KR20170142393A - Positive Electrode Active Material Particle Comprising Core Having Lithium Cobalt-based Oxide and Shell Having Lithium Nickel-based Oxide and Method of Manufacturing the Same - Google Patents

Abstract

The present invention provides a lithium secondary battery comprising: a core comprising a lithium cobalt oxide represented by the following formula (1); And a shell coated on the surface of the core and comprising a lithium nickel-based oxide expressed by the following Chemical Formula 2 or Chemical Formula 3,
Wherein the lithium transition path of the core and the lithium path of the shell are continuously connected to each other.
Li _a Co _(1-x) M _x O _{2 -he h} (1)
Li _b Ni _y Co _z Mn _{1- y z} O _{2-w w} (2)
Li _b Ni _{y '} Mn _z' M '_1-y'-z' O _{2 -w a w} (3)
In this formula,
M is at least one member selected from the group consisting of Ti, Mg, Al, Zr, Mn and Ni,
A is an oxygen-substituted halogen,
M 'is at least one member selected from the group consisting of Ti, Mg, Al and Zr,
Y? 0.8, 0.1? Z? 0.4, 0.1? 1-yz? 0.4, 0.4? Y'? 0.5, 0.4? Z'≤0.5, 0.95? B? 1.00, 0.5, 0? 1-y'-z'0.2, 0? H? 0.001, and 0? W?

Description

TECHNICAL FIELD [0001] The present invention relates to a positive electrode active material particle comprising a core containing a lithium-cobalt oxide and a shell containing a lithium-nickel-based oxide and a method for producing the same. Method of Manufacturing the Same}

The present invention relates to a cathode active material particle comprising a core containing a lithium cobalt oxide and a shell containing a lithium nickel-based oxide and a method of producing the same.

As the technology development and demand for mobile devices have increased, the demand for secondary batteries has increased sharply as an energy source. Among such secondary batteries, lithium secondary batteries having high energy density and operating potential, long cycle life, Have been commercialized and widely used.

In addition, as the interest in environmental issues grows, researches on electric vehicles and hybrid electric vehicles that can replace fossil fuel-based vehicles such as gasoline vehicles and diesel vehicles, which are one of the main causes of air pollution, . Although nickel-metal hydride secondary batteries are mainly used as power sources for such electric vehicles and hybrid electric vehicles, researches using lithium secondary batteries having high energy density and discharge voltage are being actively carried out, and they are in the commercialization stage.

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 , excellent physical properties such as high rolling density and excellent electrochemical characteristics such as high cycle characteristics have been used to date. However, LiCoO ₂ has a low charging / discharging current of about 150 mAh / g and has a problem that its crystal structure is unstable at a voltage of 4.3 V or more, resulting in rapid deterioration of lifetime characteristics and a risk of ignition due to reaction with an electrolyte .

In particular, when applying a high voltage to develop a high capacity secondary battery, the Li usage of LiCoO ₂ increases, and the possibility of surface instability and structural instability increases.

To solve this problem, conventionally, coated or doped with a metal such as Al, Ti, Mg, Zr, or on the surface of LiCoO _2, and LiCoO ₂ A technique of mixing a ternary system of a lithium nickel oxide and a technique of coating a ternary system of a lithium nickel oxide on the surface of LiCoO ₂ have been proposed. However, conventionally, only a wet method in which a ternary precursor is coated on a particle of LiCoO ₂ and heat treatment, or a method in which LiCoO ₂ particles and a metal or ternary phase particles are dry-mixed are disclosed, and the resultant product produced by this method is LiCoO ₂ And the metal or lithium tin oxide compound particles are present as separate particles, the lattice coherence of the lithium transfer path is not good, the void space exists between the interfaces between the particles, the lithium mobility decreases, There is a problem that the characteristics are rapidly reduced.

Therefore, there is a high demand for development of cathode active material based on lithium cobalt oxide which can be used stably at high voltage without deteriorating performance.

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.

The inventors of the present application have conducted intensive research and various experiments, and have found that, as will be described later, in the cathode active material particle having the shell of the lithium nickel-based oxide formed on the surface of the core including the lithium cobalt oxide, Is connected at a lattice matching ratio of 60% or more, the desired effect can be exhibited, and the present invention has been accomplished.

Accordingly, the cathode active material particle for a secondary battery according to the present invention comprises: a core comprising a lithium cobalt-based oxide represented by the following formula (1); And

A shell coated on the surface of the core and comprising a lithium-nickel-based oxide expressed by the following Chemical Formula 2 or Chemical Formula 3;

/ RTI >

And the lithium path of the core and the lithium path of the shell are continuously connected to each other.

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

Li _b Ni _y Co _z Mn _{1- y z} O _{2-w w} (2)

Li _b Ni _{y '} Mn _z' M '_1-y'-z' O _{2 -w a w} (3)

In this formula,

M is at least one member selected from the group consisting of Ti, Mg, Al, Zr, Mn and Ni,

A is an oxygen-substituted halogen,

M 'is at least one member selected from the group consisting of Ti, Mg, Al and Zr,

Y? 0.8, 0.1? Z? 0.4, 0.1? 1-yz? 0.4, 0.4? Y'? 0.5, 0.4? Z'≤0.5, 0.95? B? 1.00, 0.5, 0? 1-y'-z'0.2, 0? H? 0.001, and 0? W?

In the above formulas, A may be F, S, or N in detail.

Generally, when a lithium cobalt oxide is used as a cathode active material at a high voltage, a large amount of lithium ions are released from the lithium cobalt oxide particles, resulting in the crystal structure being defective. As a result, the unstable crystal structure is collapsed and reversibility is degraded. In addition, when Co ³⁺ or Co ⁴⁺ ions present on the surface of the lithium cobalt oxide particles are reduced by the electrolytic solution in the state in which lithium ions are released, oxygen is desorbed from the crystal structure and the above-described structural collapse is further promoted.

Therefore, in order to stably use the lithium cobalt oxide under a high voltage, even when a large amount of lithium ions are released, its crystal structure is stably maintained, and side reactions of the Co ions and the electrolyte must be suppressed.

Accordingly, the present invention provides a lithium nickel-based oxide-containing shell formed on a surface of a lithium-cobalt oxide-containing core, wherein the core and the shell are continuously connected to each other so that the lithium- The structural stability of the active material particles is improved and the migration of lithium ions is relatively facilitated to prevent deterioration of output characteristics of the secondary battery.

Here, the lithium transition passages in the core and the shell are continuously connected, which means that the lithium layers of the core and the shell are generally connected without being shifted from the central portion to the surface portion of the particles. Therefore, the lattice matching of the lithium transfer path, which will be described below, is such that when the lithium layer of the core and the lithium layer of the shell are positioned so that the lithium ions can easily move from the center portion to the surface portion of the particle, And exhibits high lattice matching. This is shown in FIG. 6 as a schematic diagram.

Based on this definition, the lattice matching ratio to be described below is determined by TEM photographs. The lattice matching ratio of the lithium layer formed on the core and the lithium layer formed on the shell The total volume is the percentage of the volume at which the core's lithium layer and the shell's lithium layer are connected in series. (1).

Lattice matching ratio (%) = (volume of continuous lithium layer / volume of total lithium layer) * 100 (One)

The cathode active material of the present invention measured on the basis thereof may be continuously connected with the lithium path of the core and the lithium path of the shell at a lattice matching ratio of 60% or more, , More than 70%, and more particularly, more than 80%.

Furthermore, the cathode active material particles of the present invention may have no boundary space between the core and the shell. In other words, the core and shell of the cathode active material particles of the present invention may have a continuous layer structure Lt; / RTI >

Therefore, there is almost no increase in the interfacial resistance, and there is an effect that deterioration of the output characteristics due to the coating is prevented.

On the other hand, in the case of forming the shell according to the conventional manufacturing method, although the structural stability can be ensured, as the shell material constituting the shell is present as particles separate from the core particles as shown in the schematic diagram shown in FIG. 6, Even if the core and the shell both have a layered structure, the lithium layer mostly deviates, and a core made of a lithium cobalt oxide is used. As the shell is later produced, there is a void space therebetween. It is necessary to move across the space formed at the interface, and the lithium layer is also out of order and has a longer travel path, so that the interfacial resistance is increased and the lithium movement is not smooth and the output characteristic is greatly deteriorated.

That is, the present invention also solves the problems in the case of using the cathode active material particles of the core-shell structure manufactured by the conventional method.

Meanwhile, in one specific example, the weight ratio (B / A) of the shell (B) to the core (A) may be 0.001 to 0.3.

When the weight ratio of the shell to the core is less than 0.001, the ratio of the shells in the cathode active material particles is too small, and the desired effect may not be sufficiently exhibited. On the contrary, There is a problem that the ratio of the shell in the cathode active material particles becomes excessively high and the rolling density becomes lower than that in the case where only lithium cobalt oxide based oxide is used so that the energy density per volume is lowered in the actual cell and the output characteristic is significantly lowered .

Further, in one specific example, the shell may be coated in an area of 50% to 100% with respect to the surface area of the core.

When the shell is coated with an area of less than 50% out of the above range with respect to the surface area of the core, the coating area of the shell is too small and the desired effect is not sufficiently exhibited.

As described below, the cathode active material particles according to the present invention undergo a process of forming a core and a shell in the precursor stage and then adding lithium and being subjected to a permeation reaction, so that the concentration of lithium in the core and the shell becomes a concentration gradient Specifically, in the case where there is a lithium deficiency on the surface of the shell, the portion of the shell where lithium is partially deficient is partially formed on the surface of the spinel phase having a fast moving speed of lithium ion, so that lithium from the lithium cobalt- It is possible to more effectively perform the role as the passage for the ions to move, and it is possible to further prevent the degradation of the output characteristics of the secondary battery, so that the concentration gradient can be continuously or discontinuously increased from the shell toward the center of the core , And more particularly, therefore, stoichiometrically, the core is in a lithium overdose state, the shell is in a lithium deficiency state Can.

In one specific example, the lithium cobalt-based oxide may be LiCoO ₂ , and the lithium nickel-based oxide may be a compound of formula (2). More specifically, the lithium nickel-based oxide may be Li _b Ni _1/3 Co _1/3 Mn _1/3 O ₂ , Li _b Ni _0.5 Co _0.2 Mn _0.3 O _2, or Li _b Ni _0.6 Co _0.2 Mn _0.2 O ₂ (where b is as defined in the above-mentioned 1).

Although the present invention is not limited to the above configuration, the combination exhibits the most excellent effect in terms of capacity.

Further, the present invention provides a method of producing the above-mentioned cathode active material particles,

(a) forming a coating layer containing a hydroxide of nickel (Ni) -manganese (Mn) or a hydroxide of nickel (Ni) -cobalt (Co) -manganese (Mn) on a lithium cobalt oxide precursor in a particle state; And

(b) mixing and firing a lithium precursor with a lithium cobalt oxide precursor having the coating layer formed thereon;

. ≪ / RTI >

That is, according to the above production method, the cathode active material particles of the present invention can be obtained by forming a nickel-based hydroxide on the lithium cobalt oxide itself and not reacting with the lithium precursor, but reacting the lithium cobalt oxide precursor with nickel (Ni) (M ') is coated with a hydroxide of nickel (Ni) - cobalt (Co) - manganese (Mn) That is to say that the particles forming the core and the shell form a core-shell structure in the precursor stage and then the lithium source penetrates into the core and the shell, as described above, A lithium layer as a lithium path can be continuously formed in the core and the shell layer, and the materials forming the core and the shell both form a core-shell structure at the precursor stage As does the interface space is not formed between the core and the shell. Therefore, the lithium nickel-based oxide may be more stably attached to the core, and further, the deterioration of the output characteristics is less than that of the conventional coating material coated on the lithium cobalt oxide.

The process (a) may be performed by dispersing a lithium cobalt oxide precursor in a particulate state in a solution in which a nickel compound, a manganese compound, or another metal (M ') compound is dissolved, and then conducting a coprecipitation reaction. And dispersing the system oxide precursor in a solution in which a nickel compound, a cobalt compound and a manganese compound are dissolved, followed by coprecipitation reaction. Which can be suitably selected depending on the material to be formed as a shell on the surface of the core.

At this time, the mixing ratio of the compounds contained in the solution may be appropriately selected stoichiometrically according to the composition of the desired shell. In detail, when the nickel compound, the manganese compound and the other metal (M ') compound are dissolved, When the nickel compound, the cobalt compound and the manganese compound are all dissolved in a molar ratio of nickel, manganese and other metal (M ') of 4: 5: 4 to 5: 0 to 2, Cobalt, and manganese in the range of 3 to 8: 1 to 4: 1 to 4.

In addition, in the step (b), the mixing ratio of the lithium cobalt oxide precursor and the lithium precursor in which the coating layer is formed may be selected by stoichiometric considerations. Specifically, the lithium precursor may have a total molar ratio of the metals contained in the precursor The amount of lithium may be 0.95 to 1.05 times the amount of lithium as a standard, or may be mixed with a little excess.

Meanwhile, the heat treatment in the process (b) may be performed at a temperature in the range of 850 to 1100 degrees Celsius for 2 to 20 hours.

If the heat treatment in the step (iii) is carried out at an excessively low temperature beyond the above range, or if the heat treatment is carried out for an excessively short time, the core-shell structure of the cathode active material particles can not be stably formed, In contrast, when the heat treatment in the step (iii) is carried out at an excessively high temperature beyond the above range, or when the heat treatment is performed for an excessively long time, the lithium cobalt oxide constituting the cathode active material particles and the lithium nickel The physical and chemical properties of the compound may be changed, which may cause deterioration in performance, which is not preferable.

In one specific example, the lithium cobalt-based oxide precursor used in the production method according to the present invention may be cobalt oxide, and its kind is not limited, but may be Co3O4 in detail.

In addition, the nickel (Ni) - manganese (Mn) - Other metals (M ') of the hydroxide is _{particularly, Li b Ni y' Mn z} 'M'1-y'-z'(OH 1-t) 2 , And the hydroxide of nickel (Ni) -cobalt (Co) -manganese (Mn) is specifically Ni _y Co _z Mn ₁ -yz (OH _{1 -t} ) ₂ (where 0.3≤y≤0.8, 0.1≤z≤ 0.4, 0.1? 1-yz? 0.4, 0.4? Y'? 0.5, 0.4? Z'0.5, 0? 1-y'-z'0.2 and 0? T? 0.5).

The lithium precursor is not limited as long as it is a compound containing a lithium source, specifically, it may be LiOH or Li ₂ CO ₃ .

In this way, a more uniform coating layer can be formed by the wet production method, and according to the manufacturing method of the present invention, since the coating is performed in the precursor step, the continuity of the lithium layer between the core and the shell allows the coating layer And it is possible to prevent the deterioration of the output characteristic by reducing the interfacial resistance due to the connection of the lithium transfer path.

The present invention also provides a positive electrode for a secondary battery comprising the positive electrode active material particles.

The positive electrode may be manufactured by, for example, applying a positive electrode mixture mixed with a positive electrode active material composed of positive electrode active material particles to a positive electrode collector, and a conductive material and a binder, and if necessary, adding a filler to the positive electrode mixture Can be added.

The cathode current collector is generally formed to a thickness of 3 to 500 탆 and is not particularly limited as long as it has high conductivity without causing chemical change in the battery. For example, stainless steel, aluminum, nickel, titanium , And a surface treated with carbon, nickel, titanium or silver on the surface of aluminum or stainless steel can be used. Specifically, aluminum can be used. The current collector may have fine irregularities on the surface thereof to increase the adhesive force of the cathode active material, and various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric are possible.

The cathode active material may be, 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 cathode active material particle; Lithium manganese oxides such as Li _{1 + x} Mn _{2 -x} O ₄ (where x is 0 to 0.33), LiMnO ₃ , LiMn ₂ O ₃ , LiMnO ₂ and the like; 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 expressed 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, and Zn, or Ta, x = 0.01 ~ 0.1 Im) or Li ₂ Mn ₃ MO ₈ (where, M = Fe, Co, Ni, Cu, or Zn); LiMn ₂ O _{4 in} which a part of Li in the formula is substituted with an alkaline earth metal ion; Disulfide compounds; Fe ₂ (MoO ₄ ) ₃ , and the like, but is not limited thereto.

The conductive material is usually added in an amount of 0.1 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 contained in the positive electrode is a component that 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 0.1 to 30 wt% 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, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene , Polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluorine rubber, various copolymers and the like.

The present invention also provides a secondary battery comprising the positive electrode, the negative electrode, and an electrolytic solution. The secondary battery 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, though the kind thereof is not particularly limited.

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.

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 collector, and if necessary, the above-described components may be selectively included.

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

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 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 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.

The lithium salt-containing nonaqueous electrolyte solution is composed of a nonaqueous electrolyte and a lithium salt. As the non-aqueous electrolyte, non-aqueous organic solvents, organic solid electrolytes, inorganic solid electrolytes, and the like are used, but the present invention is not limited thereto.

Examples of the non-aqueous organic solvent 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 nonaqueous electrolytic solution is preferably a solution prepared by dissolving or dispersing in a solvent such as pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, glyme, hexaphosphoric triamide, N, N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, aluminum trichloride and the like may be added have. In some cases, halogen-containing solvents such as carbon tetrachloride and ethylene trifluoride may be further added to impart nonflammability. In order to improve the high-temperature storage characteristics, carbon dioxide gas may be further added. FEC (Fluoro-Ethylene Carbonate, PRS (Propene sultone), and the like.

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.

The device may be, for example, a notebook computer, a netbook, a tablet PC, a mobile phone, MP3, a wearable electronic device, a power tool, an electric vehicle (EV), a hybrid electric vehicle (HEV) , A plug-in hybrid electric vehicle (PHEV), an electric bike (E-bike), an electric scooter (E-scooter), an electric golf cart, However, the present invention is not limited thereto.

As described above, the cathode active material particle according to the present invention comprises a core containing lithium cobalt oxide and a shell of a lithium nickel-based oxide formed on the surface of the core, wherein the lithium moving passages of the core and the shell are continuously connected The structural stability at high voltage can be secured by significantly reducing the contact area between the core surface and the electrolyte while suppressing the crystal structure collapse from the outer surface of the core, The lattice matching of the lithium secondary battery can be smoothly carried out and the interface resistance can be lowered to prevent the overall performance deterioration of the lithium secondary battery such as the output characteristics.

1 is an SEM photograph of a cathode active material particle according to Example 1;
2 is an SEM photograph of a cathode active material particle according to Comparative Example 1;
3 is an SEM photograph of the cathode active material particles according to Comparative Example 2;
4 is a graph of experimental results of high-temperature continuous filling of Examples and Comparative Examples according to Experimental Example 2;
5 is a graph comparing the temperatures of the cells according to Experimental Example 3 with those of Comparative Examples in the case of overcharge;
6 is a schematic diagram showing the lattice matching of the lithium transition passage of the core and the shell.

Hereinafter, the present invention will be described with reference to embodiments thereof, but it should be understood that the scope of the present invention is not limited thereto.

&Lt; Example 1 >

The nickel sulfate so that the molar ratio of 2 (NiSO ₄₎ and cobalt sulfate (CoSO ₄₎ and manganese sulfate (MnSO ₄₎ are mixed a mixed aqueous solution 500ml: Co ₃ O ₄ particles to 50g Ni: Co: Mn = 6 : 2 Ni-Co-Mn hydroxide was coprecipitated to Co ₃ O ₄ particles using sodium hydroxide. These dispersion systems were filtered and dried at 120 &lt; 0 &gt; C. A precursor sample in which Ni-Co-Mn based hydroxide was formed on the surface of Co ₃ O ₄ particles was obtained.

26.4 g of LiOH.H ₂ O was added to 50 g of the precursor such that the molar ratio of the total elements in the particle was Li: M (Ni, Co, Mn) = 1: 1, and the mixture was mixed with the zirconia balls using a ball mill, The mixture was calcined at 1050 DEG C for 15 hours at a high temperature in an air atmosphere to obtain an active material of a core-shell structure.

&Lt; Example 2 >

In the mixed aqueous solution, Ni: Co: Mn = 5 : 2: 3 nickel sulfate so that the molar ratio of (NiSO ₄₎ and cobalt sulfate (CoSO ₄₎ and manganese sulfate (MnSO ₄₎ as in Example 1 except that the mixed The active material was synthesized in the same manner.

&Lt; Example 3 >

Except that nickel sulfate (NiSO ₄ ), cobalt sulfate (CoSO ₄ ) and manganese sulfate (MnSO ₄ ) were mixed in a molar ratio of Ni: Co: Mn = 1: The active material was synthesized in the same manner.

<Example 4>

50 g of Co ₃ O ₄ particles and 0.038 g of Al ₂ O ₃ were mixed together with a zirconia ball using a ball mill and then the mixture was calcined at 1010 ° C. for 15 hours in an air atmosphere to obtain a Co ₃ O ₄ precursor Were synthesized.

Ni: Co: Mn = 6: 2: nickel sulfate so that the molar ratio of 2 (NiSO ₄₎ and cobalt sulfate (CoSO ₄₎ and manganese sulfate (MnSO ₄₎ Co using the dispersion and sodium hydroxide in the mixed aqueous mixed solution 500ml ₃ O ₄ Ni-Co-Mn hydroxide was coprecipitated to the particles. These dispersion systems were filtered and dried at 120 &lt; 0 &gt; C. A precursor sample in which Ni-Co-Mn based hydroxide was formed on the surface of Co ₃ O ₄ particles was obtained.

26.4 g of LiOH.H ₂ O was added to 50 g of the precursor so that the molar ratio of the total elements in the particle was Li: M (Ni, Co, Mn, Al) = 1: 1 and mixed with the zirconia balls using a ball mill After that, the mixture was calcined at 1050 DEG C for 15 hours at a high temperature in an air atmosphere to obtain a core-shell structure active material.

&Lt; Example 5 >

Co ₃ O ₄ particles, 50g of Ni: Mn = 1: nickel sulfate so that the molar ratio of 1 (NiSO ₄₎ and manganese sulfate (MnSO ₄₎ dispersed in a mixed aqueous mixed solution 500ml and using sodium hydroxide Co ₃ O ₄ Ni-Mn hydroxide was co-precipitated with the particles. These dispersion systems were filtered and dried at 120 &lt; 0 &gt; C. A precursor sample having Ni-Mn based hydroxide formed on the surface of Co ₃ O ₄ particles was obtained.

26.4 g of LiOH.H ₂ O was added to 50 g of the precursor such that the molar ratio of the total elements in the particle was Li: M (Ni, Co, Mn) = 1: 1, and the mixture was mixed with the zirconia balls using a ball mill, The mixture was calcined at 1050 DEG C for 15 hours at a high temperature in an air atmosphere to obtain an active material of a core-shell structure.

&Lt; Comparative Example 1 &

The average composition of the LiCoO ₂ particles 50g Ni: Co: Mn = 6 : 2: nickel sulfate so that the molar ratio of 2 (NiSO ₄₎ and cobalt sulfate (CoSO ₄₎ and manganese sulfate (MnSO ₄₎ are mixed a mixed aqueous solution 500ml And Ni-Co-Mn hydroxide was coprecipitated to Co ₃ O ₄ particles using sodium hydroxide. These dispersion systems were filtered and dried at 120 &lt; 0 &gt; C. A precursor sample in which Ni-Co-Mn based hydroxide was formed on the surface of LiCoO ₂ particles was obtained. 26.4 g of LiOH.H ₂ O was added to 50 g of the precursor to give a molar ratio of Li: M (Ni-Co-Mn) = 1: 1 of the total metal content of the Ni-Co-Mn hydroxide to the lithium, The mixture was mixed with a ball mill using a ball mill, and then the mixture was calcined at 1050 DEG C for 15 hours at a high temperature in an air atmosphere. Thus, a core-shell structure active material was synthesized.

&Lt; Comparative Example 2 &

LiCoO ₂ particles and LiNi _0.6 Mn _0.2 Co _0.2 O ₂ particles were weighed at a weight ratio of 90:10 and dry pressed to apply LiNi _0.6 Mn _0.2 Co _0.2 O ₂ to the surface of the LiCoO ₂ particles to synthesize the active material Respectively.

&Lt; Comparative Example 3 &

Using Al ₂ O ₃ as a source, particles of LiCoO ₂ coated with Al were used as an active material.

<Experimental Example 1>

SEM photographs of the active material particles prepared in Example 1 and Comparative Examples 1 and 2 are shown in FIGS. 1 to 3, and the lithium transition channel lattice matching ratios of the prepared active material particles were determined according to the criteria of the present invention, Are shown in Table 1 below.

Example 1 Comparative Example 1 Comparative Example 2 Lattice matching ratio (%) About 80 About 10 0

Referring to these figures and Table 1, it can be seen from the drawings that the active materials of Example 1 prepared according to the present invention are more uniformly coated on the surface of the core and have a high coverage, It can be confirmed that the lithium movement in the positive electrode active material is smooth.

<Experimental Example 2>

The active material particles prepared in Examples 1 to 4 and Comparative Examples 1 to 3 were used as a cathode active material, and PVdF as a binder and natural graphite as a conductive material were used. The positive electrode active material: binder: conductive material was mixed well with NMP so as to have a weight ratio of 96: 2: 2, and then applied to Al foil having a thickness of 20 탆 and dried at 130 캜 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-cell thus manufactured was continuously charged in an CC / CV mode at an upper limit voltage of 4.55 V at 60 ° C., and the time for reaching the maximum current was compared. The results are shown in Table 2 and FIG.

High temperature continuous charging Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Comparative Example 3 Maximum current arrival time (h) 152 150 154 153 125 121 80

Referring to Table 2, it can be seen that the maximum current arrival time of the embodiments at the time of high-temperature continuous charging is much longer than that of the comparative examples. The reason why the current increases with time at the high temperature continuous charging is because the leakage current due to the side reaction at the interface between the cathode material and the electrolyte is increased under high temperature / high voltage. Therefore, a long maximum current reaching time means that the anode / electrolyte side reaction is low at a high temperature / high voltage, which means that the stability is higher when the LCO is used at a high voltage. In particular, the maximum current reaching time is much higher than that of Comparative Example 3 where the LCO surface is coated with NCM, which is an Al coated LCO in the case of Examples 1-4. This is because the NCM coating layer has a surface area between the LCO surface charged with high voltage and the electrolytic solution It can be seen that a more uniform coating layer can be formed by forming the NCM coating layer according to the manufacturing method according to the present invention from the fact that the safety of the lithium secondary battery is improved.

<Experimental Example 3>

The cathode active material particles prepared in Example 1 and Comparative Example 3 were used as a cathode active material, and PVdF as a binder and natural graphite as a conductive material were used. The positive electrode active material: binder: conductive material was mixed well with NMP so as to have a weight ratio of 96: 2: 2, and then applied to Al foil having a thickness of 20 탆 and dried at 130 캜 to prepare a positive electrode.

The negative electrode was prepared by mixing artificial graphite, PVd and carbon black at a weight ratio of 96: 2: 2 in NMP, followed by coating on a 20 μm thick Cu foil and drying at 130 ° C. to prepare a negative electrode.

An electrode assembly was manufactured therebetween through a celgard and then placed in a pouch-type battery case. Using an electrolyte solution containing 1M of LiPF ₆ in a solvent of EC: DMC: DEC = 1: 2: 1, .

The thus prepared battery cells were charged in a CC / CV mode for 24 hours up to an upper limit voltage of 10 V to compare cell temperature changes. The results are shown in FIG.

Referring to FIG. 5, it can be seen that the cell temperature of the battery using the active material particles of Example 1 is lower than the cell temperature of the battery using the active material particles of Comparative Example 3, so that the high voltage stability is higher

<Experimental Example 4>

The cathode active material particles prepared in Examples 1 to 4 and Comparative Examples 1 to 3 were used as a cathode active material, and PVdF as a binder and natural graphite as a conductive material were used. The positive electrode active material: binder: conductive material was mixed well with NMP so as to have a weight ratio of 96: 2: 2, and then applied to Al foil having a thickness of 20 탆 and dried at 130 캜 to prepare a positive electrode.

As negative electrode, artificial graphite, PVdF, and carbon black were mixed well with NMP so that the weight ratio thereof was 96: 2: 2, and then coated on a Cu foil having a thickness of 20 탆 and dried at 130 캜 to prepare a negative electrode.

An electrode assembly was manufactured therebetween through a celgard and then placed in a pouch-type battery case. Using an electrolyte solution containing 1M of LiPF ₆ in a solvent of EC: DMC: DEC = 1: 2: 1, .

The output characteristics (rate characteristics) were confirmed at a ratio of 2.0 C to 0.1 C using the thus-prepared battery cells, and the results are shown in Table 3 below. The C-rate measurement criterion was 1 C of 40 mA. Charging and discharging was performed between 2.5V and 4.55V, charging was measured by CC / CV, and discharging was measured by CC.

Output Characteristics Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Comparative Example 3 2.0C / 0.1C capacity ratio (%) 91.5 91.2 91.3 91.0 88.5 87.2 92.0

Referring to Table 3, it can be seen that in the case of Examples 1-4 in which the LCO surface is coated with NCM, the output characteristics are almost the same as those in Comparative Example 3 in which the LCO is coated with Al. This is because the lithium migration path of the NCM coating layer and the LCO core of Example 1 has a lattice matching ratio of 60% or more as seen in Experimental Example 1, so that lithium migration can be performed more smoothly than Comparative Examples 1 and 2. From this, it can be seen that the NCM coating method of Example 1-4 has a great advantage in terms of the output characteristics as compared with the method of Comparative Example 1 or 2.

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 (21)

A core comprising a lithium cobalt oxide expressed by the following formula (1); And
A shell coated on the surface of the core and comprising a lithium-nickel-based oxide expressed by the following Chemical Formula 2 or Chemical Formula 3;
/ RTI &gt;
Wherein a lithium pathway of the core and a lithium pathway of the shell are continuously connected to each other.
Li _a Co _(1-x) M _x O _{2 -he h} (1)
Li _b Ni _y Co _z Mn _{1- y z} O _{2-w w} (2)
Li _b Ni _{y '} Mn _z' M '_1-y'-z' O _{2 -w a w} (3)
In this formula,
M is at least one member selected from the group consisting of Ti, Mg, Al, Zr, Mn and Ni,
A is an oxygen-substituted halogen,
M 'is at least one member selected from the group consisting of Ti, Mg, Al and Zr,
Y? 0.8, 0.1? Z? 0.4, 0.1? 1-yz? 0.4, 0.4? Y'? 0.5, 0.4? Z'≤0.5, 0.95? B? 1.00, 0.5, 0? 1-y'-z'0.2, 0? H? 0.001, and 0? W? The cathode active material particle according to claim 1, wherein there is no boundary space between the core and the shell. The lithium secondary battery according to claim 1, wherein the lithium path of the core and the lithium path of the shell are continuously connected with a lattice matching ratio of 60% or more. particle. The positive electrode active material particle according to claim 1, wherein the core and the shell have a continuous layered structure in their crystal structure. The positive electrode active material particle according to claim 1, wherein the weight ratio (B / A) of the shell (B) to the core (A) is 0.001 to 0.3. The positive electrode active material particle according to claim 1, wherein the shell is coated in an area of 50% to 100% with respect to the surface area of the core. The positive electrode active material particle according to claim 1, wherein the concentration of lithium in the core and the shell exhibits a concentration gradient that increases continuously or discontinuously toward the center of the core from the shell. The cathode active material particle of claim 1, wherein the stoichiometrically, the core is lithium overbased and the shell is lithium deficient. The cathode active material particle according to claim 1, wherein the lithium cobalt-based oxide is LiCoO ₂ . The positive electrode active material particle according to claim 1, wherein the lithium nickel oxide is a compound of the formula (2). The lithium nickel oxide according to claim 1, wherein the lithium nickel oxide is Li _b Ni _1/3 Co _1/3 Mn _1/3 O ₂ , Li _b Ni _0.5 Co _0.2 Mn _0.3 O _2, or Li _b Ni _0.6 Co _0.2 Mn _0.2 O ₂ (wherein b is the same as defined in the above item 1). A method for producing a cathode active material particle according to claim 1,
(a) a hydroxide of nickel (Ni) -manganese (Mn) -other metal (M ') in a lithium cobalt oxide precursor in a particle state (wherein M' is as defined in claim 1) or nickel ) -Cobalt (Co) -manganese (Mn); And
(b) mixing and firing a lithium precursor with a lithium cobalt oxide precursor having the coating layer formed thereon;
Wherein the positive electrode active material particles have an average particle diameter of not more than 100 nm. 13. The method of claim 12, wherein the step (a)
Dispersing a lithium cobalt oxide precursor in a particle state in a solution in which a nickel compound, a manganese compound and another metal (M ') compound are dissolved, followed by coprecipitation reaction. 13. The method of claim 12, wherein the step (a)
Dispersing a lithium cobalt oxide precursor in a particulate state in a solution in which a nickel compound, a cobalt compound and a manganese compound are dissolved, and conducting a coprecipitation reaction. 15. The method of claim 14, wherein the mixing ratio of the nickel compound, the cobalt compound, and the manganese compound ranges from 3 to 8: 1 to 4: 1 to 4 in molar ratio of nickel, cobalt, and manganese. Way. 13. The method of claim 12, wherein the lithium cobalt oxide precursor is cobalt oxide. The method of claim 12, wherein the hydroxide of nickel (Ni) -cobalt (Co) -manganese (Mn) is Ni _y Co _z Mn ₁ -yz (OH _{1 -t} ) ₂ wherein 0.3≤y≤0.8, 0.1≤ z? 0.4, 0.1? 1-yz? 0.4, and 0? t? 0.5). 13. The method according to claim 12, wherein the heat treatment in step (b) is performed at a temperature in the range of 850 to 1100 degrees Celsius for 2 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 19. A device comprising a battery pack according to claim 20.

Images