A composite carbon source coated sodium ferric pyrophosphate and a preparation method thereof

Abstract

The application provides a kind of sodium pyrophosphate iron phosphate coated with composite carbon source and a preparation method thereof, comprising the following steps: weighing inorganic sodium source, organic sodium, organic phosphonic acid, glucose and ferric phosphate according to proportion; first, add organic phosphonic acid and glucose in deionized water, stir to dissolve and form a clear and transparent solution; continue to add organic sodium, stir to dissolve and obtain a transparent solution; then add inorganic sodium source, stir to form a clear and transparent solution; finally, add ferric phosphate, stir to form a green liquid; dry the green liquid and grind to obtain a precursor dry powder; sinter the precursor dry powder under the protection of inert gas at 500-600 DEG C, and naturally cool to obtain Na4Fe3 (PO4) 2 (P2O7) / C composite material. The method is simple to operate, and the cost is reduced. The sodium pyrophosphate iron phosphate / carbon composite material with high phase purity and uniform carbon coating can be obtained by using organic sodium, glucose and organic phosphonic acid to form a composite carbon source system, which effectively improves the sodium storage performance of the material.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery technology, and particularly relates to a composite carbon source-coated sodium iron pyrophosphate and its preparation method. Background Technology

[0002] Sodium-ion batteries, with their abundant sodium resources, low raw material costs, and electrochemical working principle similar to lithium-ion batteries, are widely regarded as one of the most promising rechargeable battery technologies for large-scale energy storage systems and low-speed electric vehicles. The cathode material is a core component determining the performance and cost of sodium-ion batteries. Among various cathode materials, sodium iron phosphate pyrophosphate has low raw material cost, a stable voltage plateau, and excellent crystal structure stability; however, its intrinsic electronic conductivity is low, and its electron conduction resistance is high, resulting in poor electrochemical performance. Traditional single-carbon-source coating processes are difficult to control the carbon layer structure, and the improvement in conductivity through carbon coating is limited. Therefore, how to optimize the carbon source system and effectively improve the conductivity and rate performance of materials through carbon coating is a key problem that urgently needs to be solved in this field. Summary of the Invention

[0003] To address the aforementioned technical problems, this invention provides a composite carbon source-coated sodium iron pyrophosphate and its preparation method. The method of this invention is simple to operate and reduces costs. It uses sodium organic acid, glucose, and organic phosphonic acid to form a composite carbon source system, which can obtain sodium iron pyrophosphate / carbon composite material with high phase purity and uniform carbon coating, effectively improving the sodium storage performance of the material.

[0004] Note that the description of these objectives does not preclude the existence of other objectives. One aspect of the invention does not require achieving all of the above objectives. Objectives other than those described above can be extracted from the description, drawings, and claims.

[0005] The present invention achieves the above-mentioned technical objectives through the following technical means.

[0006] A method for preparing sodium iron pyrophosphate coated with a composite carbon source includes the following steps:

[0007] Step S1: Weigh out the inorganic sodium source, organic sodium acid, organic phosphonic acid, glucose and ferric phosphate according to the proportions; first, add organic phosphonic acid and glucose to deionized water and stir to dissolve to form a clear and transparent solution; then add organic sodium acid and stir to dissolve to obtain a transparent solution; then add inorganic sodium source and stir to form a clear and transparent solution; finally add ferric phosphate and stir to form a green liquid.

[0008] Step S2: Dry and grind the green liquid obtained in step S1 to obtain precursor powder;

[0009] Step S3: The precursor dry powder obtained in step S2 is sintered under inert gas protection at 500-600℃ and naturally cooled to obtain Na4Fe3(PO4)2(P2O7) / C composite material.

[0010] In the above scheme, in step S1, based on the amount of phosphonic acid group (-PO3H2), the molar ratio of sodium:iron:phosphate:phosphonic acid group in the inorganic sodium source, iron phosphate, organic sodium acid and organic phosphonic acid is 4:3:3:1.

[0011] In the above scheme, in step S1, the sodium organic acid is one of sodium citrate, sodium gluconate, sodium acetate, or sodium malate.

[0012] In the above scheme, in step S1, the organophosphonic acid is one of aminotrimethylenephosphonic acid, ethylenediaminetetramethylenephosphonic acid, diethylenetriaminepentamethylenephosphonic acid, or hydroxyethylidenediphosphonic acid.

[0013] In the above scheme, in step S1, the inorganic sodium source is one of sodium carbonate, sodium sulfate, sodium chloride, sodium oxalate, or sodium hydroxide.

[0014] In the above scheme, in step S1, the inorganic sodium source is sodium carbonate, the organic acid sodium is sodium citrate, and the organic phosphonic acid is aminotrimethylenephosphonic acid.

[0015] Furthermore, the amounts of raw materials used in step S1 are as follows: sodium carbonate 0.3 mol, sodium citrate 0.2 mol, aminotrimethylenephosphonic acid 0.1 mol, glucose 0.2 mol, and ferric phosphate 0.9 mol.

[0016] Furthermore, the amounts of raw materials used in step S1 are as follows: 0.24 mol sodium carbonate, 0.24 mol sodium citrate, 0.1 mol aminotrimethylenephosphonic acid, 0.16 mol glucose, and 0.9 mol ferric phosphate.

[0017] Furthermore, the amounts of raw materials used in step S1 are as follows: sodium carbonate 0.18 mol, sodium citrate 0.28 mol, aminotrimethylenephosphonic acid 0.1 mol, glucose 0.12 mol, and ferric phosphate 0.9 mol.

[0018] A sodium iron phosphate pyrophosphate / carbon composite material prepared according to the method for preparing sodium iron phosphate pyrophosphate coated with the composite carbon source, wherein the chemical composition of the sodium iron phosphate pyrophosphate / carbon composite material is Na4Fe3(PO4)2(P2O7) / C.

[0019] Compared with the prior art, the beneficial effects of the present invention are:

[0020] 1. This invention employs a composite carbon source system composed of organophosphonic acid, sodium organic acid, and glucose. The organophosphonic acid also has a chelating effect, enabling it to complex metal ions in the liquid phase and promote molecular-level mixing of the raw materials. Sodium organic acid decomposes to provide a partial sodium source and precipitates amorphous carbon. The pyrolysis of glucose helps form a continuous conductive carbon framework. The combined use of these three components facilitates the formation of a uniform and highly conductive carbon coating layer on the surface of sodium iron phosphate pyrophosphate particles.

[0021] 2. This invention employs a specific feeding sequence: first, organophosphonic acid is dissolved with glucose, then sodium organic acid, inorganic sodium source, and ferric phosphate are added sequentially, and finally, the mixture is stirred to form a uniform gel precursor. This sequence facilitates the full utilization of the chelating effect of organophosphonic acid, ensuring uniform dispersion of each component in the liquid phase, thereby obtaining a composite material with good carbon coating consistency.

[0022] 3. This invention achieves stable pure phase Na4Fe3(PO4)2(P2O7) / C by controlling the molar ratio of sodium:iron:phosphate:phosphonic acid groups to 4:3:3:1. X-ray diffraction (XRD) analysis shows that no impurity phases such as NaFePO4 were detected in the obtained product, indicating high phase purity and stable crystal structure.

[0023] 4. The sodium iron phosphate / carbon pyrophosphate composite material obtained by this invention has excellent electrochemical performance. The data from the examples show that at a rate of 0.1C, the initial discharge specific capacity can reach 111.71 mAh / g, and the initial coulombic efficiency is as high as 99.91%, demonstrating good reversible capacity and coulombic efficiency.

[0024] 5. This invention uses a full liquid-phase gel method to prepare the precursor. The carbon source is entirely derived from organophosphonic acid, sodium organic acid, and glucose. There is no need to add solid carbon materials such as carbon black and carbon nanotubes. The process is simple and easy to operate. The raw materials are all common chemicals, which helps to reduce production costs and is suitable for industrial production.

[0025] In summary, this invention provides a method for preparing sodium iron phosphate pyrophosphate coated with a composite carbon source and the resulting composite material. By using a ternary composite carbon source of organophosphonic acid, sodium organic acid, and glucose, combined with a specific feeding sequence and optimized molar ratio, the problems of low intrinsic electronic conductivity and limited coating effect of a single carbon source for sodium iron phosphate pyrophosphate are effectively solved. This results in a sodium iron phosphate pyrophosphate / carbon composite material with high phase purity, uniform carbon coating, and excellent sodium storage performance. This method is simple, low-cost, and has broad prospects for industrial application.

[0026] Note that the description of these effects does not preclude the existence of other effects. One aspect of the invention does not necessarily have all the aforementioned effects. Effects other than those described above can be readily observed and extracted from the description, drawings, claims, etc. Attached Figure Description

[0027] Figure 1 The image shown is the XRD pattern of the sample prepared in Example 1 of this invention.

[0028] Figure 2 The image shows the charge-discharge curves of the sample prepared in Example 1 of this invention at a rate of 0.1C, where the black curve is the charging curve and the red curve is the discharging curve.

[0029] Figure 3 The image shown is the XRD pattern of the sample prepared in Example 2 of this invention.

[0030] Figure 4 The graph shows the cycling performance of the sample prepared in Example 2 of this invention at a rate of 0.1C, where the black curve is the charging curve and the red curve is the discharging curve.

[0031] Figure 5 The image shown is the XRD pattern of the sample prepared in Example 3 of this invention.

[0032] Figure 6 The graph shows the cycling performance of the sample prepared in Example 3 of this invention at a rate of 0.1C, where the black curve is the charging curve and the red curve is the discharging curve.

[0033] Figure 7 The image shown is the XRD pattern of the sample prepared in Example 4 of this invention.

[0034] Figure 8 The graph shows the cycling performance of the sample prepared in Example 4 of this invention at a rate of 0.1C, where the black curve is the charging curve and the red curve is the discharging curve.

[0035] Figure 9 The image shown is the XRD pattern of the sample prepared in Example 5 of this invention.

[0036] Figure 10 The graph shows the cycling performance of the sample prepared in Example 5 of this invention at a rate of 0.1C, where the black curve is the charging curve and the red curve is the discharging curve. Detailed Implementation

[0037] The embodiments of the present invention are described in detail below. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention. Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods; unless otherwise specified, the reagents, materials, etc. used in the following embodiments are commercially available.

[0038] Example 1

[0039] A method for preparing sodium iron pyrophosphate coated with a composite carbon source includes the following steps:

[0040] Weigh out 0.3 mol sodium carbonate, 0.2 mol sodium citrate, 0.1 mol aminotrimethylenephosphonic acid, 0.2 mol glucose, and 0.9 mol ferric phosphate. First, dissolve aminotrimethylenephosphonic acid and glucose in deionized water and stir until clear; add sodium citrate and stir to dissolve to obtain a transparent solution; then add sodium carbonate and stir to dissolve to obtain a transparent solution; finally add ferric phosphate and stir to form a green liquid. Dry and grind at 80 ℃, and sinter at 600 ℃ under argon for 12 h to obtain the Na4Fe3(PO4)2(P2O7) / C composite material.

[0041] The resulting product maintains a stable color and appears as a silvery-gray powder when stored in air for an extended period. Figure 1 The XRD pattern of the product shows sharp diffraction peaks with moderate intensity. No characteristic peaks of NaFePO4 were detected, indicating that the product does not contain this impurity phase. Electrochemical tests were performed using a coin cell assembly: [Example image would be inserted here]. Figure 2 As shown, the initial discharge specific capacity at 0.1C rate is 103.95 mAh / g, and the initial coulombic efficiency is 90.91%.

[0042] Example 2

[0043] A method for preparing sodium iron pyrophosphate coated with a composite carbon source includes the following steps:

[0044] Weigh out 0.24 mol sodium carbonate, 0.24 mol sodium citrate, 0.1 mol aminotrimethylenephosphonic acid, 0.16 mol glucose, and 0.9 mol ferric phosphate. First, dissolve aminotrimethylenephosphonic acid and glucose in deionized water and stir until clear; add sodium citrate and stir to dissolve to obtain a transparent solution; then add sodium carbonate and stir to dissolve to obtain a transparent solution; finally add ferric phosphate and stir to form a green liquid. Dry and grind at 80 ℃, and sinter at 600 ℃ for 12 h under argon atmosphere to obtain the Na4Fe3(PO4)2(P2O7) / C composite material.

[0045] The product does not change color when left in the air for a long time; it is a silvery-gray powder. Figure 3 XRD results showed sharp and moderate diffraction peaks, with no NaFePO4 diffraction peaks observed, indicating extremely low content. Electrochemical performance tests showed an initial discharge specific capacity of 111.71 mAh / g at 0.1C, with an initial efficiency of 99.91%.

[0046] Example 3

[0047] A method for preparing sodium iron pyrophosphate coated with a composite carbon source includes the following steps:

[0048] Weigh out 0.18 mol sodium carbonate, 0.28 mol sodium citrate, 0.1 mol aminotrimethylenephosphonic acid, 0.12 mol glucose, and 0.9 mol ferric phosphate. First, dissolve aminotrimethylenephosphonic acid and glucose in deionized water and stir until clear; add sodium citrate and stir to dissolve to obtain a transparent solution; then add sodium carbonate and stir to dissolve to obtain a transparent solution; finally add ferric phosphate and stir to form a green liquid. Dry and grind at 80 ℃, and sinter at 600 ℃ under argon for 12 h to obtain the Na4Fe3(PO4)2(P2O7) / C composite material.

[0049] The product does not change color when left in the air for a long time, and remains silvery-gray. Figure 5 The XRD pattern showed sharp peaks with moderate intensity and no NaFePO4 diffraction peaks, indicating that its content was very low. Electrochemical test results: the initial discharge specific capacity at 0.1C was 110.39 mAh / g, and the initial efficiency was 98.91%.

[0050] Example 4

[0051] A method for preparing sodium iron pyrophosphate coated with a composite carbon source includes the following steps:

[0052] Weigh out 0.12 mol sodium carbonate, 0.32 mol sodium citrate, 0.1 mol aminotrimethylenephosphonic acid, 0.08 mol glucose, and 0.9 mol ferric phosphate. First, dissolve aminotrimethylenephosphonic acid and glucose in deionized water and stir until clear; add sodium citrate and stir to dissolve to obtain a transparent solution; then add sodium carbonate and stir to dissolve to obtain a transparent solution; finally add ferric phosphate and stir to form a green liquid. Dry and grind at 80 ℃, and sinter at 600 ℃ under argon for 12 h to obtain the Na4Fe3(PO4)2(P2O7) / C composite material.

[0053] The product does not change color when left in the air for a long time, and remains silvery-gray. Figure 7 The XRD pattern showed sharp peaks with moderate intensity and no NaFePO4 diffraction peaks, indicating that its content was very low. Electrochemical test results: the initial discharge specific capacity at 0.1C was 103.39 mAh / g, and the initial efficiency was 98.91%.

[0054] Example 5

[0055] A method for preparing sodium iron pyrophosphate coated with a composite carbon source includes the following steps:

[0056] Weigh out 0.06 mol sodium carbonate, 0.36 mol sodium citrate, 0.1 mol aminotrimethylenephosphonic acid, 0.2 mol glucose, and 0.9 mol ferric phosphate. First, dissolve aminotrimethylenephosphonic acid and glucose in deionized water and stir until clear; add sodium citrate and stir to dissolve to obtain a transparent solution; then add sodium carbonate and stir to dissolve to obtain a transparent solution; finally add ferric phosphate and stir to form a green liquid. Dry and grind at 80 ℃, and sinter at 600 ℃ under argon for 12 h to obtain the Na4Fe3(PO4)2(P2O7) / C composite material.

[0057] The product does not change color when left in the air for a long time, and remains silvery-gray. Figure 9 The XRD pattern showed sharp peaks with moderate intensity and no NaFePO4 diffraction peaks, indicating that its content was very low. Electrochemical test results: the initial discharge specific capacity at 0.1C was 101.39 mAh / g, and the initial efficiency was 98.91%.

[0058] Table 1 shows the carbon content results for each embodiment: when the carbon content is below 2.37 wt%, the conductive network is discontinuous; when it is above 2.47 wt%, the specific capacity decreases. Therefore, 2.37–2.47 wt% is preferred.

[0059] Table 1

[0060]

[0061] This invention utilizes sodium organic acid, glucose, and organophosphonic acid as a carbon source to form a uniform gel precursor in a liquid phase system. After high-temperature sintering, a carbon coating layer is formed on the surface of sodium iron phosphate pyrophosphate particles. The organophosphonic acid also has a chelating effect, capable of complexing metal ions and promoting molecular-level mixing of the raw materials; the sodium organic acid decomposes to provide a sodium source and precipitates amorphous carbon; and the pyrolysis of glucose helps form a continuous conductive network. The combined use of these three components is beneficial for obtaining a uniformly coated carbon layer structure with good conductivity.

[0062] The organophosphonic acid of this invention has a chelating effect, complexing metal ions in the liquid phase, promoting uniform mixing of materials to form a gel precursor, and further improving the uniformity of carbon coating.

[0063] This invention integrates the feeding of ternary composite carbon sources, eliminating the need for additional carbon powder. The liquid-phase preparation process is simple, the production cost is low, and the finished product exhibits excellent coulombic efficiency and reversible capacity retention.

[0064] This invention develops a liquid-phase preparation process for carbon-coated modified sodium iron phosphate pyrophosphate using composite carbon sources, fundamentally improving the inherent low electronic conductivity of sodium iron phosphate pyrophosphate. Simultaneously, organophosphonic acids exert a chelating effect, promoting uniform dispersion of all raw materials in the liquid phase to form a gel precursor, ensuring consistent carbon coating. This invention utilizes a fully liquid-phase gel preparation process, eliminating the need for external carbon powder. The process is streamlined and cost-effective, addressing the industry pain points of uncontrollable carbon layer coating and limited conductivity improvement associated with traditional single-carbon source methods. The resulting sodium-ion battery cathode material exhibits excellent rate capability and sodium storage performance, showing promising prospects for industrial application.

[0065] It should be understood that although this specification is described according to various embodiments, not every embodiment contains only one independent technical solution. This way of describing the specification is only for clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

[0066] The detailed descriptions listed above are merely specific illustrations of feasible embodiments of the present invention and are not intended to limit the scope of protection of the present invention. All equivalent embodiments or modifications made without departing from the spirit of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing sodium iron pyrophosphate coated with a composite carbon source, characterized in that, Includes the following steps: Step S1: Weigh out the inorganic sodium source, organic sodium acid, organic phosphonic acid, glucose and ferric phosphate according to the proportions; first, add organic phosphonic acid and glucose to deionized water, stir to dissolve and form a clear and transparent solution; then add organic sodium acid, stir to dissolve and obtain a transparent solution. Add an inorganic sodium source and stir to form a clear and transparent solution; finally, add ferric phosphate and stir to form a green liquid. Step S2: Dry and grind the green liquid obtained in step S1 to obtain precursor powder; Step S3: The precursor dry powder obtained in step S2 is sintered under inert gas protection at 500-600℃ and naturally cooled to obtain Na4Fe3(PO4)2(P2O7) / C composite material.

2. The method for preparing sodium iron pyrophosphate coated with a composite carbon source according to claim 1, characterized in that, In step S1, based on the amount of phosphonic acid group (-PO3H2), the molar ratio of sodium:iron:phosphate:phosphonic acid group in the inorganic sodium source, iron phosphate, organic sodium acid and organic phosphonic acid is 4:3:3:

1.

3. The method for preparing sodium iron pyrophosphate coated with a composite carbon source according to claim 1, characterized in that, In step S1, the sodium organic acid is one of sodium citrate, sodium gluconate, sodium acetate, or sodium malate.

4. The method for preparing sodium iron pyrophosphate coated with a composite carbon source according to claim 1, characterized in that, In step S1, the organophosphonic acid is one of aminotrimethylenephosphonic acid, ethylenediaminetetramethylenephosphonic acid, diethylenetriaminepentamethylenephosphonic acid, or hydroxyethylidene diphosphonic acid.

5. The method for preparing sodium iron pyrophosphate coated with a composite carbon source according to claim 1, characterized in that, In step S1, the inorganic sodium source is one of sodium carbonate, sodium sulfate, sodium chloride, sodium oxalate, or sodium hydroxide.

6. The method for preparing sodium iron pyrophosphate coated with a composite carbon source according to claim 1, characterized in that, In step S1, the inorganic sodium source is sodium carbonate, the organic sodium acid is sodium citrate, and the organic phosphonic acid is aminotrimethylene phosphonic acid.

7. The method for preparing sodium iron pyrophosphate coated with a composite carbon source according to claim 6, characterized in that, The amounts of raw materials used in step S1 are: sodium carbonate 0.3 mol, sodium citrate 0.2 mol, aminotrimethylenephosphonic acid 0.1 mol, glucose 0.2 mol, and ferric phosphate 0.9 mol.

8. The method for preparing sodium iron pyrophosphate coated with a composite carbon source according to claim 6, characterized in that, The amounts of raw materials used in step S1 are: sodium carbonate 0.24 mol, sodium citrate 0.24 mol, aminotrimethylenephosphonic acid 0.1 mol, glucose 0.16 mol, and ferric phosphate 0.9 mol.

9. The method for preparing sodium iron pyrophosphate coated with a composite carbon source according to claim 6, characterized in that, The amounts of raw materials used in step S1 are: 0.18 mol sodium carbonate, 0.28 mol sodium citrate, 0.1 mol aminotrimethylenephosphonic acid, 0.12 mol glucose, and 0.9 mol ferric phosphate.

10. A sodium iron phosphate pyrophosphate / carbon composite material prepared by the method for preparing sodium iron phosphate pyrophosphate coated with a composite carbon source according to any one of claims 1 to 9, characterized in that, The chemical composition of the sodium iron phosphate / carbon pyrophosphate composite material is Na4Fe3(PO4)2(P2O7) / C.

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