Copper-doped pyrophosphoric acid ferric phosphate sodium carbon composite material and preparation method thereof

Abstract

The invention belongs to the technical field of nano materials and electrochemistry, and particularly relates to a copper-doped pyrophosphoric acid ferric phosphate sodium carbon composite material and a preparation method thereof. The structural formula of the copper-doped pyrophosphoric acid ferric phosphate sodium carbon composite material is Na4Fe2.85Cux (PO4) 2P2O7 (at) C, x is larger than or equal to 0.03 and smaller than or equal to 0.07, the composite material belongs to an NASICON type material, the conductivity and sodium ion migration kinetics of the material are improved through a strategy of copper doping and iron defect construction, and the composite material shows excellent electrochemical performance when serving as a sodium ion battery positive electrode active material.

Description

Technical Field

[0001] This invention belongs to the field of nanomaterials and electrochemical technology, specifically relating to a copper-doped sodium iron phosphate carbon composite material and its preparation method. Background Technology

[0002] Renewable energy sources such as wind, solar, and tidal power have been widely adopted in modern industry. However, their intermittency and volatility pose significant challenges to widespread implementation, highlighting the necessity of developing cost-effective energy storage systems. With advancements in lithium-ion batteries (LIBs), portable electronic devices and electric vehicles have seen widespread application. However, the limited availability and high cost of lithium resources severely hinder their further application. In contrast, sodium-ion batteries (SIBs) have attracted widespread attention as one of the most promising candidate battery devices due to their abundant raw materials, high cost-effectiveness, and environmental friendliness. To further realize the commercialization of SIBs, the development of high-performance and low-cost cathode materials is crucial. Currently, the main cathode materials for SIBs include layered oxides, polyanionic compounds, Prussian blue analogues, and organic compounds. Among these, iron-based mixed phosphate polyanionic materials stand out due to their stable crystal structure, low cost, and cross-linked Na+. + Its diffusion channels and high, adjustable operating voltage make it a promising candidate material. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a copper-doped sodium iron phosphate carbon composite material and its preparation method, which is simple in process and meets the requirements of green chemistry. This copper-doped sodium iron phosphate carbon composite material can be used as a high-capacity, high-rate sodium-ion battery positive electrode active material and has excellent electrochemical performance when applied in sodium-ion battery positive electrode materials.

[0004] A copper-doped sodium iron phosphate carbon composite material, wherein the structural formula of the copper-doped sodium iron phosphate carbon composite material is Na₄Fe₂O₃. 2.85 Cu x (PO4)2P2O7@C, where 0.03 ≤ x ≤ 0.07.

[0005] The preparation method of the above-mentioned copper-doped sodium iron phosphate carbon composite material includes the following steps: Sodium salt, iron salt, ammonium salt, copper salt and carbon source are mixed evenly in sequence to obtain a mixed solution; the mixed solution is then dried, ground and calcined in sequence to obtain copper-doped sodium iron pyrophosphate carbon composite material.

[0006] Further, the sodium salt is CH3COONa·3H2O or Na2C2O4, and the concentration of the sodium salt is 0.2-0.5 mol / L; The iron salt is FeSO4·7H2O or Fe(NO3)3·9H2O, and the concentration of the iron salt is 0.1-0.4 mol / L.

[0007] Further, the ammonium salt is NH4H2PO4 or (NH4)2HPO, and the concentration of the ammonium salt is 0.2-0.5 mol / L.

[0008] Furthermore, the carbon source is C6H8O7·H2O or C6H 12 O6, wherein the concentration of the carbon source is 0.1-0.4 mol / L; The copper salt is CuSO4·5H2O or CuCl2, and the concentration of the copper salt is 0.001-0.01 mol / L.

[0009] Furthermore, the drying process is carried out at a temperature of 120-180 ℃ for 2-10 h.

[0010] Furthermore, the grinding method is ball milling, and the ball milling speed is 200-500 r / min, and the time is 2-6 h.

[0011] Furthermore, the calcination process is carried out in stages under an Ar / H2 or N2 atmosphere. The temperature of the first stage of calcination is 150-350 ℃ and the calcination time is 2-5 h. The temperature of the second stage of calcination is 400-600 ℃ and the calcination time is 8-12 h.

[0012] The above-mentioned copper-doped sodium iron phosphate carbon composite material is used as a positive electrode active material for sodium-ion batteries.

[0013] The copper-doped sodium iron phosphate carbon composite material can be used as a high-capacity, long-life sodium-ion battery cathode material.

[0014] The copper-doped sodium iron phosphate carbon composite material prepared in this invention effectively improves the material's conductivity and enhances its structural stability through copper ion doping; a suitable amount of iron defects significantly reduces the formation of impurity phases; furthermore, the composite with carbon materials further improves the material's conductivity. When used as a cathode material in sodium-ion batteries, it exhibits excellent electrochemical performance.

[0015] The beneficial effects of the present invention are: (1) The sodium iron phosphate pyrophosphate cathode material prepared by the present invention, Cu 2+Incorporating Fe sites not only improves structural stability but also enhances the material's conductivity. Furthermore, an appropriate amount of iron defects significantly reduces NaFePO4 impurities, effectively suppressing the formation of impurity phases and ultimately improving the material's electrochemical performance. In addition, compositing with carbon materials further enhances the material's conductivity.

[0016] (2) The sodium iron pyrophosphate cathode material prepared by the present invention exhibits excellent rate performance and cycle performance when copper-doped sodium iron pyrophosphate is applied to sodium-ion battery cathode materials.

[0017] (3) The preparation method of the present invention successfully synthesized copper-doped sodium iron phosphate carbon composite material by ball milling combined with high temperature solid-state sintering. When applied to the cathode material of sodium-ion battery, the present invention exhibits high specific capacity, high rate performance and excellent cycle performance, and is a potential application material for high power and long life sodium-ion battery.

[0018] (4) The preparation method of the present invention is simple, meets the requirements of green chemistry, has low equipment requirements, and is conducive to the market application of sodium-ion batteries. Attached Figure Description

[0019] Figure 1 This is a scanning electron microscope image of the copper-doped sodium iron phosphate carbon composite material prepared in Example 1 of the present invention; Figure 2 This is a comparison diagram of the XRD of the copper-doped sodium iron phosphate carbon composite material prepared in Example 1 of the present invention and the sodium iron phosphate carbon composite material prepared in Comparative Example 1. Figure 3 This is an EDS mapping image of the copper-doped sodium iron phosphate carbon composite material prepared in Example 1 of this invention; Figure 4 This is a comparison chart of the battery cycle performance at 0.1 C rate between the copper-doped sodium iron pyrophosphate carbon composite material prepared in Example 1 of the present invention and the sodium iron pyrophosphate carbon composite material prepared in Comparative Example 1. Figure 5 This is a comparison chart of the battery cycle performance of the copper-doped sodium iron phosphate carbon composite material prepared in Example 1 of the present invention and the sodium iron phosphate carbon composite material prepared in Comparative Example 1 at a high rate of 10 C. Figure 6 This is a comparison chart of the rate performance of the copper-doped sodium iron phosphate carbon composite material prepared in Example 1 of the present invention and the sodium iron phosphate carbon composite material prepared in Comparative Example 1. Figure 7 This is a comparison of the electrochemical impedance spectroscopy of the copper-doped sodium iron pyrophosphate carbon composite material prepared in Example 1 of this invention and the sodium iron pyrophosphate carbon composite material prepared in Comparative Example 1. Detailed Implementation

[0020] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0021] The first aspect of this invention is to protect a method for preparing copper-doped sodium iron phosphate carbon composite material, which includes the following steps: S1. Add 2-5 mmol of CH3COONa·3H2O or Na2C2O4 to 10 mL of deionized water and stir at room temperature for 10-15 min to dissolve it. Specifically, the amount of CH3COONa·3H2O or Na2C2O4 can be 2 mmol, 3 mmol, 4 mmol, or 5 mmol.

[0022] S2. Add 1-4 mmol FeSO4·7H2O or Fe(NO3)3·9H2O to the solution obtained in step S1, and stir at room temperature for 10-20 min to dissolve it; specifically, the amount of FeSO4·7H2O or Fe(NO3)3·9H2O can be 1 mmol, 2 mmol, 3 mmol, or 4 mmol.

[0023] S3. Add 2-5 mmol of NH4H2PO4 or (NH4)2HPO4 to the solution obtained in step S2 and stir at room temperature for 10-20 min to dissolve it; specifically, the amount of NH4H2PO4 or (NH4)2HPO4 can be 2 mmol, 3 mmol, 4 mmol, or 5 mmol.

[0024] S4, add 1-4 mmol of C6H8O7·H2O or C6H 12 O6 is added to the solution obtained in step S3, and stirred at room temperature for 10-20 min to dissolve it; specifically, C6H8O7·H2O or C6H 12 The amount of O6 can be 1 mmol, 2 mmol, 3 mmol, or 4 mmol.

[0025] S5. Add 0.01-1 mmol CuSO4·5H2O or CuCl2 to the solution obtained in step S4, and stir at room temperature for 10-20 min to dissolve it; specifically, the amount of CuSO4·5H2O or CuCl2 can be 0.01 mmol, 0.1 mmol, 0.4 mmol, 0.6 mmol, 0.8 mmol, or 1 mmol.

[0026] S6. Place the homogeneous solution obtained in step S5 in an oven and dry it at 120-180 ℃ for 2-10 h until it is completely dry. S7. Pour the black solid obtained in step S6 into a ball mill jar and ball mill it at a speed of 200-500 r / min for 2-6 hours to obtain a black powder. S8. Place the black powder obtained from grinding in step S7 into a tube furnace and calcine it in stages under an Ar / H2 or N2 atmosphere. The first stage of calcination is carried out at a temperature of 150-350 ℃ for 2-5 h, and the second stage of calcination is carried out at a temperature of 400-600 ℃ for 8-12 h, finally obtaining a black powdery copper-doped iron phosphate sodium carbon composite material Na4Fe. 2.85 Cu x (PO4)2P2O7@C, where 0.03 ≤ x ≤ 0.07.

[0027] The second aspect of this invention is to protect the copper-doped sodium iron phosphate carbon composite material obtained by the above preparation method, whose structural formula is Na₄Fe₂O₃. 2.85 Cu x (PO4)2P2O7@C, where 0.03 ≤ x ≤ 0.07.

[0028] The third aspect of this invention is to protect the application of copper-doped sodium iron phosphate carbon composite material as a positive electrode active material for sodium-ion batteries.

[0029] <Comparative Example 1> The preparation method of sodium iron phosphate carbon pyrophosphate composite material includes the following steps: S1. Add 4 mmol CH3COONa·3H2O to 10 mL of deionized water and stir for 10 min at room temperature to dissolve it. S2. Add 2.85 mmol FeSO4·7H2O to the solution obtained in step S1 and stir at room temperature for 10 min to dissolve it. S3. Add 4 mmol of NH4H2PO4 to the solution obtained in step S2 and stir at room temperature for 10 min to dissolve it. S4. Add 2 mmol C6H8O7·H2O to the solution obtained in step S3 and stir for 10 min at room temperature to dissolve it. S5. Place the homogeneous solution obtained in step S4 in an oven and dry it at 160 °C for 4 h to ensure it is completely dried. S6. Pour the black solid obtained in step S5 into a ball mill jar and ball mill it at a speed of 400 r / min for 4 h to obtain a black powder. S7. The black powder obtained from grinding in step S6 is placed in a tube furnace and calcined in stages under an Ar / H2 atmosphere. The first stage calcination temperature is 300 ℃ and the calcination time is 3 h. The second stage calcination temperature is 550 ℃ and the calcination time is 10 h. Finally, a black powdery sodium iron phosphate carbon pyrophosphate composite material Na4Fe is obtained. 2.85 (PO4)2P2O7@C.

[0030] Taking the sodium iron phosphate carbon composite material prepared in this comparative example as the positive electrode material of sodium-ion battery, a charge-discharge test was conducted at a low rate of 0.1 C. After 50 cycles, the discharge specific capacity was 104 mAh / g.

[0031] <Example 1> The preparation method of copper-doped sodium iron phosphate carbon composite material includes the following steps: S1. Add 4 mmol CH3COONa·3H2O to 10 mL of deionized water and stir for 10 min at room temperature to dissolve it. S2. Add 2.90 mmol FeSO4·7H2O to the solution obtained in step S1 and stir at room temperature for 10 min to dissolve it. S3. Add 4 mmol of NH4H2PO4 to the solution obtained in step S2 and stir at room temperature for 10 min to dissolve it. S4. Add 2 mmol C6H8O7·H2O to the solution obtained in step S3 and stir for 10 min at room temperature to dissolve it. S5. Add 0.05 mmol CuSO4·5H2O to the solution obtained in step S4 and stir at room temperature for 10 min to dissolve it. S6. Place the homogeneous solution obtained in step S5 in an oven and dry it at 160 °C for 4 h to ensure it is completely dried. S7. Pour the black solid obtained in step S6 into a ball mill jar and ball mill it at a speed of 400 r / min for 4 h to obtain a black powder. S8. The black powder obtained from grinding in step S7 is placed in a tube furnace and calcined in stages under an Ar / H2 atmosphere. The first stage calcination temperature is 300 ℃ and the calcination time is 3 h. The second stage calcination temperature is 550 ℃ and the calcination time is 10 h. Finally, a black powdery copper-doped sodium iron pyrophosphate composite material Na4Fe is obtained. 2.85 Cu 0.05 (PO4)2P2O7@C.

[0032] The copper-doped sodium iron phosphate carbon composite material Na4Fe prepared in this embodiment was obtained respectively.2.85 Cu 0.05 The electron microscopy, XRD pattern, and EDS mapping of (PO4)2P2O7@C are shown below. Figure 1-3 As shown.

[0033] Depend on Figure 1 It can be seen that the copper-doped sodium iron phosphate carbon composite material prepared in this embodiment has an irregular particle morphology, exhibits a relatively smooth particle surface, and has a particle size of 500 nm.

[0034] like Figure 2 and Figure 3 As shown, XRD indicates that the characteristic peaks of the copper-doped sodium iron pyrophosphate material match well with the standard card (PDF: #89-0579), and the elements are uniformly distributed in the bulk phase, proving that the target material was synthesized without other impurities.

[0035] The copper-doped sodium iron pyrophosphate carbon composite material prepared in this example is used as the positive electrode active material of a sodium-ion battery. The preparation method of the sodium-ion battery of this invention is existing technology. The preparation method of the electrode sheet is as follows: the copper-doped sodium iron pyrophosphate carbon composite material prepared in this example and the sodium iron pyrophosphate carbon composite material prepared in Comparative Example 1 are used as active materials, Super P as a conductive agent, and polyvinylidene fluoride (PVDF) as a binder. The mass ratio of active material, Super P and PVDF is 7:2:1. After they are fully mixed in proportion to form a slurry, it is then uniformly coated on aluminum foil and dried in an oven at 120 °C for 12 h. The slurry is then punched into 11 mm electrode sheets for later use. A coin cell sodium-ion battery is assembled using 1M NaClO4 dissolved in ethylene carbonate (EC), diethyl carbonate (DEC) and 5% fluoroethylene carbonate (FEC) as the electrolyte, a self-made sodium sheet as the negative electrode, glass fiber as the separator, and CR2025 stainless steel as the battery casing.

[0036] Taking the copper-doped pyrophosphate sodium-carbon composite material prepared in this example as a cathode material for sodium-ion batteries, as an example... Figure 4 As shown, the material was tested at 0.1 C, and the first-cycle specific capacity reached 126.6 mAh / g, with a coulombic efficiency of 98.2%. In subsequent cycles, the coulombic efficiency approached 100%, and after 50 cycles, the discharge specific capacity reached 120 mAh / g. In contrast, the sodium iron phosphate carbon composite material of Comparative Example 1 only had a discharge capacity of 102 mAh / g after 50 cycles, which is significantly higher than that of Comparative Example 1, demonstrating excellent cycling performance.

[0037] like Figure 5As shown, the material was subjected to constant current charge-discharge test at a high rate of 10 C. After 1000 cycles, the discharge specific capacity still reached 78.6 mAh / g, while the sodium iron phosphate carbon composite material of Comparative Example 1 had a discharge capacity of less than 50 mAh / g after 1000 cycles, indicating that the material of this embodiment has good long-term cycling stability.

[0038] like Figure 6 As shown, the material was subjected to constant current charge-discharge tests at rates of 0.1 C, 0.2 C, 0.5 C, 1 C, 2 C, 5 C, 10 C, 20 C, and 30 C, and its discharge specific capacity was 125.2, 111.2, 103.1, 97.6, 93.5, 87.7, 80.6, 69.6, and 58.4 mAh / g, respectively. In contrast, the sodium iron phosphate carbon composite material of Comparative Example 1 had discharge specific capacities of 114.6, 101.9, 91.4, 87.4, 84.7, 81.1, 74.9, 62.7, and 48.0 mAh / g at the corresponding rates, indicating that the material in this embodiment exhibits excellent rate performance.

[0039] like Figure 7 As shown, the copper-doped sodium iron phosphate carbon composite material prepared in this example Rct The smaller value effectively enhances charge transfer capability. These properties demonstrate that copper-doped sodium iron phosphate carbon composite materials possess excellent high-rate characteristics and long-cycle performance, making them potential application materials for high-power, long-life sodium-ion batteries.

[0040] <Example 2> The preparation method of copper-doped sodium iron phosphate carbon composite material includes the following steps: S1. Add 4 mmol CH3COONa·3H2O to 10 mL of deionized water and stir for 10 min at room temperature to dissolve it. S2. Add 2.88 mmol FeSO4·7H2O to the solution obtained in step S1 and stir at room temperature for 10 min to dissolve it. S3. Add 4 mmol of NH4H2PO4 to the solution obtained in step S2 and stir at room temperature for 10 min to dissolve it. S4. Add 2 mmol C6H8O7·H2O to the solution obtained in step S3 and stir for 10 min at room temperature to dissolve it. S5. Add 0.03 mmol CuSO4·5H2O to the solution obtained in step S4 and stir at room temperature for 10 min to dissolve it. S6. Place the homogeneous solution obtained in step S5 in an oven and dry it at 160 °C for 4 h to ensure it is completely dried. S7. Pour the black solid obtained in step S6 into a ball mill jar and ball mill it at a speed of 400 r / min for 4 h to obtain black powder. S8. The black powder obtained from grinding in step S7 is placed in a tube furnace and calcined in stages under an Ar / H2 atmosphere. The first stage calcination temperature is 300 ℃ and the calcination time is 3 h. The second stage calcination temperature is 550 ℃ and the calcination time is 10 h, thus obtaining a black powdery copper-doped sodium iron phosphate pyrophosphate composite material Na4Fe. 2.85 Cu 0.03 (PO4)2P2O7@C.

[0041] <Example 3> The preparation method of copper-doped sodium iron phosphate carbon composite material includes the following steps: S1. Add 4 mmol CH3COONa·3H2O to 10 mL of deionized water and stir for 10 min at room temperature to dissolve it. S2. Add 2.92 mmol FeSO4·7H2O to the solution obtained in step 1) and stir for 10 min at room temperature to dissolve it. S3. Add 4 mmol of NH4H2PO4 to the solution obtained in step 2) and stir at room temperature for 10 min to dissolve it. S4. Add 2 mmol C6H8O7·H2O to the solution obtained in step 3) and stir for 10 min at room temperature to dissolve it. S5. Add 0.07 mmol CuSO4·5H2O to the solution obtained in step 4) and stir for 10 min at room temperature to dissolve it. S6. Place the homogeneous solution obtained in step 5) in an oven and dry it at 160 °C for 4 h to ensure it is completely dried. S7. Pour the black solid obtained in step 6) into a ball mill jar and ball mill it at a speed of 400 r / min for 4 h to obtain a black powder. S8. The black powder obtained from grinding in step 7) is placed in a tube furnace and calcined in stages under an Ar / H2 atmosphere. The first stage calcination temperature is 300 ℃ and the calcination time is 3 h. The second stage calcination temperature is 550 ℃ and the calcination time is 10 h. Finally, a black powdery copper-doped sodium iron pyrophosphate composite material Na4Fe is obtained. 2.85 Cu 0.07 (PO4)2P2O7@C.

[0042] Taking the copper-doped sodium iron phosphate carbon composite material prepared in this example as the positive electrode material of sodium-ion battery, a charge-discharge test was conducted at a low rate of 0.1 C. After 50 cycles, the discharge specific capacity still reached 106 mAh / g, demonstrating good electrochemical performance.

[0043] <Example 4> The preparation method of copper-doped sodium iron phosphate carbon composite material includes the following steps: S1. Add 4 mmol CH3COONa·3H2O to 10 mL of deionized water and stir for 10 min at room temperature to dissolve it. S2. Add 2.90 mmol FeSO4·7H2O to the solution obtained in step S1 and stir at room temperature for 10 min to dissolve it. S3. Add 4 mmol of NH4H2PO4 to the solution obtained in step S2 and stir at room temperature for 10 min to dissolve it. S4. Add 2 mmol C6H8O7·H2O to the solution obtained in step S3 and stir for 10 min at room temperature to dissolve it. S5. Add 0.05 mmol CuSO4·5H2O to the solution obtained in step S4 and stir at room temperature for 10 min to dissolve it. S6. Place the homogeneous solution obtained in step S5 in an oven and dry it at 160 °C for 4 h to ensure it is completely dried. S7. Pour the black solid obtained in step S6 into a ball mill jar and ball mill it at a speed of 400 r / min for 4 h to obtain a black powder. S8. The black powder obtained from grinding in step S7 is placed in a tube furnace and calcined in stages under an Ar / H2 atmosphere. The first stage calcination temperature is 300 ℃ and the calcination time is 3 h. The second stage calcination temperature is 500 ℃ and the calcination time is 10 h. Finally, a black powdery copper-doped sodium iron phosphate carbon composite material Na4Fe is obtained. 2.85 Cu 0.05 (PO4)2P2O7@C.

[0044] The copper-doped sodium iron phosphate carbon composite material Na4Fe prepared in this example 2.85 Cu 0.05 Taking (PO4)2P2O7@C as the cathode material for sodium-ion batteries as an example, after 50 cycles of charge-discharge testing at a low rate of 0.1 C, the discharge specific capacity can still reach 110 mAh / g, demonstrating good electrochemical performance.

[0045] <Example 5> The preparation method of copper-doped sodium iron phosphate carbon composite material includes the following steps: S1. Add 3 mmol Na2C2O4 to 10 mL of deionized water and stir for 10 min at room temperature to dissolve it. S2. Add 2.88 mmol Fe(NO3)3·9H2O to the solution obtained in step S1 and stir for 10 min at room temperature to dissolve it. S3. Add 4 mmol (NH4)2HPO4 to the solution obtained in step S2 and stir at room temperature for 10 min to dissolve it. S4, add 2 mmol C6H 12 O6 is added to the solution obtained in step S3 and stirred for 10 min at room temperature to dissolve it. S5. Add 0.03 mmol CuCl2 to the solution obtained in step S4 and stir for 10 min at room temperature to dissolve it. S6. Place the homogeneous solution obtained in step S5 in an oven and dry it at 160 °C for 4 h to ensure it is completely dried. S7. Pour the black solid obtained in step S6 into a ball mill jar and ball mill it at a speed of 400 r / min for 4 h to obtain black powder. S8. The black powder obtained from grinding in step S7 is placed in a tube furnace and calcined in stages under an Ar / H2 atmosphere. The first stage calcination temperature is 300 ℃ and the calcination time is 3 h. The second stage calcination temperature is 550 ℃ and the calcination time is 10 h, thus obtaining a black powdery copper-doped sodium iron phosphate pyrophosphate composite material Na4Fe. 2.85 Cu 0.03 (PO4)2P2O7@C.

[0046] <Example 6> The preparation method of copper-doped sodium iron phosphate carbon composite material includes the following steps: S1. Add 5 mmol Na2C2O4 to 10 mL of deionized water and stir for 10 min at room temperature to dissolve it. S2. Add 2.88 mmol Fe(NO3)3·9H2O to the solution obtained in step S1 and stir for 10 min at room temperature to dissolve it. S3. Add 4 mmol (NH4)2HPO4 to the solution obtained in step S2 and stir at room temperature for 10 min to dissolve it. S4, add 2 mmol C6H 12 O6 is added to the solution obtained in step S3 and stirred for 10 min at room temperature to dissolve it. S5. Add 0.03 mmol CuCl2 to the solution obtained in step S4 and stir for 10 min at room temperature to dissolve it. S6. Place the homogeneous solution obtained in step S5 in an oven and dry it at 160 °C for 4 h to ensure it is completely dried. S7. Pour the black solid obtained in step S6 into a ball mill jar and ball mill it at a speed of 400 r / min for 4 h to obtain black powder. S8. The black powder obtained from grinding in step S7 is placed in a tube furnace and calcined in stages under an Ar / H2 atmosphere. The first stage calcination temperature is 300 ℃ and the calcination time is 3 h. The second stage calcination temperature is 550 ℃ and the calcination time is 10 h, thus obtaining a black powdery copper-doped sodium iron phosphate pyrophosphate composite material Na4Fe. 2.85 Cu 0.03 (PO4)2P2O7@C.

[0047] The specific raw materials listed in this invention, as well as the upper and lower limits and ranges of values ​​for each raw material and process parameter, can all achieve this invention. Examples are not listed individually here. Where there is no conflict, the above embodiments and features described herein can be combined with each other.

[0048] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A copper-doped sodium iron phosphate carbon composite material, characterized in that, The structural formula of the copper-doped sodium iron phosphate carbon pyrophosphate composite material is Na4Fe 2.85 Cu x (PO4)2P2O7@C, where 0.03 ≤ x ≤ 0.

07.

2. A method for preparing the copper-doped sodium iron phosphate carbon composite material as described in claim 1, characterized in that, Includes the following steps: Sodium salt, iron salt, ammonium salt, copper salt and carbon source are mixed evenly in sequence to obtain a mixed solution; the mixed solution is then dried, ground and calcined in sequence to obtain copper-doped sodium iron pyrophosphate carbon composite material.

3. The method for preparing the copper-doped sodium iron phosphate carbon composite material according to claim 2, characterized in that, The sodium salt is CH3COONa·3H2O or Na2C2O4, and the concentration of the sodium salt is 0.2-0.5 mol / L; the iron salt is FeSO4·7H2O or Fe(NO3)3·9H2O, and the concentration of the iron salt is 0.1-0.4 mol / L.

4. The method for preparing the copper-doped sodium iron phosphate carbon composite material according to claim 2, characterized in that, The ammonium salt is NH4H2PO4 or (NH4)2HPO4, and the concentration of the ammonium salt is 0.2-0.5 mol / L.

5. The method for preparing the copper-doped sodium iron phosphate carbon composite material according to claim 2, characterized in that, The carbon source is C6H8O7·H2O or C6H 12 O6, wherein the concentration of the carbon source is 0.1-0.4 mol / L; The copper salt is CuSO4·5H2O or CuCl2, and the concentration of the copper salt is 0.001-0.01 mol / L.

6. The method for preparing the copper-doped sodium iron phosphate carbon composite material according to claim 2, characterized in that, The drying process is carried out at a temperature of 120-180 ℃ for 2-10 h.

7. The method for preparing the copper-doped sodium iron phosphate carbon composite material according to claim 2, characterized in that, The grinding method is ball milling, with a rotation speed of 200-500 r / min and a grinding time of 2-6 h.

8. The method for preparing the copper-doped sodium iron phosphate carbon composite material according to claim 2, characterized in that, The calcination process is carried out in stages under an Ar / H2 or N2 atmosphere. The temperature of the first stage of calcination is 150-350 ℃ and the calcination time is 2-5 h. The temperature of the second stage of calcination is 400-600 ℃ and the calcination time is 8-12 h.

9. The application of the copper-doped sodium iron phosphate carbon composite material as described in claim 1 as a positive electrode active material for sodium-ion batteries.

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