Manganese-based Prussian blue analogue positive electrode for sodium ion battery and preparation method of manganese-based Prussian blue analogue positive electrode

Abstract

The invention provides a manganese-based Prussian blue analogue positive electrode for a sodium-ion battery and a preparation method of the manganese-based Prussian blue analogue positive electrode, and belongs to the technical field of sodium-ion battery positive electrode materials. The preparation method comprises the following steps: mixing a manganese source, a chelating agent and a cyanide ferric salt aqueous solution for hydrothermal reaction to obtain a manganese-based Prussian blue analogue material, then mixing the manganese-based Prussian blue analogue material with a conductive agent and a binder to prepare positive electrode slurry, and then coating a current collector with the positive electrode slurry to prepare the positive electrode. The manganese-based Prussian blue analogue positive electrode is prepared by adopting a simple hydrothermal method, and the manganese-based Prussian blue analogue positive electrode has excellent performances of high specific capacity, high discharge platform and stable and non-inclined platform, and has ultrahigh energy density. The manganese-based Prussian blue analogue positive electrode obtained by the preparation method disclosed by the invention can obtain relatively high cycling stability under the condition of not carrying out any post-treatment. The preparation method is simple in process, easy to operate, suitable for mass production and suitable for industrial application.

Description

Technical Field

[0001] The present invention relates to the technical field of cathode materials for sodium-ion batteries, and particularly to a manganese-based Prussian blue analogue cathode for sodium-ion batteries and a preparation method thereof. Background Art

[0002] In existing energy storage technologies, lithium-ion batteries are highly favored by the market due to their excellent energy storage performance and wide application fields. However, with the large-scale application of lithium-ion batteries, drawbacks such as tight raw material supply and potential safety hazards have gradually emerged. Therefore, to ensure national resource security and people's lives, it has become extremely urgent to develop a new type of secondary energy storage battery with rich resources, low cost, and high safety to replace lithium-ion batteries. Sodium-ion batteries have become the optimal choice to replace lithium-ion batteries due to their abundant reserves and high safety.

[0003] The electrochemical performance of sodium-ion batteries is largely limited by the cathode material. This key material not only affects the energy density and safety of the battery but also is an important factor determining the overall performance of the battery. Among them, Prussian blue analogues stand out from numerous cathode materials due to their unique framework structure and excellent electrochemical performance.

[0004] Prussian blue analogues are divided into different types according to their transition metal elements. Among them, manganese-based Prussian blue analogues have the greatest potential for high capacity and high potential platforms. In recent years, researchers have developed various manganese-based Prussian blue analogues. For example, (CN116169285A) prepared a sodium-rich and low-water-content manganese-based Prussian blue analogue by introducing an inert gas during the synthesis process, achieving good cycle stability; (CN 116282073B) controlled the reaction rate by adding raw materials in batches with the assistance of a reducing agent, improving the crystallinity of the manganese-based Prussian blue analogue and achieving good cycle stability and rate performance; (CN118724015A) added a manganese-based Prussian blue analogue rich in vacancy defects to a sodium ethylenediaminetetraacetate solution for vacancy repair, enhancing the structural stability and reducing the content of lattice water, and achieving high capacity and cycle stability. However, although these strategies have achieved good results, they are still far from their theoretical capacity, and the effects on the charge-discharge platform and energy density are not mentioned. In fact, lower and sloping charge-discharge potential platforms will seriously affect their energy density and voltage stability during charge and discharge. In addition, the existing synthesis methods are too complex and the synthesis conditions are strict, which is not conducive to industrial regulation. Therefore, it is of great significance to develop a manufacturing process for a manganese-based Prussian blue analogue cathode for sodium-ion batteries with high capacity, high platform, high energy density, easy synthesis, and no post-treatment. Summary of the Invention

[0005] The object of the present invention is to provide a manganese-based Prussian blue analogue cathode for sodium-ion batteries and a preparation method thereof, which are used to solve the technical problems of low specific capacity, low energy density and complex preparation process of existing sodium-ion cathodes.

[0006] In order to achieve the above object of the invention, the present invention provides the following technical solutions:

[0007] The present invention provides a preparation method of a manganese-based Prussian blue analogue cathode for sodium-ion batteries, comprising the following steps:

[0008] 1) Mix a manganese source and a chelating agent in water to obtain solution A;

[0009] 2) Add an iron cyanide aqueous solution to solution A and stir, and perform a hydrothermal reaction on the obtained mixture to obtain a manganese-based Prussian blue analogue suspension;

[0010] 3) Centrifuge, wash and vacuum-dry the manganese-based Prussian blue analogue suspension in sequence to obtain a manganese-based Prussian blue analogue material;

[0011] 4) Mix the manganese-based Prussian blue analogue material, a conductive agent and a binder to obtain a mixed powder, and then add N-methylpyrrolidone for ball milling to obtain a manganese-based Prussian blue analogue cathode slurry;

[0012] 5) Coat the manganese-based Prussian blue analogue cathode slurry on an Al current collector, vacuum-dry and press it to obtain a manganese-based Prussian blue analogue cathode.

[0013] Further, the manganese source includes one or more of manganese sulfate, manganese acetate, manganese chloride and manganese nitrate; the chelating agent includes one or more of ethylenediaminetetraacetic acid, pyrophosphoric acid, sodium pyrophosphate, citric acid, sodium citrate, potassium citrate, acetic acid, sodium acetate, polyvinylpyrrolidone, oxalic acid and sodium oxalate.

[0014] Further, in solution A, the concentration of the manganese source is 0.005-0.5 mol / L, and the concentration of the chelating agent is 0.005-1.5 mol / L.

[0015] Further, the iron cyanide salt in the iron cyanide aqueous solution includes one or more of potassium ferricyanide, potassium ferrocyanide and sodium ferrocyanide, and the concentration of the iron cyanide aqueous solution is 0.005-0.5 mol / L.

[0016] Further, the stoichiometric ratio of Mn in solution A to Fe in the iron cyanide aqueous solution is 0.1-10, the rate of adding the iron cyanide aqueous solution to solution A is 0.05-100 L / h, and the stirring time is 3-36000 s.

[0017] Further, in step 3), the temperature of the hydrothermal reaction is 60-180°C, and the time of the hydrothermal reaction is 4-24 h;

[0018] The rotation speed of the centrifugation is 3000-15000 r / min, the time of the centrifugation is 1-60 min, the temperature of the vacuum drying is 60-180°C, the vacuum degree of the vacuum drying is -0.3 to -0.01 MPa, and the time of the vacuum drying is 6-96 h.

[0019] Further, the conductive agent includes one or more of acetylene black, conductive carbon black, single-walled carbon nanotubes, and multi-walled carbon nanotubes, and the binder includes one or more of polyacrylic acid, polyvinylidene fluoride, polyvinylidene difluoride, and sodium carboxymethyl cellulose;

[0020] The mass ratio of the manganese-based Prussian blue analogue material, the conductive agent, and the binder is 5:1-7:0.25-2.25.

[0021] Further, the mass ratio of the mixed powder and N-methylpyrrolidone is 1:3-12, the rotation speed of the ball milling is 100-600 r / min, and the time of the ball milling is 0.5-8 h.

[0022] Further, the amount of the manganese-based Prussian blue analogue relative to the Al current collector is 2-12 mg / cm 2 ;

[0023] In step 5), the temperature of the vacuum drying is 60-180°C, the vacuum degree of the vacuum drying is -0.3 to -0.01 MPa, and the time of the vacuum drying is 6-96 h.

[0024] The present invention also provides a manganese-based Prussian blue analogue positive electrode for a sodium-ion battery.

[0025] The beneficial effects of the present invention:

[0026] 1) The preparation method of the manganese-based Prussian blue analogue positive electrode of the present invention is simple, easy to operate, and suitable for industrial application.

[0027] 2) The manganese-based Prussian blue analogue positive electrode prepared by the present invention can reach a discharge specific capacity of up to 174 mAh·g -1 , which is very close to the theoretical specific capacity of this material.

[0028] 3) The manganese-based Prussian blue analogue positive electrode prepared by the present invention has a high discharge platform of 3.63 V, and the platform length is long, very stable, and the charge-discharge voltage is stable.

[0029] 4) The manganese-based Prussian blue analogue positive electrode prepared by the present invention has an energy density as high as 591.25 Wh·kg -1 . Brief Description of the Drawings

[0030] Figure 1 is the X-ray diffraction (XRD) pattern of Example 1 and Example 2;

[0031] Figure 2 is the scanning electron microscope (SEM) image of Example 1;

[0032] Figure 3 is the X-ray photoelectron spectroscopy (XPS) of Example 1, where Figure a is the narrow scan of Fe and Figure b is the narrow scan of Mn;

[0033] Figure 4 is the discharge specific capacity diagram of Example 1 at a current density of 20 mA·g -1 ;

[0034] Figure 5 is the discharge plateau diagram of Example 1 at a current density of 20 mA·g -1 ;

[0035] Figure 6 is the scanning electron microscope image of Example 2;

[0036] Figure 7 is the discharge specific capacity diagram of Example 2 at a current density of 20 mA·g -1 ;

[0037] Figure 8 is the discharge plateau diagram of Example 2 at a current density of 20 mA·g -1 ;

[0038] Figure 9 is the discharge specific capacity diagram of Example 3 at a current density of 20 mA·g -1 ;

[0039] Figure 10 is the discharge plateau diagram of Example 3 at a current density of 20 mA·g -1 ;

[0040] Figure 11 is the discharge specific capacity diagram of Example 4 at a current density of 20 mA·g -1 ;

[0041] Figure 12 is the discharge plateau diagram of Example 4 at a current density of 20 mA·g -1 ;

[0042] Figure 13 is the discharge specific capacity diagram of Example 5 at a current density of 20 mA·g -1 ;

[0043] Figure 14 The discharge plateau diagram of Example 5 at a current density of 20 mA·g -1 ;

[0044] Figure 15 The discharge specific capacity diagram of Comparative Example 1 at a current density of 50 mA·g -1 ;

[0045] Figure 16 The discharge plateau diagram of Comparative Example 1 at a current density of 50 mA·g -1 ;

[0046] Figure 17 The discharge specific capacity diagram of Comparative Example 2 at a current density of 20 mA·g -1 ;

[0047] Figure 18 The discharge plateau diagram of Comparative Example 2 at a current density of 20 mA·g -1 ; Detailed implementation method

[0048] The present invention provides a preparation method of a manganese-based Prussian blue analogue cathode for a sodium-ion battery, comprising the following steps:

[0049] 1) Mix a manganese source and a chelating agent in water to obtain solution A;

[0050] 2) Add an aqueous solution of iron(III) cyanide to solution A and stir, and perform a hydrothermal reaction on the obtained mixture to obtain a manganese-based Prussian blue analogue suspension;

[0051] 3) Centrifuge, wash, and vacuum-dry the manganese-based Prussian blue analogue suspension in sequence to obtain a manganese-based Prussian blue analogue material;

[0052] 4) Mix the manganese-based Prussian blue analogue material, a conductive agent, and a binder to obtain a mixed powder, and then add N-methylpyrrolidone for ball milling to obtain a manganese-based Prussian blue analogue cathode slurry;

[0053] 5) Coat the manganese-based Prussian blue analogue cathode slurry on an Al current collector, vacuum-dry it, and then press it into a sheet to obtain a manganese-based Prussian blue analogue cathode.

[0054] In the present invention, the manganese source includes one or more of manganese sulfate, manganese acetate, manganese chloride, and manganese nitrate, preferably one or more of manganese sulfate, manganese acetate, and manganese chloride; the chelating agent includes one or more of ethylenediaminetetraacetic acid, pyrophosphoric acid, sodium pyrophosphate, citric acid, sodium citrate, potassium citrate, acetic acid, sodium acetate, polyvinylpyrrolidone, oxalic acid, and sodium oxalate, preferably one or more of ethylenediaminetetraacetic acid, disodium ethylenediaminetetraacetate, pyrophosphoric acid, and sodium pyrophosphate.

[0055] In the present invention, in the solution A, the concentration of the manganese source is 0.005 - 0.5 mol / L, preferably 0.01 - 0.4 mol / L, and more preferably 0.1 - 0.3 mol / L; the concentration of the chelating agent is 0.005 - 1.5 mol / L, preferably 0.01 - 1.2 mol / L, more preferably 0.1 - 1.0 mol / L, and even more preferably 0.2 - 0.8 mol / L.

[0056] In the present invention, the ferric cyanide salt in the aqueous ferric cyanide solution includes one or more of potassium ferricyanide, potassium ferrocyanide, and sodium ferrocyanide, preferably potassium ferricyanide; the concentration of the aqueous ferric cyanide solution is 0.005 - 0.5 mol / L, preferably 0.01 - 0.4 mol / L, and more preferably 0.1 - 0.3 mol / L.

[0057] In the present invention, the stoichiometric ratio of Mn in the solution A to Fe in the aqueous ferric cyanide solution is 0.1 - 10, preferably 0.2 - 8, and more preferably 0.3 - 7; the rate of adding the aqueous ferric cyanide solution to the solution A is 0.05 - 100 L / h, preferably 1 - 90 L / h, and more preferably 10 - 80 L / h; the stirring time is 3 - 36000 s, preferably 30 - 30000 s, and more preferably 100 - 10000 s.

[0058] In the present invention, in the step 3), the temperature of the hydrothermal reaction is 60 - 180 °C, preferably 80 - 160 °C, and more preferably 100 - 140 °C; the time of the hydrothermal reaction is 4 - 24 h, preferably 10 - 20 h, and more preferably 15 - 18 h.

[0059] In the present invention, the rotation speed of the centrifugation is 3000 - 15000 r / min, preferably 4000 - 12000 r / min, and more preferably 5000 - 10000 r / min; the time of the centrifugation is 1 - 60 min, preferably 5 - 50 min, and more preferably 10 - 40 min; the temperature of the vacuum drying is 60 - 180 °C, preferably 80 - 160 °C, and more preferably 100 - 140 °C; the vacuum degree of the vacuum drying is -0.3 - -0.01 MPa, preferably -0.2 - -0.1 MPa; the time of the vacuum drying is 6 - 96 h, preferably 10 - 90 h, and more preferably 15 - 80 h.

[0060] In the present invention, the conductive agent includes one or more of acetylene black, conductive carbon black, single-walled carbon nanotubes, and multi-walled carbon nanotubes, preferably acetylene black; the binder includes one or more of polyacrylic acid, polyvinylidene fluoride, polyvinylidene difluoride, and sodium carboxymethyl cellulose, preferably polyacrylic acid.

[0061] In the present invention, the mass ratio of the manganese-based Prussian blue analogue material, conductive agent, and binder is 5:1 to 7:0.25 to 2.25, preferably 5:2 to 6:0.5 to 2.0, and more preferably 5:3 to 5:1.0 to 1.5.

[0062] In the present invention, the mass ratio of the mixed powder and N-methylpyrrolidone is 1:3 to 12, preferably 1:4 to 10, and more preferably 1:5 to 9; the rotation speed of the ball milling is 100 to 600 r / min, preferably 200 to 500 r / min, and more preferably 300 to 400 r / min; the ball milling time is 0.5 to 8 h, preferably 1 to 7 h, and more preferably 2 to 6 h.

[0063] In the present invention, the amount of the manganese-based Prussian blue analogue relative to the Al current collector is 2 to 12 mg / cm 2 , preferably 5 to 10 mg / cm 2 , and more preferably 6 to 8 mg / cm 2 .

[0064] In the present invention, in step 5), the temperature of the vacuum drying is 60 to 180 °C, preferably 80 to 160 °C, and more preferably 100 to 140 °C; the vacuum degree of the vacuum drying is -0.3 to -0.01 MPa, preferably -0.2 to -0.1 MPa; the vacuum drying time is 6 to 96 h, preferably 10 to 90 h, and more preferably 15 to 80 h.

[0065] The present invention also provides a manganese-based Prussian blue analogue positive electrode for a sodium ion battery.

[0066] 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 protection scope of the present invention.

[0067] Example 1

[0068] Manganese chloride, sodium citrate, and deionized water were mixed to obtain solution A, where the concentration of manganese chloride was 0.04 mol / L and the concentration of sodium citrate was 0.104 mol / L;

[0069] An aqueous solution of potassium ferrocyanide was poured into solution A at a rate of 29.88 L / h. After stirring for 20 s, the suspension was added to a reaction kettle and subjected to a hydrothermal reaction at 120 °C for 10 h, where the concentration of the aqueous solution of potassium ferrocyanide was 0.04 mol / L.

[0070] The hydrothermal product was centrifuged at 10,000 r / min for 5 min, washed alternately with deionized water and ethanol, and finally centrifuged and separated with ethanol. The obtained precipitate was placed in a vacuum drying oven with a vacuum degree of -0.1 MPa and dried at 100 °C for 24 h to obtain the PBA-1 material.

[0071] The PBA-1 material, multi-walled carbon nanotubes, and polyvinylidene fluoride were mixed evenly in a mass ratio of 7:3:2.25 to form a mixed powder. After adding N-methylpyrrolidone with a mass ratio of 1:7.71 to the mixed powder, it was ball-milled at 400 r / min for 4 h to obtain the PBA-1 positive electrode slurry.

[0072] The PBA-1 positive electrode slurry was uniformly coated onto the Al current collector at 6.5 g / cm 2 and vacuum-dried at a vacuum degree of -0.1 MPa and a temperature of 120 °C for 24 h, followed by pressing to obtain the PBA-1 positive electrode, which was then applied to a sodium-ion battery.

[0073] The XRD pattern of the above PBA-1 material is as Figure 1 shown. The sample has a high purity, no impurities, and is a typical monoclinic structure of Prussian blue analogues. The SEM is as Figure 2 shown. The sample presents a hollow cubic morphology of 200 - 300 nm, with good dispersibility, uniform particle size, and is pure without impurities. From the inductively coupled plasma mass spectrometry test results of PBA-1 in Table 1 and the Figure 3 XPS spectrum of 1.49 K 0.06 Na 6 Mn[Fe(CN) 6 can be obtained that the chemical formula of PBA-1 is. It has a relatively high alkali metal content and no vacancy defects.

[0074] Table 1 Test results

[0075] Element type Na K Fe Mn Content 0.058 1.495 1 1.004

[0076] The above PBA-1 positive electrode was assembled into a coin-type sodium-ion half-cell, and the cycle performance test was carried out at a current density of 20 mA·g -1 . The results are as Figure 4 shown. The highest specific capacity is up to 174 mAh·g -1 ; the discharge plateau is as Figure 5 shown. Its discharge plateau is as high as 3.63 V and 3.47 V, the discharge plateau is relatively long, and the plateau is almost non-inclined. The PBA-1 positive electrode has an energy density as high as 591.25 Wh·kg -1 .

[0077] Example 2

[0078] The difference from Example 1 is that potassium ferricyanide in Example 1 is replaced with potassium ferrocyanide of the same amount of substance, and the others remain unchanged, obtaining the PBA-2 positive electrode.

[0079] The XRD pattern of the above PBA-2 material is as Figure 1 shown. The sample has a high purity, no impurities, and is a typical monoclinic structure of Prussian blue analog. SEM is as Figure 6 shown. The sample presents a cubic morphology with a size of 50 - 100 nm, good dispersibility, uniform particle size, and is pure without impurities.

[0080] The above PBA-2 positive electrode is assembled into a button-type sodium-ion half-cell, and the cyclic performance test is carried out at a current density of 20 mA·g -1 . The results are as Figure 7 shown. The highest specific capacity is up to 166.3 mAh·g -1 ; the discharge platform is as Figure 8 shown. Its discharge platform is also as high as 3.63 V and 3.47 V, and the platform is long and almost has no inclination. The PBA-2 positive electrode has an energy density as high as 557.84 Wh·kg -1 .

[0081] Example 3

[0082] The difference from Example 1 is that sodium citrate in Example 1 is replaced with citric acid of the same amount of substance, and the others remain unchanged, obtaining the PBA-3 positive electrode.

[0083] The above PBA-3 positive electrode is assembled into a button-type sodium-ion half-cell, and the cyclic performance test is carried out at a current density of 20 mA·g -1 . The results are as Figure 9 shown. The highest specific capacity is up to 116.5 mAh·g -1 ; the discharge platform is as Figure 10 shown. It has three stable discharge platforms at 3.59 V, 3.45 V, and 2.79 V, and most of the platforms are relatively flat. The PBA-3 positive electrode has a high energy density of 374.75 Wh·kg -1 .

[0084] Example 4

[0085] Mix manganese chloride, sodium citrate, and deionized water to obtain solution A, where the concentration of manganese chloride is 0.5 mol / L and the concentration of sodium citrate is 1.5 mol / L;

[0086] Pour the aqueous solution of sodium ferrocyanide into solution A at a rate of 89.5 L / h. After stirring for 20 s, add the suspension into the reaction kettle and carry out hydrothermal reaction at 140 °C for 10 h, where the concentration of the aqueous solution of sodium ferrocyanide is 0.5 mol / L.

[0087] The hydrothermal product was centrifuged at 8000 r / min for 20 min, washed alternately with deionized water and ethanol, and finally centrifuged with ethanol. The obtained precipitate was placed in a vacuum drying oven with a vacuum degree of -0.1 MPa and dried at 100 °C for 24 h to obtain the PBA-4 material.

[0088] The PBA material, conductive carbon black, and polyvinylidene fluoride were mixed evenly in a mass ratio of 5:3:1.8 to form a mixed powder. After adding N-methylpyrrolidone with a mass ratio of 1:6.5 to the mixed powder, it was ball-milled at 400 r / min for 4 h to obtain the PBA-4 positive electrode slurry.

[0089] The PBA-4 positive electrode slurry was uniformly coated onto the Al current collector at 7.1 g / cm 2 After vacuum drying at a vacuum degree of -0.1 MPa and a temperature of 120 °C for 24 h, it was pressed to obtain the PBA positive electrode, which was then applied to a sodium-ion battery.

[0090] The above-mentioned PBA-4 positive electrode was assembled into a coin-type sodium-ion half-cell, and the cyclic performance test was carried out at a current density of 20 mAh·g -1 The results are as follows Figure 11 shown. The highest specific capacity was up to 115.5 mAh·g -1 ; the discharge platform is as shown in Figure 12 It has two obvious platforms at 3.53 V and 3.36 V, and the platform quality is relatively high. The PBA-4 positive electrode has a high energy density of 376.07 Wh·kg -1 .

[0091] Example 5

[0092] Manganese nitrate, potassium citrate, and deionized water were mixed to obtain solution A, where the concentration of manganese nitrate was 0.5 mol / L and the concentration of potassium citrate was 1.0 mol / L;

[0093] An aqueous solution of potassium ferrocyanide was poured into solution A at a rate of 33.6 L / h. After stirring for 20 s, the suspension was added to a reaction kettle and hydrothermally reacted at 100 °C for 10 h, where the concentration of the aqueous solution of potassium ferrocyanide was 0.1 mol / L.

[0094] The hydrothermal product was centrifuged at 12000 r / min for 3 min, washed alternately with deionized water and ethanol, and finally centrifuged with ethanol. The obtained precipitate was placed in a vacuum drying oven with a vacuum degree of -0.2 MPa and dried at 90 °C for 36 h to obtain the PBA-5 material.

[0095] Mix the PBA-5 material, conductive carbon black, and sodium carboxymethylcellulose evenly in a mass ratio of 5:4:1.8 to form a mixed powder. After adding N-methylpyrrolidone with a mass ratio of 1:10 to the mixed powder, ball mill it at a speed of 500 r / min for 4 h to obtain the PBA-5 positive electrode slurry.

[0096] Apply the PBA-5 positive electrode slurry evenly onto the Al current collector at a rate of 6.0 g / cm 2 Vacuum dry it at a vacuum degree of -0.1 MPa and a temperature of 120 °C for 24 h, then press it to obtain the PBA-5 positive electrode, and apply it to a sodium-ion battery.

[0097] Assemble the above PBA-5 positive electrode into a button-type sodium-ion half-cell and conduct a cyclic performance test at a current density of 20 mA·g -1 The results are as follows Figure 13 shown, and the highest specific capacity is up to 105.4 mAh·g -1 ; the discharge platform is as follows Figure 14 shown, with two long and stable discharge platforms at 3.50 V and 2.80 V, and the platform is relatively flat. The PBA-5 positive electrode has a high energy density of 336.85 Wh·kg -1 .

[0098] Comparative Example 1

[0099] Mix manganese acetate, disodium ethylenediaminetetraacetate, and deionized water to obtain Solution A, where the concentration of manganese acetate is 0.2 mol / L and the concentration of disodium ethylenediaminetetraacetate is 0.05 mol / L;

[0100] Pour the aqueous solution of sodium ferrocyanide into Solution A at a rate of 45.0 L / h, stir for 20 s, then add the suspension to the reaction kettle and carry out a hydrothermal reaction at 150 °C for 10 h, where the concentration of the aqueous solution of sodium ferrocyanide is 0.2 mol / L.

[0101] Centrifuge the hydrothermally treated product at a speed of 5000 r / min for 10 min, wash it alternately with deionized water and ethanol, and finally centrifuge and separate it with ethanol. Place the obtained precipitate in a vacuum drying oven with a vacuum degree of -0.1 MPa and dry it at 100 °C for 24 h to obtain the PBA-6 material.

[0102] Mix the PBA-6 material, acetylene black, and polyacrylic acid evenly in a mass ratio of 5:5:2.0 to form a mixed powder. After adding N-methylpyrrolidone with a mass ratio of 1:12 to the mixed powder, ball mill it at a speed of 400 r / min for 4 h to obtain the PBA-6 positive electrode slurry.

[0103] Apply the PBA-6 positive electrode slurry evenly onto the Al current collector at a rate of 6.5 g / cm 2Coated uniformly onto the Al current collector, vacuum-dried at a vacuum degree of -0.1 MPa and a temperature of 120 °C for 24 h, then pressed to obtain the PBA-6 positive electrode, and applied it to a sodium-ion battery.

[0104] The above PBA-6 positive electrode was assembled into a coin-type sodium-ion half-cell and subjected to a cyclic performance test at a current density of 50 mA·g -1 The results are as Figure 15 shown, the highest specific capacity is only 45.3 mAh·g -1 , and the capacity is unstable, with a relatively long activation process; the discharge plateau is as Figure 16 shown, it has two indistinct plateaus at 3.50 V and 2.70 V, the plateaus are short, and the inclination is relatively serious. Due to the low capacity, the PBA-6 positive electrode only has an energy density of 124.75 Wh·kg -1 .

[0105] Comparative Example 2

[0106] Manganese chloride, citric acid and deionized water were mixed to obtain Solution A, where the concentration of manganese chloride was 0.04 mol / L and the concentration of sodium citrate was 0.104 mol / L;

[0107] An aqueous solution of potassium ferricyanide was poured into Solution A at a rate of 29.88 L / h, stirred for 20 s without hydrothermal treatment, and the product was directly centrifuged at a speed of 10,000 r / min for 5 min, washed alternately with deionized water and ethanol, and finally centrifuged and separated with ethanol. The obtained precipitate was placed in a vacuum drying oven with a vacuum degree of -0.1 MPa and dried at 100 °C for 24 h to obtain the PBA-7 material.

[0108] The PBA-7 material, multi-walled carbon nanotubes and polyvinylidene fluoride were mixed evenly in a mass ratio of 7:3:2.25 to form a mixed powder. After adding N-methylpyrrolidone with a mass ratio of 1:7.71 to the mixed powder, ball-milled at a speed of 400 r / min for 4 h to obtain the PBA-7 positive electrode slurry.

[0109] The PBA-7 positive electrode slurry was coated uniformly onto the Al current collector at 6.5 g / cm 2 , vacuum-dried at a vacuum degree of -0.1 MPa and a temperature of 120 °C for 24 h, then pressed to obtain the PBA-7 positive electrode, and applied it to a sodium-ion battery.

[0110] The above PBA-7 positive electrode was assembled into a coin-type sodium-ion half-cell and subjected to a cyclic performance test at a current density of 20 mA·g -1 The results are as Figure 17 shown, the highest specific capacity is only 49.2 mAh·g -1 ; the discharge plateau is as Figure 18As shown, the PBA-7 positive electrode only has a relatively low plateau around 3.0V, and the slope is relatively severe. Due to the low capacity and low discharge plateau, the PBA-7 positive electrode only has an energy density of 145.04 Wh·kg -1 .

[0111] Compared with the comparative examples, the PBA positive electrodes in the examples all show higher specific capacity and better cycle stability in terms of capacity, which means longer battery life; in terms of voltage plateau, the PBAs in the examples all show ideal discharge plateaus with high potential, smoothness and longer length, which means stable voltage during discharge. Under the combined action of the above factors, the samples in the examples all show ultra-high energy density.

[0112] As can be seen from the above examples, the present invention provides a manganese-based Prussian blue analogue positive electrode for sodium-ion batteries and its preparation method. The present invention adopts a simple hydrothermal method to prepare a manganese-based Prussian blue analogue positive electrode, which has excellent properties such as high specific capacity, high discharge plateau, stable and non-inclined plateau, and ultra-high energy density. The manganese-based Prussian blue analogue positive electrode obtained by the present invention can obtain high cycle stability without any post-treatment. The preparation method has a simple process, is easy to operate, can be mass-produced, and is suitable for industrial application.

[0113] The above are only the preferred embodiments of the present invention. It should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing a manganese-based Prussian blue analogue positive electrode for a sodium ion battery, characterized in that: The following steps are involved: 1) mixing a manganese source and a chelating agent in water to obtain a solution A; 2) adding an aqueous solution of ferric cyanide salt to solution A and stirring, and subjecting the obtained mixed solution to a hydrothermal reaction to obtain a suspension of a manganese-based Prussian blue analog; 3) centrifuging, washing, and vacuum drying the manganese-based Prussian blue analog suspension in sequence to obtain a manganese-based Prussian blue analog material; 4) mixing a manganese-based Prussian blue analog material, a conductive agent and a binder to obtain a mixed powder, and then adding N-methylpyrrolidone for ball milling to obtain a manganese-based Prussian blue analog positive electrode slurry; 5) coating the manganese-based Prussian blue analogue positive electrode slurry on an Al current collector, vacuum drying and then pressing the sheet to obtain a manganese-based Prussian blue analogue positive electrode.

2. The preparation method according to claim 1, characterized in that: The manganese source comprises one or more of manganese sulfate, manganese acetate, manganese chloride and manganese nitrate; the chelating agent comprises one or more of ethylenediaminetetraacetic acid, pyrophosphoric acid, sodium pyrophosphate, citric acid, sodium citrate, potassium citrate, acetic acid, sodium acetate, polyvinylpyrrolidone, oxalic acid and sodium oxalate.

3. The preparation method according to claim 2, characterized in that: In the solution A, the concentration of the manganese source is 0.005-0.5 mol / L, and the concentration of the chelating agent is 0.005-1.5 mol / L.

4. The preparation method according to claim 2 or 3, characterized in that: The ferric cyanide salt in the ferric cyanide salt aqueous solution comprises one or more of potassium ferrocyanide, potassium ferrocyanide and sodium ferrocyanide, and the concentration of the ferric cyanide salt aqueous solution is 0.005-0.5 mol / L.

5. The preparation method according to claim 4, characterized in that: The stoichiometric ratio of Mn in the solution A to Fe in the ferric cyanide aqueous solution is 0.1-10, the rate of adding the ferric cyanide aqueous solution into the solution A is 0.05-100 L / h, and the stirring time is 3-36000 s.

6. The preparation method according to claim 1, 2 or 5, characterized in that: In the step 3), the temperature of the hydrothermal reaction is 60 to 180° C., and the time of the hydrothermal reaction is 4 to 24 hours; The centrifugal speed is 3000-15000 r / min, the centrifugal time is 1-60 min, the vacuum drying temperature is 60-180° C., the vacuum degree of vacuum drying is -0.3--0.01 MPa, and the vacuum drying time is 6-96 h.

7. The preparation method according to claim 6, characterized in that: The conductive agent comprises one or more of acetylene black, conductive carbon black, single-walled carbon nanotubes and multi-walled carbon nanotubes, and the binder comprises one or more of polyacrylic acid, polyvinylidene fluoride, polyvinylidene fluoride and sodium carboxymethyl cellulose; The mass ratio of the manganese-based Prussian blue analog material, the conductive agent and the binder is 5:1-7:0.25-2.

25.

8. The preparation method according to claim 5 or 7, characterized in that: The mass ratio of the mixed powder to N-methylpyrrolidone is 1:3-12, the rotation speed of the ball mill is 100-600 r / min, and the ball milling time is 0.5-8 h.

9. The preparation method according to claim 8, characterized in that: The amount of the manganese-based Prussian blue analogue relative to the Al current collector is 2 to 12 mg / cm 2 ; In the step 5), the vacuum drying temperature is 60 to 180° C., the vacuum degree of the vacuum drying is -0.3 to -0.01 MPa, and the vacuum drying time is 6 to 96 hours.

10. A manganese-based Prussian blue analogue positive electrode for a sodium ion battery prepared by the preparation method according to any one of claims 1 to 9.

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