KR101471417B1 - Method for Preparing Cathode Active Material for Secondary Battery and Cathode Active Material Using the Same - Google Patents

Abstract

The present invention relates to a method for producing lithium iron phosphate of an olivine crystal structure, comprising the steps of: (1) preparing primary particles having an olivine crystal structure; (2) preparing a mixture of the primary particles and the conductive material; And (3) a step of drying the mixture and agglomerating the primary particles to prepare secondary particles having a structure in which the conductive material is dispersed among the lithium iron phosphate particles; and a method for producing lithium iron phosphate .

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for preparing a cathode active material for a secondary battery and a cathode active material for the cathode active material,

The present invention relates to a process for producing lithium iron phosphate having an olivine crystal structure, and more particularly, to a process for preparing primary particles having an olivine crystal structure, a process for preparing a mixture of the primary particles and a conductive material, And a step of drying the mixture and agglomerating the primary particles to prepare secondary particles having a structure in which the conductive material is dispersed among the lithium iron phosphate particles. .

Background Art [0002] As a negative electrode active material of a lithium secondary battery, which has recently been rapidly used, a carbon material is mainly used, and use of lithium metal, a sulfur compound, a silicon compound, and a tin compound is also considered. Lithium-containing cobalt oxide (LiCoO ₂ ) is mainly used as a cathode active material of such a lithium secondary battery, and a lithium-containing manganese oxide such as LiMnO _{2 having a} layered crystal structure and LiMn ₂ O _{4 having a} spinel crystal structure, The use of oxide (LiNiO ₂ ) is also considered.

Although LiCoO ₂ is excellent in various physical properties such as cycle characteristics, it is used at present, but its safety is low and it is expensive due to the resource limit of cobalt as a raw material, so there is a limit to mass use as a power source for fields such as electric vehicles. LiNiO ₂ is difficult to apply to actual mass production process at a reasonable cost due to its characteristics depending on the production method thereof, and lithium manganese oxides such as LiMnO ₂ and LiMn ₂ O ₄ have poor cycle characteristics.

Recently, a method of using a lithium transition metal phosphate as a cathode active material has been studied. Lithium transition metal phosphates are classified into Nasicon structure Li _x M ₂ (PO ₄ ) ₃ and olivine structure LiMPO ₄ , which are superior to conventional LiCoO ₂ in terms of high temperature stability. . At present, Li ₃ V ₂ (PO ₄ ) ₃ is known among the nacicon structure compounds, and LiFePO ₄ and Li (Mn, Fe) PO ₄ are the most widely studied among the olivine structure compounds.

Of the olivine-structured compounds, LiFePO ₄ , in particular, has a high bulk density of ~3.5 V vs. 3.6 g / cm ³ versus lithium and a high theoretical stability at a theoretical capacity of 170 mAh / g as compared to cobalt (Co) Since Fe is used as a raw material at low cost, it is highly likely to be applied to a cathode active material for a lithium secondary battery in the future.

However, due to the characteristics of the active material used in the lithium secondary battery, high density and excellent rate characteristics are required. In the case of LiFePO ₄ , it shows a very low Li ⁺ diffusion rate and electric conductivity. Therefore, when LiFePO ₄ is used as the positive electrode active material, there is a problem that the internal resistance of the battery increases, and the amount of the active material is reduced by increasing the conductive material content in the preparation of the mixture, The polarization potential is increased to reduce the battery capacity.

In order to solve this problem, some prior arts such as Japanese Patent Application Laid-Open No. 2001-110414 disclose a technique of adding a conductive material to olivine-type metal phosphate for improving conductivity.

However, the conventional LiFePO ₄ is Li ₂ bar, the firing process by the carbon source to be added to the lithium source and the conductivity increase is produced through such as CO ₃ or LiOH high conventional method, using a lithium source hydrothermal method Li ₂ CO ₃ There is a problem in that a large amount is generated.

Such Li ₂ CO ₃ decomposes at the time of charging or reacts with the electrolyte to generate CO ₂ gas, which is disadvantageous in that excessive gas is generated during storage or cycling. Thereby causing a swelling phenomenon of the battery and deteriorating high-temperature safety.

Another approach is to use a method of reducing the diffusion distance by making the particle size of LiFePO ₄ small, but in this case, a large BET value is expensive to manufacture the battery.

In addition, although a method of adding a carbon precursor to coat the surface of particles of LiFePO ₄ with carbon (C) has been used, it is necessary to form a mixture together with another conductive material even in the case of lithium iron phosphate thus produced. Therefore, as the content of the conductive material increases, the content of the active material decreases and the capacity decreases.

As a result, there is a high need for a method for producing lithium iron phosphate which does not require the addition of a conductive material separately or to which a small amount of conductive material can be added.

SUMMARY OF THE INVENTION Accordingly, the present invention has been made to solve the above-mentioned problems of the prior art and the technical problems required from the past.

The inventors of the present application have conducted intensive research and various experiments and have found that when secondary particles are produced by dispersing a conductive material in a primary particle slurry instead of a conventional carbon precursor, The inventors have confirmed that they are uniformly dispersed and have high conductivity, and have completed the present invention.

Accordingly, the method for producing lithium iron phosphate of the olivine crystal structure according to the present invention comprises:

(1) a process for producing primary particles having an olivine crystal structure;

(2) preparing a mixture of the primary particles and the conductive material; And

(3) a step of drying the mixture and agglomerating the primary particles to prepare secondary particles having a structure in which the conductive material is dispersed among the lithium iron phosphate particles;

.

As described above, by preparing the lithium iron phosphate of the olivine crystal structure by adding the conductive material before the secondary particle production step, not only the primary particles of the lithium iron phosphate but also the conductive particles And can have a uniformly dispersed configuration.

When the lithium iron phosphate thus prepared is used as a cathode active material, the conductive material is not added to the positive electrode active material when the lithium iron phosphate is used as a cathode active material, It does not fall. Therefore, the content of the cathode active material can be relatively increased, and thus the capacity can be increased compared with the conventional cathode active material.

The mixture of the above process (2) may further comprise a binder. The binder may serve to more easily bind the conductive material to the surface of the primary particles.

In addition, the mixture of the above process (2) may further comprise a solvent. When the primary particles in the above process (1) are in a slurry state, a separate solvent may not be used, but in other cases, it is preferable to disperse the primary particles and the conductive material using an additional solvent.

In the above production method, the method of preparing the primary particles of the process (1) is not limited, and for example, a solid phase method, coprecipitation method, hydrothermal method, or the like can be used.

The oligo-modified lithium iron phosphate according to the present invention may be prepared by any method as long as the above-described particle shape can be produced.

Preferably, the olivine-type lithium iron phosphate may be prepared through a rapid reaction of a short reaction time. The lithium ion conductivity can be improved by growing asymmetrically along a thermodynamically stable crystal plane in a rapid reaction condition without limiting the content of the present invention. For example, in the layered structure of lithium iron phosphate, the particles continue to grow from the end of the layer, while the growth in the interlayer direction perpendicular to the layer is relatively limited to form a macroscopically long rod-like structure have. The reaction time for this rapid reaction can be, for example, from 0.5 seconds to 1 minute, and preferably from 1 second to 10 seconds.

In one preferred example, the rapid reaction may be carried out by a supercritical hydrothermal process or a microwave process. The supercritical hydrothermal method may be a continuous supercritical hydrothermal method.

The supercritical hydrothermal method is, for example,

(a) precipitating transition metal hydroxides by primary mixing of precursors as raw materials and alkylating agents;

(b) synthesizing and drying lithium iron phosphate by secondary mixing of the mixture under the supercritical or subcritical condition with the mixture of step (a); And

(c) calcination of selectively synthesized lithium iron phosphate;

. ≪ / RTI >

Li ₂ CO _{3 ,} Li (OH), Li (OH) .H ₂ O, LiNO ₃ and the like can be used as the lithium precursor as the raw material in the process (a) is a divalent compound _{FeSO 4, FeC 2 O 4 ·} 2H 2 O, may take advantage of a FeCl _2, such as, phosphorus (P) precursor, an ammonium salt _{H 3 PO 4, NH 4 H} 2 PO 4, (NH 4) 2 HPO ₄ , P ₂ O ₅ and the like can be used.

Examples of the alkalizing agent include alkali metal hydroxides, alkaline earth metal hydroxides, and ammonia compounds.

In the process (b), the water under the supercritical or subcritical condition may be water in the range of 200 to 700 ° C under a pressure of 180 to 550 bar, and the calcining temperature in the process (c) may be 600 to 1200 ° C.

In one preferred example of the present invention, a washing process for removing impurities remaining in the primary particles before the process (2) may be added. The impurity may be an impurity salt such as NH ₄ NO ₃ or an ionic impurity such as NO ₃ ^- or SO ₄ ^{2 -} decomposed from a metal precursor.

The drying and the preparation of the secondary particles may be performed simultaneously in the step (3). For example, various methods such as spray drying, fluidized bed drying and vibration drying may be used. Particularly, the rotary spray drying method in the spray drying method is preferable because the secondary particles can be made spherical so that the tap density of the electrode can be increased accordingly.

The drying temperature may be 120 to 200 ° C, and the step (3) may be performed in an inert gas atmosphere such as Ar and N ₂ .

In one preferred example, the step (3) may further include a step of baking after drying. The crystallinity of the lithium iron phosphate of the olivine structure can be enhanced by the calcination.

The conductive material of the above-mentioned process (2) is not limited as long as it can be generally used as a conductive material. Preferably, it is a hydrophilic conductive material in order to disperse well in a slurry of primary particles prepared by the hydrothermal method or in an added solvent. In the case of the hydrophobic conductive material, it may be undesirable because it is not well dispersed and aggregates and secondary particles are formed in a form in which the conductive material is not dispersed evenly in the production of lithium iron phosphate, and a relatively large amount of conductive material is used.

In addition, the conductive material in the above process (2) may be a powdery conductive material. The conductive material of the process (2) may have an average particle diameter of 5 to 500 nm. When the average particle diameter of the conductive material is less than 5 nm, the particle size is too small to process. On the other hand, when the conductive material is more than 500 nm, it may be difficult to disperse among the primary particles.

The kind of the hydrophilic conductive material is not particularly limited, but may be one or more selected from the group consisting of, for example, channel black, furnace black, and oxidation-treated carbon materials.

The present invention also provides a method for producing lithium iron phosphate of an olivine crystal structure,

(a ') a process of precipitating transition metal hydroxides by primary mixing of precursors as raw materials with an alkalizing agent;

(b ') a step of synthesizing lithium iron phosphate by secondary mixing of water under supercritical or subcritical conditions with the mixture of step (a');

(c ') adding and dispersing a conductive material to the lithium iron phosphate slurry synthesized in the process (b'); And

(d ') drying and calcinating the slurry;

And a method for producing the lithium iron phosphate.

By this method, lithium iron phosphate of an olivine crystal structure in which the conductive material is uniformly dispersed among the lithium iron phosphate particles can be produced.

The present invention also relates to a lithium iron phosphate secondary particle having an olivine crystal structure, wherein lithium iron phosphate primary particles having an olivine crystal structure in which a powder conductive material is dispersed on the surface of lithium iron phosphate primary particles It provides iron phosphate.

The lithium iron phosphate is uniformly dispersed in the conductive material between the particles, so that the conductivity is improved. In addition, due to the improved conductivity, a separate conductive material may not be added or only a small amount may be added in the preparation of the cathode mixture, and thus the capacity of the same volume of the electrode may be increased.

The lithium iron phosphate of the olivine crystal structure may preferably have a porosity of 15 to 40% of the secondary particles.

In the case of secondary particles having a high porosity, it was confirmed that the shape of the secondary particles could be at least partially collapsed during the pressing process in the production of the electrode and returned to the primary particles, thereby further improving the electric conductivity .

That is, when the primary particles have a high porosity while they have aggregated secondary particles, they exhibit high electrical conductivity and density, which are the advantages of the primary particles, have. Specifically, the secondary particles can be used to reduce the amount of binder and solvent used in the preparation of the electrode mixture, and to shorten the mixing and drying time. Thus, ultimately, the capacity and energy density of the electrode and the battery can be maximized.

When the porosity of the secondary particles is less than 15%, it is not preferable since the secondary particles can be refined only when a pressure higher than the pressure normally applied in the pressing process of the electrode is applied. If the porosity exceeds 40%, there is a problem that the bonding force between the primary particles is low and the handling is not easy. Furthermore, it is more preferable that the porosity of the secondary particles is 20 to 30% in terms of uniform dispersion of primary particles and process efficiency.

On the other hand, in order to exhibit excellent electrical conductivity, stability of crystal structure, and high tap density even in the case where secondary particles disintegrate in the production of electrodes and return to primary granulation in the present invention, primary particles in a crystallized state are used To form secondary particles. That is, it is preferable that the primary particles each independently have an olivine-type crystal structure.

On the other hand, when the primary particles are aggregated and then crystallized by sintering, secondary pressurization is required to return to the primary particles due to the high binding force between the primary particles, The collapse of the crystal structure also occurs when the particles are collapsed, so that it is difficult to exhibit the effect of improving the conductivity due to the small particle size.

Further, in terms of facilitating return to the primary particles, the primary particles are not chemically bonded such as a covalent bond or an ionic bond, but are aggregated by physical bonding such as van der Waals attraction force to form secondary particles desirable.

Considering that an average particle size of the primary particles is too large, the desired ion conductivity can not be improved. On the other hand, considering that particles having an excessively small particle diameter are not easily produced, the average particle size (D50) To 550 nm, and more preferably from 100 to 300 nm.

If the average particle size of the secondary particles is too large, the void ratio between the secondary particles becomes large and the tap density is lowered. On the contrary, if the particle diameter is too small, the process efficiency can not be obtained. (D50). Particularly, considering the slurry mixing and the smoothness of the surface of the electrode, it is preferable to have an average particle diameter of 5 to 40 mu m, and when it is more than 40 mu m, sedimentation occurs slowly during slurry mixing, not.

The secondary particles preferably have a specific surface area (BET) of 10 m ² / g.

The shape of the secondary particles is not particularly limited, but is preferably spherical in view of the tap density.

The present invention also provides a cathode mixture for a secondary battery comprising the lithium iron phosphate of the olivine crystal structure as a cathode active material. In addition to the positive electrode active material, the positive electrode mixture may optionally contain a conductive material, a binder, a filler, and the like.

The conductive material may be generally added in an amount of 0 to 30% by weight based on the total weight of the mixture including the cathode active material. Such a conductive material is not particularly limited as long as it has electrical conductivity without causing a chemical change in the battery, and includes, for example, graphite; Carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskey such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used. Concrete examples of commercially available conductive materials include acetylene black series such as Chevron Chemical Company, Denka Singapore Private Limited, Gulf Oil Company, etc.), Ketjenblack, EC (Armak Company), Vulcan XC-72 (Cabot Company), and Super P (Timcal).

The binder is a component which assists in bonding of the active material and the conductive material and bonding to the current collector, and is usually added in an amount of 1 to 30% by weight based on the total weight of the mixture containing the cathode active material. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene , Polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butylene rubber, fluorine rubber, and various copolymers.

The filler is optionally used as a component for suppressing the expansion of the electrode, and is not particularly limited as long as it is a fibrous material without causing any chemical change in the battery. Examples of the filler include olefin-based polymerizers such as polyethylene and polypropylene; Fibrous materials such as glass fibers and carbon fibers are used.

On the other hand, the cathode active material may be composed of only the olivine-type lithium iron phosphate according to the present invention, and in some cases, it may be composed of other lithium-containing transition metal oxides.

Examples of the lithium-containing transition metal oxide include a layered compound such as lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), or a compound substituted with one or more transition metals; Lithium manganese oxides such as Li _{1 + y} Mn _2-y O ₄ (where y is 0 to 0.33), LiMnO ₃ , LiMn ₂ O ₃ and LiMnO ₂ ; Lithium copper oxide (Li ₂ CuO ₂ ); Vanadium oxides such as LiV ₃ O ₈ , LiFe ₃ O ₄ , V ₂ O ₅ and Cu ₂ V ₂ O ₇ ; Formula _{LiNi 1-y M y O 2} ( where, the M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, y = 0.01 ~ 0.3 Im) Ni site type lithium nickel oxide which is represented by; Formula _{LiMn 2-y M y O 2} ( where, M = Co, Ni, Fe , Cr, and Zn, or Ta, y = 0.01 ~ 0.1 Im) or Li ₂ Mn ₃ MO ₈ (where, M = Fe, Co, Ni, Cu, or Zn); LiMn ₂ O _{4 in} which a part of Li in the formula is substituted with an alkaline earth metal ion; Disulfide compounds; Fe ₂ (MoO ₄ ) ₃ , and the like. However, the present invention is not limited to these.

The present invention provides a positive electrode in which the positive electrode mixture is applied on a current collector.

The positive electrode for a secondary battery can be produced, for example, by applying a slurry prepared by mixing the positive electrode material mixture with a solvent such as NMP, onto a positive electrode collector, followed by drying and rolling.

The cathode current collector is generally made to have a thickness of 3 to 500 mu m. Such a positive electrode collector is not particularly limited as long as it has conductivity without causing chemical change to the battery, and may be formed on the surface of stainless steel, aluminum, nickel, titanium, sintered carbon or aluminum or stainless steel Carbon, nickel, titanium, silver, or the like may be used. The current collector may have fine irregularities on the surface thereof to increase the adhesive force of the cathode active material, and various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric are possible.

The present invention provides a lithium secondary battery comprising the positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte containing a lithium salt.

The negative electrode is prepared, for example, by applying a negative electrode mixture containing a negative electrode active material on a negative electrode collector and then drying the same. The negative electrode mixture may contain a conductive material, a binder, a filler, May be included.

The negative electrode collector is generally made to have a thickness of 3 to 500 mu m. The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical change in the battery. Examples of the negative electrode current collector include copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless steel Surface-treated with carbon, nickel, titanium, silver or the like, aluminum-cadmium alloy, or the like can be used. In addition, like the positive electrode collector, fine unevenness can be formed on the surface to enhance the bonding force of the negative electrode active material, and it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams and nonwoven fabrics.

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

The separation membrane is interposed between the anode and the cathode, and an insulating thin film having high ion permeability and mechanical strength is used. The pore diameter of the separator is generally 0.01 to 10 mu m, and the thickness is generally 5 to 300 mu m. Such separation membranes include, for example, olefinic polymers such as polypropylene, which are chemically resistant and hydrophobic; A sheet or nonwoven fabric made of glass fiber, polyethylene or the like is used. When a solid electrolyte such as a polymer is used as an electrolyte, the solid electrolyte may also serve as a separation membrane.

The lithium salt-containing nonaqueous electrolyte solution is composed of an electrolyte solution and a lithium salt. As the electrolyte solution, a nonaqueous organic solvent, an organic solid electrolyte, and an inorganic solid electrolyte may be used.

Examples of the non-aqueous organic solvent include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma -Butyrolactone, 1,2-dimethoxyethane, tetrahydroxyfuran, 2-methyltetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane , Acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate Nonionic organic solvents such as tetrahydrofuran derivatives, ethers, methyl pyrophosphate, ethyl propionate and the like can be used.

Examples of the organic solid electrolyte include a polymer electrolyte such as a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphate ester polymer, an agitation lysine, a polyester sulfide, a polyvinyl alcohol, a polyvinylidene fluoride, A polymer containing an ionic dissociation group and the like may be used.

Examples of the inorganic solid electrolyte include Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, LiSiO ₄ , LiSiO ₄ -LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Nitrides, halides and sulfates of Li such as Li ₄ SiO ₄ -LiI-LiOH and Li ₃ PO ₄ -Li ₂ S-SiS ₂ can be used.

The lithium salt is a material that is readily soluble in the non-aqueous electrolyte, for example, LiCl, LiBr, LiI, LiClO 4, LiBF 4, LiB 10 Cl 10, LiPF 6, LiCF 3 SO 3, LiCF 3 CO 2, LiAsF _{6, LiSbF 6, LiAlCl 4,} CH 3 SO 3 Li, CF 3 SO 3 Li, (CF 3 SO 2) 2 NLi, chloroborane lithium, lower aliphatic carboxylic acid lithium, lithium tetraphenyl borate and imide have.

For the purpose of improving the charge / discharge characteristics and the flame retardancy, the electrolytic solution is preferably mixed with an organic solvent such as pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, glyme, Benzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N, N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, . In some cases, halogen-containing solvents such as carbon tetrachloride and ethylene trifluoride may be further added to impart nonflammability. In order to improve the high-temperature storage characteristics, carbon dioxide gas may be further added. FEC (Fluoro-Ethylene Carbonate, PRS (Propene sultone), and the like.

The lithium secondary battery according to the present invention can be manufactured by a conventional method known in the art. In the lithium secondary battery according to the present invention, the structure of the positive electrode, the negative electrode and the separator is not particularly limited. For example, each of the sheets may be formed into a cylindrical shape by a winding type or a stacking type, Or inserted into a case of a pouch type.

Also, the present invention provides a middle- or large-sized battery module including the lithium secondary battery as a unit battery, and a battery pack including the battery module.

The battery pack may be used in a variety of mid- to large-sized devices requiring particularly high rate characteristics and high-temperature safety, for example, a power tool that is powered by an electric motor and moves; An electric vehicle including an electric vehicle (EV), a hybrid electric vehicle (HEV), and a plug-in hybrid electric vehicle (PHEV); Electric motorcycle including E-bike, E-scooter; An electric golf cart, or the like, and may be used in a power storage system, but the present invention is not limited thereto.

As described above, the process for producing lithium iron phosphate having an olivine crystal structure according to the present invention can produce lithium iron phosphate secondary particles having a structure in which a conductive material is dispersed among particles, There is an advantage that the ash can not be added, or a small amount of conductive material can be added, thereby increasing the capacity of the battery.

1 is a flow chart of a method for producing lithium iron phosphate according to one embodiment of the present invention;
FIG. 2 is a schematic view showing a method of producing lithium iron phosphate according to an embodiment of the present invention. FIG.

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

FIG. 1 shows a flowchart of a method for producing lithium iron phosphate according to one embodiment of the present invention.

Referring to FIG. 1, the method for producing lithium iron phosphate according to the present invention comprises three steps.

The process (1) is a process for preparing primary particles having an olivine crystal structure, and the method is not limited as long as lithium iron phosphate having an olivine crystal structure can be produced. However, for example, , Coprecipitation method, hydrothermal method, and the like can be used. Preferably a continuous supercritical hydrothermal process.

The process (2) is a process for preparing a mixture of the primary particles and the conductive material. When the primary particles are in a slurry state, the conductive material may be mixed immediately, but a separate solvent may be further included. In addition, the mixture may further comprise a binder so that the conductive material can easily bind to the surface of the primary particles.

The process (3) is a process for producing secondary particles having a structure in which the mixture is dried and primary particles are agglomerated and the conductive material is dispersed among the lithium iron phosphate particles, wherein the conductive material is a mixture of primary particles The amount of the conductive material can be reduced or eliminated in the preparation of the electrode material mixture, so that it is possible to obtain a large capacity in terms of volume. The drying may be selected from the group consisting of, for example, a spray drying method, a fluidized bed drying method, and a vibration drying method. Particularly, it is preferable to use the spin-spray drying method among the spray drying method in that the secondary particles can be spherically formed, thereby increasing the tap density of the electrode.

As a preferable example, there is further included a step of calcining after drying in the step (3). During the firing process, the crystallinity of the lithium iron phosphate of the olivine structure is enhanced.

FIG. 2 schematically shows a stepwise state of a method for producing lithium iron phosphate according to one embodiment of the present invention.

Referring to FIG. 2, in the state where lithium iron phosphate primary particles and conductive material particles are dispersed, secondary particles are formed through spray drying, and the crystallinity is strengthened through firing, so that the conductive material particles are lithium iron phosphate Secondary particles having a structure dispersed among the cargo particles can be produced.

Those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims (22)

A process for producing lithium iron phosphate of olivine crystal structure,
(1) a process for producing primary particles having an olivine crystal structure;
(2) preparing a mixture of the primary particles and the conductive material; And
(3) a step of drying the mixture and agglomerating the primary particles to prepare secondary particles having a structure in which the conductive material is dispersed among the lithium iron phosphate particles;
/ RTI >
The above process (1) uses a supercritical or subcritical hydrothermal method,
A cleaning process for removing impurities remaining in the primary particles is added before the process (2)
The conductive material is at least one selected from the group consisting of channel black, furnace black, and oxidation-treated carbon materials as the hydrophilic conductive material,
The conductive material of the process (2) has an average particle diameter of 5 nm to 500 nm,
Wherein the porosity of the secondary particles is 15% to 40%. The method of claim 1, wherein the mixture of step (2) further comprises a binder. 2. The method of claim 1, wherein the mixture of step (2) further comprises a solvent. delete The method according to claim 1, wherein the drying and the preparation of the secondary particles are simultaneously performed in the step (3). [6] The method of claim 5, wherein the drying of step (3) is performed in at least one selected from the group consisting of a spray drying method, a fluidized bed drying method, and a vibration drying method. [7] The method according to claim 6, wherein the drying of step (3) is carried out by a spray drying method in a spray drying method. The method according to claim 1, further comprising a step of calcining after drying in the step (3). delete The method of producing a lithium iron phosphate according to claim 1, wherein the conductive material in the step (2) is a powdery conductive material. delete delete delete delete delete A positive electrode material mixture comprising the lithium iron phosphate produced by the method according to claim 1 as a positive electrode active material. A positive electrode for a secondary battery, characterized in that the positive electrode mixture according to claim 16 is applied on a current collector. A lithium secondary battery comprising the positive electrode according to claim 17. A battery module comprising the lithium secondary battery according to claim 18 as a unit cell. A battery pack comprising the battery module according to claim 19. The battery pack according to claim 20, wherein the battery pack is used as a power source for a middle- or large-sized device. 22. The battery pack of claim 21, wherein the middle- or large-sized device is an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, or a power storage system.

Images