Doped Prussian blue analogue material and preparation method thereof

Abstract

The invention discloses a doped Prussian blue analogue material and a preparation method thereof, and belongs to the technical field of sodium ion battery positive electrode materials, and the preparation method comprises the following steps: sequentially putting transition metal salt, a complexing agent and a reducing agent into deionized water according to different proportions, and stirring until the transition metal salt, the complexing agent and the reducing agent are fully dissolved to obtain a mixed solution A; sodium ferrocyanide and a complexing agent are dissolved in a sodium chloride solution, and a mixed solution B is obtained after the sodium ferrocyanide and the complexing agent are stirred to be fully dissolved; slowly dropwise adding the solution B into the solution A through a peristaltic pump, wherein the whole process is completed in an inert gas atmosphere; meanwhile, violently stirring for water-phase reaction; after dropwise adding is completed, standing for a period of time, removing supernate, carrying out centrifugal washing for multiple times to obtain a precipitate, and drying to obtain a final product, namely the different-proportion doped Prussian blue analogue material. By adopting the steps, the prepared prussian blue analogue is stable in structure and good in cycle performance.

Description

Technical Field

[0001] The invention relates to the technical field of sodium ion battery positive electrode materials, in particular to a doped Prussian blue analog material and a preparation method thereof. Background Art

[0002] With the exhaustion of traditional fossil energy, the booming development of many 3C products such as mobile phones, computers, and automobiles, efficient electrochemical energy storage plays an important role in the development of contemporary society. The most widely used secondary battery at present is the lithium-ion battery. However, due to the scarcity of lithium resources and uneven geographical distribution, lithium-ion batteries are not the best choice for large-scale energy storage devices. Therefore, the market urgently needs new batteries with unlimited resources and guaranteed safety. Since sodium-ion batteries have similar working mechanisms to lithium-ion batteries and have advantages such as sufficient and cheap resources, they have become one of the new electrochemical energy storage systems with the greatest potential for large-scale industrial applications. Like lithium-ion batteries, the electrochemical performance of sodium-ion batteries depends to a large extent on electrode materials, especially positive electrode materials. At present, the main positive electrode materials of sodium-ion batteries are layered oxides, polyanionic compounds, Prussian blue analogs, etc., and Prussian blue analogs stand out among many positive electrode materials due to their unique electronic structure, open three-dimensional ion channels, environmental friendliness, and low cost.

[0003] However, Prussian blue analogs face many challenges when used as positive electrodes for sodium-ion batteries: First, the reaction rate is extremely fast during the preparation of Prussian blue analogs, the crystallinity is poor and vacancies are easily generated. The presence of vacancy defects will destroy the structural integrity and reduce the Na + active storage sites, changing the electron transfer path; secondly, during the preparation process, water molecules will enter the lattice, hindering the Na + The insertion and extraction of ions lead to a decrease in reversible capacity, resulting in problems such as low capacity utilization and poor cycle stability. Summary of the invention

[0004] The purpose of the present invention is to provide a doped Prussian blue analog material and a preparation method thereof, so as to solve the problems of low capacity utilization and poor cycle stability of positive electrode materials for sodium ion batteries.

[0005] To achieve the above object, the present invention provides a doped Prussian blue analog material, the structural formula of which is Na x Cu[Fe(CN) 6 ] y ·zH 2 O, particle size is 10-15μm.

[0006] Preferably, the method for preparing the above-mentioned doped Prussian blue analog material comprises the following steps:

[0007] S1. Put two transition metal salts, a complexing agent and a reducing agent in different proportions into deionized water in turn, and stir until fully dissolved to obtain a mixed solution A;

[0008] S2, dissolving sodium ferroxine and the complexing agent in a sodium chloride solution, stirring and fully dissolving to obtain a mixed solution B;

[0009] S3, slowly adding solution B to solution A by a peristaltic pump, and the whole process is completed under an inert gas atmosphere, while vigorously stirring to react the aqueous phase;

[0010] S4. After the addition is completed, let it stand for a while, remove the supernatant, wash it by centrifugation several times to obtain a precipitate, and then dry it to obtain the final product - Prussian blue analog materials doped in different proportions.

[0011] Preferably, in the above-mentioned method for preparing a doped Prussian blue analog material, in step S1, the transition metal salt is MnCl 2 、FeCl 2 、CoCl 2 、NiCl 2 , CuCl 2 、ZnCl 2、 MnSO 4 、FeSO 4 、CuSO 4 、ZnSO 4 The concentration of the transition metal salt in the mixed solution is 6-60 mmol / L; the molar ratio of the two transition metal salts in the mixed solution is 1:1-3.

[0012] Preferably, in the above-mentioned method for preparing a doped Prussian blue analog material, in step S1, the concentration of the complexing agent in the mixed solution is 15-40 mmol / L; the complexing agent includes one or more of sodium citrate, sodium tartrate, sodium gluconate, sodium alginate, sodium tripolyphosphate, sodium pyrophosphate and sodium hexametaphosphate; and the molar ratio of the complexing agent to the transition metal salt is 1:0.1-1.

[0013] Preferably, in the above method for preparing a doped Prussian blue analog material, in step S1, the concentration of the reducing agent in the mixed solution is 2-10 mmol / L.

[0014] Preferably, in the above method for preparing a doped Prussian blue analog material, in step S2, the concentration of the sodium ferroxanthate solution is 6-60 mmol / L.

[0015] Preferably, in the above-mentioned method for preparing a doped Prussian blue analog material, in step S2, the concentration of the complexing agent in the mixed solution is 15-40 mmol / L; the complexing agent includes one or more of sodium citrate, sodium tartrate, sodium gluconate, sodium alginate, sodium tripolyphosphate, sodium pyrophosphate and sodium hexametaphosphate.

[0016] Preferably, in the above method for preparing a doped Prussian blue analog material, in step S2, the sodium chloride solution is 1 mol / L.

[0017] Preferably, in the above method for preparing a doped Prussian blue analog material, in step S3, the reaction temperature is 50-90° C., and the reaction time is 2-8 h.

[0018] Preferably, in the above method for preparing a doped Prussian blue analog material, in step S4, the drying temperature is 120-150°C.

[0019] Therefore, the present invention adopts a doped Prussian blue analog material of the above structure and a preparation method thereof, and its beneficial effects are:

[0020] (1) The use of sodium salt solution as a reaction solvent in the present invention can effectively increase the content of sodium ions in the material and reduce vacancy defects in the material.

[0021] (2) The present invention uses a chelating agent during the reaction to reduce the transition metal ions and [Fe(CN) 6 ] 4- The rate of ion contact slows down the nucleation rate of crystal particles and improves the crystallinity of the material.

[0022] (3) In the present invention, sodium ascorbate is added as a reducing agent during the reaction to inhibit the high-spin Fe 2+ Being oxidized to prevent Fe 3+ Rejection of Na + Enter the lattice.

[0023] (4) The doped Prussian blue analogue prepared by the present invention has improved structural stability and electrochemical performance.

[0024] (5) This method has a simple preparation process, low cost and high yield, and has broad prospects for large-scale production and application.

[0025] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a SEM image of the Prussian blue analog material in Example 1 of a doped Prussian blue analog material and a preparation method thereof of the present invention;

[0027] Figure 2 This is a SEM image of the Prussian blue analog material in Example 2 of a doped Prussian blue analog material and a preparation method thereof of the present invention;

[0028] Figure 3 This is a SEM image of the material in Comparative Example 1 of a doped Prussian blue analog material and a preparation method thereof of the present invention;

[0029] Figure 4 This is a SEM image of the material in Comparative Example 2 of a doped Prussian blue analog material and a preparation method thereof of the present invention;

[0030] Figure 5 XRD spectra of Example 1, Example 2, Comparative Example 1 and Comparative Example 2 of a doped Prussian blue analog material and a preparation method thereof of the present invention;

[0031] Figure 6 The figure is a rate performance diagram of Example 1 and Example 2 of a doped Prussian blue analog material and a preparation method thereof of the present invention;

[0032] Figure 7 It is a rate performance diagram of Example 1 and Comparative Example 1 of a doped Prussian blue analog material and a preparation method thereof of the present invention;

[0033] Figure 8 It is a rate performance diagram of Example 1 and Comparative Example 2 of a doped Prussian blue analog material and a preparation method thereof of the present invention;

[0034] Fig. 9 The cycle performance diagrams of the doped Prussian blue analog material and the preparation method thereof in Example 1 and Example 2 of the present invention;

[0035] Fig.10 The cycle performance diagram of Example 1 and Comparative Example 1 of a doped Prussian blue analog material and a preparation method thereof of the present invention;

[0036] Fig.11 This is a cycle performance diagram of Example 1 and Comparative Example 2 of a doped Prussian blue analog material and a preparation method thereof of the present invention. DETAILED DESCRIPTION

[0037] In order to better understand the above technical solution, the above technical solution will be described in detail below in conjunction with the accompanying drawings and specific implementation methods. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0038] The terms used in the embodiments of the present invention are only for the purpose of describing specific embodiments, and are not intended to limit the present invention. The singular forms "a", "said" and "the" used in the embodiments of the present invention and the appended claims are also intended to include plural forms, unless the context clearly indicates other meanings, and "multiple" generally includes at least two.

[0039] It should also be noted that the term "includes", "comprising" or any other variation thereof is intended to cover non-exclusive inclusion, so that a commodity or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such commodity or device. In the absence of more restrictions, the elements defined by the sentence "comprising a ..." do not exclude the existence of other identical elements in the commodity or device including the elements.

[0040] The present invention provides a doped Prussian blue analog material, the structural formula of which is Na x Cu[Fe(CN) 6 ] y ·zH 2 O, particle size is 10-15μm.

[0041] The method for preparing the above-mentioned doped Prussian blue analog material comprises the following steps:

[0042] S1. Put two transition metal salts, a complexing agent and a reducing agent in different proportions into deionized water in turn, stir until fully dissolved to obtain a mixed solution A; the transition metal salt is MnCl 2 、FeCl 2 、CoCl 2 、NiCl 2 , CuCl 2 、ZnCl 2、 MnSO 4 、FeSO 4 、CuSO 4 、ZnSO 4 The present invention relates to a method for preparing a chelating agent for treating a chelating agent. The chelating agent comprises two or more of the chelating agents; the concentration of the transition metal salt in the mixed solution is 6-60 mmol / L; the molar ratio of the two transition metal salts in the mixed solution is 1:1-3. The concentration of the complexing agent in the mixed solution is 15-40 mmol / L; the complexing agent comprises one or more of sodium citrate, sodium tartrate, sodium gluconate, sodium alginate, sodium tripolyphosphate, sodium pyrophosphate and sodium hexametaphosphate; the molar ratio of the complexing agent to the transition metal salt is 1:0.1-1. The concentration of the reducing agent in the mixed solution is 2-10 mmol / L.

[0043] S2, dissolving sodium ferroxanthate and a complexing agent in a sodium chloride solution, stirring and fully dissolving to obtain a mixed solution B; the concentration of the sodium ferroxanthate solution is 6-60 mmol / L. The concentration of the complexing agent in the mixed solution is 15-40 mmol / L; the complexing agent includes one or more of sodium citrate, sodium tartrate, sodium gluconate, sodium alginate, sodium tripolyphosphate, sodium pyrophosphate and sodium hexametaphosphate. The sodium chloride solution is 1 mol / L.

[0044] S3. Solution B is slowly added dropwise to solution A through a peristaltic pump, and the entire process is completed under an inert gas atmosphere, while vigorously stirring the aqueous phase for reaction; the reaction temperature is 50-90°C, and the reaction time is 2-8h.

[0045] S4. After the addition is completed, the mixture is allowed to stand for a period of time, the supernatant is removed, and the precipitate is obtained by centrifugation and washing for multiple times. The final product - Prussian blue analog material doped in different proportions - is obtained after drying; the drying temperature is 120-150°C.

[0046] In order to more clearly and in detail introduce a doped Prussian blue analog material and a preparation method thereof provided by an embodiment of the present invention, a description will be given below in conjunction with specific embodiments.

[0047] Example 1

[0048] S1, 4 mmol FeSO 4 7H 2 O, 2 mmol CuCl 2 ·2H 2 O, 17 mmol sodium citrate, and 2.5 mmol sodium ascorbate were sequentially placed into 100 ml deionized water, and stirred until fully dissolved to obtain a mixed solution A;

[0049] S2, dissolving 6 mmol sodium ferrate and 17 mmol sodium citrate in 1 mol / L sodium chloride solution, stirring and fully dissolving to obtain a mixed solution B;

[0050] S3, solution B was slowly added to solution A by a peristaltic pump, the dropping speed was 1 ml / min and the whole process was completed under an inert gas atmosphere. At the same time, the aqueous phase was vigorously stirred for reaction, the reaction temperature was 80°C, and the reaction time was 3 hours.

[0051] S4. After the addition is completed, the mixture is allowed to stand for 4 hours, the supernatant is removed, and the precipitate is obtained by centrifugation and washing for multiple times, and the precipitate is dried to obtain the Prussian blue analog. The drying temperature is 120° C. and the drying time is 24 hours.

[0052] Example 2

[0053] S1, 6 mmol FeSO4 7H 2 O, 17 mmol sodium citrate, and 2.5 mmol sodium ascorbate were sequentially placed into 100 ml deionized water, and stirred until fully dissolved to obtain a mixed solution A;

[0054] S2, dissolving 6 mmol sodium ferrate and 17 mmol sodium citrate in 1 mol / L sodium chloride solution, stirring and fully dissolving to obtain a mixed solution B;

[0055] S3, solution B was slowly added to solution A by a peristaltic pump, the dropping speed was 1 ml / min and the whole process was completed under an inert gas atmosphere. At the same time, the aqueous phase was vigorously stirred for reaction, the reaction temperature was 80°C, and the reaction time was 3 hours.

[0056] S4. After the addition is completed, the mixture is allowed to stand for 4 hours, the supernatant is removed, and the precipitate is obtained by centrifugation and washing for multiple times, and the precipitate is dried to obtain the Prussian blue analog. The drying temperature is 120° C. and the drying time is 24 hours.

[0057] Comparative Example 1

[0058] The difference between this comparative example and Example 1 is that 3 mmol CuCl 2 ·2H 2 O, and FeSO 4 7H 2 The molar ratio of O is 1:1, the total amount of substance is 6 mmol, and the remaining steps are the same as in Example 1.

[0059] Comparative Example 2

[0060] The difference between this comparative example and Example 1 is that 2 mmol CuCl 2 ·2H 2 O, and FeSO 4 7H 2 The molar ratio of O is 1:3, the total amount of substance is 6 mmol, and the remaining steps are the same as in Example 1.

[0061] Test Example 1

[0062] a. Scanning electron microscope test

[0063] SEM images of the Prussian blue analogs obtained in Examples 1 and 2, Figure 1 It is a copper-doped Prussian blue analogue. Figure 2 It is an undoped copper analog of Prussian blue. Figure 1 and Figure 2 It can be seen that the Prussian blue analogues are in a cubic stacking morphology, and the secondary particles after doping are larger and more irregular.

[0064] Figure 3 and Figure 4 They are SEM images of the materials of Comparative Example 1 and Comparative Example 2 respectively. Figure 3 As shown, the particles in Comparative Example 1 are larger, more irregular in shape, and are formed by the accumulation of numerous cubic particles. Figure 4 That is, the grain shape of Comparative Example 2 is larger, the secondary particles are no longer angular, the agglomeration phenomenon is more serious, and the irregular secondary particles are all about 15um.

[0065] b. X-ray diffractometer test

[0066] Figure 5 The XRD spectra of Example 1, Example 2, Comparative Example 1 and Comparative Example 2 are shown in Figure 1. As can be seen from the figure, Example 1, Example 2, Comparative Example 1 and Comparative Example 2 are all monoclinic phases, and no impurity peaks are detected, indicating that Prussian blue is successfully prepared and the prepared samples have no impurity phases, and the diffraction peaks of the four materials all show good crystallinity.

[0067] c. Electrochemical performance test

[0068] The synthesized Prussian blue analog material, the conductive agent and the binder were prepared into an electrode sheet in a ratio of 7:2:1, Super P was the conductive agent and polyvinylidene fluoride was the binder. 1MNaCl O 4 (EC:PC=1:1) as electrolyte, Whatman GF / C as battery separator, CR2032 button battery assembly work was carried out in an argon-filled glove box. Battery charge and discharge tests were carried out on a CT / CTE-4000-5V test system, with a charge and discharge potential range of 2-4.2V.

[0069] Depend on Figure 6 It can be seen that Figure 6 The figure is a rate comparison chart of Example 1 and Example 2. Example 1 is slightly behind Example 2 in initial capacity comparison, but as the current density increases, the capacity of Example 1 gradually exceeds that of Example 2 at a rate of 10C, and even at a high current density, it still has a capacity of 82 mAh·g -1 Specific capacity.

[0070] Depend on Figure 7 It can be seen that the specific capacity of Example 1 at each current density is higher than that of Comparative Example 1, and it still has a specific capacity of 82 mAh / g at a rate of 10C. In contrast, Comparative Example 1 has a specific capacity of only 53 mAh / g at a rate of 10C, indicating that Example 1 has better rate performance.

[0071] Depend on Figure 8It can be seen that the specific capacity of Example 1 at each current density is higher than that of Comparative Example 2, and it still has a specific capacity of 82 mAh / g at a rate of 10C. In contrast, Comparative Example 1 has a specific capacity of only 70 mAh / g at a rate of 10C, indicating that Example 1 has better rate performance.

[0072] Depend on Fig. 9 It can be seen that the capacity retention rate of Example 1 after 200 cycles is 76%, and the capacity retention rate of Example 2 after 200 cycles is 44%. Therefore, the cycle stability of Example 1 is more excellent.

[0073] Depend on Fig.10 It can be seen that the capacity retention rate of Example 1 after 200 cycles is 76%, and the capacity retention rate of Comparative Example 1 after 200 cycles is 71%. Therefore, the cycle stability of Example 1 is more excellent.

[0074] Depend on Fig.11 It can be seen that the capacity retention rate of Example 1 after 200 cycles is 76%, and the capacity retention rate of Comparative Example 2 after 200 cycles is 43%. Therefore, the cycle stability of Example 1 is more excellent.

[0075] The above tests show that, compared with Example 2 in which copper is not doped, the Prussian blue analogue prepared by the preparation method provided by the present invention has better cycle stability. The preparation method of the present invention has a simple process and is easy to apply to large-scale industrialization. The prepared Prussian blue analogue has a relatively stable structure, low water content and good crystallinity.

[0076] Therefore, the present invention adopts a doped Prussian blue analog material of the above structure and a preparation method thereof, and uses a sodium salt solution as a reaction solvent, which can effectively increase the content of sodium ions in the material and reduce vacancy defects in the material. In the reaction process, a chelating agent is used to reduce the reaction between transition metal ions and [Fe(CN) 6 ] 4- The rate of ion contact slows down the nucleation rate of crystal particles and improves the crystallinity of the material. Sodium ascorbate is added as a reducing agent during the reaction to inhibit the high-spin Fe 2+ Being oxidized to prevent Fe 3+ Rejection of Na + The doped Prussian blue analogue obtained by the preparation has improved structural stability and electrochemical performance. The preparation process is simple, low cost and high yield, and has broad prospects for large-scale production and application.

[0077] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A doped Prussian blue analog material, characterized in that: Its structural formula is Na x Cu[Fe(CN)6] y zH2O, particle size is 10-15μm.

2. A method for preparing the doped Prussian blue analog material according to claim 1, characterized in that: The following steps are involved: S1. Put two transition metal salts, a complexing agent and a reducing agent in different proportions into deionized water in turn, and stir until fully dissolved to obtain a mixed solution A; S2, dissolving sodium ferroxine and the complexing agent in a sodium chloride solution, stirring and fully dissolving to obtain a mixed solution B; S3, slowly adding solution B to solution A by a peristaltic pump, and the whole process is completed under an inert gas atmosphere, while vigorously stirring to react the aqueous phase; S4. After the addition is completed, let it stand for a while, remove the supernatant, wash it by centrifugation several times to obtain a precipitate, and then dry it to obtain the final product - Prussian blue analog materials doped in different proportions.

3. The method for preparing a doped Prussian blue analog material according to claim 2, characterized in that: In step S1, the transition metal salt is MnCl2, FeCl2, CoCl2, NiCl2, CuCl2, ZnCl 2、 Two or more of MnSO4, FeSO4, CuSO4, and ZnSO4; the concentration of the transition metal salt in the mixed solution is 6-60 mmol / L; the molar ratio of the two transition metal salts in the mixed solution is 1:1-3.

4. The method for preparing a doped Prussian blue analog material according to claim 3, characterized in that: In step S1, the concentration of the complexing agent in the mixed solution is 15-40mmol / L; the complexing agent includes one or more of sodium citrate, sodium tartrate, sodium gluconate, sodium alginate, sodium tripolyphosphate, sodium pyrophosphate and sodium hexametaphosphate; the molar ratio of the complexing agent to the transition metal salt is 1:0.1-1.

5. The method for preparing a doped Prussian blue analog material according to claim 4, characterized in that: In step S1, the concentration of the reducing agent in the mixed solution is 2-10 mmol / L.

6. The method for preparing a doped Prussian blue analog material according to claim 5, characterized in that: In step S2, the concentration of the sodium ferroxine solution is 6-60 mmol / L.

7. The method for preparing a doped Prussian blue analog material according to claim 6, characterized in that: In step S2, the concentration of the complexing agent in the mixed solution is 15-40 mmol / L; the complexing agent includes one or more of sodium citrate, sodium tartrate, sodium gluconate, sodium alginate, sodium tripolyphosphate, sodium pyrophosphate and sodium hexametaphosphate.

8. The method for preparing a doped Prussian blue analog material according to claim 7, characterized in that: In step S2, the sodium chloride solution is 1 mol / L.

9. The method for preparing a doped Prussian blue analog material according to claim 8, characterized in that: In step S3, the reaction temperature is 50-90° C. and the reaction time is 2-8 h.

10. The method for preparing a doped Prussian blue analog material according to claim 9, characterized in that: In step S4, the drying temperature is 120-150°C.

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