Manganese oxide for aqueous zinc ion battery and its preparation method and application

Abstract

The present invention belongs to the field of ion batteries, and specifically relates to a manganese oxide for aqueous zinc ion batteries, and a preparation method and application thereof. The present invention slowly forms alkaline conditions by slightly dissolving magnesium oxide in water, making the reaction process more controllable and stable, easy to operate, low in cost, high in safety factor, and suitable for mass production. Acidified multi-walled carbon nanotubes can significantly expand the battery capacity. Multi-walled carbon nanotubes containing rich hydroxyl groups surround prismatic β-MnO2, increasing the surface area of ​​the material. Acidified multi-walled carbon nanotubes can also control the growth direction of β-MnO2, improve the ionic conductivity of the overall material, and inhibit the structural collapse of β-MnO2. Too much acidified multi-walled carbon nanotubes will cause serious agglomeration, thereby separating from the prismatic β-MnO2. The β-MnO2-WMCNT prepared by the present invention is used as the positive electrode of an aqueous zinc ion battery, greatly improving the capacity and cycle stability.

Description

Technical Field

[0001] The present invention belongs to the field of ion batteries, and in particular relates to a manganese oxide for aqueous zinc ion batteries, a preparation method thereof, and an application thereof. Background Art

[0002] As time goes by, commercial lithium-ion batteries have gradually become exposed to challenges, such as the low earth abundance of lithium, flammable and explosive electrolytes, and high prices. Research has gradually shifted to other new energy battery options. Aqueous zinc-ion batteries, with their low cost, minimal operating requirements, high theoretical capacity, moderate redox potential, and high safety and stability, have become a promising alternative to lithium-ion batteries.

[0003] Zinc ion cathode materials have been widely studied, with vanadium oxides and manganese oxides being the main materials. Manganese is abundant in the earth's crust, and its oxides have very high redox activity (Mn 2+ 、Mn 3+ 、Mn 4+ 、Mn 7+ ), Mn 7+ Not as good as Mn 4+ Stable, so MnO2 has become the focus of research. Its crystal form includes five main crystal forms (α, β, γ, δ, ε), which are less affected by air and suitable for various preparation conditions. In addition, MnO2 has high Faraday activity and a high potential window. The average operating voltage in aqueous zinc-ion batteries is about 1.2V. In current research, β-MnO2 is easy to form rods and has high crystallinity characteristics. As a positive electrode material for aqueous zinc-ion batteries, it has high capacity and energy density. However, the preparation of β-MnO2 often uses potassium permanganate as a manganese source or Mn 2+ Potassium permanganate is used as a manganese source, along with ammonium persulfate as a strong oxidant. However, potassium permanganate is prone to explosion when exposed to organic substances such as ethanol or easily oxidized substances, while ammonium persulfate readily forms ammonium sulfide in air, which is corrosive. Furthermore, conventional preparation methods, which typically utilize alkaline solutions, result in a violent reaction and poor controllability. Therefore, a safe and stable oxidant is urgently needed for the synthesis of β-MnO2. Furthermore, while MnO2 has a high theoretical capacity, its practical application requires improvement, a factor that valence engineering can address.

[0004] Magnesium oxide has a solubility of 0.00062g / 100mL in water and can continuously hydrolyze in aqueous solutions, creating alkaline conditions. In the absence of other reactants, magnesium oxide will slowly form magnesium hydroxide. The addition of manganese sulfate, due to its smaller solubility product constant, preferentially reacts with hydroxide ions in the aqueous solution to form a precipitation of Mn(OH)2. The oxidant sodium persulfate is non-corrosive, stable in air, and much cheaper than other oxidants. It can oxidize the Mn(OH)2 precipitate into the MnO2 phase. Multi-walled carbon nanotubes, through an acidification reaction, readily attach hydroxyl groups to their surfaces, which can entangle around the MnO2, directly increasing its specific surface area. This allows for the adsorption of more zinc ions, increasing capacity, and directly stabilizing the MnO2 structure. The doping of multi-walled carbon nanotubes can also improve the material's conductivity. Summary of the Invention

[0005] In order to improve the electrochemical performance of MnO2 and ensure the safety of the experimental process, the present invention improves the capacity and cycle stability of MnO2 as a cathode material for aqueous zinc ion batteries through a new synthesis method and valence engineering.

[0006] The present invention provides a method for preparing manganese oxide (β-MnO2-WMCNT, the same below) for aqueous zinc ion batteries, comprising the following steps:

[0007] S11: adding multi-walled carbon nanotubes to a mixed solvent, heating, and separating to obtain acidified multi-walled carbon nanotubes; the mixed solvent is obtained by mixing nitric acid and sulfuric acid and then adding water;

[0008] S12: adding the acidified multi-walled carbon nanotubes to a salt solution, mixing, and obtaining a solution to be reacted; the solute of the salt solution includes magnesium oxide, manganese chloride, and sodium persulfate, and the solvent of the salt solution is water;

[0009] S13: hydrothermally reacting the solution at 140-180° C. for 10-14 hours and then separating the solution to obtain the manganese oxide for aqueous zinc ion battery.

[0010] Preferably, in the mixed solvent, the volume ratio of nitric acid to sulfuric acid is 1:1-3.

[0011] Preferably, in step S11, the heating time is 4-8 hours.

[0012] Preferably, in step S11, the heating temperature is 80-100° C.; during the heating process, water needs to be added from time to time to ensure sufficient moisture.

[0013] Preferably, in step S11, the separation method is centrifugal separation at a speed of 9000-11000 rpm, and then vacuum drying at 50-70° C. for 20-30 hours.

[0014] Preferably, in step S12, the mass ratio of magnesium oxide, manganese chloride and sodium persulfate is 0.5-0.8:2.5-3.5:3-4.

[0015] Preferably, in step S12, the mixing time is 5-20 minutes.

[0016] Preferably, in step S13, the separation method is centrifugal separation at a speed of 5000-7000 rpm.

[0017] Preferably, in step S13, after separation, the mixture is vacuum dried at 50-70° C. for 20-30 hours.

[0018] The present invention also provides a manganese oxide (β-MnO2-WMCNT) for aqueous zinc ion batteries prepared by the above preparation method.

[0019] The present invention also provides an aqueous zinc ion battery positive electrode sheet, which is obtained by mixing acetylene black, polyvinylidene fluoride (PVDF), N-methylpyrrolidone and the above-mentioned manganese oxide for aqueous zinc ion batteries and then coating the mixture on titanium foil.

[0020] Specifically, the aqueous zinc ion battery positive electrode sheet is prepared by the following method: β-MnO2-WMCNT, acetylene black and PVDF are mixed evenly, ground and added with N-methylpyrrolidone, stirred evenly to obtain a slurry, the slurry is scraped on a titanium foil, dried and baked to obtain the aqueous zinc ion battery positive electrode sheet.

[0021] Preferably, the mass ratio of manganese oxide, acetylene black and PVDF for aqueous zinc ion batteries is 6-8:1-2:1-2.

[0022] Specifically, the mass ratio of the β-MnO2-WMCNT, acetylene black and PVDF is 7:2:1.

[0023] The technical solution of the present invention has the following advantages over the prior art:

[0024] This invention improves the battery capacity and cycle stability of MnO2 in aqueous zinc-ion batteries by controlling alkaline conditions for slow formation, ensuring a safe and stable oxidant, and through valence engineering. Compared with existing solutions, it offers economical pricing, stable reactions, simple operation, and significantly improved performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is the X-ray diffraction pattern (XRD) of the material prepared in Comparative Example 1.

[0026] Figure 2This is the X-ray diffraction pattern (XRD) of the material prepared in Example 1.

[0027] Figure 3 This is a capacity diagram of aqueous zinc ion batteries assembled with materials obtained from Comparative Example 1 (MnO2), Example 1 (MnO2-0.4gWMCNT), Example 2 (MnO2-0.2gWMCNT) and Example 3 (MnO2-0.6gWMCNT) of the present invention and tested at a current of 0.1A / g.

[0028] Figure 4 Figure g is the capacity graph of aqueous zinc ion batteries tested at a current of 0.1-3 A / g when the materials obtained from Comparative Example 1 (MnO2), Example 1 (MnO2-0.4gWMCNT), Example 2 (MnO2-0.2gWMCNT) and Example 3 (MnO2-0.6gWMCNT) of the present invention are assembled.

[0029] Figure 5 This is a capacity diagram of aqueous zinc ion batteries tested at a current of 2 A / g assembled with materials obtained from Comparative Example 1 (MnO2), Example 1 (MnO2-0.4gWMCNT), Example 2 (MnO2-0.2gWMCNT) and Example 3 (MnO2-0.6gWMCNT) of the present invention.

[0030] Figure 6 This is a scanning electron microscope (SEM) characterization image of β-MnO2 formed in Comparative Example 1 of the present invention.

[0031] Figure 7 Scanning electron microscope (SEM) characterization image of β-MnO2-0.2gWMCNT formed in Example 2 of the present invention.

[0032] Figure 8 Scanning electron microscope (SEM) characterization image of β-MnO2-0.4gWMCNT formed in Example 1 of the present invention.

[0033] Figure 9 Scanning electron microscope (SEM) characterization image of β-MnO2-0.6gWMCNT formed in Example 3 of the present invention. DETAILED DESCRIPTION

[0034] The present invention will be further described below with reference to the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it. However, the embodiments are not intended to limit the present invention.

[0035] Figures 3 to 5 The number marked in the middle is the constant current charge and discharge current, the unit is A / g.

[0036] Example 1

[0037] Step (1): Prepare 40 mL of a solution of nitric acid and sulfuric acid in a volume ratio of 1:3 and add deionized water to 200 mL.

[0038] Step (2): Add the solution obtained in step (1) to multi-walled carbon nanotubes, heat in an oil bath at 90° C. for 6 h, and add deionized water from time to time.

[0039] Step (3): The solution obtained in step (2) was centrifuged at 10,000 rpm with ethanol to obtain acidified multi-walled carbon nanotubes, which were then dried in a vacuum drying oven at 60° C. for 24 h.

[0040] Step (4): Dissolve 0.6 g of magnesium oxide in 100 mL of deionized water and stir for 10 min.

[0041] Step (5): Add 2.97 g of manganese chloride to the solution obtained in step (4) and stir for 10 minutes.

[0042] Step (6): 3.57 g of sodium persulfate was added to the solution obtained in step (5), and the mixture was stirred for 10 min. Then, 0.4 g of acidified carbon nanotubes was added and the mixture was stirred for another 10 min.

[0043] Step (7): Transfer the solution obtained in step (6) to a polytetrafluoroethylene liner and react with hot water at 160°C for 12 hours.

[0044] Step (8): The solution obtained in step (7) was centrifuged at 6000 rpm with deionized water, and dried in a vacuum drying oven at 60° C. for 24 h to obtain β-MnO2-WMCNT.

[0045] Example 2

[0046] Step (1): Prepare 40 mL of a solution of nitric acid and sulfuric acid in a volume ratio of 1:3 and add deionized water to 200 mL.

[0047] Step (2): Add the solution obtained in step (1) to multi-walled carbon nanotubes, heat in an oil bath at 90° C. for 6 h, and add deionized water from time to time.

[0048] Step (3): The solution obtained in step (2) was centrifuged at 10,000 rpm with ethanol to obtain acidified multi-walled carbon nanotubes, which were then dried in a vacuum drying oven at 60° C. for 24 h.

[0049] Step (4): Dissolve 0.6 g of magnesium oxide in 100 mL of deionized water and stir for 10 min.

[0050] Step (5): Add 2.97 g of manganese chloride to the solution obtained in step (4) and stir for 10 minutes.

[0051] Step (6): 3.57 g of sodium persulfate was added to the solution obtained in step (5), and the mixture was stirred for 10 min. Then, 0.2 g of acidified carbon nanotubes was added and the mixture was stirred for another 10 min.

[0052] Step (7): Transfer the solution obtained in step (6) to a polytetrafluoroethylene liner and react in hot water at 160°C for 12 hours;

[0053] Step (8): The solution obtained in step (7) was centrifuged at 6000 rpm with deionized water, and dried in a vacuum drying oven at 60° C. for 24 h to obtain β-MnO2-WMCNT.

[0054] Example 3

[0055] Step (1): Prepare 40 mL of a solution of nitric acid and sulfuric acid in a volume ratio of 1:3 and add deionized water to 200 mL.

[0056] Step (2): Add the solution obtained in step (1) to multi-walled carbon nanotubes, heat in an oil bath at 90° C. for 6 h, and add deionized water from time to time.

[0057] Step (3): The solution obtained in step (2) was centrifuged at 10,000 rpm with ethanol to obtain acidified multi-walled carbon nanotubes, which were then dried in a vacuum drying oven at 60° C. for 24 h.

[0058] Step (4): Dissolve 0.6 g of magnesium oxide in 100 mL of deionized water and stir for 10 min.

[0059] Step (5): Add 2.97 g of manganese chloride to the solution obtained in step (4) and stir for 10 minutes.

[0060] Step (6): 3.57 g of sodium persulfate was added to the solution obtained in step (5), and the mixture was stirred for 10 min. Then, 0.6 g of acidified carbon nanotubes was added and the mixture was stirred for another 10 min.

[0061] Step (7): Transfer the solution obtained in step (6) to a polytetrafluoroethylene liner and react in hot water at 160°C for 12 hours;

[0062] Step (8): The solution obtained in step (7) was centrifuged at 6000 rpm with deionized water, and dried in a vacuum drying oven at 60° C. for 24 h to obtain β-MnO2-WMCNT.

[0063] Example 4

[0064] The β-MnO2-WMCNT, acetylene black and PVDF prepared in Example 1 were mixed in a ratio of 7:2:1, and then N-methylpyrrolidone was added after thorough grinding. The entire mixture was transferred to a 10 mL sample bottle, sealed and stirred for 6 h to form a slurry; the active material slurry was scraped onto a 100 μm titanium foil, dried under an infrared lamp for 60 min, and dried at 60°C under vacuum for 12 h. The wafers were cut into 14 mm diameter discs to obtain electrode sheets, which were used as the positive electrode of aqueous zinc ion batteries and assembled into CR2032 button batteries for testing;

[0065] The electrolyte is prepared by dissolving zinc sulfate and manganese sulfate in deionized water to form a battery electrolyte, wherein the concentration of zinc sulfate is 3M and the concentration of manganese sulfate is 0.3M.

[0066] Example 5

[0067] The β-MnO2-WMCNT, acetylene black and PVDF prepared in Example 2 were mixed in a ratio of 7:2:1, and then N-methylpyrrolidone was added after thorough grinding. The entire mixture was transferred to a 10 mL sample bottle, sealed and stirred for 6 h to form a slurry; the active material slurry was scraped onto a 100 μm titanium foil, dried under an infrared lamp for 60 min, and dried at 60°C under vacuum for 12 h. The wafers were cut into 14 mm diameter discs to obtain electrode sheets, which were used as the positive electrode of aqueous zinc ion batteries and assembled into CR2032 button batteries for testing;

[0068] The electrolyte is prepared by dissolving zinc sulfate and manganese sulfate in deionized water to form a battery electrolyte, wherein the concentration of zinc sulfate is 3M and the concentration of manganese sulfate is 0.3M.

[0069] Example 6

[0070] The β-MnO2-WMCNT, acetylene black and PVDF prepared in Example 3 were mixed uniformly in a ratio of 7:2:1, and then N-methylpyrrolidone was added after thorough grinding. All the mixture was transferred to a 10 mL sample bottle, sealed and stirred for 6 hours to form a slurry; the active material slurry was scraped onto a 100 μm titanium foil, dried under an infrared lamp for 60 minutes, and dried at 60°C under vacuum for 12 hours. The wafers were cut into 14 mm diameter wafers to obtain electrode sheets, which were used as the positive electrode of aqueous zinc ion batteries and assembled into CR2032 button batteries for testing.

[0071] The electrolyte is prepared by dissolving zinc sulfate and manganese sulfate in deionized water to form a battery electrolyte, wherein the concentration of zinc sulfate is 3M and the concentration of manganese sulfate is 0.3M.

[0072] Example 7

[0073] Step (1): Prepare 40 mL of a solution of nitric acid and sulfuric acid in a volume ratio of 1:1 and add deionized water to 200 mL.

[0074] Step (2): Add the solution obtained in step (1) to multi-walled carbon nanotubes, heat in an oil bath at 80° C. for 4 h, and add deionized water from time to time.

[0075] Step (3): The solution obtained in step (2) was centrifuged at 9000 rpm with ethanol to obtain acidified multi-walled carbon nanotubes, which were then dried in a vacuum drying oven at 50° C. for 20 h.

[0076] Step (4): Dissolve 0.5 g of magnesium oxide in 100 mL of deionized water and stir for 10 min.

[0077] Step (5): Add 3.5 g of manganese chloride to the solution obtained in step (4) and stir for 10 minutes.

[0078] Step (6): 4 g of sodium persulfate was added to the solution obtained in step (5), and the mixture was stirred for 10 min. Then, 0.4 g of acidified carbon nanotubes was added and the mixture was stirred for another 10 min.

[0079] Step (7): transfer the solution obtained in step (6) into a polytetrafluoroethylene liner and react with hot water at 140°C for 10 hours;

[0080] Step (8): The solution obtained in step (7) was centrifuged at 5000 rpm with deionized water, and dried in a vacuum drying oven at 50° C. for 20 h to obtain β-MnO2-WMCNT.

[0081] Example 8

[0082] Step (1): Prepare 40 mL of a solution of nitric acid and sulfuric acid in a volume ratio of 1:2 and add deionized water to 200 mL.

[0083] Step (2): Add the solution obtained in step (1) to multi-walled carbon nanotubes, heat in an oil bath at 100° C. for 8 h, and add deionized water from time to time.

[0084] Step (3): The solution obtained in step (2) was centrifuged at 11000 rpm with ethanol to obtain acidified multi-walled carbon nanotubes, which were then dried in a vacuum drying oven at 70°C for 30 hours.

[0085] Step (4): Dissolve 0.8 g of magnesium oxide in 100 mL of deionized water and stir for 10 min.

[0086] Step (5): Add 3.5 g of manganese chloride to the solution obtained in step (4) and stir for 10 minutes.

[0087] Step (6): 3 g of sodium persulfate was added to the solution obtained in step (5), and the mixture was stirred for 10 min. Then, 0.4 g of acidified carbon nanotubes was added and the mixture was stirred for another 10 min.

[0088] Step (7): Transfer the solution obtained in step (6) to a polytetrafluoroethylene liner and react in hot water at 180°C for 14 hours;

[0089] Step (8): The solution obtained in step (7) was centrifuged at 7000 rpm with deionized water, and dried in a vacuum drying oven at 70° C. for 30 h to obtain β-MnO2-WMCNT.

[0090] Comparative Example 1

[0091] Step (1): Dissolve 0.6 g of magnesium oxide in 100 mL of deionized water and stir for 10 min.

[0092] Step (2): Add 2.97 g of manganese chloride to the solution obtained in step (1) and stir for 10 minutes.

[0093] Step (3): Add 3.57 g of sodium persulfate to the solution obtained in step (2) and stir for 10 minutes.

[0094] Step (4): transfer the solution obtained in step (3) into a polytetrafluoroethylene liner and react in hot water at 160°C for 12 hours;

[0095] Step (5): The solution obtained in step (4) was centrifuged at 6000 rpm with deionized water, and dried in a vacuum drying oven at 60° C. for 24 h to obtain β-MnO2.

[0096] Comparative Example 2

[0097] The β-MnO2, acetylene black and PVDF of Comparative Example 1 were mixed evenly in a ratio of 7:2:1, and then N-methylpyrrolidone was added after thorough grinding. All the mixtures were transferred to a 10mL sample bottle, sealed and stirred for 6 hours to form a slurry; the active material slurry was scraped onto a 100um titanium foil, dried under an infrared lamp for 60 minutes, and dried at 60°C under vacuum for 12 hours. The discs were cut into 14mm diameter wafers to obtain electrode sheets, which were used as the positive electrode of aqueous zinc ion batteries and assembled into CR2032 button batteries for testing.

[0098] The electrolyte is prepared by dissolving zinc sulfate and manganese sulfate in deionized water to form a battery electrolyte, wherein the concentration of zinc sulfate is 3M and the concentration of manganese sulfate is 0.3M.

[0099] Effect evaluation 1

[0100] By analyzing the above examples and comparative examples, it can be found that the present invention makes the reaction process more controllable and stable by slowly forming alkaline conditions by slightly dissolving magnesium oxide in water. It is also convenient to operate, low in cost, high in safety, and suitable for mass production.

[0101] Through valence engineering, β-MnO2 with varying amounts of acidified multi-walled carbon nanotubes was modified and subjected to material characterization and electrochemical testing. The analytical results indicate that acidified multi-walled carbon nanotubes can significantly increase battery capacity. The primary mechanism is as follows: hydroxyl-rich multi-walled carbon nanotubes surround the prismatic β-MnO2, increasing the material's surface area and mitigating irreversible ZnMn2O4 deposition. The acidified multi-walled carbon nanotubes also control the growth direction of β-MnO2, improving the overall material's ionic conductivity and inhibiting its structural collapse. Excessive acidified multi-walled carbon nanotubes can lead to severe agglomeration, resulting in the detachment of the prismatic β-MnO2. Therefore, the β-MnO2-WMCNT prepared by the present invention, when used as the positive electrode for aqueous zinc-ion batteries, significantly improves capacity and cycling stability.

[0102] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A method for preparing manganese oxide for aqueous zinc ion batteries, characterized in that: The steps include: S11: adding multi-walled carbon nanotubes to a mixed solvent, heating, and separating to obtain acidified multi-walled carbon nanotubes; the mixed solvent is obtained by mixing nitric acid and sulfuric acid and then adding water; in the mixed solvent, the volume ratio of nitric acid to sulfuric acid is 1:1-3, and the volume ratio of the total amount of nitric acid and sulfuric acid to water is 1:4; S12: adding the acidified multi-walled carbon nanotubes to a salt solution, mixing, and obtaining a solution to be reacted; the solute of the salt solution includes magnesium oxide, manganese chloride, and sodium persulfate, and the solvent of the salt solution is water; S13: hydrothermally reacting the solution at 140-180° C. for 10-14 hours and then separating to obtain the manganese oxide for aqueous zinc ion battery; in the step S11, the heating time is 4-8 hours and the heating temperature is 80-100° C.; in the step S12, the mass ratio of magnesium oxide, manganese chloride and sodium persulfate is 0.5-0.8:2.5-3.5:3-4.

2. The preparation method according to claim 1, wherein In step S13, the separation method is centrifugal separation at a speed of 5000-7000 rpm.

3. The preparation method according to claim 1, wherein In the step S13, after separation, the product is vacuum dried at 50-70° C. for 20-30 h.

4. A manganese oxide for aqueous zinc ion batteries prepared by the preparation method according to any one of claims 1 to 3.

5. A positive electrode sheet for an aqueous zinc ion battery, characterized in that: The aqueous zinc ion battery positive electrode sheet is obtained by mixing acetylene black, PVDF, N-methylpyrrolidone and the manganese oxide for aqueous zinc ion batteries according to claim 4 and coating the mixture on a titanium foil.

6. The aqueous zinc ion battery positive electrode sheet according to claim 5, wherein: The mass ratio of manganese oxide, acetylene black and PVDF for aqueous zinc ion batteries is 6-8:1-2:1-2.

Images