KR20190117049A - Positive electrode active material for secondary battery, method for preparing the same, and secondary battery comprising the same - Google Patents

Abstract

The present invention relates to a method for manufacturing positive electrode active materials which comprises following steps of: preparing a lithium composite transition metal oxide represented by chemical formula 1: LiNi_aCo_bMn_cM_dO_2; cleaning the lithium composite transition metal oxide; and mixing the washed lithium composite transition metal oxide with a coating raw material, followed by heat treating to coat the same, wherein the coating raw material contains at least one selected from an oxide-based coating raw material and a carbide-based coating raw material, and a hydrate-based coating raw material.

Description

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

The present invention relates to a cathode active material for a secondary battery including a composite coating layer having excellent coating properties, a method for preparing the same, and a lithium secondary battery including the same.

As technology development and demand for mobile devices increase, the demand for secondary batteries as a source of energy is rapidly increasing. Among such secondary batteries, lithium secondary batteries having high energy density and voltage, long cycle life, and low self discharge rate have been commercialized and widely used.

Lithium transition metal composite oxide is used as a positive electrode active material of a lithium secondary battery, and among these, lithium cobalt composite metal oxide of LiCoO ₂ having a high operating voltage and excellent capacity characteristics is mainly used. However, since LiCoO ₂ is very poor in thermal properties due to destabilization of crystal structure due to de-lithium and is expensive, there is a limit to using LiCoO ₂ as a power source in fields such as electric vehicles.

As a material for replacing LiCoO ₂ , lithium manganese composite metal oxides (such as LiMnO ₂ or LiMn ₂ O ₄ ), lithium iron phosphate compounds (such as LiFePO ₄ ), or lithium nickel composite metal oxides (such as LiNiO ₂ ) have been developed. Among them, research and development of lithium nickel composite metal oxides having a high reversible capacity of about 200mAh / g, which is easy to implement a large-capacity battery, are being actively studied. However, LiNiO ₂ has a poor thermal stability compared to LiCoO _2, and when an internal short circuit occurs due to pressure from the outside in a charged state, the positive electrode active material itself decomposes, causing a battery to rupture and ignite.

Accordingly, as a method for improving low thermal stability while maintaining excellent reversible capacity of LiNiO ₂ , a nickel cobalt manganese-based lithium composite transition metal oxide in which a part of Ni is substituted with Mn and Co (hereinafter, simply referred to as 'NCM-based lithium oxide') Has been developed. However, NCM-based lithium oxides, which have been developed up to now, have insufficient capacity characteristics, have a layered crystal structure, have low structural stability, and elute transition metal components by reaction with an electrolyte solution, thereby rapidly deteriorating battery performance. There is a problem.

In order to solve this problem, techniques for preventing contact with the electrolyte by forming a coating layer on the surface of the NCM-based lithium oxide have been proposed. For example, Japanese Patent Application Laid-Open No. 10-2016-0050835 discloses a method of forming a coating layer by mixing an NCM-based lithium oxide in a solution containing a tungsten precursor, removing a solvent, and then performing a heat treatment at 250 ° C to 500 ° C.

As such, conventionally, the surface of the positive electrode active material has been modified by coating a single material, but there is a problem in that the coating property is inferior according to the coating raw material. Therefore, there is a problem that the coating on the surface of the positive electrode material is not well at the time of low temperature coating. However, when a high temperature process is used to coat the materials, there is a problem in that the powder characteristics such as the specific surface area of the cathode material and the electrochemical performance are different.

Therefore, there is a demand for development of a technology capable of obtaining excellent coating properties even at low temperatures.

Patent Publication No. 10-2016-0050835

An object of the present invention is to provide a method for producing a positive electrode active material that can form a coating layer exhibiting excellent coating properties for a lithium composite transition metal oxide even at low temperatures.

Another object of the present invention is to provide a positive electrode active material including a coating layer having excellent coating properties prepared by the method of manufacturing the positive electrode active material.

Another object of the present invention is to provide a cathode and a lithium secondary battery comprising the cathode active material.

The present invention to prepare a lithium composite transition metal oxide represented by the formula (1) to solve the above problems; Cleaning the lithium composite transition metal oxide; And mixing the washed lithium composite transition metal oxide with a coating raw material, followed by heat treatment to coat the coating raw material, wherein the coating raw material is one or more selected from an oxide-based coating raw material and a carbide-based coating raw material; It provides a method for producing a positive electrode active material comprising a hydrate-based coating raw material.

[Formula 1]

LiNi _a Co _b Mn _c M _d O ₂

(a> 0.75, 0 <b <0.25, 0 <c <0.25, 0 ≦ d ≦ 0.2, a + b + c + d = 1, and M is W, Cu, Fe, V, Cr, Ti, Zr, At least one doping element selected from the group consisting of Zn, Al, In, Ta, Y, In, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo)

In addition, the present invention, in order to solve the other problem, a positive electrode active material prepared by the method for producing a positive electrode active material, comprising a lithium composite transition metal oxide represented by the formula (1), the surface of the lithium composite transition metal oxide A coating layer comprising two or more coating elements is formed in the coating element, and the coating element is derived from at least one selected from an oxide-based coating raw material and a carbide-based coating raw material, and a hydrate-based coating raw material. It provides a positive electrode active material, which is a material.

In addition, the present invention provides a lithium secondary battery comprising a positive electrode for a lithium secondary battery including the positive electrode active material and the positive electrode for a lithium secondary battery in order to solve the another problem.

According to the present invention, since the coating layer is formed on the lithium composite transition metal oxide using at least one selected from an oxide-based coating raw material and a carbide-based coating raw material, and a coating raw material including a hydrate-based coating raw material, the coating layer is Excellent coating properties can be exhibited.

The following drawings, which are attached to this specification, illustrate exemplary embodiments of the present invention, and together with the contents of the present invention serve to further understand the technical idea of the present invention, the present invention is limited to the matters described in such drawings. It should not be construed as limited.
1 is a scanning electron microscope (SEM) photograph of the positive electrode active material according to Example 1. FIG.

The terms or words used in this specification and claims are not to be construed as limiting in their usual or dictionary meanings, and the inventors may appropriately define the concept of terms in order to best explain their invention in the best way possible. It should be interpreted as meaning and concept corresponding to the technical idea of the present invention based on the principle that the present invention.

The terminology used herein is for the purpose of describing exemplary embodiments only and is not intended to be limiting of the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise.

As used herein, the terms "comprise", "comprise" or "have" are intended to indicate that there is a feature, number, step, component, or combination thereof, that is, one or more other features, It should be understood that it does not exclude in advance the possibility of the presence or addition of numbers, steps, components, or combinations thereof.

As used herein, "%" means weight percent unless otherwise indicated.

In the present specification, the "average particle diameter (D ₅₀ )" means a particle size corresponding to 50% of the cumulative number of particles in the particle size distribution curve of the particles. The average particle diameter D ₅₀ may be measured using, for example, a laser diffraction method.

Method for producing a cathode active material of the present invention comprises the steps of preparing a lithium composite transition metal oxide represented by the formula (1); Cleaning the lithium composite transition metal oxide; And mixing the washed lithium composite transition metal oxide with a coating raw material, followed by coating by heat treatment.

[Formula 1]

LiNi _a Co _b Mn _c M _d O ₂

(a> 0.75, 0 <b <0.25, 0 <c <0.25, 0 ≦ d ≦ 0.2, a + b + c + d = 1, and M is W, Cu, Fe, V, Cr, Ti, Zr, At least one doping element selected from the group consisting of Zn, Al, In, Ta, Y, In, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo)

A represents an atomic fraction of nickel in the lithium composite transition metal oxide, and may be a> 0.75, specifically 0.75 <a <1, and more specifically 0.8 ≦ a ≦ 0.95.

B represents an atomic fraction of cobalt in the lithium composite transition metal oxide, and may be 0 <b <0.25, and specifically 0.05 ≦ b <0.2.

C represents an atomic fraction of manganese in the lithium composite transition metal oxide, and may be 0 <c <0.25, and specifically 0.05 ≦ c <0.2.

The d represents an atomic fraction of the M element in the lithium composite transition metal oxide, and may be 0 ≦ d ≦ 0.2, and specifically 0 ≦ d ≦ 0.1.

(1) preparing a lithium composite transition metal oxide represented by Formula 1

The lithium composite transition metal oxide may be prepared by using a commercially available lithium composite transition metal oxide or by a method for preparing a lithium composite transition metal oxide known in the art.

For example, the lithium composite transition metal oxide represented by Formula 1 may be prepared by mixing a transition metal precursor and a lithium raw material, optionally a raw material containing M element, and then firing.

The transition metal precursor may be a hydroxide, an oxy hydroxide, a carbonate, or an organic complex including Ni, Co, and Mn. Specifically, the transition metal precursor may be nickel-cobalt hydroxide, nickel-cobalt oxy hydroxide, nickel-cobalt-manganese hydroxide, nickel-cobalt-manganese oxy hydroxide, or M or doped with the hydroxide or oxy hydroxide, It is not limited to this.

The lithium raw material may be lithium-containing carbonate (e.g. lithium carbonate), hydrate (e.g. lithium hydroxide I hydrate (LiOHH ₂ O), etc.), hydroxide (e.g. lithium hydroxide, etc.), nitrate (e.g. , Lithium nitrate (LiNO ₃ ), etc.), chlorides (eg, lithium chloride (LiCl), etc.), but are not limited thereto.

The M-containing raw material may be an oxide, hydroxide, sulfide, oxyhydroxide, halide or mixtures thereof containing M elements. For example, the M-containing raw material is ZnO, Al ₂ O ₃ , Al (OH) ₃ , AlSO ₄ , AlCl ₃ , Al-isopropoxide (Al-isopropoxide), AlNO ₃ , TiO ₂ , WO _{3 ,} AlF, H ₂ BO ₃ , HBO ₂ , H ₃ BO ₃ , H ₂ B ₄ O _{7 ,} B ₂ O ₃ , C ₆ H ₅ B (OH) ₂ , (C ₆ H ₅ O) ₃ B, [(CH ₃ ( CH ₂ ) ₃ O) ₃ B, C ₃ H ₉ B ₃ O ₆ , (C ₃ H ₇ O ₃ ) B, Li ₃ WO ₄ , (NH ₄ ) ₁₀ W ₁₂ O ₄₁ 5H ₂ O, NH ₄ H ₂ PO ₄ Etc., but is not limited thereto.

Meanwhile, the firing may be performed at 600 ° C. to 1000 ° C., preferably 700 ° C. to 900 ° C. for 5 hours to 30 hours, preferably 10 hours to 20 hours.

(2) cleaning the lithium composite transition metal oxide

The lithium composite transition metal oxide has residual lithium which is not reacted in the manufacturing process, and thus requires a process for cleaning the surface.

Composite transition metal oxides containing nickel, in particular composite hydroxides containing nickel or composite oxides containing nickel, and lithium composite transition metal oxides obtained by firing lithium compounds are unreacted on the surfaces of primary particles and / or secondary particles. Lithium compounds are present. Therefore, it is possible to remove excess unreacted lithium compounds such as lithium hydroxide or lithium carbonate and other impurity elements that deteriorate battery characteristics from the lithium composite transition metal oxide particles through the washing process.

Therefore, when the preparation of the lithium composite transition metal oxide is performed, the step of cleaning the lithium composite transition metal oxide is performed. The cleaning may be performed using, for example, washing water including water. In this case, water is imparted to the surface of the lithium composite transition metal oxide in the cleaning step so that the reactivity with the hydrate-based coating raw material may be reduced in the subsequent coating layer formation step. Can be increased.

In addition, the washing may include a process of obtaining the lithium composite transition metal oxide washed by mixing the lithium composite transition metal oxide with washing water, washing with water, followed by filtration and solid-liquid separation. For example, the lithium composite transition metal oxide powder may be mixed with water to form a slurry, and then filtered and solid-liquid separated to obtain a washed lithium composite transition metal oxide.

The washing water introduced in the washing process may be used in an amount of 0.5 times or more and less than 4 times the weight of the lithium composite transition metal oxide, and the temperature in the washing process may be 0 ° C. to 30 ° C., specifically, 10 C may be 25 ° C.

When the amount of the washing water is used in relation to the weight of the lithium composite transition metal oxide, the lithium compound existing on the surface of the lithium composite transition metal oxide particles may be removed. When the amount of the washing water is used, the unreacted lithium compound may be removed. Since it may remain, the washing can be more effectively performed when the amount of the washing water is in the above range. In addition, since the solubility of the unreacted lithium compound varies depending on the temperature of the washing water, and the inside and surface properties of the lithium composite transition metal oxide particles may vary, the unreacted lithium compound may be more effectively removed when the washing is performed in the above temperature range. have.

(3) Cleaned  Mixing the lithium composite transition metal oxide and the coating raw material, followed by heat treatment to coat

The cleaned lithium composite transition metal oxide may have unstable defects on the surface of the lithium composite transition metal oxide, and thus, after cleaning, a coating layer may be used to control defects on the surface of the lithium composite transition metal oxide. Shall be.

The coating layer may be formed by mixing the washed lithium composite transition metal oxide and the coating raw material, and then heat treatment, the coating raw material is at least one selected from an oxide-based coating raw material and a carbide-based coating raw material, Hydrate based coating raw materials.

The coating raw material may be 0.01 part by weight to 2 parts by weight, specifically 0.01 part by weight to 1.5 parts by weight, and more specifically 0.01 part by weight to 1 part by weight based on 100 parts by weight of the cleaned lithium composite transition metal oxide. Can be. When the coating raw material is insufficiently used, it is difficult to stabilize the surface of the lithium composite transition metal oxide, so that it is difficult to control the specific surface area to an appropriate level and the life may be reduced. When the coating raw material is used too much, the coating layer is electrically inert. Since a problem of reducing capacity may occur, when mixed with the cleaned lithium composite transition metal oxide in the above range, a coating layer for surface stability may be formed to an appropriate degree. Such a coating layer may have a thickness of 1 nm to 500 nm, specifically 1 nm to 200 nm, and more specifically may have a thickness of 1 nm to 100 nm.

The heat treatment may be performed at a temperature of 400 ° C. or less, specifically 100 ° C. to 400 ° C., and more specifically 250 ° C. to 350 ° C. When the heat treatment temperature is less than 400 ℃ to improve the surface stability of the lithium composite transition metal oxide to control the specific surface area, it can exhibit the effect of improving the life characteristics.

The oxide coating raw material is one selected from the group consisting of tungsten oxide (WO ₃ ), boron oxide (B ₂ O ₃ ), alumina (Al ₂ O ₃ ), titanium dioxide (TiO ₂ ) and magnesium oxide (MgO). It may be abnormal.

In addition, the carbide-based coating material may be at least one selected from the group consisting of boron carbide (B ₄ C), tungsten carbide (WC), aluminum carbide (Al ₄ C ₃ ) and titanium carbide (TiC).

In addition, the hydrate-based coating raw material may be at least one selected from the group consisting of boric acid (H ₃ BO ₃ ), tungstic acid (H ₂ WO ₄ ), and molybdate acid (H ₂ MoO ₄ ).

In general, since the oxide-based coating raw material and the carbide-based coating raw material react at a high temperature of 1,000 ° C. or more, it is not easy to coat these materials on the positive electrode active material. However, according to the researches of the present inventors, when the oxide coating raw material and / or carbide coating raw material is coated together with a hydrate coating raw material, the oxide coating raw material and / or carbide coating raw material at low temperature It has been found that can be coated on the surface of the positive electrode active material. In addition, after the lithium composite transition metal oxide was washed with water, the affinity with the hydrate-based coating raw material was improved, and the reactivity was further improved. In this way, when the coating property is increased, the service life of the battery may be improved, and when the reactivity of the lithium composite transition metal oxide and the hydrate-based coating raw material is improved, the specific surface area of the lithium composite transition metal oxide is controlled at low temperature. It may have the advantage of being easy to do.

In addition, when the lithium composite transition metal oxide is washed with water and then coated with only the oxide-based coating material and the carbide-based coating material alone at low temperature, it is difficult to control the specific surface area of the cathode active material, and the hydrate The service life is lower compared to the case where the system coating raw material is used together.

The coating raw material may be one or more selected from the oxide coating raw material and the carbide coating raw material, and the hydrate coating raw material may be included in a weight ratio of 1: 1.2 to 1: 5, specifically 1: It may be included in a weight ratio of 1.5 to 1: 3.

When too much of the proportional hydrate-based coating raw material is added, too much electrical inert coating layer may be made, which may cause a problem of capacity reduction, and at least one selected from the oxide-based coating raw material and the carbide-based coating raw material; When the hydrate-based coating raw material is included in the weight ratio, it may exhibit more excellent long-term stability without lowering the electrical capacity.

In one example of the present invention, the oxide-based coating raw material may be tungsten oxide (WO ₃ ), the hydrate-based coating raw material may be boric acid (H ₃ BO ₃ ).

In addition, in one example of the present invention, the carbide-based coating raw material may be boron carbide (B ₄ C), the hydrate-based coating raw material may be tungstic acid (H ₂ WO ₄ ).

Tungsten oxide (WO ₃ ) is used as the oxide-based coating raw material, boric acid (H ₃ BO ₃ ) is used as the hydrate-based coating raw material, and boron carbide (B ₄ C) as the carbide-based coating raw material When tungstic acid (H ₂ WO ₄ ) is used as the hydrate-based coating raw material, a coating layer containing tungsten (W) and a boron compound may be formed on the surface of the lithium transition metal oxide.

Specifically, the coating layer may include a lithium tungsten oxide combined with lithium and tungsten, the lithium tungsten oxide, for example, Li ₂ WO ₄ And at least one of Li ₆ W ₂ O ₉ . Among various lithium-tungsten compounds, Li ₂ WO ₄ And since Li ₆ W ₂ O ₉ has a low lithium migration barrier energy, when the coating layer comprises tungsten in the form, there is an advantage that the desorption of lithium ions smoothly.

The tungsten may be included in an amount of 200 ppm to 4,000 ppm, specifically 500 ppm to 2,000 ppm, and more specifically 500 ppm to 1,000 ppm of the cathode active material. When the content of the tungsten satisfies the above range, the crystal transition in the lithium composite transition metal oxide surface layer portion occurs smoothly, and the deterioration of the capacitance characteristics can be suppressed.

In addition, the coating layer may include a boron compound containing boron and oxygen. The boron compound may be lithium borate, boron oxide, boric acid, boric acid oxo acid, boron oxo acid salt, and the like, specifically, LiBO ₂ , Li ₂ B ₄ O ₇ , LiB ₅ O ₈ , Li ₂ B ₂ O ₅ , Ortho boric acid, boric acid, ammonium borate, and the like, but is not limited thereto. When the boron compound is included in the coating layer, the thermal stability of the cathode active material may be further improved.

The boron compound may be included in an amount of 100 ppm to 2,000 ppm, specifically 100 ppm to 1,500 ppm, and more specifically 300 ppm to 1,000 ppm in the cathode active material. When the content of the boron compound satisfies the above range, it is possible to exert excellent long-life characteristics, and to suppress a decrease in capacity and an increase in resistance.

The present invention also provides a cathode active material produced by the method for producing the cathode active material.

The cathode active material includes a lithium composite transition metal oxide represented by Formula 1 below, and a coating layer including two or more coating elements is formed on a surface of the lithium composite transition metal oxide, and the coating element is an oxide-based coating raw material. It is a substance derived from the at least 1 sort (s) chosen from a substance and a carbide-type coating raw material, and a substance derived from the hydrate-type coating raw material.

[Formula 1]

LiNi _a Co _b Mn _c M _d O ₂

(a> 0.75, 0 <b <0.25, 0 <c <0.25, 0 ≦ d ≦ 0.2, a + b + c + d = 1, and M is W, Cu, Fe, V, Cr, Ti, Zr, At least one doping element selected from the group consisting of Zn, Al, In, Ta, Y, In, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo)

In the cathode active material according to an example of the present invention, the coating layer may include tungsten and a boron compound, and specifically, the tungsten may be included in the form of lithium-tungsten oxide in which lithium and tungsten are combined.

In addition, the cathode active material may include the tungsten in an amount of 200 ppm to 4,000 ppm (by weight), specifically 500 ppm to 2,000 ppm, and more specifically 500 ppm to 1,000 ppm. When the content of the tungsten satisfies the above range, the crystal transition in the lithium composite transition metal oxide surface layer portion occurs smoothly, and the deterioration of the capacitance characteristics can be suppressed.

In addition, the cathode active material may include the boron compound in an amount of 100 ppm to 2,000 ppm, specifically 100 ppm to 1,500 ppm, more specifically 300 ppm to 1,000 ppm. When the content of the boron compound satisfies the above range, it can exhibit excellent long-term life characteristics, it is possible to suppress the decrease in capacity and increase in resistance.

The positive electrode active material for a secondary battery according to the present invention may be usefully used for the production of a positive electrode for a secondary battery.

Specifically, the secondary battery positive electrode according to the present invention includes a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector, wherein the positive electrode active material layer includes the positive electrode active material according to the present invention.

The positive electrode may be manufactured according to a conventional positive electrode manufacturing method except for using the positive electrode active material according to the present invention. For example, the positive electrode may be prepared by dissolving or dispersing components constituting the positive electrode active material layer, that is, the positive electrode active material, a conductive material and / or a binder, and the like in a solvent, and manufacturing the positive electrode material by combining the positive electrode material with the positive electrode current collector. After coating on at least one surface, it may be produced by drying and rolling, or by casting the positive electrode mixture on a separate support, and then laminating the film obtained by peeling from the support onto a positive electrode current collector.

At this time, the positive electrode current collector is not particularly limited as long as it has conductivity without causing chemical changes in the battery, for example, stainless steel, aluminum, nickel, titanium, calcined carbon or carbon or nickel on the surface of aluminum or stainless steel Surface treated with titanium, silver, or the like can be used. In addition, the positive electrode current collector may have a thickness of typically 3 μm to 500 μm, and may form fine irregularities on the surface of the current collector to increase adhesion of the positive electrode active material. For example, it can be used in various forms, such as a film, a sheet, a foil, a net, a porous body, foam, a nonwoven body.

At least one surface of the current collector includes a cathode active material according to the present invention, and if necessary, a cathode active material layer further including at least one of a conductive material and a binder is positioned.

The positive electrode active material includes a surface treatment layer including a positive electrode active material according to the present invention, that is, a lithium composite metal oxide represented by Chemical Formula 1 and cobalt-lithium composite particles attached to a surface of the lithium composite metal oxide. Specific details of the positive electrode active material according to the present invention are the same as described above, and thus a detailed description thereof will be omitted.

The cathode active material may be included in an amount of 80 to 99% by weight, more specifically 85 to 98% by weight based on the total weight of the cathode active material layer. When included in the above content range may exhibit excellent capacity characteristics.

The conductive material is used to impart conductivity to the electrode, and in the battery constituted, any conductive material may be used as long as it has electronic conductivity without causing chemical change. Specific examples thereof include graphite such as natural graphite and artificial graphite; Carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black and carbon fiber; Metal powder or metal fibers such as copper, nickel, aluminum, and silver; Conductive whiskers such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Or conductive polymers such as polyphenylene derivatives, and the like, or a mixture of two or more kinds thereof may be used. The conductive material may be included in an amount of 1 wt% to 30 wt% with respect to the total weight of the positive electrode active material layer.

In addition, the binder serves to improve adhesion between the positive electrode active material particles and the adhesion between the positive electrode active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC). ), Starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubbers, or various copolymers thereof, and the like, and one or a mixture of two or more thereof may be used. The binder may be included in an amount of 1 wt% to 30 wt% with respect to the total weight of the positive electrode active material layer.

On the other hand, the solvent used to prepare the positive electrode mixture may be a solvent generally used in the art, for example, dimethyl sulfoxide (DMSO), isopropyl alcohol (isopropyl alcohol), N-methylpyrroli Don (NMP), acetone (acetone) or water or the like may be used alone or in combination thereof. The amount of the solvent used may be appropriately adjusted in consideration of the coating thickness of the slurry, the production yield, the viscosity, and the like.

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

The secondary battery according to the present invention includes a positive electrode, a negative electrode positioned to face the positive electrode, a separator and an electrolyte interposed between the positive electrode and the negative electrode, wherein the positive electrode is the positive electrode according to the present invention described above.

The secondary battery may further include a battery container accommodating the electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member sealing the battery container.

In the secondary battery, the negative electrode includes a negative electrode current collector and a negative electrode active material layer positioned on at least one surface of the negative electrode current collector.

The negative electrode may be prepared according to a conventional negative electrode manufacturing method generally known in the art. For example, the negative electrode may be prepared by dissolving or dispersing components constituting the negative electrode active material layer, that is, the negative electrode active material, a conductive material and / or a binder, and the like in a solvent, and preparing the negative electrode mixture of the negative electrode current collector. After coating on at least one surface, it may be produced by drying and rolling, or by casting the negative electrode mixture on a separate support, and then laminating the film obtained by peeling from the support onto a negative electrode current collector.

The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical change in the battery. For example, the negative electrode current collector may be formed on a surface of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper, or stainless steel. Surface-treated with carbon, nickel, titanium, silver, and the like, aluminum-cadmium alloy and the like can be used. In addition, the negative electrode current collector may have a thickness of about 3 μm to 500 μm, and like the positive electrode current collector, fine concavities and convexities may be formed on the surface of the current collector to enhance the bonding force of the negative electrode active material. For example, it can be used in various forms, such as a film, a sheet, a foil, a net, a porous body, a foam, a nonwoven body.

As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fibers, and amorphous carbon; Metallic compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys or Al alloys; Metal oxides capable of doping and undoping lithium, such as SiO _v (0 <v <2), SnO ₂ , vanadium oxide, lithium vanadium oxide; Or a composite including the metallic compound and the carbonaceous material, such as a Si-C composite or a Sn-C composite, and any one or a mixture of two or more thereof may be used. In addition, a metal lithium thin film may be used as the anode active material. As the carbon material, both low crystalline carbon and high crystalline carbon can be used. Soft crystalline carbon and hard carbon are typical low crystalline carbon, and high crystalline carbon is amorphous, plate, scaly, spherical or fibrous natural graphite or artificial graphite, Kish graphite (Kish) graphite, pyrolytic carbon, mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches and petroleum or coal tar pitch High-temperature calcined carbon such as derived cokes is typical.

In addition, the binder and the conductive material may be the same as described above in the positive electrode.

On the other hand, in the secondary battery, the separator separates the negative electrode and the positive electrode and provides a passage for the movement of lithium ions, and can be used without particular limitation as long as it is usually used as a separator in the secondary battery, in particular with respect to the ion movement of the electrolyte It is preferable that it is resistance and excellent in electrolyte solution moisture-wetting ability. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin-based polymer such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer and ethylene / methacrylate copolymer, or the like Laminate structures of two or more layers may be used. In addition, a conventional porous nonwoven fabric, for example, a non-woven fabric made of high melting glass fibers, polyethylene terephthalate fibers, or the like may be used. In addition, a coated separator containing a ceramic component or a polymer material may be used to secure heat resistance or mechanical strength, and may be optionally used as a single layer or a multilayer structure.

Meanwhile, the electrolyte may be an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel polymer electrolyte, a solid inorganic electrolyte, a molten inorganic electrolyte, or the like, which can be used in manufacturing a secondary battery, but is not limited thereto.

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

The organic solvent may be used without particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvent may be an ester solvent such as methyl acetate, ethyl acetate, γ-butyrolactone or ε-caprolactone; Ether solvents such as dibutyl ether or tetrahydrofuran; Ketone solvents such as cyclohexanone; Aromatic hydrocarbon solvents such as benzene and fluorobenzene; Dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), propylene carbonate, Carbonate solvents such as PC); Alcohol solvents such as ethyl alcohol and isopropyl alcohol; Nitriles, such as Ra-CN (Ra is a C2-C20 linear, branched, or ring-shaped hydrocarbon group, and may contain a double bond aromatic ring or an ether bond); Amides such as dimethylformamide; Dioxolanes such as 1,3-dioxolane; Or sulfolanes may be used. Of these, carbonate-based solvents are preferable, and cyclic carbonates having high ionic conductivity and high dielectric constant (for example, ethylene carbonate or propylene carbonate) that can improve the charge and discharge performance of a battery, and low viscosity linear carbonate compounds ( For example, a mixture of ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate and the like is more preferable. In this case, when the cyclic carbonate and the chain carbonate are mixed and used in a volume ratio of about 1: 1 to 9, the performance of the electrolyte may be excellent.

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

The electrolyte includes, in addition to the electrolyte components, haloalkylene carbonate-based compounds such as difluoroethylene carbonate for the purpose of improving the life characteristics of the battery, suppressing the reduction of the battery capacity, and improving the discharge capacity of the battery; Or pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphate triamide, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N, N One or more additives such as -substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol or aluminum trichloride may be included. In this case, the additive may be included in an amount of 0.1 wt% to 5 wt% based on the total weight of the electrolyte.

As described above, the secondary battery including the cathode active material according to the present invention has excellent capacity characteristics and stability even under high voltage, and is a portable device such as a mobile phone, a notebook computer, a digital camera, and a hybrid electric vehicle (HEV). It can be usefully applied to the electric vehicle field such as).

In addition, the secondary battery according to the present invention can be used as a unit cell of the battery module, the battery module can be applied to a battery pack. The battery module or the battery pack is a power tool (Power Tool); Electric vehicles including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); Or it can be used as a power source for any one or more of the system for power storage.

Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily practice 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.

Example

Example 1

Lithium compound (LiOH) and transition metal precursor [Ni _{0 . 90} Co _{0 . 07} Mn _{0 . 03} (OH) ₂ ] uniformly mixed at a molar ratio of 1.05: 1, and then the mixture was calcined at 740 ° C. for 12 hours to prepare a lithium transition metal oxide LiNi _0.90 Co _0.07 Mn _0.03 O ₂ .

200 g of the lithium transition metal oxide and 200 g of water were added thereto, followed by stirring for 30 minutes while maintaining a stirring speed of 200 rpm in the reactor. After the stirring was completed, the lithium transition metal oxide was filtered and dried at 150 ° C. for 1 hour to obtain a cleaned positive electrode active material.

Since the positive electrode active material 100 g and H ₃ BO ₃ 0.34 g and 0.25 g of WO ₃ were mixed, followed by heat treatment at 300 ° C. for 3 hours to prepare a cathode active material. The prepared cathode active material was photographed using a scanning electron microscope (SEM), which is shown in FIG. 1.

Example 2

After preparing a lithium transition metal oxide in the same manner as in Example 1, after the washing step 100 g of the positive electrode active material and H ₂ WO ₄ After mixing 0.14 g, B ₄ C 0.05 g, and heat-treated at 300 ℃ for 3 hours to prepare a positive electrode active material.

Comparative Example 1

After obtaining the cleaned positive electrode active material, a positive electrode active material was prepared in the same manner as in Example 1 except that 100 g of the positive electrode active material and 0.25 g of WO ₃ were mixed and heat treated.

Comparative Example 2

After obtaining the washed cathode active material, a cathode active material was prepared in the same manner as in Example 1 except that 100 g of the cathode active material and 0.05 g of B ₄ C were mixed and heat treated.

Experimental Example 1-Lithium Secondary Battery Capacity Characteristics Evaluation

Coin half cells (using a negative electrode of Li metal) prepared by using the positive electrode active materials prepared in Examples 1 and 2 and Comparative Examples 1 and 2, respectively, will be 4.25 V at a constant current (CC) of 0.2 C at 25 ° C., respectively. The battery was charged until it was charged, and then charged at a constant voltage (CV) of 4.25 V, and the first charge was performed until the charging current became 0.05 mAh to measure the charging capacity. Thereafter, the sample was left for 20 minutes and then discharged until reaching 2.5 V at a constant current of 0.2 C. The discharge capacity of the first cycle was measured. The charge / discharge efficiency of the first cycle was evaluated. Then, rate characteristics were evaluated by varying the discharge conditions at 2 C. The results are shown in Table 1.

First charge and discharge Charge capacity (mAh / g) Discharge Capacity (mAh / g) Charge / discharge efficiency (%) Example 1 234.5 216.3 92.2 Example 2 234.4 211.2 90.1 Comparative Example 1 234.3 209.7 89.5 Comparative Example 2 235.0 209.5 89.1

Experimental Example  2 - Lithium secondary battery  Long-term stability characterization

The coin half cells prepared in Experimental Example 1 were charged at 45 ° C. in CC / CV mode until 0.3 C and 4.3 V, respectively, and discharged until they reached 2.5 V with a constant current of 0.3 C. Capacity retention (Capacity Retention [%]) and resistance increase rate (DCIR-resistance [%]) were evaluated while the results are shown in Table 2 below.

Capacity maintenance rate (%) % Increase in resistance Example 1 92.0 239.1 Example 2 92.1 232.7 Comparative Example 1 88.0 268.5 Comparative Example 2 90.6 254.0

Referring to Tables 1 and 2, the cells manufactured using the positive electrode active materials of Examples 1 and 2 are superior to the cells manufactured using the positive electrode active materials of Comparative Examples 1 and 2, and have a high capacity retention rate and It can be seen that the low rate of resistance increase.

Experimental Example  3- Cathode material  Determination of the elemental component ratio according to the etching time of the surface

Examples 1 and 2 and the positive electrode active material prepared in Comparative Examples 1 and 2, respectively, using a EQC0124: VG Scientific ESCALAB 250 device, the Depth Profile was performed up to 500 seconds, and the results are shown in Table 3 below. In Table 3 below, tungsten (W) and boron (B) represent the elements analyzed in the positive electrode active material of each Example or Comparative Example.

Etching Time (sec) Example 1 Example 2 Comparative Example 1 Comparative Example 2 Tungsten (W) Boron (B) Tungsten (W) Boron (B) 0 0.7 1.5 0.6 1.6 10 0.7 0.8 0.5 1.2 30 0.7 0.7 0.5 0.5 50 0.7 0.6 0.4 0 100 0.6 0.3 0.4 0 200 0.6 0 0.3 0 300 0.6 0 0.2 0 500 0.5 0 0.2 0

Referring to Table 3, as the coating raw material, WO ₃ which is an oxide coating raw material and H ₃ BO ₃ which is a hydrate coating raw material To Example 1, which was used together with the coating, showed that the amount of W contained in the coating layer was higher than that of Comparative Example 1, which was coated with only WO _3, which is an oxide-based coating raw material. It can be seen that W maintains its content relatively long and shows better coating properties.

Similarly, B ₄ C, a carbide-based coating raw material, and H ₂ WO ₄ , a hydrate-based coating raw material, are used as coating raw materials. In Example 2, which was used together with the coating process, B was maintained for a relatively long time, even though the etching time was increased, compared to Comparative Example 2, which was coated using only the carbide-based coating material B ₄ C. It was confirmed that the sex.

Claims (14)

Preparing a lithium composite transition metal oxide represented by Formula 1;
Cleaning the lithium composite transition metal oxide; And
And mixing the washed lithium composite transition metal oxide with a coating raw material and subjecting it to heat treatment.
The coating raw material is a method of producing a positive electrode active material comprising at least one selected from oxide coating raw material and carbide coating raw material and a hydrate coating raw material.
[Formula 1]
LiNi _a Co _b Mn _c M _d O ₂
(a> 0.75, 0 <b <0.25, 0 <c <0.25, 0 ≦ d ≦ 0.2, a + b + c + d = 1, and M is W, Cu, Fe, V, Cr, Ti, Zr, At least one doping element selected from the group consisting of Zn, Al, In, Ta, Y, In, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo)
The method of claim 1,
Wherein the coating raw material is 0.01 parts by weight to 2 parts by weight based on 100 parts by weight of the cleaned lithium composite transition metal oxide, a method of producing a positive electrode active material.
The method of claim 1,
The heat treatment is carried out at a temperature of 400 ° C or less, a method for producing a positive electrode active material.
The method of claim 1,
The oxide coating raw material is one selected from the group consisting of tungsten oxide (WO ₃ ), boron oxide (B ₂ O ₃ ), alumina (Al ₂ O ₃ ), titanium dioxide (TiO ₂ ) and magnesium oxide (MgO). The manufacturing method of the positive electrode active material which is above.
The method of claim 1,
The carbide-based coating raw material is at least one selected from the group consisting of boron carbide (B ₄ C), tungsten carbide (WC), aluminium carbide (Al ₄ C ₃ ) and titanium carbide (TiC), the method of producing a positive electrode active material. .
The method of claim 1,
The hydrate-based coating raw material is at least one member selected from the group consisting of boric acid (H ₃ BO ₃ ), tungstic acid (H ₂ WO ₄ ), and molybdate (H ₂ MoO ₄ ).
The method of claim 1,
The oxide-based coating raw material is tungsten oxide (WO ₃ ), the hydrate-based coating raw material is boric acid (H ₃ BO ₃ ), the manufacturing method of the positive electrode active material.
The method of claim 1,
The carbide-based coating raw material is boron carbide (B ₄ C), the hydrate-based coating raw material is tungstic acid (H ₂ WO ₄ ), the manufacturing method of the positive electrode active material.
The method of claim 1,
At least one selected from the oxide-based coating raw material and the carbide-based coating raw material and the hydrate-based coating raw material are included in a weight ratio of 1: 1.2 to 1: 5.
To include a lithium composite transition metal oxide represented by the formula (1),
On the surface of the lithium composite transition metal oxide is formed a coating layer containing two or more coating elements,
The coating element is a positive electrode active material which is a material derived from at least one selected from an oxide-based coating raw material and a carbide-based coating raw material, and a material derived from a hydrate-based coating raw material.
[Formula 1]
LiNi _a Co _b Mn _c M _d O ₂
(a> 0.75, 0 <b <0.25, 0 <c <0.25, 0 ≦ d ≦ 0.2, a + b + c + d = 1, and M is W, Cu, Fe, V, Cr, Ti, Zr, At least one doping element selected from the group consisting of Zn, Al, In, Ta, Y, In, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo)
The method of claim 10,
The coating layer comprises a tungsten and a boron compound, a positive electrode active material.
The method of claim 10,
The cathode active material comprises 200 ppm to 4,000 ppm of tungsten.
A cathode for a lithium secondary battery comprising the cathode active material of claim 10.
A lithium secondary battery comprising the positive electrode for a lithium secondary battery of claim 13.

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