Prussian blue-based sodium-ion battery cathode material, preparation method and application thereof

Abstract

This invention relates to a Prussian blue-based sodium-ion battery cathode material, its preparation method, and its application. The Prussian blue-based sodium-ion battery cathode material comprises: a Prussian blue analogue, and a conductive carbon material layer coated on the surface of the Prussian blue analogue; preferably, the conductive carbon material layer is composed of at least one of graphene, conductive graphite, carbon nanotubes, and conductive carbon black.

Description

Technical Field

[0001] This invention relates to a Prussian blue sodium-ion battery cathode material, its preparation method, and its application, belonging to the field of energy materials technology. Background Technology

[0002] Due to the depletion of traditional fossil fuels and the environmental pollution caused by their use, the research and development of new clean energy sources has become urgent. Currently, new clean energy sources such as wind, solar, and tidal power are being vigorously developed and have already occupied a certain share of the energy market. However, due to their intermittent nature, these new clean energy sources are subject to certain limitations in terms of time and space, and cannot effectively play their due role. Therefore, it is necessary to study large-scale energy storage technologies that can store energy generated in localized areas and release it when needed, achieving peak shaving and valley filling of energy generation, thereby enabling the effective utilization of these new clean energy sources.

[0003] Among various energy storage methods, electrochemical energy storage is the simplest and most efficient, becoming the mainstream of energy storage technology development. Lithium-ion batteries, with their outstanding advantages such as high energy density, high operating voltage, long cycle life, low self-discharge rate, and environmental friendliness, are widely used in mobile phones, laptops, digital cameras, and power tools. However, the growth of the lithium-ion battery market has led to lithium resource shortages and rising lithium prices. Therefore, there is a need to develop new energy storage systems that are abundant in resources and inexpensive. Sodium-ion batteries are another type of energy storage battery with a similar working mechanism and battery structure to lithium-ion batteries, and they have recently received increasing attention. Sodium resources are far more abundant than lithium, evenly distributed globally, and inexpensive and stable, with no development bottlenecks. Because sodium is readily available and inexpensive, and because sodium batteries can use aluminum foil as the negative electrode current collector instead of copper foil like lithium batteries, sodium-ion batteries have a significant potential price advantage. The material cost of sodium-ion batteries can be reduced by 30%-40% compared to lithium-ion batteries. As research continues, the potential advantages of sodium-ion batteries are being discovered, especially their excellent performance at high and low temperatures and their high safety, which lays a solid foundation for their application in energy storage and power fields.

[0004] The mainstream negative electrode materials for sodium-ion batteries are hard carbon and NaTi2(PO4)3, both of which have been extensively studied and possess characteristics such as long cycle life and high capacity. The electrolyte for sodium-ion batteries has also been well-developed, mainly composed of sodium salts such as NaPF6 and NaClO4 with ester solvents, exhibiting properties similar to lithium-ion battery electrolytes. Unlike the above two, the positive electrode material remains a bottleneck for sodium-ion batteries. Extensively studied sodium-ion battery positive electrodes can be divided into three categories: transition metal oxides, polyanionic compounds, and Prussian blue analogues. Transition metal oxides and polyanionic compounds, due to the presence of fluorine and oxygen bonds in their crystal structures, make Na… + Transport processes within the crystal lattice are subject to significant chemical binding energy, affecting insertion / extraction at the cathode and resulting in low rate performance. Furthermore, transition metal oxides are prone to structural damage during cycling, leading to electrode loosening or failure, and consequently, a severe reduction in cycle life. Polyanionic compounds, due to the large molecular weight of their anions, generally exhibit low specific capacity. The synthesis of both typically involves high-temperature solid-state methods, requiring substantial energy consumption.

[0005] The composition of Prussian blue (PB) and its derivatives (PBAs) can be represented by the general formula AxM[M'(CN)6]y·zH2O (A represents alkali metal ions such as Li, Na, and K, and M and M' represent transition metals such as Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Ba, and Sr, 0≤x≤2, y≤1). M and M' can be different elements or the same element, usually distinguished by their valence state. Since the two transition metal elements are located in different ligand fields of different central ions, they will exhibit different spin states. A diameter of approximately [missing information] is located in the (100) direction. It has large ion channels, therefore, it has up to 10 -9 ~10 -8 cm 2 s -1 Its high diffusion coefficient allows it to accommodate larger sodium ions and achieve faster sodium ion migration. More importantly, due to its stable and spacious three-dimensional structure, its lattice strain is almost zero during the insertion and extraction of sodium ions. Theoretically, one mole of material can achieve the insertion and extraction of two moles of sodium ions, providing a high theoretical specific capacity generated by two-electron transfer. Taking a typical Na₂FeFe(CN)₆ as an example, its theoretical specific capacity is approximately 170 mAh g⁻¹. -1 Compared to the 100-150 mAh g of typical transition metal oxide materials -1 The specific capacity and 120mAh g of phosphate materials -1The specific capacity is much higher. Furthermore, the interaction between Prussian blue-based materials and interstitial cations is very small, and the transition metal sites in their structure can be replaced by many other redox-active transition metal elements without disrupting the crystal structure. Therefore, Prussian blue and its derivatives are promising cathode materials for sodium-ion batteries. However, Prussian blue also has the following drawbacks: 1) Prussian blue-based cathode materials have low conductivity, and due to their poor thermal stability, they are difficult to carbon-coat at high temperatures; 2) During the synthesis of Prussian blue and its derivatives, structural defects such as numerous vacancies and coordinated water are easily generated, reducing the material's capacity and cycle performance; 3) Coordinated water in the crystal lattice of Prussian blue and its derivatives may transfer into the electrolyte, causing electrochemical decomposition, leading to electrolyte degradation and even safety hazards. Summary of the Invention

[0006] To address the above problems, this invention provides a Prussian blue sodium-ion battery cathode material, its preparation method, and its application.

[0007] On one hand, the present invention provides a Prussian blue-based sodium-ion battery cathode material, comprising: a Prussian blue analogue, and a conductive carbon material layer coated on the surface of the Prussian blue analogue; preferably, the conductive carbon material layer is composed of at least one of graphene, conductive graphite, carbon nanotubes, and conductive carbon black.

[0008] Preferably, the chemical formula of the Prussian blue analogue is Na. x M[Fe(CN)6] z ·wH2O, where M is n transition metal elements, n≥1, 0.1≤w≤4.0, 1.40≤x≤1.95, 0.90≤z≤0.98, and each transition metal element is labeled as y1, y2, y3…yn, and y1+y2+y3…+yn=1.

[0009] Preferably, n≥2, and when M is at least 2 transition metal elements, the subscript range of each transition metal element is 0.01 to 0.90, preferably 0.2 to 0.5.

[0010] Preferably, the particle size of the Prussian blue analogue is 10–60 μm.

[0011] Preferably, the thickness of the conductive carbon material layer is 200 nm to 2 μm.

[0012] Preferably, the conductive carbon material layer accounts for 1 to 30 wt% of the total mass of the Prussian blue sodium-ion battery cathode material.

[0013] In another aspect, the present invention provides a method for preparing a Prussian blue-type sodium-ion battery cathode material, comprising:

[0014] (1) Prussian blue analogue, conductive carbon material solution and deionized water are mixed to obtain Prussian blue analogue / conductive carbon material dispersion;

[0015] (2) The obtained Prussian blue analog / conductive carbon material dispersion is spray-dried to remove moisture and simultaneously coat the conductive carbon material on the surface of Prussian blue to obtain the Prussian blue sodium-ion battery cathode material.

[0016] Preferably, in step (1), the mixing method is ultrasonic oscillation and / or stirring; the power of ultrasonic oscillation is 200-700W and the time does not exceed 6h; the stirring time does not exceed 48h.

[0017] Preferably, in step (1), the conductive carbon material solution has a mass fraction of 1wt% to 20wt%.

[0018] The mass ratio of the conductive carbon material solution to the Prussian blue analogue is (0.1–10):1;

[0019] The concentration ratio of the Prussian blue analogue to deionized water is 1 g: (10-500) mL.

[0020] Preferably, the parameters of the spray drying include: a temperature of 180–300°C; and a peristaltic pump feed rate of (10–2000) mL / h.

[0021] Preferably, the method for preparing the Prussian blue analogue includes:

[0022] S1: Dissolve the sodium hexacyano salt, sodium salt, antioxidant and surface dispersant of transition metal N in deionized water by stirring to obtain a transparent and clear solution A;

[0023] S2: Dissolve the transition metal M salt and the complexing agent in deionized water by stirring to obtain a clear and transparent solution B;

[0024] S3: Add transparent clear solution B dropwise to transparent clear solution A, stir and react, then age the mixture, and finally separate the solid and liquid components by centrifugation, wash and dry to obtain the Prussian blue analogue.

[0025] Preferably, in step S1:

[0026] The sodium hexacyano salt of the transition metal N is one of sodium ferrocyanide decahydrate, sodium manganese cyanide decahydrate, and sodium cobalt cyanide decahydrate.

[0027] The concentration of sodium hexacyanocyanate of transition metal N in the transparent and clear solution A is 0.01–10 M;

[0028] The stirring process is carried out in a protective atmosphere at 25–95°C; the protective gas is one of air, nitrogen, and argon; the stirring speed is 200–1500 rpm.

[0029] The antioxidant is at least one of butylated hydroxyanisole, butylated hydroxytoluene, linolenic acid, tert-butylhydroquinone, or ascorbic acid, and the concentration of the antioxidant in the transparent clear solution A is 0.001-0.1M.

[0030] The sodium salt is at least one of sodium fluoride, sodium chloride, sodium bromide, sodium iodide, sodium acetate, sodium nitrate, sodium sulfate, sodium oxalate, and disodium ethylenediaminetetraacetate, and the weight ratio of the sodium salt to the transition metal M salt is (1-10):1.

[0031] The surface dispersant is at least one selected from polyvinylpyrrolidone, hexadecyltrimethylammonium bromide, polycyclic aromatic hydrocarbons, and sodium dodecylbenzenesulfonate. The concentration of the surface dispersant in the transparent and clear solution A is 0.1 g to 100 g / L. The use of the surface dispersant, on the one hand, further promotes the orderly growth of grains and prevents aggregation during the synthesis of Prussian blue; on the other hand, the addition of the surface dispersant improves the distribution, regulates the overall microstructure of the material, achieves larger sizes, and increases the particle size; thereby obtaining a uniform single-phase structure with high crystallinity and regular large-sized crystals.

[0032] Preferably, in step S2:

[0033] The concentration of the transition metal M salt in the transparent and clear solution B is 0.01–10 M;

[0034] The sodium salt of the complexing agent is selected from at least one of sodium citrate, 2,2'-bipyridine, 1-10-o-phenanthroline, ethylenediamine, ethylenediaminetetraacetic acid, trisodium aminotriacetate, sodium oxalate, disodium ethylenediaminetetraacetate, sodium gluconate, sodium tartrate, or sodium acetate, and the weight ratio of the complexing agent to the transition metal M salt is (1-10):1;

[0035] The stirring process is carried out in a protective atmosphere at 25–95°C; the protective gas is at least one of air, nitrogen, and argon; the stirring speed is 200–1500 rpm.

[0036] Preferably, in step S3;

[0037] The dropwise addition process is carried out at 25–95°C in a protective atmosphere; the protective gas is at least one of air, nitrogen, and argon.

[0038] The dropwise flow rate of the transparent and clear solution B is 1 mL / min to 50 mL / min;

[0039] The stirring reaction is carried out at a temperature of 25–95°C for a duration of 0.5–12 hours.

[0040] The aging temperature is 25–95°C, and the time is 2–72 hours;

[0041] The centrifugation speed for the centrifugation solid-liquid separation method is 6000-10000 rpm, and the time is 5-10 minutes;

[0042] The drying process is vacuum drying, with a vacuum degree of 10. -6 ~10 -2 The drying temperature is 100-220℃, and the drying time is 6-24h.

[0043] In another aspect, the present invention provides a sodium-ion battery, comprising: a positive electrode containing the above-mentioned Prussian blue sodium-ion battery positive electrode material.

[0044] Beneficial effects of this invention:

[0045] 1. This invention uses a co-precipitation method to prepare Prussian blue cathode materials. By controlling the sodium salt complexing agent in the reaction system, as well as the reaction temperature and the addition of sodium salt, the slow growth of the material crystals and the number of vacancies are achieved during the synthesis process. Subsequently, a spray drying method is used to remove the water of crystallization inside the material system, resulting in a low-water-content, low-vacancy Prussian blue sodium-ion battery cathode material. This solves the problem of coordinated water in conventional Prussian blue cathode materials, thereby improving the electrochemical performance of sodium-ion batteries.

[0046] 2. In this invention, the method of spray drying and coating the Prussian blue surface with conductive carbon material effectively overcomes the problem of poor conductivity in Prussian blue complexes, increases the conductivity of the Prussian blue cathode, reduces polarization, and significantly improves the cycle stability of the Prussian blue cathode. In particular, due to the doping of inert components in the multi-component Prussian blue, its cycle stability and rate performance are far superior to those of iron-based Prussian blue. Attached Figure Description

[0047] Figure 1 Figure ac is an SEM image of the carbon-encapsulated anhydrous Prussian blue sodium-ion battery cathode material prepared in Examples 1-3, and Figure d is an SEM image of the Prussian blue sodium-ion battery cathode material prepared in Comparative Example 1.

[0048] Figure 2 Figure ac shows the XRD patterns of the carbon-encapsulated anhydrous Prussian blue sodium-ion battery cathode materials prepared in Examples 1-3, and Figure d shows the XRD pattern of the Prussian blue sodium-ion battery cathode material prepared in Comparative Example 1.

[0049] Figure 3The graph shows the cycling performance of the sodium-ion half-cell with Prussian blue-like material as the positive electrode in the organic electrolyte system prepared in Example 1 at a current density of 500 mA / g.

[0050] Figure 4 The graph shows the cycling performance of the sodium-ion half-cell with Prussian blue-like material as the positive electrode in the organic electrolyte system prepared in Example 2 at a current density of 500 mA / g.

[0051] Figure 5 The graph shows the cycling performance of the sodium-ion half-cell with Prussian blue-like material as the positive electrode in the organic electrolyte system prepared in Example 3 at a current density of 500 mA / g.

[0052] Figure 6 The graph shows the cycling performance of the sodium-ion half-cell with Prussian blue-like material as the positive electrode in the organic electrolyte system prepared in Example 4 at a current density of 500 mA / g.

[0053] Figure 7 The graph shows the cycling performance of the sodium-ion half-cell with Prussian blue-like material as the positive electrode in the organic electrolyte system prepared in Comparative Example 1 at a current density of 500 mA / g.

[0054] Figure 8 The graph shows the cycling performance of the sodium-ion half-cell with Prussian blue-like material as the positive electrode prepared in Comparative Example 2, under an organic electrolyte system at a current density of 500 mA / g. Detailed Implementation

[0055] The present invention will be further illustrated by the following embodiments. It should be understood that the following embodiments are for illustrative purposes only and are not intended to limit the present invention.

[0056] In this disclosure, a Prussian blue-based cathode material is prepared using a co-precipitation method. By controlling the sodium salt complexing agent and the reaction temperature in the reaction system, slow crystal growth is achieved, reducing the formation of vacancy. Then, a spray drying method is used to remove the water of crystallization inside the material system, resulting in a low-water-content, low-vacancy Prussian blue-based sodium-ion battery cathode material. At the same time, a layer of conductive carbon material (preferably graphene) is coated on the surface of the Prussian blue, solving the problem of coordinated water in conventional Prussian blue-based cathode materials and alleviating the problem of low conductivity of Prussian blue-based cathode materials, thereby improving the electrochemical performance of sodium-ion batteries.

[0057] In this invention, a more stable Prussian blue-based sodium-ion battery cathode material is formed through a combination of pre-inert element doping and post-synthesis. The preparation method of the Prussian blue-based sodium-ion battery cathode material is illustrated below.

[0058] Under a specific temperature and protective atmosphere, soluble sodium hexacyanoate, sodium salt, antioxidant, and surface dispersant of transition metal N are dissolved in deionized water. After stirring, a transparent and clear solution A is obtained. The specific temperature range is 25–95°C; the protective gas is one or more of air, nitrogen, and argon; and the stirring speed is 200–1500 rpm.

[0059] In an optional embodiment, the sodium hexacyanocyanate of the transition metal N is one of sodium ferrocyanide decahydrate, sodium manganese cyanide decahydrate, or sodium cobalt cyanide decahydrate. The concentration of the soluble sodium hexacyanocyanate of the transition metal N in solution A is 0.01–10 M. The concentration of the antioxidant in solution B is 0.001–0.1 M; the weight ratio of the sodium salt to the transition metal M salt is (1–10):1; the concentration of the surface dispersant in solution B is 0.1 g–100 g / L. The complexing agent sodium salt is selected from at least one of sodium citrate, 2,2'-bipyridine, 1,10-phenanthroline, ethylenediamine, ethylenediaminetetraacetic acid, trisodium aminotriacetate, sodium oxalate, disodium ethylenediaminetetraacetate, sodium gluconate, sodium tartrate, or sodium acetate. The antioxidant is at least one of butylated hydroxyanisole, butylated hydroxytoluene, linolenic acid, tert-butylhydroquinone, or ascorbic acid. The sodium salt is at least one selected from sodium fluoride, sodium chloride, sodium bromide, sodium iodide, sodium acetate, sodium nitrate, sodium sulfate, sodium oxalate, and disodium ethylenediaminetetraacetate. The surface dispersant is at least one selected from polyvinylpyrrolidone, hexadecyltrimethylammonium bromide, polycyclic aromatic hydrocarbons, and sodium dodecylbenzenesulfonate.

[0060] Under a specific temperature and protective atmosphere, a soluble transition metal M salt, a complexing agent, and deionized water are dissolved to obtain a clear, transparent solution B. The specific temperature range is 25–95°C; the protective gas is one or more of air, nitrogen, and argon.

[0061] In an optional embodiment, the concentration of the soluble transition metal M salt in solution B is 0.01–10 M; the weight ratio of the complexing agent to the transition metal M salt is (1–10):1.

[0062] Under a specific temperature and protective atmosphere, solution B is slowly added dropwise to solution A. After stirring and reacting, the mixture is aged. Finally, solid-liquid separation, washing, and drying are performed by centrifugation to obtain the Prussian blue analogue to be treated. The specific temperature range is 25–95°C; the protective gas is one or more of air, nitrogen, and argon.

[0063] In an optional embodiment, the flow rate of solution B added dropwise to solution A is 1 mL / min to 50 mL / min. The centrifugal solid-liquid separation method uses a centrifugal speed of 6000 to 10000 rpm for 5 to 10 minutes. The drying is vacuum drying at a vacuum degree of 10. -6 ~10 -2 The drying temperature is 100-220℃, and the drying time is 6-24h.

[0064] The Prussian blue analogue and conductive carbon material composite slurry to be treated were added to water and dispersed thoroughly by ultrasonic vibration / stirring to obtain a Prussian blue analogue / conductive carbon material dispersion. The ultrasonic vibration time was 0–6 h, and the stirring time was 0–48 h.

[0065] In an optional embodiment, the mass fraction of the conductive carbon material composite slurry is 1 wt% to 10 wt%. The mass ratio of the conductive carbon material composite slurry to the Prussian blue analogue to be treated is (0.1 to 10) g / g. The concentration ratio of the Prussian blue analogue to water is 1 g / (10 to 500) mL.

[0066] A Prussian blue analog / conductive carbon material dispersion was spray-dried to obtain a low-water-content conductive carbon material encapsulating a Prussian blue-based sodium-ion battery cathode material. The spray-drying temperature was 180–300°C, and the peristaltic pump feed rate during spray-drying was (10–2000) mL / h.

[0067] In this invention, the Prussian blue sodium-ion battery cathode material can be used as the cathode of a sodium-ion battery, which can effectively improve the electrochemical performance of the sodium-ion battery.

[0068] The following examples further illustrate the present invention in detail. It should also be understood that the following examples are only for further explanation of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention are within the scope of protection of the present invention. The specific process parameters, etc., in the following examples are merely examples within a suitable range; that is, those skilled in the art can make appropriate selections within the appropriate range based on the description herein, and are not intended to be limited to the specific values ​​in the examples below.

[0069] Example 1:

[0070] Precursor solution A was prepared by dissolving 2 mol sodium ferrocyanide decahydrate, 10 g polyvinylpyrrolidone, 1 g ascorbic acid, and 1 mol sodium chloride in 1 L of deionized water. Precursor solution B was prepared by dissolving 1.5 mol manganese sulfate, 0.5 mol copper sulfate, and 5 mol sodium citrate in 1 L of deionized water. Precursor solution B was slowly added dropwise to container A at a rate of 10 mL / min using a peristaltic pump through a silicone tube. The reaction temperature was room temperature, and the stirring rate was 400 rpm. After the addition of precursor B was complete, the mixture was stirred continuously at room temperature for 8 h and then allowed to stand for 40 h to obtain a sample suspension. The sample suspension was centrifuged at 6000 rpm for 10 min. The resulting sample precipitate was washed multiple times with deionized water and ethanol. The product was then dried in a vacuum oven at 160 °C and a vacuum degree of 1 Pa for 10 h to obtain a Prussian blue analogue.

[0071] 40g of Prussian blue analogue and 20g of graphene composite slurry with a mass fraction of 20wt% were added to 1L of deionized water. After ultrasonic vibration for 2 hours, the mixture was stirred vigorously for 2 hours. During the spray drying process, the peristaltic pump feed rate was 200mL / h, and the drying temperature was 250℃ to obtain carbon-encapsulated anhydrous Prussian blue.

[0072] The chemical formula of the material was determined to be Na by inductively coupled plasma optical emission spectroscopy (ICP-OES), CHN elemental analysis, and thermogravimetric analysis. 1.72 Mn 0.75 Cu 0.25 [Fe(CN)6] 0.97 □ 0.03 ·0.15H2O@0.1C (□ means vacancy, 0.1 means 10wt%).

[0073] SEM analysis revealed that the carbon-encapsulated Prussian blue sodium-ion battery cathode material prepared in this embodiment exhibits a spherical polyhedral morphology, with an average crystal length of 40 μm. SEM images are shown below. Figure 1 As shown in (a).

[0074] XRD analysis revealed that the carbon-encapsulated Prussian blue sodium-ion battery cathode material exhibits high crystallinity. The X-ray diffraction pattern is shown below. Figure 2 As shown in (a).

[0075] The carbon-coated roszan blue sodium-ion battery cathode material prepared in Example 1 was assembled into a sodium-ion half-cell, and its cycle performance was tested. Figure 3 As shown, the material has a maximum discharge capacity of 108.5 mAh / g at a current density of 500 mA / g, and the specific capacity retention rate is 92.44% after 500 cycles, demonstrating excellent cycle performance.

[0076] Example 2:

[0077] Precursor solution A was prepared by dissolving 3 mol sodium ferrocyanide decahydrate, 5 g sodium dodecylbenzenesulfonate, 2 g butylated hydroxyanisole, and 2 mol sodium bromide in 2 L of deionized water. Precursor solution B was prepared by dissolving 0.4 mol manganese acetate, 0.4 mol copper acetate, 0.4 mol cobalt acetate, 0.4 mol zinc acetate, 0.4 mol ferric acetate, and 10 mol sodium oxalate in 2 L of deionized water. Precursor solution B was slowly added dropwise to container A at a rate of 50 mL / min using a peristaltic pump through a silicone tube at room temperature and a stirring rate of 600 rpm. After the addition of precursor solution B was complete, the mixture was stirred continuously at room temperature for 6 h and then allowed to stand for 66 h to obtain a sample suspension. The sample suspension was centrifuged at 8000 rpm for 5 min, and the resulting precipitate was washed multiple times with deionized water and ethanol. The product was then dried in a vacuum oven at 200 °C and a vacuum degree of 10 Pa for 12 h to obtain a Prussian blue analogue.

[0078] 40g of Prussian blue analogue and 60g of graphene composite slurry with a mass fraction of 10wt% were added to 2L of deionized water. After ultrasonic vibration for 4 hours, the mixture was stirred vigorously for 2 hours. During the spray drying process, the peristaltic pump feed rate was 400mL / h, and the drying temperature was 280℃ to obtain carbon-encapsulated anhydrous Prussian blue.

[0079] The chemical formula of the material was determined to be Na by inductively coupled plasma optical emission spectroscopy (ICP-OES), CHN elemental analysis, and thermogravimetric analysis. 1.56 Mn 0.2 Fe 0.2 Co 0.2 Zn 0.2 Cu 0.2 [Fe(CN)6] 0.96 □ 0.04 ·0.11H2O@0.15C (□ means vacancy, 0.15 means 15wt%).

[0080] SEM analysis revealed that the carbon-encapsulated Prussian blue sodium-ion battery cathode material prepared in this embodiment exhibits a spherical polyhedral morphology, with an average crystal length of 30 μm. SEM images are shown below. Figure 1 As shown in (b).

[0081] XRD analysis revealed that the carbon-encapsulated Prussian blue sodium-ion battery cathode material exhibits high crystallinity. The X-ray diffraction pattern is shown below. Figure 2 As shown in (b).

[0082] The carbon-coated roszan blue sodium-ion battery cathode material prepared in Example 2 was assembled into a sodium-ion half-cell, and its cycle performance was tested. Figure 4 As shown, the material has a maximum discharge capacity of 90.1 mAh / g at a current density of 500 mA / g, and the specific capacity retention rate is 94.89% after 500 cycles, demonstrating excellent cycle performance.

[0083] Example 3:

[0084] Precursor solution A was prepared by dissolving 6 mol sodium ferrocyanide decahydrate, 8 g hexadecyltrimethylammonium bromide, 0.5 g linolenic acid, and 5 mol sodium sulfate in 1 L of deionized water. Precursor solution B was prepared by dissolving 2 mol ferric chloride, 2 mol cobalt chloride, 2 mol nickel chloride, and 20 mol sodium oxalate in 2 L of deionized water. Precursor solution B was slowly added dropwise to container A at a rate of 20 mL / min using a peristaltic pump through a silicone tube. The reaction temperature was room temperature, and the stirring speed was 800 rpm. After the addition of precursor B was complete, the mixture was stirred continuously at room temperature for 12 h and then allowed to stand for 36 h to obtain a sample suspension. The sample suspension was centrifuged at 10,000 rpm for 5 min. The resulting sample precipitate was washed multiple times with deionized water and ethanol. The product was then dried in a vacuum oven at 180 °C and a vacuum degree of 30 Pa for 12 h to obtain a Prussian blue analogue.

[0085] Take 30g of Prussian blue analogue and 60g of graphene composite slurry with a mass fraction of 5wt% and add it to 1L of deionized water. After ultrasonic vibration for 0.5h, stir vigorously for 4h. During the spray drying process, the peristaltic pump feed rate is 300mL / h and the drying temperature is 260℃ to obtain carbon-encapsulated anhydrous Prussian blue.

[0086] The chemical formula of the material was determined to be Na by inductively coupled plasma optical emission spectroscopy (ICP-OES), CHN elemental analysis, and thermogravimetric analysis. 1.58 Fe 0.33 Co 0.33 Ni 0.33 [Fe(CN)6] 0.92 □ 0.08 ·0.13H2O@0.1C (□ means vacancy, 0.1 means 10wt%).

[0087] SEM analysis revealed that the carbon-encapsulated Prussian blue sodium-ion battery cathode material prepared in this embodiment exhibits a spherical polyhedral morphology, with an average crystal length of 40 μm. SEM images are shown below. Figure 1 As shown in (c).

[0088] XRD analysis revealed that the carbon-encapsulated Prussian blue sodium-ion battery cathode material exhibits high crystallinity. The X-ray diffraction pattern is shown below. Figure 2 As shown in (c).

[0089] The carbon-coated roszan blue sodium-ion battery cathode material prepared in Example 3 was assembled into a sodium-ion half-cell, and its cycle performance was tested. Figure 5 As shown, the material has a maximum discharge capacity of 91.3 mAh / g at a current density of 500 mA / g, and the specific capacity retention rate is 92.1% after 500 cycles, demonstrating excellent cycle performance.

[0090] Example 4:

[0091] Precursor solution A was prepared by dissolving 2 mol sodium ferrocyanide decahydrate, 10 g polyvinylpyrrolidone, 1 g ascorbic acid, and 1 mol sodium chloride in 1 L of deionized water. Precursor solution B was prepared by dissolving 2 mol ferrous acetate and 5 mol sodium citrate in 1 L of deionized water. Precursor solution B was slowly added dropwise to container A at a rate of 10 mL / min using a peristaltic pump through a silicone tube. The reaction temperature was room temperature, and the stirring rate was 400 rpm. After the addition of precursor B was complete, the mixture was stirred continuously at room temperature for 8 h and then allowed to stand for 40 h to obtain a sample suspension. The sample suspension was centrifuged at 6000 rpm for 10 min. The resulting precipitate was washed multiple times with deionized water and ethanol. The product was then dried in a vacuum oven at 160 °C and a vacuum degree of 1 Pa for 10 h to obtain a Prussian blue analogue.

[0092] 40g of Prussian blue analogue and 20g of graphene composite slurry with a mass fraction of 20wt% were added to 1L of deionized water. After ultrasonic vibration for 2 hours, the mixture was stirred vigorously for 2 hours. During the spray drying process, the peristaltic pump feed rate was 200mL / h, and the drying temperature was 250℃ to obtain carbon-encapsulated anhydrous Prussian blue.

[0093] The chemical formula of the material was determined to be Na by inductively coupled plasma optical emission spectroscopy (ICP-OES), CHN elemental analysis, and thermogravimetric analysis. 1.95 Fe 0.95 [Fe(CN)6] 0.95 □ 0.05 ·0.25H2O@0.1C (□ means vacancy, 0.1 means 10wt%).

[0094] SEM analysis revealed that the carbon-encapsulated Prussian blue sodium-ion battery cathode material prepared in this embodiment exhibits a spherical polyhedral morphology, with an average crystal length of 40 μm. SEM images are shown below. Figure 1 As shown in (d).

[0095] XRD analysis revealed that the carbon-encapsulated Prussian blue sodium-ion battery cathode material exhibits high crystallinity. The X-ray diffraction pattern is shown below. Figure 2 As shown in (d).

[0096] The carbon-coated roszan blue sodium-ion battery cathode material prepared in Example 4 was assembled into a sodium-ion half-cell, and its cycle performance was tested. Figure 6 As shown, the material has a maximum discharge capacity of 112.6 mAh / g at a current density of 500 mA / g, and the specific capacity retention rate is 86.32% after 500 cycles, demonstrating excellent cycle performance.

[0097] Comparative Example 1:

[0098] In Comparative Example 1, the preparation process of the Prussian blue sodium-ion battery cathode material is the same as in Example 1, except that: 2 mol sodium ferrocyanide decahydrate, 10 g polyvinylpyrrolidone, 1 g ascorbic acid, and 1 mol sodium chloride were dissolved in 1 L of deionized water to form precursor solution A; 1.5 mol manganese sulfate, 0.5 mol copper sulfate, and 5 mol sodium citrate were dissolved in 1 L of deionized water to obtain precursor solution B; precursor solution B was slowly added dropwise to container A at a rate of 10 mL / min through a silicone tube using a peristaltic pump, the reaction temperature was room temperature, and the stirring rate was 400 rpm. After the precursor B was added, the mixture was stirred continuously at room temperature for 8 hours and then allowed to stand for 40 hours to obtain a sample suspension. The sample suspension was centrifuged at 6000 rpm for 10 minutes. The resulting sample precipitate was washed multiple times with deionized water and ethanol. The product was then dried in a vacuum oven at 160°C and 1 Pa for 10 hours to obtain a Prussian blue analogue, which was not subsequently coated with graphene.

[0099] The chemical formula of the material prepared in Comparative Example 1 was determined to be Na by inductively coupled plasma optical emission spectroscopy (ICP-OES), CHN elemental analysis, and thermogravimetric analysis. 1.72 Mn 0.75 Cu 0.25 [Fe(CN)6] 0.97 □ 0.03 ·2.15H2O.

[0100] The Prussian blue prepared in Comparative Example 1 was used as the positive electrode material in a sodium-ion battery assembly to form a sodium-ion half-cell, and its cycle performance was tested. Figure 7 As shown, the maximum discharge capacity of the material at a current density of 500 mA / g is 103.5 mAh / g, and the specific capacity retention rate after 500 cycles is 80.2%, indicating poor cycle stability.

[0101] Comparative Example 2:

[0102] In Comparative Example 2, the preparation process of the Prussian blue-based sodium-ion battery cathode material is the same as in Example 4, except that: 2 mol sodium ferrocyanide decahydrate, 10 g polyvinylpyrrolidone, 1 g ascorbic acid, and 1 mol sodium chloride were dissolved in 1 L of deionized water to form precursor solution A; 2 mol ferrous sulfate and 5 mol sodium citrate were dissolved in 1 L of deionized water to obtain precursor solution B; precursor solution B was slowly added dropwise to container A at a rate of 10 mL / min using a peristaltic pump through a silicone tube, the reaction temperature was room temperature, and the stirring rate was 400 rpm. After the precursor solution B was completely added, the mixture was stirred continuously at room temperature for 8 h and then allowed to stand for aging for 40 h to obtain a sample suspension; the sample suspension was centrifuged at 6000 rpm for 10 min, and the resulting sample precipitate was washed multiple times with deionized water and ethanol. The product was then placed in a vacuum oven at 160°C and a vacuum degree of 1 Pa and dried for 10 h to obtain a Prussian blue analogue, without subsequent graphene coating.

[0103] The chemical formula of the material prepared in Comparative Example 2 was determined to be Na by inductively coupled plasma optical emission spectroscopy (ICP-OES), CHN elemental analysis, and thermogravimetric analysis. 1.95 Fe[Fe(CN)6] 0.95 □ 0.05 ·2.05H2O.

[0104] The Prussian blue prepared in Comparative Example 2 was used as the positive electrode material in a sodium-ion battery assembly to form a sodium-ion half-cell, and its cycle performance was tested. Figure 8 As shown, the maximum discharge capacity of the material at a current density of 500 mA / g is 111.6 mAh / g, and the specific capacity retention rate after 500 cycles is 75.20%, indicating poor cycle stability.

Claims

1. A method for preparing a Prussian blue-based sodium-ion battery cathode material, characterized in that, The Prussian blue-based sodium-ion battery cathode material comprises a Prussian blue analogue and a conductive carbon material layer coated on the surface of the Prussian blue analogue; the chemical formula of the Prussian blue analogue is Na. x M[Fe(CN)6] z ·wH₂O, wherein M is n transition metal elements, n≥1, 0.1≤w≤4.0, 1.40≤x≤1.95, 0.90≤z≤0.98, and each transition metal element is subscripted as y₁, y₂, y₃…yn, and y₁+y₂+y₃…+yn=1; the preparation method includes: (1) Prussian blue analogue, conductive carbon material composite slurry and deionized water are mixed to obtain Prussian blue analogue / conductive carbon material dispersion; (2) The obtained Prussian blue analog / conductive carbon material dispersion is spray-dried to remove moisture and coat the conductive carbon material on the surface of Prussian blue to obtain the Prussian blue sodium-ion battery cathode material. The method for preparing the Prussian blue analogue includes: S1: Dissolve sodium ferrocyanide decahydrate, sodium salt, antioxidant and surface dispersant in deionized water by stirring to obtain a clear and transparent solution A; S2: Dissolve the transition metal M salt and the complexing agent in deionized water by stirring to obtain a clear and transparent solution B; S3: Add transparent clear solution B dropwise to transparent clear solution A, stir and react, then age the mixture, and finally separate the solid and liquid components by centrifugation, wash and dry to obtain the Prussian blue analogue.

2. The preparation method according to claim 1, characterized in that, The conductive carbon material layer is composed of at least one of graphene, conductive graphite, carbon nanotubes, and conductive carbon black.

3. The preparation method according to claim 1, characterized in that, n≥2, and when M is at least 2 transition metal elements, the subscript range of each transition metal element is 0.01~0.

90.

4. The preparation method according to claim 3, characterized in that, n≥2, and when M is at least 2 transition metal elements, the subscript range of each transition metal element is 0.2 to 0.

5.

5. The preparation method according to claim 1, characterized in that, The particle size of the Prussian blue analogue is 10–60 μm.

6. The preparation method according to claim 1, characterized in that, The thickness of the conductive carbon material layer is 200 nm to 2 μm; the conductive carbon material layer accounts for 1 to 30 wt% of the total mass of the Prussian blue sodium-ion battery cathode material.

7. The preparation method according to claim 1, characterized in that, In step (1), the mixing method is ultrasonic oscillation and / or stirring; the power of ultrasonic oscillation is 200-700W and the time does not exceed 6h; the stirring time does not exceed 48h.

8. The preparation method according to claim 1, characterized in that, In step (1), the mass fraction of the conductive carbon material composite paste is 1wt% to 20wt%. The mass ratio of the conductive carbon composite paste to the Prussian blue analogue is (0.1-10):1; The concentration ratio of the Prussian blue analogue to deionized water is 1 g: (10-500) mL.

9. The preparation method according to claim 1, characterized in that, The parameters for spray drying include: temperature of 180–300℃; and peristaltic pump feed rate of (10–2000) mL / h.

10. The preparation method according to claim 1, characterized in that, In step S1: The concentration of sodium ferrocyanide decahydrate in the transparent and clear solution A is 0.01–10 M; The stirring process is carried out in a protective atmosphere at 25–95°C; the protective gas is one of air, nitrogen, or argon; the stirring speed is 200–1500 rpm. The antioxidant is at least one of butylated hydroxyanisole, butylated hydroxytoluene, linolenic acid, tert-butylhydroquinone, or ascorbic acid, and the concentration of the antioxidant in the transparent clear solution A is 0.001-0.1M. The sodium salt is at least one of sodium fluoride, sodium chloride, sodium bromide, sodium iodide, sodium acetate, sodium nitrate, sodium sulfate, sodium oxalate, and disodium ethylenediaminetetraacetate, and the weight ratio of the sodium salt to the transition metal M salt is (1-10):1; The surface dispersant is at least one of polyvinylpyrrolidone, hexadecyltrimethylammonium bromide, polycyclic aromatic hydrocarbons, and sodium dodecylbenzenesulfonate, and the concentration of the surface dispersant in the transparent and clear solution A is 0.1 g to 100 g / L.

11. The preparation method according to claim 1, characterized in that, In step S2: The concentration of the transition metal M salt in the transparent and clear solution B is 0.01–10 M; The complexing agent is selected from at least one of sodium citrate, 2,2'-bipyridine, 1-10-o-phenanthroline, ethylenediamine, ethylenediaminetetraacetic acid, trisodium aminotriacetate, sodium oxalate, disodium ethylenediaminetetraacetate, sodium gluconate, sodium tartrate, or sodium acetate, and the weight ratio of the complexing agent to the transition metal M salt is (1-10):1; The stirring process is carried out in a protective atmosphere at 25–95°C; the protective gas is at least one of air, nitrogen, and argon; and the stirring speed is 200–1500 rpm.

12. The preparation method according to claim 1, characterized in that, In step S3; The dropwise addition process is carried out at 25–95°C in a protective atmosphere; the protective gas is at least one of air, nitrogen, and argon. The dropwise flow rate of the transparent and clear solution B is 1 mL / min to 50 mL / min; The stirring reaction is carried out at a temperature of 25–95°C for a duration of 0.5–12 hours. The aging temperature is 25–95°C, and the time is 2–72 hours; The centrifugation speed for solid-liquid separation is 6000-10000 rpm, and the time is 5-10 minutes. The drying process is vacuum drying, with a vacuum degree of 10. -6 ~10 -2 The drying temperature is 100-220℃, and the drying time is 6-24h.

Images