CN114628660A - Hydrothermal synthesis method of lithium ferric manganese phosphate nanoparticles - Google Patents

Hydrothermal synthesis method of lithium ferric manganese phosphate nanoparticles Download PDF

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CN114628660A
CN114628660A CN202210431899.7A CN202210431899A CN114628660A CN 114628660 A CN114628660 A CN 114628660A CN 202210431899 A CN202210431899 A CN 202210431899A CN 114628660 A CN114628660 A CN 114628660A
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lithium
manganese
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iron
hydrothermal synthesis
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�田一弘
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Shenzhen Warren New Energy Co.,Ltd.
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • H01M4/625—Carbon or graphite
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive electrodes

Abstract

The invention relates to the technical field of preparation of lithium ion battery anode materials, in particular to a hydrothermal synthesis method of lithium ferric manganese phosphate nanoparticles, which comprises the following steps: preparing raw material solutions of lithium, iron, manganese and phosphorus sources, and mixing the raw material solutions to obtain mixed slurry; conveying the mixed slurry to a preheating unit for preheating, and then conveying the heated mixed slurry into a reaction kettle; carrying out hydrothermal synthesis reaction in a reaction kettle; filtering, washing and drying the product to obtain lithium manganese iron phosphate powder; and uniformly mixing the lithium iron manganese phosphate powder with a carbon source to obtain the carbon-coated lithium iron manganese phosphate. The method has the advantages that the mixed slurry of the reaction raw materials is preheated outside the reaction kettle and then is sent into the reaction kettle for continuous reaction, so that the retention time of the reaction system in a low-temperature section is shortened, the appearance and the particle size of the product are fundamentally controlled, the prepared material has uniform particles, the appearance is changed from a sheet shape to a sphere-like shape, the size can reach a nanometer level, and the rate capability and the low-temperature performance of the material are improved.

Description

Hydrothermal synthesis method of lithium ferric manganese phosphate nanoparticles
Technical Field
The invention relates to the technical field of preparation of lithium ion battery anode materials, in particular to a hydrothermal synthesis method of lithium ferric manganese phosphate nanoparticles.
Background
Lithium manganese iron phosphate has been widely used in the field of electric vehicles because of its high specific capacity, safety, environmental friendliness, long life, and the like. However, the low-temperature discharge performance and rate performance indexes of the lithium ferric manganese phosphate material still need to be improved. In addition to optimizing the conductive material coating, particle nanocrystallization is the most effective method to improve its performance. Many studies have shown that nanoscale positive electrode materials exhibit specific capacities close to their theoretical capacities. The nano-material needs to be ensured by a preparation process, and the hydrothermal method has unique advantages in the aspect of preparing nano-particles.
Generally, the morphology and size of the particles can be controlled by controlling the hydrothermal synthesis conditions, for example, the patent with publication number CN111777051A uses glycol as a solvent and also serves as a surfactant, the patent with publication number CN104583130A uses glycerol as a solvent, and the patent with publication number CN104918888A uses various alcohols as solvents; the partial organic solvent is used for replacing water, so that the pressure of a reaction system can be reduced, and the aim of refining particles can be fulfilled. However, the solubility of the reaction raw materials in the organic solvent is lower than that in water, so that the reaction concentration which is originally not high is reduced, the productivity or production efficiency of unit equipment is low, and the problems of explosion prevention of workshops and equipment and organic wastewater treatment also exist.
In the aspect of production technology, the existing method for preparing lithium manganese iron phosphate by hydrothermal method mainly comprises the steps of dissolving soluble ferrous salt and manganese salt, phosphoric acid and lithium hydroxide according to a certain proportion, mixing in a reaction kettle, heating to 120-374 ℃ (critical temperature of water), and preparing lithium manganese iron phosphate crystal in a wider temperature range. In the prior art, the reaction conditions in the preparation process, such as temperature, solvent (water or organic solvent, corresponding to the autogenous pressure of water and solvent), reaction time, pH value of the reaction system, etc. are focused. In general, the higher the reaction temperature, the smaller the particles of the prepared crystals, and the better the electrochemical properties. However, in fact, the technical solutions of increasing the reaction temperature and using a surfactant or an organic solvent do not fundamentally solve the problem of particle size control in the crystallization process. Apparently, the raw materials participating in the hydrothermal reaction are first dissolved and then added into the reaction kettle, and the molecular mixing is performed between the raw materials, however, at normal temperature or slightly higher than the normal temperature, a new precipitate mixture is formed immediately after the reaction raw material solution is mixed, and the reaction is as follows:
LiOH+H3PO4+FeSO4→Li3PO4↓+Fe3(PO4)2·nH2O↓+Li2SO4
with increasing temperature, Li3PO4Precipitation and Fe3(PO4)2·nH2The O precipitates are successively dissolved, releasing Li+、Fe2+And PO4 3-These ions are recombined to produce lithium iron phosphate. In the case of partial replacement of iron by manganese, the mechanism is the same, except that the dissolution temperature is slightly lowered. In this process, it is difficult to achieve molecular-level mixing of the raw materials in the actual reaction, and a large number of crystal nuclei cannot be formed in a short time, so that the particle size is difficult to decrease due to the small number of crystal nuclei.
It has been reported (Chemical and pharmaceutical transformation through hydro thermal process for LiFePO)4preparation in organic-free system, Electrochimica Acta, (96) 2013: 230-236) lithium iron phosphate crystal can be formed from 120 ℃, but at low temperature, mixed arrangement of iron ions and lithium ions is easy to generate in the crystal, which is not favorable for ion conduction in the crystal. Therefore, the reaction system should be avoided as much as possible in a low-temperature stage (from 120 ℃ to 140 ℃). On the other hand, as the reaction volume is increased, for example, the reaction vessel volume is increased by 100 times, the surface heat transfer area of the reaction vessel is theoretically increased by only 21 times (if the internal jacket heat transfer is calculated, the value is not deviated too much), and therefore, for industrial mass production, there is a need to solve the problem of rapid temperature rise. The patent publication No. CN105060266A discloses a hydrothermal synthesis technique in which a hydrothermal reaction vessel is directly heated by high-temperature steam, but heating by steam results in a decrease in the concentration of the reaction system and a decrease in the unit productivity, and if the delivery of steam is increased by steam alone as the volume of the single vessel is increased, disturbance is generated in the mass transfer and transmission in the vesselThis is disadvantageous in terms of production operation control.
The above problems need to be solved.
Disclosure of Invention
In order to solve the problems, the invention provides a hydrothermal synthesis method of lithium ferric manganese phosphate nanoparticles, which comprises the steps of preheating a mixture of raw materials outside a kettle, and adding the mixture into a reaction kettle heated to a set value, so as to overcome the problem of insufficient heat transfer power caused by the volume expansion of equipment, shorten the retention time of a reaction system in a low-temperature section, fundamentally realize the control of the product appearance and particle size, and achieve the purposes of nano-crystallization and sphericization.
The invention adopts the following technical scheme.
A hydrothermal synthesis method of lithium ferric manganese phosphate nanoparticles comprises the following steps:
(1) adding a mixture of a lithium source and a phosphorus source into a batching kettle, purging air in the dead volume of the kettle by using inert gas, and sealing the batching kettle; opening a feed valve and an exhaust valve of the batching kettle, adding a pure mixed solution of an iron source and a manganese source under stirring, sealing the batching kettle after the feeding is finished, and continuously stirring for 10-30 minutes to obtain a mixed slurry of the raw materials;
(2) conveying the mixed slurry in the batching kettle to a preheating unit for preheating, wherein the temperature of the slurry at an outlet of the preheating unit is 140-160 ℃, then conveying the heated mixed slurry to a reaction kettle preheated to 140-160 ℃, wherein the reaction kettle uses inert gas to sweep air in the dead volume in the kettle in advance, and after all the mixed slurry is heated and conveyed, sealing the reaction kettle;
(3) stirring the slurry in a reaction kettle, keeping the reaction for 2-4 hours at the temperature of 140-160 ℃, stopping heating, cooling, and cooling to 70-80 ℃;
(4) opening a discharge valve of the reaction kettle, filtering the resultant, washing until no sulfate ions exist to obtain a filter cake and a mother liquor, and drying the filter cake to obtain lithium ferric manganese phosphate powder;
(5) uniformly mixing lithium iron manganese phosphate powder with a carbon source, and roasting for 4 hours at 700 ℃ under the protection of inert gas to obtain carbon-coated lithium iron manganese phosphate;
wherein the manganese source accounts for 0-70% of the total molar weight of the iron source and the manganese source.
Furthermore, the preheating unit is formed by connecting a plurality of tubular preheaters in parallel, and the tubular preheaters are heated by adopting a high-temperature oil bath or an electric heating mode. Specifically, the overall feed rate is controlled by controlling the number of tubular preheaters connected in parallel.
Further, the inlet slurry temperature of the preheating unit is 20-30 ℃, the outlet slurry temperature is 140-160 ℃, and the heating time of the slurry in the preheating unit is not more than 30 minutes.
Further, in the step (2), the preheating temperature of the reaction kettle is lower than the outlet slurry temperature of the preheating unit.
Further, the molar ratio of the materials added in the step (1) is Li to M (Fe + Mn) and P is 3.0, (0.99-1.0) and 1.0; the total concentration of the ferro-manganese elements is 0.5-0.7mol/L after the feeding is finished.
Further, in the step (1), lithium hydroxide is dissolved in water and mixed with phosphoric acid to be used as a lithium source and a phosphorus source; or mixing lithium phosphate obtained by recovering the mother liquor with lithium hydroxide solution and phosphoric acid which need to be supplemented to be used as a lithium source and a phosphorus source; or lithium phosphate alone as a lithium source and a phosphorus source.
And (3) further, combining the mother liquor obtained by filtering in the step (4) with the primary washing water for washing the filter cake, evaporating and concentrating, and recovering the lithium phosphate.
Further, the iron source is ferrous sulfate crystals or liquid before crystallization, the manganese source is manganese sulfate, and particularly, the molar ratio of the iron source to the manganese source is preferably 3:7-7: 3.
Further, in the step (5), the iron-manganese-lithium phosphate powder and a carbon source are mixed according to the proportion of 100: (10-15) mixing in a mass ratio. Specifically, the dried lithium iron manganese phosphate powder is mixed with a carbon source to prepare a slurry with a solid content of 30-60%, and then spray drying is performed to obtain a mixture of the lithium iron phosphate powder and the carbon source.
Further, the carbon source is glucose.
Compared with the prior art, the invention has the following beneficial effects:
(1) according to the hydrothermal synthesis method of lithium manganese iron phosphate nanoparticles, the mixed slurry of the reaction raw materials is preheated outside the kettle, and compared with indirect heating or direct heating by steam inside the kettle, the hydrothermal synthesis method solves the problem of insufficient heat transfer power caused by expansion of the reaction kettle, does not reduce the concentration of reactants, and does not reduce the capacity of unit equipment. Meanwhile, the slurry is rapidly heated by the preheating unit and then sent into the reaction kettle for continuous reaction, so that the retention time of the reaction system in a low-temperature section is shortened, the control on the morphology and the particle size of the product is fundamentally realized, the prepared material has uniform particles, the morphology is converted from a sheet shape to a sphere-like shape, the size can reach a nanometer level, and the rate capability and the low-temperature performance of the material are improved.
(2) The hydrothermal synthesis method of lithium manganese iron phosphate nanoparticles has mild operation conditions, and by carrying out preheating operation at the temperature of 140-160 ℃, the corresponding pressure is lower, so that the adverse effect on equipment caused by adopting overhigh reaction temperature (corresponding to higher autogenous pressure) is avoided, and the method has the advantages of small equipment investment, simple and controllable process and good batch stability of products.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
FIG. 1 is a topographic map of lithium manganese iron phosphate prepared according to example 1 of the present invention;
FIG. 2 is a graph showing the morphology of lithium manganese iron phosphate prepared in comparative example 1 according to the present invention;
FIG. 3 is a graph showing the charge and discharge curves at 25 ℃ and 0.2C for the batteries prepared in examples 1 to 3 of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be described clearly and completely with reference to the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Example 1
A hydrothermal synthesis method of lithium ferric manganese phosphate nanoparticles comprises the following steps:
the first step is as follows: preparing mixed slurry of lithium, iron, manganese and phosphorus raw materials
(1) Preparing phosphorus source and lithium source mixed slurry: dissolving 3kmol of lithium hydroxide monohydrate in water, adding water to make the volume of the solution be 1m3Adding into a batching kettle 1, adding 75L of 1kmol phosphoric acid under stirring, purging air in the dead volume of the kettle with inert gas after adding, sealing the batching kettle 1 to obtain slurry A with the volume of about 1.07m3；
(2) Preparing a mixed solution of an iron source and a manganese source: 0.3kmol ferrous sulfate heptahydrate and 0.7kmol manganese sulfate dihydrate are taken and added with water until the volume is 1m3Stirring until all the components are dissolved, filtering by a pipeline type precision filter, and transferring to a batching kettle 2 to obtain slurry B with the volume of about 1.0m3；
(3) Mixing slurry A and slurry B: stirring at room temperature, opening the liquid-sealed exhaust valve of the batching kettle 1, adding the solution in the batching kettle 2 into the batching kettle 1, and continuously stirring for 20-30 minutes after the addition is finished to obtain slurry C with the volume of about 2m3；
The molar ratio of the added substances is Li: m (Fe + Mn): p ═ 3.0:1.0: 1.0; wherein, Fe: mn (molar ratio) 3: 7. After the feeding is finished, the total concentration of the iron and manganese elements in the solution is about 0.5 mol/L.
The second step: preheating and conveying of raw material slurry
(1) Conveying the slurry C obtained in the first step into preheating unit equipment by using a high-pressure pump, wherein the temperature of inlet slurry of the preheating unit equipment is 25 ℃, the temperature of outlet slurry of the preheating unit equipment is 155 ℃, the retention time of the slurry in the preheating unit is 16min, the heating rate is 8 ℃/min, the retention time and the outlet temperature of the slurry in the preheating unit are controlled by outlet flow regulation, and the preheating unit equipment is four parallel tubular preheaters;
(2) simultaneously purging air in dead volume of the high-pressure reaction kettle by using inert gas, heating the high-pressure reaction kettle to 150 ℃, wherein the volume of the high-pressure reaction kettle is 3m3After the feeding is finished, the filling coefficient of the reaction kettle is about 0.7;
(3) directly adding the slurry from the preheating unit into a high-pressure reaction kettle with stirring through a pipeline, and sealing the reaction kettle after all the slurry is added;
the third step: hydrothermal synthesis reaction
Heating the mixture by a jacket and a sleeve of the reaction kettle (220 ℃ oil bath), maintaining the reaction temperature at 150 ℃ and reacting for 2 hours;
the fourth step: filtering, washing and drying the resultant
After the reaction is finished, cooling the reaction kettle to 80 ℃ by cooling oil through a coil pipe, opening an emptying valve and a discharge valve, filtering the resultant to obtain a filter cake and mother liquor, and then washing the filter cake three times by using water with the same volume as the mother liquor to obtain LiFe0.3Mn0.7PO4White powder; mixing the powder with 12% glucose by solid content to prepare slurry with solid content of about 40%, and spray drying; the mother liquor is washed once and then enters a recovery tank, sodium phosphate is added after evaporation and concentration, and lithium phosphate is recovered;
the fifth step: carbon coating treatment
Calcining the spray-dried powder obtained in the fourth step for 4 hours at 700 ℃ under the protection of nitrogen to obtain carbon-coated lithium iron phosphate (LiFe)0.3Mn0.7PO4C) products.
The lithium/carbon ferric manganese phosphate prepared by the method is used as a battery anode material, and the charge and discharge performance of the battery anode material is tested. Specifically, the method comprises the following steps: and mixing the lithium manganese iron phosphate/carbon, the acetylene black and the 60% polytetrafluoroethylene emulsion according to the mass ratio of 7:2:1, rolling into a sheet with the thickness of 0.10-0.15 mm, pressing the sheet and an aluminum foil together, and performing vacuum drying at 120 ℃ for 12 hours to obtain the battery anode. Lithium metal sheet cathode, 1M LiPF6The solution is electrolyte, the cell gard 2300 is a diaphragm, and the solution and the anode are assembled into a buttonThe battery is charged and discharged at a rate of 0.2C and 1C at 25 ℃, and then discharged at 0.2C at-20 ℃, and the voltage range of charging and discharging is 4.5-2.3V.
The scanning electron microscope image of the material is shown in figure 1, the particles of the visible material are uniform, the appearance is similar to a sphere, and the dimension can reach the nanometer level; electrochemical performance test results are shown in table 1 and fig. 3, and the prepared lithium ion battery has good rate capability and low-temperature capability as the positive active material.
Example 2
The lithium source and phosphorus source in slurry a in example 1 were replaced with lithium phosphate recovered from a part of the mother liquor, and the remainder was supplemented with lithium phosphate obtained by a neutralization reaction between lithium hydroxide and phosphoric acid.
Specifically, the hydrothermal synthesis method of lithium ferric manganese phosphate nano particles comprises the following steps:
the first step is as follows: preparing mixed slurry of lithium, iron, manganese and phosphorus raw materials
(1) Preparing phosphorus source and lithium source mixed slurry: adding 0.6kmol (calculated by dry basis) of lithium phosphate wet crystal obtained by recovering mother liquor into the proportioning kettle 1 directly, adding 1.2kmol of lithium hydroxide monohydrate into the proportioning kettle 1, adding water for dissolving to ensure that the volume of the solution is 1m3Adding 0.4kmol phosphoric acid (about 30L) under stirring, purging air in dead volume of the kettle with inert gas, sealing the batching kettle 1 to obtain slurry A with volume of about 1.0m3；
(2) Preparing a mixed solution of an iron source and a manganese source: adding 0.3kmol ferrous sulfate heptahydrate and 0.7kmol manganese sulfate dihydrate into water to a volume of 1m3Stirring until all the components are dissolved, filtering by a pipeline type precision filter, and transferring to a batching kettle 2 to obtain slurry B with the volume of about 1.0m3；
(3) Mixing slurry A and slurry B: stirring at room temperature, opening the liquid-sealed exhaust valve of the batching kettle 1, adding the solution in the batching kettle 2 into the batching kettle 1, and continuously stirring for 20-30 minutes after the addition is finished to obtain slurry C with the volume of about 2m3；
The molar ratio of the added substances is Li: m (Fe + Mn): p ═ 3.0:1.0: 1.0; wherein, Fe: mn (molar ratio) 3: 7. After the feeding is finished, the total concentration of the iron and manganese elements in the solution is about 0.5 mol/L.
The other preparation steps are the same as example 1, and the test method is the same as example 1.
The electrochemical performance test results are shown in table 1 and fig. 3. It can be seen that the product obtained in example 2 exhibited almost the same electrochemical performance as in example 1; therefore, the lithium manganese iron phosphate prepared by the preheating mode of the invention by replacing the lithium phosphate newly prepared on site with the lithium phosphate with relatively coarse particles obtained by recovery does not influence the performance of the product.
Example 3
The hydrothermal synthesis reaction temperature in example 1 was set to 160 ℃ and the reactant concentration was increased.
Specifically, the hydrothermal synthesis method of lithium ferric manganese phosphate nanoparticles comprises the following steps:
the first step is as follows: preparation of mixed slurry of lithium, iron, manganese and phosphorus raw materials
(1) Preparing phosphorus source and lithium source mixed slurry: 1.584kmol of lithium hydroxide monohydrate is added into a batching kettle 1, and 0.56m of water is added3Dissolving, adding 0.528kmol phosphoric acid (about 30L) under stirring; then adding 0.792kmol (calculated on a dry basis) of lithium phosphate wet crystals obtained by recovering the mother liquor into the batching kettle 1 directly, after the addition is finished, purging air in the dead volume of the kettle by using inert gas, sealing the batching kettle 1 to obtain slurry A with the volume of about 0.64m3；
(2) Preparing a mixed solution of an iron source and a manganese source: 0.528kmol of ferrous sulfate heptahydrate and 0.792kmol of manganese sulfate dihydrate are taken and added with water to the volume of 1.32m3Stirring until all the components are dissolved, filtering by a pipeline type precision filter, transferring to a batching kettle 2 to obtain slurry B with the volume of about 1.32m3；
(3) Mixing slurry A and slurry B: stirring at room temperature, opening the liquid-sealed exhaust valve of the batching kettle 1, adding the solution in the batching kettle 2 into the batching kettle 1, and continuously stirring for 20-30 minutes after the addition is finished to obtain slurry C with the volume of about 1.96m3；
The molar ratio of the added substances is Li: m (Fe + Mn): p is 3.0:1.0: 1.0; wherein, Fe: mn (molar ratio) 4: 6. After the feeding is finished, the total concentration of the ferro-manganese elements in the solution is about 0.67 mol/L.
The second step is that: preheating and conveying of raw material slurry
(1) Conveying the slurry C obtained in the first step into preheating unit equipment by using a high-pressure pump, wherein the temperature of inlet slurry of the preheating unit equipment is 25 ℃, the temperature of outlet slurry of the preheating unit equipment is 160 ℃, the retention time of the slurry in the preheating unit is 17min, the heating rate is 8 ℃/min, the retention time and the outlet temperature of the slurry in the preheating unit are controlled by adjusting outlet flow, and the preheating unit equipment is four parallel tubular preheaters;
(2) simultaneously, purging air in dead volume of the high-pressure reaction kettle by using inert gas, heating the high-pressure reaction kettle to 155 ℃, wherein the volume of the high-pressure reaction kettle is 3m3After the feeding is finished, the filling coefficient of the reaction kettle is about 0.7;
(3) directly adding the slurry from the preheating unit into a high-pressure reaction kettle with a stirrer through a pipeline, and sealing the reaction kettle after all the slurry is added;
the third step: hydrothermal synthesis reaction
Heating the reaction kettle to 160 ℃ by a jacket and a sleeve of the reaction kettle (220 ℃ oil bath), and maintaining the reaction for 2 hours;
the other steps are the same as example 1, and the performance test method is the same as example 1.
The electrochemical performance test results are shown in table 1 and fig. 3. It can be seen that the product obtained in example 3 exhibited almost the same electrochemical performance as in example 1; therefore, the lithium iron manganese phosphate prepared by the preheating mode of the invention by replacing the lithium phosphate newly prepared on site with the lithium phosphate with relatively coarse particles obtained by recovery does not influence the performance of the product. Meanwhile, the concentration of reactants can be improved, so that the production efficiency of a single kettle can be improved, and the water consumption and the energy consumption can be reduced.
Comparative example 1
And carrying out hydro-thermal synthesis according to a conventional feeding technology.
Specifically, the hydrothermal synthesis method of lithium manganese iron phosphate comprises the following steps:
the first step is as follows: the same as in example 1.
The second step: the slurry C obtained in the first step is conveyed by a high-pressure pump into a reactor with a volume of 3m3In the high-pressure reaction kettle, the heating mode of the reaction kettle is electric heating of a jacket, and is limited by heating power (the influence of heat exchange area, oil temperature, equipment wall thickness and the like), the temperature of the reaction kettle is increased from 20 ℃ to 150 ℃ for 70 minutes, which is equivalent to that the temperature increasing speed is 1.86 ℃/min;
the third step: hydrothermal synthesis reaction
Heating by a jacket and a sleeve of the reaction kettle (220 ℃ oil bath), maintaining the reaction temperature at 150 ℃ and reacting for 2 hours;
the other steps are the same as example 1, and the performance test method is the same as example 1.
The scanning electron microscope image of the material is shown in fig. 2, and it can be seen that the lithium manganese iron phosphate prepared by the conventional hydrothermal synthesis method has large particles, cannot reach the nanoscale, and has poor particle uniformity. The electrochemical performance test results are shown in table 1, and the electrochemical performance is significantly reduced.
Comparative example 2
The raw material ratio is the same as that of example 2, namely, the recovered lithium phosphate is adopted, and the preparation method is the same as that of comparative example 1.
Specifically, the hydrothermal synthesis method of lithium ferric manganese phosphate nanoparticles comprises the following steps:
the first step is as follows: preparing mixed slurry of lithium, iron, manganese and phosphorus raw materials
(1) Preparing phosphorus source and lithium source mixed slurry: adding 0.6kmol (calculated by dry basis) of lithium phosphate wet crystal obtained by recovering mother liquor into the proportioning kettle 1 directly, adding 1.2kmol of lithium hydroxide monohydrate into the proportioning kettle 1, adding water for dissolving to ensure that the volume of the solution is 1m3Adding 0.4kmol phosphoric acid (about 30L) under stirring, purging air in dead volume of the kettle with inert gas, sealing the batching kettle 1 to obtain slurry A with volume of about 1.0m3；
(2) Preparing a mixed solution of an iron source and a manganese source: adding 0.3kmol ferrous sulfate heptahydrate and 0.7kmol manganese sulfate dihydrate into water to a volume of 1m3Stirring until all the components are dissolved, filtering by a pipeline type precision filter, and transferring to a batching kettle 2Obtaining slurry B with a volume of about 1.0m3；
(3) Mixing slurry A and slurry B: stirring at room temperature, opening the liquid-sealed exhaust valve of the batching kettle 1, adding the solution in the batching kettle 2 into the batching kettle 1, and continuously stirring for 20-30 minutes after the addition is finished to obtain slurry C with the volume of about 2m3；
The molar ratio of the added substances is Li: m (Fe + Mn): p is 3.0:1.0: 1.0; wherein, Fe: mn (molar ratio) 3: 7. After the feeding is finished, the total concentration of the ferro-manganese elements in the solution is about 0.5 mol/L.
The second step: the slurry C obtained in the first step is conveyed by a high-pressure pump into a reactor with a volume of 3m3In the high-pressure reaction kettle, the heating mode of the reaction kettle is jacket electric heating, and is limited by heating power (the influence of heat exchange area, oil temperature, equipment wall thickness and the like), the temperature of the reaction kettle is increased from 20 ℃ to 150 ℃ for 70 minutes, which is equivalent to the temperature increasing speed of 1.86 ℃/min;
the third step: hydrothermal synthesis reaction
Heating the mixture by a jacket and a sleeve of the reaction kettle (220 ℃ oil bath), maintaining the reaction temperature at 150 ℃ and reacting for 2 hours;
the other steps are the same as example 1, and the performance test method is the same as example 1.
In this comparative example, the obtained lithium manganese iron phosphate particles were coarse, and the slurry after discharge in the third step was immediately separated. Compared with comparative example 1, the electrochemical performance of the obtained product is more deteriorated, and the specific test results are shown in table 1. It follows that lithium manganese iron phosphate is produced at a relatively low rate of temperature increase by replacing lithium phosphate freshly produced on-site with lithium phosphate of relatively coarse size obtained by recovery, and the particle size of the starting lithium phosphate also adversely affects the properties of the final product.
TABLE 1 electrochemical Performance test results
0.2C specific capacity/mAhg-1 Specific capacity of 0.2C/mAhg at-20 ℃-1
Example 1 149.9 120.2
Example 2 149.4 119.5
Example 3 153.6 124.5
Comparative example 1 118.4 --
Comparative example 2 112.2 --
From the data, compared with the in-kettle heating mode in the prior art, the preheating unit in the invention has the advantages that the heat transfer is fast, the problem of reactant concentration reduction is avoided compared with the direct water vapor heating mode, the adverse effect caused by the large lithium phosphate particles obtained by recovering the mother solution can be overcome, the reactant concentration can be improved, and the productivity of unit equipment can be improved. The prepared material has uniform particles, the shape is converted from a sheet shape to a sphere-like shape, the dimension can reach a nanometer level, and the rate performance and the low-temperature performance of the material are good and stable. By controlling the heating link, the problem of dislocation of the lithium iron ions in the product particle size, morphology and crystal structure is fundamentally solved, and the overhigh pressure-resistant requirement on equipment caused by increasing the reaction high temperature is avoided. The method has the advantages of relatively mild reaction conditions, simple and controllable process and good batch stability of the product, and provides technical support for large-scale industrial production.
The present invention has been further described with reference to specific embodiments, but it should be understood that the detailed description should not be construed as limiting the spirit and scope of the present invention, and various modifications made to the above-described embodiments by those of ordinary skill in the art after reading this specification are within the scope of the present invention.

Claims (10)

1. A hydrothermal synthesis method of lithium ferric manganese phosphate nanoparticles is characterized by comprising the following steps:
(1) adding a mixture of a lithium source and a phosphorus source into a batching kettle, purging air in the dead volume of the kettle by using inert gas, sealing the batching kettle, opening a feed valve and an exhaust valve of the batching kettle, adding a pure mixed solution of an iron source and a manganese source under stirring, sealing the batching kettle after the feeding is finished, and continuously stirring for 10-30 minutes to obtain mixed slurry;
(2) conveying the mixed slurry in the batching kettle to a preheating unit for preheating, wherein the temperature of the slurry at an outlet of the preheating unit is 140-160 ℃, then conveying the heated mixed slurry to a reaction kettle preheated to 140-160 ℃, wherein the reaction kettle uses inert gas to sweep air in the dead volume in the kettle in advance, and after all the mixed slurry is heated and conveyed, sealing the reaction kettle;
(3) keeping the reaction kettle at the temperature of 140 ℃ and 160 ℃ for reaction for 2-4 hours under stirring, stopping heating, cooling, and cooling to 70-80 ℃;
(4) opening a discharge valve of the reaction kettle, filtering the resultant, washing until no sulfate ions exist to obtain a filter cake and a mother solution, and drying after washing the filter cake to obtain lithium manganese iron phosphate powder;
(5) uniformly mixing lithium iron manganese phosphate powder with a carbon source, and roasting at 700 ℃ for 4 hours under the protection of inert gas to obtain carbon-coated lithium iron manganese phosphate;
wherein the manganese source accounts for 0-70% of the total molar weight of the iron source and the manganese source.
2. The hydrothermal synthesis method of lithium ferric manganese phosphate nanoparticles as claimed in claim 1, wherein the preheating unit is composed of a plurality of tubular preheaters connected in parallel, and the tubular preheaters are heated by high temperature oil bath or electric heating.
3. The hydrothermal synthesis method of lithium iron manganese phosphate nanoparticles as claimed in claim 1, wherein the inlet slurry temperature of the preheating unit is 20-30 ℃, the outlet slurry temperature is 140-160 ℃, and the slurry is heated in the preheating unit for no more than 25 minutes.
4. The hydrothermal synthesis method of lithium iron manganese phosphate nanoparticles as claimed in claim 1, wherein the preheating temperature of the reaction kettle in the step (2) is lower than the outlet slurry temperature of the preheating unit.
5. The hydrothermal synthesis method of lithium ferric manganese phosphate nanoparticles as claimed in claim 1, wherein the molar ratio of the substances added in step (1) is Li: M (Fe + Mn): P ═ 3.0, (0.99-1.0): 1.0; the total concentration of the ferro-manganese elements is 0.5-0.7mol/L after the feeding is finished.
6. The hydrothermal synthesis method of lithium manganese iron phosphate nanoparticles according to claim 1, characterized in that in step (1), lithium hydroxide is dissolved in water and mixed with phosphoric acid as a lithium source and a phosphorus source; or mixing lithium phosphate obtained by recovering the mother liquor with lithium hydroxide solution and phosphoric acid which need to be supplemented to be used as a lithium source and a phosphorus source; or lithium phosphate alone as a lithium source and a phosphorus source.
7. The hydrothermal synthesis method of lithium manganese iron phosphate nanoparticles as claimed in claim 1, characterized in that the mother liquor obtained by filtration in step (4) and the primary washing water for washing the filter cake are combined, evaporated and concentrated, and then the lithium phosphate is recovered.
8. The hydrothermal synthesis method of lithium ferric manganese phosphate nanoparticles as claimed in claim 1, wherein the iron source is ferrous sulfate crystals or liquid before crystallization, and the manganese source is manganese sulfate.
9. The hydrothermal synthesis method of lithium ferric manganese phosphate nanoparticles as claimed in claim 1, wherein in step (5), the ratio of lithium ferric manganese phosphate powder to carbon source is determined according to a ratio of 100: (10-15) mixing in a mass ratio.
10. The hydrothermal synthesis method of lithium ferric manganese phosphate nanoparticles as claimed in claim 1, wherein the carbon source is glucose.
CN202210431899.7A 2022-04-22 2022-04-22 Hydrothermal synthesis method of lithium ferric manganese phosphate nanoparticles Pending CN114628660A (en)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN115806282A (en) * 2022-11-22 2023-03-17 贵州雅友新材料有限公司 Flaky lithium manganese iron phosphate and synthesis method and application thereof

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN115806282A (en) * 2022-11-22 2023-03-17 贵州雅友新材料有限公司 Flaky lithium manganese iron phosphate and synthesis method and application thereof

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