TWI415324B - Method for making electrode material of lithium battery - Google Patents

Abstract

The invention relates to a method for making an electrode material of lithium battery. In the method, a lithium vanadium phosphate electrode material is provided. The lithium vanadium phosphate electrode material includes a plurality of lithium vanadium phosphate particles. A lithium iron phosphate electrode material is coated on the surface of the lithium vanadium phosphate particles to form the lithium iron phosphate/lithium vanadium phosphate composite electrode material.

Description

Method for preparing lithium battery electrode material

The invention relates to a preparation method of a lithium battery electrode material, in particular to a preparation method of a lithium iron phosphate/vanadium phosphate composite electrode material.

Lithium iron phosphate (LiFePO ₄ ) and lithium vanadium phosphate (Li ₃ V ₂ (PO ₄ ) ₃ ) electrode materials have attracted much attention due to their structural stability, safety and resource. At the same time, studies have shown that the two electrode materials also have other inherent characteristics. The lithium iron phosphate electrode material has good high temperature performance and cycle performance, and has a high theoretical specific capacity, but its lithium ion insertion and extraction is performed in one dimension. Therefore, the ionic conductivity is poor, the high rate charge and discharge performance and the low temperature performance are poor; the lithium ion diffusion in the lithium vanadium phosphate electrode material is performed in the three-dimensional direction, so the ion diffusion performance in the low voltage range is good, and the high rate charge and discharge is performed. Excellent performance and low temperature performance, but low electronic conductivity and theoretical specific capacity.

For the disadvantage that the ionic conductivity of lithium iron phosphate is poor and the theoretical specific capacity of lithium vanadium phosphate is low, it has been reported in the literature to obtain a lithium iron phosphate/lithium vanadium phosphate composite cathode material by a method of combining lithium iron phosphate and lithium vanadium phosphate. Thereby achieving the complementary advantages of the two. See "Improving electrochemical properties of lithium iron phosphate by additon of vanadium", Yang MR, Ke W, Wu S H. J Power Sources, 2007, 165: 646-650, by using lithium iron phosphate and lithium vanadium phosphate The precursor is uniformly mixed and calcined to form a bulk composite lithium iron phosphate/vanadium phosphate composite cathode material. After electrochemical performance test, it is found that the lithium iron phosphate is added due to the addition of lithium vanadium phosphate with good ion conductivity. The specific capacity of the lithium vanadium phosphate composite electrode material at a high rate is higher than that of the single phase of lithium iron phosphate and lithium vanadium phosphate.

However, when the composite positive electrode material is used in a lithium battery, since lithium iron phosphate and lithium vanadium phosphate are uniformly distributed in the bulk lithium iron phosphate/vanadium phosphate composite positive electrode material, a part of the electrolyte cannot be combined with Lithium iron phosphate is directly contacted, so that lithium iron phosphate having poor lithium ion diffusion performance is insufficiently contacted with the electrolyte, so that lithium ions of lithium iron phosphate in the lithium iron phosphate/vanadium phosphate composite cathode material are not easily diffused sufficiently In the electrolyte, the electrochemical performance of the entire lithium iron phosphate/vanadium phosphate composite cathode material is lowered.

In view of this, it is necessary to provide a method for preparing a lithium iron phosphate/vanadium phosphate composite electrode material, and the lithium ion of lithium iron phosphate in the obtained lithium iron phosphate/vanadium phosphate composite electrode material can be obtained by the preparation method. Fully spread.

A method for preparing a lithium battery electrode material, comprising the steps of: preparing a vanadium phosphate monophosphate electrode material comprising a plurality of lithium vanadium phosphate particles; and coating a surface of the lithium vanadium phosphate particles with a lithium iron phosphate electrode material, thereby A lithium iron phosphate/vanadium phosphate composite electrode material is formed.

A method for preparing a lithium battery electrode material, comprising the steps of: providing a vanadium phosphate monophosphate electrode material comprising a plurality of lithium vanadium phosphate particles; providing an iron salt and a phosphorus source, and dissolving the iron salt and the phosphorus source a solvent is formed to form a mixed solution; the mixture is continuously fed into a reactor at a flow rate of 100 ml/hr to 150 ml/hr; the pH of the mixture is adjusted to 1.5 to 5, and the temperature of the reactor is 25 ° C ~ 50 ° C, the reaction time of the mixture in the reactor is 40 minutes to 2 hours, thereby forming iron phosphate precursor particles; in an inert gas atmosphere, in the temperature range of 400 ° C ~ 700 ° C Said iron phosphate precursor particles for 2 hours to 24 hours; providing a lithium source solution and a reducing agent, uniformly mixing the lithium source solution, the iron phosphate precursor particles and the reducing agent to form a mixed slurry; The lithium vanadium phosphate particles are uniformly dispersed in the mixed slurry, and the mixed slurry is uniformly coated on the surface of the lithium vanadium phosphate particles, and then the vanadium phosphate particles coated with the mixed slurry are filtered and dried. Make the phosphorus The mixed slurry on the surface of the vanadium lithium particles is solidified to form a composite; the composite is heated in an inert gas atmosphere at a temperature of 500 ° C to 850 ° C for 8 hours to 40 hours to form iron phosphate Lithium/vanadium phosphate composite electrode material.

Compared with the prior art, in the lithium iron phosphate/vanadium phosphate composite electrode material obtained by the method for preparing the lithium battery electrode material, the lithium iron phosphate particle layer having poor lithium ion diffusion property is located in the “shell layer”, thereby making the phosphoric acid When the iron lithium/vanadium phosphate composite electrode material is used in a lithium battery, the electrolyte is in sufficient contact with the lithium iron phosphate particles in the lithium iron phosphate particle layer, so that the lithium ions therein can be sufficiently diffused into the electrolyte, thereby effectively improving The electrochemical performance of the entire lithium iron phosphate/vanadium phosphate composite electrode material.

The lithium battery electrode material provided by the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

Referring to FIG. 1 and FIG. 2, an embodiment of the present invention provides a lithium iron phosphate/lithium vanadium phosphate (LiFePO ₄ /Li ₃ V ₂ (PO ₄ ) ₃ ) composite electrode material 10, which comprises a plurality of uniformly distributed lithium iron phosphate/ The lithium vanadium phosphate composite particles 100, each of the lithium iron phosphate/vanadium phosphate composite particles 100 comprising lithium vanadium phosphate (Li ₃ V ₂ (PO ₄ ) ₃ ) particles 102 and uniformly coated on the surface of the lithium vanadium phosphate particles 102 Lithium iron phosphate monophosphate (LiFePO ₄ ) particle layer 104.

In each of the lithium iron phosphate/vanadium phosphate composite particles 100, the vanadium phosphate vanadium particles 102 preferably have a spherical or spheroidal shape and a diameter of 1 micrometer to 50 micrometers, preferably 5 micrometers to 20 micrometers. In one example, the lithium vanadium phosphate particles 102 have a diameter of 10 microns. The lithium iron phosphate particle layer 104 includes a plurality of lithium iron phosphate particles 1042, and the morphology of each of the lithium iron phosphate particles 1042 is preferably spherical or spheroidal, and has a diameter of 50 nm to 10 μm, preferably 100 nm. At 500 nm, the size of the lithium iron phosphate particles 1042 is not too large, and is too large to fall off. In the present embodiment, the lithium iron phosphate particles 1042 have a diameter of 100 nm to 200 nm. The outer surface of the lithium vanadium phosphate particles 102 in the lithium iron phosphate/vanadium phosphate composite particles 100 is formed with a plurality of complex lithium iron phosphate particles 1042 to form a "core-shell structure".

In each of the lithium iron phosphate/vanadium phosphate composite particles 100 described above, the mass ratio of the lithium iron phosphate particle layer 104 to the lithium vanadium phosphate particles 102 is greater than or equal to 1.5. In addition, the thickness of the lithium iron phosphate particle layer 104 should not be too thick, and too thick will increase the migration resistance of lithium ions by the lithium iron phosphate particle layer 104, and easily cause agglomeration and shedding of the lithium iron phosphate particles 1042 therein, and The thickness of the lithium iron phosphate particle layer 104 is not too thin, and if it is too thin, it is difficult to cause the lithium iron phosphate particle layer 104 to function in the lithium iron phosphate/vanadium phosphate composite electrode material 10. Therefore, the thickness of the lithium iron phosphate particle layer 104 is preferably 10 μm or less under the condition that the mass ratio of the lithium iron phosphate particle layer 104 to the lithium vanadium phosphate particles 102 is 1.5 or more. In this embodiment, the lithium iron phosphate particle layer 104 has a thickness of 2 μm.

In the above lithium iron phosphate/vanadium phosphate composite electrode material 10 having a "core-shell structure", the lithium iron phosphate particle layer 104 located in the "shell layer" includes a plurality of lithium iron phosphate particles 1042, which is a thin porous structure, and The lithium iron phosphate particles 1042 have the characteristics of small particle diameter and large specific surface area. Therefore, when the lithium iron phosphate/vanadium phosphate composite electrode material 10 is used in a lithium battery, lithium ions are made by the thinner one. The lithium iron phosphate particle layer 104 of the shell layer has a short diffusion path, and the "shell layer" having a porous structure can be sufficiently contacted with the electrolyte, so that lithium ions in the lithium iron phosphate particles 1042 having poor lithium ion diffusion properties can be Fully diffuse into the electrolyte. While the "core" lithium vanadium phosphate particles 102 have good lithium ion migration properties, the lithium vanadium phosphate particles 102 provide a highly active support for the "shell" lithium iron phosphate particle layer 104. It is advantageous for lithium ions to diffuse deep into the lithium iron phosphate/vanadium phosphate composite particles 100.

Referring to FIG. 3, in order to further improve the electronic conductivity of the lithium iron phosphate/vanadium phosphate composite electrode material 10, the lithium iron phosphate/vanadium phosphate composite electrode material 10 may be further doped with carbon 106, the carbon 106. It consists of amorphous carbon. The carbon 106 may be doped with the lithium vanadium phosphate particles 102 and/or the lithium iron phosphate particle layer 104 in the lithium iron phosphate/vanadium phosphate composite electrode material 10. Specifically, the surface of the lithium vanadium phosphate particles 102 may be coated with a carbon layer, or the lithium iron phosphate particle layer 104 may be doped with carbon particles. The carbon particles doped in the lithium iron phosphate particle layer 104 may be uniformly dispersed between the lithium iron phosphate particles 1042 in the lithium iron phosphate particle layer 104, or may be coated on the surface of the lithium iron phosphate particles 1042. Therefore, the specific structure of the carbon-doped lithium iron phosphate/vanadium phosphate composite electrode material 10 may include: lithium vanadium phosphate particles 102 coated with a carbon layer, and carbon doped on the surface of the lithium vanadium phosphate particles 102. The hetero-lithium iron phosphate particle layer 104, wherein the carbon 106 in the lithium iron phosphate particle layer 104 may be coated on the surface of each of the lithium iron phosphate particles or uniformly dispersed between the lithium iron phosphate particles. Alternatively, the carbon 106 may be incorporated only into the lithium iron phosphate particle layer 104 or coated on the surface of the lithium vanadium phosphate particles 102. When the surface of the lithium vanadium phosphate particles 102 is coated with a carbon layer, and the lithium iron phosphate particle layer 104 is also doped with carbon particles, the lithium iron phosphate particles 1042 located in the "shell layer" are located between The "shell" lithium iron phosphate particles 1042 are connected and fixed together by the carbon 106 between the surface of the "core" lithium vanadium phosphate particles 102 to form a continuous conductive network, with monodisperse iron phosphate. Compared with the lithium particles 1042, the contact resistance between the lithium iron phosphate particles 1042 and the lithium iron phosphate particles 1042 and the lithium vanadium phosphate particles 102 is smaller, thereby greatly increasing the entire lithium iron phosphate/vanadium phosphate composite electrode material 10 Electronic conductivity. However, due to the low density of carbon, too much carbon 106 is incorporated, which will lower the energy density and tap density of the lithium iron phosphate/vanadium phosphate composite electrode material 10, so that each lithium iron phosphate/vanadium phosphate In the lithium composite particles 100, the mass of the carbon 106 doped into the lithium vanadium phosphate particles 102 and the lithium iron phosphate particle layer 104 is 0.5% to 10% of the mass of the lithium vanadium phosphate particles 102 and the lithium iron phosphate particle layer 104, respectively. It is preferably 2% to 5%.

In order to further increase the lithium ion diffusion coefficient of the "shell" lithium iron phosphate particles 1042, thereby improving the rate performance and cycle performance of the entire lithium iron phosphate/vanadium phosphate composite electrode material 10, in the lithium iron phosphate particle layer 104 The iron-site of the lithium iron phosphate particle 1042 is doped with a metal cation such as nickel ion (Ni ²⁺ ), cobalt ion (Co ²⁺ ), magnesium ion (Mg ²⁺ ) or vanadium ion (V ³⁺ ), the metal The doping of the cation can effectively weaken the average binding energy of the lithium-oxygen bond (Li-O) in the lithium iron phosphate particle 1042, making the insertion and extraction of the lithium ion more free, thereby increasing the diffusion coefficient of the lithium ion. The shell material obtained after the doping has the general formula LiFe _1-x M _x PO ₄ (or lithium iron phosphate with an M doping amount of x), wherein M can be nickel (Ni), cobalt (Co), Magnesium (Mg) or vanadium (V), etc., and are not limited thereto, and x is preferably 0.01 to 0.08, that is, the lithium iron phosphate is doped with 1% to 8% of a metal cation. In this embodiment, M is vanadium (V), and x is 0.03, that is, the shell material obtained after the doping has a molecular formula of LiFe _0.97 V _0.03 PO ₄ .

Referring to FIG. 4, this embodiment measures a lithium iron phosphate/vanadium phosphate composite electrode material and a vanadium doped 3% lithium iron phosphate at a voltage range of 2.5 volts to 4.3 volts at a magnification of 0.1 C. The charge-discharge performance of lithium vanadium phosphate composite electrode material, the charge specific capacity of lithium iron phosphate/vanadium phosphate composite electrode material and vanadium doped 3% lithium iron phosphate/vanadium phosphate composite electrode material measured at 0.1C rate They were 140 mAh/g and 145 mAh/g, respectively, and the discharge specific capacities were 138.9 mAh/g and 145 mAh/g, respectively. Referring to FIG. 5, the specific capacity-cycle curve of different magnifications is also measured in the voltage range of 2.5 volts to 4.3 volts, and the cadmium-doped 3% lithium iron phosphate/vanadium phosphate composite electrode material is measured. The specific capacity is higher than the lithium iron phosphate/vanadium phosphate composite electrode material, which is related to the incorporation of vanadium in the lithium iron phosphate particle layer to improve the diffusion performance of lithium ions.

Referring to FIG. 6, a first embodiment of the present invention provides a method for preparing the above lithium iron phosphate/vanadium phosphate composite electrode material, which comprises:

Step 1: preparing a vanadium phosphate monophosphate electrode material, which comprises a plurality of lithium vanadium phosphate particles;

Step 2: coating a surface of the lithium vanadium phosphate particles with a lithium iron phosphate electrode material to form a lithium iron phosphate/vanadium phosphate composite electrode material.

The above steps will be introduced separately below.

step one

The preparation method of the lithium vanadium phosphate electrode material may be a high temperature solid phase method, a sol-gel method or a microwave method. Wherein, the high-temperature solid phase method may select a hydrogen reduction method and a high-temperature carbothermal reduction method, and the high-temperature carbothermal reduction method may select a pure solid phase carbothermal reduction method, a sol-gel-carbothermic reduction method or spray granulation- Carbothermal reduction method, etc. In this embodiment, the vanadium phosphate phosphate electrode material is prepared by a spray granulation-carbothermal reduction method.

The preparation method specifically includes: S1, providing a lithium source, a vanadium source and a phosphorus source, and dissolving the lithium source, the vanadium source and the phosphorus source in a solvent to form a uniform mixture; and S2, providing a carbon thermal reduction And uniformly mixing the carbon thermal reducing agent with the above mixture to form a sol; S3, spray drying the sol to obtain a precursor particle; and S4, heat treating the precursor particle to obtain a vanadium phosphate monophosphate electrode material .

In the above step S1, the solvent is dissolved in a ratio of lithium element, vanadium element and phosphorus element (Li:V:P) of from 3:2:3 to 3.3:2:3. Both the lithium source and the phosphorus source are preferably soluble in water. The lithium source may include lithium hydroxide or a lithium salt, and the lithium salt may include lithium carbonate, lithium sulfate, lithium nitrate or lithium chloride, and the like, and is not limited to the ones listed. The vanadium source may include ammonium metavanadate, vanadium pentoxide, vanadium dioxide or vanadium tetrachloride. The phosphorus source may include phosphoric acid, dihydrogen phosphate or diammonium hydrogen phosphate. The solvent may be water, ethanol or acetone, etc., the solvent is preferably water, and the water is preferably deionized water or distilled water to avoid introduction of other impurity elements.

In this embodiment, the lithium source is lithium hydroxide, the vanadium source is ammonium metavanadate, the phosphorus source is phosphoric acid, and the molar ratio of the three elements according to lithium element, vanadium element and phosphorus element is 3: The ratio of 2:3 was dissolved in a deionized water to form a mixed solution. To uniformly mix the mixed solution, the mixture was further stirred by magnetic stirring for 2 hours.

In the above step S2, the carbothermal reducing agent is an organic compound which is pyrolyzable to form carbon, and the carbothermal reducing agent may include sucrose, glucose, phenolic resin, polyacrylic acid, polyacrylonitrile, polyethylene glycol or polyvinyl alcohol. Wait. The amount of the carbothermal reducing agent added to the mixed solution may be such that the pentavalent vanadium ion (V ⁵⁺ ) in the ammonium metavanadate is completely reduced to the trivalent vanadium ion (V ³⁺ ), and is also suitable In excess, it is preferred that the carbothermal reducing agent is added in a ratio of lithium element, vanadium element, phosphorus element to carbon element in a ratio of 3:2:3:2 to 3.3:2:3:2.6. And in order to form a uniformly stable sol, the mixture may be further heated at a temperature ranging from 60 ° C to 85 ° C to evaporate part of the solvent before or during the addition of the carbon source reducing agent to the above mixture, and In the heating process, in order to uniformly mix the lithium source, the vanadium source, the phosphorus source and the carbon source reducing agent in the mixed liquid, the mixed solution may be further processed by magnetic stirring, ball mill ball milling or ultrasonic dispersion for a certain time until the The carbon source reducing agent completely dissolves and forms a sol.

In this embodiment, the carbothermal reducing agent is sucrose, and the sucrose is added in a ratio of lithium element, vanadium element, phosphorus element to carbon element ratio of 3:2:3:2.4. Before adding the sucrose to the above mixture, first, the mixture is heated at a constant temperature of 80 ° C, and the mixture is stirred by magnetic stirring for 2 hours until a uniform and stable sol is formed, and the sol is added thereto. Sucrose is described and stirring is continued until the sucrose is completely dissolved.

In the above step S3, the spray drying process uses a gas flow spray dryer having an atomizing device using a dual flow nozzle, and the air flow spray dryer adopts a cocurrent drying method. dry.

Specifically, the sol is used to input the sol into the airflow spray dryer under the action of a stream of hot air; the sol is atomized by the dual-flow nozzle atomizing device to form a misty liquid. The droplets formed are cocurrent with the hot air, and in the hot air, the mist droplets are instantaneously evaporated to almost all of the water, thereby forming a plurality of spherical or spheroidal precursor particles.

The spray drying method can disperse the sol into extremely fine mist droplets, so that the atomized sol has a large specific surface area, and when the mist droplets generate intense heat exchange with hot air, The porous spherical precursor particles having a plurality of particle diameters of 5 μm to 20 μm can be obtained by rapidly removing moisture in the mist droplets in a few seconds to several tens of seconds. The plurality of porous spherical precursor particles have the advantages of relatively uniform particle size distribution, good fluidity, good processability and regular morphology.

In this embodiment, each of the spherical precursor particles is a composite particle composed of ammonium vanadate, lithium hydroxide, a carbothermal reducing agent and phosphoric acid.

In the above step S4, the heat treatment is specifically carried out by heating the precursor particles in a temperature range of 500 ° C to 1000 ° C for 10 hours to 20 hours under an inert gas atmosphere, thereby obtaining the vanadium phosphate electrode. material. In this example, the precursor particles were heated at 800 ° C for 16 hours under a protective atmosphere of nitrogen. During the heat treatment, the sucrose is cleaved to form carbon, and at the same time, due to the presence of the carbon, the pentavalent vanadium ions in the precursor particles can be further reduced by the carbon to trivalent vanadium ions, thereby forming a plurality A lithium vanadium phosphate electrode material composed of lithium vanadium phosphate particles. It can be seen that during the reaction of the carbon with the pentavalent vanadium ion, the carbon is gradually oxidized to form carbon monoxide or carbon dioxide, and when the added carbon source reducing agent is excessive, it can be residual in the formed lithium vanadium phosphate cathode material. A small amount of carbon. Referring to FIG. 7, since the vanadium phosphate particles are formed directly from the spherical or spheroidal precursor particles during the heat treatment, the lithium vanadium phosphate particles have a morphology similar to that of the precursor particles described above. That is spherical or spheroidal.

Step two

The second step may specifically include: A1, providing a lithium iron phosphate precursor mixed slurry; A2, coating the lithium iron phosphate precursor mixed slurry on the surface of the lithium vanadium phosphate particles and solidifying to form a composite A3, heat-treating the dried composite to form a lithium iron phosphate/vanadium phosphate composite electrode material.

In the above step A1, the preparation method of the lithium iron phosphate precursor mixed slurry is not limited, and it can be prepared by a coprecipitation method or a sol-gel method. In this embodiment, the preparation method comprises the following steps:

B1, providing an iron salt and a phosphorus source, dissolving the iron salt and the phosphorus source in a solvent to form a mixed solution;

B2, adding a plurality of microparticle fillers to the mixture, uniformly mixing the plurality of microparticle fillers with the mixture, and adjusting the pH of the mixture to 1.5 to 5 during the uniform mixing to react the mixture Forming iron phosphate precursor particles;

B3, providing a lithium source solution and a reducing agent, uniformly mixing the lithium source solution, the iron phosphate precursor particles and the reducing agent to form a lithium iron phosphate precursor mixed slurry.

The respective steps of B1 to B3 will be described in detail below.

In the step B1, the iron salt and the phosphorus source are dissolved in a solvent in a molar ratio of iron to phosphorus of 1:0.8 to 1:1.2. The iron salt may be dissolved in the solvent, which may be one or a mixture of iron chloride, iron nitrate, and iron sulfate, and is not limited to the ones listed. The phosphorus source is soluble in the solvent and may form a phosphate ion, which may be a mixture of one or more of phosphoric acid, ammonium phosphate, ammonium hydrogen phosphate, and ammonium dihydrogen phosphate. The solvent may be water, ethanol or acetone, etc., the solvent is preferably water, and the water is preferably deionized water or distilled water to avoid introduction of other impurity elements. The concentration of the iron salt and the phosphorus source in the mixed solution is preferably from 0.1 mol/L to 3 mol/L. In the mixed solution of the present embodiment, the iron salt is ferric nitrate, the phosphorus source is phosphoric acid, the solvent is deionized water, and the concentration of the ferric nitrate and phosphoric acid is 0.2 mol/L.

In the step B2, the plurality of microparticle fillers are composed of a hard material which is insoluble in the above solvent and does not react with the above iron source and phosphorus source. Specifically, the material of the plurality of microparticle fillers may be one or more of ceramics, quartz, and glass, and is not limited thereto. The particle diameter of each of the microparticle fillers is preferably larger than the diameter of the subsequently formed iron phosphate precursor particles, and may be 20 micrometers to 1 millimeter, and the volume of the plurality of microparticle fillers accounts for 15% to 50% of the volume of the mixture. .

The step B2 may specifically be performed by using a controlled crystallization process to prepare the iron phosphate precursor particles, which may specifically include the following substeps:

First, the above mixture is continuously fed to a reactor at a flow rate of 100 ml/hr to 150 ml/hr, and the reactor may be vacant or pre-filled with a certain amount of solvent. In this embodiment, the flow rate is 120 ml/hr, and the reactor is filled with 60% by volume of a solvent, and the solvent may be deionized water, distilled water or ethanol, etc., preferably, the solvent and the above mixture are The solvent is the same, ie deionized water.

Next, the plurality of microparticle fillers are added to the reactor before or during the introduction of the above mixture into the reactor, and the mixture is uniformly mixed with the plurality of microparticle fillers. Specifically, the mixing solution and the plurality of micro-particle fillers are uniformly mixed by a stirring method, and the specific manner of the stirring is not limited, and may be mechanical stirring, magnetic stirring or ultrasonic dispersion, etc., in this embodiment, a magnetic stirring method is adopted. The above mixture was stirred at a power of ~60 watts/liter.

Again, the pH of the mixture input to the reactor was adjusted to 1.5 to 5 to form hydrated iron phosphate precursor particles. Specifically, in the process of stirring the mixed liquid and continuously injecting the mixed liquid in the reactor, the pH may be adjusted by continuously injecting an alkaline solution into the mixed liquid, and the alkaline solution may be ammonia water or sodium hydroxide. Solution, etc. In this embodiment, the alkaline solution is ammonia water, and the pH of the mixed liquid in the reactor is adjusted to 2.3. During the entire reaction, since the mixed liquid is continuously injected into the reactor at a certain flow rate, the hydrated iron phosphate precursor particles formed by the reaction after the mixed liquid input to the reactor reacts for a certain period of time The hydrated iron phosphate precursor particles outside the overflow reactor are collected, which naturally overflows the reactor due to continuous input of the mixed liquid.

During the agitation process, the plurality of microparticle fillers and the formed hydrated iron phosphate precipitate collide and collide with each other, thereby increasing the mixing strength of the iron salt and the phosphorus source in the mixture, and is more favorable for forming a spherical or spheroidal shape. The hydrated iron phosphate precursor particles inhibit the agglomeration and growth of the hydrated iron phosphate precursor particles. It can be understood that if the step does not add the plurality of microparticles, the hydrated iron phosphate precursor particles can be obtained, and the final product lithium iron phosphate/vanadium phosphate composite electrode material can also be formed, which is added only during the reaction. The morphology and particle size of the hydrated iron phosphate precursor particles are more effectively controlled, and the electrochemical performance of the lithium iron phosphate material as the "shell" in the lithium iron phosphate/vanadium phosphate composite electrode material is optimized.

Further, in order to better control the particle size of the formed hydrated iron phosphate precursor particles, the temperature of the mixed liquid input into the reactor may be controlled to be 25 ° C to 50 ° C by controlling the flow rate of the mixed liquid and the reactor. The volume is sized to control the reaction time of the mixture in the reactor, i.e., the residence time is between 40 minutes and 2 hours. The reaction temperature and reaction time will affect the particle size of the final hydrated iron phosphate precursor particles. The higher the reaction temperature, the longer the reaction time will promote the growth of crystal grains, thereby forming the particles of the iron phosphate precursor particles. The diameter is large. In this embodiment, the reaction temperature is controlled at 25 ° C and the reaction time is controlled at 1 hour.

Further, the step B2 may further comprise the step of filtering, washing and drying the iron phosphate precursor particles. Specifically, the hydrated iron phosphate precursor particles obtained by the above collection may be sieved by a centrifuge, and the sieved iron phosphate precursor particles are washed with deionized water or distilled water, and then the washed iron phosphate precursor is washed. The bulk particles are dried at a temperature of 70 ° C to 100 ° C for 2 to 4 hours to obtain hydrated iron phosphate precursor particles having a particle diameter of 20 nm to 10 μm.

In addition, since the microparticle filler does not participate in the reaction, the microparticle filler is still present in the hydrated iron phosphate precursor particles, so the microparticle filler can be further sieved out, specifically, due to the microparticle filler. The particle diameter is 20 μm to 1 mm, which is larger than the particle size of the formed hydrated iron phosphate precursor particles. Therefore, a diameter smaller than the smallest microparticle in the microparticle filler can be used and is larger than the formed hydrated iron phosphate precursor. A filter of the diameter of the largest microparticles in the bulk particles screens the microparticulate filler to form pure hydrated iron phosphate precursor particles.

Referring to FIG. 8 and FIG. 9, the controlled crystallization process effectively controls the growth process of the hydrated iron phosphate crystal grains by controlling the reaction temperature of the mixed solution in the reactor, the reaction time, and adding the microparticle filler to the mixed solution. The final formed hydrated iron phosphate precursor particle diameter can reach a controllable range of 20 nm to 10 μm, and the morphology of the hydrated iron phosphate precursor particle is spherical or spheroidal, and has no agglomeration and dispersibility. Good and so on. It can be understood that the morphology, particle size and dispersibility of the hydrated iron phosphate precursor particles are related to the morphology, particle size and dispersibility of the finally formed lithium iron phosphate electrode material, and the hydrated iron phosphate precursor particles The smaller the particle size, the better the dispersibility, and the closer the morphology is to a spherical or spheroidal shape, the smaller the particle size of the finally formed lithium iron phosphate electrode material, the better the dispersibility and the closer the morphology to the sphere or class. It is spherical, and the spherical or spheroidal lithium iron phosphate electrode material having a small particle size and good dispersibility is more easily supported on the surface of the above spherical lithium vanadium phosphate particles. In this embodiment, the hydrated iron phosphate precursor particles have a diameter of 100 to 200 nm.

In addition, the step may further include the step of heat-treating the hydrated iron phosphate precursor particles, that is, heating the hydrated iron phosphate precursor particles in a temperature range of 400 ° C to 700 ° C for 2 hours to 24 in an inert gas atmosphere. In the hour, this example was heated under a nitrogen atmosphere at a temperature of 520 ° C for 10 hours to remove crystal water in the hydrated iron phosphate precursor particles to obtain anhydrous iron phosphate precursor particles.

In the above step B3, the lithium source solution is formed by dissolving a lithium salt or lithium hydroxide (LiOH) in a solvent. The lithium salt is a soluble lithium salt, and may be lithium carbonate, lithium sulfate, lithium nitrate or lithium chloride, and is not limited to the ones listed. The solvent may be water, ethanol or acetone or the like. The solvent is preferably water, and the water is preferably deionized water or distilled water to avoid introduction of other impurity elements. The reducing agent may be ascorbic acid, stannous chloride, sodium borohydride or a carbothermal reducing agent, preferably a carbothermal reducing agent, which is a reducing organic compound soluble in the above solvent, and the organic compound may be cleaved In the formation of carbon, the carbothermal reducing agent is uniformly mixed in a molar ratio of lithium element, phosphorus element and carbon element of 1:1:1 to 1.2:1:1. The carbothermal reducing agent may be sucrose, glucose, phenolic resin, polyacrylic acid, polyacrylonitrile, polyethylene glycol or polyvinyl alcohol. In this embodiment, the lithium source solution is a lithium hydroxide solution, and the reducing agent is sucrose.

In order to uniformly mix the lithium source solution, the reducing agent and the iron phosphate precursor particles, the lithium iron phosphate precursor mixed slurry may be further stirred for a certain period of time, specifically by ball milling, mechanical stirring, magnetic stirring or ultrasonic dispersion. The mixed slurry. In this embodiment, the mixed slurry was ball milled by ball milling for 2 hours.

It can be seen that the lithium iron phosphate precursor mixed slurry obtained by the above steps B1 to B3 is a mixture of iron phosphate precursor particles, a lithium source solution and a reducing agent.

Specifically, the step A2 may include: uniformly dispersing the lithium vanadium phosphate particles in the lithium iron phosphate precursor mixed slurry, and uniformly loading the mixed slurry on the surface of the lithium vanadium phosphate particles; The surface is loaded with lithium vanadium phosphate particles mixed with a slurry; the vanadium phosphate particles loaded with the mixed slurry on the surface are dried to solidify the mixed slurry on the surface of the lithium vanadium phosphate particles. The entire process can be repeated by performing a plurality of coatings so that the lithium iron phosphate precursor mixed slurry can be sufficiently coated on the surface of the lithium vanadium phosphate particles. In this embodiment, the coating is three times, specifically: (1), the lithium iron phosphate precursor mixed slurry is evenly divided into three equal parts, which are respectively the first, second and third mixed slurry; (2) Dispersing the lithium vanadium phosphate particles uniformly in the first mixed slurry to uniformly load the mixed slurry on the surface of the lithium vanadium phosphate particles; (3) loading the surface with a mixed slurry The lithium vanadium phosphate particles are filtered and dried at a temperature for a certain period of time to solidify the mixed slurry on the surface to form a first composite; (4) dispersing the first composite in the second mixed slurry , the mixed slurry is uniformly supported on the surface of the first composite, and then the above step (3) is repeated to form a second composite; and (5) the second composite is dispersed in the third mixed slurry. The mixed slurry is uniformly supported on the surface of the second composite, and then the above step (3) is repeated to form a third composite.

In the above coating process, the mixed slurry and the lithium vanadium phosphate particles are supplied in a mass ratio of the iron phosphate precursor particles to the lithium vanadium phosphate particles in the finally obtained composite of 5.5:4 to 6.5:4. In the above step (2), the step (4) and the step (5), in order to uniformly load the mixed slurry on the surface of each of the vanadium phosphate particles, the lithium vanadium phosphate particles dispersed may be stirred by stirring. The mixed slurry, the stirring method is not limited, and may be magnetic stirring or ultrasonic dispersion, etc., and the stirring method can also prevent the iron phosphate precursor particles from sticking to each other, so that the finally obtained composite has a comparative Good dispersion. In the above step (3), the lithium vanadium phosphate particles coated with the mixed slurry may be heated in a temperature range of 60 ° C to 90 ° C for 10 minutes to 30 minutes to cure the mixed slurry.

By repeating the above-mentioned repeated coating and repeated curing, the mixed slurry can be solidified and then firmly and uniformly coated on the surface of the lithium vanadium phosphate particles to form a stable composite.

In addition, in order to firmly bond the slurry to the surface of the vanadium phosphate vanadium particles, a small amount of a water-soluble binder such as a starch binder, a polyurethane binder or a resin binder may be further added to the mixed sol. .

In the above step A3, the heat treatment is specifically carried out by heating the composite at a temperature of 500 ° C to 850 ° C for 8 hours to 40 hours in an inert gas atmosphere, thereby allowing the composite to be in a reducing agent. The reduction reaction occurs to form a lithium iron phosphate/vanadium phosphate composite electrode material composed of lithium vanadium phosphate particles and a lithium iron phosphate electrode material coated on the surface of the lithium vanadium phosphate particles. This example was heated for 16 hours under a nitrogen atmosphere at 700 °C. Referring to FIG. 10, during the high-temperature heating, the reducing agent in the composite, ie, sucrose, is cracked to generate carbon, and the iron ions (Fe ³⁺ ) in the iron phosphate precursor particles are reduced by the carbon. Forming ferrous ions (Fe ²⁺ ) and reacting with a lithium source to form lithium iron phosphate. The carbon formed during the high-temperature heat treatment can also inhibit grain growth and agglomeration, thereby forming the finally formed iron phosphate. The lithium particles have a small particle size and good dispersibility, and if the carbon has a residue, the residual carbon can be coated on the surface of the lithium iron phosphate particles, thereby further improving the electronic conductivity of the lithium iron phosphate electrode material. At the same time, since the iron phosphate precursor particles have the characteristics of small particle size, spherical shape or spheroidal shape, the lithium iron phosphate particles formed by the reaction of the iron phosphate precursor particles also have the characteristics of small particle size, spherical shape or spheroidal shape. .

In addition, the lithium iron phosphate material prepared by the redox method can be used not only as a "shell layer" of the lithium iron phosphate/vanadium phosphate composite electrode material, but also as an electrode material for a lithium battery, and the iron phosphate can be simply prepared. The method of the lithium electrode material only needs to remove the step A2 in the above step 2, and dry the mixed slurry to completely evaporate the water therein, and then directly perform the above step A3.

Since the lithium iron phosphate particles prepared by the redox method have the characteristics of small particle size, good dispersibility, spherical or spheroidal shape, which is advantageous for use as a lithium battery electrode material, the bulk density is improved, and lithium ions are shortened. The diffusion path in the solid phase particles. Moreover, the redox method uses a relatively inexpensive carbon source as a reducing agent, which is low in cost and safer, and the entire preparation process takes a short time, which is advantageous for industrial production. Please refer to FIG. 11 for the cycle performance curve of the lithium iron phosphate electrode material with a particle diameter of about 100 nm to 200 nm in a voltage range of 2.5 to 4.2 volts at a 1 C rate. It can be seen from the figure that the first charge-discharge specific capacity of lithium iron phosphate electrode material at 10C rate is 106.4 mAh/g, the reversible specific capacity decreases to 95 mAh/g after 50 cycles, and the capacity retention rate is as high as 90%, indicating that phosphoric acid The fineness of the particles of the iron-lithium electric material maintains excellent cycle performance.

In addition, since the lithium iron phosphate material as the "shell layer" in the lithium iron phosphate/vanadium phosphate composite electrode material has the above advantages, the electrochemical performance of the entire lithium iron phosphate/vanadium phosphate composite electrode material can be further improved, and When the lithium iron phosphate/vanadium phosphate composite electrode material is used in a lithium battery, since the lithium iron phosphate material has the characteristics of small particle diameter, large specific surface area, and being located in the shell layer, it can be sufficiently contacted with the electrolyte. Lithium ions can be fully diffused, which effectively compensates for the shortcomings of poor conductivity of lithium iron phosphate electrical materials. At the same time, the "core" lithium vanadium phosphate has excellent lithium ion diffusion performance, so that the ionic conductivity and high rate performance of the whole lithium iron phosphate / vanadium phosphate composite electrode material are significantly improved. Referring to FIG. 12 to FIG. 15 , the discharge curve of the lithium iron phosphate electrode material and the lithium iron phosphate/vanadium phosphate composite electrode material in the voltage range of 2.5V to 4.3V at different magnifications is measured. It can be seen that the lithium iron phosphate/vanadium phosphate composite electrode material has a significantly higher discharge specific capacity and discharge voltage platform at 0.1C, 1C, 5C and 10C ratios than the lithium iron phosphate electrode material.

The second embodiment of the present invention provides a method for preparing the lithium iron phosphate/vanadium phosphate composite electrode material, and the first step is the same as the first step of the first embodiment, and will not be described herein. The difference is that the embodiment The second step is to prepare a vanadium-doped lithium iron phosphate electrode material to form a vanadium-doped lithium iron phosphate/vanadium phosphate composite electrode material. The step 2 specifically includes the following steps: C1, providing a vanadium-doped lithium iron phosphate precursor mixed slurry; C2, coating the vanadium-doped lithium iron phosphate precursor mixed slurry on the lithium vanadium phosphate The surface of the particles is cured to form a composite; C3, the composite is heat treated.

In the above steps, only the step C1 is different from the step A1 in the first embodiment, and the other steps C2 to C3 are substantially the same as the steps A2 to A3 in the first embodiment, and are not described herein again.

In the step C1, further comprising: D1, providing a vanadium source, an iron salt and a phosphorus source, dissolving the vanadium source, the iron salt and the phosphorus source in a solvent to form a mixed solution; D2, making the mixed liquid uniform Mixing, during the uniform mixing, adjusting the pH of the mixture to 1.5 to 5 to react the mixture to form a vanadium-doped iron phosphate precursor particle; D3, providing a lithium source solution and a reducing agent, The lithium source solution, the vanadium-doped iron phosphate precursor particles and the reducing agent are uniformly mixed to form a vanadium-doped lithium iron phosphate precursor mixed slurry. The steps of D2 to D3 are the same as the steps B2 to B3 in the foregoing first embodiment, and will not be described again. Wherein, in the step D1, the vanadium source, the iron salt and the phosphorus source are dissolved in a ratio of a molar ratio of the vanadium element to the iron element to the molar number of the phosphorus element of 1:0.8 to 1:1.2. In the solvent. The vanadium source may be ammonium metavanadate, vanadium pentoxide, vanadium dioxide or vanadium tetrachloride, etc., and the iron salt may be one or a mixture of ferric chloride, iron nitrate and iron sulfate. The solvent may be water, ethanol or acetone, etc., the solvent is preferably water, and the water is preferably deionized water or distilled water to avoid introduction of other impurity elements. In the mixed solution of this embodiment, the vanadium source is ammonium metavanadate, the iron salt is ferric nitrate, the phosphorus source is phosphoric acid, and the solvent is deionized water. The ammonium metavanadate is provided in an amount of 1% to 8% of the vanadium-doped iron phosphate precursor particles obtained according to the molar fraction X (V) of the vanadium element, and X(V) in this embodiment is respectively 1%, 3% and The ammonium metavanadate is provided in 5%.

In addition, in this embodiment, the plurality of microparticle fillers may be uniformly doped into the mixed liquid in the step D2 to more effectively control the particle morphology of the formed vanadium-doped lithium iron phosphate precursor particles. , particle size and dispersion characteristics. The specific method of adding the microparticle filler is the same as the step B2 of the first embodiment, and details are not described herein again.

Referring to FIG. 16 and FIG. 17, it can be seen that the vanadium-doped hydrated iron phosphate precursor particles have smaller particle size and better dispersion than the vanadium-doped hydrated iron phosphate precursor particles, mainly because The doping of vanadium inhibits grain growth and prevents agglomeration during vanadium-doped hydrated iron phosphate precursor particles. Meanwhile, since the present embodiment is the same as the first embodiment, both are prepared by controlling the crystallization process, so that the obtained vanadium-doped iron phosphate precursor particles also have a spherical or spheroidal shape and a small particle diameter. , the characteristics of better dispersion. In addition, since the vanadium source, the iron salt and the phosphorus source are uniformly mixed in a solvent, the vanadium source, the iron salt and the phosphorus source can be uniformly mixed at an atomic level, so that the vanadium can be uniformly doped into the chamber. The iron phosphate precursor particles are formed, thereby finally forming a lithium iron phosphate/vanadium phosphate composite electrode material uniformly doped with vanadium.

In addition, the vanadium-doped lithium iron phosphate electrode material prepared by the redox method can be used not only as a "shell layer" of the lithium iron phosphate/vanadium phosphate composite electrode material, but also as a positive electrode material for a lithium battery. The method for simply preparing the vanadium-doped lithium iron phosphate electrode material only needs to remove the A2 step in the above step 2, and drying the mixed slurry to completely evaporate the water therein, and then directly performing the above step A3. Referring to FIG. 18, the XRD spectrum of the non-vanadium-doped lithium iron phosphate material and the doped vanadium 1%, 3% and 5% lithium iron phosphate materials is measured, and the spectrum shows vanadium doping. The lithium iron phosphate material is consistent with the pure phase lithium iron phosphate spectrum, and no hetero peaks appear, indicating that the vanadium in the vanadium-doped lithium iron phosphate material is completely doped to the iron level, and no additional materials are formed.

Referring to FIG. 19 to FIG. 22, in this embodiment, a vanadium-doped 3% lithium iron phosphate/vanadium phosphate composite electrode material and a vanadium-doped 3% lithium iron phosphate electrode material are measured in a voltage range of 2.5V to 4.3V. Inside, the discharge curve at different magnifications. The discharge specific capacities of vanadium doped 3% lithium iron phosphate electrode materials at 0.1C, 1C, 5C and 10C ratios are 148.6mAh/g, 135.3 mAh/g, 105.0 mAh/g and 74.3mAh/g, respectively. The discharge specific capacities of 3% lithium iron phosphate/vanadium phosphate composite electrode materials at 0.1C, 1C, 5C and 10C ratios were 145.0 mAh/g, 136.2 mAh/g, 115.0 mAh/g and 89.0 mAh/g, respectively. It can be seen that at lower magnifications (0.1C and 1C), the discharge specific capacity of vanadium doped 3% lithium iron phosphate electrode material and vanadium doped 3% lithium iron phosphate/vanadium phosphate composite electrode material are basically the same. When the charge-discharge rate is increased to 5C or 10C, the vanadium-doped 3% lithium iron phosphate/vanadium phosphate composite electrode material has a higher specific capacity and discharge voltage platform than the vanadium-doped 3% lithium iron phosphate electrode material.

In addition, the preparation methods of the first embodiment and the second embodiment may directly provide iron phosphate precursor particles or vanadium-doped iron phosphate precursor particles, and the iron phosphate precursor particles or vanadium-doped iron phosphate precursors The bulk particles are not limited to the above-described controlled crystallization process, and may be a sol-gel method or a coprecipitation method.

In summary, the present invention has indeed met the requirements of the invention patent, and has filed a patent application according to law. However, the above description is only a preferred embodiment of the present invention, and it is not possible to limit the scope of the patent application of the present invention. Equivalent modifications or variations made by those skilled in the art in light of the spirit of the invention are intended to be included within the scope of the following claims.

10‧‧‧Lithium iron phosphate/vanadium phosphate composite electrode material

100‧‧‧Lithium iron phosphate/vanadium phosphate composite particles

102‧‧‧Lithium vanadium phosphate particles

104‧‧‧ Lithium iron phosphate particle layer

1042‧‧‧Lithium iron phosphate particles

106‧‧‧carbon

1 is a schematic structural view of a lithium iron phosphate/vanadium phosphate composite electrode material according to an embodiment of the present invention.

2 is a scanning electron micrograph of a lithium iron phosphate/vanadium phosphate composite electrode material according to an embodiment of the present invention.

3 is a schematic structural view of a carbon-doped lithium iron phosphate/vanadium phosphate composite electrode material according to an embodiment of the present invention.

4 is a specific capacity of charge and discharge of a lithium iron phosphate/vanadium phosphate composite electrode material and a vanadium-doped lithium iron phosphate/vanadium phosphate composite electrode material as positive electrodes at a rate of 0.1 C, respectively, according to an embodiment of the present invention. Test the graph.

5 is a specific capacity-cycle test of a lithium iron phosphate/vanadium phosphate composite electrode material and a vanadium-doped lithium iron phosphate/vanadium phosphate composite electrode material as positive electrodes at different ratios, respectively, according to an embodiment of the present invention. Graph.

6 is a flow chart of a method for preparing a lithium iron phosphate/vanadium phosphate composite electrode material according to a first embodiment of the present invention.

Figure 7 is a scanning electron micrograph of a lithium vanadium phosphate material prepared in accordance with a first embodiment of the present invention.

Figure 8 is a scanning electron micrograph of a ferric phosphate precursor particle prepared in accordance with a first embodiment of the present invention.

Figure 9 is a transmission electron micrograph of a ferric phosphate precursor particle prepared in accordance with a first embodiment of the present invention.

Figure 10 is a scanning electron micrograph of a lithium iron phosphate material prepared in accordance with a first embodiment of the present invention.

Fig. 11 is a graph showing a specific capacity-cycle test of a battery of lithium iron phosphate prepared as a positive electrode of the first embodiment of the present invention at a 1C rate.

12 to FIG. 15 are graphs showing discharge specific capacity tests of batteries of lithium iron phosphate prepared by the first embodiment of the present invention and lithium iron phosphate/vanadium phosphate composite electrode materials as positive electrodes at different magnifications.

Figure 16 is a scanning electron micrograph of an undoped vanadium-doped iron phosphate precursor particle prepared in accordance with a first embodiment of the present invention.

Figure 17 is a scanning electron micrograph of a vanadium-doped iron phosphate precursor particle prepared in accordance with a second embodiment of the present invention.

Figure 18 is a XRD comparative spectrum of a vanadium-doped 1%, 3%, and 5% lithium iron phosphate material prepared by the first embodiment of the present invention.

19 to FIG. 22 are discharge ratios of vanadium doped 3% lithium iron phosphate material prepared by using the second embodiment of the present invention and vanadium doped 3% lithium iron phosphate/vanadium phosphate composite electrode material at different ratios. Capacity test curve.

Claims (20)

A method for preparing a lithium battery electrode material, comprising the steps of: providing a vanadium phosphate monophosphate electrode material comprising a plurality of lithium vanadium phosphate particles; and coating a surface of each of the lithium vanadium phosphate particles to form a lithium iron phosphate layer Thereby, a lithium iron phosphate/vanadium phosphate composite electrode material is formed. The method for preparing a lithium battery electrode material according to claim 1, wherein the method of coating the surface of the lithium iron phosphate particles with the lithium iron phosphate layer further comprises the step of: providing a lithium iron phosphate precursor mixed slurry The lithium iron phosphate precursor mixed slurry is coated on the surface of the lithium vanadium phosphate particles and solidified to form a composite; the composite is heat-treated to form a lithium iron phosphate/vanadium phosphate composite electrode material. The method for preparing a lithium battery electrode material according to claim 2, wherein the method for preparing the lithium iron phosphate precursor mixed slurry further comprises the steps of: providing iron phosphate precursor particles; providing a lithium source solution and a The reducing agent uniformly mixes the lithium source solution, the iron phosphate precursor particles and the reducing agent to form the lithium iron phosphate precursor mixed slurry. The method for producing a lithium battery electrode material according to claim 3, wherein the iron phosphate precursor particles are prepared by a sol-gel method, a coprecipitation method or a controlled crystallization method. The method for preparing a lithium battery electrode material according to claim 4, wherein the preparing the iron phosphate precursor particles by using the controlled crystallization process further comprises the steps of: providing an iron salt and a phosphorus source, the iron The salt and phosphorus source are dissolved in a solvent to form a mixed solution; during the above mixing, the pH of the mixed solution is adjusted to 1.5 to 5 to react the mixed solution to form iron phosphate precursor particles. The method for producing a lithium battery electrode material according to claim 5, wherein the iron salt and the phosphorus source are dissolved in the solvent in a ratio of a molar ratio of iron element to phosphorus element of 1:0.8 to 1:1.2. . The method for producing a lithium battery electrode material according to claim 5, wherein a plurality of fine particle fillers are further added to the mixed liquid to uniformly mix the plurality of fine particle fillers with the mixed liquid. The method for producing a lithium battery electrode material according to claim 7, wherein the fine particle filler is composed of a hard material which is insoluble in the above solvent and does not react with the iron source and the phosphorus source. The method for preparing a lithium battery electrode material according to claim 8, wherein the material of the microparticle filler is one or more of ceramic, quartz and glass. The method for producing a lithium battery electrode material according to claim 7, wherein the microparticle filler has a diameter of 20 μm to 1 mm. The method for preparing a lithium battery electrode material according to claim 5, wherein the reaction temperature of the mixed solution is further controlled to be 25 ° C to 50 ° C, and the reaction time is 40 minutes to 2 hours. A method for preparing a lithium battery electrode material according to claim 5, wherein the method The step of preparing the iron phosphate precursor particles further comprises: heating the iron phosphate precursor particles in an inert gas atmosphere at a temperature ranging from 400 ° C to 700 ° C for 2 hours to 24 hours, thereby obtaining an anhydrous iron phosphate precursor The step of granules. The method for producing a lithium battery electrode material according to claim 3, wherein the reducing agent is a carbothermal reducing agent, and the carbothermal reducing agent is a reducing organic compound. The method for producing a lithium battery electrode material according to claim 13, wherein the lithium source solution is in a ratio of a lithium element, a phosphorus element and a carbon element in a molar ratio of 1:1:1 to 1.2:1:1.3. The iron phosphate precursor particles and the carbothermal reducing agent are uniformly mixed. The method for producing a lithium battery electrode material according to claim 3, wherein the iron phosphate precursor particles are vanadium-doped iron phosphate precursor particles. The method for preparing a lithium battery electrode material according to claim 2, wherein the method of coating the lithium iron phosphate precursor mixed slurry on the surface of the lithium vanadium phosphate particles to form a composite comprises the following steps: The lithium vanadium phosphate particles are uniformly dispersed in the lithium iron phosphate precursor mixed slurry, and the mixed slurry is uniformly supported on the surface of the lithium vanadium phosphate particles; and the vanadium phosphate loaded with the mixed slurry is filtered. Lithium particles; the vanadium phosphate particles loaded with the mixed slurry on the surface are dried to solidify the mixed slurry on the surface of the lithium vanadium phosphate particles. The method for producing a lithium battery electrode material according to claim 16, wherein the lithium vanadium phosphate particles coated with the mixed slurry are heated in a temperature range of 60 ° C to 90 ° C for 10 minutes to 30 minutes, thereby The mixed slurry is cured. The method for preparing a lithium battery electrode material according to claim 2, wherein the above The step of forming a composite further includes the following steps: dividing the mixed slurry into three equal portions, respectively being first, second, and third mixed slurries; uniformly dispersing the vanadium phosphate vanadium particles in the first In the mixed slurry, the mixed slurry is uniformly supported on the surface of the lithium vanadium phosphate particles; the lithium vanadium phosphate particles loaded with the mixed slurry on the surface are filtered and dried to solidify the mixed slurry on the surface. Forming a first composite; dispersing the first composite in the second mixed slurry, uniformly loading the mixed slurry on a surface of the first composite; and loading the surface with a mixed slurry The first composite of the material is filtered and dried to solidify the mixed slurry of the surface to form a second composite; the second composite is dispersed in the third mixed slurry to make the mixed slurry The material is evenly supported on the surface of the second composite; the second composite loaded with the mixed slurry on the surface is filtered and dried to solidify the mixed slurry of the surface to form a third composite. The method for preparing a lithium battery electrode material according to claim 2, wherein the step of heat-treating the composite body is: heating the composite body 8 at a temperature of 500 ° C to 850 ° C in an inert gas atmosphere. Hours ~ 40 hours. A method for preparing a lithium battery electrode material, comprising the steps of: providing a vanadium phosphate monophosphate electrode material comprising a plurality of lithium vanadium phosphate particles; providing an iron salt and a phosphorus source, and dissolving the iron salt and the phosphorus source a solvent is formed to form a mixed solution; the mixture is continuously fed into a reactor at a flow rate of 100 ml/hr to 150 ml/hr; the pH of the mixture is adjusted to 1.5 to 5, and the temperature of the reactor is 25 ° C ~ 50 ° C, The reaction time of the mixed solution in the reactor is 40 minutes to 2 hours to form iron phosphate precursor particles; the iron phosphate precursor particles are heated in an inert gas atmosphere at a temperature ranging from 400 ° C to 700 ° C. 2 hours to 24 hours; providing a lithium source solution and a reducing agent, uniformly mixing the lithium source solution, the iron phosphate precursor particles and the reducing agent to form a mixed slurry; uniformly dispersing the vanadium phosphate particles In the mixed slurry, the mixed slurry is uniformly coated on the surface of each of the vanadium phosphate particles; the vanadium phosphate particles coated with the mixed slurry are filtered and dried to make the vanadium phosphate The mixed slurry on the surface of the particles is solidified to form a composite; the composite is heated in an inert gas atmosphere at a temperature of 500 ° C to 850 ° C for 8 hours to 40 hours to make each of the phosphoric acid The surface of the vanadium lithium particles is coated with a lithium iron phosphate layer to form a lithium iron phosphate/vanadium phosphate composite electrode material.