Prussian blue crystal with controllable vacancy content as well as preparation method and application of Prussian blue crystal

Abstract

The invention discloses a vacancy content controllable Prussian blue crystal as well as a preparation method and application thereof, and belongs to the technical field of material synthesis. In order to solve the technical problems that the vacancy content of a prussian blue material is difficult to accurately control and a vacancy-free material is difficult to prepare, the invention provides a series of prussian blue crystals with controllable vacancy content, and the preparation method comprises the following steps: mixing sodium ferrocyanide, a complexing agent, a sodium salt and water to obtain a solution A; mixing soluble manganese salt, soluble ferrous salt, a complexing agent, sodium salt and water to obtain a solution B; and controlling the sodium ion concentration and the reaction atmosphere and temperature, adding the solution A into the solution B, reacting, and aging to obtain the Prussian blue crystal. According to the method, the sodium ion concentration, the reaction atmosphere and the temperature are regulated and controlled by changing the addition amount of the sodium salt and the like, and the crystal growth speed and the ion transmission speed in the coprecipitation reaction are controlled, so that the purpose of accurately controlling the vacancy content is achieved, and a material without vacancy and first-stage crystal water can be prepared.

Description

Technical Field

[0001] This invention belongs to the field of materials synthesis technology, specifically relating to a Prussian blue-like crystal with controllable vacancy content, its preparation method, and its application. Background Technology

[0002] With increasing concern about the sustainability of fossil fuels and their environmental impact, the large-scale utilization of renewable energy has become a research hotspot for next-generation energy storage and conversion technologies. Although lithium-ion batteries (LIBs) are widely used, the high cost and scarcity of lithium resources limit their development in grid-scale energy systems. Benefiting from the widespread availability and low cost of sodium resources, sodium-ion batteries (SIBs), as an economical alternative to LIBs, are being actively developed for energy storage applications. However, the practical application of SIBs still faces key challenges, one of which is the development of high-performance cathode materials.

[0003] Prussian blue analogues (PBAs), compared to other SIB candidates (such as polyanionic compounds, layered oxides, and organic compounds), exhibit rapid Na+ uptake due to their 3D open framework structure. + Advantages of transport. Furthermore, PBAs possess high theoretical capacity (~170 mAh / g) and output voltage (~3.5 V), and can be synthesized via a low-cost, mature co-precipitation method, making them a promising cathode material choice for large-scale production of SIBs. The general chemical formula of PBAs is usually represented as A x M1[M2(CN)6] y □ 1-y •zH₂O, where A represents an alkali metal (such as Na), M1 and M2 are transition metals, and □ represents [M₂(CN)₆]. 4- Vacancies. M1 and M2 are alternately connected to C≡N to form a rigid open framework, with sodium ions located in larger interstitial positions. This three-dimensional network of channels facilitates the rapid insertion / extraction of sodium ions. Theoretically, based on the electrochemical activity of M1 and M2 ions, each unit transfers two electrons, thus exhibiting high specific capacity. However, during co-precipitation, TM... 2+ Ions and [M2(CN)6] 4- Rapid ion binding results in a large amount of [M2(CN)6] in the material. 4- Vacancies reduce the sodium content in the crystal lattice, and the unoccupied sites formed by vacancies increase the probability of water molecule adsorption.

[0004] However, the impact of vacancies on electrochemical performance remains controversial. Some researchers believe that low vacancy content and high sodium content can lead to excellent electrochemical performance, while others believe that vacancies can positively influence the electrochemical performance of PBAs by promoting sodium ion transport. Due to limitations in synthetic methods, it is difficult to precisely control the vacancy content of PBAs. Therefore, it is crucial to find a way to directly prepare materials with precisely controllable vacancy content in one step through synthetic design. Summary of the Invention

[0005] The purpose of this invention is to solve the problem of [Fe(CN)6] in Prussian blue materials in the prior art. 4- The technical challenges include the difficulty in precisely controlling vacancy defects and preparing vacancy-free materials.

[0006] To address the aforementioned technical problems, this invention first proposes a method for preparing Prussian blue-like crystals with precisely controllable vacancy content, comprising the following steps:

[0007] A. Add sodium ferrocyanide, complexing agent and sodium salt to the mixture and mix thoroughly to obtain solution A;

[0008] B. Add soluble manganese salt, soluble ferrous salt, complexing agent and sodium salt to water, mix thoroughly to obtain solution B;

[0009] C. Under an inert atmosphere, add solution A dropwise to solution B. After the addition is complete, carry out the aging reaction at 55~65℃ under an inert atmosphere or under an inert atmosphere followed by an air atmosphere.

[0010] D. After aging, Prussian blue crystals are obtained through cooling, solid-liquid separation, washing and drying.

[0011] The total sodium ion concentration in solutions A and B is 3.4–12 mol / L.

[0012] When the total sodium ion concentration in solutions A and B is less than 7.4 mol / L (3.4 mol / L ≤ total concentration of sodium ions in solutions A and B), and the proportion of the inert atmosphere time in step C to the total dropping and aging time is less than 50%, the vacancy content of the Prussian blue-like crystals obtained in step D is 13% < vacancy content ≤ 20%, and the general chemical formula is Na. x1 Mn p1 Fe q1 [Fe(CN)6] 1-y1 □ y1 ·z1H2O, 1.3≤x1<1.5, 0≤p1<1, 0<q1≤1, p1+q1=1, 0.13<y1≤0.2, 2≤z1≤3;

[0013] When the total sodium ion concentration in solutions A and B is less than 7.4 mol / L and 50% ≤ the proportion of the inert atmosphere time in step C to the total dropping and aging time is less than 100%, or when the total sodium ion concentration in solutions A and B is less than 10 mol / L and 20% ≤ the proportion of the inert atmosphere time in step C to the total dropping and aging time is less than 50%, the vacancy content of the Prussian blue crystals obtained in step D is 7% < vacancy content ≤ 13%, and the general chemical formula is Na. x2 Mn p2 Fe q2 [Fe(CN)6] 1-y2 □ y2 ·z2H2O, 1.5≤x2<1.75, 0≤p2<1, 0<q2≤1, p2+q2=1, 0.07<y2≤0.13, 2≤z2≤3;

[0014] When the total sodium ion concentration in solutions A and B is less than 10 mol / L (7.4 mol / L ≤ total sodium ion concentration in solutions A and B), and 50% ≤ the proportion of the inert atmosphere time in step C to the total dropping and aging time is less than 100%; or when the total sodium ion concentration in solutions A and B is less than 12 mol / L (10 mol / L ≤ total sodium ion concentration in solutions A and B), and 20% ≤ the proportion of the inert atmosphere time in step C to the total dropping and aging time is less than 50%, the vacancy content of the Prussian blue crystals obtained in step D is 0% < vacancy content ≤ 7%, and the chemical formula is Na. x3 Mn p3 Fe q3 [Fe(CN)6] 1-y3 □ y3 ·z3H2O, 1.75≤x3<2.0, 0≤p3<1, 0<q3≤1, p3+q3=1, 0<y3≤0.07, 1.9≤z3≤2;

[0015] When the total sodium ion concentration in solutions A and B is ≤12 mol / L (10 mol / L ≤ 12 mol / L), and the inert atmosphere time in step C accounts for ≤100% of the total dropping and aging time, the vacancy content of the Prussian blue crystals obtained in step D is 0%, and the chemical formula is Na. x4 Mn p4 Fe q4 [Fe(CN)6] y4 ·z4H2O, 2.0≤x4≤2.2, 0≤p4<1, 0<q4≤1, p4+q4=1, 1.0≤y4≤1.1, 1.8≤z4≤1.9.

[0016] In this invention, the total sodium ion concentration in solution A and solution B refers to the sum of the total molar amount of sodium ions in sodium ferrocyanide, complexing agent, and sodium salt in solution A, plus the total molar amount of sodium ions in complexing agent and sodium salt in solution B, divided by the total volume of solutions A and B.

[0017] This invention discovers that sodium salts can provide a sufficient sodium source for the reaction process, reducing the vacancy content. Simultaneously, the sodium ion concentration in sodium ferrocyanide, the complexing agent, and the sodium salt can affect the vacancy content. Furthermore, in the method of this invention, ferrous ions are oxidized to ferric ions in an air atmosphere, affecting the vacancy content. Manganese ions are stable in air, and changing the atmosphere makes it difficult to alter the vacancy content. Therefore, soluble ferrous salts must be added to solution B of this invention, while soluble manganese salts can be added or not. This allows for the control of the reaction atmosphere and the utilization of the specific properties of ferrous ions to change the vacancy content.

[0018] In the preparation method of the Prussian blue crystal with controllable vacancy content, the concentration of sodium ferrocyanide in solution A is 0.02~0.1 mol / L, the concentration of complexing agent is 0.02~0.1 mol / L, and the concentration of sodium salt is 3~12 mol / L.

[0019] In the method for preparing Prussian blue-like crystals with controllable vacancy content, in step A, the complexing agent is selected from at least one of sodium citrate, sodium oxalate, disodium ethylenediaminetetraacetate, or sodium acetate, and the sodium salt is selected from at least one of sodium chloride, sodium sulfate, sodium nitrate, sodium oxalate, or sodium acetate.

[0020] In the preparation method of the Prussian blue crystal with controllable vacancy content, the concentration of soluble manganese salt in solution B is 0~0.1 mol / L, the concentration of soluble ferrous salt is 0.01~0.1 mol / L, the concentration of complexing agent is 0~0.1 mol / L, and the concentration of sodium salt is 3~12 mol / L.

[0021] In the method for preparing Prussian blue-like crystals with controllable vacancy content, in step B, the soluble manganese salt is selected from at least one of manganese chloride, manganese sulfate, manganese nitrate, manganese oxalate, or manganese acetate; the soluble ferrous salt is selected from at least one of ferrous chloride, ferrous sulfate, ferrous nitrate, ferrous oxalate, or ferrous acetate; the complexing agent is selected from at least one of sodium citrate, sodium oxalate, disodium ethylenediaminetetraacetate, or sodium acetate; and the sodium salt is selected from at least one of sodium chloride, sodium sulfate, sodium nitrate, sodium oxalate, or sodium acetate.

[0022] The complexing agent and sodium salt in step A of the method of the present invention may be the same as or different from those in step B. The concentrations of the complexing agent and sodium salt in step A of the method of the present invention may also be the same as or different from those in step B.

[0023] In the preparation method of the Prussian blue-like crystal with controllable vacancy content, in step C, the volume ratio of solution A to solution B during dropwise addition is 1~2:2~1.

[0024] In the preparation method of Prussian blue-like crystals with controllable vacancy content, in step C, the temperature of solution A and solution B is maintained at 55~65℃ during dropwise addition.

[0025] In the preparation method of the Prussian blue-like crystals with controllable vacancy content, the dropping rate in step C is 1.5~2.5 mL / min.

[0026] In the method for preparing Prussian blue-like crystals with controllable vacancy content, step C involves a stirring speed of 300-600 rpm and a total addition and aging time of 18-30 hours. In step C of this invention, a stirrer or magnetic stirrer can be used for stirring during the addition and aging reactions.

[0027] In step D of the method of the present invention, after washing with pure water 2 to 3 times, the product is placed in an oven at 60 to 80°C and dried for 12 to 24 hours to obtain Prussian blue compounds.

[0028] Using the above method, this invention can prepare a series of Prussian blue-like crystals with controllable vacancy content, and in particular, a series of materials without vacancies and without first-stage water of crystallization. Therefore, this invention also provides a series of Prussian blue-like crystals with controllable vacancy content, especially those without vacancies and without first-stage water of crystallization.

[0029] This invention also provides the application of the above-mentioned Prussian blue-like crystals with controllable vacancy content in sodium-ion secondary batteries.

[0030] The beneficial effects of this invention are:

[0031] This invention uses soluble manganese salt, ferrous salt, and sodium ferrocyanide as raw materials. By comprehensively controlling the amount of complexing agent, sodium salt, and reaction temperature, and further controlling the reaction atmosphere, the precise controllability of the product vacancy content is achieved. The complexing agent slows down the crystal growth rate during the reaction process, preventing excessive vacancies caused by rapid crystal nucleation and growth. The sodium salt provides a sufficient sodium source for the reaction process. By adjusting the sodium salt concentration, the sodium ion concentration is controlled, thereby regulating the vacancy content. Controlling the reaction temperature to 55-65℃ accelerates ion transport and reduces vacancy content. Furthermore, by adjusting the reaction atmosphere, ferrous ions are converted... By controlling the vacancy content using ferric ions, and through the synergistic control of multiple key parameters, the vacancy content can be precisely controlled. Repeated verification has shown that this method achieves precise control of the product vacancy content from 0-20% and the water of crystallization content from 9-18%, enabling the preparation of Prussian blue-like crystals without vacancies or first-stage water of crystallization. This invention addresses the technical challenge of precisely controlling the vacancy and water of crystallization content in Prussian blue-like materials, retaining the advantages of the co-precipitation method, and further enhancing its industrialization potential through parameter optimization, demonstrating significant economic and application value. Attached Figure Description

[0032] Figure 1 The image shown is a 300nm scanning electron microscope image of the material obtained in Example 1.

[0033] Figure 2 The thermogravimetric analysis curve of the material obtained in Example 1 is shown.

[0034] Figure 3 The image shown is a 300nm scanning electron microscope image of the material obtained in Example 2.

[0035] Figure 4 The thermogravimetric analysis curve of the material obtained in Example 2 is shown.

[0036] Figure 5 This is a 300nm scanning electron microscope image of the material obtained in Example 3.

[0037] Figure 6 The thermogravimetric analysis curve of the material obtained in Example 3 is shown.

[0038] Figure 7 This is a 300nm scanning electron microscope image of the material obtained in Example 4.

[0039] Figure 8 The thermogravimetric analysis curve of the material obtained in Example 4 is shown.

[0040] Figure 9 This is a 300nm scanning electron microscope image of the material obtained in Example 5.

[0041] Figure 10The thermogravimetric analysis curve of the material obtained in Example 5 is shown.

[0042] Figure 11 The image shown is a 300nm scanning electron microscope image of the material obtained in Example 6.

[0043] Figure 12 The thermogravimetric analysis curve of the material obtained in Example 6 is shown.

[0044] Figure 13 This is a 300nm scanning electron microscope image of the material obtained in Example 7.

[0045] Figure 14 The thermogravimetric analysis curve of the material obtained in Example 7 is shown.

[0046] Figure 15 This is a 300nm scanning electron microscope image of the material obtained in Example 8.

[0047] Figure 16 The thermogravimetric analysis curve of the material obtained in Example 8 is shown.

[0048] Figure 17 This is a 300nm scanning electron microscope image of the material obtained in Example 9.

[0049] Figure 18 The thermogravimetric analysis curve of the material obtained in Example 9 is shown.

[0050] Figure 19 The image shown is a 300nm scanning electron microscope image of the material obtained in Example 10.

[0051] Figure 20 The thermogravimetric analysis curve of the material obtained in Example 10 is shown. Detailed Implementation

[0052] The present invention will be further described in detail below through embodiments, but the scope of protection of the present invention is not limited to the embodiments described herein. The following embodiments only list some of the experiments of the present invention.

[0053] Example 1

[0054] Step 1: Dissolve 0.012 mol sodium ferrocyanide decahydrate, 0.012 mol sodium citrate dihydrate and 0.821 mol sodium chloride in 240 mL of deionized water to obtain solution A. Keep the temperature of solution A at 60℃.

[0055] Step 2: Dissolve 0.006 mol manganese sulfate monohydrate, 0.006 mol ferrous sulfate heptahydrate and 0.821 mol sodium chloride in 240 mL of deionized water to obtain solution B. Keep the temperature of solution B at 60℃.

[0056] Step 3: Under a nitrogen atmosphere, solution A is slowly added dropwise to solution B at a rate of 2 ml / min using a peristaltic pump over a period of 2 hours. After the addition is complete, the solution is aged under a nitrogen atmosphere for 5 hours, and then the reaction atmosphere is switched to air for 17 hours. During the addition and aging process, the reaction temperature is maintained at 60°C and the stirring speed is 300 r.

[0057] Step 4: After aging, the crystals are cooled, separated from their solid state, washed, and finally dried in a vacuum oven at 80°C for 24 hours to obtain Prussian blue-like crystals with the molecular formula Na. 1.44 Mn 0.55 Fe 0.45 [Fe(CN)6] 0.86 •2.50H2O.

[0058] Figure 1 These are scanning electron microscope images of the materials obtained in this embodiment; Figure 2 The thermogravimetric analysis curve of the material shows that its water of crystallization content is 16.68%. Inductively coupled plasma atomic emission spectrometry (ICP-AES) analysis determined the molecular formula of the material to be Na. 1.32 Mn 0.55 Fe 0.45 [Fe(CN)6] 0.83 • 2.90H2O, with a vacancy content of 17%.

[0059] In this embodiment, the sodium ion concentration in solution A is 3.77 mol / L, the total sodium ion concentration in solution B is 3.42 mol / L, and the total sodium ion concentration of solutions A and B is 3.60 mol / L, with the total sodium ion concentration ranging from 3.4 to 7.4 mol / L. Simultaneously, the total time under nitrogen is 7 hours, less than 12 hours, accounting for less than 50% of the total time, resulting in an increased vacancy content of 13%-20%. Experiments show that by controlling the total sodium ion concentration between 3.4 and 7.4 mol / L (excluding 7.4 mol / L) and the total time under nitrogen less than 50%, this invention can obtain Prussian blue-like crystals with a vacancy content of 13%-20% (excluding 13%).

[0060] Example 2

[0061] Compared to Example 1, the only differences are as follows:

[0062] Step 1: Dissolve 0.012 mol sodium ferrocyanide decahydrate, 0.012 mol sodium citrate dihydrate and 1.281 mol sodium chloride in 240 mL of deionized water to obtain solution A. Keep the temperature of solution A at 60℃.

[0063] Step 2: Dissolve 0.006 mol manganese sulfate monohydrate, 0.006 mol ferrous sulfate heptahydrate and 1.281 mol sodium chloride in 240 mL of deionized water to obtain solution B. Keep the temperature of solution B at 60℃.

[0064] Figure 3 These are scanning electron microscope images of the materials obtained in this embodiment; Figure 4 The thermogravimetric analysis curve of the material shows that its water of crystallization content is 15.34%. Inductively coupled plasma atomic emission spectrometry (ICP-AES) analysis determined the molecular formula of the material to be Na. 1.41 Mn 0.59 Fe 0.41 [Fe(CN)6] 0.85 • 2.70H2O, with a vacancy content of 15%.

[0065] In this embodiment, the sodium ion concentration in solution A is 5.688 mol / L, and the total sodium ion concentration in solution B is 5.338 mol / L. The total sodium ion concentration of solutions A and B is 5.513 mol / L, which is between 3.4 and 7.4 mol / L. Simultaneously, the total time under nitrogen is 7 hours, less than 12 hours, accounting for less than 50% of the total time, resulting in an increased vacancy content of 13%-20%. Experiments show that by controlling the total sodium ion concentration between 3.4 and 7.4 mol / L (excluding 7.4 mol / L) and the total time under nitrogen less than 50%, this invention can obtain Prussian blue-like crystals with a vacancy content of 13%-20% (excluding 13%).

[0066] Example 3

[0067] Compared to Example 1, the only differences are as follows:

[0068] Step 1: Dissolve 0.012 mol sodium ferrocyanide decahydrate, 0.012 mol sodium citrate dihydrate and 1.68 mol sodium chloride in 240 mL of deionized water to obtain solution A. Keep the temperature of solution A at 60℃.

[0069] Step 2: Dissolve 0.006 mol manganese sulfate monohydrate, 0.006 mol ferrous sulfate heptahydrate, and 1.68 mol sodium chloride in 240 mL of deionized water to obtain solution B. Keep the temperature of solution B at 60℃.

[0070] Figure 5 These are scanning electron microscope images of the materials obtained in this embodiment; Figure 6 The thermogravimetric analysis curve of the material shows that its water of crystallization content is 14.25%. Inductively coupled plasma atomic emission spectrometry (ICP-AES) analysis determined the molecular formula of the material to be Na. 1.44 Mn0.55 Fe 0.45 [Fe(CN)6] 0.86 • 2.50H2O, with a vacancy content of 14%.

[0071] In this embodiment, the sodium ion concentration in solution A is 7.35 mol / L, and the total sodium ion concentration in solution B is 7 mol / L. The total sodium ion concentration of solutions A and B is 7.175 mol / L, which is between 3.4 and 7.4 mol / L. Simultaneously, the total time under nitrogen is 7 hours, less than 12 hours, accounting for less than 50% of the total time, resulting in an increased vacancy content of 13%-20%. Experiments show that by controlling the total sodium ion concentration between 3.4 and 7.4 mol / L (excluding 7.4 mol / L) and the total time under nitrogen less than 50%, this invention can obtain Prussian blue-like crystals with a vacancy content of 13%-20% (excluding 13%).

[0072] Example 4

[0073] Compared to Example 1, the only differences are as follows:

[0074] Step 3: Under a nitrogen atmosphere, solution A is slowly added dropwise to solution B at a rate of 2 ml / min using a peristaltic pump over a period of 2 hours. After the addition is complete, the solution is aged under a nitrogen atmosphere for 22 hours. During the addition and aging process, the reaction temperature is maintained at 60℃ and the stirring speed is 300 r.

[0075] Figure 7 These are scanning electron microscope images of the materials obtained in this embodiment; Figure 8 The thermogravimetric analysis curve of the material shows that its water of crystallization content is 13.77%. Inductively coupled plasma atomic emission spectrometry (ICP-AES) analysis determined the molecular formula of the material to be Na. 1.56 Mn 0.52 Fe 0.48 [Fe(CN)6] 0.89 • 2.06H2O, with a vacancy content of 11%.

[0076] In this embodiment, the sodium ion concentration in solution A is 3.77 mol / L, the total sodium ion concentration in solution B is 3.42 mol / L, and the total sodium ion concentration of solutions A and B is 3.60 mol / L, which is between 3.4 and 7.4 mol / L. Simultaneously, nitrogen gas is used throughout the entire process, with a total time under nitrogen gas of 24 hours (100% of the total time), resulting in a reduction in vacancy content to 7%-13%. Experiments have shown that by controlling the total sodium ion concentration between 3.4 and 7.4 mol / L (excluding 7.4 mol / L) and the total time under nitrogen gas to 100% or greater than or equal to 50%, Prussian blue-like crystals with a vacancy content of 7%-13% (excluding 7%) can be obtained.

[0077] Example 5

[0078] Compared to Example 3, the only differences are as follows:

[0079] Step 3: Under a nitrogen atmosphere, solution A is slowly added dropwise to solution B at a rate of 2 ml / min using a peristaltic pump over a period of 2 hours. After the addition is complete, the solution is aged under a nitrogen atmosphere for 22 hours. During the addition and aging process, the reaction temperature is maintained at 60℃ and the stirring speed is 300 r.

[0080] Figure 9 These are scanning electron microscope images of the materials obtained in this embodiment; Figure 10 The thermogravimetric analysis curve of the material shows a crystal water content of 12.29%. Inductively coupled plasma atomic emission spectrometry (ICP-AES) analysis confirmed the molecular formula of the material as Na. 1.69 Mn 0.51 Fe 0.49 [Fe(CN)6] 0.92 • 2.25H2O, with a vacancy content of 8%.

[0081] In this embodiment, the sodium ion concentration in solution A is 7.35 mol / L, and the total sodium ion concentration in solution B is 7 mol / L. The total sodium ion concentration of solutions A and B is 7.175 mol / L, which is between 3.4 and 7.4 mol / L. Simultaneously, nitrogen gas is used throughout the entire process, with a total time under nitrogen gas of 24 hours (100% of the total time), resulting in a reduction in vacancy content to 7%-13%. Experiments show that by controlling the total sodium ion concentration between 3.4 and 7.4 mol / L (excluding 7.4 mol / L) and the total time under nitrogen gas to 100% or greater than 50%, Prussian blue-like crystals with a vacancy content of 7%-13% (excluding 7%) can be obtained.

[0082] Example 6

[0083] Compared to Example 1, the only differences are as follows:

[0084] Step 1: Dissolve 0.012 mol sodium ferrocyanide decahydrate, 0.012 mol sodium citrate dihydrate and 1.8 mol sodium chloride in 240 mL of deionized water to obtain solution A. Keep the temperature of solution A at 60℃.

[0085] Step 2: Dissolve 0.006 mol manganese sulfate monohydrate, 0.006 mol ferrous sulfate heptahydrate and 1.8 mol sodium chloride in 240 mL of deionized water to obtain solution B. Keep the temperature of solution B at 60℃.

[0086] Figure 11These are scanning electron microscope images of the materials obtained in this embodiment; Figure 12 The thermogravimetric analysis curve of the material shows that its water of crystallization content is 14.26%. Inductively coupled plasma atomic emission spectrometry (ICP-AES) analysis determined the molecular formula of the material to be Na. 1.53 Mn 0.57 Fe 0.43 [Fe(CN)6] 0.88 • 2.56H2O, with a vacancy content of 12%.

[0087] In this embodiment, the sodium ion concentration in solution A is 7.85 mol / L, the total sodium ion concentration in solution B is 7.5 mol / L, and the total sodium ion concentration of solutions A and B is 7.675 mol / L, which is between 7.4 and 10 mol / L. Simultaneously, the total time under nitrogen is 7 hours, less than 12 hours, accounting for less than 50% of the total time, resulting in an increased vacancy content of 7%-13%. Experiments show that by controlling the total sodium ion concentration between 7.4 and 10 mol / L (excluding 10 mol / L) and the total time under nitrogen less than 50%, Prussian blue-like crystals with a vacancy content of 7%-13% (excluding 7%) can be obtained.

[0088] Example 7

[0089] Compared to Example 1, the only differences are as follows:

[0090] Step 1: Dissolve 0.012 mol sodium ferrocyanide decahydrate, 0.012 mol sodium citrate dihydrate and 2.3 mol sodium chloride in 240 mL of deionized water to obtain solution A. Keep the temperature of solution A at 60℃.

[0091] Step 2: Dissolve 0.006 mol manganese sulfate monohydrate, 0.006 mol ferrous sulfate heptahydrate, and 2.3 mol sodium chloride in 240 mL of deionized water to obtain solution B. Keep the temperature of solution B at 60℃.

[0092] Figure 13 These are scanning electron microscope images of the materials obtained in this embodiment; Figure 14 The thermogravimetric analysis curve of the material shows that its water of crystallization content is 14.19%. Inductively coupled plasma atomic emission spectrometry (ICP-AES) analysis determined the molecular formula of the material to be Na. 1.67 Mn 0.57 Fe 0.43 [Fe(CN)6] 0.92 • 2.64H2O, with a vacancy content of 8%.

[0093] In this embodiment, the sodium ion concentration in solution A is 9.93 mol / L, the total sodium ion concentration in solution B is 9.58 mol / L, and the total sodium ion concentration of solutions A and B is 9.755 mol / L, which is between 7.4 and 10 mol / L. Simultaneously, the total time under nitrogen is 7 hours, less than 12 hours, accounting for less than 50% of the total time, resulting in an increased vacancy content of 7%-13%. Experiments show that by controlling the total sodium ion concentration between 7.4 and 10 mol / L (excluding 10 mol / L) and the total time under nitrogen less than 50%, Prussian blue-like crystals with a vacancy content of 7%-13% (excluding 7%) can be obtained.

[0094] Example 8

[0095] Compared to Example 7, the only differences are as follows:

[0096] Step 3: Under a nitrogen atmosphere, solution A is slowly added dropwise to solution B at a rate of 2 ml / min using a peristaltic pump over a period of 2 hours. After the addition is complete, the solution is aged under a nitrogen atmosphere for 22 hours. During the addition and aging process, the reaction temperature is maintained at 60℃ and the stirring speed is 300 r.

[0097] Figure 15 These are scanning electron microscope images of the materials obtained in this embodiment; Figure 16 The thermogravimetric analysis curve of this material shows a water of crystallization content of 10.24%. Inductively coupled plasma atomic emission spectrometry (ICP-AES) analysis confirmed the molecular formula of the material to be Na. 1.85 Mn 0.51 Fe 0.49 [Fe(CN)6] 0.96 • 1.92H2O, with a vacancy content of 4%.

[0098] In this embodiment, the sodium ion concentration in solution A is 9.93 mol / L, the total sodium ion concentration in solution B is 9.58 mol / L, and the total sodium ion concentration of solutions A and B is 9.755 mol / L, which is between 7.4 and 10 mol / L. Simultaneously, nitrogen gas is used throughout the entire process, with a total time under nitrogen gas of 24 hours (100% of the total time), resulting in a reduction in vacancy content to 0-7%. Experiments have shown that by controlling the total sodium ion concentration between 7.4 and 10 mol / L (excluding 10 mol / L) and the total time under nitrogen gas of 100% or greater than or equal to 50%, Prussian blue-like crystals with a vacancy content of 0-7% (excluding 0) can be obtained.

[0099] Example 9

[0100] Compared to Example 7, the only differences are as follows:

[0101] Step 1: Dissolve 0.012 mol sodium ferrocyanide decahydrate, 0.012 mol sodium citrate dihydrate and 2.6 mol sodium chloride in 240 mL of deionized water to obtain solution A. Keep the temperature of solution A at 60℃.

[0102] Step 2: Dissolve 0.006 mol manganese sulfate monohydrate, 0.006 mol ferrous sulfate heptahydrate and 2.6 mol sodium chloride in 240 mL of deionized water to obtain solution B. Keep the temperature of solution B at 60℃.

[0103] Step 3: Under a nitrogen atmosphere, solution A is slowly added dropwise to solution B at a rate of 2 ml / min using a peristaltic pump over a period of 2 hours. After the addition is complete, the solution is aged under a nitrogen atmosphere for 22 hours. During the addition and aging process, the reaction temperature is maintained at 60℃ and the stirring speed is 300 r.

[0104] Figure 17 These are scanning electron microscope images of the materials obtained in this embodiment; Figure 18 The thermogravimetric analysis curve of this material shows a water of crystallization content of 9.54%. Inductively coupled plasma atomic emission spectrometry (ICP-AES) analysis confirmed the molecular formula of the material as Na. 2.04 Mn 0.51 Fe 0.49 [Fe(CN)6] 1.01 • 1.86H₂O, vacancy content is 0. From Figure 18 It can be seen that the crystal structure of the defect-free material in this embodiment is more complete, there is no coordination water, only interstitial water, and the content of crystal water is lower.

[0105] In this embodiment, the sodium ion concentration in solution A is 11.18 mol / L, and the total sodium ion concentration in solution B is 10.83 mol / L. The total sodium ion concentration of solutions A and B is 11 mol / L, which is between 10⁻¹² mol / L. Simultaneously, nitrogen gas is used throughout the entire process, with a total time under nitrogen gas of 24 hours (100% of the total time), resulting in reduced vacancy content and the absence of vacancy-containing crystals. Experiments have shown that by controlling the total sodium ion concentration between 10⁻¹² mol / L and maintaining a total time under nitrogen gas of 100% or greater than 50%, this invention can obtain Prussian blue-like crystals with zero vacancy content.

[0106] Example 10

[0107] Compared to Example 9, the only differences are as follows:

[0108] Step 1: Dissolve 0.012 mol sodium ferrocyanide decahydrate, 0.012 mol sodium citrate dihydrate and 2.8 mol sodium chloride in 240 mL of deionized water to obtain solution A. Keep the temperature of solution A at 60℃.

[0109] Step 2: Dissolve 0.012 mol ferrous sulfate heptahydrate and 2.8 mol sodium chloride in 240 mL of deionized water to obtain solution B. Keep the temperature of solution B at 60℃.

[0110] Figure 19 These are scanning electron microscope images of the materials obtained in this embodiment; Figure 20 The thermogravimetric analysis curve of the material showed a water of crystallization content of 9.21%. Inductively coupled plasma atomic emission spectrometry (ICP-AES) determined the molecular formula of the material to be Na. 2.13 Fe[Fe(CN)6] 1.03 • 1.82H₂O, vacancy content is 0. From Figure 20 It can be seen that the crystal structure of the defect-free material in this embodiment is more complete, there is no coordination water, only interstitial water, and the content of crystal water is lower.

[0111] In this embodiment, the sodium ion concentration in solution A is 12.02 mol / L, the total sodium ion concentration in solution B is 11.67 mol / L, and the total sodium ion concentration of solutions A and B is 11.85 mol / L, which is between 10⁻¹² mol / L. Simultaneously, nitrogen gas is used throughout the entire process, with a total time under nitrogen gas of 24 hours (100% of the total time), resulting in reduced vacancy content and the absence of vacancy-containing crystals. Experiments have shown that by controlling the total sodium ion concentration between 10⁻¹² mol / L and maintaining a total time under nitrogen gas of 100% or greater than 50%, this invention can obtain Prussian blue-like crystals with zero vacancy content.

[0112] As can be seen from the above embodiments, the present invention effectively controls the ion transport rate during the precipitation reaction by adjusting key parameters such as the reaction atmosphere and the amount of PVP added, based on the control of the total sodium ion concentration in solutions A and B. This achieves the goal of precise control of vacancy content and can prepare Prussian blue materials with vacancy content suitable for actual production. It breaks through the technical problem of the difficulty in precisely controlling vacancy content and has good application value.

Claims

1. A method for preparing Prussian blue-like crystals with controllable vacancy content, characterized in that: Includes the following steps: A. Add sodium ferrocyanide, complexing agent and sodium salt to the mixture and mix thoroughly to obtain solution A; B. Add soluble manganese salt, soluble ferrous salt, complexing agent and sodium salt to water, mix thoroughly to obtain solution B; C. Under an inert atmosphere, add solution A dropwise to solution B. After the addition is complete, carry out the aging reaction at 55~65℃ under an inert atmosphere or under an inert atmosphere followed by an air atmosphere. D. After aging, Prussian blue crystals are obtained through cooling, solid-liquid separation, washing and drying. The total sodium ion concentration in solutions A and B is 3.4–12 mol / L. When the total sodium ion concentration in solutions A and B is less than 7.4 mol / L (3.4 mol / L ≤ total concentration of sodium ions in solutions A and B), and the proportion of the inert atmosphere time in step C to the total dropping and aging time is less than 50%, the vacancy content of the Prussian blue-like crystals obtained in step D is 13% < vacancy content ≤ 20%, and the general chemical formula is Na. x1 Mn p1 Fe q1 [Fe(CN)6] 1-y1 □ y1 ·z1H2O, 1.3≤x1<1.5, 0≤p1<1, 0<q1≤1, p1+q1=1, 0.13<y1≤0.2, 2≤z1≤3; When the total sodium ion concentration in solutions A and B is less than 7.4 mol / L and 50% ≤ the proportion of the inert atmosphere time in step C to the total dropping and aging time is less than 100%, or when the total sodium ion concentration in solutions A and B is less than 10 mol / L and 20% ≤ the proportion of the inert atmosphere time in step C to the total dropping and aging time is less than 50%, the vacancy content of the Prussian blue crystals obtained in step D is 7% < vacancy content ≤ 13%, and the general chemical formula is Na. x2 Mn p2 Fe q2 [Fe(CN)6] 1-y2 □ y2 ·z2H2O, 1.5≤x2<1.75, 0≤p2<1, 0<q2≤1, p2+q2=1, 0.07<y2≤0.13, 2≤z2≤3; When the total sodium ion concentration in solutions A and B is less than 10 mol / L (7.4 mol / L ≤ total sodium ion concentration in solutions A and B), and 50% ≤ the proportion of the inert atmosphere time in step C to the total dropping and aging time is less than 100%; or when the total sodium ion concentration in solutions A and B is less than 12 mol / L (10 mol / L ≤ total sodium ion concentration in solutions A and B), and 20% ≤ the proportion of the inert atmosphere time in step C to the total dropping and aging time is less than 50%, the vacancy content of the Prussian blue crystals obtained in step D is 0% < vacancy content ≤ 7%, and the chemical formula is Na. x3 Mn p3 Fe q3 [Fe(CN)6] 1-y3 □ y3 ·z3H2O, 1.75≤x3<2.0, 0≤p3<1, 0<q3≤1, p3+q3=1, 0<y3≤0.07, 1.9≤z3≤2; When the total sodium ion concentration in solutions A and B is ≤12 mol / L (10 mol / L ≤ 12 mol / L), and the inert atmosphere time in step C accounts for ≤100% of the total dropping and aging time, the vacancy content of the Prussian blue crystals obtained in step D is 0%, and the chemical formula is Na. x4 Mn p4 Fe q4 [Fe(CN)6] y4 ·z4H2O, 2.0≤x4≤2.2, 0≤p4<1, 0<q4≤1, p4+q4=1, 1.0≤y4≤1.1, 1.8≤z4≤1.

9.

2. The method for preparing Prussian blue-like crystals with controllable vacancy content according to claim 1, characterized in that: In solution A, the concentration of sodium ferrocyanide is 0.02~0.1 mol / L, the concentration of the complexing agent is 0.02~0.1 mol / L, and the concentration of the sodium salt is 3~12 mol / L.

3. The method for preparing Prussian blue-like crystals with controllable vacancy content according to claim 1, characterized in that: In step A, the complexing agent is selected from at least one of sodium citrate, sodium oxalate, disodium ethylenediaminetetraacetate, or sodium acetate, and the sodium salt is selected from at least one of sodium chloride, sodium sulfate, sodium nitrate, sodium oxalate, or sodium acetate.

4. The method for preparing Prussian blue-like crystals with controllable vacancy content according to claim 1, characterized in that: In solution B, the concentration of soluble manganese salt is 0~0.1 mol / L, the concentration of soluble ferrous salt is 0.01~0.1 mol / L, the concentration of complexing agent is 0~0.1 mol / L, and the concentration of sodium salt is 3~12 mol / L.

5. The method for preparing Prussian blue-like crystals with controllable vacancy content according to claim 1, characterized in that: In step B, the soluble manganese salt is selected from at least one of manganese chloride, manganese sulfate, manganese nitrate, manganese oxalate, or manganese acetate; the soluble ferrous salt is selected from at least one of ferrous chloride, ferrous sulfate, ferrous nitrate, ferrous oxalate, or ferrous acetate; the complexing agent is selected from at least one of sodium citrate, sodium oxalate, disodium ethylenediaminetetraacetate, or sodium acetate; and the sodium salt is selected from at least one of sodium chloride, sodium sulfate, sodium nitrate, sodium oxalate, or sodium acetate.

6. The method for preparing Prussian blue-like crystals with controllable vacancy content according to claim 1, characterized in that: In step C, the volume ratio of solution A to solution B during dropwise addition is 1~2:2~1.

7. The method for preparing Prussian blue-like crystals with controllable vacancy content according to claim 1, characterized in that: In step C, during the dropwise addition, the temperature of solutions A and B is maintained at 55~65℃.

8. The method for preparing Prussian blue-like crystals with controllable vacancy content according to claim 1, characterized in that: In step C, the dropping rate is 1.5~2.5 mL / min; in step C, the stirring speed is 300~600 rpm, and the total time for dropping and aging is 18~30 h.

9. A Prussian blue-like crystal with controllable vacancy content prepared by the preparation method according to any one of claims 1 to 8.

10. The application of the Prussian blue-like crystal with controllable vacancy content as described in claim 9 in sodium-ion secondary batteries.

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