WO2016053053A1 - Cathode active material for lithium secondary battery, preparation method therefor and lithium secondary battery comprising same - Google Patents

Abstract

The present invention provides a cathode active material for a lithium secondary battery, comprising particles of a lithium cobalt oxide, wherein the particles of the lithium cobalt oxide comprises, on the particle surface and in a region corresponding to a distance of 0% or more and less than 100% from the particle surface with respect to a distance (r) from the surface to the center of the particle, a lithium defective lithium cobalt oxide, of which the mole ratio of Li/Co is less than 1 and a space group belongs to Fd-3m, and having a cubic crystalline structure. The cathode active material for a lithium secondary battery according to the present invention facilitates intercalation and deintercalation of lithium at the particle surface, thereby improving output characteristics and rate characteristics when applied to a battery. Consequently, excellent lifetime characteristics are exhibited and the amount of generated gas can be minimized even when the cathode active material is a large particle.

Description

Cathode active material for lithium secondary battery, manufacturing method thereof and lithium secondary battery comprising same

Citation with Related Applications

This application claims the benefit of priority based on Korean Patent Application Nos. 2014-0133428 and 2014-0133429 dated October 2, 2014, and Korean Patent Application No. 2015-0138746 dated October 1, 2015. All content disclosed in the patent application is included as part of this specification.

Technical Field

The present invention relates to a cathode active material for a lithium secondary battery, a manufacturing method thereof, 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.

However, a lithium secondary battery has a problem in that its life is rapidly decreased as charging and discharging are repeated. In particular, this problem is more serious at high temperatures. This is due to the phenomenon that the electrolyte is decomposed or the active material is deteriorated due to moisture or other influences inside the battery, and the internal resistance of the battery is increased.

Accordingly, the positive electrode active material for lithium secondary batteries currently being actively researched and developed is LiCoO ₂ having a layered structure. LiCoO ₂ is easy to synthesize and is most used because of its excellent electrochemical performance including lifespan characteristics. However, LiCoO ₂ has a limited structural stability and thus is not applicable to high capacity battery technology.

As a cathode active material for replacing this, various lithium transition metal oxides such as LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , or LiFePO ₄ have been developed. Among them, LiNiO ₂ has the advantage of exhibiting battery characteristics of high discharge capacity, but the synthesis is difficult by a simple solid phase reaction, there is a problem of low thermal stability and low cycle characteristics. In addition, lithium manganese oxides such as LiMnO ₂ or LiMn ₂ O ₄ have advantages in that they are excellent in thermal safety and inexpensive, but have a small capacity and low temperature characteristics. In particular, in the case of LiMn ₂ O ₄ but a part merchandising products to low cost, since the Mn ^{+ 3} structure modification (Jahn-Teller distortion) due to the not good life property. In addition, LiFePO ₄ has a low price and excellent safety, and a lot of research is being made for hybrid electric vehicles (HEV), but it is difficult to apply to other fields due to low conductivity.

Due to this situation, the most popular material for LiCoO _{2 as} an alternative cathode active material is lithium nickel manganese cobalt oxide, Li (Ni _x Co _y Mn _z ) O ₂ (At this time, X, y, and z are atomic fractions of independent oxide composition elements, respectively, where 0 <x ≦ 1, 0 <y ≦ 1, 0 <z ≦ 1, and 0 <x + y + z ≦ 1. This material is cheaper than LiCoO ₂ and has advantages in that it can be used for high capacity and high voltage, but has disadvantages of poor rate characteristics and high lifetime characteristics at high temperatures. Therefore, in order to increase the structural stability of lithium nickel manganese cobalt oxide, it is used by including the content of Li higher than the content of the transition metal contained in the oxide.

Recently, as portable devices such as mobile phones and tablet PCs are becoming smaller and smaller, batteries to which they are applied are also required to be miniaturized, high in capacity and energy. In order to increase the energy per unit volume of the battery, the packing density of the active material must be increased. In addition, in order to increase the packing density, it is preferable to use an active material having large particles. However, since the active material of such a large particle has a relatively low surface area, the active area in contact with the electrolyte is also narrow. This narrow active area has a kinetic disadvantage, resulting in relatively low rate properties and initial capacity.

The first technical problem to be solved by the present invention is to facilitate the insertion and detachment of lithium ions on the particle surface to improve the output characteristics and rate characteristics when applying the battery, and even with the improved lifetime characteristics, even if the alleles, It is to provide a cathode active material for a lithium secondary battery that can minimize the amount of gas generated.

The second technical problem to be solved by the present invention is to provide a manufacturing method for producing the positive electrode active material.

The third technical problem to be solved by the present invention is to provide a positive electrode including the positive electrode active material.

The fourth technical problem to be solved by the present invention is to provide a lithium secondary battery, a battery module and a battery pack including the positive electrode.

In order to solve the above problems, according to an embodiment of the present invention, the particles of lithium cobalt oxide, the particles of lithium cobalt oxide is on the surface of the particles, and the distance (r) from the surface of the particles to the center Lithium cobalt oxide of a lithium defect having a cubic crystal structure with a molar ratio of Li / Co of less than 1, a space group of Fd-3m, and a cubic crystal structure within a region corresponding to a distance of 0% or more and less than 100% from the particle surface. It provides a cathode active material for a lithium secondary battery comprising a.

In addition, according to another embodiment of the present invention, mixing the cobalt raw material and the lithium raw material in an amount such that 1≤Li / Co molar ratio to prepare a particle of the second lithium cobalt oxide by primary heat treatment, And it provides a method for producing a cathode active material for a lithium secondary battery comprising the step of performing the secondary heat treatment for the particles of the second lithium cobalt oxide at least once.

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

Furthermore, according to another embodiment of the present invention, there is provided a lithium secondary battery, a battery module, and a battery pack including the positive electrode.

Other specific details of the embodiments of the present invention are included in the following detailed description.

The positive electrode active material for a lithium secondary battery according to the present invention includes a lithium defect structure that is easy to insert and detach lithium ions on the surface side of the active material particles, thereby improving the rate characteristics when the battery is applied by increasing the movement speed of lithium ions, In addition, the reduction in resistance on the surface of the active material can improve capacity characteristics without fear of lowering the initial capacity. In addition, even if the alleles can exhibit excellent life characteristics, at the same time the energy density of the battery can be improved by increasing the anode density. Accordingly, the cathode active material for a lithium secondary battery according to the present invention may be particularly useful as a cathode active material of a high voltage battery of 4.4V or more.

The following drawings, which are attached to this specification, illustrate preferred embodiments of the present invention, and together with the contents of the present invention serve to further understand the technical spirit 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 photograph of the lithium distribution on the particle surface side using an atomic probe tomography (APT) for the cathode active material prepared in Preparation Example 2.

FIG. 2 is a photograph of a crystal structure observed using a transmission electron microscope (TEM) for the cathode active material prepared in Preparation Example 2. FIG.

FIG. 3 is a graph illustrating initial charge and discharge characteristics during charge and discharge of a lithium secondary battery including the cathode active materials prepared in Preparation Example 1 and Comparative Example 1, respectively.

4 is a graph illustrating the rate characteristics during charge and discharge of a lithium secondary battery including the cathode active materials prepared in Preparation Example 1 and Comparative Example 1, respectively.

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

The terms or words used in this specification and claims are not to be construed as being limited to their ordinary or dictionary meanings, and the inventors may appropriately define the concept of terms in order to best describe their invention. 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.

In general, the rate characteristic of the positive electrode active material is generally determined by the interfacial reaction rate between the positive electrode active material and the electrolyte. The present invention provides a lithium deficient structure that facilitates the insertion and desorption of lithium ions and the three-dimensional movement of lithium ions on the outside of the lithium cobalt oxide particles, that is, on the surface side of the cathode active material. Rate characteristics can be improved when the battery is applied. In addition, the output characteristics can be improved by reducing the resistance on the surface of the active material particles. Accordingly, even if the cathode active material is an allele, excellent life characteristics may be exhibited, and the energy density of the battery may be improved by increasing the anode density.

That is, the cathode active material for a lithium secondary battery according to an embodiment of the present invention,

Contains particles of lithium cobalt oxide,

The particles of lithium cobalt oxide are in the area of the particle surface, i.e., the surface of the particle and the area corresponding to a distance of 0% or more and less than 100% from the particle surface to the distance r from the surface of the particle to the center r The molar ratio of / Co is less than 1, the space group belongs to Fd-3m, and contains lithium cobalt oxide of lithium defects having a cubic crystal structure.

Specifically, in the positive electrode active material according to an embodiment of the present invention, the lithium cobalt oxide particles, lithium cobalt of lithium defects having a molar ratio of Li / Co less than 1, more specifically 0.95 or more to 1 on the particle surface side. Oxides.

Unlike the usual lithium cobalt oxide having a layered crystal structure, the lithium cobalt oxide of the lithium defect has a cubic crystal structure in which the space group belongs to Fd-3m, and the lattice constant a0 is 7.992 to 7.994 (25 ° C). Can be. The crystal structure is similar to the spinel crystal structure, so that lithium ions can be moved in three dimensions as in the spinel crystal structure. Accordingly, compared with the layered structure in which the lithium ions can be moved in two dimensions, the lithium ions can be more smoothly moved and have a higher speed. As a result, the insertion and desorption of the lithium ions can be easier. In the present invention, the lithium crystalline cobalt oxide having the above-described crystal structure of the lithium defect is located on the surface side of the lithium cobalt oxide particles, so that the movement of lithium ions can be facilitated, thereby improving the rate characteristic during battery application. In addition, output characteristics can be improved due to a decrease in resistance at the active material surface side.

The crystal structure of the lithium cobalt oxide of the lithium defect can be confirmed according to a conventional crystal structure checking method, and specifically, the crystal structure can be confirmed using a transmission electron microscope.

More specifically, the lithium cobalt oxide of the lithium defect may include the first lithium cobalt oxide of Formula 1.

[Formula 1]

Li _1-a CoM _x O ₂

In Formula 1, a and x are atomic fractions of the oxide composition elements, respectively, 0 <a ≦ 0.05 and x is 0 ≦ x ≦ 0.02.

In Formula 1, M is any one or two or more metals selected from the group consisting of W, Mo, Zr, Ti, Mg, Ta, Al, Fe, V, Cr, Ba, Ca, and Nb as a doping element. An element may be included and included in the content of x in the first lithium cobalt oxide, that is, 0 ≦ x ≦ 0.02. As described above, when the metal element is further doped into the lithium cobalt oxide of the lithium defect, the structural stability is improved, and there is no fear of lowering the structural stability of the cathode active material due to the lithium defect, and the output characteristics of the battery can be improved. In addition, the improvement effect may be further improved by doping with the above-mentioned content.

More specifically, in the cathode active material for a lithium secondary battery according to an embodiment of the present invention, the particles of the lithium cobalt oxide may have a core-shell structure, wherein the shell portion of the first lithium of the lithium defect of Formula 1 Cobalt oxide, and the core portion may include a second lithium cobalt oxide of the formula (2).

[Formula 1]

Li _1-a CoM _x O ₂

[Formula 2]

Li _b CoM ' _y O ₂

(In Chemical Formulas 1 and 2,

M and M 'each independently include any one or two or more metal elements selected from the group consisting of W, Mo, Zr, Ti, Mg, Ta, Al, Fe, V, Cr, Ba, Ca and Nb,

a, b, x and y are atomic fractions of the independent oxide composition elements, respectively, and may be 0 <a ≦ 0.05, 1 ≦ b ≦ 1.2, 0 ≦ x ≦ 0.02 and 0 ≦ y ≦ 0.02.)

When the conditions of 0 <a ≤ 0.05 and 1 ≤ b ≤ 1.2 at the same time in Formula 1, a rate characteristic according to the formation of a lithium defect structure improvement compared to the active material when a exceeds 0.05 or b exceeds 1.2 The effect may be further improved by 10% or more. In addition, compared to lithium cobalt oxide (LiCOO ₂ ) that does not form a lithium defect structure, the rate characteristic improvement effect can be improved up to 30%.

In the lithium cobalt oxide particles, the first lithium cobalt oxide has a spinel like structure, that is, a space group belongs to Fd-3m, has a cubic crystal structure, as described above, and The second lithium cobalt oxide may have a layered structure.

As described above, the positive electrode active material according to the embodiment of the present invention includes lithium cobalt oxide having a defect structure capable of three-dimensional movement of lithium ions on the surface side of the active material particles, that is, the shell portion in relation to the movement of lithium ions. As a result, the lithium may be smoothly moved, and the initial battery internal resistance of the lithium secondary battery may be reduced to improve the rate characteristic and the output characteristic of the battery. In addition, by including lithium rich lithium cobalt oxide having a Li / Co ratio of 1 or more in the inside of the active material particles, that is, the core part, the structural stability of the active material, in particular, the structural stability at high temperatures, is improved, and capacity deterioration at high temperatures is achieved. You can prevent it. This effect is more effective as the positive electrode active material of the alleles.

Considering the remarkable control of the Li / Co ratio according to the position in the active material particles and the improvement effect according to, as described above, in Formulas 1 and 2, may be 0.01 <a ≤ 0.05, 1 ≤ b ≤ 1.05.

More specifically, in the cathode active material of the core-shell structure as described above, the core portion and the shell portion may include lithium distributed in a concentration gradient gradually increasing toward the center of the lubricant particles in each region. .

In this case, the gradient of the concentration gradient of lithium in the core portion and the shell portion may be a first-order function or a second-order function that varies depending on the thickness of the particles independently from the center of the active material particles. The gradient of the concentration gradient of lithium in the core portion and the gradient of the concentration gradient of lithium in the shell portion may be the same as or different from each other.

On the other hand, in the cathode active material of the core-shell structure as described above, the core portion and the shell portion may include lithium present in one concentration value in each region. In this case, the lithium concentration contained in the core portion may be higher than the concentration of lithium included in the shell portion.

In addition, as described above, when the lithium concentration distributions in the core portion and the shell portion are different from each other independently, the height difference according to the difference in the lithium concentration in the core portion and the shell portion may be formed at the contact interface between the core portion and the shell portion. have.

On the other hand, the cathode active material of the core-shell structure as described above may include lithium distributed throughout the active material particles, that is, with a concentration gradient gradually increasing from the surface of the particles to the center. In this case, in Chemical Formulas 1 and 2, a may decrease toward the center of the particle within the range of 0 <a ≦ 0.05, and b may increase toward the center of the particle within the range of 1 ≦ b ≦ 1.2. In addition, the gradient of the concentration gradient of lithium may be a first-order function that varies depending on the thickness of the particles from the center of the active material particles, or may be a second-order function. By having a concentration gradient throughout the particle as described above, there is no abrupt phase boundary region from the center to the surface, so that the crystal structure is stabilized and the thermal stability is increased. In addition, when the gradient of the concentration gradient of the metal is constant, the effect of improving the structural stability may be further improved.

On the other hand, in the present invention, the change in the concentration of lithium on the surface and the inside of the particles can be measured according to a conventional method, specifically, the concentration of each element including lithium present on the surface is X-ray photoelectron analysis (X -ray Photoelectron Spectroscopy (XPS), Transmission Electron Microscopy (TEM) or Energy Dispersve x-ray spectroscopy (EDS). In addition, the lithium composition of lithium cobalt oxide can be measured by Inductively Coupled Plasma-Atomic Emission Spectrometer (ICP-AES), and is a time of flight secondary ion mass spectrometer. Spectrometry (ToF-SIMS) can determine the form of lithium cobalt oxide.

In addition, in the present invention, the 'surface side' of the lithium cobalt oxide particles means a surface and an area close to the surface except the center of the particles, and specifically, the distance from the surface of the lithium cobalt oxide particles to the center, that is, lithium cobalt It means a region corresponding to a distance of 0% or more and less than 100% from the particle surface with respect to the semi-diameter of the oxide. The shell portion of the lithium cobalt oxide particles is an area corresponding to a distance from the surface of the lithium cobalt oxide particles to the center, that is, a distance of 0% to 99% from the particle surface with respect to the semi-diameter of the particles, more specifically. It means an area corresponding to a distance of 0% to 95%. Accordingly, the core part is present inside the shell part, and means a region excluding the shell part in lithium cobalt oxide particles.

Specifically, in the lithium cobalt oxide particles, the semi-diameter of the core portion and the thickness of the shell portion may have a thickness ratio of 1: 0.01 to 1: 0.1. If the semi-diameter of the core portion is too large outside the above ratio range, the effect of increasing the mobility of lithium ions according to the formation of the shell portion including lithium cobalt oxide of lithium defect and the effect of improving the battery characteristics are insignificant, and the thickness ratio If the thickness of the shell portion is too thick, the stability of the structure inside the active material particles may be insignificant due to the relative reduction of the core portion. More specifically, the thickness of the shell portion may be 1 to 500 nm, or 10 to 450 nm under the condition of the thickness ratio of the semi-diameter of the core portion and the shell portion.

In addition, in the cathode active material for a lithium secondary battery according to an embodiment of the present invention, the second lithium cobalt oxide of the lithium defect structure may be included in 10 to 30% by weight based on the total weight of the cathode active material. When the content of the second lithium cobalt oxide is less than 10% by weight, the improvement effect due to the formation of the lithium defect structure is insignificant, and when the content of the second lithium cobalt oxide is more than 30% by weight, there is a fear of capacity reduction and structure collapse.

In the present invention, the content of the second lithium cobalt oxide of the lithium defect structure is to determine the Li surface defect structure in the shell through the analysis using a transmission electron microscope (TEM), and check the thickness to determine the mass ratio through the total volume ratio Or by adjusting the time to dissolve in weak acid during ICP analysis, dissolving little by little from the surface of lithium cobalt oxide particles and analyzing the ratio of Li / transition metal (eg, cobalt (Co), etc.) through the filtrate. After determining the content of the second lithium cobalt oxide by measuring the weight of the undissolved amount.

In addition, the cathode active material according to an embodiment of the present invention has a monolithic structure consisting of primary particles of lithium cobalt oxide.

In the present invention, the "monolith structure" refers to a structure in which particles exist in an independent phase in which particles do not aggregate with each other in a morphology phase. Particle structures, in contrast to these monolithic structures, include structures in which small-sized particles ('primary particles') are physically and / or chemically aggregated to form relatively large particle forms ('secondary particles'). Can be.

In general, in order to increase the capacity of the battery, it is preferable to have a large particle size of the positive electrode active material. However, in this case, the surface area is relatively low, and thus there is a problem in that the rate characteristic and the initial capacity are reduced due to the decrease in the active area in contact with the electrolyte. In order to solve this problem, a cathode active material of secondary particles in which primary particles of fine particles are assembled is mainly used. However, in the case of the secondary particles of the positive electrode active material, lithium ions move to the surface of the active material and react with moisture or CO ₂ in the air to easily form surface impurities such as Li ₂ CO ₃ and LiOH. Water has a serious problem in high temperature stability because it causes a swelling phenomenon of the battery by reducing the battery capacity or decomposing in the battery to generate gas. On the other hand, the positive electrode active material according to an embodiment of the present invention has a monolithic structure, so there is no fear of a problem that the positive electrode active material having secondary particles has.

In addition, the positive electrode active material of the monolithic structure as described above may have an average particle diameter (D ₅₀ ) of 3 ㎛ to 50 ㎛ in consideration of the specific surface area and the positive electrode mixture density, due to the structural features that facilitate the insertion and removal of lithium ions The average particle diameter (D ₅₀ ) of 10 μm to 50 μm higher than that of the related art may have a higher particle size than that of the related art.

In the present invention, the average particle diameter (D ₅₀ ) of the particles of the lithium cobalt oxide may be defined as the particle size at 50% of the particle size distribution. The average particle diameter (D ₅₀ ) of the particles of the lithium cobalt oxide may be measured using, for example, a laser diffraction method. Specifically, the particles of lithium cobalt oxide are dispersed in a dispersion medium, and then introduced into a commercially available laser diffraction particle size measuring apparatus (for example, Microtrac MT 3000) and irradiated with an ultrasonic wave of about 28 kHz at an output of 60 W, and then to the measuring apparatus. The average particle diameter D ₅₀ at the 50% reference of the particle size distribution in the sample can be calculated.

In the cathode active material according to the embodiment of the present invention as described above, the cobalt raw material and the lithium raw material are mixed in an amount such that 1 ≦ Li / Co molar ratio, followed by primary heat treatment to form particles of the second lithium cobalt oxide. It may be prepared by a manufacturing method comprising the step of preparing (step 1), and the step (step 2) of performing a second heat treatment on the particles of the second lithium cobalt oxide. Accordingly, according to another embodiment of the present invention, a method of manufacturing the cathode active material for a lithium secondary battery is provided.

Hereinafter, each step will be described in detail, Step 1 is a step of preparing the particles of the second lithium cobalt oxide.

Specifically, the particles of the first lithium cobalt oxide may be prepared by mixing the cobalt raw material and the lithium raw material in an amount such that a molar ratio of 1 ≦ Li / Co, followed by primary heat treatment.

In this case, the cobalt raw material may be specifically cobalt-containing oxide, hydroxide, oxyhydroxide, halide, nitrate, carbonate, acetate, oxalate, citrate or sulfate, and more specifically Co (OH) ₂ , CoO , CoOOH, Co (OCOCH ₃ ) ₂ 4H ₂ O, Co (NO ₃ ) ₂ 6H ₂ O or Co (SO ₄ ) ₂ ㆍ 7H ₂ O, and the like, and any one or a mixture of two or more thereof may be used. have.

In addition, the lithium raw material may be specifically a lithium-containing oxide, hydroxide, oxyhydroxide, halide, nitrate, carbonate, acetate, oxalate, citrate or sulfate, and more specifically, Li ₂ CO ₃ , LiNO ₃ , LiNO _2, LiOH, LiOH and _{H 2 O, LiH, LiF,} LiCl, LiBr, LiI, CH 3 COOLi, Li 2 O, Li 2 SO 4, CH 3 COOLi, or Li ₃ C ₆ H ₅ O ₇ or the like Any one or a mixture of two or more of these may be used.

The cobalt raw material and the lithium raw material may be mixed in an amount such that the Li / Co molar ratio satisfies the condition of 1 ≦ Li / Co molar ratio. When mixed in the above content range, a core including a lithium rich lithium cobalt oxide having a layered structure may be formed. More specifically, considering the remarkable improvement effect, the cobalt raw material and the lithium raw material have a Li / Co molar ratio of 1 ≦ Li / Co molar ratio ≦ 1.2, and more specifically 1 ≦ Li / Co molar ratio ≦ 1.1. It may be mixed in an amount to meet. In addition, the particle center in the particles of the second lithium cobalt oxide is added by reducing the Li / Co molar ratio within the range of 1 ≦ Li / Co molar ratio ≦ 1.2 with time when the cobalt raw material and the lithium raw material are added. It can be made to have a concentration gradient that decreases the concentration of lithium toward the surface from.

In addition, when the manufactured second lithium cobalt oxide is doped, a raw material of the doping metal element (M ′) may be selectively added when the cobalt raw material mulch and the lithium raw material are mixed.

The raw material of the doping metal element (M ') is specifically any one selected from the group consisting of W, Mo, Zr, Ti, Mg, Ta, Al, Fe, V, Cr, Ba, Ca and Nb or Two or more metals, or oxides, hydroxides, oxyhydroxides, halides, nitrates, carbonates, acetates, oxalates, citrates or sulfates, and the like, including any one or a mixture of two or more thereof.

In addition, the first heat treatment for the mixture of the above raw materials may be carried out at a temperature from 800 ℃ to 1100 ℃. If the heat treatment temperature is lower than 800 ° C, there may be a decrease in discharge capacity per unit weight, cycle characteristics, and a decrease in operating voltage due to the remaining of unreacted raw materials. There is a fear of lowering the discharge capacity, lowering the cycle characteristics and lowering the operating voltage.

In addition, the first heat treatment may be performed at a lower temperature than the subsequent second heat treatment within the above temperature range, it may be easy to control the diffusion rate of lithium.

In addition, the primary heat treatment may be carried out in the air or under an oxygen atmosphere, and may be carried out for 5 to 30 hours so that the diffusion reaction between the particles of the mixture is sufficient.

Next, step 2 is a step of forming the first lithium cobalt oxide of the lithium defect on the surface of the particles of the second lithium cobalt oxide prepared in step 1.

Specifically, the first lithium cobalt oxide of the lithium defect is subjected to at least one second heat treatment at 800 ° C. to 1100 ° C. with respect to the particles of the second lithium cobalt oxide prepared in Step 1, more specifically, one to three times. It can be formed by performing once, more specifically once or twice. At this time, the temperature during each heat treatment may be the same or different within the above temperature range.

In this secondary heat treatment, lithium present on the surface of the second lithium cobalt oxide particles reacts with oxygen in air to form lithium oxide, thereby forming the lithium-defected first lithium cobalt oxide. In addition, as the number of times of the second heat treatment increases, lithium defects in the lithium cobalt oxide also increase, and as a result, a concentration gradient in which lithium concentration decreases from the center of the first lithium cobalt oxide to the surface is formed. .

In addition, during the second heat treatment, cobalt raw material, or cobalt raw material and lithium raw material may be selectively added. The materials may be added in batches at specific stages during the second heat treatment, or may be added in the same or different amounts at each stage.

Specifically, in the case where only the cobalt raw material is selectively added, cobalt in the cobalt raw material reacts with lithium present on the surface of the second lithium cobalt oxide particles to form lithium cobalt oxide of lithium defects having a molar ratio of Li / Co of less than one. Can be formed. At this time, the cobalt raw material may be the same as described above, the amount of use may be appropriately adjusted according to the concentration gradient of Li.

In addition, when the cobalt raw material and the lithium raw material are selectively added, the cobalt raw material and the lithium raw material are 0 <Li / Co molar ratio <1, 0.95≤Li / Co molar ratio <1, more specifically 0.95 It may be added in an amount so as to satisfy the condition of? Li / Co molar ratio ≦ 0.99. When the cobalt raw material and the lithium raw material are mixed in the above content range, a layer containing lithium cobalt oxide of lithium defect is formed. At this time, the cobalt raw material and the lithium raw material may be the same as in step 1.

In addition, when the manufactured first lithium cobalt oxide is doped, a raw material of the doping metal element (M) may be optionally further added when the cobalt raw mulch and the lithium raw material are mixed.

The raw material of the doping metal element (M) is specifically any one selected from the group consisting of W, Mo, Zr, Ti, Mg, Ta, Al, Fe, V, Cr, Ba, Ca, and Nb or Two or more metals, or oxides, hydroxides, oxyhydroxides, halides, nitrates, carbonates, acetates, oxalates, citrates or sulfates, and the like, including any one or a mixture of two or more thereof.

On the other hand, the second heat treatment in step 2 may be carried out at a temperature from 800 ℃ to 1100 ℃. If the heat treatment temperature is less than 800 ° C., the crystallization of the lithium cobalt oxide formed on the surface is not sufficiently performed, and there is a fear that the movement of lithium ions may be disturbed. In addition, when the heat treatment temperature exceeds 1100 ° C., there is a fear of excessive crystallization or unstable structure formation by Li evaporation in the crystal structure. Accordingly, in order to prevent the lowering of the discharge capacity per unit weight, the cycle characteristics and the lowering of the operating voltage due to the residual or side reaction products of the unreacted raw materials and the uncrystallized or overcrystallized lithium cobalt oxide. More specifically, the heat treatment may be carried out at a temperature of 1000 ℃ to 1100 ℃.

In addition, the higher the temperature during the secondary heat treatment promotes the movement and diffusion of lithium in the active material, so that the distribution of lithium in the positive electrode active material can be controlled according to the secondary heat treatment temperature. Specifically, when the temperature during the second heat treatment is 1000 ° C. or more and 1000 ° C. to 1100 ° C. within the above temperature range, lithium in the active material may be distributed with a concentration gradient.

In addition, the secondary heat treatment may be carried out in the air or under an oxygen atmosphere, and may be performed for 7 to 50 hours. If the heat treatment time is too long, the evaporation of lithium and the crystallinity of the metal oxide layer formed on the surface may be increased, leading to the movement of lithium ions. There is a risk of problems.

Method for producing the positive electrode active material according to an embodiment of the present invention is a dry method without using a solvent.

The wet method using a solvent in the preparation and surface treatment process of the positive electrode active material is easy to change the pH of the solvent because the metal precursor is dissolved in the solvent, thereby changing the size of the final positive electrode active material or particle breakage It may cause. In addition, lithium ions are eluted from the surface of the positive electrode active material containing lithium, and various oxides may be formed on the surface as side reaction materials. On the contrary, in the present invention, the cathode active material is prepared by a dry method. There is no fear of occurrence of the above problems due to the use of a solvent, and it is superior in terms of production efficiency and process ease of active material. In addition, since the surface treatment method by the dry method does not use a binder, there is no fear of side reactions caused by the use of the binder.

The positive electrode active material produced by the above-described manufacturing method includes a lithium cobalt oxide having a lithium defect structure in which lithium is easily inserted and detached on the surface side of lithium cobalt oxide particles having a monolithic structure, thereby providing excellent output characteristics and rate characteristics. Can be represented. In addition, since the lithium defect structure is kinetically advantageous by being formed on the particle surface side, even if it is a large particle, it can exhibit the outstanding output and discharge rate characteristics. In addition, the specific surface area decreases as the size of the active material increases, and the lithium cobalt oxide content decreases due to the formation of a lithium defect structure, thereby lowering the reactivity with the electrolyte, thereby reducing the amount of gas generated when the battery is driven.

Accordingly, according to another embodiment of the present invention provides a cathode and a lithium secondary battery including the cathode active material.

Specifically, the positive electrode is formed on the positive electrode current collector and the positive electrode current collector, and includes a positive electrode active material layer containing the positive electrode active material.

The positive electrode current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery. For example, carbon, nickel, titanium on the surface of stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel Surface treated with silver, silver or the like can be used. In addition, the positive electrode current collector may have a thickness of about 3 to 500 μm, and may form fine irregularities on the surface of the current collector to increase the 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, a foam, a nonwoven body.

The positive electrode active material layer may include a conductive material and a binder together with the positive electrode active material. At this time, the positive electrode active material is the same as described above.

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, summer black and carbon fiber; Metal powder or metal fibers such as copper, nickel, aluminum, and silver; Conductive whiskeys 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 typically be included in an amount of 1 to 30% by weight based on 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 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 to 30% by weight based on the total weight of the positive electrode active material layer.

The positive electrode having the structure as described above may be manufactured according to a conventional positive electrode manufacturing method except for using the positive electrode active material described above. Specifically, the positive electrode active material, the binder and the conductive material may be prepared by dissolving and dispersing the composition for forming a positive electrode active material layer prepared by dissolving in a solvent, followed by drying and rolling. In this case, the type and content of the cathode active material, the binder, and the conductive material are as described above.

In addition, the solvent in the composition for forming the positive electrode active material layer may be a solvent generally used in the art, dimethyl sulfoxide (DMSO), isopropyl alcohol (isopropyl alcohol), N-methylpyrroli Don (NMP), acetone (acetone) or water, and the like, one of these alone or a mixture of two or more may be used. The amount of the solvent is sufficient to dissolve or disperse the positive electrode active material, the conductive material, and the binder in consideration of the coating thickness of the slurry and the production yield, and to have a viscosity that can exhibit excellent thickness uniformity during application for the production of the positive electrode. Do.

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

According to another embodiment of the present invention, an electrochemical device including the anode is provided. The electrochemical device may be specifically a battery or a capacitor, and more specifically, may be a lithium secondary battery.

The lithium secondary battery specifically 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, and the positive electrode is as described above. The lithium secondary battery may further include a battery container for accommodating the electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member for sealing the battery container.

In the lithium secondary battery, the negative electrode includes a negative electrode current collector and a negative electrode active material layer positioned on the negative electrode current collector.

The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical 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 or silver, or the like, or an aluminum-cadmium alloy may be used. In addition, the negative electrode current collector may have a thickness of about 3 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, or a nonwoven body.

The negative electrode active material layer optionally includes a binder and a conductive material together with the negative electrode active material. For example, the negative electrode active material layer is coated with a negative electrode active material, and optionally a composition for forming a negative electrode including a binder and a conductive material on a negative electrode current collector and dried, or casting the negative electrode forming composition on a separate support It may be produced by laminating a film obtained by peeling from this support onto a negative electrode current collector.

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 _x (0 <x <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 lithium secondary battery, the separator is to separate the negative electrode and the positive electrode and to provide a passage for the movement of lithium ions, if it is usually used as a separator in a lithium secondary battery can be used without particular limitation, in particular to the ion movement of the electrolyte It is desirable to have a low resistance against the electrolyte and excellent electrolytic solution-moisture capability. 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, conventional porous nonwoven fabrics such as nonwoven fabrics made of high melting point glass fibers, polyethylene terephthalate fibers and 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.

In addition, examples of the electrolyte used in the present invention include an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel polymer electrolyte, a solid inorganic electrolyte, a molten inorganic electrolyte, and the like, which can be used in manufacturing a lithium secondary battery. It doesn't happen.

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; Dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate, Carbonate solvents such as PC); Alcohol solvents such as ethyl alcohol and isopropyl alcohol; Nitriles such as R-CN (R is a C2 to C20 linear, branched or cyclic hydrocarbon group, which may include 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, the cyclic carbonate and the chain carbonate may be mixed and used in a volume ratio of about 1: 1 to about 1: 9, so that 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 0.1 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.

In addition to the electrolyte components, the electrolyte includes, for example, haloalkylene carbonate-based compounds such as difluoro ethylene carbonate, pyridine, tri, etc. for the purpose of improving battery life characteristics, reducing battery capacity, and improving discharge capacity of the battery. Ethyl phosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphate triamide, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N, N-substituted imida One or more additives such as zolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxy ethanol or aluminum trichloride may be included. In this case, the additive may be included in 0.1 to 5% by weight based on the total weight of the electrolyte.

As described above, since the lithium secondary battery including the cathode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics, and capacity retention rate, portable devices such as mobile phones, notebook computers, digital cameras, and hybrid electric vehicles ( It is useful for electric vehicle fields such as hybrid electric vehicle (HEV).

Accordingly, according to another embodiment of the present invention, a battery module including the lithium secondary battery as a unit cell and a battery pack including the same are provided.

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.

[ Production Example  One: Of positive electrode active material  Produce]

The Li ₂ CO ₃ powder and Co ₃ O ₄ powder is mixed in an amount such that the Li / Co molar ratio gradually decreases over time within the range of Li / Co molar ratio 1.0 to 1.02, followed by primary treatment at 900 ° C. for 10 hours. Heat treatment. The resulting powder was ground and classified to prepare particles of a second lithium cobalt oxide.

Li ₂ CO ₃ powder and Co ₃ O ₄ powder was dry-mixed in an amount such that the Li / Co molar ratio is 0.95 with respect to the second lithium cobalt oxide particles prepared above, followed by secondary heat treatment at 1050 ° C. for 20 hours. , A monolithic cathode active material (average particle size: 10㎛) was prepared, having a concentration gradient that decreases as lithium goes from the particle center to the surface throughout the particle.

Preparation Example 2: Preparation of Cathode Active Material

Li ₂ CO ₃ powder and Co ₃ O ₄ powder was mixed in an amount such that the Li / Co molar ratio of 1 and heat-treated at 900 ℃ for 10 hours to prepare a particle of the second lithium cobalt oxide.

The prepared second lithium cobalt oxide was repeatedly subjected to heat treatment at 900 ° C. for 5 hours in an oxygen atmosphere twice, whereby lithium cobalt oxide having a lithium defect structure was distributed with a concentration gradient on the surface of the particle. An active material (average particle diameter: 10 mu m) was prepared.

Preparation Example 3: Preparation of Cathode Active Material

Li ₂ CO ₃ powder and Co ₃ O ₄ powder was mixed in an amount such that the Li / Co molar ratio of 1 and heat-treated at 900 ℃ for 10 hours to prepare a particle of the second lithium cobalt oxide.

The second lithium cobalt oxide was repeatedly subjected to heat treatment for 5 hours at 900 ° C. under oxygen atmosphere. At this time, Co ₃ O ₄ was added in amounts of 0.05 mol and 0.25 mol for each heat treatment step. As a result, a positive electrode active material (average particle size: 10 mu m) having a monolithic structure was prepared in which lithium cobalt oxide having a lithium defect structure was distributed with a concentration gradient on the particle surface side.

Preparation Example 4: Preparation of Cathode Active Material

The Li ₂ CO ₃ powder and Co ₃ O ₄ powder were mixed in an amount such that the Li / Co molar ratio was 1.02, followed by primary heat treatment at 900 ° C. for 10 hours. The resulting powder was ground and classified to prepare particles of a second lithium cobalt oxide.

Li ₂ CO ₃ powder and Co ₃ O ₄ powder was dry-mixed in an amount such that the Li / Co molar ratio is 0.95 with respect to the second lithium cobalt oxide particles prepared above, followed by secondary heat treatment at 1050 ° C. for 20 hours. A monolithic cathode active material (average particle size: 12 μm) was prepared, having a concentration gradient that decreases as lithium goes from the particle center to the surface throughout the particle.

Preparation Example 5 Preparation of Cathode Active Material

The Li ₂ CO ₃ powder and Co ₃ O ₄ powder were mixed in an amount such that the Li / Co molar ratio was 1, and then subjected to primary heat treatment at 900 ° C. for 10 hours. The resulting powder was ground and classified to prepare particles of a second lithium cobalt oxide.

For the second lithium cobalt oxide particles prepared above, Li ₂ CO ₃ powder and Co ₃ O ₄ powder is dry-mixed in an amount such that the Li / Co molar ratio is 0.95, and the secondary heat treatment at 900 ℃ 20 hours Thus, a positive electrode active material (average particle size: 12 mu m) having a monolithic structure containing a first lithium cobalt oxide having a lithium defect structure on the particle surface side was prepared.

Preparation Example 6 Preparation of Cathode Active Material

The Li ₂ CO ₃ powder and Co ₃ O ₄ powder were mixed in an amount such that the Li / Co molar ratio was 1, and then subjected to primary heat treatment at 900 ° C. for 10 hours. The resulting powder was ground and classified to prepare particles of a second lithium cobalt oxide.

Li ₂ CO ₃ powder and Co ₃ O ₄ powder were dry mixed in an amount such that a Li / Co molar ratio of 0.95 was added to the second lithium cobalt oxide particles prepared above, and the ZrO ₂ powder was further added to 1 mol of Li. After adding and mixing the Zr metal in an amount of 0.01 mol, the second heat treatment was performed at 1050 ° C. for 20 hours to distribute lithium cobalt oxide having a concentration gradient on the surface of the particle with a concentration gradient. The lithium cobalt oxide of Zr doped to prepare a positive electrode active material (average particle size: 12㎛) of a monolithic structure.

Preparation Example 7 Preparation of Cathode Active Material

The Li ₂ CO ₃ powder and Co ₃ O ₄ powder were mixed in an amount such that the Li / Co molar ratio was 1, and then subjected to primary heat treatment at 900 ° C. for 10 hours. The resulting powder was ground and classified to prepare particles of a second lithium cobalt oxide.

Li ₂ CO ₃ powder and Co ₃ O ₄ powder were dry mixed in an amount such that a Li / Co molar ratio of 0.95 was added to the second lithium cobalt oxide particles prepared above, and additionally, 1 mol of MgO and TiO ₂ powder were added. Mg and Ti metals were added in an amount of 0.01 mol each to mix and mix, followed by a secondary heat treatment at 1050 ° C. for 20 hours, so that lithium had a concentration gradient decreasing from the particle center to the surface throughout the particle. A positive electrode active material (average particle size: 12 mu m) having a monolithic structure including a first lithium cobalt oxide having a lithium-deficient structure doped with Mg and Ti in a shell portion was prepared.

[Examples 1 to 7: Preparation of the lithium secondary battery]

A lithium secondary battery was manufactured using the cathode active materials prepared in Preparation Examples 1 to 7, respectively.

In detail, the positive electrode active material, the carbon black conductive material, and the PVdF binder prepared in Preparation Examples 1 to 7 were mixed in an N-methylpyrrolidone solvent in a ratio of 90: 5: 5 by weight in a composition for forming a positive electrode. (Viscosity: 5000 mPa · s) was prepared, which was applied to an aluminum current collector, and then dried and rolled to prepare a positive electrode.

In addition, MCMB (mesocarbon microbead), carbon black conductive material and PVdF binder, which are artificial graphite as a negative electrode active material, were mixed in an N-methylpyrrolidone solvent in a weight ratio of 85: 10: 5 to prepare a composition for forming a negative electrode, This was applied to a copper current collector to prepare a negative electrode.

An electrode assembly was manufactured by interposing a separator of porous polyethylene between the positive electrode and the negative electrode prepared as described above, the electrode assembly was placed in a case, and an electrolyte solution was injected into the case to prepare a lithium secondary battery. At this time, the electrolyte solution is lithium hexafluoro of 1.15 M concentration in an organic solvent consisting of ethylene carbonate (EC) / dimethyl carbonate (DMC) / ethyl methyl carbonate (EMC) (mixed volume ratio of EC / DMC / EMC = 3/4/3) Prepared by dissolving phosphate (LiPF ₆ ).

Comparative Example 1: Manufacture of Lithium Secondary Battery

A lithium secondary battery was manufactured in the same manner as in Example 1, except that LiCoO ₂ (average particle diameter: 10 μm) was used as the cathode active material.

Comparative Example 2: Fabrication of Lithium Secondary Battery

The Li ₂ CO ₃ powder and Co ₃ O ₄ powder were mixed in an amount such that the Li / Co molar ratio was 1, and then subjected to primary heat treatment at 900 ° C. for 10 hours. The resulting powder was ground and classified to prepare particles of a second lithium cobalt oxide.

Li ₂ CO ₃ powder and Co ₃ O ₄ powder is dry-mixed in an amount such that the Li / Co molar ratio is 1.2 with respect to the second lithium cobalt oxide particles prepared above, followed by secondary heat treatment at 1050 ° C. for 20 hours. On the surface of the second lithium cobalt oxide particles, a positive electrode active material (average particle diameter: 10 μm) containing lithium cobalt oxide (Li _a CoO ₂ , 0 <a ≦ 0.2) having _a higher concentration of lithium than the core was formed.

Experimental Example 1

Li / Co according to the depth profile from the surface of the active material particles to the inside using X-ray photoelectron spectroscopy (XPS) for the cathode active materials prepared in Preparation Examples 1 to 5 above The molar ratio change was observed. The results are shown in Tables 1 and 2 below.

Depth from the surface of the anode active material particle (nm) Li / Co molar ratio Preparation Example 1 Preparation Example 2 Preparation Example 3 30 0.95 0.97 0.95 50 0.95 0.98 0.95 150 0.96 0.99 0.96 250 0.96 0.99 0.97 300 0.97 1.00 0.98 450 0.98 1.00 0.99 500 1.00 1.00 1.00 1000 1.00 1.00 1.00 1500 1.01 1.00 1.00 2000 1.01 1.00 1.00 2500 1.01 1.00 1.00 3000 1.02 1.00 1.00 3500 1.02 1.00 1.00 4000 1.02 1.00 1.00 4500 1.02 1.00 1.00 5000 (particle center) 1.02 1.00 1.00

Depth from Particle Surface of Lithium Cobalt Oxide (nm) Molar ratio of Li / Co Preparation Example 4 Preparation Example 5 50 0.95 0.95 150 0.96 0.95 250 0.98 0.95 300 0.98 0.95 450 0.99 0.95 500 1.00 1.00 1000 1.00 1.00 1500 1.00 1.00 2000 1.00 1.00 2500 1.00 1.00 3000 1.00 1.00 3500 1.00 1.00 4000 1.02 1.00 4500 1.02 1.00 5000 1.02 1.00 5500 1.02 1.00 6000 (particle center) 1.02 1.00

As shown in Tables 1 and 2, a shell including the first lithium cobalt oxide having a lithium defect structure was formed in a region corresponding to a distance ratio of 0.05 to 0.1 from the surface of the particles based on the radius of the active material particles.

In addition, the positive electrode active material distributed during the manufacturing process has a concentration gradient that decreases from the center of the particle to the surface of the lithium through the control of the heat treatment temperature and the continuous change of the content ratio of the input material (Preparation Examples 1 and 4), 2 By repeating the secondary heat treatment, lithium cobalt oxide having a lithium defect structure having a concentration gradient only on the particle surface side (manufacture examples 2 and 3), and no concentration gradient throughout the particle, and lithium defect only on the particle surface side Cathode active materials (manufacture example 5) containing lithium cobalt oxide were prepared, respectively. In addition, in the case of the positive electrode active material of Preparation Example 3, in addition to repeating the secondary heat treatment, by introducing cobalt oxide reacting with lithium in each heat treatment step, the thickness of the shell portion including the lithium defect structure is thicker, and Li / The change of Co molar ratio was abrupt.

Experimental Example 2

For lithium cobalt oxide particles prepared in Preparation Example 2, the lithium distribution on the surface of the particles was observed using an atomic probe tomography (APT). The results are shown in FIG.

In FIG. 1, a) shows the lithium distribution on the particle surface side (from the particle surface to 50 nm in the center direction) of lithium cobalt oxide in Preparation Example 2 in APT, and b) shows 3D information in a) in 2D. The image is measured by measuring the density.

As shown in Figure 1, it can be seen that the density of lithium increases toward the particle center of the lithium cobalt oxide. Meanwhile, the yellow lithium rich portion shown in the upper right part in FIG. 1 is due to an error during the experiment.

Experimental Example 3

For the lithium cobalt oxide particles prepared in Preparation Example 2, the crystal structures on the surface side and inside of the active material were observed using a transmission electron microscope. The results are shown in FIG.

As shown in FIG. 2, in the case of the first lithium cobalt oxide present on the surface side of the lithium cobalt oxide particles (A) similar to the spinel crystal structure, it can be confirmed that it has a cubic crystal structure of the space group Fd-3m. . On the other hand, in the case of the second lithium cobalt oxide present in the active material particles (C) it can be confirmed that it has a layered crystal structure of the space group R_3m.

Experimental Example 4

Coin cell (using Li metal cathode) was prepared using the cathode active materials prepared in Preparation Example 1 and Comparative Example 1, and after initial charge and discharge at room temperature (25 ° C.) under 0.1C / 0.1C conditions The properties were evaluated. The results are shown in FIG. 3.

As a result of the experiment, as shown in FIG. 3, the positive electrode active material of Preparation Example 1 having a lithium defect structure on the particle surface side of the lithium cobalt oxide, that is, the shell portion, was nearly compared with the positive electrode active material of Comparative Example 1 having no lithium defect structure. Equivalent charge and discharge characteristics were shown. However, in the case of the positive electrode active material of Preparation Example 1, the breakage of the voltage profile, that is, the inflection point was observed between 4.05 and 4.15V due to the lithium defect structure present in the shell portion.

Experimental Example 5

After charging and discharging the coin cell (using a negative electrode of Li metal) prepared by using the cathode active material prepared in Preparation Example 1 under conditions of 0.1C and 0.5C at room temperature (25 ° C), respectively, rate characteristics were evaluated. . The results are shown in FIG. 4.

As a result, as shown in Figure 4, the lithium secondary battery including the positive electrode active material of Preparation Example 1 having a lithium defect structure in the shell, the lithium of Comparative Example 1 containing a positive electrode active material of LiCoO ₂ does not have a lithium defect structure Compared to the secondary battery showed improved rate characteristics.

Experimental Example 6

Battery characteristics of the lithium secondary batteries prepared in Examples 1 and 2 and Comparative Example 1 were evaluated in the following manner.

Specifically, for the lithium secondary batteries prepared in Examples 1 and 2 and Comparative Example 1, the charge-discharge rate characteristics under the condition of 2C / 0.1C within the range of 3V to 4.4V driving voltage at room temperature (25 ° C) and Cycle capacity retention ratio, which is the ratio of the discharge capacity at the 50th cycle to the initial capacity after 50 charge / discharge cycles are performed under the conditions of 0.5C / 1C at a high temperature (60 ° C.) within a range of 3V to 4.4V retention) was measured and shown in Table 3 below.

Room temperature (25 ℃) rate characteristic (2C / 0.1C,%) 50 cycle capacity retention rate at high temperature (60 ℃) Comparative Example 1 91.5 94.4 Example 1 97.1 96.2 Example 2 97.1 96.2

As a result of the experiment, the batteries of Examples 1 and 2 containing lithium cobalt oxide having a lithium defect structure, compared with the battery of Comparative Example 1 containing lithium cobalt oxide without a lithium defect structure as a positive electrode active material, improved rate characteristics and lifetime Characteristics.

Experimental Example 7: Evaluation of Gas Generation in Lithium Secondary Battery

After charging / discharging 50 times with respect to the lithium secondary batteries prepared in Example 1 and Comparative Examples 1 and 2 under a condition of 0.5C / 1C at a high temperature (60 ° C.) within a range of 3 to 4.4V driving voltage, the battery The amount of gas generated in the chamber was measured. The results are shown in Table 4 below.

Gas generation amount (µl / mg) Comparative Example 1 3 Comparative Example 2 5 Example 1 One

As a result of the experiment, the battery of Example 1 containing lithium cobalt oxide having a lithium defect structure in the shell of the core, Comparative Example 1 containing lithium cobalt oxide having no lithium defect structure as a positive electrode active material and in lithium cobalt oxide in the shell Compared to the battery of Comparative Example 2, the concentration of lithium was higher than that of the core, which showed a significantly reduced amount of gas generation.

Claims (26)

Contains particles of lithium cobalt oxide, The particle of the lithium cobalt oxide has a molar ratio of Li / Co in the area of the particle and in an area corresponding to a distance of 0% or more and less than 100% from the particle surface with respect to the distance r from the surface to the center of the particle. Less than 1, the space group belongs to Fd-3m, and comprises a lithium cobalt oxide of lithium defects having a cubic crystal structure, a cathode active material for a lithium secondary battery. The method of claim 1, The lithium cobalt oxide of the lithium defect is a positive electrode active material for a lithium secondary battery containing the first lithium cobalt oxide of the formula (1). [Formula 1] Li _1-a CoM _x O ₂ (In Formula 1, M includes one or two or more metal elements selected from the group consisting of W, Mo, Zr, Ti, Mg, Ta, Al, Fe, V, Cr, Ba, Ca, and Nb) a is 0 <a≤0.05, x is 0≤x≤0.02) The method of claim 1, The particles of lithium cobalt oxide has a core portion and a core-shell structure of a shell portion located on the surface of the core portion, The shell part includes a first lithium cobalt oxide of Formula 1, The core part of the positive electrode active material for a lithium secondary battery containing a second lithium cobalt oxide of the formula (2). [Formula 1] Li _1-a CoM _x O ₂ [Formula 2] Li _b CoM ' _y O ₂ (In Formulas 1 and 2, M and M 'are each independently selected from the group consisting of W, Mo, Zr, Ti, Mg, Ta, Al, Fe, V, Cr, Ba, Ca, and Nb) Or two or more metal elements, a, b, x and y being 0 <a≤0.05, 1≤b≤1.2, 0≤x≤0.02 and 0≤y≤0.02) The method of claim 3, The first lithium cobalt oxide is a space group belongs to Fd-3m, has a cubic crystal structure, The second lithium cobalt oxide is a positive electrode active material for a lithium secondary battery having a layered crystal structure. The method of claim 3, Wherein the shell portion is a region corresponding to the distance of 0% to 99% from the surface with respect to the distance from the surface to the center of the lithium cobalt oxide particles. The method of claim 3, The core part and the shell part has a thickness ratio of 1: 0.01 to 1: 0.1. The method of claim 3, Wherein the core portion and the shell portion is a positive electrode active material for a lithium secondary battery, each containing lithium distributed in increasing concentration gradient toward the center of the particles of lithium cobalt oxide. The method of claim 3, The gradient of the concentration gradient of lithium in the core portion and the gradient of the concentration gradient of lithium in the shell portion are the same or different inclination value for a lithium secondary battery positive electrode active material. The method of claim 3, The core portion contains a higher concentration of lithium than the shell portion, At least one of the core portion and the shell portion includes a lithium present in one concentration value in the region of the positive electrode active material for a lithium secondary battery. The method of claim 3, The lithium cobalt oxide particles are distributed in a concentration gradient in which lithium gradually increases from the surface to the center, In Chemical Formulas 1 and 2, a decreases toward the particle center within a range of 0 <a ≦ 0.05, and b increases toward the particle center within a range of 1 ≦ b ≦ 1.2. The method of claim 1, A cathode active material for a lithium secondary battery having a monolithic structure having a mean particle size of 3 to 50 μm. The method of claim 1, The positive electrode active material for a lithium secondary battery having an inflection point in the voltage range of 4.0V to 4.2V when measuring the voltage profile according to the charge and discharge. Preparing a particle of a second lithium cobalt oxide by mixing the cobalt raw material and the lithium raw material in an amount such that a ratio of 1 ≦ Li / Co ≦ 1.2 and then heat treatment; And Performing a second heat treatment at least once on the particles of the second lithium cobalt oxide Method for producing a cathode active material for a lithium secondary battery according to claim 1 comprising a. The method of claim 13, In the particle preparation step of the second lithium cobalt oxide, W, Mo, Zr, Ti, Mg, Ta, Al, Fe, V, Cr, Ba, Ca, and Nb when mixing the cobalt raw material and the lithium raw material A method for producing a cathode active material for a lithium secondary battery further comprising any one or two or more metal element-containing raw materials selected from the group. The method of claim 13, The primary heat treatment is a method for producing a cathode active material for a lithium secondary battery that is carried out by heating at 800 ℃ to 1100 ℃ temperature in the atmosphere or oxygen atmosphere. The method of claim 13, The secondary heat treatment is a method for producing a cathode active material for a lithium secondary battery that is carried out by heating at 800 ℃ to 1100 ℃ temperature in the atmosphere or oxygen atmosphere. The method of claim 13, The secondary heat treatment is carried out twice at a temperature of 800 ℃ to 1100 ℃, each temperature during the heat treatment method for producing a positive electrode active material for a lithium secondary battery. The method of claim 13, A method of manufacturing a cathode active material for a lithium secondary battery, further comprising adding a cobalt raw material or a cobalt raw material and a lithium raw material during the second heat treatment. The method of claim 13, The method of manufacturing a cathode active material for a lithium secondary battery further comprises adding a cobalt raw material and a lithium raw material in an amount such that 0.95 <Li / Co molar ratio <1 during the second heat treatment. The method of claim 13, Further adding one or more metal element-containing raw materials selected from the group consisting of W, Mo, Zr, Ti, Mg, Ta, Al, Fe, V, Cr, Ba, Ca, and Nb during the second heat treatment Method for producing a cathode active material for a lithium secondary battery. A cathode for a lithium secondary battery comprising the cathode active material according to any one of claims 1 to 12. A lithium secondary battery comprising the positive electrode according to claim 21. A battery module comprising the lithium secondary battery according to claim 22 as a unit cell. A battery pack comprising the battery module according to claim 23. The method of claim 24, Battery pack that is used as a power source for medium and large devices. The method of claim 25, The medium-to-large device is a battery pack that is selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles and power storage systems.

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