Method for preparing low-defect Prussian blue

Abstract

A method for preparing low-defect Prussian blue belongs to the technical field of new energy, and specifically comprises the following steps: step 1, preparing a sodium ferrocyanide solution marked as a solution A, preparing a complexing solution containing transition metal ions I marked as a solution B1, and preparing a complexing solution containing transition metal ions II marked as a solution B2; step 2, sequentially and alternately adding the solution B1 and the solution B2 together with the solution A in equal quantity into a pre-added solution, uniformly mixing, and carrying out a co-precipitation reaction; 3, after the reaction is finished, lower-layer precipitates are subjected to centrifugal washing and vacuum drying, low-defect Prussian blue is obtained, and the transition metal ions I comprise one or a combination of two of manganese ions and ferrous ions; the transition metal ions II comprise one or a combination of manganese ions and ferrous ions, the manganese ions and the ferrous ions in the transition metal ions I and the transition metal ions II are mixed in any proportion, but the proportions of iron and manganese in the transition metal ions I and the transition metal ions II are different.

Description

Technical Field

[0001] The invention belongs to the field of new energy technology, relates to the field of sodium ion battery technology, and specifically relates to a method for preparing low-defect Prussian blue. Background Art

[0002] Nowadays, with the vigorous development of new energy and the extensive use of electronic devices, a low-cost battery is needed to meet the energy storage needs. Sodium-ion batteries can be used as the next generation of battery technology due to their abundant resources and excellent electrochemical performance. The main cathode materials for sodium-ion batteries are transition metal oxides, polyanion compounds, and Prussian blue analogs. Among them, Prussian blue has the advantages of low cost, high energy density, good environmental performance, excellent rate performance and low temperature performance, and is expected to occupy a place in the future sodium-ion battery cathode material market. Therefore, exploring the performance of Prussian blue has become a current research hotspot.

[0003] Prussian blue has a three-dimensional open framework and is generally prepared by coprecipitation. However, due to the rapid reaction rate, vacancy defects will be generated, thereby forming coordinated water. The coordinated water will hinder the diffusion of sodium ions during the charge and discharge process, resulting in a low specific capacity. Generally, a complexing agent is added during the reaction to reduce the reaction rate, and low-defect Prussian blue can be prepared. However, to further improve the cycle performance, methods such as doping and coating are required. Among the many doped transition metal elements, the doping of Mn and Fe is the first choice for Prussian blue. How to reasonably arrange the doping of Mn and Fe elements remains a question.

[0004] In addition, controlling the reaction rate at a low level causes the particle size of Prussian blue to grow larger, especially for Prussian blue with high manganese content. Too large a particle size is not conducive to the diffusion of sodium ions, and also has a great impact on the electrode preparation process, such as the tap density and the sedimentation rate of the material during homogenization. Adjusting the reaction rate can control the particle size, and adjusting factors such as temperature, drip rate, and concentration is essentially adjusting the reaction rate. Increasing the reaction rate can reduce the particle size, but at the same time it will introduce more vacancy defects, which will affect the electrochemical performance. How to reduce the particle size while keeping the temperature, drip rate, and concentration conditions unchanged has become a process problem. Summary of the invention

[0005] In order to solve the problem of how to reduce the particle size of the particles under the condition of unchanged temperature, dripping rate and concentration in the process of preparing Prussian blue as described in the background art, the present invention provides a method for preparing low-defect Prussian blue, which can arrange the doping of transition metal elements more reasonably and further improve the cycle stability. In addition, under the condition of keeping the concentration, temperature, dripping rate and other conditions unchanged, the purpose of reducing the particle size of Prussian blue particles can be achieved by designing a scheme of alternating addition.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for preparing low-defect Prussian blue comprises the following steps:

[0008] Step 1: prepare a sodium ferrocyanide solution, which is referred to as solution A; prepare a complex solution containing transition metal ion I, which is referred to as solution B1; prepare a complex solution containing transition metal ion II, which is referred to as solution B2;

[0009] Step 2: Alternately add solution B1 and solution B2 together with solution A in equal amounts into the pre-added liquid and mix them evenly to cause a coprecipitation reaction;

[0010] Step 3: After the reaction is completed, the lower precipitate is centrifuged and washed and vacuum dried to obtain low-defect Prussian blue; the transition metal ion I includes one or a combination of manganese ions and ferrous ions; the transition metal ion II includes one or a combination of manganese ions and ferrous ions, and the manganese ions and ferrous ions in the transition metal ions I and transition metal ions II are mixed in any proportion, but the iron-manganese ratios in the transition metal ions I and transition metal ions II are different.

[0011] Preferably, when preparing low-defect manganese-based Prussian blue, the transition metal ion I is a manganese ion, the transition metal ion II includes a manganese ion and a ferrous ion, or the transition metal ion I is a manganese ion and a ferrous ion, and the transition metal ion II is a manganese ion; wherein the molar ratio of the manganese ion to the ferrous ion is set according to the product design.

[0012] Preferably, when preparing low-defect manganese-based Prussian blue, the transition metal ion I includes manganese ion and ferrous ion, and the transition metal ion II includes manganese ion and ferrous ion, and the molar ratio of the manganese ion to the ferrous ion is set according to product design.

[0013] Preferably, when preparing low-defect iron-based Prussian blue, the transition metal ion I is a ferrous ion, the transition metal ion II includes a ferrous ion and a manganese ion, or the transition metal ion I includes a ferrous ion and a manganese ion, the transition metal ion II includes a ferrous ion, and the molar ratio of the manganese ion to the ferrous ion is set according to the product design.

[0014] Preferably, when preparing low-defect iron-based Prussian blue, the transition metal ion I is manganese ion and ferrous ion, the transition metal ion II includes manganese ion and ferrous ion, and the molar ratio of the manganese ion to the ferrous ion is set according to product design.

[0015] Furthermore, in step 1, the concentration of sodium ferrocyanide in solution A, the concentration of transition metal ion I in solution B1, and the concentration of transition metal ion II in solution B2 are all 0.1 to 0.625 mol / L.

[0016] Furthermore, the concentration of the complexing agent in solution B1 and solution B2 is 0.4-1.5 mol / L.

[0017] Furthermore, in step 1, the complexing agent selected in solution B1 and solution B2 includes a combination of one or more of sodium citrate, EDTA and HEDP.

[0018] Furthermore, in step 2, the pre-added liquid is deionized water, and the pre-added liquid also includes a complexing agent, and the concentration of the complexing agent is 0 to 1.5 mol / L.

[0019] Furthermore, in step 2, solution B1 and solution B2 are alternated at least three times.

[0020] Furthermore, in step three, the vacuum drying temperature is 120-250° C. and the time is 2-12 h.

[0021] The chemical formula of the prepared Prussian blue is Na x M A [Fe(CN)6] y ·zH2O,M A is one or more transition metal elements, wherein y>0.7, 2>x>1.4, 4>z>2. The composition of the prepared Prussian blue is relatively uniform.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] Prussian blue with high iron content is more inclined to nucleate when generated, while Prussian blue with high manganese content is more inclined to grow when generated. When using this difference to alternately add components with different iron-manganese ratios, since one of the components has a higher iron content, the number of nuclei will be greater than that of a homogeneous mixture, and accordingly, the particle size will decrease. In addition, the number of alternations is different, and the amount of each component added is also different. When the amount of the component with high iron content is more, the number of nuclei will increase accordingly, and the particle size will decrease. Therefore, adjusting the number of alternations can achieve the purpose of adjusting the particle size. The unit cell parameters of Prussian blue with different iron-manganese ratios are different. When the iron-manganese ratio in the solution changes continuously, it is not conducive to crystal growth.

[0024] The invention can destroy the long-range order of Prussian blue, relieve the volume strain in the charge and discharge process, and improve the long-cycle performance by only changing the reaction process in the process of synthesizing Prussian blue and alternately adding transition metal ion solutions containing different components into the reactor. The particle size of Prussian blue can be controlled by adjusting the components of the transition metal ion solution. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a cycle performance diagram of the sodium ion battery positive electrode prepared in Example 1, Example 2 and Comparative Example 1. DETAILED DESCRIPTION

[0026] The technical solution of the present invention will be clearly and completely described below in conjunction with the drawings and embodiments. Obviously, the described embodiments are only part of the embodiments of the invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0027] Embodiment 1:

[0028] A method for preparing low-defect manganese-based Prussian blue comprises the following steps:

[0029] (1) Dissolve sodium ferrocyanide in deionized water to prepare 600 mL of a 0.2 mol / L sodium ferrocyanide solution, referred to as solution A;

[0030] (2) preparing 300 mL of a complexing solution of transition metal ion I with a concentration of 0.2 mol / L, denoted as solution B1, wherein the transition metal ion I is a manganese ion and the concentration of the complexing agent is 1 mol / L;

[0031] (3) Prepare 300 mL of a complex solution of transition metal ion II with a concentration of 0.2 mol / L, denoted as solution B2, wherein the transition metal ion II includes manganese ions and ferrous ions, with a molar ratio of Mn 2+ :Fe 2+ =8:2, the concentration of complexing agent is 1 mol / L;

[0032] (4) preparing 600 mL of complexing agent solution as a pre-addition solution, wherein the concentration of the complexing agent is 1 mol / L;

[0033] (5) At 25°C, solution B1 and solution B2 were added to the pre-added liquid alternately and simultaneously with solution A at a rate of 1.5 mL / min. Solution B2 was added 6 times and solution B1 was added 5 times until all the solutions were added to the pre-added liquid. The mixture was stirred for 16 h, the lower precipitate was washed by centrifugation, and then dried under vacuum at 120°C for 12 h to obtain Na2Mn 0.9 Fe 0.1 [Fe(CN)6] (denoted as MFPB1).

[0034] MFPB1 was tested as a cathode for sodium-ion batteries.

[0035] Embodiment 2:

[0036] A method for preparing low-defect manganese-based Prussian blue comprises the following steps:

[0037] (1) Dissolve sodium ferrocyanide in deionized water to prepare 600 mL of a 0.2 mol / L sodium ferrocyanide solution, referred to as solution A;

[0038] (2) preparing 300 mL of a complexing solution of transition metal ion I with a concentration of 0.2 mol / L, denoted as solution B1, wherein the transition metal ion I is a manganese ion and the concentration of the complexing agent is 1 mol / L;

[0039] (3) Prepare 300 mL of a complex solution of transition metal ion II with a concentration of 0.2 mol / L, denoted as solution B2, wherein the transition metal ion II includes manganese ions and ferrous ions, with a molar ratio of Mn 2+ :Fe 2+ =7:3, the complexing agent concentration is 1 mol / L.

[0040] (4) preparing 600 mL of complexing agent solution as a pre-addition solution, wherein the concentration of the complexing agent is 1 mol / L;

[0041] (5) At 25°C, solution B1 and solution B2 were added to the pre-added liquid alternately at the same time as solution A at a rate of 1.5 mL / min. Solution B1 was added 6 times and solution B2 was added 5 times until all the solutions were added to the pre-added liquid. The mixture was stirred for 16 h, the lower precipitate was washed by centrifugation, and then dried under vacuum at 120°C for 12 h to obtain Na2Mn 0.9 Fe 0.1 [Fe(CN)6] (denoted as MFPB2).

[0042] MFPB2 was tested as a cathode for sodium-ion batteries.

[0043] Embodiment 3:

[0044] A method for preparing low-defect iron-based Prussian blue comprises the following steps:

[0045] (1) Dissolve sodium ferrocyanide in deionized water to prepare 600 mL of a 0.2 mol / L sodium ferrocyanide solution, referred to as solution A;

[0046] (2) Prepare 300 mL of a complex solution of transition metal ion I with a concentration of 0.2 mol / L, denoted as solution B1, wherein the transition metal ion I includes manganese ions and ferrous ions, with a molar ratio of Mn 2+ :Fe 2+ =0.5:9.5, the concentration of complexing agent is 1 mol / L;

[0047] (3) Prepare 300 mL of a complex solution of transition metal ion II with a concentration of 0.2 mol / L, denoted as solution B2, wherein the transition metal ion II includes manganese ions and ferrous ions, with a molar ratio of Mn 2+ :Fe 2+ =2.5:7.5, the concentration of complexing agent is 1 mol / L;

[0048] (4) preparing 600 mL of complexing agent solution as a pre-addition solution, wherein the concentration of the complexing agent is 1 mol / L;

[0049] (5) At 25°C, solution B1 and solution B2 were added to the pre-added liquid alternately at the same time as solution A at a rate of 1.5 mL / min. Solution B1 was added 10 times and solution B2 was added 10 times until all the solutions were added to the pre-added liquid. The mixture was stirred for 16 h, the lower precipitate was washed by centrifugation, and then dried under vacuum at 120°C for 12 h to obtain Na2Mn 0.1 Fe 0.9 [Fe(CN)6] (denoted as MFPB3).

[0050] MFPB3 was tested as a cathode for sodium-ion batteries.

[0051] Comparative Example 1:

[0052] A method for preparing Prussian blue comprises the following steps:

[0053] (1) Dissolve sodium ferrocyanide in deionized water to prepare 600 mL of a 0.2 mol / L sodium ferrocyanide solution, referred to as solution A;

[0054] (2) preparing 600 ml of a 0.2 mol / L transition metal ion III complex solution, referred to as solution C, wherein the transition metal ion III includes manganese ions and ferrous ions, with a molar ratio of Mn:Fe=9:1, and a complexing agent concentration of 1 mol / L;

[0055] (3) preparing 600 mL of complexing agent solution as a pre-addition solution, wherein the concentration of the complexing agent is 1 mol / L;

[0056] (4) At 25°C, solution C and solution A were added to the pre-added solution at the same time and in equal amounts at a rate of 1.5 mL / min, stirred for 16 h, the lower precipitate was centrifuged and washed, and then vacuum dried at 120°C for 12 h to obtain Na2Mn 0.9 Fe 0.1 [Fe(CN)6] (denoted as MFPB4). MFPB4 was tested as the positive electrode of sodium ion battery.

[0057] Comparative Example 2:

[0058] A method for preparing Prussian blue comprises the following steps:

[0059] (1) Dissolve sodium ferrocyanide in deionized water to prepare 600 mL of a 0.2 mol / L sodium ferrocyanide solution, referred to as solution A;

[0060] (2) preparing 600 ml of a 0.2 mol / L transition metal ion VI complex solution, referred to as solution D, wherein the transition metal ion VI includes manganese ions and ferrous ions, with a molar ratio of Mn:Fe=1:9, and a complexing agent concentration of 1 mol / L;

[0061] (3) preparing 600 mL of complexing agent solution as a pre-addition solution, wherein the concentration of the complexing agent is 1 mol / L;

[0062] (4) At 25°C, solution D and solution A were added to the pre-added solution at the same time and in equal amounts at a rate of 1.5 mL / min, stirred for 16 h, the lower precipitate was centrifuged and washed, and then vacuum dried at 120°C for 12 h to obtain Na2Mn 0.1 Fe 0.9 [Fe(CN)6] (denoted as MFPB5). MFPB5 was tested as the positive electrode of sodium ion battery.

[0063]

[0064]

[0065] in conclusion:

[0066] like Figure 1 As shown, compared with comparative example 1, the cycle performance of the two embodiments at the 150th cycle is improved by about 1%, the long cycle performance is significantly improved, and the particle size is reduced. Therefore, the alternating design adopted in the present invention has a significant improvement in the cycle performance of Prussian blue (the capacity retention rate of MFPB4 in comparative example 1 is 80% at about 1200 cycles, and the capacity retention rate of MFPB1 in embodiment 1 is 80% at about 1500 cycles); the particle size can be adjusted by adjusting the proportion of transition metal ions.

[0067] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A method for preparing low-defect Prussian blue, characterized in that: The following steps are involved: Step 1: prepare a sodium ferrocyanide solution, which is referred to as solution A; prepare a complex solution containing transition metal ion I, which is referred to as solution B1; prepare a complex solution containing transition metal ion II, which is referred to as solution B2; Step 2: Alternately add solution B1 and solution B2 together with solution A in equal amounts into the pre-added liquid and mix them evenly to cause a coprecipitation reaction; Step 3: After the reaction is completed, the lower precipitate is centrifuged and washed and vacuum dried to obtain low-defect Prussian blue, wherein the transition metal ion I includes one or a combination of manganese ions and ferrous ions; the transition metal ion II includes one or a combination of manganese ions and ferrous ions, and the manganese ions and ferrous ions in the transition metal ions I and transition metal ions II are mixed in any proportion, but the iron-manganese ratios in the transition metal ions I and transition metal ions II are different.

2. A method for preparing low-defect Prussian blue according to claim 1, characterized in that: When preparing low-defect manganese-based Prussian blue, the transition metal ion I is a manganese ion, the transition metal ion II includes a manganese ion and a ferrous ion, or the transition metal ion I is a manganese ion and a ferrous ion, and the transition metal ion II is a manganese ion; wherein the molar ratio of the manganese ion to the ferrous ion is set according to the product design.

3. A method for preparing low-defect Prussian blue according to claim 1, characterized in that: When preparing low-defect manganese-based Prussian blue, the transition metal ion I includes manganese ion and ferrous ion, and the transition metal ion II includes manganese ion and ferrous ion. The molar ratio of manganese ion to ferrous ion is set according to product design.

4. A method for preparing low-defect Prussian blue according to claim 1, characterized in that: When preparing low-defect iron-based Prussian blue, the transition metal ion I is a ferrous ion, the transition metal ion II includes a ferrous ion and a manganese ion, or the transition metal ion I includes a ferrous ion and a manganese ion, the transition metal ion II includes a ferrous ion, and the molar ratio of the manganese ion to the ferrous ion is set according to the product design.

5. The method for preparing low-defect Prussian blue according to claim 1, characterized in that: When preparing low-defect iron-based Prussian blue, the transition metal ion I is manganese ion and ferrous ion, the transition metal ion II includes manganese ion and ferrous ion, and the molar ratio of manganese ion and ferrous ion is set according to product design.

6. A method for preparing low-defect Prussian blue according to claim 1, characterized in that: In step 1, the concentration of sodium ferrocyanide in solution A, the concentration of transition metal ion I in solution B1, and the concentration of transition metal ion II in solution B2 are all 0.1 to 0.625 mol / L.

7. A method for preparing low-defect Prussian blue according to claim 1, characterized in that: The concentration of the complexing agent in solution B1 and solution B2 is 0.4-1.5 mol / L.

8. A method for preparing low-defect Prussian blue according to claim 1, characterized in that: In step 1, the complexing agent selected in solution B1 and solution B2 includes a combination of one or more of sodium citrate, EDTA and HEDP.

9. A method for preparing low-defect Prussian blue according to claim 1, characterized in that: In step 2, the pre-added liquid is deionized water, and the pre-added liquid also includes a complexing agent, and the concentration of the complexing agent is 0 to 1.5 mol / L.

10. The method for preparing low-defect Prussian blue according to claim 1, characterized in that: In step 3, the vacuum drying temperature is 120-250° C. and the time is 2-12 hours.

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