KR20160080243A - Method for Preparing Lithium Manganese Iron Phosphate and Product of Olivine Type Obtained from the Same - Google Patents

Abstract

The present invention relates to a preparation method of lithium manganese iron phosphate, and lithium manganese iron phosphate prepared by the method. More particularly, the preparation method of lithium manganese iron phosphate comprises the following steps of: (a) manufacturing a mixture solution by injecting a lithium precursor, an iron precursor, a manganese precursor, and a phosphorous precursor to a polyol solvent; (b) conducting a reaction by injecting the mixture solution into an atmospheric reactor; and (c) obtaining lithium manganese iron phosphate from the reaction solvent. The preparation method of lithium manganese iron phosphate controls particle morphology and crystal direction of the prepared lithium manganese iron phosphate through a simple process.

Description

TECHNICAL FIELD The present invention relates to a method for producing lithium iron-manganese phosphorus oxide and an olivine-type lithium iron-manganese phosphorus oxide prepared therefrom,

The present invention relates to a process for producing lithium iron-manganese phosphorus oxide (LiMn _x Fe _{1 - x} PO ₄ ) and an olivine-type lithium iron-manganese phosphorus oxide prepared therefrom, which can be easily and safely carried out using a polyol reaction solvent The present invention relates to a process for producing lithium iron-manganese phosphorus oxides and an olivine-type lithium iron-manganese phosphorus oxide prepared therefrom.

As technology development and demand for mobile devices increase, the demand for secondary batteries as energy sources is rapidly increasing. Among such secondary batteries, lithium secondary batteries having a high energy density and voltage, a long cycle life, and a low self-discharge rate are commercially available and widely used.

The conventional lithium secondary battery uses lithium-containing cobalt oxide (LiCoO ₂ ) as a main component of the cathode active material. However, since the lithium-containing cobalt oxide has low stability and high cost, it has been difficult to mass-produce a lithium secondary battery.

In recent years, LiBiPO ₄ and Li (LiFePO ₄₎ , which have a 3.5V voltage vs. lithium, a high bulk density of 3.6 g / cm ³ and a theoretical capacity of 170 mAh / g, (Mn, Fe) PO ₄ cathode active materials have been studied.

Since the cathode active material of the olivine structure is different from the layered system and the spinel type cathode material, the electrochemical characteristics of the lithium ion are limited to the 1D channel, Length) and crystal direction (1D channel direction).

On the other hand, the olivine-based cathode active material has a relatively low electric conductivity as compared with other cathode active materials including lithium. Specifically, in comparison with lithium cobalt oxide (LiCoO ₂ ) having an electric conductivity of 10 ^-4 S / cm and lithium manganese oxide (LiMn ₂ O ₄ ) having an electric conductivity of 10 ^-5 S / cm, olivine type cathode active material ) Has an electric conductivity of 10 ^-9 S / cm which is 10,000 times smaller. Accordingly, in order to improve the low electrical conductivity of the olivine-based cathode active material and to improve the Li conductivity, it is necessary to reduce the length of the Li ion path by making the anode material particles small in the nano-size, A method of forming a conductive layer, for example, a carbon coating layer, and the like have been proposed. In addition, LiMnPO ₄ having a discharge voltage of about 4.2 V compared to LiFePO ₄ having a discharge voltage of 3.4 V level is added to produce a composite oxide (LiFe _x Mn _1-x PO ₄ ), whereby a variety of materials for increasing the energy density of the cathode material Efforts are continuing to develop methods.

In order to solve the above-mentioned problems, the present invention is a simple process in two steps of preparing a lithium iron-manganese phosphorus oxide by using a polyol reaction solvent and then heat-treating the lithium iron-manganese phosphorus oxide. Iron-manganese phosphorus oxide.

Also, in the present invention, an olivine-type lithium iron-manganese phosphorus oxide containing a carbon coating layer on the surface of the particles produced by the above method is to be provided.

In one embodiment to achieve the above object,

(a) preparing a mixed solution by adding a lithium precursor, an iron precursor, a manganese precursor and a phosphorus precursor to a polyol solvent;

(b) charging the mixed solution into an atmospheric pressure reactor and reacting; And

(c) obtaining a lithium iron-manganese phosphorus oxide from the reaction solvent.

The method may further include the step of (d) heat-treating the obtained lithium iron-manganese phosphorus oxide to prepare a carbon-coated lithium iron-manganese phosphorus oxide.

In addition, an embodiment of the present invention provides a lithium iron-manganese phosphorus oxide comprising a carbon coating layer produced by the above method.

Also, in one embodiment of the present invention, there is provided a positive electrode comprising a lithium iron-manganese phosphorus oxide containing the carbon coating layer and a lithium secondary battery comprising the same.

According to the method of the present invention, a carbon-coated lithium iron-manganese phosphorus oxide with controlled particle shape and crystal orientation can be easily produced in a simple and safe manner without using a high-temperature high-pressure reactor. In addition, a lithium secondary battery improved in capacity and stability can be manufactured using the anode comprising the carbon-coated lithium iron-manganese phosphorus oxide.

1 is an electron microscope (SEM) photograph of a lithium iron-manganese phosphorus oxide prepared according to Example 1 of the present invention.
2 is an electron microscope (SEM) photograph of the lithium iron-manganese phosphorus oxide prepared according to Example 2 of the present invention.
3 is an X-ray diffraction (XRD) graph of lithium iron-manganese phosphorus oxide prepared according to Example 2 of the present invention.
4 is an electron microscope (SEM) photograph of the lithium iron-manganese phosphorus oxide prepared according to Comparative Example 1 of the present invention.
Figure 5 shows electron micrograph (SEM) photographs of carbon coated lithium iron-manganese phosphorus oxides prepared according to Example 3 of the present invention.
6 is an electron micrograph (SEM) photograph of a carbon coated lithium iron-manganese phosphorus oxide prepared according to Example 4 of the present invention.
7 is a graph showing the lattice constants of the lithium iron-manganese phosphorus oxides prepared in Examples 2 to 4 according to the content of manganese.

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

The terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms and the inventor may appropriately define the concept of the term in order to best describe its invention It should be construed as meaning and concept consistent with the technical idea of the present invention.

Conventionally, solid-state reaction and sol-gel were used to synthesize lithium iron-manganese phosphorus oxide (LiMn _x Fe _1-x PO ₄ ). Since the oxidation number of iron and manganese in the lithium iron-manganese phosphorus oxide is divalent, there is a difficulty in maintaining a reducing atmosphere in the synthesis of lithium iron-manganese phosphorus oxide. That is, in the solid-phase method, even if a reducing agent is added, oxygen must be maintained at 1012 ppm or less, and the dissolved oxygen must be lowered similarly in a liquid phase method based on an aqueous solution. However, in the present invention, since a polyol solvent which is a nonaqueous solvent liquid is used as a reaction solvent, the oxidation problem can be solved without the use of a reducing agent by synthesizing under a boiling point. In addition, unlike the hydrothermal synthesis method and the conventional glycothermal method, the carbon-coated lithium iron-manganese phosphorus having uniform particle shape and crystal orientation can be easily synthesized by a simple and safe method without using a high-temperature high-pressure reactor have.

Specifically, in one embodiment of the present invention

(a) preparing a mixed solution by adding a lithium precursor, an iron precursor, a manganese precursor and a phosphorus precursor to a polyol solvent;

(b) charging the mixed solution into an atmospheric pressure reactor and reacting; And

(c) obtaining a lithium iron-manganese phosphorus oxide from the reaction solvent.

The method may further include the step of (d) heat-treating the obtained lithium iron-manganese phosphorus oxide to prepare a carbon-coated lithium iron-manganese phosphorus oxide.

Hereinafter, the present invention will be described in detail by steps.

The mixed solution preparation step (step a)

First, a lithium precursor, an iron precursor, a manganese precursor and a phosphor precursor are prepared and put into a polyol reaction solvent to prepare a uniform mixed solution.

The lithium precursor is lithium acetate dihydrate (CH ₃ COOLi.H ₂ O), lithium hydroxide monohydrate (LiOH.H ₂ O), lithium hydroxide (LiOH), lithium carbonate (Li ₂ CO ₃ ) , Lithium phosphate (Li ₃ PO ₄ ), lithium phosphate dodecahydrate (Li ₃ PO ₄ .2H ₂ O), and lithium oxalate (Li ₂ C ₂ O ₄ ) .

The iron precursor that is introduced is citric acid ferric _{(FeC 6 H 5 O 7)} , citric acid iron (III) hydrate _{(FeC 6 H 5 O 7 ·} nH 2 O), ferrous sulfate heptahydrate (FeSO ₄ · H ₂ O ) oxalate, iron dihydrate _{(FeC 2 O 4 · H 2} O), iron acetylacetonate _{(Fe (C 5 H 7 O} 2) 3), ferric phosphate dihydrate (FePO ₄ · H ₂ O) and hydroxide And ferric iron (FeO (OH) 2).

The input manganese precursor may be selected from the group consisting of manganese acetate tetrahydrate, magnesium nitrate hexahydrate, manganese (IV) oxide, and manganese (II) sulfate pentahydrate), or a mixture of two or more thereof.

The precursor is introduced is tri-ammonium phosphate trihydrate _{((NH 4) 3 PO 4} · H 2 O), ammonium phosphate _{((NH 4) 2 HPO 4} ), ammonium dihydrogen phosphate (NH ₄ H ₂ PO ₄ ), And phosphoric acid (H ₃ PO ₄ ).

In the present invention, when the mixing ratio of the iron precursor and the manganese precursor is 1, the mixing ratio of the iron precursor and the manganese precursor is 0.1 to 0.9: 0.1 to 0.9, respectively, And manganese precursor in a molar ratio of about 0.9 to about 1.5 based on the sum of the manganese precursor and the manganese precursor. The lithium precursor may be added in a ratio of 2 to 5 mol based on the manganese precursor.

Specifically, the molar ratio of the lithium precursor: iron precursor: manganese precursor and phosphorus precursor is 1: 2.3 to 0.2: 0.8: 0.2 to 0.8: 1, wherein the molar ratio of the manganese precursor: lithium precursor is 1: 2 to 5 . More specifically, the molar ratio of the lithium precursor: iron precursor: manganese precursor and phosphorus precursor may be 1: 0.8: 0.2: 1, 2.3: 0.2: 0.8: 1 or 2.25: 0.5: 0.5: 1.

When the molar ratio of the lithium precursor: iron precursor: manganese precursor and phosphorus precursor is 1: 2.3 to 0.2: 0.8: 0.2 to 0.8: 1, the charging ratio of the manganese precursor: lithium precursor is 1: 2 to 5 When the manganese precursor: lithium precursor is introduced at a ratio of 1: 1.5 or less, a manganese precursor, for example, tetraphosphates in which H ₂ O present in Mn (CH ₃ COO) ₂ .4H ₂ O is present in the solution, And reacts with anions to give H ⁺ ions as shown in Reaction Scheme 1 below.

P ₄ O ₁₂ ^{4 -} + 12H ₂ O? 4PO ₄ ^{3 -} + 8H ₃ O ⁺ (Scheme 1)

As described above, the acetate groups present in the H ⁺ and manganese precursors generated through the above reaction scheme 1 affect the pH of the solvent and lower the overall pH, so that it is difficult to form uniform sized particles.

If the ratio of the lithium precursor to the manganese precursor is within the above range, the -OH group of the lithium precursor introduced in an excessively large amount reacts with the H ⁺ ion from the above reaction formula 1 to exist in the H ⁺ or manganese precursor The effect on the pH of the solvent is insignificant, so that a uniform plate-like lithium iron-manganese phosphorus oxide can be synthesized.

When the amount of the polyol solvent to be used is 1 part by weight, the iron precursor may be added in an amount of about 0.005 to 10 parts by weight, and the lithium precursor, the manganese precursor, and the phosphorus precursor may be added to the molar portion corresponding to the iron precursor . ≪ / RTI >

In the preparation of the mixed solution, the method may further include stirring the lithium, iron, manganese, and phosphorus precursors so as to be uniformly dispersed in the polyol solvent.

On the other hand, in the present invention, the polyol solvent can be used as a nonaqueous solution for butanediol, which is a solvent having a relatively high boiling point. Typical examples of the polyol solvent include 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2-butanediol, , 2,3-butanediol, and isomers thereof. [0035]

The 1,2-butanediol has a boiling point of about 195 ° C, the 1,3-butanediol has a boiling point of about 204 ° C, the 1,4-butanediol has a boiling point of about 235 ° C, Lt; / RTI >

The reaction step (step b)

Next, the mixed solution is charged into the reactor and allowed to react. In this step, an amorphous lithium iron-manganese phosphorus oxide is produced.

The reactor may be a reactor commonly used in the art to produce lithium iron-manganese phosphorus oxides, and the kind thereof is not particularly limited. For example, an open reactor or an enclosed reactor.

The step (b) may be conducted at a temperature below the boiling point of the reaction solvent used under the pressure of 10 bar or less, for example, a temperature range of 120 to 235 ° C, and may be conducted for 0.1 to 48 hours.

In one embodiment of the present invention, when 1,4-butanediol is used as the reaction solvent, the step (b) may be carried out at a temperature of 120 to 235 ° C for 0.1 to 24 hours, more specifically, 150 to 235 Lt; 0 > C for 1 hour to 5 hours.

On the other hand, it has been confirmed that lithium iron-manganese phosphorus oxides can be synthesized at a temperature of about 150 ° C or higher. Specifically, in the present invention, when the polyol solvent is used for the synthesis of the lithium iron-manganese phosphorus oxide, the reaction can proceed at a temperature not higher than the boiling point of the reaction solvent (235 ° C) The degree of vaporization is reduced. As a result, the pressure rise due to the solvent vaporized during the course of the reaction is very small compared with the conventional hydrothermal synthesis method. This improves the overall safety of the process.

In addition, since the polyol solvent that can be used is a non-aqueous solution, there is an advantage that the problem of oxidation of iron can be solved even without using a reducing agent.

The step of obtaining (step c)

Meanwhile, in order to obtain the lithium iron-manganese phosphorus oxide prepared in the step (b), one or more steps selected from a cooling step, a washing step and a drying step are carried out.

For example, the nanoside particles may be first cooled and then washed sequentially using acetone and methanol.

In addition, the washed nanoside particles may be subjected to a drying step. The drying method in the drying step is not particularly limited. For example, the drying may be performed at a temperature of 20 to 160 ° C for 2 to 40 hours.

The heat treatment step (step d)

In one embodiment of the present invention, the lithium iron-manganese phosphorus oxide prepared by the above method may be heat-treated to prepare a lithium iron-manganese phosphorus oxide containing a carbon coating layer.

That is, when the lithium iron-manganese phosphorus oxide (c) obtained through the step (c) is heat-treated under an inert atmosphere (d), a lithium iron-manganese phosphorus oxide coated with part or all of carbon on the particle surface can be produced.

The heat treatment may be performed by heating to a temperature range of 400 ° C to 900 ° C, and the heat treatment time is not particularly limited, but may be, for example, within 0.5 to 5 hours.

Meanwhile, the heat treatment step may be performed under an inert atmosphere, for example, under argon (Ar) or nitrogen (N ₂ ) atmosphere.

Also, in the step (d), the lithium iron-manganese phosphorus oxide not crystallized by the step (b) may be crystallized by the heat treatment.

At the same time as the crystallization, a carbon coating layer is formed on a part or all of the surface of the formed particles.

In detail, the precursor of the carbon coating layer can be used for the used reaction day, which remains on the particle surface. Particularly, the reaction solvent used may remain partially on the surface of the particles even after the drying step, and they are carbonized through a heat treatment process in a temperature range of 400 ° C to 900 ° C to form a carbon coating layer on the particle surface.

On the other hand, the organic material of the remaining polyol solvent can be carbonized at the time of heat treatment (baking) without using a conductivity imparting agent (carbon black) or the like as a precursor of the carbon coating layer to form a uniform coating layer.

Further, a separate organic compound may be used in order to enhance the coating efficiency, and the step of introducing the separate organic compound to form a carbon coating layer on the surface of lithium iron-manganese oxide particles is not particularly limited.

In one embodiment of the present invention, the organic compound may be added together with a lithium precursor, an iron precursor, and a phosphorus precursor in a solvent to prepare a mixed solution.

In still another embodiment, the lithium iron-manganese phosphorus oxide may be added after the washing and drying steps, or may be added during the heat treatment of step (d).

The organic compound is not particularly limited and includes, for example, 1 or 2 selected from the group consisting of glucose, sucrose, galactose, proctose, lactose, starch, mannose, ribose, aldohexose, kedohexose, It may be a mixture of two or more.

On the other hand, the organic compound may be added in an amount of 0.1 to 5 wt% based on the total weight of the lithium iron-manganese phosphorus oxide, and when added in excess of the above range, the carbon coating layer may be unnecessarily thickened There is a problem.

The carbon coating layer formed on the surface of the lithium iron-manganese phosphorus oxide produced through the above step may have a thickness of 10 nm or less, for example, 1 to 5 nm.

Since the lithium iron-manganese phosphorus oxide has a low electrical conductivity, the carbon coating layer is formed on a part or the whole surface of the produced fine lithium iron-manganese phosphorus oxide, There is an effect to supplement.

The lithium iron-manganese phosphorus oxide synthesized through the series of steps has an olivine structure, and a carbon coating layer is formed on part or all of the surface of the particles.

On the other hand, the particle diameter and particle size distribution of the lithium iron-manganese phosphorus oxide produced can be controlled by varying the reaction temperature and the reaction time of the step (b) and the kind of the lithium precursor, iron precursor and phosphorus precursor. Can be controlled through the heat treatment temperature and the heat treatment time in the step (c). Generally, when the heat treatment temperature is high or the heat treatment time is long, the particles become large.

The carbon-coated lithium iron-manganese phosphorus oxide produced by the heat treatment process may have an average secondary particle diameter of 30 to 300 nm and an average particle size distribution of 50% or less.

Implementation of lithium secondary battery

In addition, the present invention can provide a cathode active material comprising the lithium iron-manganese phosphorus oxide having the olivine crystal structure. The cathode active material may further include a conductive material, a binder, a filler, and the like in addition to the lithium iron-manganese phosphorus oxide.

The 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 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 conductive material may be typically contained in an amount of 1 to 30% by weight based on the total weight of the mixture including the cathode active material.

The binder is not particularly limited as long as it is a component that assists in bonding between the active material and the conductive material and bonding to the current collector. Examples of the binder include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, Polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber, fluorocarbon rubber, various types of airborne polystyrene, And the like.

The binder may typically comprise from 1 to 30% by weight, based on the total weight of the mixture comprising the cathode active material.

The filler may be selectively used as a component for suppressing the expansion of the electrode, and is not particularly limited as long as it is a fibrous material that does not cause chemical change in the battery. Examples of the filler include olefin polymers such as polyethylene and polypropylene; Fibrous materials such as glass fiber, carbon fiber and the like can be used.

Also, in an embodiment of the present invention, there is provided a positive electrode for a lithium secondary battery in which the positive electrode active material is coated on a current collector.

The positive electrode for a lithium secondary battery can be prepared, for example, by dissolving the positive electrode active material in a solvent to prepare a slurry, applying the slurry on a collector, followed by drying and rolling.

The positive electrode current collector is not particularly limited as long as it has conductivity without causing chemical changes in the battery. For example, carbon, nickel, titanium, , Silver or the like may be used.

On the other hand, the collector may have a thickness of 3 to 500 탆, and fine unevenness may be formed on the surface of the current collector to increase the adhesion of the cathode active material. For example, it can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric.

Also, in an embodiment of the present invention, a lithium secondary battery comprising a positive electrode containing the positive electrode active material, a negative electrode, a separator, and a non-aqueous electrolyte containing a lithium salt may be provided.

The negative electrode is prepared, for example, by coating a negative electrode mixture containing a negative electrode active material on a negative electrode collector and then drying the mixture. The negative electrode mixture may contain a conductive material, a binder, a filler ≪ / RTI >

The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. For example, the negative electrode current collector may be formed on the surface of copper, stainless steel, aluminum, nickel, titanium, sintered carbon, Carbon, nickel, titanium, silver or the like, aluminum-cadmium alloy, or the like may be used.

On the other hand, the current collector may have a thickness of 3 to 500 탆, and similarly to the positive electrode collector, fine concavity and convexity may be formed on the current collector surface to enhance the bonding force of the negative electrode active material. For example, it can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric.

The separation membrane is interposed between the anode and the cathode, and an insulating thin film having high ion permeability and mechanical strength can be used.

The pore diameter of the separator is generally 0.01 to 10 mu m, and the thickness may be generally 5 to 300 mu m.

The separation membrane may be, for example, an olefin-based polymer such as polypropylene, which is chemically resistant and hydrophobic; A sheet or nonwoven fabric made of glass fiber, polyethylene, or the like can be 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 nonaqueous electrolyte solution is composed of an electrolyte solution and a lithium salt. As the electrolyte solution, a nonaqueous organic solvent or an organic solid electrolyte may be used.

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 derivatives, Tetrahydrofuran derivatives, ether, 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, Polymers containing ionic dissociation groups, and the like 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 C 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) 2 NLi, chloroborane lithium, lower aliphatic carboxylic acid lithium, 4-phenyl lithium 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, 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.

As described above, the carbon-coated lithium iron-manganese phosphorus oxide production method of the present invention is capable of producing a lithium iron-manganese phosphorus oxide by the use of a novel reaction solvent as a nonaqueous solution and, in comparison with the conventional hydrothermal synthesis method, It is possible to easily produce a lithium iron-manganese phosphorus having a uniform particle size and controlled particle size distribution while securing the safety and economy of the process without using a high-temperature / high-pressure reactor. have.

In addition, a lithium iron-manganese phosphorus oxide having a controlled particle size and particle size distribution can be prepared by a simple two-step process in which nano-seed particles are first prepared and then heat-treated, and at the same time, a carbon coating layer So that the process is economical and has an advantage in mass production. In addition, the lithium iron-manganese phosphorus oxide prepared by the above method is industrially useful because it improves the characteristics as a cathode active material by supplementing the insufficient electric conductivity.

Example

Hereinafter, the present invention will be described in detail by way of examples with reference to the following examples. However, the embodiments according to the present invention can be modified into various other forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. The embodiments of the present invention are provided to enable those skilled in the art to more fully understand the present invention.

(Example 1)

(H ₃ PO ₄ ), lithium hydroxide (LiOH), ferric citrate (FeC ₆ H ₅ O ₇ .nH ₂ O), manganese acetate ((CH ₃ COO) ₂ Mn · 4H ₂ O) (Butanediol) in the ratio of 1: 0.8: 0.2: 1 molar ratio (manganese precursor: lithium precursor molar ratio 1: 5) based on the weight of the starting material (0.05 mol). The mixed solution sufficiently stirred was put into a 500 ml atmospheric pressure reactor and reacted at 190 ° C for 24 hours.

After completion of the reaction, the remaining reaction solution was cooled, and washed successively with acetone and methanol. After the washing, the product was dried with a vacuum drier. The reaction product obtained after the washing / drying was analyzed using an electron microscope. As a result, it was confirmed that the reaction product was a lithium iron-manganese phosphorus oxide having a uniform (particle size) size of 50 nm to 100 nm 1).

(Example 2)

The lithium iron-manganese phosphorus oxide obtained in Example 1 was heat-treated at 600 ° C for 2 hours in an argon (Ar) atmosphere furnace. The product obtained by the heat treatment was analyzed using an electron microscope. As a result, it was confirmed that a carbon-coated lithium iron-manganese phosphorus oxide composed of uniform particles (see FIG. 2) having a diameter of 50 nm formed with a carbon coating layer of several nm was obtained .

Further, the reaction product was analyzed by X-ray diffraction spectroscopy. As shown in FIG. 3, it was confirmed that the (020) crystal plane in which Li ions migrate in the olefin structure is more dominant than the other crystal directions. (The peak intensity ratio of XRD is I ₍₀₂₀₎ / I ₍₂₀₀₎ = 4.25)

(Comparative Example 1)

Except that the molar ratio of lithium precursor: manganese precursor: phosphoric precursor was 1: 0.2: 0.8: 1 (manganese precursor: molar ratio of lithium precursor = 1: 1.25) in the production process of Example 1 Lithium iron-manganese phosphorus oxide was prepared in the same manner as in Example 1. Thereafter, the reaction product obtained after washing / drying was analyzed using an electron microscope. As a result, it was confirmed that the reaction product was a plate-shaped lithium iron-manganese phosphorus oxide having a non-uniform size ranging from 50 nm to 40 nm 4).

(Example 3)

Except that the molar ratio of lithium precursor: iron precursor: manganese precursor: phosphate precursor was 2.3: 0.2: 0.8: 1 (molar ratio of manganese precursor: lithium precursor = 1: 2.875) -Manganese phosphorus oxide, the obtained lithium iron-manganese phosphorus oxide was heat-treated at 600 ° C for 2 hours in an argon (Ar) atmosphere furnace. In Comparative Example 1, the ratio of iron to manganese to lithium was 1, while in Example 3, the ratio of iron to manganese to lithium was about 2.3.

After the completion of the reaction, the obtained product was analyzed by an electron microscope. As a result, the reaction product was found to have a lithium iron-manganese phosphorus oxide having a uniform (particle size) size of 100 nm to 150 nm in which a carbon coating layer of several nm was formed (See Fig. 5).

At this time, the -OH group of the lithium precursor (LiOH), which is excessively added to Comparative Example 1, reacts with the H ⁺ ion from the Reaction Scheme 1 to prevent the pH of the solvent from becoming too low and uniform nano- - contributed to the synthesis of manganese phosphorus oxide.

(Example 4)

 Lithium iron (II) was prepared in the same manner as in Example 3, except that the molar ratio of lithium precursor: iron precursor: manganese precursor: phosphate precursor was 2.25: 0.5: 0.5: 1 (manganese precursor: lithium precursor molar ratio: - manganese phosphorus oxide was prepared.

After the completion of the reaction, the obtained product was analyzed using an electron microscope. As a result, the reaction product was found to have a uniform (particle size) lithium iron-manganese phosphorus oxide of 50 nm to 100 nm in which a carbon coating layer of several nm was formed (See Fig. 6).

7 shows the lattice parameter of the lithium iron-manganese phosphorus oxide prepared in Example 2 (FIG. 7A), Example 3 (FIG. 7B) and Example 4 (FIG. 7C) ) Were calculated based on XRD refinement and plotted.

As can be seen from the above Examples and Comparative Examples, the lithium iron-manganese phosphorus oxide produced according to the method of the present invention has a small particle size and uniformity, and can control the particle shape and crystal orientation. Therefore, in the case of a cathode active material containing the same, it is considered that the lithium iron phosphate has a contrast energy density.

Claims (18)

(a) preparing a mixed solution by adding a lithium precursor, an iron precursor, a manganese precursor and a phosphorus precursor to a polyol solvent;
(b) charging the mixed solution into an atmospheric pressure reactor and reacting; And
(c) obtaining a lithium iron-manganese phosphorus oxide from the reaction solvent.
The method according to claim 1,
The method further comprises, after step (c), (d) heat treating the obtained lithium iron-manganese phosphorus oxide to produce a carbon-coated lithium iron-manganese phosphorus oxide. Gt;
The method according to claim 1,
The lithium precursor is a single substance selected from the group consisting of lithium acetate dihydrate, lithium hydroxide monohydrate, lithium hydroxide, lithium carbonate, lithium phosphate, lithium phosphate dodecahydrate and lithium oxalate, or a mixture of two or more thereof ≪ / RTI > wherein the lithium iron-manganese phosphorus oxide is produced by a method comprising:
The method according to claim 1,
Wherein the iron precursor is selected from the group consisting of ferric citrate, ferric citrate ferric sulfate, ferrous sulfate heptahydrate, iron oxalate dihydrate, ferrous acetylacetonate, ferric phosphate dibasic and ferric hydroxide, or 2 Wherein the lithium iron-manganese phosphorus oxide is a mixture of two or more kinds of lithium iron-manganese phosphorus oxides.
The method according to claim 1,
Wherein the manganese precursor is a single substance selected from the group consisting of manganese acetate tetrahydrate, manganese nitrate hexahydrate, manganese oxide and manganese sulfate pentahydrate or a mixture of two or more thereof.
The method according to claim 1,
Wherein the phosphorus precursor is a single substance selected from the group consisting of tri-ammonium phosphate trihydrate, ammonium phosphate, ammonium dihydrogen phosphate, and phosphoric acid, or a mixture of two or more thereof.
The method according to claim 1,
The molar ratio of the lithium precursor: iron precursor: manganese precursor: phosphorus precursor is 1: 2.3: 0.2 to 0.8: 0.2 to 0.8: 1, wherein the molar ratio of the manganese precursor: lithium precursor is 1: 2 to 5 ≪ / RTI > wherein the lithium iron-manganese phosphorus oxide is produced by a method comprising:
The method of claim 7,
Wherein the molar ratio of the lithium precursor to the iron precursor to the manganese precursor to the phosphorus precursor is 1: 0.8: 0.2: 1, 2.3: 0.2: 0.8: 1 or 2.25: 0.5: 0.5: Gt;
The method according to claim 1,
The polyol solvent is selected from the group consisting of 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol (2 , 3-butanediol), and isomers thereof. 2. The process for producing lithium iron-manganese dioxide according to claim 1,
The method according to claim 1,
Wherein the step (b) is carried out at a temperature below the boiling point of the polyol solvent under a pressure of 10 bar or less.
The method according to claim 1,
Wherein the step (b) is carried out at a temperature of 120 ° C to 235 ° C for 0.1 to 48 hours.
The method according to claim 1,
The method for producing lithium iron-manganese phosphorus oxide according to claim 1, wherein the step (c) further comprises at least one step selected from a cooling step, a washing step and a drying step.
The method of claim 2,
Wherein the heat treatment step (d) is performed in an inert atmosphere at a temperature ranging from 400 ° C to 900 ° C within 0.5 to 5 hours.
A carbon coated lithium iron-manganese phosphorus oxide prepared by the method of claim 2.
15. The method of claim 14,
The carbon coated lithium iron-manganese phosphorus oxide as claimed in claim 1, wherein the thickness of the carbon coating layer is 10 nm or less.
The method of claim 14,
Wherein the lithium iron-manganese phosphorus oxide containing the carbon coating layer has an average particle diameter of 30 to 300 nm.
A cathode active material comprising a carbon-coated lithium iron-manganese phosphorus oxide according to claim 14,
Optionally further comprising at least one selected from a conductive material, a binder and a filler.
A lithium secondary battery comprising a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and a nonaqueous electrolyte solution containing a lithium salt,
And the positive electrode comprises the positive electrode according to claim 17.

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