Preparation method of low-defect low-water-content Prussian white type potassium ion battery positive electrode material

Abstract

The invention discloses a preparation method for efficiently preparing a low-defect low-water-content Prussian white type potassium ion battery positive electrode material, which comprises the following steps: introducing chelating agents with different proportions into synthesis of a Prussian white type material, and carrying out coprecipitation to obtain the high-quality low-defect low-water-content Prussian white type positive electrode material on a large scale. Wherein the chelating agent slows down the precipitation growth rate in the precipitation reaction process, and can provide additional potassium ions at the same time. The preparation method provided by the invention is simple in synthesis process and suitable for batch and large-scale production of the high-quality, low-defect and low-water-content Prussian white potassium ion positive electrode material.

Description

Technical Field

[0001] The invention belongs to the technical field of positive electrode materials for potassium ion batteries, and in particular relates to a method for efficiently preparing a low-defect and low-water-content Prussian white type potassium ion battery positive electrode material. Background Art

[0002] Compared with the scarce lithium element, the sodium and potassium elements are abundant and inexhaustible. The development of potassium ion batteries and sodium ion batteries is a very promising research work. + Relative to Na + With a higher standard potential, when matched with the negative electrode to form a full battery, the potassium ion battery will provide a higher voltage platform, thereby increasing the energy density of the battery. Therefore, the potassium ion battery is considered to be a low-cost high-voltage battery system.

[0003] Iron-based Prussian white analog K x Fe[Fe(CN) 6 As a positive electrode material for potassium ion batteries, it has a theoretical capacity of 156 mAh / g. Its three-dimensional open dioctahedral skeleton ensures the adaptability of volume change during potassium ion insertion and extraction, which makes K x Fe[Fe(CN) 6 ]It has better rate performance, cycle stability, etc. than other positive electrode materials (including polyanion compounds and layered oxides, etc.).

[0004] The preparation of such Prussian white cathode materials is generally synthesized by direct precipitation of transition metal cations and metal hexacyanide anions from aqueous solutions. This will introduce defects and vacancies in the lattice, especially [Fe(CN) 6 ] 4- Vacancies. These fatal defects not only reduce the active sites, but also reduce the rate / cycling performance. To alleviate this severe problem, the use of chelating agents has become the most widely used strategy because they have a strong coordination effect with metal ions. Potassium citrate (KCA), as one of the mainstream chelating agents, can improve the crystallinity of Prussian white cathode materials. However, the chelating strength between the citric acid ligand and the metal ions is too weak, and the prepared cathode materials contain a large number of crystal defects; usually, an excess amount of citrate (e.g., KCA / K 4 Fe(CN) 6 The feed ratio is >5:1), which may cause cost issues and pollution footprint. In addition, potassium ethylenediaminetetraacetate (EDTA-2K) has also been explored as another chelating agent. Unfortunately, a large number of transition metal ion vacancies are usually formed in the resulting Prussian white analogs. In summary, the Prussian white analog positive electrode materials obtained by the above methods cannot be prepared on a large scale with high quality. Summary of the invention

[0005] The present invention uses a double chelating agent in the process of material synthesis. The chelating agent can slow down the rate of precipitation and crystallization, and also serves as an additional potassium source to provide a potassium-rich environment for the material during the precipitation reaction. The present invention can be performed by co-precipitating the required compound raw material and the added double chelating agent. The preparation method has the characteristics of simple process, easy reaction control, low cost, and can be prepared in large quantities continuously, which is very suitable for large-scale production.

[0006] The technical problem to be solved by the present invention is to overcome the deficiencies and defects mentioned in the above background technology. The present invention provides a simple and large-scale method for preparing a Prussian white analog positive electrode material for potassium ion batteries by using a double chelating agent during the material synthesis process.

[0007] The object of the present invention is achieved through the following steps:

[0008] (1) mixing a soluble divalent iron salt, a chelating agent, ascorbic acid and deionized water in corresponding proportions to obtain a solution A, wherein the molar ratio of potassium citrate to dipotassium ethylenediaminetetraacetate is 1:(0-3); wherein the chelating agent controls the crystallization rate to inhibit the formation of defects and provides additional potassium ions for the reaction;

[0009] (2) mixing potassium ferrocyanide and deionized water to obtain solution B;

[0010] (3) pumping the solution B obtained in step (2) into the solution A through a peristaltic pump to carry out a coprecipitation reaction, and after a period of reaction, carrying out an aging reaction at room temperature to obtain a precursor;

[0011] (4) The precursor aged in step (3) is centrifuged, washed and dried in sequence to obtain a Prussian white potassium ion battery positive electrode material.

[0012] In particular, the divalent iron salt in step (1) can be selected from one or more of ferrous sulfate, ferrous chloride, ferrous nitrate, ferrous oxalate, ferrous stearate, ferrous succinate, and ferrous gluconate; the chelating agent can be selected from one or more of ethylenediaminetetraacetic acid, dipotassium ethylenediaminetetraacetic acid, nitrilotriacetic acid, diethylenetriaminepentaacetic acid, N-hydroxyethylethylaminetriacetic acid, citric acid, potassium citrate, tartaric acid, and potassium tartrate.

[0013] Particularly, the molar ratio of the divalent iron salt to potassium ferrocyanide is 1:9 to 9:1; and the volume ratio of solution A to solution B is 1:9 to 9:1.

[0014] Particularly, the ratio of the sum of the molar amounts of potassium citrate and dipotassium ethylenediaminetetraacetate to the molar amount of potassium ferrocyanide in the chelating agent is 1:1; and the molar ratio of potassium citrate to dipotassium ethylenediaminetetraacetate is 9:1 to 1:9.

[0015] Particularly, the molar ratio of the divalent iron salt to potassium ferrocyanide is 1:4 to 4:1; and the volume ratio of solution A to solution B is 1:4 to 4:1.

[0016] Particularly, the molar ratio of potassium citrate to dipotassium ethylenediaminetetraacetate is 1:4 to 4:1.

[0017] In particular, argon is introduced into the reactions of step (1) and step (3) as a protective gas to prevent the divalent iron salt from being oxidized.

[0018] In particular, the coprecipitation reaction temperature in step (3) is 25° C., the reaction time is 2 h, and the aging time is 12 h.

[0019] In particular, in step (4), the rotation speed of the centrifuge is 9000 rpm, the centrifugation time is 6 min, the drying temperature is 120° C., and the drying time is 12 h. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0021] Figure 1 KCA prepared by co-precipitation reaction by adding different ratios of chelating agent (KCA:EDTA-2K=1:0, 3:1, 1:1, 1:3, 0:1; named KCA, KCA75, KCA50, KCA25, EDTA-2K, respectively) in Example 1 of the present invention x Fe[Fe(CN) 6 ]X-ray diffraction pattern of Prussian white analogue cathode material;

[0022] Figure 2 K prepared by coprecipitation reaction in Example 1 of the present invention by adding potassium citrate and dipotassium ethylenediaminetetraacetate in a molar ratio of 3:1 x Fe[Fe(CN) 6 ]Thermogravimetric curve of Prussian white analogue positive electrode material;

[0023] Figure 3 K prepared in Example 1 of the present invention x Fe[Fe(CN)6 ]Fe K-edge FT-EXAFS oscillation curve of Prussian white analog cathode material;

[0024] Figure 4 K prepared in Example 1 of the present invention x Fe[Fe(CN) 6 ] Cycling performance diagram in potassium ion battery; DETAILED DESCRIPTION

[0025] In order to facilitate the understanding of the present invention, the present invention will be described more comprehensively and meticulously below in conjunction with the accompanying drawings and preferred embodiments of the present invention, but the protection scope of the present invention is not limited to the following specific embodiments.

[0026] Unless otherwise defined, all professional terms used hereinafter have the same meaning as those generally understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention. The preferred implementation methods and materials described herein are for demonstration purposes only. Several improvements and modifications may be made without departing from the principles of the embodiments of the present invention, and these improvements and modifications are also considered to be within the scope of protection of the present invention.

[0027] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0028] A specific implementation of the present invention is to add a double chelating agent during the material synthesis process to prepare a high-quality, low-defect, low-water content Prussian white potassium ion positive electrode material by a coprecipitation method.

[0029] Example 1

[0030] In this embodiment, K was prepared by adjusting different proportions of chelating agents (the molar ratio of potassium citrate to dipotassium ethylenediaminetetraacetate was 1:0). 1.88 Fe[Fe(CN) 6 ], specifically including the following steps:

[0031] (1) 4 mmol of ferrous sulfate and 4 mmol of ascorbic acid were mixed with deionized water, and potassium citrate and dipotassium ethylenediaminetetraacetate were added thereto in a molar ratio of 3:1 (named KCA75), and mixed to obtain 100 mL of solution A.

[0032] (2) Mix 4 mmol of potassium ferrocyanide with deionized water to obtain 100 mL of solution B;

[0033] (3) The solution B obtained in step (2) was pumped into the solution A at a dropping rate of 0.5 mL / min through a peristaltic pump to carry out a coprecipitation reaction. After reacting for 2 hours, the solution was aged at room temperature for another 12 hours to obtain a precursor.

[0034] (4) The precursor aged in step (3) was centrifuged at 9000 rpm for 6 min. After repeated centrifugation, the obtained material was placed in a vacuum drying oven and dried at 120° C. for 12 h to obtain K 1.88 Fe[Fe(CN) 6 ]powder.

[0035] Taking the KCA75 material obtained in this embodiment as an example, the constant current charge and discharge test results of 20 mAh / g show that its initial charge and discharge specific capacity can reach 124.3 mAh / g, and the capacity remains at 121.6 mAh / g after 100 cycles.

[0036] Example 2

[0037] A method for efficiently preparing a low-defect, low-water-content Prussian white potassium ion battery positive electrode material, wherein the preparation method is the same as that of Example 1, except that the chelating agent added in step (1) is a chelating agent of potassium citrate and dipotassium ethylenediaminetetraacetate in a molar ratio of 1:1.

[0038] Taking the KCA50 material obtained in this embodiment as an example, the constant current charge and discharge test results of 20 mAh / g show that its initial charge and discharge specific capacity can reach 105 mAh / g, and the capacity remains at 91.9 mAh / g after 100 cycles.

[0039] Example 3

[0040] A method for efficiently preparing a low-defect, low-water-content Prussian white potassium ion battery positive electrode material, wherein the preparation method is the same as that of Example 1, except that: the chelating agent (the molar ratio of potassium citrate to dipotassium ethylenediaminetetraacetate is 1:3) added in step (1)

[0041] Taking the KCA25 material obtained in this embodiment as an example, the constant current charge and discharge test results of 20 mAh / g show that its initial charge and discharge specific capacity can reach 105 mAh / g, and the capacity remains at 100.8 mAh / g after 100 cycles.

[0042] Comparative Example 1

[0043] A method for efficiently preparing a low-defect, low-water-content Prussian white potassium ion battery positive electrode material, wherein the preparation method is the same as that of Example 1, except that: the chelating agent (the molar ratio of potassium citrate to dipotassium ethylenediaminetetraacetate is 1:0) added in step (1)

[0044] Taking the KCA material obtained in this comparative example as an example, the constant current charge and discharge test results of 20 mAh / g show that its initial charge and discharge specific capacity can reach 92 mAh / g, and the capacity is maintained at 87.9 mAh / g after 100 cycles.

[0045] Comparative Example 2

[0046] A method for efficiently preparing a low-defect, low-water-content Prussian white potassium ion battery positive electrode material, wherein the preparation method is the same as that of Example 1, except that: the chelating agent (the molar ratio of potassium citrate to dipotassium ethylenediaminetetraacetate is 0:1) added in step (1)

[0047] Taking the EDTA-2K material obtained in this comparative example as an example, the constant current charge and discharge test results of 20 mAh / g show that its initial charge and discharge specific capacity can reach 110 mAh / g, and the capacity remains at 109 mAh / g after 100 cycles.

[0048] The XRD patterns of the materials prepared in Examples 1, 2, 3 and Comparative Examples 1 and 2 are shown in Figure 1 As shown. Figure 1 It can be seen that all samples can be retrieved as face-centered cubic phase PDF#31-1000, space group Fm-3m, indicating that different ratios of potassium citrate and dipotassium ethylenediaminetetraacetate do not affect the structure of the prepared samples.

[0049] The thermogravimetric curves of the materials prepared in Examples 1, 2, 3 and Comparative Examples 1 and 2 at 25-400°C are as follows: Figure 2 The water content obtained by thermogravimetry is shown in Table 1

[0050] Table 1: Calculation and statistics of water content of Examples 1, 2, 3, and Comparative Examples 1 and 2 by thermogravimetric (TGA) curve

[0051] sample Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Water content (%) 8.55 5.76 6.38 7.26 7.4

[0052] According to the thermogravimetric curves of the materials prepared in Examples 1, 2, 3 and Comparative Examples 1 and 2 at 25-400°C, the water content in Example 1 reached the lowest at 5.76%. This is because the ratio of the dual chelating agent KCA to EDTA-2K in Example 1 is 3:1, which can not only coordinate with the divalent iron ions during the synthesis process, but also provide additional K + , so that the reaction system reaches a potassium-rich environment, and the excess K + It enters the octahedral voids of the unit cell and is stored, thereby effectively achieving the interstitial water content in Example 1.

[0053] Fe K-edge Fourier transform k of materials prepared in Examples 1, 2, 3 and Comparative Examples 1 and 2 2 The Fourier transform of the weighted EXAFS oscillation is Figure 3 As shown. Figure 3 It can be seen that two obvious peaks can be observed in the R space, corresponding to Fe-C and Fe-N bonds; those connected to C are low-spin Fe (LS-Fe), and those connected to N are high-spin Fe (HS-Fe). According to the expression K x Fe[Fe(CN) 6 ] y □ 1-y ·zH 2 O, y is the ratio of LS-Fe to HS-Fe, and the content of defect □ is 1-y. 2 The weighted EXAFS oscillation curve is subjected to peak fitting to obtain the ratio of LS-Fe to HS-Fe, as shown in Table 2. According to Table 2, the LS-Fe / HS-Fe value in Example 1 is the highest, and thus the defect content is the lowest.

[0054] Table 2: LS-Fe / HS-Fe ratio obtained by fitting the Fe-C peak and Fe-N peak of the XAFS curve

[0055] sample Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 LS-Fe / HS-Fe 0.79 0.70 0.62 0.56 0.61 <![CDATA[Fe(CN) 6 2- Defect content]]> 0.21 0.30 0.38 0.44 0.39

[0056] The cycle performance of the materials prepared in Example 1 and Comparative Example 1 in a potassium ion battery (assembled into a half-cell, the negative electrode of which is a potassium sheet, and the electrolyte is 2.5M KFSI in TEP) (cycle performance test at a current density of 20mA / g) is as follows: Figure 2 , after 100 cycles, their capacities remained at 120.8 and 86 mAh / g, respectively.

[0057] In summary, the present invention can slow down the precipitation anti-crystallization rate by adding different proportions of chelating agents during the material synthesis process, provide additional potassium ions during the material synthesis process to achieve a potassium-rich environment, and facilitate the synthesis of high-quality and low-water content Prussian white analog positive electrode materials. This method is based only on the synthesis point of view, and can achieve arbitrary regulation of defect content within a certain range without increasing the experimental cost. The method is simple and easy to operate, low cost, high purity, excellent repeatability, and strong product controllability.

[0058] The above is only a preferred embodiment of the present invention and does not limit the present invention in any form. Therefore, any simple modification, equivalent change and modification made to the above embodiment according to the technical essence of the present invention without departing from the content of the technical solution of the present invention shall fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for preparing a low-defect, low-water-content Prussian white potassium ion battery positive electrode material, characterized in that: The general formula of the positive electrode material is K x Fe[Fe(CN)6] y ·□ 1-y ·zH2O, where 0 < x ≤ 2, 0 < y ≤ 1, and it can be prepared by adjusting the ratio of different chelating agents; among them, the chelating agent is any one or two of citric acid, potassium citrate, dipotassium ethylenediaminetetraacetate, and tartaric acid.

2. The method for efficiently preparing a low-defect, low-water-content Prussian white potassium ion battery positive electrode material according to any one of claim 1, characterized in that: The steps include: (1) mixing a soluble divalent iron salt, a chelating agent, ascorbic acid and deionized water in corresponding proportions to obtain a solution A, wherein the molar ratio of potassium citrate to dipotassium ethylenediaminetetraacetate is 1:(0-3); (2) mixing potassium ferrocyanide and deionized water to obtain solution B; (3) pumping the solution B obtained in step (2) into the solution A through a peristaltic pump to carry out a coprecipitation reaction, and after a period of reaction, carrying out an aging reaction at room temperature to obtain a precursor; (4) The precursor aged in step (3) is centrifuged, washed and dried in sequence to obtain a Prussian white potassium ion battery positive electrode material.

3. The method for efficiently preparing a low-defect, low-water-content Prussian white potassium ion battery positive electrode material according to claim 2, characterized in that The divalent iron salt in step (1) can be selected from one or more of ferrous sulfate, ferrous chloride, ferrous nitrate, ferrous oxalate, ferrous stearate, ferrous succinate, and ferrous gluconate; the chelating agent can be selected from one or more of ethylenediaminetetraacetic acid, dipotassium ethylenediaminetetraacetic acid, nitrilotriacetic acid, diethylenetriaminepentaacetic acid, N-hydroxyethylethylaminetriacetic acid, citric acid, potassium citrate, tartaric acid, and potassium tartrate. The divalent iron salt is ferrous sulfate; the chelating agent is potassium citrate and dipotassium ethylenediaminetetraacetic acid.

4. The method for efficiently preparing a low-defect, low-water-content Prussian white potassium ion battery positive electrode material according to claim 2, characterized in that The molar ratio of the divalent iron salt to potassium ferrocyanide is 1:9 to 9:1; the volume ratio of solution A to solution B is 1:9 to 9:

1.

5. The method for efficiently preparing a low-defect, low-water-content Prussian white potassium ion battery positive electrode material according to claim 2, characterized in that The ratio of the sum of the molar amounts of potassium citrate and dipotassium ethylenediaminetetraacetate to the molar amount of potassium ferrocyanide in the chelating agent is 1:1; and the molar ratio of potassium citrate to dipotassium ethylenediaminetetraacetate is 9:1-1:

9.

6. A method for efficiently preparing a low-defect, low-water-content Prussian white potassium ion battery positive electrode material according to claim 2 or 5, characterized in that The molar ratio of the divalent iron salt to potassium ferrocyanide is 1:4 to 4:1; the volume ratio of solution A to solution B is 1:4 to 4:

1.

7. A method for efficiently preparing a low-defect, low-water-content Prussian white potassium ion battery positive electrode material according to claim 2 or 5, characterized in that The molar ratio of the potassium citrate to dipotassium ethylenediaminetetraacetate is 1:4 to 4:

1.

8. The method for efficiently preparing a low-defect, low-water-content Prussian white potassium ion battery positive electrode material according to claim 2, characterized in that Argon is introduced into the reactions of step (1) and step (3) as a protective gas to prevent the divalent iron salt from being oxidized.

9. The method for efficiently preparing a low-defect, low-water-content Prussian white potassium ion battery positive electrode material according to claim 2, characterized in that The coprecipitation reaction temperature in step (3) is 25-40° C., the reaction time is 1-6 h, and the aging time is 4-12 h.

10. The method for efficiently preparing a low-defect, low-water-content Prussian white potassium ion battery positive electrode material according to claim 2, characterized in that In step (4), the rotation speed of the centrifuge is 5000-12000 rpm, the centrifugation time is 5-15 min, the drying temperature is 60-120° C., and the drying time is 10-15 h.

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