KR101280319B1 - The manufacturing method of producing lithium manganese complex oxide by hydrothermal reaction, lithium manganese complex oxide manufactured by the method, and electrochemical device using the same - Google Patents

Abstract

The present invention relates to Li _{1 + x} Mn _2-xy M _y O ₄ (0 ≦ _x ≦ 0.1, 0.01 ≦ _y ≦ 0.5, M = Al, Mg and Ni, Co, which is a lithium manganese composite oxide used as an active material of a lithium secondary battery). Hydrothermal synthesis method of the same transition metal), and thus, Li _{1 + x} Mn _{2 -x- y} M _y O ₄ (0 _{≦ x} ≦ 0.1, 0.01 ≦ _y ≦ 0.5, M = Al, Mg and Ni, Co, etc. Metal) and electrochemical devices using the same.

Description

Method for synthesizing lithium manganese composite oxide using hydrothermal synthesis method, the lithium manganese composite oxide prepared by the same and electrochemical device using the same METHOD, AND ELECTROCHEMICAL DEVICE USING THE SAME}

The present invention relates to a method for synthesizing a lithium manganese composite oxide using a hydrothermal synthesis method, a lithium manganese composite oxide prepared thereby and an electrochemical device using the same, more specifically Li _{1 +} used as an active material of a lithium secondary battery Hydrothermal synthesis of _x Mn _{2 -x- y} M _y O ₄ (0 _{≦ x} ≦ 0.1, 0.01 ≦ _y ≦ 0.5, M = Al, Mg and Ni, Co, etc. transition metals), thereby preparing Li _{1 + x} Mn _{2 -xy} M _y O ₄ (0≤x≤0.1, 0.01≤y≤0.5, M = Al, Mg and transition metals such as Ni, Co) and the electrochemical device using the same.

As a power source for portable electronic devices such as PDAs, mobile phones, and notebook computers for information and communication, electric bicycles, and electric vehicles, the demand for secondary batteries that are repeatedly charged and discharged is rapidly increasing. In particular, the demand for high performance batteries is very large because their product performance depends on batteries, which are the key components. The characteristics required for the battery have various aspects such as charge and discharge characteristics, life, high rate characteristics, and stability at high temperatures. Lithium secondary batteries have the highest voltage and high energy density and are the most attracting attention.

Lithium secondary batteries have been reported by Mizushima et al in 1980 as a cathode active material for lithium secondary batteries (Material Research Bulletin vol 115, pages 783 to 789 (1980)). Research and development on the composite oxides are actively underway, and lithium cobalt, lithium nickelate, and lithium manganate are known as cathode active materials. Among them, lithium manganate (LiMn ₂ O ₄ ) has been proposed in the past because of the low cost of raw materials and low manufacturing cost compared to lithium cobalt or lithium nickelate.

Such lithium manganate LiMn ₂ O ₄ is generally synthesized by using a solid phase method, but this is produced by several steps of mixing and baking these powders using carbonates or hydroxides of each element as raw materials. However, the solid-phase reaction method has a disadvantage in that it is difficult to form a solid solution of the solid phases, has a high inflow of impurities during mixing, difficult to control the size of the particles constantly, and has a high temperature and a long manufacturing time in manufacturing.

Conventionally, wet processes such as co-precipitation, sol-gel, and hydrothermal synthesis have been used to solve these problems. However, co-precipitation during such a wet process has a disadvantage of synthesizing a precursor after synthesis of a lithium salt and heat treatment. Gel method has a problem due to volume expansion during the synthesis process. In addition, in the hydrothermal synthesis method of the wet process, it is difficult to obtain LiMn ₂ O ₄ having a long synthesis time and high crystallinity using only water as a solvent, and thus has to undergo a separate heat treatment process.

SUMMARY OF THE INVENTION The present invention has been made to solve such problems in the related art, and an object of the present invention is to provide a new hydrothermal synthesis method capable of increasing the crystallinity of the produced lithium manganese composite oxide, obtaining particles having a uniform shape, and reducing manufacturing time. .

The present invention is a method for synthesizing a lithium manganese composite oxide in order to solve the above problems, by mixing the lithium compound, manganese compound and M element compound as a raw material in a stoichiometric ratio, using water and a cosolvent as a solvent, 160 Li _{1 + x} Mn _{2 -xy} M _y O ₄ (0 ≦ _x ≦ 0.1, 0.01 ≦ _y ≦ 0.5, M = Al, using a hydrothermal synthesis method characterized by hydrothermal treatment at 1 to 4 days at 250 ° C.). Provided is a method for synthesizing Mg and transition metals such as Ni and Co.

In the present invention, the cosolvent may be used in substances such as methanol, ethanol, isopropanol, benzoyl alcohol, monoethanolamine, diethanolamine, triethanolamine, carbon tetrachloride, acetone, methyl ethyl ketone, tetrahydrofuran and the like. It is characterized by the fact that it is one kind alone or a mixture of two or more kinds.

In the present invention, the cosolvent is used at 0.5 to 5% by volume based on the water.

In another embodiment of the present invention is manufactured by the manufacturing method _{Li 1 + x Mn 2 -x- y} M y O 4 (0≤x≤0.1, 0.01≤y≤0.5, M = Al, Mg , and Ni, Co And the like transition metal).

In another embodiment of the present invention Li _{1 + x} Mn _{2 -xy} M _y O ₄ (0≤x≤0.1, 0.01≤y≤0.5, M = Al, Mg and Ni, Co, etc. prepared by this manufacturing method Provided is an electrochemical device using a transition metal) as a cathode active material.

In the present invention, the electrochemical device is Li _{1 + x} Mn _{2 -xy} M _y O ₄ of claim 4, characterized in that the lithium secondary battery or a hybrid capacitor (0≤x≤0.1, 0.01≤y≤0.5, M It provides an electrochemical device using =, Al, Mg and transition metals such as Ni, Co) as a cathode active material.

Hereinafter, the present invention will be described in more detail.

The present invention is a method for synthesizing Li _{1 + x} Mn _{2 -x- y} M _y O ₄ (0≤x≤0.1, 0.01≤y≤0.5, M = Al, Mg and Ni, Co and other transition metals) by hydrothermal synthesis In this regard, hydrothermal synthesis is a method of crystallizing amorphous powders under high temperature and high pressure (Byrappa, K., Handbook of Crystal Growth, Vol. 2, 1994, edited by Hurl, DTJ). It was discovered while studying the formation of the crust ores. The process and principle of crystal formation in hydrothermal synthesis is that the constituents of the crystals ionize in aqueous solution under high temperature and high pressure, and these ions produce and grow the most stable crystal phase under given conditions.

Generally, in hydrothermal synthesis, the raw material is placed in an autoclave, filled with a substantial portion of water, and then sealed to heat to a high temperature. In the present invention, a lithium compound, a manganese compound, and an M element compound are mixed at stoichiometric ratios as raw materials, placed in an autoclave container, and then water and cosolvent as solvents are used at 160 to 250 ° C. for 1 to 4 days. _Hydrothermal treatment synthesizes Li _{1 + x} Mn _{2 -x- y} M _y O ₄ (0 _{≦ x} ≦ 0.1, 0.01 ≦ _y ≦ 0.5, M = Al, Mg and Ni, Co and other transition metals).

In the present invention, by promoting the reaction between the lithium compound and manganese compound using a co-solvent, Li _{1 + x} Mn _{2 -xy} M having a high crystallinity and uniform shape in a short time than the conventional method using only water as a solvent _y 0 ₄ (0 ≦ _x ≦ 0.1, 0.01 ≦ _y ≦ 0.5, M = Al, Mg, and transition metal such as Ni, Co) particles can be made. The cosolvent usable in the present invention may be used in substances such as methanol, ethanol, isopropanol, benzoyl alcohol, monoethanolamine, diethanolamine, triethanolamine, carbon tetrachloride, acetone, methyl ethyl ketone, tetrahydrofuran and the like. It is single 1 type or a mixture of 2 or more types. Such cosolvent is preferably used at 0.5 to 5% by volume with respect to water.

As for the hydrothermal temperature in this invention, 160-250 degreeC, and hydrothermal treatment time are 1 day-4 days are preferable. There is a problem that the crystal does not grow at 160 ℃ or less, the solvent is boiled at 250 ℃ or more, there is a problem that the production of crystal is not enough when the hydrothermal treatment time is less than 1 day, Li ₁ produced when more than 4 days _{+ x} Mn _{2 -x- y} M _y O ₄ There is a problem that the size distribution of the powder is large.

The present invention also provides a lithium secondary battery comprising such a positive electrode. Methods for producing a lithium secondary battery by the construction of a positive electrode, a negative electrode, a separator, and a lithium salt-containing nonaqueous electrolyte are known in the art.

As described above, the positive electrode is prepared by applying a mixture of a positive electrode mixture of a positive electrode active material, a conductive agent and a binder and a ferroelectric material on a positive electrode current collector, and then drying it, and optionally adding a filler to the mixture. do.

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 conductive agent 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 agent is not particularly limited as long as it has electrical conductivity without causing a chemical change in the battery, and examples thereof include graphite such as natural graphite and 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 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 which assists in binding of the active material and the conductive agent and bonding to the current collector, and is usually added in an amount of 1 to 50% by weight based on the total weight of the mixture containing the cathode active material. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, Polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene 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 produced by applying and drying the negative electrode material on the negative electrode current collector. In some cases, a conductive agent, a binder, a filler, or the like as in the positive electrode mixture may be optionally included.

The negative electrode collector is generally made to have a thickness of 3 to 500 mu m. Such a negative electrode current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery. For example, 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 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 negative electrode 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 Mep _{1 - x} Me ' _y O _z (Mep: 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 alloy; Silicon-based alloys; Tin alloy; _{SnO, SnO 2, PbO, PbO} 2, Pb 2 O 3, Pb 3 O 4, Sb 2 O 3, Sb 2 O 4, Sb 2 O 5, GeO, GeO 2, Bi 2 O 3, Bi 2 O 4 , and Bi ₂ O ₅ and the like; Conductive polymers such as polyacetylene; Li-Co-Ni-based materials and the like can be used.

The separator is interposed between the cathode and the cathode, and an insulating thin film having high ion permeability and mechanical strength is used.

The pore diameter of the membrane is generally 0.01 ~ 10 ㎛ ㎛, thickness is generally 5 ~ 300 ㎛. 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 lithium salt-containing non-aqueous electrolyte consists of a nonaqueous electrolyte and lithium. As the non-aqueous electrolyte, a non-aqueous electrolyte, a solid electrolyte, an inorganic solid electrolyte and the like are used.

As said non-aqueous electrolyte, N-methyl- 2-pyrrolidinone, a propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyl Low lactone, 1,2-dimethoxy ethane, tetrahydroxy franc, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolon, formamide, dimethylformamide, dioxolon, aceto Nitrile, nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxy methane, dioxorone derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative , Aprotic organic solvents such as tetrahydrofuran derivatives, ethers, methyl pyroionate, 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, Polymers containing ionic dissociation groups, and the like can be used.

As the inorganic solid electrolyte, for example, 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 be dissolved 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 3 Li, (CF 3 SO 2) 2NLi, chloroborane lithium, lower aliphatic carboxylic acid lithium, lithium tetraphenyl borate and imide .

In addition, the non-aqueous electrolyte includes pyridine, triethyl phosphite, triethanol amine, 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 added to impart nonflammability, or a carbon dioxide gas may be further added to improve high-temperature storage characteristics.

Li _{1 + x} Mn _{2 -x- y} M _y O ₄ (0 _{≦ x} ≦ 0.1, 0.01 ≦ _y ≦ 0.5, M = Al, Mg and Ni, Co, etc.) according to the hydrothermal synthesis method according to the present invention In this case, not only can shorten the manufacturing time, but also obtain crystal particles with high crystallinity and uniform size. In the case of the secondary battery including the cathode active material, capacity and rate characteristics are improved.

Figure 1 shows a SEM photograph of LiMn ₂ O ₄ prepared by the embodiment of the present invention.
Figure 2 shows a SEM photograph of LiMn ₂ O ₄ prepared by the comparative example of the present invention.
Figure 3 shows an XRD photograph of LiMn ₂ O ₄ prepared by the Examples and Comparative Examples of the present invention.
Figure 4 shows the rate (C-rate) characteristics of a cell made of the positive electrode active material of Examples and Comparative Examples of the present invention.

Hereinafter, the content of the present invention will be described in detail by way of examples, but the scope of the present invention is not limited thereto.

<Examples>

Ethanol was mixed with water as a cosolvent so that the volume ratio of ethanol was 1.5%, and LiOH and MnO ₂ (EMD) were added in a molar ratio of 1: 2, followed by stirring. Then, the stirred mixture was placed in an autoclave and hydrothermally treated at 200 ° C. for 4 days, and then washed and dried to obtain LiMn ₂ O ₄ .

<Comparative Example>

LiMn ₂ O ₄ was obtained in the same manner as in the above example except that only water was used as the solvent.

<SEM photo measurement>

LiMn ₂ O ₄ of Examples and Comparative Examples thus prepared were taken by a SEM photograph, and the results are shown in FIGS. 1 and 2.

In the case of LiMn ₂ O ₄ prepared according to an embodiment of the present invention using a cosolvent, uniform particles having a level of 1 micron can be obtained as shown in FIG. 1, while in the comparative example of FIG. 2 using only water without a cosolvent Small particles of several tens of nanometers in size were found to be heavily aggregated.

<XRD measurement>

The XRD of LiMn ₂ O ₄ of Examples and Comparative Examples thus prepared was compared, and the results are shown in FIG. 3.

As shown in Figure 3, when the hydrothermal treatment for 4 days when using a co-solvent according to an embodiment of the present invention, it has a much higher crystallinity, in the case of the comparative example without the co-solvent is low in crystallinity and MnO _It was confirmed that impurities such as ₂ existed.

<Production of test cell>

The positive electrode active material of the examples and comparative examples thus prepared, polyvinylidene fluoride (PVDF) as a binder, super P (Super P) as a conductive material, solvent (N-methylpyrrolidone in a weight ratio of 80:10:10) ) And a positive electrode active material composition slurry was prepared, and the slurry was cast in the form of a tape to prepare an electrode plate.

A coin cell type half cell was produced using Li-foil as a counter electrode for this electrode plate and using a 1: 1 volume ratio mixture of ethylene carbonate and dimethyl carbonate and an electrolyte solution containing LiPF ₆ .

<Charge / Discharge Test>

The cell obtained as described above is represented by [Li ₂ MnO ₄ / LiPF ₆ (1 M) in EC ⁺² EMC / Li], and the rate (C-rate) characteristics of the cell were evaluated.

To evaluate the rate characteristics, charge and discharge experiments were conducted at room temperature (30 ℃), 3.0 ~ 4.3V potential range, and various current density conditions using an electrochemical analyzer (Toscat3000U, Japan, Toyo). The capacity change with the cycle is shown in FIG. 4.

In the case of the embodiment of the present invention containing a co-solvent, as shown in Figure 4, the initial capacity of 127mAh / g level can be obtained in terms of rate characteristics, in terms of rate characteristics, about 70% of 0.1 C-rate at 10 C-rate The capacity retention rate can be obtained, but in the comparative example without the co-solvent, a capacity retention rate of 64% compared to 0.1 C-rate was obtained at an initial capacity of 97mAh / g and 10 C-rate. That is, in the case of the embodiment to add a co-solvent, it can be confirmed that a higher initial capacity and excellent rate characteristics can be obtained, and that the synthesis period is 2 days, which is much shorter than 10 days when no co-solvent is added.

Claims (6)

As a method for synthesizing lithium manganese composite oxide,
As a raw material, a lithium compound, a manganese compound, and an M element compound are mixed in a stoichiometric ratio, and water and a cosolvent are used as a solvent, and the cosolvent is methanol, ethanol, isopropanol, benzoyl alcohol, monoethanolamine, diethanolamine, triethanolamine , At least one selected from the group consisting of carbon tetrachloride, acetone, methyl ethyl ketone, and tetrahydrofuran, and the mixing ratio of the cosolvent is 0.5 to 5% by volume with respect to the water, and 1 to 4 at 160 to 250 ° C. Lithium manganese composite oxide Li _{1 + x} Mn _2-xy M _y O ₄ (0 ≦ _x ≦ 0.1, 0.01 ≦ _y ≦ 0.5, M = Al, Mg and Ni, using a hydrothermal synthesis method characterized in that the hydrothermal treatment for a day) Transition metals such as Co).
delete delete Li _{1 + x} Mn _2-xy M _y O ₄ prepared by the method of claim ₁ (0 ≦ _x ≦ 0.1, 0.01 ≦ _y ≦ 0.5, M = Al, Mg, Ni, Co and other transition metals).
Electric using Li _{1 + x} Mn _{2 -x- y} M _y O ₄ (0≤x≤0.1, 0.01≤y≤0.5, M = Al, Mg and Ni, Co, etc.) of claim 4 as a cathode active material Chemical element.
The method of claim 5, wherein
The electrochemical device is Li _{1 + x} Mn _2-xy M _y O ₄ (0≤x≤0.1, 0.01≤y≤0.5, M = Al, Mg and Ni, Co, characterized in that the lithium secondary battery or a hybrid capacitor) Electrochemical device using a transition metal) as a cathode active material.

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