KR102095520B1 - Positive Electrode Active Material for Lithium Secondary Battery Comprising Lithium Cobalt Oxide with Core-Shell Structure and Method of Manufacturing the Same - Google Patents

Abstract

The present invention is a cathode active material for a lithium secondary battery comprising a core-shell structured lithium cobalt doped oxide,
The lithium cobalt doped oxide of the core and the lithium cobalt doped oxide of the shell each independently contain three types of dopants;
It relates to a positive electrode active material and a method for manufacturing the same, characterized in that the ratio of the average oxidation number of the dopants present in the core and the average oxidation number of the dopants present in the shell satisfies the following condition (1).
0.7 ≤ r (ratio) = OC / OS <0.95 (1)
Here, the OC is the average oxidation number of the dopants present in the core, and the OS is the average oxidation number of the dopants present in the shell.

Description

Positive Electrode Active Material for Lithium Secondary Battery Comprising Lithium Cobalt Oxide with Core-Shell Structure and Method of Manufacturing the Same}

The present invention relates to a cathode active material for a lithium secondary battery comprising a core-shell structured lithium cobalt oxide and a method for manufacturing the same.

As the technology development and demand for mobile devices increases, the demand for secondary batteries as an energy source is rapidly increasing, and among such secondary batteries, a lithium secondary battery exhibiting high energy density and operating potential, long cycle life, and low self-discharge rate Has been commercialized and widely used.

In addition, as interest in environmental problems has increased, research into electric vehicles and hybrid electric vehicles capable of replacing fossil fuel vehicles such as gasoline vehicles and diesel vehicles, which are one of the main causes of air pollution, has been conducted. . As a power source for such electric vehicles and hybrid electric vehicles, nickel-metal hydride secondary batteries are mainly used, but studies using lithium secondary batteries having a high energy density and discharge voltage are actively being conducted, and are in some commercialization stages.

At present, LiCoO ₂ , Samsung branch (NMC / NCA), LiMnO ₄ , and LiFePO ₄ are used as cathode materials for lithium secondary batteries. Among them, in the case of LiCoO ₂ , the advantages such as high rolling density are clearly present, and thus LiCoO ₂ is still used a lot, and research is being conducted to increase the use voltage to develop a high-capacity secondary battery. However, LiCoO ₂ has a low charge / discharge current of about 150 mAh / g, and has a problem in that its crystal structure is unstable at a voltage of 4.3 V or higher, resulting in a rapid decrease in life characteristics, and there is a risk of ignition due to reaction with an electrolyte. .

To solve this problem, in the prior art, wherein the LiCoO ₂ doped with a metal such as Al, Ti, Mg, Zr, or a technique of coating a metal such as Al, Ti, Mg, Zr on the surface of LiCoO ₂ also used, but , All of these prior arts only disclose a method of doping the doping element within 50 ppm to 8000 ppm, and there is still a problem that structural stability cannot be maintained at a high voltage of more than 4.5 V. In the case of the coating layer made of the metal, Li during charging and discharging Interfering with the movement of ions or reducing the capacity of LiCoO ₂ , rather deteriorating the performance of the secondary battery, there was still a problem in stability and life characteristics at high temperature and high voltage.

Therefore, there is a high need to develop a positive electrode active material based on lithium cobalt oxide with high life characteristics and enhanced stability even in a high temperature and high voltage environment.

The present invention aims to solve the problems of the prior art as described above and the technical problems requested from the past.

After extensive research and various experiments, the inventors of the present application have an average oxidation number ratio of three types of dopants independently doped to the lithium cobalt doped oxide of the core and the lithium cobalt doped oxide of the shell, as described later. When the condition (1) of claim 1 is satisfied, the structural stability of the crystal structure is improved even in the operating voltage range of more than 4.5 V, and the crystal structure is maintained. .

Accordingly, the positive electrode active material for a secondary battery according to the present invention is a positive electrode active material for a lithium secondary battery comprising a lithium cobalt doped oxide having a core-shell structure,

The lithium cobalt doped oxide of the core and the lithium cobalt doped oxide of the shell each independently contain three types of dopants;

The ratio of the average oxidation number of the dopants present in the core to the average oxidation number of the dopants present in the shell is characterized by satisfying the following condition (1).

0.7 ≤ r (ratio) = OC / OS <0.95 (1)

Here, the OC is the average oxidation number of the dopants present in the core, and the OS is the average oxidation number of the dopants present in the shell.

In general, when a lithium cobalt oxide for driving a battery of 4.35V, 4.4V, or 4.45V as a positive electrode active material is used as a high voltage, the lithium cobalt oxide is doped with Al, Ti, Zr, Mg, P, Ca, F, Co, etc. Alternatively, structural durability and surface stability were realized in a high voltage environment by coating. Specifically, lithium cobalt oxide as the essential characteristics from Li _x CoO ₂ in the x <50 situation Co ³⁺ increases the structural stress due to the ionic radius of, small Co ^{4+ 4+} As oxidized to Co, and continue to When charging is reduced to around x = 20, a structure change from the O3 structure to the H1-3 structure occurs in the 4.53V region based on the coin half-cell voltage. This structural change occurs irreversibly during charging and discharging, and the inferiority of efficiency, discharge rate characteristics, and life characteristics at 4.55 V or higher is remarkably confirmed. Of course, in the existing 4.2V to 4.45V cell development, charging and discharging was performed without significant change from the O3 structure (of course, there is a change to the mono-clinic phase, but this is reversible and does not affect the lifespan), but the battery is 4.5V or more In order to drive, there is a problem that a structure change to the H1-3 should be prevented.

Accordingly, the inventors of the present application, after repeated in-depth research, as the core-shell structured lithium cobalt doped oxide, the core lithium cobalt doped oxide and the shell lithium cobalt doped oxide each have three types of dopants. When the average oxidation number of the dopants doped into the core and the shell is adjusted by controlling the average oxidation number, the surface structure change is suppressed under high temperature and high voltage to improve the structural stability of the positive electrode active material particles, thereby significantly improving the life characteristics. Turned out to be.

In the specification of the present application, the driving voltage is written on a half coin cell basis.

Here, when the r (ratio) is outside the range of condition (1), a large number of irreversible crystal structure changes occur, and thus, inferiority also appears in the lifespan characteristics, and thus the desired effect of the present invention cannot be obtained. More specifically, the r (ratio) may satisfy the condition of 0.8 ≤ r <0.95.

The core-shell structured lithium cobalt-doped oxide that satisfies these conditions can maintain a crystal structure without phase change in a range in which the anode potential at full charge is greater than 4.5 V based on the Li potential.

First, the lithium cobalt doped oxide of the core may have a composition of Formula 1 below.

Li _a Co _1-xyz M1 _x M2 _y M3 _z O ₂ (1)

In the above formula,

M1, M2 and M3 are each independently one element selected from the group consisting of Ti, Mg, Al, Zr, Ba, Ca, Ta, Nb, Mo, Ni, Zn, Si, V and Mn;

0.95≤a≤1.05;

0 <x≤0.04, 0 <y≤0.04, and 0 <z≤0.04.

Similarly, the lithium cobalt doped oxide of the shell may have the composition of Formula 2 below.

Li _b Co _1-stw M1 ' _s M2' _t M3 ' _w O ₂ (1)

In the above formula,

M1 ', M2' and M3 'are each independently selected from the group consisting of Ti, Mg, Al, Zr, Ba, Ca, Ta, Nb, Mo, Ni, Zn, Si, V and Mn ;

0.95≤b≤1.05;

0 <s≤0.04, 0 <t≤0.04, and 0 <w≤0.04.

That is, as shown in the above formula, the composition formulas of the core and the shell are all three types of dopants doped at the cobalt site, and do not differ significantly in the type and amount of doping elements.

Therefore, as can be seen from the above, the concept of the shell is not a completely independent phase separate from the core, but can be regarded as the same concept as surface doping due to a change in composition and / or content, so long as it can distinguish between the core and the shell. Surface-doped constructions are also within the scope of the present invention.

At this time. The thickness of the shell having a difference in composition different from the core may be 50 to 2000 nm, and specifically, 50 to 200 nm.

Outside the above range, if the thickness of the shell is too thick, the resistance may be large due to the influence of a large shell, and there may be a problem in that the resistance and rate characteristics may be negative due to the disconnection of the Li ion transport passage, If the thickness is too thin, it may not be possible to guarantee high voltage stability by the shell, which is not preferable.

The types of dopants substituted in the cobalt sites of the core and the shell may be the same in all (M1 = M1 ', M2 = M2', M3 = M3 '), and different (M1 ≠ M1' ≠ M2 ≠ M2 '≠ M3 ≠) M3 '), and some may be the same, for example, M1 = M1', M2 = M2 ', M3_M3', and any combination is possible and is not limited to the above example. When all kinds of dopants are the same, the content is determined in a range that satisfies the above condition (1), so some or all of them are different.

Even if the types of dopants substituted in the cobalt sites of the core and the shell are different, some or all of the elements having the same oxidation number of the respective dopants can be selected, so that the content is the same in the range that satisfies the condition (1). , Or may be different.

Moreover, M1, M2, and M3, and M1 ', M2', and M3 'are selected from the above dopants, and M1, M2, and M3, or M1', M2 ', and M3' have the same oxidation number. The number may be different, but in detail, each dopant substituted at the cobalt site of the core and the shell may have a different oxidation number, and in detail, M1 and M1 'are +2 metals of oxidation number, and M2 and M2 'Is a metal of +3 valence oxidation water, and M3 and M3' may be a metal of +4 valence oxidation water.

As described above, when the dopants doped in the core and the shell have different oxidation numbers from other elements doped together, so that +2, +3, and +4 all have oxidation water, it is more advantageous for the structural stability intended by the present invention. Do.

Specifically, the metal of +2 is oxidized water, the doped metal is oxidized before Co ³⁺ , to prevent the oxidation to Co ⁴⁺ to prevent the occurrence of structural stress can improve the structural stability, +3 is oxidized water The metal maintains the structure in place of the cobalt oxidized with Co ⁴⁺ and also improves the surface stability, and the metal of +4 valent oxidation water suppresses the change in surface structure under high temperature and high voltage, and the movement of lithium ions is relatively It is easy to prevent the degradation of the output characteristics of the secondary battery. By the combination of these dopants, the lithium cobalt doped oxide according to the present invention can maintain structural stability even in an operating range of more than 4.5V.

That is, the dopants having different oxidation numbers doped in each of the above partially replace the cobalt site of the lithium cobalt oxide, thereby serving to improve structural safety according to each time and situation.

In this case, the metals M1 and M1 'of the +2 valence oxidation water are each independently one element selected from the group consisting of Mg, Ca, Ni and Ba; The metals M2 and M2 'of the +3 valence oxide are each independently one element selected from the group consisting of Ti, Al, Ta and Nb; The metals M3 and M3 'of the +4 valent oxidation water are each independently selected from the group consisting of Ti, Ta, Nb, Mn and Mo, and may be elements different from M2 and M2', and more specifically, +2 is the oxidation water The metal (M1) of Mg is, the metal of the +3 valence oxidation water (M2) is Ti or Al, and the metal (M3) of the +4 valence oxidation water may be Ti, Nb or Mo.

Moreover, the structural stability does not continue to increase even if all of these dopants are included in an excessive amount, and the average oxidation number of the core and the shell does not exceed 12% based on the molar ratio in the core and the shell, respectively, without the total content of the doped dopants being increased. As described above, it is possible to exert improved structural stability when the ratio satisfies the condition (1).

Meanwhile, the respective dopants may be uniformly doped throughout the core and shell of the lithium cobalt doped oxide to prevent local structural changes in the particles, although not limited.

In addition, in order to further improve the stabilization of the surface structure of the lithium cobalt doped oxide, Al ₂ O ₃ having a thickness of 50 nm to 100 nm may be coated on the surface of the lithium cobalt doped oxide.

In addition, the present invention provides a method for preparing a lithium-cobalt-doped oxide having a core-shell structure of the positive electrode active material,

(i) a process of preparing a doped cobalt precursor containing three types of dopants by coprecipitation; And

(ii) a process of mixing the doped cobalt precursor and a lithium precursor and performing primary firing to produce core particles; And

(iii) preparing a core-shell structured lithium cobalt-doped oxide by mixing the core particles, cobalt precursor, lithium precursor, and three types of dopant precursors and performing secondary firing to form a shell on the surface of the core particles;

It may include.

According to the above manufacturing method, the core-shell structured lithium cobalt-doped oxide is first prepared by co-precipitating a doped cobalt precursor containing a dopant, and then firing the doped cobalt precursor and lithium precursor Through the process, since doping is performed on the cobalt precursor itself during core production, it is generated by reacting with the lithium precursor, so that the dopant can react with the lithium precursor evenly distributed in the cobalt, and there are fewer by-products to obtain the present invention The yield of lithium cobalt doped oxide containing dopants is high.

Here, in the process (i), after dissolving the salts and cobalt salts containing the dopant element in water, the solution is converted to a basic atmosphere to prepare a doped cobalt oxide as a doped cobalt precursor by coprecipitation. At this time, the content of the salts containing the dopant element and the content of the cobalt salt may be determined by considering the composition of the final product core.

Salts and cobalt salts containing the dopant element for preparing the doped cobalt precursor of step (i) are not limited as long as they are capable of performing a co-precipitation process, for example, in the form of carbonate, sulfate, or nitrate. And, in particular, sulfate.

In the process (iii), the content of the cobalt precursor, lithium precursor, and three types of dopant precursor may be determined by considering the composition of the shell. At this time, it is of course mixed to satisfy the above condition (1).

For additional metal coating on the lithium cobalt doped oxide, for example, an oxide such as Al ₂ O ₃ may be dry or wet mixed, and the method disclosed in the art is not limited.

In addition, the present invention provides another method for producing a lithium-cobalt-doped oxide having a core-shell structure of the positive electrode active material, and specifically, the manufacturing method,

(i) a process of mixing the cobalt precursor, the lithium precursor, and the three types of dopant precursors and performing primary firing to produce core particles; And

(ii) the core particle, the cobalt precursor, the lithium precursor, and independently of the process (i), three types of dopant precursors are mixed and secondary fired to form a shell on the surface of the core particle to form a shell on the surface of the core particle, lithium Preparing a cobalt doped oxide;

It may include.

According to the above manufacturing method, a cobalt precursor, a lithium precursor, and a dopant precursor are mixed together and fired from the core to the shell to produce a lithium cobalt doped oxide in a more convenient manner.

At this time, in each of the above steps, the content of the dopant precursors and the content of the cobalt precursors may determine the mixing ratio in consideration of the final product. In addition, the mixing ratio of the dopant precursors in steps (i) and (ii) may be set to satisfy the condition (1).

On the other hand, it is possible to prepare the core-shell structured lithium cobalt-doped oxide of the present invention by any of the above methods, wherein the cobalt precursor may be cobalt oxide, for example, Co ₃ O ₄ , and the dopant precursor These may be metals, metal oxides or metal salts for dopants, and the lithium precursors are also not limited, but may be one or more selected from the group consisting of LiOH and Li ₂ CO ₃ .

As described above, the dopants of the three types of dopant precursors may have the same or different oxidation numbers if they are different types, but in various ways at high voltage, in order to exhibit more improved structural stability, in detail, different oxidation numbers It may have, and, more specifically, +2 may be a metal of oxidized water, +3 of a metal of oxidized water, and +4 of a oxidized metal.

Meanwhile, the primary firing for obtaining the lithium cobalt doped oxide of the core is performed for 8 to 12 hours at a temperature of 850 ° C to 1100 ° C, and the secondary firing for forming a shell is at a temperature of 700 ° C to 1100 ° C 5 hours to 12 hours.

When the primary firing is performed at an excessively low temperature outside the above range or when performed for an excessively short period of time, the lithium source may not sufficiently penetrate and the positive electrode active material may not be stably formed. , When it is performed for an excessively high temperature or an excessively long time out of the above range, the physical and chemical properties of the lithium cobalt oxide in which the doping is performed may be changed, which may cause performance degradation.

Similarly, when the secondary firing is performed for an excessively low temperature or an excessively short time outside the above range, precursors constituting the shell may remain between the positive electrode active materials without reacting to cause deterioration of the battery performance, Conversely, when the secondary firing is performed for an excessively high temperature or too long time outside the above range, the dopant component of the shell may be doped into the core portion, in which case the condition (1) is satisfied. It is not desirable because it is difficult to manufacture.

As a result, in the core-shell structured lithium cobalt-doped oxide, the ratio of the average oxidation number of the dopants present in the core and the average oxidation number of the dopants present in the shell may satisfy the condition (1), and the present invention Exert the intended effect.

The present invention also provides a positive electrode characterized in that it is produced by applying a slurry containing the positive electrode active material, a conductive material, and a binder to a current collector. If necessary, a filler may be further added to the slurry.

The positive electrode current collector is generally manufactured to a thickness of 3 to 500 μm, and is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium , And may be used one selected from carbon, nickel, titanium or silver surface treatment on the surface of aluminum or stainless steel, specifically aluminum may be used. The current collector may also increase the adhesion of the positive electrode active material by forming fine irregularities on its surface, and various forms such as a film, sheet, foil, net, porous body, foam, and nonwoven fabric are possible.

The positive electrode active material may include, for example, a layered compound such as lithium nickel oxide (LiNiO ₂ ) or a compound substituted with one or more transition metals, in addition to the positive electrode active material particles; Lithium manganese oxides such as the formula Li _{1 + x} Mn _2-x O ₄ (where x is 0 to 0.33), LiMnO ₃ , LiMn ₂ O ₃ , LiMnO ₂ ; Lithium copper oxide (Li ₂ CuO ₂ ); Vanadium oxides such as LiV ₃ O ₈ , LiV ₃ O ₄ , V ₂ O ₅ and Cu ₂ V ₂ O ₇ ; A Ni-site type lithium nickel oxide represented by the formula LiNi _1-x M _x O ₂ (where M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, and x = 0.01 to 0.3); Formula LiMn _2-x M _x O ₂ (where M = Co, Ni, Fe, Cr, Zn or Ta, x = 0.01 to 0.1) or Li ₂ Mn ₃ MO ₈ (where M = Fe, Co, Lithium manganese composite oxide represented by Ni, Cu or Zn); LiMn ₂ O _{4 in} which part of Li in the formula is substituted with alkaline earth metal ions; Disulfide compounds; Fe ₂ (MoO ₄ ) _{3 And the like} , it is not limited to these.

The conductive material is usually added in 1 to 30% by weight based on the total weight of the positive electrode mixture containing the positive electrode active material. The conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the battery. For example, graphite such as natural graphite or artificial graphite; Carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black; Conductive fibers such as carbon fibers and metal fibers; Metal powders such as carbon fluoride powder, aluminum powder, and nickel powder; Conductive whiskey such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives may be used.

The binder is a component that assists in bonding the active material and the conductive material and the like to the current collector, and is usually added at 1 to 30% by weight based on the total weight of the mixture containing the positive electrode active material. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropyl cellulose, recycled cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene , Polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluorine rubber, and various copolymers.

The filler is optionally used as a component that inhibits the expansion of the positive electrode, and is not particularly limited as long as it is a fibrous material without causing chemical changes in the battery, and includes, for example, an olefinic polymer such as polyethylene and polypropylene; Fibrous materials such as glass fibers and carbon fibers are used.

The present invention also provides a secondary battery comprising the positive electrode, the negative electrode and the electrolyte. The secondary battery is not particularly limited in its kind, but as a specific example, it may be a lithium secondary battery such as a lithium ion battery or a lithium ion polymer battery having advantages such as high energy density, discharge voltage, and output stability.

Generally, a lithium secondary battery is composed of a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte containing lithium salt.

Hereinafter, other components of the lithium secondary battery will be described.

The negative electrode is manufactured by applying and drying a negative electrode active material on a negative electrode current collector, and if necessary, components as described above may be optionally further included.

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

The negative active material includes, for example, carbon such as non-graphitized carbon and graphite-based carbon; Li _x Fe ₂ O ₃ (0≤x≤1), Li _x WO ₂ (0≤x≤1), Sn _x Me _1-x Me ' _y O _z (Me: Mn, Fe, Pb, Ge; Me' : Al, B, P, Si, group 1, group 2, group 3 elements of the periodic table, halogen; metal composite oxides such as 0 <x≤1;1≤y≤3;1≤z≤8); Lithium metal; Lithium alloys; Silicon-based alloys; Tin-based alloys; SnO, SnO ₂ , PbO, PbO ₂ , Pb ₂ O ₃ , Pb ₃ O ₄ , Sb ₂ O ₃ , Sb ₂ O ₄ , Sb ₂ O ₅ , GeO, GeO ₂ , Bi ₂ O ₃ , Bi ₂ O ₄ , and Bi ₂ O ₅ ; Conductive polymers such as polyacetylene; Li-Co-Ni based materials and the like can be used.

The separator is interposed between the anode and the cathode, and an insulating thin film having high ion permeability and mechanical strength is used. The pore diameter of the separator is generally 0.01 to 10 micrometers, and the thickness is generally 5 to 30 micrometers. Examples of the separator include olefin-based polymers such as polypropylene, which are chemically resistant and hydrophobic; Sheets or non-woven fabrics made of glass fiber or polyethylene are used. When a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte may also serve as a separator.

The electrolyte solution may be a lithium salt-containing non-aqueous electrolyte, and the lithium salt-containing non-aqueous electrolyte is composed of a non-aqueous electrolyte and a lithium salt, and the non-aqueous electrolyte includes a non-aqueous organic solvent, an organic solid electrolyte, and an inorganic solid electrolyte. It is not limited to.

Examples of the non-aqueous organic solvent include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, and gamma. -Butyl lactone, 1,2-dimethoxy ethane, tetrahydroxyfuran, 2-methyl tetrahydrofuran, dimethylsulfoxide, 1,3-dioxorun, formamide, dimethylformamide, dioxorun, acetonitrile , Nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxy methane, dioxoren derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, Aprotic organic solvents such as tetrahydrofuran derivatives, ethers, methyl pyropionate, and ethyl propionate can be used.

Examples of the organic solid electrolyte include polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphoric acid ester polymers, poly agitation lysine, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, and ions. A polymerization agent containing a sex dissociating group and the like can be used.

Examples of the inorganic solid electrolyte include Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, LiSiO ₄ , LiSiO ₄ -LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Li ₄ nitrides such as SiO ₄ -LiI-LiOH, Li ₃ PO ₄ -Li ₂ S-SiS ₂ , halides, sulfates, and the like can be used.

The lithium salt is a material that is soluble in the nonaqueous electrolyte, for example, LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF ₆ , LiSbF ₆ , LiAlCl ₄ , CH ₃ SO ₃ Li, (CF ₃ SO ₂ ) ₂ NLi, lithium chloroborane, lower aliphatic lithium carboxylate, lithium 4-phenyl borate, imide, and the like.

In addition, the non-aqueous electrolyte solution has the purpose of improving charge / discharge properties, flame retardancy, etc., for example, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme (glyme), hexaphosphate triamide, Nitrobenzene derivatives, sulfur, quinone imine dye, N-substituted oxazolidinone, N, N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxy ethanol, aluminum trichloride, etc. may be added. have. In some cases, in order to impart non-flammability, a halogen-containing solvent such as carbon tetrachloride or ethylene trifluoride may be further included, or carbon dioxide gas may be further included to improve high temperature storage characteristics, and FEC (Fluoro-Ethylene) Carbonate), PRS (Propene sultone), etc. may be further included.

In one specific example, lithium salts such as LiPF ₆ , LiClO ₄ , LiBF ₄ , and LiN (SO ₂ CF ₃ ) ₂ are formed of a cyclic carbonate of EC or PC as a highly dielectric solvent and DEC, DMC or EMC of a low viscosity solvent. A lithium salt-containing non-aqueous electrolyte may be prepared by adding it to a mixed solvent of linear carbonate.

As described above, in the positive electrode active material according to the present invention, the lithium cobalt doped oxide of the core and the lithium cobalt doped oxide of the shell are each independently doped with three types of dopants, and the average oxidation number ratio of the doped dopants is as follows: By satisfying the condition (1), the structural stability of the crystal structure is improved even in the operating voltage range of more than 4.5V, and the crystal structure is maintained. have.

1 is a graph showing the capacity retention rate when the upper limit voltage is charged to 4.55V at 25 ° C according to Experimental Example 1.

In the following, description will be made with reference to examples of the present invention, but this is for easier understanding of the present invention, and the scope of the present invention is not limited thereto.

<Production Example 1>

MgO 0.94 g, Al ₂ O ₃ 0.535 g, TiO ₂ 1.73 g, Co ₃ O ₄ 200 g, and Li ₂ CO ₃ 81.9 g were dry mixed and calcined in a furnace at 1,050 ° C. for 10 hours for Mg, Al, Ti-doped lithium cobalt-doped oxide Li _1.02 Co _0.94 Mg _0.04 Al _0.01 Ti _0.01 O ₂ was prepared.

<Production Example 2>

MgO 0.141 g, Al ₂ O ₃ 2.14 g, TiO ₂ 1.73 g, Co ₃ O ₄ 200 g, and Li ₂ CO ₃ 81.9 g were dry mixed and calcined in a furnace at 1,050 ° C. for 10 hours for Mg, Al, Ti-doped lithium cobalt-doped oxide Li _1.02 Co _0.944 Mg _0.006 Al _0.04 Ti _0.01 O ₂ was prepared.

<Production Example 3>

Co ₃ (SO ₄ ) ₄ , magnesium sulfate (MgSO ₄ ), aluminum sulfate (Al ₂ (SO ₄ ) ₃ ), titanium sulfate (Ti (SO ₄ ) ₂ ) Co: Mg: Al: Ti = 0.94: 0.04: Dispersed in a mixed aqueous solution of 0.01: 0.01, and coprecipitated with sodium hydroxide to obtain precursor particles of (Co _0.94 Mg _0.04 Al _0.01 Ti _0.01 ) (OH) ₂ .

After adding 41 g of LiOH.H ₂ O so that the molar ratio of total elements in the particles to the precursor 100 g is a molar ratio of Li: M (Co, Mg, Al, Ti) = 1.02: 1, and then mixing with a zirconia ball using a ball mill , The mixture was first calcined at 1010 ° C. for 12 hours at a high temperature in an air atmosphere to prepare lithium cobalt doped oxide Li _1.02 Co _0.94 Mg _0.04 Al _0.01 Ti _0.01 O ₂ doped with Mg, Al, and Ti.

<Production Example 4>

MgO 0.705 g, Al ₂ O ₃ 0.214 g, TiO ₂ 0.346 g Co ₃ O ₄ 200 g, and Li ₂ CO ₃ 81.9 g were dry mixed and calcined in a furnace at 1,050 ° C. for 10 hours for Mg, Al, Ti. The doped lithium cobalt doped oxide Li _1.02 Co _0.964 Mg _0.03 Al _0.004 Ti _0.002 O ₂ was prepared.

<Example 1>

200 g of lithium cobalt doped oxide prepared in Preparation Example 1, MgO 0.035 g, Al ₂ O ₃ 0.535 g, TiO ₂ 0.43 g, Co ₃ O ₄ 50 g, and Li ₂ CO ₃ 20.475 g after dry mixing Lithium cobalt doped oxide doped with Mg, Al, Ti by firing at 950 ° C for 10 hours in a furnace, Li _1.02 Co _0.944 Mg _0.006 Al _0.04 Ti _0.01 O2 is formed on the core of Li _1.02 Co _0.94 Mg _0.04 Al _0.01 Ti _0.01 O2 A cathode active material having a core-shell structure was prepared.

<Example 2>

Al ₂ O ₃ having an average particle diameter of 50 nm was added to the lithium cobalt-doped oxide prepared in Example 1 by 0.05% by weight based on the total mass of the positive electrode active material, followed by secondary calcination at 570 ° C for 6 hours to produce 500 aluminum. A coating layer of ppm was formed. At this time, the aluminum coating layer was formed to an average thickness of approximately 50 nm.

<Comparative Example 1>

200 g of lithium cobalt-doped oxide prepared in Preparation Example 2, MgO 0.076 g, Al ₂ O ₃ 0.267 g, TiO ₂ 0.43 g, Co ₃ O ₄ 50 g, and Li ₂ CO ₃ 20.475 g after dry mixing Lithium cobalt doped oxide doped with Mg, Al, Ti by firing for 10 hours at 950 ° C in a furnace, Li _1.02 Co _0.957 Mg _0.013 Al _0.02 Ti _0.01 O2 is in the core of Li _1.02 Co _0.944 Mg _0.006 Al _0.04 Ti _0.01 O ₂ A positive electrode active material having a formed core-shell structure was prepared.

<Comparative Example 2>

After 200 g of lithium cobalt doped oxide prepared in Preparation Example 4, MgO 0.07 g, Al ₂ O ₃ 0.53 g, TiO ₂ 1.73 g, Co ₃ O ₄ 50 g, and Li ₂ CO ₃ 20.475 g after dry mixing The core formed on the core of Li _1.02 Co _0.908 Mg _0.012 Al _0.04 Ti _0.04 O2 is Li _1.02 Co _0.964 Mg _0.03 Al _0.004 Ti _0.002 O ₂ by calcining at 950 ° C. for 10 hours in a furnace, and doped with Al and Ti. -A cathode active material having a shell structure was prepared.

Table 1 below shows the average oxidation number (up to the first decimal point) and the ratio of the doping elements of Example 1 and Comparative Examples 1 to 2.

OC OS r Example 1 2.5 3.1 0.81 Comparative Example 1 3.1 2.9 1.07 Comparative Example 2 2.2 3.3 0.67

<Experimental Example 1>

The oxide particles prepared in Example 1 and Comparative Examples 1 to 2 were used as a positive electrode active material, and PVdF as a binder and natural graphite as a conductive material were used. Cathode active material: Binder: Conductive material was mixed well in NMP such that the weight ratio was 96: 2: 2, and then applied to a 20 μm thick Al foil, followed by drying at 130 ° C. to prepare a positive electrode. Lithium foil was used as the negative electrode, and half coin cells were prepared using an electrolyte containing 1 M LiPF ₆ in a solvent of EC: DMC: DEC = 1: 2: 1.

The half-coin cells prepared above were charged at 25 ° C at 0.5C with an upper limit voltage of 4.55V, and then discharged to a lower limit voltage of 3C at 1.0C with one cycle, and the capacity retention rate of 50 cycles was measured. The results are shown in Figure 1 below.

1, the capacity retention rate of the battery using the positive electrode active material of the embodiment according to the present invention represents a capacity retention rate of 90% or more, whereas the capacity retention rate of the battery using the positive electrode active material of Comparative Examples is about 85% or less This is not good, it can be seen that the embodiments satisfying the conditions of the present invention have higher high-voltage high-temperature life characteristics, which can be expected to accelerate the difference as the cycle progresses.

Although described above with reference to the embodiments of the present invention, those skilled in the art to which the present invention pertains will be able to perform various applications and modifications within the scope of the present invention based on the above.

Claims (19)

A cathode active material for a lithium secondary battery comprising a core-shell structured lithium cobalt doped oxide,
The lithium cobalt doped oxide of the core and the lithium cobalt doped oxide of the shell each independently contain three types of dopants;
The ratio of the average oxidation number of the dopants present in the core and the average oxidation number of the dopants present in the shell satisfies the following condition (1),
The three types of dopants include a positive electrode active material comprising a metal of +2 valence oxidation water, a metal of +3 valence oxidation water and a metal of +4 valence oxidation water:
0.7 ≤ r (ratio) = OC / OS <0.95 (1)
Here, the OC is the average oxidation number of the dopants present in the core, and the OS is the average oxidation number of the dopants present in the shell. The positive electrode active material according to claim 1, wherein the core-shell structured lithium cobalt doped oxide maintains a crystal structure without phase change in a range in which the positive electrode potential at full charge is greater than 4.5 V based on the Li potential. The positive electrode active material according to claim 1, wherein the r (ratio) satisfies the condition of 0.8 ≤ r <0.95. According to claim 1, The lithium cobalt doped oxide of the core is a positive electrode active material, characterized in that it has a composition of formula (1):
Li _a Co _1-xyz M1 _x M2 _y M3 _z O ₂ (1)
In the above formula,
M1, M2 and M3 are each independently an element selected from the group consisting of Ti, Mg, Al, Zr, Ba, Ca, Ta, Nb, Mo, Ni, Zn, Si, V and Mn, and the M1 Silver +2 is a metal of oxidized water, M2 is +3 a metal of oxidized water, M3 is +4 a oxidized metal;
0.95≤a≤1.05;
0 <x≤0.04, 0 <y≤0.04, and 0 <z≤0.04. The cathode active material of claim 1, wherein the lithium cobalt doped oxide of the shell has a composition of Formula 2 below:
Li _b Co _1-stw M1 ' _s M2' _t M3 ' _w O ₂ (1)
In the above formula,
M1 ', M2' and M3 'are each independently selected from the group consisting of Ti, Mg, Al, Zr, Ba, Ca, Ta, Nb, Mo, Ni, Zn, Si, V and Mn , M1 'is +2 is a metal of oxidized water, M2' is +3 is a metal of oxidized water, M3 'is +4 is a metal of oxidized water;
0.95≤b≤1.05;
0 <s≤0.04, 0 <t≤0.04, and 0 <w≤0.04. delete The method of claim 4 or 5,
M1 and M1 'are each independently an element selected from the group consisting of Mg, Ca, Ni and Ba;
M2 and M2 'are each independently an element selected from the group consisting of Ti, Al, Ta and Nb;
The M3 and M3 'are each independently selected from the group consisting of Ti, Ta, Nb, Mn, and Mo, and are positive electrode active materials characterized in that they are different elements from M2 and M2'. The cathode active material according to claim 1, wherein the thickness of the shell is 50 to 2000 nm. The cathode active material according to claim 1, wherein Al ₂ O ₃ having a thickness of 50 nm to 100 nm is coated on the surface of the shell. A method for manufacturing a lithium-cobalt-doped oxide having a core-shell structure of the positive electrode active material for a secondary battery according to claim 1,
(i) a process of preparing a doped cobalt precursor containing three types of dopants by coprecipitation; And
(ii) a process of mixing the doped cobalt precursor and a lithium precursor and performing primary firing to produce core particles; And
(iii) a process of preparing a lithium-cobalt-doped oxide having a core-shell structure by mixing the core particles, a cobalt precursor, a lithium precursor, and three types of dopant precursors and performing secondary firing to form a shell on the surface of the core particles;
Including,
The three types of dopants are +2 oxidized water metal, +3 oxidized water metal and +4 oxidized water metal. The method of claim 10, wherein in step (i), after dissolving the salts and cobalt salts containing the dopant element in water, the solution is converted to a basic atmosphere to prepare a doped cobalt oxide as a doped cobalt precursor by coprecipitation. Manufacturing method characterized in that. The method of claim 11, wherein the salts and cobalt salts containing the dopant element are in the form of carbonate, sulfate, or nitrate. A method for manufacturing a lithium-cobalt-doped oxide having a core-shell structure of the positive electrode active material for a secondary battery according to claim 1,
(i) a process of mixing the cobalt precursor, the lithium precursor, and the three types of dopant precursors and performing primary firing to produce core particles; And
(ii) the core particle, the cobalt precursor, the lithium precursor, and independently of the process (i), three types of dopant precursors are mixed and secondary fired to form a shell on the surface of the core particle to form a shell on the surface of the core particle, lithium Preparing a cobalt doped oxide;
Including,
The three types of dopants are +2 valence oxidation metal, +3 valence oxidation metal and +4 valence oxidation metal. The method of claim 10, wherein the cobalt precursor is cobalt oxide, the dopant precursors are metals, metal oxides or metal salts for dopants, and the lithium precursor is at least one selected from the group consisting of LiOH, and Li ₂ CO ₃ Manufacturing method. delete delete The method of claim 10, wherein the primary firing is performed for 8 to 12 hours at a temperature of 850 ° C to 1100 ° C, and the secondary firing is performed for 5 hours to 12 hours at a temperature of 700 ° C to 1100 ° C. Manufacturing method characterized by. A positive electrode characterized by being prepared by applying a slurry containing the positive electrode active material according to claim 1, a conductive material, and a binder to a current collector. A secondary battery comprising the positive electrode according to claim 18.

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