Preparation method of iron-based prussian blue nanomaterial and application thereof

Abstract

The application belongs to the technical field of electrode materials, and particularly relates to a preparation method of iron-based Prussian blue nanomaterial and application thereof, and the method comprises the following steps: S1: firstly, Na salt is dissolved in a mixed solution of ethanol and deionized water to form a solution A, then a chelating agent is optionally added into the solution A to form a solution B under the condition of magnetic stirring, and then Na4Fe(CN)6 and an optional non-ionic surfactant are added into the solution B; after the solution is uniformly mixed, acid is added drop by drop, and a clear solution is obtained after 1h of vigorous stirring; S2: the clear solution is transferred into a hydrothermal kettle, a hydrothermal reaction is carried out at a temperature of 80 DEG C, a precipitate is obtained, and the target product is obtained after washing and vacuum drying. Through the above method, the particle size of the obtained iron-based Prussian blue nanomaterial is controlled in the range of 300nm-2mu m, and the iron-based Prussian blue nanomaterial can be applied to a water-based sodium ion battery as an electrode material, and when the current density is 1Ag ‑1 , the capacity retention rate is above 92% after 500 cycles.

Description

Technical Field

[0001] This invention belongs to the field of electrode material technology, and particularly relates to a method for preparing iron-based Prussian blue nanomaterials and their application in aqueous sodium-ion batteries. Background Technology

[0002] Environmental pollution and resource scarcity have become two major problems facing modern society. With increasing concern about fossil fuel consumption and environmental challenges, traditional energy sources are gradually revealing their limitations in the process of rapid development. Vigorously developing new energy sources is considered a primary task for achieving sustainable development of human society, in which energy storage technology plays a crucial role, and large-scale energy storage has become a critical link. Currently, energy storage mainly relies on lithium-ion batteries. With the widespread use of lithium, the global cost and scarcity of lithium resources have attracted significant attention. To address this issue, in recent years, there has been considerable focus on finding low-cost and resource-rich alternatives for emerging energy storage. Among various secondary energy systems, sodium-ion batteries have received considerable attention due to the abundance and low price of sodium. Sodium-ion batteries are classified into three types based on their electrolytes: organic, aqueous, and all-solid-state. Organic electrolytes are the most common type of sodium-ion battery electrolyte, but they are volatile and flammable, posing potential safety risks. Solid-state electrolyte batteries, on the other hand, suffer from problems such as low conductivity and structural instability. Aqueous electrolytes have advantages such as high safety, low cost, environmental friendliness, and higher ion conduction rate, making them more attractive in the field of large-scale energy storage compared to other battery systems.

[0003] Electrode materials are a bottleneck restricting the development of aqueous sodium-ion batteries. During electrochemical reactions, the large hydrated ionic radius of sodium ions (0.358 nm) makes insertion / extraction difficult in the active material structure, leading to instability and easy decomposition. This is especially true for cathode materials, which need to meet requirements such as high voltage, high stability, and high specific capacity. Currently, research focuses primarily on transition metal oxides, polyanionic materials, and Prussian blue-based materials. Transition metal oxides still face challenges in structural stability, sodium ion diffusion kinetics, and air stability, requiring further exploration. Polyanionic materials exhibit high redox potentials due to the inductive effect of their anions and high thermal stability due to the strong covalent bonds binding oxygen atoms in their framework structure; however, their intrinsic electronic conductivity is low, resulting in less than ideal rate performance.

[0004] Prussian Blue M x N y[Fe(CN)6](Prussian Blue, PB) is a simple metal-organic framework complex, where M is an alkali metal such as sodium or potassium, and N is a transition metal such as iron. With further research, the scope has expanded to Prussian blue analogs, which can be divided into single-electron transfer and two-electron transfer types. Single-electron transfer Prussian blue analogs mainly include Ni[Fe(CN)6] and Zn[Fe(CN)6], with a theoretical specific capacity of 85 mAh g⁻¹. -1 The two-electron-transfer types mainly include Co[Fe(CN)6], Mn[Fe(CN)6], Fe[Fe(CN)6], and Mn[Mn(CN)6], with a theoretical specific capacity of 170 mAh g. -1 Among them, PB has attracted widespread attention and become one of the preferred cathode materials for sodium-ion batteries due to its complete cubic crystal structure and the presence of a large number of coordination vacancies, which are conducive to the insertion and extraction of alkali metal ions in the crystal lattice. At the same time, PB has abundant porosity, excellent redox activity, high theoretical specific capacity, simple synthesis method, and low cost. However, some difficulties have also been encountered in the research process. The main problems include the presence of a large number of water molecules and vacancies in the crystal structure, which reduces the storage sites of sodium ions, and the fact that transition metal ions in the Prussian blue framework are prone to precipitation during cycling, resulting in limited sodium storage capacity and poor cycle stability of PB cathode materials. In 2015, Wu et al. studied the electrochemical performance of FeFe(CN)6 in aqueous sodium-ion batteries (Wu X, Luo Y, Sun M, et al. Low-defect Prussian blue nanocubes as highcapacity and long-life cathodes for aqueous Na-ion batteries[J]. Nano Energy, 2015, 13: 117-123.). Their results showed that FeFe(CN)6 could cycle for 500 cycles at a current density of 10C with a capacity retention of 83%. However, it still suffers from low capacity and poor long-cycle stability. Therefore, improving the structural stability and electrochemical performance of PB in aqueous sodium-ion batteries has become a critical issue that urgently needs to be addressed. Summary of the Invention

[0005] In view of the aforementioned deficiencies in the prior art, the technical problem to be solved by the present invention is how to improve the structural stability of PB, thereby improving its electrochemical performance in aqueous sodium-ion batteries. The inventors have discovered that by using a mixed solution of ethanol and deionized water to dissolve Na salt, adjusting the pH value of the PB growth environment, and controlling the hydrothermal reaction time, it is possible to obtain PB nanomaterials with suitable capacity, improved structural stability, and maintained capacity after long-term cycling in aqueous sodium-ion batteries, thus completing the present invention.

[0006] Therefore, in a first aspect, the present invention provides a method for preparing iron-based Prussian blue nanomaterials, the method comprising:

[0007] S1: First, dissolve the Na salt in a mixed solution of ethanol and deionized water to form solution A. Then, under magnetic stirring, optionally add a chelating agent to solution A to form solution B. Next, add Na4Fe(CN)6 and optionally a nonionic surfactant to solution B. After the solution is mixed evenly, add acid dropwise and stir vigorously for 1 hour to obtain a clear solution.

[0008] S2: Transfer the clarified solution to a hydrothermal reactor and carry out a hydrothermal reaction at 80°C. After the reaction is complete, a precipitate is obtained. The precipitate is washed 3-5 times with deionized water and ethanol by centrifugation at 10000 r / min for 4 min. Then, the precipitate is dried under vacuum at 80°C for 12 h to obtain the target product.

[0009] In a preferred embodiment, in S1, the volume ratio of deionized water to ethanol in the mixed solution of ethanol and deionized water is 4 to 1:1.

[0010] In a preferred embodiment, in S1, the Na salt is one or more of Na2NO3, NaCl, and Na2CO3.

[0011] In a preferred embodiment, in S1, the molar mass ratio of Na4Fe(CN)6 to sodium salt is 1:1 to 10.

[0012] In a preferred embodiment, in step S1, a chelating agent is added to solution A to form solution B. The chelating agent is one or more of trisodium citrate, sodium citrate, and sodium ascorbate. When the chelating agent is added, the molar mass ratio of Na₄Fe(CN)₆ to the chelating agent is 1:1 to 7.

[0013] In a preferred embodiment, in S1, the optional nonionic surfactant is one or more of polyvinylpyrrolidone, sucrose ester, and alkylolamide, or no nonionic surfactant is added.

[0014] In a preferred embodiment, in S1, the acid is hydrochloric acid or sulfuric acid.

[0015] In a preferred embodiment, in S1, acid is added dropwise to lower the pH of the reaction solution to 0.5-2.

[0016] In a preferred embodiment, the hydrothermal reaction time in S2 ranges from 4 to 10 hours, preferably from 4 to 8 hours, and more preferably from 4 to 6 hours.

[0017] In a second aspect, the present invention provides iron-based Prussian blue nanomaterials obtained by the above-described preparation method.

[0018] In a preferred embodiment, the iron-based Prussian blue nanomaterial has a cubic structure, uniform morphology, and small particle size, ranging from 300 nm to 2 μm.

[0019] In a third aspect, the present invention provides the application of the iron-based Prussian blue nanomaterial in an aqueous sodium-ion battery.

[0020] In a preferred embodiment, in an aqueous sodium-ion battery, the iron-based Prussian blue nanomaterial serves as an electrode material at a current density of 1 A g. -1 When the capacity is maintained for 500 cycles, the capacity retention rate is above 92%, preferably 95%.

[0021] Technical effect

[0022] This invention employs a single iron source synthesis method, under acidic conditions, to synthesize Fe in Na4Fe(CN)6. 2+ It can be released slowly, which slows down the nucleation rate of Prussian blue, forming Prussian blue with lower bound water and fewer vacancies, thus improving cycle stability.

[0023] This invention dissolves sodium salt in a mixed solution of ethanol and deionized water. Compared to deionized water, the hydroxyl groups in ethanol adsorb onto the surface of certain Prussian blue crystals, coordinating with metal ions in the Prussian blue crystal structure, inhibiting crystal nucleus growth, and forming PB with uniform morphology and small particle size. Furthermore, a chelating agent can be added during the preparation of Prussian blue as a crystal nucleus growth inhibitor, which can slow down the reaction rate while replenishing the sodium source. More sodium ions enter the framework, effectively reducing vacancies and coordinated water, increasing the sodium ion content of structural units, stabilizing their structure, and preparing high-capacity, structurally stable Prussian blue, thus improving cycling stability and efficiency.

[0024] This invention controls the grain size of Prussian blue during the reaction process by adjusting the hydrothermal reaction time to 4–10 hours, resulting in Prussian blue with controllable grain size. This preparation of Prussian blue with suitable grain size increases active sites, reduces ion transport distance, and improves electrochemical performance. Too short a hydrothermal time will prevent Prussian blue from nucleating; too long a hydrothermal time will lead to inconsistent Prussian blue particle size, changing from nanometer to micrometer scale.

[0025] The present invention can also adjust the dispersibility by adding nonionic surfactants, forming micelles in the solution, avoiding secondary aggregation of particles, and preparing Prussian blue with good crystallinity and dispersibility.

[0026] This invention optimizes the preparation process to obtain Prussian blue nanomaterials with good crystallinity, a typical cubic structure, uniform morphology, and small particle size, suitable for aqueous sodium-ion batteries. As an electrode material, it exhibits good performance at a current density of 1 A g. -1 At this stage, the capacity retention rate is above 92% after 500 cycles, even reaching as high as 95%. Compared with organic sodium-ion batteries, PB does not have the problem of removing bound water in aqueous electrolytes, and has advantages such as high safety, low cost, environmental friendliness, and higher ion conduction rate, achieving significant progress. Attached Figure Description

[0027] Figure 1 This is a scanning electron microscope image of PB obtained in Example 1 of the present invention;

[0028] Figure 2 The invention illustrates the use of PB obtained in Example 1 as an electrode material in 1Ag. -1 Under normal cyclic performance;

[0029] Figure 3 This is a scanning electron microscope image of PB obtained in Example 2 of the present invention;

[0030] Figure 4 The PB obtained in Example 2 of the present invention is shown as an electrode material in 1Ag. -1 Under normal cyclic performance;

[0031] Figure 5 The PB obtained in Example 3 of the present invention is shown as an electrode material in 1Ag. -1 Under normal cyclic performance;

[0032] Figure 6 This is a scanning electron microscope image of PB obtained in Comparative Example 2 of the present invention;

[0033] Figure 7 This is a scanning electron microscope image of PB obtained in Comparative Example 3 of the present invention;

[0034] Figure 8 The invention illustrates PB obtained in Comparative Example 3 as an electrode material in 1Ag. -1 Under normal cyclic performance;

[0035] Figure 9 This is a comparison diagram of the XRD pattern of PB obtained in Example 1 and Comparative Example 3 of the present invention with that of the standard card;

[0036] Figure 10 This is a scanning electron microscope image of PB obtained in Comparative Example 4 of the present invention;

[0037] Figure 11 The results of Comparative Example 4 of the present invention, using PB as an electrode material, are shown in 1 A g.-1 The loop performance is as follows. Detailed Implementation

[0038] The following description, with reference to the accompanying drawings, illustrates several preferred embodiments of the present invention to make its technical content clearer and easier to understand. The present invention can be embodied in many different forms, and the scope of protection of the present invention is not limited to the embodiments mentioned herein.

[0039] Example 1

[0040] Preparation of Prussian blue (PB) nanomaterials by hydrothermal synthesis:

[0041] First, dissolve 1g of NaCl in a mixed solution of 80mL of deionized water and 20mL of ethanol. Then, under magnetic stirring, add 0.36g of Na4Fe(CN)6 and 1g of polyvinylpyrrolidone (K30) to the sodium chloride solution. After the solution is mixed evenly, add 2.0mL of hydrochloric acid (37%) (solution pH=0.5) dropwise. After stirring vigorously for 1 hour, a clear solution is obtained.

[0042] The clarified solution was transferred to a 100 mL hydrothermal reactor and hydrothermally reacted at 80 °C for 10 h. After the reaction was completed, the precipitate was obtained and washed 3 to 5 times with deionized water and ethanol by centrifugation at 10,000 r / min for 4 min. Then, the precipitate was vacuum dried at 80 °C for 12 h to obtain the target product.

[0043] The obtained scanning electron microscope image of PB is as follows: Figure 1 As shown.

[0044] The prepared sample, Ketjen black, and polytetrafluoroethylene emulsion were ground and mixed evenly at a mass ratio of 7:2:1 to prepare a slurry. The slurry was then evenly pressed onto a stainless steel current collector and vacuum dried in a vacuum drying oven at 120℃ for 5 hours using 1 mol L... -1 Na₂SO₄ solution was used as the electrolyte, and Prussian blue electrode material (Prussian blue loading: 2 mg cm⁻¹) was used. -1 A complete aqueous battery testing system is constructed using an Ag / AgCl electrode as the reference electrode, with an excess of activated carbon as the counter electrode and an Ag / AgCl electrode as the reference electrode.

[0045] The PB prepared in this embodiment was used as an electrode material at 1A g. -1 Cyclic performance such as Figure 2 As shown, when the current density is 1Ag -1 At that time, the capacity of PB was 81mAh g. -1 After 400 cycles, the capacity retention rate was 97%.

[0046] Example 2

[0047] Preparation of Prussian blue (PB) nanomaterials by hydrothermal synthesis:

[0048] First, dissolve 1g of NaCl in a mixed solution of 80mL of deionized water and 20mL of ethanol. Then, under magnetic stirring, add 0.36g of Na4Fe(CN)6 and 1g of polyvinylpyrrolidone (K30) to the sodium chloride solution. After the solution is mixed evenly, add 2.0mL of hydrochloric acid (37%) (solution pH=0.5) dropwise. After stirring vigorously for 1 hour, a clear solution is obtained.

[0049] The clarified solution was transferred to a 100 mL hydrothermal reactor and hydrothermally reacted at 80 °C for 4 h. After the reaction was completed, the precipitate was obtained and washed 3 to 5 times with deionized water and ethanol by centrifugation at 10,000 r / min for 4 min. Then, the precipitate was vacuum dried at 80 °C for 12 h to obtain the target product.

[0050] The obtained scanning electron microscope image of PB is as follows: Figure 3 As shown. Compared to Example 1, the reaction time was shortened from 10h to 4h. As the reaction time decreased, the particle size of PB decreased to about 300nm. The smaller grain size can effectively increase the active sites, reduce the ion transport distance, and improve the electrochemical performance.

[0051] The prepared sample, Ketjen black, and polytetrafluoroethylene emulsion were ground and mixed evenly at a mass ratio of 7:2:1 to prepare a slurry. The slurry was then evenly pressed onto a stainless steel current collector and vacuum dried in a vacuum drying oven at 120℃ for 5 hours using 1 mol L... -1 Na₂SO₄ solution was used as the electrolyte, and Prussian blue electrode material (Prussian blue loading: 2 mg cm⁻¹) was used. -1 A complete aqueous battery testing system is constructed using an Ag / AgCl electrode as the reference electrode, with an excess of activated carbon as the counter electrode and an Ag / AgCl electrode as the reference electrode.

[0052] The PB prepared in this embodiment was used as an electrode material at 1A g. -1 Cyclic performance such as Figure 4 As shown, when the current density is 1A g -1 At that time, the capacity of PB was 113mAh g. -1 After 500 cycles, the capacity retention rate is 95%.

[0053] Example 3

[0054] Preparation of Prussian blue (PB) nanomaterials by hydrothermal synthesis:

[0055] First, dissolve 1g of NaCl in a mixed solution of 80mL of deionized water and 20mL of ethanol. Then, under magnetic stirring, add 0.36g of Na4Fe(CN)6 and 1.76g of sodium citrate to the mixed solution. After the solution is mixed evenly, add 2.0mL of hydrochloric acid (37%) (solution pH=0.5) dropwise. After stirring vigorously for 1 hour, a clear solution is obtained.

[0056] The clarified solution was transferred to a 100 mL hydrothermal reactor and hydrothermally reacted at 80 °C for 10 h. After the reaction was completed, the precipitate was obtained and washed 3 to 5 times with deionized water and ethanol by centrifugation at 10,000 r / min for 4 min. Then, the precipitate was vacuum dried at 80 °C for 12 h to obtain the target product.

[0057] The prepared sample, Ketjen black, and polytetrafluoroethylene emulsion were ground and mixed evenly at a mass ratio of 7:2:1 to prepare a slurry. The slurry was then evenly pressed onto a stainless steel current collector and vacuum dried in a vacuum drying oven at 120℃ for 5 hours. 1 mol L... -1 Na₂SO₄ solution was used as the electrolyte, and Prussian blue electrode material (Prussian blue loading: 2 mg cm⁻¹) was used. -1 A complete aqueous battery testing system is constructed using an Ag / AgCl electrode as the reference electrode, with an excess of activated carbon as the counter electrode and an Ag / AgCl electrode as the reference electrode.

[0058] The PB prepared in this embodiment was used as an electrode material at 1A g. -1 Cyclic performance such as Figure 5 As shown, when the current density is 1Ag -1 At that time, the capacity of PB was 84mAh g. -1 After 500 cycles, the capacity retention rate was 92%.

[0059] Comparative Example 1

[0060] Preparation of Prussian blue (PB) nanomaterials by hydrothermal synthesis:

[0061] First, dissolve 1g NaCl in 100mL of deionized water. Then, under magnetic stirring, add 0.36g Na4Fe(CN)6 and 1g polyvinylpyrrolidone (K30) to the sodium chloride solution. After the solution is mixed evenly, add 0.5mL of hydrochloric acid (37%) (solution pH=2) dropwise. Stir vigorously for 1 hour to obtain a clear solution.

[0062] The clarified solution was transferred to a 100 mL hydrothermal reactor and hydrothermally reacted at 80 °C for 10 h. After the reaction, a precipitate was obtained, which was washed 3–5 times with deionized water and ethanol by centrifugation at 10,000 r / min for 4 min. Then, it was vacuum dried at 80 °C for 12 h to obtain the target product. The yield of PB was low and the morphology was irregular.

[0063] The prepared sample, Ketjen black, and polytetrafluoroethylene emulsion were ground and mixed evenly at a mass ratio of 7:2:1 to prepare a slurry. The slurry was then evenly pressed onto a stainless steel current collector and vacuum dried in a vacuum drying oven at 120℃ for 5 hours. 1 mol L... -1 Na₂SO₄ solution was used as the electrolyte, and Prussian blue electrode material (Prussian blue loading: 2 mg cm⁻¹) was used. -1 A complete aqueous battery testing system is constructed using an Ag / AgCl electrode as the reference electrode, with excess activated carbon as the counter electrode and an Ag / AgCl electrode as the reference electrode. However, when the current density is 1A g... -1 At that time, the capacity of PB was relatively low.

[0064] Comparative Example 2

[0065] Preparation of Prussian blue (PB) nanomaterials by hydrothermal synthesis:

[0066] First, dissolve 1g NaCl in 100mL of deionized water. Then, under magnetic stirring, add 0.36g Na4Fe(CN)6 and 1g polyvinylpyrrolidone (K30) to the sodium chloride solution. After the solution is mixed evenly, add 1.0mL of hydrochloric acid (37%) (solution pH=1) dropwise. Stir vigorously for 1 hour to obtain a clear solution.

[0067] The clarified solution was transferred to a 100 mL hydrothermal reactor and hydrothermally reacted at 80 °C for 10 h. After the reaction was completed, the precipitate was obtained and washed 3 to 5 times with deionized water and ethanol by centrifugation at 10,000 r / min for 4 min. Then, the precipitate was vacuum dried at 80 °C for 12 h to obtain the target product.

[0068] The obtained scanning electron microscope image of PB is as follows: Figure 6 As shown, no ethanol was added during the preparation process, and the pH was high, resulting in a low yield and irregular morphology of PB.

[0069] The prepared sample, Ketjen black, and polytetrafluoroethylene emulsion were ground and mixed evenly at a mass ratio of 7:2:1 to prepare a slurry. The slurry was then evenly pressed onto a stainless steel current collector and vacuum dried in a vacuum drying oven at 120℃ for 5 hours using 1 mol L... -1 Na₂SO₄ solution was used as the electrolyte, and Prussian blue electrode material (Prussian blue loading: 2 mg cm⁻¹) was used. -1A complete aqueous battery testing system is constructed using an Ag / AgCl electrode as the working electrode, excess activated carbon as the counter electrode, and Ag / AgCl electrode as the reference electrode. However, when the current density is 1Ag... -1 At that time, the capacity of PB was relatively low.

[0070] Comparative Example 3

[0071] Preparation of Prussian blue (PB) nanomaterials by hydrothermal synthesis:

[0072] First, dissolve 1g of NaCl in 100mL of deionized water. Then, under magnetic stirring, add 0.36g of Na4Fe(CN)6 and 1g of polyvinylpyrrolidone (K30) to the sodium chloride solution. After the solution is mixed evenly, add 2.0mL of hydrochloric acid (37%) (solution pH=0.5) dropwise. Stir vigorously for 1 hour to obtain a clear solution.

[0073] The clarified solution was transferred to a 100 mL hydrothermal reactor and hydrothermally reacted at 80 °C for 10 h. After the reaction was completed, the precipitate was obtained and washed 3 to 5 times with deionized water and ethanol by centrifugation at 10,000 r / min for 4 min. Then, the precipitate was vacuum dried at 80 °C for 12 h to obtain the target product.

[0074] The obtained scanning electron microscope image of PB is as follows: Figure 7 As shown. Compared to Comparative Example 2, lowering the pH of the mixed solution resulted in an increased yield of PB and a more regular morphology.

[0075] Furthermore, the comparison diagrams of the XRD patterns of PB obtained in Example 1 and Comparative Example 3 of this invention with the standard card are shown below. Figure 9 As shown, both samples exhibit good crystallinity, with diffraction peaks matching the standard card and displaying a typical cubic structure. Furthermore, compared to Comparative Examples 1, 2, and 3, Example 1 of this invention adds ethanol to the mixed solution. The hydroxyl groups in the ethanol adsorb onto the surface of some Prussian blue crystals, coordinating with metal ions in the Prussian blue crystal structure, inhibiting crystal nucleus growth, and forming PB with uniform morphology and small particle size.

[0076] The prepared sample, Ketjen black, and polytetrafluoroethylene emulsion were ground and mixed evenly at a mass ratio of 7:2:1 to prepare a slurry. The slurry was then evenly pressed onto a stainless steel current collector and vacuum dried in a vacuum drying oven at 120℃ for 5 hours using 1 mol L... -1 Na₂SO₄ solution was used as the electrolyte, and Prussian blue electrode material (Prussian blue loading: 2 mg cm⁻¹) was used. -1 A complete aqueous battery testing system is constructed using an Ag / AgCl electrode as the reference electrode, with an excess of activated carbon as the counter electrode and an Ag / AgCl electrode as the reference electrode.

[0077] The PB prepared in this embodiment was used as an electrode material in 1Ag -1 Cyclic performance such as Figure 8 As shown, when the current density is 1Ag -1 At that time, the capacity of PB was 58mAh g. -1 When used in aqueous sodium-ion batteries, the capacity is relatively low, but the capacity retention rate is 100% after 300 cycles, and the cycle stability is improved.

[0078] Comparative Example 4

[0079] Preparation of Prussian blue (PB) nanomaterials by hydrothermal synthesis:

[0080] First, dissolve 1g of NaCl in a mixed solution of 80mL of deionized water and 20mL of ethanol. Then, under magnetic stirring, add 0.36g of Na4Fe(CN)6 and 1g of polyvinylpyrrolidone (K30) to the sodium chloride solution. After the solution is mixed evenly, add 2.0mL of hydrochloric acid (37%) (solution pH=0.5) dropwise. After stirring vigorously for 1 hour, a clear solution is obtained.

[0081] The clarified solution was transferred to a 100 mL hydrothermal reactor and hydrothermally reacted at 80 °C for 16 h. After the reaction was completed, the precipitate was obtained and washed 3 to 5 times with deionized water and ethanol by centrifugation at 10,000 r / min for 4 min. Then, the precipitate was vacuum dried at 80 °C for 12 h to obtain the target product.

[0082] The obtained scanning electron microscope image of PB is as follows: Figure 10 As shown, compared to Example 1, the reaction time was increased from 10h to 16h. With the increase of reaction time, the particle size of PB increased to about 1μm, and the particle size was inconsistent.

[0083] The prepared sample, Ketjen black, and polytetrafluoroethylene emulsion were ground and mixed evenly at a mass ratio of 7:2:1 to prepare a slurry. The slurry was then evenly pressed onto a stainless steel current collector and vacuum dried in a vacuum drying oven at 120℃ for 5 hours using 1 mol L... -1 Na₂SO₄ solution was used as the electrolyte, and Prussian blue electrode material (Prussian blue loading: 2 mg cm⁻¹) was used. -1 A complete aqueous battery testing system is constructed using an Ag / AgCl electrode as the reference electrode, with an excess of activated carbon as the counter electrode and an Ag / AgCl electrode as the reference electrode.

[0084] The PB prepared in this embodiment was used as an electrode material in 1Ag -1 Cyclic performance such as Figure 11 As shown, when the current density is 1Ag -1 At that time, the capacity of PB was 73mAh g.-1 After 500 cycles, the capacity retention rate is only 55%.

[0085] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A method for preparing an iron-based Prussian blue nanomaterial, the method comprising: S1: firstly dissolving a Na salt in a mixed solution of ethanol and deionized water to form a solution A, then adding a chelating agent to the solution A under magnetic stirring to form a solution B, and then adding Na4Fe(CN) 6 and an optional non-ionic surfactant to the solution B; after the solution is mixed uniformly, adding an acid drop by drop to reduce the pH of the reaction solution to 0.5, and then stirring vigorously for 1 h to obtain a clear solution; S2: transferring the clear solution into an autoclave, and performing a hydrothermal reaction at a temperature of 80 ℃, and then obtaining a precipitate after the reaction is completed, and then washing the precipitate with deionized water and ethanol by centrifugation for 3-5 times, and then drying the precipitate at 80 ℃ under vacuum for 12 h to obtain a target product; in S1, the volume ratio of deionized water to ethanol in the mixed solution of ethanol and deionized water is 4-1:1; in S2, the hydrothermal reaction is performed for 4-10 h.

2. The production method according to claim 1, wherein in S1, the Na salt is one or more of NaCl and Na2CO3.

3. The production method according to claim 1, wherein in S1, a chelating agent is added to the solution A to form the solution B.

4. The production method according to claim 3, wherein the chelating agent is one or more of trisodium citrate, sodium citrate, and sodium ascorbate.

5. The production method according to claim 1, wherein in S1, the optional non-ionic surfactant is one or more of polyvinylpyrrolidone, sucrose ester, and alkylolamide, or no non-ionic surfactant is added. 6.An iron-based Prussian blue nanomaterial obtained by the method according to any one of claims 1-5, having a particle size ranging from 300 nm to 2 μm.

7. The application of the iron-based Prussian blue nanomaterial in claim 6 in a water-based sodium ion battery, wherein the capacity retention rate of the iron-based Prussian blue nanomaterial as an electrode material is above 92% when the current density is 1 A g -1 for 500 cycles.

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