A manganese-doped iron-based prussian blue material, a preparation method and application thereof

Abstract

The application provides a manganese-doped iron-based Prussian blue material and a preparation method and application thereof. The ultrasonic-assisted synthesis technology is used to utilize cavitation effect and heat effect, optimize crystallinity and dispersibility of the manganese-doped iron-based Prussian blue material, reduce structural defects and agglomeration phenomenon, and improve ion diffusion kinetic performance. Results show that the discharge specific capacity of KFeMnPB-40 is as high as 102.4 mAh / g after 1000 cycles at 0.5 C ‑1 When cycled at 2 C for 500 cycles, the discharge specific capacity of KFeMnPB-40 is as high as 89.7 mAh / g ‑1 , which is much higher than that of KFeMnPB without ultrasonic assistance. Meanwhile, the preparation process is simple, does not require high-temperature and high-pressure equipment, has mild reaction conditions, is highly controllable, is suitable for industrial large-scale production, and has a wide application prospect.

Description

Technical Field

[0001] This invention relates to the field of cathode material technology, specifically to a manganese-doped iron-based Prussian blue material, its preparation method, and its application. Background Technology

[0002] With the dual demands of the new energy market and the large-scale energy storage market, relying solely on lithium batteries to meet the ever-growing market demand is simply unsustainable. At this juncture, sodium, as a group element of lithium, offers similar chemical properties to lithium batteries, and sodium batteries are also similar in nature. Furthermore, sodium resources are abundant and inexpensive, making it a suitable and necessary supplement to lithium batteries.

[0003] Among numerous cathode materials, Prussian blue possesses a unique open-frame structure, which facilitates sodium ion insertion / extraction. Furthermore, its synthesis is simple, inexpensive, and exhibits ideal performance, meeting commercialization requirements. However, the most common method for synthesizing Prussian blue is coprecipitation, but materials synthesized using this method typically exhibit suboptimal electrochemical performance. From a synthetic perspective, the reaction is time-consuming, energy-intensive, and requires stringent reaction conditions. From a material perspective, the synthesized materials often exhibit uneven particle size and agglomeration. This is because controlling the nucleation rate during synthesis is difficult, resulting in unevenly synthesized materials that severely impact electrochemical performance. These issues pose significant challenges to the commercialization of iron-manganese-based Prussian blue. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings and deficiencies of the existing technology and to provide a manganese-doped iron-based Prussian blue material, its preparation method and application.

[0005] The technical solution adopted by this invention is as follows: The first aspect of this invention provides a method for preparing manganese-doped iron-based Prussian blue material, comprising the following steps: S1. Dissolve potassium citrate, soluble iron salt and soluble manganese salt in water to obtain solution A, and dissolve potassium citrate and potassium ferrocyanide in water to obtain solvent B; S2. Add solution A dropwise into solution B, and simultaneously perform ultrasonic treatment with an ultrasonic amplitude of 20-100kHz. After titration, a mixed solution is obtained. S3. Continue stirring the mixed solution, age it, wash and dry it to obtain manganese-doped iron-based Prussian blue material.

[0006] Preferably, in step S1, the concentration of potassium citrate in solution A is 0.05-0.5 mol / L, the concentration of soluble iron salt in solution A is 0.05-0.5 mol / L, and the concentration of soluble manganese salt in solution A is 0.001-0.03 mol / L.

[0007] Preferably, in step S1, the concentration of potassium citrate in solution B is 0.05-0.5 mol / L, and the concentration of potassium ferrocyanide in solution B is 0.01-0.5 mol / L.

[0008] Preferably, in step S2, solution A is dispensed at a rate of 1-50 mL / min. -1 It is added dropwise to solution B at a rate of [missing information].

[0009] Preferably, in step S3, the stirring time is 1-12 h.

[0010] Preferably, in step S3, the product is aged at 20-30°C for 12-48 hours.

[0011] Preferably, in step S3, the product is dried at a temperature of 100-140 °C for 6-24 h.

[0012] A second aspect of the present invention provides a manganese-doped iron-based Prussian blue material, which is prepared by the preparation method described above.

[0013] A third aspect of the present invention provides the application of the manganese-doped iron-based Prussian blue material as described above in sodium-ion batteries.

[0014] A fourth aspect of the present invention provides a positive electrode sheet comprising the manganese-doped iron-based Prussian blue material as described above.

[0015] The beneficial effects of this invention are as follows: 1. The ultrasound-assisted synthesis technique employed in this invention utilizes cavitation and thermal effects to optimize the crystallinity and dispersion of manganese-doped iron-based Prussian blue materials, reducing structural defects and agglomeration, and improving ion diffusion kinetics. Results show that after 1000 cycles at 0.5 C, the discharge specific capacity of KFeMnPB-40 reaches as high as 102.4 mAh / g. -1 After 500 cycles at 2C, KFeMnPB-40 exhibited the highest discharge specific capacity, at 89.7 mAh / g. -1 The KFeMnPB is far from being ultrasound-assisted.

[0016] 2. The preparation process of this invention is simple, requires no high temperature and high pressure equipment, has mild reaction conditions, is highly controllable, and is suitable for large-scale industrial production.

[0017] 3. The manganese-doped iron-based Prussian blue material prepared by this invention has excellent electrochemical performance, outstanding cycle stability and rate performance, and is suitable for sodium-ion battery anode materials for large-scale energy storage, with broad application prospects. Attached Figure Description

[0018] 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.

[0019] Figure 1 This is a schematic diagram of the synthesis process in Embodiment 1 of the present invention; Figure 2 The image shows the XPS pattern of the KFeMnPB-40 material prepared in Example 1 of this invention. Figure 3 The image shows the EDS diagram of the KFeMnPB-40 material prepared in Example 1 of this invention. Figure 4 The images show the XRD patterns and magnified views of KFePB materials synthesized with different Mn doping concentrations according to the present invention. Figure 5 (a) FTIR and (b) thermogravimetric analysis of KFePB materials synthesized with different Mn doping amounts according to the present invention. Figure 6 The images show (a) XRD pattern, (b) FTIR pattern, and (c) thermogravimetric diagram of KFeMnPB materials synthesized with different ultrasonic amplitudes according to the present invention. Figure 7 TEM images of KFeMnPB materials synthesized with different ultrasonic amplitudes according to the present invention at different magnifications: (a) KFeMnPB-0, (b) KFeMnPB-20, (c) KFeMnPB-40, (d) KFeMnPB-60, (e) KFeMnPB-0, (f) KFeMnPB-20, (g) KFeMnPB-40, (h) KFeMnPB-60; Figure 8 The graphs show (a) the first charge-discharge curves at 0.1 C and (b) the first charge-discharge curves at 0.1 mV s for KFePB materials synthesized with different Mn doping amounts according to this invention. -1 Comparison of CV curves, (c) electrochemical impedance spectroscopy in the range of 0.01-105 Hz; Figure 9 Comparison of KFePB materials synthesized with different Mn doping amounts according to the present invention: (a) comparison of rate performance, (b) comparison of cycling stability at 0.5 C, and (c) comparison of cycling stability at 2 C; Figure 10 The following are images of KFeMnPB materials synthesized with different ultrasonic amplitudes according to this invention: (a) First-cycle charge-discharge curve at 0.1 C, (b) Electrochemical impedance spectroscopy, (c) Na +Diffusion coefficient curve and GITT curve of KFeMnPB-40; Figure 11 The figures show (a) rate performance, (b) cycling stability at 0.5 C, and (c) cycling stability at 2 C for the KFeMnPB materials synthesized with different ultrasonic amplitudes according to the present invention. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings.

[0021] Example 1 This embodiment provides a manganese-doped iron-based Prussian blue material, the preparation method of which includes the following steps: (1) Dissolve 0.01 mol potassium citrate, 0.0054 mol ferrous sulfate and 0.0006 mol manganese sulfate in 100 mL of deionized water to prepare solution A. Then dissolve 0.01 mol potassium citrate and 0.005 mol potassium ferrocyanide in 100 mL of deionized water to prepare solution B.

[0022] (2) Before the titration begins, stir the prepared solutions A and B at 500 rpm for 1 h respectively. Set the volumetric flow rate of one side of the advection pump to 5 mL / min. -1 Solution A is added dropwise to solution B at a constant rate. Simultaneously, solution B needs to be sonicated at an amplitude of 40 kHz.

[0023] (3) After titration, the resulting mixture was stirred for 6 h and then aged at room temperature for 24 h. After aging, the sample was washed three times each with deionized water and anhydrous ethanol, and then dried in a 120℃ oven for 12 h. The resulting product was divided into two portions and labeled as KFeMnPB-40 and KFe, respectively. 0.9 Mn 0.1 PB.

[0024] Example 2 This embodiment provides a manganese-doped iron-based Prussian blue material. The preparation method differs from that of Example 1 only in that: in step (1), the molar amounts of ferrous sulfate and manganese sulfate are 0.0057 mol and 0.0003 mol, respectively, the iron-manganese ratio is 0.95:0.05, and the obtained product is labeled as KFe. 0.95 Mn 0.05 PB.

[0025] Example 3 This embodiment provides a manganese-doped iron-based Prussian blue material. The preparation method differs from that of Example 1 only in that: in step (1), the molar amounts of ferrous sulfate and manganese sulfate are 0.0048 mol and 0.0012 mol, respectively, the iron-manganese ratio is 0.8:0.2, and the obtained product is labeled as KFe. 0.8 Mn 0.2 PB.

[0026] Example 4 This embodiment provides a manganese-doped iron-based Prussian blue material. The difference between its preparation method and that of Example 1 is only that in step (2), solution B is sonicated under an amplitude of 20 kHz, and the resulting product is labeled as KFeMnPB-20.

[0027] Example 5 This embodiment provides a manganese-doped iron-based Prussian blue material. The difference between its preparation method and that of Example 1 is only that in step (2), solution B is sonicated under an amplitude of 60 kHz, and the resulting product is labeled as KFeMnPB-60.

[0028] Comparative Example 1 This comparative example provides a manganese-free iron-based Prussian blue, the preparation method of which differs from that of Example 1 only in that: in step (1), 0.01 mol potassium citrate and 0.0054 mol ferrous sulfate are dissolved in 100 mL of deionized water to prepare solution A, that is, solution A does not contain manganese sulfate.

[0029] Comparative Example 2 This comparative example provides a manganese-doped iron-based Prussian blue material. The difference between its preparation method and that of Example 1 is that in step (2), solution B is not subjected to ultrasound, and the resulting product is labeled as KFeMnPB-0.

[0030] Microscopic characterization Figure 2 The image shows the XPS diagram of the FeMnPB material prepared in Example 1. It can be seen from the image that the material contains K, Fe, Mn, C, N and O elements.

[0031] Figure 3 The image shows the EDS diagram of the FeMnPB material prepared in Example 1. The uniform co-distribution of C and N elements verifies the uniformity of the CN framework in the Prussian blue structure. The uniform distribution of K, Fe, and Mn elements also verifies the successful synthesis of the KFeMnPB material. The small distribution of Mn elements indicates that Mn element was indeed successfully doped and the doping amount was small.

[0032] Figure 4 The XRD patterns of KFePB materials synthesized with different Mn doping amounts prepared in Examples 1-3 and Comparative Example 1 are shown in the figure. The diffraction peak positions of the four groups of materials are 17.7°, 24.9°, 35.6°, and 39.8°, which correspond to the (200), (220), (400), and (420) crystal planes of the cubic phase material Fe4[Fe(CN)6]3 (PDF#52-1907).

[0033] Figure 5 FTIR and thermogravimetric analyses of KFePB materials synthesized with different Mn doping levels prepared in Examples 1-3 and Comparative Example 1 are shown. Figure 5 As shown in (a), the four samples were at 2000-2100 cm⁻¹ -1 Strong absorption peaks were observed in all samples, corresponding to the stretching vibration of the C≡N bond. Meanwhile, the 500-700 cm⁻¹ peaks... -1 There is also a weak absorption peak at each position, corresponding to the bending vibration of the Fe-C≡N bond, which strongly supports the fact that low-dose Mn doping does not change the basic framework structure of Prussian blue. Moreover, compared with KFePB, the peak sharpness and intensity of the material synthesized by manganese doping are improved, and KFe 0.9 Mn 0.1 The peak shape of PB is the sharpest, indicating that the introduction of Mn improves the long-range order of the crystal and reduces lattice defects and structural distortions. For example... Figure 5 As shown in (b), among the four samples, KFe 0.9 Mn 0.1 PB exhibits the best thermal stability, while undoped KFePB has the worst thermal stability and the highest water content is 7.21%. As the Mn doping concentration increases, the thermal stability of the material first improves and then decreases.

[0034] Figure 6 The XRD, FTIR, and thermogravimetric analyses of KFeMnPB materials synthesized using different ultrasonic amplitudes in Examples 1, 4, 5, and Comparative Example 2 are shown. Figure 6 As shown in (a), the characteristic peaks of all four materials correspond to the standard KMnFe(CN)6•2H2O (PDF#51-1896), and no impurity peaks are generated, indicating that ultrasound-assisted synthesis does not introduce impurities or cause the formation of new phases. Secondly, as the ultrasonic amplitude increases to 40kHz, the intensity of the diffraction peaks significantly increases, and the peak shape becomes sharper, indicating that the crystallinity of the material also improves to some extent with the increase of the ultrasonic amplitude. However, when the ultrasonic amplitude increases to 60kHz, the intensity of the diffraction peaks decreases. Figure 6 As shown in (b), the samples were all between 2000 and 2100 cm. -1The appearance of a strong absorption peak corresponds to the stretching vibration of the C≡N bond, while the 500-700 cm⁻¹ peak... -1 Each peak exhibits a weak absorption peak, corresponding to the bending vibration of the Fe-C≡N bond. This precisely demonstrates that ultrasound-assisted synthesis does not alter the material's fundamental framework structure. Furthermore, as the amplitude increases, the peak shapes gradually strengthen and become sharper, with KFeMnPB-40 exhibiting the sharpest peak, indicating that its framework is the most stable. However, when the amplitude increases to 60, the peak intensity actually weakens. Figure 6 As shown in (c), with the increase of ultrasonic amplitude, the thermal stability of KFeMnPB-20 and KFeMnPB-40 was improved to some extent compared with KFeMnPB-0. However, when the amplitude reached 60kHz, the thermal stability decreased significantly, and even became worse than that of KFeMnPB-0.

[0035] Figure 7 The images are TEM images of KFeMnPB materials synthesized using different ultrasonic amplitudes in Examples 1, 4, 5 and Comparative Example 2 at different magnifications. Figure 7 (ad) and Figure 7 Figures (ef) show the morphology of the four materials at 20 nm and 5 nm, respectively. It can be observed that KFeMnPB-0 particles exhibit irregular large-scale agglomeration with blurred boundaries and uneven size. This indicates that without ultrasound-assisted synthesis, the mass transfer in the reaction system is not ideal, leading to severe particle agglomeration. As the ultrasonic amplitude increases, the particle boundaries gradually become clearer. When the ultrasonic amplitude increases to 40 kHz, the particle size is very uniform, and the boundaries are even clearer, with no obvious large-scale agglomeration. When the ultrasonic amplitude continues to increase to 60 kHz, the size distribution widens, and amorphous regions and agglomeration reappear. This demonstrates that ultrasound-assisted synthesis can avoid precursor agglomeration, ensuring ordered crystal growth and resulting in uniform crystal size and complete structure. Furthermore, a moderate ultrasonic amplitude, to a certain extent, balances mass transfer and crystal growth, yielding excellent materials with high crystallinity and regular structure. However, if the ultrasonic amplitude is continuously increased, high amplitude will generate strong shear forces, which may cause crystal breakage and damage the structural integrity.

[0036] Sodium storage performance study and testing Figure 8(a) The first charge-discharge curves of the KFePB materials prepared in Examples 1-3 and Comparative Example 1 at 0.1C show that the discharge ratio increases with the increase of the Mn doping ratio, indicating that Mn doping can expand the sodium storage sites of the material and improve the capacity. Furthermore, the charging plateau of all materials is around 3.0V and 3.6V, while the discharge plateau increases with the increase of the Mn doping ratio, with the charging plateau around 3.0V and 3.5V. The charge-discharge plateau increases to varying degrees with the change of the Mn doping ratio, but the highest discharge plateau is observed in KFePB. 0.9 Mn 0.1 PB combines the advantages of high voltage, high capacity, and low polarization, resulting in excellent performance. Figure 8 (b) KFePB materials prepared for Examples 1-3 and Comparative Example 1 at 0.1 mV s -1 Comparing the initial CV curves, it is evident that as the Mn doping ratio increases, the oxidation peak shifts towards higher voltages. Among these four materials, KFe... 0.9 Mn 0.1 PB has the sharpest peak shape, the best symmetry, and the smallest potential difference between the oxidation and reduction peaks. This indicates that KFe 0.9 Mn 0.1 PB exhibits good reversibility and superior reaction kinetics compared to KFe. 0.9 Mn 0.1 PB materials, KFePB and KFe 0.95 Mn 0.05 The PB material exhibits a wider peak shape and a significantly lower peak current, indicating that appropriate Mn doping effectively enhances the electrochemical reactivity of Fe sites. Meanwhile, KFe... 0.8 Mn 0.2 Although the PB material has a large peak current, it exhibits obvious peak splitting in the 3.4V range. This may be due to lattice distortion caused by excessive Mn doping, which triggers side reactions or structural instability. Figure 8 (c) shows the impedance comparison of the four materials. All curves have a semicircle in the high-frequency region, which corresponds to the charge transfer impedance R. ct Furthermore, it was found that the undoped KFePB semicircle was the largest, indicating the highest charge transfer impedance. With lower Mn doping content, R... ct Gradually decrease and KFe 0.9 Mn 0.1 PB has the smallest R ct The slashed part corresponds to Na. + Diffusion resistance within the material, KFe 0.9 Mn 0.1The steepest slope of PB indicates that it has the best ion diffusion performance. This demonstrates that Mn doping, within certain limits, can reduce the interfacial charge transfer impedance and ion diffusion impedance of materials, thereby improving electrochemical reaction kinetics.

[0037] Figure 9 (a) is a comparison of the rate performance of KFePB materials prepared in Examples 1-3 and Comparative Example 1 at different current densities. Most of the materials obtained after manganese doping have higher discharge specific capacities at different current densities than undoped KFePB. 0.9 Mn 0.1 PB exhibits the best rate performance. Its discharge specific capacities at current densities of 0.1, 0.2, 0.5, 1, 2, 3, 5, and 10 C are 138.7, 135.2, 127.7, 120.3, 110.2, 103.3, 93.1, and 81.2 mAh g⁻¹, respectively. -1 . Figure 9 (b) and Figure 9 (c) represents the cycling stability of these four materials at current densities of 0.5 C and 2 C. After 250 cycles at a current density of 0.5 C, KFe... 0.9 Mn 0.1 The discharge specific capacity of PB is 109.5 mAh g. -1 The capacity retention rate is as high as 87.74%, while the discharge specific capacity of undoped KFePB is only 79.4 mAh g⁻¹. -1 The capacity retention rate was only 69.95%. As the Mn doping ratio reached its maximum, KFe... 0.8 Mn 0.2 PB has the lowest discharge specific capacity, at only 75.0 mAh / g. -1 After 1000 cycles at a high current density of 2C, KFe 0.9 Mn 0.1 PB's discharge specific capacity can reach 73.9 mAh / g -1 It is far greater than that of KFePB material (56.2 mAh / g). -1 This demonstrates that appropriate Mn doping can not only improve the rate performance of materials, but also increase the capacity of materials to a certain extent, enhance the structural stability of materials, and thus extend cycle life.

[0038] Figure 10(a) Comparison of the first-cycle charge-discharge curves of KFeMnPB materials synthesized using different ultrasonic amplitudes in Examples 1, 4, 5, and Comparative Example 2 at a current density of 0.1C and a voltage window of 2.0-4.2 V. It can be observed that the charge-discharge plateaus of the four materials are roughly similar, indicating that the ultrasonic amplitude did not introduce impurities or generate new phases. Furthermore, comparing the discharge specific capacity of the four materials reveals a certain correlation with the ultrasonic amplitude; the discharge specific capacity of the unultrasonicated KFeMnPB-0 is only 123.2 mAh / g. -1 When the ultrasonic amplitude is 20 kHz, the discharge specific capacity of KFeMnPB-20 is 133.6 mAh / g. -1 Compared to KFeMnPB-0, it shows a certain improvement. When the ultrasonic amplitude continues to increase to 40kHz, KFeMnPB-40 exhibits the highest discharge specific capacity, at 145.0 mAh / g. -1 Furthermore, the discharge platform was improved to some extent. At an ultrasonic amplitude of 60 kHz, the discharge specific capacity of KFeMnPB-60 was 141.2 mAh / g. -1 It decreased compared to KFeMnPB-40. Figure 10 (b) shows the impedance comparison diagram of the four materials. In the high-frequency region, KFeMnPB-0 has the largest semicircular diameter and the largest charge transfer impedance. Through ultrasound-assisted synthesis with different amplitudes, the semicircular diameters of KFeMnPB-20, KFeMnPB-40, and KFeMnPB-60 decrease sequentially, and their charge transfer impedances also decrease sequentially. In the low-frequency region, KFeMnPB-40 has the largest slope, indicating that it has the smallest ion diffusion impedance. Although KFeMnPB-60 has the smallest transfer impedance, this may be because under high-amplitude ultrasound, the strong shear force can break down ion particles and optimize the electron transport path. However, because its slope is the smallest, even smaller than that of KFeMnPB-0, it indicates that its ion diffusion impedance is the largest. Overall, KFeMnPB-40 has the best overall impedance performance, indicating that its internal pore structure and ion transport channels are more conducive to ion diffusion compared to other materials. Figure 10 (c) is Na + The diffusion coefficient curve and the GITT curve of KFeMnPB-40 reveal the DNa content of KFeMnPB-40. + The range is 10⁻⁹.6 to 10⁻¹².2 cm. 2 / s -1 Between these values, the closest to 0 indicates the highest sodium ion diffusion coefficient, while the DNa of KFeMnPB-60 is... + The range is 10⁻⁹.9 to 10⁻¹².8 cm. 2 / s -1 Between, and even less than, the DNa of KFeMnPB-0 +The range is 10⁻⁹.8 to 10⁻¹².6 cm. 2 / s -1 The fact that KFeMnPB-40 has the lowest sodium ion diffusion coefficient also verifies that KFeMnPB-60 has the lowest ion diffusion impedance and KFeMnPB-60 has the highest ion diffusion impedance in the impedance diagram. This demonstrates that excessively high amplitude can indeed lead to structural damage in the material, which is detrimental to sodium storage performance.

[0039] Figure 11 (a) Comparison of rate performance of KFeMnPB synthesized with different ultrasonic amplitudes in Examples 1, 4, 5 and Comparative Example 2 at different current densities. The results show that the discharge specific capacity of KFeMnPB-40 at current densities of 0.1, 0.2, 0.5, 1, 2, 3, 4 and 5 C are 138.3, 130.7, 123.1, 115.6, 107.3, 101.0, 96.5 and 92.5 mAh / g, respectively. -1 Higher than KFeMnPB-0 materials (128.1, 122.9, 114.8, 105.9, 95.3, 88.1, 79.5 and 67.5 mAh g⁻¹). -1 Among them, the discharge specific capacity of KFeMnPB-60 at 0.1 and 0.2 C is 140.4 and 131.5 mAh / g, respectively. -1 Furthermore, when the current density returns to 0.1 C, the discharge specific capacity of KFeMnPB-60 reaches a maximum of 135.5 mAh / g. -1 It is also slightly higher than that of KFeMnPB-40 material (128.8 mAh / g). -1 However, at current densities of 0.5, 1, 2, 3, 4, and 5 C, the discharge specific capacities of KFeMnPB-60 were 121.6, 112.4, 102.7, 95.9, 90.6, and 85.8 mAh / g, respectively. -1 The specific capacity is significantly lower than that of KFeMnPB-40. This indicates that at higher amplitudes, the material is more fragmented, exposing more active sites and allowing for greater contact with the electrolyte, thus resulting in a higher discharge specific capacity at low currents. This also verifies the higher Rc of KFeMnPB-60 in the EIS plot. ct This is the smallest. However, when the current density is high, the entire process is mainly dominated by ion diffusion resistance, and KFeMnPB-40 has the lowest ion diffusion resistance. Therefore, at higher current densities, the discharge specific capacity of KFeMnPB-40 is much higher than that of other materials. Overall, KFeMnPB-40 still has superior rate performance. Figure 11(b) shows the cycling performance of the four FeMnPB materials at a current density of 0.5 C. It can be observed that the materials synthesized with ultrasonic assistance all exhibit good cycling stability. The capacity retention rates of KFeMnPB-0, KFeMnPB-20, KFeMnPB-40, and KFeMnPB-60 are 53.3%, 68.7%, 74.2%, and 59.3%, respectively. After 1000 cycles, KFeMnPB-40 exhibits the highest discharge specific capacity, reaching 102.4 mAh / g. -1 It is far higher than KFeMnPB-0 (54.5 mAh / g). -1 Furthermore, before 500 cycles, the discharge specific capacity of KFeMnPB-60 was higher than that of KFeMnPB-20. However, after more than 500 cycles, the discharge specific capacity of KFeMnPB-60 actually decreased compared to KFeMnPB-20. Even at 1000 cycles, the discharge specific capacity of KFeMnPB-60 was only 72.3 mAh / g. -1 It is lower than KFeMnPB-20 (81.9mAh / g). -1 This also verifies that under ultrasound-assisted synthesis conditions, increasing the amplitude allows the material to gain more energy and thus more capacity, but excessive amplitude also leads to the collapse of the material structure and a decrease in cycle stability. Figure 11 (c) shows the cycling performance of the four KFeMnPB types at a current density of 2 C. The general trend is similar to that at 0.5 C. After 500 cycles, the capacity retention rates of KFeMnPB-0, KFeMnPB-20, KFeMnPB-40, and KFeMnPB-60 are 71.6%, 75.1%, 76.9%, and 68.8%, respectively. Among them, KFeMnPB-40 has the highest discharge specific capacity, at 89.7 mAh / g. -1 Much higher than KFeMnPB-0 (68.9 mAh / g) -1 KFeMnPB-20 (77.0 mAh / g) -1 ) and KFeMnPB-60 (76.2 mAh / g -1 This indicates that materials synthesized with ultrasound assistance exhibit superior cycle stability under high current densities.

[0040] 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 a manganese-doped iron-based Prussian blue material, characterized in that, Includes the following steps: S1. Dissolve potassium citrate, soluble iron salt and soluble manganese salt in water to obtain solution A, and dissolve potassium citrate and potassium ferrocyanide in water to obtain solvent B; S2. Add solution A dropwise to solution B, and simultaneously perform ultrasonic treatment with an ultrasonic amplitude of 20-100kHz. After titration, a mixed solution is obtained. S3. Continue stirring the mixed solution, age it, wash and dry it to obtain manganese-doped iron-based Prussian blue material.

2. The method for preparing a manganese-doped iron-based Prussian blue material according to claim 1, characterized in that: In step S1, the concentration of potassium citrate in solution A is 0.05-0.5 mol / L, the concentration of soluble iron salt in solution A is 0.05-0.5 mol / L, and the concentration of soluble manganese salt in solution A is 0.001-0.03 mol / L.

3. The method for preparing a manganese-doped iron-based Prussian blue material according to claim 1, characterized in that: In step S1, the concentration of potassium citrate in solution B is 0.05-0.5 mol / L, and the concentration of potassium ferrocyanide in solution B is 0.01-0.5 mol / L.

4. The method for preparing a manganese-doped iron-based Prussian blue material according to claim 1, characterized in that: In step S2, solution A is dispensed at a rate of 1-50 mL / min. -1 It is added dropwise to solution B at a rate of [missing information].

5. The method for preparing a manganese-doped iron-based Prussian blue material according to claim 1, characterized in that: In step S3, the stirring time is 1-12 h.

6. The method for preparing a manganese-doped iron-based Prussian blue material according to claim 1, characterized in that: In step S3, the product is aged at 20-30℃ for 12-48 hours.

7. The method for preparing a manganese-doped iron-based Prussian blue material according to claim 1, characterized in that: In step S3, the product is dried at 100-140℃ for 6-24 hours.

8. A manganese-doped iron-based Prussian blue material, characterized in that, It is prepared by the preparation method described in any one of claims 1-7.

9. The application of the manganese-doped iron-based Prussian blue material as described in claim 8 in a sodium-ion battery.

10. A positive electrode sheet, characterized in that, It comprises the manganese-doped iron-based Prussian blue material as described in claim 8.

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