KR101145951B1 - Positive active material for lithium secondary battery and lithium secondary battery comprising the same - Google Patents

Abstract

The present invention relates to a positive electrode active material for a lithium secondary battery and a lithium secondary battery including the same, wherein the positive electrode active material is a coin-type half cell comprising a lithium metal composite oxide represented by the following formula (1) as a positive electrode and a lithium metal as a negative electrode (Coin The first cycle discharge capacity is 165mAh / g or more in the 4.3 ~ 3.0 V voltage range by the half cell configuration, and the main exotherm temperature by DSC (Differential Scanning Calorimetry) at 4.3V is 300 ℃ or more, and 4.6 It is a lithium metal composite oxide which shows that main heating temperature by DSC at V is 290 degreeC or more, and Ni ion site occupying 3a site is 1.9-3.1 in the Rietveld analysis by X-ray diffraction.

The positive electrode active material of the present invention has a high capacity and excellent thermal stability by adjusting the Li / M ratio, NiMnCo ratio and cation mixing degree.

Li [Li _z A _(1-za) D _a ] E _b O _{2-b ...} One)

Wherein A = Ni _(1-xy) M ¹ _x Co _y ,

M ¹ is at least one metal element selected from Mn, Ti, and Zr,

D is at least one metal element selected from Mg, Al, B and Zn.

E is at least one anion selected from P, F,

-0.05 ≤ z ≤ 0.1, 0 ≤ a ≤ 0.05, 0 ≤ b ≤ 0.05

0.3 ≦ x ≦ 0.4 and 0.85 <2x + y ≦ 0.9.

Positive electrode active material, cation mixing, thermal stability, lithium secondary battery, lithium metal composite oxide

Description

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

The present invention relates to a cathode active material for a lithium secondary battery and a lithium secondary battery including the same, and more particularly, to adjust an optimal Li / M ratio, NiCoMn composition ratio, and cation mixing degree, for a lithium secondary battery having high thermal stability and excellent thermal stability. It relates to a positive electrode active material and a lithium secondary battery comprising the same.

Recently, with the trend toward miniaturization and light weight of portable electronic devices, the need for high performance and high capacity of batteries used as power sources for these devices is increasing.

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

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

A lithium metal composite compound is used as a cathode active material of a lithium secondary battery, and examples thereof include a composite such as LiCoO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , LiNi _1-x Co _x O ₂ (0 <x <1), LiMnO _2, and the like. Metal oxides are being studied.

Among the cathode active materials, LiMn ₂ O ₄ is easy to synthesize, relatively low in price, and has the highest thermal stability compared to other active materials when overcharged, and is attractive because of low pollution to the environment, but has a small capacity and cycle characteristics. This is bad.

LiCoO ₂ has a good electrical conductivity and a high battery voltage of about 3.7V, and has excellent physical properties such as cycle life characteristics and discharge capacity, and thus is a representative cathode active material that is currently commercialized and commercially available. However, since LiCoO ₂ is expensive due to resource limitations, the cost of LiCoO ₂ is 30% or more of the battery price.

In addition, the secondary battery including the existing LiNiO ₂ -based positive electrode active material shows a rapid deterioration of the crystal structure due to the volume change during the process of intercalation / deintercalation of lithium ions, and this series of processes is repeated. Particles and crystal structures may be cracked or separated from each other.

In order to solve this problem, ternary lithium composite oxides of various compositions in which a part of nickel is substituted with other transition metals (Co, Mn) have been disclosed, but a composition consisting of a ratio between transition metals (Ni: Co: Mn) and a Li / M ratio The range of specific battery characteristics and thermal stability have not been presented.

When Ni content is higher, the reversible capacity is relatively increased, but thermal stability is sharply decreased. When Ni content is relatively low and Mn content is high, thermal stability is improved, but the energy density has no advantage over conventional LiCoO ₂ . do. Therefore, in order to completely replace or partially replace the conventional LiCoO ₂ , an optimal Ni: Mn: Co composition and Li / M should be selected in terms of capacity and safety.

Control of the Li / M ratio in the positive electrode active material is related to the Mn content in the composite transition metal, it is possible to insert extra lithium in the transition metal layer by a certain amount of Mn substitution amount or more. In terms of battery characteristics, the extra lithium inserted into the transition metal layer gives relatively high high-rate characteristics and lifespan characteristics. Also, in the composition system having a relatively high Mn content compared to a ternary composition including a low Mn content, It is easy to insert lithium to minimize the amount of lithium introduced during synthesis, and it is possible to control the water-soluble base content such as Li ₂ CO ₃ , LiOH remaining on the surface of the active material after firing. The residual lithium component decomposes during charging and discharging or reacts with the electrolyte to generate CO ₂ gas. As a result, a swelling phenomenon of the battery is generated, thereby lowering the high temperature stability.

In particular, when LiNiO _2- based positive electrode active material or ternary positive electrode active material containing Ni as a main component is exposed to air and moisture, impurities such as LiOH and Li ₂ CO ₃ are formed on the surface (see Schemes 1 and 2; J. Power Sources). , 134, page 293, 2004).

Scheme 1

LiNiO ₂ + yH ₂ O → Li _1-y NiO _{2-y / 2} + yLiOH

Scheme 2

LiNi _0.8 Co _0.15 Al _0.05 O ₂ + 4xO ₂ + yH ₂ O → Li _1-y Ni _0.8 Co _0.15 Al _0.05 O ₂ + 2xLi ₂ CO ₃

The residual lithium formed increases the pH when preparing the slurry of the electrode plate, and gelation occurs because the slurry containing NMP (1-methyl-2-pyrrolidinone) and the binder (Binder) starts to polymerize. It causes problems in the manufacturing process.

Therefore, many prior arts focus on improving the properties and manufacturing process of nickel-based cathode active materials. However, problems such as high production costs, process complexity, premature operation of current interrupt devices (CID devices) due to excessive gas generation in batteries, swelling phenomenon, and low thermal stability have not been sufficiently solved.

In connection with a lithium secondary battery, Japanese Laid-Open Patent Publication No. 1996-319120 discloses a binary Li _x Ni _1-y Me _y O ₂ system based on Ni (Me is a transition metal other than Ni, 0 <x <1,0 The degree of cation mixing of ≦ y <0.6) is disclosed.

However, the patent not only differs from the present invention in the composition of the active material, but also uses only LiOH, not Li ₂ CO _{3, which} is inexpensive and easily handled as a lithium source, and also calcinates in an oxygen atmosphere which is a specific reaction atmosphere. Equipped with an expensive process, there is a difference from the present invention produced in the air atmosphere using Li ₂ CO ₃ .

In addition, Korean Patent Nos. 10-0790834 and 10-0790835 have the formula Li _x [{Ni _(1-ab) (Ni _1/2 Mn _1/2 ) _a Co _b } _1-k A _k ] _y O ₂ , the ranges are 0.65 ≦ a + b ≦ 0.85 and 0.1 ≦ b ≦ 0.4, and the degree of cation mixing of the lithium composite oxide and the composition, which is limited to 0 ≦ k <0.05, is disclosed.

The oxide of the present invention is different from the above invention in the composition range, and based on the effect of the Li / M ratio of the active material (residual Li ₂ CO ₃ , pH, initial capacity, high rate characteristics, lifetime) and thermal stability even at the degree of cation mixing It is limited to the cation mixing ratio range.

The present invention is to solve the conventional problems of the three-phase cathode active material containing Ni as a main component, the search for the optimal Li / M ratio and NiCoMn composition ratio and a part of Ni ions are inserted into the lithium layer (Layer) It is to provide a positive electrode active material for a lithium secondary battery and a lithium secondary battery comprising the same by adjusting the cation mixing degree to occur, and excellent thermal stability.

Another object of the present invention is to provide a method for producing a lithium metal composite oxide of the formula (1).

Li [Li _z A _(1-za) D _a ] E _b O _{2 -b ...} (1)

Wherein A = Ni _(1-xy) M ¹ _x Co _y ,

M ¹ is at least one metal element selected from Mn, Ti, and Zr,

D is at least one metal element selected from Mg, Al, B and Zn.

E is at least one anion selected from P, F,

-0.05 ≤ z ≤ 0.1, 0 ≤ a ≤ 0.05, 0 ≤ b ≤ 0.05

0.3 ≦ x ≦ 0.4 and 0.85 <2x + y ≦ 0.9.

In order to achieve the above object, the positive electrode active material of the present invention has a composition represented by the following formula (1), the first cycle discharge in the voltage range of 4.3 ~ 3.0 V by the coin half cell (Coin Half cell) configuration of lithium metal as a negative electrode Capacity is 165 mAh / g or more, main heating peak by DSC (Differential Scanning Calorimetry) at 4.3V is 300 ℃ or higher, main heating temperature by DSC at 4.6V is 290 ℃ or higher, X In the Rietveld analysis by line diffraction, the occupancy ratio of Ni ion occupying the 3a site is 1.9 to 3.1.

Li [Li _z A _(1-za) D _a ] E _b O _{2 -b ...} (1)

Wherein A = Ni _(1-xy) M ¹ _x Co _y ,

M ¹ is at least one metal element selected from Mn, Ti, and Zr,

D is at least one metal element selected from Mg, Al, B and Zn.

E is at least one anion selected from P, F,

-0.05 ≤ z ≤ 0.1, 0 ≤ a ≤ 0.05, 0 ≤ b ≤ 0.05

0.3 ≦ x ≦ 0.4 and 0.85 <2x + y ≦ 0.9.

In the composition of Formula 1, Li [Ni _0.47 Co _0.2 Mn _0.33 ] O ₂ is preferable.

)로서 개방층(open layer)를 통해 Li이온이 가역적으로 출입할 수 있는 구조의 결정계를 나타내고, X선 회절에 의한 리트벨트 해석에 의한 측정치와 계산치의 잔류 오차(Rp)가 15% 이하이다. The lithium metal composite oxide has a layered structure in which Li ions occupy an octahedral site between layers made of octahedra.

) Represents a crystal system having a structure in which Li ions can reversibly enter and exit through an open layer, and the residual error (Rp) between the measured value and the calculated value by Rietveld analysis by X-ray diffraction is 15% or less.

In the cation mixing, transition metal ions are inserted into the lithium layer and lithium ions are inserted into the transition metal layer. Thus, divalent Ni having a similar ion radius to lithium ions among the transition metals is inserted into the lithium layer. If the amount of cation incorporation is large, the charge and discharge will be disturbed and the reversible capacity will be lowered. Therefore, the reversible capacity of the lithium metal oxide can be increased by controlling the degree of cation mixing.

The lithium metal composite oxide exhibits a main exotherm temperature of 300 ° C. or higher by DSC at 4.3 V and a main exotherm temperature of 290 ° C. or more by DSC at 4.6 V. The definition of the main exothermic temperature in the present invention is defined as the peak on the high temperature side (pyrolysis peak of the bulk of the active material) in the presence of several exothermic peaks.

Primary particles of the lithium metal composite oxide aggregate into spherical or elliptic phase to form secondary particles having an average particle diameter of 4 to 20 um.

The production method of the present invention comprises the steps of mixing Li ₂ CO ₃ and the composite transition metal hydroxide;

Baking the obtained mixture in air at a firing temperature of 700 to 1050 ° C for 12 to 24 hours to obtain a fired body;

Slowly cooling and pulverizing the resulting fired body.

In the firing step, by adjusting the flow rate of the air step by step to facilitate the emission of CO ₂ generated during the reaction characterized in that it controls the Cation mixing ratio (Cation mixing) and the residual lithium carbonate. The profile of the kiln consists of heating / maintenance / cooling sections, and each section is defined as the initial, middle, and late periods by dividing the time into three sections. When a higher flow rate than 4/5 of the initial flow rate input to the elevated temperature and maintaining the end section when it is difficult to excessive heat loss due to the air input and thus maintain the set temperature in accordance with the input is lower than the third air is CO ₂ emissions can not not smooth particle diameter Difficulties in growth and residual Li components remain in excess. Therefore, it is preferable to inject air corresponding to 4/5 to 1/3 of the initial temperature flow rate during the end of the temperature increase and the maintenance section.

The lithium metal composite oxide of the present invention is composed of an optimal Li / M ratio and NiCoMn composition range, and has a high capacity and excellent thermal stability by appropriately adjusting the cation mixing degree.

In addition, the lithium metal composite oxide of the present invention provides a cathode active material for a lithium secondary battery which is inexpensive.

The cathode active material according to the present invention includes a lithium metal composite oxide represented by the following Chemical Formula 1.

Li [Li _z A _(1-za) D _a ] E _b O _{2 -b ...} (1)

Wherein A = Ni _(1-xy) M ¹ _x Co _y ,

M ¹ is at least one metal element selected from Mn, Ti, and Zr,

D is at least one metal element selected from Mg, Al, B and Zn.

E is at least one anion selected from P, F,

-0.05 ≤ z ≤ 0.1, 0 ≤ a ≤ 0.05, 0 ≤ b ≤ 0.05

0.3 ≦ x ≦ 0.4 and 0.85 <2x + y ≦ 0.9.

In the compound of Formula 1, the initial capacity in the range of 4.3 ~ 3.0V when the coin-type half-cell (Coin Half cell) of the lithium metal as a negative electrode is preferably 165 mAh / g or more. In the case of the positive electrode active material mainly composed of nickel, since the average discharge voltage is lower than that of LiCoO ₂ , the initial capacity required is higher than that of LiCoO ₂ of 160 mAh / g. If the initial capacity is less than 165 mAh / g, there is no advantage in terms of energy density compared to LiCoO ₂ .

The lithium metal composite oxide constituting the cathode active material of the present invention has excellent thermal stability and electrochemical properties by appropriately adjusting the ratio of Li / M and NiCoMn, in particular, the ratio of Ni and Mn.

As for the average particle diameter of the said lithium metal complex oxide, 4-25 micrometers is preferable. If the average particle diameter is smaller than 4 µm, the tap density does not sufficiently occur and the thermal stability decreases due to the increase of the specific surface area. On the other hand, when the thickness exceeds 25 μm, the lithium de-insertion reactivity is lowered and the high rate characteristic is lowered.

The tap density of the lithium metal composite oxide is preferably 1.8 to 2.7 g / cc in order to realize high electrode plate density.

The composite transition metal hydroxide among the starting materials used in the production of the lithium metal composite oxide of the present invention can be produced by, for example, the method described in Japanese Patent Laid-Open No. 2002-201028.

In the preparation of the positive electrode active material according to the present invention, the compounding molar ratio of the composite transition metal hydroxide and the lithium compound (Li / Metal) is preferably 0.95 to 1.15, which is subjected to mixing, firing, and grinding.

In addition, the calcination process for producing a lithium metal composite oxide according to the present invention is a one-step calcination or heating step of 400 to 800 ℃ in a one-step calcination for 12 to 24 hours at a firing temperature of 700 ℃ to 1050 ℃. It provides a multi-step firing comprising the step of maintaining the temperature for a certain time and the main firing at a firing temperature of 700 ℃ to 1050 ℃.

The lithium metal composite oxide of the present invention can be usefully used for the positive electrode of a lithium secondary battery. The lithium secondary battery includes a negative electrode and an electrolyte including a negative electrode active material together with a positive electrode.

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

At this time, the conductive material is carbon black, graphite, metal powder, binder is vinylidene fluoride / hexafluoropropylene copolymer, polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polytetrafluoroethylene And mixtures thereof.

Moreover, N-methylpyrrolidone, acetone, tetrahydrofuran, decane, etc. are used as a solvent. In this case, the contents of the positive electrode active material, the conductive material, the binder, and the solvent are used at levels commonly used in lithium secondary batteries.

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

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

The separator may be used as long as it is commonly used in a lithium secondary battery. For example, polyethylene, polypropylene, polyvinylidene fluoride or two or more multilayer films thereof may be used. In addition, a mixed multilayer film such as polyethylene / polypropylene two-layer separator, polyethylene / polypropylene / polyethylene three-layer separator, polypropylene / polyethylene / polypropylene three-layer separator, and the like may be used.

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

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

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

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

Hereinafter, the present invention will be described in more detail with reference to specific examples. However, embodiments of the present invention are presented by way of example to illustrate the present invention, by which the present invention is not limited, the present invention is defined by the technical spirit and claims described in the detailed description.

Manufacturing example

<Production of Complex Transition Metal Hydroxide>

The sulfuric acid raw materials of nickel, cobalt, and manganese were dissolved in distilled water in a ratio such that the compositions shown in Examples 1 to 2 and Comparative Examples 1 to 5 were obtained in a reactor to prepare a solution containing nickel, cobalt, and manganese.

5.5 M sodium hydroxide was added to this solution as a precipitant, 1 M ammonia water was added as a complexing agent, and pH was maintained at 11.5. After washing / filtering the precipitate obtained according to this process, the process of removing impurities Na and S through alkaline aqueous solution and then washing / filtering with water is repeated.

If the Na content, which is an impurity, is more than 500 ppm, deterioration of sinterability and battery characteristics occurs. If SO ₄ is more than 5000 ppm, lithium sulfide is formed during the firing process and remains as an impurity. In addition, Na, SO ₄ is Reaction with moisture in the air makes electrode slurry and electrode plate difficult, and swelling occurs when the battery is left at high temperature.

The powder obtained was dried in an oven set at 120 ° C. and then ground to prepare a composite transition metal hydroxide.

Example 1

<Production of Lithium Metal Composite Oxide>

Li ₂ CO ₃ (trade name: SQM) and the composite transition metal hydroxide Ni _0.45 Co _0.2 Mn _0.35 (OH) ₂ prepared in the above Preparation Example were mixed using a mixer in a weight ratio of 1: 1.03 (M: Li). .

The resulting mixture at the end and the retaining zone temperature was raised while supplying the air of the temperature increase the reaction time of 6 hours in air, 950 ℃ in the sustain period, a seven-time total burning time is, and the more than 20 hours, temperature was raised early / mid-term is 20m ³ / h The fired body was manufactured under the condition of introducing air corresponding to 1/2 of the temperature increase initial flow rate. The resulting fired body was slowly cooled and pulverized to prepare a positive electrode active material powder of the lithium metal composite oxide of the present invention.

The initial and late stages were defined as the beginning, middle, and end by dividing the time period into three sections. The resulting fired body was slowly cooled and pulverized to prepare a positive electrode active material powder of the lithium metal composite oxide of the present invention.

Example 2

In Example 1, except that the composite transition metal hydroxide is to use _{Ni 0 .47 Co 0 .2 Mn 0} .33 (OH) 2 to prepare a sintered body in the same manner as in Example 1. The resulting fired body was slowly cooled and pulverized to prepare a positive electrode active material powder of the lithium metal composite oxide of the present invention. The battery characteristic evaluation results of the prepared active material are shown in Table 1.

TABLE 1

Sample name 2-1 2-2 2-3 2-4 2-5 2-6 Li / M 0.97 0.975 0.994 1.035 1.052 1.07 Residual Li ₂ CO ₃ 0.091 0.108 0.114 0.134 0.140 0.157 pH 11.20 11.24 11.3 11.36 11.39 11.52 Formation capacity 165.2 166.4 169.1 170.2 170.4 166.1 2C capacity 136.4 137.2 139.0 144.2 144.7 139.9 Life expectancy after 30 cycles 91.8 92.5 93.3 93.5 95.8 94.1

In the case of the composition of Example 2 (LiNi _0.47 Co _0.2 Mn _0.33 O ₂ ), since the ratio of Mn in the total metal is 30% or more, more lithium may be inserted into the transition metal layer. Therefore, it is possible to manufacture a cathode active material having a relatively high Li / M ratio, and the amount of Li ₂ CO ₃ remaining on the surface is also relatively easy compared to LiNi _0.5 Co _0.2 Mn _0.3 O ₂ .

In Table 1, as the Li / M ratio was increased, the amount of residual Li ₂ CO ₃ was increased, and when it is 1.07 or more, it can be seen that a high pH value (11.5) appears to be a problem when preparing the slurry of the electrode plate. In terms of battery characteristics, it can be seen that as the Li / M ratio is increased from 0.97 to 1.052, the formation discharge capacity is increased and 2C characteristics are improved. When the Li / M ratio is 1.07, the capacity and high rate characteristics are deteriorated. Therefore, the Li / M ratio of the active material is preferably 0.98 to 1.06 in consideration of residual lithium control and battery characteristics.

Comparative Example 1

Ni _1/3 Co _1/3 Mn _1/3 (OH) ₂ composite hydroxide was mixed using a mixer so that the molar ratio of Li ₂ CO ₃ and (Ni + Co + Mn): Li is 1: 1.03.

The resulting mixture was held and calcined at 1000 ° C. for 7 hours in a heating reaction time of 6 hours and a holding section. The obtained fired body was cooled slowly and pulverized again to prepare a positive electrode active material.

Comparative Example 2

Ni _0.4 Co _0.15 Mn _0.45 (OH) ₂ composite hydroxide was mixed using a mixer such that the molar ratio of Li ₂ CO ₃ and (Ni + Co + Mn): Li is 1: 1.04.

The resulting mixture was held and calcined at 980 ° C. for 7 hours in a heating reaction time of 6 hours and a holding section. The obtained fired body was slowly cooled and pulverized again to prepare a positive electrode active material. Table 2 shows the powder results of the active material obtained in Comparative Example 2.

Table 2

Sample name Comparative Example 2 Li / M 1.03 Residual Li ₂ CO ₃ (%) 0.095 pH 10.83

Compared with sample 2-4 of Example 2 (at the same level of Li / M ratio) shows a low residual Li ₂ CO ₃ content and pH characteristics. Compared with Examples 1 to 2, the Mn content is relatively high, so even a small amount of lithium source facilitates the excessive Li insertion into the transition metal layer, and the nickel content is also smaller than that of Examples 1 to 2, so the residual Li content is also estimated to be small. do.

Comparative Example 3

Ni _0.5 Co _0.2 Mn _0.3 (OH) ₂ composite hydroxide was mixed using a mixer so that the molar ratio of Li ₂ CO ₃ and (Ni + Co + Mn): Li is 1: 1.03.

The resulting mixture was held and calcined for 7 hours at 950 ° C. in a heating reaction time of 6 hours and a holding section. The resulting fired body was cooled slowly and pulverized again to prepare a cathode active material. Table 3 shows the powder results of the active material obtained in Comparative Example 3.

TABLE 3

Sample name Comparative Example 3 Li / M 0.99 Residual Li ₂ CO ₃ (%) 0.13 pH 11.5

Compared with Samples 2-3 of Comparative Examples 3 and 2 (compared at the same Li / M level), the residual Li ₂ CO ₃ content and pH level of Comparative Example 3 were high and the pH of Comparative Example 3 was To obtain more than 1.0 Li / M at the same level as Sample 2-6, an excessive amount of Li raw material should be added, resulting in a residual Li ₂ CO ₃ content and a rise in pH.

Comparative Example 4

The Ni _0.6 Co _0.2 Mn _0.2 (OH) ₂ composite hydroxide was mixed using a mixer such that the molar ratio of Li ₂ CO ₃ and (Ni + Co + Mn): Li is 1: 1.03.

The resulting mixture was held and calcined at 900 ° C. for 7 hours in a heating reaction time of 6 hours and a holding section. The obtained fired body was cooled slowly and pulverized again to prepare a positive electrode active material.

Comparative Example 5

Ni _0.7 Co _0.15 Mn _0.15 (OH) ₂ composite hydroxide was mixed using a mixer so that the molar ratio of Li ₂ CO ₃ and (Ni + Co + Mn): Li is 1: 1.03.

The resulting mixture was held and calcined at 820 ° C. for 7 hours in a heating reaction time of 6 hours and a holding section. The obtained fired body was cooled slowly and pulverized again to prepare a positive electrode active material.

The battery application evaluation results of the active materials obtained in Examples 1 and 2 and Comparative Examples 1 to 3 are collectively shown in Table 4.

Table 4

Sample name Example 1 Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 Formation capacity
(mAh / g) 167.5 170.4 165.2 158.2 168.2 2C capacity (mAh / g) 140.2 145.5 139.7 138.2 139.1 % Life cycle after cycle (%) 97 95.8 93.2 96.1 91.2

The compositions of Examples 1 and 2 exhibit high reversible discharge capacity characteristics when compared to the compositions of Comparative Examples 1 and 2. Comparative Example 2 showed excellent characteristics in the life retention rate, but showed an inadequate characteristic as a material for high energy density due to its low initial capacity. In comparison with Comparative Example 3, excellent life characteristics were observed in Example 1, reversible capacity equivalent to or higher in Example 2, and excellent 2C / life retention characteristics.

Example 3

Example 3-1

A high-voltage LiCoO ₂ prepared by the method described in Korean Patent No. 10-0864199 and a lithium composite oxide prepared in Example 2-4 were mixed at a weight ratio of 8: 2 to prepare an electrode plate. A coin battery was manufactured using the manufactured electrode plate as a positive electrode and lithium metal as a negative electrode. After charging to 4.3V, the cell was disassembled and DSC measurement was performed.

Example 3-2

The DSC measurement was performed in the same manner except that the LiCoO ₂ and the lithium composite oxide prepared in Example 2-5 were mixed at a ratio of 7: 3.

Rietveld analysis by X-ray diffraction

  The XRD diffraction pattern is obtained under the following measurement conditions.

  X-ray tube: Copper (Cu)

  Power: Voltage-40kV, Current-30mA

  -Temperature: 25 ℃

  -Diffraction value recording method: step-scan

  -Scanning angle range: 10 ㅀ ~ 120 ㅀ

  -Scanning interval: 0.01 ㅀ ~ 0.03 ㅀ

  -Interval of scan interval: 10 seconds ~ 60 seconds

  Reciving Slit: 0.15mm ~ 0.60mm

  Divergence Slit: 0.5 ㅀ ~ 2 ㅀ

In the case of a hexagonal compound, there are 3a, 3b, and 6c sites, and in the case of LiNiO ₂ having a complete stoichiometric composition, the 3a site is Li, the 3b site Ni, and the 6c site are each 100% occupied by O.

The Rietveld analysis method expresses the peak of the powder X-ray diffraction pattern as an exponent in order to obtain detailed lattice parameters at high resolution, intersects the space group, and refines the lattice constant by the least-squares method or Rawlay method. Powder X-ray diffraction is simulated based on structural model constructed from atomic arrangements by estimating each atomic arrangement with crystallographic knowledge and chemical composition.

<Rietveld analysis sequence>

Rietveld analysis program: Materials Studio Reflex

① Load data obtained through XRD device

② Establish structural model through crystallographic insights and elemental analysis

   Enter the space group, atomic coordinates, and lattice constant of the crystal

 Space group: R-3m

 -Enter atomic coordinates (X, Y, Z)

   Li (3a site): (0, 0, 0)

   M (3b site): (0, 0, 0.5)

   O (6c site): (0, 0, 2.4 ~ 2.45)

 Enter the grid constants (a, b, c)

   a: 2.5 ~ 2.9Å

   c: 14.0 ~ 14.9Å

③ Adjust the below factors to reduce the analysis error.

 Peak profile function

 Background function arguments

 Preferred Orientation Factor

 -Thermal oscillation factor or isotropic temperature factor

 Line Shift Factor

④ Perform simulation after checking occupancy ratio (ICP measurement) and refinement by element.

⑤ Check reliability and analysis error through R factor and refinement pattern graph.

Ni ion site occupancy occupying 3a site of the positive electrode active material of 2-2 to 2-6 of Example 2 was calculated based on Rietveld Mothed as described above and the results are shown in Table 5 below. From Table 1 and Table 5, cation occupancy is preferably 1.9 to 3.1.

Table 5

Sample name 2-2 2-3 2-4 2-5 2-6 Li / M 0.975 0.994 1.035 1.052 1.07 Cation share (%) 3.24 2.88 2.53 2.02 1.85

An X-ray diffraction pattern of the sample of the present invention was measured using an X-ray diffraction apparatus. As shown in the result of the Rietbelt analysis of the X-ray diffraction (Table 5), in Example 1 and Comparative Example 3 of the present invention, the powder characteristic values were almost similar, but the difference in the degree of cation mixing of the positive electrode active material affected the battery characteristics. You can see the madness.

 From the results shown in Table 5, it can be seen that the positive electrode active materials of Examples 1 to 2 and the positive electrode active materials of Comparative Examples 1 to 3 of the present invention have different structural properties, and these other physical properties affect thermal stability. .

* Thermal stability measurement

In order to determine the thermal stability of the positive electrode active material of Example 2-5 and the positive electrode active material according to Comparative Examples 1 to 5, by charging at 4.3V by the configuration of a coin-type half-cell (Coin Half cell) using a lithium metal as a negative electrode Differential Scanning Calorimeter (DSC) measurement was performed, and the results are shown in FIG. 1.

In addition, in order to examine the thermal stability at high voltages of Examples 2-5 and Comparative Example 3 was charged to 4.6V by a coin-type half-cell (Coin Half cell) configuration using lithium metal as a negative electrode, DSC measurement was performed The results are shown in FIG.

As shown in Example 3, LiCoO ₂ prepared by the method described in Korean Patent No. 10-0864199 and the positive electrode active material of the present invention are 8: 2 (Example 3-1) to 7: 3 (Example 3-). 2) After mixing the ratio to prepare the electrode plate was configured with a coin cell (cathode: lithium metal, electrolyte solution 1.0M LiPF ₆ EC / DMC 1: 1) and charged to 4.3 V, the differential weight thermal analysis device was measured, The results are shown in FIG.

Fan Used: Pressure Fan

Sample weight: 5-10mg

Nitrogen: 50ml / min

Measuring range: 30 ~ 350 ℃

Temperature raising rate: 5 ℃ / min

FIG. 1 is a graph illustrating measurement of thermal stability characteristics (DSC) of the cathode active materials prepared in Examples 2-5 and Comparative Examples 1 to 5 of the present invention, and as shown in FIG. 1, Example 2- of the present invention. Since the exothermic temperature of the positive electrode active material of 5 is higher than Comparative Examples 1, 3 to 5, it can be seen that the thermal stability is excellent.

FIG. 2 is a graph illustrating measurement and measurement of thermal stability (DSC) at 4.6V of the cathode active materials prepared in Examples 2-5 and Comparative Example 3 of the present invention. As shown in FIG. 2, an embodiment of the present invention. Since the exothermic temperature of the positive electrode active material of 2-5 is higher than that of Comparative Example 3, it can be seen that the thermal stability is excellent.

Figure 3 is a graph showing the measurement of the thermal stability characteristics (DSC) of Examples 3-1 and 3-2 of the present invention, as shown in Figure 3, when the coating LiCoO ₂ and the positive electrode active material of the present invention is used in combination In contrast, when used alone, it can be seen that the exothermic temperature peak moves toward the high temperature of 10 ° C or more.

The exothermic temperature is a temperature at which oxygen decomposes due to broken metal and oxygen bonds in the positive electrode active material, which means that the higher the temperature, the better the stability.

The technical problem to be achieved by the present invention is not limited to the above-mentioned technical problem, and also all simple modifications or changes of the present invention can be easily carried out by those skilled in the art and such modifications or changes Are all included in the scope of the present invention.

       1 is a graph showing the measurement of the thermal stability (DSC) at 4.3V of the positive electrode active material prepared in Examples 2-5 and Comparative Examples 1 to 5 of the present invention.

Figure 2 is a graph showing the measurement of the thermal stability (DSC) at 4.6V of the positive electrode active material prepared in Example 2-5 and Comparative Example 3 of the present invention.

Figure 3 is a graph showing the measurement of the thermal stability (DSC) at 4.3V of the positive electrode active material prepared in Example 3-1 and Example 3-2 of the present invention.

Claims (22)

The first cycle discharge capacity in the voltage range of 4.3 to 3.0 V is 165 mAh / g or more in the voltage range of 4.3 to 3.0 V by the composition represented by the following formula (1) and the lithium metal is used as a cathode. The main heat generation temperature by 290 degreeC or more, and the lithium ion composite oxide of 1.9-3.1 Ni-site occupying 3a site in the Rietveld analysis by X-ray diffraction characterized by the above-mentioned. Li [Li _z A _(1-za) D _a ] E _b O _2-b ................... (1) Wherein A = Ni _(1-xy) M ¹ _x Co _y , M ¹ is at least one metal element selected from Mn, Ti, and Zr, D is at least one metal element selected from Mg, Al, B and Zn. E is at least one anion selected from P, F, -0.05 ≤ z ≤ 0.1, 0 ≤ a ≤ 0.05, 0 ≤ b ≤ 0.05 0.3 ≦ x ≦ 0.4 and 0.85 <2x + y ≦ 0.9. The lithium metal composite oxide of claim 1, wherein the composition of Formula 1 is Li [Ni _0.47 Co _0.2 Mn _0.33 ] O ₂ . The lithium metal composite oxide of claim 1, wherein the composition of Formula 1 is Li [Ni _0.45 Co _0.2 Mn _0.35 ] O ₂ . The method of claim 1, wherein the first cycle discharge capacity is 180mAh / g or more in the voltage range of 4.4 ~ 3.0 V by using a coin half cell configuration using a lithium metal composite oxide as a positive electrode and a lithium metal as a negative electrode. Lithium metal composite oxide. The method according to claim 1, wherein the first cycle discharge capacity is 190mAh / g or more in the voltage range 4.5 ~ 3.0 V by the coin half cell configuration of the lithium metal composite oxide as a positive electrode and lithium metal as a negative electrode. Lithium metal composite oxide. The method of claim 1, wherein the lithium metal composite oxide

And a residual error (Rp) between the measured value and the calculated value by Rietveld analysis by X-ray diffraction is 15% or less. The lithium metal composite oxide of claim 1, wherein the lithium metal composite oxide aggregates in a spherical or elliptical shape with primary particles having an average particle diameter of 4 to 25 μm. The lithium metal composite oxide according to claim 1, wherein the main exothermic temperature by DSC is shifted by 10 ° C. or higher compared to the use of the lithium metal composite oxide alone by mixing the lithium metal composite oxide with LiCoO ₂ . The lithium metal composite oxide according to claim 8, wherein a mixing ratio of LiCoO ₂ and the lithium metal composite oxide is 8: 2 to 6: 4. The lithium metal composite oxide according to claim 1, wherein the main exotherm temperature by DSC at 4.3 V is 300 ° C. or higher. The lithium metal composite oxide according to claim 1, wherein a 0.1 C discharge capacity retention ratio is 83% or more compared to 2C in a voltage range of 4.3 to 3.0 V by using a coin half cell structure having lithium metal as a negative electrode. . Mixing Li ₂ CO ₃ and the composite transition metal hydroxide; Baking the obtained mixture in air at a firing temperature of 700 to 1050 ° C for 12 to 24 hours to obtain a fired body; The resulting fired body is slowly cooled and pulverized to have a composition represented by the following formula (1), and comprises a lithium metal as a negative electrode (Coin Half cell) configuration by 4.3 to 3.0 V In the voltage range, the first cycle discharge capacity is 165mAh / g or more, the main heat generation temperature by DSC at 4.3V is 300 ° C or higher, the main heat generation temperature by DSC at 4.6V is 290 ° C or higher, and it is lit by X-ray diffraction. The method for producing a lithium metal composite oxide, wherein the occupancy ratio of Ni ion occupying 3a site in the belt analysis is 1.9 to 3.1. Li [Li _z A _(1-za) D _a ] E _b O _2-b ............... (1) Wherein A = Ni _(1-xy) M ¹ _x Co _y , M ¹ is at least one metal element selected from Mn, Ti, and Zr, D is at least one metal element selected from Mg, Al, B and Zn. E is at least one anion selected from P, F, -0.05 ≤ z ≤ 0.1, 0 ≤ a ≤ 0.05, 0 ≤ b ≤ 0.05 0.3 ≦ x ≦ 0.4 and 0.85 <2x + y ≦ 0.9. The method of claim 12, wherein in the firing step, supplying air of at least 10 m ³ / h to the initial temperature / medium temperature of the heating step, the air corresponding to 4/5 to 1/3 of the initial flow rate of the temperature increase in the end of the temperature rising and the maintenance section Characterized in the manufacturing method. The method of claim 12, wherein in the firing step, the flow rate supplied to the initial / middle temperature rise section 10 to 30 m ³ / h, the air flow rate of the end of the temperature increase and the maintenance section to 4/5 to 1/3 of the initial temperature rise section Method for producing a corresponding air. The method according to claim 12, wherein in the firing step, a temperature increase reaction time is 4 to 8 hours, and a holding period is 850 ° C to 1000 ° C and 4 to 10 hours. The method of claim 12, wherein the step of maintaining the temperature at a temperature of 400 ℃ to 800 ℃ constant temperature during the firing step and the step of performing the main firing at a firing temperature of 700 ℃ to 1050 ℃ multi-step (multi step) Manufacturing method characterized in that it is manufactured as. The method according to claim 12, wherein the mixing ratio of the Li ₂ CO ₃ and the composite transition metal hydroxide is 0.97 to 1.15 in a Li / M molar ratio. The method of claim 12, wherein in the firing step, by adjusting the flow rate of air step by step to facilitate the emission of CO ₂ generated during the reaction to control the Cation mixing ratio (Cation mixing ratio) and residual lithium carbonate. . The lithium metal composite oxide of claim 1, wherein the tap density of the lithium metal composite oxide is 1.8 to 2.7 g / cc. The lithium metal composite oxide according to claim 1, wherein Na content in the lithium metal composite oxide is 500 ppm or less. The lithium metal composite oxide according to claim 1, wherein the content of SO ₄ in the lithium metal composite oxide is 5000 ppm or less. A lithium secondary battery comprising the lithium metal composite oxide according to any one of claims 1 to 11 and 19 to 21 as a positive electrode active material.

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