KR20180114412A - Positive electrode active material for secondary battery, method for producing the same, positive electrode and secondary battery comprising the same - Google Patents

Abstract

The present invention relates to: a positive electrode active material for a secondary battery which includes a lithium composite metal oxide represented by chemical formula 3: Li_x′[Ni_aCo_bMn_c]O_2, and a surface treatment layer containing cobalt-lithium composite particles attached to the surface thereof; a production method of the positive electrode active material; and a positive electrode and a secondary battery comprising the same. (In the chemical formula 3, 0.6 <= a < 1, 0 < b <= 0.3, 0 < c <= 0.3, a + b + c = 1, 0.95 <= x′ <= 1.05)

Description

TECHNICAL FIELD The present invention relates to a positive electrode active material for a secondary battery, a method for producing the same, a positive electrode and a secondary battery for a secondary battery including the positive electrode active material,

The present invention relates to a cathode active material for a secondary battery, a method for producing the same, a cathode and a secondary battery for the same, and more particularly, to a cathode active material capable of realizing excellent capacity characteristics and stability even under a high voltage, And more particularly to a positive electrode and a secondary battery for a secondary battery.

Recently, with the popularization of mobile devices and electric power tools, and the demand for environmentally friendly electric vehicles, there is an increasing requirement for an energy source for driving them. In particular, development of a cathode active material having high energy density, stable operation under high voltage, and long life characteristics is required.

Lithium transition metal composite oxides are used as the cathode active material of lithium secondary batteries, and among them lithium cobalt composite metal oxides of LiCoO ₂ having high action voltage and excellent capacity characteristics are mainly used. However, since LiCoO ₂ has a poor thermal characteristic due to destabilization of crystal structure due to depolythium, and is expensive, it can not be used as a power source in fields such as electric vehicles and the like.

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 as materials for replacing LiCoO ₂ . LiNiO ₂ has poor thermal stability as compared with LiCoO _2, and if an internal short circuit occurs due to external pressure or the like in a charged state, there is a problem that the cathode active material itself is decomposed to cause rupture and ignition of the battery.

Accordingly, a method for improving low thermal stability while maintaining an excellent reversible capacity of LiNiO ₂ is known as 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' ) Was developed. However, the conventional NCM-based lithium oxide developed to date has a limited capacity because of insufficient capacitance characteristics.

In order to overcome such a problem, studies have recently been made to increase the content of Ni in NCM-based lithium oxide. However, as the nickel content in the positive electrode active material increases, the capacity increases. However, due to the oxidation depth from Ni ^{2 +} to Ni ^{3 + / 4 + due} to the depth of charge, abrupt oxygen desorption progresses and the desorbed oxygen reacts with the electrolyte Thereby causing instability of the lattice structure, and further causing structural collapse.

Therefore, development of a cathode active material capable of realizing excellent capacity characteristics and stability even under a high voltage is required.

Korean Patent Publication No. 10-2015-0070853 (published on June 25, 2015)

Disclosure of Invention Technical Problem [8] Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a nickel cathode active material capable of realizing excellent capacity characteristics and stability even under a high voltage.

According to an aspect of the present invention, there is provided a lithium secondary battery comprising: preparing a lithium composite metal oxide represented by Formula 1 below; And mixing the lithium composite metal oxide with the cobalt-containing raw material, and then heat-treating the lithium composite metal oxide at a temperature higher than 300 ° C but lower than 400 ° C.

[Chemical Formula 1]

Li _x [Ni _a Co _b Mn _c ] O ₂

0.3, a + b + c = 1, and 1.07? X? 1.09 in the formula (1).

At this time, the step of preparing the lithium composite metal oxide represented by Formula 1 may be performed by mixing a transition metal precursor including nickel, cobalt, and manganese and a lithium-containing raw material with lithium / transition metal at an atomic ratio of 1: 1.07 to 1: 1.09 Followed by calcining at 600 ° C to 900 ° C.

The transition metal precursor may be represented by the following general formula (2).

(2)

Ni _d Co _e Mn _f (OH) ₂

In the formula (2) 0.6 <d <1, 0 <e <0.3, 0 <f <0.3, d + e + f = 1.

Also, the firing can be performed in an oxygen atmosphere.

Specifically, the firing may include a first firing step performed at 700 ° C. to 800 ° C. and a second firing step performed at 800 to 900.

In the heat treatment step, the cobalt-containing raw material may be mixed in an amount of 0.8 to 1.2 parts by weight based on 100 parts by weight of the lithium composite metal oxide, and the heat treatment is preferably performed in an atmospheric environment for 5 to 10 hours Do.

In another aspect, the present invention provides a lithium composite metal oxide represented by Formula 3 below; And a surface treatment layer comprising cobalt-lithium composite particles adhered to the surface of the lithium composite metal oxide.

(3)

Li _{x '} [Ni _a Co _b Mn _c ] O ₂

(In the formula 3, 0.6? A <1, 0 <b? 0.3, 0 <c? 0.3, a + b + c = 1, 0.95? X?

The cobalt content in the surface treatment layer may be 8000 ppm to 12000 ppm.

According to another aspect of the present invention, there is provided a secondary battery including a positive electrode for a secondary battery 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.

The cathode active material for a secondary battery according to the present invention has a surface treatment layer containing cobalt-lithium composite particles having a high lithium content and excellent output characteristics and stability on the surface thereof. Therefore, unlike the conventional high- It is structurally stable and exhibits excellent output characteristics even under high voltage.

Further, according to the method for producing a cathode active material for a secondary battery of the present invention, a cathode active material for a secondary battery having a high lithium content can be produced without performing a washing step, and thus productivity is excellent.

1 is a SEM photograph of a cathode active material prepared according to an embodiment.
FIG. 2 is a SEM photograph of a cathode active material prepared according to Comparative Example 4. FIG.
FIG. 3 is a graph showing charge-discharge characteristics of a battery manufactured according to Example and Comparative Example 1. FIG.
4 is a graph showing charge / discharge characteristics of a battery manufactured according to Examples, Comparative Examples 2 and 3;
5 is a graph showing charge-discharge characteristics of a battery manufactured according to Example and Comparative Example 4. FIG.
FIG. 6 is a graph showing the discharge capacity according to the number of cycles of the battery manufactured according to the embodiment and the comparative example 1. FIG.
7 is a graph showing the discharge capacity according to the number of cycles of the battery manufactured according to the embodiment and the comparative examples 2 and 3. FIG.

Below. The present invention will be described in more detail.

The present inventors have conducted extensive research to produce a cathode active material which is stable under a high voltage and has excellent capacity characteristics. As a result, it has been found that a lithium composite metal oxide having a nickel atomic ratio of 0.6 or more and a lithium atomic ratio of 1.07 or more and a cobalt- And then heat-treating the mixture at a specific temperature, the present invention has been accomplished.

First, a method of manufacturing a cathode active material for a secondary battery according to the present invention will be described.

Method for manufacturing cathode active material for secondary battery

The method for producing a cathode active material according to the present invention comprises the steps of: (1) preparing a lithium composite metal oxide represented by the formula (1); and (2) mixing the lithium composite metal oxide and the cobalt- Lt; RTI ID = 0.0 &gt; 0 C &lt; / RTI &gt; 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 an NMC-based lithium composite metal oxide containing nickel, cobalt and manganese as a transition metal, and has an atomic fraction of nickel in the transition metal of 0.6 or more and an atomic fraction of lithium of 1.07 to 1.09 Lithium composite metal oxide.

Specifically, the lithium composite metal oxide may be a lithium composite metal oxide represented by the following general formula (1).

[Chemical Formula 1]

Li _x [Ni _a Co _b Mn _c ] O ₂

0? B? 0.3, 0? C? 0.3, a + b + c = 1, 1.07? X?

B, and c represent the atomic fractions of Ni, Co, and Mn in the metal elements other than lithium (that is, transition metal elements), and satisfy the relationships 0.6 ≦ a ≦ 1, 0 ≦ b ≦ 0.3, and 0 <c Lt; = 0.3, and a + b + c = 1.

Specifically, a represents an atomic fraction of nickel in the transition metal elements, and a may be 0.6 or more and less than 1, preferably 0.65 or more and less than 1, more preferably 0.65 to 0.95.

B represents the atomic fraction of cobalt among the transition metal elements, and b may be more than 0 and not more than 0.3, preferably 0.001 to 0.25, more preferably 0.01 to 0.25.

C represents the atomic fraction of manganese in the transition metal elements, and c may be more than 0 and not more than 0.3, preferably 0.001 to 0.25, more preferably 0.01 to 0.25.

X represents the atomic fraction of lithium in the lithium composite metal oxide, and x is 1.07 to 1.09.

For example, the transition metal precursor including nickel, cobalt, and manganese and the lithium-containing raw material may be mixed with lithium / transition metal at an atomic ratio of 1: 1.07 to 1: 1: 1.09, and firing at 700 to 900 ° C.

The transition metal precursor may be, for example, a nickel-cobalt-manganese hydroxide. Specifically, the transition metal precursor may be a compound represented by the following general formula (2).

(2)

Ni _d Co _e Mn _f (OH) ₂

In the formula (2) 0? E? 0.3, 0? F? 0.3, and d + e + f = 1. Specifically, in the above formula (2), d may be 0.65 or more and less than 1, preferably 0.65 to 0.95, e may be 0.001 to 0.25, preferably 0.01 to 0.25, f is 0.001 to 0.25, May be 0.01 to 0.25.

The transition metal precursor may be purchased from a commercial product, or may be prepared according to the process for preparing a nickel-cobalt-manganese transition metal precursor which is well known in the art.

For example, the nickel-cobalt-manganese transition metal precursor is prepared by a coprecipitation reaction in which a complex compound containing an ammonium cation and a basic compound is added to a metal solution containing a nickel-containing starting material, a cobalt containing starting material and a manganese- .

The nickel-containing source material is, for example, nickel-containing acid salt, and the like nitrate, sulphate, halide, a sulfide, a hydroxide, an oxide or oxy-hydroxide, _{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, But is not limited thereto.

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

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

The metal solution is added to a mixed solvent of a nickel-containing raw material, a cobalt-containing raw material and a manganese-containing raw material in a solvent, specifically water or an organic solvent (e.g., alcohol or the like) Or may be produced by mixing an aqueous solution of a nickel-containing raw material, an aqueous solution of a cobalt-containing raw material, and an aqueous solution of a manganese-containing raw material.

The ammonium cation-containing complexing agent 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 , But is not limited thereto. On the other hand, the ammonium cation-containing complex-forming agent may be used in the form of an aqueous solution. As the solvent, water or a mixture of water and an organic solvent which can be uniformly mixed with water (specifically, alcohol or the like) and water may be used.

The basic compound may be a hydroxide of an alkali metal or an 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. As the solvent, water or a mixture of water and an organic solvent (specifically, alcohol or the like) which can be uniformly mixed with water may be used.

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

On the other hand, the coprecipitation reaction can be performed at a temperature of 40 to 70 in an inert atmosphere such as nitrogen or argon.

Particles of nickel-cobalt-manganese hydroxide are formed by the above-described process and precipitated in the reaction solution. The precipitated nickel-cobalt-manganese hydroxide particles can be separated and dried by a conventional method to obtain a transition metal precursor.

The transition metal precursor prepared by the above method and the lithium-containing source material are mixed and calcined at 600 ° C to 900 ° C, preferably 700 ° C to 900 ° C to obtain a lithium composite metal oxide. At this time, the transition metal precursor and the lithium-containing source material are mixed so that the atomic ratio of the lithium: transition metal is 1: 1.07 to 1: 1.09. Here, the atomic ratio of the transition metal means the total number of atoms of the transition metal that combine the numbers of atoms of nickel, cobalt and manganese.

The lithium-containing raw material may be at least one selected from the group consisting of a lithium-containing carbonate (for example, lithium carbonate), a hydrate (for example, lithium hydroxide I hydrate (LiOH.H ₂ O) (E.g., lithium nitrate (LiNO ₃ ) and the like) and chlorides (e.g., lithium chloride (LiCl) and the like), and a single or a mixture of two or more of them may be used.

Meanwhile, the firing is preferably performed in an oxygen atmosphere .

The firing may be performed in two or more stages of firing at different temperatures, including, for example, a first firing step performed at 700 ° C to 800 ° C and a second firing step performed at 800 ° C to 900 ° C Lt; / RTI &gt; In this case, the reactivity between the lithium-containing raw material and the transition metal precursor increases as compared with the case of the first-stage calcination. The transition metal precursor and lithium react with each other through the firing to obtain the lithium composite metal oxide represented by Formula 1. [

 (2) Step of heat treatment

When the lithium composite metal oxide of Formula 1 is prepared as described above, the prepared lithium composite metal oxide and the cobalt-containing raw material are mixed and heat-treated.

The heat treatment step is for forming a surface treatment layer of the lithium composite metal oxide. The cobalt reacts with the lithium by-product present in the lithium composite metal oxide by the heat treatment and the cobalt-containing raw material to form a lithium-cobalt composite A surface treatment layer containing particles is formed.

In the cobalt-containing source material, and the like cobalt-containing acid salt, a nitrate, a sulfate, a halide, a sulfide, a hydroxide, an oxide or oxy-hydroxide, specifically, the _{Co (OH) 2, CoOOH,} Co (OCOCH 3) 2 and 4H ₂ O, Co (NO ₃ ) ₂揃 6H ₂ O, Co (SO ₄ ) ₂揃 7H ₂ O, or combinations thereof. Of these, Co (OH) ₂ is particularly preferable.

The cobalt-containing raw material may be mixed in an amount of 0.8 to 1.2 parts by weight, preferably 0.8 to 1 part 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, excellent lithium byproduct formation inhibiting effect and electrical characteristics can be obtained.

On the other hand, the heat treatment is performed in a temperature range of more than 300 ° C to less than 400 ° C, preferably in a temperature range of 320 ° C to 380 ° C. If the heat treatment temperature is out of the above range, the capacity characteristics of the cathode active material may deteriorate or the surface treatment layer containing cobalt-lithium composite particles may not be formed.

Conventionally, it has been common to carry out a high-temperature treatment at a temperature of 500 ° C or higher in forming a surface treatment layer on the surface of a lithium composite metal oxide. However, since lithium complex metal oxide having a high lithium content is used in the present invention, Reaction can be smoothly performed. On the other hand, in the case of the cobalt-containing raw material used in the surface treatment of the present invention, lithium-cobalt composite particles are not formed when the heat treatment temperature is too high and are present in the form of cobalt oxide So that capacity reduction of the cathode active material may occur.

Meanwhile, the heat treatment may preferably be performed for 5 hours to 10 hours, and may be performed in an atmospheric environment. Since the heat treatment is performed at a relatively low temperature range, cobalt oxidation can be controlled even in an atmospheric environment.

Meanwhile, the method for producing a cathode active material according to the present invention does not perform a washing process. Generally, in the case of a lithium composite metal oxide having a nickel atom fraction of 0.6 or more, a large amount of lithium by-products such as LiOH and Li ₂ CO ₃ remain on the surface of the lithium composite metal oxide in the manufacturing process. There is a problem in that it causes gas generation and swelling by reacting with an electrolyte solution or the like. Therefore, in order to use a lithium composite metal oxide containing a high-concentration nickel as a cathode active material in the prior art, a water washing step for removing lithium by-products on the surface of the lithium composite metal oxide has been essentially required. However, in the case of the present invention, since the lithium by-product remaining in the lithium composite metal oxide is removed as a raw material for forming the lithium-cobalt complex in the heat treatment process, a separate washing process may not be performed. As described above, since the washing process is not performed in the present invention, the production process can be shortened compared to the conventional process, and productivity can be improved.

Cathode active material for secondary battery

Next, the cathode active material for a secondary battery according to the present invention will be described.

The cathode active material for a secondary battery according to the present invention comprises a lithium composite metal oxide represented by Chemical Formula 3 and a surface treatment layer comprising cobalt-lithium composite particles attached to the surface of the lithium composite metal oxide .

(3)

Li _{x '} [Ni _a Co _b Mn _c ] O ₂

In the above formula (3), 0.6? A <1, 0 <b? 0.3, 0 <c? 0.3, a + b + c = 1 and 0.95? X? When the composition of the lithium composite metal oxide satisfies the above range, high capacity characteristics and life characteristics can be obtained even at a high voltage of 4.3 V or more.

B, and c represent the atomic fractions of Ni, Co, and Mn in the metal elements other than lithium (that is, transition metal elements), and satisfy the relationships 0.6 ≦ a ≦ 1, 0 ≦ b ≦ 0.3, and 0 <c Lt; = 0.3, and a + b + c = 1.

Specifically, a represents an atomic fraction of nickel in the transition metal elements, and a may be 0.6 or more and less than 1, preferably 0.65 or more and less than 1, more preferably 0.65 to 0.95.

B represents the atomic fraction of cobalt among the transition metal elements, and b may be more than 0 and not more than 0.3, preferably 0.001 to 0.25, more preferably 0.01 to 0.25.

C represents the atomic fraction of manganese in the transition metal elements, and c may be more than 0 and not more than 0.3, preferably 0.001 to 0.25, more preferably 0.01 to 0.25.

X 'represents an atomic fraction of lithium in the lithium composite metal oxide, and x' is 0.95 to 1.05. Lithium in the lithium composite metal oxide represented by Chemical Formula 1 reacts with the cobalt-containing raw material, so that the lithium content of the lithium composite metal oxide contained in the finally produced cathode active material decreases as shown in Formula 3. [Formula 3]

The surface treatment layer is for improving the structural stability of the lithium composite metal oxide and includes cobalt-lithium composite particles. The cobalt-lithium composite particles are attached to the surface of the lithium composite metal oxide to prevent the separation of oxygen from the lithium composite metal oxide, thereby improving the structural stability. Further, lithium contained in the cobalt-lithium composite increases the lithium concentration on the surface of the cathode active material, thereby realizing excellent electrical characteristics.

On the other hand, the cobalt content in the surface treatment layer may be 8000 ppm to 12000 ppm, preferably 8500 ppm to 10000 ppm. When the content of cobalt in the surface treatment layer satisfies the above range, the content of lithium by-products present on the surface of the lithium composite metal oxide is effectively reduced, so that a cathode active material having an excellent electrical performance at 4.3 V or more without any water washing can be produced.

In the case of the conventional NMC-based lithium composite metal oxide, the ratio of lithium to the transition metal is generally 1.05 or less. However, such lithium composite metal oxides have a problem in that their capacity characteristics and stability are poor under a high voltage of 4.3 V or more. However, the cathode active material of the present invention has a higher lithium content than conventional ones and can realize high capacity characteristics even at a high voltage, for example, a voltage of 4.3 V or higher. As described above, lithium-cobalt It is structurally stable because the composite particles are attached.

Anode and secondary battery

The cathode active material for a secondary battery according to the present invention can be usefully used for manufacturing a cathode for a secondary battery.

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

The positive electrode may be produced according to a conventional positive electrode manufacturing method, except that the positive electrode active material according to the present invention is used. For example, the positive electrode may be prepared by dissolving or dispersing the components constituting the positive electrode active material layer, that is, the positive electrode active material, the conductive material and / or the binder, in a solvent to prepare a positive electrode composite material, Or by a method in which the film is coated on at least one side and then dried and rolled or by casting the positive electrode material on a separate support and then peeling off the support from the support to laminate the positive electrode current collector.

The positive electrode current collector is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery. For example, the positive electrode current collector may be made of a metal such as stainless steel, aluminum, nickel, titanium, sintered carbon, aluminum or stainless steel, , Titanium, silver, or the like may be used. In addition, the cathode current collector may have a thickness of 3 to 500 탆, and fine unevenness may be formed on the surface of the current collector to increase the adhesive force of the cathode 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, and a nonwoven fabric.

The current collector includes the cathode active material according to the present invention on at least one surface thereof and optionally includes at least one of a conductive material and a binder.

The cathode active material includes a surface treatment layer comprising the cathode active material according to the present invention, that is, the lithium composite metal oxide represented by Formula 1 and the cobalt-lithium composite particles adhered to the surface of the lithium composite metal oxide . Since the specific contents of the cathode active material according to the present invention are the same as those described above, detailed description thereof will be omitted.

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

The conductive material is used for imparting conductivity to the electrode. The conductive material is not particularly limited as long as it has electron conductivity without causing chemical change. Specific examples thereof include graphite such as natural graphite and artificial graphite; Carbonaceous 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; And polyphenylene derivatives. These may be used alone or in admixture of two or more. The conductive material may be included in an amount of 1% by weight to 30% by weight based on the total weight of the cathode active material layer.

In addition, the binder serves to improve the adhesion between the positive electrode active material particles and the adhesion between the positive electrode active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose ), Starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, and various copolymers thereof. One kind or a mixture of two or more kinds of them 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 cathode active material layer.

On the other hand, the solvent used in the preparation of the positive electrode material may be a solvent commonly used in the art, for example, dimethyl sulfoxide (DMSO), isopropyl alcohol, (NMP), acetone or water may be used alone or in combination. The amount of the solvent to be used can be appropriately adjusted in consideration of the application 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 disposed opposite to the positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, wherein the positive electrode is the positive electrode according to the present invention.

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

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

The negative electrode may be manufactured according to a conventional negative electrode manufacturing method generally known in the art. For example, the negative electrode may be produced by dissolving or dispersing the components constituting the negative electrode active material layer, that is, the negative electrode active material, the conductive material and / or the binder in a solvent to form a negative electrode mixture, Or a method in which the negative electrode material is coated on at least one surface and then dried or rolled or casting the negative electrode material onto a separate support and then peeling the support from the support to laminate the negative electrode current collector.

The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. For example, the negative electrode current collector may be formed on the surface of copper, stainless steel, aluminum, nickel, titanium, sintered carbon, Carbon, nickel, titanium, silver or the like, aluminum-cadmium alloy, or the like may be used. In addition, the negative electrode collector may have a thickness of 3 to 500 탆, and similarly to the positive electrode collector, fine unevenness may be formed on the surface of the collector to enhance the binding 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, and a nonwoven fabric.

As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples thereof include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber and amorphous carbon; Metal 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 such as SiO _v (0 <v <2), SnO ₂ , vanadium oxide, and lithium vanadium oxide, which can dope and dedoped lithium; Or a composite containing the metallic compound and the carbonaceous material such as Si-C composite or Sn-C composite, and any one or a mixture of two or more thereof may be used. Also, a metal lithium thin film may be used as the negative electrode active material. The carbon material may be both low-crystalline carbon and high-crystallinity carbon. Examples of the low-crystalline carbon include soft carbon and hard carbon. Examples of the highly crystalline carbon include natural graphite, artificial graphite, artificial graphite or artificial graphite, Kish graphite graphite, pyrolytic carbon, mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches and petroleum or coal tar coke derived cokes).

In addition, the binder and the conductive material may be the same as those described above for the anode.

Meanwhile, in the secondary battery, the separator separates the negative electrode and the positive electrode and provides a moving path of lithium ion. The separator can be used without any particular limitation as long as it is used as a separator in a secondary battery. Particularly, It is preferable that it is a resistance and excellent in an ability to impregnate the electrolyte. Specifically, porous polymer films such as porous polymer films made of polyolefin-based polymers such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers and ethylene / methacrylate copolymers, May be used. Further, a nonwoven fabric made of a conventional porous nonwoven fabric, for example, glass fiber of high melting point, polyethylene terephthalate fiber, or the like may be used. In order to secure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymer material may be used, and may be optionally used as a single layer or a multilayer structure.

The electrolyte may be an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, a melt-type inorganic electrolyte, and the like, which are usable in the production of a secondary battery.

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

The organic solvent may be used without limitation as long as it can act as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, examples of the organic solvent include ester solvents such as methyl acetate, ethyl acetate,? -Butyrolactone and? -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), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), propylene carbonate PC) and the like; Alcohol solvents such as ethyl alcohol and isopropyl alcohol; Ra-CN (Ra is a linear, branched or cyclic hydrocarbon group having 2 to 20 carbon atoms, which may contain a double bond aromatic ring or ether bond); Amides such as dimethylformamide; Dioxolanes such as 1,3-dioxolane; Or sulfolane may be used. Among these, a carbonate-based solvent is preferable, and a cyclic carbonate (for example, ethylene carbonate or propylene carbonate) having a high ionic conductivity and a high dielectric constant, for example, such as ethylene carbonate or propylene carbonate, For example, ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate) is more preferable. In this case, when the cyclic carbonate and the chain carbonate are mixed in a volume ratio of about 1: 1 to 9, the performance of the electrolytic solution may be excellent.

The lithium salt can 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, 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 may be used. The concentration of the lithium salt is preferably within the range of 0.1M to 2.0M. When the concentration of the lithium salt is within the above range, the electrolyte has an appropriate conductivity and viscosity, so that it can exhibit excellent electrolyte performance and the lithium ion can effectively move.

The electrolyte may contain, for example, a haloalkylene carbonate-based compound such as difluoroethylene carbonate or the like for the purpose of improving the lifetime characteristics of the battery, suppressing the reduction of the battery capacity, and improving the discharge capacity of the battery. N, N &lt; RTI ID = 0.0 &gt; (N, &lt; / RTI &gt; N, N'-tetramethyluronium hexafluorophosphate), pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, glyme, And at least one additive such as substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol or aluminum trichloride may be further included. The additive may be included in an amount of 0.1 wt% to 5 wt% based on the total weight of the electrolyte.

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

In addition, the secondary battery according to the present invention can be used as a unit cell of a battery module, and the battery module can be applied to a battery pack. The battery module or the battery pack may include a power tool; An electric vehicle including an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); Or a power storage system, as shown in FIG.

Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily carry out the present invention. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

Example

Ni _{0 . 65} Co _{0 .} Was placed in an alumina crucible so that the first, held for 5 hours at 750 ℃ in an oxygen atmosphere, and _{850 ℃: 2 Mn 0 .15 (} OH) 2 and Li ₂ CO ₃ to Li: total transition metal atom ratio of 1.07 Followed by firing for 10 hours to obtain a lithium composite metal oxide LiNi _{0 . 65} Co _{0 . 2} Mn _{1 . 5} O ₂ . The prepared lithium composite metal oxide is pulverized using induction, and then 1 part by weight of Co (OH) ₂ is added to 100 parts by weight of the lithium composite metal oxide and mixed. The mixed powders were heat-treated at 350 캜 for 7 hours in the air atmosphere. Then, the heat-treated powder was pulverized and classified using 325 mesh to prepare a final cathode active material.

The cathode active material, the carbon black conductive material and the PVdF binder thus prepared were mixed in a N-methylpyrrolidone solvent in a weight ratio of 95: 2.5: 2.5 to prepare a positive electrode mixture (viscosity: 5000 mPa · s) Coated on one side of the aluminum current collector, dried at 130 캜 and rolled to prepare a positive electrode. Then, a coin half cell was prepared using the positive electrode.

Comparative Example 1

Ni _{0 . 65} Co _{0 . 2} Mn _{0 .15} (OH) ₂ and Li ₂ CO ₃ to Li: total of the transition metal atom ratio of 1.05: 1, the positive electrode in the same manner as in Example, except for a mixing point so that the active material, the positive electrode, and the coin-half Cell battery.

Comparative Example 2

A positive electrode active material, a positive electrode and a coin half cell were produced in the same manner as in Example except that the heat treatment temperature was 300 캜.

Comparative Example 3

A positive electrode active material, a positive electrode and a coin half cell were produced in the same manner as in Example except that the heat treatment temperature was 400 占 폚.

Comparative Example 4

A positive electrode active material, a positive electrode and a coin half cell were prepared in the same manner as in Example 1, except that H ₃ BO ₃ was used instead of Co (OH) ₂ .

Experimental Example 1

The cathode active material prepared in Examples and Comparative Example 4 was photographed by SEM. FIG. 1 is a photograph of the positive electrode active material of the embodiment, and FIG. 2 is a photograph of the positive electrode active material of Comparative Example 4.

As shown in FIG. 1, in the case of the positive electrode active material prepared according to the production method of the present invention, it can be confirmed that particles-like composites are attached to the surface of the lithium composite metal oxide.

On the other hand, as shown in FIG. 2, there is no particle-shaped composite on the surface of the cathode active material of Comparative Example 4 which is boron-coated.

Experimental Example 2 - Evaluation of charge / discharge characteristics

Charge and discharge characteristics were measured by charging and discharging the coin half cell manufactured by the examples and comparative examples 1 to 4 at 25 ° C under a condition of 0.1C / 0.1C from 3.0V to 4.3V. The measurement results are shown in Figs. 3 to 5.

FIG. 3 is a graph comparing the charge-discharge characteristics of a battery manufactured according to the example and the comparative example 1, FIG. 4 is a graph comparing charge-discharge characteristics of the battery manufactured according to the example, 5 is a graph comparing charge-discharge characteristics of a battery manufactured according to Example and Comparative Example 4. Fig.

3 to 5, it can be seen that the battery using the cathode active material produced according to the method of the present invention has higher output characteristics at higher voltage than the batteries manufactured by Comparative Examples 1 to 4.

Experimental Example 3 - Evaluation of cycle characteristics

The coin half cell prepared in Examples and Comparative Examples 1 to 3 was charged and discharged at 25 DEG C for 50 cycles under the conditions of a charging end voltage of 4.3 V, a discharge end voltage of 3 V, and a voltage of 0.5 C / g). The measurement results are shown in FIGS. 6 and 7. FIG.

FIG. 6 is a graph comparing the discharge capacities according to the number of cycles of the batteries manufactured according to the example and the comparative example 1. FIG. 7 is a graph showing the discharge capacity FIG.

6 and 7, it can be confirmed that the battery of the example made according to the method of the present invention exhibits a higher discharge capacity than the batteries of Comparative Examples 1 to 3 in the entire cycle.

Claims (12)

Preparing a lithium composite metal oxide represented by Formula 1 below; And
[Chemical Formula 1]
Li _x [Ni _a Co _b Mn _c ] O ₂
0.3, a + b + c = 1, and 1.07? X? 1.09 in the formula (1).
Mixing the lithium composite metal oxide with a cobalt-containing starting material, and then heat-treating the lithium composite metal oxide at a temperature of more than 300 ° C but less than 400 ° C. The method according to claim 1,
The preparation of the lithium composite metal oxide represented by Formula 1 may be performed by mixing a transition metal precursor including nickel, cobalt, and manganese and a lithium-containing source material in such a manner that the atomic ratio of lithium to transition metal is 1: 1.07 to 1: 1.09 And calcining the resultant at 600 to 900 캜. 3. The method of claim 2,
Wherein the transition metal precursor is represented by the following formula (2).
(2)
Ni _d Co _e Mn _f (OH) ₂
In the formula (2) 0? E? 0.3, 0? F? 0.3, d + e + f = 1. 3. The method of claim 2,
Wherein the firing is performed in an oxygen atmosphere. 3. The method of claim 2,
Wherein the firing includes a first firing step performed at 700 ° C to 800 ° C and a second firing step performed at 800 ° C to 900 ° C. The method according to claim 1,
Wherein the cobalt-containing raw material is mixed in an amount of 0.8 to 1.2 parts by weight based on 100 parts by weight of the lithium composite metal oxide in the heat treatment step. The method according to claim 1,
Wherein the heat treatment is performed in an atmospheric environment for 5 hours to 10 hours. A lithium composite metal oxide represented by the following formula (3); And
And a surface treatment layer comprising cobalt-lithium composite particles adhered to the surface of the lithium composite metal oxide.
(3)
Li _{x '} [Ni _a Co _b Mn _c ] O ₂
(In the formula 3, 0.6? A <1, 0 <b? 0.3, 0 <c? 0.3, a + b + c = 1, 0.95? X? 9. The method of claim 8,
Wherein, in the formula (3), 0.65? A <1. 9. The method of claim 8,
Wherein the cobalt content in the surface treatment layer is 8000 ppm to 12000 ppm. The positive electrode for a secondary battery according to any one of claims 8 to 10, comprising a positive electrode active material for a secondary battery. 12. A secondary battery comprising a positive electrode for a secondary battery according to claim 11.

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