] Li [Li _{(1-2x) / 3} Ni _x Mn _{(2-x) / 3} ] O _2-δ Q _δ (In Formula 2, Q is a halogen element or S and 0 <x <1/3, 0≤δ≤0.1) (3) Li [Li _x Ni _y Co _1-3x-2y Mn _{2x + y} ] O _2-δ Q _δ (In Chemical Formula 3, Q is a halogen element or S and 0 <x <1/3, 0 <y <(1-3x) / 2, 0≤δ≤0.1) 10. The method of claim 9, When preparing the compound represented by Formula 1, the aqueous metal salt solution is nickel, cobalt, manganese, and optionally metal (M) (wherein M is Mg, Al, B, Ca, Na, K, Sr, Cr, A metal salt comprising V, Ti, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W, and combinations thereof); When preparing the compound represented by Formula 2, the aqueous metal salt solution contains a metal salt containing nickel, and manganese, When preparing the compound represented by Formula 3, wherein the aqueous metal salt solution contains a metal salt containing nickel, manganese, and cobalt. 10. The method of claim 9, The metal salt aqueous solution is a method of producing a positive electrode active material for lithium secondary batteries having a concentration of 1 M to 3 M. 10. The method of claim 9, The metal salt aqueous solution comprises a salt selected from the group consisting of sulfate, nitrate, acetate, halide, hydroxide, and combinations thereof. 10. The method of claim 9, The chelating agent is any one selected from the group consisting of ammonia aqueous solution, ammonium sulfate aqueous solution, and mixtures thereof. 10. The method of claim 9, The molar ratio of the chelating agent and the metal salt aqueous solution is 0.2 to 0.5: 1 manufacturing method of a positive electrode active material for lithium secondary batteries. 10. The method of claim 9, The basic aqueous solution is any one selected from the group consisting of NaOH, KOH, and combinations thereof. 10. The method of claim 9, The basic aqueous solution is a method of producing a positive electrode active material for a lithium secondary battery having a concentration of 2 M to 10 M. 10. The method of claim 9, The coprecipitation compound is prepared at a pH of 10 to 12.5. 10. The method of claim 9, When the coprecipitation compound is prepared, the drying is performed at 110 to 200 ° C., and the heat treatment is performed at 400 to 550 ° C. A method of manufacturing a cathode active material for a lithium secondary battery. 10. The method of claim 9, The lithium salt is any one selected from the group consisting of lithium nitrate, lithium acetate, lithium carbonate, lithium hydroxide, and combinations thereof. 10. The method of claim 9, The firing of the mixture of the active material precursor and the lithium salt is carried out at 700 to 1100 ℃ manufacturing method of a positive electrode active material for a lithium secondary battery. 10. The method of claim 9, The method of manufacturing a cathode active material for a lithium secondary battery further comprising the step of adding a sintering additive when the active material precursor and lithium salt mixing. The method of claim 21, The sintering additive is any one selected from the group consisting of a compound containing an ammonium ion, a metal oxide, a metal halide, and a combination thereof. The method of claim 22, The compound containing ammonium ion is any one selected from the group consisting of NH ₄ F, NH ₄ NO ₃ , (NH ₄ ) ₂ SO ₄ , and combinations thereof, The metal oxide is any one selected from the group consisting of B ₂ O ₃ , Bi ₂ O ₃ , and combinations thereof, The metal halide is any one selected from the group consisting of NiCl ₂ , CaCl ₂ , and combinations thereof. The method of claim 21, The sintering additive is a method for producing a positive electrode active material for a lithium secondary battery that is used in an amount of 0.01 to 0.2 mole per 1 mole of the active material precursor. 10. The method of claim 9, Lithium secondary further comprising the step of coating any one selected from the group consisting of a compound represented by Formula 1, a compound represented by Formula 2, a compound represented by Formula 3, and combinations thereof with a metal fluoride The manufacturing method of the positive electrode active material for batteries. The method of claim 25, The metal fluoride is LiF, NaF, KF, MgF ₂ , CaF ₂ , CuF ₂ , CdF ₂ , FeF ₂ , MnF ₂ , NiF ₂ , PbF ₂ , SnF ₂ , SrF ₂ , XeF ₂ , ZnF ₂ , AlF ₃ , _{BF 3, BiF 3, CeF 3} , CrF 3, FeF 3, InF 3, LaF 3, MnF 3, NdF 3, VOF 3, YF 3, CeF 4, GeF 4, HfF 4, SiF 4, SnF 4, TiF 4 , VF ₄ , ZrF ₄ , VF ₅ , NbF ₅ , SbF ₅ , TaF ₅ , BiF ₅ , MoF ₆ , ReF ₆ , SF ₆ , WF ₆ , and any one selected from the group consisting of a mixture thereof The manufacturing method of the positive electrode active material for secondary batteries. A lithium secondary battery comprising the cathode active material for lithium secondary battery according to any one of claims 1 to 8.

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