KR20180055379A - Positive Electrode Active Material Particle Comprising Core Part Having Lithium Cobalt Oxide and Concentration Gradient Part Having Concentration Gradient of Metal Element and Method for Manufacturing the Same - Google Patents

Abstract

The present invention relates to a positive active material particle including a lithium cobalt composite oxide represented by chemical formula 1, Li_aM^1_xM^2_yCo_(1-x-y)O_(2-h)A_h(1), which comprises: a core part containing lithium cobalt oxide; and a concentration gradient part formed on an outer surface of the core part, doped with a more chemically stable element than cobalt for a secondary battery electrolyte, and exhibiting a concentration gradient in which the concentration of a doping element continuously or discontinuously increases from the outer surface of the core part toward the surface of a positive active material particle. In the chemical formula 1, M^1 and M^2 are different elements selected from the group consisting of Al, Mg, Mn, Fe, Zr, Zn, Si, Ca, Sr, Ba, and Ti; A is an oxygen substituted halogen; and the conditions of 0.95 <= a <= 1.05, 0.01 <= x+y <= 0.1, and 0 <= h <= 0.001 are satisfied.

Description

TECHNICAL FIELD [0001] The present invention relates to a positive electrode active material particle including a core portion containing lithium cobalt oxide and a concentration gradient portion in which a metallic element exhibits a concentration gradient, and a method for producing the same. BACKGROUND ART [0002] Positive Electrode Active Material Particles Comprising Core Part Having Lithium Cobalt Oxide and Concentration Gradient Part Having Concentration Gradient of Metal Element and Method for Manufacturing the Same}

The present invention relates to a cathode active material particle containing a lithium cobalt oxide and a cathode active material particle having a concentration gradient of a metallic element and a method for producing the cathode active material particle.

In recent years, the demand for environmentally friendly alternative energy sources has become an indispensable factor for the future, as the increase in the price of energy sources due to depletion of fossil fuels and the interest in environmental pollution are amplified. Various researches on power generation technologies such as nuclear power, solar power, wind power, and tidal power have been continuing, and electric power storage devices for more efficient use of such generated energy have also been attracting much attention.

Particularly, as technology development and demand for mobile devices increase, the demand for batteries as energy sources is rapidly increasing. Recently, the use of secondary batteries as a power source for electric vehicles (EV) and hybrid electric vehicles (HEV) In addition, the use area has been expanded for use as a power auxiliary power source through a grid, and accordingly, a lot of researches on a battery that can meet various demands have been conducted.

Typically, in terms of the shape of a battery, there is a high demand for a prismatic secondary battery and a pouch-type secondary battery which can be applied to products such as mobile phones with a small thickness, and has advantages such as high energy density, discharge voltage, There is a high demand for lithium secondary batteries such as lithium ion batteries and lithium ion polymer batteries.

At present, LiCoO ₂ , ternary system (NMC / NCA), LiMnO ₄ , LiFePO ₄ and the like are used as a cathode material of a lithium secondary battery. Of these, LiCoO ₂ is expensive and has a lower capacity at the same voltage as the ternary system. Therefore, the use of ternary system is increasing to increase the capacity of the secondary battery.

However, in the case of LiCoO ₂ , since the advantages such as a high rolling density are also clearly present, LiCoO ₂ has been widely used up to now, and studies are under way to increase the operating voltage in order to develop a high capacity secondary battery.

In the case of the lithium cobalt oxide, when the high voltage of 4.5 V or more is applied for the purpose of increasing the capacity, the amount of Li of LiCoO ₂ is increased and the surface is unstable and gas is generated due to a side reaction with the electrolyte, There is a problem that the stability is deteriorated due to occurrence of a ring phenomenon, the possibility of structural instability is increased, and the lifetime characteristic is rapidly deteriorated.

In order to solve this problem, a technique of forming a separate coating layer by coating a metal such as Al, Ti, Mg or Zr on the surface of the LiCoO ₂ may be used. In the case of the coating layer made of the metal, The capacity of the LiCoO ₂ may be reduced, and the performance of the secondary battery may be deteriorated.

Therefore, there is a high need for a technique capable of fundamentally solving such problems.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems of the prior art and the technical problems required from the past.

As a result of intensive research and various experiments, the inventors of the present application have discovered that, as will be described later, the cathode active material particles include a core portion containing lithium cobalt oxide; And a concentration gradient in the outer surface of the core portion such that a more chemically stable element relative to the electrolyte solution of the secondary battery is continuously or discontinuously increased in concentration from the outer surface of the core portion toward the surface of the cathode active material particle, By containing the concentration gradient part, the reactivity with the electrolytic solution is remarkably reduced as compared with the conventional cathode active material particle containing only lithium cobalt oxide, so that the problem of the safety deterioration such as the swelling phenomenon due to gas generation can be prevented In addition, it is possible to effectively prevent the problem of capacity decrease as compared with the conventional cathode active material particles forming the coating layer and to improve the structural stability to the surface of the cathode active material particle by the presence of the doping element in a solid-solution form The problem of the above safety deterioration Point prevention can be maximized, and the present invention has been accomplished.

In order to accomplish the above object, the present invention provides a cathode active material particle,

1. A cathode active material particle comprising a lithium-cobalt composite oxide represented by the following general formula (1)

A core part comprising lithium cobalt oxide; And

And is doped with an element chemically more stable than cobalt with respect to the electrolyte solution of the secondary battery, and the concentration of the doping element increases continuously or non-continuously from the outer surface of the core portion toward the surface of the cathode active material particles A concentration gradient part that represents a concentration gradient;

: &Lt; / RTI &gt;

Li _a M ¹ _x M ² _y Co _(1-xy) O _{2 -he h h} (1)

Wherein M ¹ and M ² are different elements selected from the group consisting of Al, Mg, Mn, Fe, Zr, Zn, Si, Ca, Sr, Ba and Ti, A is an oxygen- ? A? 1.05, 0.01? X + y? 0.1, and 0? H?

As described above, when the chemically stable doping element on the outer surface of the core portion includes a concentration gradient part that is doped so as to exhibit a concentration gradient, as compared with conventional cathode active material particles containing only lithium cobalt oxide, And thus the problem of safety deterioration such as swelling due to gas generation can be prevented and the coating layer is formed of a doped lithium oxide capable of exhibiting capacity. Thus, a metal or metal oxide The problem of the capacity decrease can be effectively prevented as compared with the conventional cathode active material particles forming the coating layer of the cathode active material.

In one specific example, the core parts of lithium cobalt oxide may be LiCoO _2.

That is, the positive electrode active material particles according to the present invention maintain the above advantages based on LiCoO ₂ exhibiting the same advantages as the high rolling density, and also have a low surface stability of the LiCoO ₂ , a high reactivity with the electrolyte, It is possible to solve the problem of a decrease in safety such as a swelling phenomenon due to the presence of the catalyst.

In addition, the doping element may exist in solid-solution form in the concentration gradient portion so as to improve the surface stability of the cathode active material particles.

Here, the term of the solid solution means that atoms of different elements are uniformly distributed in a crystal of a solid to be in the same state as in the solution.

That is, since the doping element is present in a solid solution form in a state of being positioned between respective crystals together with cobalt in the concentration gradient portion, the surface stability and structural stability of the cathode active material particle can be improved, It is possible to effectively prevent the problem that the capacity is lowered as compared with the conventional cathode active material particles forming the coating layer.

On the other hand, the concentration gradient portion may be formed in an area of 50% to 100% with respect to the outer surface of the core portion, and the thickness of the concentration gradient portion may be 0.05% to 1.5% Lt; / RTI &gt;

More specifically, when considering that the cathode active material particles according to the present invention are formed at about 16 micrometers to 18 micrometers, the concentration gradient portion may be formed up to 100 nanometers from the surface toward the core portion, May be formed with a thickness of 5 to 20 nanometers, considering the capacity and lifetime characteristics of the substrate.

If the formation area of the concentration gradient portion is too small or too small beyond the above range, the proportion of the concentration gradient portion in the cathode active material particle is excessively small, and the desired effect can be sufficiently obtained On the contrary, when the formation area of the concentration gauge portion is too large beyond the above range and the thickness of the concentration gauge portion is excessively large, the ratio of the concentration gauge portion in the positive electrode active material particles becomes too large , There is a problem that the overall capacity of the cathode active material may be reduced.

In one specific example, the concentration of the doping element may increase from 5% to 15% per 10% thickness of the concentration gradient toward the outer side from the boundary between the core and the concentration gradient.

As described above, in the concentration gradient portion, the concentration gradient of the doping element is continuously or discontinuously increased from the outer surface of the core portion toward the surface of the cathode active material particle, Stability or structural stability can be improved.

If the concentration of the doping element exceeds the above range and increases to an excessively small range of less than 5% per 10% thickness of the concentration gradient portion, the content of the doping element becomes small, The concentration of the doping element increases to an excessively large range exceeding 15% per 10% of the thickness of the concentration gradient portion. If the concentration of the doping element exceeds the range, The capacity of the cathode active material may be lowered.

According to the above-described doping, the concentration gradient portion includes at least one selected from the group consisting of a metal, a metal oxide, a lithium-metal oxide, and an alloy type lithium-metal oxide, Lt; / RTI &gt;

In other words, the concentration gradient portion is a form in which the concentration of the doping element which is chemically more stable than the cobalt with respect to the electrolytic solution at the outermost portion is maximized. As a result, the outermost portion is a metal, a metal oxide, a lithium- And a lithium-metal oxide in the form of an alloy. Therefore, it is possible to maximize the surface stability and structural stability of the surface of the cathode active material particles, and accordingly, the surface of the cathode active material particle It is possible to effectively prevent the problems caused by the reactivity with the electrolytic solution and to effectively prevent the problem of the capacity drop compared with the conventional cathode active material particles including the coating layer on the surface.

In this case, the lithium-metal oxide may be a lithium-metal oxide represented by the following formula (2).

Li _a M ¹ _x M ² _y O _{2 -he h} (2)

Wherein M ¹ and M ² are different elements selected from the group consisting of Al, Mg, Mn, Fe, Zr, Zn, Si, Ca, Sr, Ba and Ti, A is an oxygen- ? A? 1.05, x + y = 1, and 0? H?

That is, the lithium-metal oxide may have a structure in which the concentration of the doping element is maximum, and unlike the core portion containing lithium cobalt oxide, the lithium-metal oxide may not include cobalt at all.

In one specific example, the cathode active material particle may have a structure including an aluminum oxide coating layer on its surface so as to compensate for the effect of the present invention.

Wherein the thickness of the aluminum oxide coating layer is 0.05% to 0.1% with respect to the diameter of the cathode active material particle.

If the thickness of the aluminum oxide coating layer is out of the above range and is too thin, the effect of the present invention may not be fully compensated through the aluminum oxide coating layer. On the contrary, if the thickness of the aluminum oxide coating layer is within the above range On the other hand, if it is excessively thick, the amount of lithium cobalt oxide is relatively small, and the capacity can be lowered

The M ¹ and M ² may have an average oxidation number of +2.5 to +3.5 in the lithium-cobalt composite oxide.

If the average oxidation number of M ¹ and M ² is out of the above range and excessively small or large, the lithium cobalt composite oxide may not maintain a stable crystal structure due to a change in reactivity.

The present invention also provides a method for producing the cathode active material particles,

(a) preparing a cobalt hydroxide precursor to form a core portion of lithium cobalt oxide by continuously introducing a cobalt source into a solvent to precipitate;

(b) when the cobalt content of the precipitated hydroxide precursor reaches 96% with respect to the cobalt content of the lithium cobalt oxide, the doping element source for forming the concentration gradient portion is continuously mixed with the cobalt source, ; And

(c) mixing the mixture of the process (b) with a lithium source and then performing heat treatment;

. &Lt; / RTI &gt;

At this time, the doping element source and the cobalt source of the process (b) may be continuously mixed and coprecipitated so that the proportion of the doping element to the cobalt element of the cobalt source is gradually increased.

More specifically, the doping element source is continuously mixed with the cobalt source and co-precipitated in the latter half of the above process during the formation of the precursor constituting the core portion of the lithium cobalt oxide so that the surface of the precursor is doped with the doping element A concentration gradient portion where the concentration is increased can be formed.

In particular, in the step (b), the doping element source and the cobalt source may be doped with a doping element such that the proportion of the doping element gradually increases, for example, from 1: 9 to 9: 1, The amount of the doping element can be increased while the amount of the cobalt element can be decreased and the mixture can be continuously mixed and coprecipitated while changing the mixing ratio.

Accordingly, the precursor can more easily form a concentration gradient in which the concentration of the doping element increases toward the surface side.

In another specific example, the method for producing the positive electrode active material particles includes:

(i) preparing a particulate cobalt precursor of lithium cobalt oxide to form a core portion;

(ii) the precursor is dispersed in a solvent so that the cobalt content reaches 96% with respect to the cobalt content of the lithium cobalt oxide, and then the doping element source for forming the concentration gradient is continuously mixed with the cobalt source and A process of inputting and coping; And

(iii) mixing lithium ions in the mixture of step (ii) and heat-treating the mixture;

. &Lt; / RTI &gt;

At this time, the doping element source and the cobalt source in the step (ii) can be continuously mixed and coprecipitated so that the proportion of the doping element to the cobalt element gradually increases.

More specifically, the doping element source is continuously mixed with the cobalt source and co-precipitated in the latter half of the above process during the dispersion process of the cobalt precursor constituting the core portion of the lithium cobalt oxide, Concentration gradient can be formed.

Particularly, in the step (ii), the doping element source and the cobalt source are mixed so that the proportion of the doping element gradually increases, for example, until the ratio of the doping element: cobalt element is 1: 9 to 9: The amount of the doping element can be increased while the amount of the cobalt source can be decreased and the mixture can be continuously mixed and coprecipitated while changing the mixing ratio.

Accordingly, the precursor can more easily form a concentration gradient in which the concentration of the doping element increases toward the surface side.

In other words, the doping element is doped at the precursor stage of the lithium cobalt oxide forming the core portion, so that the concentration gradient portion can be formed more easily. Thus, the doping element is added to the core portion containing the completed lithium cobalt oxide It is possible to exert a better effect and to eliminate or reduce the defective rate of the product as compared with the method of forming the concentration gradient portion.

The type of the particulate cobalt precursor of the lithium cobalt oxide is not limited as long as it can supply the cobalt element to the lithium cobalt oxide constituting the core portion. The type of the precursor is not particularly limited, and various conditions such as ease of handling and supply, And more particularly, Co ₃ O ₄ .

Further, the cobalt source may be a metal hydroxide containing Co or a metal sulfide, and the doping element source for forming the concentration gradient may provide an element chemically more stable than the cobalt for the secondary battery electrolyte In detail, at least one kind of metal particles selected from the group consisting of Al, Mg, Mn, Fe, Zr, Zn, Si, Ca, Sr, Ba and Ti, Metal oxides, metal hydroxides, or metal sulfides.

On the other hand, if the lithium source is capable of supplying the lithium element to the lithium cobalt oxide constituting the core portion, the kind thereof is not limited to a great extent and can be selected in consideration of various conditions such as ease of handling and supply, More specifically, it may be Li ₂ CO ₃ .

In one specific example, the doping element source may be mixed such that the ratio of the mole fraction of the doping element to the total mole fraction of cobalt and doping element is less than 10%.

If the proportion of the molar fraction of the doping element exceeds 10%, the thickness of the concentration gradient portion where the doping element exhibits a concentration gradient becomes excessively thick, and the capacity of the cathode active material may be rather reduced, At least a portion of the element may be doped not only on the surface of the coiler but also inside the core portion and may affect the physical or electrochemical performance of the cathode active material.

In addition, the heat treatment may be performed at a temperature in the range of 600 to 1100 degrees Celsius for 5 to 20 hours.

If the heat treatment is performed at an excessively low temperature beyond the above range, or if the heat treatment is performed for an excessively short time, the structure of the cathode active material particles including the concentration gradient portion may not be stably formed. On the contrary, Is carried out at an excessively high temperature beyond the above range or is carried out for an excessively long time, the physical and chemical characteristics of the lithium cobalt oxide and the doping element constituting the cathode active material particles may be changed, .

Meanwhile, the present invention provides a secondary battery including the positive electrode active material particles, the negative electrode and the electrolyte, and the secondary battery is not particularly limited in its kind, but specific examples thereof include a high energy density, A secondary battery such as a lithium ion battery, a lithium ion polymer battery or the like, which has merits such as power, 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 a lithium salt.

The positive electrode is prepared, for example, by coating a mixture of a positive electrode active material, a conductive material and a binder on a positive electrode current collector, and then drying the mixture. Optionally, a filler may be further added to the mixture.

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

The binder is a component which assists in bonding of the active material and the conductive material and bonding to the current collector, and is usually added in an amount of 1 to 30% by weight based on the total weight of the mixture containing the cathode active material. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene , Polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butylene rubber, fluorine rubber, various copolymers and the like.

The filler is optionally used as a component for suppressing the expansion of the anode, and is not particularly limited as long as it is a fibrous material without causing a chemical change in the battery. Examples of the filler include olefin polymers such as polyethylene and polypropylene; Fibrous materials such as glass fibers and carbon fibers are used.

The negative electrode is manufactured by applying and drying a negative electrode active material on a negative electrode collector, and if necessary, the above-described components may be selectively included.

Examples of the negative electrode active material include carbon such as non-graphitized carbon and graphite 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' : Metal complex oxides such as Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, Halogen, 0 < x &lt; Lithium metal; Lithium alloy; Silicon-based alloys; Tin alloy; _{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 separation membrane and the separation film are 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 mu m and the thickness is generally 5 to 300 mu m. Such separation membranes include, for example, olefinic polymers such as polypropylene, which are chemically resistant and hydrophobic; A sheet or nonwoven fabric made of glass fiber, polyethylene or the like is used. When a solid electrolyte such as a polymer is used as an electrolyte, the solid electrolyte may also serve as a separation membrane.

Further, in one specific example, in order to improve the safety of a high energy density cell, the separation membrane and / or the separation film may be an organic / inorganic composite porous SRS (Safety-Reinforcing Separators) separator.

The SRS separator is manufactured by using inorganic particles and a binder polymer on the polyolefin-based separator substrate as an active layer component. In addition to the pore structure contained in the separator substrate itself, the SRS separator is formed by interstitial volume between inorganic particles And has a uniform pore structure.

The use of such an organic / inorganic composite porous separator has the advantage of suppressing an increase in thickness of the cell due to swelling at the time of chemical conversion compared with the case of using a conventional separator, When a gelable polymer is used when liquid electrolyte is impregnated, it can also be used as an electrolyte.

In addition, the organic / inorganic composite porous separator can exhibit excellent adhesion characteristics by controlling the contents of the inorganic particles and the binder polymer in the separator, so that the cell assembly process can be easily performed.

The inorganic particles are not particularly limited as long as they are electrochemically stable. That is, the inorganic particles usable in the present invention are not particularly limited as long as the oxidation and / or reduction reaction does not occur in the operating voltage range of the applied battery (for example, 0 to 5 V based on Li / Li +). Particularly, when inorganic particles having an ion-transporting ability are used, the ion conductivity in the electrochemical device can be increased and the performance can be improved. Therefore, it is preferable that the ionic conductivity is as high as possible. In addition, when the inorganic particles have a high density, it is difficult to disperse the particles at the time of coating, and there is a problem of an increase in weight during the production of the battery. In the case of an inorganic substance having a high dielectric constant, dissociation of an electrolyte salt, for example, a lithium salt, in the liquid electrolyte also contributes to increase ionic conductivity of the electrolyte.

The nonaqueous electrolyte solution containing a lithium salt is composed of a polar organic electrolyte and a lithium salt. As the electrolytic solution, a non-aqueous liquid electrolytic solution, an organic solid electrolyte, an inorganic solid electrolyte and the like are used.

Examples of the nonaqueous liquid electrolytic solution include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma -Butyrolactone, 1,2-dimethoxyethane, tetrahydroxyfuran, 2-methyltetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane , Acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate Nonionic organic solvents such as tetrahydrofuran derivatives, ethers, methyl pyrophosphate, ethyl propionate and the like can be used.

Examples of the organic solid electrolyte include a polymer electrolyte such as a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphate ester polymer, an agitation lysine, a polyester sulfide, a polyvinyl alcohol, a polyvinylidene fluoride, Polymers containing ionic dissociation groups, 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 , Nitrides, halides and sulfates of Li such as Li ₄ SiO ₄ -LiI-LiOH and Li ₃ PO ₄ -Li ₂ S-SiS ₂ can be used.

The lithium salt is a material that is readily soluble in the non-aqueous 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 3 Li, (CF 3 SO 2) 2 NLi, chloroborane lithium, lower aliphatic carboxylic acid lithium, lithium tetraphenyl borate and imide have.

For the purpose of improving the charge-discharge characteristics and the flame retardancy, the non-aqueous liquid electrolyte may contain, for example, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, glyme, N, N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, aluminum trichloride and the like are added It is possible. In some cases, a halogen-containing solvent such as carbon tetrachloride or ethylene trifluoride may be further added to impart nonflammability, or a carbon dioxide gas may be further added to improve high-temperature storage characteristics.

The present invention also provides a battery pack including the secondary battery and a device including the battery pack. Since the battery pack and the device are known in the art, a detailed description thereof will be omitted herein. do.

INDUSTRIAL APPLICABILITY As described above, the cathode active material particle according to the present invention comprises a core portion in which the cathode active material particles contain lithium cobalt oxide; And a concentration gradient in the outer surface of the core portion such that a more chemically stable element relative to the electrolyte solution of the secondary battery is continuously or discontinuously increased in concentration from the outer surface of the core portion toward the surface of the cathode active material particle, By containing the concentration gradient part, the reactivity with the electrolytic solution is remarkably reduced as compared with the conventional cathode active material particle containing only lithium cobalt oxide, so that the problem of the safety deterioration such as the swelling phenomenon due to gas generation can be prevented In addition, it is possible to effectively prevent the problem of capacity decrease as compared with the conventional cathode active material particles forming the coating layer and to improve the structural stability to the surface of the cathode active material particle by the presence of the doping element in a solid-solution form The problem of the above safety deterioration There is an effect of maximizing the prevention of dots.

1 is a graph showing Al / Co ratios of a cathode material according to Experimental Example 1 of the present invention;
2 is a graph showing the capacity retention rate measured according to Experimental Example 2 of the present invention.

Hereinafter, the present invention will be further described with reference to Examples of the present invention, but the scope of the present invention is not limited thereto.

Cathode active material manufacturing

&Lt; Example 1 >

In the process of in order to form a precursor of LiCoO _2, precipitated successively introduced into a CoSO ₄ in 200ml water, upon reaching 96% of the cobalt content of LiCoO ₂ to the cobalt content of said precipitated precursors desired, CoSO ₄ And Al ₂ (SO ₄ ) ₃ as a doping element source for forming a concentration gradient portion were continuously mixed and charged and coprecipitated. At this time, the Al ₂ (SO ₄ ) ₃ and CoSO ₄ are continuously mixed and added so that the ratio of the Al element to the Co element increases from 1: 9 to 9: 1, ₃ O ₄ was doped with Al to form a concentration gradient showing a concentration gradient. The Li ₂ CO ₃ was added and mixed as a lithium source in a ratio of Li: Co of 1: 1 as a lithium source to the coprecipitation reaction, and then heat treatment was performed at 1000 ° C. for 10 hours to obtain a total molar fraction 3% of the ratio of the mole fraction of Al element and on the concentration sphere indicates the density gradient in the distribution that the concentration of Al gradually increased continuously to the surface direction of the particle from the core portion outer surface, the lithium element is of at least the core Co ₃ O ₄ to form cathode active material particles forming lithium cobalt oxide

&Lt; Example 2 >

As a precursor of LiCoO ₂ , 100 g of Co ₃ O _{4 in a} particle state was mixed and dispersed in 200 ml of water, and then CoSO ₄ as a cobalt source for forming a concentration gradient and Al ₂ (SO ₄ ) ₃ as a doping element source were continuously And co-precipitated. At this time, the Al ₂ (SO ₄ ) ₃ and CoSO ₄ are continuously mixed and added so that the ratio of the Al element to the Co element increases from 1: 9 to 9: 1, ₃ O ₄ was doped with Al to form a concentration gradient showing a concentration gradient. The Li ₂ CO ₃ was added and mixed as a lithium source to the solution in which the coprecipitation reaction was completed so that the Li: Co ratio became 1.05: 1, and then heat treatment was performed at 1000 ° C. for 10 hours to obtain a total molar fraction 3% of the ratio of the mole fraction of Al element and on the concentration sphere indicates the density gradient in the distribution that the concentration of Al gradually increased continuously to the surface direction of the particle from the core portion outer surface, the lithium element is of at least the core Co ₃ O ₄ to form cathode active material particles forming lithium cobalt oxide

&Lt; Comparative Example 1 &

As a precursor of LiCoO ₂ , Co ₃ O _{4 in a} particle state and Li ₂ CO ₃ as a lithium source were mixed and dispersed in 200 ml of water so that the ratio of Li / Co became 1.05, and then heat treatment was performed at 1000 ° C. for 10 hours , Thereby preparing LiCoO ₂ . Al ₂ O ₃ particles were mixed with the LiCoO ₂ so that the Al ₂ O ₃ particles were coated so as to be coated with Al at a temperature of 800 ° C. for 6 hours to prepare cathode active material particles containing the Al-coated lithium cobalt oxide.

<Experimental Example 1>

In order to measure the doping state (structure) in Examples 1 to 3 and Comparative Example 1, the depth profile was measured using XPS to confirm the ratio of Al: Co from the surface to a certain distance in the inward direction, Respectively.

<Experimental Example 2>

Life characteristics

The cathode active material particles, the PVdF binder, and the natural graphite conductive material prepared in Examples 1 and 2 and Comparative Example 1 were thoroughly mixed in NMP so as to have a weight ratio of 95: 2.5: 2.5 (cathode active material: binder: conductive material) Thick Al foil, and dried at 130 DEG C to prepare a positive electrode. Lithium foil was used as the cathode, and an electrolyte solution containing 1 M of LiPF ₆ in a solvent of EC: DMC: DEC = 1: 2: 1 was used to prepare a half coin cell.

The half-coin cells were charged and discharged for 50 cycles in a CC / CV mode with an upper limit voltage of 4.55 V at a room temperature of 25 degrees Celsius, and the capacity retention rate was measured. The results are shown in FIG.

2, in the case of Examples 1 and 2, a concentration gradient portion doped so that Al shows a concentration gradient is formed on the surface of the lithium cobalt oxide core portion, and the stability of the surface is improved. Therefore, The maintenance rate is about 96% or more. On the other hand, in the case of Comparative Example 1, although the surface of the lithium cobalt oxide contains Al, the surface is unstable and the capacity retention rate is about 93%, which is relatively low as compared with the Examples.

1 and 2, in the case of Examples 1 and 2 in which Al is doped to form a concentration gradient portion, although the distribution ratios of Al vary from a surface to a certain distance in the inward direction, they exhibit a similar effect , It is confirmed that it shows an excellent effect as compared with Comparative Example 1 in which Al is coated. Therefore, it can be easily seen that the anode active material particles exhibit better effects when doped to form a concentration gradient rather than a structure in which Al is simply coated.

While the present invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Claims (23)

1. A cathode active material particle comprising a lithium-cobalt composite oxide represented by the following general formula (1)
A core part comprising lithium cobalt oxide; And
And is doped with an element chemically more stable than cobalt with respect to the electrolyte solution of the secondary battery, and the concentration of the doping element increases continuously or non-continuously from the outer surface of the core portion toward the surface of the cathode active material particles A concentration gradient part that represents a concentration gradient;
Wherein the positive electrode active material particle comprises:
Li _a M ¹ _x M ² _y Co _(1-xy) O _{2 -he h h} (1)
Wherein M ¹ and M ² are different elements selected from the group consisting of Al, Mg, Mn, Fe, Zr, Zn, Si, Ca, Sr, Ba and Ti, A is an oxygen- ? A? 1.05, 0.01? X + y? 0.1, and 0? H? The cathode active material particle according to claim 1, wherein the lithium cobalt oxide in the core portion is LiCoO ₂ . The cathode active material particle according to claim 1, wherein the doping element exists in a solid-solution form at a concentration gradient portion so as to improve surface stability of the cathode active material particle. The positive electrode active material particle according to claim 1, wherein the concentration gradient portion is formed in an area of 50% to 100% with respect to an outer surface of the core portion. The positive electrode active material particle according to claim 1, wherein the thickness of the concentration gradient portion is 0.05% to 1.5% of the radius of the positive electrode active material particle. The doping element according to claim 1, characterized in that the concentration of the doping element increases from 5% to 15% per 10% thickness of the concentration gradient as going outward from the boundary between the core portion and the concentration gradient portion Active material particles. The lithium ion secondary battery according to claim 1, wherein the concentration gradient portion includes at least one selected from the group consisting of a metal, a metal oxide, a lithium-metal oxide, and an alloy lithium-metal oxide, As a cathode active material particle. The positive electrode active material particle according to claim 7, wherein the lithium-metal oxide is a lithium-metal oxide represented by the following formula (2)
Li _a M ¹ _x M ² _y O _{2 -he h} (2)
Wherein M ¹ and M ² are different elements selected from the group consisting of Al, Mg, Mn, Fe, Zr, Zn, Si, Ca, Sr, Ba and Ti, A is an oxygen- ? A? 1.05, x + y = 1, and 0? H? The cathode active material particle according to claim 1, wherein the cathode active material particle further comprises an aluminum oxide coating layer on the surface. The cathode active material particle according to claim 9, wherein the thickness of the aluminum oxide coating layer is 0.05% to 0.1% with respect to the diameter of the cathode active material particle. The positive electrode active material particle according to claim 1, wherein M ¹ and M ^{2 each} have an average oxidation number of +2.5 to +3.5 in the lithium-cobalt composite oxide. A method for producing a cathode active material particle according to claim 1,
(a) preparing a cobalt hydroxide precursor to form a core portion of lithium cobalt oxide by continuously introducing a cobalt source into a solvent to precipitate;
(b) when the cobalt content of the precipitated hydroxide precursor reaches 96% with respect to the cobalt content of the lithium cobalt oxide, the doping element source for forming the concentration gradient portion is continuously mixed with the cobalt source, ; And
(c) mixing the mixture of the process (b) with a lithium source and then performing heat treatment;
Wherein the positive electrode active material particles have an average particle diameter of not more than 100 nm. 13. The method according to claim 12, wherein the doping element source and the cobalt source in the step (b) are continuously mixed and coprecipitated so that the proportion of the doping element to the cobalt element gradually increases . A method for producing a cathode active material particle according to claim 1,
(i) preparing a particulate cobalt precursor of lithium cobalt oxide to form a core portion;
(ii) the precursor is dispersed in a solvent so that the cobalt content reaches 96% with respect to the cobalt content of the lithium cobalt oxide, and then the doping element source for forming the concentration gradient is continuously mixed with the cobalt source and A process of inputting and coping; And
(iii) mixing lithium ions in the mixture of step (ii) and heat-treating the mixture;
Wherein the positive electrode active material particles have an average particle diameter of not more than 100 nm. 15. The method for producing a cathode active material particle according to claim 14, wherein the doping element source and the cobalt source in the step (ii) are continuously mixed and coprecipitated so that the proportion of the doping element to the cobalt element gradually increases . 15. The method of claim 14, wherein the precursor of the lithium cobalt oxide is Co ₃ O ₄ . The doping element source for forming the concentration gradient portion of claim 12 or 14, wherein the doping element source is at least one selected from the group consisting of Al, Mg, Mn, Fe, Zr, Zn, Si, Ca, Sr, A metal oxide, a metal hydroxide, or a metal sulfide. Claim 12 according to any one of claims 14, wherein the lithium source is a method for producing a positive electrode active material particles, characterized in that Li ₂ CO _3. 15. The method of claim 12 or 14, wherein the doping element source is mixed such that the ratio of the mole fraction of the doping element to the total mole fraction of cobalt and doping element is 10% or less. The method of claim 12 or 14, wherein the heat treatment is performed at a temperature in the range of 600 to 1100 degrees Celsius for 5 to 20 hours. A secondary battery comprising a cathode, a cathode, and an electrolyte containing the cathode active material particles according to claim 1. A battery pack comprising a secondary battery according to claim 21. A device comprising a battery pack according to claim 22.

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