KR20110071653A - Method for continuous preparation of lithium-containing phospate nanoparticels for positive active materials - Google Patents

Abstract

PURPOSE: A successive manufacturing method of phosphate positive active material nanoparticles is provided to improve electrochemical features with an introduction of a metal dopant or a nonmetal dopant, and to control a formation of impurity with an introduction of a reducing agent. CONSTITUTION: The successive manufacturing method of phosphate positive active material nanoparticles includes following steps.(a) A lithium precursor solution, an iron precursor solution, a phosphoric acid precursor solution, a metal dopant or nonmetal dopant precursor solution and a reductant solution are prepared respectively.(b) The solutions of the step(a) are introduced consecutively to a mixer under a supercritical or subcritical condition. A solution containing 'phosphate positive active material nanoparticles' having a chemical formula of LiFe1-xMIxPO4 or Li1-xMIIxFePO4(0<=X<=0.3, MI andMII are a metal or a base metal) is formed.(c) The solution containing 'phosphate positive active material nanoparticles' is successively introduced to a reactor with high pressure and high temperature. The crystallinity of phosphate positive active material nanoparticles' is increased.(d) The solution containing 'phosphate positive active material nanoparticles' is cooled. (e) The phosphate positive active material nanoparticles are divided and collected.

Description

Continuous production method of phosphate-based cathode active material nanoparticles {METHOD FOR CONTINUOUS PREPARATION OF LITHIUM-CONTAINING PHOSPATE NANOPARTICELS FOR POSITIVE ACTIVE MATERIALS}

The present invention relates to a continuous method for producing a phosphate-based cathode active material nanoparticles having excellent electrochemical properties utilized in lithium secondary batteries.

BACKGROUND ART A lithium secondary battery having a high energy density is widely used as a power source used for information-related devices such as portable computers, mobile phones, cameras, or communication devices. In addition, the development of Plug-in Hybrid Vehicles (PHEVs), an eco-friendly electric vehicle that uses lithium secondary batteries as an energy source to reduce dependence on petroleum and reduce the source of greenhouse gases, has been competitively developed. Demand for large secondary batteries is expected to increase significantly in various fields such as power supply and medical devices, and research and development are actively conducted accordingly.

Currently, lithium metal composite oxides such as LiCoO ₂ , LiMn ₂ O ₄ , and LiNiO ₂ are widely used as cathode materials for secondary batteries. Among these, LiCoO ₂ is the most widely used cathode active material because of its high voltage and charge / discharge characteristics.However, the output of cobalt (Cobalt, Co), which is a raw material, is low, regionally biased, and expensive, and its production cost is high. When discharged, there are disadvantages of causing environmental pollution and stability, such as unstable with temperature and explosion at high temperatures. Therefore, in order to solve this problem, there was a study on the production of a cathode active material having a chemical formula of LiMn ₂ O ₄ or LiNiO ₂ using a relatively rich reserve manganese (Mn) or nickel (Ni). However, LiMn ₂ O ₄ has a problem in stability because manganese is dissolved in the electrolyte, and has a poor lifespan due to deterioration at high temperature. In the case of LiNiO ₂ , the crystal structure collapses during charging and discharging. Therefore, there is a problem that the battery capacity is seriously lowered and the thermal stability is low. Therefore, the demand for a new positive electrode active material having high performance, safety and reliability for increasing the size and mass production of lithium secondary batteries is increasing.

Recently, as a cathode active material for a large secondary battery, LiFe _{1 - x} M ^I _x PO ₄ having an olivine structure having high performance, safety, and reliability. Or Li _{1 - x} M ^II _x FePO ₄ (0≤X≤0.3, M ^I _, M ^II is a metal or non-metal) phosphate-based cathode active material having the formula is attracting attention. In particular, using abundant reserves and inexpensive iron, the raw material price is very low compared to LiCoO ₂ and eco-friendly because of low toxicity, and the stability of the olivine structure makes the explosion risk at high temperatures very low, and the theoretical output is 170 mAh. Since it is relatively high in / g, there is an advantage that the battery capacity per unit mass can be increased. However, the phosphate-based positive electrode active material having an olivine structure has not yet obtained satisfactory electrochemical properties to be used as a positive electrode active material of a lithium secondary battery when compared to LiCoO ₂ . This is because the rate of insertion / desorption of lithium ions is very slow during battery charging and discharging, and the rate of transfer of lithium ions in the cathode active material is very slow. Only lithium ions located on the surface of the particles are used. This is because, when the charge and discharge of the cathode active material itself is small, overvoltage occurs and battery characteristics are significantly reduced. A method of increasing charge and discharge capacity by increasing the insertion / desorption rate of lithium ions by shortening the distance between the surface and the center of the particles by manufacturing nano-sized particles as a means of overcoming the problems of the phosphate-based cathode active material, preparation of active materials To increase electrical conductivity by performing carbon coating or metal coating, to increase electrical conductivity by adding conductive materials such as carbon when manufacturing electrodes, and to Al, Cr, Co instead of the element corresponding to Li or Fe in LiFePO ₄ A method of improving conductivity by substituting with a hetero element such as Cu, Mg, Mn, Nb, Ni, Ti, W, Zn, or Zr has been proposed.

Phosphorus-based positive electrode active material synthesis method known to the olivine structure is Li ₃ PO ₄ , LiF, Li ₂ CO ₃ , LiNO ₃ Li precursors such as FeC ₂ O ₄ 2H ₂ O, Fe ₃ (PO ₄ ) ₂ 8H ₂ O, Fe (NO ₃ ) ₃ 9H ₂ O, Fe ₂ O ₃ Iron precursors such as NH ₄ H ₂ PO ₄ .H ₂ O, (NH ₄ ) ₃ PO ₄ .3H ₂ O, and the like, are mixed in a solid state by a ball mill or the like, and then 600 to 600; There is a solid-state method which is produced by firing at a temperature between 1000 ° C. for 10 hours to 48 hours. U.S. Pat.No. 5,910,382 and Padhi et al., Journal of Electrochemical Society, 1997, 144, 1188 disclose a method for preparing a phosphate-based cathode active material by a solid phase method. In order to produce a single-phase material in solid state from a mixture containing three kinds of components such as lithium, metal and phosphoric acid, a ball mill process at a high temperature is required, and a long time mixing and long firing are required, resulting in large energy consumption and an unproductive effect. And it is uneconomical, the particle size is about 30㎛ relatively large due to long-term firing at high temperature excessive crystallization is progressed, the insertion / desorption rate of lithium ions during charge and discharge is very slow, the charge and discharge capacity is low. In addition, in order to improve electrochemical properties, metals such as Mn, Mg, and Zr may also be doped using nonmetallic components, but added metals or nonmetallic components may be difficult to uniformly doped, and mixing and firing processes may be performed in a batch form. Because of this, the uniformity and productivity of the product are deteriorated, and the impurities are easily mixed by mixing and grinding, such as ball mill, and the productivity is improved because a separate long-time grinding process is required to synthesize nano-sized phosphate-based cathode active material. There is a disadvantage in that the particle distribution becomes much wider and the loss occurs in the classification of the particle size to solve this problem.

On the other hand, the synthesis method of the phosphine-based cathode active material of the olivine structure is hydrothermal method, co-precipitation, emulsion-drying, sol-gel method, spray pyrolysis method There is a solution-based method such as spray-pyrolysis. In the case of the liquid phase method, a long reaction time and a firing time of 12 to 48 hours are required, which is inefficient and unproductive, and the uniformity and productivity of the product are deteriorated because the precipitation process, the reaction process, and the firing process are performed in a batch form. As a waste acid and waste organic solvent is generated there is a problem that causes environmental pollution.

On the other hand, recently, a method of continuously producing phosphate-based cathode active material particles using supercritical water or subcritical water has been published (Xu et al., Journal of Supercritical Fluids, 2008, 44, 92). The method is to continuously pressurize the aqueous lithium hydroxide solution, aqueous iron salt solution and aqueous phosphoric acid solution to continuously introduce into the reactor maintained in supercritical water or subcritical water conditions to prepare a cathode active material. The reaction time is very short within 30 seconds and has the advantage of synthesizing nano-sized particles, but there is a problem that the electrochemical properties are not excellent because a large number of impurities are mixed in the prepared phosphate-based cathode active material.

Therefore, there is an urgent need to develop an economical and productive manufacturing method by continuously producing a phosphate-based cathode active material having excellent electrochemical properties at a high speed.

An object of the present invention is to provide a method for continuously producing a phosphate-based cathode active material having a nano-size and excellent electrochemical properties without containing impurities, such that the quality is uniform and the productivity is excellent.

This object is achieved by (a) dissolving a lithium precursor, an iron precursor, a phosphate precursor, a doped metal or a doping nonmetal precursor, and a reducing agent, respectively, in a lithium precursor solution, an iron precursor solution, a phosphoric acid precursor solution, a doping metal or doping nonmetal precursor solution, and Respectively preparing a reducing agent solution, (b) continuously feeding the lithium precursor solution, the iron precursor solution, the phosphate precursor solution, the doping metal or doping nonmetal precursor solution, and the reducing agent solution into a mixer under supercritical or subcritical conditions. Introduced LiFe _{1 - x} M ^I _x PO ₄ Or Li _{1 - x} M ^II _x FePO ₄ (0≤X≤0.3, M ^I _, M ^II is a step of forming a solution comprising a phosphate-based cathode active material nanoparticles having a chemical formula (metal or nonmetal), (c) continuously introducing a solution containing the cathode active material nanoparticles into a high temperature and high pressure reactor Increasing the crystallinity of the particles, (d) cooling the solution comprising the positive electrode active material nanoparticles, and (e) separating and recovering the positive electrode active material nanoparticles from the solution containing the positive electrode active material nanoparticles. It can be achieved by a method for producing a phosphate-based cathode active material nanoparticles.

According to the present invention, the electrochemical properties such as charge and discharge characteristics may be improved by the introduction of the doping metal or the doping nonmetal, and the formation of impurities may be suppressed by the introduction of the reducing agent. In addition, since the present invention is a continuous manufacturing method, the quality and specifications of the prepared phosphate-based cathode active material nanoparticles are uniform, and mass production is easy and economical because the nanoparticles are manufactured at a high speed. In addition, the method of the present invention is high in productivity and economical since no high temperature baking process is required.

Method for producing a phosphate-based cathode active material nanoparticles of the present invention (a) lithium precursor, iron precursor, phosphate precursor, doping metal or doping non-metal precursor and reducing agent, respectively, by dissolving lithium precursor solution, iron precursor solution, phosphate precursor solution Preparing a doping metal or doping nonmetal precursor solution and a reducing agent solution, respectively, (b) supercritical the lithium precursor solution, the iron precursor solution, the phosphate precursor solution, the doping metal or doping nonmetal precursor solution, and the reducing agent solution. Or continuously introduced into a mixer under subcritical conditions to form LiFe _1-x M ^I _x PO ₄ or Li _1-x M ^II _x FePO ₄ (0 ≦ _X ≦ 0.3, M ^I _, M ^II is a step of forming a solution comprising a phosphate-based cathode active material nanoparticles having a chemical formula (metal or nonmetal), (c) continuously introducing a solution containing the cathode active material nanoparticles into a high temperature and high pressure reactor Increasing the crystallinity of the particles, (d) cooling the solution comprising the positive electrode active material nanoparticles, and (e) separating and recovering the positive electrode active material nanoparticles from the solution containing the positive electrode active material nanoparticles. do. In step (a), a lithium precursor is dissolved in water to prepare a lithium precursor solution separately, and a mixed solution may be prepared by dissolving an iron precursor, a phosphate precursor, a doped metal or a doping nonmetal precursor, and a reducing agent together, or lithium in water. The second mixed solution may be prepared by dissolving the first mixed solution in which the precursor, the doped metal or the doping nonmetal precursor, and the reducing agent are dissolved, and the iron precursor and the phosphoric acid precursor in water. However, the lithium precursor, the iron precursor and the phosphoric acid precursor should always be prepared separately and introduced. This is because when the lithium component meets iron or phosphoric acid in the preparation of the solution, it reacts directly at room temperature to form a substance that does not dissolve in water, thereby inhibiting the tube flow of the reactor.

The lithium precursor of step (a) is a group consisting of LiOH.H ₂ O, LiCl, Li (OH) .H ₂ O, LiCH ₃ OO.2H ₂ O, Li ₂ SO ₄ , Li ₃ PO ₄ and salts thereof It may be at least one selected from. However, the present invention is not limited thereto and may be applied as long as it is dissolved in water as a lithium precursor.

The iron precursor of step (a) is FeSO ₄ 6H ₂ O, Fe (SO ₄ ) ₂ 6H ₂ O, FeCl ₂ , Fe (COO) ₂ 2H ₂ O, FeC ₂ O ₄ 2H ₂ O, FeC At least one selected from the group consisting of ₆ H ₈ O ₇ nH ₂ O, (NH ₄ ) ₂ Fe (SO ₄ ) ₂ 6H ₂ O, Fe ₃ (PO ₄ ) .8H ₂ O, and salts thereof The phosphoric acid precursor of step (a) may be NH ₄ H ₂ PO ₄ H ₂ O, (NH ₄ ) ₂ HPO ₄ , (NH ₄ ) ₃ PO ₄ 3H ₂ O, H ₃ PO ₄ It may be at least one selected from. Also, the present invention is not limited thereto and may be applicable as long as it is an iron precursor and a phosphoric acid precursor soluble in water.

The doping metal or doping non-metal precursor of step (a) is a compound comprising at least one selected from the group consisting of magnesium, aluminum, titanium, manganese, calcium, zinc, lead, tin and zirconium and salts thereof It may be at least one selected from. For example, zinc nitrate (Zn (NO ₃ ) ₂ ), aluminum nitrate (Al (NO ₃ ) ₃ ), magnesium nitrate (Mg (NO ₃ ) ₂ ), magnesium sulfate (MgSO ₄ 7H ₂ O), magnesium acetate (Mg (C ₂ H ₃ O ₂ ) ₂ 4H ₂ O), titanium sulfate (Ti (SO ₄ ) ₂ ), manganese nitrate (Mn (NO ₃ ) ₂ ), manganese acetate (Mn (CH ₃ COO) ₂ 4H ₂ O), zirconium nitrate (Zr (NO ₃ ) ₄ ), lead chloride (NbCl ₅ ), copper sulfate (CuSO ₄ 4H ₂ O), chromium nitrate (Cr (NO ₃ ) ₃ ), calcium nitrate (Ca (NO ₃ ) ₂ ) and so on.

The reducing agent of step (a) may be at least any one selected from the group consisting of sugar, hydrazine, ascrobic acid and oxalic acid, but is not limited thereto and may be applied as long as it is a reducing agent capable of preventing Fe ^II from oxidizing to Fe ^III . This is possible.

The lithium precursor in the lithium precursor solution, the iron precursor in the iron precursor solution, the phosphate precursor in the phosphate precursor solution, the concentration of the doping metal or doping nonmetal precursor in the doping metal or doping nonmetal precursor solution, the iron precursor in the mixed solution, the phosphoric acid in step (a) The concentration of the precursor, the doped metal or the doped non-metal precursor, the concentration of the lithium precursor, the doped metal or the doped non-metal precursor in the first mixed solution or the iron precursor and the phosphoric acid precursor in the second mixed solution may be 0.001 to 1 mol / l, respectively. And preferably 0.01 to 0.5 mol / L. If the concentration of the precursor is less than 0.001 mol / l, the concentration is too low, which may lead to economic deterioration. If the concentration of the precursor exceeds 1 mol / l, the viscosity of the solution becomes too high, which adversely affects the continuous flow in the tube. And as a result can lead to a decrease in productivity and quality of the produced nanoparticles.

The concentration of the reducing agent in the reducing agent solution of step (a), the concentration of the reducing agent in the mixed solution, and the concentration of the reducing agent in the first mixed solution are not particularly limited, but preferably 0.001 to 5 mol / l, more preferably. 0.01 to 1 mol / L. If the concentration of the reducing agent in the solution is less than 0.001 mol / L, the concentration is too low to carry out an effective reduction reaction, and if the concentration of the reducing agent exceeds 5 mol / L, the viscosity of the solution is too high to increase the precursor concentration as in the tube It may adversely affect the continuous flow of, resulting in a decrease in productivity and quality of the nanoparticles produced.

The supercritical or subcritical conditions of step (b) may have a reaction temperature of 200 to 600 ° C., preferably 250 to 400 ° C., and a reaction pressure of 20 to 500 bar, preferably 250 to 500 bar. If the reaction temperature is less than 200 ℃ or the reaction pressure is less than 20 bar, the size of the nanoparticles to be produced, the particle size distribution is widened and the crystallinity is low, the reaction temperature exceeds 600 ℃, the reaction If the pressure exceeds 500 bar, the increase in the cost to maintain a high temperature and high pressure leads to a decrease in economic efficiency.

LiFe _{1 - x} M ^I _x PO ₄ formed in step (b) Or Li _{1 - x} M ^II _x FePO ₄ (M ^I _, The value x of M ^II is a metal or a non-metal) is preferably 0 ≦ X ≦ 0.3. This is because if the x value is 0.3 or more, the substitution ratio is high and the olivine structure may collapse. On the other hand, the nanoparticles may be coated with carbon in order to improve the electrical conductivity of the phosphate-based positive electrode active material nanoparticles.

The diameter of the cathode active material nanoparticles of the present invention may be 10 to 1000 nm, preferably 20 to 500 nm. When the diameter of the nanoparticles exceeds 1000 nm, the properties as nanoparticles are reduced, and when the lithium secondary battery is formed, electrochemical properties such as charge and discharge characteristics are deteriorated, and when the diameter of the nanoparticles is less than 10 nm, cohesion between particles is observed. This increased and difficult handling of the produced particles can arise.

The method of recovering the phosphate-based cathode active material nanoparticles from the solution in step (e) may use filtration and centrifugation, and after separation and recovery of step (e), (f) separated and recovered phosphate-based cathode active material nano The method may further include washing and drying the particles. The washing may use organic solvents such as water, methanol, ethanol or tetrahydrofuran or other organic solvents that dissolve salts, and the drying may be vacuum drying, oven drying or freeze drying.

Figure 1 shows an example of a device for continuously producing a phosphate-based cathode active material nanoparticles in accordance with the present invention. Continuous production apparatus of phosphate-based cathode active material nanoparticles according to the present invention is a high pressure reactor (10), high pressure pumps (70, 71, 72), heaters (30, 31), preheater (20), filter (50), rear pressure A controller 60, a lithium precursor solution, an iron precursor solution, a phosphate precursor solution, a doping element precursor solution and a solution storage container 80 and 81 for storing a reducing agent solution, and a water storage container 82 for storing water.

In the present invention, the mixer in which step (b) is performed is a general T-type structure in which the flow of pure supercritical water and the flow of the phosphate positive electrode active material precursor, the doping element precursor, and the reducing agent precursor meet between 0 ^o and 180 ^o . It may be a mixer of the structure selected from the group consisting of the Y-type structure, the reverse flow structure. However, the present invention is not limited thereto and may be a structure that effectively mixes the solution without blocking the continuous flow in the pipe.

Hereinafter, a process of continuously preparing the phosphate-based cathode active material nanoparticles according to the present invention will be described in detail with reference to FIG. 1.

First, the lithium precursor, the iron precursor, the phosphate precursor, the doping element precursor and the reducing agent are dissolved in water, and then the lithium precursor solution, the iron precursor solution, the phosphate precursor solution, the doping element precursor solution and the reducing agent solution are stored in a solution container (80, 81). Is introduced. Water in the water reservoir 82 is transferred to the high pressure reactor 10 using the high pressure pump 72. At this time, the temperature of the water introduced into the high pressure reactor is controlled by using a preheater 20, the temperature of the high pressure reactor is controlled by using a heater 30, the pressure of the high pressure reactor is controlled by using a rear pressure regulator (60) The water introduced into the high pressure reactor is kept in supercritical or subcritical water. Lithium precursor solution, iron precursor solution, phosphoric acid precursor solution, doped or non-doped metal precursor solution, and reducing agent solution are continuously transferred into a mixer at a predetermined temperature and pressure to react with the supercritical or subcritical water in a mixer to phosphorylate Produce a water-based cathode active material. The resulting phosphate cathode active material is transferred to a high temperature and high pressure reactor to increase the crystallinity. In the high-pressure reactor, the temperature of the solution containing the phosphate positive electrode active material nanoparticles having increased crystallinity is lowered using the cooler 40, and then the phosphate positive electrode active material nanoparticles are separated from the cooled solution using the filter 50. Recover.

On the other hand, the method for producing an electrode using the phosphate-based positive electrode active material of the present invention is not particularly limited and can use a conventional method that can be used in the conventional lithium secondary battery device manufacturing.

Hereinafter, the present invention will be described in more detail with reference to Examples. These examples are only for illustrating the present invention in detail, and the scope of the present invention is not limited by these examples.

Example 1

LiFePO ₄ nanoparticles were prepared by using supercritical water according to the present invention and introducing a reducing agent into the mixed solution.

Water was placed in a 1000 ml glass vessel, and hydrated lithium hydroxide (LiOH.H ₂ O) as a lithium precursor was introduced to adjust the concentration to 0.09 mol / l and purged with nitrogen for at least 1 hour. Water was added to a separate 2000 ml glass vessel, where iron sulfate (Fe (SO ₄ ) .7H ₂ O) was introduced as an iron precursor, and the concentration was adjusted to 0.03 mol / l, and phosphoric acid (H ₃ as a phosphoric acid precursor. PO ₄ ) was introduced to adjust the concentration to 0.03 mol / l, and 0.005 mol / l of ascrobic acid was introduced as a reducing agent and purged with nitrogen for at least 1 hour. The lithium solution and the iron / phosphoric acid / reducing agent mixture solution thus prepared were pumped at a rate of 1.7 g / min using a high pressure pump and pressurized to 250 bar. Water was placed in another 20 liter plastic container and pumped at a rate of 9 g / min using a high pressure pump to pressurize to 250 bar and transferred to the preheater. The pressurized lithium solution, the iron / phosphate / reducing agent mixed solution and water were mixed in a mixer maintained at 400 ° C., and then the mixture was transferred to a high pressure reactor maintained at 400 ° C. for 40 seconds. The resulting solution containing LiFePO ₄ nanoparticles was cooled using a cooler, and then the LiFePO ₄ nanoparticles were separated and recovered using a filter. Unreacted precursors were separated from the recovered LiFePO ₄ nanoparticles via a centrifuge and then washed with water. The washed LiFePO ₄ nanoparticles were dried in a vacuum oven at 60 ° C. for one day to remove water.

In order to analyze the properties of the phosphate-based cathode active material nanoparticles prepared by the method of the present invention, Hitachi's Scanning Electron Microscopy (SEM) was used, and the composition of the nanoparticles was analyzed. Rigaku's X-ray Diffractor Meter (XRD) was used, and Particle size of Portal Otsuka's particle size analyzer was used to analyze nanoparticle size and particle distribution. Analyzer (hereinafter 'PSA') was used, and Belsorp's specific surface area analyzer (Brunauer, Emmet, and Teller, hereinafter 'BET') was used.

Figure 2 (a) is a view showing an XRD pattern of LiFePO ₄ nanoparticles prepared according to the production method of the present invention. Figure 3a shows an SEM image of the prepared LiFePO ₄ nanoparticles. Figure 4 (a) shows the PSA results of the LiFePO ₄ nanoparticles obtained after washing.

An anode was prepared using LiFePO ₄ prepared according to the present invention and its charge and discharge characteristics were evaluated. An anode was prepared by using acetylene black as a conductive agent and polyvinylidene fluoride (PVDF) as a binder. At this time, the ratio of the positive electrode active material: the conductive agent: the binder was 85: 10: 5 by weight ratio, the solvent was mixed by using NMP (n-methyl pyrrolidone) to prepare a slurry. The slurry thus prepared was applied to an aluminum foil in the form of a 250 μm thin electrode plate and then dried in an oven at 80 ° C. for at least 6 hours. EC (ethylene carbonate) series EC: EMC: DEC was used as an electrolyte in a ratio of 1: 1: 1, and LiPF ₆ was dissolved using Li metal as a negative electrode. Was prepared. The prepared battery was examined for the charge / discharge characteristics of the battery under the condition of 0.1 C in the voltage range of 2.5-4.3 V. Table 1 shows the discharge results of the positive electrode using the prepared LiFePO ₄ .

Comparative Example 1

Although supercritical water was used, LiFePO ₄ particles were prepared without using a reducing agent. LiFePO ₄ nanoparticles were prepared in the same manner as in Example 1, except that acrobic acid was not used as a reducing agent. The prepared nanoparticles were analyzed in the same manner as in Example 1, and the results are shown in FIGS. 2B, 3B, and 4B. Using the prepared phosphate-based positive electrode active material to prepare a positive electrode in the same manner as in Example 1 and to investigate the charge / discharge characteristics are shown in Table 1 the results.

Comparative Example 2

LiFePO ₄ particles were prepared by the solid phase method. Zirconia ball and 0.5 mol Li ₂ CO ₃ , 1 mol FeC ₂ O ₄ ㆍ 2H ₂ O, 1 mol (NH ₄ ) ₂ Precursor of 1 HPO ₄ is introduced into a zirconia bowl (1: 20) And mixed in solid state using a ball mill for 3 hours. The prepared mixture was calcined at 600 ° C. for 10 hours while flowing argon gas containing 5% hydrogen gas to prepare LiFePO ₄ particles. The prepared particles were analyzed in the same manner as in Example 1, and the results are shown in (c) of FIG. 2, (c) of FIG. 3, and (c) of FIG. Using the prepared phosphate-based positive electrode active material to prepare a positive electrode in the same manner as in Example 1 and to investigate the charge / discharge characteristics are shown in Table 1 the results. This comparative example is a known method for preparing a phosphate-based cathode active material by a conventional solid phase method, and is an experiment for comparing with the phosphate-based cathode active material particles prepared in a continuous process using a supercritical water which is a method according to the present invention.

As shown in (a) of FIG. 2, when the ascrobic acid was used as the reducing agent in Example 1, it was confirmed that no impurities were present in the prepared LiFePO ₄ nanoparticles. Fig particles prepared without the use of a reducing agent Ars croissant biksan in Comparative Example 1. As shown in 2 (b) is LiFePO ₄ in addition to _{Fe (PO 3) 3, FeH} 3 (PO 3) and 2H ₂ O, FePO ₄ It was found that Fe ^{+ 3} types of materials such as H ₂ O, β-Fe ₂ O ₃ , LiFeH ₄ (P ₂ O ₇ ) _2, and the like were mixed. Therefore, when using ascrobic acid as a reducing agent, Fe ⁺² It can be seen that the oxidation of Fe ^{+ 3} is prevented to suppress the formation of impurities. On the other hand, as shown in Figure 2c, in the case of the phosphate-based cathode active material prepared by the solid-phase method in Comparative Example 2 it was confirmed that there is no impurities other than LiFePO ₄ particles.

3 is a SEM image of the particles, looking at this, the LiFePO ₄ nanoparticles prepared in Example 1 is LiFePO ₄ prepared in Comparative Example 1 It was confirmed that the size was smaller and uniformly synthesized than the particles. Therefore, when the acrobic acid is added as a reducing agent, it can be seen that the particle size is reduced by suppressing the aggregation between particles in the process of forming the particles. On the other hand, LiFePO ₄ synthesized by using the solid-phase method in Comparative Example 2 it can be seen that there is agglomeration between particles and the particle size distribution is widely spread.

Figure 4 is a PSA results graph showing the size and size distribution of the particles, Looking at it, LiFePO ₄ nanoparticles prepared in Example 1 is smaller in particle size and size distribution than the LiFePO ₄ particles prepared in Comparative Example 1 It can be seen that it is uniform. The average diameter of the LiFePO ₄ nanoparticles prepared in Example 1 is 95 nm, the particle size distribution is 75-125 nm, while the average diameter of the LiFePO ₄ particles prepared in Comparative Example 1 is 185 nm, and the particle size distribution is 160-200 nm. Therefore, it can be seen that when the ascrobic acid is used as the reducing agent, the particle size becomes smaller and the particle size distribution becomes narrower. On the other hand, the average diameter of the LiFePO ₄ particles prepared by the solid-phase method in Comparative Example 1 is 900 nm, the particle size distribution is 200-2000 nm, compared to LiFePO ₄ nanoparticles prepared using a supercritical water according to the present invention It can be seen that the particle size is very large and the particle size distribution is very wide.

Comparing the performance of the battery formed using the particles prepared according to the Examples and Comparative Examples, as shown in Table 1, the battery using the LiFePO ₄ nanoparticles prepared in Example 1 has an initial discharge capacity of 135 mAh / g, the discharge capacity after 50 cycles was 120mAh / g showed excellent discharge characteristics, whereas the battery using LiFePO ₄ particles prepared in Comparative Example 1 the initial discharge capacity was 110 mAh / g, 50 cycles After the discharge capacity was 100 mAh / g, it was confirmed that the discharge capacity of the battery produced in Example 1. From these results, LiFePO ₄ without ascrobic acid as reducing agent was used. In addition, it can be seen that impurities are formed to deteriorate battery characteristics. On the other hand, the battery using the LiFePO ₄ positive electrode active material prepared by the solid-phase method in Comparative Example 1 shows an initial discharge capacity of 95 mAh / g, after 50 cycles shows a discharge capacity of 50 mAh / g, according to the present invention in Example 1 It can be seen that the discharge capacity is smaller than the battery formed by using the nanoparticles prepared according to the large capacity reduction due to charging and discharging. This is because the LiFePO ₄ particles prepared by the solid phase method are larger than the LiFePO ₄ nanoparticles prepared using the supercritical water according to the present invention, and the insertion / desorption rate of lithium ions during charging and discharging is very slow due to aggregation between particles, It is considered that only lithium ions located on the surface of the particles are used because the transfer rate of lithium ions is very slow, and lithium ions located at the center of the particles cannot be used. As a result, LiFePO ₄ prepared using supercritical water in Example 1 and acrobic acid as a reducing agent. It was confirmed that the nanoparticles were excellent in battery characteristics when forming a battery using the nanoparticles with a small particle size of 100 nm, high crystallinity and no impurities.

Example 2

The same conditions as in Example 1 were used, but LiFePO ₄ nanoparticles were prepared using sugar (sucrose) instead of ascrobic acid as the reducing agent. The prepared LiFePO ₄ nanoparticles were analyzed in the same manner as in Example 1, and the results are shown in Table 1.

Example 3

The conditions different from those of Example 1 were the same, but the concentration of iron sulfate (Fe (SO ₄ ) .7H ₂ O) was adjusted to 0.0294 mol / l and magnesium nitrate (Mg (NO ₃ ) ₂ .6H ₂ O) was introduced. adjusting the concentration of 0.0006 mol / ℓ to prepare a PO ₄ nanoparticles _.02 LiFe _{0 .98} Mg _0. Mg is introduced as the doping metal. Manufactured LiFe _{0 .98} Mg _{0 .02} PO ₄ Nanoparticles were analyzed in the same manner as in Example 1, and the results are shown in Figure 5 and Table 1.

Example 4

The conditions other than those of Example 1 were the same, but the concentration of lithium hydroxide (LiOH.H ₂ O) was adjusted to 0.0294 mol / L and zinc nitrate (Zn (NO ₃ ) ₂ .6H ₂ O) was introduced to adjust the concentration to 0.0006 mol. / ℓ to adjust the Li _{0 .98} Zn _{0 .02} FePO ₄ Nanoparticles were prepared. Zn is introduced as the doping metal. Manufactured Li _{0 .98} Zn _{0 .02} FePO ₄ The nanoparticles were analyzed in the same manner as in Example 1, and the results are shown in FIG. 6 and Table 1. FIG.

division Average particle size
PSA measurement (nm) BET surface area (m ² / g) Initial discharge capacity (mAh / g) Discharge capacity after 50 cycles (mAh / g) Example 1 95 15.1 135 120 Example 2 90 15.7 137 118 Example 3 110 14.5 150 120 Example 4 100 14.0 147 123 Comparative Example 1 185 7.3 110 100 Comparative Example 2 900 2.4 95 50

As shown in Table 1, the LiFePO ₄ nanoparticles prepared in Example 2 had a particle size and BET surface area of LiFePO ₄ prepared in Example 1 Similar to the nanoparticles, the battery formed using the nanoparticles prepared in Example 2, the initial discharge capacity and 50 cycles after the discharge capacity is similar to the discharge capacity of the battery formed using the nanoparticles prepared in Example 1 Confirmed. As a result, it was confirmed that sugar, like ascrobic acid, has an effect as a reducing agent.

In addition, when using Mg and Zn as the doping material in Example 3 and Example 4, the particle size is similar to the size of the particles prepared without using the dopant in Example 1 or Example 2, the initial discharge capacity is 147 The discharge capacity was -150 mAh / g and the discharge capacity was 120-123 mAh / g after 50 cycles, showing better discharge characteristics than the battery formed using the phosphate-based positive electrode active material particles prepared in Examples 1 and 2. This is considered to be because the conductivity is improved by using the doping material.

1 is a schematic view showing a device for producing a phosphate-based cathode active material nanoparticles of the present invention.

Figure 2 is a graph showing the XRD pattern of the particles prepared in Example 1 (a), Comparative Example 1 (b) and Comparative Example 2 (c).

3 is a SEM image photograph of the particles prepared in Example 1 (a), Comparative Example 1 (b) and Comparative Example 2 (c).

Figure 4 is a graph showing the PSA results of the particles prepared in Example 1 (a), Comparative Example 1 (b) and Comparative Example 2 (c).

5 is a SEM image photograph of the LiFe _{0 .98} Mg _{0 .02} PO ₄ nanoparticles prepared in Example 2.

6 is a SEM image of a photograph of a Li _{0 .98} Zn _{0 .02} FePO ₄ nanoparticles prepared in Example 3.

* Description of symbols for the main devices in the drawings

10: high pressure reactor 20: preheater

30, 31: heater 40: cooler

50 filter 60 rear pressure regulator

70, 71, 72: high pressure pump

80, 81: precursor and reducing solution storage container

82: water storage container

Claims (19)

(a) a lithium precursor, an iron precursor, a phosphate precursor, a doped metal or a doping nonmetal precursor, and a reducing agent are respectively dissolved in water to prepare a lithium precursor solution, an iron precursor solution, a phosphate precursor solution, a doping metal or doping nonmetal precursor solution, and a reducing agent solution, respectively. Preparing; (b) the lithium precursor solution, the iron precursor solution, the phosphate precursor solution, the doping metal or doping nonmetal precursor solution, and the reducing agent solution are continuously introduced into a mixer under supercritical or subcritical conditions to provide LiFe _{1 - x} M ^I _x PO ₄ Or Li _{1 - x} M ^II _x FePO ₄ (0≤X≤0.3, M ^I _, M ^II is a solution of forming a solution containing a phosphate-based cathode active material nanoparticles having a chemical formula (metal or non-metal); (c) continuously introducing a solution containing the phosphate-based cathode active material nanoparticles into a high temperature and high pressure reactor to increase the crystallinity of the phosphate-based cathode active material nanoparticles; (d) cooling the solution containing the phosphate-based cathode active material nanoparticles; And (e) separating and recovering the phosphate-based cathode active material nanoparticles from a solution containing the phosphate-based cathode active material nanoparticles; Method for producing a phosphate-based cathode active material nanoparticles comprising a. (a) dissolving a lithium precursor in water to prepare a lithium precursor solution, and preparing a mixed solution by dissolving an iron precursor, a phosphate precursor, a doped metal or a doping nonmetal precursor, and a reducing agent in water; (b) LiFe _{1 - x} M ^I _x PO ₄ by continuously introducing the lithium precursor solution and the mixed solution into the mixer under supercritical or subcritical conditions Or Li _{1 - x} M ^II _x FePO ₄ (0≤X≤0.3, M ^I _, M ^II is a solution of forming a solution containing a phosphate-based cathode active material nanoparticles having a chemical formula (metal or non-metal); (c) continuously introducing a solution containing the phosphate-based cathode active material nanoparticles into a high temperature and high pressure reactor to increase the crystallinity of the phosphate-based cathode active material nanoparticles; (d) cooling the solution containing the phosphate-based cathode active material nanoparticles; And (e) separating and recovering the phosphate-based cathode active material nanoparticles from a solution containing the phosphate-based cathode active material nanoparticles; Method for producing a phosphate-based cathode active material nanoparticles comprising a. (a) preparing a first mixed solution by dissolving a lithium precursor, a doped metal or a doping nonmetal precursor, and a reducing agent in water, and preparing a second mixed solution by dissolving an iron precursor and a phosphoric acid precursor in water; (b) LiFe _{1 - x} M ^I _x PO ₄ by continuously introducing the first and second mixed solution into the mixer under supercritical or subcritical conditions Or Li _{1 - x} M ^II _x FePO ₄ (0≤X≤0.3, M ^I _, M ^II is a solution of forming a solution containing a phosphate-based cathode active material nanoparticles having a chemical formula (metal or non-metal); (c) continuously introducing a solution containing the phosphate-based cathode active material nanoparticles into a high temperature and high pressure reactor to increase the crystallinity of the phosphate-based cathode active material nanoparticles; (d) cooling the solution containing the phosphate-based cathode active material nanoparticles; And (e) separating and recovering the phosphate-based cathode active material nanoparticles from a solution containing the phosphate-based cathode active material nanoparticles; Method for producing a phosphate-based cathode active material nanoparticles comprising a. The method according to any one of claims 1 to 3, wherein the lithium precursor in step (a) is LiOH.H ₂ O, LiCl, Li (OH) .H ₂ O, LiCH ₃ OO.2H ₂ O, Li ₂ Method for producing a phosphate-based positive electrode active material nanoparticles which is at least one selected from the group consisting of SO ₄ , Li ₃ PO ₄ and salts thereof. The method according to any one of claims 1 to 3, wherein the iron precursor of step (a) comprises FeSO ₄ .6H ₂ O, Fe (SO ₄ ) ₂ .6H ₂ O, FeCl ₂ , Fe (COO) _2. 2H ₂ O, FeC ₂ O ₄ ㆍ 2H ₂ O, FeC ₆ H ₈ O ₇ ㆍ nH ₂ O, (NH ₄ ) ₂ Fe (SO ₄ ) ₂ ㆍ 6H ₂ O, Fe ₃ (PO ₄ ) · 8H ₂ O And at least one selected from the group consisting of salts thereof. The process of claim 1, wherein the phosphate precursor of step (a) is selected from NH ₄ H ₂ PO ₄ H ₂ O, (NH ₄ ) ₂ HPO _4. And (NH ₄ ) ₃ PO ₄ ㆍ 3H ₂ O, H ₃ PO ₄ , at least one selected from the group consisting of phosphate-based positive electrode active material nanoparticles. The method of claim 1, wherein the doped or non-doped metal precursor of step (a) is selected from the group consisting of magnesium, aluminum, titanium, manganese, calcium, zinc, lead, tin and zirconium. Method for producing a phosphate-based positive electrode active material nanoparticles which is at least any one selected from the group consisting of a compound comprising at least one and salts thereof. The method of claim 1, wherein the reducing agent of step (a) is at least one selected from the group consisting of sugar, hydrazine, ascrobic acid, and oxalic acid. . The method of claim 1, wherein the lithium precursor in the lithium precursor solution, the iron precursor in the iron precursor solution, the phosphate precursor in the phosphate precursor solution, the doped metal or doped nonmetal precursor in the solution of the doped metal or doped nonmetal precursor of step (a). The concentration of the 0.001 to 1 mol / ℓ of the method for producing a phosphate-based cathode active material nanoparticles, respectively. The phosphorylation of claim 2, wherein the concentration of the lithium precursor in the lithium precursor solution of step (a) and the concentration of the iron precursor, the phosphate precursor, the doped metal or the doped nonmetal precursor in the mixed solution are 0.001 to 1 mol / L, respectively. Method for preparing water-based cathode active material nanoparticles. The method of claim 3, wherein the concentration of the lithium precursor, the doped metal or the doping nonmetal precursor in the first mixed solution of step (a), and the concentration of the iron precursor and the phosphoric acid precursor in the second mixed solution are respectively 0.001 to 1 mol / A method of producing phosphate-based cathode active material nanoparticles. The method of claim 1, wherein the concentration of the reducing agent in the reducing agent solution of step (a) is 0.001 to 5 mol / L. The method of claim 2, wherein the concentration of the reducing agent in the mixed solution of step (a) is 0.001 to 5 mol / L method for producing a phosphate-based cathode active material nanoparticles. The method of claim 3, wherein the concentration of the reducing agent in the first mixed solution of step (a) is 0.001 to 5 mol / l. According to any one of claims 1 to 3, the supercritical or subcritical conditions of step (b), the reaction temperature is 200 to 600 ℃, the reaction pressure is 20 to 500 bar phosphate-based cathode active material nano Method for Producing Particles. The method according to any one of claims 1 to 3, wherein the diameter of the phosphate positive electrode active material nanoparticles is 10 to 1,000 nm. The phosphate-based cathode active material nanoparticle according to any one of claims 1 to 3, further comprising, after step (e), (f) washing and drying the separated and recovered phosphate-based cathode active material nanoparticles. Manufacturing method. The method of claim 13, wherein the washing is performed using water, methanol, ethanol, or tetrahydrofuran solvent. The method of claim 13, wherein the drying is vacuum drying, oven drying, or freeze drying.

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