A polyanionic sodium-ion cathode material and a preparation method thereof

Abstract

The application discloses a kind of polyanionic sodium ion positive electrode materials and preparation method, it is related to sodium ion battery technical field, including the following steps: preparation ferrous sulfate precursor material;Preparation of a superfine nanometer point composite multi-dimensional porous conductive graphene;Ferrous sulfate sodium precursor material and a superfine nanometer point composite multi-dimensional porous conductive graphene are mixed, to obtain second mixture, the second mixture is dry method ball milling, to obtain third mixture, the third mixture is moved to first inert gas high-temperature environment and is sintered, after cooling, obtain the surface of multi-dimensional conductive network coated ferrous sulfate sodium material is coated.This application constructs superfine nanometer point composite multi-dimensional porous conductive graphene network and is coated with material modification, improves surface coating effect, while improving the conductivity of material, additionally increase material surface defect, improve the performance of Fe2+, improve the electrochemical performance of material to a certain extent.

Description

Technical Field

[0001] This application relates to the field of sodium-ion battery technology, and in particular to a polyanionic sodium-ion cathode material and its preparation method. Background Technology

[0002] Na₂Fe₂(SO₄)₃ has a theoretical voltage plateau of 3.8V, offering a working voltage comparable to lithium-ion batteries. This represents a significant advantage over other polyanionic sodium-ion cathode materials, effectively overcoming the low working voltage and low energy density issues of sodium-ion batteries. However, Na₂Fe₂(SO₄)₃ suffers from low conductivity and sensitivity to moisture, making it susceptible to air poisoning. Coating and carbon modification of Na₂Fe₂(SO₄)₃ are common methods to improve its performance. However, conventional carbon modification methods struggle to achieve a tight bond between the active material and the carbon substrate, resulting in low overall conductivity and difficulty meeting the requirements for high-rate charge and discharge.

[0003] For example, patent CN110336021A provides a novel method in which graphene oxide and / or acetylene black are used together as a conductive framework to composite with sodium ferrous sulfate to obtain a Na2Fe(SO4)2 / C electrode material. The presence of graphene oxide and / or acetylene black as carbon materials promotes the formation of pure-phase Na2Fe(SO4)2 and reduces the generation of impurity phases. The composite of graphene oxide and / or acetylene black enhances the electronic conductivity of the material and improves its electrochemical performance. However, this method is prepared by using a low-temperature solid-state method with ferrous sulfate and sodium sulfate. In the composite material, graphene and / or acetylene black are uniformly dispersed around the prepared sodium ferrous sulfate particles and obtained by liquid nitrogen freeze-drying technology. Pure graphene has a layered structure with large steric hindrance, and acetylene black particles are small with a large specific surface area and are prone to agglomeration and uneven dispersion.

[0004] For example, patent CN109192982A provides a method for synthesizing Na2+2xFe2-x(SO4)3 material using Na2SO4 and FeSO4·7H2O as the main raw materials. The synthesis method is simple. However, this method uses carbon black as a carbon source, which generally requires a high temperature and is not easy to uniformly coat the material surface to form a conductive network. Summary of the Invention

[0005] To address the problems of poor conductivity, uneven coating layer formation, and poor electron carrier in existing polyanionic sodium ferric sulfate (NaxFey(SO4)y) materials, this application provides a polyanionic sodium ion cathode material and its preparation method. The method improves the coating agent by constructing an ultrafine nanodot composite multidimensional porous conductive graphene network to coat the polyanionic sodium ferric sulfate material. This significantly reduces the risk of direct contact between the sodium ferric sulfate surface and space, while simultaneously creating more sites and providing more sodium ion transport channels, thus solving the problems of low conductivity and poor cycle stability.

[0006] Specifically, in order to achieve the above technical solution, firstly, this application provides a method for preparing a polyanionic sodium-ion cathode material, comprising the following steps:

[0007] Preparation of ferrous sulfate precursor materials;

[0008] Prepare a multidimensional porous conductive graphene composite of ultrafine nanodots;

[0009] The sodium ferrous sulfate precursor material and the multidimensional porous conductive graphene composite of ultrafine nanodots are mixed to obtain a second mixture. The second mixture is then dry-ball-milled to obtain a third mixture. The third mixture is then transferred to a high-temperature environment with a first inert gas for sintering. After cooling, a sodium ferrous sulfate material with a multidimensional conductive network coating on its surface is obtained.

[0010] Preferably, the preparation of the ferrous sulfate precursor material includes the following steps:

[0011] After removing impurities by dissolving ferrous sulfate in deionized water, the first solution is obtained.

[0012] Sodium sulfate is added to the first solution and mixed to obtain the second solution;

[0013] The second solution was slowly added to liquid nitrogen and freeze-dried to obtain the ferrous sulfate precursor material.

[0014] Preferably, the first solution is a ferrous sulfate solution, and the molar ratio of ferrous sulfate to sodium sulfate in the second solution is 2:1.

[0015] Preferably, the preparation of the ultrafine nanodot composite multidimensional porous conductive graphene includes the following steps:

[0016] Dissolve 0.005-0.2 parts of metal M hydrochloride compound and 0.005-0.2 parts of nitrated triacetic acid in 1.35-2.78 parts of deionized water and 0.32-0.66 parts of 2-propanol and stir for 15-30 minutes to obtain a third solution. Then, transfer the third solution to a high-pressure sealed environment at 150-190℃ for heat treatment for 4-8 hours to obtain an M-nitrated triacetic acid precursor. Separate the precursor by centrifugation and wash the product 2-4 times with deionized water and / or ethanol. Dry the product at 50℃-70℃ for 10-14 hours to obtain precursor A.

[0017] 0.005-0.2 parts of precursor A are redispersed in 1-1.2 parts of deionized water and ultrasonically treated for 10-15 minutes to obtain the first dispersion.

[0018] The first dispersion was added to an aqueous solution containing 0.005-0.3 parts of graphene oxide and dispersed. Then, it was sonicated for 10-15 minutes, an antioxidant was added, and it was stored at 92-98℃ for 1.5-2.5 hours to form a multidimensional graphene oxide gel.

[0019] The multidimensional graphene oxide gel is rinsed and then freeze-dried with liquid nitrogen to obtain a first mixture. The first mixture is then mixed with sulfur powder or selenium powder and sintered in a second inert gas high-temperature environment. After cooling, M-GO material is obtained. The M-GO material is the multidimensional porous conductive graphene composite of ultrafine nanodots.

[0020] Preferably, the inert gas in the second inert gas high-temperature environment of the M-GO material is nitrogen or helium, the temperature range of the second inert gas high-temperature environment is 300℃-500℃, and the sintering time of the M-GO material is 1-2 hours.

[0021] Preferably, the multidimensional graphene oxide gel is rinsed 2-3 times with an ethanol solution, an acetone solution, or deionized water.

[0022] Preferably, the mass ratio of sodium ferrous sulfate precursor to M-GO in the second mixture is 85-100:0-15, and the ball milling aid in the second mixture is one or more of ethanol, acetone, or N-methylpyrrolidone.

[0023] Preferably, the inert gas in the first inert gas environment of the third mixture is nitrogen or helium, the sintering temperature of the third mixture is 300℃-400℃, and the sintering time of the third mixture is 10-30h.

[0024] Preferably, the metal M hydrochloride compound is a Co hydrochloride or a Mo hydrochloride, or one or more of Sn, Cr hydrochloride compounds, etc.

[0025] Secondly, embodiments of this application also provide a ternary cathode material coated with a perovskite-type conductor, which is prepared using a method for preparing a polyanionic sodium-ion cathode material provided in any embodiment of this application.

[0026] This application has the following beneficial effects: The preparation method of this application improves the coating agent, addressing the defects of graphene oxide itself, such as large steric hindrance and layered structure; by constructing a composite nanodot porous conductive network structure to coat the material surface, the risk of direct contact between the sodium ferrous sulfate surface and space is reduced to a greater extent; using 0-dimensional SnS, CoSe2, MoS2, CoS2 and other ultrafine nanodots uniformly confined in porous carbon nanowires, providing abundant active sites and shortened ion / electron diffusion paths; one-dimensional porous carbon nanowires can effectively protect CoSe2 nanodots from polymerization, and in particular, the high conductivity and continuous three-dimensional network not only further reduce volume changes, but also provide multi-channel transport pathways for ions / electrons, solving the technical problems of sodium ferrous sulfate material being easy to absorb water, easily oxidized, easily deteriorated and easily deactivated, and overcoming the problems of low sodium storage capacity, low conductivity and poor cycle stability in practical applications. Attached Figure Description

[0027] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments of this application and their descriptions are used to explain this application and do not constitute an undue limitation of this application.

[0028] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 This is a schematic flowchart of a method for preparing a polyanionic sodium-ion cathode material according to an embodiment of this application. Detailed Implementation

[0030] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0031] In the description of this application, the terms "first", "second", and "A" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0032] The Chinese meanings of the following English abbreviations

[0033] FCC: First charge capacitor; FDC: First discharge capacitor;

[0034] PVDF: Polyvinylidene fluoride homopolymer or copolymer of vinylidene fluoride with other small amounts of fluorinated vinyl monomers;

[0035] NMP: N-methylpyrrolidone is an organic compound.

[0036] Please see Figure 1 A preferred embodiment of this application discloses a method for preparing a polyanionic sodium-ion cathode material, comprising the following steps:

[0037] S1: Preparation of ferrous sulfate precursor material; In this step, the preparation of ferrous sulfate precursor material includes the following steps: S11: Dissolve titanium dioxide ferrous sulfate in deionized water to remove impurities, and then obtain the first solution;

[0038] S12: Add sodium sulfate to the first solution and mix to obtain a second solution; S13: Slowly add the second solution to liquid nitrogen and freeze dry to obtain the ferrous sulfate precursor material; wherein, the first solution is a ferrous sulfate solution, and the molar ratio of ferrous sulfate to sodium sulfate in the second solution is 2:1.

[0039] S2: Preparation of an ultrafine nanodot composite multidimensional porous conductive graphene; In this step, the preparation of the multidimensional porous conductive graphene includes the following steps: S21: Dissolve 0.005-0.2 parts of metal M hydrochloride compound and 0.005-0.2 parts of nitrated triacetic acid in 1.35-2.78 parts of deionized water and 0.32-0.66 parts of 2-propanol and stir for 15-30 minutes to obtain a third solution. Then, transfer the third solution to a high-pressure sealed environment at 150-190℃ for heat treatment for 4-8 hours to obtain an M-nitrated triacetic acid precursor. Separate by centrifugation and wash the product 2-4 times with deionized water and / or ethanol. Dry at 50℃-70℃ for 10-14 hours to obtain precursor A. In this precursor A, the metal M hydrochloride compound is one or more of Co hydrochloride, Mo hydrochloride, or Sn, Cr hydrochloride compounds, etc.; S22: Dissolve 0.0 S23: 0.5-0.2 parts of precursor A are redispersed in 1-1.2 parts of deionized water and ultrasonically treated for 10-15 minutes to obtain a first dispersion; S24: The first dispersion is added to an aqueous solution containing 0.005-0.3 parts of graphene oxide and dispersed, then ultrasonically treated for 10-15 minutes, an antioxidant is added, and the mixture is stored at 92-98℃ for 1.5-2.5 hours to form a multidimensional graphene oxide gel; S25: The multidimensional graphene oxide gel is rinsed 2-3 times with ethanol solution, acetone solution, or deionized water. After rinsing, it is freeze-dried with liquid nitrogen to obtain a first mixture. The first mixture is mixed with sulfur powder or selenium powder and sintered in an inert gas environment such as nitrogen or helium at a temperature of 300℃-500℃ for 1-2 hours. After cooling, M-GO material is obtained, wherein the M-GO material is the multidimensional porous conductive graphene composite of ultrafine nanodots.

[0040] S3: Ferrous sulfate precursor material is treated with multidimensional porous conductive graphene to obtain a sodium ferrous sulfate material with a multidimensional conductive network coating on its surface; specifically, the sodium ferrous sulfate precursor material and a multidimensional porous conductive graphene composite of ultrafine nanodots are mixed at a mass ratio of 85-100:0-15 to obtain a second mixture. The second mixture is then dry-milled with ethanol, acetone, or N-methylpyrrolidone to obtain a third mixture. The third mixture is then sintered in an inert gas environment such as nitrogen or helium at a temperature of 300℃-400℃ for 10-30 hours. After cooling, the sodium ferrous sulfate material with a multidimensional conductive network coating on its surface is obtained.

[0041] Example

[0042] Step 1: Preparation of sodium ferrous sulfate precursor material; Ferrous sulfate of titanium dioxide is dissolved in deionized water to remove impurities, obtaining a ferrous sulfate solution with low impurity content (first solution). Ferrous sulfate and sodium sulfate are mixed according to the stoichiometric ratio to obtain a second solution, wherein the molar ratio of ferrous sulfate to sodium sulfate is 2:1; the above solution is slowly added to liquid nitrogen for freeze-drying to obtain the precursor material.

[0043] Step 2: Dissolve 0.1 mol of SnCl₅H₂O and 0.05 mol of nitrated triacetic acid in 25 ml of deionized water and 30 ml of 2-propanol, and stir magnetically for 15 minutes to obtain a third solution. Then, place the third solution in a sealed high-pressure reactor lined with polytetrafluoroethylene (PTFE). The solvothermal reaction temperature is controlled at 160°C, and the reaction proceeds for 6 hours to obtain a Sn-nitrated triacetic acid precursor. After centrifugation, the product is washed three times with deionized water and ethanol, and then dried in a vacuum drying oven at 50°C for 12 hours to obtain precursor A.

[0044] Step 3: Take 0.005 mol of precursor A and redisperse it in 20 mL of deionized water and sonicate for 10 minutes to form a low concentration dispersion. Then, add graphene oxide (GO) aqueous solution to the above dispersion for dispersion, followed by sonication. Add 2 mL of antioxidant ascorbic acid and store at 95°C for 2 hours to form a multidimensional graphene oxide gel.

[0045] Step 4: The multidimensional graphene oxide gel obtained in Step 3 is rinsed twice with ethanol solution, acetone solution or deionized water, and then freeze-dried with liquid nitrogen to obtain a freeze-dried product. Finally, the freeze-dried product is mixed with sulfur powder and sintered at 400℃ for 2 hours under inert gas N2 protection, and then cooled to room temperature to obtain an ultrafine nanodot SnS composite nano-multidimensional porous conductive graphene, which is the M-GO material.

[0046] Step 5: Mix the sodium ferrous sulfate precursor material and the M-GO material with a mass fraction of ferrous sulfate precursor: M-GO = 90:10. Perform dry ball milling with ethanol as a ball milling aid. Sinter under inert gas N2 protection at a temperature of 400℃ for 20 hours. After cooling to room temperature, obtain the desired sodium ferrous sulfate material with a multi-dimensional conductive network coating.

[0047] Comparative Example

[0048] Following steps 1-5, where M-GO is replaced by ordinary graphene oxide, the sodium ferrous sulfate precursor material and GO material are mixed with a mass fraction of ferrous sulfate precursor:GO = 90:10. The mixture is then dry-ball-milled with ethanol as a ball-milling aid and sintered under inert gas N2 protection at a temperature of 400℃ for 20 hours. After cooling to room temperature, the comparative sodium ferrous sulfate material is obtained.

[0049] The two positive electrode materials obtained by the above method were evaluated for their electrical performance. A mass ratio formulation with the main material as sp:PVDF = 80:10:10 was used. The formulation was tested using NMP as solvent, and homogenized on a centrifugal dispersion device. The coating surface density was controlled at 80-100 m² / g. After baking, the materials were assembled into 2025-type button batteries, with a sodium metal sheet as the negative electrode. Electrical performance tests were conducted using sodium perchlorate as the solute and ethylene carbonate and dimethyl carbonate as solvents. The electrical performance was tested on a CTE-1000 testing chamber in Chengde at a temperature of 25±2℃ and a voltage range of 2.0-4.4V. Simultaneously, the powder conductivity of the modified powder was tested. Details are shown in Table 1, which compares the electrical performance of the proportions and examples.

[0050] Table 1: Electrical performance tests of comparative examples and embodiments

[0051]

[0052] As shown in Table 1, the conductivity of the embodiments of this application reaches 3.47 S / cm, which is higher than that of the comparative example (2.55 S / cm). Furthermore, in both FCC and FDC tests, the results show that the embodiments of this application are superior to the comparative example. Therefore, this application constructs an ultrafine nanodot composite multidimensional porous conductive graphene network to coat the polyanionic sodium ferric sulfate material, which greatly reduces the risk of direct contact between the surface of sodium ferric sulfate and space, while forming more sites and providing more sodium ion transport channels, thus solving the problems of low conductivity and poor cycle stability.

[0053] The above are merely preferred embodiments of this application; however, the scope of protection of this application is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in this application, based on the technical solution and its improved concept, should be covered within the scope of protection of this application.

Claims

1. A method for preparing a polyanionic sodium-ion cathode material, characterized in that, Includes the following steps: Preparation of sodium ferrous sulfate precursor materials; Preparation of multidimensional porous conductive graphene composed of ultrafine nanodots; The sodium ferrous sulfate precursor material and the ultrafine nanodot composite multidimensional porous conductive graphene are mixed to obtain a second mixture. The second mixture is then dry ball-milled to obtain a third mixture. The third mixture is then transferred to a first inert gas high-temperature environment for sintering. After cooling, a sodium ferrous sulfate material with a multidimensional conductive network coating on its surface is obtained. The preparation of the ultrafine nanodot composite multidimensional porous conductive graphene includes the following steps: Dissolve 0.005-0.2 parts of metal M hydrochloride compound and 0.005-0.2 parts of nitrated triacetic acid in 1.35-2.78 parts of deionized water and 0.32-0.66 parts of 2-propanol and stir for 15-30 minutes to obtain a third solution. Then, transfer the third solution to a high-pressure sealed environment at 150-190℃ for heat treatment for 4-8 hours to obtain M-nitrated triacetic acid precursor. Separate by centrifugation and wash the product 2-4 times with deionized water and / or ethanol. Dry at 50℃-70℃ for 10-14 hours to obtain precursor A. 0.005-0.2 parts of precursor A are redispersed in 1-1.2 parts of deionized water and ultrasonically treated for 10-15 minutes to obtain the first dispersion. The first dispersion was added to an aqueous solution containing 0.005-0.3 parts of graphene oxide and dispersed. Then, it was sonicated for 10-15 minutes, an antioxidant was added, and the mixture was stored at 92-98℃ for 1.5-2.5 hours to form a multidimensional graphene oxide gel. The multidimensional graphene oxide gel is rinsed and then freeze-dried with liquid nitrogen to obtain a first mixture. The first mixture is then mixed with sulfur powder or selenium powder and sintered in a second inert gas high-temperature environment. After cooling, M-GO material is obtained. The M-GO material is a multidimensional porous conductive graphene composite of ultrafine nanodots.

2. The method for preparing a polyanionic sodium-ion cathode material according to claim 1, characterized in that, The preparation of the sodium ferrous sulfate precursor material includes the following steps: After removing impurities by dissolving ferrous sulfate in deionized water, the first solution is obtained. Sodium sulfate is added to the first solution and mixed to obtain the second solution; The second solution was slowly added to liquid nitrogen and freeze-dried to obtain the sodium ferrous sulfate precursor material.

3. The method of claim 2, wherein the poly-anionic sodium-ion cathode material is prepared by the following steps: (1) preparing a precursor of the poly-anionic sodium-ion cathode material; (2) mixing the precursor with a solvent; (3) heating the mixture to obtain the poly-anionic sodium-ion cathode material. The first solution is a ferrous sulfate solution, and the molar ratio of ferrous sulfate to sodium sulfate in the second solution is 2:

1.

4. The method of claim 1, wherein the poly-anionic sodium-ion cathode material is prepared by the following steps: (1) preparing a precursor of the poly-anionic sodium-ion cathode material; (2) mixing the precursor with a solvent; (3) heating the mixture to obtain the poly-anionic sodium-ion cathode material. The inert gas in the second inert gas high-temperature environment of the M-GO material is nitrogen or helium, the temperature range of the second inert gas high-temperature environment is 300℃-500℃, and the sintering time of the M-GO material is 1-2 hours.

5. The method of claim 4, wherein the poly-anionic sodium-ion cathode material is prepared by the following steps: (1) preparing a precursor of the poly-anionic sodium-ion cathode material; (2) mixing the precursor with a solvent; (3) heating the mixture to obtain the poly-anionic sodium-ion cathode material. Multidimensional graphene oxide gel is rinsed 2-3 times with ethanol solution, acetone solution, or deionized water.

6. The method of claim 1, wherein the poly-anionic sodium-ion cathode material is prepared by the following steps: (1) preparing a precursor of the poly-anionic sodium-ion cathode material; (2) mixing the precursor with a solvent; (3) heating the mixture to obtain the poly-anionic sodium-ion cathode material. The mass ratio of sodium ferrous sulfate precursor to multidimensional porous conductive graphene composited with ultrafine nanodots in the second mixture is 85-100:0-15, and the ball milling aid of the second mixture is one or more of ethanol, acetone, or N-methylpyrrolidone.

7. The method of claim 6, wherein the poly-anionic sodium-ion cathode material is prepared by the following steps: (1) preparing a precursor of the poly-anionic sodium-ion cathode material; (2) mixing the precursor with a solvent; (3) heating the mixture to obtain the poly-anionic sodium-ion cathode material. The inert gas in the first inert gas environment of the third mixture is nitrogen or helium, the sintering temperature of the third mixture is 300-400 DEG C, and the sintering time of the third mixture is 10-30h.

8. The method of claim 1, wherein the poly-anionic sodium-ion cathode material is prepared by the following steps: (1) preparing a precursor of the poly-anionic sodium-ion cathode material; (2) mixing the precursor with a solvent; (3) heating the mixture to obtain the poly-anionic sodium-ion cathode material. The metal M hydrochloride compound is a hydrochloride of Co or Mo, or one or more of hydrochloride compounds of Sn, Cr.

9. A perovskite-type conductor-coated ternary cathode material, characterized by Prepared by any one of the preparation methods of the polyanionic sodium ion cathode material in claims 1-8.

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