Ketjen black cross-linked silicate substituted sodium ferric sulfate positive electrode material and preparation method thereof

Abstract

The invention discloses a ketjen black cross-linked silicate substituted sodium ferric sulfate positive electrode material and a preparation method thereof, and relates to the technical field of sodium ion battery positive electrode materials. The material comprises a sodium ferric sulfate matrix and ketjen black, sulfate radicals of the sodium ferric sulfate matrix are partially replaced by silicate radicals, the sodium ferric sulfate matrix and the ketjen black are compounded in a cross-linking mode, the chemical formula of the material is Na < 2.6 > Fe < 1.7 > (SO4) < 3-2x > (SiO4) x (at) C, x is equal to 0.05-0.1, and C is ketjen black. The electronic conductivity and sodium ion migration ability of the material are effectively improved, meanwhile, the stability of a crystal structure in the cycle process is enhanced, and the prepared positive electrode material has excellent electrochemical performance, good rate capability, high reversible capacity and stable cycle life, and is suitable for high-performance sodium ion batteries, such as lithium ion batteries, lithium ion batteries, lithium ion batteries, lithium ion batteries, lithium ion batteries, lithium ion batteries, lithium ion batteries, lithium ion batteries, lithium ion batteries and lithium ion batteries. Good application prospects are realized.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery cathode material technology, and in particular to a Ketjen Black crosslinked silicate-substituted sodium iron sulfate cathode material and its preparation method. Background Technology

[0002] The urgent global demand for clean energy is driving the accelerated development of energy storage technologies. Sodium-ion batteries, as a potential complement to lithium-ion batteries, demonstrate broad application prospects in large-scale energy storage due to the wide availability of sodium resources, significant cost-effectiveness, and excellent overall electrochemical performance.

[0003] In the performance composition of sodium-ion batteries, the cathode material plays a crucial and decisive role. Its cycle life, operating voltage, thermal safety, reversible capacity, and power output directly affect the battery's practical application efficiency. Polyanionic compounds are a class of cathode materials that have attracted much attention, with their core advantages being structural stability, high voltage platform, and excellent ion diffusion performance. Among them, sodium iron sulfate, with its outstanding characteristics such as low raw material price, simple synthesis process, low environmental impact, and energy-saving production process, is considered one of the important candidate cathode materials for promoting the commercialization of sodium-ion batteries.

[0004] However, sodium ferric sulfate has inherent technical shortcomings that are difficult to avoid: firstly, its charge mobility is insufficient, which directly limits the material's actual output capacity, high-rate discharge performance, and long-cycle stability; secondly, its thermodynamic stability is poor, and the material will gradually decompose when the temperature rises above 400℃. It is worth noting that the currently widely used strategy of constructing an in-situ conductive network through high-temperature (typically 500℃ to 800℃) carbonization conflicts with the heat-sensitive characteristics of sodium ferric sulfate, making this traditional strategy difficult to directly apply to the preparation of sodium ferric sulfate-based cathode materials. Summary of the Invention

[0005] The purpose of this invention is to provide a Ketjenblack cross-linked silicate-substituted sodium iron sulfate cathode material and its preparation method, thereby solving the problems existing in the prior art. By introducing Ketjenblack and silicate substitution, this invention greatly improves the conductivity and stability of sodium iron sulfate, resulting in a sodium-ion battery cathode material with high reversible specific capacity, high rate performance, and good cycle stability, which is a Ketjenblack cross-linked silicate-substituted sodium iron sulfate material.

[0006] To achieve the above objectives, the present invention provides the following solution: One of the technical solutions of the present invention is to provide a sodium ferric sulfate cathode material with cross-linked silicate substitution by Ketjen black, comprising a sodium ferric sulfate matrix with silicate partially replacing sulfate and Ketjen black, wherein the sodium ferric sulfate matrix and Ketjen black are cross-linked composite. The chemical formula of the Ketjen Black crosslinked silicate-substituted sodium ferric sulfate cathode material is: Na 2.6 Fe 1.7 (SO4) 3-2x (SiO4) x @C, x=0.05-0.1, where C is Ketjen Black.

[0007] As a further preferred embodiment of the present invention, x = 0.05, 0.07 or 0.1.

[0008] As a further preferred embodiment of the present invention, the mass percentage of Ketjen black in the cross-linked silicate-substituted sodium ferric sulfate cathode material is 10 wt%.

[0009] The second technical solution of the present invention provides a method for preparing the above-mentioned Ketjen Black crosslinked silicate-substituted sodium ferric sulfate cathode material, comprising the following steps: (1) According to the stoichiometric ratio, ascorbic acid, anhydrous sodium sulfate, sodium acetate trihydrate, ferrous sulfate heptahydrate and tetraethyl orthosilicate are mixed in a solvent to obtain a mixed solution; (2) Add a dispersant to the mixed solution, then add Ketjen black and disperse to obtain a precursor solution; (3) The precursor solution is dried to obtain the precursor; (4) The precursor is heat-treated under a reducing protective atmosphere to obtain the Ketjen black crosslinked silicate-substituted sodium iron sulfate cathode material.

[0010] Furthermore, the amount of Ketjen black added is 10 wt% of the theoretical yield of the cross-linked silicate-substituted sodium ferric sulfate cathode material.

[0011] As a further preferred embodiment of the present invention, the dispersant comprises hexadecyl dimethyl ethyl ammonium bromide (EHDAB).

[0012] Furthermore, the amount of the dispersant added is 10 wt% of the theoretical yield of the Ketjen black crosslinked silicate-substituted sodium ferric sulfate cathode material.

[0013] As a further preferred embodiment of the present invention, the mass ratio of hexadecyl dimethyl ethyl ammonium bromide to Ketjen black is 1:1.

[0014] In the preparation process of this invention, the dispersant promotes the uniform dispersion of Ketjenblack in the solution; subsequent spray drying treatment forms a microsphere structure with uniform cross-linking of sodium ferric sulfate and Ketjenblack. This design can more efficiently improve the conductivity of the composite material, thereby significantly enhancing the reversible specific capacity and cycle stability of the material under high current conditions.

[0015] As a further preferred embodiment of the present invention, the heat treatment temperature is 350-400°C and the heat treatment time is 6-12 hours.

[0016] As a further preferred embodiment of the present invention, the heat treatment temperature is 350-380°C and the heat treatment time is 8-10 hours.

[0017] As a further preferred embodiment of the present invention, the reducing protective atmosphere is a hydrogen-argon mixture.

[0018] As a further preferred embodiment of the present invention, the volume ratio of hydrogen to argon in the hydrogen-argon mixed atmosphere is 5:95.

[0019] In this invention, by introducing silicate (SiO4) to partially replace sulfate (SO4), the anionic framework structure of sodium iron sulfate materials is effectively controlled. Since the tetrahedral volume of silicate is larger than that of sulfate, its substitution effect, without compromising the overall crystal structure stability, causes adjustments to the local lattice environment and a redistribution of strain. This results in the contraction of the FeO6 octahedral structure adjacent to the silicate, manifested as a decrease in Fe–O bond length and octahedral volume. This structural change enhances the interaction between Fe–O bonds and improves the structural stability of the Fe–O framework. Simultaneously, the introduction of Si–O bonds into the silicate alters the local electronic environment of oxygen atoms, adjusting the distribution of oxygen-related electronic states and promoting electronic coupling between Fe and O. This anionic structure control method can also improve the local coordination environment of sodium ions to a certain extent without hindering their migration channels, thus contributing to improved electrochemical reaction kinetics and cycle stability. The Ketjen Black crosslinked silicate-substituted sodium iron sulfate cathode material of this invention exhibits excellent electrochemical performance and good structural stability.

[0020] The Ketjen Black crosslinked silicate-substituted sodium ferric sulfate cathode material prepared by this invention possesses high reversible specific capacity, excellent rate performance, and good cycle stability. Compared with pure sodium ferric sulfate material, this composite material not only achieves a high reversible specific capacity close to the theoretical specific capacity, but also significantly improves the capacity retention capability under high current charge and discharge conditions, successfully solving the core technical problems of insufficient cycle stability and poor rate performance of traditional sodium ferric sulfate materials.

[0021] This invention achieves precise control of the anionic framework structure of sodium ferric sulfate materials by introducing silicate (SiO4) to partially replace sulfate (SO4) in sodium ferric sulfate, laying a structural foundation for optimizing the electrochemical performance of the materials.

[0022] The third technical solution of the present invention provides the application of the above-mentioned Ketjen Black crosslinked silicate-substituted sodium iron sulfate cathode material in sodium-ion batteries.

[0023] As a further preferred embodiment of the present invention, the sodium-ion battery includes an energy storage battery and a power battery.

[0024] The present invention discloses the following technical effects: This invention significantly improves the electronic conductivity and structural stability of sodium ferric sulfate by introducing silicate ions to partially replace sulfate ions in the sodium ferric sulfate crystal structure and achieving uniform cross-linking with Ketjen black conductive agent. The introduction of silicate ions not only optimizes the lattice arrangement and enhances the unimpeded flow of sodium ion migration channels, but also effectively suppresses structural collapse caused by volume changes during charge and discharge, thereby improving the material's cycle performance. Simultaneously, the cross-linking composite formed between Ketjen black and the active material matrix significantly reduces interfacial impedance and improves electrode reaction kinetic efficiency. The synergistic effect of these two factors allows the resulting cathode material to maintain high specific capacity while exhibiting excellent rate performance and long cycle life.

[0025] This invention balances ion / electron conductivity with structural durability, providing a reliable technical path for developing high-performance sodium-ion battery cathode materials. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 The images show the XRD patterns of sodium ferric sulfate materials prepared in Examples 1-3 and Comparative Examples 1-2 of this invention.

[0028] Figure 2 In the image, from left to right, are SEM images of the Ketjen Black crosslinked sodium ferric sulfate materials prepared by Comparative Example 2, Comparative Example 1, and Example 1 of this invention.

[0029] Figure 3 The above figures show the rate performance of sodium ferric sulfate materials prepared in Examples 1-3 and Comparative Examples 1-2 of this invention.

[0030] Figure 4 The diagram shows the cycling performance of sodium ferric sulfate materials prepared in Examples 1-3 and Comparative Example 1 of this invention. Detailed Implementation

[0031] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0032] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0033] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0034] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be readily apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0035] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0036] Unless otherwise specified, the room temperature in this invention is 25±2℃.

[0037] All raw materials used in the embodiments of this invention were obtained through commercial purchase.

[0038] It should be noted that all aspects not described in detail in this invention are conventional operating methods in the field and are not the focus of this invention. For example, specific methods such as ultrasonic dispersion and spray drying are all completed using conventional methods.

[0039] The Ketjen black crosslinked silicate-substituted sodium ferric sulfate cathode material of the present invention uses Ketjen black as the conductive component and hexadecyl dimethyl ethyl ammonium bromide as the dispersant, so that sodium ferric sulfate and Ketjen black can be uniformly crosslinked, which greatly improves the conductivity of the composite material. Furthermore, bulk doping is introduced, and silicate partially replaces sulfate to enhance the intrinsic conductivity and air stability of sodium ferric sulfate, thereby overcoming the defects of poor conductivity and poor air stability of the material, and improving the specific capacity, rate performance and cycle stability of the sodium ferric sulfate cathode material.

[0040] The first aspect of the present invention is to provide a cross-linked sodium ferric sulfate cathode material with substituted silicate in the form of Ketjen black, comprising a sodium ferric sulfate matrix with silicate partially substituted sulfate and Ketjen black, wherein the sodium ferric sulfate matrix and Ketjen black are cross-linked and composite. The chemical formula of the Ketjen Black crosslinked silicate-substituted sodium ferric sulfate cathode material is: Na 2.6 Fe 1.7 (SO4) 3-2x (SiO4) x @C, x=0.05-0.1, where C is Ketjen Black.

[0041] In a preferred embodiment of the present invention, x = 0.05, 0.07 or 0.1.

[0042] In a preferred embodiment of the present invention, the mass percentage of Ketjen black in the cross-linked silicate-substituted sodium ferric sulfate cathode material is 10 wt%.

[0043] A second aspect of the present invention provides a method for preparing the above-mentioned Ketjen Black crosslinked silicate-substituted sodium ferric sulfate cathode material, comprising the following steps: (1) According to the stoichiometric ratio, ascorbic acid, anhydrous sodium sulfate, sodium acetate trihydrate, ferrous sulfate heptahydrate and tetraethyl orthosilicate are mixed in a solvent to obtain a mixed solution; (2) Add a dispersant to the mixed solution, then add Ketjen black and disperse to obtain a precursor solution; (3) The precursor solution is dried to obtain the precursor; (4) The precursor is heat-treated under a reducing protective atmosphere to obtain the Ketjen black crosslinked silicate-substituted sodium iron sulfate cathode material.

[0044] In a preferred embodiment of the present invention, the amount of Ketjen black added is 10 wt% of the theoretical yield of the cross-linked silicate-substituted sodium ferric sulfate cathode material.

[0045] In a preferred embodiment of the invention, the dispersant comprises hexadecyl dimethyl ethyl ammonium bromide (EHDAB).

[0046] In a preferred embodiment of the present invention, the amount of the dispersant added is 10 wt% of the theoretical yield of the Ketjen black crosslinked silicate-substituted sodium ferric sulfate cathode material.

[0047] In a preferred embodiment of the present invention, the mass ratio of hexadecyl dimethyl ethyl ammonium bromide to Ketjen black is 1:1.

[0048] In the preparation process of this invention, cetyldimethylethylammonium bromide is used as a dispersant to promote the uniform dispersion of Ketjen black in the solution. Subsequent spray drying forms a spherical precursor with uniform cross-linking of sodium ferric sulfate and Ketjen black. This design more efficiently improves the conductivity of the composite material, thereby significantly enhancing the reversible specific capacity and cycle stability under high current conditions. Simultaneously, this invention uses tetraethyl orthosilicate and sodium acetate as raw materials, successfully achieving partial substitution of sulfate with silicate ions without introducing impurities. This further improves the air stability and intrinsic conductivity of the material, synergistically optimizing its overall performance.

[0049] In a preferred embodiment of the present invention, the heat treatment temperature is 350-400°C and the heat treatment time is 6-12 hours; more preferably, the heat treatment temperature is 350-380°C and the heat treatment time is 8-10 hours.

[0050] In a preferred embodiment of the present invention, the reducing protective atmosphere is a hydrogen-argon mixture.

[0051] In a preferred embodiment of the present invention, the volume ratio of hydrogen to argon in the hydrogen-argon mixed atmosphere is 5:95.

[0052] In a preferred embodiment of the present invention, the ultrasonic dispersion time is 30 min-60 min, preferably 50 min-60 min, and more preferably 60 min.

[0053] In a preferred embodiment of the present invention, spray drying is selected as the drying method.

[0054] The present invention will be further described in detail below with reference to specific embodiments: Example 1 A method for preparing a Ketjen Black crosslinked silicate-substituted sodium ferric sulfate cathode material, comprising the following steps: (1) Dissolve 0.68 mmol ascorbic acid, 4.64 mmol sodium sulfate, 6.8 mmol ferrous sulfate heptahydrate, 1.12 mmol sodium acetate trihydrate and 0.28 mmol tetraethyl orthosilicate in 100 mL of deionized water and stir to dissolve to form a solution; (2) Add 0.142 g of hexadecyl dimethyl ethyl ammonium bromide (EHDAB) and 0.142 g of Ketjen black to the solution obtained in step (1) in sequence. After dissolving, ultrasonically disperse for 60 min to obtain a uniform black precursor solution. (3) The above precursor solution was spray-dried to obtain the precursor product; (4) The precursor product was heat-treated in a tube furnace at 380°C for 8 hours under a hydrogen-argon mixed gas condition (volume ratio of hydrogen to argon of 5:95) to obtain the Ketjen Black crosslinked silicate-substituted sodium ferric sulfate material Na. 2.6 Fe 1.7 (SO4) 2.86 (SiO4) 0.07 @C, the product is denoted as NFSS@C-0.07.

[0055] Example 2 The only difference from Example 1 is that the amount of sodium sulfate added is 4.8 mmol, the amount of sodium acetate trihydrate added is 0.8 mmol, and the amount of tetraethyl orthosilicate added is 0.2 mmol. The resulting product Na... 2.6 Fe 1.7 (SO4) 2.9 (SiO4) 0.05 @C is denoted as NFSS@C-0.05.

[0056] Example 3 The only difference from Example 1 is that the amount of sodium sulfate added is 4.4 mmol, the amount of sodium acetate trihydrate added is 1.6 mmol, and the amount of tetraethyl orthosilicate added is 0.4 mmol. The resulting product Na... 2.6 Fe 1.7 (SO4) 2.8 (SiO4) 0.1 @C is denoted as NFSS@C-0.1.

[0057] Comparative Example 1 The only difference from Example 1 is that tetraethyl orthosilicate and sodium acetate trihydrate were not added, and the amount of sodium sulfate added was 5.2 mmol. The resulting product Na 2.6 Fe 1.7 (SO4)3@C is denoted as NFS@C.

[0058] Comparative Example 2 The only difference from Example 1 is that tetraethyl orthosilicate, sodium acetate trihydrate, hexadecyl dimethyl ethyl ammonium bromide and Ketjen black were not added, and the amount of sodium sulfate added was 5.2 mmol; pure sodium ferric sulfate cathode material was obtained, and the product was labeled as NFS.

[0059] The XRD images of the sodium ferric sulfate materials prepared in Examples 1-3 and Comparative Examples 1-2 are as follows: Figure 1 As shown, the XRD patterns of the samples prepared by this invention are basically consistent, indicating that the addition of Ketjen black and the partial substitution of silicate groups did not change the phase of the material, and the purity is very high.

[0060] SEM images of the Ketjen Black crosslinked sodium ferric sulfate material prepared in Example 1 are shown below. Figure 2 As shown, the results indicate that a microsphere structure uniformly cross-linked with sodium ferric sulfate and Ketjen black was successfully synthesized by spray drying, which can significantly improve the conductivity and structural stability of the composite material.

[0061] The materials prepared in each embodiment and comparative example were used as positive electrode materials for battery assembly, as detailed below: The positive electrode materials prepared in each embodiment or comparative example were mixed with conductive carbon black (Super P) and polyvinylidene fluoride (PVDF) in a mass ratio of 7:2:1. After thorough grinding and mixing, the mixture was dissolved in N-methylpyrrolidone (NMP) solution and magnetically stirred for 4 h to form a uniform slurry. The slurry was then uniformly coated onto aluminum foil using a scraper method and dried at 80 °C for 12 h under vacuum. The resulting material was then cut into electrode sheets to serve as the positive electrode. Sodium sheets were used as the negative electrode. The electrolyte was a 1 M sodium perchlorate (NaClO4) solution, with a solvent consisting of ethylene carbonate / diethyl carbonate (EC / DEC) in a volume ratio of 1:1, and 5 wt% fluoroethylene carbonate (FEC) was added. The separator was made of glass fiber. The cells were assembled into a 2032 type button cell in an argon-filled glove box.

[0062] The rate performance graphs of sodium ferric sulfate materials prepared in Examples 1-3 and Comparative Examples 1-2 are shown below. Figure 3 As shown in the rate performance diagram, NFSS@C-0.07 has the best rate performance, maintaining a high reversible specific capacity even at high currents. In contrast, in the comparative example without the addition of Ketjenblack, the capacity drops rapidly as the current density increases, and its stability is poor even when Ketjenblack is added but no silicate is introduced.

[0063] The cycling performance diagrams of the sodium ferric sulfate materials prepared in Examples 1-3 and Comparative Example 1 are shown below. Figure 4 As shown in the cycling performance diagram, NFSS@C-0.05 exhibits the best cycling stability, which can be attributed to the synergistic effect of Ketjen black and silicate substitution on conductivity enhancement and structural stability.

[0064] The test results for each embodiment and the comparative assembly of the batteries are shown in Table 1.

[0065] Table 1 As can be seen from Table 1, the sodium iron sulfate cathode material with cross-linked silicate prepared in this invention can achieve high reversible specific capacity, excellent rate performance and cycle stability when used as the cathode of sodium-ion batteries.

[0066] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A Ketjen Black crosslinked silicate-substituted sodium ferric sulfate cathode material, characterized in that, The product comprises a sodium ferric sulfate matrix with silicate partially substituted sulfate and Ketjen black, wherein the sodium ferric sulfate matrix is ​​cross-linked with Ketjen black. The chemical formula of the Ketjen Black crosslinked silicate-substituted sodium ferric sulfate cathode material is: Na 2.6 Fe 1.7 (SO4) 3-2x (SiO4) x @C, x=0.05-0.1, where C is Ketjen Black.

2. The Ketjen Black crosslinked silicate-substituted sodium ferric sulfate cathode material according to claim 1, characterized in that, x = 0.05, 0.07, or 0.

1.

3. The Ketjen Black crosslinked silicate-substituted sodium ferric sulfate cathode material according to claim 1, characterized in that, The mass percentage of Ketjen black in the cross-linked silicate-substituted sodium ferric sulfate cathode material is 10 wt%.

4. The method for preparing the Ketjen Black crosslinked silicate-substituted sodium ferric sulfate cathode material according to any one of claims 1-3, characterized in that, Includes the following steps: (1) According to the stoichiometric ratio, ascorbic acid, anhydrous sodium sulfate, sodium acetate trihydrate, ferrous sulfate heptahydrate and tetraethyl orthosilicate are mixed in a solvent to obtain a mixed solution; (2) Add a dispersant to the mixed solution, then add Ketjen black and disperse to obtain a precursor solution; (3) The precursor solution is dried to obtain the precursor; (4) The precursor is heat-treated under a reducing protective atmosphere to obtain the Ketjen black crosslinked silicate-substituted sodium iron sulfate cathode material.

5. The preparation method according to claim 4, characterized in that, The dispersant includes hexadecyl dimethyl ethyl ammonium bromide.

6. The preparation method according to claim 4, characterized in that, The heat treatment temperature is 350-400℃, and the heat treatment time is 6-12h.

7. The preparation method according to claim 4, characterized in that, The reducing protective atmosphere is a hydrogen-argon mixture.

8. The application of the Ketjen black crosslinked silicate-substituted sodium iron sulfate cathode material as described in any one of claims 1-3 in sodium-ion batteries.

9. The application according to claim 8, characterized in that, The sodium-ion battery includes energy storage batteries and power batteries.

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