KR20190041715A - Positive electrode active material for lithium secondary battery, preparing method of the same, positive electrode and lithium secondary battery including the same - Google Patents

Abstract

The present invention relates to a positive electrode material, a method for manufacturing the positive electrode material, a positive electrode for a lithium secondary battery comprising the positive electrode material, and a lithium secondary battery. The positive electrode material comprises: a first positive electrode active material having an average particle diameter (D50) of 10 μm or more; and a second positive electrode active material having an average particle diameter (D50) of 4-8 μm. The first positive electrode active material and the second positive electrode active material each independently comprises lithium nickel cobalt manganese oxide having a nickel content of 50 mol% or more based on the total moles of transition metals excluding lithium. The second positive electrode active material has a single particle form.

Description

TECHNICAL FIELD The present invention relates to a positive electrode material for a lithium secondary battery, a method for producing the same, a positive electrode for a lithium secondary battery, and a lithium secondary battery including the same. BACKGROUND OF THE INVENTION 1. Field of the Invention [0001]

The present invention relates to a positive electrode material for a lithium secondary battery, a method for producing the positive electrode material, a positive electrode for a lithium secondary battery including the positive electrode material, and a lithium secondary battery comprising the same.

As technology development and demand for mobile devices increase, the demand for secondary batteries as energy sources is rapidly increasing. Among such secondary batteries, lithium secondary batteries having a high energy density and voltage, a long cycle life, and a low self-discharge rate are commercially available and widely used.

Lithium transition metal composite oxides are used as the positive electrode active material of lithium secondary batteries. Among them, LiCoO ₂ Lithium cobalt composite metal oxide is mainly used. However, LiCoO ₂ has a poor thermal characteristic due to destabilization of crystal structure due to depolythium, and is expensive, so that it can not be used as a power source in fields such as electric vehicles.

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 . Among them, research and development on a lithium nickel composite metal oxide having a high reversible capacity of about 200 mAh / g and facilitating the realization of a large capacity battery has been actively researched. However, LiNiO ₂ has a lower thermal stability than LiCoO _2, and if an internal short circuit occurs due to external pressure or the like in a charged state, the cathode active material itself is decomposed to cause rupture and ignition of the battery. Accordingly, a lithium nickel cobalt manganese oxide in which a part of Ni is substituted with Mn and Co has been developed as a method for improving the low thermal stability while maintaining excellent reversible capacity of LiNiO ₂ .

However, in the case of the lithium nickel cobalt manganese oxide, the rolling density of the particles is low, and especially when the content of Ni is increased to increase the capacity characteristics, the rolling density of the particles is further lowered. When the electrode is strongly rolled in order to increase the rolling density, breakage of the current collector and cracking of the cathode material occur.

Therefore, development of a cathode material capable of improving the rolling density of the lithium nickel cobalt manganese oxide has been demanded.

Korean Patent Publication No. 2016-0080244

In order to solve the above problems, a first technical object of the present invention is to provide a cathode material for a lithium secondary battery which contains a high content of lithium nickel cobalt manganese oxide and can improve a rolling density.

A second technical object of the present invention is to provide a method for producing the cathode material.

A third object of the present invention is to provide a positive electrode for a lithium secondary battery including the positive electrode material.

A fourth aspect of the present invention is to provide a lithium secondary battery including the positive electrode for a lithium secondary battery.

The present invention provides a lithium secondary battery comprising a first cathode active material having an average particle diameter (D ₅₀ ) of 10 μm or more and a second cathode active material having an average particle diameter (D ₅₀ ) of 4 μm to 8 μm, wherein the first cathode active material and the second cathode active material And lithium nickel cobalt manganese oxide having a nickel content of 50 mol% or more with respect to the total number of moles of transition metals other than lithium, respectively, and the second cathode active material has a single particle form.

Also, the present invention provides a method for producing a cathode active material, comprising: preparing a nickel cobalt manganese hydroxide precursor having an average particle diameter (D ₅₀ ) of 10 μm or more and a lithium-containing raw material at a temperature lower than 800 ° C. to 930 ° C. to produce a first cathode active material; Preparing a nickel cobalt manganese hydroxide precursor having an average particle diameter (D ₅₀ ) of 4 탆 to 8 탆 and a lithium-containing raw material under a temperature of 930 캜 to 1,000 캜 to prepare a second cathode active material having a single particle form; And mixing the first positive electrode active material and the second positive electrode active material.

Further, there is provided a positive electrode for a lithium secondary battery comprising the positive electrode material according to the present invention.

Further, there is provided a lithium secondary battery comprising a positive electrode according to the present invention.

According to the present invention, a first cathode active material having an average particle diameter (D ₅₀ ) of 10 μm or more and a second cathode active material having a small particle diameter of an average particle diameter (D ₅₀ ) of 4 μm to 8 μm are mixed and used , And the second cathode active materials are filled between the empty spaces of the first cathode active materials to provide a cathode having an excellent rolling density. Particularly, by manufacturing the second cathode active material having a small particle diameter in the form of a single particle, the particles can be maintained without being broken even by rolling with a strong force, and the rolling density is further improved.

In addition, it is possible to provide a secondary battery having improved life characteristics when a cathode material having improved rolling density is applied to a secondary battery.

1 is a graph showing changes in rolling density according to pressure of a cathode material prepared in Example 1 and Comparative Examples 2 and 3 of the present invention.
2 is a graph showing lifetime characteristics of the cathode material produced in Example 1 and Comparative Example 1 of the present invention.
3 is a graph showing the amount of gas generated in the cathode material produced in Example 1 and Comparative Example 1 of the present invention.

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

The terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms and the inventor may appropriately define the concept of the term in order to best describe its invention It should be construed as meaning and concept consistent with the technical idea of the present invention.

In the case of lithium nickel cobalt manganese oxide used as a cathode material for a lithium secondary battery in the past, the rolling density of the particles is low. Especially, when the content of nickel is increased for the production of the high capacity cathode material, the rolling density of the particles is further lowered. When the electrode is strongly rolled to increase the rolling density, there is a problem that breakage of the current collector and breakage of the cathode material occur.

The present inventors have conducted intensive studies to develop a cathode material having a high rolling density while containing nickel in a high content. As a result, it has been found that two kinds of cathode active materials having different average particle diameters are used, It is possible to effectively improve the rolling density of the cathode material containing nickel in a high content by using the cathode active material in the form of a single particle.

More specifically, the cathode material according to the present invention includes a first cathode active material having an average particle diameter (D ₅₀ ) of 10 μm or more and a second cathode active material having an average particle diameter (D ₅₀ ) of 4 μm to 8 μm, The first cathode active material and the second cathode active material each independently comprise lithium nickel cobalt manganese oxide having a nickel content of 50 mol% or more based on the total moles of transition metals except lithium, and the second cathode active material has a single particle form will be.

Specifically, the cathode material according to the present invention comprises a first cathode active material and a second cathode active material, wherein the first cathode active material and the second cathode active material each independently comprise lithium nickel cobalt manganese oxide represented by the following formula Can:

[Chemical Formula 1]

Li _{1 + a} Ni _x Co _y Mn _(1-xy) O ₂

In Formula 1, -0.1? A? 0.1, 0.5? X? 0.8, 0.1? Y? 0.4, 0.6? X + y?

Preferably, the first cathode active material and the second cathode active material each independently include lithium nickel cobalt manganese oxide having a nickel content of 50 mol% or more based on the total moles of transition metals except lithium. For example, the first cathode active material and second cathode active materials are, each independently, LiNi _{0. 5} Co _{0 . 2} Mn _{0 . 3} O ₂ , LiNi _{0 . 5} Co _{0 . 3} Mn _{0 . 2} O ₂ , LiNi _0.6 Co _0.2 Mn _0.2 O ₂ , and LiNi _{0 . 8} Co _{0 . 1} Mn _{0 . 1} < RTI ID = 0.0 &_gt; O2. ≪ / RTI >

When the first cathode active material and the second cathode active material each independently include the lithium nickel cobalt manganese oxide, a cathode material having excellent capacity characteristics and lifetime characteristics can be provided.

The cathode material may be formed in a bimodal form. For example, small-sized second cathode active material particles having an average particle diameter (D ₅₀ ) of 4 탆 to 8 탆 in an empty space between first cathode active material particles having an average particle diameter (D ₅₀ ) of 10 탆 or larger It can be a filled form. Even when the voids between the first cathode active material particles are filled with the particles of the second cathode active material so that nickel is contained in a high content for the production of a high capacity cathode material, the rolling density of the cathode material according to the present invention is improved Lt; / RTI >

The first cathode active material may have an average particle diameter (D ₅₀ ) of 10 μm or more, preferably 10 μm to 15 μm, and more preferably 10 μm to 12 μm. For example, when the average particle diameter (D ₅₀ ) of the first cathode active material is less than 10 탆, the rolling density of the first cathode active material is reduced, thereby making it difficult to realize a high electrode density.

The average particle diameter (D ₅₀ ) of the first cathode active material can be defined as a particle diameter at a standard of 50% of the particle diameter distribution. For example, the average particle diameter (D ₅₀ ) of the first cathode active material may be measured using a laser diffraction method. The laser diffraction method generally enables measurement of a particle diameter from a submicron region to several millimeters, resulting in high reproducibility and high degradability. For example, a method of measuring the average particle diameter (D ₅₀ ) of the first cathode active material is a method of measuring the average particle size (D ₅₀ ) of the first cathode active material by introducing the first cathode active material into a commercially available laser diffraction particle size analyzer (for example, Microtrac MT 3000) Is irradiated at an output of 60 W, the average particle diameter (D ₅₀ ) at the 50% reference of the particle diameter distribution in the measuring apparatus can be calculated.

The first cathode active material is a secondary particle type in which a plurality of primary particles are aggregated.

In the present invention, 'primary particle' refers to a primary structure of a single particle, and 'secondary particle' refers to a physical structure between primary particles without intentional agglomeration or assembly process for primary particles constituting secondary particles Or an aggregate, i.e., a secondary structure, in which primary particles are agglomerated by chemical bonding.

For example, the first cathode active material may be a secondary particle formed by agglomerating primary particles having crystal grains of 1 nm to 500 nm, preferably 50 nm to 300 nm. Since the first cathode active material is formed of secondary particles in which primary particles are aggregated, a high rolling density can be achieved at the same time while having the high specific surface area, and the energy density per volume of the electrode can be increased.

At this time, the first cathode active material has a rolling density of 2.6 g / cc to 3.0 g / cc when rolled under a force of 400 kgf to 2,000 kgf, and is compressed into the pellet shape at the rolling density, 90 mu S / cm to 200 mu S / cm.

Since the first cathode active material is produced in the form of secondary particles in which primary particles are agglomerated, the contact area between the first cathode active material and the electrolyte is wide, the moving distance of lithium ions in the first cathode active material is short, Can be easily displayed. Also, as the contact points between the particles are increased, the first positive electrode active material is pressurized to form a pellet shape, and the measured electric conductivity may exhibit an excellent value applicable to the positive electrode.

For example, the rolling density of the first cathode active material can be measured by, for example, introducing the first cathode active material into a rolling density measuring device (HPRM-1000, Hankook, Korea) and then applying a force of 400 kgf to 2,000 kgf And can be measured by rolling. The electrical conductivity of the first cathode active material may be measured by, for example, compressing the first cathode active material at a rolling density of 400 kgf to 2,000 kgf to obtain a pellet, and then measuring the electrical conductivity of the first cathode active material using a commercially available electrical conductivity meter (MCP- T610, Mitsubishi, Japan).

In addition, the second cathode active material may have an average particle diameter (D ₅₀ ) of 4 탆 to 8 탆, preferably 4 탆 to 6 탆. When the average particle diameter (D ₅₀ ) of the second cathode active material is out of the range and is less than 4 탆 or more than 8 탆, the effect of improving the rolling density due to bimodalization of the cathode material hardly occurs, Can not be implemented.

The average particle diameter (D ₅₀ ) of the second cathode active material can be defined as a particle diameter at a 50% of the particle diameter distribution, and the average particle diameter of the second cathode active material is the same as the average particle diameter of the first cathode active material Can be measured.

Specifically, the second cathode active material is in the form of a single particle. Even when the second cathode active material is formed as a single particle, even if the average particle diameter (D ₅₀ ) is in the range of about 4 탆 to about 8 탆, the particle strength is excellent. Accordingly, even when the second cathode active material is rolled with a high force of 400 kgf to 2,000 kgf, the phenomenon of particulate increase in the electrode due to the breakage of the particles is alleviated, thereby improving the lifetime characteristics of the battery.

At this time, the second cathode active material has a rolling density of 2.7 g / cc to 3.1 g / cc when rolled under a force of 400 kgf to 2,000 kgf, and the electrical conductivity measured after the rolling is compressed to the powder density is 5 mu S / cm to 50 mu S / cm. The rolling density and electrical conductivity of the second cathode active material may be measured using the same method as the rolling density and electrical conductivity of the first cathode active material.

Since the second cathode active material is prepared in the form of a single particle, the moving distance of lithium ions in the second cathode active material is increased, and thus the mobility of lithium ions in the second cathode active material is decreased. Also, the contact point between the second cathode active material particles decreases due to the low rolling density, and the second cathode active material exhibits a lower electric conductivity than the first cathode active material.

Meanwhile, the cathode material is prepared by mixing the first cathode active material and the second cathode active material in a weight ratio of 9: 1 to 6: 4, preferably 8: 2 to 6: 4, more preferably 8: 2 to 7: May include. In the case of the positive electrode material including the first positive electrode active material and the second positive electrode active material within the above range, the electric conductivity is improved as compared with the case where only the second positive electrode active material is contained, and the output characteristic and the rate characteristic improvement effect of the lithium secondary battery using the same You can expect.

As described above, in the case where only the second cathode active material in the form of a single particle is included, the electrical conductivity measured after the pellet is formed is as low as about 5 μS / cm to 50 μS / cm. When the positive electrode active material constituting the electrode has an electrical conductivity of 5 μS / cm to 50 μS / cm, the resistance becomes high, and the output characteristics and rate characteristics of the battery may be deteriorated. Accordingly, by including at least 60 wt% of the first cathode active material having a high electrical conductivity with respect to the total weight of the cathode active material, the low powder electrical conductivity of the second cathode active material can be canceled.

Specifically, the cathode material includes the first cathode active material and the second cathode active material in a weight ratio of 9: 1 to 6: 4, preferably 8: 2 to 6: 4, more preferably 8: 2 to 7: 3 Cm 2 to 1,000 μS / cm, and more preferably 100 μS / cm to 500 μS / cm when compressed into a pellet shape by compressing with a force of 400 kgf to 2,000 kgf. In particular, the cathode material may exhibit an electrical conductivity of 150 μS / cm to 1,000 μS / cm when compressed into a pellet shape with a force of 2,000 kgf.

Further, the cathode material includes the first cathode active material and the second cathode active material in a ratio of from 9: 1 to 6: 4, thereby achieving a rolling density of 2.75 g / cc to 3.2 g / cc when rolling at a force of 400 kgf to 2,000 kgf Lt; / RTI >

Meanwhile, a method for producing a cathode material according to the present invention comprises: preparing a nickel cobalt manganese hydroxide precursor having an average particle diameter (D ₅₀ ) of 10 μm or more and a lithium-containing raw material at a temperature lower than 800 ° C. to 930 ° C. to produce a first cathode active material step; A nickel cobalt manganese hydroxide precursor having an average particle diameter (D ₅₀ ) of 3 탆 to 8 탆, and a lithium-containing raw material is calcined at 930 캜 to 1,000 캜 to prepare a second cathode active material having a single particle form; And mixing the first cathode active material and the second cathode active material.

Specifically, the nickel cobalt manganese hydroxide precursor used in the production of the first cathode active material and the second cathode active material is prepared by controlling only the average particle diameter (D ₅₀ ) by varying the precursor coprecipitation time, and the nickel cobalt manganese hydroxide precursor May be produced in the same manner.

First, the preparation method of the nickel cobalt manganese hydroxide precursor will be described in more detail. A transition metal-containing solution is prepared.

The transition metal-containing solution may be prepared by adding a nickel raw material, a cobalt raw material, and a manganese raw material to a mixture of an organic solvent (such as an alcohol) and water that can be uniformly mixed with a solvent, specifically, water or water, An aqueous solution containing each of the metal-containing raw materials may be prepared and then mixed and used.

As the raw materials of the nickel, cobalt and manganese, sulfates, nitrates, acetates, halides, hydroxides, or oxyhydroxides containing the respective metal elements may be used. If they are soluble in the above-mentioned solvents such as water, Can be used without limitation.

Specifically, the cobalt raw material may be Co (OH) ₂ , CoOOH, CoSO ₄ , Co (OCOCH ₃ ) ₂揃 4H ₂ O, Co (NO ₃ ) ₂揃 6H ₂ O, or Co (SO ₄ ) ₂揃 7H ₂ < RTI ID = 0.0 > O. < / RTI >

In addition, the nickel raw material is _{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 or nickel halide.

The raw materials for manganese include manganese oxides such as Mn ₂ O ₃ , MnO ₂ , and Mn ₃ O ₄ ; Manganese salts such as MnCO ₃ , Mn (NO ₃ ) ₂ , MnSO ₄ , manganese acetate, manganous dicarboxylate, manganese citrate and manganese fatty acid; Oxyhydroxide, or manganese chloride.

Next, the transition metal-containing solution, the ammonium ion-containing solution and the basic aqueous solution are added and subjected to a coprecipitation reaction to prepare a nickel cobalt manganese hydroxide precursor.

The ammonium ion-containing solution may comprise at least one or more selected from the group consisting of NH ₄ OH, (NH ₄ ) ₂ SO ₄ , NH ₄ NO ₃ , NH ₄ Cl, CH ₃ COONH ₄ , and NH ₄ CO ₃ have. At this time, a mixture of water and an organic solvent (specifically, alcohol or the like) which can be mixed with water uniformly and water can be used as the solvent.

The basic aqueous solution may contain at least one or more selected from the group consisting of NaOH, KOH, and Ca (OH) ₂ , and examples of the solvent include water or an organic solvent that can be uniformly mixed with water Etc.) and water may be used.

The precursor of nickel cobalt manganese hydroxide prepared by the above process for producing a precursor of nickel cobalt manganese hydroxide may be represented by the following formula 2:

(2)

[Ni _x1 Co _y1 Mn _(1-x1-y1) ] (OH) ₂

0.5? X1? 0.8, 0? Y1? 0.4, 0.6? X1 + y1? 0.9.

In order to produce the cathode material according to the present invention, first, a nickel cobalt manganese hydroxide precursor having an average particle diameter (D ₅₀ ) of 10 μm or more and a lithium-containing raw material are heated at a temperature of 800 ° C. to less than 930 ° C., preferably 900 ° C. to 930 ° C. For 10 to 24 hours to prepare a first cathode active material. The average particle diameter (D ₅₀ ) of the precursor of nickel cobalt manganese hydroxide represented by Formula 2 may be 10 탆 or more, preferably 10 탆 to 15 탆, more preferably 10 탆 to 12 탆 Mu m.

For example, the lithium-containing raw material is not particularly limited as long as it is a compound containing a lithium source, but lithium carbonate (Li ₂ CO ₃ ), lithium hydroxide (LiOH), LiNO ₃ , CH ₃ COOLi, Li ₂ (COO) ₂ can be used.

The nickel cobalt manganese hydroxide precursor and the lithium-containing raw material may be mixed at a molar ratio of 1: 1.0 to 1: 1.3, preferably 1: 1.0 to 1: 1.1. When the nickel cobalt manganese hydroxide precursor and the lithium-containing raw material are mixed in the above range, the first cathode active material to be produced may exhibit excellent capacity characteristics.

When the firing temperature and the firing time satisfy the above range, the first cathode active material is produced in the form of secondary particles in which primary particles are aggregated, so that the first cathode active material having a high specific surface area, Particles can be produced.

Next, a nickel cobalt manganese hydroxide precursor having an average particle diameter (D ₅₀ ) of 4 탆 to 8 탆 and a lithium-containing raw material are calcined at 930 캜 to 1,000 캜, preferably 950 캜 to 980 캜 for 10 hours to 24 hours Thereby preparing a second cathode active material having a single particle form. The average particle diameter (D ₅₀ ) of the precursor of nickel cobalt manganese hydroxide represented by Formula 2 may be 4 탆 to 8 탆, preferably 4 탆 to 6 탆, by reducing the coacervation time in the production of the precursor.

In the production of the second cathode active material, the second cathode active material may be produced in the form of a single particle by carrying out the calcining at 930 ° C. to 1,000 ° C. for 10 hours to 24 hours. In the case where the second cathode active material is recrystallized and formed into a single particle in the case of performing the preforming for 10 hours to 24 hours at a high temperature of 930 to 1,000 ° C as described above. As a result, the second positive electrode active material exhibits excellent particle strength, so that even when compressed with a binding force of 400 kgf to 2,000 kgf, the particles are not broken and the shape can be maintained. As a result, the increase in the number of fine particles in the electrode due to the breakage of the particles is suppressed, thereby improving the lifetime characteristics of the battery.

In addition, since the second cathode active material is fired at a high temperature of 930 DEG C or more, the amount of lithium remaining on the surface of the second cathode active material is reduced. This residual lithium reduction effect can reduce the generation of gas due to the reaction between the residual lithium and the electrolytic solution.

Finally, the first cathode active material and the second cathode active material are mixed.

The first cathode active material and the second cathode active material may be mixed in a weight ratio of 9: 1 to 6: 4, preferably 8: 2 to 6: 4, more preferably 8: 2 to 7: 3.

When the first cathode active material and the second cathode active material are mixed in the above range, the second cathode active material particles having a relatively small average particle diameter are filled between the spaces between the first cathode active material particles having an average particle diameter, Even when nickel is contained in a high content for the production of a high capacity cathode material, a cathode material having an excellent rolling density can be produced.

The present invention also provides a positive electrode for a lithium secondary battery comprising the positive electrode material. Specifically, the cathode for a secondary battery includes a cathode current collector, a cathode material layer formed on the cathode current collector, and the cathode material layer includes the cathode material according to the present invention.

At this time, by using a cathode material including the same first cathode active material and the second cathode active material as the above-mentioned cathode material, a cathode having a high rolling density is provided.

Since the cathode material is the same as that described above, a detailed description thereof will be omitted, and only the remaining constitution will be described in detail below.

The positive electrode current collector is not particularly limited as long as it has conductivity without causing chemical changes in the battery. For example, carbon, nickel, 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 irregularities may be formed on the surface of the current collector to increase the adhesive strength of the cathode 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 cathode material layer may include a conductive material and, optionally, a binder optionally together with the cathode material.

At this time, the cathode material may be contained in an amount of 80 to 99% by weight, more specifically 85 to 98.5% by weight based on the total weight of the anode 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; Carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, summer black and carbon fiber; Metal powder or metal fibers such as copper, nickel, aluminum and silver; Conductive whiskey 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 contained in an amount of 0.1 to 15% by weight based on the total weight of the cathode material layer.

The binder serves to improve the adhesion between the cathode material particles and the adhesion between the anode 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 0.1 to 15% by weight based on the total weight of the anode material layer.

The positive electrode may be produced according to a conventional positive electrode manufacturing method, except that the positive electrode material is used. Specifically, a cathode active material composition prepared by dissolving or dispersing the above-described cathode material and optionally a binder and a conductive material in a solvent may be coated on the cathode current collector, followed by drying and rolling. At this time, the cathode material according to the present invention has a high rolling density, so that even if compressed with a strong force of 400 kgf to 2000 kgf, the first cathode active material and the second cathode active material contained in the cathode material do not break As a result, it is possible to provide a positive electrode having improved stability.

Examples of the solvent include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, and the like. Water and the like, and one kind or a mixture of two or more kinds can be used. The amount of the solvent to be used is sufficient to dissolve or disperse the cathode material, the conductive material and the binder in consideration of the coating thickness of the slurry and the production yield, and to have a viscosity capable of exhibiting excellent thickness uniformity at the time of application for cathode production Do.

Alternatively, the anode may be produced by casting the composition for forming a cathode layer on a separate support, and then laminating a film obtained by peeling the support from the support onto a cathode current collector.

In addition, the present invention can produce an electrochemical device including the positive electrode. The electrochemical device may be specifically a battery, a capacitor, or the like, and more specifically, it may be a lithium secondary battery.

Specifically, the lithium secondary battery includes a positive electrode, a negative electrode disposed opposite to the positive electrode, and a separation membrane and an electrolyte interposed between the positive electrode and the negative electrode. The positive electrode is the same as that described above, Only the remaining configuration will be described in detail below.

The lithium secondary battery may further include a battery container for housing the electrode assembly of the anode, the cathode, and the separator, and a sealing member for sealing the battery container.

The lithium secondary battery according to the present invention uses a positive electrode material having a high rolling density and a low residual lithium to provide a lithium secondary battery having a high rolling rate and improved lifetime characteristics and reduced gas generation amount can do.

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

The anode active material layer optionally includes a binder and a conductive material together with the anode active material.

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 capable of doping and dedoping lithium such as SiO? (0 <? <2), SnO ₂ , vanadium oxide, and lithium vanadium oxide; 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).

The negative electrode active material may include 80% by weight to 99% by weight based on the total weight of the negative electrode active material layer.

The binder is a component for assisting the bonding between the conductive material, the active material and the current collector, and is usually added in an amount of 0.1% by weight to 10% by weight based on the total weight of the negative electrode active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene Examples thereof include ethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluorine rubber and various copolymers thereof.

The conductive material may be added in an amount of 10 wt% or less, preferably 5 wt% or less, based on the total weight of the negative electrode active material layer, as a component for further improving the conductivity of the negative electrode active material. Such a conductive material is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery, for example, graphite such as natural graphite or artificial graphite; Carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskey such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used.

For example, the negative electrode active material layer is prepared by applying and drying a composition for forming a negative electrode active material layer, which is prepared by dissolving or dispersing a negative electrode active material on a negative electrode current collector, and optionally a binder and a conductive material in a solvent, Casting a composition for forming an active material layer on a separate support, and then laminating a film obtained by peeling from the support onto a negative electrode current collector.

The negative electrode active material layer may be formed by applying and drying a composition for forming a negative electrode active material layer prepared by dissolving or dispersing a negative electrode active material on a negative electrode collector and optionally a binder and a conductive material in a solvent, Casting the composition on a separate support, and then peeling the support from the support to laminate a film on the negative electrode current collector.

Meanwhile, in the lithium secondary battery, the separation membrane separates the cathode and the anode and provides a passage for lithium ion. The separation membrane can be used without any particular limitation as long as it is used as a separation membrane in a lithium secondary battery. Particularly, It is preferable to have a low resistance and an excellent 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 the separator may be selectively used as a single layer or a multilayer structure.

Examples of the electrolyte used in the present invention include an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, and a molten inorganic electrolyte that can be used in the production of a lithium secondary battery. It is not.

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. Specific examples of the organic solvent include methyl acetate, ethyl acetate,? -Butyrolactone,? -Caprolactone,? -Valerolactone,? Ester solvents such as valerolactone, dimethoxyethane, diethoxyethane methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate and butyl propionate; 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; R-CN (R is a linear, branched or cyclic hydrocarbon group having 2 to 20 carbon atoms, which may contain a double bond aromatic ring or an 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 about 1: 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 in the range of 0.1 to 2.0 M. 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 further include an additive 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, in addition to the electrolyte components, if necessary. For example, the additive may be a haloalkylene carbonate compound such as difluoroethylene carbonate, vinylene carbonate (VC), 1,3-propane sultone (PS), pyridine, triethylphosphite, triethanolamine, cyclic ether , Ethylenediamine, glyme, hexametriamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N, N-substituted imidazolidines, ethylene glycol dialkyl ethers, One or more additives such as an ammonium salt, pyrrole, 2-methoxyethanol or aluminum trichloride may be further included. 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, since the lithium secondary battery including the cathode material according to the present invention stably exhibits excellent discharge capacity, output characteristics and life characteristics, it can be applied to portable devices such as mobile phones, notebook computers, digital cameras, and hybrid electric vehicles hybrid electric vehicle (HEV)).

According to another embodiment of the present invention, there is provided a battery module including the lithium secondary battery as a unit cell and a battery pack including the same.

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.

The external shape of the lithium secondary battery of the present invention is not particularly limited, but may be a cylindrical shape, a square shape, a pouch shape, a coin shape, or the like using a can.

The lithium secondary battery according to the present invention can be used not only in a battery cell used as a power source of a small device but also as a unit cell in a middle- or large-sized battery module including a plurality of battery cells.

Hereinafter, the present invention will be described in detail by way of examples with reference to the following examples. However, the embodiments according to the present invention can be modified into various other forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. The embodiments of the present invention are provided to enable those skilled in the art to more fully understand the present invention.

Example

Example  One

Ni _{0 & lt ; /} RTI &gt; having an average particle diameter (D ₅₀ ) of 12 μm as the first cathode active material precursor _{. 5} Co _{0 . 2} Mn _{0 .3} (OH) ₂ and Li ₂ CO ₃ 1: 1.02 were mixed in a molar ratio, and calcining at 920 ℃ for 10 hours, the average particle diameter (D ₅₀₎ is 12㎛ the first positive electrode active material (LiNi _{0. 5 Co 0. 2 Mn 0.} 3 O 2) was prepared.

Next, as a second cathode active material precursor, Ni _0.5 Co _0.2 Mn _0.3 (OH) ₂ having an average particle diameter (D ₅₀ ) of 6 μm and Li ₂ CO ₃ were mixed at a molar ratio of 1: 1.02 and calcined at 960 ° C. for 10 hours to prepare a mean particle size (D ₅₀₎ is 6.4㎛ the second positive electrode active material _{(LiNi 0. 5 Co 0.} 2 Mn 0. 3 O 2).

The first cathode active material and the second cathode active material prepared above were mixed at a weight ratio of 7: 3 to prepare a cathode material for a secondary battery.

The cathode material, the carbon black conductive material, and the PVdF binder prepared above were mixed at a weight ratio of 96: 2: 2 and mixed in an NMP solvent to prepare a composition for forming an anode. The composition for forming an anode was applied to an aluminum foil having a thickness of 12 占 퐉, dried, and rolled to produce a positive electrode.

On the other hand, graphite, a carbon conductive material (SuperC65) and a PVdF binder were mixed as a negative electrode active material at a weight ratio of 95.6: 0.75: 3.65, and this was added to NMP as a solvent to prepare a negative electrode composition. The composition for forming an anode was coated on a copper foil having a thickness of 20 占 퐉, dried, and then rolled to produce a negative electrode.

The positive electrode and the negative electrode prepared above were laminated together with a polyolefin separator to produce an electrode assembly. The electrode assembly was placed in a battery case and mixed with 100 parts by weight of a mixed solvent of ethylene carbonate: propyl propionate: diethyl carbonate in a ratio of 3: 1: 6 An electrolyte solution in which 1 M of LiPF ₆ , 0.5 part of vinylene carbonate (VC) and 1.0 part of 1-3 of propane sultone (PS) had been dissolved was injected into a lithium secondary battery.

Example  2

A first cathode active material having an average particle diameter of _{11㎛ (LiNi 0. 5 Co 0} . 3 Mn 0. 2 O 2) and the second cathode active material having an average particle diameter of _{6.8㎛ (LiNi 0. 5 Co 0} . 3 Mn 0. 2 O ₂ ) was used as a positive electrode material, and a lithium secondary battery including the positive electrode material for a secondary battery was prepared.

Comparative Example  One

A cathode material and a lithium secondary battery including the cathode material were prepared in the same manner as in Example 1, except that the second cathode active material was prepared by firing at 920 ° C for 10 hours in the production of the second cathode active material.

Comparative Example  2

A cathode material and a lithium secondary battery including the cathode material were prepared in the same manner as in Example 1, except that only 100% of the first cathode active material prepared in Example 1 was used.

Comparative Example  3

A cathode material and a lithium secondary battery including the cathode material were prepared in the same manner as in Example 1, except that only 100% of the second cathode active material prepared in Example 1 was used.

Experimental Example  1: Rolling density measurement

Example 1 and Comparative Example 2 A positive electrode material prepared in 2-3 (the area of the die: 3.14 cm ^2), respectively, using the rolling density meter (HPRM-1000, hantek社, Korea) 400kgf, 800kgf, 1200kgf, 1600kgf , And a rolling force of 2,000 kgf at the time of rolling were measured, which is shown in Fig.

As shown in Fig. 1, Comparative Example 2 is a comparative example in which the average particle diameter (D ₅₀₎ includes only the under-6.4㎛ St. the small particle size cathode active material including only the average particle diameter (D ₅₀₎ 12㎛ substituted diameter of the positive electrode active material 3 shows excellent rolling density over the entire pressure range. This is because it is easy to obtain a higher rolling density as the particle size is larger.

Also, as in Example 1, when the first positive electrode active material and the second positive electrode active material having a small particle diameter were mixed, the rolling density was improved as the first and second positive electrode active materials were formed in a bimodal form . Specifically, the second positive electrode active material particles filled in the gap between the void spaces between the first positive electrode active material particles of the larger diameter improved the rolling density of Comparative Example 2 and Comparative Example 3.

Experimental Example  2: Determination of life characteristics of lithium secondary battery

The life characteristics of the lithium secondary batteries produced in Example 1 and Comparative Example 1 were measured.

Specifically, each of the lithium secondary batteries prepared in Example 1 and Comparative Example 1 was charged at a constant current of 0.7 C at a room temperature of 25 캜 to a voltage of 4.35 V at a cut off of 0.05 C. Thereafter, discharging was performed until the voltage reached 3.0 V at a constant current of 0.5C. The charging and discharging behaviors were set as one cycle. After repeating this cycle 135 times, the life characteristics of the lithium secondary battery according to Example 1 and Comparative Example 1 were measured.

As shown in FIG. 2, the lifetime characteristics of the secondary battery of Example 1, which was overheated at a high temperature of 930 ° C or higher in the production of the second cathode active material, were superior to those of Comparative Example 1 in which the second cathode active material was fired at a relatively low temperature. This is because, in the case of the secondary battery manufactured in Example 1, when the second cathode active material is fired at a high temperature of 930 DEG C or higher in the production of the second cathode active material, excellent rolling density can be obtained by using the second cathode active material having a high mechanical strength. The generation of fine particles in the electrode which deteriorates the life characteristic is suppressed. The falling peak near 20 cycles in the graph of FIG. 2 is an error as the condition in the laboratory unit is changed at the time of measurement.

Experimental Example  3: Confirmation of gas generation amount of lithium secondary battery

The amount of gas generated in each of the lithium secondary batteries manufactured in Example 1 and Comparative Example 1 was confirmed.

Specifically, each of the lithium secondary batteries prepared in Example 1 and Comparative Example 1 was charged at 0.7 C to 4.35 V, and then stored at 60 ° C. for 3 weeks. After storing for 3 weeks, the amount of gas generated in the cell was measured and shown in FIG.

As shown in FIG. 3, it was confirmed that a smaller amount of gas was generated in the case of the secondary battery of Example 1, which was over-heated at a high temperature of 930 ° C or higher in the production of the second cathode active material. This is because, in the case of Example 1, the residual lithium amount on the surface of the second cathode active material was decreased by the inclusion of the second cathode active material which was underreduced, thereby reducing the side reaction with the electrolyte.

Claims (9)

A first cathode active material having an average particle diameter (D ₅₀ ) of 10 탆 or more and a second cathode active material having an average particle diameter (D ₅₀ ) of 4 탆 to 8 탆,
Wherein the first cathode active material and the second cathode active material each independently comprise lithium nickel cobalt manganese oxide having a nickel content of 50 mol% or more based on the total moles of transition metals excluding lithium,
Wherein the second cathode active material has a single particle form.
The method according to claim 1,
Wherein the first cathode active material and the second cathode active material each independently comprise a lithium nickel cobalt manganese oxide represented by the following formula 1:
[Chemical Formula 1]
Li _{1 + a} Ni _x Co _y Mn _(1-xy) O ₂
In Formula 1,
-0.1? A? 0.1, 0.5? X? 0.8, 0.1? Y? 0.4, 0.6? X + y? 0.9.
The method according to claim 1,
Wherein the first cathode active material and the second cathode active material are contained in a weight ratio of 9: 1 to 6: 4.
The method according to claim 1,
Wherein the cathode material has a rolling density of 2.75 g / cc to 3.2 g / cc upon rolling at a force of 400 kgf to 2,000 kgf.
Preparing a first cathode active material by calcining a nickel-cobalt manganese hydroxide precursor having an average particle diameter (D ₅₀ ) of 10 μm or more and a lithium-containing raw material at a temperature lower than 800 ° C. to 930 ° C.;
Preparing a nickel cobalt manganese hydroxide precursor having an average particle diameter (D ₅₀ ) of 4 탆 to 8 탆 and a lithium-containing raw material under a temperature of 930 캜 to 1,000 캜 to prepare a second cathode active material having a single particle form; And
And mixing the first cathode active material and the second cathode active material.
6. The method of claim 5,
Wherein the nickel cobalt manganese hydroxide precursor is represented by the following formula (2): < EMI ID =
(2)
[Ni _x1 Co _y1 Mn _(1-x1-y1) ] (OH) ₂
In Formula 2,
0.5? X1? 0.8, 0 <y1? 0.4, 0.6? X1 + y1? 0.9.
6. The method of claim 5,
Wherein the first cathode active material and the second cathode active material are mixed at a weight ratio of 9: 1 to 6: 4.
A positive electrode for a lithium secondary battery, comprising the positive electrode material according to any one of claims 1 to 4.
A lithium secondary battery comprising the positive electrode according to claim 8.

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