阅读说明：本技术 制备二次电池用正极活性材料的方法 (Method for preparing positive electrode active material for secondary battery ) 是由 李银熙 金成培 朴英洙 林一朗 于 2019-06-07 设计创作，主要内容包括：本发明涉及一种制备二次电池用正极活性材料的方法,所述方法包括以下步骤：提供包含核部和壳部的正极活性材料前体,其中所述核部包含镍(Ni)、钴(Co)和锰(Mn),并且所述壳部包含钴(Co)并且围绕所述核部；以及通过将所述正极活性材料前体与锂原料混合以获得混合物并在970℃以上的温度下烧制所述混合物来形成单粒子形式的锂复合过渡金属氧化物。(The present invention relates to a method for preparing a positive electrode active material for a secondary battery, the method comprising the steps of: providing a positive active material precursor including a core portion and a shell portion, wherein the core portion includes nickel (Ni), cobalt (Co), and manganese (Mn), and the shell portion includes cobalt (Co) and surrounds the core portion; and forming a lithium composite transition metal oxide in a single particle form by mixing the positive electrode active material precursor with a lithium raw material to obtain a mixture and firing the mixture at a temperature of 970 ℃ or higher.)

1. A method of preparing a positive electrode active material for a secondary battery, the method comprising the steps of:

providing a positive active material precursor including a core portion and a shell portion, wherein the core portion includes nickel (Ni), cobalt (Co), and manganese (Mn), and the shell portion includes cobalt (Co) and surrounds the core portion;

forming a lithium composite transition metal oxide in a single particle form by mixing the positive electrode active material precursor with a lithium raw material to obtain a mixture and firing the mixture at a temperature of 970 ℃ or higher.

2. The method for preparing a positive electrode active material for a secondary battery according to claim 1, wherein the firing temperature is 980 ℃ to 1050 ℃.

3. The method of preparing a positive electrode active material for a secondary battery according to claim 1, wherein the core part is formed by Co-precipitating a first transition metal solution including nickel (Ni), cobalt (Co), and manganese (Mn).

4. The method of preparing a positive active material for a secondary battery according to claim 1, wherein the shell part is formed by Co-precipitating a second transition metal solution including cobalt (Co).

5. The method of preparing a cathode active material for a secondary battery according to claim 1, wherein the shell portion has 5 parts by volume to 30 parts by volume based on 100 parts by volume of the cathode active material precursor.

6. The method for producing a positive electrode active material for a secondary battery according to claim 1, wherein the positive electrode active material precursor is in the form of secondary particles in which primary particles are aggregated.

7. The method of preparing a positive electrode active material for a secondary battery according to claim 1, wherein the positive electrode active material precursor has a nickel (Ni) content of 60 mol% or less in the entire transition metal, and a cobalt (Co) content is greater than a manganese (Mn) content.

8. The method for producing a positive electrode active material for a secondary battery according to claim 1, wherein the firing is performed in such a manner that the positive electrode active material contains primary particles having an average particle diameter (D50) of 2 μm to 10 μm.

9. The method of producing a positive electrode active material for a secondary battery according to claim 1, wherein the firing is performed in such a manner that the positive electrode active material has a crystallite size of 210nm or more.

10. The method for producing a positive electrode active material for a secondary battery according to claim 1, wherein the lithium raw material is mixed in such a manner that a molar ratio (Li/M) of lithium (Li) in the lithium raw material to all metal elements (M) contained in the lithium composite transition metal oxide is 1.06 or less.

11. The method for preparing a positive electrode active material for a secondary battery according to claim 1, further comprising the steps of: forming a coating part by mixing a coating material with the lithium composite transition metal oxide and heat-treating, the coating material including at least one selected from the group consisting of: al, B, Zr, Ti, Mg, Ta, Nb, Mo, W and Cr.

Technical Field

Cross Reference to Related Applications

This application claims the benefit of korean patent application No. 10-2018-0065528, filed by the korean intellectual property office at 7.6.2018, the disclosure of which is incorporated herein by reference in its entirety.

Background

In recent years, with the rapid spread of electronic devices using batteries, such as mobile phones, laptop computers, electric vehicles, and the like, the demand for secondary batteries that are small in size, light in weight, and relatively high in capacity has rapidly increased.

In a state where an organic electrolyte or a polymer electrolyte is filled between a positive electrode and a negative electrode made of an active material capable of intercalating and deintercalating lithium ions, the lithium secondary battery generates electric energy through oxidation and reduction reactions while lithium ions are intercalated into and deintercalated from the positive electrode and the negative electrode.

As a positive electrode active material of a lithium secondary battery, lithium cobalt oxide (LiCoO) is used₂) Lithium nickel oxide (LiNiO)₂) Lithium manganese oxide (LiMnO)₂Or LiMn₂O₄) Lithium iron phosphate compound (LiFePO)₄) And the like. Among them, lithium cobalt oxide (LiCoO)₂) Due to high working voltage and excellent capacityThe advantage of the quantity characteristic is widely used and is used as a positive electrode active material for high voltage. However, there is a limitation in large-scale use as a power source in fields such as electric vehicles due to rising prices and unstable supply of cobalt (Co). Therefore, a need has arisen to develop a positive electrode active material capable of overcoming such a limitation.

Therefore, a nickel-cobalt-manganese-based lithium composite transition metal oxide (hereinafter, simply referred to as "NCM-based lithium composite transition metal oxide") in which a part of Co is replaced with nickel (Ni) and manganese (Mn) has been developed. However, the conventionally developed NCM-based lithium composite transition metal oxide in the form of secondary particles in which primary particles are aggregated has limitations of large specific surface area, low particle strength, large gas generation during battery operation due to high content of lithium by-products, and low stability. In other words, the conventionally developed NCM-based lithium composite transition metal oxide is limited in use for a high voltage battery because stability thereof cannot be ensured. Therefore, there is still a need to develop a positive electrode active material containing an NCM-based lithium composite transition metal oxide that can be applied to a high-voltage lithium secondary battery.

Disclosure of Invention

Technical problem

The present invention relates to a method for preparing a positive electrode active material containing an NCM-based lithium composite transition metal oxide, which can be applied to a high-voltage lithium secondary battery. In particular, the present invention provides a method for preparing a positive active material containing an NCM-based lithium composite transition metal oxide, which can reduce a specific surface area, improve particle strength, and reduce the amount of gas generation in battery operation by reducing the content of lithium by-products.

In addition, when the cathode material in the form of single particles is prepared by firing at high temperature, there is a limitation such that disintegration is difficult due to strong cohesive force between particles. The present invention provides a method of preparing a positive active material that can overcome such a limitation.

Technical scheme

The present invention provides a method for preparing a positive electrode active material for a secondary battery, the method comprising the steps of: providing a positive active material precursor including a core portion and a shell portion, wherein the core portion includes nickel (Ni), cobalt (Co), and manganese (Mn), and the shell portion includes cobalt (Co) and surrounds the core portion; forming a lithium composite transition metal oxide in a single particle form by mixing the positive electrode active material precursor with a lithium raw material to obtain a mixture and firing the mixture at a temperature of 970 ℃ or higher.

Advantageous effects

The NCM-based positive active material prepared according to the present invention can reduce the specific surface area, improve the particle strength, and reduce the amount of gas generation in the battery operation by reducing the content of lithium by-products. The NCM-based positive electrode active material according to the present invention can ensure excellent stability, and thus can be applied to a high-voltage lithium secondary battery.

Further, according to the present invention, it is possible to easily prepare a single-particle-form NCM-based positive electrode active material by firing only once, and it is possible to improve the degree of disintegration of particles, and thus it is possible to improve productivity and processing easiness, although the single-particle-form particles are prepared by firing at high temperature.

Drawings

Fig. 1 to 4 are Scanning Electron Microscope (SEM) photographs (enlarged for observation) showing the positive electrode active materials prepared in example 1 and comparative example 1 after disintegration.

Fig. 5 is a graph showing changes in particle size before and after pressurization of the positive electrode active materials prepared in example 1 and comparative example 1.

Detailed Description

Hereinafter, the present invention will be described in more detail to allow the present invention to be more clearly understood. Here, it should be understood that the words or terms used in the specification and claims should not be construed as meaning defined in a general dictionary. It should be further understood that the words or terms should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and technical idea of the invention, based on the principle that the inventor can appropriately define the meaning of the words or terms to best explain the present invention.

<Method for preparing positive electrode active material>

The method for preparing the positive active material for the secondary battery of the present invention comprises the steps of: providing a positive active material precursor including a core portion and a shell portion, wherein the core portion includes nickel (Ni), cobalt (Co), and manganese (Mn), and the shell portion includes cobalt (Co) and surrounds the core portion; forming a lithium composite transition metal oxide in a single particle form by mixing the positive electrode active material precursor with a lithium raw material to obtain a mixture and firing the mixture at a temperature of 970 ℃ or higher.

A method of preparing the positive electrode active material will be described in detail step by step.

First, a positive active material precursor including a core portion and a shell portion is provided, wherein the core portion includes nickel (Ni), cobalt (Co), and manganese (Mn), and the shell portion includes cobalt (Co) and surrounds the core portion.

The core portion may be formed by Co-precipitating a first transition metal solution including nickel (Ni), cobalt (Co), and manganese (Mn), and the shell portion may be formed by Co-precipitating a second transition metal solution including cobalt (Co).

More specifically, the core portion of the precursor may be generated by a coprecipitation reaction by adding a complexing agent containing ammonium cations and a basic compound to a first transition metal solution having a nickel-containing raw material, a cobalt-containing raw material, and a manganese-containing raw material.

The nickel-containing raw material may be, for example, nickel-containing acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide or oxyhydroxide, and specifically may be Ni (OH)₂、NiO、NiOOH、NiCO₃·2Ni(OH)₂·4H₂O、NiC₂O₂·2H₂O、Ni(NO₃)₂·6H₂O、NiSO₄、NiSO₄·6H₂O, nickel salts of fatty acids, nickel halides, or combinations thereof, but is not limited thereto.

The cobalt-containing material may be, for example, cobalt-containing acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide, oxyhydroxide, or the likeAnd may be, specifically, Co (OH)₂、CoOOH、Co(OCOCH₃)₂·4H₂O、Co(NO₃)₂·6H₂O、CoSO₄、Co(SO₄)₂·7H₂O or a combination of the above materials, but 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, and specifically, may be: oxides of manganese, e.g. Mn₂O₃、MnO₂And Mn₃O₄(ii) a Manganese salts, e.g. MnCO₃、Mn(NO₃)₂、MnSO₄Manganese acetate, manganese dicarboxylate, manganese citrate, and manganese fatty acid salt; manganese oxyhydroxide; manganese chloride; or combinations of the above materials, but are not limited thereto.

The first transition metal solution may be produced by adding a nickel-containing raw material, a cobalt-containing raw material, and a manganese-containing raw material to a solvent, specifically, water or a mixed solvent of water and an organic solvent (e.g., alcohol, etc.) that can be uniformly mixed with water, or may be produced by mixing an aqueous solution of a nickel-containing raw material, an aqueous solution of a cobalt-containing raw material, and an aqueous solution of a manganese-containing raw material.

The complexing agent for the ammonium cation may be, for example, NH₄OH、(NH₄)₂SO₄、NH₄NO₃、NH₄Cl、CH₃COONH₄、(NH₄)₂CO₃Or combinations of the above materials, but are not limited thereto. On the other hand, the complexing agent containing an ammonium cation may be used in the form of an aqueous solution, and here, water or a mixture of water and an organic solvent (specifically, alcohol or the like) which can be uniformly mixed with water may be used as the solvent.

The basic compound may be: hydroxides of alkali metals or alkaline earth metals, e.g. NaOH, KOH or Ca (OH)₂(ii) a A hydrate thereof; or combinations of the above materials. The basic compound may be used in the form of an aqueous solution, and here, water or a mixture of water and an organic solvent (specifically, alcohol or the like) which can be uniformly mixed with water may be usedThe product is used as a solvent.

The basic compound is added to adjust the pH of the reaction solution, and may be added in an amount such that the pH of the metal solution becomes 10 to 12.5.

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

Through the above process, nickel-cobalt-manganese hydroxide particles are generated and precipitated in the reaction solution.

Thereafter, in order to form the shell portion around the core portion, a coprecipitation reaction may be performed by adding a second transition metal solution having a cobalt-containing raw material, a complexing agent containing ammonium cations, and an alkaline compound to the nickel-cobalt-manganese hydroxide.

The cobalt-containing raw material may be, for example, cobalt-containing acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide or oxyhydroxide, and specifically may be Co (OH)₂、CoOOH、Co(OCOCH₃)₂·4H₂O、Co(NO₃)₂·6H₂O、CoSO₄、Co(SO₄)₂·7H₂O or a combination of the above materials, but not limited thereto.

The second transition metal solution may be produced by adding a cobalt-containing raw material to a solvent, specifically water or a mixed solvent of water and an organic solvent (e.g., alcohol, etc.) that can be uniformly mixed with water.

The description of the complexing agent containing an ammonium cation and the basic compound is the same as that given in the formation of the core portion, and therefore, it is omitted.

The basic compound in the formation of the shell portion may be added in an amount such that the pH of the metal solution becomes 10 to 12.5.

On the other hand, the coprecipitation reaction in the formation of the shell portion may be performed at a temperature of 40 ℃ to 70 ℃ under an inert atmosphere such as nitrogen or argon.

Through the above process, particles including a nickel cobalt manganese hydroxide core portion and a cobalt hydroxide shell portion are generated and precipitated in the reaction solution. The positive electrode active material precursor can be obtained by separating and drying the precipitated particles by a conventional method.

The thus-produced positive active material precursor forms a core-shell structure including a core portion and a shell portion, wherein the core portion includes nickel (Ni), cobalt (Co), and manganese (Mn), and the shell portion includes cobalt (Co).

In the case of conventional particles in the form of single particles prepared by firing at high temperature, there are problems such as difficulty in disintegration due to strong cohesive force between particles. Since particles in the form of a single particle are prepared by using a positive electrode active material of a core-shell structure formed of a shell portion containing cobalt (Co) on a core portion, the present invention can improve the disintegration degree to increase the ease of processing. In other words, according to the present invention, although particles in the form of single particles are prepared by high-temperature firing, it is possible to widen the range of usable crushers and to improve productivity. In addition, the content of lithium by-products can be further reduced.

Here, the shell portion may be formed to have 5 to 30 parts by volume based on 100 parts by volume of the cathode active material precursor. More preferably, the shell portion may be formed to have 5 to 20 parts by volume, more preferably 5 to 15 parts by volume. In the formation of the shell section, the shell section may be prepared to have a weight ratio within the above-described range by controlling the concentration of the second transition metal solution and the coprecipitation time of the coprecipitation reaction. By forming in such a manner that the weight ratio of the shell portion is within the above range, the effects of reducing the lithium by-product content and improving the disintegration degree can be achieved.

On the other hand, the cathode active material precursor may be prepared to have a composition in which a nickel (Ni) content is 60 mol% or less in the entire transition metal and a cobalt (Co) content is greater than a manganese (Mn) content. Here, the composition may be based on the entire composition of the precursor containing the core/shell portion. In preparing the precursor, the precursor may be prepared to have the above-described composition by controlling the concentrations of the nickel-containing raw material, the cobalt-containing raw material, and the manganese-containing raw material, and the coprecipitation time of the core/shell portions. More preferably, the nickel (Ni) content may be 55 mol% or less, more preferably 50 mol% or less. In addition, more preferably, the cobalt (Co) content may be higher than manganese (Mn) by at least 5 mol%, and more preferably, the cobalt (Co) content may be higher than manganese (Mn) by at least 10 mol%. If the positive electrode active material satisfying the above composition is used, the NCM-based positive electrode active material in the form of single particles can be easily formed by firing only once at a temperature of 970 ℃ or higher.

The precursor of the positive electrode active material prepared in the same manner as described above is in the form of secondary particles in which primary particles are aggregated, and the average particle diameter (D) of the secondary particles of the precursor₅₀) May be 3 μm to 8 μm, more preferably 3 μm to 7 μm, further preferably 3 μm to 6 μm. In the present invention, "primary particles" refer to a single-particle primary structure, and "secondary particles" refer to an aggregate, i.e., a secondary structure, in which primary particles are aggregated by physical or chemical bonding of the primary particles without an intentional aggregation or assembly step for the primary particles constituting the secondary particles.

Next, the positive electrode active material precursor and the lithium raw material are mixed, and the resulting mixture is fired at a temperature of 970 ℃ or higher to form the lithium composite transition metal oxide in a single particle form. The NCM-based positive electrode active material in the form of single particles thus prepared may allow a reduction in specific surface area, an increase in particle strength, and a reduction in gas generation amount in battery operation by reducing the lithium byproduct content. In addition, the NCM-based positive electrode active material prepared according to the present invention can ensure excellent stability, and thus can be applied to a high-voltage lithium secondary battery.

As the lithium raw material, sulfate, nitrate, acetate, carbonate, oxalate, citrate, halide, hydroxide, oxyhydroxide, or the like containing lithium may be used, and the lithium raw material is not particularly limited as long as it can be dissolved in water. Specifically, the lithium source may be Li₂CO₃、LiNO₃、LiNO₂、LiOH、LiOH·H₂O、LiH、LiF、LiCl、LiBr、LiI、CH₃COOLi、Li₂O、Li₂SO₄、CH₃COOLi or Li₃C₆H₅O₇And the like, and any one of the above materials or a mixture of two or more thereof may be used.

The lithium raw material may be mixed so that the molar ratio (Li/M) of lithium (Li) in the lithium raw material to all metal elements (M) contained in the lithium composite transition metal oxide is 1.06 or less. More preferably, the lithium raw material may be mixed in such a manner that Li/M is 1 to 1.05, more preferably 1 to 1.04. When Li/M satisfies this range, a lithium composite transition metal oxide in a single particle form and having a layered crystal structure represented by a space group of R3M can be formed.

By mixing the positive electrode active material with the lithium raw material and firing the resulting mixture at a temperature of 970 ℃ or higher, it is possible to easily form the NCM-based positive electrode active material in the form of single particles by firing only once. In other words, although the precursor is in the form of secondary particles, in the case of firing under specific conditions using the precursor according to the present invention, a single particle form and an average particle diameter (D) of primary particles can be prepared by the firing process₅₀) 2 μm to 10 μm of an NCM-based positive electrode active material. Further, there has been a problem that it is difficult to perform disintegration when a cathode material is prepared by high-temperature firing, and the present invention can improve the disintegration degree of a cathode material in the form of a single particle prepared by using a precursor of a core-shell structure including a shell portion containing cobalt (Co) in the same manner as described above. On the other hand, in order to prepare a single-particle type NCM-based positive electrode active material, since the composition including the concentration gradient of nickel (Ni), cobalt (Co), and manganese (Mn) becomes uniform, the cobalt (Co) shell portion of the precursor disappears by undergoing a firing process at a temperature of 970 ℃ or higher, and thus the finally prepared lithium composite transition metal oxide positive electrode active material may not have a core-shell structure.

The firing temperature may preferably be 970 ℃ or more to form a single particle, and the firing temperature is more preferably 980 ℃ to 1050 ℃, and further preferably 980 ℃ to 1020 ℃. If the firing temperature is less than 970 ℃, it may be difficult to prepare a single-particle type of NCM-based positive electrode active material, and an NCM-based positive electrode active material in the form of aggregated secondary particles may be prepared.

Firing may be performed under an atmosphere of air or oxygen, and may be performed for 5 hours to 13 hours.

The primary particles of the single-particle type NCM-based positive electrode active material prepared may have an average primary particle diameter (D) of 2 to 10 μm₅₀) Firing is performed in the manner described above. More preferably, the average particle diameter (D) of the primary particles may be made such that₅₀) Firing is performed in a manner of 3 μm to 9 μm, more preferably 4 μm to 8 μm. The single-particle type positive electrode active material has the average primary particle diameter (D)₅₀) In the case of (2), the particle strength may be increased to suppress particle breakage during rolling processing, the rolling density may be improved, the specific surface area may be reduced, and the amount of gas generated due to a side reaction with the electrolyte may be reduced because the lithium by-product is reduced.

In the present invention, the average particle diameter (D) may be₅₀) As the particle size corresponding to 50% volume accumulation in the particle size distribution curve. The average particle diameter (D) can be measured using, for example, a laser diffraction method₅₀). For example, the average particle diameter (D) for measuring the positive electrode active material may be prepared in the following manner₅₀) The method of (1): the positive electrode active material particles were dispersed in a dispersion medium, and then the dispersed positive electrode active material particles were introduced into a commercially available laser diffraction particle size measuring instrument (e.g., Microtrac MT 3000), the dispersed positive electrode active material particles were irradiated with an ultrasonic wave of about 28kHz at an output of 40W, and an average particle diameter (D) corresponding to 50% cumulative volume was calculated in the measuring instrument₅₀)。

Further, firing may be performed so that the single-particle type NCM-based positive electrode active material has a crystallite size of 210nm or more. More preferably, firing may be performed so that the single-particle type NCM-based positive electrode active material has a crystallite size of 215nm or more, more preferably 220nm or more. The cathode active material satisfying the crystallite size according to the embodiment of the present invention can suppress particle breakage caused by roll processing, and can improve the life characteristics and stability.

In the present invention, "particles" refer to particles in units of micrometers, and when the particles are observed at a magnified scale, "grains" having a crystal shape of several tens of nanometers can be resolved. If the particles are viewed at a further enlarged scale, it can be seen that the atoms form partitions of the lattice structure in a particular direction, said partitions being called "crystallites". The size of the particles observed by XRD is defined as the crystallite size. The method for measuring the crystallite size can estimate the crystallite size by using the peak broadening of XRD data, and can quantitatively calculate the crystallite size by Scherrer's formula.

Next, optionally, the coating portion may be formed by mixing the lithium composite transition metal oxide with a coating raw material containing at least one element selected from the group consisting of: al, B, Zr, Ti, Mg, Ta, Nb, Mo, W and Cr. The coating raw material may more preferably contain Al, B and/or W, and further preferably contain Al. In the case of a coating material, for example, Al (OH) can be used₃、Al₂O₃、AlPO₄、AlCl₃、Al₂(SO₄)₃And the like.

The heat treatment may be performed at a temperature of 300 ℃ to 700 ℃, more preferably 400 ℃ to 600 ℃. The heat treatment may be performed for 1 hour to 6 hours.

By further forming the coating portion, lithium by-products on the particle surface are reduced, and the amount of gas generation in the battery operation can be further reduced.

<Positive electrode and secondary battery>

A positive electrode for a lithium secondary battery and a lithium secondary battery may be manufactured by using the positive electrode active material prepared according to one embodiment of the present invention.

Specifically, the positive electrode includes a positive electrode current collector and a positive electrode active material layer that is formed on the positive electrode current collector and includes a positive electrode active material.

In the positive electrode, the positive electrode current collector is not particularly limited as long as it has conductivity without causing chemical changes in the battery, and for example: stainless steel; aluminum; nickel; titanium; firing carbon; or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like. In addition, the positive electrode current collector may generally have a thickness of 3 to 500 μm, and fine irregularities may be formed on the surface of the positive electrode current collector to improve adhesion of the positive electrode active material. For example, various shapes of the positive electrode current collector such as a film, a sheet, a foil, a mesh, a porous body, a foam, a nonwoven fabric body, and the like can be used.

Further, the positive electrode active material layer may include a conductive material and a binder in addition to the above-described positive electrode active material.

In this case, a conductive material is used to provide conductivity to the electrode, wherein any conductive material may be used without particular limitation so long as it has conductivity and does not cause chemical changes in the battery constituted. Specific examples of the conductive material may be: graphite such as natural graphite or artificial graphite, etc.; carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber, and the like; powders or fibers of metals such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide whiskers and potassium titanate whiskers, and the like; conductive metal oxides such as titanium oxide and the like; or a conductive polymer such as a polyphenylene derivative or the like, and one of the above materials or a mixture of two or more thereof may be used. The conductive material may be generally included in an amount of 1 to 30 wt% based on the total weight of the positive electrode active material layer.

In addition, the binder improves the adhesion between the particles of the positive electrode active material and the adhesion between the positive electrode active material and the positive electrode current collector. Specific examples of binders may be: polyvinylidene fluoride (PVDF), a vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, Ethylene Propylene Diene Monomer (EPDM), sulfonated EPDM, Styrene Butadiene Rubber (SBR), fluororubber, or various copolymers thereof, and one of the above materials or a mixture of two or more thereof may be used. The binder may be included in an amount of 1 to 30 wt% based on the total weight of the positive electrode active material layer.

The positive electrode may be manufactured according to a typical method of preparing a positive electrode, in addition to using the above-described positive electrode active material. Specifically, the composition for forming a positive electrode active material layer, which includes the above-described positive electrode active material and optionally a binder and a conductive material, may be coated on a positive electrode current collector, and then a positive electrode may be prepared by drying and roll-pressing the coated positive electrode current collector. In this case, the types and amounts of the positive electrode active material, the binder, and the conductive material are the same as those previously described.

The solvent may be a solvent generally used in the art. The solvent may include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and one of the above materials or a mixture of two or more thereof may be used. In view of the coating thickness and manufacturing yield of the slurry, the amount of the solvent used may be sufficient if the solvent can dissolve or disperse the positive electrode active material, the conductive material, and the binder, and can be allowed to have a viscosity that provides excellent thickness uniformity during the subsequent coating for preparing the positive electrode.

Further, as another method, a positive electrode may be prepared by casting the composition for forming a positive electrode active material layer on a separate support and then laminating a film separated from the support on a positive electrode current collector.

According to another embodiment of the present invention, there is provided an electrochemical device including the positive electrode. The electrochemical device may be specifically a battery or a capacitor, and more specifically may be a lithium secondary battery.

The lithium secondary battery specifically includes a positive electrode, a negative electrode facing the positive electrode, a separator provided between the positive electrode and the negative electrode, and an electrolyte, wherein the positive electrode is the same positive electrode as described above. In addition, the lithium secondary battery may further optionally include: a battery container accommodating an electrode assembly of a positive electrode, a negative electrode, and a separator; and a sealing member sealing the battery container.

In the lithium secondary battery, the anode includes an anode current collector and an anode active material layer disposed on the anode current collector.

The anode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, there may be used: copper; stainless steel; aluminum; nickel; titanium; burning the charcoal; copper or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like; and aluminum-cadmium alloys. In addition, the anode current collector may generally have a thickness of 3 to 500 μm, and similar to the cathode current collector, fine irregularities may be formed on the surface of the current collector to improve adhesion of the anode active material. For example, negative electrode current collectors of various shapes such as a film, a sheet, a foil, a mesh, a porous body, a foam, a nonwoven fabric body, and the like may be used.

The anode active material layer selectively contains a binder and a conductive material in addition to the anode active material. As one embodiment, the anode active material layer may be prepared by: the composition for forming an anode, which selectively includes a binder and a conductive material and includes an anode active material, is coated on an anode current collector and the coated anode current collector is dried, or an anode active material layer may be prepared by casting the composition for forming an anode on a separate support and then laminating a film separated from the support on the anode current collector.

As the negative electrode active material, a compound capable of reversibly intercalating and deintercalating lithium may be used. Specific examples of the anode active material may be: carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, amorphous carbon, and the like; (semi) metallic materials capable of forming an alloy with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy, Al alloy, or the like; metal oxides, e.g. SiO, which may or may not be doped with lithium_β(0<β<2)、SnO₂Vanadium oxide and lithium vanadium oxide; or a composite material containing a (semi) metal-based material and a carbonaceous material, such as a Si-C composite material or a Sn-C composite material, and either one of the above materials or a mixture of two or more thereof may be used. In addition, as the negative electrode active material, a metallic lithium thin film may be used. Further, as the carbon material, low crystalline carbon and high crystalline carbon may be used. Typical examples of the low crystalline carbon may be soft carbon and hard carbon, and typical examples of the high crystalline carbon may be irregular, planar, flakyNatural or artificial graphite in the form of spheres or fibers; condensing graphite; pyrolytic carbon; mesophase pitch-based carbon fibers; mesophase carbon microbeads; mesophase pitch; and high temperature sintered carbons such as petroleum or coal tar pitch derived coke, and the like.

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

Meanwhile, in the lithium secondary battery, a separator separates a negative electrode and a positive electrode and provides a moving path of lithium ions, wherein any separator may be used as the separator without particular limitation as long as it is generally used in the lithium secondary battery, and in particular, a separator having a high moisture-retaining ability to an electrolyte and a low resistance to migration of electrolyte ions may be desired. Specifically, it is possible to use: porous polymer films such as those made from polyolefin-based polymers (e.g., ethylene homopolymers, propylene homopolymers, ethylene/butene copolymers, ethylene/hexene copolymers, and ethylene/methacrylate copolymers), and the like; or a laminated structure having two or more layers of the above porous polymer film. In addition, a typical porous nonwoven fabric, such as a nonwoven fabric formed of high-melting glass fibers or polyethylene terephthalate fibers, may be used. In addition, a coated separator including a ceramic component or a polymer material may be used to secure heat resistance or mechanical strength, and a separator having a single-layer or multi-layer structure may be selectively used.

In addition, the electrolyte used in the present invention may include, but is not limited to, an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, a melt-type inorganic electrolyte, or the like, which may be used in the preparation of a lithium secondary battery.

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

Any organic solvent may be used as the organic solvent without particular limitation so long as it can serve as a medium through which ions participating in the electrochemical reaction of the battery can move. Specifically, the following substances may be used as the organic solvent: ester solvents such as methyl acetate, ethyl acetate, gamma-butyrolactone, and-caprolactone, etc.; ether solvents such as dibutyl ether or tetrahydrofuran, etc.; ketone solvents such as cyclohexanone, etc.; aromatic hydrocarbon solvents such as benzene and fluorobenzene, etc.; carbonate-based solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (MEC), Ethyl Methyl Carbonate (EMC), Ethylene Carbonate (EC), and Propylene Carbonate (PC); alcohol solvents such as ethanol and isopropanol, etc.; nitriles such as R-CN (where R is a linear, branched or cyclic C2-C20 hydrocarbyl group and may include double bonds, aromatic rings or ether linkages); amides such as dimethylformamide and the like; dioxolanes such as 1, 3-dioxolane and the like; or sulfolane. Among these solvents, a carbonate-based solvent may be desirable, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ion conductivity and high dielectric constant, which can improve charge and discharge characteristics of a battery, and a low-viscosity linear carbonate-based compound (e.g., ethylene methyl carbonate, dimethyl carbonate, diethyl carbonate, etc.) may be further desirable. In this case, when the cyclic carbonate and chain carbonate are present in a ratio of about 1: 1 to about 1: 9, the electrolyte may be excellent in performance when mixed.

The lithium salt may be used without particular limitation as long as it is a compound capable of providing lithium ions used in the lithium secondary battery. Specifically, as the lithium salt, LiPF may be used₆、LiClO₄、LiAsF₆、LiBF₄、LiSbF₆、LiAlO₄、LiAlCl₄、LiCF₃SO₃、LiC₄F₉SO₃、LiN(C₂F₅SO₃)₂、LiN(C₂F₅SO₂)₂、LiN(CF₃SO₂)₂LiCl, LiI or LiB (C)₂O₄)₂And the like. The lithium salt may be used in a concentration range of 0.1M to 2.0M. In the case where the lithium salt concentration is included within the above range, since the electrolyte may have appropriate conductivity and viscosity, excellent performance of the electrolyte may be obtained and lithium ions may be efficiently moved.

In addition to the electrolyte component, in order to improve the life characteristics of the battery, suppress the decrease in the battery capacity, and improve the discharge capacity of the battery, at least one additive, such as: halogenated alkylene carbonate compounds (e.g., difluoroethylene carbonate, etc.), pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, (glycidyl) glyme, hexamethylphosphoric triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, etc. In this case, the additive may be included in an amount of 0.1 to 5 wt% based on the total weight of the electrolyte.

As described above, since the lithium secondary battery including the cathode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics, and capacity retention rate, the lithium secondary battery is suitably used in the following fields: portable devices such as mobile phones, laptop computers, digital cameras, and the like; and electric vehicles such as Hybrid Electric Vehicles (HEVs) and the like; and so on.

Thus, according to another embodiment of the present invention, there are provided a battery module including the lithium secondary battery as a unit cell and a battery pack including the battery module.

The battery module or the battery pack may be used as a power source for at least one of medium-and large-sized devices: an electric tool; electric vehicles, including Electric Vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or an electrical power storage system.

Hereinafter, embodiments of the present invention will be described in detail so that those of ordinary skill in the art to which the present invention pertains can easily practice the present invention. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

[ example 1]

In a batch 40L reactor set at 50 deg.C, by passing NiSO₄、CoSO₄And MnSO₄So that the ratio of nickel: cobalt: of manganeseThe molar ratio is 57: 20: 23 were mixed in water to prepare a first transition metal solution having a concentration of 2.4M.

13 liters of deionized water was added to the coprecipitation reactor (capacity: 40L) and nitrogen was purged into the reactor at a rate of 25 liters/minute to remove dissolved oxygen from the water and create a non-oxidizing atmosphere in the reactor. Thereafter, 83g of a 25% strength aqueous NaOH solution was added thereto, and the mixture was stirred at a temperature of 50 ℃ and a stirring speed of 700rpm to maintain the pH at 11.5.

Thereafter, the first transition metal solution was separately fed at a rate of 1.9L/hr, and NaOH aqueous solution, NH were added₄An aqueous OH solution was added together therewith, and at the same time, a coprecipitation reaction was carried out for 41.8 hours to produce a core portion of nickel cobalt manganese hydroxide.

Then, by adding CoSO₄Mixed in water to prepare a second transition metal solution having a concentration of 2.2M. Feeding the second transition metal solution at a rate of 1.9L/hr, and adding NaOH aqueous solution and NH₄An aqueous OH solution was added therewith, and simultaneously, a coprecipitation reaction was performed for 6.2 hours to produce a shell portion.

The hydroxide particles were separated and washed, and then dried in an oven at 120 ℃ for 12 hours to prepare a positive electrode active material. The positive active material precursor prepared in the same manner as described above had a core-shell structure, and was formed to have an overall composition of Ni_0.5Co_0.3Mn_0.2(OH)₂Nickel-cobalt-manganese-containing hydroxide particles of (1).

The positive electrode active material precursor and the lithium source Li prepared in the same manner as described above were mixed in such a manner that the molar ratio of Li/M (Ni, Co, Mn) became 1.02₂CO₃Was fed into a Henschel mixer (20L), and then mixed at 300rpm, which is the rpm of the center portion, for 20 minutes. The mixed powder was input into an alumina crucible having a size of 330mm x 330mm, and fired at 990 ℃ for 21 hours under an air atmosphere to prepare a positive electrode active material of a lithium composite transition metal oxide.

[ example 2]

Will be prepared in the same manner as in example 1Lithium composite transition metal oxide and Al₂O₃And (4) mixing. The mixed mixture was heat-treated at 500 ℃ for 3 hours under an air atmosphere to prepare a positive electrode active material in which an Al coating portion was formed.

Comparative example 1

In a batch 40L reactor set at 50 deg.C, by passing NiSO₄、CoSO₄And MnSO₄So that the ratio of nickel: cobalt: the molar ratio of manganese is 50: 30: an amount of 20 is mixed in water to prepare a precursor forming solution.

13 liters of deionized water was added to the coprecipitation reactor (capacity: 40L) and nitrogen was purged into the reactor at a rate of 25 liters/minute to remove dissolved oxygen from the water and create a non-oxidizing atmosphere in the reactor. Thereafter, 83g of a 25% strength aqueous NaOH solution was added thereto, and the mixture was stirred at a temperature of 50 ℃ and a stirring speed of 700rpm to maintain the pH at 11.5.

Thereafter, the precursor forming solution was separately fed at a rate of 1.9L/hr, and an aqueous NaOH solution, NH₄An aqueous OH solution was added together therewith, and at the same time, a coprecipitation reaction was carried out for 48 hours to produce nickel-cobalt-manganese-containing hydroxide particles (Ni)_0.5Co_0.3Mn_0.2(OH)₂). The hydroxide particles were separated and washed, and then dried in an oven at 120 ℃ to prepare a positive electrode active material.

The positive electrode active material precursor and the lithium source Li prepared in the same manner as described above were mixed in such a manner that the molar ratio of Li/M (Ni, Co, Mn) became 1.02₂CO₃Was fed into a Henschel mixer (20L), and then mixed at 300rpm, which is the rpm of the center portion, for 20 minutes. The mixed powder was input into an alumina crucible having a size of 330mm x 330mm, and fired at 990 ℃ for 21 hours under an air atmosphere to prepare a positive electrode active material of a lithium composite transition metal oxide.

[ Experimental example 1: degree of disintegration of positive electrode active material ]

The positive electrode active materials prepared in example 1 and comparative example 1 were coarsely pulverized by a roll mill, 100g of which was input into a hand mixer, and then disintegrated for 2 minutes. Next, fig. 1 and 2 (example 1), fig. 3 and 4 (comparative example 1) are photographs of the disintegrated positive electrode active material observed at an enlarged scale by a Scanning Electron Microscope (SEM).

Referring to fig. 1 to 4, the cathode active materials prepared in example 1 and comparative example 1 were both of a single particle type, however, although example 1 (fig. 1 and 2) showed that particles using a precursor having a cobalt (Co) shell portion were well disintegrated and not aggregated, comparative example 1 (fig. 3 and 4) showed that particles without a cobalt (Co) shell portion in the precursor were aggregated in a large amount due to poor disintegration.

[ Experimental example 2: particle diameter and crystallite size of primary particles of positive electrode active material ]

The positive electrode active materials prepared in examples 1 and 2 and comparative examples 1 and 2 were coarsely pulverized by a roll mill, 100g of which was input into a hand mixer, and then disintegrated for 2 minutes. Thereafter, the average particle diameter (D) of the primary particles of the disintegrated positive electrode active material was measured₅₀) And crystallite size. The average particle diameter (D) of the primary particles in examples 1 and 2 was measured using a laser diffraction method (Microtrac)₅₀) The crystallite size was measured using xrd (ultima iv) and the value was calculated.

[ Table 1]

Referring to table 1, although single particles were formed in both examples 1 and 2 and comparative example 1, the difference was that the positive electrode active materials of examples 1 and 2 using the precursors having a cobalt (Co) shell portion had a small D of less than 7.0 μm after disintegration₅₀Whereas the positive electrode active material of comparative example 1, which has no cobalt (Co) shell portion in the precursor, has a large D of 7.7 μm after disintegration₅₀. In examples 1 and 2 using a precursor having a cobalt (Co) shell portion, it was confirmed that D was caused due to high disintegration after disintegration₅₀And decreases.

[ Experimental example 3: particle size distribution after pressure disintegration ]

The positive electrode active materials prepared in example 1 and comparative example 1 were pressurized by Carver _ 4350. Specifically, 3g of the positive electrode active materials prepared in example 1 and comparative example 1 were placed in cylindrical molds, respectively, and then the molds containing the positive electrode active materials were pressurized. After that, the particle size of the positive electrode active material disintegrated by pressurization was measured using a laser diffraction method (Microtrac), and the results are shown in table 2 and fig. 5.

[ Table 2]

Referring to table 2 and fig. 5, the cathode active material of example 1 using the precursor having a cobalt (Co) shell portion had a small D after disintegration without pressurization of 1.6₅₀And D after 2.5 tons of pressure application (i.e., in a pressure-disintegrated state)₅₀The positive electrode active material of comparative example 1, which has no cobalt (Co) shell portion in the precursor, has a large D of 2.3₅₀The difference value. When disintegration was performed without pressurization, it was thus seen that the degree of disintegration of comparative example 1 was lower than that of example 1.

[ Experimental example 4: measurement of lithium by-product

5g of each of the positive electrode active materials prepared in example 1 and comparative example 1 was dispersed in 100mL of water, and then titrated with 0.1M HCl while measuring a change in pH value, to obtain a pH titration curve. The LiOH residue content and Li in each positive electrode active material were calculated using the pH titration curves₂CO₃The residue contents, and the sum total value thereof was evaluated as the total lithium by-product residue content, as shown in table 3 below.

[ Table 3]

	Total residual lithium by-product content (% by weight)
		Example 1	0.106
Comparative example 1	0.153

Referring to table 3, the cathode active material of example 1 had a lithium byproduct content of 0.15 wt% or less, which was reduced as compared to the cathode active material of comparative example 1.