Preparation method and application of sodium iron vanadate sulfate positive electrode material with wide temperature range

Abstract

The application relates to a preparation method and application of a wide-temperature-range sodium vanadium iron sulfate positive electrode material, and relates to a preparation method and application of a positive electrode material. In order to solve the problem of insufficient cycle stability of an existing sodium iron sulfate positive electrode material, the preparation method comprises the following steps: a sodium source, a vanadium source, an iron source, a sulfate and a carbon source are mixed according to a stoichiometric ratio, and ball milling treatment is carried out under a rotating speed of 300-600 r / min to obtain a precursor; the precursor is subjected to first-stage sintering at 150-200 DEG C, and then subjected to second-stage sintering at 650 DEG C to obtain a NaVFe(SO4)3 positive electrode material with a carbon-coated structure. Through optimization of a ball milling process and a segmented sintering system, the crystallinity and structural integrity of the material are effectively improved, the prepared NaVFe(SO4)3 positive electrode material is uniform in particle size, the carbon-coated layer is complete, and the material exhibits excellent structural stability, high-rate performance, wide-temperature-range performance and significantly improved energy density. The application belongs to the technical field of secondary battery electrode materials.

Description

Technical Field

[0001] This invention relates to a method for preparing a positive electrode material and its application, belonging to the field of secondary battery electrode material technology. Background Technology

[0002] With the rapid development of renewable energy and smart grids, large-scale energy storage systems are placing higher demands on the cost, safety, and resource sustainability of rechargeable batteries. While lithium-ion batteries dominate the market, the scarcity and uneven geographical distribution of metal resources such as lithium and cobalt limit their widespread application in large-scale energy storage. Therefore, sodium-ion batteries, with their abundant resources and low cost, are considered a highly promising alternative. Research on sodium-ion battery cathode materials mainly focuses on three systems: layered oxides, Prussian blue analogues, and polyanionic compounds. Among these, polyanionic compounds, with their robust three-dimensional framework structure and adjustable operating voltage, exhibit significant advantages in cycle stability.

[0003] Sodium ferric sulfate (Na2Fe2(SO4)3), as an important member of the polyanionic family, is characterized by its unique [SO4]² - The polyanionic groups provide high electronegativity, enabling iron ions to pair with (Fe²⁺) + / Fe³ + It can achieve a high redox potential (approximately 3.8 V vs. Na). + The sodium vanadium sulfate (Na₂F) material, while possessing a crystal structure that provides ample channels for sodium ion diffusion, theoretically offers considerable capacity. However, its intrinsic electronic and ionic conductivity are relatively low, limiting its rate performance. Furthermore, the significant volume change and iron ion dissolution during the charge-discharge phase transition result in poor cycle life. Therefore, developing a novel sodium vanadium sulfate material with high stability is crucial for the development of high-performance sodium-ion battery materials.

[0004] Chinese patent application CN115838162B, filed on December 21, 2022, discloses a sodium vanadium iron phosphate cathode material and its preparation method. The method includes: using a solid-phase iron source with two particle size distributions as a carrier, mixing the iron source with a sodium source, a vanadium source, a phosphorus source, and a carbon source to obtain a sodium vanadium iron phosphate precursor, and then sintering it using a solid-phase method to obtain sodium vanadium iron phosphate cathode materials with different particle size distributions; wherein the melting point temperature of the iron source is higher than the sintering temperature; the median particle size of the large particles in the iron source is 800–900 nm, and the median particle size of the small particles is 350–450 nm. This invention, by controlling the melting point of the iron source to act as a carrier in the reaction system and optimizing the composition of the median particle size of the iron source, can improve the electrochemical performance of the sodium vanadium iron phosphate cathode material while achieving a high solid density.

[0005] However, the aforementioned patented technologies still cannot solve the problem of insufficient cycle stability of sodium ferric sulfate cathode materials. Summary of the Invention

[0006] To address the problem of insufficient cycle stability of existing sodium ferric sulfate cathode materials, this invention proposes a method for preparing and applying sodium ferric vanadium sulfate cathode materials with a wide temperature range.

[0007] The technical solution adopted by the present invention to solve the above problems is as follows: The steps of the method for preparing a wide-temperature-range sodium vanadium iron sulfate cathode material according to the present invention include:

[0008] Step 1: Weigh out sodium source, vanadium source, iron source and sulfate by molar ratio, add carbon source, mechanically activate and mix the raw materials evenly; Step 2: In an inert atmosphere, the precursor obtained in Step 1 is placed in a tube furnace for pretreatment, followed by high-temperature sintering to obtain NaVFe(SO4)3 cathode material.

[0009] Furthermore, the sodium source in step 1 is one or more of sodium sulfate, sodium carbonate, and sodium hydroxide.

[0010] Furthermore, the vanadium source in step 1 is one or more of vanadium sulfate, ammonium metavanadate sulfate, and vanadium pentoxide.

[0011] Furthermore, the iron source in step 1 is one or more of ferrous sulfate monohydrate and ferrous sulfate heptahydrate.

[0012] Furthermore, the sulfate in step 1 is one or more of sodium sulfate and ferrous sulfate.

[0013] Furthermore, the carbon source in step 1 is one or more of oxalic acid, citric acid, glucose, carbon black, graphene, and carbon nanotubes.

[0014] Furthermore, in step 1, the mass fraction of the carbon source is 1% to 10%, and the mechanical activation lasts for 0.5 to 24 hours.

[0015] Furthermore, the inert gas in step 2 is either argon or nitrogen.

[0016] Furthermore, in step 2, the pretreatment temperature of the precursor in the tube furnace is 150~200℃, the pretreatment time is 4~6h, the high-temperature sintering temperature is 650℃, and the sintering time is 12~20h.

[0017] The sodium vanadium iron sulfate cathode material prepared by the wide-temperature-range sodium vanadium sulfate cathode material preparation method described in this invention is used in the preparation of sodium-ion battery cathodes.

[0018] The beneficial effects of this invention are: 1. This invention marks the first successful synthesis of a novel polyanionic compound, NaVFe(SO4)3, as a cathode material for sodium-ion batteries via a solid-state method. The preparation process is simple and reproducible, and the obtained product exhibits uniform micron-sized particle morphology and a fully coated carbon layer structure, effectively improving electronic conductivity. Sodium half-cells assembled with this material demonstrate excellent cycle stability, wide temperature range performance, and high rate capability, possessing a solid foundation for industrial application.

[0019] 2. Compared to other polyanionic cathode materials, the NaVFe(SO4)3 material provided by this invention exhibits a significant high voltage plateau around 3.8 V and 4.2 V, corresponding to Fe²⁺. + / Fe³ + With V³ + / V 4+ The material exhibits a high average operating voltage and superior structural stability due to its multi-electron redox reaction. It also demonstrates low capacity decay during cycling, significantly improving the energy density of full cells and showing clear advantages in large-scale fabrication and commercial applications. Attached Figure Description

[0020] Figure 1 This is a scanning electron microscope image of the sample from Example 1; Figure 2 This is a comparison graph of the long-cycle performance of Example 1 and Comparative Sample 1 at room temperature; Figure 3 This is a comparison chart of the rate performance of Example 2 and Comparative Sample 2; Figure 4 This is a graph showing the cycling performance of the sample from Example 1 at 60°C; Figure 5 This is a graph showing the cycling performance of the sample from Example 1 at -30°C.

[0021] Example Example 1 High-performance sodium vanadium iron sulfate cathode material is produced according to the following steps: Step 1: Weigh out sodium sulfate, vanadium sulfate, and ferrous sulfate monohydrate by molar ratio, and add 3% oxalic acid and 5% citric acid as reducing agents and carbon sources. Place the weighed reagents into agate balls, add agate balls of different sizes at a ball-to-material ratio of 20:3, and add anhydrous ethanol as a ball milling aid. Set the ball milling speed to 300 rpm and the milling time to 12 hours to mix thoroughly. Place the milled precursor into a vacuum oven at 120℃ and dry for 12 hours. Store the dried reagents in a vacuum desiccator.

[0022] Step 2: The precursor prepared in Step 1 is evenly spread inside the corundum boat and compacted. The boat is placed in the center of the tube furnace, and argon gas is introduced as a protective gas. The tube furnace is set to heat at 5℃ / min, hold at 150℃ for 10h, hold at 650℃ for 10h, and then cool with the furnace.

[0023] like Figure 1 As shown, the NaVFe(SO4)3 material prepared by ball milling has uniform particle morphology and concentrated particle size distribution, with an average size of about 1 micrometer, showing good physical consistency, which is beneficial to the uniform dispersion and interfacial contact of active materials during electrode preparation.

[0024] To further evaluate the electrochemical performance of this material in sodium-ion batteries, electrode sheets were prepared according to a mass ratio of active material (NaVFe(SO4)3), conductive agent (Super-P), and binder (PVDF) of 7:2:1, and then assembled into coin cells for testing. Figure 2 As shown, the prepared NaVFe(SO4)3 electrode material exhibits excellent discharge specific capacity, reaching 104 mAh / g, at a current rate of 1 C. It is particularly noteworthy that this material shows excellent discharge specific capacity at approximately 3.8 V and 4.2 V (vs. NaVFe(SO4)3). + A distinct and stable voltage plateau is observed near / Na, which, according to analysis, corresponds to Fe² + / Fe³ + With V³ + / V 4+ The redox couple reaction. The presence of these two high-voltage plateaus indicates that the material has high operating voltage characteristics, providing an important foundation for achieving high energy density in sodium-ion batteries and showing good application prospects.

[0025] Example 2 High-performance sodium vanadium iron sulfate cathode material is produced according to the following steps: Step 1: Weigh out sodium sulfate, ammonium metavanadate sulfate, and ferrous sulfate heptahydrate by molar ratio, and add 5% glucose and 1% graphene as reducing agent and carbon source. Place the weighed reagents into a steel container, add steel balls at a ball-to-material ratio of 7:1, and add anhydrous ethanol as a ball milling aid. Set the ball mill speed to 600 rpm and the milling time to 6 hours to mix thoroughly. Place the ball-milled precursor into a 120℃ vacuum oven and dry for 10 hours. Store the dried reagents in a vacuum desiccator.

[0026] Step 2: The precursor prepared in Step 1 is evenly spread inside the corundum boat and compacted. The boat is placed in the center of the tube furnace, and argon gas is introduced as a protective gas. The tube furnace is set to heat at 5℃ / min, hold at 200℃ for 6 hours, hold at 650℃ for 15 hours, and then cool with the furnace.

[0027] To further evaluate the material's performance, its long-cycle performance over an ultra-wide temperature range of 60°C and -30°C was tested. Figure 4 As shown, the prepared NaVFe(SO4)3 electrode material exhibits a high capacity of 110 mAh / g at an ultra-high temperature of 60℃. Figure 5 The electrode exhibits excellent performance at -30℃, maintaining a capacity of 96 mAh / g, and retaining 91% of its capacity after 100 cycles. These electrochemical properties demonstrate the potential of NaVFe(SO4)3 electrode materials for applications over an ultra-wide temperature range.

[0028] Example 3 This example prepares a high-performance sodium vanadium iron sulfate, which differs from Example 1 in that only 10% by mass of glucose is added in step 1.

[0029] Example 4 This example prepares a high-performance sodium vanadium ferric sulfate. The specific difference from Example 1 is that in step 1, vanadium oxide sulfate is replaced with vanadium pentoxide.

[0030] Example 5 This example prepares a high-performance sodium vanadium iron sulfate. The specific difference from Example 1 is that in step 2, the temperature is kept at 200℃ for 6 hours and at 650℃ for 12 hours.

[0031] Comparative Example Comparative Example 1 This example prepares a Na2Fe2(SO4)3 cathode material. The specific difference from Example 1 is that vanadium oxide sulfate is not added in step 1.

[0032] Figure 2 The graphs for the cycling stability of Example 1 and Comparative Example 1 at room temperature show that NaVFe(SO4)3 has higher specific capacity and capacity retention.

[0033] Comparative Example 2 This example prepares a Na2Fe2(SO4)3 cathode material. The specific difference from Example 2 is that ammonium metavanadate sulfate is not added in step 1.

[0034] Figure 3 The rate performance graphs for Example 2 and Comparative Example 2 show that, due to the addition of vanadium with high conductivity, NaVFe(SO4)3 exhibits superior rate performance, displaying a capacity of 58 mAh / g at a 10 C rate.

[0035] In summary, this invention prepares a novel polyanionic compound, NaVFe(SO4)3, using a solid-state method, which has the following outstanding advantages as a cathode material for sodium-ion batteries: 1. The material has a stable structure and maintains good reversibility during sodium ion insertion / extraction; 2. It exhibits excellent rate performance, cycle stability, and wide temperature range performance; 3. The values ​​around 3.8 V and 4.2 V correspond to Fe² + / Fe³ + and V³ + / V 4+ Redox pairs exhibit a typical high voltage plateau, giving the material high energy density characteristics; The solid-phase process used is simple and the conditions are easy to control, making it suitable for large-scale industrial production.

[0036] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent substitutions, and improvements made to the above embodiments without departing from the scope of the present invention, based on the technical essence of the present invention and within the spirit and principles of the present invention, shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing a wide-temperature-range sodium vanadium iron sulfate cathode material, characterized in that, The specific steps include: Step 1: Weigh out sodium source, vanadium source, iron source and sulfate by molar ratio, add carbon source, mechanically activate and mix the raw materials evenly; Step 2: In an inert atmosphere, the precursor obtained in Step 1 is placed in a tube furnace for pretreatment, followed by high-temperature sintering to obtain NaVFe(SO4)3 cathode material.

2. The method for preparing a wide-temperature-range sodium vanadium iron sulfate cathode material according to claim 1, characterized in that, The sodium source in step 1 is one or more of sodium sulfate, sodium carbonate, and sodium hydroxide.

3. The method for preparing a wide-temperature-range sodium vanadium iron sulfate cathode material according to claim 1, characterized in that, The vanadium source in step 1 is one or more of vanadium sulfate, ammonium metavanadate sulfate, and vanadium pentoxide.

4. The method for preparing a wide-temperature-range sodium vanadium iron sulfate cathode material according to claim 1, characterized in that, The iron source in step 1 is one or more of ferrous sulfate monohydrate and ferrous sulfate heptahydrate.

5. The method for preparing a wide-temperature-range sodium vanadium iron sulfate cathode material according to claim 1, characterized in that, The sulfate in step 1 is one or more of sodium sulfate and ferrous sulfate.

6. The method for preparing a wide-temperature-range sodium vanadium iron sulfate cathode material according to claim 1, characterized in that, The carbon source in step 1 is one or more of oxalic acid, citric acid, glucose, carbon black, graphene, and carbon nanotubes.

7. The method for preparing a wide-temperature-range sodium vanadium iron sulfate cathode material according to claim 1, characterized in that, In step 1, the mass fraction of the carbon source is 1% to 10%, and mechanical activation takes 0.5 to 24 hours.

8. The method for preparing a wide-temperature-range sodium vanadium iron sulfate cathode material according to claim 1, characterized in that, The inert gas in step 2 is either argon or nitrogen.

9. The method for preparing a wide-temperature-range sodium vanadium iron sulfate cathode material according to claim 1, characterized in that, In step 2, the pretreatment temperature of the precursor in the tube furnace is 150~200℃, the pretreatment time is 4~6h, the high-temperature sintering temperature is 650℃, and the sintering time is 12~20h.

10. The application of a sodium vanadium iron sulfate cathode material prepared by the method according to any one of claims 1 to 9, characterized in that, The sodium vanadium iron sulfate cathode material is used in the preparation of the cathode for sodium-ion batteries.

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