KR101515363B1 - Electrode Active Material for Secondary Battery and the Method for Preparing the Same - Google Patents

Abstract

The present invention provides, as an electrode active material for a secondary battery, an electrode active material for a secondary battery in which the surface of a lithium metal oxide represented by the general formula (1) is carbon-coated to improve conductivity.
Li _a M ' _b O _{4-ca c} (1)
In the above formula, M 'is at least one element selected from the group consisting of Ti, Sn, Cu, Pb, Sb, Zn, Fe, In, Al and Zr;
a and b are 0.1? a? 4; Is determined according to the oxidation number of M 'in the range of 0.2? B? 4;
c is determined according to the oxidation number in the range of 0? c <0.2;
A is one or more of an anion of -1 or -2.

Description

[0001] The present invention relates to an electrode active material for a secondary battery,

The present invention relates to an electrode active material for a secondary battery, wherein a surface of a lithium metal oxide represented by a specific formula is carbon-coated to improve conductivity.

As technology development and demand for mobile devices have increased, there has been a rapid increase in demand for secondary batteries as energy sources. Among such secondary batteries, lithium secondary batteries, which exhibit high energy density and operational potential, long cycle life, Batteries have been commercialized and widely used.

In recent years, there has been a growing interest in environmental issues, and as a result, electric vehicles (EVs) and hybrid electric vehicles (HEVs), which can replace fossil-fueled vehicles such as gasoline vehicles and diesel vehicles, And the like. Although a nickel metal hydride (Ni-MH) secondary battery is mainly used as a power source for such an electric vehicle (EV) and a hybrid electric vehicle (HEV), a lithium secondary battery having a high energy density, a high discharge voltage, Research is being actively carried out, and some are commercialized.

The lithium secondary battery has a structure in which a non-aqueous electrolyte containing a lithium salt is impregnated in an electrode assembly having a porous separator interposed between a positive electrode and a negative electrode coated with an active material on an electrode current collector.

At present, a carbon-based material is mainly used as a cathode for a lithium secondary battery. However, the carbon-based material has a low electric potential of 0 V compared to lithium, thereby reducing the amount of the electrolytic solution and generating gas. In order to solve such a problem, a lithium metal oxide having a relatively high potential is used as an anode active material.

However, also in this case, in order to improve the conductivity of the electrode material mixture, a conductive material is used, and activated carbon which maximizes the surface area is mainly used. This active carbon used as a conductive material can cause a side reaction with the electrolyte solution. Particularly, in the case of lithium-titanium oxide among the lithium metal oxides, a phenomenon occurs in which the potential drops sharply at the time of 100% charging. At this time, the carbon-based material can react.

Therefore, there is a great need for a technique capable of preventing a side reaction of an electrolyte during operation of the battery, particularly, a technique capable of solving the above-described problems while using lithium-titanium oxide having poor conductivity as an electrode active material.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems of the prior art and the technical problems required from the past.

The inventors of the present application have conducted intensive research and various experiments and have found that when a lithium metal oxide represented by a specific chemical formula is carbon-coated on a surface of a lithium battery and the conductivity is improved by using a separate conductive material It is possible to achieve the above-mentioned desired effect, and the present invention has been accomplished.

Accordingly, the present invention provides an electrode active material for a secondary battery, wherein the surface of a lithium metal oxide represented by the following formula (1) is carbon-coated to improve conductivity.

Li _a M ' _b O _{4-ca c} (1)

In the above formula, M 'is at least one element selected from the group consisting of Ti, Sn, Cu, Pb, Sb, Zn, Fe, In, Al and Zr;

a and b are 0.1? a? 4; Is determined according to the oxidation number of M 'in the range of 0.2? B? 4;

c is determined according to the oxidation number in the range of 0? c <0.2;

A is one or more of an anion of -1 or -2.

In one specific example, the lithium metal oxide of Formula 1 may be lithium-titanium oxide (LTO) represented by the following Formula 2, specifically Li _0.8 Ti _2.2 O ₄ , Li _2.67 Ti _1.33 O ₄ , LiTi ₂ O ₄ , Li _1.33 Ti _1.67 O ₄ , Li _1.14 Ti _1.71 O _4, and the like, but there is no particular limitation on the composition and kind of lithium ions capable of intercalating / deintercalating lithium ions, and more specifically, It may be a spinel structure Li _1.33 Ti _1.67 O ₄ or LiTi ₂ O ₄ having a small change in structure and excellent in reversibility.

Li _a Ti _b O ₄ (2)

In the above formula, 0.5? A? 3, 1? B? 2.5.

In particular, the lithium-titanium oxide has been attracting attention as an electrode active material for a middle- or large-sized battery pack because it exhibits excellent performance in rapid charging. However, the lithium-titanium oxide has a disadvantage that its conductivity is low. Therefore, in order to compensate for this, the above-described disadvantages can be overcome by coating the surface of the lithium titanium oxide with carbon having excellent conductivity.

In one specific example, the carbon coated on the surface of the lithium metal oxide may not be activated carbon, which is mainly used as a separate conductive material, but may be carbon produced by carbonizing an organic material, and thus the precursor of the carbon may be an organic material .

When the lithium metal oxide, particularly lithium titanium oxide, is used as an anode active material, the activated carbon mainly used as the conductive material can react with lithium while the potential is lowered at 100% charging. In this case, carbon is used as an active material The safety of the secondary battery may be lowered due to the decomposition reaction of electrolytic solution and the like, which is not preferable.

The organic material may be any material capable of carbonizing and coating carbon on the surface of the lithium metal oxide, but may be, for example, Sucrose or Lactose.

In one specific example, the carbon may be coated on all or a portion of the surface of the lithium metal oxide, wherein the coating thickness of the carbon is in particular from 0.1 to 10 탆, more specifically from 1 to 5 탆 . Within the above range, carbon can be uniformly coated on the surface of the lithium metal oxide, desorption and insertion of lithium ions can be appropriately performed, and it is possible to have electrochemical characteristics of a desired level or higher.

The present invention provides an electrode mixture for a secondary battery, which contains the electrode active material and does not contain an additional conductive material.

Since the electrode active material is coated with carbon having excellent conductivity, the electrochemical performance of the electrode active material is not deteriorated even when no additional conductive material is included.

The present invention also provides an electrode for a secondary battery, wherein the electrode mixture is applied to an electrode current collector. The electrode for the secondary battery may be an anode or a cathode.

When the lithium metal oxide is lithium titanium oxide, the lithium metal oxide has a high potential relative to lithium and can be used as a cathode active material and also as an anode active material. Specifically, the lithium-titanium oxide may be used as a negative electrode active material. In this case, it is preferable to solve the safety problem caused by using carbon as the negative electrode active material.

Therefore, the electrode for the secondary battery may be a negative electrode including a negative electrode active material.

The present invention provides a rechargeable battery including the electrode, specifically, a lithium secondary battery having a structure in which an electrode assembly having a separator interposed between an anode and a cathode is impregnated with a lithium salt-containing electrolyte.

The positive electrode for a secondary battery is prepared by applying a mixture of a positive electrode active material, a conductive material and a binder on a positive electrode current collector, followed by drying and pressing. If necessary, a filler may be further added to the mixture.

The cathode current collector generally has a thickness of 3 to 500 mu m. Such a positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. Examples of the positive electrode current collector include stainless steel, aluminum, nickel, titanium, sintered carbon, aluminum or stainless steel A surface treated with carbon, nickel, titanium, silver or the like may be used. The current collector may have fine irregularities on the surface thereof to increase the adhesive force of the cathode active material, and various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric are possible.

The cathode active material may be a layered compound such as lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), or a compound substituted with one or more transition metals; Lithium manganese oxides such as Li _{1 + x} Mn _{2 -x} O ₄ (where x is 0 to 0.33), LiMnO ₃ , LiMn ₂ O ₃ , LiMnO ₂ and the like; Lithium copper oxide (Li ₂ CuO ₂ ); Vanadium oxides such as LiV ₃ O ₈ , LiFe ₃ O ₄ , V ₂ O ₅ and Cu ₂ V ₂ O ₇ ; A Ni-site type lithium nickel oxide expressed by the formula LiNi _1-x M _x O ₂ (where M = Co, Mn, Al, Cu, Fe, Mg, B or Ga and x = 0.01 to 0.3); Formula _{LiMn 2-x M x O 2} ( where, M = Co, Ni, Fe , Cr, and Zn, or Ta, x = 0.01 ~ 0.1 Im) or Li ₂ Mn ₃ MO ₈ (where, M = Fe, Co, Ni, Cu, or Zn); A lithium manganese composite oxide having a spinel structure represented by LiNi _x Mn _2-x O ₄ ; LiMn ₂ O _{4 in} which a part of Li in the formula is substituted with an alkaline earth metal ion; Disulfide compounds; Fe ₂ (MoO ₄ ) ₃ , and the like. However, the present invention is not limited to these.

In one specific example, a lithium manganese composite oxide having a spinel structure which corresponds to a high potential of the lithium metal oxide may be used as the cathode active material. The lithium manganese composite oxide may be represented by the following formula (3).

Li _x M _y Mn _2-y O _{4 -z z} (3)

Wherein 0 < y < 2, 0 z < 0.2,

M is at least one element selected from the group consisting of Al, Mg, Ni, Co, Fe, Cr, V, Ti, Cu, B, Ca, Zn, Zr, Nb, Mo, Sr, Sb, W, ;

A is one or more of an anion of -1 or -2.

In detail, the lithium manganese composite oxide may be a lithium nickel manganese complex oxide (LNMO) represented by the following general formula (4), more specifically LiNi _0.5 Mn _1.5 O ₄ or LiNi _0.4 Mn _1.6 O ₄ &lt; / RTI &gt;

Li _x Ni _y Mn _2-y O ₄ (4)

In the above formula, 0.9? X? 1.2 and 0.4? Y? 0.5.

The conductive material is usually added in an amount of 1 to 50% by weight based on the total weight of the mixture including the cathode active material. Such a conductive material is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery, for example, graphite such as natural graphite or artificial graphite; Carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskey such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used.

The binder is a component that assists in bonding of the active material and the conductive material and bonding to the current collector, and is usually added in an amount of 1 to 50 wt% based on the total weight of the mixture containing the cathode active material. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene , Polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butylene rubber, fluorine rubber, various copolymers and the like.

The filler is optionally used as a component for suppressing the expansion of the anode, and is not particularly limited as long as it is a fibrous material without causing a chemical change in the battery. Examples of the filler include olefin polymers such as polyethylene and polypropylene; Fibrous materials such as glass fibers and carbon fibers are used.

On the other hand, the negative electrode is manufactured by applying, drying and pressing a carbon-coated lithium metal oxide as a negative electrode active material on an anode current collector, and may optionally further include a binder, a filler, and the like as described above.

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

The separation membrane is interposed between the anode and the cathode, and an insulating thin film having high ion permeability and mechanical strength is used. The pore diameter of the separator is generally 0.01 to 10 mu m and the thickness is generally 5 to 300 mu m. Such separation membranes include, for example, olefinic polymers such as polypropylene, which are chemically resistant and hydrophobic; A sheet or nonwoven fabric made of glass fiber, polyethylene or the like is used. When a solid electrolyte such as a polymer is used as an electrolyte, the solid electrolyte may also serve as a separation membrane.

The electrolyte solution containing the lithium salt is composed of an electrolyte solution and a lithium salt. The electrolyte solution may be a non-aqueous organic solvent, an organic solid electrolyte, or an inorganic solid electrolyte, but is not limited thereto.

Examples of the non-aqueous organic solvent include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma -Butyrolactone, 1,2-dimethoxyethane, tetrahydroxyfuran, 2-methyltetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane , Acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate Nonionic organic solvents such as tetrahydrofuran derivatives, ethers, methyl pyrophosphate, ethyl propionate and the like can be used.

Examples of the organic solid electrolyte include a polymer electrolyte such as a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphate ester polymer, an agitation lysine, a polyester sulfide, a polyvinyl alcohol, a polyvinylidene fluoride, A polymer containing an ionic dissociation group and the like may be used.

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

The lithium salt is a material that is readily soluble in the non-aqueous electrolyte, for example, LiCl, LiBr, LiI, LiClO 4, LiBF 4, LiB 10 Cl 10, LiPF 6, LiCF 3 SO 3, LiCF 3 CO 2, LiAsF _{6, LiSbF 6, LiAlCl 4,} CH 3 SO 3 Li, (CF 3 SO 2) 2 NLi, chloroborane lithium, lower aliphatic carboxylic acid lithium, lithium tetraphenyl borate and imide.

For the purpose of improving the charge / discharge characteristics and the flame retardancy, the electrolytic solution is preferably mixed with an organic solvent such as pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, glyme, Benzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N, N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, . In some cases, halogen-containing solvents such as carbon tetrachloride and ethylene trifluoride may be further added to impart nonflammability. In order to improve the high-temperature storage characteristics, carbon dioxide gas may be further added. FEC (Fluoro-Ethylene Carbonate, PRS (Propene sultone), and the like.

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

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

The battery pack may be used as a power source for devices requiring high temperature stability, long cycle characteristics, and high rate characteristics.

Specific examples of the device include a power tool which is powered by an electric motor and moves; An electric vehicle including an electric vehicle (EV), a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), and the like; An electric motorcycle including an electric bike (E-bike) and an electric scooter (E-scooter); An electric golf cart; And a power storage system, but the present invention is not limited thereto.

As described above, since the surface of the electrode active material for a secondary battery according to the present invention is coated with carbon and no additional conductive material is used, the safety problem due to electrolytic solution reduction can be solved.

1 is a graph showing experimental results of capacity retention rate and resistance increase rate according to Experimental Example 1. FIG.

Hereinafter, the present invention will be described in more detail with reference to embodiments thereof, but the scope of the present invention is not limited thereto.

&Lt; Example 1 >

Cathode manufacturing

After mixing the precursor powder for the anode active material with lithium carbonate (Li ₂ CO ₃ ) and mixing 3 parts by weight of sucrose as a carbon source, the mixture was calcined at 800 ° C for 15 hours at a rate of 2 to 5 ° C / min the carbon-coated negative electrode active material _{(Li 1.33 Ti 1.67 O 4 /} C) to prepare a, and a negative electrode active material _{(Li 1.33 Ti 1.67 O 4 /} C) and a binder (PVdF) 93: negative electrode put in NMP mixed in a weight ratio of 7 After the mixture was prepared, the negative electrode mixture was coated to a thickness of 200 mu m on a copper foil having a thickness of 20 mu m, rolled and dried to prepare a negative electrode.

Manufacture of Secondary Battery

The anode mixture was prepared by mixing LiNi _0.5 Mn _1.5 O ₄ as a cathode active material, a conductive material (Denka black) and a binder (Solef 6020) in NMP at a weight ratio of 88: 8.5: 3.5, , Rolled and dried to prepare a positive electrode.

After the electrode assembly was manufactured through the separator (thickness: 20 占 퐉) between the thus-prepared positive electrode and the negative electrode, the electrode assembly was housed in the pouch-shaped battery case, and a carbonate-based composite containing 1 M of LiPF ₆ The solution was injected into the electrolyte and then sealed to prepare a lithium secondary battery.

&Lt; Comparative Example 1 &

The negative electrode active material (Li _1.33 Ti _1.67 O ₄ ), the conductive material (Denka black) and the binder (PVdF) were mixed in NMP at a weight ratio of 91.5: 3: 5.5 in Example 1, A lithium secondary battery was prepared in the same manner as in Example 1, except that the mixture was prepared.

<Experimental Example 1>

The capacity and the discharge resistance of the secondary battery according to Example 1 and Comparative Example 1 were measured by charging and discharging at 1 C in the range of 2 V to 3.35 V and the batteries were stored at 60 ° C. for 4 weeks in an SOC of 100% After that, the capacity and discharge resistance were measured again, and the results are shown in Table 1 and Fig.

1 ^st discharge 60 ° C, 4week, SOC 100% Capacity increase and decrease
(%) Increase / decrease of resistance (%) 1C Capacity (mAh) Discharge resistance
(mΩ) 1C Capacity (mAh) Discharge resistance
(mΩ) Example 1 18.23 1.91 17.98 2.79 98.62 145.95 Comparative Example 1 19.47 1.70 18.27 2.34 93.83 137.42

Referring to Table 1 and FIG. 1, it can be seen that the secondary battery of Example 1 is higher than the secondary battery of Comparative Example 1 in terms of the initial resistance and the rate of increase in resistance, while the rate of capacity reduction due to high temperature storage is low.

The reason why the initial resistance and the rate of increase in resistance of Example 1 is higher than that of Comparative Example 1 is because the content of the binder is 2% higher than that of Comparative Example 1 while the amount of moisture adsorbed on the carbon due to the carbon coating . On the other hand, the secondary battery of Example 1 does not require a conductive material separately due to the carbon coating, so that the side reaction that may occur at the interface between the electrode active material and the electrolyte is minimized, I will exert.

It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

Claims (16)

1. A lithium secondary battery comprising: a cathode active material for a secondary battery, the cathode active material having a surface of lithium titanium oxide (LTO) represented by the following formula (2) A negative electrode coated with a thickness of 占 퐉 and coated with a negative electrode material mixture not containing additional conductive material; And
And a positive electrode coated with a positive electrode material mixture comprising a positive electrode active material for a secondary battery represented by the following formula (4): &lt; EMI ID =
Li _a Ti _b O ₄ (2)
In the above formula, 0.5? A? 3, 1? B? 2.5.
Li _x Ni _y Mn _2-y O ₄ (4)
In the above formula, 0.9? X? 1.2 and 0.4? Y? 0.5. delete The secondary battery according to claim 1, wherein the lithium titanium oxide is Li _1.33 Ti _1.67 O ₄ or LiTi ₂ O ₄ . delete The secondary battery according to claim 1, wherein the organic material is sucrose or lactose. delete The secondary battery according to claim 1, wherein the carbon is coated on all or a part of the surface of the lithium metal oxide. delete delete delete delete The secondary battery according to claim 1, wherein the secondary battery is a lithium secondary battery. A battery module comprising a secondary battery according to claim 12 as a unit cell. A battery pack comprising the battery module according to claim 13. A device comprising a battery pack according to claim 14. 16. The device of claim 15, wherein the device is an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, or a system for power storage.

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