A potassium ferric sulfate electrode material, its preparation method and application

Abstract

This invention provides a potassium ferric sulfate electrode material, its preparation method, and its application, relating to the field of cathode materials for sodium-ion batteries. The preparation method of the potassium ferric sulfate electrode material includes the following steps: mixing potassium permanganate, a polymer, and water for a hydrothermal reaction to obtain manganese hydroxide; mixing manganese hydroxide with anhydrous ethanol to prepare an alcoholic solution of manganese hydroxide, and reacting this solution with a mixed solution containing ferrous sulfate and potassium sulfate to obtain potassium ferric sulfate. The preparation method of the potassium ferric sulfate electrode material disclosed in this invention does not require the use of strong acid solutions, has mild reaction conditions, a simple process, and is easy to operate, showing good prospects for industrial application. When used as a cathode material for sodium-ion batteries, it exhibits excellent electrochemical performance, good long-term cycle stability, and high rate performance.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery cathode materials, and in particular to a potassium ferric sulfate electrode material, its preparation method, and its application. Background Technology

[0002] In recent years, the shortage and uneven distribution of lithium resources have become increasingly prominent. In contrast, sodium-ion batteries have seen a continuous rise in research interest due to their abundant raw material sources and low cost. In sodium-ion battery systems, the performance of the cathode material directly affects the battery's energy density and production cost. Therefore, developing cathode materials with high energy density, high safety, and low cost is particularly important. Iron-based sulfate cathodes (such as jaundice) have attracted much attention due to their abundant raw material sources, low cost, and high operating voltage. Furthermore, the layered crystal structure of jaundice provides a rapid ion diffusion channel. While there have been reports on the preparation of jaundice in recent years, most methods employ hydrothermal or solvothermal processes and utilize strong acid solutions during synthesis. These methods are complex, time-consuming, and inherently dangerous. Therefore, there is an urgent need to develop a green, environmentally friendly method for preparing jaundice with mild reaction conditions. Summary of the Invention

[0003] The purpose of this invention is to provide a potassium ferric alum electrode material, its preparation method and application, to solve the problems that the preparation of existing potassium ferric alum electrode materials requires strong acid solutions and the methods are complicated and time-consuming.

[0004] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0005] This invention provides a method for preparing a potassium ferric sulfate electrode material, comprising the following steps:

[0006] 1) A hydrothermal reaction is carried out by mixing potassium permanganate, a polymer and water to obtain manganese hydroxyoxide;

[0007] 2) Prepare an alcoholic solution of manganese hydroxyoxide by mixing manganese hydroxyoxide with anhydrous ethanol, and react it with a mixed solution containing ferrous sulfate and potassium sulfate to obtain jaundice iron alum electrode material.

[0008] Preferably, the mass ratio of potassium permanganate, polymer and water in step 1) is 0.15-0.3g: 0.05-0.1g: 150-170mL;

[0009] The polymer includes one or more of polyvinylpyrrolidone, polyvinyl alcohol, and polyacrylic acid.

[0010] Preferably, the hydrothermal reaction in step 1) is carried out at a temperature of 120–160°C for 25–30 hours.

[0011] Preferably, the molar ratio of manganese hydroxide, ferrous sulfate, and potassium salt in step 2) is 3:2 to 3:1;

[0012] The ratio of manganese hydroxyoxide to anhydrous ethanol was 0.0045 mol: 40–60 mL;

[0013] The ratio of ferrous sulfate, potassium sulfate and water is 0.003-0.0045 mol: 0.0015 mol: 15-40 mL.

[0014] Preferably, the reaction temperature in step 2) is 60–90°C and the reaction time is 3–12 h.

[0015] Preferably, the potassium salt in step 2) includes one or more of potassium nitrate, potassium chloride, and potassium sulfate;

[0016] The ferrous sulfate salt includes one or more of ferrous sulfate, ferrous sulfate pentahydrate, ferrous ammonium sulfate hexahydrate, and ferrous sulfate heptahydrate.

[0017] The present invention also provides a potassium ferric sulfate electrode material prepared by the above preparation method.

[0018] This invention also provides an application of the above-mentioned potassium ferric sulfate electrode material in the positive electrode material of sodium-ion batteries. The preparation method of the sodium-ion battery positive electrode material is as follows:

[0019] A suspension was prepared by mixing potassium ferric sulfate electrode material, water, and carbon nanotubes. The suspension was then filtered to obtain a potassium ferric sulfate self-supporting electrode.

[0020] Preferably, the mass ratio of the potassium ferric sulfate electrode material to the carbon nanotubes is 1:31.25 to 125.

[0021] The present invention has at least the following beneficial effects:

[0022] 1. The method for preparing the potassium ferric sulfate electrode material disclosed in this invention does not require the use of strong acid solutions, has mild reaction conditions, simple process, and easy operation, and has good prospects for industrial application.

[0023] 2. The potassium ferrous sulfate prepared by this invention exhibits good electrochemical performance, good long-term cycle stability, and high rate performance when used as a cathode material for sodium-ion batteries. It is an ideal cathode material for sodium-ion batteries with broad commercial application prospects.

[0024] 3. The substrate-free self-supporting potassium ferric sulfate electrode does not contain inert binder particles, has a continuous electronic conductivity path, and the active material is tightly wrapped in a three-dimensional conductive network, which improves the electronic conductivity of the material. Attached Figure Description

[0025] Figure 1 The X-ray diffraction pattern of manganese hydroxyoxide prepared in Example 1;

[0026] Figure 2 A scanning electron microscope image of manganese hydroxyl oxide prepared in Example 1;

[0027] Figure 3 The X-ray diffraction pattern of the potassium ferric sulfate prepared in Example 1;

[0028] Figure 4 This is a scanning electron microscope image of the potassium ferric sulfate prepared in Example 1;

[0029] Figure 5 The X-ray photoelectron spectrum of the potassium ferric sulfate prepared in Example 1 is shown below.

[0030] Figure 6 The infrared spectrum of the potassium ferric sulfate prepared in Example 1;

[0031] Figure 7 The cyclic voltammetry curve of the potassium ferric sulfate self-supporting electrode prepared in Example 1 in an organic sodium-ion battery;

[0032] Figure 8 The charge-discharge curves of the potassium ferric sulfate self-supporting electrode prepared in Example 1 in an organic sodium-ion battery are shown.

[0033] Figure 9 The rate performance of the potassium ferric sulfate self-supporting electrode prepared in Example 1 in an organic sodium-ion battery is shown in the graph.

[0034] Figure 10 The cycling curve of the potassium ferric sulfate self-supporting electrode prepared in Example 1 in an organic sodium-ion battery is shown. Detailed Implementation

[0035] This invention provides a method for preparing a potassium ferric sulfate electrode material, comprising the following steps:

[0036] 1) A hydrothermal reaction is carried out by mixing potassium permanganate, a polymer and water to obtain manganese hydroxyoxide;

[0037] 2) Prepare an alcoholic solution of manganese hydroxyoxide by mixing manganese hydroxyoxide with anhydrous ethanol, and react it with a mixed solution containing ferrous sulfate and potassium sulfate to obtain jaundice iron alum electrode material.

[0038] In this invention, the mass ratio of potassium permanganate, polymer and water in step 1) is 0.15-0.3g:0.05-0.1g:150-170mL, preferably 0.17-0.28g:0.06-0.09g:155-165mL, more preferably 0.2-0.25g:0.07-0.08g:158-163mL, and even more preferably 0.22-0.24g:0.07-0.08g:160mL.

[0039] In this invention, the temperature of the hydrothermal reaction in step 1) is 120-160°C, preferably 125-155°C, more preferably 130-150°C, and even more preferably 135-140°C; the time is 25-30h, preferably 26-29h, and even more preferably 27-28h.

[0040] In this invention, the molar ratio of manganese hydroxyoxide, ferrous sulfate and potassium salt in step 2) is 3:2 to 3:1, preferably 3:2.2 to 2.8:1, more preferably 3:2.4 to 2.6:1, and even more preferably 3:2.5:1.

[0041] In this invention, the ratio of manganese hydroxyoxide to anhydrous ethanol is 0.0045 mol: 40-60 mL, preferably 0.0045 mol: 45-55 mL, and more preferably 0.0045 mol: 50 mL.

[0042] In this invention, the addition ratio of ferrous sulfate, potassium sulfate and water is 0.003-0.0045 mol: 0.0015 mol: 15-40 mL, preferably 0.0032-0.0042 mol: 0.0015 mol: 20-35 mL, and more preferably 0.0035-0.004 mol: 0.0015 mol: 25-30 mL.

[0043] In this invention, the reaction temperature in step 2) is 60-90°C, preferably 65-85°C, more preferably 70-80°C, and even more preferably 75°C; the reaction time is 3-12 hours, preferably 5-10 hours, more preferably 6-9 hours, and even more preferably 7-8 hours.

[0044] In this invention, the potassium salt mentioned in step 2) includes one or more of potassium nitrate, potassium chloride, and potassium sulfate;

[0045] In this invention, the ferrous sulfate salt includes one or more of ferrous sulfate, ferrous sulfate pentahydrate, ferrous ammonium sulfate hexahydrate, and ferrous sulfate heptahydrate.

[0046] The present invention also provides a potassium ferric sulfate electrode material prepared by the above preparation method.

[0047] This invention also provides an application of the above-mentioned potassium ferric sulfate electrode material in the positive electrode material of sodium-ion batteries. The preparation method of the sodium-ion battery positive electrode material is as follows:

[0048] A suspension was prepared by mixing potassium ferric sulfate electrode material, water, and carbon nanotubes. The suspension was then filtered to obtain a potassium ferric sulfate self-supporting electrode.

[0049] In this invention, the mass ratio of the potassium ferric sulfate electrode material to the carbon nanotubes is 1:31.25 to 125, preferably 1:40 to 110, more preferably 1:50 to 100, and even more preferably 1:60 to 90.

[0050] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0051] Example 1

[0052] 1) Dissolve 0.084 g of polyvinylpyrrolidone and 0.168 g of potassium permanganate in 160 mL of deionized water. After stirring for 50 min, transfer the solution to a 200 mL reactor and heat at 140 °C for 25 h in an electric drying oven for a hydrothermal reaction. After the reaction, separate the solvent and dry to obtain manganese hydroxyl oxide nanowires. The X-ray diffraction pattern of the manganese hydroxyl oxide nanowires is shown below. Figure 1 As shown, from Figure 1 As can be seen, the diffraction peaks are sharp and intense. All diffraction peaks of the product are consistent with the standard diffraction peaks of manganese hydroxide (JCPDS Card No. 41-1379). No impurity absorption peaks were observed, indicating that the product has high purity. The scanning electron microscope image of the manganese hydroxide nanowires is shown below. Figure 2 As shown, from Figure 2 It can be seen that the manganese hydroxyoxide nanowires are grown very neatly and smoothly, and are on a large scale. The length of the manganese hydroxyoxide nanowires is about 5 to 10 μm, and the diameter is about 70 to 100 nm.

[0053] 2) 0.393 g (0.0045 mol) of manganese hydroxyoxide was ultrasonically dispersed in 50 mL of anhydrous ethanol to obtain a homogeneous dispersion. Then, 1.2552 g (0.0045 mol) of ferrous sulfate heptahydrate and 0.1526 g (0.0015 mol) of potassium nitrate were dissolved in 30 mL of deionized water to obtain a mixed solution of iron and potassium ions. This solution was added dropwise to the ethanol dispersion, and then stirred until homogeneous at room temperature to obtain the reaction precursor solution.

[0054] 3) The obtained reaction precursor solution was transferred to a sealed glass bottle and placed in a 90℃ water bath. After heating and stirring for 3 hours, the mixture was allowed to cool naturally. The reaction solution was then filtered using a vacuum filtration device. The solution was washed with deionized water and anhydrous ethanol to obtain a yellow powder. Finally, the powder was dried in an 80℃ forced-air drying oven for 24 hours to obtain the potassium ferric sulfate electrode material. The X-ray diffraction pattern of the potassium ferric sulfate electrode material is shown below. Figure 3 As shown, from Figure 3 As can be seen from the image, the obtained product completely matches the standard card (JCPDSCard No. 22-0827), with no impurity peaks, indicating that the synthesized substance is indeed potassium ferric sulfate. Furthermore, the sharp diffraction peaks indicate good crystallinity of the product. The scanning electron microscope image of the potassium ferric sulfate electrode material is shown below. Figure 4 As shown, from Figure 4 It can be seen that a large number of polyhedral structures are formed, indicating a good crystal structure; the X-ray photoelectron spectrum of the potassium ferric sulfate electrode material is shown in the figure. Figure 5 As shown, from Figure 5 Characteristic peaks for K, Fe, S, and O can be observed, and no other impurity peaks are present, proving that the synthesized sample has high purity; the infrared spectrum of the potassium ferric sulfate electrode material is shown below. Figure 6 As shown, from Figure 6 It can be seen that the height ranges from 500 to 1400 cm. -1 The range is SO4 2- Overlapping vibration modes, 1100cm -1 The nearby zone is attributed to tetrahedral SO4. 2- Asymmetric stretching, and located at 1010cm -1 The peak reflects SO4 2- Tensile vibration, approximately 3450cm -1 The peak at that location corresponds to OH — The vibration.

[0055] Preparation and performance testing of self-supporting potassium ferric sulfate cathode:

[0056] 10 mg of the potassium ferric alum electrode material prepared in this embodiment was weighed and placed in a glass bottle. 15 mL of deionized water was added, and the mixture was ultrasonically dispersed for 10 min using an ultrasonic cell disruptor to obtain a uniform yellow suspension. 0.625 g of carbon nanotube slurry (0.4 wt% carbon nanotubes, water as dispersant) was added to this suspension, and the mixture was ultrasonically dispersed again for 40 min using an ultrasonic cell disruptor to obtain a black suspension containing potassium ferric alum and carbon nanotubes. This black suspension was quickly filtered using a sintered glass funnel. After filtration, a black film was obtained on the filter membrane. The film was dried in a cool, shaded place indoors. After drying, the black film detached from the filter membrane, yielding the potassium ferric alum sodium-ion battery cathode material.

[0057] The above-mentioned potassium iron alum sodium ion battery positive electrode material was pressed into a 12mm electrode sheet using a tablet press. An electrolyte with a concentration of 1mol / L was prepared using glass fiber as the separator, diethylene glycol dimethyl ether as the solvent and sodium hexafluorophosphate as the electrolyte. A pure sodium sheet was used as the counter electrode. The cells were assembled into a coin cell and the electrochemical performance was tested.

[0058] Figure 7 The cyclic voltammetry curves of the coin cell prepared in this embodiment at different scan rates show that the cyclic voltammetry curves have broad but indistinct redox peaks, indicating obvious pseudocapacitive behavior. Furthermore, the peak position shift is very small as the scan rate increases.

[0059] Figure 8 The charge-discharge curves of the coin cell prepared in this embodiment at different rates show that no plateaus exist at either the lower (0.1C) or higher (30C) rates. This is consistent with... Figure 7 The broad and indistinct redox peaks in the cyclic voltammetry curves correspond to the prepared potassium ferric sulfate, proving that it is a pseudocapacitive electrode material.

[0060] Figure 9 The diagram shows the rate performance of the coin cell prepared in this embodiment. The rate increases from 0.2C to 0.5C, 1C, 2C, 5C, 10C, 20C, and 30C (1C = 160.5 mAg). -1 The reversible capacities were 120.5, 118.0, 109.8, 106.9, 95.9, 88.4, 78.9, and 72.2 mAh g, respectively. -1 When the current density returns to 0.2C, the reversible capacity increases to 119.2 mAh g. -1 Even at a rate as high as 30C, it still has a capacity of 72.2 mAh g. -1 The specific capacity (approximately 61.18% at 0.5C) indicates that the prepared potassium ferric sulfate cathode exhibits excellent rate performance.

[0061] Figure 10 for mA g -1 The cycling performance graph shows that after 1000 cycles at 2C and 5C rates, the capacities are 58.87 mAh g and 58.87 mAh g, respectively. -1 and 52.0mAh g -1 The specific capacity indicates that the prepared potassium ferric sulfate cathode exhibits good cycle stability.

[0062] Example 2

[0063] 1) Dissolve 0.090g of polyvinylpyrrolidone and 0.18g of potassium permanganate in 160mL of deionized water, stir for 50min, transfer to 200mL of reaction vessel, and then heat at 140℃ for 28h in an electric heating drying oven to carry out hydrothermal reaction. After the reaction is completed, separate the solvent and dry to obtain manganese hydroxy oxide nanowires.

[0064] 2) 0.393 g (0.0045 mol) of manganese hydroxyoxide was ultrasonically dispersed in 40 mL of anhydrous ethanol to obtain a homogeneous dispersion. Then, 0.8368 g (0.003 mol) of ferrous sulfate heptahydrate and 0.1526 g (0.0015 mol) of potassium nitrate were dissolved in 35 mL of deionized water to obtain a mixed solution of iron and potassium ions. This solution was added dropwise to the ethanol dispersion, and then stirred until homogeneous at room temperature to obtain the reaction precursor solution.

[0065] 3) The obtained reaction precursor solution was transferred to a sealed glass bottle container and placed in an 80°C water bath. After heating and stirring for 5 hours, the mixture was allowed to cool naturally. The reaction solution was then filtered using a vacuum filtration device. The solution was then washed with deionized water and anhydrous ethanol to obtain a yellow powder. Finally, the powder was dried in an 80°C forced-air drying oven for 24 hours to obtain the potassium ferric sulfate electrode material.

[0066] Preparation and performance testing of self-supporting potassium ferric sulfate cathode:

[0067] 10 mg of the potassium ferric alum electrode material prepared in this embodiment was weighed and placed in a glass bottle. 15 mL of deionized water was added, and the mixture was ultrasonically dispersed for 10 min using an ultrasonic cell disruptor to obtain a uniform yellow suspension. 0.625 g of carbon nanotube slurry (0.4 wt% carbon nanotubes, water as dispersant) was added to this suspension, and the mixture was ultrasonically dispersed again for 40 min using an ultrasonic cell disruptor to obtain a black suspension containing potassium ferric alum and carbon nanotubes. This black suspension was quickly filtered using a sintered glass funnel. After filtration, a black film was obtained on the filter membrane. The film was dried in a cool, shaded place indoors. After drying, the black film detached from the filter membrane, yielding the potassium ferric alum sodium-ion battery cathode material.

[0068] The above-mentioned potassium ferric sulfate sodium ion battery positive electrode material was pressed into a 12mm electrode sheet using a tablet press. A 1mol / L electrolyte was prepared using glass fiber as the separator, diethylene glycol dimethyl ether as the solvent, and sodium hexafluorophosphate as the electrolyte. A pure sodium sheet was used as the counter electrode. A coin cell was assembled and its electrochemical performance was tested. At a current density of 0.5C, its reversible capacity was 113.8 mAh g. -1 After 1000 cycles at 2C and 5C rates, the capacities were 58.42 mAh g and 58.42 mAh g, respectively. -1 and 54.06mAh g -1 .

[0069] Example 3

[0070] 1) Dissolve 0.1g of polyvinyl alcohol and 0.3g of potassium permanganate in 170mL of deionized water, stir for 50min, transfer to 200mL of reaction vessel, and then heat at 140℃ for 25h in an electric heating drying oven to carry out hydrothermal reaction. After the reaction is completed, separate the solvent and dry to obtain manganese hydroxy oxide nanowires.

[0071] 2) 0.393 g (0.0045 mol) of manganese hydroxyoxide was ultrasonically dispersed in 50 mL of anhydrous ethanol to obtain a homogeneous dispersion. Then, 1.2552 g (0.0045 mol) of ferrous sulfate heptahydrate and 0.1526 g (0.0015 mol) of potassium nitrate were dissolved in 40 mL of deionized water to obtain a mixed solution of iron and potassium ions. This solution was added dropwise to the ethanol dispersion, and then stirred until homogeneous at room temperature to obtain the reaction precursor solution.

[0072] 3) The obtained reaction precursor solution was transferred to a sealed glass bottle container and placed in a 60°C water bath. After heating and stirring for 10 hours, it was naturally cooled. The reaction solution was filtered using a vacuum filtration device. Then, it was washed with deionized water and anhydrous ethanol to obtain a yellow powder. Finally, it was dried in an 80°C forced-air drying oven for 24 hours to obtain the potassium ferric sulfate electrode material.

[0073] Preparation and performance testing of self-supporting potassium ferric sulfate cathode:

[0074] 10 mg of the potassium ferric alum electrode material prepared in this embodiment was weighed and placed in a glass bottle. 15 mL of deionized water was added, and the mixture was ultrasonically dispersed for 10 min using an ultrasonic cell disruptor to obtain a uniform yellow suspension. 0.625 g of carbon nanotube slurry (0.4 wt% carbon nanotubes, water as dispersant) was added to this suspension, and the mixture was ultrasonically dispersed again for 40 min using an ultrasonic cell disruptor to obtain a black suspension containing potassium ferric alum and carbon nanotubes. This black suspension was quickly filtered using a sintered glass funnel. After filtration, a black film was obtained on the filter membrane. The film was dried in a cool, shaded place indoors. After drying, the black film detached from the filter membrane, yielding the potassium ferric alum sodium-ion battery cathode material.

[0075] The above-mentioned potassium ferric sulfate sodium ion battery positive electrode material was pressed into a 12mm electrode sheet using a tablet press. A 1mol / L electrolyte was prepared using glass fiber as the separator, diethylene glycol dimethyl ether as the solvent, and sodium hexafluorophosphate as the electrolyte. A pure sodium sheet was used as the counter electrode. A coin cell was assembled and its electrochemical performance was tested. At a current density of 0.5C, its reversible capacity was 123.1 mAh g. -1 After 1000 cycles at 2C and 5C rates, the capacities were 57.33 mAh g and 57.33 mAh g, respectively. -1and 52.74mAh g -1 .

[0076] Example 4

[0077] 1) Dissolve 0.065g of polyvinylpyrrolidone and 0.25g of potassium permanganate in 150mL of deionized water, stir for 50min, transfer to 200mL of reaction vessel, and then heat at 140℃ for 25h in an electric heating drying oven to carry out hydrothermal reaction. After the reaction is completed, separate the solvent and dry to obtain manganese hydroxy oxide nanowires.

[0078] 2) 0.393 g (0.0045 mol) of manganese hydroxyoxide was ultrasonically dispersed in 50 mL of anhydrous ethanol to obtain a homogeneous dispersion. Then, 1.2552 g (0.0045 mol) of ferrous sulfate heptahydrate and 0.1526 g (0.0015 mol) of potassium nitrate were dissolved in 30 mL of deionized water to obtain a mixed solution of iron and potassium ions. This solution was added dropwise to the ethanol dispersion, and then stirred until homogeneous at room temperature to obtain the reaction precursor solution.

[0079] 3) The obtained reaction precursor solution was transferred to a sealed glass bottle container and placed in a 70°C water bath. After heating and stirring for 12 hours, it was naturally cooled. The reaction solution was filtered using a vacuum filtration device. Then, it was washed with deionized water and anhydrous ethanol to obtain a yellow powder. Finally, it was dried in an 80°C forced-air drying oven for 24 hours to obtain the potassium ferric sulfate electrode material.

[0080] Preparation and performance testing of self-supporting potassium ferric sulfate cathode:

[0081] 10 mg of the potassium ferric alum electrode material prepared in this embodiment was weighed and placed in a glass bottle. 15 mL of deionized water was added, and the mixture was ultrasonically dispersed for 10 min using an ultrasonic cell disruptor to obtain a uniform yellow suspension. 0.625 g of carbon nanotube slurry (0.4 wt% carbon nanotubes, water as dispersant) was added to this suspension, and the mixture was ultrasonically dispersed again for 40 min using an ultrasonic cell disruptor to obtain a black suspension containing potassium ferric alum and carbon nanotubes. This black suspension was quickly filtered using a sintered glass funnel. After filtration, a black film was obtained on the filter membrane. The film was dried in a cool, shaded place indoors. After drying, the black film detached from the filter membrane, yielding the potassium ferric alum sodium-ion battery cathode material.

[0082] The above-mentioned potassium ferric sulfate sodium ion battery positive electrode material was pressed into a 12mm electrode sheet using a tablet press. A 1mol / L electrolyte was prepared using glass fiber as the separator, diethylene glycol dimethyl ether as the solvent, and sodium hexafluorophosphate as the electrolyte. A pure sodium sheet was used as the counter electrode. A coin cell was assembled and its electrochemical performance was tested. At a current density of 0.5C, its reversible capacity was 124.8 mAh g. -1After 1000 cycles at 2C and 5C rates, the capacities were 56.92 mAh g and 56.92 mAh g, respectively. -1 and 51.55mAh g -1 .

[0083] Comparative Example 1

[0084] Weigh 2.5104 g of ferrous sulfate heptahydrate and 0.3052 g of potassium nitrate and dissolve them in 200 mL of 0.01 mol / L dilute sulfuric acid aqueous solution. Disperse and mix evenly by ultrasonication to obtain a reaction precursor solution. Place the beaker in a 90℃ water bath and heat and stir for 3 h. After natural cooling, filter the reaction solution using a vacuum filtration device. Then wash and filter three times with deionized water and ethanol respectively to obtain a yellow powder. Finally, dry it in an 80℃ forced-air drying oven for 24 h to obtain the jaundice iron alum electrode material.

[0085] 10 mg of the potassium ferric alum electrode material prepared in this comparative example was weighed and placed in a glass bottle. 15 mL of deionized water was added, and the mixture was ultrasonically dispersed for 10 min using an ultrasonic cell disruptor to obtain a uniform yellow suspension. 0.625 g of carbon nanotube slurry (0.4 wt% carbon nanotubes, water as dispersant) was added to this suspension, and the mixture was ultrasonically dispersed again for 40 min using an ultrasonic cell disruptor to obtain a black suspension containing potassium ferric alum and carbon nanotubes. This black suspension was quickly filtered using a sintered glass funnel. After filtration, a black film was obtained on the filter membrane. The film was dried in a cool, shaded place indoors. After drying, the black film detached from the filter membrane, yielding the potassium ferric alum sodium-ion battery cathode material.

[0086] The above-mentioned potassium ferric sulfate sodium ion battery positive electrode material was pressed into a 12mm electrode sheet using a tablet press. A 1mol / L electrolyte was prepared using glass fiber as the separator, diethylene glycol dimethyl ether as the solvent, and sodium hexafluorophosphate as the electrolyte. A pure sodium sheet was used as the counter electrode. A coin cell was assembled and its electrochemical performance was tested. At a current density of 0.5C, its reversible capacity was 118.16 mAh g. -1 After 1000 cycles at 2C and 5C rates, the capacities were 52.095 mAh g and 52.095 mAh g, respectively. -1 and 50.1925mAh g -1 .

[0087] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a potassium ferric sulfate electrode material, characterized in that, Includes the following steps: 1) Potassium permanganate, a polymer, and water are mixed and subjected to a hydrothermal reaction to obtain manganese hydroxyoxide; 2) Prepare an alcoholic solution of manganese hydroxide by mixing manganese hydroxide with anhydrous ethanol, and react it with a mixed solution containing ferrous sulfate and potassium sulfate to obtain jaundice iron alum electrode material. The polymer includes one or more of polyvinylpyrrolidone, polyvinyl alcohol, and polyacrylic acid.

2. The method for preparing a potassium ferrous sulfate electrode material according to claim 1, characterized in that, The mass ratio of potassium permanganate, polymer and water in step 1) is 0.15~0.3g:0.05~0.1g:150~170mL.

3. The method for preparing a potassium ferrous sulfate electrode material according to claim 2, characterized in that, The hydrothermal reaction in step 1) is carried out at a temperature of 120~160℃ for 25~30h.

4. A method for preparing a potassium ferrous sulfate electrode material according to any one of claims 1 to 3, characterized in that, In step 2), the molar ratio of manganese hydroxide, ferrous sulfate, and potassium salt is 3:2 to 3:

1. The ratio of manganese hydroxyoxide to anhydrous ethanol was 0.0045 mol: 40~60 mL; The ratio of ferrous sulfate, potassium sulfate and water is 0.003~0.0045mol:0.0015mol:15~40mL.

5. The method for preparing a potassium ferrous sulfate electrode material according to claim 4, characterized in that, The reaction temperature in step 2) is 60~90℃, and the reaction time is 3~12h.

6. The method for preparing a potassium ferrous sulfate electrode material according to claim 5, characterized in that, The potassium salt mentioned in step 2) includes one or more of potassium nitrate, potassium chloride, and potassium sulfate; The ferrous sulfate salt includes one or more of ferrous sulfate, ferrous sulfate pentahydrate, ferrous ammonium sulfate hexahydrate, and ferrous sulfate heptahydrate.

7. The potassium ferrous alum electrode material prepared by the method described in any one of claims 1 to 6.

8. The application of the potassium ferrous sulfate electrode material according to claim 7 in the positive electrode material of sodium-ion batteries, characterized in that, The preparation method of sodium-ion battery cathode material is as follows: A suspension was prepared by mixing potassium ferric sulfate electrode material, water, and carbon nanotubes. The suspension was then filtered to obtain a potassium ferric sulfate self-supporting electrode.

9. The application of the potassium ferrous sulfate electrode material according to claim 8 in the positive electrode material of sodium-ion batteries, characterized in that, The mass ratio of the potassium ferric sulfate electrode material to carbon nanotubes is 1:31.25~125.

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