2218 results about "Manganese phosphate" patented technology

A lithium manganese iron phosphate positive electrode material, which comprises first lithium manganese iron phosphate particles and second lithium manganese iron phosphate particles, wherein in the first lithium manganese iron phosphate particles, the molar ratio of Mn to Fe elements is greater than or equal to 1; and in the second lithium manganese iron phosphate particles, the molar ratio of Mn to Fe elements is less than or equal to that in the first lithium manganese iron phosphate particles. The particle size of the first lithium manganese iron phosphate particles is less than or equal to that of the second lithium manganese iron phosphate particles. A preparation method for the lithium manganese iron phosphate positive electrode material and the use thereof. A first precursor having a manganese content larger than or equal to the iron content thereof inhibits crystal growth during sintering, and has a small particle size; and a second precursor having a manganese-iron ratio less than or equal to the ratio in the first precursor is beneficial to crystal growth during sintering, and has a large particle size, thereby forming particle size grading, improving the space utilization rate of particle accumulation, and improving the compaction density and the volume specific capacity of the lithium manganese iron phosphate positive electrode material.

The invention provides a positive plate, a preparation method thereof and a battery. The positive plate comprises a positive current collector, and a first positive active coating and a second positive active coating which are sequentially arranged on at least one side of the positive current collector, the first positive electrode active coating is close to one side of the positive electrode current collector, and the first positive electrode active coating comprises a first manganese iron lithium phosphate active material and a nickel-cobalt-manganese ternary active material; in the first positive electrode active coating, the mass ratio of the first lithium manganese iron phosphate active material to the nickel-cobalt-manganese ternary active material is (80-90): (8-15); the second positive electrode active coating is far away from one side of the positive electrode current collector, and the second positive electrode active coating comprises a second lithium manganese iron phosphate active material; the surface density rho1 of the first positive electrode active coating and the surface density rho2 of the second positive electrode active coating meet the following conditions: rho1 is greater than or equal to 240 g / m < 2 >, and rho2 is greater than or equal to 240 g / m < 2 >; and rho1-rho2 is less than or equal to 5g / m < 2 >. The positive plate has relatively high electron conduction and ion conduction performance, meanwhile, the polarization of the positive plate is effectively reduced, and the cycle performance and the thermal stability of the battery are greatly improved.

The invention discloses a preparation method of a high-compaction lithium manganese iron phosphate positive electrode material, which comprises the following steps: placing a manganese source, an iron source and a phosphorus source in deionized water, stirring, carrying out primary high-speed ball milling, carrying out constant-temperature water bath, adding an oxidizing agent, stirring and oxidizing, and drying the slurry to obtain manganese iron phosphate precursor powder; carrying out primary sintering on the ferromanganese phosphate precursor powder to obtain a ferromanganese phosphate primary sintering material; putting the ferromanganese phosphate primary sintering material into deionized water, adding a lithium source and a carbon source at the same time, and performing stirring, secondary high-speed ball milling and drying to obtain lithium ferromanganese phosphate precursor powder; and carrying out secondary sintering on the lithium manganese iron phosphate precursor powder to obtain the high-compaction lithium manganese iron phosphate positive electrode material. The void ratio is well reduced and good carbon coating is realized by means of secondary grinding and secondary sintering, and compared with the prior art, the method has the advantages that good capacity can be maintained, the powder compaction density of the material can be improved, the conductivity can be improved, and the specific surface area of the material can be effectively reduced.

The invention provides a positive electrode material and a preparation method thereof, a positive electrode plate and a battery, the positive electrode material comprises lithium manganese iron phosphate particles, a first shell layer and a second shell layer, the first shell layer and the second shell layer sequentially coat the surfaces of the lithium manganese iron phosphate particles, the material of the first shell layer comprises nanoscale SiO2 particles, and the material of the second shell layer comprises nanoscale TiO2 particles. The surfaces of the lithium manganese iron phosphate particles are sequentially coated with the SiO2 layer and the TiO2 layer, so that the contact between the lithium manganese iron phosphate particles and an electrolyte can be reduced, the side reaction between the lithium manganese iron phosphate particles and the electrolyte in the electrochemical reaction process is reduced, the cycle life attenuation of the battery is relieved, the dissolution of Mn element is reduced, and the service life of the battery is prolonged. Therefore, the battery impedance increase caused by deposition of Mn < 2 + > on the negative electrode in the circulation process is relieved.

The invention relates to the technical field of lithium ion batteries, in particular to a lithium iron manganese phosphate-ternary material composite positive electrode lithium ion battery formation method and a lithium ion battery, the formation method comprises the following steps: S1, allowing a soft package cell to stand in a vacuum environment; s2, applying a first pressure and heating, and then carrying out constant current charging to 20%-40% SOC at a small current of 0.02-0.05 C; s3, second pressure is applied, heating is conducted, then constant current charging is conducted to 50%-70% SOC with the large current of 0.1-0.2 C, and the second pressure is larger than the first pressure; s4, applying a third pressure and heating, and then performing constant-current discharge at the current of 0.2-0.5 C until the SOC is 30-50%; and S5, performing high-temperature aging on the soft package battery cell. According to the formation method provided by the invention, the cycle performance of the lithium iron manganese phosphate-ternary material composite positive electrode lithium ion battery is improved.

The invention discloses a lithium manganese iron phosphate positive electrode material with a core-shell structure, which is prepared by the following steps: mixing a manganese source, an iron source, a phosphorus source, lithium carbonate and a carbon source, grinding and drying to prepare a pre-sintered material; then carrying out gas crushing on the pre-sintered material to obtain a pre-gas crushed material, and carrying out heat preservation at the temperature of 200-600 DEG C; putting the pre-gas crushed material subjected to heat preservation into an iron salt solution for quenching reaction to obtain iron compound coated lithium manganese iron phosphate; and finally, mixing the lithium iron manganese phosphate coated with the iron compound, a lithium source, a phosphorus source and a carbon source, grinding, drying, and carrying out secondary calcination to obtain the lithium iron manganese phosphate material with the core-shell structure. During preparation of the lithium manganese iron phosphate positive electrode material, a lithium manganese iron phosphate pre-sintered body and an iron salt solution are subjected to a quenching reaction to form an iron compound coated lithium manganese iron phosphate pre-sintered body, and then the iron compound coated lithium manganese iron phosphate pre-sintered body and other raw materials of lithium iron phosphate are subjected to a secondary calcination reaction to generate the composite positive electrode material with a core-shell structure. A coating structure is formed, the reaction between manganese and electrolyte is reduced, the dissolution of manganese is inhibited, the Gingtaler effect of manganese is relieved, and the stability of the material is improved; and the material has the advantages of high energy density, high power density, excellent cycle performance and strong core-shell interface bonding force.

The invention provides a battery monomer, a battery device and a power utilization device. The battery monomer comprises an electrode assembly, wherein the electrode assembly comprises a positive plate, a negative plate and a non-aqueous electrolyte; the positive plate comprises a positive current collector and a positive film layer, and the negative plate comprises a negative current collector and a negative film layer; the positive electrode film layer comprises a positive electrode active material, and the positive electrode active material comprises a lithium manganese iron phosphate material and a nickel cobalt lithium manganate material; in the nickel cobalt lithium manganate material, the molar ratio of Ni in the sum of the three elements of Ni, Co and Mn is 0.5-0.95; the non-aqueous electrolyte comprises vinylene carbonate, and the mass content of the vinylene carbonate in the non-aqueous electrolyte is 0.5%-2%; the non-aqueous electrolyte comprises at least one of linear carbonic ester and linear carboxylic ester, and the conductivity of the non-aqueous electrolyte is 9-14 mS / cm. The energy density, the cycle performance and the power performance of the battery monomer are improved at the same time.

The invention discloses a transition metal nitride and amorphous carbon composite coated and modified lithium manganese iron phosphate composite material as well as a preparation method and application thereof, and belongs to the technical field of lithium ion batteries. The vanadium nitride / amorphous carbon is adopted to perform composite coating modification on the lithium manganese iron phosphate material, so that the composite positive electrode material is more stable in structure. The use of vanadium nitride reduces the coating amount of carbon, and avoids the problems of coating layer thickening caused by high carbon content and Li < + > diffusion hindering caused by reduction of tap density of active substances. Vanadium nitride not only has good conductivity, but also has good Li < + > conductivity transmission performance, Li < + > de-intercalation can be rapidly achieved, the conductivity of the material is improved, meanwhile, a Li < + > diffusion channel on the surface of the positive electrode material is further dredged and increased, and the capacity loss of the modified material is reduced.

The invention provides a lithium iron manganese phosphate positive electrode material and a preparation method and application thereof, the lithium iron manganese phosphate positive electrode material comprises a doped type iron manganese phosphate inner core and a coating layer coating the surface of the doped type iron manganese phosphate inner core, and the coating layer is a lithium-containing carbon layer; the doped iron manganese phosphate inner core comprises doped ions, and in the particles of the doped iron manganese phosphate inner core from inside to outside, the content gradient of manganese ions and iron ions is reduced, and the content gradient of the doped ions is increased. According to the lithium manganese iron phosphate positive electrode material with the structure, a series of problems caused by poor phase structure stability, poor conductivity and Jahn-Teller effect and manganese dissolution of the material in the lithium manganese iron phosphate positive electrode material can be effectively improved; further, the conductivity of the lithium manganese iron phosphate positive electrode material and the comprehensive performance of gram volume, cycling stability and the like when the lithium manganese iron phosphate positive electrode material is applied to a battery are improved.

The invention relates to a comprehensive recovery method of lithium iron phosphate black powder, and belongs to the technical field of lithium iron phosphate battery recovery. The technical problem to be solved by the invention is to provide the lithium iron phosphate black powder comprehensive recovery method. The method comprises the following steps: mixing lithium iron phosphate black powder with acid, and adding an oxidizing agent for reaction to obtain iron phosphorus slag; the iron phosphorus slag is subjected to acid pickling and then acid leaching to obtain secondary acid leaching liquid; and dropwise adding the secondary acid leaching solution into bottom water to generate a precipitate, and adjusting the molar ratio of phosphorus to iron or the molar ratio of phosphorus to (iron and manganese) to obtain battery-grade iron phosphate or ferromanganese phosphate. According to the method, alkali is not adopted as a precipitator, iron powder is not introduced, iron phosphate or the ferromanganese phosphate precursor is obtained through a normal-pressure one-step method, the problems that mixing is not uniform when the ferromanganese phosphate precursor is prepared through a solid-phase method, and alkali is needed as the precipitator or organic matter is introduced in a liquid-phase method are solved, use of alkaline chemical reagents and generation treatment of by-products are reduced, and the method is suitable for industrial production. The method has the advantages of simple process, low equipment use requirements, battery grade and high purity of the prepared product, improves the utilization rate of the phosphorus source, and has high yield.

The invention provides a lithium ion battery and electric equipment, the lithium ion battery comprises a positive pole piece and an electrolyte, active substances in the positive pole piece comprise a phosphate lithium positive pole material and nickel cobalt manganese lithium oxide, and the electrolyte comprises a positive pole film-forming agent, a negative pole film-forming agent and a lithium salt, the lithium salt comprises lithium hexafluorophosphate and lithium bis (fluorosulfonyl) imide, the lithium ion battery meets the following formula: # imgabs0 #, NL is the mass ratio of the lithium nickel cobalt manganese oxide to the lithium phosphate positive electrode material, Salt is the sum of the molar concentrations of the lithium hexafluorophosphate and the lithium bis (fluorosulfonyl) imide in the electrolyte by taking mol / L as the unit, and the sum of the molar concentrations of the lithium hexafluorophosphate and the lithium bis (fluorosulfonyl) imide in the electrolyte is the sum of the molar concentrations of the lithium hexafluorophosphate and the lithium bis (fluorosulfonyl) imide. Add is the mass ratio of the positive electrode film-forming agent to the negative electrode film-forming agent. When the ternary material is doped in the lithium manganese iron phosphate or the lithium iron phosphate, the proportion of the positive and negative electrode film-forming agents and the proportion of the heat-resistant high-lithium salt can be adjusted according to the mixing proportion of the lithium manganese iron phosphate and the lithium iron phosphate, so that the cycle performance of the battery is improved.

The invention discloses a lithium manganese iron phosphate composite material, a preparation method thereof and a lithium ion battery containing the lithium manganese iron phosphate composite material. The preparation method comprises the following steps: grinding, sintering and crushing a mixture of the lithium iron manganese phosphate, the lithium iron phosphate precursor and water to form the lithium iron manganese phosphate composite material, the sintering temperature is 650 DEG C to 750 DEG C; wherein the lithium manganese iron phosphate forms an inner core of the lithium manganese iron phosphate composite material, and the average particle size of the inner core is 600 nm to 1200 nm; the lithium iron phosphate precursor forms a lithium iron phosphate coating layer and a carbon coating layer of the lithium manganese iron phosphate composite material. The lithium manganese iron phosphate composite material provided by the invention can effectively improve the ginger-Taylor effect of the lithium manganese iron phosphate and improve the electrochemical cycle performance of the material at the same time.

The invention provides a lithium manganese iron phosphate battery. The battery comprises a positive pole piece, a negative pole piece and a non-aqueous electrolyte, the positive pole piece comprises a positive active material and a positive active coating arranged on at least one surface of the positive active material; the positive electrode active material comprises lithium manganese iron phosphate LiMnxFe1-xPO4 coated with a carbon coating layer, and x is more than or equal to 0.5 and less than or equal to 0.8; the negative pole piece comprises a negative active material and a negative active coating arranged on at least one surface of the negative active material; the battery satisfies the following relational expressions: 4.5 < = (a / 20 + d) / (b + c) < = 12.8; a is a coated diaphragm resistor of the positive pole piece; b is the compaction density of the positive pole piece; c is the mass percentage content of vinylene carbonate in the positive electrode slurry; and d is the mass percentage content of the lithium bis (fluorosulfonyl) imide in the non-aqueous electrolyte. By optimizing the composition of the lithium ion battery, the low-temperature discharge performance of the battery is improved, and meanwhile, the high-temperature cycle performance is considered.

The invention provides an anion-cation co-doped modified lithium manganese phosphate positive electrode material and a preparation method thereof, the lithium manganese phosphate positive electrode material comprises anion-cation doped lithium manganese phosphate and a carbon layer, the carbon layer is coated on the surface of the anion-cation doped lithium manganese phosphate, the chemical general formula is LiMn < 0.6 > Fe < 0.4-x > M < x > PO < 4-y > Fy, 0.001 < = x < = 0.03, 0.01 < = y < = 0.5, and 0 < = y < = 0.5. M is a cation, and Y is a fluorine ion. According to the preparation method, carbon layer coating and anion and cation co-doping modification of the lithium manganese iron phosphate positive electrode material are simultaneously realized through a one-step hydrothermal method, and the prepared lithium manganese iron phosphate positive electrode material is in an irregular spherical shape, relatively smooth in particle surface, and relatively high in large and small particle grading and compaction; after a performance test, compared with an electrode material which is not doped with anions and cations, the material disclosed by the invention has the advantages that the stability and the discharge capacity of the material are remarkably improved, and the electrochemical performance of the lithium manganese iron phosphate positive electrode material is effectively improved.

Provided are a lithium manganese iron phosphate material and a preparation method therefor, a positive electrode sheet, and a lithium ion battery. The lithium manganese iron phosphate material comprises a core and a coating layer that coats the surface of the core. The chemical formula of the material of the core is LiaMnbFecMdPO4, wherein M comprises at least one element among magnesium, calcium, strontium, cobalt, titanium, zirconium, molybdenum, vanadium, niobium, nickel, scandium, chromium, copper, zinc, beryllium, lanthanum and aluminum. The coating layer is formed by sintering a carbon source, and the carbon coating layer comprises graphitized carbon.

The invention provides a positive active material and a preparation method thereof, a positive plate and a battery, and belongs to the technical field of batteries, the positive active material comprises a ternary material and lithium manganese iron phosphate; wherein the mass of the lithium manganese iron phosphate is A, the total mass of the ternary material and the lithium manganese iron phosphate is B, and A / B is more than 0 and less than 50%; the lithium manganese iron phosphate is of a hollow spherical structure, and the median particle size of the lithium manganese iron phosphate is 0.5-3 microns. According to the positive electrode active material provided by the embodiment of the invention, the cost of the positive electrode active material can be reduced, relatively high rate capability, cycle performance and energy density are considered, and the comprehensive electrochemical performance is improved.

The invention relates to the technical field of electrochemistry, and particularly discloses a positive pole piece, an electrochemical device comprising the positive pole piece and an electric device. The positive pole piece comprises a first active material with a particle size of 4-20 [mu] m and a second active material with a particle size of 200-600 nm, the first active material comprises lithium manganese iron phosphate with the manganese content of m%, the second active material comprises lithium manganese iron phosphate and / or lithium iron phosphate with the manganese content of n%, and m and n meet the condition that m-n is larger than or equal to 15 and smaller than or equal to 85. According to the invention, by controlling the particle size distribution in the positive electrode active material and the manganese content relationship, the electrochemical device containing the positive electrode plate has excellent fast charging performance and energy density.

The invention discloses a modified carbon-coated sodium manganese ferric phosphate pyrophosphate / sodium ferric phosphate pyrophosphate positive electrode material as well as a preparation method and application thereof, and relates to the technical field of new energy materials. The preparation method comprises the following steps: preparing MnFe-MOF from a manganese source, a first iron source and a first organic ligand under a hydrothermal reaction; a second iron source, the MnFe-MOF and a second organic ligand are subjected to a hydrothermal reaction, and MnFe-MOF / Fe-MOF is obtained; uniformly mixing with a sodium source and a phosphorus source, and sintering to obtain a positive electrode material; and carrying out high-temperature gas-phase etching treatment to obtain the fluorine-doped carbon-coated modified sodium manganese ferric phosphate pyrophosphate / sodium ferric phosphate pyrophosphate positive electrode material. The material disclosed by the invention has a coating modified structure, so that an interface side reaction caused by direct contact between sodium ferromanganese phosphate and an electrolyte can be effectively avoided, a manganese dissolution phenomenon is reduced, and the structural stability of the material is improved; and meanwhile, the material has high conductivity, excellent structural stability, excellent long cycle life and excellent rate capability.

The invention relates to a positive electrode active material, a preparation method, a battery monomer, a battery device and a power utilization device. The positive electrode active material comprises an inner core and a first coating layer arranged on at least part of the surface of the inner core, the inner core comprises lithium manganese iron phosphate; the first coating layer comprises lithium iron phosphate; an X-ray diffraction pattern of the positive electrode active material comprises a diffraction peak of a (020) crystal face and a diffraction peak of a (200) crystal face, the diffraction peak of the (020) crystal face and the diffraction peak of the (200) crystal face meet the condition that I (020) / I (200) is larger than or equal to 3.5, I (020) represents the intensity of the diffraction peak of the (020) crystal face, and I (200) represents the intensity of the diffraction peak of the (200) crystal face. The positive electrode active material provided by the embodiment of the invention has good lithium ion diffusion performance, and when the positive electrode active material is used for a battery, the battery can have good rate capability.

The invention belongs to the technical field of new energy materials, and particularly relates to a low-sulfur metal cation doped ammonium manganese ferric phosphate precursor, carbon-coated modified sodium manganese ferric pyrophosphate and a preparation method and application thereof. According to the invention, the low-sulfur metal cation doped ammonium manganese ferric phosphate precursor is successfully prepared. A proper amount of phosphoric acid source is added into the prepared metal cation doped ammonium manganese ferric phosphate precursor for treatment, so that the sulfur content of the precursor is remarkably reduced, and the molar ratio of manganese, iron, doped elements and phosphorus elements is regulated and controlled to be slightly smaller than 1. The atomic-scale distribution of elements in the precursor is realized, the tap density is also improved, and the subsequent preparation of a high-performance carbon-coated modified manganese ferric sodium phosphate pyrophosphate material is facilitated. The sodium ion battery constructed based on the material has excellent charge-discharge capacity, capacity retention ratio and cycling stability. In addition, the preparation method of the precursor is simple and convenient to operate and easy to control, and has the advantage of wide application.

The invention discloses a gradient composite coated modified lithium manganese iron phosphate positive electrode material and a preparation method thereof, and belongs to the technical field of positive electrode materials. An LMFP precursor is pretreated through a citric acid-ethanol mixed solution, an active crystal face is exposed, and then a three-dimensional gradient coating structure of a polydopamine (PDA) chemical bonding layer, an MXene nanosheet middle layer and a polyaniline (PANI) conductive outer layer is sequentially constructed on the surface of the material, so that the electronic conductivity of the lithium manganese iron phosphate positive electrode material is increased to 10 <-3 > S / cm magnitude, and the performance of the lithium manganese iron phosphate positive electrode material is improved. The capacity retention ratio (1C) of 500 cycles is larger than 90%, the coating layer is not prone to falling off, and meanwhile dissolution of manganese ions is effectively inhibited.

The invention provides a positive pole piece. The positive pole piece comprises a positive current collector, a first material layer arranged on at least one surface of the positive current collector, and a second material layer arranged on the surface, far away from the positive current collector, of the first material layer, the first material layer comprises an active material A and an active material B; the second material layer comprises an active material C; the active material A is selected from lithium iron phosphate and / or lithium manganese iron phosphate; the active material B is selected from one or more of nickel cobalt lithium manganate, lithium cobalt oxide, lithium manganate and nickel lithium manganate; the active material C is selected from one or more of nickel cobalt lithium manganate, lithium cobalt oxide, lithium manganate and nickel lithium manganate; by using the positive pole piece provided by the invention, the interface impedance of the pole piece can be reduced, the problem that the expansion rates of different areas of the pole piece are different is solved, and the cycle life of the battery is prolonged.

The invention discloses a method for regenerating waste lithium iron phosphate into a lithium manganese iron phosphate positive electrode material under assistance of element doping. According to the method, the waste lithium iron phosphate is successfully regenerated into the lithium manganese iron phosphate material with excellent performance through solid-phase sintering and element doping. Compared with a traditional repairing and regenerating method, the method has the advantages that upgrading and regenerating of the waste lithium iron phosphate are realized, and the market competitiveness of regenerated products is improved. Compared with other methods, the method does not need an acid leaching step, and the recovery process is simpler and more environment-friendly. And an element doping modification means is introduced, so that the performance of the regenerated lithium manganese iron phosphate material is further improved. The invention aims to provide a green, efficient and high-valued method for upgrading and regenerating the waste lithium iron phosphate positive electrode material into the lithium iron manganese phosphate positive electrode material with industrial application prospects.

The invention belongs to the technical field of lithium batteries, and discloses a fluorine-doped lithium iron manganese phosphate positive electrode material and a preparation method thereof.The preparation method comprises the steps that hydrofluoric acid, manganese sulfate monohydrate, ferrous sulfate heptahydrate, lithium hydroxide monohydrate and phosphoric acid serve as raw materials, and a fluorine-doped lithium iron manganese phosphate precursor is prepared through a microwave-hydrothermal synthesis method; and forming a coating layer on the surface of the precursor by using SnO2-doped chitosan gel, and calcining to obtain the fluorine-doped lithium iron manganese phosphate positive electrode material. The positive electrode material comprises fluorine-doped lithium manganese iron phosphate particles and a SnO2 / C coating layer, doping of fluorine promotes diffusion of lithium ions of the positive electrode material, the structure of the material is more stable, SnO2 is doped in chitosan serving as a carbon source, the conductivity of the positive electrode material is improved, and on the basis of the synergistic effect of the fluorine element and metal ions of the coating layer, the conductivity of the positive electrode material is improved. A uniform and tightly combined carbon coating layer is formed on the surface of the material. The fluorine-doped lithium iron manganese phosphate positive electrode material prepared by the preparation method has excellent cycle performance and rate capability.

The invention discloses a method for preparing a manganese iron phosphate precursor by recycling waste lithium manganese iron phosphate, and belongs to the technical field of lithium ion batteries. The invention provides a method for preparing a manganese iron phosphate precursor by recycling waste lithium manganese iron phosphate, which comprises the following steps: by taking waste lithium manganese iron phosphate battery powder as a raw material, carrying out acid dissolution and filtration to remove graphite and part of impurities; adjusting the pH value of the filtrate to obtain a lithium-ion-rich solution and a ferromanganese precipitate, and adding sodium carbonate into the lithium-ion-rich solution for concentration and crystallization to obtain battery-grade lithium carbonate; carrying out acid dissolution on the ferromanganese precipitate, removing copper and aluminum impurities in the solution, adjusting the ratio of ferromanganese to phosphorus, and mixing with liquid caustic soda in a nitrogen atmosphere to obtain a ferromanganese phosphate precursor; according to the method, the problems of incomplete recovery and insufficient impurity removal of the manganese iron phosphate lithium battery are solved, the battery-grade lithium carbonate and the manganese iron phosphate precursor are prepared during recovery, the value of the recovered product is improved, and the production requirement of the lithium ion battery is met.

The invention provides a modified lithium iron manganese phosphate positive electrode material and a preparation method thereof, a positive plate and a lithium ion battery. The modified lithium manganese iron phosphate positive electrode material comprises transition metal element-doped lithium manganese iron phosphate and a silicon hydroxyl-containing carbon coating layer, wherein the surface of the transition metal element-doped lithium manganese iron phosphate is coated with the silicon hydroxyl-containing carbon coating layer. And the transition metal element replaces the position of an iron element in the lithium manganese iron phosphate, so that the ion diffusion coefficient of the lithium manganese iron phosphate and the compaction density of the modified lithium manganese iron phosphate positive electrode material can be improved. The existence of the silicon hydroxyl-containing carbon coating layer is beneficial for improving the electronic conductivity and the structural stability of the lithium manganese iron phosphate positive electrode material, so that the manganese dissolution rate of the lithium manganese iron phosphate positive electrode material in the high-temperature cycle process of the battery is reduced. Therefore, the modified lithium manganese iron phosphate positive electrode material disclosed by the invention has relatively high ion diffusion coefficient, electronic conductivity, compaction density, rate capability, energy density and cycling stability.

The invention discloses a preparation method of a lithium manganese iron phosphate precursor, which comprises the following steps: mixing a manganese source and an iron source according to the molar ratio of Mn < 2 + > to Fe < 2 + > of (1.5-4): 1, adding water to prepare a manganese and iron ion mixed solution with the total concentration of Mn < 2 + > and Fe < 2 + > of 1-2mol / L, then dropwise adding the manganese and iron ion mixed solution and a precipitator into a base solution at the same time to obtain a reaction mixed solution, carrying out heat preservation and aging on the reaction mixed solution, then carrying out solid-liquid separation to obtain a filter cake, sequentially washing, drying and calcining the filter cake to obtain ferromanganese oxide, and then preparing a lithium iron manganese phosphate material by taking the obtained ferromanganese oxide as a lithium iron manganese phosphate precursor; according to the method, the soluble manganese source and the iron source are adopted for coprecipitation, and the manganese-iron ratio, the reaction rate, the pH and the reaction temperature are controlled, so that stable manganese-iron oxide with uniformly mixed manganese and iron is prepared, the stability of the further prepared lithium manganese-iron phosphate material is higher, and the electrochemical performance of the lithium manganese-iron phosphate material is effectively improved.

The invention provides a lithium manganese iron phosphate material as well as a preparation method and application thereof. The lithium manganese iron phosphate material sequentially comprises a lithium manganese iron phosphate matrix inner core, a first coating layer and a second coating layer from inside to outside, the first coating layer comprises a carbon material, the second coating layer comprises a composite material, and the composite material comprises carbon nitride and a conductive polymer. Through doping and coating of the carbon material in the first coating layer and synergistic cooperation of the conductive polymer and the carbon nitride in the second coating layer, the conductivity of the lithium manganese iron phosphate material is improved, and the cycling stability, the capacity and the rate capability of the lithium manganese iron phosphate material are improved.

The invention relates to a lithium manganese iron phosphate positive electrode material and a preparation method thereof, and an electrochemical device, the preparation method of the lithium manganese iron phosphate positive electrode material comprises the following steps: mixing a manganese source, an iron source, a first phosphorus source, a lithium source, a first carbon source and a magnesium source, and carrying out primary grinding to obtain a first slurry; carrying out primary sintering on the first slurry to obtain a lithium manganese iron phosphate precursor; mixing the lithium manganese iron phosphate precursor, a second phosphorus source, a second carbon source and a niobium source, and performing secondary grinding to obtain second slurry; the second slurry is subjected to secondary sintering, the lithium manganese iron phosphate positive electrode material is obtained, the magnesium element exists in a bulk phase of the lithium manganese iron phosphate positive electrode material in a doping mode, and the niobium element exists in a coating layer of the lithium manganese iron phosphate positive electrode material in a coating mode. According to the preparation method, magnesium and niobium are co-doped and coated, and through the synergistic effect of magnesium and niobium, the electron and ion conductivity, the specific capacity and the cycle performance of the lithium manganese iron phosphate positive electrode material are jointly improved.

The invention provides composite positive electrode slurry, a positive electrode and a preparation method thereof, and relates to the field of lithium batteries. The solid content of the slurry is 40-60wt%, and the slurry comprises the following raw materials in parts by weight: 1-5 parts of a binder, 2-4 parts of a conductive agent, 100 parts of a blended positive electrode active material and the balance of a solvent; the binder comprises hydrogenated butadiene-acrylonitrile rubber emulsion, and the mass fraction of the hydrogenated butadiene-acrylonitrile rubber emulsion combined with acrylonitrile is 10-50%; the blending type positive electrode active material comprises the following components in percentage by mass: 10-90% of lithium manganese iron phosphate and 10-90% of high-nickel ternary layered oxide. The positive electrode comprises an aluminum foil current collector and composite positive electrode slurry, and the composite positive electrode slurry is coated on the surface of the aluminum foil current collector. According to the present invention, the positive electrode of the positive electrode slurry composed of the HNBR binder, the conductive agent and the solvent is combined with the blending type positive electrode active material composed of the lithium manganese iron phosphate and the high-nickel ternary layered oxide, and the positive electrode is applied to the lithium ion secondary battery, and the battery has high energy density and high-voltage cycle stability.