A prussian blue material with core-shell structure, preparation method and application

Abstract

The application relates to a Prussian blue material with a core-shell structure, a preparation method and application, which comprises the following steps: dissolving a divalent transition metal M salt and a chelating agent in a solvent to obtain solution A; dissolving sodium ferrocyanide in a solvent to obtain solution B; mixing solution B with solution A, heating and stirring for a period of time to obtain a suspension C containing Na x MFe(CN)6 and free hexacyanoferrate; pouring the acid solution into the suspension C, heating and stirring for a period of time, and then centrifuging, washing and drying to obtain the Prussian blue material with a core-shell structure MHCF@FeHCF. The core in the application is prepared by a coprecipitation method, and the shell is obtained by spontaneously and slowly growing on the surface of the core through acid treatment on the original solution after a simple coprecipitation reaction, so that the preparation cost and the complexity of the process flow are reduced.

Description

Technical Field

[0001] This application relates to the field of sodium-ion battery electrode materials, and in particular to a core-shell structured Prussian blue material, its preparation method, and its application. Background Technology

[0002] With severe global environmental pollution, countries are calling for cleaner and more renewable energy sources. Energy storage systems are a crucial component, converting and storing renewable energy and releasing it pollution-free when needed. As a promising rechargeable battery, sodium-ion batteries have received increasing attention in large-scale energy storage in recent years due to the low cost, abundant availability, and wide distribution of sodium resources. However, the large diameter of sodium ions limits their diffusion rate in electrodes, resulting in lower capacity and poor rate performance. The larger ion diameter also makes it easier to damage the material's structure, leading to poor cycle performance in sodium-ion batteries. Therefore, finding suitable sodium-ion intercalation electrode materials has become an urgent task.

[0003] Currently, hard carbon materials have a clear advantage in sodium-ion battery anode materials, but a highly advantageous material has yet to be identified in the cathode field, which is the top priority for the commercial application of sodium-ion batteries. Sodium-ion battery cathode materials mainly fall into four categories: polyanionic, layered oxide, organic compound, and Prussian blue.

[0004] Compared to other types of materials, Prussian blue analogues (PBAs) have inexpensive raw materials, are simple to synthesize, and have low costs. They also possess a unique large-gap, open-frame 3D structure, which is beneficial for Na+. + Its rapid transport and long cycle performance make it a promising cathode material for sodium-ion batteries.

[0005] Currently, the main methods for synthesizing PBAs are hydrothermal synthesis, single iron source synthesis, and high-energy ball milling. However, these methods have complex processes, low yields, and are difficult to commercialize.

[0006] In contrast, the coprecipitation method offers a simpler synthesis process and higher yield, making it the most promising method for large-scale production of PBAs. However, due to the rapid precipitation reaction, the synthesized PBAs often have many defects. Therefore, finding a simple and efficient way to improve the coprecipitation synthesis method is crucial for the commercial application of sodium-ion batteries.

[0007] In some related technologies, a monoclinic Prussian blue material core is first prepared by coprecipitation, and then a cubic Prussian blue material shell is prepared by coprecipitation.

[0008] This approach significantly increases the fabrication cost of core-shell PBAs and makes the process more complex. Therefore, simplifying the fabrication method of core-shell PBAs and reducing the cost is a crucial issue worth considering. Summary of the Invention

[0009] This application provides a core-shell structured Prussian blue material, its preparation method, and its application, in order to solve the problems of high preparation cost and complex process flow in related technologies where both the core and shell are prepared by co-precipitation.

[0010] In a first aspect, a method for preparing a core-shell structured Prussian blue material is provided, comprising the following steps:

[0011] A solution A is obtained by dissolving a divalent transition metal M salt and a chelating agent in a solvent;

[0012] Sodium ferrocyanide was dissolved in a solvent to obtain solution B;

[0013] Solution B was mixed with solution A, and the mixture was heated and stirred for a period of time to obtain a solution containing Na. x Suspension C of MFe(CN)6 and free hexacyanoferrate ions;

[0014] The acid solution was poured into suspension C, heated and stirred for a period of time, then centrifuged, washed and dried to obtain the core-shell structured Prussian blue material MHCF@FeHCF.

[0015] In some embodiments, Na, as the kernel x In MFe(CN)6, M is selected from at least one of Co, Mn, Ni, Fe, and Cu, and 1 < x ≤ 2.

[0016] In some embodiments, M is selected from Mn.

[0017] In some embodiments, the chelating agent includes one or more of sodium citrate, EDTA, and IDHA;

[0018] And / or, the solvent is one or more of deionized water, tap water, and mineral water;

[0019] And / or, the acid solution includes one or more of hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, citric acid, and acetic acid;

[0020] And / or, divalent transition metal M salts include one or more of the following: sulfates, nitrates, and halides of divalent transition metal M.

[0021] In some embodiments, the molar ratio of the divalent transition metal M salt to the chelating agent is 1:(1-2);

[0022] And / or, the molar ratio of sodium ferrocyanide to divalent transition metal M salt is (1.5–4):1.

[0023] In some embodiments, the heating temperature after mixing solution B and solution A is 25–80°C, and the stirring time is 5–8 hours.

[0024] In some embodiments, the acid solution is poured into suspension C, heated to 25–80°C, and stirred for 12–48 hours.

[0025] Secondly, a core-shell structured Prussian blue material is provided, which is prepared using any of the above-described methods for preparing core-shell structured Prussian blue materials.

[0026] In some embodiments, the core is MHCF and the shell is FeHCF. The core is a cubic phase with a side length of 1 to 3 μm, and the FeHCF shell is uniformly grown on the surface of the MHCF core with a thickness of 100 to 300 nm.

[0027] Thirdly, a method for preparing a core-shell structured Prussian blue material as described above is provided, and the application of the prepared core-shell structured Prussian blue material in sodium-ion battery electrode materials is provided.

[0028] The beneficial effects of the technical solution provided in this application include:

[0029] This application provides a core-shell structured Prussian blue material, its preparation method, and its application. The core is prepared by a co-precipitation method, while the shell is obtained by acid treatment of the original solution synthesized by a simple co-precipitation reaction, which allows the core to grow spontaneously and slowly on the surface of the core. Therefore, this application reduces the preparation cost and the complexity of the process. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 This is a scanning electron microscope (SEM) image of MnHCF@FeHCF prepared in Example 1 of this application;

[0032] Figure 2 This is a scanning electron microscope (SEM) image of pure MnHCF prepared in Comparative Example 1 of this application.

[0033] Figure 3 This is a scanning electron microscope (SEM) image of pure FeHCF prepared in Comparative Example 2 of this application.

[0034] Figure 4 XRD patterns of MnHCF@FeHCF prepared in Example 1 of this application, MnHCF prepared in Comparative Example 1, and FeHCF prepared in Comparative Example 2.

[0035] Figure 5 XPS full spectrum of MnHCF@FeHCF prepared in Example 1 of this application;

[0036] Figure 6 The Mn 2p energy spectrum of MnHCF@FeHCF prepared in Example 1 of this application;

[0037] Figure 7 The Fe 2p energy spectrum of MnHCF@FeHCF prepared in Example 1 of this application;

[0038] Figure 8 TEM EDS image of MnHCF@FeHCF prepared in Example 1 of this application;

[0039] Figure 9 Cyclic voltammetry curves of the sodium-ion battery assembled from MnHCF@FeHCF prepared in Example 1 of this application during the first four charge-discharge cycles;

[0040] Figure 10 The charge-discharge curves of the sodium-ion battery assembled from MnHCF@FeHCF prepared in Example 1 of this application during the first three charge-discharge cycles.

[0041] Figure 11 The specific capacity-efficiency curve of the sodium-ion battery assembled from MnHCF@FeHCF prepared in Example 1 of this application at a current density of 50 mA / g;

[0042] Figure 12 The specific capacity-efficiency curve of the sodium-ion battery assembled from MnHCF@FeHCF prepared in Example 1 of this application at a high current density of 1A / g. Detailed Implementation

[0043] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0044] This application provides a method for preparing a core-shell structured Prussian blue material, which includes the following steps:

[0045] 101: Dissolve a soluble divalent transition metal M salt and a chelating agent in a solvent to obtain solution A; dissolve sodium ferrocyanide in a solvent to obtain solution B.

[0046] The amount of divalent transition metal M salt and chelating agent can be determined according to actual needs. For example, as a preferred example, the molar ratio of divalent transition metal M salt to chelating agent is 1:(1~2); a better ratio is 1:1.

[0047] The amount of sodium ferrocyanide and divalent transition metal M salt can be determined according to actual needs. For example, as a preferred example, the molar ratio of sodium ferrocyanide to divalent transition metal M salt is (1.5-4):1; a better ratio is 2:1.

[0048] 102: Mix solution B with solution A, heat and stir for a period of time to obtain a solution containing Na. x A suspension of MFe(CN)6 and free hexacyanoferrate ions C.

[0049] In solution B, sodium ferrocyanide is in excess relative to the divalent transition metal M salt. In other words, in suspension C, there is still excess sodium ferrocyanide, and thus there is still unreacted free hexacyanoferrate ions.

[0050] As a preferred example, the heating temperature after mixing solution B and solution A is 25–80°C, and the stirring time is 5–8 hours. Preferably, the heating temperature is 80°C, and the stirring time is 5 hours.

[0051] 103: Pour the acid solution into suspension C, heat and stir for a period of time, then centrifuge, wash and dry to obtain the core-shell structured Prussian blue material MHCF@FeHCF.

[0052] As a preferred example, in step 103, after the acid solution is poured into suspension C, the heating temperature is 25–80°C, and the stirring time is 12–48 h. Preferably, the heating temperature is 80°C, and the stirring time is 24 h.

[0053] The principle of this application is as follows:

[0054] This application employs chelating agents and divalent transition metal M. 2+ Ion binding reduces the amount of free M in the solution. 2+ The ion concentration was adjusted, and then excess sodium ferrocyanide was added to induce a co-precipitation reaction, during which M gradually dissociated and released in solution. 2+ Ions and Fe(CN)6 hexacyanoferrate 4- Slow combination to form a precipitate: 2Na + +M 2+ +Fe(CN)6 4- =Na2MII Fe II (CN)6, of which Na2M II Fe II (CN)6 is the core MHCF, thus yielding suspension C. Due to the excess sodium ferrocyanide, suspension C also contains a certain amount of free hexacyanoferrate ions Fe(CN)6. 4- Finally, acid is added, which reacts with the remaining free Fe(CN)6 hexacyanoferrate ions. 4- Reaction occurs: 6H + +2Na + +2Fe(CN)6 4- =Na2Fe II Fe II (CN)6+6HCN, thereby slowly generating a uniform and dense Na2Fe on the surface of the MHCF core. II Fe II (CN)6. Because ferrous ions are readily oxidized to ferric ions in acidic open systems, some of the initially formed Na₂Fe₂ ions... II Fe II (CN)6 will also be oxidized to NaFe. III Fe II (CN)6, therefore Na2Fe II Fe II (CN)6 and NaFe III Fe II (CN)6 is collectively referred to as the outer shell FeHCF. The final product is Na2M with FeHCF uniformly coated on its surface. II Fe II (CN)6 core-shell structure material, named MHCF@FeHCF.

[0055] As can be seen, the core of this application is prepared by coprecipitation, while the shell is obtained by acid treatment of the original solution synthesized by simple coprecipitation reaction, so that it can grow spontaneously and slowly on the surface of the core. Therefore, this application reduces the preparation cost and the complexity of the process.

[0056] The acid treatment method described in this application produces a shell with high crystallinity and low defects, which can prevent the occurrence of electrode side reactions during electrode cycling. The low sodium content of the shell reduces the material's moisture absorption and facilitates storage.

[0057] It should be noted that, as mentioned earlier, the kernel is Na. x MFe(CN)6, 1<x≤2. Since x=2 is the most perfect crystal, but it is not easy to achieve, based on these practical factors, the reaction equation in the above principle is written as Na2MFe(CN)6 in an ideal state, which is also easier to understand.

[0058] The material prepared by the above method in this application has a core of MHCF and a shell of FeHCF. The core is a micron-sized blocky cubic phase with a side length of 1 to 3 μm. The FeHCF shell is uniformly grown on the surface of the core MHCF and has a thickness of 100 to 300 nm.

[0059] In this application, Na serves as the kernel. x In MFe(CN)6, M is selected from at least one of Co, Mn, Ni, Fe, and Cu, where 1 < x ≤ 2. As a preferred example, M is selected from Mn.

[0060] In this application, the chelating agent can be made of various materials, which can be selected according to actual preparation needs. For example, the chelating agent includes one or more of sodium citrate, ethylenediaminetetraacetic acid (EDTA), and tetrasodium iminodisuccinate (IDHA). For example, as a preferred example, IDHA is used as the chelating agent.

[0061] In this application, the solvent material has a variety of options and can be selected according to the actual preparation needs. For example, the solvent can be one or more of deionized water, tap water, and mineral water.

[0062] In this application, the acid solution can be made of various materials, which can be selected according to actual preparation needs. For example, the acid solution includes one or more of hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, citric acid, and acetic acid.

[0063] For example, as an example, the acid solution is prepared by diluting concentrated hydrochloric acid with deionized water, wherein the volume of concentrated hydrochloric acid is 0.25 to 2 ml per 1 g of sodium ferrocyanide, preferably 1 mL.

[0064] In this application, there are various options for the materials of the divalent transition metal M salt, which can be selected according to actual preparation needs. For example, as an example, the divalent transition metal M salt includes one or more of the sulfate, nitrate and halide of the divalent transition metal M.

[0065] For example, manganese chloride can be chosen.

[0066] Example 1

[0067] A method for preparing a core-shell structured Prussian blue material, comprising the following steps:

[0068] S1. Dissolve 3 mmol of manganese chloride and 3 mmol of IDHA in 100 mL of deionized water to obtain solution A;

[0069] Solution B is obtained by dissolving 6 mmol of sodium ferrocyanide in 100 mL of deionized water.

[0070] S2. Solution B is added dropwise to solution A at a rate of 1 mL / min using a peristaltic pump, and the mixture is heated and stirred at 80 °C for 5 h to obtain a suspension C containing MnHCF precipitate.

[0071] S3. Pour 50 mL of 0.5 mol / L dilute hydrochloric acid into suspension C, heat at 80 °C and stir vigorously for 24 h, wash the reaction precipitate three times by centrifugation with 100 mL of deionized water and 100 mL of anhydrous ethanol respectively, and dry under vacuum at 120 °C for 18 h to obtain the core-shell structured Prussian blue material MnHCF@FeHCF.

[0072] Comparative Example 1

[0073] This comparative example is basically the same as Example 1, except that in step S3, 50 mL of distilled water is poured in to replace 50 mL of 0.5 mol / L dilute hydrochloric acid.

[0074] The obtained sample is denoted as pure phase MnHCF.

[0075] Comparative Example 2

[0076] The cathode material in this comparative example was prepared using the following method:

[0077] Dissolve 6 mmol of sodium ferrocyanide in 200 mL of deionized water, and then pour in 50 mL of 0.5 mol / L dilute hydrochloric acid while stirring.

[0078] The obtained sample is denoted as pure phase FeHCF.

[0079] Figure 1 The image shows a scanning electron microscope (SEM) image of MnHCF@FeHCF prepared in Example 1. It can be seen that the material has a layered structure, with a FeHCF layer uniformly growing and covering the surface of the bulk crystalline MnHCF in a stepped manner.

[0080] Table 1 below shows the ICP-OES test results of MnHCF@FeHCF prepared in Example 1. The test results show that the material has a high sodium content overall, and the Fe / Mn element ratio in the material is 1.47:1. Due to the outer FeHCF shell, the Fe element content is significantly higher than that of Mn.

[0081] Table 1

[0082] Na / Mn Fe / Mn Na / Fe / Mn MnHCF@FeHCF 1.73 1.47 1.73 / 1.47 / 1

[0083] Figure 2 The scanning electron microscope (SEM) image of pure MnHCF prepared for Comparative Example 1 is shown below. Figure 2 It can be seen that without the addition of hydrochloric acid, the generated MnHCF is a flat cube with no obvious stepped coating layer on the surface as seen in Example 1.

[0084] Figure 3 This is a scanning electron microscope (SEM) image of pure FeHCF prepared for Comparative Example 2. This image shows that FeHCF also has a cubic structure similar to MnHCF.

[0085] Figure 4 The XRD patterns of MnHCF@FeHCF prepared in Example 1, MnHCF prepared in Comparative Example 1, and FeHCF prepared in Comparative Example 2 are shown. The figures show that MnHCF@FeHCF matches the theoretical XRD diffraction peaks of MnHCF and FeHCF, and has a single crystal phase, indicating that this material has good crystallinity.

[0086] Figure 5 The XPS full spectrum of MnHCF@FeHCF prepared in Example 1 shows that it mainly contains Na, Fe, Mn, N, O and C elements.

[0087] Figure 6 The Mn 2p energy spectrum of MnHCF@FeHCF prepared in Example 1 shows that the binding energies of the two Mn 2p orbitals are 641.6 eV and 653.8 eV, respectively.

[0088] Figure 7 The Fe 2p energy spectrum of MnHCF@FeHCF prepared in Example 1 shows that the binding energies of the two Fe 2p orbitals are 708.7 eV and 721.5 eV, respectively.

[0089] Figure 8 The TEM EDS image of MnHCF@FeHCF prepared in Example 1 shows that the material has a distinct core-shell structure, with a high Mn content in the core and abundant Fe, Na, C, and N elements in the shell. This confirms the core-shell structure of the MnHCF@FeHCF material, and the Na, C, and N element concentration distribution indicates that the shell material has better crystallinity and a denser structure.

[0090] Electrochemical characterization was performed on the above-described embodiments and comparative examples.

[0091] The methods for electrochemical characterization are as follows:

[0092] The positive electrode materials prepared in Example 1, Comparative Examples 1 and 2, conductive carbon black, and polyvinylidene fluoride were mixed uniformly at a mass ratio of 7:2:1 and dispersed in N-methyl-2-pyrrolidone (NMP) solvent to form a uniform slurry. This slurry was then coated onto aluminum foil using a doctor blade or a four-sided coating applicator to form a positive electrode sheet. Finally, CR2016 coin cells were assembled in a glove box, and the electrochemical performance of the assembled cells was monitored using a Blue Battery testing system.

[0093] Figure 9 The figure shows the cyclic voltammetry (CV) curves of the sodium-ion battery assembled from MnHCF@FeHCF prepared in Example 1 during the first four charge-discharge cycles. The figure shows the peak generated by the formation of the SEI film during the first discharge, as well as the positions of the two oxidation peaks and two reduction peaks corresponding to the charge and discharge cycles, respectively.

[0094] Figure 10 The charge-discharge curves of the sodium-ion battery assembled from MnHCF@FeHCF prepared in Example 1 during the first three charge-discharge cycles clearly show two voltage plateaus corresponding to both charging and discharging. These plateau voltages correspond one-to-one with the peak potentials shown in the cyclic voltammetry curves, which together prove the reliability of the material's reaction mechanism.

[0095] Figure 11 The specific capacity-efficiency curve of the sodium-ion battery assembled from MnHCF@FeHCF prepared in Example 1 at a current density of 50 mA / g shows good cycle stability and a specific capacity of up to 108 mAh / g.

[0096] Figure 12 Sodium-ion batteries assembled from MnHCF@FeHCF prepared in Example 1, pure MnHCF prepared in Comparative Example 1, and pure FeHCF prepared in Comparative Example 2 exhibit excellent long-cycle performance at a high current density of 1 A / g, maintaining a specific capacity of up to 78.7 mAh / g after 350 cycles.

[0097] Experimental results show that the sodium-ion battery assembled from MnHCF@FeHCF prepared in Example 1 exhibits good cycle performance and high specific capacity, maintaining a high specific capacity of 78.7 mAh / g after 350 cycles at a current density of 1 A / g. In contrast, MnHCF, used as the experimental precursor, only retained a low specific capacity of 59 mAh / g after 350 cycles at a current density of 1 A / g.

[0098] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for preparing a core-shell structured Prussian blue material, characterized in that, It includes the following steps: A solution A is obtained by dissolving a divalent transition metal M salt and a chelating agent in a solvent; Sodium ferrocyanide was dissolved in a solvent to obtain solution B; Solution B was mixed with solution A, and the mixture was heated and stirred for a period of time to obtain a solution containing Na. x Suspension C of MFe(CN)6 and free hexacyanoferrate ions; The acid solution was poured into suspension C, heated and stirred for a period of time, centrifuged, washed and dried to obtain the core-shell structured Prussian blue material MHCF@FeHCF; Na as the kernel x In MFe(CN)6, M is selected from at least one of Co, Mn, Ni, Fe, and Cu, and 1 < x ≤ 2.

2. The method for preparing the core-shell structured Prussian blue material as described in claim 1, characterized in that: M is selected from Mn.

3. The method for preparing the core-shell structured Prussian blue material as described in claim 1, characterized in that: The chelating agent includes one or more of sodium citrate, EDTA, and IDHA; And / or, the solvent is one or more of deionized water, tap water, and mineral water; And / or, the acid solution includes one or more of hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, citric acid, and acetic acid; And / or, divalent transition metal M salts include one or more of the following: sulfates, nitrates, and halides of divalent transition metal M.

4. The method for preparing the core-shell structured Prussian blue material as described in claim 1, characterized in that: The molar ratio of divalent transition metal M salt to chelating agent is 1:(1~2); And / or, the molar ratio of sodium ferrocyanide to divalent transition metal M salt is (1.5–4):

1.

5. The method for preparing the core-shell structured Prussian blue material as described in claim 1, characterized in that: The heating temperature after mixing solution B and solution A is 25-80℃, and the stirring time is 5-8h.

6. The method for preparing the core-shell structured Prussian blue material as described in claim 1, characterized in that: Pour the acid solution into suspension C, heat it to 25–80°C, and stir for 12–48 hours.

7. A core-shell structured Prussian blue material, characterized in that: It is prepared using the method for preparing Prussian blue material with a core-shell structure as described in any one of claims 1 to 6.

8. The Prussian blue material with a core-shell structure as described in claim 7, characterized in that: Its core is MHCF and its shell is FeHCF. The core is a cubic phase with a side length of 1 to 3 μm. The FeHCF shell is uniformly grown on the surface of the MHCF core and has a thickness of 100 to 300 nm.

9. The application of a core-shell structured Prussian blue material prepared by a method according to any one of claims 1 to 6 in sodium-ion battery electrode materials.

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