KR20160126840A - Cathode Active Material Particles Comprising One or More Coating Layer and Method for Preparation of the Same - Google Patents

Abstract

The present invention relates to positive electrode active material particles, and to a preparation method thereof. The positive electrode active material particles comprises: a core including lithium-containing metal oxide which can occlude and discharge lithium ions; a first coating layer placed on an outer surface of the core, and containing a first metal oxide for improving electrical conductivity of the positive electrode active material; and a second coating layer placed on an outer surface of the first coating layer, and containing a second metal oxide for stabilizing the surface of the positive electrode active material particles against an electrolyte.

Description

[0001] The present invention relates to a cathode active material particle comprising at least one coating layer and a method for producing the cathode active material particle,

The present invention relates to a cathode active material particle comprising at least one coating layer and a method for producing the same.

A rechargeable secondary battery is widely used as an energy source for wireless mobile devices. In addition, the secondary battery is an electric vehicle (EV), a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (HEV), and the like, which are proposed as solutions for air pollution of existing gasoline vehicles and diesel vehicles using fossil fuels (Plug-In HEV) and the like.

In particular, a lithium secondary battery used in an electric vehicle should have a high energy density and a capability to exhibit a large output in a short time, and can be used for more than 10 years under harsh conditions. Therefore, Life characteristics are inevitably required.

As a negative electrode active material of such a lithium secondary battery, a carbon material is mainly used, and the use of lithium metal, a sulfur compound and the like are also considered. In addition, lithium-containing cobalt oxide (LiCoO ₂ ) is mainly used as the positive electrode active material, and a lithium-containing manganese oxide such as LiMnO _{2 having a} layered crystal structure and LiMn ₂ O _{4 having a} spinel crystal structure and a lithium- ₂ ) is also considered.

Among the above cathode active materials, LiCoO ₂ is most widely used because it has excellent lifetime characteristics and charge / discharge efficiency, but it has a disadvantage that its structural stability is poor and its cost competitiveness is limited due to resource limitations of cobalt used as a raw material Electric vehicles and the like.

LiNiO ₂ has a relatively low cost and exhibits a high discharge capacity, but has a problem that rapid phase transition of the crystal structure occurs depending on the volume change accompanying the charging / discharging cycle, and safety is drastically lowered when exposed to air and moisture .

In addition, lithium manganese oxides such as LiMnO ₂ and LiMn ₂ O ₄ have an advantage that they are excellent in thermal stability and low in cost, but have a small capacity, poor cycle characteristics, and poor high temperature characteristics.

Therefore, many studies have been made on a new cathode active material having a different structure.

For example, in a lithium transition metal oxide containing a high Mn content, the content of lithium is higher than that of the transition metal, and an excess lithium oxide having a high capacity of 270 mAh / g or more is used under a high voltage of 4.5 V or more There was an attempt to do.

However, since the above-mentioned oxide having an excess lithium composition has a large irreversible capacity, it also escapes from the active material structure to oxygen in addition to lithium at the time of high voltage activation in order to utilize excess lithium. Therefore, the active material structure collapses, sagging phenomenon occurs, and it is found that the battery cell has a problem of promoting degradation of the battery cell.

In addition, a method of using a layered cathode active material containing Li ₂ MnO ₃ to secure the structural stability of the layered positive electrode active material has been disclosed. In this case, the material has a merit that it contains a large amount of Mn and is very inexpensive and has a large capacity and stability at a high voltage. However, after the activation period for the flat section of 4.4 to 4.6 V, Since the transition occurs in the spinel structure and the contact between the domains is loosened, there is room for improvement in improving the electrical characteristics due to a severe structural change.

As described above, the configuration of a secondary battery having a desired level of output characteristics, cycle characteristics, and energy density has not yet been proposed.

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, as will be described later, have found out that a core comprising a lithium-containing metal oxide capable of intercalating / deintercalating lithium ions; A first coating layer containing a first metal oxide for improving electrical conductivity of a cathode active material and positioned on an outer surface of the core; And a second coating layer containing a second metal oxide for stabilizing the particle surface of the positive electrode active material with respect to the electrolyte and positioned on the outer surface of the first coating layer, the output characteristics of the secondary battery, The characteristics and the energy density are remarkably improved, and the present invention has been accomplished.

Accordingly, the cathode active material particle according to the present invention comprises a core comprising a lithium-containing metal oxide capable of intercalating / deintercalating lithium ions; A first coating layer containing a first metal oxide for improving electrical conductivity of a cathode active material and positioned on an outer surface of the core; And a second coating layer containing a second metal oxide for stabilizing the particle surface of the cathode active material with respect to the electrolytic solution and positioned on the outer surface of the first coating layer.

That is, the first coating layer is positioned on the outer surface of the core to improve the electric conductivity of the cathode active material particles, thereby improving the output characteristics of the secondary battery.

In addition, since the electric conductivity of the cathode active material particles is improved, the loading amount of the cathode mixture can be increased while maintaining a constant output, and the energy density of the secondary battery is improved.

However, the first coating layer for improving electrical conductivity may be detached from the surface of the core during use of the secondary battery. In this case, the output characteristics and the energy density are lowered. Therefore, in order to prevent detachment of the first coating layer and to prevent deterioration of the overall performance of the secondary battery such as output characteristics and energy density even when the secondary battery is used for a long time, the second coating layer for surface stabilization is formed on the outer surface of the first coating layer .

Thus, when the second coating layer is placed on the outer surface of the first coating layer, the surface of the cathode active material is stabilized and the cycle characteristics of the secondary battery are improved.

The lithium-containing metal oxide constituting the core is not particularly limited as long as it is a material capable of intercalating / deintercalating lithium ions, and examples thereof include a lithium metal oxide, a lithium transition metal oxide, a lithium transition metal composite oxide, Oxide, an over-lithium oxide, and the like.

Specifically, the lithium-containing metal oxide may be a layered compound such as lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), or a compound substituted with one or more transition metals; 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 ); LiV ₃ O ₈ , LiFe ₃ O ₄ , lithium vanadium oxide; Lithium iron phosphate; 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; Fe ₂ (MoO ₄ ) ₃ , and the like. However, the present invention is not limited to these.

The first metal oxide contained in the first coating layer may be a material capable of improving the electrical conductivity of the cathode active material. In one specific example, the first metal oxide may be ruthenium oxide.

The ruthenium oxide has been found to be particularly excellent in improving the electric conductivity of the cathode active material particles as compared with other metal oxides.

The thickness of the first coating layer may be 1 nm to 50 nm, more specifically 5 nm to 30 nm, and more specifically 10 nm to 20 nm.

If the thickness of the first coating layer is less than 1 nm, the effect of improving the electrical conductivity is not significant, and if the thickness is more than 50 nm, the specific gravity of the core for determining the capacity of the secondary battery in the positive electrode active material particles is reduced, The capacity of the battery may be reduced.

Also, the cathode active material particle may be composed of 0.08 wt% to 4.00 wt%, specifically 0.1 wt% to 2 wt%, and more specifically 0.2 wt%, based on the total weight of the cathode active material particle, To 0.7% by weight, in particular 0.5% to 0.7% by weight.

In one specific example, the second metal oxide contained in the second coating layer is not particularly limited as long as it can stabilize the surface of the cathode active material particles without causing a reaction with the electrolytic solution and lithium ions, May be aluminum oxide.

Aluminum oxide is superior to other metal oxides in stabilizing the surface, and it is confirmed that the aluminum oxide has excellent retention on the surface of the cathode active material particles due to the structural stability.

The thickness of the second coating layer may be 0.2 nm to 2 nm, specifically 0.4 nm to 1.5 nm, and more specifically, 0.6 nm to 0.8 nm.

When the thickness of the second coating layer is less than 0.2 nm, the thickness of the second coating layer is too thin to sufficiently stabilize the surface, and the second coating layer can easily be removed due to external influences, so that it is difficult to improve the cycle characteristics of the secondary battery. The formation of the second coating layer takes time and expense excessively, and the content of the cathode active material in the particles is relatively decreased, which may lead to a reduction in capacity of the secondary battery.

The cathode active material particles may contain 0.01 to 0.5% by weight, specifically 0.01 to 0.1% by weight, more specifically 0.03 to 0.05% by weight, based on the total weight of the cathode active material particles, %.

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

A method for producing a cathode active material particle according to the present invention comprises:

(a) preparing a lithium-containing metal oxide particle capable of intercalating / deintercalating lithium ions;

(b) a step of administering a lithium-containing metal oxide particle to a solution containing a first metal oxide precursor, an oxidizing agent, and a fuel for reaction promotion, 1 < / RTI > metal oxide; And

(c) annealing the cathode active material particles having the first coating layer formed thereon.

In the step (b), the reaction is carried out by adding the lithium-containing metal oxide particles to the solution containing the first metal oxide precursor, the oxidizing agent, and the fuel for promoting reaction, and when the solvent is evaporated after the reaction is completed, An oxide of the first metal oxide precursor, i.e., a first metal oxide, is coated.

Thereafter, the intermediate products that are not completely oxidized to the first metal oxide in the first metal oxide precursor can be completely oxidized by the heat treatment, and the first metal oxides included in the first coating layer form a crystal structure, The effect of improving electrical conductivity and the structural stability are further increased.

At this time, the fuel is included in the first coating layer after the step (b), and the activation energy of the oxidation reaction is lowered in the heat treatment process of the step (c) to accelerate the reaction rate. It allows you to proceed. It is possible to complete the heat treatment process in a shorter time by the fuel, thereby increasing the efficiency of the process and reducing the manufacturing cost.

In one specific example, the first metal oxide precursor may be at least one selected from the group consisting of, for example, ruthenium chloride, ruthenium chloride hydrate, ruthenium nitrate, ruthenium acetate, and the like, Ruthenium chloride hydrate.

In one specific example, the oxidizing agent is not particularly limited as long as it can oxidize the first metal oxide precursor to the first metal oxide and does not seriously cause a side reaction. For example, ammonium nitrate, ruthenium nitrate, and organic nitrate nitrate), and more specifically, it may be ammonium nitrate.

In one specific example, the solution may comprise at least one solvent selected from the group consisting of 2-methoxyethanol, anhydrous ethanol, and anhydrous methanol, and specifically may include 2-methoxyethanol .

In one specific example, the fuel may be at least one member selected from the group consisting of urea, acetyl acetone, and ketone group-containing organic compounds, and may be an element in particular.

In one specific example, the concentration of the first metal oxide precursor may be 0.01 M to 0.2 M, specifically 0.02 M to 0.1 M, and if it is less than 0.01 M, the reaction rate is slow and the reaction time is too long If it is more than 0.2 M, the thickness of the first coating layer may become unnecessarily large, and it may be difficult to coat the first coating layer with a uniform thickness.

The molar ratio of the first metal oxide precursor, the oxidizer and the fuel may be 1.0 to 2.0: 1.0 to 2.0: 1.0 to 2.0, more specifically 1.0 to 1.5: 1.0 to 1.5: 1.0 to 1.5. The reaction can take place at an appropriate rate, and the first coating layer can be formed with a uniform thickness.

In one specific example, the heat treatment may be performed at a temperature of 250 ° C to 800 ° C for 1 to 5 hours, and more specifically, at a temperature of 400 ° C to 500 ° C.

When the reaction temperature of the heat treatment is less than 250 ° C, the reaction rate is slow, the reaction takes a long time, the crystal structure of the first metal oxide is not developed, and when the reaction temperature exceeds 800 ° C, It is difficult to manage, and the cost for maintaining a high temperature is high.

Meanwhile, the method for manufacturing the cathode active material particle may further include the following step (d) after the step (c):

(d) forming a second coating layer on the outer surface of the first coating layer, the second coating layer including a second metal oxide for stabilizing the particle surface of the cathode active material with respect to the electrolytic solution.

In one specific example, in step (d), a second coating layer may be formed by atomic layer deposition.

Since the second coating layer is for stabilizing the surface of the particles of the cathode active material, if the thickness is more than the predetermined thickness, the desired effect can be achieved. Therefore, it is efficient in terms of energy density to coat the coating layer as thin as possible.

The atomic layer deposition method can control the thickness of the coating layer by approximately 0.1 nm, so that the second coating layer can be thinly coated, and the energy density of the secondary battery can be remarkably improved.

In order to form the second coating layer with a desired thickness, the second coating layer may be formed by performing the atomic layer deposition method for 1 cycle to 10 cycles, specifically, 3 cycles to 4 cycles in step (d).

In one specific example, the first coating layer is applied to 50% to 90% of the entire outer surface of the core, and the second coating layer is applied to the entire outer surface including the core and the first coating layer.

When the atomic layer deposition method is used to form the second coating layer, the positive electrode active material particles are not formed in a fixed position, and the second coating layer may be formed on the entire outer surface including the core and the first coating layer. The atomic layer deposition method can be performed while changing the position of the particles.

The present invention also provides a lithium secondary battery including the positive electrode active material particles, the binder and the conductive agent, a positive electrode mixture for the positive electrode mixture coated on the current collector, and a positive electrode for the rechargeable battery .

Hereinafter, other components of the lithium secondary battery according to the present invention will be described.

The anode is prepared, for example, by applying a mixture of a cathode active material, a conductive material and a binder to both surfaces of a cathode current collector, followed by drying and pressing, and if necessary, a filler is further added to the mixture.

The cathode current collector generally has a thickness of 3 to 300 탆 and is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. Examples of the cathode current collector include 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 conductive material is usually added in an amount of 1 to 30% by weight based on the total weight of the positive electrode material mixture containing the positive electrode 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-butadiene 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.

On the other hand, the negative electrode may be manufactured by applying a negative electrode mixture containing a negative electrode active material, a conductive material, and a binder to a negative electrode collector, and a filler or the like may further be optionally included.

The negative electrode current collector is not particularly limited as long as it has electrical conductivity without causing a chemical change in the battery. For example, the negative electrode current collector may be formed on the surface of copper, stainless steel, aluminum, nickel, titanium, sintered carbon, 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.

In the present invention, the thickness of the anode current collector may be the same within the range of 3 to 300 탆, but they may have different values depending on the case.

The negative electrode active material may include, for example, carbon such as non-graphitized carbon or 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 membrane is generally 0.01 to 10 micrometers, and the thickness is generally 5 to 30 micrometers. 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 electrolyte solution may be a non-aqueous electrolyte containing a lithium salt, and the non-aqueous electrolyte containing a lithium salt is composed of a non-aqueous electrolyte and a lithium salt. Non-aqueous organic solvents, organic solid electrolytes, inorganic solid electrolytes, 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 derivatives, Tetrahydrofuran derivatives, ether, 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 A polymer containing an acid dissociation group and the like may 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 substance that is soluble in the nonaqueous electrolyte and includes, 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, chloroborane lithium, lower aliphatic carboxylate lithium, lithium tetraphenylborate, and imide.

The nonaqueous electrolyte may contain, for the purpose of improving charge / discharge characteristics, flame retardancy, etc., 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 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.

In one specific _{example, LiPF 6, LiClO 4, LiBF} 4, LiN (SO 2 CF 3) 2 , such as a lithium salt, a highly dielectric solvent of DEC, DMC or EMC Fig solvent cyclic carbonate and a low viscosity of the EC or PC of And then adding it to a mixed solvent of linear carbonate to prepare a lithium salt-containing nonaqueous electrolyte.

The present invention also provides a battery pack including the secondary battery as a unit cell, and a device including the battery pack as a power source.

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.

The structure and manufacturing method of such a device are well known in the art, so a detailed description thereof will be omitted herein.

As described above, the cathode active material particles according to the present invention have the first coating layer positioned on the outer surface of the core to improve the electric conductivity of the cathode active material particles and improve the output characteristics of the secondary battery.

Further, the electric conductivity of the cathode active material particles can be improved, the loading amount of the cathode mixture can be increased while maintaining a constant output, and the energy density of the secondary battery can be improved.

Furthermore, the second coating layer stabilizes the surface of the positive electrode active material with respect to the electrolyte, thereby improving the cycle characteristics of the secondary battery.

FIG. 1 is a schematic view sequentially showing a method of manufacturing a first coating layer of a cathode active material particle according to an embodiment of the present invention; FIG.
FIGS. 2 and 3 are energy dispersive spectroscopy (EDS) results of the cathode active material particles having the first coating layer formed according to the manufacturing method of FIG. 1;
4 is a photograph of LNMO before ruthenium oxide coating and LNMO after ruthenium oxide coating by transmission electron microscope (TEM);
5 is a schematic view showing a structure of a cathode active material particle having a first coating layer and a second coating layer according to an embodiment of the present invention;
6 is a graph showing the results of low energy ion scattering (LEIS) analysis of Example 1, Comparative Example 1 and Comparative Example 2 of the present invention;
FIGS. 7 and 8 are graphs showing the results of measuring the electrical conductivities of Example 1 and Comparative Example 1 of the present invention, respectively;
FIG. 9 is a graph showing the charge-discharge capacity measured in the charge-discharge cycles of Example 4, Example 5, and Comparative Example 3 twice;
10 is a graph showing changes in capacitance with changes in the C-rate in Example 4, Example 5, and Comparative Example 3 of the present invention;
FIG. 11 is a graph showing changes in coulombic efficiency according to the number of times of charging and discharging of Example 4, Example 5, and Comparative Example 3 of the present invention; FIG.
FIGS. 12 and 13 are graphs showing capacitance changes according to C-rate changes in Examples 4, 6, 7, 8, 4 and 5 of the present invention;
FIGS. 14 and 15 are graphs showing capacitance changes according to the C-rate changes of Examples 7, 9, 10, 5, 6, and 7 of the present invention;
FIGS. 16 and 17 are graphs showing changes in capacitance according to the progression of cycles of Example 7, Example 9, Comparative Example 5, Comparative Example 6, Comparative Example 8, and Comparative Example 9 of the present invention;
FIGS. 18 and 19 are graphs showing changes in coulombic efficiency according to the cycle progression of Example 7, Example 9, Comparative Example 5, Comparative Example 6, Comparative Example 8, and Comparative Example 9 of the present invention.

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

&Lt; Preparation Example 1 &

Preparation of first coating layer - wet process

LiNi _0.75 Mn _0.25 O ₂ , which is a lithium-containing metal oxide to be used as a core, was prepared. A precursor solution having a concentration of ruthenium chloride of 0.05 M was prepared by mixing ruthenium chloride hydrate, ammonium nitrate and urea in a molar ratio of 1: 1: 1 to 2-methoxyethanol as a solvent. The precursor solution was reacted with LiNi _0.75 Mn _0.25 O ₂ by a wet method and the solvent was evaporated using a rotary evaporator. The reaction product obtained by evaporating the solvent is annealed at a temperature of 250 ° C to 800 ° C for 1 to 5 hours to form a cathode active material particle having a ruthenium oxide coating layer formed on the surface of the LiNi _0.75 Mn _0.25 O ₂ core Cathode active material particle).

&Lt; Preparation Example 2 &

Preparation of Second Coating Layer - Atomic Layer Deposition

The cathode active material particles having the first coating layer formed therein were placed in a reactor, and vacuum was applied to remove air inside the reactor. TMA was deposited on the surface of the cathode active material particle on which the first coating layer was formed by injecting trimethylaluminium (TMA) into the reactor, and vacuum was applied to the reactor to remove residual TMA (surface reaction). Water (H ₂ O) was injected into the reactor and reacted with TMA deposited on the surface to form a thin film. Vacuum was applied again to remove residues and by-products (water treatment reaction). The surface reaction and the water treatment reaction were performed in one cycle, and the atomic layer deposition method was performed for 1 cycle to 10 cycles to prepare cathode active material particles having the second coating layer formed thereon.

&Lt; Preparation Example 3 &

Manufacture of Secondary Battery

The positive electrode slurry was prepared by mixing the positive electrode active material particles, PVDF (KF1100, binder), and super P (conductive material) at a certain ratio based on the weight and put into NMP (solvent), coating on one side of the aluminum foil, And a positive electrode having a constant loading amount was prepared.

Lithium metal with a thickness of 0.6 mm was used as the cathode.

A LiPF ₆ electrolyte was added to a mixed solvent of ethyl carbonate (EMC) and dimethyl carbonate (DMC) in a ratio of 3: 4: 3 based on the weight of the porous polyethylene separator interposed between the prepared positive and negative electrodes. The electrolyte solution dissolved in a concentration of 1 M was added to prepare a lithium secondary battery.

&Lt; Example 1 >

According to Production Example 1 and Production Example 2, cathode active material particles having a core: first coating layer: second coating layer = 99.38: 0.57: 0.05 were prepared on the basis of weight.

&Lt; Example 2 >

In Example 1, cathode active material particles having a core: first coating layer: second coating layer = 99.3: 0.6: 0.1 were prepared on the basis of weight.

&Lt; Example 3 >

Cathode active material particles having a core: first coating layer: second coating layer = 99.88: 0.07: 0.05 were prepared on the basis of weight in Example 1.

<Example 4>

Performed by using the positive electrode active material particle of Example 1, according to Preparation Example 3, the positive electrode active material particles, by weight: binder: conductive material = 95: 4: a ratio of 1, and the loading amount of 4.9 mg / cm ² of the anode Was prepared. &Lt; tb &gt;&lt; TABLE &gt;

&Lt; Example 5 >

A secondary battery was produced in the same manner as in Example 4, except that the cathode active material particles of Example 2 were used instead of the cathode active material particles of Example 1 in Example 4.

&Lt; Example 6 >

A secondary battery was prepared in the same manner as in Example 4, except that the mixture was mixed with the cathode active material particles: binder: conductive material = 94: 4: 2 by weight in Example 4.

&Lt; Example 7 >

A secondary battery was produced in the same manner as in Example 4, except that the weight ratio of the positive electrode active material particles: the binder: the conductive material was changed to 92: 4: 4 by weight in Example 4.

&Lt; Example 8 >

A secondary battery was produced in the same manner as in Example 4, except that the cathode active material particles of Example 3 were used in place of the cathode active material particles of Example 1 in Example 4.

&Lt; Example 9 >

A secondary battery was prepared in the same manner as in Example 7, except that the loading amount of the positive electrode mixture was changed to 9.1 mg / cm ² .

&Lt; Example 10 >

A secondary battery was manufactured in the same manner as in Example 7 except that the loading amount of the positive electrode mixture was changed to 15.8 mg / cm ² .

&Lt; Comparative Example 1 &

A positive electrode active material particle was prepared in the same manner as in Example 1, except that the first coating layer and the second coating layer were not formed in Example 1.

&Lt; Comparative Example 2 &

According to Production Example 1, on the basis of weight, a cathode active material particle having a core: first coating layer = 99.4: 0.6 was prepared.

&Lt; Comparative Example 3 &

A secondary battery was produced in the same manner as in Example 4, except that the cathode active material particles of Comparative Example 2 were used instead of the cathode active material particles of Example 1 in Example 4.

&Lt; Comparative Example 4 &

A secondary battery was produced in the same manner as in Example 4 except that the cathode active material particles of Comparative Example 1 were used instead of the cathode active material particles of Example 1.

&Lt; Comparative Example 5 &

A secondary battery was produced in the same manner as in Example 7 except that the cathode active material particles of Comparative Example 1 were used instead of the cathode active material particles of Example 1.

&Lt; Comparative Example 6 >

In Comparative Example 5, a secondary battery was manufactured in the same manner as in Comparative Example 5 except that the loading amount of the positive electrode mixture was changed to 9.1 mg / cm ² .

&Lt; Comparative Example 7 &

In Comparative Example 5, a secondary battery was manufactured in the same manner as in Comparative Example 5, except that the loading amount of the positive electrode mixture was 15.5 mg / cm ² .

&Lt; Comparative Example 8 >

A secondary battery was produced in the same manner as in Example 7 except that the cathode active material particles of Comparative Example 2 were used instead of the cathode active material particles of Example 1.

&Lt; Comparative Example 9 &

In Comparative Example 8, a secondary battery was manufactured in the same manner as in Comparative Example 8, except that the loading amount of the positive electrode mixture was 9.1 mg / cm ² .

<Experimental Example 1>

The electric conductivity of each of the cathode active material particles prepared in Examples 1, 3 and Comparative Example 1 was measured using a quadrupole method. The results are shown in FIG. 7, FIG. 8, and Table 1, respectively.

Ruthenium oxide content (wt%) Electrical Conductivity (S / cm) 0.00 1.9 × 10 ^-6 0.07 4.5 × 10 ^-6 0.57 2.7 x 10 ^-1

7, 8 and Table 1, the lithium-containing metal oxide used in Example 1, Example 3 and Comparative Example 1 was the same as LiNi _0.75 Mn _0.25 O ₂ , but there was a large difference in electric conductivity Can be confirmed. The electrical conductivity of Comparative Example 1 was 1.9 × 10 ^-6 S / cm, whereas the electrical conductivity of Example 3 was 4.5 × 10 ^-6 S / cm. Even if the amount of ruthenium oxide contained was very small, the electrical conductivity It can be confirmed that it is improved more than 2 times. Moreover, it can be seen that the electrical conductivity of Example 1 was remarkably increased to 2.7 x 10 &lt; ^-1 &gt; S / cm. From these results, it is considered that the ruthenium oxide coating layer increases the electric conductivity of the cathode active material particles, thereby improving the output characteristics, cycle characteristics and energy density as shown in the following experimental examples.

<Experimental Example 2>

The charge and discharge capacities of the secondary batteries prepared in Examples 4 and 5 and Comparative Example 3 were measured by charging and discharging the secondary batteries at a rate of 0.1 C from 3 V to 5 V twice. .

<Experimental Example 3>

The C-rate was sequentially set to 0.1 C-rate, the C-rate was set at 0.1 C-rate based on the discharge capacity (about 140 mA / g) when the secondary battery prepared in each of Example 4, Example 5, The capacitance change was measured while varying at 0.5 C-rate, 1 C-rate, 2 C-rate, 3 C-rate, 4 C-rate, 7 C-rate and 10 C-rate. .

<Experimental Example 4>

The secondary batteries manufactured in Examples 4, 5 and Comparative Example 3 were subjected to the same operation as in Example 1, except that the secondary batteries were manufactured at 0.1 C-rate, 0.5 C-rate, 1 C-rate, 2 C-rate, 3 C- C-rate and 10 C-rate, and the change in coulombic efficiency was measured according to the charge-discharge rate. The results are shown in FIG.

9 and 10, Comparative Example 3 had no second coating layer having a low electrical conductivity, so that the electric conductivity of the cathode active material particles was relatively higher than that of Example 4 and Example 5, It can be confirmed that the initial capacity and the output characteristics affected by the second embodiment are relatively better than those of the fourth and fifth embodiments.

Referring to FIG. 11, in Comparative Example 3, since the second coating layer is not formed, it is confirmed that the coulomb efficiency, which is the discharge capacity in relation to the charging capacity, is relatively low as compared with the fourth and fifth embodiments. That is, in the case of Comparative Example 3, the energy efficiency during charging and discharging was inferior and the surface was not stabilized. As a result, the capacity of the battery decreased with use of the secondary battery, have.

Since the secondary battery is not a one-time consumable, when the initial capacity and the output characteristic are satisfied only at a certain level or more, the lower the capacity and the lower the coulomb efficiency are, the more effective it is when the charging and discharging are repeated.

From these results, it can be concluded that Comparative Example 3, which has a relatively low initial coulomb efficiency and cycle characteristics, is difficult to be industrially used although the initial capacity and output characteristics are relatively excellent. It can be seen that Examples 4 and 5, which are excellent in efficiency and cycle characteristics, are more suitable for industrial application.

<Experimental Example 5>

The secondary batteries prepared in Example 6, Example 7, Example 8, Comparative Example 4 and Comparative Example 5 were sequentially charged at a C-rate of 0.1 C-rate The results are shown in FIG. 12 and FIG. 12. The results are shown in FIG. 12 and FIG. 14. The results are shown in FIG. 12 and FIG. 13.

Referring to FIG. 12, in the case of Examples 4, 6 and 7, it can be seen that the output characteristics are partially improved because the capacity retention ratio is relatively high even when the content of the conductive material is increased and the C-rate is increased. However, considering that the amount of the conductive material contained in each of Examples 4, 6, and 7 is increased by two times, the increase in the output characteristics is not significant. From these results, In Examples 6 and 7, since the first coating layer is formed, the electric conductivity is improved, and it can be understood that sufficient output characteristics can be obtained even if the conductive material is used in a small amount, and a relatively large amount of the cathode active material So that the energy density can be increased.

12 and 13, it can be seen from the results of Example 4, Example 8, and Comparative Example 4 that the output characteristics of the secondary battery are lowered when the thickness of the first coating layer is too thin or not formed . Therefore, it is more preferable that the amount of ruthenium oxide contained in the first coating layer is 0.2 wt% to 0.7 wt%, based on the total weight of the cathode active material particles, from the viewpoints of improvement of output characteristics and improvement of energy density.

In addition, it can be confirmed from Example 4 and Comparative Example 5 that similar output characteristics are exhibited even though the amount of the conductive material contained in the positive electrode material mixture is about four times as large. From these results, it can be seen that the output characteristics of the cathode active material particles are remarkably improved by the coating layer of the present invention, the content of the cathode active material can be increased when exhibiting the same output characteristics, and thus the energy density can be remarkably improved .

<Experimental Example 6>

The secondary batteries manufactured in Examples 7, 9, 10, 5, and 6 and Comparative Example 7 were each subjected to a C-rate in sequential order based on the discharge capacity at 0.1 C-rate The capacitance changes were measured while varying at 0.1 C-rate, 0.5 C-rate, 1 C-rate, 2 C-rate, 3 C-rate, 4 C-rate, 7 C-rate and 10 C- Are shown in Fig. 14 and Fig.

Referring to FIG. 14, in the case of Comparative Example 5, Comparative Example 6, and Comparative Example 7, since the first coating layer for improving electrical conductivity is not formed, the internal resistance increases as the loading amount of the positive electrode material mixture increases, Of the total number of patients.

Referring to FIG. 15 in comparison with FIG. 14, in the case of the seventh embodiment, the ninth embodiment, and the tenth embodiment, it is confirmed that the output characteristics are maintained even when the loading amount is increased by the first coating layer and the second coating layer. Therefore, it can be seen that when using the cathode active material particles of the present invention, the energy density of the secondary battery can be improved while maintaining the output characteristics.

<Experimental Example 7>

The secondary batteries prepared in Example 7, Example 9, Comparative Example 5, Comparative Example 6, Comparative Example 8, and Comparative Example 9 were charged and discharged at 0.1 C rate for 2 cycles, The discharge capacity was measured while charging and discharging during the cycle. The results are shown in Fig. 16 and Fig.

Referring to FIG. 16, in the case of Comparative Example 5, the capacity tends to decrease slightly as the cycle progresses. However, the loadings of Example 7, Comparative Example 5, and Comparative Example 8 were as low as 4.9 mg / cm ² , indicating that the capacity of the initial capacity was kept high even after 130 cycles.

17, the capacity of the initial capacity of Example 9 is maintained at the highest level during the course of 130 cycles, the capacity retention rate of Comparative Example 6 is rather low, and the capacity of Comparative Example 9 is about 80 cycles It can be confirmed that the capacity is rapidly reduced thereafter.

Therefore, in the case of Comparative Example 9 in which there is no second coating layer as a stabilizing layer as the amount of loading increases, there is a problem that the capacity retention rate is drastically reduced. In order to manufacture a battery having a high capacity, a second coating layer It can be seen that it is necessary.

<Experimental Example 8>

The secondary batteries prepared in Example 7, Example 9, Comparative Example 5, Comparative Example 6, Comparative Example 8, and Comparative Example 9 were charged and discharged at 0.1 C rate for 2 cycles, Coulomb efficiency was measured while charging and discharging during the cycle. The results are shown in Fig. 18 and Fig.

Referring to FIG. 18, the initial coulombic efficiency of Example 7, Comparative Example 5, and Comparative Example 8 is low. In the case of Example 7 and Comparative Example 8, the first coating layer for improving electrical conductivity is included. In the case of Comparative Example 5, the increase in coulomb efficiency is relatively slow.

Referring to FIG. 19 in comparison with FIG. 18, it can be confirmed from the results of Example 7 and Example 9 that the Coulomb efficiency increase pattern is similar despite the difference in the amount of loading when the first coating layer and the second coating layer are included . From the results of Comparative Example 5 and Comparative Example 6, it can be confirmed that even when the first coating layer and the second coating layer are not included, the Coulomb efficiency increase pattern is similar regardless of the difference in the loading amount. Comparative Example 8 and Comparative Example 9, which did not include the second coating layer as the stabilizing layer, showed different Coulomb efficiency patterns. From the results of Comparative Example 9, when the loading amount was increased, the durability of the first coating layer was decreased, It can be seen that there is a problem that the coulomb efficiency fluctuates more and the coulomb efficiency decreases.

Therefore, in the case of Comparative Example 9 in which there is no second coating layer as a stabilizing layer as the amount of loading increases, there is a problem that the coulombic efficiency is reduced. Therefore, in order to manufacture a high capacity and high efficiency battery, a second coating layer Able to know.

FIG. 6 is a graph showing the results of low energy ion scattering (LEIS) analysis of Example 1, Comparative Example 1 and Comparative Example 2, whereby a second coating layer is formed on the surface of the active material particle It is possible to know whether or not it is uniformly applied.

Referring to FIG. 6, in the graph on the left side of FIG. 6, it can be seen that in Comparative Example 1 and Comparative Example 2, Al peaks do not appear, whereas in Example 1, Al peaks appear. From this, it can be seen that a second coating layer containing aluminum oxide was formed on the particle surface of Example 1.

In the right graph of FIG. 6, the Mn peaks of Comparative Example 1 and Comparative Example 2 are high, whereas the Mn peak of Example 1 is very low. From this, it can be seen that in Example 1, the second coating layer containing aluminum oxide is uniformly coated on the outer surface of the active material particles, so that the Mn of the core is not exposed to the outside.

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 (24)

A core comprising a lithium-containing metal oxide capable of intercalating / deintercalating lithium ions;
A first coating layer containing a first metal oxide for improving electrical conductivity of a cathode active material and positioned on an outer surface of the core; And
A second coating layer containing a second metal oxide for stabilizing the particle surface of the positive electrode active material with respect to the electrolytic solution and positioned on the outer surface of the first coating layer;
And a positive electrode active material particle. The lithium secondary battery according to claim 1, wherein the lithium-containing metal oxide is at least one selected from the group consisting of a lithium metal oxide, a lithium-transition metal oxide, a lithium-transition metal composite oxide, and an over-lithium oxide Cathode active material particle. The positive electrode active material particle according to claim 1, wherein the lithium-containing metal oxide comprises at least one compound selected from the group consisting of the following formula (1)
LiNi _1-x M _x O ₂ (1)
In this formula,
M = Co, Mn, Al, Cu, Fe, Mg, B or Ga,
x = 0.01 to 0.3. The cathode active material particle according to claim 1, wherein the first metal oxide is ruthenium oxide. The cathode active material particle according to claim 1, wherein the first coating layer has a thickness of 1 nm to 50 nm, and more specifically 5 nm to 30 nm. The cathode active material particle according to claim 1, wherein the second metal oxide is aluminum oxide. The cathode active material particle according to claim 1, wherein the thickness of the second coating layer is 0.2 nm to 2 nm, more specifically 0.4 nm to 1.5 nm. The positive electrode active material particle according to claim 1, wherein the first metal oxide is 0.08 wt% to 4.00 wt%, and more preferably 0.1 wt% to 2 wt%, based on the total weight of the positive electrode active material particles. The cathode active material particle according to claim 1, wherein the second metal oxide is contained in an amount of 0.01 to 0.5% by weight, and more preferably 0.01 to 0.1% by weight, based on the total weight of the cathode active material particles. The positive electrode active material according to claim 1, wherein the first coating layer is applied to 50% to 90% of the entire outer surface of the core, and the second coating layer is applied to the entire outer surface including the core and the first coating layer. particle. A positive electrode material mixture comprising the positive electrode active material particles according to claim 1, a binder, and a conductive material. The positive electrode for a secondary battery according to claim 11, wherein the positive electrode material mixture is applied on a current collector. A lithium secondary battery comprising a positive electrode for a secondary battery according to claim 12. (a) preparing a lithium-containing metal oxide particle capable of intercalating / deintercalating lithium ions;
(b) applying a lithium-containing metal oxide particle to a solution containing a first metal oxide precursor, an oxidizing agent, and a fuel for reaction promotion to improve electric conductivity on the surface of the lithium-containing metal oxide particle as a core Forming a first coating layer of a first metal oxide for the first metal oxide layer; And
(c) annealing the cathode active material particles having the first coating layer formed thereon;
Wherein the positive electrode active material particles have an average particle diameter of not more than 100 nm. 15. The method of claim 14, wherein the first metal oxide precursor is at least one selected from the group consisting of ruthenium chloride, ruthenium chloride hydrate, ruthenium nitrate, and ruthenium acetate. 15. The method of claim 14, wherein the oxidizing agent is at least one selected from the group consisting of ammonium nitrate, ruthenium nitrate, and organic nitrate, and more particularly, ammonium nitrate. 15. The positive active material particle of claim 14, wherein the solution comprises at least one solvent selected from the group consisting of 2-methoxyethanol, anhydrous ethanol, and anhydrous methanol, particularly 2-methoxyethanol &Lt; / RTI &gt; 15. The method of producing cathode active material particles according to claim 14, wherein the fuel is at least one selected from the group consisting of urea, acetyl acetone, and ketone group-containing organic compounds. 15. The method of claim 14, wherein the concentration of the first metal oxide precursor is 0.01 M to 0.2 M, specifically 0.02 M to 0.1 M. 15. The method of claim 14, wherein the molar ratio of the first metal oxide precursor to the oxidant to the fuel is 1.0 to 2.0: 1.0 to 2.0: 1.0 to 2.0, and more specifically 1.0 to 1.5: 1.0 to 1.5: 1.0 to 1.5. By weight based on the total weight of the positive electrode active material particles. 15. The method of claim 14, wherein the heat treatment is performed at a temperature of 250 ° C to 800 ° C for 1 to 5 hours, and more specifically at a temperature of 400 ° C to 500 ° C. The method of claim 14, further comprising the following step (d) after the step (c):
(d) forming a second coating layer on the outer surface of the first coating layer, the second coating layer including a second metal oxide for stabilizing the particle surface of the cathode active material with respect to the electrolytic solution. The method according to claim 22, wherein in the step (d), a second coating layer is formed by atomic layer deposition. 24. The method according to claim 23, wherein in the step (d), the atomic layer deposition is performed for 1 cycle to 10 cycles, specifically 3 cycles to 4 cycles to form a second coating layer.

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