A potassium-sodium co-doped manganese dioxide nanomaterial and its preparation method and application

Abstract

The present invention discloses a potassium-sodium co-doped manganese dioxide nanomaterial and its preparation and application. The present invention comprises the steps of dissolving silicate and manganese salt and mixing them to prepare a precursor; and treating the precursor by alkali etching. The potassium ions and sodium ions pre-embedded between the manganese dioxide layers stabilize the layered structure of the crystal, widen the interlayer spacing, and make the embedding and extraction of zinc ions and hydrogen ions smoother through electrostatic shielding. At the same time, the prepared potassium-sodium co-doped manganese dioxide nanomaterial has a unique nano-flower sheet structure, which increases the contact area of ​​the reaction. The electrochemical test results show that the potassium-sodium co-doped manganese dioxide nanomaterial has a good reversible specific capacity as a positive electrode material for zinc ion batteries. At a current density of 0.5 A / g, the high specific capacity can reach up to 239.1 mAh / g after 600 cycles.

Description

Technical Field

[0001] The present invention relates to a potassium-sodium co-doped manganese dioxide nanomaterial and a preparation method thereof, as well as application of the potassium-sodium co-doped manganese dioxide nanomaterial as a positive electrode material for a zinc ion battery, belonging to the technical field of battery materials. Background Art

[0002] In recent years, with the continuous deepening of energy use, energy storage technology has played a vital role in energy storage and rational energy utilization. With the development of new energy technologies, ion batteries have been widely studied as excellent energy storage devices.

[0003] Among various ion battery energy storage devices, aqueous zinc-ion batteries are considered to be one of the new technologies most likely to replace lithium-ion batteries due to their advantages such as high operating voltage, high energy density, excellent rate performance, low pollution and high safety.

[0004] Layered manganese dioxide (δ-MnO2) is a promising cathode material for aqueous zinc-ion batteries. Its layered structure allows for efficient storage of charged particles. However, structural collapse during charge and discharge in manganese-based cathode materials has limited their further development. Appropriate ion doping can improve the stability and electrochemical performance of manganese-based layered materials. Summary of the Invention

[0005] In view of the defects of the prior art, the primary purpose of the present invention is to provide a method for preparing potassium-sodium co-doped manganese dioxide nanomaterials. The method has the advantages of simple process, low cost, and potential for industrial production. Moreover, the method can prepare manganese dioxide layered structures with better crystallinity.

[0006] The preparation method of the potassium-sodium co-doped manganese dioxide nanomaterial is as follows: silicate and manganese salt are dissolved and mixed to prepare a precursor; the precursor is treated by alkali etching to obtain the material; the sources of the co-doped potassium and sodium include: silicate and / or alkali solution used for alkali etching.

[0007] The method for preparing the potassium-sodium co-doped manganese dioxide nanomaterial: the sources of the co-doped potassium and sodium also include compounds containing potassium and / or sodium that are added during the preparation process.

[0008] The source of the co-doped potassium and sodium in the present invention can be the alkali solution used for silicate and / or alkali etching, or a compound containing potassium and / or sodium added during the preparation process, preferably during the precursor preparation process. When the alkali solution used for silicate and / or alkali etching contains sufficient amounts of doped potassium and sodium, there is no need to add a compound containing potassium and / or sodium.

[0009] Further,

[0010] The silicate includes at least one of sodium silicate, potassium silicate or manganese silicate.

[0011] The manganese salt includes at least one of manganese sulfate, manganese chloride or manganese nitrate.

[0012] The alkaline solution used for the alkaline etching includes at least one of potassium hydroxide or sodium hydroxide.

[0013] Further,

[0014] The compound containing potassium and / or sodium includes potassium salt and / or sodium salt; potassium salt includes at least one of potassium chloride, potassium sulfate and potassium nitrate; sodium salt includes at least one of sodium chloride, sodium sulfate and sodium nitrate.

[0015] In the method for preparing potassium-sodium co-doped manganese dioxide nanomaterials, the silicate concentration is 50-100 mmoL / L, preferably 60-80 mmoL / L. The manganese salt concentration is 40-75 mmoL / L, preferably 40-60 mmoL / L. Excessively high silicate or manganese salt concentrations can result in an overly concentrated precursor suspension, leading to insufficient subsequent alkaline etching reaction. Excessively low silicate or manganese salt concentrations can result in low precursor yield.

[0016] The concentration of the alkali solution is 0.5 to 3 mol / L, more preferably 1 to 2 mol / L. Too high an alkali concentration will result in excessive etching, forming nanoblocks rather than nanoflowers. Too low an alkali concentration will result in insufficient etching, failing to fully convert the precursor into manganese dioxide.

[0017] Further,

[0018] The volume ratio of the silicate to manganese salt solution is in the range of 0.5 to 2:1.

[0019] The liquid-to-solid ratio of the alkali solution to the precursor is 100-120 mL / 0.2 g.

[0020] Further,

[0021] The molar ratio of potassium doped in the product is in the range of 3-12%.

[0022] The molar ratio of sodium doping in the product is in the range of 3-12%.

[0023] Further,

[0024] The mixing temperature during the preparation of the precursor is 10-80°C, more preferably 35-55°C, and the mixing time is 0.5-3 hours, more preferably 1-2 hours. Too low a temperature or too short a time will lead to insufficient reaction and reduce the precursor yield. Too high a temperature or too long a time will lead to solvent evaporation and waste of resources, and the resulting precursor yield will not be improved.

[0025] The temperature of the alkaline etching is 70-100°C, more preferably 80-90°C, and the time is 8-24h, more preferably 10-14h. The alkali solution can react with the precursor silicon manganese salt to dissolve the silicon-containing part to obtain manganese dioxide, and layered manganese dioxide can be obtained by alkaline etching. If the etching temperature is too high or the time is too long, it will lead to excessive etching, and the precursor will be etched into nanoblocks instead of nanoflowers. If the etching temperature is too low or the time is too short, it will lead to insufficient etching, and the precursor cannot be completely converted into manganese dioxide.

[0026] Further,

[0027] After the precursor is treated by alkali etching, the product is obtained by washing, filtering and drying.

[0028] The drying is vacuum drying, the drying temperature is 60-100° C., and the drying time is 12-24 hours.

[0029] As a preferred solution, the present invention provides a method for preparing a potassium-sodium co-doped manganese dioxide nanomaterial, which specifically comprises the following steps:

[0030] 1) Dissolve silicate in deionized water and stir until completely dissolved to prepare solution A with a concentration of 50-100 mmol / L;

[0031] 2) Dissolve the manganese salt in deionized water and stir until completely dissolved to prepare a solution B with a concentration of 40-75 mmol / L;

[0032] 3) At a temperature of 10-80°C, slowly mix solutions A and B (the volume ratio of silicate to manganese salt solution is in the range of 0.5-2:1). Sodium salt and / or potassium salt may be added and stirred for 0.5-3 hours to obtain a light brown suspension.

[0033] 4) The light brown suspension was separated by centrifugation, washed three times with deionized water and ethanol respectively, and dried at 60-100° C. overnight to obtain a precursor;

[0034] 5) Using at least one of potassium hydroxide and / or sodium hydroxide as the precursor at a concentration of 0.5 to 3 mol / L, with a liquid-to-solid ratio of 100 to 120 mL / 0.2 g, the precursor is etched at a temperature of 70 to 100°C for 8 to 24 hours. After etching, the precipitate is separated by centrifugation, washed at least three times with deionized water and ethanol, respectively, dried in a vacuum at 60 to 100°C for 12 to 24 hours, and thoroughly ground to obtain the product.

[0035] A second object of the present invention is to provide a potassium-sodium co-doped manganese dioxide nanomaterial prepared by the above method. The pre-embedding of sodium and potassium can increase the interlayer spacing of the material. Potassium poses a relatively small barrier to zinc ion migration, but due to its larger radius, it can easily cause the layered structure to collapse. Pre-embedding sodium between the layers can stabilize the structure. Under the synergistic effect of potassium and sodium, the material has good stability, a larger interlayer spacing of manganese dioxide, and exhibits superior electrochemical cycling performance, while also slowing the consumption of zinc ions by the byproduct hydroxide ions.

[0036] The third object of the present invention is to provide an application of potassium-sodium co-doped manganese dioxide nanomaterials, which are used as positive electrode materials in zinc ion batteries. The material has good reversible specific capacity and can reach a high specific capacity of 239.1 mAh / g after 600 cycles at a current density of 0.5 A / g.

[0037] Potassium and sodium co-doped manganese dioxide nanomaterials are used as positive electrode materials for zinc ion batteries, and are prepared by the following steps:

[0038] 1) Potassium and sodium co-doped layered manganese dioxide nanomaterials, acetylene black, and polyvinylidene fluoride were mixed in a ratio of 7:2:1, prepared into a paste with N-methylpyrrolidone, and evenly coated on a titanium foil;

[0039] 2) Dry in a vacuum oven at 100°C for 12 hours.

[0040] The test method for the electrochemical performance of the electrode material is as follows:

[0041] 1) The simulated battery used a CR2025 button cell system, the electrolyte was a mixed aqueous solution of 1M zinc sulfate and 0.2M manganese sulfate, the negative electrode was a round zinc sheet, and the battery separator was glass fiber;

[0042] 2) The reversible capacity and cycle performance of the electrode material were tested and analyzed using a constant current charge-discharge test method with a charge-discharge regime of: voltage range: 0.8-1.8 V; cycle number: 1-600 times.

[0043] Compared with the existing technology, the technical solution of the present invention brings the following beneficial technical effects:

[0044] 1) The potassium-sodium co-doped manganese dioxide nanomaterial provided by the present invention stabilizes the layered structure of manganese dioxide crystals by pre-embedding potassium ions and sodium ions between manganese dioxide layers, significantly improves the capacity and rate performance of the manganese dioxide material, and improves the cycle stability of the positive electrode material.

[0045] 2) The potassium-sodium co-doped manganese dioxide nanomaterial provided by the present invention has a flower-like nanosheet structure, which provides sufficient contact area for the embedding and extraction of zinc ions, and is more conducive to improving the electrochemical performance of manganese dioxide.

[0046] 3) When the potassium-sodium co-doped manganese dioxide nanomaterial provided by the present invention is applied to a zinc ion battery, due to the action of potassium and sodium bimetallic doping of manganese dioxide, a unique basic potassium sulfate intermediate is produced during the charge and discharge process, which can combine with the hydroxide ions generated at the positive electrode during the reaction process, thereby inhibiting the formation of basic zinc sulfate to a certain extent. The electrochemical test results also show that the potassium-sodium co-doped manganese dioxide nanomaterial has good reversible specific capacity as a positive electrode material for zinc ion batteries. At a current density of 0.5 A / g, the highest specific capacity can reach 239.1 mAh / g after 600 cycles, which is higher than most of the currently reported manganese-based positive electrode materials for aqueous zinc ion batteries.

[0047] 4) The preparation method of the present invention is highly operable, low-cost, and suitable for large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 This is a diagram of the electrochemical performance of potassium-sodium co-doped manganese dioxide nanomaterial prepared in Example 1.

[0049] Figure 2 This is the SEM image of the potassium-sodium co-doped manganese dioxide nanomaterial prepared in Example 1.

[0050] Figure 3 This is the XRD pattern of the potassium-sodium co-doped layered manganese dioxide nanomaterial prepared in Example 1.

[0051] Figure 4 This is the full XPS spectrum of the potassium-sodium co-doped manganese dioxide nanomaterial prepared in Example 1.

[0052] Figure 5 The potassium-sodium co-doped manganese dioxide nanomaterial prepared in Example 1 is used as the positive electrode of a zinc ion battery. The charge and discharge cycle curves at different current densities in the rate test are shown. The test current increases from right to left.

[0053] Figure 6 This is a CV test curve diagram of the potassium-sodium co-doped manganese dioxide nanomaterial prepared in Example 1 at different scan rates. DETAILED DESCRIPTION

[0054] The present invention will be further described below with reference to the accompanying drawings and specific examples, but the examples do not limit the present invention in any way. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in the art.

[0055] Unless otherwise specified, the reagents and materials used in the following examples were commercially available.

[0056] Example 1

[0057] A method for preparing a potassium-sodium co-doped layered manganese dioxide nanomaterial comprises the following steps:

[0058] 1) Add 3 mmol of sodium silicate to 40 mL of deionized water and stir until completely dissolved to prepare solution A;

[0059] 2) Dissolve 3 mmol of manganese chloride in 60 mL of deionized water and stir until completely dissolved to prepare solution B;

[0060] 3) At room temperature, slowly mix solutions A and B to obtain a light brown suspension, and stir for 1 h.

[0061] 4) After the reaction process is completed, the solution is centrifuged, washed three times with deionized water and ethanol respectively, dried at 60°C for 24 hours, and ground to obtain the precursor material;

[0062] 5) Dissolve 0.2 mol potassium hydroxide in 100 mL of deionized water and stir to obtain a 2 mol / L potassium hydroxide solution. Add the precursor to the potassium hydroxide solution, heat in an oil bath at 90°C, and stir for 12 hours. After etching, separate the precipitate by centrifugation, wash three times with deionized water, three times with ethanol, filter, and dry at 60°C for 12 hours to obtain potassium-sodium co-doped layered manganese dioxide nanomaterials.

[0063] In order to verify the electrochemical performance of potassium-sodium co-doped layered manganese dioxide nanomaterials, and further apply them as positive electrode materials for zinc ion batteries: the prepared potassium-sodium co-doped layered manganese dioxide nanomaterials were dissolved in N-methylpyrrolidone with the binder polyvinylidene fluoride and the conductive agent acetylene black at a ratio of 7:2:1 to prepare a slurry, coated on titanium foil, and vacuum dried at 100°C for 12 hours to assemble zinc ion batteries as electrode materials. The electrolyte used was a mixed aqueous solution of 1M zinc sulfate and 0.2M manganese sulfate, the negative electrode was a circular zinc sheet, and the battery separator was glass fiber; the electrochemical performance was analyzed by constant current charge and discharge test, and the voltage range was 0.8~1.8V. By testing its electrochemical performance, the results are shown Figure 1 It can be observed that at a current density of 0.5 A / g, the highest specific capacity can reach 239.1 mAh / g after 600 cycles, which is at the leading level among zinc-ion battery positive electrode materials.

[0064] Figure 2 It is clearly shown that the potassium-sodium co-doped manganese dioxide nanomaterial prepared in this example is a flower-like nanosheet structure.

[0065] Figure 3 It can be observed that the structure of the potassium-sodium co-doped manganese dioxide nanomaterial prepared in this example is δ-MnO2, and the layered structure can enable zinc ions to be inserted and removed more efficiently.

[0066] Figure 4 It shows the manganese, oxygen, potassium, sodium and other elements contained in the material, indicating that potassium ions and sodium ions have been successfully doped into the material.

[0067] Figure 5 It can be seen that the material has good rate performance.

[0068] Figure 6 The corresponding peaks of the two-step embedding of zinc ions and hydrogen ions can be seen, indicating that the prepared potassium-sodium co-doped manganese dioxide nanomaterial can be successfully applied to the positive electrode of zinc ion batteries.

[0069] A method for preparing a potassium-sodium co-doped layered manganese dioxide nanomaterial comprises the following steps:

[0070] 1) Add 3 mmol of potassium silicate to 40 mL of deionized water and stir until completely dissolved to prepare solution A;

[0071] 2) Dissolve 3 mmol of manganese chloride in 60 mL of deionized water and stir until completely dissolved to prepare solution B;

[0072] 3) At room temperature, slowly mix solutions A and B to obtain a light brown suspension, and stir for 1 h.

[0073] 4) After the reaction process is completed, the solution is centrifuged, washed three times with deionized water and ethanol respectively, dried at 60°C for 24 hours, and ground to obtain the precursor material;

[0074] 5) Dissolve 0.2 mol of sodium hydroxide in 100 mL of deionized water and stir to obtain a 2 mol / L potassium hydroxide solution. Add the precursor to the potassium hydroxide solution, heat in an oil bath at 90°C, and stir for 12 hours. After etching, separate the precipitate by centrifugation, wash three times with deionized water, three times with ethanol, filter, and dry at 60°C for 12 hours to obtain a potassium-sodium co-doped layered manganese dioxide nanomaterial.

[0075] To verify the electrochemical performance of the potassium-sodium co-doped layered manganese dioxide nanomaterial and further apply it as a positive electrode material for a zinc-ion battery, the prepared potassium-sodium co-doped layered manganese dioxide nanomaterial was dissolved in N-methylpyrrolidone at a ratio of 7:2:1 with a binder of polyvinylidene fluoride and a conductive agent of acetylene black. This slurry was coated onto titanium foil and vacuum-dried at 100°C for 12 hours before being assembled into a zinc-ion battery. The electrolyte was a mixed aqueous solution of 1M zinc sulfate and 0.2M manganese sulfate, the negative electrode was a circular zinc sheet, and the battery separator was glass fiber. The electrochemical performance was analyzed using galvanostatic charge-discharge tests over a voltage range of 0.8 to 1.8 V. The electrochemical performance showed a maximum capacity of 220.2 mAh / g at a current density of 0.5 A / g over 600 cycles.

[0076] Example 3

[0077] A method for preparing a potassium-sodium co-doped layered manganese dioxide nanomaterial comprises the following steps:

[0078] 1) Add 4 mmol of sodium silicate to 40 mL of deionized water and stir until completely dissolved to prepare solution A;

[0079] 2) Dissolve 3 mmol of manganese nitrate in 60 mL of deionized water and stir until completely dissolved to prepare solution B;

[0080] 3) At room temperature, slowly mix solutions A and B to obtain a light brown suspension, then add 3 mmol of potassium chloride and stir for 1.5 h.

[0081] 4) After the reaction process is completed, the solution is centrifuged, washed three times with deionized water and ethanol respectively, dried at 60°C for 24 hours, and ground to obtain the precursor material;

[0082] 5) Dissolve 0.1 mol potassium hydroxide in 100 mL of deionized water and stir to obtain a 1 mol / L potassium hydroxide solution. Add the precursor to the potassium hydroxide solution, heat in an oil bath at 80°C, and stir for 10 hours. After etching, separate the precipitate by centrifugation, wash three times with deionized water, three times with ethanol, filter, and dry at 60°C for 12 hours to obtain potassium-sodium co-doped layered manganese dioxide nanomaterials.

[0083] To verify the electrochemical performance of the potassium-sodium co-doped layered manganese dioxide nanomaterial and further apply it as a positive electrode material for a zinc-ion battery, the prepared potassium-sodium co-doped layered manganese dioxide nanomaterial was dissolved in N-methylpyrrolidone at a ratio of 7:2:1 with a binder of polyvinylidene fluoride and a conductive agent of acetylene black. This slurry was coated onto titanium foil and vacuum-dried at 100°C for 12 hours before being assembled into a zinc-ion battery. A mixed aqueous solution of 1M zinc sulfate and 0.2M manganese sulfate was used as the electrolyte, a circular zinc sheet was used as the negative electrode, and a glass fiber separator was used. Galvanostatic charge-discharge tests were performed over a voltage range of 0.8 to 1.8 V to analyze its electrochemical performance. The results showed that the maximum capacity reached 218.7 mAh / g at a current density of 0.5 A / g over 600 cycles.

[0084] Example 4

[0085] A method for preparing a potassium-sodium co-doped layered manganese dioxide nanomaterial comprises the following steps:

[0086] 1) Add 3 mmol of sodium silicate to 40 mL of deionized water and stir until completely dissolved to prepare solution A;

[0087] 2) Dissolve 4 mmol of manganese chloride in 60 mL of deionized water and stir until completely dissolved to prepare solution B;

[0088] 3) At room temperature, slowly mix solutions A and B to obtain a light brown suspension, and stir for 1 h.

[0089] 4) After the reaction process is completed, the solution is centrifuged, washed three times with deionized water and ethanol respectively, dried at 60°C for 24 hours, and ground to obtain the precursor material;

[0090] 5) Dissolve 0.1 mol potassium hydroxide in 100 mL of deionized water and stir to obtain a 1 mol / L potassium hydroxide solution. Add the precursor to the potassium hydroxide solution, heat in an oil bath at 80°C, and stir for 9 hours. After etching, separate the precipitate by centrifugation, wash three times with deionized water, three times with ethanol, filter, and dry at 60°C for 12 hours to obtain potassium-sodium co-doped layered manganese dioxide nanomaterials.

[0091] To verify the electrochemical performance of the potassium-sodium co-doped layered manganese dioxide nanomaterial and further apply it as a positive electrode material for a zinc-ion battery, the prepared potassium-sodium co-doped layered manganese dioxide nanomaterial was dissolved in N-methylpyrrolidone with a binder and a conductive agent in a ratio of 7:2:1 to prepare a slurry. The slurry was coated on titanium foil and vacuum-dried at 100°C for 12 hours before being assembled into a zinc-ion battery. The electrolyte was a mixed aqueous solution of 1M zinc sulfate and 0.2M manganese sulfate. The negative electrode was a circular zinc sheet, and the battery separator was a glass fiber. The electrochemical performance was analyzed using galvanostatic charge-discharge tests over a voltage range of 0.8 to 1.8 V. The electrochemical performance showed a maximum capacity of 228.0 mAh / g at a current density of 0.5 A / g over 600 cycles.

[0092] Example 5

[0093] A method for preparing a potassium-sodium co-doped layered manganese dioxide nanomaterial comprises the following steps:

[0094] 1) Add 3 mmol of sodium silicate to 40 mL of deionized water and stir until completely dissolved to prepare solution A;

[0095] 2) Dissolve 3 mmol of manganese sulfate in 60 mL of deionized water and stir until completely dissolved to prepare solution B;

[0096] 3) At room temperature, slowly mix solutions A and B to obtain a light brown suspension, and stir for 1 h.

[0097] 4) After the reaction process is completed, the solution is centrifuged, washed three times with deionized water and ethanol respectively, dried at 60°C for 24 hours, and ground to obtain the precursor material;

[0098] 5) Dissolve 0.1 mol potassium hydroxide and 0.1 mol sodium hydroxide in 100 mL of deionized water and stir to obtain a 1 mol / L potassium hydroxide and 1 mol / L sodium hydroxide mixed alkaline solution. Add the precursor to the mixed alkaline solution, heat in an oil bath at 90°C, and stir for 10 hours. After etching, separate the precipitate by centrifugation, wash three times with deionized water, three times with ethanol, filter, and dry at 60°C for 12 hours to obtain potassium-sodium co-doped manganese dioxide nanomaterial.

[0099] To verify the electrochemical performance of the potassium-sodium co-doped layered manganese dioxide nanomaterial and further apply it as a positive electrode material for a zinc-ion battery, the prepared potassium-sodium co-doped layered manganese dioxide nanomaterial was dissolved in N-methylpyrrolidone at a ratio of 7:2:1 with a binder of polyvinylidene fluoride and a conductive agent of acetylene black. This slurry was coated onto titanium foil and vacuum-dried at 100°C for 12 hours. A zinc-ion battery was assembled using a mixture of 1M zinc sulfate and 0.2M manganese sulfate as the electrolyte, a circular zinc sheet as the negative electrode, and a glass fiber separator. Galvanostatic charge-discharge tests were used to analyze the electrochemical performance of the material over a voltage range of 0.8 to 1.8 V. The results showed that the material achieved a maximum capacity of 230.8 mAh / g at a current density of 0.5 A / g over 600 cycles.

[0100] Comparative Example 1

[0101] A method for preparing a layered manganese dioxide nanomaterial comprises the following steps:

[0102] 1) 0.84 g of manganese sulfate monohydrate was stirred in 150 mL of deionized water until completely dissolved to obtain a manganese sulfate solution;

[0103] 2) Add 1.98 g of potassium permanganate to the manganese sulfate solution and stir at room temperature for 3 h;

[0104] 3) The suspension was collected by centrifugation, washed with deionized water three times, washed with ethanol three times, filtered, and dried at 60° C. for 12 h to obtain undoped manganese dioxide nanomaterials.

[0105] To verify the electrochemical performance of the undoped manganese dioxide nanomaterial, it was further applied as a positive electrode material for a zinc-ion battery. The prepared potassium-sodium co-doped layered manganese dioxide nanomaterial was dissolved in N-methylpyrrolidone at a ratio of 7:2:1 with a binder of polyvinylidene fluoride and a conductive agent of acetylene black. This slurry was coated onto titanium foil and vacuum-dried before being assembled into a zinc-ion battery. The electrolyte used was a mixed aqueous solution of 1M zinc sulfate and 0.2M manganese sulfate. The negative electrode was a zinc sheet, and the separator was a glass fiber. The electrochemical performance was analyzed using galvanostatic charge-discharge tests over a voltage range of 0.8 to 1.8 V. The electrochemical performance showed a maximum capacity of 143.7 mAh / g at a current density of 0.5 A / g over 600 cycles.

[0106] Comparative Example 2

[0107] A method for preparing a potassium-sodium co-doped lamellar manganese dioxide nanomaterial comprises the following steps:

[0108] 1) Add Na2SO3 to distilled water and stir to obtain a Na2SO3 solution with a concentration of 1 g / L for later use;

[0109] 2) Add KMnO4 to distilled water and stir to obtain a KMnO4 solution with a concentration of 1 g / L. Set aside.

[0110] 3) The KMnO4 solution obtained in step 2) was added dropwise to the Na2SO3 solution obtained in step 1), and the mixture was stirred for 0.5 h for coprecipitation to obtain a brown granular precipitate suspension. The volume ratio of the KMnO4 solution to the Na2SO3 solution was 2:4.

[0111] 4) The brown granular precipitate suspension obtained in step 3) was filtered and washed with distilled water, and dried at 15° C. for 12 h to obtain potassium-sodium co-doped lamellar manganese dioxide.

[0112] To verify the electrochemical performance of the potassium-sodium co-doped manganese dioxide nanomaterial prepared by this method and further applied it as a positive electrode material for zinc-ion batteries, the potassium-doped layered manganese dioxide nanomaterial was dissolved in N-methylpyrrolidone with a binder and a conductive agent in a ratio of 7:2:1 to prepare a slurry. The slurry was coated on titanium foil and vacuum-dried before being assembled into a zinc-ion battery. The electrolyte used was a mixed aqueous solution of 1M zinc sulfate and 0.2M manganese sulfate. The negative electrode was a zinc sheet, and the separator was glass fiber. The electrochemical performance was analyzed using galvanostatic charge-discharge tests over a voltage range of 0.8 to 1.8 V. The electrochemical performance showed a maximum capacity of 153.5 mAh / g at a current density of 0.5 A / g over 600 cycles. The layered manganese dioxide prepared by this method exhibited poor crystallinity, resulting in low structural stability and capacity retention.

[0113] Comparative Example 3

[0114] A method for preparing layered manganese dioxide nanomaterials by a one-step thermal decomposition method comprises the following steps:

[0115] 1) Place 3 g of potassium permanganate in a porcelain crucible and heat it to 300°C in a nitrogen atmosphere at a heating rate of 50°C / h using a tube furnace and keep it at this temperature for 5 h.

[0116] 2) After cooling, the powder was taken out, washed with deionized water three times, washed with ethanol three times, filtered, and dried at 60° C. for 12 h to obtain a manganese dioxide nanomaterial prepared by thermal decomposition.

[0117] To verify the electrochemical performance of the thermally decomposed manganese dioxide nanomaterial, it was further applied as a positive electrode material for a zinc-ion battery. The prepared manganese dioxide nanomaterial was dissolved in N-methylpyrrolidone at a ratio of 7:2:1 with a binder (polyvinylidene fluoride) and a conductive agent (acetylene black). This slurry was coated onto titanium foil and vacuum-dried before being assembled into a zinc-ion battery. The electrolyte used was a mixed aqueous solution of 1M zinc sulfate and 0.2M manganese sulfate. The negative electrode was a zinc sheet, and the separator was glass fiber. The electrochemical performance was analyzed using galvanostatic charge-discharge tests over a voltage range of 0.8 to 1.8 V. The electrochemical performance showed a maximum capacity of 107.1 mAh / g at a current density of 0.5 A / g over 600 cycles.

[0118] Comparative Example 4

[0119] A method for preparing a sodium-doped layered manganese dioxide nanomaterial comprises the following steps:

[0120] 1) Add 3 mmol of sodium silicate to 40 mL of deionized water and stir until completely dissolved to prepare solution A;

[0121] 2) Dissolve 3 mmol of manganese chloride in 60 mL of deionized water and stir until completely dissolved to prepare solution B;

[0122] 3) At room temperature, mix solutions A and B to obtain a light brown suspension, and stir for 1 h.

[0123] 4) After the reaction process is completed, the solution is centrifuged, washed three times with deionized water and ethanol respectively, dried at 60°C for 24 hours, and ground to obtain the precursor material;

[0124] 5) Dissolve 0.2 mol of sodium hydroxide in 100 mL of deionized water and stir evenly to obtain a 2 mol / L sodium hydroxide solution; add the precursor to the sodium hydroxide solution, heat in an oil bath to maintain 90° C., and stir for 12 h. After the reaction is completed, wash the product with deionized water three times, wash it with ethanol three times, filter it, and dry it at 60° C. for 12 h to obtain a sodium-doped layered manganese dioxide nanomaterial.

[0125] To verify the electrochemical performance of sodium-doped layered manganese dioxide nanomaterials and further apply them as cathode materials for zinc-ion batteries, the prepared sodium-doped layered manganese dioxide nanomaterials were dissolved in N-methylpyrrolidone at a ratio of 7:2:1 with a binder (polyvinylidene fluoride) and a conductive agent (acetylene black). The resulting slurry was coated onto titanium foil and vacuum-dried before being assembled into a zinc-ion battery. A mixed aqueous solution of 1M zinc sulfate and 0.2M manganese sulfate was used as the electrolyte, a zinc sheet was used as the negative electrode, and a glass fiber separator was used. Galvanostatic charge-discharge tests were performed over a voltage range of 0.8 to 1.8 V to analyze the electrochemical performance. The results showed a maximum capacity of 179.8 mAh / g at a current density of 0.5 A / g over 600 cycles.

[0126] Comparative Example 5

[0127] A method for preparing potassium-doped layered manganese dioxide nanomaterials comprises the following steps:

[0128] 1) Add 3 mmol of potassium silicate to 40 mL of deionized water and stir until completely dissolved to prepare solution A;

[0129] 2) Dissolve 3 mmol of manganese chloride in 60 mL of deionized water and stir until completely dissolved to prepare solution B;

[0130] 3) At room temperature, slowly mix solutions A and B to obtain a light brown suspension, and stir for 1 h.

[0131] 4) After the reaction process is completed, the solution is centrifuged, washed three times with deionized water and ethanol respectively, dried at 60°C for 24 hours, and ground to obtain the precursor material;

[0132] 5) Dissolve 0.2 mol potassium hydroxide in 100 mL of deionized water and stir to obtain a 2 mol / L potassium hydroxide solution. Add the precursor to the potassium hydroxide solution, heat in an oil bath at 90°C, and stir for 12 hours. After etching, separate the precipitate by centrifugation, wash three times with deionized water, three times with ethanol, filter, and dry at 60°C for 12 hours to obtain potassium-doped layered manganese dioxide nanomaterials.

[0133] In order to verify the electrochemical properties of potassium-doped layered manganese dioxide nanomaterials, it was further applied as the positive electrode material of zinc ion batteries: the prepared potassium-doped layered manganese dioxide nanomaterials were dissolved in N-methylpyrrolidone with the binder polyvinylidene fluoride and the conductive agent acetylene black at a ratio of 7:2:1 to prepare a slurry, coated on titanium foil, and vacuum dried at 100°C for 12 hours to assemble zinc ion batteries as electrode materials. The electrolyte used was a mixed aqueous solution of 1M zinc sulfate and 0.2M manganese sulfate, the negative electrode was a circular zinc sheet, and the battery separator was glass fiber; the electrochemical performance was analyzed by constant current charge and discharge test, and the voltage range was 0.8~1.8V. By testing its electrochemical performance, the results are shown Figure 1 It can be observed that at a current density of 0.5A / g, the specific capacity can reach a maximum of 178.5mAh / g after 600 cycles, but the capacity retention rate is only 69%. This is because the large radius of potassium ions affects the stability of the layered structure when doped alone, which also leads to a very low capacity retention rate. Zinc ions cannot be efficiently inserted and removed, resulting in its poor electrochemical performance.

[0134] By comparing Example 1 with Comparative Examples 1, 2, and 3, it can be seen that in terms of the selection of the preparation method, the method of the present invention can produce a manganese dioxide layered structure with better crystallinity than other synthesis methods, which is more suitable for use as an ion co-doped material. The prepared potassium-sodium co-doped manganese dioxide material exhibits better electrochemical properties as a positive electrode material for zinc ion batteries.

[0135] By comparing Example 1 with Comparative Examples 4 and 5, it can be seen that compared with sodium or potassium doping alone, potassium and sodium co-doping can make the manganese dioxide nanomaterial have more excellent electrochemical properties.

[0136] Comparative Example 6

[0137] This comparative example differs from Example 1 only in that the oil bath was heated at 40°C and stirred for 6 hours during the alkaline etching process. Under the same test conditions as Example 1, a maximum capacity of 114.4 mAh / g was achieved at a current density of 0.5 A / g over 600 cycles.

[0138] Comparative Example 7

[0139] This comparative example differs from Example 1 only in that the oil bath was heated at 120°C and stirred for 12 hours during the alkaline etching process. Under the same test conditions as Example 1, a maximum capacity of 106.0 mAh / g was achieved at a current density of 0.5 A / g over 600 cycles.

Claims

1. An application of potassium-sodium co-doped manganese dioxide nanomaterial in preparing positive electrode materials for zinc ion batteries, characterized in that: The preparation method of the potassium and sodium co-doped manganese dioxide nanomaterial: 1) Add 3 mmol of sodium silicate to 40 mL of deionized water and stir until completely dissolved to prepare solution A; 2) Dissolve 3 mmol of manganese chloride in 60 mL of deionized water and stir until completely dissolved to prepare solution B; 3) At room temperature, slowly mix solutions A and B to obtain a light brown suspension, and stir for 1 h. 4) After the reaction process is completed, the solution is centrifuged, washed three times with deionized water and ethanol respectively, dried at 60°C for 24 hours, and ground to obtain the precursor material; 5) Dissolve 0.2 mol potassium hydroxide in 100 mL of deionized water and stir evenly to obtain a 2 mol / L potassium hydroxide solution; add the precursor to the potassium hydroxide solution, heat in an oil bath to maintain 90° C., stir for 12 h. After etching, separate the precipitate by centrifugation, wash it three times with deionized water, wash it three times with ethanol, filter it, and dry it at 60° C. for 12 h; and obtain potassium-sodium co-doped layered manganese dioxide nanomaterials.

2. Application of potassium-sodium co-doped manganese dioxide nanomaterial in preparing positive electrode material for zinc ion batteries, characterized in that: The preparation method of the potassium and sodium co-doped manganese dioxide nanomaterial: 1) Add 3 mmol of potassium silicate to 40 mL of deionized water and stir until completely dissolved to prepare solution A; 2) Dissolve 3 mmol of manganese chloride in 60 mL of deionized water and stir until completely dissolved to prepare solution B; 3) At room temperature, slowly mix solutions A and B to obtain a light brown suspension, and stir for 1 h. 4) After the reaction process is completed, the solution is centrifuged, washed three times with deionized water and ethanol respectively, dried at 60°C for 24 hours, and ground to obtain the precursor material; 5) Dissolve 0.2 mol of sodium hydroxide in 100 mL of deionized water and stir evenly to obtain a 2 mol / L potassium hydroxide solution; add the precursor to the potassium hydroxide solution, heat in an oil bath to maintain 90° C., stir for 12 h. After etching, separate the precipitate by centrifugation, wash it three times with deionized water, wash it three times with ethanol, filter it, and dry it at 60° C. for 12 h; and obtain a potassium-sodium co-doped layered manganese dioxide nanomaterial.

3. Application of potassium-sodium co-doped manganese dioxide nanomaterial in the preparation of positive electrode materials for zinc ion batteries, characterized in that: The preparation method of the potassium and sodium co-doped manganese dioxide nanomaterial: 1) Add 4 mmol of sodium silicate to 40 mL of deionized water and stir until completely dissolved to prepare solution A; 2) Dissolve 3 mmol of manganese nitrate in 60 mL of deionized water and stir until completely dissolved to prepare solution B; 3) At room temperature, slowly mix solutions A and B to obtain a light brown suspension, then add 3 mmol of potassium chloride and stir for 1.5 h. 4) After the reaction process is completed, the solution is centrifuged, washed three times with deionized water and ethanol respectively, dried at 60°C for 24 hours, and ground to obtain the precursor material; 5) Dissolve 0.1 mol potassium hydroxide in 100 mL of deionized water and stir evenly to obtain a 1 mol / L potassium hydroxide solution; add the precursor to the potassium hydroxide solution, heat in an oil bath to maintain 80° C., stir for 10 h. After etching, separate the precipitate by centrifugation, wash it three times with deionized water, wash it three times with ethanol, filter it, and dry it at 60° C. for 12 h; and obtain potassium-sodium co-doped layered manganese dioxide nanomaterials.

4. Application of potassium-sodium co-doped manganese dioxide nanomaterial in preparing positive electrode material for zinc ion batteries, characterized in that: The preparation method of the potassium and sodium co-doped manganese dioxide nanomaterial: 1) Add 3 mmol of sodium silicate to 40 mL of deionized water and stir until completely dissolved to prepare solution A; 2) Dissolve 4 mmol of manganese chloride in 60 mL of deionized water and stir until completely dissolved to prepare solution B; 3) At room temperature, slowly mix solutions A and B to obtain a light brown suspension, and stir for 1 h. 4) After the reaction process is completed, the solution is centrifuged, washed three times with deionized water and ethanol respectively, dried at 60°C for 24 hours, and ground to obtain the precursor material; 5) Dissolve 0.1 mol potassium hydroxide in 100 mL of deionized water and stir evenly to obtain a 1 mol / L potassium hydroxide solution; add the precursor to the potassium hydroxide solution, heat in an oil bath to maintain 80°C, and stir for 9 hours. After etching, the precipitate is separated by centrifugation, washed with deionized water 3 times, washed with ethanol 3 times, filtered, and dried at 60°C for 12 hours to obtain potassium-sodium co-doped layered manganese dioxide nanomaterials.

5. Application of potassium-sodium co-doped manganese dioxide nanomaterial in preparing positive electrode material for zinc ion batteries, characterized in that: The preparation method of the potassium and sodium co-doped manganese dioxide nanomaterial: 1) Add 3 mmol of sodium silicate to 40 mL of deionized water and stir until completely dissolved to prepare solution A; 2) Dissolve 3 mmol of manganese sulfate in 60 mL of deionized water and stir until completely dissolved to prepare solution B; 3) At room temperature, slowly mix solutions A and B to obtain a light brown suspension, and stir for 1 h. 4) After the reaction process is completed, the solution is centrifuged, washed three times with deionized water and ethanol respectively, dried at 60°C for 24 hours, and ground to obtain the precursor material; 5) Dissolve 0.1 mol potassium hydroxide and 0.1 mol sodium hydroxide in 100 mL of deionized water and stir evenly to obtain a mixed alkaline solution of 1 mol / L potassium hydroxide and 1 mol / L sodium hydroxide; add the precursor to the mixed alkaline solution, heat in an oil bath to maintain 90°C, stir for 10 hours, and after etching, separate the precipitate by centrifugation, wash with deionized water 3 times, wash with ethanol 3 times, filter, and dry at 60°C for 12 hours to obtain potassium-sodium co-doped manganese dioxide nanomaterials.

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