KR101564131B1 - Cathode active material for lithium secondary battery and manufacturing method thereof - Google Patents

Abstract

The present invention relates to a cathode active material for a lithium secondary battery and a method of manufacturing the same, and more particularly, to a method for manufacturing a cathode active material for a lithium secondary battery by coating a surface of Mn-rich with LBO glass to prevent a rapid capacity decrease under high- To a cathode active material for a lithium secondary battery capable of remarkably reducing the amount of a solvent used for producing a positive electrode slurry and a method for producing the same.

Description

TECHNICAL FIELD [0001] The present invention relates to a cathode active material for a lithium secondary battery, and a cathode active material for a lithium secondary battery,

The present invention relates to a cathode active material for a lithium secondary battery and a method of manufacturing the same.

2. Description of the Related Art In recent years, lithium secondary batteries have been used in many fields including portable electronic devices such as mobile phones, PDAs, and laptop computers. Especially, as the interest in environmental problems grows, it is one of the main causes of air pollution. As a driving source of electric vehicles that can replace fossil fuel vehicles such as gasoline vehicles and diesel vehicles, lithium secondary batteries Research on batteries has been actively conducted, and some of them are in the commercialization stage. On the other hand, in order to use lithium secondary battery as a driving source of such electric vehicles, it is necessary to maintain a stable output in a wide range of state of charge (SOC) in addition to a high output.

LiCoO ₂ , which is a typical positive electrode material as a cathode material of a high capacity lithium secondary battery, has reached the practical limit of an increase in energy density and output characteristics. Especially, when it is used in a high energy density application field, State, it releases oxygen in the structure and generates an exothermic reaction with the electrolyte in the cell, thereby becoming the main cause of the explosion of the battery. In order to solve the safety problem of LiCoO ₂ , a lithium-containing manganese oxide such as a layered crystal structure of LiMnO ₂ , a spinel crystal structure of LiMn ₂ O ₄ and LiNiO ₂ Recently, the use of lithium manganese oxide (LiMnO2), which is a high-capacity material, is added to a layered lithium manganese oxide as a necessary transition metal in a larger amount than manganese (Mn) (Hereinafter abbreviated as "Mn-rich").

As described above, Mn-rich is attracting attention as a cathode material of a lithium secondary battery having a high capacity and a large capacity. However, the capacity of the material is drastically reduced at high charge and discharge conditions for practical application, unlike other conventional layered cathode materials. Further, It is recognized that the slow response rate of the material also adversely affects the life characteristics.

Accordingly, a new cathode material capable of preventing deterioration of capacity during high-speed charging and discharging and improving battery characteristics while maintaining favorable characteristics of Mn-rich, and a method for manufacturing such a cathode material effectively and economically Is required.

Korean Patent Laid-Open No. 10-2009-0006897

Disclosure of the Invention The present invention has been made to solve the above-mentioned problems and conventional problems, and it is an object of the present invention to provide a positive electrode material and a manufacturing method thereof which are excellent in cycle characteristics and lifetime characteristics without rapid capacity decrease, The present invention also provides a method for providing the above-described method.

In order to achieve the above object, the present invention provides a cathode active material for a lithium secondary battery, wherein the surface of the lithium manganese oxide represented by Chemical Formula 1 is coated with an LBO glass (Li ₂ OB ₂ O ₃ glass)

[Chemical Formula 1]

xLi ₂ MnO ₃ (1-x) Li _y MO ₂

In Formula 1,

0 &lt; x < 1,

0.9? Y? 1.2,

M is at least one element selected from the group consisting of Mn, Ni, Co, Fe, Cr, V, Cu, Zn, Ti, Al,

The present invention also provides a method for preparing lithium manganese oxide, comprising: a) mixing the lithium manganese oxide represented by Formula 1 with lithium hydroxide and boric acid; And b) chemically surface-coating the mixture. The method of manufacturing the cathode active material according to claim 1,

According to another aspect of the present invention, there is provided a positive electrode for a lithium secondary battery, comprising the positive electrode active material.

According to still another aspect of the present invention, there is provided a battery module or a battery pack, comprising a lithium secondary battery including the positive electrode, and a plurality of the lithium secondary batteries electrically connected to each other.

The cathode active material for a lithium secondary battery according to the present invention is not only rapidly prevented from deterioration in capacity under fast charging and discharging cycle conditions due to LBO surface coating, but also has excellent cycle characteristics and service life characteristics.

In addition, there is an advantage that the amount of a solvent (for example, NMP) used in the preparation of the positive electrode slurry containing the positive electrode active material can be remarkably reduced.

1 is a graph showing a rate capability of a lithium secondary battery according to Examples and Comparative Examples.
2 is a graph showing the cycle characteristics of a lithium secondary battery according to Examples and Comparative Examples.

Hereinafter, the present invention will be described in detail.

Surface coated Cathode active material

The cathode active material for a lithium secondary battery is a lithium manganese oxide represented by the following general formula (1) coated on an LBO glass (lithium boron oxide glass; Li ₂ OB ₂ O ₃ -based glass).

[Chemical Formula 1]

xLi ₂ MnO ₃ (1-x) Li _y MO ₂

In Formula 1,

x is a molar ratio, 0 < x < 1,

0.9? Y? 1.2 (more specifically, y = 1)

M is at least one element selected from the group consisting of Mn, Ni, Co, Fe, Cr, V, Cu, Zn, Ti, Al,

The lithium manganese oxide represented by the above formula (1) is a kind of layer-structured lithium transition metal oxide containing Mn as an essential transition metal, and the content of Mn is larger than the content of other metals except lithium.

Mn contained as an essential transition metal in Mn-rich is contained in a larger amount than other metals (excluding lithium), and it is preferably 50 to 80 mol% based on the total amount of metals except lithium. If the content of Mn is too small, the safety is lowered, the manufacturing cost is increased, and it may be difficult to exhibit the unique characteristics of only Mn-rich. Conversely, if the content of Mn is too large, the cycle stability may be deteriorated.

The Mn-rich may be a composite of a layered structure or may be in the form of a solid solution. In addition, Mn-rich is non-toxic and relatively inexpensive compared with LiCoO ₂ , and when used as a cathode active material, there is an advantage that a high capacity secondary battery can be provided. In this respect, M in Formula 1 is preferably Mn, Ni and Co.

On the other hand, Mn-rich provides lithium ions that are consumed in the initial irreversible reaction on the surface of the cathode, and lithium ions which were not used in the irreversible reaction at the cathode during the subsequent discharge may move to the anode to provide an additional lithium source Material.

In addition, Mn-rich is a material that exhibits a large capacity when overcharged at high voltage. In other words, Mn-rich has a flat level at a certain level above the oxidation / reduction potential, which is indicated by the change in the oxidation number of constituents in the cathode active material. Specifically, at a high voltage of 4.45 V or more based on the anode potential, And a flat level section in the V region.

In particular, Mn-rich is advantageous in that it has a lower cost and higher capacity than a cathode material for a lithium secondary battery having a general layered structure.

However, in the high-speed discharge condition for practical application, such merits of Mn-rich are not manifested and the capacity is sharply reduced, and it is recognized that the slow response speed of the material in the battery adversely affects the life characteristics.

Therefore, in order to prevent the rapid decrease in capacity and to improve the lifespan characteristics under high-speed charge and discharge conditions while maintaining the characteristic merits of only Mn-rich, the present invention provides a positive electrode active material for a lithium secondary battery in which the surface of Mn- to provide. That is, the present inventors have found that when the Mn-rich surface is coated with LBO glass, the rate characteristic and the cycle characteristic are improved, the interfacial resistance is reduced, and further, a desired viscosity is obtained even with a small amount of solvent The amount of the solvent (for example, NMP) used in the preparation of the positive electrode slurry can be drastically reduced to about 2/3.

The molar ratio of Li ₂ O: B ₂ O ₃ in the LBO glass can be appropriately controlled in consideration of the kind and degree of the required characteristics. In one embodiment, the molar ratio of Li ₂ O: B ₂ O ₃ may be 1: 3 to 3: 1, specifically Li ₂ O- ₂ B ₂ O ₃ with a molar ratio of 1: 2.

The LBO glass used for the surface coating of Mn-rich may be 0.5 to 15% by weight based on the total weight of the cathode active material. If the content of the LBO glass is less than 0.5% by weight, it may be difficult to obtain the above effects. If the content exceeds 15% by weight, the relative content of Mn-rich may decrease, have.

The method of coating the surface of Mn-rich with LBO glass is not particularly limited, and coating can be performed by applying a surface treatment method of a cathode active material commonly used in the art.

In one embodiment, the present invention provides a method for preparing a lithium battery, comprising the steps of: a) mixing lithium manganese oxide (Mn-rich) represented by Formula 1 with lithium hydroxide and boric acid; And b) chemically surface-coating the mixture. The present invention also provides a method for producing the cathode active material.

In step a), lithium hydroxide may be LiOH, LiOH.H ₂ O or a mixture thereof. Examples of the boric acid include orthoboric acid (H ₃ BO ₃ ), metaboric acid (HBO ₂ ) and tetraboric acid (H ₂ B ₄ O ₇ ) may be used singly or in combination of two or more. It is also preferred that the mixing is carried out in a liquid phase (e.g. methanol).

The chemical surface coating in step b) may be performed, for example, by heat treating the mixture obtained in step a) at a temperature of 250 ° C to 1000 ° C.

anode

According to another aspect of the present invention, there is provided a positive electrode for a lithium secondary battery comprising the above-mentioned positive electrode active material.

The positive electrode of the present invention can be produced by a conventional method known in the art using Mn-rich surface-coated with LBO glass as a cathode active material. For example, a slurry is prepared by dispersing and mixing the above-mentioned cathode active material, conductive material, binder, (if necessary) filler and the like in a dispersion medium (solvent) and applying the slurry to the cathode current collector, followed by drying and rolling, Can be prepared.

According to the present invention, when Mn-rich surface-coated with LBO glass is used as a cathode active material, a desired viscosity can be obtained even with a small amount of solvent, so that the amount of a solvent (for example, NMP) have.

The conductive material is not particularly limited as long as it does not cause a side reaction in the internal environment of the lithium secondary battery and does not cause chemical change in the battery but has excellent electrical conductivity. Typically, graphite or conductive carbon may be used.

For example, graphite such as natural graphite and artificial graphite; Carbon black such as carbon black, acetylene black, ketjen black, black black, thermal black, channel black, furnace black, lamp black, and summer black; A carbon-based material whose crystal structure is graphene or graphite; Conductive fibers such as carbon fiber and metal fiber; Carbon fluoride; Metal powders such as aluminum and nickel powder; Conductive whiskey such as zinc oxide and potassium titanate; Conductive oxides such as titanium oxide; And polyphenylene derivatives may be used singly or in combination of two or more, but the present invention is not limited thereto.

The conductive material is usually added in an amount of 0.5 to 50 parts by weight, specifically 1 to 15 parts by weight, more specifically 3 to 10 parts by weight, based on 100 parts by weight of the total weight of the cathode material including the cathode active material. If the content of the conductive material is less than 0.5 parts by weight, the effect of improving electrical conductivity may not be expected or the electrochemical characteristics of the battery may deteriorate. If the content of the conductive material exceeds 50 parts by weight, the amount of the cathode active material And the capacity and the energy density may be lowered.

The method of incorporating the conductive material into the cathode material is not particularly limited, and conventional methods known in the art such as coating on the cathode active material can be used. In some cases, since the conductive second coating layer is added to the positive electrode active material, the addition of the conductive material as described above may be substituted.

The binder is a component that assists in bonding of the positive electrode active material and the conductive material, and bonding to the current collector.

Examples of the binder include polyvinylidene fluoride (PVdF), polyvinylidene fluoride-polyhexafluoropropylene copolymer (PVdF / HFP), polyvinyl acetate, polyvinyl alcohol, polyvinyl ether, polyethylene, polyethylene oxide, (Meth) acrylate, polyethyl (meth) acrylate, polytetrafluoroethylene (PTFE), polyvinyl chloride, polyacrylonitrile, polyvinylpyridine, polyvinylpyrrolidone, Butadiene rubber, ethylene-propylene-diene monomer (EPDM) rubber, sulfonated EPDM rubber, styrene-butylene rubber, fluorine rubber, carboxymethylcellulose (CMC), starch, hydroxy At least one selected from the group consisting of polyvinylpyrrolidone, propylcellulose, regenerated cellulose, and mixtures thereof may be used, But is not limited thereto.

The binder is usually added in an amount of 1 to 50 parts by weight, more specifically 3 to 15 parts by weight based on 100 parts by weight of the total weight of the cathode material including the cathode active material. If the content of the binder is less than 1 part by weight, the adhesive force between the electrode active material and the current collector may be insufficient. If the amount of the binder is more than 50 parts by weight, the adhesive strength may be improved, but the content of the electrode active material may be decreased.

The positive electrode material constituting the positive electrode of the present invention may optionally contain a filler as a component for suppressing the expansion of the positive electrode.

The filler is not particularly limited as long as it can inhibit the expansion of the electrode without causing chemical changes in the battery, and examples thereof include olefin polymers such as polyethylene and polypropylene; Fibrous materials such as glass fibers and carbon fibers; Etc. may be used.

The dispersion medium may be N-methyl-2-pyrrolidone (DMF), dimethyl formamide (DMF), dimethyl sulfoxide (DMSO), ethanol, isopropanol, water or mixtures thereof.

The positive electrode current collector may be formed of a metal such as platinum (Pt), gold (Au), palladium (Pd), iridium (Ir), silver (Ag), ruthenium (Ru), nickel (Ni), stainless steel (STS) ), Molybdenum (Mo), chromium (Cr), carbon (C), titanium (Ti), tungsten (W), ITO (In doped SnO ₂ ), FTO (F doped SnO ₂ ) , A surface of aluminum (Al) or a stainless steel surface treated with carbon (C), nickel (Ni), titanium (Ti) or silver (Ag) may be used. The form of the anode current collector may be in the form of foil, film, sheet, punched, porous body, foam or the like.

Lithium secondary battery

According to another aspect of the present invention, there is provided a lithium secondary battery including the positive electrode.

Generally, a lithium secondary battery is composed of a positive electrode composed of a positive electrode material and a current collector, a negative electrode composed of a negative electrode material and a current collector, and a separator for blocking electrical contact between the positive electrode and the negative electrode and moving lithium ions, Includes an electrolyte solution for conducting lithium ions.

The cathode can be produced by a conventional method known in the art. For example, a negative electrode can be prepared by dispersing and mixing a negative electrode active material, a conductive material, a binder, and a filler (if necessary) in a dispersion medium (solvent) to form a slurry, applying the dispersion to an anode current collector, have.

Examples of the negative electrode active material include lithium metal, a lithium alloy (e.g., an alloy of lithium and aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium or indium), amorphous carbon, crystalline carbon, And SnO ₂ may be used, but are not limited thereto.

The negative electrode collector may be formed of at least one selected from the group consisting of Pt, Au, Pd, Ir, Ag, Ru, Ni, STS, ), Molybdenum (Mo), chromium (Cr), carbon (C), titanium (Ti), tungsten (W), ITO (In doped SnO ₂ ), FTO (F doped SnO ₂ ) (C), nickel (Ni), titanium (Ti), or silver (Ag) on the surface of copper, copper or stainless steel may be used. The anode current collector may be in the form of a foil, a film, a sheet, a punched, a porous body, a foam or the like.

The separation membrane is interposed between the positive electrode and the negative electrode to prevent a short circuit therebetween and to provide a movement path of lithium ions.

As the separation membrane, an olefin-based polymer such as polyethylene or polypropylene, glass fiber or the like may be used in the form of a sheet, a multilayer, a microporous film, a woven fabric and a nonwoven fabric, but is not limited thereto. On the other hand, when a solid electrolyte such as a polymer (for example, an organic solid electrolyte, an inorganic solid electrolyte or the like) is used as the electrolyte, the solid electrolyte may also serve as a separation membrane. Specifically, an insulating thin film having high ion permeability and mechanical strength is used. The pore diameter of the separator is generally in the range of 0.01 to 10 mu m, and the thickness may generally be in the range of 5 to 300 mu m.

As the electrolyte solution, carbonate, ester, ether, or ketone may be used alone or as a mixture of two or more of them as a non-aqueous liquid electrolyte (non-aqueous organic solvent), but the present invention is not limited thereto.

Examples of the solvent include dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, methyl ethyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, Such as ethyl acetate, n-propyl acetate, phosphoric acid triester, dibutyl ether, N-methyl-2-pyrrolidinone, 1,2-dimethoxyethane, tetrahydroxyfurfane, 2-methyltetrahydrofuran Dimethylformamide, dioxolane and derivatives thereof, acetonitrile, nitromethane, methyl formate, methyl acetate, trimethoxymethane, sulfolane, methyl sulfolane, 1,3-dioxolane, - dimethyl-2-imidazolidinone, methyl propionate, ethyl propionate and the like can be used but are not limited thereto It is not.

(Lithium salt-containing non-aqueous electrolyte solution), and the lithium salt may be a known one which is soluble in the non-aqueous electrolyte, for example, LiCl, LiBr, LiI, LiClO _{4 , LiBF 4, LiB 10 Cl 10} , LiPF 6, LiCF 3 SO 3, LiCF 3 CO 2, LiAsF 6, LiSbF 6, LiPF 3 (CF 2 CF 3) 3, LiAlCl 4, CH 3 SO 3 Li, CF 3 SO ₃ Li, (CF ₃ SO ₂ ) ₂ NLi, chloroborane lithium, lower aliphatic carboxylate lithium, lithium tetraphenylborate, imide, and the like, but not always limited thereto.

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

The lithium secondary battery of the present invention can be produced by a conventional method in the art. For example, a porous separator may be placed between the anode and the cathode, and a non-aqueous electrolyte may be added.

The lithium secondary battery according to the present invention not only exhibits improved capacity characteristics (rapid capacity decrease prevention) under high-speed charge and discharge cycle conditions, but also excellent cycle characteristics, rate characteristics and lifetime characteristics, And may be suitably used as a unit cell of a battery module which is a power source of a medium and large-sized device.

In this respect, the present invention also provides a battery module in which the lithium secondary battery 2 or more is electrically connected (in series or parallel connection). It is needless to say that the number of lithium secondary batteries included in the battery module may be variously controlled in consideration of the use and capacity of the battery module.

Further, the present invention provides a battery pack in which the battery module is electrically connected according to a conventional technique.

The battery module and the battery pack may include a power tool; An electric vehicle including an electric vehicle (EV), a hybrid electric vehicle (HEV), and a plug-in hybrid electric vehicle (PHEV); Electric truck; Electric commercial vehicle; Or a power storage system, but is not limited thereto.

Hereinafter, the present invention will be described more specifically by way of examples. However, these examples are provided only for the understanding of the present invention, and the scope of the present invention is not limited to these examples in any sense.

Example

Surface coated Cathode active material  Produce

_{0.5Li 2 MnO 3 · 0.5Li (Mn} 0 .32 Ni 0 .44 Co 0 .24) to a mixture of O ₂ · H ₂ O and from LiOH H ₃ BO ₃ and methanol liquid and then, the mixture at a temperature of 500 ℃ And then heat treated for 10 hours to prepare a chemically surface-coated Mn-rich cathode active material.

Manufacture of anode

90 wt% of the surface-coated cathode active material; 5% by weight of Super-P as a conductive material; And 5% by weight of KF1100 as a binder were added together to NMP to form a slurry. This was coated on an aluminum (Al) foil as a positive electrode collector, rolled and dried to prepare a positive electrode for a lithium secondary battery. (Loading = 4.0 mAh / cm2)

Cathode manufacturing

88 wt% of SiO _x (0 <x <2) and graphite (MAGV2) (weight ratio of SiO _x : black graphite = 33:67) as the negative electrode active material; 4% by weight of CNT as a conductive material; 8% by weight of LSR (Liquid Silicone Rubber) and CMC as a binder were added together to NMP to prepare a slurry. This was coated on a copper (Cu) foil as an anode current collector, rolled and dried to prepare a negative electrode for a lithium secondary battery. (Loading = 3.6 mAh / cm2)

The lithium secondary battery  Produce

(1.2 M of LiPF ₆ , ethylene carbonate (EC): dimethyl carbonate (DMC): ethyl methyl carbonate (EMC) = 1: 1) was placed between the prepared positive electrode and negative electrode with a separator of porous polyethylene interposed therebetween. 2: 4: 4 in volume ratio) was injected to prepare a polymer type lithium secondary battery.

Comparative Example

Except that 0.5Li ₂ MnO ₃ · 0.5Li (Mn _{0 .32} Ni _{0 .44} Co _{0 .24} ) O ₂ , which was not coated with a surface active material, was used as the positive electrode active material, Respectively.

Experimental Example

The capacity and lifetime of the lithium secondary battery manufactured according to the above Examples and Comparative Examples were tested for each discharge speed, and the results are shown in Figs. 1 and 2. Fig.

Referring to FIG. 1, it can be seen that in the case of the embodiment, the reduction width of the capacitance is greatly reduced at a high C-rate compared to the comparative example.

Referring to FIG. 2, it can be seen that the cycle characteristics of the Examples are superior to those of the Comparative Examples.

Also, in the case of the examples, a positive electrode slurry having the same viscosity could be produced only by using about 2/3 of the solvent (NMP) as compared with the comparative example.

The foregoing description is merely illustrative of the technical idea of the present invention, and various changes and modifications may be made by those skilled in the art without departing from the essential characteristics of the present invention. The scope of the present invention should be interpreted based on the scope of the following claims, and all technical ideas within the scope of equivalents thereof should be interpreted in accordance with the following claims: It is to be understood that the invention is not limited thereto.

Claims (13)

The surface of the lithium manganese oxide represented by the following formula (1) is coated with an LBO glass (Li ₂ OB ₂ O ₃ glass)
The LBO glass is contained in an amount of 0.5 to 15 wt% based on the total weight of the cathode active material,
The LBO glass is Li ₂ O-2B ₂ O ₃ in the lithium secondary battery positive electrode active material, characterized:
[Chemical Formula 1]
xLi ₂ MnO ₃ (1-x) Li _y MO ₂
In Formula 1,
0 &lt; x < 1,
0.9? Y? 1.2,
M is at least one element selected from the group consisting of Mn, Ni, Co, Fe, Cr, V, Cu, Zn, Ti, Al,
delete delete delete A positive electrode for a lithium secondary battery, comprising the positive electrode active material according to claim 1.
6. The method of claim 5,
Wherein the positive electrode further comprises conductive carbon and a binder.
A lithium secondary battery comprising the positive electrode according to claim 5.
The battery module according to claim 7, wherein the plurality of lithium secondary batteries are electrically connected to each other.
9. The method of claim 8,
The battery module includes a power tool; An electric vehicle including an electric vehicle (EV), a hybrid electric vehicle (HEV), and a plug-in hybrid electric vehicle (PHEV); Electric truck; Electric commercial vehicle; Or a power storage system, as a power source for a middle- or large-sized device.
a) mixing lithium manganese oxide represented by the following formula (1) with lithium hydroxide and boric acid; And
b) chemically surface-coating the mixture. The method of claim 1,
[Chemical Formula 1]
xLi ₂ MnO ₃ (1-x) Li _y MO ₂
In Formula 1,
0 &lt; x < 1,
0.9? Y? 1.2,
M is at least one element selected from the group consisting of Mn, Ni, Co, Fe, Cr, V, Cu, Zn, Ti, Al,
11. The method of claim 10,
Wherein the boric acid is at least one selected from the group consisting of H ₃ BO ₃ , HBO ₂ and H ₂ B ₄ O ₇ in the step a).
11. The method of claim 10,
Wherein the chemical surface coating in step b) is carried out by heat treatment at a temperature of 250 ° C to 1000 ° C.
9. A battery pack in which the battery module according to claim 8 or 9 is electrically connected.

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