WO2018124781A1 - Positive electrode active material for secondary battery, preparation method therefor, positive electrode comprising same for secondary battery, and secondary battery - Google Patents

Abstract

The present invention relates to a positive electrode active material for a secondary battery, a preparation method therefor, a positive electrode comprising the same, and a secondary battery, the positive electrode active material comprising: a lithium composite metal oxide represented by chemical formula 1; and a cobalt-rich layer formed on a surface of the lithium composite metal oxide and having a higher cobalt content than the lithium composite metal oxide.

Description

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

[Citations with Related Applications]

This application claims the benefit of priority based on Korean Patent Application No. 10-2016-0181027, filed on December 28, 2016, all the contents disclosed in the Korean patent application document is included as part of this specification.

[Technical Field]

The present invention relates to a positive electrode active material for a secondary battery, a method for manufacturing the same, a positive electrode for a secondary battery and a secondary battery including the same, and more particularly, a high concentration having a low amount of lithium by-products remaining on the surface of the active material, and having excellent high temperature stability, capacity characteristics, and lifetime characteristics. The present invention relates to a nickel (Ni-rich) cathode active material, a method of manufacturing the same, and a cathode and a secondary battery for a secondary battery including the same.

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

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

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

Accordingly, as a method for improving low thermal stability while maintaining excellent reversible capacity of LiNiO ₂ , a nickel cobalt manganese-based lithium composite metal oxide in which a part of Ni is substituted with Mn and Co (hereinafter, simply referred to as 'NCM-based lithium oxide') Has been developed. However, the conventional NCM-based lithium oxide developed to date has a limitation in application due to insufficient capacity characteristics.

In order to improve such a problem, researches have recently been made to increase the content of Ni in NCM-based lithium oxide. However, in the case of a high nickel content of a high concentration of the nickel positive electrode active material, there is a problem that the structural stability and chemical stability of the active material is lowered, the thermal stability is sharply lowered. In addition, as the nickel content in the active material increases, the amount of lithium by-products present in the form of LiOH and Li ₂ CO ₃ on the surface of the positive electrode active material increases, resulting in gas generation and swelling, thereby improving battery life and stability. The problem of deterioration also arises.

Accordingly, there is a demand for development of a high-density nickel (Ni-rich) cathode active material having high residual capacity and low residual amount of lithium by-products while meeting high capacity.

[Preceding technical literature]

1. Korean Patent Publication No. 10-2016-0063982 (published: 2016.06.07)

The present invention is to solve the above problems, a low amount of lithium by-products, cobalt-rich layer (Co-rich layer) is formed on the surface of the high-concentration nickel cathode active material that can simultaneously realize excellent capacity characteristics and high temperature stability And, to provide a manufacturing method, and a positive electrode and a secondary battery for a secondary battery comprising the same.

In one aspect, the present invention is a lithium composite metal oxide represented by the formula (1); And a cobalt-rich layer formed on the surface of the lithium composite metal oxide and having a higher cobalt content than the lithium composite metal oxide.

[Formula 1]

Li _{1 + x} [Ni _a Co _b Mn _c M _d ] _1-x O _2-y X _y

In Formula 1, 0.7 <a <1, 0 <b <0.3, 0 <c <0.1, 0 <d <0.1, a + b + c + d = 1, 0 ≦ x ≦ 0.05, 0 ≦ y ≦ 0.2 M is one metal element selected from the group consisting of Al, Mg, Ge, V, Mo, Nb, Si, Ti, Zr and W, and X is P or F.

The ratio of the number of atoms of cobalt to the sum of the number of atoms of nickel, cobalt, manganese and M in the cobalt-rich layer and the number of atoms of cobalt to the sum of the number of atoms of nickel, cobalt, manganese and M in the lithium composite metal oxide The difference in ratio of may be 0.05 to 0.2, preferably 0.05 to 0.15.

Specifically, the ratio of the number of atoms of cobalt to the sum of the number of atoms of nickel, cobalt, manganese and M in the cobalt-rich layer may be 0.05 to 0.45, and preferably 0.05 to 0.35.

The cobalt rich layer may have a thickness of 10 to 100 nm, preferably 10 to 70 nm.

On the other hand, the positive electrode active material when the heat flow (Heat Flow) measured by differential scanning calorimetry (DSC), a peak appears in the temperature range of 230 ℃ to 250 ℃, preferably 235 ℃ to 245 ℃, The maximum value of the heat flow may be 1000 mW or less, preferably 600 mW or less, and more preferably 400 mW or less.

In addition, the lithium by-product content in the positive electrode active material may be 1% by weight or less, preferably 0.5% by weight or less, and more preferably 0.3% by weight or less.

In another aspect, the present invention comprises the steps of preparing a lithium composite metal oxide represented by the formula (1); Washing the lithium composite metal oxide; And it provides a method for producing a positive electrode active material for a secondary battery comprising the step of mixing the washed lithium composite metal oxide and cobalt-containing raw material and heat treatment at an temperature of 700 ℃ or more in an oxidizing atmosphere.

At this time, the step of preparing a lithium composite metal oxide represented by the formula (1), a nickel-cobalt precursor, a manganese-containing raw material, M-containing raw material, and a lithium-containing raw material mixed and fired at 600 ℃ to 900 ℃ It can be performed as. The washing step may be performed at a temperature of 20 ℃ or less.

In the heat treatment step, the cobalt-containing raw material may be mixed to 0.001 to 0.01 parts by weight, preferably 0.002 to 0.008 parts by weight based on 100 parts by weight of the lithium composite metal oxide.

In addition, the heat treatment may be performed within 10 hours at 700 ℃ to 800 ℃ temperature.

In another aspect, the present invention provides a secondary battery positive electrode including the positive electrode active material for a secondary battery according to the present invention, and a secondary battery comprising the positive electrode for the secondary battery.

In the positive electrode active material for a secondary battery according to the present invention, a cobalt-rich layer including a high content of cobalt having excellent output characteristics and stability is formed on the surface thereof, unlike the conventional high concentration nickel positive electrode active material, it is not only structurally stable but also repeatedly charged. Even when the secondary battery is excellent in capacity characteristics and has a small resistance increase rate.

In addition, when the cobalt-containing raw material is mixed after washing with water and subjected to high temperature heat treatment in an oxidizing atmosphere, the residual amount of lithium by-products is reduced, structural stability is improved while recrystallization occurs, and thus has excellent high temperature stability. A positive electrode active material can be manufactured.

1 is a graph showing the heat flow (Heat Flow) according to the temperature of the positive electrode active material of Example 1 and Comparative Example 3.

FIG. 2 is a graph showing pH titration curves of the positive electrode active materials of Example 1, Comparative Examples 1 and 4 to 6. FIG.

3 is a graph showing capacity retention rates according to charge and discharge cycles of battery cells prepared using the cathode active materials of Example 1 and Comparative Examples 2 and 3. FIG.

4 is a graph showing the resistance increase rate according to the charge and discharge cycle of the battery cell prepared using the positive electrode active material of Example 1 and Comparative Examples 2 and 3.

Below. The present invention is described in more detail.

The inventors of the present invention have been researched to produce a high-density nickel-based positive electrode active material having a low residual amount of lithium by-products and excellent high temperature stability. As a result, a lithium composite metal oxide containing a specific metal element M in an appropriate composition ratio together with nickel, cobalt, and manganese is used. After washing with water, the mixture was mixed with the cobalt-containing raw material and then heat treated at an temperature of 700 ° C. or higher in an oxidizing atmosphere to find a high concentration nickel-based cathode active material having low residual amount of lithium by-product and excellent high temperature stability. It was.

First, the manufacturing method of the positive electrode active material for secondary batteries which concerns on this invention is demonstrated.

Manufacturing method of positive electrode active material for secondary batteries

Method for producing a positive electrode active material according to the present invention comprises the steps of (1) preparing a lithium composite metal oxide represented by the formula (1), (2) washing the lithium composite metal oxide and (3) the washed lithium composite metal oxide Mixing the cobalt-containing raw material and heat-treating at an temperature of 700 ° C. or higher in an oxidizing atmosphere. Hereinafter, each step of the present invention will be described in more detail.

(1) preparing a lithium composite metal oxide

First, a lithium composite metal oxide is prepared.

The lithium composite metal oxide used in the present invention is nickel, cobalt, manganese, and four components of M, which is one metal element selected from the group consisting of Al, Mg, Ge, V, Mo, Nb, Si, Ti, Zr, and W. It is a four-component lithium composite metal oxide containing essential as a high concentration nickel (high-nickel) four-component lithium composite metal oxide in which the molar ratio of nickel in the said four components exceeds 0.7.

Specifically, the lithium composite metal oxide may be a lithium composite metal oxide represented by Formula 1 below.

[Formula 1]

Li _{1 + x} [Ni _a Co _b Mn _c M _d ] _1-x O _2-y X _y

In Formula 1, M is one metal element selected from the group consisting of Al, Mg, Ge, V, Mo, Nb, Si, Ti, Zr, and W, X is P or F.

A, b, c, and d are the atomic fractions of each of Ni, Co, Mn, and M elements among the metal elements excluding lithium, that is, the sum of the atomic numbers of Ni, Co Mn, and M, respectively. It represents ratio of 0.7 <a <1, 0 <b <0.3, 0 <c <0.1, 0 <d <0.1, a + b + c + d = 1.

Specifically, a represents an atomic fraction of nickel among the metal elements excluding lithium, and a may be greater than 0.7 but less than 1, preferably 0.8 to 0.95, and more preferably 0.8 to 0.9.

B represents an atomic fraction of cobalt among metal elements excluding lithium, and b may be greater than 0 and less than 0.3, preferably 0.001 to 0.25, more preferably 0.01 to 0.2.

C represents an atomic fraction of manganese among metal elements excluding lithium, and c may be greater than 0 and less than 0.1, preferably 0.001 to 0.05.

The d represents an atomic fraction of the M element among the metal elements excluding lithium, and d may be greater than 0 and less than 0.1, preferably 0.001 to 0.05.

On the other hand, x represents the extent to which some of the metal elements except lithium are replaced by lithium, and y represents the extent to which oxygen is replaced by the X element, 0≤x≤0.1, 0≤y≤ 0.5. Preferably 0 ≦ x ≦ 0.05, 0 ≦ y ≦ 0.2.

The lithium composite metal oxide having the composition as shown in [Formula 1] is relatively high in structural stability, while implementing a high capacity characteristic compared to the conventional NMC-based lithium oxide. Specifically, the lithium composite metal oxide of [Formula 1] has a high nickel content having a high capacity characteristic, thereby realizing excellent capacity characteristics, and Mn and M elements are doped inside the active material, compared to the conventional NMC-based lithium oxide. Structurally stable. In addition, when oxygen is replaced with P or F, desorption of oxygen is prevented during charge and discharge of the lithium secondary battery, and interfacial reaction with the electrolyte is suppressed, thereby improving surface stability.

The lithium composite metal oxide of [Formula 1] is not limited thereto, but for example, a nickel-cobalt precursor, a manganese-containing raw material, a M-containing raw material, and a lithium-containing raw material are mixed, and 700 ° C. to 900 ° C. It may be prepared by the method of firing at ℃.

In this case, the nickel-cobalt precursor may be, for example, nickel-cobalt hydroxide, specifically, a compound represented by Ni _{a '} Co _b' OOH, wherein a 'is 0.7 to 0.95, preferably Preferably it may be 0.8 to 0.95, the b 'may be 0.05 to 0.3, preferably 0.05 to 0.2. The nickel-cobalt precursor may be purchased by using a commercially available nickel-cobalt hydroxide, or may be prepared according to a method for preparing a nickel-cobalt precursor well known in the art.

For example, the nickel-cobalt precursor may be prepared by coprecipitation reaction by adding an ammonium cation-containing complex former and a basic compound to a metal solution containing a nickel-containing raw material and a cobalt-containing raw material.

The nickel-containing raw material may be, for example, nickel-containing acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide or oxyhydroxide, and the like, specifically, Ni (OH) ₂ , NiO, NiOOH, NiCO _3. 2Ni (OH) ₂ 4H ₂ O, NiC ₂ O ₂ 2H ₂ O, Ni (NO ₃ ) ₂ 6H ₂ O, NiSO ₄ , NiSO ₄ 6H ₂ O, fatty acid nickel salts, nickel halides or their It may be a combination, but is not limited thereto.

The cobalt-containing raw material may be cobalt-containing acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide or oxyhydroxide, and the like, specifically, Co (OH) ₂ , CoOOH, Co (OCOCH ₃ ) ₂ ㆍ 4H ₂ O , Co (NO ₃ ) ₂ ㆍ 6H ₂ O, Co (SO ₄ ) ₂ ㆍ 7H ₂ O or a combination thereof, but is not limited thereto.

The metal solution is prepared by adding a nickel-containing raw material and a cobalt-containing raw material to a solvent, in particular water, or a mixed solvent of an organic solvent (eg, alcohol, etc.) that can be mixed uniformly with water, or It may be prepared by mixing an aqueous solution of the nickel-containing raw material and an aqueous solution of the cobalt-containing raw material.

The ammonium cation-containing complex former may be, for example, NH ₄ OH, (NH ₄ ) ₂ SO ₄ , NH ₄ NO ₃ , NH ₄ Cl, CH ₃ COONH ₄ , NH ₄ CO _3, or a combination thereof. It is not limited to this. On the other hand, the ammonium cation-containing complex forming agent may be used in the form of an aqueous solution, wherein a solvent may be a mixture of water or an organic solvent (specifically, alcohol, etc.) that can be uniformly mixed with water.

The basic compound may be a hydroxide of an alkali metal or alkaline earth metal such as NaOH, KOH or Ca (OH) ₂ , a hydrate thereof, or a combination thereof. The basic compound may also be used in the form of an aqueous solution, and as the solvent, a mixture of water or an organic solvent (specifically, alcohol, etc.) that can be uniformly mixed with water may be used.

On the other hand, although not essential, if necessary, the basic compound may be used by dissolving an anionic compound including the X element, that is, P and / or F. In this case, while the X element derived from the anionic compound is partially substituted at the oxygen position of the precursor, it is possible to obtain the effect of suppressing oxygen desorption and reaction with the electrolyte during charging and discharging of the secondary battery.

The basic compound is added to adjust the pH of the reaction solution, and may be added in an amount such that the pH of the metal solution is 11 to 13.

On the other hand, the coprecipitation reaction may be carried out at a temperature of 40 ℃ to 70 ℃ under an inert atmosphere such as nitrogen or argon.

By the above process, particles of nickel-cobalt hydroxide are produced and precipitated in the reaction solution. The precipitated nickel-cobalt hydroxide particles can be separated according to a conventional method and dried to obtain a nickel-cobalt precursor.

The nickel cobalt precursor prepared by the above method, a manganese-containing raw material, an M-containing raw material and a lithium-containing raw material are mixed and calcined at 600 ° C to 900 ° C, preferably 600 ° C to 800 ° C to form a lithium composite metal oxide. You can get it.

In this case, the manganese-containing raw material may be, for example, manganese-containing acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide, oxyhydroxide or a combination thereof, and specifically Mn ₂ O ₃ , MnO ₂ Manganese oxides such as Mn ₃ O ₄ and the like; Manganese salts such as MnCO ₃ , Mn (NO ₃ ) ₂ , MnSO ₄ , manganese acetate, manganese dicarboxylic acid, manganese citrate, fatty acid manganese; Manganese oxy hydroxide, manganese chloride or a combination thereof, but is not limited thereto.

In addition, the M-containing raw material may be acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide, oxyhydroxide or a combination thereof containing M element, specifically, Al ₂ O ₃ , AlSO ₄ , AlCl ₃ , Al-isopropoxide, AlNO ₃ , or a combination thereof, but is not limited thereto.

The lithium-containing raw material may be a lithium-containing carbonate (e.g., lithium carbonate), a hydrate (e.g., lithium hydroxide I hydrate (LiOH, H ₂ O), etc.), a hydroxide (e.g., lithium hydroxide, etc.), a nitrate ( For example, lithium nitrate (LiNO ₃ ), etc.), chlorides (for example, lithium chloride (LiCl), etc.), and the like may be used alone, or a mixture of two or more thereof may be used.

On the other hand, the mixing of the nickel-cobalt precursor, the manganese containing raw material, the M containing raw material, and the lithium containing raw material may be made by solid phase mixing such as jet milling. Meanwhile, the mixing ratio of the nickel-cobalt precursor, the manganese-containing raw material, the M-containing raw material, and the lithium-containing raw material may be determined in a range satisfying the atomic fraction of each metal component in the finally manufactured lithium composite metal oxide.

In addition, although not essential, in order to dope some of the oxygen of the lithium composite metal oxide with the element X, the X-containing raw material may be further mixed during the firing. In this case, the X-containing raw material may be, for example, Na ₃ PO ₄ , K ₃ PO ₄ , Mg ₃ (PO ₄ ) ₂ , AlF ₃ , NH ₄ F, LiF, and the like, but is not limited thereto.

As described above, when a part of oxygen is replaced by the element X, the effect of suppressing oxygen desorption and reaction with the electrolyte during charging and discharging of the secondary battery can be obtained.

(2) Flushed  step

When the lithium composite metal oxide is prepared in the same manner as above, the lithium composite metal oxide is washed with water to remove lithium by-products remaining in the lithium composite metal oxide.

Lithium composite metal oxides containing high concentrations of nickel are more structurally unstable than lithium composite metal oxides with low nickel content, resulting in more lithium byproducts such as unreacted lithium hydroxide or lithium carbonate in the manufacturing process. Specifically, in the case of a lithium composite metal oxide having a nickel fraction of less than 80 atomic%, the amount of lithium byproducts after synthesis is about 0.5 to 0.6 wt%, whereas in the case of a lithium composite metal oxide having a nickel fraction of 80 atomic% or more, lithium after synthesis The amount of by-products appears as high as 1% by weight. On the other hand, when a large amount of lithium by-products are present in the positive electrode active material, lithium by-products and electrolytes react to generate gas and swelling, and thus high temperature stability is significantly lowered. Therefore, a washing process for removing lithium by-products from lithium composite metal oxides containing high concentrations of nickel is essential.

The washing step may be performed, for example, by adding a lithium composite metal oxide to ultrapure water and stirring the mixture. In this case, the washing temperature may be 20 ℃ or less, preferably 10 ℃ to 20 ℃, the washing time may be about 10 minutes to 1 hour. When the water washing temperature and the water washing time satisfy the above range, lithium by-products can be effectively removed.

(3) heat treatment step

After the washing is completed, the washed lithium composite metal oxide and the cobalt-containing raw material are mixed and heat-treated. At this time, the heat treatment is performed at a temperature of 700 ℃ or more in an oxidizing atmosphere. The heat treatment step is to improve the structural stability and thermal stability by further removing lithium by-products, and recrystallization of the metal elements in the positive electrode active material through high temperature heat treatment.

The cobalt-containing raw material may include cobalt-containing acetates, nitrates, sulfates, halides, sulfides, hydroxides, oxides, or oxyhydroxides, and specifically, Co (OH) ₂ , CoOOH, Co (OCOCH ₃ ) ₂ ㆍ 4H. _{2 O, Co (nO 3)} 2 and _{6H 2 O, Co (SO 4} ) 2 and 7H ₂ O, or the like may be used a combination thereof, and the like.

Meanwhile, the cobalt-containing raw material may be mixed in an amount of 0.001 to 0.01 parts by weight, preferably 0.002 to 0.008 parts by weight, based on 100 parts by weight of the lithium composite metal oxide. When the content of the cobalt-containing raw material satisfies the above range, the output characteristics can be effectively improved without inhibiting the capacity characteristics of the lithium composite metal oxide. Specifically, when the amount is less than 0.001 part by weight, the effect of improving the output is insignificant. When the amount exceeds 0.01 part by weight, nickel in the lithium composite metal oxide may be replaced with cobalt to deteriorate capacity characteristics.

When the heat treatment is performed by additionally adding the cobalt-containing raw material, the cobalt component is coated on the surface of the lithium composite metal oxide during the heat treatment process, and thus the cobalt-rich layer having a relatively higher cobalt content than the inside of the lithium composite metal oxide ( Cobalt-Rich Layer is formed. As such, when the cobalt-rich layer is formed on the surface of the lithium composite metal oxide, an output characteristic may be improved.

On the other hand, the heat treatment is carried out in an oxidizing atmosphere, for example, an oxygen atmosphere. Specifically, the heat treatment may be performed while supplying oxygen at a flow rate of 0.5 to 10 L / min, preferably 1 to 5 L / min. When the heat treatment is performed in an oxidizing atmosphere as in the present invention, lithium by-products are effectively removed. According to the researches of the present inventors, the effect of removing lithium by-products is remarkably decreased when heat treatment is performed in the air. In particular, when heat treatment is performed at 700 or more in the air, the amount of lithium by-products increases rather than before heat treatment.

In addition, the heat treatment is preferably performed within 10 hours, for example, 1 hour to 10 hours at 700 ℃ or more, for example, 700 ℃ to 800 ℃ temperature. When the heat treatment temperature and time satisfy the above range, the effect of improving the thermal stability is excellent. According to the researches of the present inventors, it was found that when the heat treatment temperature is less than 700 ° C., there is little effect of improving thermal stability.

Cathode Active Material for Secondary Battery

Next, the positive electrode active material for secondary batteries which concerns on this invention is demonstrated.

The cathode active material for a secondary battery of the present invention manufactured according to the above method includes a lithium composite metal oxide represented by the following Chemical Formula 1, and a cobalt-rich layer formed on the surface of the lithium composite metal oxide.

[Formula 1]

Li _{1 + x} [Ni _a Co _b Mn _c M _d ] _1-x O _2-y X _y

In Formula 1, M is one metal element selected from the group consisting of Al, Mg, Ge, V, Mo, Nb, Si, Ti, Zr and W, X is P or F, 0.7 <a <1 , 0 <b <0.3, 0 <c <0.1, 0 <d <0.1, a + b + c + d = 1, 0 ≦ x ≦ 0.05, 0 ≦ y ≦ 0.2. Specific specifications of the lithium composite metal oxide represented by the above [Formula 1] are the same as those described in the above manufacturing method, and thus, detailed description thereof will be omitted.

Meanwhile, the cobalt-rich layer is a layer formed by coating a surface of a lithium composite metal oxide with a cobalt component derived from a cobalt-containing raw material in a process of mixing and heat treating a lithium composite metal oxide and a cobalt-containing raw material. It is a layer containing more cobalt than metal oxide.

Specifically, the ratio of the number of atoms of cobalt to the total number of atoms (ie, sum of the number of atoms of nickel, cobalt, manganese, and M) of metal elements excluding lithium of the cobalt-rich layer (hereinafter, referred to as' cobalt atomic fraction) ') And the cobalt atomic fraction of the lithium composite metal oxide may be 0.05 to 0.2, preferably 0.05 to 0.15. More specifically, the atomic fraction of cobalt among nickel, cobalt, manganese, and M in the cobalt-rich layer (ie, the ratio of the number of atoms of cobalt to the sum of the number of atoms of nickel, cobalt, manganese, and M) is 0.05 to 0.45, preferably 0.05 to 0.35. When the cobalt atomic fraction in the cobalt rich layer satisfies the above range, the output characteristics can be effectively improved without disturbing the capacity characteristics of the lithium composite metal oxide.

On the other hand, the cobalt rich layer may have a thickness of 10 to 100nm, preferably 30nm to 70nm. When the thickness of the cobalt rich layer satisfies the above range, when the thickness of the cobalt rich layer exceeds 100 nm, the initial discharge capacity may decrease, and when the thickness of the cobalt rich layer is less than 10 nm, output and cycle characteristics may be degraded. Can be.

The cathode active material according to the present invention as described above is manufactured through a process of high temperature heat treatment in an oxidizing atmosphere after washing with water, the residual amount of lithium by-products is significantly less than the conventional high concentration nickel-containing cathode active material, it is possible to implement excellent high temperature stability.

Specifically, the positive electrode active material according to the present invention, when the heat flow (Heat Flow) is measured by differential scanning calorimetry (DSC), in the temperature range of 230 ℃ to 250 ℃, preferably in the temperature range of 235 ℃ to 245 ℃ A peak appears, and the maximum value of the heat flow is 1000 mW or less, preferably 600 mW or less, more preferably 400 mW or less. If the heat treatment is not performed after washing, or even if the heat treatment temperature and atmosphere does not satisfy the conditions of the present invention, the peak appears at a lower temperature, that is, less than 230 ℃, a high heat flow value of more than 1000mW. As such, when a peak appears in a low temperature range and a cathode active material having a high maximum heat flow amount is used, when the temperature inside the battery increases due to overcharging or the like, an explosion may occur while the heat flow rate increases rapidly. On the other hand, the positive electrode active material of the present invention has a relatively high temperature range in which peaks appear and a small maximum amount of heat flow, so that the explosion risk is small even when the internal temperature of the battery rises due to overcharge or the like.

In addition, the positive electrode active material according to the present invention has a lithium byproduct content of 1% by weight or less, preferably 0.5% by weight or less, more preferably 0.3% by weight or less. Therefore, when the secondary battery is manufactured using the cathode active material according to the present invention, gas generation and swelling phenomenon during charging and discharging can be effectively suppressed.

Positive and Secondary Batteries

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

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

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

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

At least one surface of the current collector includes a cathode active material according to the present invention, and optionally a cathode active material layer further comprising at least one of a conductive material and a binder.

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

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

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

In addition, the binder serves to improve adhesion between the cathode active material particles and adhesion between the cathode 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% by weight to 30% by weight based on the total weight of the positive electrode active material layer.

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

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

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

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

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

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

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

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

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

On the other hand, in the secondary battery, the separator separates the negative electrode and the positive electrode and provides a passage for the movement of lithium ions, and can be used without particular limitation as long as it is usually used as a separator in the secondary battery, in particular with respect to the ion movement of the electrolyte It is preferable that it is resistance and excellent in electrolyte solution moisture-wetting ability. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin-based polymer such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer and ethylene / methacrylate copolymer or the like Laminate structures of two or more layers may be used. In addition, 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.

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

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

The organic solvent may be used without particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvent may be an ester solvent such as methyl acetate, ethyl acetate, γ-butyrolactone or ε-caprolactone; Ether solvents such as dibutyl ether or tetrahydrofuran; Ketone solvents such as cyclohexanone; Aromatic hydrocarbon solvents such as benzene and fluorobenzene; 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; R _a -CN nitriles, such as (R _a may include a straight, branched, or a hydrocarbon group of a cyclic structure, an aromatic ring or a double bond, ether bond, having 2 to 20 carbon atoms); 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 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 0.1M to 2.0M. When the concentration of the lithium salt is included in the above range, since the electrolyte has an appropriate conductivity and viscosity, it can exhibit excellent electrolyte performance, and lithium ions can move effectively.

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

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

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

Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily practice the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention.

Example  One

Ni _{0 . 9} Co _{0 . 1 OOH, Mn 3 O 4,} Al 2 O 3 , and then a solution of the solid phase the LiOH, then fired at 750 ℃ lithium-metal composite oxide _{Li (Ni 0. 86 Co 0} . 1 Mn 0. 02 Al 0. 02) O 2 Was prepared.

300 g of the lithium composite metal oxide was added to 300 mL of ultrapure water, washed with stirring for 30 minutes, and filtered for 20 minutes. The filtered lithium composite metal oxide was dried at 130 ° C. in a vacuum oven, followed by sieving. Then, Co (OH) ₂ was added to the lithium composite metal oxide at a concentration of 5000 ppm, and heat treatment was performed at 700 ° C. for 5 hours while supplying oxygen at a flow rate of 1 L / min to prepare a cathode active material.

Comparative example  One

A positive electrode active material was prepared in the same manner as in Example 1 except that heat treatment was not performed.

Comparative example  2

A positive electrode active material was prepared in the same manner as in Example 1 except that Co (OH) ₂ was not added during the heat treatment.

Comparative example  3

A positive electrode active material was manufactured in the same manner as in Example 1, except that Co (OH) ₂ was not added during the heat treatment and heat-treated at 300 ° C. without oxygen supply.

Comparative example  4

A positive electrode active material was manufactured in the same manner as in Example 1, except that Co (OH) ₂ was not added during the heat treatment and heat-treated at 500 ° C. without oxygen supply.

Comparative example  5

A positive electrode active material was manufactured in the same manner as in Example 1, except that Co (OH) ₂ was not added during the heat treatment and heat-treated at 600 ° C. without oxygen supply.

Comparative example  6

A positive electrode active material was manufactured in the same manner as in Example 1, except that Co (OH) ₂ was not added during the heat treatment and heat-treated at 700 ° C. without oxygen supply.

Experimental Example  One - Heat flow  evaluation

Differential scanning calorimetry (SETARAM Instrumentation, Sensys evo DSC) to measure the heat flow (Heat Flow) according to the temperature of the positive electrode active material of Example 1 and Comparative Example 3. Specifically, 16 mg of the positive electrode active material of Example 1 and Comparative Example 3 was added to a pressure-resistant pen for DSC measurement, and 20 μL of electrolyte (EVPS) was injected. The temperature range for DSC analysis was 25 to 400 ° C., and the temperature increase rate was 10 / min. DSC measurements were performed three times or more on each positive electrode active material, and the average value was calculated.

The measurement result is shown in FIG. 1, the positive electrode active material of Example 1 showed a peak at 240 ° C., and the maximum amount of heat flow was less than 200 mW, whereas the positive electrode active material of Comparative Example 3 showed a peak at 225 ° C., and the maximum value of heat flow exceeded 1000 mW. can confirm. This shows that the positive electrode active material of Example 1 has excellent high temperature stability compared to the positive electrode active material of Comparative Example 3.

Experimental Example  2-Lithium By-Product Residue Evaluation

5 g of the positive electrode active material prepared according to Example 1 and Comparative Examples 1, 2, 4 to 6 was dispersed in 100 mL of water, and titrated with 0.1 M HCl, and the pH titration curve was measured by measuring the change in pH value. Got it. The pH titration curve is shown in FIG. 2.

Residual LiOH and LiCO ₃ residues in each cathode active material were calculated using the pH titration curve, and the sum of these values was evaluated as total lithium byproduct residues, and is shown in Table 1 below.

	Residual LiOH (wt%)	Residual LiCO 3 (wt%)	Total Lithium By-Product Residues (wt%)
Example 1	0.158	0.063	0.221
Comparative Example 1	0.165	0.119	0.284
Comparative Example 4	0.111	0.334	0.445
Comparative Example 5	0.146	0.372	0.518
Comparative Example 6	0.228	0.605	0.833

[Table 1], the lithium by-product residual amount of the positive electrode active material of Example 1 satisfying the heat treatment conditions of the present invention does not perform the heat treatment process (Comparative Example 1), or when the heat treatment is performed without oxygen supply (Comparative Example Compared to 4 ~ 6) it can be seen that significantly falling. In addition, when the heat treatment is performed in the air atmosphere without supplying oxygen as in Comparative Examples 4 to 6, it can be seen that the residual amount of lithium by-products increases rather than Comparative Example 1 without heat treatment.

Experimental Example  3-battery performance evaluation

Each positive electrode active material, carbon black conductive material, and PVdF binder prepared by Example 1, Comparative Example 2 and Comparative Example 3 were mixed in an N-methylpyrrolidone solvent in a ratio of 95: 2.5: 2.5 by weight in a positive electrode mixture (Viscosity: 5000 mPa · s) was prepared, which was applied to one surface of an aluminum current collector, dried at 130 ° C., and rolled to prepare a positive electrode.

In addition, as a negative electrode active material, a natural graphite, a carbon black conductive material, and a PVdF binder were mixed in an N-methylpyrrolidone solvent in a ratio of 85: 10: 5 in a weight ratio to prepare a composition for forming a negative electrode active material layer, and the copper current collector It was applied to one side of to prepare a negative electrode.

An electrode assembly was manufactured between the positive electrode and the negative electrode prepared as described above through a separator of porous polyethylene, 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 is prepared by dissolving 1.0M concentration of lithium hexafluorophosphate (LiPF ₆ ) in an organic solvent consisting of ethylene carbonate / dimethyl carbonate / ethyl methyl carbonate (mixing volume ratio of EC / DMC / EMC = 3/4/3). It was.

Capacity retention rate (%) and resistance increase rate of the lithium secondary battery prepared as described above while charging and discharging 50 cycles at 45 ° C. under a charge end voltage of 4.25V, a discharge end voltage of 2.5V, and 0.5C / 0.5C. (DCR Incress [%]) was measured. The measurement results are shown in FIGS. 3 and 4. 3 is a graph showing a capacity retention rate, and FIG. 4 is a graph showing a resistance increase rate.

3 and 4, in the case of the secondary battery to which the cathode active material of Example 1 is applied, the capacity reduction rate and the resistance increase rate are remarkably increased at 50 charge / discharge cycles, compared to the secondary batteries to which the cathode active materials of Comparative Examples 2 and 3 are applied. You can see the low.

Claims (14)

1. A lithium composite metal oxide represented by Formula 1 below; And

   A cathode active material for a secondary battery formed on the surface of the lithium composite metal oxide and including a cobalt-rich layer having a higher cobalt content than the lithium composite metal oxide.

   [Formula 1]

   Li _{1 + x} [Ni _a Co _b Mn _c M _d ] _1-x O _2-y X _y

   In Formula 1, 0.7 <a <1, 0 <b <0.3, 0 <c <0.1, 0 <d <0.1, a + b + c + d = 1, 0 = x ≦ 0.05, 0 ≦ y ≦ 0.2 M is one metal element selected from the group consisting of Al, Mg, Ge, V, Mo, Nb, Si, Ti, Zr and W, and X is P or F.
2. The method of claim 1,

   The ratio of the number of atoms of cobalt to the sum of the number of atoms of nickel, cobalt, manganese and M in the cobalt-rich layer and the atoms of cobalt to the sum of the number of atoms of nickel, cobalt, manganese and M in the lithium composite metal oxide The positive electrode active material for secondary batteries whose difference of ratio of numbers is 0.05-0.2.
3. The method of claim 1,

   The positive electrode active material for secondary batteries, wherein the ratio of the number of atoms of cobalt to the sum of the number of atoms of nickel, cobalt, manganese, and M in the cobalt-rich layer is 0.05 to 0.45.
4. The method of claim 1,

   The cobalt rich layer is a positive electrode active material for a secondary battery having a thickness of 10nm to 100nm.
5. The method of claim 1,

   The positive electrode active material is a positive electrode active material for secondary batteries, the peak appears in the temperature range of 230 ℃ to 250 ℃ when the heat flow (Heat Flow) measured by differential scanning calorimetry (DSC).
6. The method of claim 1,

   The cathode active material is a cathode active material for secondary batteries, the maximum value of the heat flow (Heat Flow) measured by differential scanning calorimetry (DSC) is 1000mW or less.
7. The method of claim 1,

   A cathode active material for a secondary battery having a lithium byproduct content of 1% by weight or less in the cathode active material.
8. Preparing a lithium composite metal oxide represented by Formula 1;

   [Formula 1]

   Li _{1 + x} [Ni _a Co _b Mn _c M _d ] _1-x O _2-y X _y

   (In Formula 1, 0.7 <a <1, 0 <b <0.3, 0 <c <0.1, 0 <d <0.1, a + b + c + d = 1, 0 ≦ x ≦ 0.05, 0 ≦ y ≦ 0.2, M is one metal element selected from the group consisting of Al, Mg, Ge, V, Mo, Nb, Si, Ti, Zr and W, and X is P or F.

   Washing the lithium composite metal oxide; And

   After mixing the washed lithium composite metal oxide and cobalt-containing raw material and heat treatment at an temperature of 700 ℃ or more in an oxidizing atmosphere.
9. The method of claim 8,

   The preparing of the lithium composite metal oxide represented by Chemical Formula 1 may include mixing a nickel-cobalt precursor, a manganese-containing raw material, an M-containing raw material, and a lithium-containing raw material, and firing at 600 ° C to 900 ° C. Method for producing a positive active material for a secondary battery that is carried out.
10. The method of claim 8,

    The washing step is a method of manufacturing a positive electrode active material for a secondary battery that is carried out at a temperature of 20 ℃ or less.
11. The method of claim 8,

    In the heat treatment step, the cobalt-containing raw material is mixed with 0.001 to 0.01 parts by weight based on 100 parts by weight of the lithium composite metal oxide.
12. The method of claim 8,

    The heat treatment is a method of manufacturing a positive electrode active material for a secondary battery that is performed within 10 hours at 700 ℃ to 800 ℃ temperature.
13. The positive electrode for secondary batteries containing the positive electrode active material for secondary batteries of any one of Claims 1-7.
14. A secondary battery comprising the positive electrode for secondary battery of claim 13.

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