KR20140025103A - Cathode active material for lithium secondary battery and manufacturing method thereof - Google Patents

Abstract

The present invention relates to a positive electrode active material for a lithium secondary battery and a manufacturing method thereof, and more specifically to: a positive electrode active material for a lithium secondary battery which prevents a sudden capacity decrease in a high-speed charging and discharging cycle condition by coating the surface of Mn-rich with LiBO_2, and remarkably reduces the amount of solvent for producing a positive electrode slurry by improving cycle and lifetime properties; and a manufacturing method thereof. [Reference numerals] (AA) Comparative example; (BB) Dotted line: charge capacity, Solid line: discharge capacity

Description

Cathode active material for lithium secondary battery and manufacturing method thereof {CATHODE ACTIVE MATERIAL FOR LITHIUM SECONDARY BATTERY AND MANUFACTURING METHOD THEREOF}

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

Recently, lithium secondary batteries have been used in various fields including portable electronic devices such as mobile phones, PDAs, and laptop computers. In particular, as interest in environmental issues grows, lithium secondary batteries with high energy density and discharge voltage can be used as a driving source of electric vehicles that can replace fossil fuels such as gasoline and diesel vehicles, which are one of the main causes of air pollution. Research on batteries is actively underway and some commercialization stages are in progress. On the other hand, in order to use a lithium secondary battery as a driving source of such an electric vehicle, it must be able to stably maintain power in a wide range of state of charge (SOC) as well as high output.

As a cathode material of a high capacity lithium secondary battery, LiCoO ₂ , which is a representative cathode material, has reached an increase in energy density and a practical limit of output characteristics, and especially when used in a high energy density application, high temperature charge due to its structural instability. In the state, along with structural modification, oxygen is released in the structure, causing exothermic reaction with the electrolyte in the battery, which is the main cause of battery explosion. In order to improve the safety problem of LiCoO ₂ , lithium-containing manganese oxides such as LiMnO _{2 having} a layered crystal structure and LiMn ₂ O _{4 having a} spinel crystal structure, and LiNiO ₂ Lithium-containing nickel oxides have been considered, and recently, lithium manganese oxides in which manganese (Mn) is added to the layered lithium manganese oxide as a mandatory transition metal in a higher capacity than other transition metals (except lithium) as a mandatory transition metal. Many studies have been conducted (hereinafter, abbreviated as "Mn-rich").

As such, Mn-rich has been spotlighted as a cathode material of a lithium secondary battery having a large capacity for its price, but has a problem in that its capacity decreases rapidly unlike other general layered cathode materials under high speed charging and discharging conditions. It is recognized that the slow reaction rate of the material adversely affects the life characteristics.

Therefore, development of a new cathode material capable of preventing capacity deterioration and improving battery characteristics at high speed while maintaining Mn-rich's inherent advantageous properties, and a method for producing such cathode material effectively and economically It is required.

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

The present invention has been made to solve the above-mentioned demands and conventional problems, and has a rapid capacity reduction during high-speed charging and discharging, excellent cycle characteristics and life characteristics, and a cathode material which can reduce the cost required for anode production and its manufacture. It is a technical task to provide a method.

In order to achieve the above technical problem, the present invention provides a cathode active material for a lithium secondary battery, characterized in that the surface of the lithium manganese oxide represented by the formula (1) is coated with LiBO ₂ :

[Chemical Formula 1]

xLi ₂ MnO ₃ (1-x) Li _y MO ₂

In Formula 1,

0 <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, Mg and B.

In addition, the present invention a) mixing the lithium manganese oxide represented by the formula (1) with LiBO ₂ ; And b) chemically surface-coating the mixture.

In addition, another aspect of the present invention provides a lithium secondary battery positive electrode comprising the positive electrode active material.

In another aspect, the present invention provides a battery module or a battery pack comprising a lithium secondary battery including the positive electrode, and a plurality of lithium secondary batteries electrically connected to each other.

The cathode active material for a lithium secondary battery according to the present invention not only prevents a sudden drop in capacity under fast charge and discharge cycle conditions due to the LiBO ₂ surface coating, but also has excellent cycle characteristics and life characteristics.

In addition, there is an advantage that can significantly reduce the amount of a solvent (eg, NMP) used in the production of a positive electrode slurry containing the positive electrode active material.

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

Hereinafter, the present invention will be described in detail.

Surface coated Cathode active material

In the cathode active material for a lithium secondary battery, a surface of a lithium manganese oxide represented by Chemical Formula 1 is coated with LiBO ₂ .

[Chemical Formula 1]

xLi ₂ MnO ₃ (1-x) Li _y MO ₂

In Formula 1,

x is a mole ratio and 0 <x <1,

0.9≤y≤1.2 (in detail, y = 1),

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

The lithium manganese oxide represented by Formula 1 (Mn-rich) includes Mn as an essential transition metal, and Mn is a kind of layered lithium transition metal oxide having a content of Mn higher than that of other metals except lithium.

Mn, which is included as an essential transition metal in Mn-rich, is included in a larger amount than other metals (except lithium), and is preferably 50 to 80 mol% based on the total amount of metals except lithium. Too little Mn content can lead to reduced safety, increased manufacturing costs and difficult Mn-rich unique properties. Conversely, if the content of Mn is too large, the cycle stability may be deteriorated.

The Mn-rich may be a layered composite or may be in the form of a solid solution. In addition, Mn-rich is non-toxic, relatively inexpensive compared to LiCoO ₂ , when used as a cathode active material has the advantage of providing a high capacity secondary battery. In this aspect, 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 at the negative electrode surface, and then during discharge, lithium ions that were not used for the irreversible reaction at the negative electrode may move to the positive electrode to provide an additional lithium source. It is a substance.

In addition, Mn-rich is a material that expresses a large capacity when overcharged at high voltage. That is, Mn-rich has a flat level of a certain range above the oxidation / reduction potential indicated by the change of oxidation number of the constituents in the positive electrode active material. Specifically, 4.45 to 4.8 at high voltage of 4.45 V or higher based on the anode potential. It has a flat level section in the V region.

In particular, Mn-rich has the advantage of having a low price and high capacity compared to the cathode material for a lithium secondary battery of the general layer structure.

However, in the high-speed discharge conditions for practical application, there is a problem that the capacity of the Mn-rich is not manifested and the capacity is rapidly reduced, and it is recognized that the life time characteristics are adversely affected by the slow reaction speed of the material in the battery.

Accordingly, in the present invention, Mn-rich has a characteristic advantage of the lithium secondary battery positive electrode active material coated with LiBO ₂ in order to prevent the sudden drop in capacity under fast charging and discharging conditions and also improve the life characteristics to provide. That is, the present inventors improve the rate (rate) and cycle characteristics when the Mn-rich surface is coated with LiBO ₂ , and furthermore, the desired viscosity can be obtained even with a small amount of solvent, such as a solvent used for preparing a positive electrode slurry (eg, In addition, it is confirmed that the amount of NMP can be significantly reduced to about 2/3 of the previous level.

LiBO ₂ used for the surface coating of Mn-rich may be 0.5 to 15% by weight based on the total weight of the positive electrode active material. If the content of LiBO ₂ is less than 0.5% by weight it may be difficult to obtain the above effects, if the content exceeds 15% by weight the capacity of the battery can be reduced or the energy density is reduced due to the relative content of Mn-rich have.

The method of coating the surface of Mn-rich with LiBO ₂ is not particularly limited, and the coating may be performed by applying a surface treatment method of a cathode active material commonly used in the art.

In one embodiment, the present invention comprises the steps of: a) mixing lithium manganese oxide (Mn-rich) represented by the formula (1) with LiBO ₂ ; And b) chemically surface-coating the mixture. Here, the mixing is preferably carried out in a liquid phase (eg methanol).

The chemical surface coating in step b) may be performed by, for example, heat treatment 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 cathode for a lithium secondary battery comprising the cathode active material as described above.

The positive electrode of the present invention can be prepared according to conventional methods known in the art using Mn-rich surface-coated with LiBO ₂ as the positive electrode active material. For example, the positive electrode active material, the conductive material, the binder, and the filler (if necessary) are dispersed and mixed in a dispersion medium (solvent) to form a slurry, which is coated on a positive electrode current collector, followed by drying and rolling to produce a slurry. Can be prepared.

According to the present invention, when Mn-rich surface-coated with LiBO ₂ is used as a cathode active material, a desired viscosity can be obtained even with a small amount of solvent, thereby significantly reducing the amount of solvent (eg, NMP) used in the production of a cathode slurry. have.

The conductive material is not particularly limited as long as it has excellent electrical conductivity without causing side reactions in the internal environment of the lithium secondary battery and without causing chemical changes to the battery. Typically, graphite or conductive carbon may be used.

For example, graphite, such as natural graphite and artificial graphite; Carbon blacks such as carbon black, acetylene black, ketjen black, denca black, thermal black, channel black, furnace black, lamp black and summer black; Carbon-based materials 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 conductive polymers such as polyphenylene derivatives; may be used alone or in combination of two or more thereof, but is not necessarily limited thereto.

The conductive material is typically added in an amount of 0.5 to 50 parts by weight, specifically 1 to 15 parts by weight, and 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, it is difficult to expect the effect of improving electrical conductivity, or the electrochemical characteristics of the battery may be lowered. If the content of the conductive material is more than 50 parts by weight, the amount of the positive electrode active material is relatively high. Capacity and energy density can be reduced.

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

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

As the binder, polyvinylidene fluoride (PVdF), polyvinylidene fluoride-polyhexafluoropropylene copolymer (PVdF / HFP), polyvinylacetate, polyvinyl alcohol, polyvinyl ether, polyethylene, polyethylene oxide, alkylation Polyethylene oxide, polypropylene, polymethyl (meth) acrylate, polyethyl (meth) acrylate, polytetrafluoroethylene (PTFE), polyvinylchloride, polyacrylonitrile, polyvinylpyridine, polyvinylpyrrolidone, Styrene-butadiene rubber, acrylonitrile-butadiene rubber, ethylene-propylene-diene monomer (EPDM) rubber, sulfonated EPDM rubber, styrene-butylene rubber, fluorine rubber, carboxymethylcellulose (CMC), starch, hydroxy One or more selected from the group consisting of propylcellulose, regenerated cellulose, and mixtures thereof may be used, but must It is not limited.

The binder is usually added 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 positive electrode material including the positive electrode active material. When the content of the binder is less than 1 part by weight, the adhesion between the electrode active material and the current collector may be insufficient. When the content of the binder exceeds 50 parts by weight, the adhesion may be improved, but the content of the electrode active material may decrease, thereby lowering the battery capacity.

A filler may be selectively added to the cathode material constituting the cathode of the present invention as a component for inhibiting expansion of the anode.

The filler is not particularly limited as long as it can suppress the swelling of the electrode without causing chemical change in the battery, for example, olefin polymers such as polyethylene and polypropylene; Fibrous materials such as glass fibers and carbon fibers; Etc. may be used.

The dispersant may be N-methyl-2-pyrrolidone (NMP), dimethyl formamide (DMF), dimethyl sulfoxide (DMSO), ethanol, isopropanol, water, and mixtures thereof, but is not limited thereto.

The positive electrode current collector is platinum (Pt), gold (Au), palladium (Pd), iridium (Ir), silver (Ag), ruthenium (Ru), nickel (Ni), stainless steel (STS), aluminum (Al) ), Molybdenum (Mo), chromium (Cr), carbon (C), titanium (Ti), tungsten (W), ITO (In doped SnO ₂ ), FTO (F doped SnO ₂ ), and alloys thereof The surface treated with carbon (C), nickel (Ni), titanium (Ti), or silver (Ag) may be used on the surface of aluminum (Al) or stainless steel, but is not limited thereto. The positive electrode current collector may be in the form of a foil, a film, a sheet, a punched one, a porous body, a foam, or the like.

Lithium secondary battery

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

In general, a lithium secondary battery includes 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 that blocks electrical contact between the positive electrode and the negative electrode and moves lithium ions. Void contains electrolyte for conduction of lithium ion.

The negative electrode may be prepared according to conventional methods known in the art. For example, a negative electrode may be prepared by dispersing and mixing a negative electrode active material, a conductive material, a binder, and a filler (as needed) in a dispersion medium (solvent) to make a slurry, and then applying the same to a negative electrode current collector, followed by drying and rolling. have.

The negative electrode active material may be lithium metal, a lithium alloy (eg, an alloy of lithium with a metal such as aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, or indium), amorphous carbon, crystalline carbon, carbon composite material And SnO ₂ can be used, but is not necessarily limited thereto.

The negative electrode current collector is platinum (Pt), gold (Au), palladium (Pd), iridium (Ir), silver (Ag), ruthenium (Ru), nickel (Ni), stainless steel (STS), copper (Cu ), Molybdenum (Mo), chromium (Cr), carbon (C), titanium (Ti), tungsten (W), ITO (In doped SnO ₂ ), FTO (F doped SnO ₂ ), and alloys thereof The surface of carbon (C), nickel (Ni), titanium (Ti), or silver (Ag) may be used on the surface of copper (Cu) or stainless steel, but is not limited thereto. The negative electrode current collector may be in the form of a foil, a film, a sheet, a punched material, a porous body, a foam, or the like.

The separator is interposed between the positive electrode and the negative electrode to prevent a short circuit therebetween and serves to provide a movement passage of lithium ions.

As the separator, an olefin 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 (eg, an organic solid electrolyte, an inorganic solid electrolyte, etc.) is used as the electrolyte, the solid electrolyte may also serve as a separator. Specifically, an insulating thin film having high ion permeability and mechanical strength is used. The pore diameter of the separator is generally 0.01 ~ 10㎛, the thickness may generally range from 5 ~ 300㎛.

The electrolyte may be used alone or as a mixture of two or more kinds of carbonate, ester, ether or ketone as a non-aqueous electrolyte (non-aqueous organic solvent), but is not limited thereto.

For example, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, methylethyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, γ-butylolactone, n-methyl acetate, n- Such as ethyl acetate, n-propyl acetate, phosphoric acid triesters, dibutyl ether, N-methyl-2-pyrrolidinone, 1,2-dimethoxy ethane, tetrahydroxy franc, 2-methyl tetrahydrofuran Tetrahydrofuran derivatives, dimethyl sulfoxide, formamide, dimethylformamide, dioxolon and derivatives thereof, acetonitrile, nitromethane, methyl formate, methyl acetate, trimethoxy methane, sulfolane, methyl sulfolane, 1,3 Aprotic organic solvents such as dimethyl-2-imidazolidinone, methyl propionate and ethyl propionate may be used, but are not limited thereto. It is not.

Lithium salt may be further added to the electrolyte solution (so-called lithium salt-containing non-aqueous electrolyte solution), and the lithium salt may be well-known in the non-aqueous electrolyte solution, for example, LiCl, LiBr, LiI, and 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, lithium chloroborane, lower aliphatic lithium carbonate, lithium 4-phenylborate, imide, and the like, but are not necessarily limited thereto.

In the (non-aqueous) electrolyte, pyridine, triethyl phosphite, 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, etc. It may be. In some cases, a halogen-containing solvent such as carbon tetrachloride or ethylene trifluoride may be further included to impart nonflammability, and carbon dioxide gas may be further included to improve high temperature storage characteristics.

The lithium secondary battery of the present invention can be manufactured according to a conventional method in the art. For example, a porous separator may be placed between the positive electrode and the negative electrode, and the nonaqueous electrolyte may be added.

The lithium secondary battery according to the present invention not only exhibits an improved capacity characteristic (prevents a sudden drop in capacity) under high-speed charging and discharging cycle conditions, but also has excellent cycle characteristics, rate characteristics, and life characteristics. Of course, the present invention can be particularly suitably used as a unit cell of a battery module which is a power source for medium and large devices.

In this aspect, the present invention also provides a battery module comprising two or more of the lithium secondary battery is electrically connected (serial or parallel connection). The number of lithium secondary batteries included in the battery module may be variously adjusted in consideration of the purpose and capacity of the battery module.

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

The battery module and the battery pack is a power tool (Power Tool); Electric vehicles including electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs); Electric truck; Electric commercial vehicle; Or, any one or more of the power storage system can be used as a medium-large device power supply, but is not necessarily 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, and then, the surface of the mixture to chemical and heat treated for 2 hours at a temperature of 600 ℃ mixing (Mn Ni _{0 .32 0 .44 0 .24} Co) O ₂ in methanol liquid and LiBO ₂ Coated Mn-rich cathode active material was prepared.

Manufacture of anode

90 wt% of the surface-coated cathode active material; 5 wt% Super-P as the conductive material; And 5% by weight of KF1100 as a binder; were added together to NMP to make 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 / cm 2)

Cathode manufacturing

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

The lithium secondary battery  Produce

And interposing a porous polyethylene separator between the positive electrode and the negative electrode prepared as described above, a lithium salt-containing non-aqueous liquid electrolyte (LiPF ₆ of 1.2M ethylene carbonate (EC): dimethyl carbonate (DMC): ethyl methyl carbonate (EMC) = And dissolved in an organic solvent mixed in a volume ratio of 2: 4: 4 to prepare a polymer type lithium secondary battery.

Comparative Example

Producing an image, and is a lithium secondary battery in the same manner as in Example, except that a cathode active material with a surface coating is not a _{0.5Li 2 MnO 3 · 0.5Li (Mn} 0 .32 Ni 0 .44 Co 0 .24) O 2 It was.

Experimental Example

The capacity and lifespan of the lithium secondary batteries manufactured according to the Examples and Comparative Examples were tested for each discharge rate, and the results are shown in FIGS. 1 and 2.

Referring to FIG. 1, in the case of the embodiment, it can be seen that the decrease in capacity is greatly reduced at higher C-rate than the comparative example.

Referring to FIG. 2, it can be seen that in the case of the example, the cycle characteristics are superior to those of the comparative example.

In addition, in the case of the embodiment it was possible to prepare a positive electrode slurry of the same viscosity only by using a solvent (NMP) of about 2/3 compared to 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 (10)

A cathode active material for a lithium secondary battery, characterized in that the surface of the lithium manganese oxide represented by Formula 1 is coated with LiBO ₂ :
[Chemical Formula 1]
xLi ₂ MnO ₃ (1-x) Li _y MO ₂
In Formula 1,
0 <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, Mg and B.
The method of claim 1,
The LiBO ₂ is a positive electrode active material, characterized in that it comprises 0.5 to 15% by weight based on the total weight of the positive electrode active material.
A cathode for a lithium secondary battery comprising the cathode active material according to claim 1.
The method of claim 3,
A cathode for a lithium secondary battery, further comprising conductive carbon and a binder.
A lithium secondary battery comprising the positive electrode according to claim 3.
A battery module or a battery pack comprising a plurality of lithium secondary batteries according to claim 5 electrically connected.
The method according to claim 6,
The battery module or the battery pack is a power tool (Power Tool); Electric vehicles including electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs); Electric truck; Electric commercial vehicle; Or a battery module or a battery pack, characterized in that used as a power source for any one or more of the system for power storage.
a) mixing the lithium manganese oxide represented by Formula 1 with LiBO ₂ ; And
b) a method for producing a cathode active material according to claim 1, comprising chemically surface coating the mixture:
[Chemical Formula 1]
xLi ₂ MnO ₃ (1-x) Li _y MO ₂
In Formula 1,
0 <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, Mg and B.
9. The method of claim 8,
Mixing of step a) is characterized in that the manufacturing method is carried out in the liquid phase.
9. The method of claim 8,
Chemical surface coating in the step b) is characterized in that it is carried out by heat treatment at a temperature of 250 ℃ ~ 1000 ℃.

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