275 results about "Iron pyrophosphate" patented technology

The invention provides a doped and coated composite sodium battery positive electrode material as well as a preparation method and application thereof. The doped and coated composite sodium battery positive electrode material comprises an inner core and a coating layer on the surface of the inner core, the chemical general formula of the inner core is NabNixFeyMnzMjO2, x + y + z + j = 1, 0.2 < = x < = 0.6, 0.2 < = y < = 0.5, 0.2 < = z < = 0.5, 0 < j < = 0.2, 0.8 < = b < = 1.2; the coating layer comprises a ferric sodium pyrophosphate material; raw materials for preparing the doped and coated composite sodium battery positive electrode material comprise an inner core, a phosphoric acid ferric sodium pyrophosphate precursor material and a sodium source. The metal elements are doped in the inner core, and the surface is coated with the ferric sodium pyrophosphate material with relatively high stability, so that the inner core can be prevented from being in direct contact with an electrolyte, and the cycle performance of the sodium battery positive electrode material is improved.

The invention relates to a preparation method and application of high-compaction-density composite sodium ferric phosphate. The preparation method comprises the following steps: weighing a sodium source, an iron source and a phosphorus source according to a stoichiometric ratio of [xNa + (a-x) A]: [yFe + (b-y) B]: P = a: b: (c + 2), mixing and dispersing the iron source, the sodium source, the phosphorus source and a chelating agent into pure water, reacting for a period of time at a certain temperature, transferring into a sand mill for grinding, adding a dispersing agent, cane sugar, the dopants A and B, and obtaining slurry F after grinding; and carrying out spray drying on the slurry F to obtain powder K. The powder K is transferred to a tubular furnace, and the oxygen content is 1t under the N2 protective atmosphere; and calcining at the temperature of 450-600 DEG C under the pressure of 50 ppm, and then carrying out air jet pulverization to obtain sodium ferric pyrophosphate positive electrode material powder with high compaction density and a molecular formula of (NaxAa-x) (FeyBb-y) (PO4) cP2O7. When the product is used, the compaction density is high, the dynamic performance of the material is enhanced, the thermal stability and chemical stability of the material are improved, and the electrochemical performance is good.

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 provides a sodium ferric phosphate pyrophosphate positive electrode material and a preparation method thereof, and a sodium ion battery, the molecular formula of the sodium ferric phosphate pyrophosphate positive electrode material is Na4Fe3 (PO4) 2P2O7 / D1D2, D1 is a first conductive agent, the first conductive agent is a metal oxide, the second conductive agent is phosphate, D2 is a second conductive agent, and D1D2 is a metal oxide. And the molar ratio of the sodium element to the iron element to the phosphorus element to the first conductive agent to the second conductive agent in the ferric sodium phosphate pyrophosphate positive electrode material is (4.0 to 4.1) to (2.8 to 3.0) to (3.0 to 3.1) to (0.001 to 0.0.005) to (0.05 to 0.10). According to the embodiment of the invention, the first conductive agent increases the lattice volume, so that conduction channels of Na < + > and doped ions are increased, and higher electronic conductivity is achieved; and the phosphate of the second conductive agent forms coating points on the surface layers of the sodium iron phosphate particles, so that the interfacial effect in the electrochemical reaction process of the sodium iron phosphate pyrophosphate positive electrode material is slowed down, the electrochemical performance of the sodium iron phosphate pyrophosphate positive electrode material is further improved, and the electrochemical specific capacity is improved.

The invention discloses a ferric sodium pyrophosphate positive electrode material, a preparation method thereof and a battery, and relates to the technical field of batteries. Pre-sintering is performed; sanding and spray drying; and high-temperature sintering. Wherein the pH value of the reaction is controlled by using a Tris-HCl buffer solution in the hydrothermal reaction, so that the precursor is uniformly crystallized and has high crystallinity, and low-temperature segmented presintering is adopted later, so that the compaction density of the material can be controlled, and the related electrical properties of the material are relatively good. In the preparation process, a carbon source and a doping element are supplemented twice, so that carbon coating is uniform in the sintering process, the compaction density of the NFPP positive electrode material is further improved, the properties such as theoretical specific capacity of the positive electrode material are better through doping and carbon coating modification, and the high-compaction and high-capacity ferric sodium pyrophosphate positive electrode material is obtained.

The invention belongs to the technical field of preparation of electrode materials, and particularly relates to a high-tap-density spherical ferric sodium pyrophosphate electrode material and a preparation method thereof. According to the preparation method, a uniform precursor is prepared by utilizing solution gel, and a strategy of combining spray drying with secondary sintering is adopted, so that uniform carbon coating and doping modification of ferric sodium pyrophosphate can be successfully realized, and the strategy provides an important experimental basis for an industrialization process of a sodium ion battery. And the method has great potential of large-scale preparation.

The invention provides a sodium ferric phosphate pyrophosphate composite material, a preparation method and application thereof, and a sodium ion battery, and relates to the technical field of positive electrode materials, the preparation method comprises the following steps: carrying out solid phase mixing on carbon-coated sodium ferric phosphate pyrophosphate and an organic carbon source, and then carrying out sintering treatment to obtain the sodium ferric phosphate pyrophosphate composite material; the temperature of the sintering treatment is 400-580 DEG C. The technical problems that in the prior art, according to a carbon source coating method, carbon source coating is not uniform, the porosity between materials is difficult to effectively reduce, the compaction performance of the materials cannot be remarkably improved, and the crystal structure of the materials is prone to change are solved, and the purposes of reducing the powder resistance of the materials and improving the compaction performance of the materials are achieved. The carbon coating uniformity is effectively improved, the porosity of the material is effectively reduced, the compaction performance of the material is remarkably improved, the water absorption of the material is reduced, and the crystal structure of the material is improved, so that the technical effect of comprehensively improving the performance of the material is achieved.

A positive electrode material, and a preparation method therefor and the use thereof. The positive electrode material has a core-shell structure, wherein a core part comprises a carbon-coated Cu2+-doped iron-based phosphate sodium-ion material, and a shell layer is CuO. The iron-based phosphate sodium-ion material is selected from ferric sodium pyrophosphate, ferric sodium phosphate or ferric sodium phosphate pyrophosphate. The preparation method for the positive electrode material comprises: mixing the carbon-coated iron-based phosphate sodium-ion material, a copper source and a first solvent, and then subjecting the mixture to first drying and first calcination.

The invention relates to a preparation method of a nickel ion doped modified ferric sodium pyrophosphate positive electrode material, and belongs to the technical field of sodium ion battery positive electrode materials. The nickel ion doped modified ferric sodium pyrophosphate positive electrode material is prepared by adopting an integrated process system of liquid phase uniform mixing, spray granulation and precise segmented calcination. According to the process system, atomic-scale uniform doping of nickel ions and a specific microstructure of a precursor are realized through spray drying, and a plurality of inherent key technical problems of low electronic conductivity, low ion diffusion rate, impurity phase generation and the like of an NFPP material are solved together through a synergistic effect with a subsequent calcining process; furthermore, the discharge capacity of the ferric sodium phosphate pyrophosphate composite material at high rate is improved, so that the battery has relatively high cycling stability.

The invention discloses a method for synthesizing ferric phosphate pyrophosphate and preparing a sodium ferric phosphate pyrophosphate positive electrode material. The method comprises the following steps: S1, preparing a raw material solution; s2, adding the ferric salt solution, the phosphate radical solution and the pyrophosphate radical solution into the reaction base solution, controlling the pH value, and carrying out coprecipitation reaction; s3, filtering and washing, adding water, and pulping again; s4, heating and crystallizing; s5, filtering and drying; s6, sintering to obtain ferric pyrophosphate Fe6 (PO4) 2 (P2O7) 3; s7, adding ferric pyrophosphate, a sodium source and a carbon source into water, pulping, and sanding; s8, spray drying; and S9, sintering is carried out, such that Na4Fe3 (PO4) 2 (P2O7) / C is obtained. According to the method, a precursor Fe6 (PO4) 2 (P2O7) 3 is synthesized firstly, long-range ordered mixing of Fe and P elements on the atomic scale is achieved, the morphology and particle size of the precursor are controllable, the problem of generation of inactive impure-phase NaFePO4 in the synthesis process of ferric sodium pyrophosphate can be effectively solved, the raw material utilization rate is high, and the synthesized positive electrode material is large in tap density and compaction density and excellent in electrochemical performance.

The invention discloses ferric sodium pyrophosphate, a preparation method, a positive pole piece and a sodium ion battery, and belongs to the technical field of secondary batteries. The preparation method comprises the following steps: S1, mixing a phosphorus element, an iron element, a sodium element and a carbon element in a phosphorus source, an iron source, a sodium source and a carbon source according to a molar ratio of (1-5): (1-3): (1-5): (0.1-0.5); adding a dispersing agent and an organic solvent; s2, carrying out ball milling on the mixture obtained in the step S1; s3, carrying out vacuum drying on the mixture subjected to ball milling; and S4, sintering the material treated in the step S3 to obtain the ferric sodium pyrophosphate. The preparation method of the ferric sodium pyrophosphate comprises the following steps: uniformly mixing a phosphorus source, an iron source, a sodium source and a carbon source through ball milling, and sintering to obtain the ferric sodium pyrophosphate. The ferric sodium pyrophosphate is prepared by adopting a solid phase method, the preparation steps are simple, and large-scale production is easier.

The invention discloses an in-situ formed sodium ferric phosphate coated sodium ion positive electrode layered oxide material, a sodium ion battery positive electrode and a sodium ion battery, the method comprises the following steps: preparing a sodium ion positive electrode layered oxide material to be coated, and measuring the residual alkali content of the sodium ion positive electrode layered oxide material; the method comprises the following steps: mixing ferric pyrophosphate with the content equal to that of residual alkali with a raw material for preparing a sodium ion positive electrode layered oxide to form a premix, sintering and slowly cooling, and forming a sodium ferric phosphate coating layer on the sodium ion positive electrode layered oxide material in situ by a residual sodium substance separated out from the surface of the sodium ion positive electrode layered oxide material and ferric pyrophosphate to prepare the sodium ion positive electrode layered oxide material. The sodium iron phosphate in-situ coated sodium ion positive electrode layered oxide material is prepared. According to the sodium ion positive electrode layered oxide material, a dense, uniform and thickness-controllable sodium ferric phosphate coating layer is formed in situ, so that residual alkali on the surface of the material can be effectively reduced, the pH value is reduced, meanwhile, the cell processing performance of the material is improved, the electrolyte corrosion resistance of the surface of the material is effectively enhanced, and the service life of the material is prolonged. The subsequent complicated process flow for reducing the residual alkali is reduced, the capacity of the sodium-ion battery positive electrode material is improved, and the production cost of the sodium-ion battery positive electrode material is reduced.

The invention provides sodium vanadium ferric phosphate pyrophosphate as well as a preparation method and application thereof. The sodium vanadium ferric phosphate pyrophosphate comprises an inner core and a coating layer coating at least part of the surface of the inner core; the molecular formula of the inner core is as shown in formula 1; na (10 + 6x) / 3 Fe (7-3x) / 3 V2x (PO4) (6x + 4) / 3 (P2O7) Formula 1; wherein x is greater than or equal to 0.25; the coating layer comprises a carbon element, a boron element and a nitrogen element. The sodium ferric vanadium phosphate pyrophosphate has excellent reversible capacity and conductivity.

The invention discloses a sodium ferric pyrophosphate material with a sodium storage dominant crystal face regulated and controlled by cation doping as well as a preparation method and application of the sodium ferric pyrophosphate material. The chemical formula of the prepared sodium ferric pyrophosphate material with the regulated and controlled crystal structure is Na < 4 > Fe < 2.97 > M < 0.03 > (PO4) < 2 > P < 2 > O < 7 >. Wherein M = Sr, or Sr and a second doping element, and the second doping element is selected from one of Cd, Bi, Mo, Ni and Al. The material is prepared by adopting a sol-gel method, an iron source, a chelating agent, a sodium source, a phosphorus source and doping elements are dissolved in deionized water, and stirring is performed until a gel state is formed; and drying and calcining twice to obtain a final product. The sodium ferric pyrophosphate electrode material prepared by the invention has more sodium storage dominant crystal faces, shows good electrochemical performance, has the advantages of simple preparation process, easily available raw materials and low cost, has remarkable industrial application value, and is easy for large-scale production.

The invention provides a ferric sodium pyrophosphate positive electrode material as well as a preparation method and application thereof. The D50 of the sodium ferric phosphate pyrophosphate positive electrode material is 2-10 [mu] m, and the maximum particle size of the sodium ferric phosphate pyrophosphate positive electrode material is less than 25 [mu] m; the internal porosity of the ferric sodium pyrophosphate positive electrode material is less than 14%, and the compaction density is greater than 2.17 g / cm < 3 >. According to the invention, the compaction density of the ferric sodium pyrophosphate positive electrode material can be improved.

The invention belongs to the field of battery materials, and discloses a ferric sodium pyrophosphate material as well as a preparation method and application thereof. The preparation method of the ferric sodium pyrophosphate comprises the following steps: step 1, mixing a phosphorus source, an iron source, a sodium source, a biomass carbon source and an alcohol additive, and uniformly stirring to obtain a mixed material A; step 2, carrying out hydrothermal reaction on the mixed material A, and then centrifuging and drying to obtain an intermediate product B; and 3, roasting the intermediate product C in a protective atmosphere to obtain the carbon-coated ferric sodium pyrophosphate. A three-dimensional conductive network is formed after the biomass carbon source and the NFPP are compounded, the interface resistance is reduced, the charge transfer efficiency is improved, and after the biomass carbon source is carbonized, biomass carbon with mechanical supporting and buffering effects can relieve volume expansion of the NFPP in the charge-discharge or reaction process and inhibit material pulverization, so that the cycling stability is improved.

The invention discloses a preparation method of a carbon-coated single-crystal sodium ferric pyrophosphate positive electrode material, which is specifically implemented according to the following steps: step 1, dissolving sodium salt, ferric salt and phosphate in deionized water in proportion, then adding a carbon source into the solution, and uniformly stirring to obtain a mixed solution; step 2, fully drying the mixed solution obtained in the step 1 to obtain precursor powder; and 3, carrying out heat treatment on the precursor powder in a protective atmosphere, and cooling to obtain the carbon-coated single-crystal sodium ferric pyrophosphate positive electrode material. The invention also discloses a coating prepared by the method, a single-crystal structure is combined with uniform carbon coating, grain boundary defects are eliminated, conductivity is improved, high specific capacity and long cycle life are realized, single-crystal growth and carbon layer in-situ coating are synchronously realized by a synthesis process, and structural integrity and efficient conductive network construction can be ensured.

The invention provides a ferric sodium pyrophosphate positive electrode material, a preparation method thereof and a sodium ion battery, and relates to the field of sodium ion batteries. The ferric sodium phosphate pyrophosphate positive electrode material comprises ferric sodium phosphate pyrophosphate and a coating layer located on the outer surface of the ferric sodium phosphate pyrophosphate, wherein the coating layer comprises conductive carbon and SiO2. The SiO2 in the coating layer can separate the ferric sodium pyrophosphate to achieve the effect of refining the size of the material, and the conductive carbon in the coating layer can achieve the effects of enhancing the conductivity and improving the rate capability. SiO2 and conductive carbon are matched with each other, so that the specific capacity and the rate capability of the positive electrode material can be improved.

The invention provides a sodium ferric phosphate pyrophosphate-based composite material as well as a preparation method and application thereof, and relates to the technical field of sodium ion battery electrode materials. The composite material is of a core-shell structure and sequentially comprises a base material, a heterogeneous interface layer and a coating layer from inside to outside, the chemical formula of the base material is Na4Fex( PO4) 2P2O7, the heterogeneous interface layer is iron-based phosphide nanoparticles distributed on the surface of the base material, and the coating layer is a carbon layer; the iron-based phosphide is prepared from at least one of FeP and Fe2P; 3 < = x < = 4; iron-based phosphide nanoparticles are generated on the surface of the ferric sodium phosphate pyrophosphate material through in-situ reduction, a tightly-combined heterogeneous interface network is formed, the electron and ion transmission performance of the material is remarkably improved, and the rate performance is improved; the preparation method is simple and easy to implement on a large scale.

The invention provides a sodium ferric pyrophosphate positive electrode diaphragm as well as a dry preparation method and application thereof. The dry preparation method comprises the following steps: dividing the conductive agent into a conductive agent A and a conductive agent B; mixing the conductive agent A with the ferric sodium pyrophosphate positive electrode material, and performing first stirring to obtain a first material; mixing a conductive agent B with sodium trifluoromethanesulfonate, and performing second stirring to obtain a second material; mixing the first material with the second material, and performing third stirring to obtain a third material; mixing the third material with a binder, and performing fourth stirring to obtain a fourth material; and the fourth material is subjected to fibrosis treatment and rolling in sequence to obtain the sodium ferric pyrophosphate positive electrode diaphragm. By designing the contents and proportions of the sodium ferric pyrophosphate positive electrode material, the conductive agent, the binder and the sodium trifluoromethanesulfonate and controlling the mixing method, sequence and steps, the sodium ferric pyrophosphate positive electrode diaphragm with high compaction density, high conductivity and excellent ion transmission channels is prepared.

The invention provides a method for preparing a high-stability fast-charging ferric sodium pyrophosphate / rGO composite positive electrode material with a heterogeneous symbiotic structure through one-step sintering. According to the method, a raw material mechanical mixing and one-step calcination treatment process is adopted, phosphate is used as a raw material, pyrophosphate raw materials are not needed to be added, presintering treatment is not needed, and the non-stoichiometric ferric sodium pyrophosphate and ferric sodium pyrophosphate heterosymbiotic graphene composite material is directly prepared. The method specifically comprises the following steps: dispersing graphene oxide (GO) nanosheets in an organic medium, mixing the GO nanosheets with a sodium source, an iron source and phosphate through mechanical ball milling, so that the GO nanosheets can be in full contact with Fe < 2 + > in the iron source, the Fe < 2 + > is anchored by using rich oxygen-containing functional groups of the GO nanosheets, the Fe < 2 + > is subjected to in-situ combination reaction with the sodium source and the phosphate in a subsequent one-step sintering process, and the graphene oxide nanosheets are obtained. Meanwhile, phosphate is partially reduced into pyrophosphate, and GO is reduced into reduced graphene oxide (rGO), so that the ferric sodium pyrophosphate / rGO composite material with a heterogeneous symbiotic structure is obtained. The composite material can be used as a sodium ion battery positive electrode active material, and has excellent rate capability and cycling stability.

The present invention discloses a method for preparing a composite sodium ferric pyrophosphate cathode material, which relates to the technical field of sodium batteries and includes the following steps: Step S1, preparing a precursor; Step S2, combining it with a carbon source; and Step S3, sintering it. The composite sodium ferric pyrophosphate cathode material disclosed in the present invention has excellent electrochemical performance, good electrical conductivity, strong cycle performance and rate performance, and high initial charge and discharge efficiency.

The preparation method comprises the following steps: (1) weighing a sodium source, an iron source, a phosphorus source and a carbon source, quickly and uniformly mixing, and then pre-sintering at low temperature to obtain a precursor; wherein the low-temperature presintering comprises two stages, in the first stage, the temperature is increased to 60-150 DEG C and kept for 1-3 h, and in the second stage, the temperature is increased to 200-350 DEG C and kept for 1-8 h; and (2) adding a carbon source into the precursor to prepare slurry, sanding the slurry, carrying out centrifugal spray drying, and carrying out high-temperature sintering to obtain the ferric sodium pyrophosphate positive electrode material. The precursor of the high-solid-content slurry can be prepared, the problem that the solid content of the slurry is low in the grinding stage of the sodium ferric pyrophosphate positive electrode material prepared by a solid-phase method is effectively solved, the solid content of the slurry is increased, the yield of the precursor is increased, the production cost is reduced, and meanwhile, the product quality is improved. The prepared ferric sodium pyrophosphate positive electrode material has relatively high compaction density, capacity and other performances, and the performance of the product is improved.

The invention discloses a preparation method of a high-compaction ferric sodium pyrophosphate positive electrode material and a vehicle, and belongs to the technical field of synthesis of sodium ion battery positive electrode materials. The preparation method specifically comprises the following steps: uniformly mixing a metal compound, a non-metal compound, second-phase nanoparticles and deionized water, adding a slurry dispersing aid, stirring at a high speed, sanding, spray-drying and carrying out air jet pulverization to obtain the high-compaction ferric sodium pyrophosphate positive electrode material. The positive electrode material is applied to the vehicle sodium ion battery; the slurry dispersing aid at least comprises a tetraphenylethylene-based quaternary ammonium salt derivative and an amido pyridine compound, the tetraphenylethylene-based quaternary ammonium salt derivative has a vinyl group and a quaternary ammonium group, and the amido pyridine compound has an amide group and a pyridine group. The invention relates to a preparation method of a high-compaction ferric sodium pyrophosphate positive electrode material with high compaction density and high reversible capacity and a vehicle.

According to the double-site doped ferric sodium pyrophosphate / carbon composite positive electrode material and the preparation method thereof, tungstate is introduced in the raw material mixing process, and the Fe site and the PO4 site are respectively occupied in the forms of W < 6 + > and WO4 < 2-> in the synthesis process; the chemical formula of the obtained double-site doped ferric pyrophosphate sodium / carbon composite positive electrode material is Na4Fe3-xWx (PO4) 2-y (WO4) y (P2O7) / C, x is greater than or equal to 0 and less than or equal to 0.3, and y is greater than or equal to 0 and less than or equal to 0.3. The invention also comprises a preparation method of the double-site doped ferric sodium pyrophosphate / carbon composite positive electrode material. According to the double-site doped ferric pyrophosphate sodium / carbon composite positive electrode material, the phase purity is greatly improved, non-active marmite type ferric phosphate sodium and low-capacity ferric pyrophosphate sodium impurity phases do not exist, and sodium-iron antisite defects in the structure are obviously reduced. The positive electrode material is good in electronic conductivity and ionic conductivity, high in specific capacity, good in rate capability and long in cycle life, and the high and low temperature performance is also remarkably improved.

The invention belongs to the technical field of sodium ion battery positive electrode materials, and discloses a preparation method of a high-performance ferric pyrophosphate sodium positive electrode material. Performing high-energy ball milling on a sodium source, an iron source, a phosphorus source, an A source and a carbon source to obtain a precursor; and then annealing the precursor in argon to obtain the ferric sodium pyrophosphate positive electrode material doped with high-valence transition metal elements and subjected to iron defect engineering. Through doping of high-valence transition metal elements and regulation and control of iron defect sites, the technical problems that the ferric sodium phosphate pyrophosphate type positive electrode material is poor in conductivity, poor in ionic conductivity and low in compaction density, inactive impurities are easily generated in the preparation process, and the electrochemical performance of the ferric sodium phosphate pyrophosphate type positive electrode material is affected are solved.

The invention relates to the technical field of sodium-ion battery positive electrode materials, in particular to a titanium-doped high-density spherical nano sodium ferric pyrophosphate sodium-ion battery positive electrode material and a preparation method of the titanium-doped high-density spherical nano sodium ferric pyrophosphate sodium-ion battery positive electrode material. The chemical general formula of the titanium-doped high-density spherical nano sodium ferric pyrophosphate sodium ion battery positive electrode material is NaFe3-xTix (PO) PO), x is more than or equal to 0.05 and less than or equal to 0.2, the particle size of the positive electrode material is 20-300 nm, and the surface of the positive electrode material is coated with a layer of carbon. Through multi-dimensional innovation of material-process-structure, the invention provides a high-performance positive electrode solution for commercialization of the sodium ion battery, and has both technical advancement and engineering potential.

The invention discloses a high-magnification ferric sodium pyrophosphate composite material as well as a preparation method and application thereof, and belongs to the technical field of sodium ion battery positive electrode materials. According to the positive electrode material, phosphoric acid and ferric pyrophosphate sodium nano-microspheres grow on multi-walled carbon nanotubes (MCNTs), so that the MCNTs are coated with the phosphoric acid and ferric pyrophosphate sodium nano-microspheres, and a composite material composed of a matrix MCNTS and a phosphoric acid and ferric pyrophosphate sodium microsphere coating layer is formed. The chemical formula of the material is Na4Fe3 (PO4) P2O7 (at) MCNTS. The ultrahigh-rate ferric sodium phosphate pyrophosphate composite material comprises an MCNTS carrier and a coating layer coated on the surface of the MCNTS. According to the pyrophosphate and ferric phosphate sodium nanosphere coated multi-walled carbon nanotube composite material provided by the invention, due to a cross-linked three-dimensional network structure, a sodion deintercalation path is greatly shortened, electrons are transferred among nanospheres at an ultra-fast speed, and aggregation of the nanospheres is also inhibited. Due to ultrahigh electronic and ionic conductivity, the nanospheres show remarkable high capacity, ultrahigh rate capability and super-long cycle performance.

The preparation method comprises the following steps: mixing a sodium source, an iron source, a manganese source, a phosphorus source, a carbon source, water and a polyethylene glycol additive with the weight-average molecular weight of 5000-6000, and carrying out sanding, drying, sintering, crushing and other operations on the obtained mixed slurry to obtain the sodium ferromanganese pyrophosphate positive electrode material. The sodium ferromanganese pyrophosphate positive electrode material is obtained. The sodium ferromanganese pyrophosphate positive electrode material is prepared by adopting a wet ball milling-carbon thermal reduction method, and polyethylene glycol with the weight-average molecular weight of 5000-6000 is added as an additive in the preparation process, so that the prepared sodium ferromanganese pyrophosphate positive electrode material is nano spherical particles which are uniform in size distribution and have an excellent carbon conductive network structure. When the material is applied to a sodium-ion battery, the material has good electronic and ionic conductivity, and the electrochemical performance such as discharge capacity, platform voltage, rate capability and cycle performance can be greatly improved.

The invention discloses a method for reducing pores formed among particles during sintering of composite ferric sodium pyrophosphate, which comprises the following steps: step 1, preparation of precursor slurry: mixing, stirring and grinding an iron source, a phosphorus source, a sodium source, a carbon source and deionized water to obtain the precursor slurry; wherein the stoichiometric ratio of the iron source to the phosphorus source to the sodium source is 3: 4: 4, and the chemical formula of the synthesized composite ferric sodium pyrophosphate is Na4Fe3 (PO4) 2P2O7; 2, carrying out spray drying on the precursor slurry to obtain a dried precursor; and step 3, loading the dried precursor in a graphite sagger, and then feeding the dried precursor into a roller kiln for sintering to obtain the composite ferric sodium pyrophosphate material. According to the invention, the solid content of the slurry is reduced to realize that the spray-dried composite phosphoric acid ferric pyrophosphate precursor forms thin-wall secondary spherical particles, and then through a unique sintering process curve, volatile components of the precursor are smoothly discharged in the sintering process, so that the composite phosphoric acid ferric pyrophosphate product without pores among particles is obtained.