KR102128011B1 - 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 is a lithium composite metal oxide represented by the following formula (3); And it relates to a positive electrode active material for a secondary battery comprising a surface treatment layer comprising a cobalt-lithium composite particles attached to the lithium composite metal oxide surface, a method for manufacturing the same, and a positive electrode and a secondary battery including the same.
[Formula 3]
Li _x' [Ni _a Co _b Mn _c ]O ₂
(In Formula 3, 0.6≤a<1, 0<b≤0.3, 0<c≤0.3, a+b+c=1, 0.95≤x'≤1.05.)

Description

Anode active material for a secondary battery, a manufacturing method thereof, and a cathode and a secondary battery for a secondary battery including the same 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 specifically, a positive electrode active material capable of realizing excellent capacity characteristics and stability even under high voltage, and a method for manufacturing the same It relates to a positive electrode for a secondary battery and a secondary battery.

Recently, as the popularity of mobile devices and power tools and the demand for eco-friendly electric vehicles have increased, the conditions for the energy source to drive them have gradually increased. In particular, development of a positive electrode active material having high energy density, stable driving under high voltage, and long life characteristics is required.

Lithium transition metal composite oxide is used as the positive electrode active material of the lithium secondary battery, and among them, lithium cobalt composite metal oxide of LiCoO ₂ having a high working voltage and excellent capacity characteristics is mainly used. However, LiCoO ₂ has very poor thermal properties due to destabilization of the crystal structure due to de-lithium, and is expensive, and thus has a limitation in mass use 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, LiNiO ₂ has 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 is decomposed to cause the battery to burst and ignite.

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

In order to improve such a problem, research has 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, but rapid oxygen desorption proceeds due to oxidation from Ni ^{2 +} to Ni ^{3 +/4+} depending on the filling depth, and the desorbed oxygen reacts with the electrolytic solution. There is a problem that the intrinsic properties of the lattice structure are changed and the structure collapses.

Accordingly, there is a need to develop a positive electrode active material capable of realizing excellent capacity characteristics and stability even under high voltage.

Korean Patent Publication No. 10-2015-0070853 (Publication date: 2015.06.25)

The present invention is to solve the above problems, and to provide a nickel positive electrode active material capable of realizing excellent capacity characteristics and stability even under high voltage, a manufacturing method thereof, and a positive electrode and a secondary battery for a secondary battery including the same.

In one aspect, the present invention, preparing a lithium composite metal oxide represented by the following formula (1); And mixing the lithium composite metal oxide and the cobalt-containing raw material and then heat-treating the mixture over 300°C and below 400°C.

[Formula 1]

Li _x [Ni _a Co _b Mn _c ]O ₂

(In Formula 1, 0.6≤a<1, 0<b≤0.3, 0<c≤0.3, a+b+c=1, 1.07≤x≤1.09.)

At this time, the step of preparing the lithium composite metal oxide represented by the formula (1), the transition metal precursor and the lithium-containing raw material containing nickel, cobalt, and manganese lithium: the atomic ratio of the transition metal is 1.07:1 to 1.09:1 It can be carried out by mixing and firing at 600°C to 900°C if possible.

In addition, the transition metal precursor may be represented by the following formula (2).

[Formula 2]

Ni _d Co _e Mn _f (OH) ₂

In Chemical Formula 2 0.6<d<1, 0<e<0.3, 0<f<0.3, d+e+f=1.

Further, the firing may be performed under an oxygen atmosphere.

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

In addition, 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 step is preferably performed for 5 to 10 hours in an atmospheric atmosphere. Do.

In another aspect, the present invention is a lithium composite metal oxide represented by the following formula (3); And a surface treatment layer comprising cobalt-lithium composite particles attached to the lithium composite metal oxide surface.

[Formula 3]

Li _x' [Ni _a Co _b Mn _c ]O ₂

(In Formula 3, 0.6≤a<1, 0<b≤0.3, 0<c≤0.3, a+b+c=1, 0.95≤x'≤1.05.)

In addition, the cobalt content in the surface treatment layer may be 8000ppm to 12000ppm.

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

The positive electrode active material for a secondary battery according to the present invention has a high lithium content, and a surface treatment layer including cobalt-lithium composite particles containing cobalt having excellent output characteristics and stability is formed on the surface, unlike the conventional high concentration nickel positive electrode active material Not only is it structurally stable, it shows excellent output characteristics even under high voltage.

In addition, according to the method of manufacturing a positive electrode active material for a secondary battery of the present invention, a positive electrode active material for a secondary battery having a high lithium content can be produced without performing a water washing process, and thus productivity is excellent.

1 is a SEM photograph of a positive electrode active material prepared according to an embodiment.
2 is a SEM photograph of a positive electrode active material prepared according to Comparative Example 4.
3 is a graph showing the charge and discharge characteristics of the battery prepared according to Example and Comparative Example 1.
4 is a graph showing the charge and discharge characteristics of the batteries prepared according to Examples and Comparative Examples 2 and 3.
5 is a graph showing the charge and discharge characteristics of the battery prepared according to Example and Comparative Example 4.
6 is a graph showing the discharge capacity according to the number of cycles of the battery prepared according to Example and Comparative Example 1.
7 is a graph showing the discharge capacity according to the number of cycles of the batteries prepared according to Examples and Comparative Examples 2 and 3.

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

The present inventors have repeatedly studied to produce a positive electrode active material that is stable under high voltage and has excellent capacity characteristics. As a result, a lithium composite metal oxide and a cobalt-containing raw material having a nickel atomic ratio of 0.6 or higher and an atomic ratio of lithium of 1.07 or higher After mixing the heat treatment at a specific temperature, it was found that the above object can be achieved and the present invention has been completed.

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

Method for manufacturing positive electrode active material for secondary battery

The method for preparing a positive electrode active material according to the present invention comprises: (1) preparing a lithium composite metal oxide represented by Chemical Formula 1, and (2) mixing the lithium composite metal oxide and a cobalt-containing raw material, and then exceeding 300° C. to 400° C. And heat-treating to a lower temperature. Hereinafter, each step of the present invention will be described in more detail.

(1) Step of 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 the transition metal, wherein the atomic fraction of nickel in the transition metal is 0.6 or more and the atomic fraction of lithium is 1.07 to 1.09. It is a lithium composite metal oxide.

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

[Formula 1]

Li _x [Ni _a Co _b Mn _c ]O ₂

In Formula 1, 0.6≤a<1, 0<b≤0.3, 0<c≤0.3, a+b+c=1, and 1.07≤x≤1.09.

The a, b, and c represent atomic fractions of Ni, Co, and Mn among metal elements (ie, transition metal elements) excluding lithium, respectively. 0.6≤a<1, 0<b≤0.3, 0<c ≤0.3, a+b+c=1.

Specifically, a represents the atomic fraction of nickel among 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, and more preferably 0.65 to 0.95.

The b represents an atomic fraction of cobalt among transition metal elements, and the b may be greater than 0 and less than 0.3, preferably 0.001 to 0.25, and more preferably 0.01 to 0.25.

The c represents an atomic fraction of manganese among transition metal elements, and the c may be greater than 0 and less than 0.3, preferably 0.001 to 0.25, and more preferably 0.01 to 0.25.

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

The lithium composite metal oxide of the above [Formula 1] is, but is not limited to, for example, a transition metal precursor containing nickel, cobalt, manganese and a lithium-containing raw material lithium: the atomic ratio of the transition metal is 1.07:1 to It may be prepared by mixing to be 1.09:1, and firing at 700°C to 900°C.

In this case, the transition metal precursor may be, for example, nickel-cobalt-manganese hydroxide, or specifically, a compound represented by the following Chemical Formula 2.

[Formula 2]

Ni _d Co _e Mn _f (OH) ₂

In Chemical Formula 2 0.6≤d<1, 0<e≤0.3, 0<f≤0.3, d+e+f=1. Specifically, in Chemical 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, and f is 0.001 to 0.25, preferably It may be 0.01 to 0.25.

The transition metal precursor may be purchased according to a commercially available product, or may be prepared according to a method of manufacturing a nickel-cobalt-manganese transition metal precursor well known in the art.

For example, the nickel-cobalt-manganese transition metal precursor is prepared by coprecipitation reaction by adding an ammonium cation-containing complexing agent and a basic compound to a metal solution containing a nickel-containing raw material, a cobalt-containing raw material, and a manganese-containing raw material. It can be.

The nickel-containing raw material may be, for example, nickel-containing acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide or oxyhydroxide, and 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 salt, nickel halide 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 specifically Co(OH) ₂ , CoOOH, Co(OCOCH ₃ ) ₂ ㆍ4H ₂ O , Co(NO ₃ ) ₂ ㆍ6H ₂ O, Co(SO ₄ ) ₂ ㆍ7H ₂ O, or a combination thereof, but is not limited thereto.

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

The metal solution is a nickel-containing raw material, a cobalt-containing raw material and a manganese-containing raw material are added to a solvent, specifically water, or a mixed solvent of an organic solvent (for example, alcohol) that can be uniformly mixed with water. Or an aqueous solution of a nickel-containing raw material, an aqueous solution of a cobalt-containing raw material, or an aqueous solution of a manganese-containing raw material.

The ammonium cation-containing complex forming 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 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, and at this time, as a solvent, a mixture of water or an organic solvent (specifically, alcohol, etc.) uniformly mixed with water and water may be used.

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

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

Meanwhile, the co-precipitation reaction may be performed at a temperature of 40 to 70 under an inert atmosphere such as nitrogen or argon.

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

A lithium composite metal oxide can be obtained by mixing the transition metal precursor prepared by the above method with a lithium-containing raw material, and firing at 600°C to 900°C, preferably at 700°C to 900°C. At this time, the transition metal precursor and the lithium-containing raw material are mixed so that the atomic ratio of lithium:transition metal is 1.07:1 to 1.09:1. Here, the atomic ratio of the transition metal refers to the total number of atoms of the transition metal summing the atomic number of nickel, cobalt, and manganese.

The lithium-containing raw materials include lithium-containing carbonates (for example, lithium carbonate), hydrates (for example, lithium hydroxide I-hydrate (LiOHH ₂ O), etc.), hydroxides (for example, lithium hydroxide), nitrates ( For example, lithium nitrate (LiNO ₃ ), etc., chloride (eg, lithium chloride (LiCl), etc.), and the like, one of these, or a mixture of two or more thereof may be used.

Meanwhile, it is preferable that the firing is performed under an oxygen atmosphere .

In addition, the firing may consist of two or more firing processes with different temperatures, for example, including a primary firing step performed at 700°C to 800°C and a secondary firing step performed at 800°C to 900°C. It can be done. When the two-step firing process is performed as described above, the reactivity of the lithium-containing raw material and the transition metal precursor is increased compared to the one-step firing. Through the firing, the transition metal precursor reacts with lithium to obtain a lithium composite metal oxide represented by Chemical Formula 1.

(2) Heat treatment

When the lithium composite metal oxide of Chemical Formula 1 is prepared in the same manner 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 to form a surface treatment layer of a lithium composite metal oxide, and lithium by-products present in the lithium composite metal oxide and cobalt of a cobalt-containing raw material react by heat treatment to form a lithium-cobalt composite on the surface of the lithium composite metal oxide. A surface treatment layer containing particles is formed.

The cobalt-containing raw material may be cobalt-containing acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide or oxyhydroxide, and specifically Co(OH) ₂ , CoOOH, Co(OCOCH ₃ ) ₂ ㆍ4H ₂ O, Co(NO ₃ ) ₂ ㆍ6H ₂ O, Co(SO ₄ ) ₂ ㆍ7H ₂ O, or a combination thereof may be used. Of these, Co(OH) ₂ is particularly preferred.

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, it is possible to obtain excellent lithium by-product production suppression effect and electrical properties.

Meanwhile, the heat treatment is performed in a temperature range of more than 300°C and less than 400°C, preferably in a temperature range of 320°C to 380°C. When the heat treatment temperature is out of the above range, the capacity characteristics of the positive electrode active material are lowered, or it is impossible to form a surface treatment layer containing cobalt-lithium composite particles.

Conventionally, when forming a surface treatment layer on the surface of a lithium composite metal oxide, it was common to perform a high temperature treatment of 500°C or higher, but in the case of the present invention, lithium and cobalt are used even at a relatively low heat treatment temperature because lithium composite metal oxide having a high lithium content is used. The reaction can be made smoothly. On the other hand, in the case of the raw material containing cobalt used in the surface treatment of the present invention, since it is easily decomposed and oxidized at high temperature and converted to oxide, lithium-cobalt composite particles are not formed when the heat treatment temperature is too high, and exist in the form of cobalt oxide Thus, a decrease in the capacity of the positive electrode active material may occur.

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

On the other hand, the manufacturing method of the positive electrode active material according to the present invention does not perform a water washing process. In general, in the case of a lithium composite metal oxide having a high nickel atomic 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 reacts with an electrolyte and causes gas generation and swelling. Therefore, in the related art, in order to use a lithium composite metal oxide containing high concentration nickel as a positive electrode active material, a water washing process for removing lithium by-products on the surface of the lithium composite metal oxide is essential. However, in the case of the present invention, since the lithium by-product remaining in the lithium composite metal oxide is used as a raw material for forming a lithium-cobalt composite in the heat treatment process, it is not necessary to perform a separate washing process. As described above, since the present invention does not perform a water washing process, it is possible to shorten the production process compared to the prior art, thereby obtaining an effect of improving productivity.

Anode active material for secondary batteries

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

The positive electrode active material for a secondary battery of the present invention manufactured according to the above method includes a surface treatment layer comprising a lithium composite metal oxide represented by the following Chemical Formula 3 and cobalt-lithium composite particles attached to the surface of the lithium composite metal oxide .

[Formula 3]

Li _x' [Ni _a Co _b Mn _c ]O ₂

In Chemical Formula 3, 0.6≤a<1, 0<b≤0.3, 0<c≤0.3, a+b+c=1, 0.95≤x'≤1.05, and preferably 0.65≤a<1. When the composition of the lithium composite metal oxide satisfies the above range, high capacity characteristics and life characteristics can be obtained even under a high voltage of 4.3 V or higher.

The a, b, and c represent atomic fractions of Ni, Co, and Mn among metal elements (ie, transition metal elements) excluding lithium, respectively. 0.6≤a<1, 0<b≤0.3, 0<c ≤0.3, a+b+c=1.

Specifically, a represents the atomic fraction of nickel among 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, and more preferably 0.65 to 0.95.

The b represents the atomic fraction of cobalt among the transition metal elements, and the b may be greater than 0 and less than 0.3, preferably 0.001 to 0.25, and more preferably 0.01 to 0.25.

The c represents an atomic fraction of manganese among transition metal elements, and the c may be greater than 0 and 0.3 or less, preferably 0.001 to 0.25, and more preferably 0.01 to 0.25.

On the other hand, x'represents the atomic fraction of lithium in the lithium composite metal oxide, and x'is 0.95 to 1.05. Since lithium of the lithium composite metal oxide represented by Chemical Formula 1 reacts with the cobalt-containing raw material, the lithium content of the lithium composite metal oxide contained in the finally produced positive electrode active material decreases as in Chemical 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, thereby preventing oxygen from being desorbed from the lithium composite metal oxide, thereby improving structural stability. In addition, lithium concentration on the surface of the positive electrode active material is increased by lithium contained in the cobalt-lithium composite, thereby realizing excellent electrical properties.

Meanwhile, 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 the 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 positive electrode active material having excellent electrical performance at 4.3 V or more can be produced without additional washing.

In the case of the conventional NMC-based lithium composite metal oxide, it was common that the ratio of lithium to transition metal was 1.05 or less, but in the case of such lithium composite metal oxides, there was a problem that capacity characteristics and stability were poor under high voltage of 4.3 V or more. However, the positive electrode active material of the present invention has a higher lithium content than the prior art, and thus can achieve high capacity characteristics even under a high voltage, for example, a voltage of 4.3 V or higher, and lithium-cobalt on the surface of the lithium composite metal oxide as described above. It is structurally stable because the composite particles are attached.

Anode and secondary battery

The positive electrode active material for a secondary battery according to the present invention can be usefully used for preparing a positive electrode for a secondary battery.

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

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

In this case, 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 aluminum or stainless steel surfaces , Titanium, silver or the like may be used. In addition, the positive electrode current collector may typically have a thickness of 3 μm to 500 μm, and may form fine irregularities on the surface of the current collector to increase the adhesion of the positive electrode active material. For example, it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics.

A positive electrode active material layer comprising a positive electrode active material according to the present invention on at least one surface of the current collector, and optionally further comprising at least one of a conductive material and a binder, if necessary.

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

The positive electrode active material may be included in an amount of 80 to 99% by weight, more specifically 85 to 98% by weight relative to the total weight of the positive electrode active material layer. When included in the above-described content range, it can exhibit excellent capacity characteristics.

The conductive material is used to impart conductivity to the electrode, and in a battery configured, it can be used without particular limitation as long as it has electronic conductivity without causing chemical changes. Specific examples 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 powders 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, etc. are mentioned, and 1 type of these or mixtures of 2 or more types can be used. The conductive material may be included in 1 to 30% by weight based on the total weight of the positive electrode 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, and carboxymethyl cellulose (CMC) ), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluorine rubber, or various copolymers thereof, and one of these may be used alone or as a mixture of two or more. The binder may be included in 1 to 30% by weight relative to the total weight of the positive electrode active material layer.

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

Next, the 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 opposite to 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.

On the other hand, the secondary battery may further include a battery container for storing the electrode assembly of the positive electrode, the negative electrode, 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 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 is prepared by dissolving or dispersing the components constituting the negative electrode active material layer, that is, the negative electrode active material, a conductive material, and/or a binder, in a solvent to prepare a negative electrode mixture, and the negative electrode mixture of the negative electrode current collector. After coating on at least one surface, it can be produced by drying or rolling, or by casting the negative electrode mixture on a separate support, and then laminating the film obtained by peeling from the support on the negative electrode current collector.

The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surfaces Carbon, nickel, titanium, silver or the like, aluminum-cadmium alloy, or the like may be used. In addition, the negative electrode current collector may have a thickness of usually 3 μm to 500 μm, and like the positive electrode current collector, fine irregularities 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 films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics.

As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples include artificial graphite, natural graphite, graphitized carbon fibers, carbonaceous materials such as amorphous carbon; Metal compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy or Al alloy; Metal oxides capable of doping and dedoping lithium such as SiO _v (0<v<2), SnO ₂ , vanadium oxide, and lithium vanadium oxide; Or a complex containing the above-described metallic compound and a carbonaceous material, such as a Si-C composite or a Sn-C composite, etc., 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 negative electrode active material. In addition, both low crystalline carbon and high crystalline carbon may be used as the carbon material. Soft carbon and hard carbon are typical examples of low crystalline carbon, and amorphous or plate-like, scaly, spherical or fibrous natural graphite or artificial graphite, and kissy graphite are examples of high crystalline carbon. graphite), pyrolytic carbon, mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches and petroleum or coal tar pitch derived cokes).

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

On the other hand, in the secondary battery, the separator separates the negative electrode from the positive electrode and provides a passage for lithium ions. If the battery is normally used as a separator in a secondary battery, it can be used without particular limitation. It is preferable that it is excellent in resistance and electrolyte-moisturizing ability. Specifically, porous polymer films such as ethylene homopolymer, propylene homopolymer, ethylene/butene copolymer, ethylene/hexene copolymer and ethylene/methacrylate copolymer, etc. A laminate structure of two or more layers of may be used. In addition, a conventional porous nonwoven fabric, for example, a high melting point glass fiber, a polyethylene terephthalate fiber, or the like may be used. In addition, a coated separator containing a ceramic component or a polymer material may be used to secure heat resistance or mechanical strength, and may be used in a single-layer or multi-layer structure.

Meanwhile, as the electrolyte, an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel polymer electrolyte, a solid inorganic electrolyte, a molten inorganic electrolyte, and the like that can be used in manufacturing a secondary battery may be used, but are 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, methyl acetate (methyl acetate), ethyl acetate (ethyl acetate), γ-butyrolactone (γ-butyrolactone), ε-caprolactone (ε-caprolactone), such as ester solvents; Ether-based solvents such as dibutyl ether or tetrahydrofuran; Ketone solvents such as cyclohexanone; Aromatic hydrocarbon-based solvents such as benzene and fluorobenzene; Dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (ethylmethylcarbonate, EMC), ethylene carbonate (EC), propylene carbonate (propylene carbonate, PC) and other carbonate-based solvents; Alcohol-based solvents such as ethyl alcohol and isopropyl alcohol; Nitriles such as Ra-CN (Ra is a straight-chain, branched or cyclic hydrocarbon group having 2 to 20 carbon atoms, and may include a double bond aromatic ring or ether bond); Amides such as dimethylformamide; Dioxolanes such as 1,3-dioxolane; Alternatively, sulfolanes may be used. Of these, carbonate-based solvents are preferred, and cyclic carbonates (for example, ethylene carbonate or propylene carbonate) having high ionic conductivity and high dielectric constant that can improve the charge and discharge performance of the battery, and low-viscosity linear carbonate-based compounds ( For example, a mixture of ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate) is more preferable. In this case, the mixture of the cyclic carbonate and the chain carbonate in a volume ratio of about 1: 1 to 9 may be used to exhibit excellent electrolyte performance.

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 be effectively moved.

In addition to the electrolyte components, the electrolyte may include haloalkylene carbonate-based compounds such as difluoroethylene carbonate or the like for the purpose of improving the life characteristics of the battery, suppressing the reduction in 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 further included. At this time, the additive may be included in an amount of 0.1 to 5% by weight based on the total weight of the electrolyte.

As described above, the secondary battery including the positive electrode active material according to the present invention has excellent capacity characteristics and stability even under high voltage, portable devices such as mobile phones, notebook computers, digital cameras, and hybrid electric vehicles (HEVs). ) 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 a battery module, and the battery module can be applied to a battery pack. The battery module or battery pack includes a power tool; An electric vehicle including an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); Alternatively, it can be used as a power source for any one or more medium-to-large devices in a power storage system.

Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art to which the present invention pertains can easily practice. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein.

Example

Ni _0.65 Co _0.2 Mn _0.15 (OH) ₂ and Li ₂ CO ₃ were placed in an alumina crucible such that the atomic ratio of Li:total transition metal was 1.07:1, and maintained at 750°C in an oxygen atmosphere for 5 hours, 850°C It was fired for 10 hours to prepare a lithium composite metal oxide. The prepared lithium composite metal oxide is pulverized using a mortar, 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 powder was heat-treated at 350°C for 7 hours in an atmosphere. Then, the resultant heat-treated powder was pulverized and then classified using 325 mesh to prepare a final positive electrode active material.

A positive electrode mixture (viscosity: 5000 mPa·s) was prepared by mixing the positive electrode active material, carbon black conductive material, and PVdF binder prepared as described above in a ratio of 95:2.5:2.5 in a weight ratio in N-methylpyrrolidone solvent. After coating on one side of the aluminum current collector, dried at 130° C., and rolled to prepare an anode. Then, a coin half cell battery was manufactured 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 cells were prepared.

Comparative Example 2

A positive electrode active material, a positive electrode, and a coin half-cell battery were manufactured in the same manner as in Example, except that the heat treatment temperature was 300°C.

Comparative Example 3

A positive electrode active material, a positive electrode, and a coin half-cell battery were manufactured in the same manner as in Example, except that the heat treatment temperature was 400°C.

Comparative Example 4

A positive electrode active material, a positive electrode, and a coin half-cell battery 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 positive electrode active material prepared by Example and Comparative Example 4 was photographed by SEM. 1 shows a photo of the positive electrode active material of the embodiment, and FIG. 2 shows a photo of the positive electrode active material of Comparative Example 4.

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

On the other hand, as shown in Figure 2, the surface of the positive electrode active material of the boron-coated Comparative Example 4 does not have a composite in the form of particles.

Experimental Example 2-Evaluation of charge/discharge characteristics

The coin half-cell batteries prepared in Examples and Comparative Examples 1 to 4 were charged and discharged at 25C to 3.0V to 4.3V under 0.1C/0.1C conditions to measure charge/discharge characteristics. Measurement results are shown in FIGS. 3 to 5.

Figure 3 is a graph comparing the charge and discharge characteristics of the battery prepared according to Example and Comparative Example 1, Figure 4 is a graph comparing the charge and discharge characteristics of the battery prepared according to Examples, Comparative Examples 2 and 3, 5 is a graph comparing the charge and discharge characteristics of the battery prepared according to Example and Comparative Example 4.

3 to 5, in the case of a battery using a positive electrode active material prepared according to the method of the present invention, it can be seen that it has a higher output characteristic under high voltage than the batteries produced by Comparative Examples 1 to 4.

Experimental Example 3-Evaluation of cycle characteristics

Discharge capacity (mAh/) of the coin half-cell battery prepared in Examples and Comparative Examples 1 to 3 at 25° C. while performing 50 cycles of charging and discharging under the conditions of a charge termination voltage of 4.3 V, a discharge termination voltage of 3 V, and 0.5 C/1.0 C. g) was measured The measurement results are shown in FIGS. 6 and 7.

6 is a graph comparing the discharge capacity according to the number of cycles of the battery manufactured according to Examples and Comparative Examples 1, and FIG. 7 is a discharge capacity according to the number of cycles of the batteries manufactured according to Examples and Comparative Examples 2 and 3 It is a graph comparing.

6 and 7, it can be seen that in the case of the battery of the embodiment prepared according to the method of the present invention, it exhibits a higher discharge capacity than the batteries of Comparative Examples 1 to 3 in all cycles.

Claims (12)

Preparing a lithium composite metal oxide represented by the following Chemical Formula 1; And
[Formula 1]
Li _x [Ni _a Co _b Mn _c ]O ₂
(In Formula 1, 0.6≤a<1, 0<b≤0.3, 0<c≤0.3, a+b+c=1, 1.07≤x≤1.09.)
A method of manufacturing a positive electrode active material for a secondary battery, comprising mixing the lithium composite metal oxide and the cobalt-containing raw material and heat-treating the mixture at a temperature of 300°C or higher and less than 400°C. According to claim 1,
The step of preparing the lithium composite metal oxide represented by Chemical Formula 1 includes mixing a transition metal precursor containing nickel, cobalt, and manganese and a lithium-containing raw material such that the atomic ratio of lithium:transition metal is 1.07:1 to 1.09:1. And it is carried out by a method of firing at 600 ℃ to 900 ℃ method for producing a positive electrode active material for a secondary battery. According to claim 2,
The transition metal precursor is a method for producing a positive electrode active material for a secondary battery represented by the following formula (2).
[Formula 2]
Ni _d Co _e Mn _f (OH) ₂
In Chemical Formula 2 0.6≤d<1, 0<e≤0.3, 0<f≤0.3, d+e+f=1. According to claim 2,
The firing is a method for producing a positive electrode active material for a secondary battery that is performed under an oxygen atmosphere. According to claim 2,
The firing method comprising a primary firing step performed at 700°C to 800°C and a secondary firing step performed at 800°C to 900°C. According to claim 1,
In the heat treatment step, the cobalt-containing raw material is a method of manufacturing a positive electrode active material for a secondary battery that is mixed with 0.8 to 1.2 parts by weight based on 100 parts by weight of lithium composite metal oxide. According to claim 1,
The heat-treating step is a method for producing a positive electrode active material for a secondary battery, which is performed for 5 to 10 hours under an atmospheric atmosphere. delete delete delete delete delete

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