KR20100086413A - Anion-deficient non-stoichiometric lithium transition metal polyacid compound as electrode active material, method for preparing the same, and electrochemical device using the same - Google Patents

Abstract

PURPOSE: A lithium transition metal polyacid compound is provided to ensure high mechanical and chemical stability and to suppress impurity generation. CONSTITUTION: A method for manufacturing anion-deficient non-stoichiometric lithium transition metal polyacid comprises: a step of mixing Fe precursor compound, polyacid comound containing one or more atom A selected from a group consisting of atoms having four coordinated structure, alkalizing agents, and lithium precursor for generating lithium transition metal polyacid compound precursor; a step of reacting the compound precursor with water at 200-700 °C and 180~550 bar to form non-stoichiometric lithium transition metal polyacid compound and drying; and a step of calcinating or granulating before calcinating.

Description

Anion-deficient non-stoichiometric lithium transition metal polyacid compound as an electrode active material, a method for manufacturing the same, and an electrochemical device using the same DEVICE USING THE SAME}

The present invention relates to an anion-deficient non-stoichiometric lithium transition metal polyacid compound as an electrode active material, a method for producing the same, and an electrochemical device using the same.

Lithium ion secondary batteries have advantages of being lighter and higher in capacity than other secondary batteries such as nickel cadmium batteries (Ni // Cd) and nickel-hydrogen batteries (Ni // MH). Therefore, it serves as a power source for portable electric and electronic devices such as mobile phones, notebook computers, game consoles, and vacuum cleaners. Recently, the market is rapidly expanding to high power medium and large size lithium secondary batteries for electric bicycles, electric scooters, service robots, electric vehicles, and power storage devices for power plants.

BACKGROUND ART Lithium ion secondary batteries have been generally manufactured using lithium cobaltate (LiCoO ₂ ) as a positive electrode active material, carbon material as a negative electrode active material, lithium hexafluorophosphate (LiPF ₆ ) as an electrolyte, and the like. However, lithium cobalt as a main positive electrode active material is not only unstable in the supply and demand of cobalt as a main component, but also has a high cost of cobalt, it is economically impossible to be applied to the medium-large size lithium secondary battery that requires a large amount. Therefore, spinel-structured lithium manganate (LiMn ₂ O ₄ ), etc., in which cobalt is replaced with another low-cost transition metal, has been commercially used, and lithium transition, which can be represented by olivine-type lithium iron phosphate (LiFePO ₄ ) Commercialization of metal polyacid compounds is ongoing.

The lithium transition metal polyacid compound having an olivine structure has high stability to crystal structure and chemical reactions, but it is not easily commercialized even though it has advantages of high capacity, long life, and low cost of the battery. This is because of the disadvantages of low electron conductivity, low ionic conductivity and generation of impurities by side reactions. Among these drawbacks, low electron conductivity can be overcome by coating of conductive carbon, and low ion conductivity can be overcome by shortening the lithium ion diffusion path by ultra-fine particle size. However, since the composition of the lithium transition metal polyacid compound is sensitively changed according to the preparation method, it is difficult to overcome the disadvantage that a product containing impurities other than the desired composition or transition metal oxide water is obtained. As a result, the material and battery properties are poor, resulting in low productivity, reliability and economics.

For example, in the case of lithium iron phosphate (LiFePO ₄ ), impurities such as Fe ₂ O ₃ , Li ₃ Fe ₂ (PO ₄ ) ₃ , Fe ₂ P are additionally generated, and most of the iron contained in the impurities is oxidized water. It is in the state of +3, because iron has a strong tendency for the oxidation state to be +3 rather than +2, and is easily oxidized during the calcination process.

When lithium iron phosphate contains iron in an oxidation state of +3, lithium iron phosphate containing impurities other than the olivine structure is produced. Since impurities do not have electrochemical activity, lithium iron phosphate containing iron in an oxidation state of +3 shows poorer material and battery characteristics than lithium iron phosphate composed of only +2 iron. Therefore, efforts have been made to make iron oxides +2.

The present invention relates to an anion deficient non-stoichiometric lithium transition metal polyacid compound in which iron production, which is an oxidation state of +3, is suppressed. Although there are prior art documents that disclose non-stoichiometric lithium transition metal polyacid compounds, the non-stoichiometric compounds disclosed in these prior arts differ from the present invention in that they are not anion deficient, but are cationic or cationic. Do.

Specifically, EP-A-1,094,532 discloses a method for producing a compound represented by Li _x M _y PO ₄ , where 0 <x ≦ 2, 0.8 ≦ y ≦ 1.2, and M is a 3d orbital. at least one metal having orbitals.

EP-A-1,094,533 discloses a compound represented by the general formula Li _x M _y PO ₄ , wherein 0 <x ≦ 2, 0.8 ≦ y ≦ 1.2, and M contains a 3d transition state. The grains of Li _x M _y PO ₄ are less than 10 micrometers.

U.S. Patent Application Publication 2006 / 0263286A1 discloses a process for producing Li _{1 + x} Fe _{1 + y} PO ₄ having an olivine structure, where −0.2 ≦ x ≦ 0.2 and −0.2 ≦ _y ≦ 0.2. The method comprises the steps of (A) adding iron powder, lithium salt and phosphate to an acid solution to form a mixture in which the molar ratio of Li ⁺ : Fe ^{2 +} : PO ₄ ^{3 -} is 1 + x: 1 + y: y, (B A) stirring the mixture, (C) drying the mixture to obtain a solid precursor, and (D) heating the solid precursor at at least 500 ° C. to obtain a powder of olivine structure.

US Patent Application Publication No. 2007 / 0207080A1 discloses a method for preparing a Li _x M _y PO ₄ compound having an olivine structure. The method produces a solution comprising the ions, Li ⁺ ions and PO ₄ ^{3 −} ions of the transition metal M, drying the solution to form starting material particles and having an olivine structure from the starting material particles. Form Li _x M _y PO ₄ compound particles (0.8 ≦ _x ≦ 1.2 and 0.8 ≦ _y ≦ 1.2) and form Li _x M _y PO ₄ Coating the carbon layer on the compound particles.

However, the lithium compounds disclosed in the above-mentioned four patent documents are all cationic excess or cation deficient compounds in which the molar ratio of PO ₄ as an anion is 1 and the molar ratio of M as a cation is varied, such as Li _x M _y PO _4. It is different from the anion deficient nonstoichiometric lithium transition metal polyacid compound according to the invention. The anion-deficient non-stoichiometric lithium transition metal polyacid compound is a compound in which the molar ratio of M as a cation is 1 and the molar ratio of PO _{4 as} an anion is less than 1, for example, as in Li _x M (PO ₄ ) _1-a . to be.

In this regard, non-stoichiometric iron phosphate is described as follows.

Ceramic material such as lithium iron phosphate has a cation (M ^{y +)} and an anion (X ^{y -)} point defects (point defects), which is an ionic compound consisting of the ionic compound may be present in non-stoichiometric forms of the all four .

The first is a cationic excess nonstoichiometric compound and the formula is represented by M _{1 + z} X. In the chemical formula, the composition ratio of anion (X ^{y −} ) is 1, which means that all the lattice points where anion (X ^{y −} ) should be present in the MX crystal structure are all disposed and cation (M ^{y +} ) The composition ratio of 1 + z means that all the lattice points to which cations (M ^{y +} ) should be filled and the excess z moles of cations (M ^{y +} ) are arranged at interstitial sites rather than magnetic sites. it means. Such point defects are called Frenkel defects in crystallography, more particularly inter-grid cation defects. In addition to the chemical composition ratio, the factors to be considered are the laws of charge neutrality. When there is 1 mole of negatively charged anion (X ^{y −} ) of -y and 1 + z mole of positively charged cation (M ^{y +} ) of ^{+ y} , charge neutralization cannot be achieved. Therefore, the cation is + y '(y' = y / (1 + z)) cation (M ^{y ' +} ) rather than the positive charge of + y the oxidation number of the cation decreases from + y to + y'.

The second is a cation deficient nonstoichiometric compound and the formula is represented by M _{1 - z} X. It is the composition ratio is 1, the anion (X ^{y -)} in MX crystal structure ^- anion (X ^y) in the formula means a state that is arranged both to all the grid points should be, and the composition ratio of the cation (M ^{y +)} 1 -z means that all the lattice points to which cations (M ^{y +} ) should not be filled and vacancies as much as z moles are formed. Such point defects are called Schottky defects in crystallography, more specifically cationic vacancy defects. anion with a negative charge of -y ^(y X ^-) is 1 mol and + y positive charge when the cation (M ^{y +)} is less than 1 mol with 1-z of not be able to achieve charge neutrality. Therefore, the cation is + y '(y' = y / (1-z)) cation (M ^{y ' +} ), not the positive charge of + y, the oxidation number of the cation increases from + y to + y'.

Third is an anion deficient nonstoichiometric compound and the formula is represented by MX _{1 -z} . In this chemical formula, the composition ratio of cation (M ^{y +} ) is 1, which means that all the lattice points where cation (M ^{y +} ) should be present in the MX crystal structure are all arranged, and the composition ratio of anion (X ^{y −} ) is 1 being the -z anion (X ^{y -)} did not fill all of the all of the grid points to have the means to condition the replacement for as long as z moles formed. These defects are called Schottky defects in crystallography, and more specifically anion vacancies defects. When there is 1 mole of positively charged positive ion (M ^{y +} ) and 1 mole of negatively charged anion (X ^{y −} ) less than 1, charge neutrality cannot be achieved. Common cations in ceramic materials are transition metal cations, and the oxidation number of the transition metal can be changed in a certain region, but the oxidation number of the anion is difficult to change. Thus, the cation is not positive charge of + y but + y '(y' = y (1-z)) cation (M ^{y ' +} ), the oxidation number of the cation decreases from + y to + y'. For quick understanding, for example, the olivine crystal structure of anion-deficient non-stoichiometric lithium iron phosphate, which is a kind of anion-deficient non-stoichiometric lithium transition metal polyacid compound according to the present invention, is the same as that of FIG. An illustration of where anion vacancies defects can occur in olivine iron phosphate is shown.

Fourth is an anion excess nonstoichiometric compound and the formula is represented by MX _{1 + z} . In this chemical formula, the composition ratio of cation (M ^{y +} ) is 1, which means that all the lattice points where cation (M ^{y +} ) should be present in the MX crystal structure are all arranged, and the composition ratio of anion (X ^{y −} ) is 1 + z means that all the lattice points where anions (X ^{y −} ) should be present are filled, and the excess z moles of anions (X ^{y −} ) are arranged at positions between lattice positions rather than magnetic sites. This point defect is called a Frenkel defect in crystallography, more particularly an inter-grid anion defect. When there is 1 mole of positively charged cation (M ^{y +} ) and 1 mole of positively charged anion (X ^{y −} ) greater than 1, charge neutrality cannot be achieved. Therefore, the cation is + y '(y' = y (1 + z)) cation (M ^{y ' +} ), not the positive charge of + y, the oxidation number of the cation increases from + y to + y'.

As such, in order to produce lithium iron phosphate composed only of +2 oxide iron, which is relatively excellent in electrochemical properties, the cation excess non-stoichiometric lithium iron phosphate (Frenkel defect, interstitial cation defect) can reduce the oxidation number of cations The process design can be selected from among the anion-deficient non-stoichiometric iron phosphate (Schottky defect, anion void defect). The disadvantage is that the energy that activates the Frenkel defect is significantly higher than the energy that activates the Schottky defect.

The anion deficient non-stoichiometric lithium transition metal polyacid compound according to the present invention has the advantages of high capacity, long life and low cost.

The problem to be solved by the present invention is that the physical and chemical stability is higher than the conventional stoichiometric lithium transition metal polyacid compound to suppress the generation of impurities, to achieve high capacity, long life and improved output characteristics of the battery The present invention provides a compound capable of producing a homogeneous electrode plate, which can reduce battery manufacturing defect rate and improve battery life characteristics, and a method of manufacturing the same.

The present inventors have found that the oxidation state of the transition metal, which may have a great influence on the generation of impurities, can be controlled by adjusting the proportion of anions in the preparation of the lithium transition metal polyacid compound.

The present invention provides an anion deficient non-stoichiometric lithium transition metal polyacid compound, and also provides a method for producing the same, an electrode using the same, and an electrochemical device having the electrode.

The compound according to the present invention is an anion deficient non-stoichiometric lithium transition metal polyacid compound represented by the following general formulas (1) to (3).

[Formula 1]

Li _{1 - x} FeA _{1 - a} O _{4 -b} (0≤x≤0.15, 0 <a≤0.05, 0 <b≤0.2)

[Formula 2]

_{Li 1 - y B z FeA 1} - a O 4 -b (0≤y≤0.2, 0≤z≤0.05, 0 <a≤0.05, 0 <b≤0.2)

(3)

Li _{1 - x} Fe (PO ₄ ) _1-a (0 ≦ _x ≦ 0.15, 0 <a ≦ 0.05)

In the above formulas, A is at least one element selected from the group consisting of elements having a coordination structure, and B is at least one element selected from the group consisting of alkaline earth metal elements and group 3B elements.

In another aspect, the present invention provides a method for producing an anion-deficient non-stoichiometric lithium transition metal polyacid compound as follows.

(a) a polyacid compound, an alkalizing agent comprising A, which is at least one element selected from the group consisting of Fe precursor compounds which are reactants, elements having a four coordination structure, in order to obtain the composition ratio specified in the above Chemical Formulas 1 to 3 Mixing the lithium precursor compound to produce a lithium transition metal polyacid compound precursor;

(b) mixing and producing a non-stoichiometric lithium transition metal multiacid compound by mixing the lithium transition metal multiacid compound precursor of step (a) with water under a reaction condition of a temperature of 200 to 700 ° C. and a pressure of 180 to 550 bar. ;

(c) calcining the result of step (b) or granulating and calcining.

The present invention provides an anion-deficient non-stoichiometric lithium transition metal multiacid compound that provides improved battery characteristics over conventional stoichiometric lithium transition metal multiacid compounds, a method for preparing the same, and an electrode using the same, and a high capacity and a long lifespan. It provides an electrochemical device representing.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

Anion-deficient non-stoichiometric lithium transition metal polyacid compound of the specified composition ratio of the present invention is represented by the following general formula (1) and (2).

Li _{1 - x} FeA _{1 - a} O _{4 -b} (0≤x≤0.15, 0 <a≤0.05, 0 <b≤0.2)

_{Li 1 - y B z FeA 1} - a O 4 -b (0≤y≤0.2, 0≤z≤0.05, 0 <a≤0.05, 0 <b≤0.2)

In the above formula, A is at least one element selected from the group consisting of elements having a coordination structure, and B is at least one element selected from the group consisting of alkaline earth metal elements and group 3B elements.

In Formula 1 or Formula 2, A having a coordination structure may be P, Ti, V, Si, or the like. In addition, B may be Al, Mg, Ti or the like. However, the present invention is not limited thereto.

In formulas (1) and (2), a is preferably 0.01 ≦ a ≦ 0.05, and more preferably 0.03 ≦ a ≦ 0.05.

Specific examples of the anion-deficient non-stoichiometric lithium transition metal polyacid compound according to the present invention are compounds represented by the following formula (3).

Li _{1 - x} Fe (PO ₄ ) _1-a

In the above formula, 0 ≦ x ≦ 0.15 and 0 <a ≦ 0.05. Also preferably, it is 0.01 ≦ a ≦ 0.05, and more preferably 0.03 ≦ a ≦ 0.05.

In the above Chemical Formulas 1, 2 and 3, the range of the lithium ion molar ratio is for lithium ions as a constituent of the anion deficient non-stoichiometric lithium transition metal polyacid compound. In order to compensate for the volatilized lithium during the calcination process or to maximize the discharge capacity of the lithium secondary battery when preparing the lithium transition metal polyacid compound, which is actually an electrode active material, an excess lithium precursor compound is generally introduced as a reactant, thereby producing a lithium transition. The molar ratio of lithium ions contained in the metal polyacid compound may be higher than the lithium ion molar ratio in the above formulas. However, lithium ions introduced for the above purpose are not contained in the anion-deficient non-stoichiometric lithium transition metal polyacid compound according to the present invention but exist in the form of impurities having electrochemical activity. A representative example is lithium ions present in crystal surface defects.

The form of the anion-deficient non-stoichiometric lithium transition metal polyacid compound prepared according to the present invention is not particularly limited, but is preferably spherical. In this case, the size of the particles before granulation is preferably in the range of 0.01 μm to 1 μm, but is not limited thereto. The size of the particles after granulation is preferably in the range of 1 μm to 20 μm. If the particle size is less than 1 μm, the specific surface area may be too large and the electrode may not be easy to manufacture. If the particle size exceeds 20 μm, it may be difficult to form a homogeneous slurry, and the thickness uniformity of the thin layer may be degraded during electrode production, thereby preventing battery defects. There is a concern. The anion-deficient non-stoichiometric lithium transition metal polyacid compound is capable of controlling their shape, size and size distribution under a range showing structural stability and excellent physical properties.

The anion-deficient non-stoichiometric lithium transition metal polyacid compound described above is suitable as an electrode active material, particularly as a cathode active material of a secondary battery.

As the method for preparing the electrode, a conventional method known in the art may be used. For example, the anion-deficient non-stoichiometric lithium transition metal polyacid compound may be used as a positive electrode active material. An electrode may be prepared by preparing an electrode slurry after mixing and coating the prepared electrode slurry on a current collector. At this time, a conductive agent can also be used.

The present invention provides an electrochemical device comprising (a) a positive electrode comprising an anion-deficient non-stoichiometric lithium transition metal polyacid compound, (b) a negative electrode, (c) a separator, and (d) an electrolyte. Electrochemical devices include all devices that undergo an electrochemical reaction, and specific examples thereof include various secondary cells, fuel cells, solar cells, memory devices, and capacitors including hybrid capacitors (P-EDLC). In particular, a lithium secondary battery including a lithium metal secondary battery, a lithium ion secondary battery, a lithium ion polymer secondary battery, or a lithium metal polymer secondary battery is preferable.

The electrochemical device of the present invention may be prepared by inserting a porous separator between an anode and a cathode by a conventional method known in the art, and then introducing an electrolyte.

The negative electrode, the electrolyte, and the separator to be applied together with the positive electrode of the present invention are not particularly limited, and conventional ones that may be used in the conventional electrochemical device may be used.

The anion-deficient non-stoichiometric lithium transition metal polyacid compound of the specified composition ratio of the present invention is based on the hydrothermal synthesis method using subcritical or supercritical water known in the art, and the reaction mixture ratio and reaction temperature (200-700 ° C.) In addition, the reaction pressure (180 ~ 550bar) can be prepared through a process change.

If the reaction temperature is less than 200 ℃ unsuitable to obtain a single-phase high crystalline anion deficient non-stoichiometric lithium transition metal polyacid compound, if the temperature is higher than 700 ℃ the material cost of the manufacturing apparatus increases.

Alkali metal hydroxides such as lithium, sodium, and potassium have high solubility in water at room temperature and atmospheric pressure, but when the density of water decreases due to high temperature and high pressure, the solubility decreases significantly. In the case of LiOH, it is necessary to maintain a pressure of 180 to 550 bar and a temperature of 200 to 700 ° C. together to significantly reduce the solubility.

Typically, the lithium transition metal polyacid compound may be prepared by various methods such as solid phase reaction, melt sintering, sol-gel, spray pyrolysis, coprecipitation-sintering, wet precipitation, and hydrothermal methods. However, the lithium transition metal polyacid compound does not have a desired composition or transition metal oxide number depending on the preparation method, but has various impurity contents, thereby showing a large variation in material and battery characteristics.

For example, in the wet precipitation method, the crystallization rate of each component constituting the non-stoichiometric multicomponent lithium transition metal polyacid compound is different from each other to obtain a crystal structure in which solid solution properties are lowered, and the particle size is increased. Too small in nano units makes it difficult to utilize as an electrode active material.

Accordingly, in the present invention, the anion-deficient non-stoichiometric multicomponent lithium transition metal multiacid compound ultrafine particles having a specified composition ratio are produced by calcining hydrothermal synthesis using subcritical water or supercritical water, or calcined, or calcined and calcined and then crystallized. And preparing a homogeneous anion deficient non-stoichiometric lithium transition metal polyacid compound with improved adhesion between the crystals, and according to the method for preparing the anion deficient non-stoichiometric lithium transition metal polyacid compound according to the dry firing method and wet precipitation. It is possible to form a homogeneous solid solution more easily than the law.

In addition, the lithium transition metal polyacid compound by the wet precipitation method such as the existing coprecipitation method requires a product preparation time of about 12 to 48 hours, and the compound does not contain a lithium component, thereby preventing lithium diffusion and crystal formation. Sufficient heat treatment time is required. In contrast, in the present invention, the anion-deficient non-stoichiometric lithium transition metal polyacid compound may be formed by treatment for several seconds at high temperature and high pressure. In addition, since the lithium component is already contained before the heat treatment, a separate mixing process is not required, and a time for generating the final electrode active material through heat treatment may be shortened. In particular, when a small particle size is required, such as an olivine crystal structure type anion deficient non-stoichiometric lithium transition metal polyacid compound having low ion conductivity, ultrafine particles can be easily generated without a separate ultrafine atomization process.

The difference between the wet precipitation method such as the existing coprecipitation method and the manufacturing method of the present invention can be easily distinguished by the difference between the two reaction mechanisms.

For example, the reaction mechanism by the conventional coprecipitation method is divided into two steps as follows.

(a) coprecipitation _{step: 3LiNO 3 + 3Fe (NO 3} ) 2 · nH 2 O + 3 (NH 4) 2 HPO 4 → Fe 3 (PO 4) 2 · nH 2 O + Li 3 PO 4 + 6NH 3 + 9HNO ₃ ;

(b) calcination process: Fe ₃ (PO ₄ ) ₂ · nH ₂ O + Li ₃ PO ₄ → 3LiFePO ₄ + nH ₂ O.

Expressed on the basis of the stoichiometric lithium iron phosphate for convenient understanding of the reaction mechanism by the production method of the present invention is as follows.

FeSO ₄ 7H ₂ O + H ₃ PO ₄ + LiOH → LiFePO ₄ + H ₂ SO ₄ + 8H ₂ O.

As can be seen from the difference between the two reaction mechanisms, in the case of the conventional coprecipitation method, Fe ₃ (PO ₄ ) ₂ nH ₂ O and Li ₃ PO ₄ generated in the wet process are subjected to dry calcination process only through solid phase reaction of the two products. While the olivine crystal structure type lithium iron phosphate (LiFePO ₄ ) can be obtained, in the case of the production method of the present invention, an anion-deficient non-stoichiometric lithium iron phosphate polyacid compound can be obtained by a single wet process. The anion-deficient non-stoichiometric lithium iron phosphate polyacid compound of the present invention includes a calcination process, but this is for improving the crystallinity of the produced anion-free non-stoichiometric lithium iron phosphate.

Composition ratio control parameters for obtaining the anion-deficient non-stoichiometric multicomponent lithium transition metal polyacid compound having a specific composition ratio include a mixture ratio of the transition metal precursor compound, the polyacid compound, the alkalizing agent, the lithium precursor compound and water, and the mixed solution. Since there are pH, reaction temperature, and reaction pressure, the composition ratio of the anion-deficient non-stoichiometric multicomponent lithium transition metal polyacid compound can be specified according to the combination of these variables. However, since the composition ratio of the anion-deficient non-stoichiometric multicomponent lithium transition metal multiacid compound may vary according to the combination of variables, an optimal value for each variable for a specific composition ratio may be determined. It is not limited.

For a preferred embodiment of the manufacturing method, (a) to obtain a composition ratio specified in the formulas (1) to (3) is a Fe precursor compound, a reactant, A is at least one element selected from the group consisting of elements having a coordination structure Mixing a multiacid compound, an alkalizing agent, and a lithium precursor compound including a specific ratio to produce a lithium transition metal multiacid compound precursor; (b) mixing the lithium transition metal polyacid compound precursor of step (a) with water under subcritical or supercritical conditions to produce and dry a non-stoichiometric lithium transition metal multiacid compound; (c) calcining the result of step (b) or calcining after granulation to improve crystallinity and adhesion between the crystals.

Each step will be described in more detail below.

Step a): mixing a reactant Fe precursor compound, a polyacid compound including A, an alkalizing agent and a lithium precursor compound in a specific ratio to generate a lithium transition metal polyacid compound precursor

The Fe precursor compound is not particularly limited as long as it is a compound capable of ionizing as a salt containing Fe. It is preferably a water-soluble compound. Non-limiting examples of such Fe precursor compounds include alkoxides, nitrates, acetates, halides, oxides, carbonates, oxalates, sulfates containing salts, or salts including combinations thereof. In particular, nitrate, sulfate, acetate, etc. are preferable.

The polyacid compound is not particularly limited as long as it is a compound capable of ionizing as a salt containing polyacid. It is preferably a water-soluble compound. Non-limiting examples of the polyacid compound include polyacids, ammonium, hydrogenammonium, alkoxides, nitrates, acetates, halides, hydroxides, oxides, carbonates, oxalates, sulfates, and the like including polyacids. The polyacid salts may contain one or more or a mixture thereof.

The alkalizing agent is not particularly limited as long as the reaction solution is made alkaline. Non-limiting examples of the alkalizing agent include alkali metal hydroxides (NaOH, KOH, etc.), alkaline earth metal hydroxides (Ca (OH) ₂ , Mg (OH) _2, etc.), ammonia compounds (ammonia water, ammonium nitrate, etc.) or mixtures thereof Etc.

The lithium precursor compound may be used without limitation as long as it contains a lithium and ionizable water-soluble salt, non-limiting examples thereof include lithium nitrate, lithium acetate, lithium hydroxide, lithium sulfate and the like. In particular, lithium hydroxide is preferable because it not only serves as a lithium source but also increases alkalinity. The molar ratio of Li / Fe is suitably 1.0 to 20, preferably 1.0 to 10. If the molar ratio of Li / Fe is too small, small amounts of lithium to form the non-stoichiometric lithium transition metal polyacid compound participate in the reaction, resulting in impurities such as transition metal compounds that cannot react with lithium, such as oxide transition metals. This lowers the purity of the target material. If the ratio is too large, lithium remains and economical efficiency is lowered because it has to be recovered or discarded from the discharge liquid.

The alkali equivalent ratio of the mixture is preferably 1 to 10, but is not limited thereto. In this case, the alkali equivalent ratio is defined as the equivalent ratio of the number of equivalents of hydroxyl ions coming from the alkalizing agent and lithium hydroxide, and the acid groups (NO ₃ , SO ₄ ) coming from the Fe precursor compound and the lithium precursor compound. When the alkali equivalence ratio is too small, impurities are present in the product, and when the alkali equivalence ratio is too large, the alkaline component of the wastewater becomes excessively high.

When the Fe precursor compound, the polyacid compound and the alkalizing agent and the lithium precursor compound are mixed, they may be mixed with water or mixed with water at once, or the Fe precursor compound and the polyacid compound may be added with the alkalizing agent and the lithium precursor. The compound may be mixed first and then mixed with water.

Step b) : Mixing the lithium transition metal polyacid compound precursor with water under subcritical or supercritical conditions to produce and dry anion deficient non stoichiometric lithium transition metal multiacid compound

The reaction pressure and reaction temperature should be suitable for the production of anion-deficient non-stoichiometric lithium transition metal polyacid compound of the specified composition ratio. At this time, the subcritical or supercritical conditions means a pressure of 180 to 550 bar at a high temperature in the range of 200 to 700 ℃, it is appropriate to maintain the conditions continuously, it is more preferable if the continuous.

Moreover, it is preferable that pH at the time of reaction is larger than 4.0 and 9.0 or less. If the pH is 4.0 or less, it is not preferable because the prepared anion-deficient non-stoichiometric lithium transition metal polyacid compound is dissolved in a low pH range, and if it exceeds 9.0, an excessive amount of alkalizing agent for pH control should be added. Economics are reduced because of the need for additional additional processes for cleaning, flushing and effluent treatment. Mixing is also suitable for continuous mixers, such as in the form of tubes. As such, the anion-deficient non-stoichiometric lithium transition metal polyacid compound is homogeneously formed in the mixer.

Step c): The resultant of step b) is calcined after drying or calcined after granulation

The anion-deficient non-stoichiometric lithium transition metal polyacid compound produced in step b) is very fine because of insufficient crystallinity and a particle size of about 0.01 to 1 μm, which is not suitable for use as a positive electrode active material of a lithium secondary battery. Therefore, in step c), the crystallinity is improved and appropriately sized granules are suitable for use as the positive electrode active material. It is preferable that the positive electrode active material of the lithium secondary battery has a particle size of about 1 to 20 μm.

Granulation methods can usually be carried out simultaneously with drying, and various methods known in the art, such as spray drying, fluidized bed drying, and vibration drying, can be used. In particular, the spray drying method is preferable because the spherical production can increase the tap density of the granules. Impurity salt to remain in and drying the concentrate concentrate prior to the granulation (e.g., NH ₄ NO ₃ salt, etc.), ionic impurities (for ^{_{example, NO 3 -, SO 4 2}} - , etc.) removal and the like Can be washed with clean water.

In addition, since the calcination step serves to improve the crystallinity of the anion-deficient non-stoichiometric lithium transition metal polyacid compound and to improve the adhesion between them, it is preferable that the calcination step be performed immediately after the step (b). Particularly, when the granulation and calcining steps are continuously performed, the primary particles constituting the granules are grown while being crystallographically stabilized. If the calcination process is not carried out, the crystals are not stabilized and the initial charge / discharge performance of the battery is very poor. This is especially the case of such a phenomenon that the surface of the unstable collapse of the phenomenon. In addition, since the specific surface area of the positive electrode active material is large and the tap density is low, the capacity per volume is low as the positive electrode active material, which is not preferable.

There is no particular limitation on the calcination temperature range, but 500 to 1200 ° C is preferred. When the temperature is lower than 500 ° C., primary particle crystallinity may be insufficient and sintering between the primary particles may not be completed, resulting in a large specific surface area and lower tap density. In addition, the improvement of crystallinity is insufficient and the material is not sufficiently stabilized, thereby degrading battery performance such as charge / discharge battery life and output. If it exceeds 1200 DEG C, excessive sintering results in disadvantages such as phase decomposition.

Binder, sintering aid, dopant, coating agent, reducing agent, oxidizing agent, acid, carbon or carbon precursor, metal oxide and lithium before, after or during one or more of the steps a), b) and c) One or more additives selected from the group consisting of compounds may be added.

The binder may be used for sphericalization of the granules and for improving particle size, and non-limiting examples thereof include water, aqueous ammonia, poly vinly alcohol (PVA), or a mixture thereof. The sintering aid may be used to lower the firing temperature or increase the sintering density when the granules are calcined at a high temperature. Non-limiting examples thereof include metal oxides such as alumina, B ₂ O ₃ , MgO, or precursors thereof, LiF, Li compounds such as LiOH, Li ₂ CO ₃ and the like. The dopant and the coating agent are used to dope the metal oxide inside the cathode active material structure or to coat the metal oxide ultrafine particles on the outside of the crystal to improve durability when the fired body is used in the battery. Non-limiting examples thereof include metal oxides such as alumina, zirconia, titania, magnesia or precursors thereof.

Reducing or oxidizing agents can be used to control the atmosphere of each manufacturing step to a reducing or oxidizing atmosphere. In particular, in the case of an anion-deficient non-stoichiometric lithium transition metal polyacid compound in which the transition metal is Fe and the polyacid is phosphoric acid, a reducing agent may be appropriately used in the manufacturing process for the purpose of improving electrical conductivity and suppressing oxidation of Fe. Non-limiting examples of reducing agents include hydrazine, oxalic acid, sugars, fructose, ascorbic acid, hydrogen, carbon, hydrocarbons or mixtures thereof. Non-limiting examples of oxidants include oxygen, hydrogen peroxide, ozone or mixtures thereof. Acids are used to participate as reactants of phosphoric acid compounds, sulfuric acid compounds, nitric acid compounds and the like. Non-limiting examples of acids include phosphoric acid, sulfuric acid, nitric acid or mixtures thereof. Carbon or carbon precursor may be coated on the surface of the material to be produced to improve electrical conductivity or to give a reducing atmosphere. It is particularly useful in the case of anion-deficient non-stoichiometric lithium transition metal polyacid compounds having an olivine-type crystal structure. Non-limiting examples of carbon or carbon precursors include sugar, ascorbic acid, cellulose, polyvinyl alcohol (PVA), polyethylene glycol (PEG), or mixtures thereof.

The lithium compound may participate in the reaction in the calcining step when it is desired to increase the content of lithium in the anion deficient non-stoichiometric lithium transition metal polyacid compound precursor. Non-limiting examples thereof include LiF, LiOH, LiNO ₃ , Li ₂ CO ₃ or mixtures thereof.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. However, the following examples are for illustrating the present invention, and the scope of the present invention is not limited thereto.

Example  One

The molar ratio of phosphoric acid (85 wt%) to iron sulfate (FeSO ₄ · 7H ₂ O) is 1: 1, and the sugar is weighed in a 10% weight ratio to iron sulfate to make an aqueous solution. The aqueous solution of ammonia water and lithium hydroxide was weighed in a molar ratio of 1: 1.1 and 1: 2, respectively, to prepare an aqueous solution separate from the aqueous solution. Each of the two aqueous solutions was pumped under pressure at 250 bar at room temperature at a flow rate of 8 g / min and mixed in a mixer to produce a lithium iron phosphate precursor.

Ultrapure water heated to about 450 [deg.] C. in the precursor is mixed under pressure by pumping it at 250 bar and a flow rate of 96 g / min. The final mixture was held for 7 seconds in a reactor maintained at 380 ° C. and 250 bar to produce low crystalline anion deficient non-stoichiometric lithium iron phosphate, followed by cooling and concentration. The pH of the concentrate was 6.1, which means that the concentrations of iron sulfate, phosphoric acid, ammonia water and lithium hydroxide in the two aqueous solutions were controlled to pH 6.1 as well as the mixed molar ratio of iron sulfate, phosphoric acid, aqueous ammonia and lithium hydroxide.

Sugar was mixed in the concentrate at a 10% weight ratio compared to lithium iron phosphate, and spray drying and granules were formed through a spray dryer. The formed dry granular particles were heat-treated at 700 ° C. for 10 hours to obtain anion-deficient non-stoichiometric lithium iron phosphate having improved crystallinity due to calcination and improved adhesion between crystals. The calcination process is a process for improving the crystallinity and the adhesion between the crystals of the anion-deficient non-stoichiometry, which is an electrode active material, which improves the battery characteristics of the lithium transition metal polyacid compound. There is no change in the composition of the transition metal polyacid compound.

Induced coupling plasma spectroscopy (ICP) analysis, super conducting quantum interference device (SQUID) analysis, and Mossbauer spectroscopic analysis were performed on the prepared anion-deficient non-stoichiometric lithium transition metal polyacid compound. It was confirmed that the molar ratio of Fe: P is 0.880: 1: 0.960 (As mentioned above, an excessive amount of Li may be added in the preparation of the lithium transition metal polyacid compound for the purpose of maximizing the discharge capacity of the lithium secondary battery. The Li content in the molar ratio of Li: Fe: P refers to the amount of Li constituting the lithium transition metal polyacid compound according to the present invention, excluding the Li content added in such an excess. The same is true for the Li content in the other examples below). In addition, it was confirmed that the lithium transition metal polyacid compound prepared according to the present example using a transmission electron microscope (TEM) has an anion deficient defect.

Example  2

The molar ratio of phosphoric acid (85 wt%) to iron sulfate (FeSO ₄ · 7H ₂ O) is 1: 1, and the sugar is weighed in a 10% weight ratio to iron sulfate to make an aqueous solution. The aqueous solution of ammonia water and lithium hydroxide were weighed in a molar ratio of 1: 1.3 and 1: 2, respectively, to prepare an aqueous solution separate from the aqueous solution. Each of the two aqueous solutions was pumped under pressure at 250 bar at room temperature at a flow rate of 8 g / min and mixed in a mixer to produce a lithium iron phosphate precursor.

Ultrapure water heated to about 450 [deg.] C. in the precursor is mixed under pressure by pumping it at 250 bar and a flow rate of 96 g / min. The final mixture was held for 7 seconds in a reactor maintained at 380 ° C. and 250 bar to produce low crystalline anion deficient non-stoichiometric lithium iron phosphate, followed by cooling and concentration. The pH of the concentrate was 8.4, which means that the concentration of iron sulfate, phosphoric acid, ammonia water and lithium hydroxide in the two aqueous solutions was controlled to pH 8.4 as well as the mixed molar ratio of iron sulfate, phosphoric acid, aqueous ammonia and lithium hydroxide.

Sugar was mixed in the concentrate at a 10% weight ratio compared to lithium iron phosphate, and spray drying and granules were formed through a spray dryer. The formed dry granular particles were subjected to heat treatment at 700 ° C. for 10 hours.

Induced coupled plasma spectroscopy (ICP) analysis, superconducting quantum interference device analysis and Mossbauer spectroscopic analysis were performed on the prepared anion-deficient non-stoichiometric lithium transition metal polyacid compound to obtain a molar ratio of Li: Fe: P of 0.877: 1: It was confirmed that the 0.959, using a transmission electron microscope (TEM) was confirmed to have an anion-deficient defect.

Example  3

The molar ratio of phosphoric acid (85 wt%) to iron sulfate (FeSO ₄ · 7H ₂ O) is 1: 1, and the sugar is weighed in a 10% weight ratio to iron sulfate to make an aqueous solution. The aqueous solution of ammonia water and lithium hydroxide was weighed in a molar ratio of 1: 1.5 and 1: 2, respectively, to prepare an aqueous solution separate from the aqueous solution. Each of the two aqueous solutions was pumped under pressure at 250 bar at room temperature at a flow rate of 8 gl / min and mixed in a mixer to produce a lithium iron phosphate precursor.

Ultrapure water heated to about 450 [deg.] C. in the precursor is mixed under pressure by pumping it at 250 bar and a flow rate of 96 g / min. The final mixture was held for 7 seconds in a reactor maintained at 380 ° C. and 250 bar to produce low crystalline anion deficient non-stoichiometric lithium iron phosphate, followed by cooling and concentration. The pH of the concentrate was 8.5, which means that the concentration of iron sulfate, phosphoric acid, ammonia water and lithium hydroxide in the two aqueous solutions was controlled to pH 8.5, as well as the mixed molar ratio of iron sulfate, phosphoric acid, aqueous ammonia and lithium hydroxide.

Sugar was mixed in the concentrate at a 10% weight ratio compared to lithium iron phosphate, and spray drying and granules were formed through a spray dryer. The formed dry granular particles were subjected to heat treatment at 700 ° C. for 10 hours.

Induced coupling plasma spectroscopy (ICP) analysis, superconducting quantum interference device analysis and Mossbauer spectroscopic analysis were performed on the prepared anion-deficient non-stoichiometric lithium transition metal polyacid compound to obtain a molar ratio of Li: Fe: P of 0.868: 1: It was confirmed that it is 0.956, and it was confirmed that it has an anion deficient defect using a transmission electron microscope (TEM).

Example  4

The molar ratio of phosphoric acid (85 wt%) to iron sulfate (FeSO ₄ · 7H ₂ O) is 1: 1.1, and the sugar is weighed in a 10% weight ratio to iron sulfate to make an aqueous solution. The aqueous solution of ammonia water and lithium hydroxide was weighed in a molar ratio of 1: 1.1 and 1: 2, respectively, to prepare an aqueous solution separate from the aqueous solution. The two aqueous solutions were pumped under pressure at 250 bar at room temperature at a flow rate of 8 g / min, respectively, and mixed in a mixer to produce a lithium iron phosphate precursor.

Ultrapure water heated to about 450 [deg.] C. in the precursor is mixed under pressure by pumping it at 250 bar and a flow rate of 96 g / min. The final mixture was held for 7 seconds in a reactor maintained at 380 ° C. and 250 bar to produce low crystalline anion deficient non-stoichiometric lithium iron phosphate, followed by cooling and concentration. The pH of the concentrate was 5.2, which means that the concentration of iron sulfate, phosphoric acid, ammonia water and lithium hydroxide in the two aqueous solutions was controlled to pH 5.2 as well as the mixed molar ratio of iron sulfate, phosphoric acid, aqueous ammonia and lithium hydroxide.

Sugar was mixed in the concentrate at a 10% weight ratio compared to lithium iron phosphate, and spray drying and granules were formed through a spray dryer. The formed dry granular particles were subjected to heat treatment at 700 ° C. for 10 hours.

Induced coupled plasma spectroscopy (ICP) analysis, superconducting quantum interference device analysis and Mossbauer spectroscopic analysis were performed on the prepared anion-deficient non-stoichiometric lithium transition metal polyacid compound to obtain a molar ratio of Li: Fe: P of 0.931: 1: It was confirmed that it is 0.977, using a transmission electron microscope (TEM) was confirmed to have an anion-deficient defect.

Example  5

The molar ratio of phosphoric acid (85 wt%) to iron sulfate (FeSO ₄ · 7H ₂ O) is 1: 1.1, and the sugar is weighed in a 10% weight ratio to iron sulfate to make an aqueous solution. The aqueous solution of ammonia water and lithium hydroxide were weighed in a molar ratio of 1: 1.3 and 1: 2, respectively, to prepare an aqueous solution separate from the aqueous solution. Each of the two aqueous solutions was pumped under pressure at 250 bar at room temperature at a flow rate of 8 g / min and mixed in a mixer to produce a lithium iron phosphate precursor.

Ultrapure water heated to about 450 [deg.] C. in the precursor is mixed under pressure by pumping it at 250 bar and a flow rate of 96 g / min. The final mixture was held for 7 seconds in a reactor maintained at 380 ° C. and 250 bar to produce low crystalline anion deficient non-stoichiometric lithium iron phosphate, followed by cooling and concentration. The pH of the concentrate was 7.3, which means that the concentration of iron sulfate, phosphoric acid, ammonia water and lithium hydroxide in the two aqueous solutions was controlled to pH 7.3 as well as the mixed molar ratio of iron sulfate, phosphoric acid, aqueous ammonia and lithium hydroxide.

Sugar was mixed in the concentrate at a 10% weight ratio compared to lithium iron phosphate, and spray drying and granules were formed through a spray dryer. The formed dry granular particles were subjected to heat treatment at 700 ° C. for 10 hours.

Induced coupling plasma spectroscopy (ICP) analysis, superconducting quantum interference device analysis and Mossbauer spectroscopic analysis were performed on the prepared anion-deficient non-stoichiometric lithium transition metal polyacid compound to obtain a molar ratio of Li: Fe: P of 0.907: 1: It was confirmed that it is 0.969, and it was confirmed that it has an anion deficiency defect using a transmission electron microscope (TEM).

Example  6

The molar ratio of phosphoric acid (85 wt%) to iron sulfate (FeSO ₄ · 7H ₂ O) is 1: 1.1, and the sugar is weighed in a 10% weight ratio to iron sulfate to make an aqueous solution. The aqueous solution of ammonia water and lithium hydroxide were weighed in a molar ratio of 1: 1.5 and 1: 2, respectively, to iron sulfate to prepare a separate aqueous solution. Each of the two aqueous solutions was pumped under pressure at 250 bar at room temperature at a flow rate of 8 g / min and mixed in a mixer to produce a lithium iron phosphate precursor.

Ultrapure water heated to about 450 [deg.] C. in the precursor is mixed under pressure by pumping it at 250 bar and a flow rate of 96 g / min. The final mixture was held for 7 seconds in a reactor maintained at 380 ° C. and 250 bar to produce low crystalline anion deficient non-stoichiometric lithium iron phosphate, followed by cooling and concentration. The pH of the concentrate was 8.1, which means that the concentration of iron sulfate, phosphoric acid, ammonia water and lithium hydroxide in the two aqueous solutions was controlled to pH 8.1 as well as the mixed molar ratio of iron sulfate, phosphoric acid, aqueous ammonia and lithium hydroxide.

Sugar was mixed in the concentrate at a 10% weight ratio compared to lithium iron phosphate, and spray drying and granules were formed through a spray dryer. The formed dry granular particles were subjected to heat treatment at 700 ° C. for 10 hours.

Induced coupled plasma spectroscopy (ICP) analysis, superconducting quantum interference device analysis and Mossbauer spectroscopic analysis were performed on the prepared anion-deficient non-stoichiometric lithium transition metal polyacid compound to obtain a molar ratio of Li: Fe: P of 0.880: 1: It was confirmed that it is 0.960, and it was confirmed that it has an anion deficient defect using a transmission electron microscope (TEM).

Example  7

The molar ratio of phosphoric acid (85 wt%) to iron sulfate (FeSO ₄ · 7H ₂ O) is 1: 1.2, and the sugar is weighed in a 10% weight ratio to iron sulfate to make an aqueous solution. The aqueous solution of ammonia water and lithium hydroxide was weighed in a molar ratio of 1: 1.1 and 1: 2, respectively, to prepare an aqueous solution separate from the aqueous solution. Each of the two aqueous solutions was pumped under pressure at 250 bar at room temperature at a flow rate of 8 g / min and mixed in a mixer to produce a lithium iron phosphate precursor.

Ultrapure water heated to about 450 [deg.] C. in the precursor is mixed under pressure by pumping it at 250 bar and a flow rate of 96 g / min. The final mixture was held for 7 seconds in a reactor maintained at 380 ° C. and 250 bar to produce low crystalline anion deficient non-stoichiometric lithium iron phosphate, followed by cooling and concentration. The pH of the concentrate was 4.3, which means that the concentration of iron sulfate, phosphoric acid, ammonia water and lithium hydroxide in the two aqueous solutions was controlled to pH 4.3 as well as the mixed molar ratio of iron sulfate, phosphoric acid, ammonia water and lithium hydroxide.

Sugar was mixed in the concentrate at a 10% weight ratio compared to lithium iron phosphate, and spray drying and granules were formed through a spray dryer. The formed dry granular particles were subjected to heat treatment at 700 ° C. for 10 hours.

Induced coupling plasma spectroscopy (ICP) analysis, superconducting quantum interference device analysis and Mossbauer spectroscopic analysis were performed on the prepared anion-deficient non-stoichiometric lithium transition metal polyacid compound to obtain a molar ratio of Li: Fe: P of 0.955: 1: It was confirmed that it is 0.985, using a transmission electron microscope (TEM) was confirmed to have an anion-deficient defect.

Example  8

The molar ratio of phosphoric acid (85 wt%) to iron sulfate (FeSO ₄ · 7H ₂ O) is 1: 1.2, and the sugar is weighed in a 10% weight ratio to iron sulfate to make an aqueous solution. The aqueous solution of ammonia water and lithium hydroxide were weighed in a molar ratio of 1: 1.3 and 1: 2, respectively, to prepare an aqueous solution separate from the aqueous solution. Each of the two aqueous solutions was pumped under pressure at 250 bar at room temperature at a flow rate of 8 g / min and mixed in a mixer to produce a lithium iron phosphate precursor.

Ultrapure water heated to about 450 [deg.] C. in the precursor is mixed under pressure by pumping it at 250 bar and a flow rate of 96 g / min. The final mixture was held for 7 seconds in a reactor maintained at 380 ° C. and 250 bar to produce low crystalline anion deficient non-stoichiometric lithium iron phosphate, followed by cooling and concentration. The pH of the concentrate was 5.0, which means that the concentration of iron sulfate, phosphoric acid, ammonia water and lithium hydroxide in the two aqueous solutions was controlled to pH 5.0 as well as the mixed molar ratio of iron sulfate, phosphoric acid, aqueous ammonia and lithium hydroxide.

Sugar was mixed in the concentrate at a 10% weight ratio compared to lithium iron phosphate, and spray drying and granules were formed through a spray dryer. The formed dry granular particles were subjected to heat treatment at 700 ° C. for 10 hours.

Induced coupling plasma spectroscopy (ICP) analysis, superconducting quantum interference device analysis and Mossbauer spectroscopic analysis were performed on the prepared anion-deficient non-stoichiometric lithium transition metal polyacid compound to obtain a molar ratio of Li: Fe: P of 0.940: 1: It was confirmed that it is 0.980, using a transmission electron microscope (TEM) was confirmed to have an anion-deficient defect.

Example  9

The molar ratio of phosphoric acid (85 wt%) to iron sulfate (FeSO ₄ · 7H ₂ O) is 1: 1.2, and the sugar is weighed in a 10% weight ratio to iron sulfate to make an aqueous solution. The aqueous solution of ammonia water and lithium hydroxide was weighed in a molar ratio of 1: 1.5 and 1: 2, respectively, to prepare an aqueous solution separate from the aqueous solution. Each of the two aqueous solutions was pumped under pressure at 250 bar at room temperature at a flow rate of 8 g / min and mixed in a mixer to produce a lithium iron phosphate precursor.

Ultrapure water heated to about 450 [deg.] C. in the precursor is mixed under pressure by pumping it at 250 bar and a flow rate of 96 g / min. The final mixture was held for 7 seconds in a reactor maintained at 380 ° C. and 250 bar to produce low crystalline anion deficient non-stoichiometric lithium iron phosphate, followed by cooling and concentration. The pH of the concentrate was 6.7, which means that the concentrations of iron sulfate, phosphoric acid, ammonia water and lithium hydroxide in the two aqueous solutions were controlled to pH 6.7 as well as the mixed molar ratio of iron sulfate, phosphoric acid, aqueous ammonia and lithium hydroxide.

Sugar was mixed in the concentrate at a 10% weight ratio compared to lithium iron phosphate, and spray drying and granules were formed through a spray dryer. The formed dry granular particles were subjected to heat treatment at 700 ° C. for 10 hours.

Induced coupling plasma spectroscopy (ICP) analysis, superconducting quantum interference device analysis and Mossbauer spectroscopic analysis were performed on the prepared anion-deficient non-stoichiometric lithium transition metal polyacid compound to obtain a molar ratio of Li: Fe: P of 0.937: 1: It was confirmed that the 0.979, using a transmission electron microscope (TEM) was confirmed to have an anion-deficient defect.

Comparative example  One

The molar ratio of phosphoric acid (85 wt%) to iron sulfate (FeSO ₄ · 7H ₂ O) is basis weight 1: 1.3, and the sugar is weighed in a 10% weight ratio with respect to iron sulfate to make an aqueous solution. The aqueous solution of ammonia water and lithium hydroxide was weighed in a molar ratio of 1: 1.1 and 1: 2, respectively, to prepare an aqueous solution separate from the aqueous solution. Each of the two aqueous solutions was pumped under pressure at 250 bar at room temperature at a flow rate of 8 g / min and mixed in a mixer to produce a lithium iron phosphate precursor.

Ultrapure water heated to about 450 [deg.] C. in the precursor is mixed under pressure by pumping it at 250 bar and a flow rate of 96 g / min. The final mixture was held for 7 seconds in a reactor maintained at 380 ° C. and 250 bar to produce low crystalline anion deficient non-stoichiometric lithium iron phosphate, followed by cooling and concentration. The pH of the concentrate was 4.0, which means that the concentration of iron sulfate, phosphoric acid, ammonia water and lithium hydroxide in the two aqueous solutions was controlled to pH 4.0 as well as the mixed molar ratio of iron sulfate, phosphoric acid, aqueous ammonia and lithium hydroxide.

Sugar was mixed in the concentrate at a 10% weight ratio compared to lithium iron phosphate, and spray drying and granules were formed through a spray dryer. The formed dry granular particles were subjected to heat treatment at 700 ° C. for 10 hours.

Induced coupling plasma spectroscopy (ICP) analysis, superconducting quantum interference device analysis and Mossbauer spectroscopic analysis were performed on the prepared lithium transition metal polyacid compound to confirm that the molar ratio of Li: Fe: P was 1: 1.

Comparative example  2

The molar ratio of phosphoric acid (85 wt%) to iron sulfate (FeSO ₄ · 7H ₂ O) is 1: 1, and the sugar is weighed in a 10% weight ratio to iron sulfate to make an aqueous solution. The aqueous solution of ammonia water and lithium hydroxide was weighed in a molar ratio of 1: 2.0 and 1: 2, respectively, to prepare an aqueous solution separate from the aqueous solution. Each of the two aqueous solutions was pumped under pressure at 250 bar at room temperature at a flow rate of 8 g / min and mixed in a mixer to produce a lithium iron phosphate precursor.

Ultrapure water heated to about 450 [deg.] C. in the precursor is mixed under pressure by pumping it at 250 bar and a flow rate of 96 g / min. The final mixture was held for 7 seconds in a reactor maintained at 380 ° C. and 250 bar to produce low crystalline anion deficient non-stoichiometric lithium iron phosphate, followed by cooling and concentration. The pH of the concentrate was 9.1, which means that the concentrations of iron sulfate, phosphoric acid, ammonia water and lithium hydroxide in the two aqueous solutions were controlled to pH 9.1 as well as the mixed molar ratio of iron sulfate, phosphoric acid, aqueous ammonia and lithium hydroxide.

Sugar was mixed in the concentrate at a 10% weight ratio compared to lithium iron phosphate, and spray drying and granules were formed through a spray dryer. The formed dry granular particles were subjected to heat treatment at 700 ° C. for 10 hours.

Induced coupling plasma spectroscopy (ICP) analysis, superconducting quantum interference device analysis and Mossbauer spectroscopic analysis were performed on the prepared lithium transition metal polyacid compound to confirm that the molar ratio of Li: Fe: P was 0.820: 1: 0.940.

Comparative example  3

Ferrous sulfate (FeSO ₄ · 7H ₂ O), phosphoric acid (85wt%), and lithium hydroxide (LiOH) are weighed in a molar ratio of 1: 1: 3, and the sugar is 10% by weight so that the carbon content is 2.0% of the final product. Basis weight to make an aqueous solution. Sugar was added as a reducing agent and a carbon coating during the reaction.

The mixed aqueous solution was reacted at 200 ° C. for 5 hours in an autoclave reactor in a 99.9% nitrogen atmosphere. The resulting precipitate was washed several times, concentrated and dried in a vacuum oven at 60 ° C. for 12 hours. The dried particles were heat treated at 700 ° C. for 10 hours.

ICP analysis of the prepared final product confirmed that the molar ratio of Fe: P was 1: 1.

Comparative example  4

Li ₂ CO ₃ , FeC ₂ O ₄ · 2H ₂ O, (NH ₄ ) ₂ HPO ₄ were weighed out at a molar ratio of 1.1: 2: 2 at a speed of 350 rpm using zirconia ball milling. Mix first for 8 hours. For the carbon coating, the first mixture is mixed with sugar, the carbon precursor, in a weight ratio of 2: 8. The reason for separating the primary and secondary mixtures is that homogeneous mixing is impossible when sugar is introduced in the primary mixing process because of the strong hygroscopicity of the sugar.

The secondary mixture was first calcined at 500 ° C., 99.9% nitrogen atmosphere for 8 hours to obtain carbon coated lithium iron phosphate. The primary calcination temperature was chosen as 500 ° C because the temperature at which the main reaction mechanism was terminated by thermal analysis of the mixture of reactants was 500 ° C. Carbon-coated lithium iron phosphate prepared by the first calcination was calcined for 2 hours at 675 ℃, 99.9% nitrogen atmosphere to improve the crystallinity.

ICP analysis was performed on the prepared final product to confirm that the molar ratio of Fe: P was 1: 1.

Comparative example  5

CH ₃ CO ₂ Li.H ₂ O and Fe (NO ₃ ) ₃ .9H ₂ O are weighed in a molar ratio of 1.1: 1 and dissolved in distilled water to obtain an aqueous solution 1. Apart from the aqueous solution 1, sugar (NH ₄ ) ₂ HPO ₄ and 20% by weight of lithium iron phosphate were dissolved in distilled water in a ratio of 1: 1 compared to Fe (NO ₃ ) ₃ · 9H ₂ O. Obtain an aqueous solution 2. The two aqueous solutions are mixed while slowly adding a small amount of the aqueous solution 1 to the aqueous solution 2. The reason for mixing the two aqueous solutions after separating the aqueous solution 1 and the aqueous solution 2 and then mixing the two aqueous solutions is to dissolve the four reactants in distilled water at the same time to obtain one aqueous solution. Because no mixing is possible.

When the mixed aqueous solution is stirred, it becomes a sol and gels. The resulting gel is dried for 24 hours at 80 ℃ and then micropowdered.

The fine powder is first calcined for 8 hours at 500 ° C. and 99.9% nitrogen atmosphere to obtain carbon-coated lithium iron phosphate. Lithium iron phosphate prepared by the first calcination was calcined for 2 hours at 675 ℃, 99.9% nitrogen atmosphere to improve the crystallinity.

ICP analysis was performed on the prepared final product to confirm that the molar ratio of Fe: P was 1: 1.

Measurement of the oxidation state of iron

In order to measure the susceptibility of lithium iron phosphate, the measurement was performed in the temperature range of 4 to 300K using MPMS 5 instrument for measuring the squid magnetometer of Quantum Design.

FIG. 2 shows the relative ratios of +2 and +3 oxidation state iron synthesized in Example 3 (graph a) and Comparative Example 1 (graph b), Comparative Example 4 (graph c), and Comparative Example 5 (graph d) This is the result of measuring the susceptibility of the other four lithium iron phosphates. All of the four lithium iron phosphates of FIG. 2 show that the Neel temperature is generated at an absolute temperature of 52K, all having antiferromagnetic alignment, and that all are magnetic materials of the Curie-Weiss law. According to the Curie-Weiss law (1 / χ) = (T-θ / C, the slope of the straight line in Fig. 2 is (1 / C), which is the inverse of the Curie constant. C = N _A g ² μ _B ² S (S + 1) / 3k = 0.125g ² S (S + 1), (N _A : Avogadro constant, g: Land constant, μ _B : Bohr magnetone, S: total spin quantum number, k: Boltzmann constant) and +3 oxidation S for state iron (3d ⁵ , t _2g ³ e _g ² , five unpaired electrons) is 5/2 and +2 oxidation state iron (3d ⁶ , t _2g ⁴ e _g ² , unpaired electron 4) S is 4/2, so as the ratio of iron to +3 oxide increases, the Curie constant C increases and the inverse of the Curie constant (1 / C) decreases.

And the effective magnetic moment (μ _eff ) is +2 by using the relationship of μ _eff = (3k / N _A ) ^1/2 (χT) ^1/2 = {g ² S (S +1)} ^1/2 μ _B The theoretical effective magnetic moments of and +3 iron oxide can be found. If L = 0 under the condition of a constant Lande (g) value of 2.0023, +2 and theoretical effective magnetic moments of the oxidized iron is 4.90μ _B, if the +3 oxidation state, because iron is 5.92μ _B, the graph of Fig. 2 In (a), the anion-deficient non-stoichiometric lithium iron phosphate of the present invention is 4.61μ _B at room temperature. Considering having an effective magnetic moment and changing the g value, the anion-deficient non-stoichiometric iron phosphate of the present invention consists only of +2 oxidation state iron. On the other hand, lithium iron phosphate in the graphs (c) and (d) of Figure 2 is 5.79 ~ 6.32μ _B at room temperature High effective magnetic moment. It can be seen from the graph (b) of FIG. 2 that the amount of iron in the +3 oxidation state increases as the lithium iron phosphate of (d) increases. (Graph a: 4.61 μ _B , graph b: 4.91 μ _B , graph c: 5.79 μ _B , graph d: 6.32 μ _{B in} FIG. ₂ )

Figure 3a is a Mossbauer spectroscopic analysis of lithium iron phosphate mixed with +2 and +3 iron oxide state, Figure 3b is a Mossbauer spectroscopy of the anion-deficient non-stoichiometric lithium iron phosphate of the present invention synthesized in Example 3 Analysis graph.

X-ray diffraction (XRD) pattern analysis for the characterization of the crystal structure of lithium iron phosphate was carried out using Rigaku's D / MAX 2500H. Measured over a section of ˜100 °. 4A and 4B are XRD graphs of the lithium transition metal polyacid compound synthesized in Example 3 and Comparative Example 3, respectively. Figure 4a is the result of X-ray diffraction spectroscopy of the anion-deficient non-stoichiometric lithium iron phosphate composed only of +2 oxidation state iron of the present invention, in the case of lithium iron phosphate exceeding the limit of +3 iron oxide state, Figure 4b The impurity diffraction peak (▼) appears as shown in the enlarged picture.

⁷ Li Magic Angle Spinning nuclear magnetic resonance (NMR) analysis was performed using Bruker's 400 MHz Avance II + to evaluate the oxidation state of iron through the synthesis of lithium iron phosphate and the atmosphere evaluation around lithium ions. In order to reduce the secondary and secondary chemical shift, the sample was inclined at 15 ° and the sample rotation speed was fixed at 14 kHz and measured. 1 M LiCl solution was used as a reference material. Figure 5 is a graph of the Li-NMR analysis of the lithium transition metal polyacid compound synthesized in Example 3 (graph a) and Comparative Example 3 (graph b), respectively. Since the number of the outermost electrons which do not form an electron pair according to the oxidation state of iron plays a role of shifting the position of the main peak of Li-NMR, it is necessary to examine the outermost electron arrangement for each oxidation state of iron. In the case of +3 oxide iron, three electron-paired electrons are disposed at the lower energy level of t _2g and two electron-paired electrons are disposed at the higher energy level of e _g . In this case, all four electrons (two unpaired electrons and two electron paired electrons) are placed at the lower energy level t _2g and two unpaired electrons are placed at the higher energy level e _g level. have. The unpaired electrons at the t _2g level shift the position of the Li-NMR peak per electron by -24 to -28 ppm, and the unpaired electrons at the e _g level are at the Li-NMR peak per electron. Move the position by +70 ~ + 79ppm. Therefore, the position of the Li-NMR main peak of lithium iron phosphate composed only of +2 oxide iron may be between -14 and +7 ppm. If lithium iron phosphate is composed of only +3 oxide iron, there is no Li-NMR peak because lithium is not present in the material to meet charge neutrality. However, if there is lithium, but not lithium iron phosphate, and there is a material consisting only of +3 iron oxide, the Li-NMR main peak of the material may be between -84 and -72 ppm.

5 is a result of Li-NMR measurement of the anion-deficient non-stoichiometry lithium iron phosphate of the present invention and the position of the Li-NMR main peak is at -10.9 ppm, which is an anion-deficient non-stoichiometry of the present invention. Lithium iron phosphate once more verifies that it consists only of iron in the +2 oxidation state. On the other hand, the graph b of Figure 5 shows the result of Li-NMR measurement of the stoichiometric lithium iron phosphate prepared in Comparative Example 3 and the position of the Li-NMR main peak is -46.2ppm, which is +3 oxidation of the lithium iron phosphate Shows the presence of iron in the state.

Shape of compound

In order to evaluate the particle size and shape of lithium iron phosphate, scanning electron microscope (SEM) measurements were carried out using JEOL's JSM-6300 under the conditions of accelerating voltage of 10000 kV, emission current 9500 nA and working distance 12400 μm. It was. Figure 6a is a SEM image of the granulated particles of the anion-deficient non-stoichiometric lithium transition metal polyacid compound synthesized in Example 3 shows a granule size of 19μm, Figure 6b is an anion deficient synthesized in Example 3 The type non-stoichiometric lithium transition metal polyacid compound is an enlarged SEM image showing that it is a nano-sized ultrafine particle.

Measurement of charge and discharge characteristics of compounds

Evaluation of battery characteristics of the lithium secondary battery using the anion-deficient non-stoichiometric lithium transition metal polyacid compound of the present invention was performed as follows.

The positive electrode plate composition is an anion-deficient non-stoichiometric lithium transition metal polyacid compound produced: conductive material: binder weight ratio 90: 5: 5: The conductive material is a mixture of super-P and VGCF in the same weight ratio, binding Zero was mixed using KF1100 to form an electrode slurry. The electrode slurry was applied on an aluminum thin film under application conditions of an applicator front chamber temperature of 90 ° C., a rear chamber temperature of 120 ° C., and a coating speed of 0.3 m / min, and dried to prepare a positive electrode. The electrolyte was obtained by dissolving 1 mol of LiPF ₆ in a solvent in which ethylene carbonate (EC): ethyl methyl carbonate (EMC) was mixed in a 1: 2 volume ratio. A lithium secondary battery of the coin cell type was manufactured and charged and discharged at a constant current of 0.2 C using a Maccor series 4000.

7 is a charge and discharge graph of a lithium secondary battery using the lithium transition metal polyacid compound synthesized in Comparative Examples 3, 4, 5, and Example 3 as a cathode active material. 7A, 7B and 7C are lithium iron phosphate containing +3 oxide iron in accordance with Comparative Examples 3, 4 and 5, respectively, and FIG. 7D is an anion deficient stoichiometry consisting of only +2 oxide iron according to Example 3 The charge and discharge capacity of lithium iron phosphate is shown. The former discharge capacity is 93 to 143 mAh / g, which is significantly lower than the latter discharge capacity of 163 mAh / g. In addition, a wide planar potential, which is a typical feature of the olivine structure lithium iron phosphate, can be found only in anion-deficient non-stoichiometric lithium iron phosphate composed only of +2 oxidation state iron, as shown in FIG.

Figure 8 shows a curve of charging and discharging anion-deficient non-stoichiometric iron phosphate lithium phosphate (graph VIIa) and the conventional stoichiometric lithium iron phosphate (graph VII b) prepared in Example 3 at a rate of 0.2C, It can be seen that there are two differences between the anion-deficient nonstoichiometric iron phosphate of the invention and the conventional stoichiometric lithium iron phosphate. The first difference is that the discharge capacity of the anion-deficient non-stoichiometric lithium iron phosphate of the present invention is 162.58 mAh / g, which is much higher than the discharge capacity of the conventional stoichiometric lithium iron phosphate of 148.32 mAh / g. The difference in discharge potential is that the anion-deficient non-stoichiometric iron phosphate of the present invention is much narrower than conventional stoichiometric lithium iron phosphate. Both differences mean that the anion-deficient non-stoichiometric iron phosphate of the present invention undergoes a redox reaction in a much more reversible and wider range than conventional stoichiometric lithium iron phosphate. As mentioned above, the +3 iron oxide phosphate of lithium iron phosphate containing +3 iron oxide produced during manufacture cannot form olivine-structure lithium iron phosphate as a crystal structural factor and can be produced as impurities of other crystal structures. Considering the fact that it is present and that impurities composed of +3 iron oxide do not function as a positive electrode active material, conventional stoichiometric lithium phosphate contains impurities that cannot function as positive electrode active material such as +3 iron oxide. Shows.

9 to 16 show curves in which the anion-deficient non-stoichiometric lithium iron phosphates prepared in Examples 1, 2, 4, 5, 6, 7, 8, and 9 were charged and discharged at a rate of 0.2C, respectively.

17 and 18 are charge and discharge graphs of a lithium secondary battery using the lithium transition metal polyacid compound synthesized in Comparative Example 1 and Comparative Example 2 as a cathode active material, respectively.

19 is a discharge capacity value of a lithium secondary battery using the anion-deficient non-stoichiometric lithium transition metal polyacid compound synthesized from Examples 1 to 9 including Comparative Example 1 and Comparative Example 2 as a cathode active material, compared to iron This graph shows the molar ratio of phosphorus in a variable.

19 shows that as the P / Fe molar ratio decreases, the discharge capacity of the anion-deficient non-stoichiometric lithium iron phosphate of the present invention increases. In particular, when the ratio of P / Fe is about 0.95 ≦ P / Fe ≦ about 0.99, the discharge capacity is excellent in terms of increase in discharge capacity, and about 0.95 ≦ P / Fe ≦ about 0.97. Also, when the value of P / Fe is 0.95, the discharge capacity is remarkably increased. FIG. 19 verifies that the production of lithium iron phosphate can be controlled by controlling the proportion of phosphoric acid having a −3 charge, thereby suppressing the production of +3 iron oxide.

Figure 1a shows the olivine crystal structure of the anion-deficient non-stoichiometric lithium iron phosphate, Figure 1b shows the location where an anion vacancies defect can occur in the olivine iron phosphate.

FIG. 2 is a graph of measurement of magnetization rate of lithium transition metal polyacid compound synthesized in Example 3 (graph a) and Comparative Example 1 (graph b), Comparative Example 4 (graph c), and Comparative Example 5 (graph d).

FIG. 3A is a Mossbauer spectroscopic graph of lithium iron phosphate mixed with +2 and +3 iron oxide, and FIG. 3B is a Mossbauer spectroscopic graph of anion-deficient non-stoichiometric lithium iron phosphate synthesized in Example 3. FIG.

4A is an X-ray diffraction spectrum (XRD) graph of the lithium transition metal polyacid compound synthesized in Example 3. FIG.

Figure 4b is an X-ray diffraction spectroscopy (XRD) graph of the lithium transition metal polyacid compound synthesized in Comparative Example 3.

5 is a graph showing the results of Li-nuclear magnetic resonance spectroscopy (NMR) analysis of the lithium transition metal polyacid compounds synthesized in Example 3, respectively.

Graph b of Figure 5 is a graph of the results of Li-nuclear magnetic resonance spectroscopy (NMR) analysis of the lithium transition metal polyacid compound synthesized in Comparative Example 3.

FIG. 6A is a scanning electron microscope (SEM) photograph at 4000 times magnification of granulated and calcined particles of the anion deficient non-stoichiometric lithium transition metal polyacid compound synthesized in Example 3 showing spherical particle shape.

FIG. 6B is a scanning electron microscope showing the granulation of nano-sized ultra-fine particles by granulating and calcining the calcined particles of the anion-deficient non-stoichiometric lithium transition metal polyacid compound synthesized in Example 3 at a magnification of 10000 times. (SEM) picture.

7A is a graph of charge and discharge of a lithium secondary battery using the lithium transition metal polyacid compound synthesized in Comparative Example 3 as a cathode active material.

7B is a charge / discharge graph of a lithium secondary battery using the lithium transition metal polyacid compound synthesized in Comparative Example 4 as a cathode active material.

7C is a graph of charge and discharge of a lithium secondary battery using the lithium transition metal polyacid compound synthesized in Comparative Example 5 as a cathode active material.

7D is a graph of charge and discharge of a lithium secondary battery using the lithium transition metal polyacid compound synthesized in Example 3 as a cathode active material.

8 is a comparative graph of charge and discharge of a lithium secondary battery using the lithium transition metal polyacid compound synthesized in Example 3 (graph a) and Comparative Example 3 (graph b) as a cathode active material.

9 is a charge and discharge graph of a lithium secondary battery using the anion-deficient non-stoichiometric lithium transition metal polyacid compound synthesized in Example 1 as a cathode active material.

10 is a charge and discharge graph of a lithium secondary battery using the anion-deficient non-stoichiometric lithium transition metal polyacid compound synthesized in Example 2 as a cathode active material.

11 is a charge / discharge graph of a lithium secondary battery using the anion-deficient non-stoichiometric lithium transition metal polyacid compound synthesized in Example 4 as a cathode active material.

12 is a charge and discharge graph of a lithium secondary battery using the anion-deficient non-stoichiometric lithium transition metal polyacid compound synthesized in Example 5 as a cathode active material.

FIG. 13 is a charge / discharge graph of a lithium secondary battery using the anion-deficient non-stoichiometric lithium transition metal polyacid compound synthesized in Example 6 as a cathode active material.

14 is a charge / discharge graph of a lithium secondary battery using the anion-deficient non-stoichiometric lithium transition metal polyacid compound synthesized in Example 7 as a positive electrode active material.

15 is a charge and discharge graph of a lithium secondary battery using the anion-deficient non-stoichiometric lithium transition metal polyacid compound synthesized in Example 8 as a cathode active material.

16 is a charge / discharge graph of a lithium secondary battery using the anion-deficient non-stoichiometric lithium transition metal polyacid compound synthesized in Example 9 as a cathode active material.

17 is a graph of charge and discharge of a lithium secondary battery using the lithium transition metal polyacid compound synthesized in Comparative Example 1 as a cathode active material.

18 is a charge and discharge graph of a lithium secondary battery using the lithium transition metal polyacid compound synthesized in Comparative Example 2 as a cathode active material.

19 is a discharge capacity value of a lithium secondary battery using the anion-deficient non-stoichiometric lithium transition metal polyacid compound synthesized from Examples 1 to 9 including Comparative Example 1 and Comparative Example 2 as a cathode active material, compared to iron This graph shows the molar ratio of phosphorus in a variable.

Claims (1)

The compound represented by following formula (1) which is an electrode active material.

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