A multi-metal ion doped prussian blue sodium salt material, a preparation method and application thereof

Abstract

The application provides a multi-metal ion doped prussian blue sodium salt material and a preparation method and application thereof, and relates to the technical field of sodium ions. x Mn a Fe b Co c Ni d Zn e [Fe(CN)6] y ·nH2O, formula I; wherein 0 ‑ The application provides a multi-metal doped prussian blue sodium salt material, which can exhibit excellent structural stability and electrochemical performance in a natural seawater electrolyte system, and especially in a complex ion environment with the presence of chloride ions (Cl ‑ ), effectively solves the problems of structural damage and capacity attenuation of existing prussian blue materials in a seawater environment.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery technology, and in particular to a multi-metal ion-doped Prussian blue sodium salt material, its preparation method, and its application. Background Technology

[0002] With increasing energy demand and growing environmental pressure, seawater batteries, as a low-cost, environmentally friendly, and efficient energy storage device, have attracted widespread attention in recent years. Seawater batteries utilize natural or simulated seawater as the electrolyte, offering abundant resources, low cost, and a long service life. However, existing seawater batteries face several technical challenges, particularly in the marine environment, where the structural stability and electrochemical performance of Prussian blue materials are often affected by chloride ions (Cl-). - The influence of these factors leads to poor cycle stability of the material in the seawater system and rapid degradation of battery performance.

[0003] Prussian blue materials are widely used in sodium-ion batteries due to their open-framework structure and excellent sodium-ion conductivity. However, existing Prussian blue sodium salt materials are typically modified by single-metal ion doping or equimolar ratio doping with multiple metal ions, which limits their application in seawater systems. Although some studies have explored improving the electrochemical performance of materials by doping with different metal ions, current technologies have failed to effectively address the stability issues of multi-metal ion doping in the complex environment of natural seawater, nor have they provided a Prussian blue sodium salt material that can maintain excellent electrochemical performance in seawater systems. Summary of the Invention

[0004] Therefore, the purpose of this invention is to provide a polymetallic ion-doped Prussian blue sodium salt material with a specific ratio that exhibits significant cycle stability and low capacity decay in natural seawater environments, overcoming the shortcomings of existing technologies and providing a novel and efficient cathode material for seawater sodium-ion batteries. This invention provides a multi-metal-doped Prussian blue sodium salt material that exhibits excellent structural stability and electrochemical performance in natural seawater electrolyte systems, especially in chloride ion (Cl) ion exchange. - In the complex ionic environment, this effectively solves the problems of structural damage and capacity decay of existing Prussian blue materials in seawater.

[0005] In existing technologies, Prussian blue materials, used as cathode materials in sodium-ion batteries, exhibit poor structural stability in seawater electrolyte systems, especially in the presence of chloride ions and other competing cations (such as Na+). + Mg² + K +In environments with high concentrations of Prussian blue (etc.), it exhibits low cycle life and capacity decay. Therefore, improving the stability and long-term cycling performance of Prussian blue materials in natural seawater environments remains a pressing technical challenge in the field of seawater batteries.

[0006] The technical solution of this invention is implemented as follows: A polymetallic ion-doped Prussian blue sodium salt material has the chemical composition shown in Formula I: Na x Mn a Fe b Co c Ni d Zn e [Fe(CN)6] y ·nH2O, Formula I; Among them, 0 <x ≤ 2,y=0.8~1.2,n=1~3; a: b: c: d: e =7~9: 0.3~0.8: 0.3~0.8: 0.3~0.8: 0.3~0.8.

[0007] Furthermore, a:b:c:d:e =7~9:0.4~0.6:0.4~0.6:0.4~0.6:0.4~0.6.

[0008] This invention constructs a multi-metal-doped Prussian blue sodium salt material using manganese as the main metal ion. Compared with systems based on a single metal such as iron, copper, cobalt, or nickel, manganese ions exhibit variable valence state characteristics (Mn²). + / Mn³ + / Mn 4+ During charging and discharging, it can provide more reversible redox reaction sites, which is beneficial to improving the sodium storage capacity of the material. At the same time, the Mn–N≡C–Fe bond in the manganese-based coordination structure has a moderate bond energy, which is conducive to the insertion and extraction of sodium ions, improves the ion diffusion kinetics performance, and is more suitable for application in natural seawater environment.

[0009] Furthermore, manganese is abundant, inexpensive, and environmentally friendly, which helps reduce material preparation costs and enhance its practical application value. In contrast, materials based on cobalt or nickel are more expensive, while materials based on iron or copper have limitations in capacity improvement. Therefore, this invention uses manganese as the main component and combines it with multi-metal synergistic doping, which helps to achieve comprehensive optimization in terms of structural stability, electrochemical performance, and cost.

[0010] On the one hand, the present invention also provides a method for preparing the above-mentioned multi-metal ion-doped Prussian blue sodium salt material, comprising the following steps: A metal salt precursor solution A was prepared by dissolving a metal salt precursor and a chelating agent in a glycerol-water mixed solution; a solution B was prepared by dissolving ferrocyanide in a glycerol-water mixed solution. In this process, iron salt, nickel salt, cobalt salt, zinc salt and manganese salt are mixed according to the stoichiometric ratio of Formula I to prepare a metal salt precursor. Under pH 4-5, 50-70 ℃, and inert gas conditions, a co-precipitation reaction was carried out by indirectly adding metal salt precursor solution A to solution B to obtain the polymetallic ion-doped Prussian blue sodium salt material.

[0011] In this invention, a mixed solution of glycerol and deionized water is used as the reaction medium, and the reaction process is controlled by a segmented titration method, which can better optimize the nucleation and growth behavior of Prussian blue materials. Glycerol reduces the activity of water in the system and increases the solution viscosity by constructing a stable hydrogen bond network, thereby slowing down the ion diffusion rate, inhibiting the introduction of coordinated water, and reducing crystal structure defects. Simultaneously, the segmented titration separates the nucleation and crystal growth processes in time, allowing the nuclei formed in the initial stage to fully stabilize and rearrange during the pause, followed by controlled growth, effectively avoiding particle agglomeration and compositional inhomogeneity caused by instantaneous supersaturation. The synergistic effect of these two methods not only significantly improves the uniformity of multi-metal ion doping but also enhances the crystal quality, structural stability, and electrochemical performance of the material.

[0012] Furthermore, in the glycerol-water mixed solution, the volume fraction of glycerol is 3% to 10%; The molar volume ratio of the metal salt precursor, chelating agent, and glycerol-water mixed solution is 0.003~0.007 mol : 0.003~0.007 mol : 30~70 mL; The molar volume ratio of the ferrocyanide and glycerol-water mixed solution is 0.003~0.007 mol: 120~180 mL.

[0013] Furthermore, the indirect dripping method includes dripping for 20-40 minutes, stopping dripping for 10-15 minutes, then continuing dripping for 20-40 minutes and stopping dripping for another 10-15 minutes; The indirect dripping rate is 1~3 mL / min.

[0014] Furthermore, the chelating agent comprises sodium citrate and / or diethylenetriaminepentaacetic acid; The manganese salt includes one or more of manganese chloride, manganese sulfate, manganese nitrate, and manganese acetate; The iron salt includes one or more of ferrous chloride, ferrous sulfate, ferrous nitrate, and ferrous acetate; The cobalt salt includes one or more of cobalt chloride, cobalt sulfate, cobalt nitrate, and cobalt acetate; The nickel salt includes one or more of nickel chloride, nickel sulfate, and nickel nitrate; The zinc salt includes one or more of zinc chloride, zinc sulfate, and zinc acetate.

[0015] Furthermore, the pH value is adjusted to 4-5 by adding dilute hydrochloric acid solution and / or ammonia solution to the reaction system; The concentration of the dilute hydrochloric acid solution is 0.03 mol / L to 0.1 mol / L; the concentration of the ammonia solution is 0.03 mol / L to 0.1 mol / L.

[0016] Furthermore, after the coprecipitation reaction, the reaction system is further subjected to aging, centrifugation, and drying to obtain the multi-metal ion-doped Prussian blue sodium salt material. The aging time is 20-30 h; the drying temperature is 160-190 ℃, and the drying time is 20-30 h.

[0017] On the other hand, the present invention also provides the application of the above-mentioned multi-metal ion-doped Prussian blue sodium salt material in aqueous sodium-ion batteries.

[0018] Furthermore, the above-mentioned multi-metal ion-doped Prussian blue sodium salt material is used as a cathode material in aqueous sodium-ion batteries.

[0019] The multi-metal doped Prussian blue sodium salt material of the present invention can be used as a positive electrode material in a three-electrode electrochemical testing system and in a seawater sodium ion secondary full cell.

[0020] Specific applications include: 1) Three-electrode electrochemical performance testing system: The electrode prepared by the multi-metal doped Prussian blue sodium salt material of the present invention is used as the working electrode, the carbon rod is used as the counter electrode, the Ag / AgCl electrode is used as the reference electrode, and natural seawater is used as the electrolyte to characterize the intrinsic cycling, rate and kinetic performance of the material.

[0021] 2) Seawater sodium-ion full battery system: Using the electrode prepared by the multi-metal doped Prussian blue sodium salt material of the present invention as the positive electrode, sodium titanium phosphate (NTP) electrode as the negative electrode, and natural seawater as the electrolyte, a rechargeable seawater sodium-ion secondary battery is assembled.

[0022] Through multi-metal doping and a specific ratio design, the multi-metal doped Prussian blue sodium salt material provided by this invention exhibits the following technical effects in natural seawater environments: 1) Significantly improves structural stability: Through multi-metal ion synergistic doping, the lattice stability of the material is significantly improved, which can effectively suppress the structural collapse and metal site dissolution caused by chloride ions; 2) Improved cycle performance: Compared with traditional single metal or Prussian blue materials with small or equal molar doping, the material of this invention has higher initial charge and discharge efficiency in seawater systems, and exhibits lower polarization and capacity decay. 4) Enhanced resistance to chloride ion corrosion: The material can maintain a longer cycle life in chloride ion-containing environments, significantly reducing the destructive effect of chloride ions on electrode materials; 5) Excellent rate performance: This material exhibits stable discharge performance at different rates, making it suitable for high-efficiency energy storage applications in seawater batteries.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. It helps improve the structural stability of materials in the complex ionic environment of seawater: Existing Prussian blue materials in natural seawater systems, due to the high concentration of Cl... - The combined effects of multiple competing cations can easily lead to lattice structure disturbances and metal site dissolution. This invention utilizes a specific ratio of multi-metal ion synergistic doping to regulate the lattice coordination environment, thereby improving the structural stability of multi-metal-doped Prussian blue sodium salt materials in seawater environments.

[0024] 2. Beneficial for reducing the cycling decay rate in seawater electrolytes: In the high ionic strength environment of natural seawater, traditional single-metal or low-doped Prussian blue materials experience rapid capacity decay during cycling. This invention, through synergistic regulation between the host metal and auxiliary metals, helps to mitigate structural changes during cycling, thereby improving the cycling stability of multi-metal-doped Prussian blue sodium salt materials.

[0025] 3. Enhanced resistance to chloride ion interference: The high concentration of chloride ions in seawater systems can adversely affect electrode materials. The multi-metal synergistic structure of this invention enhances the material's adaptability to chloride ion environments, thereby improving the applicability of multi-metal-doped Prussian blue sodium salt materials in seawater electrolytes.

[0026] 4. Applicable to natural seawater and simulated seawater systems: The multi-metal doped Prussian blue sodium salt material provided by this invention can be used not only in simulated seawater systems, but also in natural seawater environments, providing a suitable cathode material option for seawater sodium-ion batteries and seawater full batteries. Attached Figure Description

[0027] Figure 1 This is a scanning electron microscope image of the multi-metal ion-doped Prussian blue sodium salt material prepared in Example 1; Figure 2 This is a scanning electron microscope image of the Mn-based Prussian blue sodium salt material prepared in Comparative Example 1; Figure 3These are XRD comparison images of the multi-metal doped Prussian blue sodium salt material prepared in Example 1 and the Mn-based Prussian blue sodium salt material prepared in Comparative Example 1. Figure 4 This is a comparison chart of TG data for the multi-metal ion-doped Prussian blue sodium salt material prepared in Example 1 and the Mn-based Prussian blue sodium salt material prepared in Comparative Example 1. Figure 5 (This is a comparison of the cycling stability curves of the multi-metal ion-doped Prussian blue sodium salt materials prepared in Examples 1-3 and the Mn-based Prussian blue sodium salt material prepared in Comparative Example 1 in seawater electrolyte). Figure 6 This is a comparison of the first constant current charge-discharge curves of the multi-metal ion-doped Prussian blue sodium salt material prepared in Example 1 and the Mn-based Prussian blue sodium salt material prepared in Comparative Example 1 in seawater electrolyte. Figure 7 This is the rate performance curve of the multi-metal ion-doped Prussian blue sodium salt material prepared in Example 1; Figure 8 This is a CV diagram of the multi-metal ion-doped Prussian blue sodium salt material prepared in Example 1 in seawater electrolyte; Figure 9 This is a comparison of the cycling stability curves of the multi-metal ion-doped Prussian blue sodium salt materials prepared in Examples 1-3 and the Mn-based Prussian blue sodium salt material prepared in Comparative Example 1 in seawater electrolyte. Figure 10 This is a comparison of the first constant current charge-discharge curves of the multi-metal ion-doped Prussian blue sodium salt material prepared in Example 1 and the Mn-based Prussian blue sodium salt material prepared in Comparative Example 1 in seawater electrolyte. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0029] Unless otherwise specified, the experimental methods used in the embodiments of this invention are all conventional methods.

[0030] Unless otherwise specified, all materials and reagents used in the embodiments of this invention are commercially available.

[0031] Example 1 The specific steps for preparing polymetallic ion-doped Prussian blue sodium salt materials are as follows: 1) Weigh out each metal salt compound to a total molar amount of 0.005 mol, wherein the molar ratio of FeSO4·7H2O, NiSO4·6H2O, CoSO4·7H2O, ZnCl2, and MnSO4·H2O is 1:1:1:1:16. Specifically, weigh out 0.00025 mol FeSO4·7H2O (0.0695 g), 0.00025 mol NiSO4·6H2O (0.0657 g), 0.00025 mol CoSO4·7H2O (0.0703 g), 0.00025 mol ZnCl2 (0.03407 g), and 0.004 mol MnSO4·H2O (0.6760 g), and simultaneously weigh out 0.005 mol anhydrous sodium citrate (Na3C6H5O7, 1.2903 g). Add the above-mentioned drugs together to 50 mL of a mixed solvent of deionized water and glycerin (volume ratio of 95:5), and stir on a magnetic stirrer for 2 h until completely dissolved to form a dark green transparent solution A; 2) Weigh 0.005 mol of anhydrous sodium ferrocyanide (Na4Fe(CN)6, 1.51 g), dissolve it in 150 mL of a mixed solvent of deionized water and glycerol (volume ratio 95:5), and prepare a transparent colorless solution B in a three-necked flask; nitrogen gas is continuously introduced during the dissolution and subsequent reaction to isolate air. 3) Under constant temperature of 60 ℃, solution B was placed under continuous magnetic stirring. Solution A was added dropwise to solution B using a peristaltic pump at a rate of 2 mL / min. The dropwise addition was controlled in stages, i.e., after adding for 30 min, the addition was paused for 10-15 min, and then the addition was continued until all solution A was added. At the same time, the pH of the system was adjusted by adding 0.05 M ammonia solution dropwise to stabilize it at 4-5, and finally the reaction solution C was obtained. 4) After the addition is complete, continue the reaction for 30 min to allow the system to stabilize. Then stop stirring and let the reaction system stand at room temperature for 24 h to age. 5) After the reaction is complete, the precipitate is centrifuged (10,000 rpm, 1 min) and washed with deionized water 3 times. After each washing, centrifugation is performed to remove residual ions. 6) The obtained solid was dried in a vacuum drying oven at 175 ℃ for 24 h to obtain polymetallic ion-doped Prussian blue sodium salt powder. The obtained product was blue-green, had good crystallinity, and uniform particle distribution, and was denoted as deionized water-glycerol mixed solvent—intermittent titration—PBA-5.

[0032] Comparative Example 1 The specific steps for preparing a single manganese-based Prussian blue sodium salt are as follows: 1) The procedure was carried out according to the method described in Example 1, except that all the polymetallic salts used were replaced with manganese sulfate monohydrate (MnSO4·H2O). 0.005 mol of MnSO4·H2O (0.845 g) and 0.005 mol of anhydrous sodium citrate (Na3C6H5O7, 1.2903 g) were weighed and added to a mixed solvent of deionized water and glycerol (volume ratio 95:5, total volume 50 mL). The solution was magnetically stirred at room temperature for 2 h until completely dissolved, yielding a light pink transparent solution a. 2) Weigh 0.005 mol of anhydrous sodium ferrocyanide (Na4Fe(CN)6, 1.51 g), dissolve it in a mixed solvent of deionized water and glycerol (volume ratio 95:5, total volume 150 mL), and prepare a transparent solution b in a three-necked flask; nitrogen gas is continuously introduced during stirring and subsequent reaction to isolate air. 3) Under constant temperature of 60 ℃, solution b is placed under continuous magnetic stirring, and solution a is added dropwise to solution b at a rate of 2 mL / min using a peristaltic pump. The dropwise addition is carried out in segments, that is, after adding for 30 min, pause for 10-20 min, and then continue adding until all solution a is added. During the dropwise addition, the pH of the system is adjusted by adding 0.05 M ammonia solution to maintain it at 4-5. 4) After the addition is complete, continue the reaction for 30 min to allow the system to react fully. Then stop stirring and let the reaction system stand at room temperature for 24 h. 5) After the reaction is complete, the precipitate is centrifuged (10,000 rpm, 1 min) and washed 3 times with deionized water to remove residual impurities; 6) The obtained solid was dried in a vacuum drying oven at 175 °C for 24 h to obtain a single manganese-based Prussian blue sodium salt powder, denoted as PBA-Mn.

[0033] from Figure 1 and Figure 2As can be seen from the comparison, the multi-metal ion-doped Prussian blue sodium salt prepared in Example 1 exhibits a highly regular cubic morphology, with uniform grain size (approximately 200-800 nm), excellent dispersibility, and a complete crystal surface; while the single manganese-based Prussian blue in Comparative Example 1 has a distorted morphology, blurred edges, a large number of fine particle agglomerates, uneven grain size distribution, and a rough surface. This difference stems from the synergistic regulation of multi-metal ions, the slow nucleation effect of the glycerol-water mixed solvent, and the precise control of the segmented dropwise addition process in Example 1, which effectively guided the preferential growth of crystals along the {100} crystal plane and suppressed agglomeration; the regular cubic morphology and high crystallinity not only shortened the Na + The diffusion pathway was improved, enhancing ion and electron transport efficiency and further strengthening the material's performance in high-Cl seawater environments. - This improves structural stability under environmental conditions, thereby significantly enhancing its cycle life and rate performance.

[0034] Example 2 The difference between this embodiment and Example 1 is that the mixed solvent of deionized water and glycerol is replaced with deionized water, and the coprecipitation reaction is carried out by continuous titration. The specific steps are as follows: 1) Weigh out each metal salt compound to a total molar amount of 0.005 mol, wherein the molar ratio of FeSO4·7H2O, NiSO4·6H2O, CoSO4·7H2O, ZnCl2, and MnSO4·H2O is 1:1:1:1:16. Specifically, weigh out 0.00025 mol FeSO4·7H2O (0.0695 g), 0.00025 mol NiSO4·6H2O (0.0657 g), 0.00025 mol CoSO4·7H2O (0.0703 g), 0.00025 mol ZnCl2 (0.03407 g), and 0.004 mol MnSO4·H2O (0.6760 g), and simultaneously weigh out 0.005 mol anhydrous sodium citrate (Na3C6H5O7, 1.2903 g). Add the above-mentioned drugs together to 50 mL of deionized water, place on a magnetic stirrer and stir for 2 h until completely dissolved to form a dark green transparent solution A; 2) Weigh 0.005 mol of anhydrous sodium ferrocyanide (Na4Fe(CN)6, 1.51 g), dissolve it in 150 mL of deionized water, and prepare a transparent and colorless solution B in a three-necked flask; nitrogen gas is continuously introduced during the dissolution and subsequent reaction to isolate air. 3) Under constant temperature of 60 ℃, solution B is placed under continuous magnetic stirring. Solution A is added dropwise to solution B at a rate of 2 mL / min using a peristaltic pump until all solution A is added. At the same time, the pH of the system is adjusted by adding 0.05 M ammonia solution dropwise during the reaction to stabilize it at 4-5, and finally reaction solution C is obtained. 4) After the addition is complete, continue the reaction for 30 min to allow the system to stabilize. Then stop stirring and let the reaction system stand at room temperature for 24 h to age. 5) After the reaction is complete, the precipitate is centrifuged (10,000 rpm, 1 min) and washed with deionized water 3 times. After each washing, centrifugation is performed to remove residual ions. 6) The obtained solid was dried in a vacuum drying oven at 175 ℃ for 24 h to obtain polymetallic ion-doped Prussian blue sodium salt powder. The obtained product was blue-green, had good crystallinity, and uniform particle distribution, and was denoted as deionized water solvent-continuous titration-PBA-5.

[0035] Example 3 The difference between this embodiment and Embodiment 1 is that the mixed solvent of deionized water and glycerin is replaced with deionized water. The specific steps are as follows: 1) Weigh out each metal salt compound to a total molar amount of 0.005 mol, wherein the molar ratio of FeSO4·7H2O, NiSO4·6H2O, CoSO4·7H2O, ZnCl2, and MnSO4·H2O is 1:1:1:1:16. Specifically, weigh out 0.00025 mol FeSO4·7H2O (0.0695 g), 0.00025 mol NiSO4·6H2O (0.0657 g), 0.00025 mol CoSO4·7H2O (0.0703 g), 0.00025 mol ZnCl2 (0.03407 g), and 0.004 mol MnSO4·H2O (0.6760 g), and simultaneously weigh out 0.005 mol anhydrous sodium citrate (Na3C6H5O7, 1.2903 g). Add the above-mentioned drugs together to 50 mL of deionized water, place on a magnetic stirrer and stir for 2 h until completely dissolved to form a dark green transparent solution A; 2) Weigh 0.005 mol of anhydrous sodium ferrocyanide (Na4Fe(CN)6, 1.51 g), dissolve it in 150 mL of deionized water, and prepare a transparent and colorless solution B in a three-necked flask; nitrogen gas is continuously introduced during the dissolution and subsequent reaction to isolate air. 3) Under constant temperature of 60 ℃, solution B was placed under continuous magnetic stirring. Solution A was added dropwise to solution B using a peristaltic pump at a rate of 2 mL / min. The dropwise addition was controlled in stages, i.e., after adding for 30 min, the addition was paused for 10-15 min, and then the addition was continued until all solution A was added. At the same time, the pH of the system was adjusted by adding 0.05 M ammonia solution dropwise to stabilize it at 4-5, and finally the reaction solution C was obtained. 4) After the addition is complete, continue the reaction for 30 min to allow the system to stabilize. Then stop stirring and let the reaction system stand at room temperature for 24 h to age. 5) After the reaction is complete, the precipitate is centrifuged (10,000 rpm, 1 min) and washed with deionized water 3 times. After each washing, centrifugation is performed to remove residual ions. 6) The obtained solid was dried in a vacuum drying oven at 175 °C for 24 h to obtain polymetallic ion-doped Prussian blue sodium salt powder. The obtained product was blue-green, had good crystallinity, and uniform particle distribution, and was denoted as deionized water solvent-indirect titration-PBA-5.

[0036] Application Example 1 The multi-metal ion-doped Prussian blue sodium salt material prepared in Example 1 and the Mn-based Prussian blue sodium salt material prepared in Comparative Example 1 were assembled with carbon rods in seawater electrolyte to form a three-electrode system for electrochemical performance testing. The specific steps are as follows: 1) Take 70 mg of PBA-5 from Examples 1-3 or 70 mg of PBA-Mn from Comparative Example 1, and add them together with 20 mg of Ketjen Black into an agate mortar. Add an appropriate amount of anhydrous ethanol as a dispersion medium and grind and mix thoroughly until a uniform slurry is formed.

[0037] 2) Add 11 μL of polytetrafluoroethylene (PTFE) emulsion as a binder to the above mixed slurry, and continue grinding and stirring until uniform to obtain a black electrode paste that can form a film. Then, dry the obtained paste in a vacuum drying oven at 80 ℃ for 12 h and roll it onto a titanium mesh to obtain a PBA-5 electrode sheet or a PBA-Mn electrode sheet.

[0038] 3) Electrochemical performance was tested using PBA-5 or PBA-Mn electrode sheets as working electrodes in a three-electrode system with natural seawater as the electrolyte. A silver chloride electrode (Ag / AgCl) was used as the reference electrode, and a carbon rod as the counter electrode. All electrochemical tests were conducted at room temperature.

[0039] Test results are as follows Figures 5-8 As shown.

[0040] Figure 5 This demonstrates the performance of Prussian blue sodium salt materials at 100 mA·g under different preparation processes. - ¹ Cyclic performance at current density (left axis: specific capacity; right axis: coulombic efficiency). The process in Example 1 (deionized water-glycerol mixed solvent – ​​discontinuous titration – PBA-5) showed the best performance: initial specific capacity approximately 75 mAh·g. - ¹ After 90 cycles, the capacity retention rate reached ~86.7%, and the coulombic efficiency remained stable above 98%. In contrast, the initial specific capacity of single manganese-based PBA-Mn (deionized water-glycerol mixed solvent-intermittent titration-PBA-Mn), PBA-5 intermittently titrated with deionized water solvent, and PBA-5 continuously titrated with deionized water solvent were all lower, and the capacity decayed faster. After 90 cycles, the capacity retention rates were only ~75%, ~62.5%, and ~80%, respectively. This indicates that the synergistic effect of multi-metal doping, glycerol-water mixed solvent, and segmented titration process significantly improved the structural stability and electrochemical reversibility of the material in the seawater system.

[0041] Figure 6 The test conditions in a three-electrode system with natural seawater electrolyte (carbon rod as counter electrode, Ag / AgCl as reference electrode) were 100 mA·g. - ¹ First-cycle constant-current charge-discharge curves at current density. PBA-5 exhibits a higher reversible specific capacity (approximately 70 mAh·g). - ¹), with a smoother charge / discharge plateau and a more stable voltage range, and significantly less electrochemical polarization; while the reversible specific capacity of PBA-Mn is only about 40 mAh·g. - ¹ The charge / discharge plateau is short and the potential fluctuations are significant, indicating a greater degree of polarization. This result demonstrates that multi-metal ion doping and optimized preparation processes effectively improve the reversible sodium storage capacity of Prussian blue materials, reduce electrochemical polarization, and better suit the charge / discharge requirements of seawater sodium-ion batteries.

[0042] Figure 7 The figures show the rate performance curves of PBA-5 material in a three-electrode system (carbon rod as counter electrode, natural seawater as electrolyte), with current densities of 1, 2, 5, 10, 5, 2, and 1 A·g. - ¹. The results showed that PBA-5 in 1 A g - ¹ Specific capacity is approximately 70 mAh·g - ¹, 10 A·g - ¹ It can still maintain approximately 55 mAh·g under high current. - ¹ Capacity, when the current density recovers to 1 A·g -¹ The capacity can return to the initial level, while the coulombic efficiency remains stable at over 98%, indicating that it has excellent rate performance and structural stability, and can quickly adapt to high-current charging and discharging scenarios.

[0043] Figure 8 The PBA-5 material was tested in a three-electrode system (carbon rod as counter electrode, natural seawater as electrolyte) at 0.01 V·s. - ¹ Cyclic voltammetry (CV) curves at the scan rate, with a test potential window of 0–0.85 V. The curves show two pairs of symmetrical and clear redox peaks with regular peak shapes and good reversibility, corresponding to Na. + The embedding and extraction processes within the Prussian blue three-dimensional framework directly reflect the material's excellent ion diffusion kinetics and electrochemical reversibility, providing mechanistic support for its good rate performance.

[0044] Application Example 2 The electrochemical performance of seawater full cells assembled using PBA-5 or PBA-Mn electrode sheets prepared in Example 1 as positive electrodes and sodium titanium phosphate electrode sheets as negative electrodes was tested. The specific steps are as follows: 1) Take 70 mg of commercial sodium titanium phosphate powder and add it together with 20 mg of Ketjen black into an agate mortar. Add an appropriate amount of anhydrous ethanol as a dispersion medium and grind and mix thoroughly until a uniform slurry is formed.

[0045] 2) Add 11 μL of polytetrafluoroethylene (PTFE) emulsion as a binder to the above mixed slurry, and continue grinding and stirring until uniform to obtain a black electrode paste that can form a film. Then, dry the obtained paste in a vacuum drying oven at 80 ℃ for 12 h and roll it onto a titanium mesh to obtain sodium titanium phosphate electrode sheet, hereinafter referred to as NTP electrode sheet.

[0046] 3) Using dust-free paper as a separator, seawater along the coast of Yazhou Bay as the electrolyte, and the NTP electrode sheet from step (2) as the negative electrode sheet, and the PBA-5 electrode sheet or the PBA-Mn electrode sheet as the positive electrode sheet, secondary batteries NTP-PBA-5 or NTP-PBA-Mn are assembled respectively.

[0047] Test results are as follows Figure 9 and Figure 10 As shown.

[0048] Figure 9 The PBA-5 cathode material, PBA-Mn cathode material, and the cathode materials obtained in Examples 2 and 3 were used to assemble seawater sodium-ion secondary batteries with sodium titanium phosphate anodes, respectively, at 1 A·g -¹ Cyclic performance curves at current density. Among them, the process in Example 1 (deionized water-glycerol mixed solvent—intermittent titration—NTP-PBA-5) performed best, with an initial specific capacity of approximately 77 mAh·g. - ¹, after 50 cycles, the capacity retention was excellent and the coulombic efficiency remained stable at over 98%; while single manganese-based PBA-Mn, PBA-5 with intermittent titration in deionized water solvent and PBA-5 with continuous titration all showed faster capacity decay. This further verifies that the synergistic effect of multi-metal doping, glycerol-water mixed solvent and segmented titration process can significantly improve the cycle stability and electrochemical reversibility of the full cell.

[0049] Figure 10 The PBA-5 and PBA-Mn cathode materials were used to assemble seawater sodium-ion secondary batteries with sodium titanium phosphate anodes, respectively, at 1 A·g - ¹ First charge-discharge curves at current density. NTP-PBA-5 exhibits a higher reversible specific capacity (approximately 65 mAh). g - ¹), with a smoother charge / discharge plateau and less voltage polarization; while the reversible specific capacity of NTP-PBA-Mn is only about 40 mAh·g. - ¹ The shorter charge-discharge platform and obvious polarization indicate that multi-metal doping and optimized preparation process effectively improve the sodium storage capacity and electrochemical stability of the full battery, making it more suitable for seawater energy storage scenarios.

[0050] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A multi-metal ion-doped Prussian blue sodium salt material, characterized in that, It has the chemical composition shown in Formula I: Na x Mn a Fe b Co c Ni d Zn e [Fe(CN)6] y ·nH2O, Formula I; Among them, 0 <x ≤ 2,y=0.8~1.2,n=1~3; a: b: c: d: e =7~9: 0.3~0.8: 0.3~0.8: 0.3~0.8: 0.3~0.

8.

2. The polymetallic ion-doped Prussian blue sodium salt material according to claim 1, characterized in that a:b:c:d:e = 7~9:0.4~0.6:0.4~0.6:0.4~0.6:0.4~0.

6.

3. A method for preparing a polymetallic ion-doped Prussian blue sodium salt material as described in claim 1 or 2, characterized in that, Includes the following steps: A metal salt precursor solution A was prepared by dissolving a metal salt precursor and a chelating agent in a glycerol-water mixed solution; a solution B was prepared by dissolving ferrocyanide in a glycerol-water mixed solution. In this process, iron salt, nickel salt, cobalt salt, zinc salt and manganese salt are mixed according to the stoichiometric ratio of Formula I to prepare a metal salt precursor. Under pH 4-5, 50-70 ℃, and inert gas conditions, a co-precipitation reaction was carried out by indirectly adding metal salt precursor solution A to solution B to obtain the polymetallic ion-doped Prussian blue sodium salt material.

4. The preparation method of the multi-metal ion-doped Prussian blue sodium salt material according to claim 3, characterized in that, In the glycerol-water mixed solution, the volume fraction of glycerol is 3% to 10%. The molar volume ratio of the metal salt precursor, chelating agent, and glycerol-water mixed solution is 0.003~0.007 mol : 0.003~0.007 mol : 30~70 mL; The molar volume ratio of the ferrocyanide and glycerol-water mixed solution is 0.003~0.007 mol: 120~180 mL.

5. The method for preparing the multi-metal ion-doped Prussian blue sodium salt material according to claim 3, characterized in that, The indirect dripping method includes dripping for 20-40 minutes, stopping dripping for 10-15 minutes, then continuing dripping for 20-40 minutes and stopping dripping for another 10-15 minutes; The indirect dripping rate is 1~3 mL / min.

6. The preparation method of the multi-metal ion-doped Prussian blue sodium salt material according to claim 3, characterized in that, The chelating agent includes sodium citrate and / or diethylenetriaminepentaacetic acid; The manganese salt includes one or more of manganese chloride, manganese sulfate, manganese nitrate, and manganese acetate; The iron salt includes one or more of ferrous chloride, ferrous sulfate, ferrous nitrate, and ferrous acetate; The cobalt salt includes one or more of cobalt chloride, cobalt sulfate, cobalt nitrate, and cobalt acetate; The nickel salt includes one or more of nickel chloride, nickel sulfate, and nickel nitrate; The zinc salt includes one or more of zinc chloride, zinc sulfate, and zinc acetate.

7. The preparation method of the multi-metal ion-doped Prussian blue sodium salt material according to claim 3, characterized in that, The pH value was adjusted to 4-5 by adding dilute hydrochloric acid solution and / or ammonia solution to the reaction system; The concentration of the dilute hydrochloric acid solution is 0.03 mol / L to 0.1 mol / L; the concentration of the ammonia solution is 0.03 mol / L to 0.1 mol / L.

8. The preparation method of the multi-metal ion-doped Prussian blue sodium salt material according to claim 3, characterized in that, After the coprecipitation reaction, the reaction system is further subjected to aging, centrifugation, and drying to obtain the multi-metal ion-doped Prussian blue sodium salt material. The aging time is 20-30 h; the drying temperature is 160-190℃, and the drying time is 20-30 h.

9. The application of a polymetallic ion-doped Prussian blue sodium salt material as described in claim 1 or 2, or a polymetallic ion-doped Prussian blue sodium salt material prepared by the preparation method described in any one of claims 3 to 8, in an aqueous sodium-ion battery.

10. The application of the polymetallic ion-doped Prussian blue sodium salt material according to claim 9 as a cathode material in an aqueous sodium-ion battery.

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