CN116565165A - Bicontinuous-phase coated sodium ferric phosphate cathode material and preparation method thereof - Google Patents

Bicontinuous-phase coated sodium ferric phosphate cathode material and preparation method thereof Download PDF

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CN116565165A
CN116565165A CN202310540961.0A CN202310540961A CN116565165A CN 116565165 A CN116565165 A CN 116565165A CN 202310540961 A CN202310540961 A CN 202310540961A CN 116565165 A CN116565165 A CN 116565165A
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杨成浩
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Guangdong Guangna New Material Technology Co ltd
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Abstract

The invention belongs to the technical field of ion battery anode materials, and discloses a bicontinuous phase coated ferric sodium phosphate anode material which comprises ferric sodium phosphate (Na) 4 Fe 3 (PO 4 ) 2 (P 2 O 7 ) A coating layer (metal oxide TiNb) coated on the surface thereof 2 O 7 And a continuous composite phase formed by uniformly mixing the carbon layers). The preparation method comprises the following steps: 1) Mixing a sodium source, an iron source, a phosphorus source and a solvent to prepare slurry; 2) Spray drying the slurry to obtain a precursor; 3) Mixing the precursor with a carbon source, a titanium source and a niobium source, and grinding; 4) And (5) cooling the grinded precursor after high-temperature sintering. The invention utilizes metal oxide TiNb 2 O 7 The coating layer which is uniformly mixed with the carbon layer to form a bicontinuous phase completely wraps the sodium iron phosphate cathode material, improves the conductivity, the ion diffusion capacity and the low-temperature cycle life of the sodium iron phosphate, and is beneficial to expanding the application range of the sodium iron phosphate at low temperature.

Description

Bicontinuous-phase coated sodium ferric phosphate cathode material and preparation method thereof
Technical Field
The invention relates to the technical field of ion battery anode materials, in particular to a bicontinuous phase coated sodium ferric pyrophosphate anode material and a preparation method thereof.
Background
Lithium Ion Batteries (LIBs) are widely used as power sources for advanced portable electronic products due to their high energy density. However, the high cost and limited amount of stored lithium have prevented the use of lithium ion batteries for future large-scale energy storage. Under the background, the method is similar to the working principle, the preparation process and the engineering mass production flow of the lithium ion battery, has obvious resource, cost and safety advantages and uses Na + Sodium Ion Batteries (SIBs), which are carriers, are one of the requisite routes and best options for the development of large-scale energy storage technologies in the future.
For grid-scale energy storage systems, the power density and cycling stability of the battery modules are more important than the energy density. Based on these considerations, polyanionic materials having 3-D framework structures are of great interest because of their strong structural resistance to repeated insertion/extraction and their strong inductive effect of increasing the operating voltage. To date, polyanionic cathode materials have made many breakthroughs, such as the prussian blue family of compounds, phosphates, fluorophosphates, fluorosulfates and pyrophosphates. Wherein, NASICON type mixed phosphate material Na 4 Fe 3 (PO 4 ) 2 P 2 O 7 (NFPP) has the advantages of both phosphate and pyrophosphate. The unique dimer structure can rotate and twist to compensate the deformation of the material structure, so that the material structure is formed in Na + The crystal structure changes little during the insertion/extraction process, and the volume changes less than 4%. The iron-based material has low cost, is nontoxic and environment-friendly, and is an ideal positive electrode material of sodium ion batteries. However, the sodium ferric phosphate cathode material also faces a great challenge that the low-temperature performance of the material is relatively poor; under the low-temperature condition, the decay of the ferric sodium phosphate pyrophosphate battery is serious, and the cycle life is obviously reduced. The low-temperature performance of the battery is poor mainly because the material is an insulator, the electronic conductivity is low, the sodium ion diffusivity is poor, the internal resistance of the battery is increased, the polarization influence is large, and the charge and discharge of the battery are blocked, so that the low-temperature performance is not ideal. Therefore, how to improve the electronic conductivity and capacity and low temperature performance of such materials is a problem in the art that needs to be addressed.
At present, the electrochemical performance of the sodium iron phosphate pyrophosphate can be improved to a certain extent by means of cladding, doping or morphology control and the like, but the improvement of the charge and discharge performance of the sodium iron phosphate pyrophosphate under the low-temperature condition is very critical for expanding the application range of the sodium iron phosphate pyrophosphate under the low temperature.
Disclosure of Invention
The invention aims to provide a bicontinuous phase coated sodium ferric phosphate cathode material and a preparation method thereof, which utilize metal oxide TiNb 2 O 7 The coating layer which is uniformly mixed with the carbon layer to form a bicontinuous phase completely wraps the sodium iron phosphate cathode material, so that the conductivity, the ion diffusion capacity and the low-temperature cycle life of the sodium iron phosphate are improved, and the application range of the sodium iron phosphate at low temperature is widened; and the production process is simple, the safety coefficient is high, the method is suitable for large-scale industrial production, the prepared material battery has high capacity and long cycle life.
In order to achieve the above object, the present invention provides the following technical solutions:
the bicontinuous phase coated ferric sodium phosphate cathode material comprises ferric sodium phosphate and a coating layer coated on the surface of the ferric sodium phosphate, wherein the chemical formula of the ferric sodium phosphate is Na 4 Fe 3 (PO 4 ) 2 (P 2 O 7 ) The method comprises the steps of carrying out a first treatment on the surface of the The coating layer is metal oxide TiNb 2 O 7 And the carbon layer are uniformly mixed to form a continuous composite phase.
The preparation method of the bicontinuous phase coated sodium ferric phosphate cathode material adopts a spray drying method to prepare the cathode material, and comprises the following steps:
1) Preparation of sodium ferric phosphate slurry: uniformly mixing a sodium source, an iron source, a phosphorus source and a solvent to obtain ferric sodium phosphate slurry;
2) Spray drying the sodium ferric phosphate slurry obtained in the step 1) to obtain sodium ferric phosphate precursor;
3) Mixing the sodium ferric phosphate precursor obtained in the step 2) with a carbon source, a titanium source and a niobium source, and then carrying out grinding treatment;
4) Sintering the sodium ferric phosphate precursor obtained in the step 3) in a protective atmosphere, heating to 200-400 ℃ at a speed of 1-10 ℃/min, preserving heat for 2-10 hours, heating to 500-700 ℃ at a speed of 1-10 ℃/min, preserving heat for 6-24 hours, and then cooling; thus obtaining the required anode material.
Further, in step 1), sodium in the raw material molar ratio of the sodium iron phosphate pyrophosphate slurry is prepared: iron: phosphorus is 3.95-4.05: 3:3.95 to 4; the solvent is water or ethanol.
Further, in step 1), the sodium source is one or more of sodium carbonate, sodium hydroxide, sodium bicarbonate, sodium pyrophosphate, disodium dihydrogen pyrophosphate, and sodium citrate; the iron source is one or more of ferrous oxalate, ferric oxalate, ferrous sulfate, ferrous ammonium sulfate, ferric oxide and ferric phosphate; the phosphorus source is one or more of monoammonium phosphate, diammonium phosphate and phosphoric acid.
Further, in the step 2), the air inlet temperature of spray drying is 100-250 ℃; the air outlet temperature is 80-120 ℃; the diameter of the nozzle is 0.5-2.5 mm; the air source is compressed air, and preheating is carried out at 80-250 ℃ before entering the spray gun; the spraying feeding flow rate is 30-2000 mL/h.
Further, in step 3), the carbon source is one or more of soluble starch, cellulose, sucrose, glucose, and ascorbic acid; the addition amount of the carbon source is 5 to 25 percent of the mass of the finished product sodium ferric pyrophosphate; the titanium source is one or more of titanium n-propoxide, tetrabutyl titanate and titanium dioxide; the niobium source is one or more of ammonium niobate oxalate hydrate, niobium ethoxide, niobium pentachloride and niobium oxide.
Further, in step 4), the protective atmosphere comprises one or more of nitrogen, argon or a mixture of an inert gas and a reducing gas.
Further, in step 4), the cooling is one of air cooling, water cooling and liquid nitrogen cooling.
Further, in step 4), the mass of the metal oxide coating layer of the obtained positive electrode material is 5 to 10% of the mass of the positive electrode material.
Application of bicontinuous phase coated ferric sodium pyrophosphate positive electrode material in sodium ion battery.
The technical proposal has the beneficial effects that:
1. the bicontinuous phase coated sodium ferric phosphate cathode material provided by the invention utilizes metal oxide TiNb 2 O 7 The high-conductivity network layer with a continuous composite phase structure is formed by uniformly mixing the high-conductivity network layer with the carbon layer to form a coating layer of a continuous composite phase, so that the electronic conductivity, the low-temperature activity and the cycle life of the material are greatly improved, and the application range of the sodium ferric phosphate at low temperature is widened;
2. the invention adopts a spray drying method to prepare the bicontinuous phase coated ferric sodium phosphate cathode material, and can control the uniform morphology of the electrode material. The spray drying method has the advantages of large production capacity, high product quality and easy expansion besides the capability of full automation and continuity;
3. the bicontinuous phase coated sodium ferric phosphate anode material provided by the invention has the advantages of low raw material cost, abundant sources and contribution to industrial application.
Drawings
FIG. 1 is a flow chart of a preparation method of a bicontinuous phase coated sodium iron phosphate cathode material of the present invention;
FIG. 2 is an SEM image of the sodium iron pyrophosphate phosphate positive electrode material prepared in example 1 of the present invention;
FIG. 3 is an XRD pattern of sodium iron pyrophosphate phosphate positive electrode materials prepared in example 1 and comparative example 1 of the present invention;
FIG. 4 is a graph showing the cycle performance of the sodium iron pyrophosphate cathode materials prepared in example 1 and comparative example 1 according to the present invention at 1C;
FIG. 5 is a graph showing the low-temperature cycle performance at 0.5C of the sodium iron pyrophosphate positive electrode materials prepared in example 1 and comparative example 1 of the present invention.
Detailed Description
The invention is described in further detail below with reference to the attached drawings and embodiments:
a bicontinuous phase coated ferric sodium phosphate positive electrode material comprises ferric sodium phosphate and a coating layer coated on the surface of the ferric sodium phosphate positive electrode material, wherein the chemical formula of the ferric sodium phosphate is Na 4 Fe 3 (PO 4 ) 2 (P 2 O 7 ) The method comprises the steps of carrying out a first treatment on the surface of the The coating layer is metal oxide TiNb 2 O 7 And the carbon layer are uniformly mixed to form a continuous composite phase.
As shown in figure 1 of the drawings,
the preparation method of the bicontinuous phase coated sodium ferric phosphate cathode material adopts a spray drying method to prepare the cathode material, and comprises the following steps:
1) Preparation of sodium ferric phosphate slurry: uniformly mixing sodium carbonate, ferrous oxalate and ammonium dihydrogen phosphate in a molar ratio of 4:3:4 in ethanol to obtain sodium ferric pyrophosphate phosphate slurry S1;
2) Spray drying the sodium ferric phosphate slurry S1 obtained in the step 1), wherein the air inlet temperature of the spray drying is 100-250 ℃; the air outlet temperature is 80-120 ℃; the diameter of the nozzle is 0.5-2.5 mm; the air source is compressed air, and preheating is carried out at 80-250 ℃ before entering the spray gun; the spray feeding flow is 30-2000 mL/h, and the sodium ferric phosphate precursor S2 is obtained;
3) Mixing the sodium ferric phosphate precursor S2 obtained in the step 2) with cellulose, titanium n-propoxide and niobium ethoxide, wherein the addition amount of the cellulose is 15% of the mass of the finished sodium ferric phosphate, and then carrying out grinding treatment;
4) Sintering the sodium ferric phosphate precursor obtained in the step 3) in nitrogen atmosphere, heating to 200-400 ℃ at a speed of 1-10 ℃/min, preserving heat for 2-10 hours, heating to 500-700 ℃ at a speed of 1-10 ℃/min, preserving heat for 6-24 hours, and then cooling with liquid nitrogen; the required anode material is obtained, wherein the mass of the metal oxide coating layer is 7.5% of the mass of the anode material.
Application of bicontinuous phase coated ferric sodium pyrophosphate positive electrode material in sodium ion battery.
Example 1
105.99g of Na is weighed according to the stoichiometric ratio of 4:3:4 2 CO 3 、269.85gFeC 2 O 4 ·2H 2 O、230.06gNH 4 H 2 PO 4 Adding the mixture into 10L of water, adding and stirring each material for 0.5h, adding the next material, and stirring for 1h after all materials are added to obtain uniformly mixed sodium ferric phosphate slurry S1; the surface tension of the test slurry is 0.01N/m, the viscosity is 1500 mPa.s, and the solid content is 25%;
spray-drying sodium iron phosphate slurry S1 under the conditions that the nozzle diameter is 0.1mm, the preheated compressed air is 200 ℃, the pressure is 0.5MPa, the air inlet temperature is 150 ℃, the air outlet temperature is 85 ℃ and the feeding flow is 1200L/h, so as to prepare sodium iron phosphate precursor S2;
sodium iron phosphate pyrophosphate precursor S2 with 62.34g glucose, 25.58gC 12 H 28 O 4 Ti、54.54gC 4 H 4 NNbO 9 .nH 2 Mixing O, and then grinding to obtain a sample S3;
and sintering the sample S3 in a high-purity nitrogen atmosphere, heating to 350 ℃ at 2 ℃/min, preserving heat for 4 hours, heating to 550 ℃, preserving heat for 10 hours, and naturally cooling the obtained sample.
Comparative example 1
105.99g of Na is weighed according to the stoichiometric ratio of 4:3:4 2 CO 3 、269.85gFeC 2 O 4 ·2H 2 O、230.06gNH 4 H 2 PO 4 Adding the mixture into 10L of water, adding and stirring each material for 0.5h, adding the next material, and stirring for 1h after all materials are added to obtain uniformly mixed sodium ferric phosphate slurry S1; the test slurry had a surface tension of 0.01N/m, a viscosity of 1500 mPas and a solids content of 25%.
Spray-drying sodium iron phosphate slurry S1 under the conditions that the nozzle diameter is 0.1mm, the preheated compressed air is 200 ℃, the pressure is 0.5MPa, the air inlet temperature is 150 ℃, the air outlet temperature is 85 ℃ and the feeding flow is 1200L/h, so as to prepare sodium iron phosphate precursor S2;
mixing a sodium ferric phosphate precursor S2 with 62.34g of glucose, and then carrying out grinding treatment to obtain a sample S3;
and sintering the sample S3 in a high-purity nitrogen atmosphere, heating to 350 ℃ at 2 ℃/min, preserving heat for 4 hours, heating to 550 ℃, preserving heat for 10 hours, and naturally cooling the obtained sample.
Performance test:
the electrochemical properties of the sodium iron pyrophosphate phosphate cathode materials prepared in example 1 and comparative example 1 were tested as follows:
all tests were performed with a button cell model CR2032 as a reference, using a metallic sodium sheet as the counter electrode, glass fiber as the separator, and using NaPF 6 Is electrolyte; the method comprises the following specific steps:
(1) Mixing and grinding an active substance, a conductive agent and polyvinylidene fluoride (PVDF) according to the mass ratio of 8:1:1, and using N-methyl-2-pyrrolidone (NMP) as a solvent;
(2) Coating the slurry ground in the step (1) on aluminum foil by using a preparation device, controlling the thickness to be 200 mu m, and then transferring the aluminum foil to a vacuum furnace at 120 ℃ for drying for 12 hours;
(3) And calculating the thickness of the pole piece obtained by rolling according to the compaction density, rolling, cutting the electrode into small wafers with the diameter of 12mm, and transferring the small wafers into a glove box filled with argon gas to assemble the button cell.
As shown in a scanning electron microscope diagram of FIG. 2, the morphology of the sodium ferric pyrophosphate positive electrode material is spherical.
As shown in FIG. 3, the XRD image diffraction peak of the sodium ferric pyrophosphate anode material prepared in the embodiment 1 and the XRD standard card peak position and peak intensity are better corresponding, which fully shows that no impurity is generated in the synthesis process, the coating has no influence on the structure and purity of the material, and the sodium ferric pyrophosphate anode material is pure-phase sodium pyrophosphate.
As shown in the graph of the cycle performance of fig. 4, the voltage range is 1.5-3.8V at 1C current density, the sodium iron phosphate cathode material prepared in example 1 has no attenuation trend after 250 cycles, and exhibits excellent cycle performance, while the sodium iron phosphate cathode material prepared in comparative example 1 has a capacity retention rate of only 77.11% after 250 cycles under the same conditions.
As shown in the low-temperature cycle performance chart of fig. 5, at a current density of 0.5C, the low-temperature performance of the sodium ferric phosphate cathode material prepared in example 1 after 100 cycles is far better than that of the sodium ferric phosphate cathode material prepared in comparative example 1. From the factors influencing sodium ion batteries, the low temperature performance of sodium ion batteries is largely related to the activity of the positive electrode material and the performance of the electrolyte. The sodium ferric phosphate cathode material prepared by the work mainly constructs a good conductive network structure, reduces battery polarization and enables charge to be embedded between particles more smoothly.
Example 2:
111.29g of Na is weighed according to the stoichiometric ratio of 4.05:3:4 2 CO 3 、269.85gFeC 2 O 4 ·2H 2 O、230.06gNH 4 H 2 PO 4 Adding the mixture into 10L of water, adding and stirring each material for 0.5h, adding the next material, and stirring for 1h after all materials are added to obtain uniformly mixed sodium ferric phosphate slurry S1; the surface tension of the test slurry is 0.01N/m, the viscosity is 1500 mPa.s, and the solid content is 25%;
spray-drying sodium iron phosphate slurry S1 under the conditions that the nozzle diameter is 0.12mm, the preheated compressed air is 180 ℃, the pressure is 0.45MPa, the air inlet temperature is 250 ℃, the air outlet temperature is 95 ℃ and the feeding flow rate is 1300L/h to prepare sodium iron phosphate precursor S2;
sodium iron pyrophosphate phosphate precursor S2 with 46.75g citric acid, 30.63g C 16 H 36 O 4 Ti、54.54gC 4 H 4 NNbO 9 .nH 2 Mixing O, and then grinding to obtain a sample S3;
and sintering the sample S3 in a high-purity nitrogen atmosphere, namely heating to 350 ℃ at a speed of 4 ℃/min, preserving heat for 4 hours, heating to 500 ℃, preserving heat for 10 hours, and naturally cooling the obtained sample.
Example 3:
136.94g of Na is weighed according to the stoichiometric ratio of 4.03:3:4 4 P 2 O 7 、269.85gFeC 2 O 4 ·2H 2 O、230.06gNH 4 H 2 PO 4 Adding the mixture into 10.5L of water, adding and stirring each material for 0.5h, adding the next material, and stirring for 1h after all materials are added to obtain uniformly mixed ferric sodium pyrophosphate slurry S1; the surface tension of the test slurry is 0.01N/m, the viscosity is 1500 mPa.s, and the solid content is 25%;
spray drying S1 under the conditions that the nozzle diameter is 0.15mm, the preheated compressed air is 220 ℃, the pressure is 0.6MPa, the air inlet temperature is 200 ℃, the air outlet temperature is 100 ℃ and the feeding flow is 1000L/h, so as to prepare sodium ferric phosphate precursor S2;
mixing sodium ferric pyrophosphate precursor S2 with 31.17g sucrose and 7.19g TiO 2 、47.85gNb 2 O 5 Mixing, and grinding to obtain a sample S3;
and sintering the sample S3 in a high-purity nitrogen atmosphere, namely heating to 350 ℃ at 5 ℃/min, preserving heat for 4 hours, heating to 600 ℃, preserving heat for 8 hours, and naturally cooling the sample.
Example 4:
139.60g of Na is weighed according to the stoichiometric ratio of 4.05:3:4 4 P 2 O 7 、269.85gFeC 2 O 4 ·2H 2 O、230.06gNH 4 H 2 PO 4 Adding the mixture into 10.5L of water, adding and stirring each material for 0.5h, adding the next material, and stirring for 1h after all materials are added to obtain uniformly mixed ferric sodium pyrophosphate slurry S1; the surface tension of the test slurry is 0.02N/m, the viscosity is 800 mPa.s, and the solid content is 22%;
spray-drying sodium iron phosphate slurry S1 under the conditions that the nozzle diameter is 0.12mm, the preheated compressed air is 180 ℃, the pressure is 0.45MPa, the air inlet temperature is 250 ℃, the air outlet temperature is 95 ℃ and the feeding flow rate is 1300L/h to prepare sodium iron phosphate precursor S2;
mixing sodium ferric pyrophosphate precursor S2 with 31.17g sucrose and 3.59g TiO 2 、23.93gNb 2 O 5 Mixing, and grinding to obtain a sample S3;
and sintering the sample S3 in a high-purity nitrogen atmosphere, namely heating to 350 ℃ at 2 ℃/min, preserving heat for 4 hours, heating to 550 ℃, preserving heat for 10 hours, and naturally cooling the sample.
The foregoing is merely exemplary embodiments of the present invention, and detailed technical solutions or features that are well known in the art have not been described in detail herein. It should be noted that, for those skilled in the art, several variations and modifications can be made without departing from the technical solution of the present invention, and these should also be regarded as the protection scope of the present invention, which does not affect the effect of the implementation of the present invention and the practical applicability of the patent. The protection scope of the present application shall be subject to the content of the claims, and the description of the specific embodiments and the like in the specification can be used for explaining the content of the claims.

Claims (10)

1. A bicontinuous phase coated ferric sodium phosphate positive electrode material is characterized by comprising ferric sodium phosphate and a coating layer coated on the surface of the ferric sodium phosphate positive electrode material, wherein the chemical formula of the ferric sodium phosphate is Na 4 Fe 3 (PO 4 ) 2 (P 2 O 7 ) The method comprises the steps of carrying out a first treatment on the surface of the The coating layer is metal oxide TiNb 2 O 7 And the carbon layer are uniformly mixed to form a continuous composite phase.
2. A method for preparing the bicontinuous phase coated sodium ferric phosphate positive electrode material according to claim 1, wherein the positive electrode material is prepared by adopting a spray drying method, and the method comprises the following steps of:
1) Preparation of sodium ferric phosphate slurry: uniformly mixing a sodium source, an iron source, a phosphorus source and a solvent to obtain ferric sodium phosphate slurry;
2) Spray drying the sodium ferric phosphate slurry obtained in the step 1) to obtain sodium ferric phosphate precursor;
3) Mixing the sodium ferric phosphate precursor obtained in the step 2) with a carbon source, a titanium source and a niobium source, and then carrying out grinding treatment;
4) Sintering the sodium ferric phosphate precursor obtained in the step 3) in a protective atmosphere, heating to 200-400 ℃ at a speed of 1-10 ℃/min, preserving heat for 2-10 hours, heating to 500-700 ℃ at a speed of 1-10 ℃/min, preserving heat for 6-24 hours, and then cooling; thus obtaining the required anode material.
3. The method for producing a bicontinuous phase coated sodium iron phosphate cathode material according to claim 2, wherein in step 1), sodium in the molar ratio of raw materials for producing sodium iron phosphate slurry: iron: phosphorus is 3.95-4.05: 3:3.95 to 4; the solvent is water or ethanol.
4. The method for preparing a bicontinuous phase coated ferric sodium pyrophosphate positive electrode material according to claim 2, wherein in the step 1), the sodium source is one or more of sodium carbonate, sodium hydroxide, sodium bicarbonate, sodium pyrophosphate, disodium dihydrogen pyrophosphate and sodium citrate; the iron source is one or more of ferrous oxalate, ferric oxalate, ferrous sulfate, ferrous ammonium sulfate, ferric oxide and ferric phosphate; the phosphorus source is one or more of monoammonium phosphate, diammonium phosphate and phosphoric acid.
5. The method for preparing a bicontinuous phase coated sodium iron phosphate cathode material according to claim 2, wherein in step 2), the air inlet temperature of spray drying is 100-250 ℃; the air outlet temperature is 80-120 ℃; the diameter of the nozzle is 0.5-2.5 mm; the air source is compressed air, and preheating is carried out at 80-250 ℃ before entering the spray gun; the spraying feeding flow rate is 30-2000 mL/h.
6. The method for preparing a bicontinuous phase coated ferric sodium phosphate positive electrode material according to claim 2, wherein in the step 3), the carbon source is one or more of soluble starch, cellulose, sucrose, glucose and ascorbic acid; the addition amount of the carbon source is 5 to 25 percent of the mass of the finished product sodium ferric pyrophosphate; the titanium source is one or more of titanium n-propoxide, tetrabutyl titanate and titanium dioxide; the niobium source is one or more of ammonium niobate oxalate hydrate, niobium ethoxide, niobium pentachloride and niobium oxide.
7. The method of preparing a bicontinuous phase coated sodium iron phosphate cathode material according to claim 2, wherein in step 4), the protective atmosphere comprises one or more of nitrogen, argon or a mixture of an inert gas and a reducing gas.
8. The method for preparing a bicontinuous phase coated sodium iron phosphate positive electrode material according to claim 2, wherein in the step 4), the cooling is one of air cooling, water cooling and liquid nitrogen cooling.
9. The method for producing a bicontinuous phase coated sodium iron phosphate positive electrode material according to claim 2, wherein in step 4), the mass of the metal oxide coating layer of the positive electrode material obtained is 5 to 10% of the mass of the positive electrode material.
10. Use of the bicontinuous phase coated ferric sodium pyrophosphate positive electrode material according to claim 1 in a sodium ion battery.
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