Carbon-coated ferrophosphoric pyrophosphate precursor material and preparation method and application thereof

Abstract

The application belongs to the field of sodium ion battery positive electrode materials, and discloses a preparation method of a carbon-coated iron pyrophosphate phosphate precursor material, which comprises the following steps: mixing a phosphorus source, a carbon source and an iron source, spray drying to obtain a mixed powder, placing the mixed powder B in an inert protective gas for calcination, cooling, crushing and sieving to obtain the carbon-coated iron pyrophosphate phosphate precursor material. x (PO4) y (P2O7) z @C precursor material, the prepared material is uniform in particle size and uniform in carbon coating, and the preparation process is simple, which is beneficial to marketization. In addition, the application also provides a preparation method of a carbon-coated sodium iron pyrophosphate phosphate material, which mixes the above-mentioned iron pyrophosphate phosphate precursor material and a sodium source, calcines and cools under an inert protective gas to obtain the sodium iron pyrophosphate phosphate material, and the above-mentioned method is convenient for controlling the particle size of the material and avoids phenomena such as agglomeration and uneven particle size.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of sodium ion battery cathode materials, and relates to a cathode material precursor, in particular to a carbon-coated iron pyrophosphite phosphate precursor material and a preparation method and application thereof. BACKGROUND

[0002] Sodium ion battery cathode materials include transition metal oxides, prussian blue analogues, polyanion compounds, etc., wherein the polyanion compound of the NASICON structure is a three-dimensional framework structure composed of strong covalent bonds, has high structural stability, fast sodium ion diffusion rate, small volume change and few phase changes in the ion deintercalation process, and can be widely used to prepare cathode materials of sodium ion batteries.

[0003] CN117361482A discloses a preparation method and application of a composite iron pyrophosphite phosphate polyanion type cathode material. The sodium ion battery cathode material is prepared by sand milling and spraying. The sodium source, phosphorus source and iron source are mixed directly by sand milling. However, there are problems such as great difficulty in material morphology control and uneven carbon coating.

[0004] CN116924371A discloses a preparation method of a core-shell structure iron pyrophosphite phosphate sodium manganese cathode material. The iron pyrophosphite phosphate sodium manganese cathode material is prepared by a sol-gel method. The raw materials of the sol-gel method are expensive, some of which are organic substances. The escaping gas and organic substances during drying are harmful to the human body and can cause material shrinkage and large material deformation. Moreover, the sol-gel process has a long preparation period, which is not conducive to marketization. SUMMARY

[0005] In view of the above problems in the prior art, in a first aspect, the application provides a carbon-coated iron pyrophosphite phosphate precursor material and a preparation method thereof. In a second aspect, the application provides an iron pyrophosphite phosphate sodium and a preparation method thereof.

[0006] Firstly, the application provides a preparation method of a carbon-coated iron pyrophosphite phosphate precursor material, which comprises the following steps:

[0007] Step 1: dissolving a phosphorus source, a carbon source and an iron source in a medium solution to obtain slurry A;

[0008] Step 2: spray drying the slurry A to obtain mixed powder B;

[0009] Step 3: calcining the mixed powder B in an inert protective gas, and cooling, crushing and sieving the calcination product to obtain the carbon-coated iron pyrophosphite phosphate precursor material.

[0010] Preferably, the molar ratio of P:Fe in the phosphorus source and the iron source is 9-13:8-10.

[0011] Preferably, the phosphorus source is one or more of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, amino-tris-methylene phosphonic acid, ethylenediamine tetra-methylene phosphonic acid, hexanediamine tetra-methylene phosphonic acid, hydroxyethylidene diphosphonic acid, ferric phosphate, ferrous phosphate, ferric pyrophosphate, ferrous pyrophosphate, ferric hypophosphite, ferric glycerylphosphate.

[0012] Further preferably, the carbon source is one or more of citric acid, oxalic acid, CNTs, oleic acid, graphene, pyromellitic acid, glucose, ethylene glycol, polyethylene glycol, liquid paraffin, PVP, bituminous coal, phenolic resin, soft carbon, MCMB, polyacrylonitrile, stearic acid, ascorbic acid, PPy, Super P, polyaniline, soluble starch, cellulose, sucrose.

[0013] Further preferably, the iron source is one or more of ferrous oxalate, ferric nitrate, iron powder, ferric phosphate, ferrous citrate, ferrous acetate, ferrous formate, ferric pyrophosphate, ferrous pyrophosphate, ferrous phosphate, ferric oxide, magnetite.

[0014] Further preferably, the medium solution comprises one or more of water, anhydrous ethanol, ethylene glycol solution.

[0015] Preferably, in step 1, the stirring rate is 100-1600 rpm when dissolving the phosphorus source, carbon source, and iron source, and the stirring time is 2-10 h.

[0016] Preferably, in step 1, the solid content in the slurry A is 30%-70%.

[0017] Preferably, in step 2, the inlet air temperature of the spray drying is 200-300℃, the outlet air temperature of the spray drying is 90-150℃, the fan frequency is 30-50 Hz, and the peristaltic speed is 60-150 rpm.

[0018] Preferably, in step 3, the calcination temperature is 350-900℃, and the calcination time is 4-20 h.

[0019] Preferably, the inert protective gas is one or more of argon and nitrogen.

[0020] Preferably, in step 3, the crushing process is any one of grinding, air flow crushing, and vibration crushing.

[0021] Preferably, in step 3, the mesh size of the sieve is 50-500 mesh.

[0022] In a second aspect, based on the same inventive concept, the present application provides a ferric pyrophosphate phosphate prepared by the above preparation method.

[0023] Preferably, the carbon content in the iron pyrophosphate precursor material is 0.2% to 12%.

[0024] Preferably, the particle size D50 of ferric pyrophosphate is 3.24~4.75μm; and the specific surface area is 12~16m². 2 / g; tap density is 1.4~1.7g / cm³ 3 .

[0025] Thirdly, based on the same inventive concept, the present invention provides a sodium iron pyrophosphate material, which is obtained by mixing the above-mentioned carbon-coated sodium iron pyrophosphate precursor material with a sodium source and calcining the mixture under an inert protective gas.

[0026] Preferably, the sodium source is one or more of sodium carbonate, sodium hydroxide, sodium pyrophosphate, sodium bicarbonate, sodium dihydrogen phosphate, disodium hydrogen phosphate, and sodium phosphate.

[0027] Preferably, the mass ratio of the ferric pyrophosphate precursor material to the sodium source is 1:0.14~0.98.

[0028] Preferably, the calcination temperature is 350~1000℃ and the calcination time is 4~12h.

[0029] Further optimization is that during calcination, the heating rate is 1~10℃ / min; the cooling rate is 1~10℃ / min.

[0030] Preferably, the inert protective gas is one or both of argon and nitrogen.

[0031] Fourthly, based on the same opposite concept, the present invention provides a sodium-ion battery in which the positive electrode material is prepared by the above-mentioned method for preparing carbon-coated sodium iron pyrophosphate material.

[0032] The technical solutions provided by this invention have at least one or more of the following significant beneficial technical effects:

[0033] (1) This invention prepares carbon-coated iron pyrophosphate Fe by spray drying-calcination method. x (PO4) y (P2O7) z @C precursor materials, the prepared precursor materials exhibit no agglomeration and uniform carbon coating, using Fe x (PO4) y (P2O7) z The cathode material made from the @C precursor material has good conductivity and a simple preparation process, which is conducive to its commercialization.

[0034] (2) By mixing the iron pyrophosphate Fe prepared in this invention x (PO4)y (P2O7) z @C precursor material and sodium source, calcination, i.e. to obtain the sodium iron phosphate pyrophosphate material, the particle size distribution of the prepared sodium iron phosphate pyrophosphate material is uniform, and there is no agglomeration phenomenon.

[0035] (3) can be adjusted by adjusting the phosphorus pyrophosphate iron Fe x (PO4) y (P2O7) z @C precursor material size, specific surface area, tap density, carbon content and other parameters, adjust the related parameters of the finally prepared sodium iron phosphate pyrophosphate material.

[0036] (4) compared with the sanding + spraying process or sol-gel process for preparing sodium iron phosphate pyrophosphate material in the prior art, the synthesis preparation process of the NFPP sodium electrode precursor proposed in the application is short, the synthesis difficulty is low, the cost is low, the controllability is high, and the obtained positive electrode material has high stability. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 The XRD graph of the carbon-coated phosphorus pyrophosphate iron precursor material prepared in Example 2 of the application.

[0038] Figure 2 The SEM graph of the carbon-coated phosphorus pyrophosphate iron precursor material prepared in Example 1 of the application.

[0039] Figure 3 The SEM graph of the carbon-coated sodium iron phosphate pyrophosphate material prepared in Example 5 of the application.

[0040] Figure 4 The SEM graph of the carbon-coated phosphorus pyrophosphate iron precursor material prepared in Comparative Example 1 of the application.

[0041] Figure 5 The battery cycle performance schematic diagram of the battery prepared using the carbon-coated sodium iron phosphate pyrophosphate material prepared in Example 6 of the application.

[0042] Figure 6 The charge-discharge curve graph of the carbon-coated sodium iron phosphate pyrophosphate material prepared using Example 5 of the application. DETAILED DESCRIPTION

[0043] The application provides the following specific technical solutions.

[0044] Firstly, the application provides a preparation method of a carbon-coated phosphorus pyrophosphate iron precursor material, comprising the following steps:

[0045] Step 1, dissolve the phosphorus source, carbon source and iron source in water, mix uniformly to obtain slurry A;

[0046] Step 2, spray drying the slurry A to obtain a mixed powder B;

[0047] Step 3, calcining, cooling, crushing and sieving the mixed powder B in an inert protective gas to obtain a carbon-coated iron phosphate pyrophosphate precursor material.

[0048] Preferably, the molar ratio of P:Fe in the phosphorus source and the iron source is 9-13:8-10.

[0049] In actual cases, the addition amount of the phosphorus source, the carbon source and the iron source can be selected according to actual needs, and the molar ratio of P:Fe in the phosphorus source and the iron source is 9-13:8-10, which is only a preferred range proposed by the inventors. The inventors propose that different carbon sources have different carbon residual rates at different sintering temperatures, and therefore, when the ingredients are prepared, the amount of the carbon source can be calculated according to the theoretical carbon content required by the material, the calcination temperature and the carbon source thermogravimetric analysis.

[0050] Preferably, the phosphorus source is one or more of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, aminotri(methylene) phosphonic acid, ethylenediamine tetra(methylene) phosphonic acid, hexanediamine tetra(methylene) phosphonic acid, hydroxyethylidene diphosphonic acid, ferric phosphate, ferrous phosphate, ferric pyrophosphate, ferrous pyrophosphate, ferrous hypophosphite, and glycerophosphoric acid iron.

[0051] Preferably, the carbon source is one or more of citric acid, oxalic acid, CNTs, oleic acid, graphene, pyromellitic acid, glucose, ethylene glycol, polyethylene glycol, liquid paraffin, PVP, bituminous coal, phenolic resin, soft carbon, MCMB, polyacrylonitrile, stearic acid, ascorbic acid, PPy, Super P, polyaniline, soluble starch, cellulose, and sucrose.

[0052] Preferably, the iron source is one or more of ferrous oxalate, ferric nitrate, iron powder, ferric phosphate, ferrous citrate, ferrous acetate, ferrous formate, ferric pyrophosphate, ferrous pyrophosphate, ferrous phosphate, diiron trioxide, and triiron tetraoxide; and the medium solution includes one or more of water, anhydrous ethanol, and ethylene glycol.

[0053] Preferably, in step 1, the stirring rate is 100-1600 rpm when the phosphorus source, the carbon source and the iron source are dissolved, and the stirring time is 2-10 h.

[0054] In actual cases, the stirring rate and the stirring time can be selected according to actual needs, as long as the phosphorus source, the carbon source and the iron source are completely dissolved.

[0055] Preferably, the solid content in the slurry A is 30%-70%.

[0056] The inventors have found that, if the solid content in the slurry A is too high, it is not conducive to the dispersion of the material in the subsequent spray drying process; if the solid content is too low, it leads to an increase in the time and energy consumption of the spray drying process, and an increase in the cost. In actual applications, the solid content in the slurry A can be selected according to actual needs, and in the specific embodiments of the present application, the solid content in the slurry A can be 30%, 40%, 50%, 60%, 70%.

[0057] Preferably, in step 2, the inlet air temperature of the spray drying is 200-300℃; the outlet air temperature of the spray drying is 90-150℃; the frequency of the fan is 30-50Hz; and the peristaltic speed is 60-150rpm.

[0058] In actual applications, the inlet air temperature, outlet air temperature, frequency of the fan and peristaltic speed during the spray drying can be adjusted according to actual conditions, and in the specific embodiments of the present application, the inlet air temperature can be 200℃, 210℃, 220℃, 230℃, 240℃, 250℃, 300℃; the outlet air temperature can be 90℃, 100℃, 110℃, 120℃, 130℃, 140℃, 150℃; the frequency of the fan can be 30Hz, 35Hz, 40Hz, 45Hz, 50Hz; and the peristaltic speed can be 60rpm, 80rpm, 100rpm, 120rpm, 150rpm.

[0059] Preferably, in step 3, the calcination temperature is 350-900℃, and the calcination time is 4-20h.

[0060] In actual applications, the calcination temperature and calcination time can be adjusted according to actual needs, and in the specific embodiments of the present application, the calcination temperature can be 350℃, 400℃, 500℃, 600℃, 700℃, 850℃, 900℃; and the calcination time can be 4h, 6h, 8h, 10h, 12h, 15h, 17h, 20h.

[0061] Further preferably, in step 3, during calcination, the heating rate is 1-10℃ / min; and the cooling rate is 1-10℃ / min.

[0062] In actual applications, the heating rate and cooling rate during calcination can be selected according to actual needs, and in the specific embodiments of the present application, the heating rate can be 1℃ / min, 3℃ / min, 5℃ / min, 8℃ / min, 10℃ / min; and the cooling rate can be 1℃ / min, 3℃ / min, 5℃ / min, 7℃ / min, 8℃ / min, 10℃ / min.

[0063] Preferably, the inert protective gas is one or both of argon and nitrogen.

[0064] Preferably, in step 3, the crushing process is any one of grinding, air flow breaking, and vibration breaking.

[0065] Preferably, in step 3, the mesh size of the screen is 50-500 mesh.

[0066] In a second aspect, based on the same inventive concept, the present application provides a ferric pyrophosphate phosphate prepared by the above preparation method.

[0067] In a third aspect, based on the same inventive concept, the present application provides a preparation method of sodium ferric pyrophosphate phosphate, comprising the following steps:

[0068] Mixing the above ferric pyrophosphate phosphate and sodium source, calcining under inert protective gas, and cooling to obtain a sodium ferric pyrophosphate phosphate material.

[0069] In the prior art, the phosphorus source, carbon source, iron source, and sodium source are usually directly mixed and calcined under protective gas to prepare a sodium ferric pyrophosphate phosphate material, and the particles are easy to agglomerate and have indefinite morphology. The inventors have found that, by first preparing a ferric pyrophosphate phosphate precursor and then mixing a sodium source and calcining under inert protective gas, a sodium ferric pyrophosphate phosphate material with spherical particles is obtained, and there is no agglomeration phenomenon and the particles are uniformly distributed. Moreover, by adjusting the morphology of the ferric pyrophosphate phosphate precursor, the morphology of the sodium ferric pyrophosphate phosphate material can be controlled to some extent, the synthesis difficulty is reduced, and the controllability is improved.

[0070] Preferably, the sodium source is one or two or more of sodium carbonate, sodium hydroxide, sodium pyrophosphate, sodium bicarbonate, sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium phosphate, sodium acetate, and sodium oxalate.

[0071] Preferably, the mass ratio of the ferric pyrophosphate phosphate precursor material to the sodium source is 1:0.14-0.98.

[0072] In actual situations, the sodium source can be selected according to actual needs. The inventors have found that too much sodium source can easily lead to an increase in residual alkali in the subsequent synthesis process of sodium ferric pyrophosphate phosphate, and too little sodium source can lead to a low capacity of the material.

[0073] Preferably, the calcination temperature is 350-1000℃, and the calcination time is 4-12h.

[0074] In specific embodiments of the present application, the calcination temperature can be 350℃, 400℃, 500℃, 550℃, 600℃, or 700℃; and the calcination time can be 4h, 6h, 8h, 10h, or 12h.

[0075] Further preferably, during calcination, the heating rate is 1-10℃ / min, and the cooling rate is 1-10℃ / min.

[0076] In actual situation, the heating rate and the cooling rate can be selected according to actual needs. In the specific embodiments of the present application, the heating rate can be 1 ℃ / min, 3 ℃ / min, 5 ℃ / min, 8 ℃ / min or 10 ℃ / min; and the cooling rate can be 1 ℃ / min, 3 ℃ / min, 5 ℃ / min, 8 ℃ / min or 10 ℃ / min. In other cases, the material can also be naturally cooled.

[0077] Preferably, the inert protective gas is one or both of argon and nitrogen.

[0078] In order to make the technical problems, technical solutions and technical advantages of the present application clearer, specific examples will be described in detail below, but the protection scope of the present application is not limited to the following specific examples.

[0079] Unless otherwise defined, all the professional terms used below have the same meaning as generally understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the protection scope of the present application.

[0080] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present application can be purchased from the market or can be prepared by existing methods.

[0081] Example 1:

[0082] A preparation method of a carbon-coated iron phosphate pyrophosphate precursor material, comprising the following steps:

[0083] Step 1, mix 3 mol of iron phosphate, 1.5 mol of iron pyrophosphate and 0.75 mol of citric acid in water, set the sand mill rotation speed to 800 rpm, sand mill for 6 h, and prepare slurry A, the solid content in slurry A is 50%.

[0084] Step 2, spray dry slurry A, the feeding peristaltic speed is 100 rpm, the inlet air temperature is 240 ℃, the outlet air temperature is 120 ℃, and the fan frequency is 45 Hz, to obtain mixed powder B;

[0085] Step 3, place the mixed powder B in a nitrogen atmosphere and calcine, the internal oxygen value is 50 ppm. The heating rate is 5 ℃ / min to 700 ℃, 700 ℃ for 10 h, the cooling rate is 7 ℃ / min to room temperature, then take out, pass through airflow crushing, use a 300 mesh sieve to sieve, and obtain a carbon-coated iron phosphate pyrophosphate precursor material with a particle size of 3.66 μm.

[0086] Example 2:

[0087] Step 1, mix 4 mol of glycerophosphate iron, 2 mol of ferrous pyrophosphate, 0.5 mol of glucose, add water, and stir at a stirring rate of 100 rpm for 2 h to prepare slurry A, the solid content in slurry A is 30%.

[0088] Step 2, spray dry slurry A, the feeding peristaltic speed is 60 rpm, the inlet air temperature is 200 ℃, the outlet air temperature is 90 ℃, and the fan frequency is 30 Hz to obtain mixed powder B;

[0089] Step 3, calcine mixed powder B in an argon atmosphere, the internal oxygen value is 10 ppm, the temperature is raised to 350 ℃ at a rate of 1 ℃ / min, and the temperature is kept for 4 h, the temperature is then lowered to room temperature at a rate of 1 ℃ / min, and the product is taken out, crushed by vibration, and sieved by a 50-mesh sieve to obtain carbon-coated iron phosphate pyrophosphate precursor material with a particle size of 3.51 μm.

[0090] Example 3:

[0091] Step 1, mix 12 mol of ammonium dihydrogen phosphate, 9 mol of ferrous citrate, and 0.5 mol of sucrose, add water, and stir at a sanding rate of 1600 rpm for 10 h to prepare slurry A, the solid content in slurry A is 70%.

[0092] Step 2, spray dry slurry A, the feeding peristaltic speed is 150 rpm, the inlet air temperature is 300 ℃, the outlet air temperature is 150 ℃, and the fan frequency is 50 Hz to obtain mixed powder B;

[0093] Step 3, calcine mixed powder B in a nitrogen atmosphere, the internal oxygen value is 100 ppm, the temperature is raised to 900 ℃ at a rate of 10 ℃ / min, and the temperature is kept for 20 h, the temperature is then lowered to room temperature at a rate of 10 ℃ / min, and the product is taken out, ground, and sieved by a 500-mesh sieve to obtain carbon-coated iron phosphate pyrophosphate precursor material with a particle size of 4.42 μm.

[0094] Example 4:

[0095] Step 1, mix 9 mol of iron phosphate hydrate and 0.1 mol of ascorbic acid, add water, and stir uniformly at a sanding speed of 1600 rpm for 3.5 h to prepare slurry A.

[0096] Step 2, spray dry slurry A, the feeding peristaltic speed is 125 rpm, the inlet air temperature is 250 ℃, the outlet air temperature is 130 ℃, and the fan frequency is 50 Hz to obtain mixed powder B;

[0097] Step 3: The mixed powder B was calcined under nitrogen atmosphere with oxygen content of 100 ppm. The temperature was raised to 850℃ at a rate of 8℃ / min, and kept for 15 h. The temperature was then lowered to room temperature at a rate of 10℃ / min. The product was taken out after the temperature reached room temperature, ground, and sieved through a 500 mesh screen to obtain carbon-coated iron pyrophosphate phosphate precursor material with a particle size of 4.03 μm.

[0098] Example 5:

[0099] A method for preparing sodium iron pyrophosphate phosphate, comprising the following steps:

[0100] The 5 kg of carbon-coated iron pyrophosphate phosphate material prepared in Example 1 was mixed with 3.09 kg of sodium acetate at a mixing speed of 900 rpm for 30 min. The mixture was calcined at 550℃ for 10 h under nitrogen atmosphere to obtain sodium iron pyrophosphate phosphate.

[0101] Example 6:

[0102] A method for preparing sodium iron pyrophosphate phosphate, comprising the following steps:

[0103] The 6 kg of carbon-coated iron pyrophosphate phosphate material prepared in Example 2 was mixed with 3.8 kg of sodium carbonate and 1.5 kg of sodium phosphate at a mixing speed of 150 rpm for 15 min. The mixture was calcined at 950℃ for 4 h under nitrogen atmosphere to obtain sodium iron pyrophosphate phosphate.

[0104] Example 7:

[0105] A method for preparing sodium iron pyrophosphate phosphate, comprising the following steps:

[0106] The 4 kg of carbon-coated iron pyrophosphate phosphate material prepared in Example 3 was mixed with 2.17 kg of sodium oxalate at a mixing speed of 1000 rpm for 40 min. The mixture was calcined at 900℃ for 12 h under nitrogen atmosphere to obtain sodium iron pyrophosphate phosphate.

[0107] Example 8:

[0108] The 3 kg of carbon-coated iron pyrophosphate phosphate material prepared in Example 4 was mixed with 0.5 kg of sodium bicarbonate and 0.65 kg of sodium phosphate at a mixing speed of 150 rpm for 15 min. The mixture was calcined at 850℃ for 4 h under nitrogen atmosphere to obtain sodium iron pyrophosphate phosphate.

[0109] Comparative Example 1:

[0110] A method for preparing carbon-coated iron pyrophosphate phosphate precursor material, comprising the following steps:

[0111] Step 1, mix 3 mol of iron phosphate, 1.5 mol of iron pyrophosphate, 0.75 mol of citric acid, add water, set the sand mill speed to 800 rpm, sand mill for 6 h, and prepare slurry A, the solid content of the mixed solution is 50%.

[0112] Step 2, after vacuum drying of slurry A, calcine it under a nitrogen atmosphere, the internal oxygen value is 50 ppm. The temperature is raised to 600°C at a rate of 5°C / min for 120 min, and then calcined at 600°C for 10 h. The temperature is lowered to room temperature at a rate of 6°C / min, and then removed. After air flow crushing and sieving with a 250 mesh sieve, a carbon-coated iron phosphate pyrophosphate precursor material with a particle size of 4.99 μm is obtained.

[0113] Comparative Example 2:

[0114] Step 1, mix 4 mol of glycerol iron phosphate, 2 mol of ferrous pyrophosphate, add water, and stir at a speed of 100 rpm for 2 h to prepare slurry A, the solid content in slurry A is 30%;

[0115] Step 2, spray dry slurry A, the feeding peristaltic speed is 90 rpm, the inlet air temperature is 240°C, the outlet air temperature is 105°C, and the fan frequency is 40 Hz to obtain mixed powder B;

[0116] Step 3, mix 0.5 mol of glucose and mixed powder B to obtain mixed powder C, and calcine mixed powder C in an inert protective gas, the internal oxygen value is 10 ppm. The temperature is raised to 550°C at a rate of 1°C / min, and then held for 6 h. The temperature is lowered to room temperature at a rate of 4°C / min, and then removed. The calcined product is cooled, air flow crushed, and sieved with a 250 mesh sieve to obtain a carbon-coated iron phosphate pyrophosphate precursor material with a particle size of 4.87 μm.

[0117] Comparative Example 3:

[0118] Step 1, mix 12 mol of ammonium dihydrogen phosphate and 9 mol of ferrous citrate, add water, and stir at a speed of 1600 rpm for 10 h to prepare slurry A, the solid content in slurry A is 70%;

[0119] Step 2, spray dry slurry A, the feeding peristaltic speed is 155 rpm, the inlet air temperature is 290°C, the outlet air temperature is 150°C, and the fan frequency is 50 Hz to obtain mixed powder B;

[0120] Step 3: The mixed powder B was calcined under nitrogen atmosphere, the oxygen content was 100 ppm. The heating rate was 10°C / min to 850°C, and the holding time was 20 h. The cooling rate was 10°C / min to room temperature, and then the calcined product was mixed with 0.5 mol sucrose to obtain mixed powder C. The mixed powder C was calcined again, the heating rate was 5°C / min to 500°C, and the holding time was 5 h. The cooling rate was 6°C / min to room temperature, and then the product was cooled, crushed, and sieved to obtain the carbon-coated ferric pyrophosphate precursor material.

[0121] Comparative Example 4:

[0122] Step 1: Iron phosphate, sodium carbonate, glucose, sodium dihydrogen phosphate, and pure water were mixed to control Fe:P:Na = 3:4:4, the solid content was 60%, and the carbon content was 2%. The slurry A was obtained by sand milling at a speed of 200 rpm for 10 h.

[0123] Step 2: The slurry A was spray dried to obtain powder B, the inlet temperature of spray drying was controlled at 220°C, the peristaltic speed was 160 rpm, and the outlet temperature was 110°C.

[0124] Step 3: The mixed powder B was calcined under nitrogen atmosphere, the oxygen content was 100 ppm. The heating rate was 10°C / min to 850°C, and the holding time was 20 h. The cooling rate was 10°C / min to room temperature, and then the calcined product was mixed with 0.5 mol sucrose to obtain mixed powder C. The mixed powder C was calcined again, the heating rate was 5°C / min to 500°C, and the holding time was 5 h. The cooling rate was 6°C / min to room temperature, and then the product was cooled, crushed, and sieved to obtain the carbon-coated ferric pyrophosphate precursor material.

[0125] Comparative Example 5:

[0126] Step 1: 2.15 kg of sodium carbonate, 5.95 kg of ammonium phosphate, 1 kg of glucose, and 1 kg of stearic acid were added to deionized water to control the solid content at 55%, and stirred until a transparent solution A was obtained.

[0127] Step 2: 4.35 kg of ferrous oxalate, 8.2 kg of ethylenediaminetetraacetic acid, and 0.55 kg of cetyltrimethylammonium bromide were added to 20 l of deionized water, and magnetically stirred until a transparent solution B was obtained.

[0128] Step 3: Then, the transparent solution B was added dropwise into solution A, and stirred vigorously. Then, the mixed solution was heated in a water bath at 90°C until all the excess water was removed to obtain a sol-gel precursor:

[0129] Step 4: The precursor was ground into fine powder, and intermediate grinding was performed under a high-purity argon atmosphere at 900°C for 24 h to obtain sodium ferric pyrophosphate with a final particle size of 5.24 μm.

[0130] The conductive property testing method of the precursor material prepared in Examples 1-4 and Comparative Examples 1-3, and the positive electrode material prepared in Examples 5-8 and Comparative Examples 4-5 is as follows:

[0131] 1g of sample was weighed, the conductivity meter was calibrated using a calibration solution, and then the sample was placed between four probes to ensure good contact between the sample and the probes. The sample height was adjusted to 20mm, and when the pressure reached 8Mpa, the resistance was calculated by measuring the current and voltage drop, and the conductivity was calculated by the geometric size. The test results are shown in Table 1 below.

[0132] Table 1 - Performance parameters of the precursor material prepared in Examples 1-4 and Comparative Examples 1-3

[0133]

[0134] As can be seen from Table 1, the tap density and specific surface area of the precursor material prepared in Examples 1-4 and Comparative Examples 1-3 are larger.

[0135] Table 2 - Performance parameters of the positive electrode material prepared in Examples 5-8 and Comparative Examples 4-5

[0136]

[0137] As can be seen from Table 2, the tap density and specific surface area of the positive electrode material prepared by the preparation process of the positive electrode material provided by the application are larger. After the mixture of the precursor and the sodium source is reacted, the internal particles become larger, resulting in a thinner carbon thickness coated on the surface of the positive electrode material, which affects the electronic conductivity.

[0138] The sodium iron pyrophosphate phosphate positive electrode material prepared in Examples 5-8 and Comparative Examples 4-5 was assembled into a button cell, including the following steps:

[0139] 1) According to the ratio of active material: conductive agent: binder = 9:0.5:0.5, NMP was used as the solvent for stirring for 6h;

[0140] 2) The slurry was coated on a 16μm aluminum foil, and the coating thickness was controlled to be 150μm. The vacuum oven was baked at 105℃ for 4h;

[0141] 3) After the pole piece was rolled, it was cut into small round pieces;

[0142] 4) According to the positive electrode shell-positive electrode piece-separator-sodium piece-negative electrode shell assembly, 5 drops of sodium special electrolyte were dropped;

[0143] 5) After standing for 12h, the charge and discharge test was carried out at room temperature under a current density of 100mA / g, and the test voltage range was 0.01-3.0V.

[0144] Figure 5The battery cycle performance diagram of the battery prepared using the carbon-coated sodium iron phosphate pyrophosphate material prepared in Embodiment 6 of the present application; Figure 6 The charge-discharge curve of the carbon-coated sodium iron phosphate pyrophosphate material prepared in Embodiment 5 of the present application.

[0145] Table 2 - Cycle parameters of the button cells assembled using the sodium iron phosphate pyrophosphate positive electrode materials prepared in Embodiments 5-8 and Comparative Examples 4-5

[0146]

[0147] As can be seen from Table 2, the discharge specific capacity and cycle stability of the battery assembled using the positive electrode materials prepared in Embodiments 5-8 are more superior than those of the battery assembled using the positive electrode materials prepared in Comparative Examples 4-5.

[0148] Figure 1 The XRD diagram of the carbon-coated sodium iron phosphate pyrophosphate precursor material prepared in Embodiment 2 of the present application.

[0149] Figure 2 The SEM diagram of the carbon-coated sodium iron phosphate pyrophosphate precursor material prepared in Embodiment 1 of the present application, which shows that the particles of the precursor material prepared in Embodiment 1 are spherical. Figure 3 The SEM diagram of the carbon-coated sodium iron phosphate pyrophosphate material prepared in Embodiment 5 of the present application, which shows that the particles of the positive electrode material prepared in Embodiment 5 are spherical. Figure 2 and Figure 3 It can be seen that the morphology of the final prepared positive electrode material can be adjusted by adjusting the morphology of the precursor.

[0150] Figure 4 The SEM diagram of the carbon-coated sodium iron phosphate pyrophosphate precursor material prepared in Comparative Example 1 of the present application, which shows that the particles of the precursor material prepared in Comparative Example 1 are spherical. Figure 3 and Figure 4 The particles are more uniform in distribution, the carbon coating is uniform, and there is no agglomeration phenomenon.

[0151] The above description is only the preferred embodiments of the present application, and it should be noted that for those skilled in the art, without departing from the principles of the present application, a number of improvements and refinements can be made, and these improvements and refinements should also be considered as the protection scope of the present application.

Claims

1. A method of making a carbon-coated ferric pyrophosphated phosphate precursor material, characterized in that, The method comprises the following steps: Step 1, dissolving a phosphorus source, a carbon source and an iron source in a medium solution to obtain a slurry A; Step 2, spray drying the slurry A to obtain a mixed powder B; Step 3, calcining the mixed powder B in an inert protective gas, and cooling, crushing and sieving the calcination product to obtain a carbon-coated ferric pyrophosphate precursor material; The molar ratio of P:Fe in the phosphorus source and the iron source is 9-13:8-10.

2. The method of claim 1, wherein the carbon-coated ferric pyrophosphate precursor material is prepared by a process comprising: The phosphorus source is one or more of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, aminotri(methylene) phosphonic acid, ethylenediamine tetra(methylene) phosphonic acid, hexanediamine tetra(methylene) phosphonic acid, hydroxyethylidene diphosphonic acid, ferric phosphate, ferrous phosphate, ferric pyrophosphate, ferrous pyrophosphate, ferrous hypophosphite, and glycerophosphoric acid iron; ​ The carbon source is one or more of citric acid, oxalic acid, CNTs, oleic acid, graphene, pyromellitic acid, glucose, ethylene glycol, polyethylene glycol, liquid paraffin, PVP, bituminous coal, phenolic resin, soft carbon, MCMB, polyacrylonitrile, stearic acid, ascorbic acid, PPy, Super P, polyaniline, soluble starch, cellulose, and sucrose; The iron source is one or more of ferrous oxalate, ferric nitrate, iron powder, ferric phosphate, ferrous citrate, ferrous acetate, ferrous formate, ferric pyrophosphate, ferrous pyrophosphate, ferrous phosphate, diiron trioxide, and triiron tetraoxide; The medium solution comprises one or more of water, anhydrous ethanol, and ethylene glycol solution.

3. The method for preparing the carbon-coated iron pyrophosphate precursor material according to any one of claims 1 to 2, characterized in that, In step 1, the solid content in the slurry A is 30%-70%.

4. The method of making a carbon-coated ferric pyrophosphated phosphate precursor material of claim 1, wherein, In step 3, the calcination temperature is 350-900℃, and the calcination time is 4-20h.

5. A carbon-coated ferric pyrophosphated phosphate precursor material, characterized in that, The carbon-coated ferric pyrophosphate precursor material is prepared by the method of any one of claims 1-4; the carbon content in the ferric pyrophosphate precursor material is 0.2%-12%.

6. The ferric pyrophosphite precursor material of claim 5, wherein, The particle size D50 is 3.24-4.75 μm; the specific surface area is 12-16 m 2 / g; the tap density is 1.4-1.7 g / cm 3 .

7. A method for preparing a carbon-coated sodium iron phosphate pyrophosphate material, characterized by, The carbon-coated ferric pyrophosphate precursor material and a sodium source are mixed, and the mixture is calcined in an inert protective gas to obtain the sodium ferric pyrophosphate material.

8. The method of claim 7, wherein the carbon-coated sodium iron phosphate pyrophosphate material is prepared by a process comprising: The sodium source is one or more of sodium carbonate, sodium hydroxide, sodium pyrophosphate, sodium bicarbonate, sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium phosphate, sodium acetate, and sodium oxalate; the mass ratio of the ferric pyrophosphate precursor material to the sodium source is 1:0.14-0.98; the calcination temperature is 350-1000℃, and the calcination time is 4-12h. ​ 9. A sodium-ion battery, characterized in that, The positive electrode material is prepared by the method of any one of claims 7-8.

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