KR101567625B1 - Method for preparing metal oxide having olivine structure - Google Patents

Abstract

More particularly, the present invention relates to a process for producing an olivine structure metal oxide which is doped with a transition metal such as Ni or Ti to improve electrical conductivity, rate characteristics and output characteristics, And to an olivine-structured metal oxide produced by such a method.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a metal oxide,

More particularly, the present invention relates to a process for producing an olivine structure metal oxide which is doped with a transition metal such as Ni or Ti to improve electrical conductivity, rate characteristics and output characteristics, And to an olivine-structured metal oxide produced by such a method.

As technology development and demand for mobile devices increase, the demand for secondary batteries as energy sources is rapidly increasing. Among these secondary batteries, a lithium secondary battery having a high energy density and voltage, a long cycle life, and a low self-discharge rate has been commercialized and widely used. In addition, as the interest in environmental issues grows, researches on electric vehicles and hybrid electric vehicles that can replace fossil fuel-based vehicles such as gasoline vehicles and diesel vehicles, which are one of the main causes of air pollution, . In recent years, studies on the use of lithium secondary batteries having high energy density and discharge voltage as power sources for electric vehicles and hybrid electric vehicles have been actively conducted, and some of them are in the commercialization stage.

Particularly, in the development of a cathode material for a large-capacity lithium secondary battery for an electric vehicle, various studies are being conducted to replace LiCoO ₂ which is currently used, and recently, olivine-structured phosphoric oxide has been attracting attention. Particularly, LiFePO ₄ having an olivine structure using Fe has been widely used as a cathode active material using Fe having excellent safety and low cost. Currently, such LiFePO ₄ As a method for producing the positive electrode material, a hydrothermal synthesis method and a supercritical method are mainly used.

However, since the phosphoric acid oxide of the olivine structure itself is largely lacking in electric conductivity, it is general to use a surface-coated conductive material such as carbon and thus, although low-cost Fe is used as a transition element, And the like, which causes the material cost to increase. Furthermore, despite the above-mentioned conductive material (carbonaceous material) coating, the rate characteristics and the output characteristics of the cathode active material using the phosphoric acid oxide of the olivine structure are not very improved. In order to solve this problem, studies have been made on a phosphoric acid oxide (hereinafter also referred to as "doped-LFP") having an olivine structure in which a transition metal element such as Li and Ti is doped in LiFePO _4. However, Development efforts on methods are minimal.

Accordingly, there is a need to develop a new method for efficiently producing doped-LFP, which is a cathode material having excellent electrical conductivity, rate characteristics, and output characteristics.

Korean Patent Publication No. 10-2010-0029501

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems and conventional problems, and it is a technical object to provide a method for efficiently manufacturing doped-LFP.

In order to achieve the above technical object,

The present invention provides a process for preparing an olivine structure metal oxide represented by the following general formula (1), characterized by using a polyol process:

Li _x M _y Fe _{1 - y} X _w O ₄

X is at least one selected from the group consisting of P, Si, S, As, Sb, Bi, and combinations thereof, and 0.9? X 0.1, 0 < y < 1, and 0.9? W?

According to another aspect of the present invention, there is provided an olivine structure metal oxide represented by Formula 1, which is produced by the above method.

According to still another aspect of the present invention, there is provided a positive electrode active material including the olivine structure metal oxide, a positive electrode, and a lithium secondary battery.

The olivine structure metal oxide prepared according to the present invention can greatly improve the output characteristics and the rate characteristics of the cathode active material including the carbonaceous material even when the carbonaceous material is not coated or only a small amount of carbonaceous material is coated. The content of the positive electrode active material is relatively increased, and thus the positive electrode active material exhibiting a higher capacity can be provided.

In addition, the production method of the present invention can produce the olivine structure metal oxide at a low temperature without being subjected to a high-temperature calcination process, and the production cost thereof is greatly reduced, and the produced particles have a uniform nanostructure , And may exhibit desirable electrical conductivity even without a coating of a bar material that exhibits very good dispersibility of the doped transition metal (e.g., Ni or Ti).

In addition, the lithium secondary battery according to the present invention can provide a middle- or large-sized lithium secondary battery which can satisfactorily meet the requirements of output characteristics, capacity, and safety required when used as a power source for an electric vehicle or the like.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a flow chart showing a process for producing an olivine structure metal oxide according to the present invention.
2 is a graph showing discharge capacity test results of lithium secondary batteries according to Examples and Comparative Examples.
3 is a graph showing a rate characteristic test result of a lithium secondary battery according to Examples and Comparative Examples.

Hereinafter, the present invention will be described in detail.

The present invention relates to a process for preparing an olivine structure metal oxide (doped-LFP) represented by the following general formula (1), characterized by using a polyol process.

Li _x M _y Fe _{1 - y} X _w O ₄

M is at least one selected from transition metal elements other than Fe (for example, Ni, Ti, Co, Mn, Cr, Zr, Nb, Cu, V, Mo, W, (Wherein x is an integer of 1 or more), 0 < y < 1 (preferably, 0 or 1), Si, S, As, Sb, Bi, <y? 0.2), and 0.9? w? 1.1 (preferably, w = 1).

Specifically, the olivine structure metal oxide may be an olivine structure phosphoric oxide represented by the following formula (2), more specifically, an olivine structure phosphoric oxide represented by the following formula (3).

LiM _x Fe _{1 - x} PO ₄

In Formula 2, M is at least one selected from transition metal elements other than Fe, and 0 < x < 1.

LiM _y Fe _{1 - y} PO ₄

In Formula 3, M is at least one selected from Ni and Ti, and 0 < y? 0.2 (preferably 0 < y? 0.1).

The olivine structure phosphoric acid oxide has a high capacity and a stable crystal structure, and the cost is also low, and has recently attracted attention as a cathode material. In particular, it is widely used LiFePO ₄ (hereinafter also referred to as "LFP") having a relatively low charging potential stable crystal structure in order to ensure the discharge of the output from 3V gamut.

The LFP has a strong covalent bond with (PO ₄ ) ^3- and has excellent thermal stability and has a high discharge capacity having an average theoretical capacity of about 170 mAh / g. In addition, the discharge capacity And the standard reduction potential is 3.4V, so that the energy density can be maintained stably without being high enough to cause a side reaction such as decomposition of the electrolyte.

However, the LFP has low electrical conductivity, low diffusion rate of lithium ions, and low energy density, so that it is difficult to increase the energy of a cell using the LFP. In order to solve such a problem of the LFP, a conductive carbonaceous material is coated and used. However, there is a limit to the amount of the carbonaceous material that can be coated for high capacity and low cost of the battery. And the electrical conductivity of LiFePO ₄ is not yet satisfactory.

By doping a part of iron (Fe) in the LFP with other transition metal elements such as nickel (Ni) and titanium (Ti), excellent electrical conductivity is exhibited without coating of carbon materials, and output characteristics and rate characteristics It is possible to provide a further improved doped phosphorus (doped-LFP).

Here, the content of the doped Ni and Ti may be in the range of 20 wt% or less, preferably 0.5 to 10 wt%, based on the total amount of the transition metal. If the doping amount exceeds 20% by weight, it may be difficult to obtain a desired level of improvement in electric conductivity because the degree of dispersion of the transition metal element in the compound affects the electrical conductivity. That is, when the doping amount of Ni and Ti is more than 20% by weight, the dispersibility of Ni and Ti in the LFP is lowered, thereby making it difficult to improve the electric conductivity of the iron oxide. When the content of doped Ni and Ti is about 0.5 to 10% by weight, the dispersibility of the phosphoric acid iron oxide is the best, and thus, the olivine structure phosphoric acid iron oxide has the highest electrical conductivity.

The doped-LFP represented by the above formula (1) has excellent electrical conductivity and can exhibit a desired level of electrical conductivity even when a carbon material having a conductivity is not coated or coated with less than a conventional coating amount. It is possible to provide an excellent, inexpensive and high capacity cathode active material. Further, using the above-mentioned doped-LFP and a conventional carbon-based coating, it is possible to obtain further improved electric conductivity and output characteristics.

In one embodiment, the method of the present invention comprises the steps of: preparing a mixed solution of a transition metal compound, a phosphate ion compound, and a lithium compound in a polyol solvent; And a step of reacting the mixed solution in a reflux apparatus to obtain a product having a nanocrystal structure represented by the following formula (2), and a heat treatment step of the obtained reaction product is not required .

LiM _x Fe _{1 - x} PO ₄

In Formula 2, M is at least one selected from transition metal elements other than Fe, and 0 < x < 1.

In the case of using a conventional sol-gel method in order to obtain a uniform and uniform particle distribution of nanostructured particles and to improve the dispersibility of the doped transition metals, a process of heat treatment at a high temperature is required to synthesize a high- . Therefore, the synthesis process becomes complicated and costly, and the growth of particles may be accompanied by a decrease in electrical conductivity.

Accordingly, in the present invention, the electric conductivity of the doped-LFP can be further enhanced by not performing the heat treatment process based on the polyol process. Meanwhile, as described above, the doped-LFP according to the present invention is characterized in that the doped-LFP is produced by a liquid phase reduction process called a polyol process, but does not necessarily exclude a solid state reaction. As one example of the solid-phase reaction _{method, Li 2 CO 3 + FeC 2} O 4 · H 2 O + Ni (OH) 2 + (NH 4) wet ball milling a mixture of ₂ HPO ₄ for about 24 hours (Wet Ball Milling) The doped-LFP can be prepared by drying in a vacuum oven (120 ° C.) through a sieving (150 μm), followed by heat treatment (700 ° C. for 6 hours, 5 ° / min, in Ar).

In another embodiment, the method of manufacture of the present invention may further comprise the step of washing the mixed solution in acetone after obtaining the result. At this time, the step of cleaning the mixed solution may further include filtering the resultant and drying the resultant.

The polyol solvent may be at least one selected from the group consisting of EG (ethylene glycol), DEG (diethylene glycol), TEG (triethylene glycol), and TTEG (tetraethylene glycol).

As the transition metal compound, at least one selected from the group consisting of an Fe-based compound, a Ni-based compound and a Ti-based compound can be used.

As the Fe-based compound, at least one selected from the group consisting of Fe (CH ₃ COO) ₂ , Fe (NO ₃ ) ₂ , FeC ₂ O ₂ , FeSO ₄ , FeCl ₂ , FeI _2, and FeF ₂ , As the compound, at least one selected from the group consisting of Ni (CH ₃ COO) ₂ , Ni (NO ₃ ) ₂ , NiC ₂ O ₂ , NiSO ₄ , NiCl ₂ , NiI ₂ and NiF ₂ , TiH _2, and TTIP may be used, but the present invention is not limited thereto.

The phosphoric acid ionic compound may be at least one selected from the group consisting of NH ₄ H ₂ PO ₄ , H ₃ PO ₄ , (NH ₄ ) ₂ HPO ₄ and (NH ₄ ) ₃ PO ₄ , It is not.

The lithium-based compound is used as a lithium precursor. For example, at least one selected from the group consisting of CH ₃ COOLi, LiOH, LiNO ₃ , LiCO ₃ , Li ₃ PO ₄ and LiF may be used, It is not.

In one embodiment, the step of reacting the mixed solution in a reflux apparatus to obtain a product having a nanocrystal structure is performed by heating the mixed solution at a boiling point (for example, 250 to 350 ° C) of the polyol solvent . Particularly, when the polyol solvent is TTEG, it is appropriate that the mixed solution is heated to 250 to 350 ° C to react. On the other hand, in the reflux apparatus, the reaction can be carried out for, for example, 1 to 72 hours.

Hereinafter, a method of preparing doped-LFP using the polyol process of the present invention will be described in more detail.

First, a polyol solvent is prepared, and a mixed solution obtained by mixing a transition metal compound, a phosphate ion compound, and a lithium compound in the polyol solvent is prepared.

As used herein, the term "polyol" refers to a material having two or more OH groups in the molecule. The polyol acts not only as a solvent and a stabilizer in the production process, but also prevents particle growth and prevents aggregation of particles. In addition, the polyol solvent plays an important role in maintaining the oxidation number of the transition metal because it produces a reducing atmosphere in terms of breaking.

As the polyol solvent, the transition metal compound, the phosphate ion compound and the lithium compound, the above-mentioned kinds of compounds can be used.

Subsequently, the mixed solution is reacted in a reflux apparatus to obtain a resultant product.

The reflux apparatus includes a heating part, a magnetic stirrer, a part for preventing evaporation of a solvent through a condenser, and a round flask. The mixed solution is heated to the boiling point of the polyol solvent in the round flask of the reflux apparatus to effect the reaction. The reaction time is suitably maintained for about 1 to 72 hours.

In the present invention, the mixed solution is reacted in the reflux apparatus. However, the present invention is not limited to this, and the reaction can be performed using various apparatuses. For example, the reaction may be carried out in a beaker under atmospheric pressure, or may be carried out using a reactor equipped with a condenser for recovering the polyol solvent to be evaporated.

A doped-LFP product having a nanocrystal structure can be obtained by the above-described production method.

If necessary, after the resultant is obtained, the mixed solution may be washed and reacted to remove remaining polyol solvent or an organic compound that may be formed additionally. The cleaning process may be performed in acetone and is preferably repeated several times until all the remaining polyol solvent or organic compound is removed.

The process may further include filtering the resultant from the mixed solution, and then drying the resultant in a vacuum oven.

As described above, the doped-LFP having a nanocrystal structure can be synthesized at low temperatures without subjecting to a high temperature baking process only by reacting the mixture with a polyol solvent, and the cost is also reduced.

In the doped-LFP of the present invention produced by such a synthesis process, the particles are homogeneous and have a nanostructure with a diameter of 10 to 50 nm, and the dispersibility of the doped transition metal (for example, Ni or Ti) , And can exhibit desirable electrical conductivity even without a coating of carbonaceous material.

Also, the present invention provides a cathode active material comprising the doped-LFP of Formula 1 prepared by the above-described method.

The cathode active material according to the present invention may further include a second cathode active material in addition to the doped-LFP of Formula 1, for example, a layered compound such as lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ) Or compounds substituted with one or more transition metals; A _{spinel represented by the} formula Li _{1 + x + y} Mn _{2 -yz} M ' _z O ₄ (x = 0 to 1, y = 0 to 0.5, z = 0 to 0.2, M' = Al and Mg) A spinel lithium manganese oxide in which a lithium manganese oxide having a crystal structure or a part of Mn in the formula is substituted with lithium, or a lithium-excess spinel lithium manganese oxide and a spinel lithium manganese oxide in which a part of manganese is substituted with an alkaline earth metal ion; Layer chalcogenides such as TiS ₂ and VS ₂ ; Lithium manganese oxides such as LiMnO ₃ , LiMn ₂ O ₃ and LiMnO ₂ ; 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 ; Formula _{LiNi 1 - x M x O 2} Ni site type lithium nickel oxide which is represented by (1 or more, x = 0.01 ~ 0.3 is selected from M = Co, Mn, Al, Cu, Fe, Mg, B and Ga); Formula _{LiMn 2 - x M x O 2} (M = Co, Ni, Fe, Cr, 1 or more, x = 0.01 ~ 0.1 is selected from Zn and Ta) or _{Li 2 Mn 3 MO 8 (M} = Fe, Co, At least one selected from the group consisting of Ni, Cu and Zn); Disulfide compounds; Li _{1 + a} Ni _x M _y Co _z M _b O _{2 -c} X _c (M = at least one selected from Al and Mg, at least one selected from X = F, S and N, -0.5? A? + 0.5 , 0 <x? 0.8, 0 <y? 0.8, 0 <z? 0.8, 0.8? X + y + z? 1.2, 0? B? 0.1, 0? C? 0.1); _{Li 1 + a Fe 1 - x} M x (PO 4 -b) X b (M = Al, Mg, Ni, Co, Mn, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn , and Y At least one selected from X = F, S and N, -0.5? A? + 0.5, 0? X? 0.5, and 0? B? 0.1); Fe ₂ (MoO ₄ ) _3, and the like may be included as the second cathode active material. In this case, the second cathode active material may include at least one kind of the second cathode active material, and it is preferable that the second cathode active material is contained in an amount of less than 50% based on the total weight of the active material so that the characteristics of the olivine structure metal oxide according to the present invention can be effectively exhibited.

The present invention also provides a positive electrode material mixture comprising the positive electrode active material, the conductive agent and the binder. The positive electrode mixture may further include a filler or the like.

The binder is added to the binder in an amount of 1 to 30% by weight, based on the total weight of the mixture containing the cathode active material, as a component that assists in bonding between the active material and the conductive agent and bonding to the current collector. 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; Etc. may be used.

Specific examples of the conductive agent will be described later with respect to the cathode.

Further, the present invention provides a positive electrode for a secondary battery in which the positive electrode material mixture is applied on a current collector.

The positive electrode for a secondary battery of the present invention can be produced, for example, by applying a slurry prepared by mixing the positive electrode mixture to a solvent such as NMP, coating the positive electrode collector, followed by drying and rolling.

The cathode current collector is generally made to have a thickness of 3 to 500 mu m. The positive electrode current collector is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery. Examples of the positive electrode current collector include carbon steel such as stainless steel, aluminum, nickel, titanium, sintered carbon, or aluminum or stainless steel. , 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.

Further, the present invention provides a lithium secondary battery comprising the positive electrode. Generally, the lithium secondary battery is composed of a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte containing a lithium salt. The lithium secondary battery according to the present invention is advantageous not only in the 4V region but also in the capacity and cycle characteristics even in the range of 2.5 to 3.5 V which is the 3V region.

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 the components as described above, if necessary.

Examples of the negative electrode active material include carbon and graphite materials such as natural graphite, artificial graphite, expanded graphite, carbon fiber, hard graphitizable carbon, carbon black, carbon nanotube, fullerene and activated carbon; Metals such as Al, Si, Sn, Ag, Bi, Mg, Zn, In, Ge, Pb, Pd, Pt and Ti which can be alloyed with lithium and compounds containing these elements; Complexes of metals and their compounds and carbon and graphite materials; Lithium-containing nitrides, and the like. Among them, a carbon-based active material, a silicon-based active material, a tin-based active material or a silicon-carbon based active material is preferable, and these may be used singly or in combination of two or more.

The negative electrode material mixture may contain a conductive agent. In this case, the conductive agent may be added in an amount of 1 to 30% by weight based on the total weight of the mixture including the negative electrode active material. Such a conductive agent 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 negative electrode 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 high conductivity without causing a chemical change in the battery. For example, the anode current collector may be formed on the surface of copper, stainless steel, aluminum, nickel, titanium, sintered carbon, 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. Examples of such a separation membrane include olefin-based polymers such as polypropylene, which is 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 nonaqueous electrolyte solution is composed of an electrolyte solution and a lithium salt. As the electrolyte solution, a nonaqueous organic solvent, an organic solid electrolyte, and an inorganic 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, But are not limited to, butylolactone, 1,2-dimethoxyethane, tetrahydroxyfuran, 2-methyltetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, But are not limited to, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxy methane, dioxolane derivatives, sulfolane, methyl sulfolane, Derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, 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 polymer including an acid dissociation group, and the like can 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 , Li ₄ SiO ₄ -LiI-LiOH, Li ₃ PO ₄ -Li ₂ S-SiS _2, 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 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 ) ₂ NLi, chloroborane lithium, lower aliphatic carboxylic acid lithium, lithium tetraphenylborate, .

For the purpose of improving the charge-discharge characteristics and the flame retardancy, the electrolytic solution may contain, for example, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, glyme, hexaphosphoric triamide, N, N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, aluminum trichloride and the like may be added. 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 the high-temperature storage characteristics. FEC (Fluoro-Ethylene carbonate ), PRS (Propene sultone), FEC (Fluoro-Ethylene carbonate), and the like.

The lithium secondary battery according to the present invention can be used not only for a battery cell used as a power source of a small device but also as a unit cell for a middle- or large-sized battery module including a plurality of battery cells that can be used as a power source for a medium- Can be used.

The medium and large devices include a power tool; An electric vehicle including an electric vehicle (EV), a hybrid electric vehicle (HEV), and a plug-in hybrid electric vehicle (PHEV); Electric motorcycle including E-bike, E-scooter; Electric Golf Cart; Electric truck; Electric commercial vehicle; And a power storage system, but the present invention is not limited thereto.

Hereinafter, the present invention will be described in more detail with reference to specific examples.

Example

Transition metal Doped Olivin  Structural Phosphoric acid iron oxide ( doped - LFP ) Produce

Fe (CH ₃ COO) ₂ and Ni (CH ₃ COO) ₂ were added as a transition metal compound in a molar ratio of 0.96: 0.04 to a TTEG (tetraethylene glycol) solvent and H ₃ PO ₄ as a phosphate ion compound and CH ₃ COOLi. At this time, the molar ratio of the added transition metal compound to H ₃ PO ₄ and CH ₃ COOLi was 1: 1: 1.

Of the mixed solution was reacted for 16 hours with reflux boiling point (328 ℃) TTEG of the solvent in a round flask of resultant electrode material for a device _{(LiNi 0 .04 Fe 0 .96 PO} 4, olivine structure) was prepared.

Since the polyol solvent (TTEG) produces a reducing atmosphere in terms of breaking, it keeps the oxidation number of Fe +2. In order to remove the organic compounds that may occur during the reaction or the TTEG solvent remaining in the reaction, the mixed solution is washed several times in acetone, and then the resultant is filtered from the mixed solution using a ceramic membrane .

Subsequently, the resultant was dried in a vacuum oven at 120 DEG C for 24 hours.

The lithium secondary battery  Produce

90% by weight of LiNi _0.04 Fe _0.96 PO _4, which was prepared by the above production method and was not coated with a carbon material, 6% by weight of black black as a conductive agent and 4% by weight of PVDF as a binder were dissolved in NMP, Followed by rolling and drying to prepare a positive electrode for a secondary battery.

A polymer type coin half cell was fabricated by interposing a porous polyethylene separator between the prepared positive electrode and the lithium metal counter electrode and injecting a lithium electrolyte.

Comparative Example

A polymer type coin half cell was fabricated in the same manner as in the above example except that LiFePO ₄ was used.

Experimental Example

The discharge capacity and the rate characteristic of the lithium secondary battery fabricated by the examples and the comparative examples were tested in a voltage range of 4.2 V to 2.5 V, and the results are shown in FIG. 2 and FIG. 3, respectively.

As shown in FIGS. 2 and 3, the doped-LFP manufactured according to the present invention has a discharge capacity similar to that of the conventional pure-LFP, but has a small resistance and excellent rate characteristics.

(The detailed values shown in the graph are only examples, and these values will vary according to the specifications of the cell, so the tendency of the graph is more important than the detailed values.)

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 (21)

Preparing a mixed solution in which a polyol solvent is mixed with a transition metal compound, a phosphate ion compound, and a lithium compound; And
Reacting the mixed solution in a reflux apparatus to obtain an output having a nanocrystal structure of an olivine structure metal oxide represented by the following Chemical Formula 3,
The transition metal compound includes at least one selected from the group consisting of an Fe-based compound, a Ni-based compound and a Ti-based compound,
In the olivine structure metal oxide, the content of Ni, Ti or a combination thereof is 0.5 to 10% by weight based on the total amount of the transition metals,
Characterized in that a heat treatment step of the resultant reaction product is not necessary.
LiM _y Fe _1-y PO ₄
In Formula 3, M is at least one selected from Ni and Ti, and 0.005? Y? 0.1. delete delete delete delete The method according to claim 1,
Obtaining the result; And then washing the mixed solution in acetone. The method according to claim 6,
Washing the mixed solution; Filtering the resultant afterwards; And drying the resultant. &Lt; Desc / Clms Page number 20 &gt; The method according to claim 1,
Wherein the polyol solvent is at least one selected from the group consisting of EG (Ethylene Glycol), DEG (Diethylene Glycol), TEG (Triethylene Glycol) and TTEG (Tetraethylene Glycol). delete The method according to claim 1,
Wherein the Fe-based compound is at least one selected from the group consisting of Fe (CH ₃ COO) ₂ , Fe (NO ₃ ) ₂ , FeC ₂ O ₂ , FeSO ₄ , FeCl ₂ , FeI ₂ and FeF ₂ . Way. The method according to claim 1,
Wherein the Ni-based compound is at least one selected from the group consisting of Ni (CH ₃ COO) ₂ , Ni (NO ₃ ) ₂ , NiC ₂ O ₂ , NiSO ₄ , NiCl ₂ , NiI ₂ and NiF ₂ . Way. The method according to claim 1,
Wherein the Ti-based compound is at least one selected from the group consisting of TiH ₂ and TTIP. The method according to claim 1,
Wherein the phosphoric acid ionic compound is at least one selected from the group consisting of NH ₄ H ₂ PO ₄ , H ₃ PO ₄ , (NH ₄ ) ₂ HPO ₄ and (NH ₄ ) ₃ PO ₄ . The method according to claim 1,
The lithium-based compound, characterized in that at least one member selected from the group consisting of _{CH 3 COOLi, LiOH, LiNO 3} , LiCO 3, Li 3 PO 4 , and LiF, method. The method according to claim 1,
Reacting the mixed solution in a reflux apparatus to obtain a product having a nanocrystal structure;
And heating the mixed solution at the boiling point of the polyol solvent. 16. The method of claim 15,
Wherein the polyol solvent has a boiling point of 250 to 350 占 폚. delete delete delete delete delete

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