KR102325728B1 - Positive electrode active material for lithium secondary battery, positive electrode for lithium secondary battery and lithium secondary battery comprising the same - Google Patents

Abstract

The present invention is a first lithium transition metal oxide particles; And a second lithium-transition and including metal oxide particles, an average particle diameter of the first lithium-transition metal oxide particles (D ₅₀₎ is the second lithium-transition greater than the average particle diameter (D ₅₀₎ of the metal oxide particles, wherein the first lithium The transition metal oxide particle and the second lithium transition metal oxide particle include a transition metal including nickel (Ni) and cobalt (Co) and lithium (Li), and the total of the transition metal of the first lithium transition metal oxide particle The ratio of the number of moles of lithium (Li) to the number of moles (Li/Me) ₁ is 1.05 to 1.09, and the ratio of the number of moles of lithium (Li) to the total number of moles of transition metals of the second lithium transition metal oxide particles (Li/Me) Me) ₂ provides a positive active material for a lithium secondary battery that is greater than 1.01 and not more than 1.04.

Description

A cathode active material for a lithium secondary battery, a cathode for a lithium secondary battery including the same, and a lithium secondary battery

The present invention relates to a cathode active material for a lithium secondary battery, a cathode for a lithium secondary battery comprising the same, and a lithium secondary battery.

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

As a positive electrode active material of a lithium secondary battery, for example, a lithium transition metal composite oxide is used, and among them, a lithium cobalt oxide of _{LiCoO 2 having a high working voltage and excellent capacity characteristics is mainly used.} However, Co is expensive and has a limitation in mass use as a power source in fields such as electric vehicles due to supply instability.

In order to overcome the above limitations, a nickel-cobalt-manganese-based lithium composite metal oxide (hereinafter simply referred to as 'NCM-based lithium oxide') in which a part of Co is substituted with Ni and Mn has been developed, has low output characteristics, and There is a problem in the elution of the elements and thus deterioration of battery characteristics.

Korean Patent Application Laid-Open No. 10-2012-0079802 discloses a cathode active material, a method for manufacturing the same, and a lithium secondary battery including the same, but does not provide an alternative to the above problems.

Korean Patent Publication No. 10-2012-0079802

An object of the present invention is to provide a cathode active material for a lithium secondary battery capable of improving structural stability, output characteristics and lifespan characteristics by blending and using lithium transition metal oxides having a lithium molar ratio (Li/Me) to a specific transition metal. will be.

Another object of the present invention is to provide a positive electrode for a lithium secondary battery and a lithium secondary battery including the above-described positive electrode active material.

The present invention is a first lithium transition metal oxide particles; And a second lithium-transition and including metal oxide particles, an average particle diameter of the first lithium-transition metal oxide particles (D ₅₀₎ is the second lithium-transition greater than the average particle diameter (D ₅₀₎ of the metal oxide particles, wherein the first lithium The transition metal oxide particle and the second lithium transition metal oxide particle include a transition metal including nickel (Ni) and cobalt (Co) and lithium (Li), and the total of the transition metal of the first lithium transition metal oxide particle The ratio of the number of moles of lithium (Li) to the number of moles (Li/Me) ₁ is 1.05 to 1.09, and the ratio of the number of moles of lithium (Li) to the total number of moles of transition metals of the second lithium transition metal oxide particles (Li/Me) Me) ₂ provides a positive active material for a lithium secondary battery that is greater than 1.01 and not more than 1.04.

In addition, the present invention is a positive active material for a lithium secondary battery described above; bookbinder; And it provides a positive electrode for a lithium secondary battery comprising a conductive material.

In addition, the present invention provides a lithium secondary battery comprising the above-described positive electrode for a lithium secondary battery.

The positive active material for a lithium secondary battery of the present invention can secure high structural stability, output characteristics, and lifespan characteristics by using a mixture of first and second lithium transition metal oxides having different lithium molar ratios to specific transition metals. In particular, according to the present invention, it is possible to implement a positive electrode for a lithium secondary battery and a lithium secondary battery having high structural stability, output characteristics and lifespan characteristics even when lithium transition metal oxide containing a low amount of Co is used.

1 is a result of a relative capacity measurement experiment for lithium secondary batteries according to Examples and Comparative Examples.
2 is an experimental result of measuring resistance values according to SOC at room temperature (25° C.) for lithium secondary batteries according to Examples and Comparative Examples.
3 is an experimental result of measuring the voltage drop over time at a low temperature (-10° C.) for lithium secondary batteries according to Examples and Comparative Examples.

The present invention is a first lithium transition metal oxide particles; And a second lithium-transition and including metal oxide particles, an average particle diameter of the first lithium-transition metal oxide particles (D ₅₀₎ is the second lithium-transition greater than the average particle diameter (D ₅₀₎ of the metal oxide particles, wherein the first lithium The transition metal oxide particle and the second lithium transition metal oxide particle include a transition metal including nickel (Ni) and cobalt (Co) and lithium (Li), and the total of the transition metal of the first lithium transition metal oxide particle The ratio of the number of moles of lithium (Li) to the number of moles (Li/Me) ₁ is 1.05 to 1.09, and the ratio of the number of moles of lithium (Li) to the total number of moles of transition metals of the second lithium transition metal oxide particles (Li/Me) Me) ₂ provides a positive active material for a lithium secondary battery that is greater than 1.01 and not more than 1.04.

In general, lithium cobalt-based oxide is used as a cathode active material of a lithium secondary battery, but cobalt (Co) is expensive and has a limitation in mass use as a power source in fields such as electric vehicles due to supply instability. Accordingly, a nickel-cobalt-manganese-based lithium composite metal oxide with a lower ratio of cobalt (Co) and an increased ratio of nickel (Ni) or manganese (Mn) is used instead, but as the content of cobalt (Co) is reduced, output characteristics are lowered There was a problem being

Accordingly, the positive active material for a lithium secondary battery of the present invention is a bi-modal form by blending the first and second lithium transition metal oxide particles having different specific transition metal to lithium molar ratios (Li/Me). As a result, even when lithium transition metal oxide containing cobalt in a low content is used, the output characteristics of the battery can be improved.

In addition, the positive electrode active material for a lithium secondary battery of the present invention is _{used by blending lithium transition metal oxide particles having different average particle diameters (D 50} ), for example, a positive electrode having a high reaction area and electrical conductivity and a positive electrode even when rolling Because small particles that can contribute to the high structural stability of the battery are mixed, the durability and output characteristics of the entire battery can be improved.

Hereinafter, the present invention will be described in more detail to help the understanding of the present invention. At this time, the terms or words used in the present specification and claims should not be construed as being limited to conventional or dictionary meanings, and the inventor appropriately defines the concept of the term in order to best describe his invention. Based on the principle that it can be done, it should be interpreted as meaning and concept consistent with the technical idea of the present invention.

The positive active material for a lithium secondary battery of the present invention includes a first lithium transition metal oxide particle and a second lithium transition metal oxide particle.

The first lithium transition-average particle diameter (D ₅₀₎ of the metal oxide particle is larger than the average particle diameter (D ₅₀₎ of the second lithium transition metal oxide particle. The positive active material for a lithium secondary battery of the present invention includes _{first and second lithium transition metal oxide particles having different average particle diameters (D 50} ), thereby improving the packing density of the electrode without damaging the active material, thereby increasing energy density per volume, capacity and Lifespan characteristics can be improved. For example, the first lithium transition metal oxide particles may contain a high content of lithium (Li) by increasing the reaction area as an antagonist, thereby improving electrical conductivity and output characteristics, and the second lithium transition metal oxide The particles are small particles and can contribute to the improvement of structural stability and lifespan characteristics of the battery during rolling.

The first lithium transition metal oxide particles have an average particle diameter (D ₅₀ ) of 8.5 μm to 12 μm, preferably 9 μm to 10 μm, and the second lithium transition metal oxide particles have an average particle diameter (D ₅₀ ) of 3 μm. to 5.5 μm, preferably 4 μm to 5 μm. When it is in the above range, output characteristics, lifespan characteristics, and structural stability of the positive active material may be further improved.

In the present specification, the average particle size (D ₅₀ ) may be defined as a particle size corresponding to 50% of the cumulative volume in the particle size distribution curve of the particles. The average particle diameter (D ₅₀ ) may be measured using, for example, a laser diffraction method. The laser diffraction method is generally capable of measuring a particle diameter of several mm from a submicron region, and can obtain high reproducibility and high resolution results.

The first lithium transition metal oxide particles and the second lithium transition metal oxide particles include a transition metal including nickel (Ni) and cobalt (Co) and lithium (Li). The positive electrode active material for a lithium secondary battery includes nickel (Ni) and cobalt (Co) as transition metals, and as will be described later, lithium (Li) with respect to the total number of moles of transition metal among the first and second lithium transition metal oxide particles. By controlling the respective ranges of the mole ratio Li/Me, excellent output characteristics can be exhibited even when lithium transition metal oxide having a low cobalt (Co) content in the transition metal is used.

The first lithium transition metal oxide particles and the second lithium transition metal oxide particles each independently contain nickel (Ni) in an amount of 60 mol% or more, preferably 60 mol% or more and less than 100%, based on 100 mol% of the transition metal. and 15 mol% or less, preferably more than 0 mol% to 15 mol% or less, more preferably 10 mol% to 15 mol% of a transition metal containing cobalt (Co).

The first lithium transition metal oxide particles and the second lithium transition metal oxide particles are each independently at least one selected from the group consisting of Mn, Al, Ba, Ca, Zr, Ti, Mg, Ta, Nb and Mo. It may further include a metal.

The first lithium transition metal oxide particles may include a compound represented by Formula 1, and the second lithium transition metal oxide particles may include a compound represented by Formula 2 below. When the compound represented by Formula 1 and/or Formula 2 is included in the cathode active material, output characteristics and structural stability of the battery may be further improved by the ranges of _{(Li/Me) 1} and (Li/Me) _{2 to be described later.} .

[Formula 1]

Li _a Ni _1-xy Co _x M1 _y M2 _z O ₂

In Formula 1, 1.05 ≤ a ≤ 1.09, x < y, 0 ≤ z ≤ 0.1, 0 < x ≤ 0.15, 0 ≤ y ≤ 0.25, and M1 is at least one selected from the group consisting of Mn and Al, M2 may be at least one selected from the group consisting of Ba, Ca, Zr, Ti, Mg, Ta, Nb and Mo.

[Formula 2]

Li _a' Ni _1-x'-y' Co _x' M1'_y'M2'_z' O ₂

In Formula 2, 1.01 < a' ≤ 1.04, x' < y', 0 ≤ z' ≤ 0.1, 0 < x' ≤ 0.15, 0 ≤ y' ≤ 0.25, and M1' is selected from the group consisting of Mn and Al. At least one selected, M2' may be at least one selected from the group consisting of Ba, Ca, Zr, Ti, Mg, Ta, Nb, and Mo.

_{The ratio (Li/Me) 1} of moles of lithium (Li) to the total number of moles of transition metals of the first lithium transition metal oxide particles is 1.05 to 1.09, and the total number of moles of transition metals of the second lithium transition metal oxide particles A ratio of moles of lithium (Li) to (Li/Me) ₂ may be greater than 1.01 and less than or equal to 1.04.

The positive active material for a lithium secondary battery of the present invention has the above-described (Li/Me) ₁ and (Li/Me) ₂ ranges, thereby improving structural stability and high-temperature characteristics of large and small particles as well as improving output characteristics. can be further improved. In particular, output characteristics even when the first lithium transition metal oxide particles and the second lithium transition metal oxide particles contain cobalt (Co) in a low content, for example, 15 mol% or less of 100 mol% of the transition metal. This does not deteriorate, and the output characteristics, lifespan characteristics and structural stability of the battery can be significantly improved.

A ratio of the number of moles of lithium (Li) to the total number of moles of transition metal in the first lithium transition metal oxide particles (Li/Me) ₁ may be 1.05 to 1.09. When (Li/Me) ₁ is less than 1.05, it is disadvantageous in terms of securing the capacity of the battery, and when (Li/Me) ₁ is more than 1.09, the _{content of lithium impurities such as LiOH and Li 2} CO ₃ increases, and the output decreases or gelation occurs. (gelation), gas generation problems may be increased.

In terms of further improving the capacity characteristics and output characteristics of the battery, (Li/Me) ₁ may be 1.06 to 1.08.

A ratio of the moles of lithium (Li) to the total moles of transition metals of the second lithium transition metal oxide particles (Li/Me) ₂ may be greater than 1.01 and less than or equal to 1.04. In the above range, structural stability and lifespan characteristics of the positive active material may be improved. When (Li/Me) ₂ is 1.01 or less, the improvement in output characteristics is insignificant, and when it exceeds 1.04, _{the lithium impurity content such as LiOH and Li 2} CO ₃ increases to decrease output, and structural stability may be deteriorated.

In terms of further improving the structural stability and lifespan characteristics of the positive active material particles, (Li/Me) ₂ may preferably be 1.02 to 1.03.

The first lithium transition metal oxide particles and the second lithium transition metal oxide particles may be included in a weight ratio of 80:20 to 60:40, preferably 70:30 to 65:35 by weight. When it is in the above range, the effect of simultaneously improving the output characteristics and structural stability of the battery can be excellently implemented.

The (Li/Me) ₁ and the (Li/Me) ₂ may be implemented by appropriately adjusting the content of a precursor such as a salt of a transition metal or a lithium source during the preparation or sintering of the lithium transition metal oxide, but is limited thereto. no.

In addition, the present invention provides a positive electrode for a lithium secondary battery comprising the above-described positive electrode active material for a lithium secondary battery.

The positive electrode for a lithium secondary battery may include the above-described positive electrode active material for a lithium secondary battery, a binder, and a conductive material.

Since the positive electrode for a lithium secondary battery includes the above-described positive electrode active material for a lithium secondary battery, it is possible to secure output characteristics, structural stability, and lifespan characteristics of the battery after the positive electrode is manufactured.

A positive electrode for a lithium secondary battery may include a positive electrode current collector and a positive electrode mixture layer formed on the positive electrode current collector. In this case, the positive electrode mixture layer may include the above-described positive electrode active material for a lithium secondary battery.

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

The positive electrode current collector is not particularly limited as long as it has conductivity without causing a chemical change in the battery, and for example, stainless steel, aluminum, nickel, titanium, sintered carbon, or carbon, nickel, titanium, Those surface-treated with silver or the like may be used. In addition, the positive electrode current collector may typically have a thickness of 3 to 500 μm, and may increase the adhesion of the positive electrode active material by forming fine irregularities on the surface of the positive electrode current collector. For example, the positive electrode current collector may be used in various forms, such as a film, a sheet, a foil, a net, a porous body, a foam, a nonwoven body, and the like.

The binder may improve adhesion between particles of a positive electrode active material for a lithium secondary battery and adhesion between a positive electrode active material for a lithium secondary battery and a positive electrode current collector. For example, the binder may be included in the positive electrode mixture layer.

The binder may be a binder material known in the art without limitation, for example, polyvinyl alcohol, polyacrylonitrile (polyacrylonitrile), carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, Regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof coalescing, single one of these, or a mixture of two or more thereof.

The binder may be included in an amount of 1 to 30% by weight based on the total weight of the positive electrode mixture layer.

The conductive material is used to impart conductivity to the electrode, and may be used without any particular limitation as long as it has electronic conductivity without causing a chemical change in the battery. For example, the conductive material may include graphite such as natural graphite and artificial graphite; carbon-based materials such as carbon black, acetylene black, ketjen black, furnace black, lamp black, summer black, and carbon fiber; metal powders or metal fibers such as copper nickel and aluminum silver; conductive whiskeys 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, and one or a mixture of two or more thereof may be used. The conductive material may be included in an amount of 1 to 30% by weight based on the total weight of the positive electrode mixture layer.

In addition, the present invention provides an electrochemical device including the above-described positive electrode for a lithium secondary battery. The electrochemical device may specifically be 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 positioned to face the positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte. In this case, the positive electrode is the same as described above. In addition, the lithium secondary battery may optionally further include a battery container for accommodating 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 mixture 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 chemical change in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless steel surface. Carbon, nickel, titanium, one surface-treated with silver, an aluminum-cadmium alloy, etc. may be used. In addition, the negative electrode current collector may have a thickness of typically 3 μm to 500 μm, and similarly to the positive electrode current collector, fine irregularities may be formed on the surface of the current collector to strengthen the bonding force of the negative electrode active material. For example, it may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam body, a nonwoven body, and the like.

The negative electrode mixture layer may optionally include a binder and a conductive material together with the negative electrode active material.

As the negative 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 fiber, and amorphous carbon; metal compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy, or Al alloy; metal oxides capable of doping and dedoping lithium, such as SiO _β (0 < β < 2), SnO ₂ , vanadium oxide, lithium titanium oxide, and lithium vanadium oxide; Alternatively, a composite including the metallic compound and a carbonaceous material such as a Si-C composite or a Sn-C composite may be used, 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, as the carbon material, both low crystalline carbon and high crystalline carbon may be used. As low crystalline carbon, soft carbon and hard carbon are representative, and as high crystalline carbon, natural or artificial graphite of amorphous, plate-like, flaky, spherical or fibrous shape, and Kish graphite (Kish) graphite), pyrolytic carbon, mesophase pitch based carbon fiber, meso-carbon microbeads, liquid crystal pitches (Mesophase pitches), and petroleum and coal tar pitch (petroleum or coal tar pitch) High-temperature calcined carbon such as derived cokes) is a representative example.

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

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

On the other hand, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a passage for the movement of lithium ions, and can be used without particular limitation as long as it is normally used as a separator in a lithium secondary battery, especially for the movement of ions in the electrolyte It is preferable to have a low resistance to and excellent electrolyte moisture content. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene/butene copolymer, an ethylene/hexene copolymer, and an ethylene/methacrylate copolymer, or these A laminate structure of two or more layers of may be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high melting point glass fiber, polyethylene terephthalate fiber, etc. may be used. In addition, in order to secure heat resistance or mechanical strength, a coated separator including a ceramic component or a polymer material may be used, and may optionally be used in a single-layer or multi-layer structure.

In addition, 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 molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries, and are limited to these. it's not going to be

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

The organic solvent may be used without any 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, as the organic solvent, ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, ε-caprolactone; 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), ethylenecarbonate (EC), propylene carbonate (PC) ) carbonate solvents such as; alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may contain a double bond aromatic ring or ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; Or sulfolanes and the like may be used. Among them, a carbonate-based solvent is preferable, and a cyclic carbonate (eg, ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant capable of increasing the charge/discharge performance of the battery, and a low-viscosity linear carbonate-based compound ( For example, a mixture of ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate) is more preferable. In this case, when the cyclic carbonate and the chain carbonate are mixed in a volume ratio of about 1:1 to about 1:9, the electrolyte may exhibit excellent 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 may 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, the electrolyte may exhibit excellent electrolyte performance because it has appropriate conductivity and viscosity, and lithium ions may move effectively.

In addition to the electrolyte components, the electrolyte includes, for example, haloalkylene carbonate-based compounds such as difluoroethylene carbonate, pyridine, tri Ethyl phosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imida One or more additives such as jolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol or aluminum trichloride may be further included. In this case, the additive may be included in an amount of 0.1 to 5% by weight based on the total weight of the electrolyte.

As described above, the lithium secondary battery including the positive electrode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics and capacity retention rate, so portable devices such as mobile phones, notebook computers, digital cameras, and hybrid electric vehicles It is useful in the field of electric vehicles 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 is a power tool (Power Tool); electric vehicles, including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); Alternatively, it may be used as a power source for any one or more medium and large-sized devices in a system for power storage.

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

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

Hereinafter, embodiments of the present invention will be described in detail so that those of ordinary skill in the art can easily carry out the present invention. However, the present invention may be embodied in many different forms and is not limited to the embodiments described herein.

Examples and Comparative Examples

Example 1: Preparation of positive electrode active material and positive electrode for lithium secondary battery

1. Preparation of cathode active material for lithium secondary battery

As the first lithium transition metal oxide particles, the average particle diameter (D ₅₀ ) is 9.5 μm, (Li/Me) ₁ is 1.08 Li _1.08 Ni _0.6 Co _0.15 Mn _0.25 O ₂ Prepared, and as the second lithium transition metal oxide particles The average particle diameter (D ₅₀ ) is 4.5 μm, (Li/Me) ₂ is 1.03 Li _1.03 Ni _0.6 Co _0.15 Mn _0.25 O ₂ was prepared.

Thereafter, the first lithium transition metal oxide particles and the second lithium transition metal oxide particles were mixed in a weight ratio of 70:30 to prepare a cathode active material for a lithium secondary battery.

2. Preparation of positive electrode for lithium secondary battery

A composition for forming a positive electrode was prepared by mixing the positive electrode active material for a lithium secondary battery prepared above, carbon black, and a binder in a weight ratio of 92.5:3.5:4.0, applied to one side of an aluminum current collector, and dried at 130° C. , to prepare a positive electrode by rolling.

Example 2: Preparation of positive electrode active material and positive electrode for lithium secondary battery

1. Preparation of cathode active material for lithium secondary battery

As the first lithium transition metal oxide particles, the average particle diameter (D ₅₀ ) is 9.5 μm, (Li/Me) ₁ is 1.06 Li _1.06 Ni _0.6 Co _0.15 Mn _0.25 O ₂ Prepared, and as the second lithium transition metal oxide particles The average particle diameter (D ₅₀ ) is 4.5 μm, (Li/Me) ₂ is 1.03 Li _1.03 Ni _0.6 Co _0.15 Mn _0.25 O ₂ was prepared.

Thereafter, the first lithium transition metal oxide particles and the second lithium transition metal oxide particles were mixed in a weight ratio of 70:30 to prepare a cathode active material for a lithium secondary battery.

2. Preparation of positive electrode for lithium secondary battery

A composition for forming a positive electrode was prepared by mixing the positive electrode active material for a lithium secondary battery prepared above, carbon black, and a binder in a weight ratio of 92.5:3.5:4.0, applied to one side of an aluminum current collector, and dried at 130° C. , to prepare a positive electrode by rolling.

Comparative Example 1: Preparation of positive electrode active material and positive electrode for lithium secondary battery

1. Preparation of cathode active material for lithium secondary battery

As the first lithium transition metal oxide particles, the average particle diameter (D ₅₀ ) is 9.5 μm, (Li/Me) ₁ is 1.03 Li _1.03 Ni _0.6 Co _0.15 Mn _0.25 O ₂ Prepared, and as the second lithium transition metal oxide particles The average particle diameter (D ₅₀ ) is 4.5 μm, (Li/Me) ₂ is 1.03 Li _1.03 Ni _0.6 Co _0.15 Mn _0.25 O ₂ was prepared.

Thereafter, the first lithium transition metal oxide particles and the second lithium transition metal oxide particles were mixed in a weight ratio of 70:30 to prepare a cathode active material for a lithium secondary battery.

2. Preparation of positive electrode for lithium secondary battery

A composition for forming a positive electrode was prepared by mixing the positive electrode active material for a lithium secondary battery prepared above, carbon black, and a binder in a weight ratio of 92.5:3.5:4.0, applied to one side of an aluminum current collector, and dried at 130° C. , to prepare a positive electrode by rolling.

Comparative Example 2: Preparation of a cathode active material and a cathode for a lithium secondary battery

1. Preparation of cathode active material for lithium secondary battery

As the first lithium transition metal oxide particles, the average particle diameter (D ₅₀ ) is 9.5 μm, (Li/Me) ₁ is 1.08 Li _1.08 Ni _0.6 Co _0.15 Mn _0.25 O ₂ Prepared, and as the second lithium transition metal oxide particles The average particle diameter (D ₅₀ ) is 4.5 μm, (Li/Me) ₂ is 1.08 Li _1.08 Ni _0.6 Co _0.15 Mn _0.25 O _{2 It} was prepared.

Thereafter, the first lithium transition metal oxide particles and the second lithium transition metal oxide particles were mixed in a weight ratio of 70:30 to prepare a cathode active material for a lithium secondary battery.

2. Preparation of positive electrode for lithium secondary battery

A composition for forming a positive electrode was prepared by mixing the positive electrode active material for a lithium secondary battery prepared above, carbon black, and a binder in a weight ratio of 92.5:3.5:4.0, applied to one side of an aluminum current collector, and dried at 130° C. , to prepare a positive electrode by rolling.

Comparative Example 3: Preparation of a cathode active material for a lithium secondary battery and a cathode

1. Preparation of cathode active material for lithium secondary battery

As the first lithium transition metal oxide particles, the average particle diameter (D ₅₀ ) is 9.5 μm, (Li/Me) ₁ is 1.04 Li _1.04 Ni _0.6 Co _0.15 Mn _0.25 O ₂ Prepared, and as the second lithium transition metal oxide particles The average particle diameter (D ₅₀ ) is 4.5㎛, (Li/Me) ₂ is 1.01 Li _1.01 Ni _0.6 Co _0.15 Mn _0.25 O ₂ was prepared.

Thereafter, the first lithium transition metal oxide particles and the second lithium transition metal oxide particles were mixed in a weight ratio of 70:30 to prepare a cathode active material for a lithium secondary battery.

2. Preparation of positive electrode for lithium secondary battery

A composition for forming a positive electrode was prepared by mixing the positive electrode active material for a lithium secondary battery prepared above, carbon black, and a binder in a weight ratio of 92.5:3.5:4.0, applied to one side of an aluminum current collector, and dried at 130° C. , to prepare a positive electrode by rolling.

Experimental example

Experimental Example 1: Evaluation of high temperature life

After preparing a monocell (using a graphite negative electrode) using the positive electrode active material of Examples and Comparative Examples and the positive electrode for a lithium secondary battery prepared therefrom, high temperature life was confirmed. Specifically, the monocell was charged/discharged 400 times at a temperature of 45° C. under the conditions of 1C/1C within the driving voltage range of 3.0V to 4.25V. As a result, the cycle capacity retention, which is the ratio of the discharge capacity to the initial capacity after 400 charging and discharging at a high temperature (45° C.), is shown in Table 1 and FIG. 1 .

Experimental Example 2: Evaluation of room temperature and low temperature output characteristics

After preparing a monocell (using a graphite negative electrode) using the positive electrode active material of Examples and Comparative Examples and the positive electrode for a lithium secondary battery prepared therefrom, room temperature and low temperature output characteristics were evaluated.

(1) Evaluation of room temperature output characteristics

For the lithium secondary batteries prepared in Examples and Comparative Examples, the cell resistance was measured by conducting a charge/discharge test for 30 seconds at 25° C. with a charge termination voltage of 4.25V, a discharge termination voltage of 3.0V, and 2.5C, and when the SOC was 50% Table 1 shows the resistance value and resistance percentage of , and the resistance value for each SOC is shown in FIG. 2 .

(2) Evaluation of low temperature output characteristics

For lithium secondary batteries prepared in Examples and Comparative Examples, under the conditions of a final charge voltage of 4.25V and a final discharge voltage of 3.0V, after resting for about 3 hours at -10°C, SOC 35%, 0.4C to SOC 20% By discharging, the voltage drop, resistance value and resistance percentage were measured and shown in Table 1 below, and a voltage drop graph is shown in FIG. 3 .

High temperature life characteristics (400cycles) Room temperature output characteristics (SOC 50%) Low temperature output characteristics Capacity retention rate (%) Resistance (Ω) Resistance Percentage (%) Voltage drop (V) Resistance (Ω) Resistance Percentage (%) Example 1 86.6 1.37 94.1 0.50 31.8 85.5 Example 2 85.3 1.38 94.6 0.51 32.8 88.2 Comparative Example 1 81.2 1.46 100.0 0.58 37.2 100.0 Comparative Example 2 80.2 1.49 101.9 0.59 37.7 101.3 Comparative Example 3 79.9 1.47 100.7 0.55 35.1 94.4

Referring to Table 1 and FIGS. 1 to 3 , the positive electrode active material for a lithium secondary battery has different average particle diameters (D ₅₀ ) and uses a blend of particles having a specific Li/Me ratio, high temperature lifespan characteristics, output characteristics, and structural It can be seen that the stability is significantly improved.

However, in Comparative Examples, it can be seen that the capacity retention rate is very reduced after 400 cycles, and the resistance is increased at room temperature and low temperature, or the voltage drop width is increased, so that the output characteristics are very poor.

Claims (9)

first lithium transition metal oxide particles; and
It comprises a second lithium transition metal oxide particles,
The first lithium transition-average particle diameter (D ₅₀₎ of the metal oxide particles and the second lithium-transition greater than the average particle diameter (D ₅₀₎ of the metal oxide particles,
The first lithium transition metal oxide particles and the second lithium transition metal oxide particles include a transition metal containing nickel (Ni) and cobalt (Co) and lithium (Li),
_{The ratio (Li/Me) 1} of moles of lithium (Li) to the total number of moles of transition metals of the first lithium transition metal oxide particles is 1.05 to 1.09, and the total number of moles of transition metals of the second lithium transition metal oxide particles The ratio of the number of moles of lithium (Li) to (Li/Me) ₂ is greater than 1.01 to 1.04 or less, a positive active material for a lithium secondary battery.
The method according to claim 1, wherein the ratio of the number of moles of lithium (Li) to the total number of moles of transition metal of the first lithium transition metal oxide particles (Li / Me) ₁ is 1.06 to 1.08,
The ratio of the moles of lithium (Li) to the total moles of transition metals of the second lithium transition metal oxide particles (Li/Me) ₂ is 1.02 to 1.03 or less, a positive active material for a lithium secondary battery.
The method according to claim 1, wherein the first lithium transition metal oxide particles and the second lithium transition metal oxide particles are each independently 60 mol% or more of nickel (Ni) and 15 mol% or less of cobalt (Co) based on 100 mol% of the transition metal ) A cathode active material for a lithium secondary battery, including a transition metal comprising a.
The method according to claim 1, wherein the first lithium transition metal oxide particles and the second lithium transition metal oxide particles are each independently selected from the group consisting of Mn, Al, Ba, Ca, Zr, Ti, Mg, Ta, Nb and Mo A cathode active material for a lithium secondary battery further comprising at least one kind.
The method according to claim 1, wherein the first lithium transition metal oxide particles include a compound represented by the following formula (1),
The second lithium transition metal oxide particles include a compound represented by the following formula (2), a cathode active material for a lithium secondary battery:
[Formula 1]
Li _a Ni _1-xy Co _x M1 _y M2 _z O ₂
(in Formula 1, 1.05 ≤ a ≤ 1.09, x < y, 0 ≤ z ≤ 0.1, 0 < x ≤ 0.15, 0 ≤ y ≤ 0.25, and M1 is at least one selected from the group consisting of Mn and Al, M2 is at least one selected from the group consisting of Ba, Ca, Zr, Ti, Mg, Ta, Nb and Mo)
[Formula 2]
Li _a' Ni _1-x'-y' Co _x' M1'_y'M2'_z' O ₂
(In Formula 2, 1.01 <a' ≤ 1.04, x'<y', 0 ≤ z' ≤ 0.1, 0 <x' ≤ 0.15, 0 ≤ y' ≤ 0.25, and M1' is from the group consisting of Mn and Al. At least one selected from the group consisting of M2' is at least one selected from the group consisting of Ba, Ca, Zr, Ti, Mg, Ta, Nb and Mo).
The method according to claim 1, The first lithium transition metal oxide particles have an average particle diameter (D ₅₀ ) of 8.5 to 12㎛,
The second lithium transition metal oxide particles have an average particle diameter (D ₅₀ ) of 3 to 5.5 μm, a cathode active material for a lithium secondary battery.
The positive active material for a lithium secondary battery according to claim 1, wherein the first lithium transition metal oxide particle and the second lithium transition metal oxide particle are included in a weight ratio of 60:40 to 80:20.
The positive active material for a lithium secondary battery of any one of claims 1 to 7;
bookbinder; and
A positive electrode for a lithium secondary battery comprising a conductive material.
A lithium secondary battery comprising the positive electrode for a lithium secondary battery of claim 8.

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