Method and application for preparing hollow spherical Na4Fe3(PO4)2P2O7 from FePO4 liquid phase

Abstract

The present invention relates to a method for preparing hollow spherical Na4Fe3(PO4)2P2O7 from liquid-phase FePO4. FePO4, a carbon source, a sodium source, and a phosphorus source are sequentially added to deionized water and stirred at room temperature to obtain a suspension; the suspension is subjected to sanding; the sanded suspension is placed in a spray dryer for secondary granulation to obtain a yellow-green precursor powder; the precursor powder is subjected to staged sintering treatment to obtain carbon-coated hollow spherical Na4Fe3(PO4)2P2O7. A carbon-coated hollow spherical Na4Fe3(PO4)2P2O7 prepared by the above method. An application of the above carbon-coated hollow spherical Na4Fe3(PO4)2P2O7 in a cathode material for a sodium-ion battery. The beneficial effects are as follows: The carbon-coated hollow spherical Na4Fe3(PO4)2P2O7 has high electronic conductivity, which is beneficial to the transfer of sodium ions and the transportation of the electrolyte.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium ion batteries, and particularly relates to a method for preparing hollow spherical Na4Fe3(PO4)2P2O7 from a FePO4 liquid phase and its application. Background Art

[0002] In recent years, with the support for the new energy industry, green secondary batteries have gradually come into view. Among them, lithium ion batteries, as a representative, have largely occupied the market share of electric vehicles and portable electronic devices. However, the uneven distribution of lithium resources globally severely restricts the development of lithium ion batteries. Developing sodium ion batteries with rich resources, wide distribution and charge-discharge mechanisms similar to those of lithium ion batteries is of great significance. At present, the commercialized cathode materials for sodium ion batteries are mainly Prussian blue analogues, but they are prone to water absorption, have poor cycle performance and poor thermal stability during the preparation process. The polyanion-type material, one of the most commonly used cathode materials for sodium ion batteries, has low cost, no resource limitations, non-toxicity, high safety, and is a good choice for mass production.

[0003] The polyanion-type material is represented by sodium iron pyrophosphate phosphate (Na4Fe3(PO4)2P2O7), which not only has low cost, good cycle performance (volume change <4% during charge and discharge), high thermal stability, is not easily affected by the environment, and has a high theoretical capacity, but its electronic conductivity and ionic conductivity are relatively low, and its performance needs to be improved by nanosizing or coating. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method for preparing hollow spherical Na4Fe3(PO4)2P2O7 from a FePO4 liquid phase and its application to overcome the deficiencies in the above-mentioned prior art.

[0005] The technical solution for the present invention to solve the above technical problem is as follows: A method for preparing hollow spherical Na4Fe3(PO4)2P2O7 from a FePO4 liquid phase, comprising the following steps:

[0006] S100. FePO4, a carbon source, a sodium source and a phosphorus source are sequentially added to deionized water and stirred at room temperature to obtain a suspension;

[0007] S200. The suspension is subjected to sanding;

[0008] S300. The sanded suspension is placed in a spray dryer for secondary granulation to obtain a yellowish-green precursor powder;

[0009] S400. The precursor powder is subjected to staged sintering treatment to obtain carbon-coated hollow spherical Na4Fe3(PO4)2P2O7.

[0010] On the basis of the above technical solutions, the present invention can also be improved as follows.

[0011] Further, the sodium source includes one or more of sodium acetate, sodium carbonate, sodium bicarbonate, sodium phosphate, and sodium dihydrogen phosphate.

[0012] Further, the phosphorus source includes one or several of phosphoric acid, diammonium hydrogen phosphate, sodium dihydrogen phosphate, sodium phosphate, and diammonium dihydrogen phosphate.

[0013] Further, the carbon source includes one or several of glucose, sucrose, polyacrylonitrile, polyvinyl alcohol, and citric acid.

[0014] Further, the sanding parameters are: rotation speed of 1000 rpm to 1500 rpm, and time of 1 h to 24 h.

[0015] Further, the solid content of the suspension spray-dried by the spray dryer is 3 wt% to 40 wt%, the feeding rate is 20 mL / h to 1500 mL / h, the inlet air temperature is 105°C to 280°C, and the outlet air temperature is 60°C to 240°C.

[0016] Further, the staged sintering treatment adopts two-stage heating. First, it is heated from room temperature to 200°C to 300°C and kept warm for 1 h to 10 h, and then directly heated to 450°C to 550°C and kept warm for 3 h to 20 h.

[0017] The beneficial effects of the present invention are as follows:

[0018] 1) The technology of sanding combined with spray drying can improve the intrinsic properties of Na4Fe3(PO4)2P2O7. By regulating the solid content of the suspension and the spray drying parameters, nano-scale FePO4 primary particles can be assembled into micron-sized spheres with a hollow structure. This carbon-coated spherical structure micron sphere can not only improve the electronic conductivity of the carbon-coated hollow spherical Na4Fe3(PO4)2P2O7, but also be more conducive to the transfer of sodium ions and the transportation of electrolytes;

[0019] 2) The carbon-coated hollow spherical Na4Fe3(PO4)2P2O7 has a relatively large specific surface area, which is conducive to the conduction of internal ions and electrons, and can further improve the cycle stability of the material;

[0020] 3) The entire process is green, simple, easy to control, and can be mass-produced, providing technical support for the industrial preparation of carbon-coated hollow spherical Na4Fe3(PO4)2P2O7.

[0021] Based on the above technical solutions, the present invention also provides a carbon-coated hollow spherical Na4Fe3(PO4)2P2O7 prepared by the method as described above.

[0022] The further beneficial effects are as follows: The charge-discharge curve of the prepared carbon-coated hollow spherical Na4Fe3(PO4)2P2O7 at 0.1C has a specific capacity of up to 101 mAhg -1 , and the capacity retention rate is close to 100% after 150 cycles at 1C.

[0023] Based on the above technical solution, the present invention also provides an application of the carbon-coated hollow spherical Na4Fe3(PO4)2P2O7 prepared by the method as described above or the carbon-coated hollow spherical Na4Fe3(PO4)2P2O7 as described above in the positive electrode material of a sodium-ion battery.

[0024] The further beneficial effects are as follows: Using the prepared carbon-coated hollow spherical Na4Fe3(PO4)2P2O7 as the positive electrode material of a sodium-ion battery exhibits excellent specific capacity and cycling performance, providing technical support for the industrial preparation of polyanionic positive electrode materials for sodium-ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is the SEM image of the carbon-coated hollow spherical Na4Fe3(PO4)2P2O7 prepared in Example 1 of the present invention;

[0026] Figure 2 It is the SEM image of the carbon-coated hollow spherical Na4Fe3(PO4)2P2O7 prepared in Example 2 of the present invention;

[0027] Figure 3 It is the XRD pattern of the carbon-coated hollow spherical Na4Fe3(PO4)2P2O7 prepared in Example 2 of the present invention;

[0028] Figure 4 It is the XRD pattern of the carbon-coated hollow spherical Na4Fe3(PO4)2P2O7 prepared in Example 3 of the present invention;

[0029] Figure 5 It is the charge-discharge curve of the carbon-coated hollow spherical Na4Fe3(PO4)2P2O7 prepared in Example 2 of the present invention;

[0030] Figure 6 It is the cycling curve of the carbon-coated hollow spherical Na4Fe3(PO4)2P2O7 prepared in Example 2 of the present invention at a current density of 1C. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0031] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0032] Example 1

[0033] A method for preparing hollow spherical Na4Fe3(PO4)2P2O7 from the liquid phase of FePO4, comprising the following steps:

[0034] Using FePO4 as the iron source and phosphorus source, ammonium dihydrogen phosphate as the supplementary phosphorus source, sodium acetate trihydrate as the sodium source, and glucose as the carbon source;

[0035] Adding 14.709 g of sodium acetate trihydrate, 12.3115 g of FePO4, 3.6757 g of ammonium dihydrogen phosphate, and 21.014 g of glucose into 600 mL of deionized water, and magnetically stirring at room temperature for 16 h to obtain a suspension;

[0036] Subsequently, transferring the suspension to a sand mill for sanding, with a rotation speed of 1200 rpm and a time of 3 h;

[0037] Transferring the sanded suspension to a spray dryer for spray drying, with an inlet air temperature of 140 °C, an outlet air temperature of 90 °C, and a feeding rate of 600 mL / h to obtain a yellowish-green powder precursor;

[0038] Sintering the precursor under an inert gas protection atmosphere, with the temperature in the first stage being 300 °C and holding for 3 h, and the temperature in the second stage being 500 °C and holding for 10 h. After cooling with the furnace, carbon-coated hollow spherical Na4Fe3(PO4)2P2O7 is obtained.

[0039] Figure 1 SEM image of the carbon-coated hollow spherical Na4Fe3(PO4)2P2O7 prepared in Example 1. It can be seen from the figure that the material presents a hollow spherical shape, with a rough surface and occasional cracks.

[0040] Example 2

[0041] A method for preparing hollow spherical Na4Fe3(PO4)2P2O7 from the liquid phase of FePO4, comprising the following steps:

[0042] Using FePO4 as the iron source and phosphorus source, ammonium dihydrogen phosphate as the supplementary phosphorus source, sodium acetate trihydrate as the sodium source, and citric acid monohydrate as the carbon source;

[0043] Adding 11.9722 g of FePO4, 15.706 g of sodium acetate trihydrate, 4.1346 g of ammonium dihydrogen phosphate, and 23.074 g of citric acid monohydrate into 450 mL of deionized water, and magnetically stirring at room temperature for 12 h to obtain a suspension;

[0044] Subsequently, transferring the suspension to a sand mill for sanding, with a rotation speed of 1300 rpm and a time of 2 h;

[0045] Transfer the sanded suspension to a spray dryer for spray drying. The inlet air temperature is 120 °C, the outlet air temperature is 78 °C, and the feeding rate is 400 mL / h to obtain a yellowish-green powder precursor;

[0046] Sinter the precursor under an inert gas atmosphere. The temperature in the first stage is 300 °C and keep it for 4 h. The temperature in the second stage is 480 °C and keep it for 10 h. After furnace cooling, carbon-coated hollow spherical Na4Fe3(PO4)2P2O7 is obtained.

[0047] Assemble a button cell with the carbon-coated hollow spherical Na4Fe3(PO4)2P2O7 prepared in Example 2 in a glove box.

[0048] Figure 2 This is the SEM image of the carbon-coated hollow spherical Na4Fe3(PO4)2P2O7 prepared in this example. It can be seen from the figure that the overall material shows very regular spherical particles. The particle surface is relatively rough. The particle size distribution is 2 μm to 10 μm, and the shell thickness is 200 nm to 500 nm.

[0049] Figure 3 This is the XRD pattern of the carbon-coated hollow spherical Na4Fe3(PO4)2P2O7 prepared in this example, which confirms the synthesis of pure-phase Na4Fe3(PO4)2P2O7, and almost no impurity peaks belonging to sodium iron phosphate and sodium pyrophosphate can be observed.

[0050] Figure 5 This is the charge-discharge curve of the carbon-coated hollow spherical Na4Fe3(PO4)2P2O7 prepared in this example at 0.1C, and the specific capacity can reach 101 mAhg -1 。

[0051] Figure 6 This is the cycle curve of the carbon-coated hollow spherical Na4Fe3(PO4)2P2O7 prepared in this example at 1C. It can be seen from the figure that the capacity retention rate is close to 100% after 150 cycles.

[0052] Example 3

[0053] A method for preparing hollow spherical Na4Fe3(PO4)2P2O7 from FePO4 liquid phase, comprising the following steps:

[0054] Using FePO4 as the iron source and phosphorus source, sodium carbonate as the sodium source, phosphoric acid as the supplementary phosphorus source, and citric acid as the carbon source;

[0055] 10 mL of phosphoric acid, 9.8590 g of FePO4, 19.067 g of citric acid, and 10.321 g of sodium carbonate were added to 300 mL of deionized water, and magnetically stirred at room temperature for 5 h to obtain a suspension;

[0056] Subsequently, the suspension was transferred to a sand mill for sanding at a rotational speed of 1500 rpm for 5 h;

[0057] The sanded suspension was transferred to a spray dryer for spray drying. The inlet air temperature was 110 °C, the outlet air temperature was 65 °C, and the feeding rate was 1000 mL / h to obtain a yellowish-green powder precursor;

[0058] The precursor was sintered under an inert gas protection atmosphere. The temperature in the first stage was 250 °C and kept warm for 6 h, and the temperature in the second stage was 550 °C and kept warm for 15 h. After cooling with the furnace, carbon-coated hollow spherical Na4Fe3(PO4)2P2O7 was obtained.

[0059] Figure 4 This is the XRD pattern of the carbon-coated hollow spherical Na4Fe3(PO4)2P2O7 prepared in this example, which confirmed the synthesis of Na4Fe3(PO4)2P2O7.

[0060] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for preparing hollow spherical Na4Fe3(PO4)2P2O7 from the liquid phase of FePO4, characterized in that, It includes the following steps: S100, FePO4, a carbon source, a sodium source, and a phosphorus source are sequentially added to deionized water and stirred at room temperature to obtain a suspension; S200, the suspension is subjected to sanding, and the sanding parameters are: rotation speed of 1000 rpm to 1500 rpm, and time of 1 h to 24 h; S300, the sanded suspension is placed in a spray dryer for secondary granulation. The solid content of the suspension spray-dried by the spray dryer is 3 wt% to 40 wt%, the feeding rate is 20 mL / h to 1500 mL / h, the inlet air temperature is 105 °C to 280 °C, and the outlet air temperature is 60 °C to 240 °C, to obtain a yellow-green precursor powder. By regulating the solid content of the suspension and the spray drying parameters, nano-scale FePO4 primary particles are assembled into micron-scale spheres with a hollow structure; S400, the precursor powder is subjected to staged sintering treatment. The staged sintering treatment uses two-stage heating. First, it is heated from room temperature to 200 °C to 300 °C and kept warm for 1 h to 10 h, and then directly heated to 450 °C to 550 °C and kept warm for 3 h to 20 h, to obtain carbon-coated hollow spherical Na4Fe3(PO4)2P2O7.

2. A method for preparing hollow spherical Na4Fe3(PO4)2P2O7 from FePO4 liquid phase according to claim 1, characterized in that, The sodium source includes one or more of sodium acetate, sodium carbonate, sodium bicarbonate, sodium phosphate, and sodium dihydrogen phosphate.

3. A method for preparing hollow spherical Na4Fe3(PO4)2P2O7 from a FePO4 liquid phase according to claim 1, characterized in that, The phosphorus source includes one or several of phosphoric acid, diammonium hydrogen phosphate, sodium dihydrogen phosphate, sodium phosphate, and ammonium dihydrogen phosphate.

4. A method for preparing hollow spherical Na4Fe3(PO4)2P2O7 from FePO4 liquid phase according to claim 1, characterized in that, The carbon source includes one or several of glucose, sucrose, polyacrylonitrile, polyvinyl alcohol, and citric acid.

5. Carbon-coated hollow spherical Na4Fe3(PO4)2P2O7 prepared by the method according to any one of claims 1 to 4.

6. Application of carbon-coated hollow spherical Na4Fe3(PO4)2P2O7 prepared by the method according to any one of claims 1 to 4 or carbon-coated hollow spherical Na4Fe3(PO4)2P2O7 according to claim 5 in a cathode material for a sodium-ion battery.

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