Preparation method of sodium-rich iron-based Prussian blue material

Abstract

The present invention relates to a method for preparing a sodium-rich iron-based Prussian blue material. An Fe salt and sodium citrate are dissolved in water to form a solution A, sodium ferrocyanide decahydrate and ascorbic acid are dissolved in water to form a solution B, and polyvinyl pyrrolidone and sodium chloride are dissolved in water to form a solution C. Solution A and solution B are added to solution C under a nitrogen atmosphere while heating and stirring, and finally aged at room temperature. The solution is centrifugally washed several times with deionized water and anhydrous ethanol, and then vacuum dried to obtain an initial iron-based Prussian blue compound. The initial iron-based Prussian blue compound is dispersed in water, magnetically stirred for a certain period of time, filtered and washed, and dried to obtain a low-sodium-content water-washed iron-based Prussian blue positive electrode material. The obtained material is made into an electrode sheet and assembled into a battery. After standing for a certain period of time, the material is electrochemically pre-embedded with sodium by constant current discharge to obtain a sodium-rich iron-based Prussian blue sodium ion battery positive electrode material.

Description

Technical Field

[0001] The invention relates to a sodium-rich iron-based Prussian blue material and a preparation method thereof, belonging to the technical field of sodium ion batteries. Background Art

[0002] The key to improving the performance of sodium-ion batteries lies in the cathode material, which determines the overall battery capacity and cycling performance. However, the large ionic radius of sodium ions easily causes structural collapse of the electrode material during battery cycling, ultimately leading to extremely poor cycling and rate performance of sodium-ion batteries. Therefore, the preparation and design of cathode materials with excellent and stable cycling performance is a key issue that needs to be addressed in the development of sodium-ion batteries.

[0003] In recent years, a variety of high-performance sodium-ion battery cathode materials have been developed. Among them, iron-based Prussian blue (molecular formula: Na2Fe[Fe(CN)6], abbreviated as Fe-PB) has attracted widespread attention due to its low cost, simple processing, and open-frame structure that facilitates sodium ion transport. Fe-PB has a high specific capacity, but its cycling performance is unsatisfactory. The present invention involves dispersing an initial iron-based Prussian blue material synthesized by a sodium citrate-assisted slow coprecipitation method in a certain amount of deionized water. The material is magnetically stirred for a certain period of time, filtered and washed, and then dried to obtain a low-sodium-content, water-washed iron-based Prussian blue cathode material. The resulting material is formed into electrode sheets and assembled into a battery. After a certain period of quiescence, the material is electrochemically pre-intercalated with sodium using a constant-current discharge in an electrochemical workstation, resulting in a sodium-rich iron-based Prussian blue cathode material for sodium-ion batteries with excellent cycling performance. Summary of the Invention

[0004] The present invention aims to provide a sodium-ion battery positive electrode material prepared using a simple method. The sodium-ion battery positive electrode material comprises a sodium-ion battery positive electrode material, prepared using a simple method. The raw materials for the synthesis of the sodium-ion battery positive electrode material and its preparation method include: an iron-containing salt selected from ferrous sulfate heptahydrate (FeSO4·7H2O) (or ferrous chloride (FeCl2) or ferrous acetate (Fe(CH3COO)2), trisodium citrate dihydrate (C6H5Na3O7·2H2O), sodium ferrocyanide decahydrate (Na4Fe(CN)6·10H2O), ascorbic acid (C6H8O6), polyvinylpyrrolidone (PVP), sodium chloride (NaCl) (or sodium carbonate (Na2CO3) or sodium acetate (CH3COONa)), and water (deionized, distilled, purified, or tap water).

[0005] The specific preparation method is:

[0006] One of the technical solutions of the present invention provides a sodium-rich iron-based Prussian blue material and a preparation method thereof, comprising the following steps:

[0007] (1) Dissolve Fe-containing salt and chelating agent sodium citrate in water to prepare solution A; dissolve an appropriate amount of sodium ferrocyanide and antioxidant ascorbic acid in an appropriate amount of water to prepare solution B; dissolve the dispersant polyvinyl pyrrolidone and an appropriate amount of sodium supplement in an appropriate amount of deionized water to obtain solution C.

[0008] (2) Under N2 atmosphere and heating and stirring conditions, solution A and solution B were simultaneously added to solution C via a peristaltic pump. After the addition was complete, the solution turned into a white suspension. Heating and stirring were continued for 10-12 h, and finally, the solution was aged at room temperature for 10-30 h. After the supernatant was discarded, the white precipitate below was washed several times with water and anhydrous ethanol by centrifugation, and then vacuum dried at 100-140°C for 10-12 h to obtain a light blue initial iron-based Prussian blue compound.

[0009] (3) A certain amount of initial iron-based Prussian blue compound is dispersed in water, magnetically stirred for a certain period of time, filtered, washed, and dried to obtain a water-washed iron-based Prussian blue sodium ion battery positive electrode material.

[0010] For those skilled in the art, it should be understood that stirring is performed in a relatively excess amount of water, followed by suction filtration and washing.

[0011] (4) The washed iron-based Prussian blue sodium ion battery cathode material is mixed with acetylene black and polyvinylidene fluoride (PVDF) to form a slurry, which is then coated on aluminum foil. After drying, punching, and laminating, the cathode material is made into a pole piece and the battery is assembled. After standing for a certain period of time, the material is electrochemically pre-embedded with sodium by constant current discharge in an electrochemical workstation, and finally a sodium-rich iron-based Prussian blue sodium ion battery cathode material is obtained.

[0012] In step (1), the iron salt is one of ferrous sulfate heptahydrate FeSO4·7H2O, ferrous chloride FeCl2, or ferrous acetate Fe(CH3COO)2, and the molar ratio of the Fe-containing salt to sodium citrate is 1:1-10, and more preferably the molar ratio of the Fe-containing salt to sodium citrate is 1:5.

[0013] The molar ratio of sodium ferrocyanide Na4Fe(CN)6·10H2O, transition metal salt and ascorbic acid in step (1) is 1:0.6~1.5:3~10.

[0014] The sodium supplement in step (1) is at least one of sodium chloride NaCl, sodium carbonate Na2CO3, and sodium acetate CH3COONa, and the mass ratio of polyvinyl pyrrolidone to the sodium supplement is 1~1.5:5.5~7.

[0015] In step (2), the dropwise addition rate of solution A and solution B is controlled at 10 ml / h, the stirring speed is 400-600 rpm under N2 atmosphere, and the reaction temperature is 45-55°C.

[0016] In step (2), the white precipitate after aging is washed three times by centrifugation with deionized water and anhydrous ethanol at a centrifugal speed of ≥8000 rpm / min to obtain a clean precipitate.

[0017] The drying method in step (2) is vacuum drying at a temperature of 100-140° C. for 20-30 hours.

[0018] In step (3), the magnetic stirring time is 6 to 10 h.

[0019] In step (4), the mass ratio of the washed iron-based Prussian blue sodium ion battery positive electrode material to acetylene black and polyvinylidene fluoride (PVDF) is 7:2:1.

[0020] In step (4), the current density of the constant current discharge is 50~100 mA g -1 .

[0021] In the electrochemical pre-embedding sodium process of step (4), the sodium source comes from NaClO4 in the electrolyte.

[0022] A sodium-rich iron-based Prussian blue material is prepared by the above-mentioned electrochemical sodium pre-embedding method, and its sodium content is not less than 10%, preferably 0.1-10%.

[0023] Compared to existing technologies, the sodium-rich iron-based Prussian blue material provided by the present invention features a simple preparation method, a sodium content of no less than 10%, and superior performance to methods that utilize heteroatom doping (ZL202210671183.4) or compounding with other materials (ZL201710201857.3, ZL201810319825.8) to increase capacity and improve stability. In Examples 4 and 5, the material was physically pre-intercalated with sodium. The experimental results showed that the cycling performance of the material after physical sodium pre-intercalation was significantly lower than that of the electrochemical sodium pre-intercalation method in Example 3, demonstrating the superiority of this method. In Example 8, the electrode sheets after electrochemical sodium pre-intercalation were reassembled into a battery, and the performance was similar to that of Example 3, demonstrating that electrolyte concentration has little effect on the performance of the material after sodium pre-intercalation. This sodium-rich iron-based Prussian blue material technology also provides an effective solution to the sodium loss that has been reported in other modification processes. The preparation method of the sodium-rich iron-based Prussian blue material provided by the present invention can achieve cycling stability superior to that of the original iron-based Prussian blue material. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The XRD comparison chart of the samples prepared in Examples 1, 2, and 3 and the standard card.

[0025] Figure 2 The sample prepared in Example 1 was-1 The charge and discharge curves of the 1st, 100th and 300th cycles at a current density of .

[0026] Figure 3 The sample prepared in Example 2 was -1 The charge and discharge curves of the 1st, 100th and 300th cycles at a current density of .

[0027] Figure 4 The sample prepared in Example 3 was -1 The charge and discharge curves of the 1st, 100th and 300th cycles at a current density of .

[0028] Figure 5 The samples prepared in Examples 1, 2, and 3 were -1 Comparison of cycling performance at different current densities.

[0029] Figure 6 The samples prepared in Examples 1, 2, and 3 were -1 Comparison of cycling performance at different current densities.

[0030] Figure 7 The sample prepared in Example 4 was -1 The charge and discharge curves of the 1st, 100th and 300th cycles at a current density of .

[0031] Figure 8 The sample prepared in Example 5 was tested at 100 mA g -1 The charge and discharge curves of the 1st, 100th and 300th cycles at a current density of .

[0032] Figure 9 The samples prepared in Examples 3, 4, and 5 were tested at 100 mA g -1 Comparison of cycling performance at different current densities.

[0033] Figure 10 The sample prepared in Example 6 was -1 The charge and discharge curves of the first, second and third cycles at a current density of .

[0034] Figure 11 The sample prepared in Example 7 was -1 The charge and discharge curves of the first, second and third cycles at a current density of .

[0035] Figure 12 The samples prepared in Examples 6 and 7 were -1 Comparison of cycling performance at different current densities.

[0036] Figure 13 These are the charge-discharge curves of the sample prepared in Example 8 at the 1st, 100th, and 300th cycles at a current density of 100 mA g-1.

[0037] Figure 14 This is a cycling performance diagram of the sample prepared in Example 8 at a current density of 100 mA g-1. DETAILED DESCRIPTION

[0038] The essential features and advantages of the present invention are further illustrated below through the description of embodiments.

[0039] Example 1

[0040] 5 mmol FeSO4·7H2O and 25 mmol Na3C6H5O7·2H2O were dissolved in 50 ml of deionized water to form solution A, and 5 mmol Na4Fe(CN)6·10H2O and 1 g C6H8O6 were dissolved in 50 ml of deionized water to form solution B. 1 g polyvinylpyrrolidone (PVP) and 3 g NaCl were dissolved in deionized water to form solution C. Under N2 atmosphere and heating and stirring conditions, solution A and solution B were added to solution C simultaneously via a peristaltic pump. After the addition was complete, the solution turned into a white suspension. Heating and stirring were continued for 12 h, and finally, the solution was aged at room temperature for 24 h. After the supernatant was discarded, the white precipitate below was washed several times with deionized water and anhydrous ethanol by centrifugation, and then heated at 120 o The initial iron-based Prussian blue cathode material, labeled Fe-PB, was obtained by vacuum drying at 400 °C for 12 h. The resulting Fe-PB cathode material was mixed with acetylene black and polyvinylidene fluoride (PVDF) to form a slurry, which was then coated onto aluminum foil. After drying, punching, and lamination, the cathode material electrode sheet was fabricated. A battery was assembled using sodium metal as the counter electrode, Grade GF / D as the separator, and a 1 M NaClO₄ / (EC+DMC+EMC) (EC:DMC:EMC = 1:1:1) electrolyte containing 2 wt.% FEC. Constant current charge and discharge tests were conducted with a voltage range of 2.0–4.2 V. Figure 1 The following is a comparison of the XRD patterns of Fe-PB and the standard card. It is clear that the crystallinity of Fe-PB is good, and the diffraction peaks are basically consistent with those of the standard card (JCPDS, NO. 52-1907), but the peaks at 24.16, 38.54 and 49.46 are not consistent. o The peaks at the same locations indicate that Fe-PB is a typical monoclinic phase. ICP analysis of Fe-PB revealed that the Na content in Fe-PB is 12.33 wt.%. Figure 2 Fe-PB cathode material at 100 mA g -1The charge-discharge curves of the first, 100, and 300 cycles at a current density of 1.5 Å are shown in Figure 2. It can be seen that the first discharge capacity of Fe-PB can reach 117.1 mAh g -1 , the capacity after 100 and 300 cycles is 85.8 mAh g -1 and 54.2 mAh g -1 . Figure 5 Fe-PB at 100 mA g -1 From the cycle performance diagram under the current density of , it can be seen that after 300 cycles, its capacity retention rate is only 46.3%. Figure 6 Fe-PB at 1 A g -1 The cycling performance graph at high current density shows that after 1000 cycles, the capacity retention rate is only 44.9%. This shows that Fe-PB has low capacity and poor cycling stability.

[0041] Example 2

[0042] 200 mg of Fe-PB prepared in Example 1 was dispersed in 100 ml of deionized water, magnetically stirred for 6 h, and then filtered and washed. o The low-sodium Fe-PB-W material was obtained by drying in a C oven for 12 hours. The Fe-PB-W cathode material was mixed with acetylene black and polyvinylidene fluoride (PVDF) to form a slurry, which was then coated onto aluminum foil. After drying, punching, and lamination, the cathode material electrode sheet was fabricated. A battery was assembled using sodium metal as the counter electrode, Grade GF / D as the separator, and a 1 M NaClO₄ / (EC+DMC+EMC) (EC:DMC:EMC = 1:1:1) electrolyte containing 2 wt.% FEC. Constant current charge and discharge tests were conducted with a voltage range of 2.0–4.2 V. Figure 1 The following is a comparison of the XRD patterns of Fe-PB-W and a standard chart. Clearly, Fe-PB-W exhibits excellent crystallinity, with all diffraction peaks corresponding exactly to those of the standard chart (JCPDS, No. 52-1907). The diffraction peaks do not exhibit the peak separation observed with Fe-PB in Example 1, demonstrating a typical cubic structure. Inductively coupled plasma (ICP) analysis of Fe-PB-W revealed a Na content of 6.77 wt.%, significantly lower than that of Fe-PB. Figure 3 Fe-PB-W cathode material at 100 mA g -1 The charge and discharge curves of the 1st, 100th and 300th cycles at a current density of 1.5 and 2.8 respectively show a discharge capacity of 82.5 mAh g -1 、76.0 mAh g -1 , 60.6 mAh g -1 . Figure 5Fe-PB-W at 100 mA g -1 From the cycle performance diagram under the current density of , it can be seen that after 300 cycles, the capacity retention rate is 73.5%. Figure 6 Fe-PB-W at 1 A g -1 The cycling performance graph at high current density shows that after 1000 cycles, the capacity retention rate is 81.2%. This shows that the capacity of Fe-PB-W is very low, but the cycling stability is significantly improved compared to Fe-PB.

[0043] Example 3

[0044] The Fe-PB-W cathode material synthesized in Example 2 was mixed with acetylene black and polyvinylidene fluoride (PVDF) to form a slurry, which was then coated on aluminum foil. After drying, punching, and laminating, the cathode material pole piece was prepared. A battery was assembled using sodium metal as the counter electrode, Grade GF / D as the separator, and 1 M NaClO4 / (EC+DMC+EMC) (EC:DMC:EMC=1:1:1) containing 2 wt.% FEC as the electrolyte. The battery was then charged at 100 mA g -1 Fe-PB-W was pre-embedded with sodium by constant current discharge at a current density of , and the material Fe-PB-Y was obtained. Figure 1 The following is a comparison of the XRD patterns of Fe-PB-Y and a standard card. It shows excellent crystallinity, with diffraction peaks corresponding exactly to those in the standard card (JCPDS, No. 52-1907). After sodium pre-intercalation, the material exhibits peak separation, demonstrating a typical monoclinic phase structure. ICP testing of Fe-PB-Y revealed a sodium content of 11.07 wt.%, significantly higher than that of Fe-PB-W, indicating successful electrochemical sodium pre-intercalation. Figure 4 Fe-PB-Y cathode material at 100 mA g -1 The charge and discharge curves of the 1st, 100th and 300th cycles at a current density of 1.5 GHz and 1.6 GHz respectively show a discharge capacity of 99.8 mAh g -1 , 94.9mAh g -1 and 90.1 mAh g -1 . Figure 5 Fe-PB-Y at 100 mA g -1 From the cycle performance diagram under the current density of , it can be seen that after 300 cycles, the capacity retention rate is 90.3%. Figure 6 Fe-PB-Y at 1 A g -1 The cycling performance graph at high current density shows that after 1000 cycles, the capacity retention rate is as high as 84.7%. This shows that the sodium-rich material Fe-PB-Y has a high capacity and excellent cycling performance.

[0045] Example 4

[0046] Sodium ascorbate solution was used to physically pre-intercalate sodium into the low sodium material Fe-PB-W. 200 mg of the low sodium material Fe-PB-W prepared in Example 2 was dispersed in 100 ml of 0.8 M sodium ascorbate solution, stirred magnetically for 6 h, and then filtered and washed. o After drying in a C oven for 12 h, Fe-PB-P1 was obtained. The Fe-PB-P1 cathode material was mixed with acetylene black and polyvinylidene fluoride (PVDF) to form a slurry, which was then coated onto aluminum foil. After drying, punching, and lamination, the cathode material electrode sheet was fabricated. A battery was assembled using sodium metal as the counter electrode, Grade GF / D as the separator, and a 1 M NaClO₄ / (EC+DMC+EMC) (EC:DMC:EMC = 1:1:1) electrolyte containing 2 wt.% FEC. Constant current charge-discharge tests were performed over a voltage range of 2.0–4.2 V. Inductively coupled plasma (ICP) testing of Fe-PB-P1 revealed a Na content of 10.21 wt.%, an increase compared to Fe-PB-W, indicating successful physical pre-intercalation of sodium using the sodium ascorbate solution. Figure 7 Fe-PB-P1 cathode material at 100 mA g -1 The charge and discharge curves of the 1st, 100th and 300th cycles at a current density of 1.5 GHz and 1.6 GHz, respectively, show a discharge capacity of 127.6 mAh g -1 、86.7mAh g -1 and 58.2 mAh g -1 . Figure 9 Fe-PB-P1 at 100 mA g -1 From the cycling performance graph at a current density of , it can be seen that after 300 cycles, its capacity retention rate is only 45.6%. This shows that although Fe-PB-P1 has a high initial discharge specific capacity, its cycling performance is very poor. The performance of the sodium-rich material Fe-PB-Y obtained by electrochemical pre-intercalation of sodium is significantly better than that of the sodium-rich material Fe-PB-P1 obtained by physical pre-intercalation of sodium using a sodium ascorbate solution.

[0047] Example 5

[0048] The low sodium material Fe-PB-W was physically pre-embedded with sodium using NaNO3. 1 g of the low sodium material Fe-PB-W prepared in Example 2 and 30 mg of NaNO3 powder were ground evenly, transferred to a tube furnace, and heated at 3 ℃ under nitrogen atmosphere. o The heating rate was increased to 200 oAfter being held at 400 °C for 3 h, the material was cooled to room temperature to obtain a Prussian blue material modified with physical pre-intercalation of sodium with NaNO₃, labeled Fe-PB-P2. The Fe-PB-P2 cathode material was mixed with acetylene black and polyvinylidene fluoride (PVDF) to form a slurry, which was then coated onto aluminum foil. The cathode material was then dried, punched, and laminated to form a cathode sheet. A battery was assembled using sodium metal as the counter electrode, Grade GF / D as the separator, and a 1 M NaClO₄ / (EC+DMC+EMC) (EC:DMC:EMC = 1:1:1) electrolyte containing 2 wt.% FEC. Constant current charge-discharge tests were performed over a voltage range of 2.0–4.2 V. Inductively coupled plasma (ICP) testing of Fe-PB-P2 revealed a Na content of 10.47 wt.%, an increase compared to Fe-PB-W, demonstrating the successful physical pre-intercalation of sodium with NaNO₃. Figure 8 Fe-PB-P2 cathode material at 100 mA g -1 The charge and discharge curves of the 1st, 100th and 300th cycles at a current density of 1.5 GHz and 1.6 GHz, respectively, show a discharge capacity of 124.6 mAh g -1 , 72.9 mAh g -1 and 43.5 mAh g -1 . Figure 9 Fe-PB-P2 at 100 mA g -1 From the cycling performance graph at a current density of , it can be seen that after 300 cycles, its capacity retention rate is only 34.9%. This shows that although the initial discharge specific capacity of Fe-PB-P2 is high, its cycling performance is very poor. This also proves that the sodium-rich material Fe-PB-Y obtained by electrochemical pre-embedding of sodium performs significantly better than the sodium-rich material Fe-PB-P2 obtained by physical pre-embedding of sodium using NaNO3.

[0049] Example 6

[0050] 200 mg of Fe-PB prepared in Example 1 was dispersed in 100 ml of deionized water, stirred for 10 min, ultrasonicated for 30 min, and then 20 mg of CuCl2, 40 mg of NaHCO3 and 0.1 g of SDBS were added. o C water bath for 6 h, then filtered and heated at 80 o The composite material was dried in an oven at 3 °C overnight; the dried material was transferred to a tube furnace and heated to 3 °C under a nitrogen atmosphere. o The heating rate was increased to 200 oC, then kept warm for 3 h. After cooling to room temperature, a CuO-modified iron-based Prussian blue cathode material, labeled Fe-PB@CuO, was obtained. The Fe-PB@CuO cathode material was mixed with acetylene black and polyvinylidene fluoride (PVDF) to form a slurry, coated on aluminum foil, and then dried, punched, and laminated to form a cathode material electrode. A battery was assembled using sodium metal as the counter electrode, GradeGF / D as the separator, and a 1 M NaClO₄ / (EC+DMC+EMC) (EC:DMC:EMC = 1:1:1) electrolyte containing 2 wt.% FEC. Constant current charge-discharge tests were performed over a voltage range of 2.0–4.2 V. Inductively coupled plasma (ICP) analysis of Fe-PB@CuO revealed a Na content of 8.21 wt.%, lower than that of Fe-PB, indicating Na loss during the synthesis of Fe-PB@CuO. Figure 10 Fe-PB@CuO at 100 mA g -1 The charge and discharge curves of the first, second, and third cycles at a current density of 110.9 mAh g -1 、107.5 mAh g -1 and 106.1 mAh g -1 In addition, the first cycle charge and discharge curve shows that the material has a significant phenomenon of less charge and more discharge, that is, the sodium content is low. Figure 11 Fe-PB@CuO at 100 mA g -1 From the cycling performance diagram under the current density of , it can be seen that after 100 cycles, its capacity increases from 110.9 mAh g -1 Decay to 92.9 mAh g -1 The capacity retention rate is 83.7%. This shows that Fe-PB@CuO has a high capacity and good cycle performance.

[0051] Example 7

[0052] In order to prove the practicality of the method of preparing high sodium content Prussian blue material by electrochemical pre-embedding sodium, the Fe-PB@CuO with low sodium content synthesized in Example 6 was electrochemically pre-embedded with sodium to compare the changes in its electrochemical performance. The Fe-PB@CuO positive electrode material synthesized in Example 6 was stirred into a slurry with acetylene black and polyvinylidene fluoride (PVDF), coated on aluminum foil, and made into a positive electrode material electrode after drying, punching and pressing. The battery was assembled with metallic sodium as the counter electrode, Grade GF / D as the diaphragm, and 1 MNaClO4 / (EC+DMC+EMC) (EC:DMC:EMC=1:1:1) containing 2 wt.% FEC as the electrolyte, and then the battery was charged at 100mA g -1Fe-PB@CuO was pre-intercalated with sodium via a constant current discharge at a current density of 1.5 GHz, yielding the material Fe-PB@CuO-Y. ICP testing of Fe-PB@CuO-Y revealed an increased sodium content of 10.40 wt.% compared to Fe-PB@CuO, demonstrating successful electrochemical pre-intercalation of sodium into Fe-PB@CuO. Figure 10 Fe-PB@CuO-Y at 100 mA g -1 The charge and discharge curves of the first, second and third cycles at a current density of 118.5 mAh g -1 , 115.3 mAh g -1 and 114.0 mAh g -1 . Figure 11 Fe-PB@CuO-Y at 100 mA g -1 Cycling performance diagram under current density of 100 cycles. It can be seen that after 100 cycles, its capacity increased from 121.0 mAh g -1 Decay to 106.5 mAh g -1 , and the capacity retention rate is 88.0%. Obviously, the performance of high-sodium Fe-PB@CuO-Y prepared by electrochemical pre-intercalation of sodium is significantly better than that of low-sodium Fe-PB@CuO.

[0053] Example 8

[0054] To prove that the electrolyte concentration has little effect on the performance of the material after electrochemical pre-intercalation of sodium, the electrolyte concentration in Example 3 was 100 mA g -1 The battery after electrochemical pre-embedding of sodium at a current density of 100 nm was disassembled, the electrode sheets were cleaned with ethylene carbonate (EC), and the battery was reassembled with the same steps and the electrochemical performance was tested. Figure 13 After reassembling the battery, the -1 The charge and discharge curves of the 1st, 100th and 300th cycles at a current density of 1.5 GHz and 1.6 GHz respectively show a discharge capacity of 98.0 mAh g -1 , 92.7 mAh g -1 and 92.0 mAh g -1 . Figure 14 Is the battery at 100 mA g -1 The cycling performance graph at a current density of 1000 Å shows that after 300 cycles, the capacity retention rate is 93.8%. This shows that the cycling performance of the material after reassembly of the battery is still very good, and it can be concluded that the electrolyte concentration has little effect on the performance of the material after electrochemical pre-intercalation of sodium.

Claims

1. A method for preparing a sodium-rich iron-based Prussian blue material, characterized in that: The following steps are involved: (1) Dissolve iron salt and sodium citrate in water to form solution A, dissolve sodium ferrocyanide and antioxidant ascorbic acid in water to form solution B, and dissolve dispersant polyvinyl pyrrolidone and sodium supplement in water to form solution C; (2) Under N2 atmosphere and heating and stirring conditions, solution A and solution B are simultaneously added dropwise to solution C to react to obtain a white suspension, which is then heated and stirred evenly and then aged at room temperature. The white precipitate obtained after aging is centrifuged, washed, and vacuum-dried to obtain the initial iron-based Prussian blue compound; (3) taking a certain amount of the initial iron-based Prussian blue compound and dispersing it in water, magnetically stirring it for a certain period of time, then filtering and washing it, and drying it to obtain a washed iron-based Prussian blue sodium ion battery positive electrode material; (4) The washed iron-based Prussian blue sodium ion battery positive electrode material was stirred with acetylene black and polyvinylidene fluoride to form a slurry, which was then coated on aluminum foil. After drying, punching and pressing, the positive electrode material was made into a pole piece and the battery was assembled. After standing for a certain period of time, the material was electrochemically pre-embedded with sodium through constant current discharge in an electrochemical workstation. During the electrochemical pre-embedding of sodium, the sodium source came from NaClO4 in the electrolyte, and the current density of the constant current discharge was 100 mA g -1 Finally, a sodium-rich iron-based Prussian blue sodium ion battery positive electrode material is obtained, whose sodium content is not less than 10%.

2. The method for preparing the sodium-rich iron-based Prussian blue material according to claim 1, wherein: In step (1), the iron salt is ferrous chloride or ferrous acetate; and the molar ratio of the iron salt to sodium citrate is 1:1-10.

3. The method for preparing the sodium-rich iron-based Prussian blue material according to claim 2, wherein: Preferably, the molar ratio of iron salt to sodium citrate is 1:

5.

4. The method for preparing the sodium-rich iron-based Prussian blue material according to claim 1, wherein: The molar ratio of sodium ferrocyanide, iron salt and ascorbic acid in step (1) is 1:0.6~1.5:3~10.

5. The method for preparing the sodium-rich iron-based Prussian blue material according to claim 1, wherein: The sodium supplement in step (1) is at least one of sodium chloride NaCl, sodium carbonate Na2CO3, and sodium acetate CH3COONa, and the mass ratio of polyvinyl pyrrolidone to the sodium supplement is 1~1.5:5.5~7.

6. The method for preparing the sodium-rich iron-based Prussian blue material according to claim 1, wherein: In step (2), under N2 atmosphere, the stirring speed is 400-600 rpm, the reaction temperature is 45-55°C, and the dropwise addition rate of solution A and solution B is controlled at 8-10 mL / h.

7. The method for preparing the sodium-rich iron-based Prussian blue material according to claim 1, wherein: In step (2), the heating and stirring time at 45-55° C. is 10-12 h; the aging time at room temperature is 10-30 h; and the vacuum drying is performed at 100-140° C. for 10-12 h.

8. The method for preparing the sodium-rich iron-based Prussian blue material according to claim 1, wherein: The mass ratio of the iron-based Prussian blue sodium ion battery positive electrode material after water washing in step (4) to acetylene black and polyvinylidene fluoride is 7:2:

1.

9. A sodium-rich iron-based Prussian blue material, characterized in that: The material prepared by the method according to any one of claims 1 to 8 has a sodium content of not less than 10%.

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