A high-stability doped sodium ferric sulfate positive electrode material and a preparation method thereof

Abstract

The application discloses a kind of high-stability doped sodium sulfate positive electrode materials and preparation method thereof, belong to sodium ion battery electrode material technical field.For the current sodium sulfate in high rate under the problem of sodium storage capacity, cycle performance and poor water resistance, the high-stability doped sodium sulfate positive electrode material of the application includes sodium iron sulfate zinc calcium phosphate particles and carbon nanotube, mass ratio is 85~95:5~15.By ball milling anhydrous ferrous sulfate, anhydrous sodium sulfate, anhydrous calcium phosphate, anhydrous zinc phosphate and carbon nanotube in inert atmosphere ball mill jar to obtain calcined precursor;Then the calcined precursor is placed in inert atmosphere tube furnace at 360~400 DEG C for 16~24h, to obtain sodium iron sulfate zinc calcium phosphate composite electrode material.The electrode material provided by the application has the advantages of simple and convenient preparation method, low cost, good air stability and rate performance, good cycle stability (>6000 times) and other advantages, and has strong market competitiveness in large-scale energy storage application field.

Description

Technical Field

[0001] This invention belongs to the technical field of sodium-ion battery electrode materials, specifically relating to a highly stable doped sodium iron sulfate cathode material and its preparation method. Background Technology

[0002] Sodium-ion batteries, as electrochemical energy storage devices with low raw material costs and high safety, have broad application prospects in large-scale energy storage. The cathode, as a key component of sodium-ion batteries, has a decisive impact on the overall battery performance and cost. Currently, there are three main systems for sodium-ion battery cathode materials: transition metal layered oxides, Prussian blue analogs, and polyanionic compounds. Among them, transition metal layered oxides have high costs and undergo irreversible phase transitions during long-cycle operation, affecting their cycle stability; while Prussian blue analogs have lower costs, the uncontrollable water of crystallization in their molecular structure limits the large-scale preparation of the material. In comparison, polyanionic sodium iron sulfate cathode materials have attracted widespread attention due to their low raw material costs, high operating voltage (approximately 3.8V), and stable cycle performance. However, the poor intrinsic conductivity of sodium iron sulfate materials limits their rate charge-discharge performance. In addition, sodium ferric sulfate is sensitive to moisture. Even trace amounts of moisture in the air can be easily absorbed by sodium ferric sulfate crystals, thereby destroying their crystal structure. Therefore, the key to the large-scale application of sodium ferric sulfate is to improve its rate performance while maintaining its stability in air.

[0003] To address the poor conductivity of sodium ferric sulfate, existing research often employs modification with composite conductive carbon materials, as illustrated in (CN 117720132 A, CN 118969995 A, Science Bulletin, 2023, 68:1894–1903, Nature Communications, 2023, 14:3701). While these existing techniques can synthesize sodium ferric sulfate composites with significantly improved conductivity and good cycling stability, the sodium storage capacity, cycling performance, and water resistance at high rates remain unsatisfactory. This is primarily because the composite between sodium ferric sulfate and carbon materials is a physical contact composite, which does not address the inherent poor conductivity and water sensitivity of sodium ferric sulfate crystals. Summary of the Invention

[0004] To address the issues of poor sodium storage capacity, cycling performance, and water resistance of sodium ferric sulfate at high rates, this invention provides a novel composite electrode material of sodium ferric phosphate, zinc phosphate, calcium phosphate, and carbon nanotubes, prepared using a simple solid-phase physical ball milling and low-temperature calcination method. The composite material is made by combining sodium ferric phosphate, zinc phosphate, calcium phosphate, and carbon nanotubes with Ca, Zn, and PO4. 3- Co-doping significantly improves the intrinsic conductivity of sodium iron sulfate crystals while reducing the material's sensitivity to moisture, resulting in a sodium-ion battery composite cathode material with excellent rate performance and air stability.

[0005] To achieve the above objectives, the present invention employs the following technical solutions:

[0006] A highly stable doped sodium iron sulfate cathode material comprises sodium iron phosphate, zinc iron phosphate, calcium iron phosphate particles, and carbon nanotubes.

[0007] Furthermore, the mass ratio of the iron phosphate zinc calcium sodium sulfate particles and carbon nanotubes is 85-95:5-15.

[0008] Furthermore, the chemical formula of the sodium iron phosphate, zinc phosphate, and calcium phosphate is: Na 2+2x Ca y Zn z Fe 2-x-y-z (SO4) 3-y-z (PO4) 2(y+z) / 3 , where x ranges from 0.20 to 0.35, y ranges from 0.03 to 0.12, and z ranges from 0.03 to 0.12.

[0009] A method for preparing a highly stable doped sodium ferric sulfate cathode material includes the following steps:

[0010] Step 1: Anhydrous ferrous sulfate, anhydrous sodium sulfate, anhydrous calcium phosphate, anhydrous zinc phosphate and carbon nanotubes are ball-milled in an inert atmosphere ball mill jar to obtain calcination precursor.

[0011] Step 2: The calcination precursor is placed in an inert atmosphere tube furnace and calcined at 360-400℃ with a heating rate of 1.5-2℃ / min and a calcination time of 16-24h to obtain the iron-zinc-calcium-sodium sulfate-phosphate composite electrode material.

[0012] Furthermore, the anhydrous ferrous sulfate is obtained by heat-treating ferrous sulfate heptahydrate in an inert atmosphere tube furnace at 250°C for 8–12 hours.

[0013] Furthermore, the mass ratio of the anhydrous ferrous sulfate, anhydrous sodium sulfate, anhydrous calcium phosphate, anhydrous zinc phosphate, and carbon nanotubes is 46.93–50.88: 32.78–41.98: 0.60–2.72: 0.74–3.38: 5.00–15.00.

[0014] Furthermore, in step 1, the gas filled in the inert atmosphere ball milling jar is argon or nitrogen, and the ball milling time is 10-15 hours.

[0015] Compared with the prior art, the present invention has the following advantages:

[0016] (1) This invention addresses the problems of poor intrinsic conductivity, low rate performance, and poor air stability of current sodium ferric sulfate electrode materials. It introduces Ca, Zn, and PO43- to modify the sodium ferric sulfate lattice. The co-doping of Ca and Zn alters the sodium ferric sulfate unit cell, expanding the lattice parameters and improving its ionic conductivity, which is beneficial for sodium ion transport. Simultaneously, the interaction between the electron clouds of the two dopants and Fe atoms effectively reduces the band gap of sodium ferric sulfate, thus improving its electronic conductivity. Furthermore, the simultaneous implementation of PO43- further enhances its properties. 3- Successful doping can effectively improve the material's binding energy to water, thus enhancing its water resistance. Combined with the excellent conductive network of carbon nanotubes, the conductivity and air stability of the composite material can be significantly improved.

[0017] (2) The electrode material provided by the present invention has the advantages of simple and convenient preparation method, low cost, good air stability and rate performance, and good cycle stability (>6000 times), and has strong market competitiveness in the field of large-scale energy storage application. Attached Figure Description

[0018] Figure 1 The charge-discharge curves of the sodium-ion battery prepared from the iron-zinc-calcium-sodium sulfate composite cathode material obtained in Example 1 of this invention are shown.

[0019] Figure 2 This is a rate performance diagram of the sodium-ion battery prepared with the iron-zinc-calcium-sodium sulfate composite cathode material obtained in Example 2 of the present invention;

[0020] Figure 3 This is a long-cycle diagram of the sodium-ion battery prepared with the composite cathode material of iron phosphate, zinc, calcium and sodium sulfate obtained in Example 2 of this invention.

[0021] Figure 4 The image shows the XRD pattern of the iron phosphate, zinc phosphate, calcium phosphate, and sodium sulfate composite cathode material obtained in Example 3 of this invention.

[0022] Figure 5This is a scanning electron microscope image of the iron phosphate, zinc phosphate, calcium phosphate, and sodium sulfate composite cathode material obtained in Example 3 of the present invention;

[0023] Figure 6 The image shows the XRD pattern of the iron phosphate zinc calcium sodium composite cathode material obtained in Example 3 of this invention after being placed in air for 7 days. Detailed Implementation

[0024] To gain a deeper understanding of this invention, we will provide a comprehensive and detailed description. However, this invention has various implementations and is not limited to the specific examples listed herein. These examples are presented to enhance a full understanding of the disclosure of this invention.

[0025] Example 1

[0026] S1. 48.37 g of ferrous sulfate heptahydrate was heat-treated at 250 °C for 8 h in an inert atmosphere tube furnace to obtain 26.65 g of anhydrous ferrous sulfate.

[0027] S2, 26.65g of anhydrous ferrous sulfate, 17.04g of anhydrous sodium sulfate, 0.31g of anhydrous calcium phosphate, 0.386g of anhydrous zinc phosphate and 2.42g of carbon nanotubes were ball-milled in an inert atmosphere ball mill jar for 10h to obtain the calcined precursor.

[0028] S3. The calcination precursor was placed in an inert atmosphere tube furnace and calcined at 360℃ with a heating rate of 1.8℃ / min for 16 hours to obtain a composite electrode material of iron-zinc-calcium-sodium sulfate phosphate, wherein the molecular formula of iron-zinc-calcium-sodium sulfate phosphate is Na. 2.4 Ca 0.03 Zn 0.03 Fe 1.74 (SO4) 2.94 (PO4) 0.04 The carbon nanotube content is 5.17% wt.

[0029] The sodium-ion battery prepared from the obtained iron-zinc-calcium-sodium sulfate composite cathode material is shown in the charge-discharge curve diagram below. Figure 1 As shown, the discharge specific capacity of the material can still reach more than 85 mAh / g at a current density of 1C (120 mAh / g).

[0030] Example 2

[0031] S1. 43.37 g of ferrous sulfate heptahydrate was heat-treated at 250 °C for 10 h in an inert atmosphere tube furnace to obtain 23.71 g of anhydrous ferrous sulfate.

[0032] S2, 23.71 g of anhydrous ferrous sulfate, 17.04 g of anhydrous sodium sulfate, 1.24 g of anhydrous calcium phosphate, 1.54 g of anhydrous zinc phosphate and 3.93 g of carbon nanotubes were ball-milled in an inert atmosphere ball mill jar for 10 h to obtain the calcined precursor.

[0033] S3. The calcination precursor was placed in an inert atmosphere tube furnace and calcined at 380℃ with a heating rate of 1.9℃ / min for 18 hours to obtain a composite electrode material of iron-zinc-calcium-sodium sulfate phosphate, wherein the molecular formula of iron-zinc-calcium-sodium sulfate phosphate is Na. 2.4 Ca 0.12 Zn 0.12 Fe 1.56 (SO4) 2.76 (PO4) 0.18 The carbon nanotube content is 8.28% wt.

[0034] The rate performance diagram of the sodium-ion battery prepared with the iron-zinc-calcium-sodium sulfate composite cathode material was obtained, as follows: Figure 2 As shown, the results indicate that the material still maintains a cycle capacity of 60 mAh / g at a high rate of 100C; the corresponding long-cycle curve for the sodium-ion battery is shown below. Figure 3 As shown, the results indicate that the material retains more than 90% of its capacity after 6000 cycles at a high current of 50C, demonstrating excellent high-rate cycling stability.

[0035] Example 3

[0036] S1. 41.7g of ferrous sulfate heptahydrate was heat-treated at 250℃ for 12h in an inert atmosphere tube furnace to obtain 22.8g of anhydrous ferrous sulfate.

[0037] S2, 22.8 g of anhydrous ferrous sulfate, 19.17 g of anhydrous sodium sulfate, 1.24 g of anhydrous calcium phosphate, 0.386 g of anhydrous zinc phosphate and 5.42 g of carbon nanotubes were ball-milled in an inert atmosphere ball mill jar for 14 h to obtain the calcined precursor.

[0038] S3. The calcination precursor was placed in an inert atmosphere tube furnace and calcined at 390℃ with a heating rate of 1.5℃ / min for 24 hours to obtain a composite electrode material of iron-zinc-calcium-sodium sulfate phosphate, wherein the molecular formula of iron-zinc-calcium-sodium sulfate phosphate is Na. 2.7 Ca 0.12 Zn 0.03 Fe 1.50 (SO4) 2.85 (PO4) 0.1 The carbon nanotube content is 11.1% wt.

[0039] The XRD pattern of the iron phosphate, zinc phosphate, calcium phosphate, and sodium sulfate composite cathode material was obtained, as follows: Figure 4As shown, the XRD diffraction peaks are sharp and there are no impurity phases, proving that the crystal phase is of high purity and the crystal form is complete; the corresponding scanning electron microscope image of the iron phosphate zinc calcium sodium sulfate composite cathode material is shown below. Figure 5 As shown, the crystals of sodium iron phosphate, zinc phosphate, and calcium phosphate are clearly uniform in size, with a particle size between 1 and 10 micrometers; the XRD pattern of the sodium iron phosphate, zinc phosphate, and calcium phosphate composite cathode material after being placed in air for 7 days is shown in the figure. Figure 6 As shown, the XRD diffraction peak shape remained basically unchanged, and no new impurity phases appeared, demonstrating its excellent air stability.

[0040] Example 4

[0041] S1. 42.53 g of ferrous sulfate heptahydrate was heat-treated at 250 °C for 8 h in an inert atmosphere tube furnace to obtain 23.25 g of anhydrous ferrous sulfate.

[0042] S2, 23.25 g of anhydrous ferrous sulfate, 19.17 g of anhydrous sodium sulfate, 0.62 g of anhydrous calcium phosphate, 0.772 g of anhydrous zinc phosphate and 6.58 g of carbon nanotubes were ball-milled in an inert atmosphere ball mill jar for 15 h to obtain the calcined precursor.

[0043] S3. The calcination precursor was placed in an inert atmosphere tube furnace and calcined at 360℃ with a heating rate of 1.5℃ / min for 20 hours to obtain a composite electrode material of iron-zinc-calcium-sodium sulfate phosphate, wherein the molecular formula of iron-zinc-calcium-sodium sulfate phosphate is Na. 2.7 Ca 0.06 Zn 0.06 Fe 1.53 (SO4) 2.88 (PO4) 0.08 The carbon nanotube content is 13.1% wt.

[0044] Example 5

[0045] S1. 43.92 g of ferrous sulfate heptahydrate was heat-treated at 250 °C for 10 h in an inert atmosphere tube furnace to obtain 24.02 g of anhydrous ferrous sulfate.

[0046] S2, 24.02 g of anhydrous ferrous sulfate, 18.46 g of anhydrous sodium sulfate, 0.62 g of anhydrous calcium phosphate, 0.772 g of anhydrous zinc phosphate and 6.42 g of carbon nanotubes were ball-milled in an inert atmosphere ball mill jar for 12 h to obtain the calcined precursor.

[0047] S3. The calcination precursor was placed in an inert atmosphere tube furnace and calcined at 370℃ with a heating rate of 1.5℃ / min for 18 hours to obtain a composite electrode material of iron-zinc-calcium-sodium sulfate phosphate, wherein the molecular formula of iron-zinc-calcium-sodium sulfate phosphate is Na. 2.6 Ca 0.06 Zn0.06 Fe 1.58 (SO4) 2.88 (PO4) 0.08 The carbon nanotube content is 12.77% wt.

[0048] Contents not described in detail in this specification are prior art known to those skilled in the art. Although illustrative specific embodiments of the invention have been described above to facilitate understanding by those skilled in the art, it should be understood that the invention is not limited to the scope of the specific embodiments. Various modifications are readily apparent to those skilled in the art as long as they fall within the spirit and scope of the invention as defined and determined by the appended claims, and all inventions utilizing the concept of this invention are protected.

Claims

1. A highly stable doped sodium ferric sulfate cathode material, characterized in that: It includes sodium iron phosphate, zinc phosphate, calcium phosphate particles and carbon nanotubes; the chemical formula of the sodium iron phosphate, zinc phosphate, calcium phosphate is: Na 2+2x Ca y Zn z Fe 2-x-y-z (SO4) 3-y-z (PO4) 2(y+z) / 3 , where x ranges from 0.20 to 0.35, y ranges from 0.03 to 0.12, and z ranges from 0.03 to 0.

12.

2. The highly stable doped sodium ferric sulfate cathode material according to claim 1, characterized in that: The mass ratio of the iron phosphate, zinc phosphate, calcium phosphate particles and carbon nanotubes is 85~95:5~15.

3. The method for preparing a highly stable doped sodium ferric sulfate cathode material as described in claim 1, characterized in that, Includes the following steps: Step 1: Anhydrous ferrous sulfate, anhydrous sodium sulfate, anhydrous calcium phosphate, anhydrous zinc phosphate and carbon nanotubes are ball-milled in an inert atmosphere ball mill jar to obtain calcination precursor; Step 2: The calcination precursor is placed in an inert atmosphere tube furnace for calcination treatment to obtain the iron phosphate zinc calcium sodium sulfate composite electrode material. The mass ratio of anhydrous ferrous sulfate, anhydrous sodium sulfate, anhydrous calcium phosphate, anhydrous zinc phosphate, and carbon nanotubes is 46.93~50.88: 32.78~41.98: 0.60~2.72: 0.74~3.38: 5.00~15.

00.

4. The method for preparing a highly stable doped sodium ferric sulfate cathode material according to claim 3, characterized in that: The anhydrous ferrous sulfate is obtained by heat-treating ferrous sulfate heptahydrate in an inert atmosphere tube furnace at 250°C for 8-12 hours.

5. The method for preparing a highly stable doped sodium ferric sulfate cathode material according to claim 3, characterized in that: In step 1, the inert atmosphere ball mill jar is filled with argon or nitrogen gas, and the ball milling time is 10-15 h.

6. The method for preparing a highly stable doped sodium ferric sulfate cathode material according to claim 3, characterized in that: In step 2, the calcination temperature is 360~400℃, the heating rate is 1.5~2℃ / min, and the calcination time is 16~24 h.

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