KR20100029501A - Olivine type positive active material for lithium second battery, method for preparing the same, and lithium battery comprising the same - Google Patents

Abstract

PURPOSE: An olivine type positive active material for a lithium second battery is provided to produce a lithium secondary battery with high energy density due to a carbon coating layer with high conductivity. CONSTITUTION: An olivine type positive active material for a lithium second battery comprises a core material represented by chemical formula 1: Li_xM_yM'_zXO_(4-w)B_w and a carbon coating layer with high conductivity which surrounds the core material. The carbon coating layer includes at least one or two kinds of carbon precursor selected from polyvinylpyrrolidone, water-soluble polymer and conductive polymer.

Description

Olivine type positive electrode active material for lithium secondary batteries, a method of manufacturing the same, and a lithium secondary battery comprising the same {Olivine type positive active material for lithium second battery, Method for preparing the same, and Lithium battery comprising the same}

The present invention is to solve the problem of low electrical conductivity of the conventional olivine-type positive electrode active material, to form a carbon coating layer having a uniform conductivity in the precursor (FePO ₄ ) material of the micron size to increase the energy density per volume, the carbon coating layer As an invention completed by selecting a carbon coating material to form a form and the optimum amount of use, an olivine-type positive electrode active material for a lithium secondary battery comprising a core material and a carbon coating layer, a method of manufacturing the same, and a lithium secondary comprising the same It relates to a battery.

Recently, it is used repeatedly for charging and discharging as a power source for portable electronic devices such as mobile phones, portable personal digital assistants (PDAs), notebook computers, portable electronic devices such as digital cameras, camcorders, electric bicycles, and electric vehicles. The demand for lithium batteries is growing exponentially. Commercially available lithium batteries use LiCoO ₂ for the positive electrode and carbon for the negative electrode. Cobalt, the starting material of the positive electrode active material, is low in reserve and expensive, and development of an alternative positive electrode material is required due to toxicity and environmental pollution. have. LiNiO ₂ , LiCo _x Ni _1-x O _2, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiMn ₂ O ₄ , and the like are currently being actively researched and developed. LiNiO ₂ which has the same layered structure as LiCoO ₂ is not commercialized due to the difficulty in synthesizing the material in a stoichiometric ratio and the problem of thermal stability.

LiMn ₂ O ₄ , a 4V class spinel cathode active material, has the advantage of using manganese as a starting material, and some of them are commercialized in low-cost products, but due to the structural variation called Jahn-Teller distortion caused by manganese ³⁺ There is a problem that the life characteristics are not good. Therefore, a positive electrode active material that is more economical, stable, and has a high capacity and good cycle characteristics is desired.

Currently, it has an olivine structure as a cathode active material of a lithium battery, and has a chemical formula Li _x M _y PO ₄ (where x is 0 <x ≦ 2, y is 0.8 ≦ y ≦ 1.2, and M is a periodic table Group 3d transition metal). Studies on the compound represented by) are in progress. In addition, the use of LiFePO ₄ as a positive electrode of a lithium ion battery among the compounds represented by Li _x M _y PO ₄ is disclosed in Japanese Patent Laid-Open No. 9-171827. LiFePO ₄ is not only environmentally friendly, rich in reserves, very low raw material price, and can easily implement low power and low voltage than conventional cathode active material, and the theoretical capacity is 170 mAh / g. However, due to the low conductivity of the olivine material, many research groups increase the diffusion rate of lithium by making the particle size nanoscale, and improve the electrochemical properties by improving the electrical conductivity through carbon coating. However, because the particle size is nano-size has a disadvantage of low energy density per volume, the research to develop the particle size to the micron size is in progress. However, when the size of the precursor is a micron size, the carbon coating should be very uniform, and the coating uniformity may vary depending on the carbon coating material, thereby affecting the electrochemical properties. That is, there is a need for a method capable of uniformly coating carbon with an optimal carbon content by selecting an optimal carbon coating material.

Accordingly, the present inventors have made efforts to solve the above problems, and uniformly form a conductive carbon coating layer on the micron-sized precursor (FePO ₄ ) material, and finds the carbon material forming the carbon coating layer and its optimal amount of use. The present invention has been completed. That is, an object of the present invention is to provide an olivine-type positive electrode active material for a lithium secondary battery having improved electrical conductivity and high energy density.

The present invention for achieving the above object relates to an olivine-type positive electrode active material for a lithium secondary battery,

A core material represented by Formula 1; And a conductive carbon coating layer containing one or two or more carbon precursors selected from polyvinylpyrrolidone, a water-soluble polymer, and a conductive polymer surrounding the core material.

Li _x M _y M ' _z XO _4-w B _w

In Formula 1, M and M 'are the same as or different from each other, Fe, Ni, Co, Mn, Cr, Zr, Nb, Cu, V, Mo, Ti, Zn, Al, Ga, Mg, B and these Is an element selected from the group consisting of a combination of the above, X is an element selected from the group consisting of P, As, Bi, Sb, and combinations thereof, wherein B is a group consisting of F, S, and combinations thereof X, y, z, and w are each 0 <x≤1, 0 <y≤1, 0 <z≤1, 0 <x + y + z≤2, and 0≤w It is a real number satisfying ≤0.5.

In addition, the present invention relates to a method for manufacturing the olivine-type positive electrode active material for a lithium secondary battery,

A first step of preparing an M-X precursor represented by the following Chemical Formula 6 by first baking an aqueous solution containing the M-X precursor represented by the Chemical Formula 6;

 A second step of mixing the M-X precursor with polyvinylpyrrolidone, a water-soluble polymer and a conductive polymer selected from one or two or more carbon precursors, followed by heating and stirring to obtain a carbon-coated M-X precursor;

After mixing the carbon-coated MX precursor and a single or two or more lithium compounds selected from lithium hydroxide, lithium fluoride, lithium nitrate, lithium carbonate and lithium acetate, and then secondary firing at a temperature of 650 ℃ ~ 850 ℃ secondary cathode active material To obtain a third step; characterized in that it comprises a.

MXO _4-w B _w

In Formula 2, M is an element selected from the group consisting of Fe, Ni, Co, Mn, Cr, Zr, Nb, Cu, V, Mo, Ti, Zn, Al, Ga, Mg, B and combinations thereof X is an element selected from the group consisting of P, As, Bi, Sb, and combinations thereof, and B is an element selected from the group consisting of F, S, and combinations thereof, wherein w is 0 This is a real number satisfying ≤ w ≤ 0.5.

Since the olivine-type positive electrode active material for a lithium secondary battery of the present invention has a carbon coating layer having high electrical conductivity, it is possible to produce a lithium secondary battery having a high energy density, and to control the type and amount of the carbon precursor used. It can change the electrochemical properties of the active material.

When described in detail with respect to the olivine-type positive electrode active material for a lithium secondary battery of the present invention and a manufacturing method thereof introduced above.

The present invention relates to an olivine-type positive electrode active material for a lithium secondary battery,

A core material represented by Formula 1; And

A carbon coating layer having conductivity including polyvinylpyrrolidone surrounding the core material, a water-soluble polymer, and a conductive polymer selected from one or more carbon precursors;

It characterized by including the.

[Formula 1]

Li _x M _y M ' _z XO _4-w B _w

In Formula 1, M and M 'are the same as or different from each other, Fe, Ni, Co, Mn, Cr, Zr, Nb, Cu, V, Mo, Ti, Zn, Al, Ga, Mg, B and these Is an element selected from the group consisting of combinations, X is an element selected from the group consisting of P, As, Bi, Sb and combinations thereof, and B is selected from the group consisting of F, S and combinations thereof. Element, wherein x, y, z, and w are each 0 <x≤1, 0 <y≤1, 0 <z≤1, 0 <x + y + z≤2, and 0≤w≤0.5 It is a mistake to be satisfied.

The core material represented by Chemical Formula 1 may be selected from the group consisting of Chemical Formula 2, Chemical Formula 3, and combinations thereof, and more preferably, Chemical Formula 4, Chemical Formula 5, and combinations thereof It is better to use the one selected in.

LiFe _1-a A _a PO ₄

In Chemical Formula 2, A is an element selected from the group consisting of Ni, Co, Mn, Cr, Zr, Nb, Cu, V, Mo, Ti, Zn, Al, Ga, Mg, B, and combinations thereof. a is a real number of 0 <a <1.

Li _1-a A _a FePO ₄

In Chemical Formula 3, A is an element selected from the group consisting of Ni, Co, Mn, Cr, Zr, Nb, Cu, V, Mo, Ti, Zn, Al, Ga, Mg, B, and combinations thereof. A is a real number of 0 <a <1.

LiFe _1-a A _a PO _4-z B _z

In Formula 4, A is an element selected from the group consisting of Ni, Co, Mn, Cr, Zr, Nb, Cu, V, Mo, Ti, Zn, Al, Ga, Mg, B, and combinations thereof, B is an element selected from the group consisting of F, S, and a combination thereof, wherein a is 0 <a <1, and z is a real number of 0.01≤z≤0.5.)

Li _1-a A _a FePO _4-z B _z

In Chemical Formula 5, A is an element selected from the group consisting of Ni, Co, Mn, Cr, Zr, Nb, Cu, V, Mo, Ti, Zn, Al, Ga, Mg, B, and combinations thereof, B is an element selected from the group consisting of F, S, and a combination thereof, wherein a is 0 <a <1 and z is a real number of 0.01 ≦ z ≦ 0.5.

In the present invention, the core material of the olivine-type positive electrode active material for a lithium secondary battery may have an average particle diameter of 0.1 μm to 15 μm, preferably 0.2 μm to 10 μm, and more preferably 5 μm to 8 μm. In this case, when the average particle diameter of the core material is less than 0.1 µm, there is a problem in manufacturing the electrode due to low tap density. When the average particle diameter exceeds 15 µm, the tap density increases, but the specific surface area is too small, and the contact area with the electrolyte is also small. It is not preferable because it interferes with the intercalation and deintercalation of Li ions. In addition, the core material has a tap density of 0.5 g / cm ³ to 2.0 g / cm ³ , preferably 0.7 g / cm ³ to 1.8 g / cm ^3, and more preferably 1.2 g / cm ³ to 1.6 g /. It is good to be cm ³ . Here, the reply if a problem when a back electrode prepared a tap density of less than 0.8 g / cm ³ of binhyeong positive electrode active material, and exceeding 2.0 g / cm ^3, the capacity of the battery, because the particle diameter of the positive electrode active material becomes large as more than 15 ㎛ It is preferable to have a tap density within the above range because there is a problem of decreasing, which is not preferable. The core material is preferably spherical, where spherical may be circular or elliptical, but is not particularly limited thereto. The core material has a spherical shape because the core material is manufactured using a spherical olivine positive electrode active material precursor.

The carbon precursor included in the carbon coating layer, which is one of the components of the present invention, may be selected from polyvinylpyrrolidone, a water-soluble polymer and a conductive polymer, or two or more types thereof, and the water-soluble polymer may be polyvinyl alcohol or polyethylene. Single or two or more species selected from imine, bobbin serum albumin and polyvinylpyrrolidone may be used, and the conductive polymer may be polyaniline, polypyrrole, polyacetylene, polythiophene and One kind or two or more kinds selected from poly sulfur nitride may be used. The carbon coating layer is prepared by adding and heat treating a carbon precursor when preparing the core material. The carbon coating layer preferably has a thickness of 5 nm to 50 nm, wherein the thickness of the carbon coating layer is less than 5 nm. When the electrical conductivity is improved, the problem may be insignificant, and when the thickness exceeds 50 nm, the intercalation and deintercalation performance of lithium is reduced due to the carbon coating layer that is too thick, thereby reducing the capacity of the battery and the tap density of the positive electrode active material. It is preferable to have a thickness of the carbon coating layer in the above range because the problem of lowering may occur.

Hereinafter, a method of manufacturing the olivine-type positive electrode active material for a lithium secondary battery of the present invention will be described in detail.

[Manufacturing method of olivine-type positive electrode active material for lithium secondary battery]

Method for producing the olivine-type positive electrode active material for a lithium secondary battery of the present invention

A first step of preparing an M-X precursor represented by the following Chemical Formula 6 by first baking an aqueous solution containing the M-X precursor represented by the Chemical Formula 6;

 A second step of mixing the M-X precursor with polyvinylpyrrolidone, a water-soluble polymer and a conductive polymer selected from one or two or more carbon precursors, followed by heating and stirring to obtain a carbon-coated M-X precursor;

After mixing the carbon-coated MX precursor and a single or two or more lithium compounds selected from lithium hydroxide, lithium fluoride, lithium nitrate, lithium carbonate and lithium acetate, and then secondary firing at a temperature of 650 ℃ ~ 850 ℃ secondary cathode active material To obtain a third step; characterized in that it comprises a.

 [Formula 6]

MXO _4-w B _w

In Formula 6, M is an element selected from the group consisting of Fe, Ni, Co, Mn, Cr, Zr, Nb, Cu, V, Mo, Ti, Zn, Al, Ga, Mg, B and combinations thereof , X is an element selected from the group consisting of P, As, Bi, Sb and combinations thereof, B is an element selected from the group consisting of F, S, and combinations thereof, wherein w is 0≤ This is a real number satisfying w≤0.5.

In the first step, the hydrate containing the M-X precursor is

M compounds containing an element selected from the group consisting of Fe, Ni, Co, Mn, Cr, Zr, Nb, Cu, V, Mo, Ti, Zn, Al, Ga, Mg, B and combinations thereof; And a solvent selected from the group consisting of water, methanol, ethanol, isopropyl alcohol, and combinations thereof (hereinafter referred to as "M aqueous solution"), and P, As, Bi, Sb, and combinations thereof. X compound containing an element selected from the group; And a solvent selected from the group consisting of water, methanol, ethanol, isopropyl alcohol, and combinations thereof (hereinafter referred to as "X aqueous solution"), wherein the pH is adjusted using a pH adjuster. Maintain 2 to 5. When mixing the M aqueous solution and the X aqueous solution, each aqueous solution is added while mixing at a rate of 0.03 to 1.2 mol / h, and when mixing, it is good to mix while stirring at a speed of 500 to 1500 rpm. Herein, when the addition rate of the aqueous solution is less than 0.03 mol / h, the yield of the M-X precursor is low, which is not preferable. When the feed rate is supplied to the reactor in excess of 1.2 mol / h, the solubility may be poor and mixing may not be performed well.

The M compound contains an element selected from the group consisting of Fe, Ni, Co, Mn, Cr, Zr, Nb, Cu, V, Mo, Ti, Zn, Al, Ga, Mg, B and combinations thereof Acetate, nitrate, sulfate, carbonate, citrate, phthalate, perchlorate, acetylacetonate, acrylate, Formate, oxalate, halide, oxyhalide, boride, oxide, sulfide, peroxide, alkoxide, Hydroxide, ammonium, acetylacetone, hydrates thereof, and combinations thereof may be preferably used, more preferably iron ethylenediammonium sulfate (Iron). ethylenediammonium sulfate) Titanium bis (ammoniumlactato) dihydroxide, Manganese monoperoxyphthalate, Aluminum phnoxide, Boric acid, Boron trifluoride di One selected from the group consisting of boron trifluoride diethyl etherate, boron trifluoride-propanol, hydrates thereof, and combinations thereof can be used.

And the X compound is acetate, nitrate, sulfate, citrate, containing an element selected from the group consisting of P, As, Bi, Sb, and combinations thereof. Perchlorate, halides, oxyhalides, oxides, sulfides, alkoxides, hydrates thereof, and combinations thereof may be preferably used. More preferably, the X compound may be selected from the group consisting of phosphoric acid, bismuth neodecanoate, hydrates thereof, and combinations thereof.

The pH adjusting agent may be selected from the group consisting of ammonia aqueous solution, carbon dioxide gas, a compound containing an OH group and combinations thereof. And, when mixing the aqueous M solution and the aqueous X solution is preferably carried out at a temperature of 30 ℃ ~ 70 ℃, it is preferably carried out for 12 to 24 hours. At this time, there is a problem that it takes a long time to prepare a hydrate containing the MX precursor because the reactivity between the M aqueous solution and the X aqueous solution is low when mixing at less than 30 ℃, when the M aqueous solution and X is carried out at a temperature exceeding 70 ℃ High reactivity between the aqueous solution can reduce the reaction time, but there may be a problem that unwanted by-products are produced. In addition, the MX precursor-containing hydrate particles formed when the reaction is less than 12 hours may be non-uniform, and if it is more than 24 hours, new particles having a different size and shape other than the spherical MX precursor-containing hydrate particles to be prepared may be formed. There is a problem that can be.

The M-X precursor-containing hydrate thus prepared was washed with distilled water, and vacuum dried at 50 ° C. to 90 ° C. for 12 to 24 hours to completely remove impurities. When the temperature of the vacuum drying is less than 50 ℃ there is a problem that a long time is required to completely remove the water that is chemically adsorbed in the hydrate particles, if the temperature exceeds 90 ℃ the hydrate is oxidized if the vacuum is not stable There is a problem. In addition, when the vacuum drying time is less than 12 hours, there is a problem in that the water that is chemically adsorbed in the MX-containing hydrate particles cannot be completely removed, and if it exceeds 24 hours, the process time is wasted because it is already completely dried. Not desirable

The first firing of the first step is preferably carried out for 5 to 20 hours at a temperature of 450 ℃ to 600 ℃, at this time, there is a problem that the crystal of the MX precursor is difficult to form if the firing temperature is less than 450 ℃, 600 Since the process cost and the process time are wasted when the temperature is exceeded, it is not preferable. When the primary firing time is less than 5 hours, there is a problem in that the crystallinity of the prepared M-X precursor is not good, and when it exceeds 20 hours, it is not preferable because the process cost and process time is wasted. The primary firing may be performed in an atmosphere selected from the group consisting of a reducing atmosphere, an inert atmosphere, and a combination thereof, and the atmosphere may be nitrogen gas, argon gas, argon / hydrogen mixed gas, and combinations thereof. It is more preferable that it is the atmosphere chosen from the group which consisted of. In particular, when the primary firing is performed in a reducing atmosphere, the M-X precursor having desired crystallinity can be formed from the M-X precursor-containing hydrate, which is preferable. The M-X precursor obtained by primary firing is preferably spherical, where spherical may be selected from the group consisting of circular, elliptical, and combinations thereof, but is not particularly limited thereto. When manufacturing the positive electrode active material for lithium batteries using the said spherical M-X precursor, since a spherical olivine-type positive electrode active material can be manufactured, it is preferable.

The M-X precursor may be nano-sized primary particles, more preferably secondary particles formed by agglomeration of the primary particles.

In addition, in preparing the hydrate containing the MX precursor in the first step, an aqueous B solution containing an element selected from the group consisting of F, S, and combinations thereof may be further added in addition to the aqueous M solution and the X aqueous solution. Nickel fluoride, iron fluoride, cobalt fluoride, manganese fluoride, chromium fluoride, zirconium fluoride, niobium Niobium fluoride, Copper fluoride, Vanadium fluoride, Titanium fluoride, Zinc fluoride, Aluminum fluoride, Gallium fluoride (Gallium fluoride), manganese fluoride (Magnesium fluoride), boron fluoride (Boron trifluoride), NH ₄ F, LiF, AlF ₃ , B compounds selected from the group consisting of S, Li ₂ S, hydrates thereof, and combinations thereof; And a solvent selected from the group consisting of water, methanol, ethanol, isopropyl alcohol, and combinations thereof.

In the second step, the carbon precursor may be a single or two or more selected from polyvinylpyrrolidone, a water-soluble polymer and a conductive polymer, and the carbon precursor is polyvinyl alcohol, polyethyleneimine and bobbin serum. One or two or more selected from albumin may be used, and the conductive polymer may be selected from polyaniline, polypyrrole, polyacetylene, polythiophene, and polysulfur nitride. Selected single species or two or more species can be used. The carbon precursor may be used by adding and dispersing 1 to 3 parts by weight of the carbon precursor with respect to 100 parts by weight of the M-X precursor in the mixture of the second step. Here, if the carbon precursor is less than 1 part by weight with respect to 100 parts by weight of the MX precursor, the electrochemical properties of the positive electrode active material are reduced since the coating is not entirely coated on the precursor particles. Is slow, the electrochemical properties of the positive electrode active material is poor, it is preferable to use within the above range.

In the third step, the secondary firing is preferably fired for 10 to 24 hours at a temperature of 650 ℃ ~ 850 ℃, wherein, if the firing temperature is less than 650 ℃ positive electrode active material prepared is less crystallinity of the positive electrode active material When the capacity of P is reduced, it is not preferable, and when it exceeds 850 ° C., since impurities (Li ₃ PO ₄ , Fe ₂ P) peaks are formed, the capacity is reduced, which is not preferable. And when firing in less than 10 hours there is a problem that all the M in the MX precursor is not reduced, if more than 20 hours, there is a problem that wastes the process time and process cost. The secondary firing is preferably performed in an atmosphere selected from the group consisting of a reducing atmosphere, an inert dust, and a combination thereof, preferably a nitrogen gas, an argon gas, an argon / hydrogen mixed gas, and a combination thereof. It is preferable that the atmosphere is selected from the group. Particularly, when the secondary firing is performed in a reducing atmosphere, M is more preferably reduced in the MX precursor to form an olivine structure.

As described above, the olivine-type positive electrode active material for a lithium secondary battery of the present invention manufactured through the first step to the third step process has a carbon precursor having excellent electrical conductivity as a coating layer, and thus has a high battery capacity because of its high energy density. have.

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

Preparation of the olivine-type positive electrode active material

Example 1

Coprecipitation reactor was placed in a 4L distilled water (volume: 4L, the output of more than 90W rotary motor), iron nitrate aqueous solution (M aqueous solution), H ₃ PO ₄ aqueous solution (X solution), and ammonia water was supplied. The iron nitrate aqueous solution and the H ₃ PO ₄ aqueous solution were mixed in advance for a sufficient time so that the total molar concentration of the iron nitrate and H ₃ PO ₄ aqueous solution in the reactor was 2M, and supplied at 0.6 mol / hr. After mixing the iron nitrate aqueous solution and H ₃ PO ₄ aqueous solution in advance, the reason for supplying was to separately feed the iron nitrate aqueous solution and H ₃ PO ₄ aqueous solution up to the existing patent, in this case exactly the input rate of the two aqueous solution in the reactor Even if the feeding rate is slightly different, there is a problem in the composition of the product. In addition, ammonia water at a concentration of 6 M / L was supplied at an appropriate flow rate so that the pH inside the reactor was maintained at 2.

While maintaining the temperature in the reactor at 50 ° C., the solution was stirred at a speed of 1000 rpm to co-precipitate iron nitrate with H ₃ PO ₄ . The average residence time of the reactants in the reactor was adjusted to a flow rate of about 24 hours. After the reaction reached steady state, iron-phosphate hydrate was continuously obtained through the overflow pipe. The obtained iron-phosphate hydrate (hydrate containing MX precursor) was dried at 70 ° C. for 24 hours under vacuum atmosphere.

The iron-phosphate hydrate was calcined at 550 ° C. for 10 hours under a nitrogen atmosphere to obtain iron-phosphate (M-X precursor).

1 part by weight of polyvinylpyrrolidone (PVP) was dispersed in ethanol based on 100 parts by weight of iron-phosphate. Iron-phosphate was added to polyvinylpyrrolidone (PVP) dispersed in the ethanol and stirred until all of the ethanol was evaporated to obtain carbon-coated iron-phosphate.

LiFePO ₄ having an olivine structure by mixing the carbon-coated iron-phosphate and lithium carbonate (Li ₂ CO ₃ ) in a 1: 1 molar ratio and calcining at 750 ° C. for 15 hours at an elevated rate of 2 to 5 ° C./min. A positive electrode active material powder was obtained.

Examples 2 to 3

In the same manner as in Example 1, Example 2 was prepared by dispersing 2 parts by weight of polyvinylpyrrolidone (PVP) in 100 parts by weight of iron-phosphate in ethanol, LiFePO ₄ positive electrode active material powder, Example 3 3 parts by weight of the polyvinylpyrrolidone was used to prepare a LiFePO ₄ positive electrode active material powder having an olivine structure.

Production Example

Manufacture of Lithium Secondary Battery

Each of the positive electrode active material powders prepared in Examples 1 to 3, acetylene black as a conductive material, and polyvinylidene fluoride (PVdF) as a binder were mixed at a weight ratio of 85: 7.5: 7.5 to prepare a slurry. The slurry was uniformly applied to an aluminum foil having a thickness of 20 μm, and vacuum dried at 120 ° C. to prepare a positive electrode. The prepared anode and lithium foil were used as counter electrodes, and a porous polyethylene membrane (manufactured by Celgard ELC, Celgard 2300, thickness: 25 μm) was used as a separator, and ethylene carbonate and diethyl carbonate were 1: 1 in volume ratio. A coin battery was prepared using a liquid in which LiPF ₆ was dissolved at a concentration of 1 M in a mixed solvent as an electrolyte.

Experimental Example 1

Scanning electron microscope observation of the prepared positive electrode active material powder

The olivine-type positive electrode active material prepared in Examples 1 to 3 was observed with a scanning electron microscope (SEM, JSM 6400, JEOL Co., Ltd.), and the results are sequentially shown in FIGS. 1 to 3.

Experimental Example 2

X-ray diffraction analysis of the prepared positive electrode active material powder

X-ray diffraction analysis (XRD, Rint-2000, manufactured by Rigaku) was performed on the olivine-type positive active material prepared according to Examples 1 to 3, and the results are shown in FIGS. 4 to 6, respectively.

4 to 6, the same peaks as Card Nos. 40-1499 of Joint Committee on Powder Diffraction Standards (JCPDS) are shown, and thus the cathode active materials prepared in Examples 1, 2, and 3 are LiFePO ₄ , which has an olivine structure. You can see that it has.

In addition, as the polyvinylpyrrolidone (PVP) content increases, Fe ₂ P peaks (2θ = 40.28 °, 44.20 °, and 47.29 °) are formed, and lithium phosphate peaks (2θ = 22.32 ° and 23.16 °) are formed. It can be seen.

Experimental Example 3

Measurement of characteristics of manufactured lithium secondary battery

Each coin cell manufactured using the positive electrode active material powders prepared in Examples 1 to 3 was used in an electrochemical analyzer (Toscat 3100U, manufactured by Toyo System) at 30 ° C. and a potential region of 2.5 V to 4.3 V. The charge and discharge experiments were carried out at a current density of 15 mA g ⁻¹ . The capacity of each coin battery manufactured using the positive electrode active material powders prepared in Examples 1, 2, and 3 is shown in FIGS. 7, 8, and 9, respectively.

Referring to FIG. 7, since the charge and discharge graph has a flat surface, a charge and discharge graph of a battery including a cathode active material having a typical olivine structure is shown, and the discharge capacity is 150 mAh / g. .

Referring to FIGS. 8 and 9, it can be seen that as the carbon content increases, the discharge curve does not sharply bend and shows a slope and a capacity appears. This shows a bad effect on the electrochemical properties because the impurity peak grows large, as can be seen on XRD due to the high carbon content.

All simple modifications or changes of the present invention can be easily carried out by those skilled in the art, and all such modifications or changes can be seen to be included in the scope of the present invention.

Through the above examples and experimental examples it can be seen that the electrochemical properties of the positive electrode active material is greatly changed according to the conditions of the carbon content.

1 is a scanning electron microscope (SEM) photograph of the olivine-type positive electrode active material prepared in Example 1 of the present invention.

Figure 2 is a scanning electron micrograph of the olivine-type positive electrode active material prepared in Example 2 of the present invention.

Figure 3 is a scanning electron micrograph of the olivine-type positive electrode active material prepared in Example 3 of the present invention.

Figure 4 is a graph showing the X-ray diffraction analysis (XRD) results of the olivine-type positive electrode active material prepared in Example 1 of the present invention.

5 is a graph showing the results of X-ray diffraction analysis (XRD) of the olivine-type positive electrode active material prepared in Example 2 of the present invention.

6 is a graph showing the results of X-ray diffraction analysis of the olivine-type positive electrode active material prepared in Example 3 of the present invention.

7 is a graph showing a change in capacity according to the voltage change of a battery manufactured using the cathode active material prepared in Example 1 of the present invention.

8 is a graph showing the discharge characteristics of the battery prepared using the positive electrode active material prepared in Example 2 of the present invention.

9 is a graph showing the discharge characteristics of the battery prepared using the positive electrode active material prepared in Example 3 of the present invention.

Claims (6)

A core material represented by Formula 1; And a polyvinylpyrrolidone surrounding the core material, a conductive carbon coating layer containing one or two or more carbon precursors selected from a water-soluble polymer and a conductive polymer; an olivine type for a lithium secondary battery, characterized in that it comprises a Positive electrode active material; [Formula 1] Li _x M _y M ' _z XO _4-w B _w In Formula 1, M and M 'are the same as or different from each other, Fe, Ni, Co, Mn, Cr, Zr, Nb, Cu, V, Mo, Ti, Zn, Al, Ga, Mg, B and these Is an element selected from the group consisting of combinations, X is an element selected from the group consisting of P, As, Bi, Sb and combinations thereof, and B is selected from the group consisting of F, S, and combinations thereof Where x, y, z, and w are each 0 <x≤1, 0 <y≤1, 0 <z≤1, 0 <x + y + z≤2, and 0≤w≤0.5 Is a mistake to satisfy. The method of claim 1, The core material has a particle diameter of 5 ㎛ to 8 ㎛, tap density of 1.2 g / cm ³ ~ 1.6 g / cm ³ olivine-type positive electrode active material for a lithium secondary battery. The method of claim 1, The thickness of the carbon coating layer is an olivine-type positive electrode active material for a lithium secondary battery, characterized in that 10 to 50 nm. The method of claim 1, The water-soluble polymer is one or a mixture of two or more selected from polyvinyl alcohol, polyethyleneimine, and bobbin serum albumin, and the conductive polymer is polyaniline, polypyrrole, polyacetylene, polythiophene, and polythiophene. And olivine-type positive electrode active material for a lithium secondary battery, characterized in that the mono- or a mixture of two or more selected from poly sulfur nitride (poly sulfur nitride). A first step of preparing an M-X precursor represented by the following Chemical Formula 6 by first baking an aqueous solution containing the M-X precursor represented by the Chemical Formula 6;  A second step of mixing the M-X precursor with polyvinylpyrrolidone, a water-soluble polymer and a conductive polymer selected from one or two or more carbon precursors, followed by heating and stirring to obtain a carbon-coated M-X precursor; After mixing the carbon-coated MX precursor and a single or two or more lithium compounds selected from lithium hydroxide, lithium fluoride, lithium nitrate, lithium carbonate and lithium acetate, and then secondary firing at a temperature of 650 ℃ ~ 850 ℃ secondary cathode active material Obtaining a third step; Method for producing an olivine-type positive electrode active material for a lithium secondary battery, characterized in that it comprises a; [Formula 6] MXO _4-w B _w In Formula 6, M is an element selected from the group consisting of Fe, Ni, Co, Mn, Cr, Zr, Nb, Cu, V, Mo, Ti, Zn, Al, Ga, Mg, B and combinations thereof X is an element selected from the group consisting of P, As, Bi, Sb, and combinations thereof, and B is an element selected from the group consisting of F, S, and combinations thereof, wherein w is 0 This is a real number satisfying ≤ w ≤ 0.5. A lithium secondary battery comprising the olivine-type positive electrode active material of any one of claims 1 to 4.

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