Preparation method of low-defect manganese-based prussian blue under solid-liquid dynamic balance

Abstract

The application discloses a kind of low-defect manganese-based prussian blue under solid-liquid dynamic balance fast preparation method, comprising the following steps: S1, sodium citrate is dissolved in deionized water, then add manganese acetate and ascorbic acid, form the solution A containing manganese complex;Wherein, the molar ratio of sodium citrate, manganese acetate and ascorbic acid is (4.5-5.5): 1:(0.3-0.4);S2, sodium ferrocyanide is added to deionized water, stirring is formed at a set temperature containing unsolved sodium ferrocyanide solid supersaturated suspension B;Wherein, the addition amount of sodium ferrocyanide is far more than its saturated solubility at the temperature, so that the system maintains solid-liquid two-phase equilibrium state;Crystalline integrity is higher: thanks to "whole process dynamic saturation" environment, the manganese-based prussian blue prepared by the application has more obvious monoclinic phase characteristics (corresponding XRD double peak is obvious, intensity is obvious, signal-to-noise ratio is good) compared with comparative document, lattice vacancy and coordination water content are significantly lower than comparative document scheme, and electronic conductivity is increased by nearly 50%.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery cathode material technology, specifically to a method for preparing low-defect manganese-based Prussian blue under solid-liquid dynamic equilibrium. Background Technology

[0002] The growing demand in portable electronics, grid-scale energy storage, and electric vehicles has driven the development of rechargeable batteries. Compared to lithium-ion batteries, sodium-ion batteries have the advantages of abundant and inexpensive sodium resources, making them ideal for low-cost energy storage applications. Currently, the mainstream sodium-ion battery cathode materials include polyanionic compounds, Prussian blue, and layered transition metal oxides. Prussian blue analogues, due to their unique open-frame structure, abundant sodium storage sites, and large ion migration channels, have gradually become a research hotspot in academia and industry. However, in practical applications, Prussian blue materials still face some unresolved issues, such as a high number of vacancies and crystal defects, and difficulty in precisely controlling the lattice water content, leading to low electronic conductivity and affecting reversible capacity. Traditional slow co-precipitation synthesis is commonly used in production, but this requires precise flow rate control with a flow-limiting valve and is time-consuming, impacting costs. Currently, although some studies have proposed using high-concentration salt strategies (such as patent CN113479911A) to suppress vacancy defects in Prussian blue-like materials, this method still has significant limitations: 1. The concentration of the near-saturated solution used continuously decreases during the reaction process as ions are consumed, causing the chemical potential energy of the reaction system to be unable to be maintained in the optimal repair range, affecting the uniformity of the crystal structure. 2. Using a very high proportion of chelating agents (approximately 8.5-9 mmol of trisodium citrate per mmol of metal salt) to delay crystal growth. However, studies have found that over-reliance on excessive chelating agents not only significantly increases raw material costs, but also easily leads to an imbalance between the nucleation process and the ion replenishment rate due to excessive coordination inhibition. 3. This method requires a long aging time (e.g., 24-30 h) to ensure slow defect repair. 4. This type of technical solution usually neglects the recycling of high-concentration mother liquor, resulting in serious loss of raw materials and placing a heavy burden on subsequent environmental treatment.

[0003] Therefore, how to effectively control the crystal nucleation and growth process while shortening the synthesis time, reducing the synthesis cost, and improving the preparation efficiency, so as to obtain Prussian blue cathode materials with both high structural integrity and excellent electrochemical performance, remains one of the key technical problems that urgently need to be solved in the field of sodium-ion batteries. Summary of the Invention

[0004] While existing technologies (such as patent CN113479911A) propose methods for suppressing defects using high-concentration salt solutions, they still suffer from the following technical problems: uncontrollable concentration decay, kinetic mismatch, excessively long aging time, and low resource utilization. This invention provides a rapid preparation method for low-defect manganese-based Prussian blue under solid-liquid dynamic equilibrium, enabling controllable structural construction and stable performance improvement of Prussian blue-based cathode materials under rapid synthesis conditions. This invention deeply utilizes the synergistic regulatory effect of temperature on the "dissolution-nucleation" dual process.

[0005] Solubility side (equilibrium state): The solubility of sodium ferrocyanide increases with increasing temperature. By adjusting the temperature, the "baseline saturation concentration" of ferrocyanide ions in the liquid phase of the reaction system can be precisely changed, thereby altering the thermodynamic driving force (chemical potential) for crystal growth.

[0006] Nucleation side (kinetics): The nucleation rate of manganese-based Prussian blue is highly sensitive to temperature. Increased temperature accelerates nucleation but may also lead to an increase in crystal defects.

[0007] The innovation of this invention lies in: by optimizing the chelating component ratio, a better lattice repair effect is achieved with a lower chelating agent dosage (the molar ratio of chelating agent to manganese salt is only 5:1), and further, by controlling the temperature at 25-45°C... o Within this specific temperature range, the dissolution kinetics of sodium ferrocyanide solid are cleverly balanced with the rapid nucleation kinetics of manganese-based Prussian blue. If the temperature is too low, the solid dissolution is too slow, leading to localized concentration deficits; if the temperature is too high, nucleation is too rapid, resulting in lattice distortion. By using temperature as a variable, this invention achieves a dynamic balance of "on-demand" supply from the solid-phase reservoir to the liquid-phase reaction interface, ensuring that the product still possesses extremely low lattice defects even under rapid preparation conditions.

[0008] In a first aspect, the present invention provides a rapid preparation method for low-defect manganese-based Prussian blue under solid-liquid dynamic equilibrium, comprising the following steps:

[0009] S1, dissolve sodium citrate in deionized water, then add manganese acetate and ascorbic acid to form solution A containing manganese complex; wherein, the molar ratio of sodium citrate, manganese acetate and ascorbic acid is (4.5-5.5):1:(0.3-0.4);

[0010] S2, add sodium ferrocyanide to 100 mL of deionized water, and heat at 25-45°C. o A supersaturated suspension was formed by stirring at temperature C. The amount of sodium ferrocyanide added far exceeded its saturated solubility at the current temperature; this is denoted as solution B.

[0011] S3, quickly pour solution A into suspension B. During the rapid mixing, the system utilizes the spontaneous in-situ dissolution mechanism of undissolved particles to compensate for the ferrocyanide ions consumed in the nucleation reaction in real time, keeping the reaction interface locked at the saturation concentration point.

[0012] S4. Let the mixed solution from step S3 stand and age for a period of time at a certain temperature.

[0013] S5, after the reaction is complete, the product is first centrifuged to obtain the supernatant for later use. The product is then washed several times with deionized water and anhydrous ethanol by centrifugation, and then freeze-dried under vacuum for a period of time. Finally, a white powder is obtained, which is the repaired manganese-based Prussian blue analogue;

[0014] S6, the supernatant from step S5 is recovered and used in subsequent repeated synthesis steps.

[0015] The chelating agent in step S1 is one or more of citric acid, sodium citrate, disodium ethylenediaminetetraacetate, and sodium pyrophosphate, with sodium citrate being the preferred chelating agent.

[0016] The manganese salt in step S1 is one or more of manganese acetate, manganese sulfate, manganese nitrate, manganese carbonate, and manganese chloride, with manganese acetate being the preferred manganese salt.

[0017] Preferably, the chelating agent is 37.5 mmol, the ascorbic acid is 2.5 mmol, and the manganese salt is 7.5 mmol.

[0018] Preferably, the sodium ferrocyanide content is 150 mmol, and the preparation temperature is 25°C. o C.

[0019] Preferably, in step S3, the stirring speed is 400-500 rpm, the stirring time is 0.5-3 h, and the stirring temperature is 25-45℃. More preferably, in step S3, the stirring speed is 500 rpm, the stirring time is 2 h, and the stirring temperature is 25℃.

[0020] Preferably, the aging temperature in step S4 is 25-45 ℃ and the aging time is 3-24 h. More preferably, the aging temperature in step S4 is 25 ℃ and the aging time is 4 h.

[0021] Preferably, the freeze-drying temperature in step S5 is -30 to -60 ℃ and the freeze-drying time is 12-24 h. More preferably, the freeze-drying temperature in step S5 is -60 ℃ and the freeze-drying time is 12 h.

[0022] Compared with the prior art document CN113479911A, the technical solution of this invention is characterized by the following: This invention does not simply increase the initial solution concentration, but rather constructs a supersaturated suspension reservoir containing undissolved solids. During the S3 reaction, the temperature (25-45 ℃) is used to dynamically match the solid dissolution rate with the manganese ion nucleation rate. When liquid-phase ions are consumed, the solid dissolves in situ to replenish them, ensuring that the entire reaction process remains locked in a saturated chemical potential state, thereby achieving a deeper level of lattice repair than the prior art document.

[0023] Compared with the prior art, the present invention has the following significant advantages:

[0024] (1) Higher crystal integrity: Thanks to the “dynamic saturation throughout the process” environment, the manganese-based Prussian blue prepared by this invention has more obvious monoclinic phase characteristics compared with the comparative document (corresponding to obvious double peaks in XRD, obvious intensity, and good signal-to-noise ratio), and the content of lattice vacancies and coordination water is significantly lower than that of the comparative document scheme, and the electronic conductivity is improved by nearly 50%.

[0025] (2) Significantly improved economic benefits and process efficiency: The comparative patent uses an extremely high proportion of chelating agent (approximately 8.5-9 mmol of trisodium citrate per 1 mmol of metal salt) to delay crystal growth; while the present invention uses only 5 times the amount of chelating agent. This achieves a better lattice repair effect with a lower amount of chelating agent. The comparative patent scheme usually requires an aging time of more than 24 hours; the present invention utilizes the self-regulating effect of solid-liquid dynamic equilibrium to complete rapid repair within 0.5-4 hours, and supports rapid material pouring without the need for complex flow-limiting equipment.

[0026] (3) Superior performance: Due to the complete repair of lattice defects, the material of this invention has a performance of -40°C. o It still exhibits excellent discharge capacity retention even at extremely low temperatures of C, while at 25°C... o The discharge capacity and polarization voltage at C are significantly better than those in the comparison document.

[0027] (4) Achieving a true closed-loop cycle: This invention utilizes the physical properties of saturated mother liquor to achieve 100% recycling of precursor fluid through step S6, significantly reducing raw material costs. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, obtaining other drawings based on these drawings without creative effort still falls within the scope of the present invention.

[0029] Figure 1Comparison of X-ray powder diffraction (XRD) images of MHCF-R and MHCF-I powders prepared in Examples 1-2 of this invention.

[0030] Figure 2 The images show a comparison of scanning electron microscopy (SEM) results of the MHCF-R and MHCF-I powders prepared in Examples 1-2 of this invention.

[0031] Figure 3 This is a comparison of the Raman spectra of MHCF-R and MHCF-I powders prepared in Examples 1-2 of this invention.

[0032] Figure 4 This is a comparison of the thermogravimetric (TG) values ​​of MHCF-R and MHCF-I powders prepared in Examples 1-2 of this invention.

[0033] Figure 5 This is a comparison chart of the powder conductivity of MHCF-R and MHCF-I powders prepared in Examples 1-2 of the present invention under different pressures.

[0034] Figure 6 This is a comparison of the electronic conductivity of the MHCF-R and MHCF-I electrode sheets prepared in Examples 1-2 of the present invention under a pressure of 25 MPa.

[0035] Figure 7 The electrode sheets of MHCF-R and MHCF-I prepared in Examples 1-2 of this invention are used at a current density of 10 mAg. -1 A comparison of the first-cycle charge-discharge curves.

[0036] Figure 8 The electrode sheets of MHCF-R and MHCF-I prepared in Examples 1-2 of this invention are used at a current density of 100 mAg. -1 The following is a comparison chart of cycles.

[0037] Figure 9 The electrode sheets of MHCF-R prepared in Examples 1-2 of this invention are used at a current density of 1000 mA g. -1 The following is a graph showing the cyclic performance.

[0038] Figure 10 The electrode sheets of MHCF-R prepared in Examples 1-2 of this invention are used at a current density of 1000 mA g. -1 The following is a charge / discharge curve.

[0039] Figure 11 The electrode sheets of MHCF-R and MHCF-I prepared in Examples 1-2 of this invention are used at a current density of 50 mAg. -1 Below, the temperature is -20 oComparison chart of cycle curves under C.

[0040] Figure 12 The electrode sheets of MHCF-R and MHCF-I prepared in Examples 1-2 of this invention are used at a current density of 100 mAg. -1 Below, the temperature is 55 o Comparison chart of cycle curves under C.

[0041] Figure 13 The electrode sheets of MHCF-R and MHCF-I prepared for Examples 1-2 of this invention were subjected to a temperature of -40°C. o C-55 o Between C, the current density is 10 mA g -1 The following is a comparison chart of the first-round capacity.

[0042] Figure 14 The XRD comparison diagrams show the MHCF-C-1, MHCF-C-2 and MHCF-C-3 powders prepared in Example 3 of the present invention.

[0043] Figure 15 Raman comparison images of MHCF-C-1, MHCF-C-2 and MHCF-C-3 powders prepared in Example 3 of the present invention.

[0044] Figure 16 The electrode sheets of MHCF-C-1, MHCF-C-2, and MHCF-C-3 prepared in Example 3 of this invention were subjected to a current density of 100 mA g. -1 The following is a comparison chart of cycles.

[0045] Table 1 is a comparison table of the concentrations of sodium ferrocyanide solutions prepared in Examples 1-2 of the present invention before and after the reaction with those of the comparative patent (CN113479911A). Detailed Implementation

[0046] The present invention will be further described below with reference to embodiments, but these embodiments are not intended to limit the invention in any way. Any simple modifications, equivalent changes, and alterations made to the following examples based on the technical essence of the present invention shall still fall within the scope of the present invention.

[0047] Example 1

[0048] S1, dissolve sodium citrate in 100 mL of deionized water, then add manganese acetate and ascorbic acid to the solution, wherein sodium citrate is 37.5 mmol, manganese acetate is 7.5 mmol, and ascorbic acid is 2.5 mmol, denoted as solution A;

[0049] S2, at 25 oIn step C, sodium ferrocyanide is added to 100 mL of deionized water and stirred. The amount of sodium ferrocyanide is 150 mmol. A supersaturated suspension is formed, which is denoted as solution B.

[0050] S3, Quickly pour the solution from step S1 into the solution S2 and stir at 25°C for 2 hours;

[0051] S4, let the mixed solution from step S3 stand for aging, wherein the aging temperature is 25℃ and the aging time is 4h;

[0052] S5, after the reaction is complete, the product is first centrifuged to obtain the supernatant for later use. The product is then washed several times by centrifugation with deionized water and anhydrous ethanol, and then freeze-dried under vacuum at a temperature of -60°C. o C, freeze-drying time is 12h, finally obtaining powdered manganese-based Prussian blue analogue (denoted as MHCF-R).

[0053] S6, Electrode Preparation: The MHCF-R material, Ketjen Black (conductive agent), and water-based adhesive (binder) from step S3 were mixed in a 7:2:1 (wt%) ratio. The resulting mixture was transferred to a shaking tube. Six 3 mm zirconia beads were added and the mixture was shaken thoroughly to obtain a uniform slurry. This slurry was then applied using a coating machine (MSK). AFA I) The solvent is evenly coated onto aluminum foil and placed in a vacuum drying oven at 100 °C for 12 h to allow complete solvent evaporation. The resulting electrode is then compacted using a roller press to achieve a density of 1.4 g / cm³. -3 The electrode was cut into circular pieces with a diameter of 10 mm using a cutting machine (MSK-T10), and the mass of the active material was calculated to be ~1.5 mg.

[0054] S7, Electrochemical Performance Testing: All battery assembly was completed in an inert atmosphere (O2 wt% ≤ 0.01, H2O wt% ≤ 0.01) in a glove box. Constant current charge-discharge testing and long-cycle testing of CR2032 button cells were performed using Neware CT4000, with a test voltage window of 2.0-4.0 V.

[0055] Example 2

[0056] The difference between this embodiment and Example 1 is that the sodium ferrocyanide in step S2 is changed to 7.5 mmol, while the other conditions are exactly the same as in Example 1. The product (denoted as MHCF-I) is obtained and its electrochemical performance is tested.

[0057] Example 3

[0058] The difference between this embodiment and Embodiments 1 and 2 is that, after centrifuging the solution in step S5 of Embodiment 1, 100 mL of the supernatant was taken, and 7.5 mmol of sodium ferrocyanide was added, denoted as solution C; solution A from step S1 was quickly poured into solution C. All other conditions were exactly the same as in Embodiment 1, achieving 100% recovery and reuse of the precursor fluid. The product after centrifugation was denoted as MHCF-C-1, and the products synthesized by reusing the supernatant twice and three times were denoted as MHCF-C-2 and MHCF-C-3, respectively.

[0059] Figure 1 The XRD comparison diagrams of MHCF-R and MHCF-I prepared in Examples 1-2 of this invention show that the double peaks of MHCF-I around ~24° are relatively weak, while the peaks of MHCF-R are strong and sharp, indicating a clear monoclinic phase.

[0060] Figure 2 The images show a comparison of SEM images of MHCF-R and MHCF-I prepared in Examples 1-2 of this invention. It can be seen that the two are similar in terms of grain size.

[0061] Figure 3 The images show a comparison of Raman spectroscopy planes of MHCF-R and MHCF-I prepared in Examples 1-2 of this invention. It can be seen that MHCF-I has a spectral density of 2062.7 cm⁻¹. -1 The position of the vacancy peak is obvious, while MHCF-R does not have obvious vacancy peaks.

[0062] Figure 4 The TG comparison charts of MHCF-R and MHCF-I prepared in Examples 1-2 of this invention show that the water content of the repaired materials is significantly reduced and can be controlled at around 9.3%.

[0063] Figure 5 The image shows a comparison of the powder conductivity of MHCF-R and MHCF-I prepared in Examples 1-2 of this invention. It can be seen that under different pressures, the conductivity of MHCF-R is nearly 50% higher than before the repair.

[0064] Figure 6 The graph shows a comparison of the electronic conductivity of the electrode sheets of MHCF-R and MHCF-I prepared in Examples 1-2 of this invention under a pressure of 25 MPa. It can be seen that the electronic conductivity of the electrode sheet of MHCF-R is much greater than that of MHCF-I.

[0065] Figure 7 The graph shows a comparison of the charge-discharge curves of the MHCF-R and MHCF-I electrode sheets prepared in Examples 1-2 of this invention at a current density of 10 mA g⁻¹. It can be seen that the capacity of MHCF-R is 25.2 mAh g⁻¹ higher than that of MHCF-I.-1 .

[0066] Figure 8 The electrode sheets of MHCF-R and MHCF-I prepared in Examples 1-2 of this invention were subjected to a 100 mA g test. -1 The comparison chart of cycling performance under current density shows that the discharge capacity of MHCF-R in the first cycle and the discharge capacity after 300 cycles are both higher than those of MHCF-I.

[0067] Figure 9 The MHCF-R electrode sheets prepared in Examples 1-2 of this invention are subjected to a temperature of 1000 mA g. -1 The cycling performance graph at current density shows that the first cycle has a current density of 130.6 mAh g⁻¹. -1 The discharge capacity remains at 92.1 mAh g after 300 cycles at a high rate. -1 The capacity contribution.

[0068] Figure 10 The electrode sheets of MHCF-R prepared in Examples 1-2 of this invention were subjected to a temperature of 1000 mA g. -1 The charge-discharge curves at the given current density show that the charge-discharge plateau remains relatively stable.

[0069] Figure 11 The electrode sheets of MHCF-R and MHCF-I prepared in Examples 1-2 of this invention are used at a current density of 50 mAg. -1 Below, the temperature is -20 o The comparison chart of the cycle curves under C shows that the MHCF-R has a better capacity than the MHCF-I, both in the first lap and after 200 laps.

[0070] Figure 12 The electrode sheets of MHCF-R and MHCF-I prepared in Examples 1-2 of this invention are used at a current density of 100 mAg. -1 Below, the temperature is 50 o The comparison chart of the cycle curves under C shows that the MHCF-R has a better capacity than the MHCF-I, both in the first lap and after 200 laps.

[0071] Figure 13 The electrode sheets of MHCF-R and MHCF-I prepared for Examples 1-2 of this invention were subjected to a temperature of -40°C. o C-55 o At C, with a current density of 10 mA g -1 Under these conditions, the first-cycle discharge capacity of MHCF-R at all temperatures is higher than that of MHCF-I.

[0072] Figure 14The XRD comparison diagrams of MHCF-C-1, MHCF-C-2 and MHCF-C-3 prepared in Example 3 of the present invention show that the peaks of the three materials are very strong and sharp, and are monoclinic phases consistent with MHCF-R.

[0073] Figure 15 The image shows a Raman comparison of MHCF-C-1, MHCF-C-2, and MHCF-C-3 prepared in Example 3 of this invention. It can be seen that the three materials have a similar growth rate at 2062.7 cm⁻¹. -1 No empty peaks were found at any of the positions, and the shapes of the other two peaks were consistent with MHCF-R.

[0074] Figure 16 The electrode sheets of MHCF-C-1, MHCF-C-2, and MHCF-C-3 prepared in Example 3 of this invention were subjected to a 100 mA g test. -1 The comparison chart of cycling performance at current densities shows that the three materials and MHCF-R have almost the same first-cycle capacity at the same current density.

[0075] Table 1 compares the concentrations of the sodium ferrocyanide solution prepared in Examples 1-2 of this invention before and after the reaction with those in the comparative patent (CN113479911A). It can be seen that MHCF-R, compared to MHCF-I, has a lower concentration at 25°C. o The concentration before and after the reaction at C is almost constant, while the comparative patent shows that the concentration at 40 is different. o At point C, the mixture is unsaturated, and after the reaction, the concentration decreases significantly, resulting in a more unsaturated state.

[0076]

[0077] Table 1

[0078] The above description discloses only preferred embodiments of the present invention and should not be construed as limiting the scope of the present invention. Therefore, equivalent variations made in accordance with the claims of the present invention are still within the scope of the present invention.

Claims

1. A method for preparing low-defect manganese-based Prussian blue under solid-liquid dynamic equilibrium, characterized in that, Includes the following steps: S1, dissolve sodium citrate in deionized water, then add manganese acetate and ascorbic acid to form solution A containing manganese complex; wherein, the molar ratio of sodium citrate, manganese acetate and ascorbic acid is (4.5-5.5):1:(0.3-0.4); S2, sodium ferrocyanide is added to deionized water and stirred at a set temperature to form a supersaturated suspension B containing undissolved sodium ferrocyanide solid; wherein the amount of sodium ferrocyanide added far exceeds its saturation solubility at the set temperature, so that the system maintains a solid-liquid two-phase equilibrium state. S3, quickly pour solution A into suspension B, and wait 20-30 seconds. o The reaction is stirred at C for 0.5-3 h. During this process, the in-situ dynamic dissolution of undissolved sodium ferrocyanide solid in the solution is used to compensate for the ferrocyanide ions consumed by the nucleation reaction in real time, so that the reaction system is always in a constant high chemical potential saturation state of ferrocyanide, and reaches a dynamic equilibrium with the nucleation and growth of manganese Prussian blue. S4, allow the mixed solution from step S3 to stand for aging, wherein the aging temperature is 25°C. o C, aging time is 0.5-4 hours; S5. After the reaction is complete, the product is first centrifuged to obtain the supernatant for later use. The product is then washed several times by centrifugation with deionized water and anhydrous ethanol, followed by vacuum freeze-drying at a temperature of -30 to -60°C. o C, freeze-drying time is 12-24 h, finally obtaining monoclinic phase powder manganese-based Prussian blue analogue; S6. The supernatant from step S5 is recovered, and after replenishing the consumed manganese source and adjusting the solid-liquid equilibrium of sodium ferrocyanide, it is recycled for the next synthesis reaction.

2. The method for preparing low-defect manganese-based Prussian blue under solid-liquid dynamic equilibrium as described in claim 1, wherein the concentration control in step S3 is achieved by adjusting the reaction temperature to balance the dissolution rate of sodium ferrocyanide solid and the nucleation rate of manganese-based Prussian blue: utilizing the difference in solubility of sodium ferrocyanide at different temperatures, combined with the nucleation kinetics characteristics of manganese-based Prussian blue at corresponding temperatures, the reaction temperature is adjusted to 25-45°C. o C matches the dynamic dissolution rate of sodium ferrocyanide solid with the reaction consumption rate, thereby locking the concentration of ferrocyanide ions in the liquid phase at the saturation point at the corresponding temperature in real time, achieving steady-state control of the crystal growth process.

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