KR102045495B1 - Cathode Active Material Particles Comprising One or More Coating Layer and Method for Preparation of the Same - Google Patents

Abstract

The present invention is a core (core) comprising a lithium-containing metal oxide capable of occluding / releasing lithium ions; A first coating layer containing a first metal oxide for improving electrical conductivity of the positive electrode 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 an electrolyte solution and positioned on an outer surface of the first coating layer. .

Description

Cathode Active Material Particles Comprising One or More Coating Layer and Method for Preparation of the Same}

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

Recently, secondary batteries capable of charging and discharging have been widely used as energy sources of wireless mobile devices. In addition, the secondary battery is an electric vehicle (EV), a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle that has been proposed as a solution for air pollution of existing gasoline and diesel vehicles using fossil fuel. It is attracting attention as a power source such as (Plug-In HEV).

In particular, lithium secondary batteries used in electric vehicles have high energy density and high power output in a short time, and should be able to be used for 10 years or more under severe conditions. Lifespan 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, etc. is also considered. In addition, lithium-containing cobalt oxide (LiCoO ₂ ) is mainly used as the positive electrode active material, and lithium-containing manganese oxides such as LiMnO _{2 having a} layered crystal structure and LiMn ₂ O _{4 having a} spinel crystal structure, and lithium-containing nickel oxide (LiNiO). The use of ₂ ) is also under consideration.

Among the positive electrode active materials, LiCoO ₂ is most used because of its excellent life characteristics and charging and discharging efficiency, but it has a disadvantage in that its price competitiveness is limited because its structural stability is low and it is expensive due to the resource limitation of cobalt used as a raw material. There is a limit to mass use as a power source in fields such as electric vehicles.

LiNiO ₂ is relatively inexpensive and exhibits high discharge capacity. However, LiNiO ₂ has a sudden phase transition of the crystal structure due to the volume change associated with the charge / discharge cycle. .

In addition, lithium manganese oxides such as LiMnO ₂ and LiMn ₂ O ₄ have the advantages of excellent thermal safety and low price, but have a problem of small capacity, poor cycle characteristics, and poor high temperature characteristics.

Therefore, much research has been conducted on new positive electrode active materials having a structure different from this.

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

However, the oxide having a lithium excess composition not only has a large irreversible capacity, but also escapes out of the active material structure to oxygen in addition to lithium at the time of high voltage activation for utilizing excess lithium, so that the active material structure collapses and the resulting voltage drop It has been found to have a problem of accelerating degeneration of a battery cell due to a sagging) phenomenon.

In addition, a method of using a layered positive electrode active material containing Li ₂ MnO ₃ has been disclosed in order to secure structural stability of the layered positive electrode active material. In this case, the material contains a lot of Mn, the price is very low, has the advantage of high capacity and stable at high voltage, but after the activation section for the flat section of 4.4 ~ 4.6V after the layer structure Since the transition to the spinel structure causes loosening of contact between domains, structural changes are severe and there is room for improvement in improving electrical properties.

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

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

The inventors of the present application, after repeated in-depth studies and various experiments, as described later, a core containing a lithium-containing metal oxide capable of occluding / releasing lithium ions; A first coating layer containing a first metal oxide for improving electrical conductivity of the positive electrode 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 electrolyte and positioned on an outer surface of the first coating layer. It was confirmed that the characteristics and energy density were significantly improved, and the present invention was completed.

Accordingly, the cathode active material particle according to the present invention includes a core including a lithium-containing metal oxide capable of occluding / discharging lithium ions; A first coating layer containing a first metal oxide for improving electrical conductivity of the positive electrode 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 electrolyte and positioned on an outer surface of the first coating layer.

That is, the first coating layer is located on the outer surface of the core to improve the electrical conductivity of the positive electrode active material particles, thereby improving the output characteristics of the secondary battery.

In addition, the electrical conductivity of the positive electrode active material particles is improved, so that the loading amount of the positive electrode mixture can be increased while maintaining a constant output, thereby improving the energy density of the secondary battery.

However, the first coating layer for improving the electrical conductivity may be detached from the surface of the core during the use of the secondary battery, in this case, the output characteristics and energy density is reduced. Therefore, in order to prevent detachment of the first coating layer and to prevent degradation 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, a second coating layer for surface stabilization may be formed on the outer surface of the first coating layer. Place it in

As such, when the second coating layer is positioned on the outer surface of the first coating layer, the surface of the positive electrode active material is stabilized, thereby improving cycle characteristics of the secondary battery.

The lithium-containing metal oxide constituting the core is not particularly limited as long as it is a substance capable of occluding / releasing lithium ions. For example, lithium metal oxide, lithium transition metal oxide, lithium transition metal composite oxide, and lithium excess content It may be one or more selected from the group consisting of oxides (over-lithium oxide).

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 ; Lithium copper oxide (Li ₂ CuO ₂ ); LiV ₃ O ₈ , LiFe ₃ O ₄ , lithium vanadium oxides; Lithium iron phosphate; Ni-site type lithium nickel oxide represented by the formula LiNi _1-x M _x O ₂ , wherein 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 (wherein M = Co, Ni, Fe, Cr, Zn or Ta and x = 0.01 to 0.1) or Li ₂ Mn ₃ MO ₈ (wherein M = Fe, Co, Lithium manganese composite oxide represented by Ni, Cu or Zn); LiMn ₂ O _{4 in} which a part of Li in the formula is substituted with alkaline earth metal ions; Fe ₂ (MoO ₄ ) ₃ and the like, but are not limited to these.

The first metal oxide contained in the first coating layer may be used as long as it is a material capable of improving the electrical conductivity of the positive electrode active material. In one specific example, the first metal oxide may be ruthenium oxide.

The ruthenium oxide was found to be particularly excellent in effect of improving the electrical conductivity of the positive electrode active material particles, compared to other metal oxides.

The first coating layer may have a thickness of about 1 nm to about 50 nm, in detail about 5 nm to about 30 nm, and more specifically about 10 nm to about 20 nm.

If the thickness of the first coating layer is less than 1 nm, it is easy to be detached from the surface of the core, and the effect of improving electrical conductivity is not great. If the thickness of the first coating layer is greater 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, thereby reducing secondary May result in a reduced capacity of the battery.

In addition, the cathode active material particles may be 0.08% to 4.00% by weight, specifically 0.1% to 2% by weight of the first metal oxide, based on the total weight of the cathode active material particles, more specifically 0.2% by weight 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 positive electrode active material particles without causing a reaction with an electrolyte solution and lithium ions. May be aluminum oxide.

Aluminum oxide has a superior surface stabilization effect than other metal oxides, and has been confirmed to have excellent retention on the surface of the cathode active material particles due to its 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 is too thin to stabilize the surface sufficiently, and the second coating layer may be easily detached due to external influence, making it difficult to improve cycle characteristics of the secondary battery. There is an excessive amount of time and cost in the formation of the second coating layer, the content of the positive electrode active material in the particles can be relatively reduced can lead to a decrease in the capacity of the secondary battery.

In addition, the positive electrode active material particles may be 0.01 wt% to 0.5 wt%, specifically 0.01 wt% to 0.1 wt%, and more specifically 0.03 wt% to 0.05 wt% of the second metal oxide based on the total weight of the cathode active material particles. May contain%.

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

Method for producing a positive electrode active material particles according to the present invention,

(a) preparing lithium-containing metal oxide particles capable of occluding / releasing lithium ions;

(b) A method for improving electrical conductivity on the surface of lithium-containing metal oxide particles as a core by administering lithium-containing metal oxide particles to a solution containing a first metal oxide precursor, an oxidant, and a fuel for reaction promotion. 1 forming a first coating layer of a metal oxide; And

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

In the process (b), the lithium-containing metal oxide particles are administered to the solution containing the first metal oxide precursor, the oxidant, and the fuel for promoting the reaction, and the reaction is completed. The oxide of the first metal oxide precursor, ie the first metal oxide, is coated on.

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

At this time, the fuel is included in the first coating layer after the step (b), and in the heat treatment of step (c) lowers the activation energy of the oxidation reaction to promote the reaction rate, the reaction is carried out at a relatively low temperature Allow it to proceed The fuel can finish the heat treatment process in a shorter time, thereby increasing the efficiency of the process and reducing the manufacturing cost.

In one specific example, the first metal oxide precursor is not particularly limited, but may be, for example, one or more selected from the group consisting of ruthenium chloride, ruthenium chloride hydrate, ruthenium nitrate, ruthenium acetate, and the like, in detail Ruthenium chloride hydrate.

In one specific example, the oxidant is capable of oxidizing the first metal oxide precursor to the first metal oxide, and is not particularly limited so long as it does not cause severe side reactions. nitrate) and one or more selected from the group consisting of ammonium nitrate.

In one specific example, the solution may include one or more selected from the group consisting of 2-methoxyethanol, anhydrous ethanol, anhydrous methanol, and the like as a solvent, and in detail, may include 2-methoxyethanol. .

In one specific example, the fuel may be at least one selected from the group consisting of urea, acetylacetone, and ketone group-containing organic compounds, and in detail, may be urea.

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, if less than 0.01 M reaction time is too long and the time required for the reaction is too long In the case of more than 0.2 M, the thickness of the first coating layer may be thicker than necessary and may be difficult to coat with a uniform thickness.

The molar ratio of the first metal oxide precursor: oxidant: fuel may be 1.0 to 2.0: 1.0 to 2.0: 1.0 to 2.0, and specifically 1.0 to 1.5: 1.0 to 1.5: 1.0 to 1.5, and in this ratio range, The reaction may occur at an appropriate rate, and the first coating layer may be formed to a uniform thickness.

In one specific example, the heat treatment may be performed for 1 to 5 hours at a temperature of 250 ℃ to 800 ℃, in detail may be carried out at a temperature of 400 ℃ to 500 ℃.

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 does not develop, and when the reaction temperature is above 800 ° C, the reaction rate is too fast, resulting in process quality. It is difficult to manage and costly to maintain high temperature.

On the other hand, the method for producing the positive electrode active material particles may further include the following process (d) after the process (c):

(d) forming a second coating layer comprising a second metal oxide for stabilizing the particle surface of the positive electrode active material with respect to the electrolyte and located on an outer surface of the first coating layer.

In one specific example, in the process (d), it is possible to form the second coating layer by atomic layer deposition (atomic layer deposition).

Since the second coating layer is for stabilization of the particle surface of the positive electrode active material, the desired effect can be achieved if the thickness is greater than or equal to a predetermined thickness. Therefore, the thin coating is efficient in terms of energy density.

The atomic layer deposition method can adjust the thickness of the coating layer in approximately 0.1 nm unit, it is possible to coat the second coating layer thin, it is possible to significantly improve the energy density of the secondary battery.

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

In one specific example, the first coating layer is applied to 50% to 90% of the entire outer surface of the core, the second coating layer may have a structure that 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 second coating layer may be formed on the entire outer surface including the core and the first coating layer, rather than being performed in a fixed position of the positive electrode active material particles. The atomic layer deposition method can be performed while changing the position of the particles.

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

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

The positive electrode is prepared by, for example, applying a mixture of a positive electrode active material, a conductive material, and a binder to both surfaces of a positive electrode current collector, followed by drying and pressing, and optionally adding a filler to the mixture.

The positive electrode current collector is generally manufactured to a thickness of 3 ~ 300 ㎛, and is not particularly limited as long as it has a high conductivity without causing chemical changes in the battery, for example, stainless steel, aluminum, nickel, titanium , And one selected from surface treated with carbon, nickel, titanium, or silver on the surface of aluminum or stainless steel may be used, and in detail, aluminum may be used. The current collector may form fine irregularities on its surface to increase the adhesion of the positive electrode active material, and may be in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric.

The conductive material is typically added in an amount of 1 to 30% by weight based on the total weight of the positive electrode mixture including the positive electrode active material. Such a conductive material is not particularly limited as long as it has conductivity without causing chemical change in the battery, and examples thereof include graphite such as natural graphite and artificial graphite; Carbon blacks such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and summer black; Conductive fibers such as carbon fibers and metal fibers; Metal powders such as carbon fluoride powder, aluminum powder and nickel powder; Conductive whiskeys 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 that assists the bonding of the active material and the conductive material to the current collector, and is generally added in an amount of 1 to 30 wt% based on the total weight of the mixture including the positive electrode active material. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, 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 inhibiting expansion of the positive electrode, and is not particularly limited as long as it is a fibrous material without causing chemical change in the battery. Examples of the filler include olefinic polymers such as polyethylene and polypropylene; Fibrous materials, such as glass fiber and carbon fiber, are used.

On the other hand, the negative electrode may be manufactured by applying a negative electrode mixture including a negative electrode active material, a conductive material, and a binder to the negative electrode current collector, and may further include a filler and the like.

The negative electrode current collector is not particularly limited as long as it has conductivity without causing 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, calcined carbon, copper, or stainless steel. Surface-treated with carbon, nickel, titanium, silver and the like, aluminum-cadmium alloy and the like can be used. In addition, like the positive electrode current collector, fine concavities and convexities may be formed on the surface to enhance the bonding strength of the negative electrode active material, and may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric.

In the present invention, the thickness of the negative electrode current collector may be all the same within the range of 3 to 300 ㎛, in some cases may have a different value.

The negative electrode active material may be, for example, carbon such as hardly 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 ≦ 1; 1 ≦ y ≦ 3; 1 ≦ z ≦ 8); Lithium metal; Lithium alloys; Silicon-based alloys; Tin-based alloys; SnO, SnO ₂ , PbO, PbO ₂ , Pb ₂ O ₃ , Pb ₃ O ₄ , Sb ₂ O ₃ , Sb ₂ O ₄ , Sb ₂ O ₅ , GeO, GeO ₂ , Bi ₂ O ₃ , Bi ₂ O ₄ , And metal oxides such as Bi ₂ O ₅ ; Conductive polymers such as polyacetylene; Li-Co-Ni-based materials and the like can be used.

The separator is interposed between the anode and the cathode, and an insulating thin film having high ion permeability and mechanical strength is used. The pore diameter of the separator is generally from 0.01 to 10 micrometers, the thickness is generally from 5 to 30 micrometers. As such a separator, for example, olefin polymers such as chemical resistance and hydrophobic polypropylene; Sheets made of glass fibers or polyethylene, nonwoven fabrics, and the like are used. When a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte may also serve as a separator.

The electrolyte may be a lithium salt-containing non-aqueous electrolyte, the lithium salt-containing non-aqueous electrolyte is composed of a non-aqueous electrolyte and a lithium salt, the non-aqueous organic solvent, an organic solid electrolyte, an inorganic solid electrolyte and the like are used, but these It is not limited only.

As the non-aqueous organic solvent, for example, N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma Butyl lactone, 1,2-dimethoxy ethane, tetrahydroxyfuran, 2-methyl tetrahydrofuran, dimethylsulfoxide, 1,3-dioxolon, formamide, dimethylformamide, dioxolon, acetonitrile Nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxy methane, dioxoron derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, Aprotic organic solvents such as tetrahydrofuran derivatives, ethers, methyl pyroionate and ethyl propionate can be used.

Examples of the organic solid electrolyte include polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate ester polymers, polyedgetion lysine, polyester sulfides, polyvinyl alcohol, polyvinylidene fluoride, and ions. Polymerizers containing a sex dissociation group and the like can be used.

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

The lithium salt is a good material to dissolve in the nonaqueous electrolyte, for example, LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF ₆ , LiSbF ₆ , LiAlCl ₄ , CH ₃ SO ₃ Li, (CF ₃ SO ₂ ) ₂ NLi, chloroborane lithium, lower aliphatic lithium carbonate, lithium tetraphenylborate, imide and the like can be used.

In addition, nonaqueous electrolytes include pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphate triamide, for the purpose of improving charge and discharge characteristics, flame retardancy, and the like. Nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N, N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrroles, 2-methoxy ethanol, aluminum trichloride and the like may be added. have. In some cases, in order to impart nonflammability, a halogen-containing solvent such as carbon tetrachloride or ethylene trifluoride may be further included, and carbon dioxide gas may be further included to improve high temperature storage characteristics, and FEC (Fluoro-Ethylene) may be further included. Carbonate), PRS (Propene sultone) may be further included.

In one specific example, lithium salts such as LiPF ₆ , LiClO ₄ , LiBF ₄ , LiN (SO ₂ CF ₃ ) _2, and the like, may be prepared by cyclic carbonate of EC or PC, which is a highly dielectric solvent, and DEC, DMC, or EMC, which are low viscosity solvents. Lithium salt-containing nonaqueous electrolyte can be prepared by adding to a mixed solvent of linear carbonate.

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 laptop computer, a netbook, a tablet PC, a mobile phone, an MP3, a wearable electronic device, a power tool, an electric vehicle (EV), or a hybrid electric vehicle (HEV). , Plug-in hybrid electric vehicles (PHEVs), electric bikes (E-bikes), electric scooters (E-scooters), electric golf carts, or power storage systems However, of course, it is not limited only to these.

Since the structure and fabrication method of such a device are known in the art, detailed description thereof will be omitted herein.

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

In addition, by improving the electrical conductivity of the positive electrode active material particles, it is possible to increase the loading amount of the positive electrode mixture while maintaining a constant output, it is possible to improve the energy density of the secondary battery.

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

1 is a schematic view sequentially showing a method for producing a first coating layer of the positive electrode active material particles according to an embodiment of the present invention;
2 and 3 are energy dispersive spectroscopy (EDS) results of the positive electrode active material particles having the first coating layer prepared according to the manufacturing method of FIG. 1;
4 is a photograph taken with a transmission electron microscope (TEM) of LNMO before ruthenium oxide coating and LNMO after ruthenium oxide coating;
5 is a schematic diagram showing the structure of the positive electrode active material particles formed with the first coating layer and the 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;
7 and 8 are graphs showing the results of measuring the electrical conductivity of Example 1 and Comparative Example 1 of the present invention, respectively;
9 is a graph measuring charge and discharge capacity during two charge and discharge cycles of Examples 4, 5 and Comparative Example 3 of the present invention;
10 is a graph measuring capacity change according to change of C-rate of Example 4, Example 5 and Comparative Example 3 of the present invention;
11 is a graph measuring a change in the coulombic efficiency according to the number of charge and discharge cycles of Examples 4, 5, and Comparative Example 3 of the present invention;
12 and 13 are graphs of the capacity change according to the C-rate change of Example 4, Example 6, Example 7, Example 8, Comparative Example 4, and Comparative Example 5 of the present invention;
14 and 15 are graphs of the capacity change according to the C-rate change of Example 7, Example 9, Example 10, Comparative Example 5, Comparative Example 6, and Comparative Example 7 of the present invention;
16 and 17 are graphs measuring the capacity change according to the progress of the cycle of Example 7, Example 9, Comparative Example 5, Comparative Example 6, Comparative Example 8, and Comparative Example 9 of the present invention;
18 and 19 are graphs measuring the coulombic efficiency change according to the progress of the cycle of Example 7, Example 9, Comparative Example 5, Comparative Example 6, Comparative Example 8, and Comparative Example 9 of the present invention.

In the following, with reference to the embodiments of the present invention, this is for easier understanding of the present invention, the scope of the present invention is not limited thereto.

<Manufacture example 1>

Preparation of the first coating layer-wet method

LiNi _0.75 Mn _0.25 O ₂ , a lithium-containing metal oxide to be used as a core, was prepared. Ruthenium chloride hydrate, ammonium nitrate, and urea were mixed with a solvent of 2-methoxyethanol in a molar ratio of 1: 1: 1 to prepare a precursor solution having a concentration of 0.05 M of ruthenium chloride. After reacting the precursor solution with LiNi _0.75 Mn _0.25 O ₂ by a wet method, the solvent was evaporated using a rotary evaporator. Cathode active material particles having a ruthenium oxide coating layer formed on the surface of the LiNi _0.75 Mn _0.25 O ₂ core by annealing the reactant after evaporation of the solvent at a temperature of 250 ° C. to 800 ° C. for 1 to 5 hours. Positive electrode active material particles) was prepared.

<Manufacture example 2>

Preparation of Second Coating Layer-Atomic Layer Deposition

The cathode active material particles on which the first coating layer was formed were placed in a reactor, and vacuum was removed to remove air in the reactor. Trimethylaluminum (TMA) was injected into the reactor to deposit TMA on the surface of the positive electrode active material particles having the first coating layer, and then 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, and again vacuum was applied to remove residues and by-products (water treatment reaction). Using the surface reaction and the water treatment reaction as one cycle, the atomic layer deposition method was performed 1 cycle to 10 cycles to prepare cathode active material particles having a second coating layer.

<Manufacture example 3>

Manufacture of Secondary Battery

The positive electrode active material particles, PVDF (KF1100, binder), and super P (conductor) were mixed at a ratio by weight, and placed in NMP (solvent) to prepare a positive electrode slurry, coating drying on one side of aluminum foil and pressing The process was performed to produce a positive electrode having a constant loading.

As the negative electrode, lithium metal having a thickness of 0.6 mm was used.

The LiPF ₆ electrolyte was added to a mixed solvent having a porous polyethylene separator between the prepared positive electrode and the negative electrode, and based on weight, EC (ethyl carbonate): EMC (ethylmethyl carbonate): DMC (dimethyl carbonate) = 3: 4: 3. An electrolyte dissolved at a concentration of 1 M was added to prepare a lithium secondary battery.

<Example 1>

According to Preparation Example 1 and Preparation Example 2, positive electrode active material particles having a core: first coating layer: second coating layer = 99.38: 0.57: 0.05 based on weight were prepared.

<Example 2>

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

<Example 3>

In Example 1, based on the weight, positive electrode active material particles having a core: first coating layer: second coating layer = 99.88: 0.07: 0.05 were prepared.

<Example 4>

Using the positive electrode active material particles of Example 1, according to Preparation Example 3, the positive electrode active material particles: binder: conductive material = 95: 4: 1 in a ratio of mixing, the positive electrode having a loading of 4.9 mg / cm ² To prepare a lithium secondary battery comprising a.

Example 5

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

<Example 6>

A secondary battery was prepared in the same manner as in Example 4, except that the active material particles: binder: conductor = 94: 4: 2 were mixed so as to be weighed in Example 4.

<Example 7>

In Example 4, a secondary battery was manufactured in the same manner as in Example 4 except for mixing by weight of the cathode active material particles: binder: conductor = 92: 4: 4.

<Example 8>

In Example 4, a secondary battery was manufactured in the same manner as in Example 4, except that the cathode active material particles of Example 3 were used instead of the cathode active material particles of Example 1.

Example 9

In Example 7, a secondary battery was manufactured in the same manner as in Example 7, except that the loading amount of the positive electrode mixture was 9.1 mg / cm ² .

<Example 10>

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

Comparative Example 1

Except not forming the first coating layer and the second coating layer in Example 1, positive electrode active material particles were prepared in the same manner as in Example 1.

Comparative Example 2

According to Preparation Example 1, positive electrode active material particles having a core: first coating layer = 99.4: 0.6 based on weight were prepared.

Comparative Example 3

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

<Comparative Example 4>

In Example 4, a secondary battery was manufactured 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.

Comparative Example 5

In Example 7, a secondary battery was manufactured 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.

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 9.1 mg / cm ² .

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 .

<Comparative Example 8>

In Example 7, a secondary battery was manufactured 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.

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

Electrical conductivity of the cathode active material particles prepared in Example 1, Example 3, and Comparative Example 1 was measured using a four-pole method, and the results are shown in FIGS. 7, 8, and Table 1, respectively.

Ruthenium Oxide Content (wt%) Conductivity (S / cm) 0.00 1.9 × 10 ^-6 0.07 4.5 × 10 ^-6 0.57 2.7 × 10 ^-1

7, 8, and Table 1, the lithium-containing metal oxide used in Example 1, Example 3 and Comparative Example 1 is the same as LiNi _0.75 Mn _0.25 O ₂ , but there is a big difference in electrical conductivity You can check it. The electrical conductivity of Comparative Example 1 is 1.9 × 10 ^-6 S / cm, whereas in Example 3, the electrical conductivity is 4.5 × 10 ^-6 S / cm, even if it contains a very small amount of ruthenium oxide It can be seen that the improvement is more than twice. Moreover, it can be seen that the electrical conductivity of Example 1 was significantly increased to 2.7 × 10 ⁻¹ S / cm. From these results, it is thought that the ruthenium oxide coating layer increases the electrical conductivity of the positive electrode active material particles, thereby improving output characteristics, cycle characteristics, and energy density, as can be seen in the following experimental examples.

Experimental Example 2

Charge and discharge of the secondary batteries prepared in Examples 4, 5 and Comparative Example 3, respectively, from 3 V to 5 V at 0.1 C-rate were measured, and the results are shown in FIG. 9. It was.

Experimental Example 3

Based on the discharge capacity (about 140 mA / g) of the secondary batteries prepared in Examples 4, 5, and Comparative Example 3 at 0.1 C-rate, the C-rate was sequentially 0.1 C-rate, Dose changes were measured while changing to 0.5 C-rate, 1 C-rate, 2 C-rate, 3 C-rate, 4 C-rate, 7 C-rate and 10 C-rate, and the results are shown in FIG. It was.

Experimental Example 4

The secondary batteries prepared in Example 4, Example 5, and Comparative Example 3, respectively, 0.1 C-rate, 0.5 C-rate, 1 C-rate, 2 C-rate, 3 C-rate, 4 C-rate, 7 Charging and discharging with C-rate and 10 C-rate, the change of the coulombic efficiency according to the charge and discharge rate was measured, the results are shown in FIG.

9 and 10, in Comparative Example 3, since the second coating layer having low electrical conductivity was not formed, the electrical conductivity of the positive electrode active material particles was relatively higher than that of Examples 4 and 5, and thus, electrical conductivity It can be seen that the initial capacity and output characteristics affected by are relatively good as compared with Examples 4 and 5.

However, referring to FIG. 11, in Comparative Example 3, since the second coating layer is not formed, it can be confirmed that the coulombic efficiency, which means the discharge capacity versus the charge capacity, is relatively low as compared with Examples 4 and 5. That is, in case of Comparative Example 3, the energy efficiency decreases during charging and discharging, and the surface is not stabilized, and thus the capacity of the battery decreases according to the use of the secondary battery. have.

Since the secondary battery is not a one-time consumable, if the initial capacity and output characteristics satisfy only a certain level or more, the lower the capacity and the lower the coulombic efficiency when the charge and discharge are repeated, the more effective.

Therefore, from these results, Comparative Example 3, which is relatively excellent in initial capacity and output characteristics, but has low coulombic efficiency and cycle characteristics, is difficult to be used industrially, while the initial capacity and output characteristics satisfy certain conditions. It can be seen that Example 4 and Example 5 having excellent efficiency and cycle characteristics are more suitable for industrial use.

Experimental Example 5

C-rate is sequentially 0.1 C-rate based on the discharge capacity when the secondary batteries manufactured in Example 6, Example 7, Example 8, Comparative Example 4, and Comparative Example 5 are 0.1 C-rate, respectively. Dose changes were measured while changing to 0.5 C-rate, 1 C-rate, 2 C-rate, 3 C-rate, 4 C-rate, 7 C-rate, and 10 C-rate, and the results are shown in FIGS. 13 is shown.

Referring to FIG. 12, in the case of Example 4, Example 6, and Example 7, it can be seen that the higher the content of the conductive material, the higher the retention rate of the capacity, the higher the C-rate, the higher the output characteristics. However, considering that the amount of the conductive material contained in each of Examples 4, 6, and 7 is increased by 2 times, it can be seen that the increase in output characteristics is not large. In Example 6 and Example 7, since the first coating layer is formed, the electrical conductivity is improved, and it can be seen that even if less conductive material is used, it can have sufficient output characteristics. This can increase the energy density.

12 and 13, it can be seen from the results of Examples 4, 8, and Comparative Example 4 that if the thickness of the first coating layer is too thin or is not produced, the output characteristics of the secondary battery are deteriorated. . Therefore, the amount of ruthenium oxide included in the first coating layer is more preferably 0.2 wt% to 0.7 wt% based on the total weight of the positive electrode active material particles in terms of output characteristics and energy density.

In addition, from Example 4 and Comparative Example 5, although the amount of the conductive material contained in the positive electrode mixture differs by about four times, it can be seen that similar output characteristics. From these results, it can be seen that the coating layer of the present invention significantly improves the output characteristics of the positive electrode active material particles, and can increase the content of the positive electrode active material when exhibiting the same output characteristics, thereby significantly improving the energy density. It can be seen.

Experimental Example 6

Based on the discharge capacity when the secondary batteries manufactured in Example 7, Example 9, Example 10, Comparative Example 5, Comparative Example 6, and Comparative Example 7 were 0.1 C-rate, C-rate was sequentially Dose changes were measured with 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-rate. Are shown in FIGS. 14 and 15.

Referring to FIG. 14, in Comparative Example 5, Comparative Example 6, and Comparative Example 7, since the first coating layer for improving the electrical conductivity is not formed, the internal resistance increases as the loading amount of the positive electrode mixture increases, resulting in output characteristics. It can be seen that this decrease.

Referring to FIG. 15 in comparison with FIG. 14, it can be seen that in Example 7, Example 9, and Example 10, the output characteristics are maintained even when the loading amount is increased by the first coating layer and the second coating layer. Therefore, when using the positive electrode active material particles of the present invention, it can be seen that the energy density of the secondary battery can be improved while maintaining the output characteristics.

Experimental Example 7

After charging and discharging the secondary batteries prepared in Example 7, Example 9, Comparative Example 5, Comparative Example 6, Comparative Example 8, and Comparative Example 9 at 0.1 C-rate for 2 cycles, about 130 at 0.5 C-rate While charging and discharging during the cycle, the discharge capacity was measured. The results are shown in FIGS. 16 and 17.

Referring to FIG. 16, in Comparative Example 5, the capacity tends to decrease slightly as the cycle progresses. However, in Example 7, Comparative Example 5, and Comparative Example 8, the loading amount was 4.9 mg / cm ^{2 It} can be confirmed that the capacity is maintained high compared to the initial capacity even after 130 cycles.

Referring to FIG. 17 in comparison with FIG. 16, while 130 cycles are in progress, the capacity of the ninth capacity is maintained to be the highest as compared to the initial capacity of Example 9. It can be seen that the dose is drastically reduced afterwards.

Therefore, in the case of Comparative Example 9 without the second coating layer, which is the stabilization layer, as the loading amount increases, there is a problem that the capacity retention rate is drastically reduced. In order to manufacture a high-capacity, high-life battery, the second coating layer, which is the stabilization layer, as in Example 9 It can be seen that it is necessary.

Experimental Example 8

After charging and discharging the secondary batteries prepared in Example 7, Example 9, Comparative Example 5, Comparative Example 6, Comparative Example 8, and Comparative Example 9 at 0.1 C-rate for 2 cycles, about 130 at 0.5 C-rate Coulomb efficiency was measured while charging and discharging during the cycle. The results are shown in FIGS. 18 and 19.

Referring to FIG. 18, Example 7, Comparative Example 5, and Comparative Example 8 all have low initial coulombic efficiency. In Example 7 and Comparative Example 8, since the first coating layer for improving the electrical conductivity is increased, the coulombic efficiency is initially increased quickly, and in Comparative Example 5, it can be seen that the coulombic efficiency is relatively slow.

Referring to FIG. 19 in comparison with FIG. 18, it can be seen from the results of Example 7 and 9 that the coulombic efficiency increase pattern is similar despite the difference in loading amount when the first coating layer and the second coating layer are included. . In addition, even when the first coating layer and the second coating layer are not included from the results of Comparative Example 5 and Comparative Example 6, it can be seen that the coulombic efficiency increase pattern is similar despite the difference in loading amount. However, Comparative Example 8 and Comparative Example 9, which does not include the second coating layer, which is a stabilization layer, show different coulombic efficiency patterns, and when the loading amount increases from the result of Comparative Example 9, the durability of the first coating layer decreases and the cycle is increased. As the process progresses, the coulomb efficiency fluctuates, and the coulomb efficiency decreases.

Therefore, in the case of Comparative Example 9 without the second coating layer, which is the stabilization layer, as the loading amount increases, the coulombic efficiency decreases. Able to know.

On the other hand, Figure 6 is a graph showing the results of low energy ion scattering (LEIS) analysis of Example 1, Comparative Example 1 and Comparative Example 2, through which the second coating layer on the surface of the active material particles It can be seen whether it is applied uniformly.

Referring to FIG. 6, in the left graph of FIG. 6, Comparative Example 1 and Comparative Example 2 do not show an Al peak, whereas Example 1 shows that an Al peak appears. From this, it can be seen that the second coating layer containing aluminum oxide is formed on the particle surface of Example 1.

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

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

Claims (24)

A core comprising a lithium-containing metal oxide capable of occluding / releasing lithium ions;
A first coating layer containing ruthenium oxide for improving electrical conductivity of the positive electrode active material and positioned on an outer surface of the core; And
A second coating layer containing aluminum oxide for stabilizing the particle surface of the positive electrode active material with respect to the electrolyte solution and located on the outer surface of the first coating layer.
Cathode active material particles comprising a. The method of claim 1, wherein the lithium-containing metal oxide is at least one selected from the group consisting of lithium metal oxide, lithium transition metal oxide, lithium transition metal complex oxide, and lithium over-lithium oxide. Positive electrode active material particles. The cathode active material particle of claim 1, wherein the lithium-containing metal oxide comprises one or more compounds selected from Formula 1 below:
LiNi _1-x M _x O ₂ (1)
Where
M = Co, Mn, Al, Cu, Fe, Mg, B or Ga,
x = 0.01 to 0.3. delete The cathode active material particle of claim 1, wherein the first coating layer has a thickness of about 1 nm to about 50 nm. delete The cathode active material particle of claim 1, wherein the thickness of the second coating layer is 0.2 nm to 2 nm. The cathode active material particle of claim 1, wherein the ruthenium oxide is present in an amount of 0.08% to 4.00% by weight based on the total weight of the cathode active material. The cathode active material according to claim 1, wherein the aluminum oxide is included in an amount of 0.01 wt% to 0.5 wt% based on the total weight of the cathode active material particles. The cathode 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 mixture comprising the positive electrode active material particles according to claim 1, a binder, and a conductive material. The positive electrode mixture for secondary batteries is coated on a current collector according to claim 11. A lithium secondary battery comprising the secondary battery positive electrode according to claim 12. (a) preparing lithium-containing metal oxide particles capable of occluding / releasing lithium ions;
(b) administering lithium-containing metal oxide particles to a solution containing a ruthenium oxide precursor, an oxidizing agent, and a fuel for promoting reaction, thereby improving electrical conductivity on the surface of the lithium-containing metal oxide particles as a core; Forming a first coating layer of ruthenium oxide;
(c) annealing the cathode active material particles having the first coating layer formed thereon; And
(d) forming a second coating layer comprising aluminum oxide for stabilizing the particle surface of the positive electrode active material with respect to the electrolyte and positioned on an outer surface of the first coating layer;
Method for producing a positive electrode active material particles comprising a. 15. The method of claim 14, wherein the ruthenium 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. 15. The method of claim 14, wherein the solution contains at least one selected from the group consisting of 2-methoxyethanol, anhydrous ethanol, and anhydrous methanol as a solvent. 15. The method of claim 14, wherein the fuel is at least one selected from the group consisting of urea, acetylacetone, and a ketone group-containing organic compound. 15. The method of claim 14, wherein the concentration of the ruthenium oxide precursor is 0.01 M to 0.2 M. 15. The method of claim 14, wherein the molar ratio of ruthenium oxide precursor: oxidant: fuel is 1.0 to 2.0: 1.0 to 2.0: 1.0 to 2.0. 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. delete 15. The method of claim 14, wherein in the step (d), a second coating layer is formed by atomic layer deposition. 24. The method of claim 23, wherein in the step (d), the second coating layer is formed by performing the atomic layer deposition method 1 cycle to 10 cycles, specifically 3 cycles to 4 cycles.

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