KR102120393B1 - Method for preparing positive electrode active material, positive electrode active material for secondary battery prepared by the same and lithium secondary battery comprising the same - Google Patents

Abstract

The present invention is a step of introducing a positive electrode active material precursor and a lithium raw material into the kiln; A heating step of raising and firing the firing temperature of the firing furnace; And when the heating is completed, the holding step of maintaining and firing the heated firing temperature; includes, wherein the heating step, the firing under a gas atmosphere containing at least 20% by volume of pure oxygen and the atmosphere (Air) And, the maintenance step provides a method for producing a positive electrode active material to perform firing in an atmosphere (Air).

Description

Manufacturing method of positive electrode active material, positive electrode active material for secondary battery manufactured as described above, and lithium secondary battery including the same

The present invention relates to a method for manufacturing a positive electrode active material, a positive electrode active material for a secondary battery thus manufactured, and a lithium secondary battery comprising the same.

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

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

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

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

In order to improve this problem, recently, research has been made to increase the content of Ni in the NCM-based lithium oxide. However, such a high-concentration nickel-containing lithium transition metal oxide has an advantage of being relatively excellent in capacity characteristics, but the cycle characteristics are rapidly reduced during long-term use, and problems such as low chemical stability are not sufficiently solved. As the nickel content in the positive electrode active material increases, impurities such as Li ₂ CO ₃ and LiOH formed by reacting with moisture or CO ₂ in the air as lithium ions move to the surface of the active material, or a raw material for manufacturing lithium transition metal oxide remains. The residual amount of the formed lithium-containing impurities increases, thereby causing gas generation and swelling, thereby deteriorating the life characteristics and stability of the battery.

Accordingly, there is a high need for a technology capable of solving the problem of chemical characteristics and thermal stability while also providing high capacity with excellent charge/discharge characteristics by reducing lithium-containing impurities remaining on the surface of the positive electrode active material.

US Publication No. 2012-0301390

The present invention is to solve the problems as described above, by reducing the residual amount of lithium-containing impurities, while realizing high capacity with excellent charge and discharge capacity characteristics, at the same time, it is possible to secure excellent life characteristics and chemical and thermal stability, and also the manufacturing cost It is intended to provide a method for manufacturing a positive electrode active material that can be reduced, and a lithium secondary battery including the positive electrode active material thus manufactured.

The present invention is a step of introducing a positive electrode active material precursor and a lithium raw material into the kiln; A heating step of raising and firing the firing temperature of the firing furnace; And when the heating is completed, the holding step of maintaining and firing the heated firing temperature; includes, wherein the heating step, the firing under a gas atmosphere containing at least 20% by volume of pure oxygen and the atmosphere (Air) And, the maintenance step provides a method for producing a positive electrode active material to perform firing in an atmosphere (Air).

In addition, the present invention is a positive electrode active material prepared as described above, the positive electrode active material provides a positive electrode active material for a secondary battery having a content of lithium carbonate (Li ₂ CO ₃ ) of less than 0.4% by weight among lithium-containing impurities remaining on the surface.

In addition, the present invention provides a positive electrode and a lithium secondary battery comprising the positive electrode active material.

According to the present invention, it is possible to reduce the residual amount of lithium-containing impurities on the surface of the positive electrode active material, thereby realizing high capacity with excellent charge and discharge capacity characteristics, while at the same time ensuring excellent life characteristics and chemical and thermal stability, while effectively reducing manufacturing costs. Can be.

1 is a graph showing the results of measuring the residual amount of lithium-containing impurity Li ₂ CO _{3 on} the surface of a positive electrode active material prepared as in Examples 1 to 4 and Comparative Example 1.
2 is a graph showing a capacity retention rate according to a charge/discharge cycle of a battery cell manufactured using the positive electrode active material prepared as in Examples 1 to 4 and Comparative Example 1.

Hereinafter, the present invention will be described in more detail to help understanding of the present invention. In this case, the terms or words used in the present specification and claims should not be interpreted as being limited to ordinary or dictionary meanings. In order to explain one's invention in the best way, it should be interpreted as a meaning and concept consistent with the technical idea of the present invention based on the principle that the concept of terms can be properly defined.

The method for manufacturing the positive electrode active material of the present invention comprises the steps of introducing a positive electrode active material precursor and a lithium raw material into a kiln; A heating step of raising and firing the firing temperature of the firing furnace; And when the heating is completed, the holding step of maintaining and firing the heated firing temperature; includes, wherein the heating step, the firing under a gas atmosphere containing at least 20% by volume of pure oxygen and the atmosphere (Air) And performing the firing under the air atmosphere.

During the production of the positive electrode active material, lithium-ion impurities formed by reacting with moisture or CO ₂ in the air while lithium ions move to the surface of the positive electrode active material, or lithium-containing impurities formed by remaining lithium raw materials remain on the surface of the positive electrode active material. Gas generation and swelling phenomena have occurred due to contained impurities, and thus there has been a problem of deteriorating the life characteristics and stability of the battery. In particular, as the nickel content in the positive electrode active material increases, the residual amount of lithium-containing impurities on the surface of the positive electrode active material further increases due to the influence of high concentration nickel inside, and thus there are many difficulties in securing capacity, life characteristics, and stability, and there are ways to improve it. It was necessary.

Accordingly, in the present invention, a method of reducing the residual amount of lithium-containing impurities on the surface of the positive electrode active material by performing firing under an oxygen atmosphere in the temperature raising step and firing in the air atmosphere in the holding step in the firing of the positive electrode active material to provide. The oxygen atmosphere means a gas atmosphere in which the concentration of oxygen is greater than that of a general atmosphere (Air).

Conventionally, when firing a positive electrode active material, it was generally fired under an atmosphere of air or fired under an oxygen atmosphere to reduce lithium-containing impurities. When firing under an atmosphere of air, the residual amount of lithium-containing impurities increases and particle size It was also difficult to control, and there was a problem in that the capacity of the battery was lowered, and the life characteristics and stability were also deteriorated. When firing under an oxygen atmosphere, the manufacturing cost was greatly increased.

However, the present invention contains lithium by firing under an atmosphere of air in the holding step of growing the crystal while maintaining the firing temperature, and then firing in an oxygen atmosphere in the heating step of raising the firing temperature during the firing process of the positive electrode active material. Reducing the residual amount of impurities and facilitating particle size control to ensure capacity characteristics, life characteristics, and stability while effectively reducing manufacturing costs.

In the firing process of the positive electrode active material, since the reaction of the lithium raw material and the positive electrode active material precursor is mostly made during the heating step, lithium transition metal oxide is formed, and in the subsequent holding step, crystals are grown in the oxygen atmosphere only during the heating step. Even if the entire calcination process is carried out in an oxygen atmosphere, the residual amount of lithium-containing impurities can be reduced to an equivalent level, and the manufacturing cost is less than about 20% compared to the case where calcination was performed in an oxygen atmosphere in the entire calcination process. The level can be significantly reduced.

Specifically, in the present invention, the positive electrode active material precursor and the lithium raw material are first introduced into the kiln.

The positive electrode active material precursor may include any one or more transition metals selected from the group consisting of nickel (Ni), manganese (Mn), and cobalt (Co), and may be hydroxides, carbonates, carbonate hydroxides, and the like.

For example, the positive electrode active material precursor may be represented by Formula 1 below.

[Formula 1]

_{Ni 1-bc Mn b Co c} M 'x (OH) 2

In Chemical Formula 1, 0<b<0.5, 0<c<0.5, 0≤x≤0.2, and M'is composed of Al, Zr, Ti, Mo, W, Nb, Ta, Sr, Ca, Ba, and B. It may include any one or more selected from the group.

In the positive electrode active material precursor of Formula 1, Ni may be included in a content corresponding to 1-b-c, for example, 0.6≤1-b-c<1. When the content of Ni in the positive electrode active material precursor of Formula 1 is 0.6 or more, a sufficient amount of Ni is secured to contribute to charging and discharging, so that high capacity can be achieved. More preferably, Ni may be included as 0.6≤1-b-c≤0.9. As described above, when the molar ratio of nickel in the total molar ratio of the transition metal of the positive electrode active material precursor used in the present invention is a high-concentration nickel (0.6) or higher concentration, the problem of residual lithium-containing impurities is greater, so that the lithium transition metal during the firing process It is more important to reduce the residual amount of lithium-containing impurities by controlling under an oxygen atmosphere at an elevated temperature step in which the oxide is formed.

In the positive electrode active material precursor of Formula 1, Mn may improve the structural stability of the active material, and as a result, the stability of the battery. When considering the effect of improving the life characteristics according to the inclusion of Mn, the Mn may be included in a content corresponding to b, that is, a content of 0<b<0.5. If the b in the positive electrode active material precursor of Formula 1 exceeds 0.5, there is a fear that the output characteristics and capacity characteristics of the battery are lowered.

In the positive electrode active material precursor of Formula 1, Co may be included in a content corresponding to c, that is, 0<c<0.5. When the content of Co in the positive electrode active material precursor of Chemical Formula 1 exceeds 0.5, there is a fear of increasing costs. Considering the remarkable effect of improving the capacity characteristics according to the inclusion of Co, the Co may be more specifically included in an amount of 0.10≦c≦0.35.

In the positive electrode active material precursor of Formula 1, in order to improve the battery characteristics through control of the distribution of the transition metal element in the positive electrode active material, it may be partially substituted or doped by another element, that is, M'. The M'may be any one or more elements specifically selected from the group consisting of Al, Zr, Ti, Mo, W, Nb, Ta, Sr, Ca, Ba and B. Among the M'elements described above, in the case of Al, it is possible to improve the life characteristics of the battery by maintaining the average oxidation number of the positive electrode active material. The element of M'may be included in an amount corresponding to x, i.e., 0<x≤0.2, within a range that does not degrade the properties of the positive electrode active material. The element of M'may be located inside and/or outside the positive electrode active material precursor.

The lithium raw material may be any one or more selected from the group consisting of lithium-containing carbonate, lithium-containing hydroxide, lithium-containing nitrate and lithium-containing chloride. More specifically, the lithium-containing carbonate (for example, lithium carbonate), hydrate (for example, lithium hydroxide I hydrate (LiOH · H ₂ O), etc.), hydroxide (for example, lithium hydroxide, etc.), nitrate (for example For example, lithium nitrate (LiNO ₃ ) and the like, chlorides (eg, lithium chloride (LiCl), etc.), and the like, one or a mixture of two or more of them may be used, more preferably Lithium carbonate can be used.

The positive electrode active material precursor and the lithium raw material may be introduced in a molar ratio of 1:1 to 1:1.5, more preferably in a molar ratio of 1:1 to 1:1.3, and most preferably in a molar ratio of 1:1 to 1:1.1. have.

The said baking furnace is a batch type or a continuous type. As a continuous kiln, a belt furnace, a rotary kiln, a roller hearth kiln, etc. are mentioned, Although it is not specifically limited, Preferably, a roller hearth kiln can be used.

Next, as a step of raising the temperature, the firing temperature of the firing furnace is raised while firing. At this time, the atmosphere at the temperature rising step is a gas atmosphere containing 20% by volume or more of pure oxygen, and the rest (80% by volume or less) containing the atmosphere (Air).

Since the temperature raising step is a section in which the positive electrode active material precursor and the lithium raw material react mostly to form a lithium transition metal oxide, the residual amount of lithium-containing impurities on the surface of the positive electrode active material generated by proceeding under an oxygen atmosphere can be reduced.

The heating step may more preferably be under a gas atmosphere containing 25 to 100% by volume of pure oxygen and the rest (75% by volume or less) containing air, most preferably 30 to 80% by volume. The calcination can be performed under a gas atmosphere containing% pure oxygen and the rest (70 to 20% by volume) containing air.

At this time, the temperature raising step may be heated to a target firing temperature, for example, to a temperature of firing of 800 to 1,000°C.

When the temperature is raised to the target firing temperature, it may be desirable to control the temperature increase rate. For example, the temperature is increased at a heating rate of 3 to 6° C./min to a relatively low firing temperature of 600 to 700° C. In the state of relatively high temperature after 600 to 700°C, the temperature may be increased at a rate of 0.1 to 2°C/min. In the section after the firing temperature of 600 to 700°C, CO ₂ gas may be generated in large quantities during the reaction, and thus the rate of temperature rise is reduced and the generated CO ₂ gas is reduced compared to the section at a relatively low firing temperature of 600 to 700°C. It may be more desirable to discharge.

As such, the heating step of firing under an oxygen atmosphere may be performed for 3 to 7 hours, more preferably 4 to 7 hours, and most preferably 5 to 6 hours.

Next, as the holding step, when the temperature is raised to the target firing temperature, firing is performed while maintaining the heated firing temperature. At this time, in the maintenance step, firing is performed under an air atmosphere.

In the holding step, since the reaction between the positive electrode active material precursor and the lithium raw material is mostly completed in the temperature raising step, and then the crystal is grown, the entire firing process is performed under an oxygen atmosphere even if firing is performed in an atmosphere of air. In contrast to the case, the reduction effect of lithium-containing impurities can be realized at an equal level, and excellent performance can be realized at an equivalent level in terms of capacity characteristics, life characteristics, and stability of the cathode active material to be manufactured. On the other hand, by firing in the air atmosphere in the maintenance step as described above, in terms of lithium-containing impurity reduction and positive electrode active material performance, while showing an excellent effect at the same level as when the entire firing process was performed under an oxygen atmosphere, the manufacturing cost is about Significant savings of less than 20% are possible.

The holding step is, for example, while maintaining the firing temperature of 800 to 1,000 ℃, more preferably 800 to 950 ℃ firing temperature, most preferably 830 to 930 ℃ firing temperature, 7 to 30 hours, more preferably It can be calcined for 8 to 24 hours.

In addition, the present invention provides a positive electrode active material for a secondary battery manufactured according to an embodiment of the present invention. In the positive electrode active material of the present invention, the content of lithium carbonate (Li ₂ CO ₃ ) among the lithium-containing impurities remaining on the surface is 0.4% by weight or less. The present invention reduces the content of lithium carbonate (Li ₂ CO ₃ ) in lithium-containing impurities to 0.4% by weight or less, thereby increasing the capacity compared to the positive electrode active material prepared by firing under an atmosphere of air, and improving the life characteristics and stability. Can be. In addition, compared to the case of firing with an oxygen atmosphere in the entire firing process, performances such as capacity characteristics, life characteristics, and stability can be realized at an equivalent level while significantly reducing manufacturing costs.

The positive electrode active material of the present invention may be represented by the following formula (2).

[Formula 2]

_{Li 1 + a Ni 1-bc} Mn b Co c M 'x O 2

In Formula 2, 0<a<0.33, 0<b<0.5, 0<c<0.5, 0≤x≤0.2, M'is Al, Zr, Ti, Mo, W, Nb, Ta, Sr, Ca , Ba and B may include any one or more selected from the group consisting of.

In addition, in Chemical Formula 2, Ni may be included in a content corresponding to 1-bc, for example, 0.6≤1-bc<1, and more preferably, Ni may be included in 0.6≤1-bc≤0.9. . In this way, the positive electrode active material prepared in the present invention may be a high-concentration nickel (high-nickel) system in which the molar ratio of nickel in the total molar ratio of transition metal is 0.6 or more.

In the positive electrode active material of the lithium transition metal oxide of Chemical Formula 2, Li may be included in an amount corresponding to 1+a, and a may be 0<a<0.33. If a is less than 0, there is a fear that the capacity is lowered. If it exceeds 0.33, particles may be sintered in the firing process, and thus it may be difficult to prepare a positive electrode active material. When considering the balance of the effect of improving the capacity characteristics of the positive electrode active material according to the control of the Li content and the sinterability during the production of the active material, the a may be more preferably 0≤a≤0.15.

In the positive electrode active material of the lithium transition metal oxide of Formula 2, the preferred composition of Ni, Mn, Co, and M'may be the same as the range of the composition of the positive electrode active material precursor described above.

According to another embodiment of the present invention, there is provided a positive electrode comprising the positive electrode active material.

Specifically, the positive electrode includes a positive electrode current collector, and a positive electrode active material layer on at least one surface of the positive electrode current collector and including the positive electrode active material.

The positive electrode current collector is not particularly limited as long as it does not cause a chemical change in the battery and has conductivity. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or carbon, nickel, titanium on aluminum or stainless steel surfaces , Surface treatment with silver or the like can be used. In addition, the positive electrode current collector may have a thickness of usually 3 to 500 μm, and may form fine irregularities on the current collector surface to increase the adhesive force of the positive electrode active material. For example, it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics.

The positive electrode active material layer may include a conductive material and a binder together with the positive electrode active material described above.

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

At this time, the conductive material is used to impart conductivity to the electrode, and in the battery configured, it can be used without particular limitation as long as it has electronic conductivity without causing a chemical change. Specific examples include graphite such as natural graphite and artificial graphite; Carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, summer black, and carbon fiber; Metal powders 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; Or a conductive polymer, such as a polyphenylene derivative, and the like, or a mixture of two or more of them may be used. The conductive material may be included in 1 to 30% by weight relative to the total weight of the positive electrode active material layer.

The binder serves to improve the adhesion between the positive electrode active material particles and the adhesion between the positive electrode active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, and carboxymethyl cellulose (CMC) ), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluorine rubber, or various copolymers thereof, and one of these may be used alone or as a mixture of two or more. The binder may be included in 1 to 30% by weight relative to the total weight of the positive electrode active material layer.

The positive electrode may be manufactured according to a conventional positive electrode manufacturing method except for using the positive electrode active material. Specifically, the positive electrode active material and, optionally, a binder and a conductive material may be prepared by dissolving or dispersing in a solvent to apply a composition for forming a positive electrode active material layer on a positive electrode current collector, followed by drying and rolling. At this time, the types and contents of the positive electrode active material, the binder, and the conductive material are as described above.

The solvent may be a solvent generally used in the art, dimethyl sulfoxide (dimethyl sulfoxide, DMSO), isopropyl alcohol (isopropyl alcohol), N-methylpyrrolidone (NMP), acetone (acetone) or Water and the like, and among these, one kind alone or a mixture of two or more kinds can be used. The amount of the solvent used is sufficient to dissolve or disperse the positive electrode active 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 after coating for positive electrode manufacturing. Do.

In addition, in another method, the positive electrode may be produced by casting the composition for forming the positive electrode active material layer on a separate support, and then laminating the film obtained by peeling from the support on the positive electrode current collector.

According to another example of the present invention, an electrochemical device including the anode is provided. The electrochemical device may be specifically a battery, a capacitor, or the like, and more specifically, a lithium secondary battery.

The lithium secondary battery specifically includes a positive electrode, a negative electrode facing the positive electrode, a separator and an electrolyte interposed between the positive electrode and the negative electrode, and the positive electrode is as described above. In addition, the lithium secondary battery may further include a battery container for storing the electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member for sealing the battery container.

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

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

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

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

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

The negative electrode active material layer is, for example, a negative electrode active material, and optionally a binder and a conductive material are dissolved or dispersed in a solvent on a negative electrode current collector to apply and dry a composition for forming a negative electrode active material layer, or for drying the negative electrode active material layer. It can also be prepared by casting the composition on a separate support and then laminating the film obtained by peeling from the support on a negative electrode current collector.

On the other hand, in the lithium secondary battery, the separator separates the negative electrode from the positive electrode and provides a passage for lithium ions, and is usually used as a separator in a lithium secondary battery, and can be used without particular limitation, especially for ion migration of electrolytes. It is desirable to have low resistance and excellent electrolyte-moisturizing ability. Specifically, porous polymer films such as ethylene homopolymers, propylene homopolymers, ethylene/butene copolymers, ethylene/hexene copolymers and polyolefin polymers such as ethylene/methacrylate copolymers or the like. A laminate structure of two or more layers of may be used. In addition, a conventional porous non-woven fabric, for example, a high-melting point glass fiber, a polyethylene terephthalate fiber or the like may be used. In addition, a coated separator containing a ceramic component or a polymer material may be used to secure heat resistance or mechanical strength, and may optionally be used in a single layer or multilayer structure.

Further, examples of the electrolyte used in the present invention include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, and melted inorganic electrolytes that can be used in the manufacture of lithium secondary batteries. It does not work.

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

The organic solvent may be used without particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvent, methyl acetate (methyl acetate), ethyl acetate (ethyl acetate), γ-butyrolactone (γ-butyrolactone), ε-caprolactone (ε-caprolactone), such as ester-based solvents; Ether-based solvents such as dibutyl ether or tetrahydrofuran; Ketone solvents such as cyclohexanone; Aromatic hydrocarbon-based solvents such as benzene and fluorobenzene; Dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), propylene carbonate (propylene carbonate, PC) and other carbonate-based solvents; Alcohol-based solvents such as ethyl alcohol and isopropyl alcohol; Nitriles such as R-CN (R is a straight-chain, branched or cyclic hydrocarbon group having 2 to 20 carbon atoms, and may include a double bond aromatic ring or ether bond); Amides such as dimethylformamide; Dioxolanes such as 1,3-dioxolane; Alternatively, sulfolanes may be used. Of these, carbonate-based solvents are preferred, and cyclic carbonates (for example, ethylene carbonate or propylene carbonate) having high ionic conductivity and high dielectric constant that can improve the charge and discharge performance of the battery, and low-viscosity linear carbonate-based compounds ( For example, a mixture of ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate) is more preferable. In this case, the mixture of the cyclic carbonate and the chain carbonate in a volume ratio of about 1:1 to about 1:9 may be used to exhibit excellent electrolyte performance.

The lithium salt may be used without particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the lithium salt is LiPF ₆ , LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiSbF ₆ , LiAl0 ₄ , LiAlCl ₄ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN(C ₂ F ₅ SO ₃ ) ₂ , LiN(C ₂ F ₅ SO ₂ ) ₂ , LiN(CF ₃ SO ₂ ) ₂ . LiCl, LiI, or LiB(C ₂ O ₄ ) ₂ and the like can be used. The concentration of the lithium salt is preferably used within the range of 0.1 to 2.0M. When the concentration of the lithium salt is included in the above range, since the electrolyte has an appropriate conductivity and viscosity, it can exhibit excellent electrolyte performance, and lithium ions can be effectively moved.

In addition to the electrolyte components, the electrolyte includes haloalkylene carbonate-based compounds such as difluoro ethylene carbonate, pyridine, and tree for the purpose of improving the life characteristics of the battery, suppressing the decrease in battery capacity, and improving the discharge capacity of the battery. Ethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphate triamide, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imida One or more additives such as zolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxy ethanol or aluminum trichloride may be further included. At this time, the additive may be included in an amount of 0.1 to 5% by weight based on the total weight of the electrolyte.

Since the lithium secondary battery comprising the positive electrode active material according to the present invention as described above stably exhibits excellent discharge capacity, output characteristics and capacity retention rate, portable devices such as mobile phones, notebook computers, digital cameras, and hybrid electric vehicles ( It is useful for electric vehicle fields such as hybrid electric vehicle (HEV).

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

The battery module or battery pack includes a power tool; An electric vehicle including an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); Alternatively, it can be used as a power supply for any one or more medium-to-large devices among power storage systems.

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 or a coin shape using a can.

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

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

Example One

Anode active material precursor Ni _{0 . 6} Mn _{0 . 2 Co 0 .2 (OH) 2} 180kg , and a lithium raw material In the Li ₂ CO ₃ 74.16kg in a Henschel mixer (700L), followed by mixing (mixing) 20 minutes at the center of 300rpm. The mixed powder was put in an alumina crucible having a size of 330 mm x 330 mm, and calcined while heating the calcination temperature under an oxygen atmosphere mixed with oxygen: air = 20:80 vol%. At this time, the temperature was raised to 4°C/min to 600°C, and the temperature was increased from 600°C to 860°C at 2°C/min and calcined for 5 hours. After reaching 860° C., the positive electrode active material was prepared by firing for 10 hours under an atmosphere of air while maintaining the firing temperature.

Example 2

A positive electrode active material was prepared in the same manner as in Example 1, except that calcination was performed in an oxygen atmosphere mixed with oxygen:atmosphere (Air)=40:60% by volume at the temperature rising step.

Example 3

A cathode active material was prepared in the same manner as in Example 1, except that calcination was performed in an oxygen atmosphere mixed with oxygen:atmosphere (Air)=60:40% by volume at the temperature rising step.

Example 4

A cathode active material was prepared in the same manner as in Example 1, except that calcination was performed in an oxygen atmosphere mixed with oxygen:atmosphere (Air)=80:20% by volume at the temperature rising step.

Comparative example One

A positive electrode active material was prepared in the same manner as in Example 1, except that firing was performed in an atmosphere of air in both the temperature raising step and the maintenance step.

[ Experimental Example 1: lithium-containing impurities ( Li ₂ CO ₃ ) Residual amount measurement]

After dispersing 10 g of the positive electrode active material prepared in Examples 1 to 4 and Comparative Example 1 in 100 mL of water, the pH value was measured by measuring the change in pH while titrating with 0.1 M HCl to obtain a pH titration curve. The residual amount of Li ₂ CO _{3 in} each positive electrode active material was calculated using the pH titration curve, and the results are shown in FIG. 1.

Referring to FIG. 1, in the case of Comparative Example 1 in which the entire firing process was performed under an atmosphere of air, the content of lithium-containing impurity Li ₂ CO ₃ was significantly higher than 1% by weight, whereas, during the firing process In the temperature raising step, the calcination was performed under an oxygen atmosphere, and in the case of Examples 1 to 4, the holding step was conducted under an air atmosphere, the content of lithium-containing impurity Li ₂ CO ₃ was significantly reduced to 0.4% by weight or less. In the case of Examples 1 to 4, since the calcination is performed in an air atmosphere in the holding step, the manufacturing cost can be significantly reduced than in the case of calcination under an oxygen atmosphere in the entire calcination process, while the lithium-containing impurity Li ₂ CO ₃ is 0.4 wt. It can be reduced to less than% to prevent degradation of battery performance due to lithium-containing impurities.

[ Experimental Example 2: Battery life characteristic evaluation]

Each of the positive electrode active materials prepared by Examples 1 to 4 and Comparative Example 1, the carbon black conductive material, and the PVdF binder were mixed in a ratio of 95:2.5:2.5 by weight ratio in an N-methylpyrrolidone solvent to prepare a positive electrode mixture ( Viscosity: 5000 mPa·s) was prepared, coated on one surface of an aluminum current collector, dried at 130° C., and rolled to prepare an anode.

Further, as a negative electrode active material, natural graphite, carbon black conductive material, and PVdF binder were mixed in a ratio of 85:10:5 by weight in an N-methylpyrrolidone solvent to prepare a composition for forming a negative electrode active material layer, and this was a copper current collector. A negative electrode was prepared by coating on one surface of the electrode.

An electrode assembly was manufactured by interposing a separator of porous polyethylene between the positive electrode and the negative electrode prepared as described above, and after placing the electrode assembly inside the case, an electrolyte was injected into the case to prepare a lithium secondary battery. At this time, the electrolytic solution was prepared by dissolving lithium hexafluorophosphate (LiPF ₆ ) at a concentration of 1.0 M in an organic solvent consisting of ethylene carbonate/dimethyl carbonate/ethyl methyl carbonate (mixed volume ratio of EC/DMC/EMC=3/4/3). Did.

The capacity of the lithium secondary battery prepared as described above was measured at 45° C. while carrying out 30 cycles of charging and discharging under the conditions of a charge termination voltage of 4.25 V, a discharge termination voltage of 3.0 V, and 0.5 C/1.0 C. . The measurement results are shown in FIG. 2.

Referring to FIG. 2, compared to Comparative Example 1 in which the entire firing process was performed under an atmosphere of air, the heating step in the firing process proceeded with firing under an oxygen atmosphere, and the maintenance step was performed under an atmosphere of air. In the case of Examples 1 to 4, it can be confirmed that the capacity reduction rate is remarkably low during 50 charge/discharge cycles.

Claims (15)

Introducing a positive electrode active material precursor and a lithium raw material into a kiln;
A heating step of raising and firing the firing temperature of the firing furnace; And
When the heating is completed, the holding step of maintaining and firing while maintaining the heated firing temperature; includes,
The heating step includes 30 to 80% by volume of pure oxygen, and the remaining 70 to 20% by volume performs firing under a gas atmosphere containing air,
The holding step is a method of manufacturing a positive electrode active material to perform firing under an atmosphere (Air).
delete According to claim 1,
The heating step is a method of manufacturing a positive electrode active material to heat up to a firing temperature of 800 to 1,000 ℃.
According to claim 1,
The heating step is a method for producing a positive electrode active material that is heated to a heating rate of 3 to 6°C/min up to a firing temperature of 600 to 700°C, and then heated to a heating rate of 0.1 to 2°C/min after the 600 to 700°C.
According to claim 1,
The heating step is a method of manufacturing a positive electrode active material is 3 to 7 hours.
According to claim 1,
The holding step is a method for producing a positive electrode active material that is fired at a firing temperature of 800 to 1,000°C for 7 to 30 hours.
According to claim 1,
The positive electrode active material precursor is nickel (Ni), manganese (Mn) and cobalt (Co) method for producing a positive electrode active material containing any one or more transition metals selected from the group consisting of.
According to claim 1,
The positive electrode active material precursor is a method of manufacturing a positive electrode active material represented by the following formula (1).
[Formula 1]
_{Ni 1-bc Mn b Co c} M 'x (OH) 2
(In Chemical Formula 1, 0<b<0.5, 0<c<0.5, 0≤x≤0.2, and M'is Al, Zr, Ti, Mo, W, Nb, Ta, Sr, Ca, Ba, and B. It includes any one or more selected from the group consisting of.)
The method of claim 8,
In Formula 1, a method of manufacturing a positive electrode active material satisfying 0.6≤1-bc<1.
According to claim 1,
The lithium raw material is a method for producing a positive electrode active material of any one or more selected from the group consisting of lithium-containing carbonate, lithium-containing hydroxide, lithium-containing nitrate and lithium-containing chloride.
A positive electrode active material prepared according to any one of claims 1, 3 to 10,
The positive electrode active material is a positive electrode active material for a secondary battery having a content of lithium carbonate (Li ₂ CO ₃ ) of less than 0.4% by weight among the lithium-containing impurities remaining on the surface.
The method of claim 11,
The positive electrode active material is a positive electrode active material for a secondary battery represented by the following formula (2).
[Formula 2]
_{Li 1 + a Ni 1-bc} Mn b Co c M 'x O 2
(In the formula 2, 0 <a <0.33, 0 <b <0.5, 0 <c <0.5, 0 ≤ x ≤ 0.2, M'is Al, Zr, Ti, Mo, W, Nb, Ta, Sr, It includes any one or more selected from the group consisting of Ca, Ba and B.)
The method of claim 12,
In Chemical Formula 2, the positive electrode active material for a secondary battery that satisfies 0.6≤1-bc<1.
A cathode for a secondary battery comprising the cathode active material according to claim 11.
A lithium secondary battery comprising the positive electrode according to claim 14.

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