Sodium ferric phosphate pyrophosphate-based composite material as well as preparation method and application thereof

Abstract

The invention provides a sodium ferric phosphate pyrophosphate-based composite material as well as a preparation method and application thereof. The method comprises the following steps: respectively weighing a sodium source, a phosphorus source, an iron source, a carbon source, a doping source, a reducing agent and a dispersing agent according to a stoichiometric ratio; adding a doping source and a reducing agent into water, mixing and reacting to obtain a mixed solution; adding a sodium source, a phosphorus source, an iron source, a carbon source and a dispersing agent into the mixed solution, fully mixing, and then carrying out ball milling to obtain mixed slurry; carrying out spray drying on the mixed slurry to obtain precursor particles; carrying out tabletting treatment on the precursor particles, and pressing the precursor particles into tablets; and sintering the pressed precursor particles in a weak reducing atmosphere to obtain the sodium ferric phosphate pyrophosphate-based composite material. The sodium ferric phosphate pyrophosphate-based composite material prepared by the method disclosed by the invention is applied to an electrochemical energy storage device and shows excellent electrochemical performance.

Description

Technical Field

[0001] The present invention relates to the technical field of electrode materials, and more particularly to a sodium iron phosphate pyrophosphate-based composite material, a preparation method thereof, and applications thereof. Background Art

[0002] Energy and environmental crises have become two major, long-standing challenges for human development. The continued development of new energy storage and power batteries with high energy density and low pollution levels is a key solution. The commercialization and large-scale application of lithium-ion batteries also demonstrate the practicality of these rocking-chair batteries. However, the increasing scarcity of lithium and cobalt ores makes lithium-ion batteries expensive, hindering their large-scale application and long-term development. Consequently, a growing number of researchers are turning their attention to sodium-ion batteries, which offer superior performance, lower cost, and abundant resources.

[0003] Among them, sodium iron phosphate pyrophosphate (Na4Fe3(PO4)2(P2O7)) of the phosphate system has become one of the most promising positive electrode materials for sodium ion batteries due to its high safety, long life, environmental friendliness and low cost. However, the inherent disadvantages of phosphate positive electrode materials, such as poor electronic conductivity and ionic conductivity and low energy density, affect their large-scale industrial application. In addition, side reactions such as transition metal dissolution in the electrolyte will affect their battery life. Therefore, it is necessary to seek effective modification methods to improve their electrochemical performance. Carbon coating is a low-cost and common improvement method, but its main function is to improve its conductivity while improving its stability to a certain extent, but it has no obvious effect on modifying the energy density of the material.

[0004] Therefore, how to improve the energy density of sodium iron pyrophosphate materials to enhance their electrochemical performance has become one of the key issues in sodium ion battery related technologies. Summary of the Invention

[0005] Based on the above technical problems existing in the prior art, the present invention provides a method for preparing sodium iron phosphate pyrophosphate-based composite materials. Through process adjustment, the originally chemically inert high-valent doping elements are activated, thereby improving the structural stability of the composite material and increasing its energy density.

[0006] In order to achieve the above object, the technical solution of the present invention is as follows:

[0007] A method for preparing a sodium iron phosphate pyrophosphate-based composite material comprises the following steps:

[0008] S1. Weigh the sodium source, phosphorus source, iron source, carbon source, doping source, reducing agent and dispersant according to the stoichiometric ratio;

[0009] S2, adding the doping source and the reducing agent into water, mixing and reacting to obtain a mixed solution;

[0010] S3, adding a sodium source, a phosphorus source, an iron source, a carbon source and a dispersant to the mixed solution, mixing thoroughly, and then ball milling to obtain a mixed slurry;

[0011] S4, spray drying the mixed slurry to obtain precursor particles;

[0012] S5, pressing the precursor particles into tablets;

[0013] S6. Sintering the pressed precursor particles in a weak reducing atmosphere to obtain a sodium iron phosphate pyrophosphate-based composite material.

[0014] In some embodiments, in step S1, the sodium source is at least one of sodium carbonate, sodium hydroxide, sodium bicarbonate, sodium dihydrogen phosphate, sodium pyrophosphate, disodium dihydrogen pyrophosphate, sodium acetate, and sodium citrate.

[0015] In some embodiments, the phosphorus source is at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and phosphoric acid.

[0016] In some embodiments, the iron source is at least one of ferric chloride, ferrous oxalate, ferrous oxalate, ferrous sulfate, ferrous ammonium sulfate, diammonium hydrogen phosphate, and phosphoric acid.

[0017] In some embodiments, the carbon source is at least one of cellulose, sucrose, and glucose.

[0018] In some embodiments, the dispersant is at least one of polyvinyl pyrrolidone, polyethylene glycol, and polyvinyl alcohol.

[0019] In some embodiments, the reducing agent is catechol and / or ascorbic acid.

[0020] In some embodiments, the doping source is at least one of ammonium molybdate tetrahydrate, sodium molybdate, molybdenum dioxide, and molybdenum trioxide.

[0021] The present invention also provides a sodium iron phosphate pyrophosphate-based composite material obtained by the preparation method of any of the above embodiments, wherein the sodium iron phosphate pyrophosphate-based composite material comprises a molybdenum-doped sodium iron phosphate pyrophosphate matrix material and a carbon coating layer coated on the surface of the matrix material, and the general structural formula of the matrix material is: Na4Fe 3-x Mo x (PO4)2(P2O7), where 0<x≤0.3.

[0022] The present invention also provides a positive electrode active material, which includes the composite material.

[0023] The present invention also provides a positive electrode material, which includes the positive electrode active material.

[0024] The present invention also provides a positive electrode, which comprises the positive electrode material.

[0025] The present invention also provides an electrochemical energy storage device, comprising the above-mentioned positive electrode. Specifically, the electrochemical energy storage device includes but is not limited to a sodium ion battery, a sodium ion capacitor, and the like.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] The present invention dopes the sodium ferric phosphate pyrophosphate material through a specific method. Through process control, the originally chemically inert Mo is activated, so that low-valent and high-valent molybdenum ions coexist in the sodium ferric phosphate pyrophosphate matrix material. The low-valent molybdenum ions can provide additional electron transfer to the high-valent molybdenum ions, thereby increasing the energy density of the composite material. The high-valent molybdenum ions provide stable structural support by strongly binding with O, thereby improving the structural stability of the composite material. The composite material of the present invention is used as a positive electrode active material in an electrochemical energy storage device, which can have a high specific capacity and excellent cycle stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a SEM image of the sodium iron phosphate pyrophosphate-based composite material prepared in Example 1;

[0029] Figure 2 is the XRD pattern of the sodium iron phosphate pyrophosphate-based composite material prepared in Example 1;

[0030] Figure 3 This is an energy spectrum diagram of the sodium iron phosphate pyrophosphate-based composite material prepared in Example 1;

[0031] Figure 4 Graph showing the initial charge and discharge specific capacity of the sodium iron pyrophosphate-based composite material prepared in Example 1 and Comparative Example 1;

[0032] Figure 5 This is a graph showing the cycling performance of the sodium iron pyrophosphate-based composite material prepared in Example 1 and Comparative Example 1 at a current density of 2C. DETAILED DESCRIPTION

[0033] The following description sets forth numerous specific details to facilitate a thorough understanding of the present invention. However, the present invention can be implemented in many other ways than those described herein, and those skilled in the art may make similar modifications without departing from the scope of the present invention. Therefore, the present invention is not limited to the specific implementations disclosed below.

[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in this specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0035] Example 1

[0036] A method for preparing a sodium iron phosphate pyrophosphate-based composite material comprises the following steps:

[0037] S1. Weigh sodium carbonate, ferric phosphate, sodium dihydrogen phosphate, ammonium molybdate tetrahydrate, citric acid, ascorbic acid, and polyvinyl pyrrolidone according to the stoichiometric ratio;

[0038] S2. Add 5 g of ammonium molybdate tetrahydrate and 3 g of ascorbic acid to 20 ml of deionized water, stir and react to obtain a mixed solution;

[0039] S3, 62.3g sodium carbonate, 177g ferric phosphate, 52.8g sodium dihydrogen phosphate, 13g citric acid, 5g polyvinyl pyrrolidone were added to 1L of the mixed solution and stirred evenly; after the stirring was completed, the mixture was transferred to the sand milling section, firstly coarsely polished with 0.5-0.6mm zirconium beads for 1-2h, and then transferred to the fine grinding section, using 0.3-0.4mm zirconium beads for fine grinding for 5-10h to obtain a slurry;

[0040] S4, transferring the slurry into a spray dryer for spray drying to obtain precursor particles; wherein, during the spray drying process, the feed rate is set to 1000 ml / h, the inlet air temperature is set to 200° C., and the outlet air temperature is set to 100° C.;

[0041] S5. Sieve the precursor particles through a 150-mesh sieve, take the particles under the sieve, and press them into tablets under a pressure of 20 MPa;

[0042] S6. The pressed precursor particles were placed in a tube furnace, and in an argon atmosphere containing 5% (v / v) hydrogen, the temperature was first raised to 350°C at a rate of 2°C / min for pre-sintering for 2 hours, and then the temperature was raised to 750°C at a rate of 5°C / min for sintering for 10 hours; after the sintering was completed, the pellets were cooled to room temperature, taken out, and then sieved through a 150-mesh sieve to obtain the target product, molybdenum-doped sodium iron phosphate pyrophosphate-based composite material (Na4Fe 2.85 Mo 0.15 (PO4)2(P2O7)).

[0043] The molybdenum-doped sodium iron phosphate pyrophosphate-based composite material obtained in this example was characterized. The results are as follows: Figure 1-Figure 3 shown.

[0044] Comparative Example 1

[0045] A method for preparing a sodium iron phosphate pyrophosphate-based composite material comprises the following steps:

[0046] S1. Weigh sodium carbonate, ferric phosphate, sodium dihydrogen phosphate, citric acid, ascorbic acid, and polyvinyl pyrrolidone according to the stoichiometric ratio;

[0047] S2, 64g sodium carbonate, 180g ferric phosphate, 48g sodium dihydrogen phosphate, 13g citric acid, 3g ascorbic acid and 3g polyvinyl pyrrolidone were added to 1L of the mixed solution and stirred evenly; after the stirring was completed, the mixture was transferred to the sand milling section, first coarsely polished with 0.5-0.6mm zirconium beads for 1-2h, and then transferred to the fine grinding section, and finely ground with 0.3-0.4mm zirconium beads for 5-10h to obtain a slurry;

[0048] S3. Transferring the slurry into a spray dryer for spray drying to obtain precursor particles; wherein, during the spray drying process, the feed rate is set to 1000 ml / h, the inlet air temperature is set to 200° C., and the outlet air temperature is set to 100° C.;

[0049] S4. Sieve the precursor particles through a 150-mesh sieve, take the particles under the sieve, and press them into tablets under a pressure of 20 MPa;

[0050] S5. Place the pressed precursor particles in a tubular furnace, and in an argon atmosphere containing 5% (v / v) hydrogen, first heat them to 350°C at a rate of 2°C / min for pre-sintering for 2 hours, and then heat them to 750°C at a rate of 5°C / min for sintering for 10 hours; after sintering, cool them to room temperature with the furnace, take them out, and then pass them through a 150-mesh sieve to obtain the target product, sodium iron phosphate pyrophosphate-based composite material (Na4Fe3(PO4)2(P2O7)).

[0051] Comparative Example 2

[0052] A method for preparing a sodium iron phosphate pyrophosphate-based composite material comprises the following steps:

[0053] S1. Weigh sodium carbonate, ferric phosphate, sodium dihydrogen phosphate, ammonium molybdate tetrahydrate, citric acid, and polyvinyl pyrrolidone according to the stoichiometric ratio;

[0054] S2, 62.3g sodium carbonate, 177g ferric phosphate, 52.8g sodium dihydrogen phosphate, 13g citric acid, 5g ammonium molybdate tetrahydrate and 5g polyvinyl pyrrolidone were added to 1L of the mixed solution and stirred evenly; after the stirring was completed, the mixture was transferred to the sand milling section, first coarsely polished with 0.5-0.6mm zirconium beads for 1-2h, and then transferred to the fine grinding section, and finely ground with 0.3-0.4mm zirconium beads for 5-10h to obtain a slurry;

[0055] S3. Transferring the slurry into a spray dryer for spray drying to obtain precursor particles; wherein, during the spray drying process, the feed rate is set to 1000 ml / h, the inlet air temperature is set to 200° C., and the outlet air temperature is set to 100° C.;

[0056] S4. The pressed precursor particles were placed in a tube furnace, and in an argon atmosphere containing 5% (v / v) hydrogen, the temperature was first raised to 350°C at a rate of 2°C / min for pre-sintering for 2 hours, and then the temperature was raised to 750°C at a rate of 5°C / min for sintering for 10 hours; after the sintering was completed, the pellets were cooled to room temperature, taken out, and then sieved through a 150-mesh sieve to obtain the target product, molybdenum-doped sodium iron phosphate pyrophosphate-based composite material (Na4Fe 2.85 Mo 0.15 (PO4)2(P2O7)).

[0057] Comparative Example 3

[0058] A method for preparing a sodium iron phosphate pyrophosphate-based composite material comprises the following steps:

[0059] S1. Weigh sodium carbonate, ferric phosphate, sodium dihydrogen phosphate, molybdenum dioxide, ammonium molybdate heptahydrate, citric acid, ascorbic acid, and polyvinylpyrrolidone according to the stoichiometric ratio;

[0060] S3, 62.3g sodium carbonate, 177g ferric phosphate, 52.8g sodium dihydrogen phosphate, 13g citric acid, 1.5g molybdenum dioxide, 1.5g ammonium molybdate heptahydrate, 3g ascorbic acid and 3g polyvinyl pyrrolidone were added to the mixed solution and stirred evenly; after stirring was completed, the mixture was transferred to the sand milling section, first coarsely polished with 0.5-0.6mm zirconium beads for 1-2h, and then transferred to the fine grinding section, and finely ground with 0.3-0.4mm zirconium beads for 5-10h to obtain a slurry;

[0061] S4, transferring the slurry into a spray dryer for spray drying to obtain precursor particles; wherein, during the spray drying process, the feed rate is set to 1000 ml / h, the inlet air temperature is set to 200° C., and the outlet air temperature is set to 100° C.;

[0062] S5. Sieve the precursor particles through a 150-mesh sieve, take the particles under the sieve, and press them into tablets under a pressure of 20 MPa;

[0063] S6. The pressed precursor particles were placed in a tube furnace, and in an argon atmosphere, the temperature was first raised to 350°C at a rate of 2°C / min for pre-sintering for 2 hours, and then the temperature was raised to 750°C at a rate of 5°C / min for sintering for 10 hours. After the sintering was completed, the pellets were cooled to room temperature, taken out, and then passed through a 150-mesh sieve to obtain the target product, molybdenum-doped sodium iron phosphate pyrophosphate-based composite material (Na4Fe 2.85 Mo 0.15(PO4)2(P2O7)).

[0064] The composite materials obtained in Example 1 and Comparative Examples 1-3 were used as positive electrode active materials in electrochemical energy storage devices, and electrochemical performance tests were performed as follows:

[0065] The positive electrode active material, conductive agent carbon black: binder PVDF were mixed in a mass ratio of 8:1:1. After thorough grinding, an appropriate amount of NMP was added to obtain a uniform slurry. The slurry was coated on an aluminum foil current collector, placed in a vacuum drying oven, dried at 120°C, then taken out and cut into discs. A metallic sodium sheet was used as the counter electrode. 1M NaClO4 / EC:DMC:EMC (1:1:1) was used as the electrolyte. After assembling button cells, the electrochemical performance was tested with a test voltage range of 1.7-4.3V.

[0066] The test results are shown in Table 1. Figure 4-Figure 5 shown.

[0067] like Figure 4 The composite material prepared in Example 1 of the present invention is used as a positive electrode active material, and the discharge specific capacity at a voltage of 1.7-4.3V and a current density of 0.1C is 131mAh / g; the composite material prepared in Comparative Example 1 is used as a positive electrode active material, and the discharge specific capacity at a voltage of 1.7-4.3V and a current density of 0.1C is 104mAh / g.

[0068] like Figure 5 The composite material prepared in Example 1 of the present invention is used as a positive electrode active material. It is cycled 300 times at a current density of 2C under the conditions of a voltage of 1.7-4.3V and a high temperature of 60°C, and the capacity retention rate is 93.89%; the composite material prepared in Comparative Example 1 is used as a positive electrode active material. It is cycled 300 times at a current density of 2C under the conditions of a voltage of 1.7-4.3V and a high temperature of 60°C, and the capacity retention rate is 62.06%.

[0069] Table 1 Electrochemical performance test results of the composite materials of Examples and Comparative Examples

[0070]

[0071] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0072] The above-described embodiments merely illustrate several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that a person skilled in the art would be able to make numerous modifications and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A method for preparing a sodium iron phosphate pyrophosphate-based composite material, characterized in that: The following steps are involved: S1. Weigh the sodium source, phosphorus source, iron source, carbon source, doping source, reducing agent and dispersant according to the stoichiometric ratio; S2, adding the doping source and the reducing agent into water, mixing and reacting to obtain a mixed solution; S3, adding a sodium source, a phosphorus source, an iron source, a carbon source and a dispersant to the mixed solution, mixing thoroughly, and then ball milling to obtain a mixed slurry; S4, spray drying the mixed slurry to obtain precursor particles; S5, pressing the precursor particles into tablets; S6. Sintering the pressed precursor particles in a weak reducing atmosphere to obtain a sodium iron phosphate pyrophosphate-based composite material.

2. The method for preparing the sodium iron phosphate pyrophosphate based composite material according to claim 1, wherein In step S1, the sodium source is at least one of sodium carbonate, sodium hydroxide, sodium bicarbonate, sodium dihydrogen phosphate, sodium pyrophosphate, disodium dihydrogen pyrophosphate, sodium acetate, and sodium citrate; and / or the phosphorus source is at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and phosphoric acid; and / or the iron source is at least one of ferric chloride, ferrous oxalate, ferrous oxalate, ferrous sulfate, ammonium ferrous sulfate, diammonium hydrogen phosphate, and phosphoric acid; and / or the carbon source is at least one of cellulose, sucrose, and glucose; and / or the dispersant is at least one of polyvinyl pyrrolidone, polyethylene glycol, and polyvinyl alcohol; and / or the reducing agent is catechol and / or ascorbic acid; and / or the doping source is at least one of ammonium molybdate heptahydrate, sodium molybdate, molybdenum dioxide, and molybdenum trioxide.

3. The method for preparing the sodium iron phosphate pyrophosphate based composite material according to claim 1, wherein In step S4, during the spray drying process, the feed rate is 1000-1500 ml / h, the air inlet temperature is 170-240°C, and the air outlet temperature is 80-120°C.

4. The method for preparing the sodium iron phosphate pyrophosphate composite material according to claim 1, wherein In step S5, before tableting, the precursor particles are first sieved through a 140-200 mesh sieve, and the particles under the sieve are pressed into tablets under a pressure of 15-30 MPa.

5. The method for preparing the sodium iron phosphate pyrophosphate based composite material according to claim 1, wherein In step S6, the weak reducing atmosphere is a mixed gas atmosphere containing 2-10% reducing gas; the mixed gas is composed of reducing gas and protective gas, the reducing gas is hydrogen or CO, and the protective gas is one of nitrogen, argon, and helium.

6. The composite material obtained by the preparation method according to any one of claims 1 to 5.

7. A positive electrode active material, characterized in that The composite material according to claim 6.

8. A cathode material, characterized in that Comprising the positive electrode active material according to claim 7.

9. A positive electrode, characterized in that Comprising the positive electrode material according to claim 8.

10. An electrochemical energy storage device, characterized in that Comprising the positive electrode according to claim 9.

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