72 results about "Iron(II) phosphate" patented technology

The invention relates to the technical field of lithium iron phosphate production, and discloses a carbon-coated titanium-doped lithium iron phosphate positive electrode material and a preparation method thereof.The preparation method comprises the following steps that 1, a ferrous solution and a phosphorus source solution are mixed in proportion, dopamine hydrochloride is added, a pH regulator is dropwise added in the stirring state, the pH of the solution is adjusted to 4.0-5.5, a reaction is conducted, a titanium source solution is added, and a reaction solution is obtained; after uniformly stirring, continuously dropwise adding a pH regulator to regulate the pH value of the solution to 5.5-6.5; the iron phosphate octahydrate coated with the titanium-embedded polydopamine is obtained; 2) calcining the titanium-embedded polydopamine-coated ferrous phosphate octahydrate in an inert gas atmosphere to obtain carbon-coated titanium-doped anhydrous ferrous phosphate; 3) mixing the carbon-coated titanium-doped anhydrous ferrous phosphate with lithium phosphate and a carbon source, ball-milling, mixing, spray-drying and calcining to obtain a carbon-coated titanium-doped lithium iron phosphate positive electrode material; the synthesis process is simple, and energy consumption is reduced.

The invention discloses a method for preparing battery-grade iron phosphate by recovering lithium iron phosphate battery black powder, which comprises the following steps of: performing reduction acid leaching on the lithium iron phosphate battery black powder to obtain acid leaching liquid; adding sodium silicate into the acid leaching solution to adjust the pH value of the solution to 2.5-4, removing aluminum and titanium to obtain a primary impurity-removed solution, deeply removing aluminum and titanium from the impurity-removed solution by adopting ion exchange resin, and removing copper and filtering by adopting sulfide to obtain a copper-removed solution; supplementing iron is added into the copper removal liquid, the pH is adjusted to 3.5-6.5, ferrous phosphate reacts and is separated out, and ferrous phosphate is obtained; the method comprises the following steps: carrying out acid leaching on ferrous phosphate to obtain a leaching solution, adjusting the molar ratio of iron to phosphorus in the leaching solution, carrying out oxidation precipitation, adjusting the pH value of the solution again, aging, filtering, washing and drying to obtain iron phosphate dihydrate, and finally calcining to obtain the anhydrous iron phosphate. According to the method, a process route for producing iron phosphate by an ammonium method is used for reference, iron and phosphorus in the black powder of the lithium iron phosphate battery are recycled and converted into battery-grade iron phosphate in a ferrous phosphate form, impurities such as aluminum, titanium and copper are effectively removed, and the impurities are prevented from being entrained in the iron phosphate.

The invention discloses a method for preparing high-quality iron phosphate in a short process, and belongs to the field of battery material manufacturing. The method comprises the following steps: dissolving iron powder with phosphoric acid to prepare a ferrous phosphate solution, then transferring the solution into a pressurized reaction kettle, blowing high-speed oxygen to oxidize ferrous phosphate into ferric phosphate, adding ammonia water to control the pH value to be 1.5-2.0, and carrying out solid-liquid separation to obtain the water-containing amorphous ferric phosphate, after washing is finished, a water-containing material is fed into a muffle furnace to be subjected to stepped calcination, dehydration and crystal transformation are completed, and the alpha monoclinic system iron phosphate is obtained. The method provided by the invention is short in process flow and low in energy consumption, the oxidant is easy to obtain and safe, the particle size uniformity of reaction materials is good, and the prepared iron phosphate is uniform in particle size, regular in structure and stable in iron-phosphorus ratio and is a high-quality precursor material.

The invention relates to a high-compaction lithium iron phosphate positive electrode material, a preparation method thereof and a lithium ion battery, and belongs to the technical field of batteries, the method adopts a two-step synthesis method, the first step adopts ferrous phosphate high-grinding sintering to prepare first-sintering large particles, and adopts in-situ doped iron phosphate low-grinding to prepare first-sintering small particles; 2, performing high grinding on the first-fired large particles, performing low grinding on the first-fired small particles, accurately controlling the sizes of the small particles, and stripping C3N4 through grinding to form g-C3N4; the large and small particles are mixed according to a certain mass ratio, and then secondary sintering is carried out to prepare the high-compaction high-capacity long-circulation lithium iron phosphate material, the advantages of different precursors are utilized, the particle composition is optimized, and the roundness of the large and small particles is better; meanwhile, the nitrogen-doped carbon layer is prepared by taking defect-type graphene and high-molecular organic nitride which are converted from C3N4 in a secondary sintering process as carbon sources, so that the conductivity and the cycle performance of the material are improved.

The present invention relates to a modified sodium iron phosphate pyrophosphate composite material and its preparation method and application, belonging to the technical field of sodium ion batteries. The preparation method of the present invention comprises the following steps: S1, adding a soluble doped metal salt solution and a surfactant to a ferrous phosphate solution, and dripping a hydrogen peroxide solution and a hydrofluoric acid solution within 40min-80min under the conditions of 60°C-80°C, reacting at 85°C-98°C for 2h-5h after the dropwise addition, and washing and calcining to obtain a flaky composite precursor; S2, dissolving the flaky composite precursor, a sodium source, a phosphorus source, and a carbon source in water, and obtaining a modified sodium iron phosphate pyrophosphate composite material through sand milling, spray drying, and heat treatment. Element doping and material modification are successfully achieved during the precursor synthesis, thereby achieving optimization of the crystal phase, reduction of the impurity phase, improvement of the energy density, conductivity, and other physical and chemical properties of the NFPP material, and reduction of its water absorption.

The invention provides a preparation method of a three-dimensional structure ferrous phosphate pigment with corrosion early warning capability, which comprises the following steps: preparing a ferrous ion-containing solution for providing ferrous ions, the ferrous ion-containing solution contains soluble ferrite and a surfactant and does not contain oxidizing ions, the ferrous ion-containing solution is in an acidic environment; preparing an initial mixed solution for providing phosphate ions and ammonium ions; atomizing and spraying the initial mixed solution into a ferrous ion-containing solution to obtain an intermediate mixed solution, carrying out ultrasonic refining on the intermediate mixed solution by utilizing an ultrasonic oscillation and microwave heating auxiliary device, heating and carrying out heat preservation to obtain a final mixed solution; and filtering the precipitate in the final mixed solution, transferring the precipitate to a vacuum environment, and carrying out high-temperature heating treatment to obtain the three-dimensional structure ferrous phosphate pigment with the corrosion early-warning capability, which can have the corrosion early-warning capability.

The present solution provides a preparation method for a three-dimensional structured ferrous phosphate pigment with corrosion early warning capability, including following steps: preparing a ferrous ion-containing solution for providing ferrous ions, where the ferrous ion-containing solution includes a soluble ferrous salt and a surfactant but no oxidizing ions, and the ferrous ion-containing solution is maintained in an acidic environment; preparing an initial mixed solution for providing phosphate ions and ammonium ions; and performing ultrasonic refinement, heating, and holding on the intermediate mixed solution using an auxiliary device with ultrasonic oscillation and microwave heating functions to obtain a final mixed solution; and filtering out precipitates from the final mixed solution, and then transferring the precipitates to a vacuum environment for high-temperature heating treatment to obtain a three-dimensional structured ferrous phosphate pigment with corrosion early warning capability.

The invention provides a preparation method for preparing a high-compaction lithium iron phosphate positive electrode material by utilizing double-iron-source composite grade matching. The preparation method comprises the following steps: adding ferrous sulfate and phosphoric acid into pure water, and fully mixing to obtain a solution; dividing the solution into a solution A and a solution B; adding a certain amount of a metal doping source material, an oxidizing agent and phosphoric acid into the solution A, and controlling the pH to be 1-3 to obtain iron phosphate; adding a certain amount of metal doped source material and ammonia water into the solution B, and controlling the pH to be 5-6 to obtain ferrous phosphate; the preparation method comprises the following steps: respectively sanding and spraying iron phosphate and ferrous phosphate with a lithium source, a carbon source and pure water according to a molar ratio to obtain a lithium iron phosphate yellow material A and a lithium iron phosphate yellow material B; calcining the yellow material A in a furnace to obtain a precursor A, calcining the yellow material B in the furnace to obtain a precursor B, mixing the precursor A and the precursor B according to a certain mass ratio, and calcining to obtain a finished product. The method is simple in technological process, can be combined with actual production, and is very effective for improving the compaction density and the electrical property.

The invention belongs to the field of battery positive electrode materials, and particularly relates to a preparation method of a ferrous phosphate precursor, a Fe < 3 + > solution and a phosphate radical source solution with the Fe / P element ratio of 3: (1.8-2.1) are mixed and subjected to a first-stage precipitation reaction in advance, and the initial pH A of the first-stage precipitation reaction is 0.5-2; then supplementing an alkaline substance to carry out a second-stage precipitation reaction under the condition that the pH value is 2.5-5, and then carrying out solid-liquid separation to obtain an iron phosphate-Fe (OH) 3 composite material; and compounding the iron phosphate Fe (OH) 3 composite material with a carbon source, and carrying out reduction roasting treatment to obtain the ferrous phosphate precursor. The invention also comprises a preparation method and application of the material. According to the method, the performance of the prepared material can be improved, and the low-temperature and batch quality stability of the material is particularly facilitated.

The invention discloses a method for preparing battery-grade iron phosphate from wet-process crude phosphoric acid and raffinate acid, which comprises the following steps of: mixing and leaching an iron source and wet-process crude phosphoric acid or wet-process crude phosphoric acid and raffinate acid to obtain ferrous dihydrogen phosphate containing metal impurities, ferrous phosphate leachate I and leaching residue; carrying out pH regulation and control on the leachate I to precipitate and remove aluminum in the form of aluminum phosphate, and carrying out multi-stage precipitation to remove aluminum until the content of aluminum ions is lower than 500ppm, so as to obtain leachate II; hydrofluoric acid is added into the leachate II, the pH value is adjusted to 1.6-2.5 with refined phosphoric acid, Al ions are precipitated, and leachate III is obtained after solid-liquid separation; an oxidizing agent is added into the leachate III for a precipitation reaction, and iron phosphate dihydrate and a phosphoric acid solution are obtained; and calcining the iron phosphate dihydrate to obtain the iron phosphate dihydrate. Crude phosphoric acid and raffinate acid can be directly utilized to produce battery-grade iron phosphate, the process is simple, compared with a traditional iron-method iron phosphate production process, the raw material cost is greatly reduced, generation of waste water and waste acid in the refining process is avoided, and the method is suitable for industrial production.

The invention specifically discloses a method for preparing ferric sodium pyrophosphate by taking ferrous phosphate as a precursor. The method comprises the following steps: S100, preparing a ferrous phosphate powder precursor through a reverse titration coprecipitation method; s200, the ferrous phosphate powder precursor, sodium pyrophosphate and a carbon source are placed in a ball milling container for a ball milling reaction, and a ferric sodium pyrophosphate precursor is prepared; and S300, calcining the obtained ferric sodium pyrophosphate precursor under a second preset temperature condition, and cooling after the calcination is finished, so as to obtain the ferric sodium pyrophosphate powder. The method for preparing the ferric sodium pyrophosphate with the ferrous phosphate as the precursor is easy to operate, low in cost and beneficial to industrial production, in addition, the ferric sodium pyrophosphate prepared through the method has the advantages of being uniform in particle size, uniform in morphology and high in purity, and the method is suitable for industrial production. And when being applied to the sodium-ion battery, the sodium-ion battery shows relatively high capacity, good rate capability and excellent cycle performance.

The invention discloses a process for preparing iron phosphate from pure iron, and relates to the technical field of chemical production. The method comprises the following specific steps: firstly, dissolving pure iron blocks in a phosphoric acid solution, and carrying out solid-liquid separation to obtain ferrous phosphate mother liquor; a proper amount of surfactant is added into the ferrous phosphate mother liquor, so that the dispersity and uniformity of particles in subsequent reaction are improved. Mixing the ferrous phosphate mother liquor with hydrogen peroxide, and adjusting with ammonia water to carry out oxidation reaction to obtain an iron phosphate crude product; and washing the crude product with hot water, mixing with water and phosphoric acid, and aging. And after aging, carrying out solid-liquid separation, washing with hot water, and drying to obtain high-purity iron phosphate. The method has the advantages of simple process, mild reaction conditions and stable product quality, and is suitable for industrial production.

The invention relates to the technical field of industrial solid waste resource utilization, in particular to a method for preparing ferrous phosphate octahydrate by taking pyrite cinder as a raw material, which comprises the following steps: 1) taking pyrite cinder as a raw material, and carrying out ball milling to obtain fine powder; 2) rinsing the fine powder with dilute acid and water respectively to obtain red slag; 3) mixing the red slag with a reducing agent, and calcining to obtain reducing slag; (4) under the protection of inert gas, leaching the reducing slag with sulfuric acid, filtering to obtain a leaching solution, and adjusting the iron ion concentration and the iron-phosphorus ratio to obtain an iron-phosphorus solution; (5) under the protection of inert gas, dilute alkali is added into the iron-phosphorus solution to adjust the pH value, filtering is performed after full reaction, and an iron-phosphorus purified solution is obtained; (6) under the protection of inert gas, dilute alkali is added into the iron-phosphorus purified liquid to adjust the pH value, filtering is performed after full reaction, and a filter cake is obtained; and 7) washing the filter cake, and carrying out vacuum drying to obtain ferrous phosphate octahydrate. The problems of environmental pollution and serious resource waste caused by difficult recycling of pyrite cinder can be solved.

This invention provides a lithium iron phosphate cathode material, its preparation method, and its application. The preparation method includes the following steps: (1) mixing ferrous salt and phosphorus source with an alcohol solvent, heating and stirring, and adding a first lithium source solution to obtain a mixed solution; adjusting the pH of the mixed solution to obtain a mixed precursor; (2) mixing a complexing agent, ferric salt, a second lithium source, phosphorus source, and surfactant with water, stirring to form a sol solution; mixing the mixed precursor obtained in step (1) with the sol solution, heating and stirring to obtain a gel precursor; (3) sintering the gel precursor to obtain the lithium iron phosphate cathode material; wherein the mixed precursor includes lithium phosphate and ferrous phosphate. This invention can achieve lithium iron phosphate gradation of different particle sizes through a single production line, improving the uniformity and compaction density of the material, and avoiding performance differences and poor stability between different batches.

The application provides a preparation method of high-density lithium iron phosphate positive electrode material by using double-iron-source complex level matching, and the method comprises the following steps: adding ferrous sulfate and phosphoric acid into pure water and fully mixing to obtain a solution; the solution is divided into solution A and solution B; solution A is added into a certain amount of metal doping source material, an oxidizing agent and phosphoric acid, and the pH is controlled to be 1-3 to obtain iron phosphate; solution B is added into a certain amount of metal doping source material and ammonia water, and the pH is controlled to be 5-6 to obtain ferrous phosphate; the iron phosphate and the ferrous phosphate are respectively sand-mixed, sprayed with lithium source, carbon source and pure water according to a molar ratio to obtain yellow materials A and B; the yellow material A is calcined in a furnace to obtain a precursor A, the yellow material B is calcined in a furnace to obtain a precursor B, and the precursors A and B are mixed according to a certain mass ratio and then calcined to obtain a finished product. The process flow of the application is simple, can be combined with actual production, and is very effective for improving the compaction density and the electrical performance.

A process for the production of iron phosphate, comprising the following steps: (1) Mixing an iron phosphide waste, an acidic liquid, an oxidizing agent and an adsorbent with stirring, heating to leaching and subjecting the resulting mixture to solid-liquid separation to obtain a first filtrate and a first filter residue; (2) Adding an alkaline liquid to the first filtrate to adjust the pH of the first filtrate, maintaining a temperature of the resulting mixture, and subjecting the resulting mixture to solid-liquid separation to obtain a second filter residue and a second filtrate; and subjecting the second filter residue to heat treatment to obtain iron oxide; (3) Subjecting the iron oxide to high-energy ball milling and adding a surfactant for activation to obtain a slurry; (4) Adding an extraction agent and an acidic liquid to the second filtrate obtained in step (2), carrying out an extraction and separation on a resulting mixture and subjecting a resulting organic phase to back-extraction to obtain phosphoric acid; and (5) Mixing the slurry obtained in step (3) with the phosphoric acid, heating to enable a reaction, subjecting the resulting mixture to solid-liquid separation to obtain a solid, and washing and sintering the solid to obtain the iron phosphate; where in step (1) the iron phosphide waste comprises a mixture of FeP and Fe2P; in step (1) the acidic liquid contains at least two from the following group: nitric acid, sulfuric acid and hydrochloric acid; In step (1) the oxidizing agent is at least one selected from the group consisting of hydrogen peroxide, oxygen, nitric acid and sodium persulfate; wherein in step (2) the alkaline liquid is at least one selected from the group consisting of a NaOH solution, a KOH solution, ammonia water, a urea solution, NH4Cl, NH4HCO3, Na2CO3 and NaHCO3; In step (2) the pH of the first filtrate is adjusted to 2.5 to 5; and In step (5) the molar ratio of Fe in the slurry to P in the phosphoric acid is 1:1–2; heating to enable a reaction is carried out at a temperature of 50 °C to 80 °C for 20 to 60 min; and the iron phosphate has a D 50 from 2 µm to 6 µm, a tapped density of 0.80 g / cm³ 3 up to 1.30 g / cm³ 3 , and a specific surface area of ​​4 m² 2 / g up to 8 m 2 / g indicates.

The application provides a method for preparing cobalt-doped ferromanganese subphosphate by using iron phosphate sewage treatment sludge, and comprises the following steps: adding acid liquor into the iron phosphate sewage treatment sludge, performing acid leaching reaction, performing solid-liquid separation, and obtaining filtrate A; adding an extraction agent into the filtrate A, and performing extraction to obtain an extracted organic phase and a raffinate; performing multistage impurity removal on the raffinate to obtain a cobalt-manganese-phosphorus-containing solution, supplementing an iron source and a phosphorus source, and using a hydrothermal synthesis method to obtain a cobalt-doped ferromanganese subphosphate crude product, which is washed, dried and calcined to obtain the cobalt-doped ferromanganese subphosphate. The method can comprehensively recycle and utilize P, Mn and Co elements in the iron phosphate sewage treatment sludge, and reduces the production cost of the cobalt-doped ferromanganese subphosphate.

There is provided a method for producing ferrous sulphate and phosphoric acid comprising treating ferrous phosphate with sulphuric acid for obtaining ferrous sulphate and phosphoric acid. Additionally, there is provided a use of sulphuric acid for treating ferrous phosphate for obtaining ferrous sulphate and phosphoric acid.

The application provides a battery monomer, a preparation method thereof, a battery and a power utilization device, and belongs to the technical field of sodium batteries. The battery monomer comprises a positive electrode sheet, the positive electrode sheet comprises a positive electrode film layer, the positive electrode film layer comprises an active substance, the active substance comprises 96-99 wt% of sodium iron pyrophosphate phosphate, 0-1.9 wt% of sodium ferrous phosphate and 0.6-4 wt% of sodium iron pyrophosphate, and the mass ratio of sodium iron pyrophosphate in the active substance is greater than the mass ratio of sodium ferrous phosphate. The battery monomer of the application controls the content of the main phase and the impurity phase in the active substance in the above range, which can not only improve the compaction density of the positive electrode active material, but also is beneficial to improving the compaction density of the positive electrode sheet, and can improve the charge gram capacity and the discharge gram capacity of the positive electrode active material. When the mass ratio of sodium iron pyrophosphate in the active substance is greater than the mass ratio of sodium ferrous phosphate in the active substance, the energy density and the cycle performance of the battery monomer can be further improved.

The invention relates to the field of lithium ion battery positive electrode materials, and particularly discloses a preparation method and application of a co-doped ferrous phosphate precursor material.The preparation method comprises the steps that an antioxidant solution and a salt solution containing doped metal ions are added into a ferrite solution, and an iron source mixed solution is obtained; mixing and reacting a phosphorus source, an iron source and an alkaline solution to obtain blue ferrous phosphate slurry; and then filtering, washing, drying and crushing to obtain the doped ferrous phosphate precursor material. According to the invention, doping and morphology regulation and control are integrated in a single reaction system through a metal ion doping process, so that the preparation process is greatly simplified, and the compaction density and the rate capability of the prepared lithium iron phosphate positive electrode material are remarkably improved.

The invention discloses a carbon-coated sodium ferrous fluorophosphate positive electrode material and a preparation method thereof. A phosphorus source, an iron source, an organic carbon source, a sodium source and a surfactant are mixed, stirred and heated, a fluorine source solution is added after reaction, a conductive carbon source is added after continuous stirring, and the sodium ferrous fluorophosphate positive electrode material is obtained through dispersion, drying and high-temperature sintering. Compared with an existing synthesis method, the method provided by the invention is small in pollution and simple in process, the conductivity of the prepared positive electrode material is greatly improved after the positive electrode material is subjected to carbon coating modification, and the specific capacity can reach 80% or above of a theoretical value.

The application relates to the technical field of lithium ion batteries, in particular to a preparation method of lithium iron phosphate. The preparation method of the lithium iron phosphate comprises the following steps: reacting a mixed solution containing ferrous phosphate and ferrous biphosphate, and performing first grinding to obtain slurry; and sequentially performing second grinding, spray drying, calcination and crushing on a mixture of the slurry, a lithium source, a carbon source and a dopant to obtain the lithium iron phosphate. The two ferrous salts of the ferrous phosphate and the ferrous biphosphate are adopted, and superfine grinding can be realized under the dual action of physical grinding and chemical reaction; the generation of strong reducing gas is avoided, and the content of magnetic substances in the product is reduced. The lithium iron phosphate prepared by adopting the preparation method has the characteristics of small primary particle size, high rate performance, low powder resistivity and excellent low-temperature performance.

The present disclosure relates to a method for preparing ferroboron alloy-coated lithium iron phosphate, comprising: preparing ferrous phosphate and lithium phosphate, then mixing ferrous phosphate and lithium phosphate and adding a hydrazine hydrate solution to obtain a mixture which is then subjected to grinding, drying and then calcining to obtain a calcined mateiral, adding pure water to the calcined material and grinding the calcined material in water to obtain a slurry, to which PEG, ferrous sulfate crystals and disodium EDTA are added and stirred to dissolve, then adding a sodium borohydride solution and a sodium hydroxide solution while stirring and maintaining a pH in the process at 8.5-10.5, reacting for 15-30 min to obtain a product, and filtering, washing and vacuum drying the product to obtain the ferroboron alloy-coated lithium iron phosphate. The method may reduce interface resistance while improving conductivity, corrosion resistance, oxidation resistance and density of the product.

The invention provides an integrated multi-stage tubular reactor and a continuous reaction system, and relates to the technical field of chemical equipment, the integrated multi-stage tubular reactor comprises a reaction container, the reaction container is made of a non-metal material; the microwave heating device is arranged in the reaction container and is used for heating a solution in the reaction container; the gas stirring device is arranged in the reaction container and is used for stirring a solution in the reaction container; wherein the microwave heating devices are uniformly distributed in the reaction container. Compared with the prior art, the problem that the crystallinity of ferrous phosphate is not ideal due to uneven heating of the reaction solution can be effectively solved, the crystallization quality of ferrous phosphate is improved, and then the particle uniformity and phase purity of subsequent iron phosphate are improved.

The present invention belongs to the field of electrode material technology, and relates to a sodium ferrous fluorophosphate / N-CNT composite positive active material, including N-CNT, and sodium ferrous fluorophosphate composited on N-CNT. In addition, the present invention further relates to a method for preparing the material, which mixes iron phosphate and carbon nanotubes and then performs ammoniation roasting to obtain an iron phosphate / N-CNT intermediate; then the iron phosphate / N-CNT intermediate, a fluorine source and a sodium source are mixed, and then roasting treatment is performed to obtain the sodium ferrous fluorophosphate / N-CNT composite positive active material. The technical solution of the present invention, pre-ammoniation roasting of iron and phosphorus with iron phosphate phases is carried on the N-CNT structure, and then subsequent sodiumization and fluorination roasting are involved, so that the sodium ferrous fluorophosphate crystal phase structure can be controlled, the unit cell size can be controlled, the material morphology can be improved, and the ion and electronic conduction network construction can be effectively constructed, thereby effectively improving the capacity, rate and cycle stability of the material.

The invention relates to a preparation method of high-purity ferrous phosphate and lithium iron phosphate, which comprises the following steps: heating dilute phosphoric acid, weighing iron powder, slowly adding the iron powder into the dilute phosphoric acid, carrying out stirring reaction, carrying out filter pressing to obtain reaction liquid, and taking filtrate to obtain a clear ferrous solution; when the temperature of the ferrous solution reaches a first temperature, adjusting the pH value of the reaction solution to a first numerical value by using ammonia water with a first concentration, preserving heat, heating the slurry, adjusting the pH value of the reaction solution to a second numerical value by using ammonia water with a second concentration, preserving heat to obtain ferrous phosphate octahydrate slurry, and carrying out filter pressing on the ferrous phosphate octahydrate slurry to obtain a ferrous phosphate octahydrate filter cake and a mother solution, the first concentration is lower than the second concentration, the first numerical value is lower than the second numerical value, and the first heat preservation time is shorter than the second heat preservation time. According to the method, phosphoric acid and iron powder are taken as raw materials, and the pH value of each stage of the reaction process is adjusted, so that the ferrous phosphate octahydrate with relatively high purity and relatively good crystallinity can be directly prepared.

The invention discloses a preparation method of lithium manganese iron phosphate with a composite polycrystalline structure. The method comprises the following steps: adding a phosphorus source and a carbon-containing substance in an amount of 3% to 10% by mass of the ferrous sulfate to a ferrous sulfate solution, reacting the mixture in an oxygen-free environment with a pH value of 5 to 10, and filtering to obtain a wet ferrous phosphate material containing carbon compounds; the carbon-containing substances comprising at least two substances; adding an oxidant and an aerogel to a manganese sulfate solution for reaction to obtain a manganese dioxide nanomaterial; mixing the graphene-containing ferrous phosphate wet material and the manganese dioxide nanomaterial, and reacting the mixture with a lithium salt and an adhesion promoter in an oxygen-free environment to obtain a lithium manganese iron phosphate precursor; and sequentially subjecting the lithium manganese iron phosphate precursor to ball milling, drying, sintering, and cooling to obtain the lithium manganese iron phosphate with the composite polycrystalline structure. The prepared lithium manganese iron phosphate has good charge and discharge performance, compaction density, and processing performance, and is worthy of promotion in the battery field.

The invention relates to ferrous phosphate based on mixed acid and iron powder and a preparation method and system thereof.The preparation method comprises the steps that dilute phosphoric acid and dilute sulfuric acid are mixed, pure iron powder is added into the mixed acid according to the ratio of n (p) to n (Fe) being (0.67-1): 1, and an iron dissolving reaction is conducted after a certain temperature is reached; taking the temperature as a starting point, sampling once every time period, analyzing the content of Fe < 2 + > in the obtained sample, and obtaining a ferrous liquid when the content of Fe < 2 + > in the sample reaches 3.5-5.0%; adding ammonia water into the ferrous liquid until the pH value of a reaction system reaches 5.0-6.5 to obtain slurry; and aging the slurry, and carrying out filter pressing, washing and drying to obtain the ferrous phosphate octahydrate. According to the method, the content of sulfate radicals in the obtained product can be effectively controlled while the use amount of phosphoric acid is reduced, the product quality is effectively improved, meanwhile, the thickness distribution uniformity of a ferrous phosphate octahydrate crystal lamellar structure is controlled, the thickness of the lamellar structure is reduced, the product quality is improved, and the compaction density of lithium iron phosphate is improved.

The present invention relates to a lithium iron phosphate material and a preparation method thereof, and a positive electrode material for lithium-ion batteries, and relates to the technical field of battery materials. The preparation method of the lithium iron phosphate material comprises the following steps: 1) a first solution containing a phosphorus source and polyethylene glycol is subjected to a co-precipitation reaction with a second solution containing an iron source to obtain a polyethylene glycol-coated ferrous phosphate precursor; 2) a third solution containing a lithium source and a polyethylene glycol-coated ferrous phosphate precursor are subjected to a hydrothermal crystallization reaction to obtain a reaction product, lithium iron phosphate; 3) the reaction product, lithium iron phosphate, is calcined under a reducing atmosphere to obtain a lithium iron phosphate material. The present invention first in-situ coats ferrous phosphate with polyethylene glycol, and uses a hydrothermal crystallization method to synthesize the reaction product, lithium iron phosphate crystals, with low antisite defects, and then calcines under a reducing atmosphere to reduce the Li + Diffusion impedance, improved electronic conductivity, and demonstrated excellent rate and capacity performance.