Oxygen vacancy-containing manganese dioxide and preparation method thereof

Abstract

According to the oxygen vacancy-containing manganese dioxide and the preparation method thereof, the manganese dioxide is subjected to a reduction reaction under the reduction condition to obtain the oxygen vacancy-containing manganese dioxide, the oxygen vacancy-containing manganese dioxide is used as a raw material to prepare an aqueous zinc-manganese battery, and the cycling stability, the conductivity and the specific capacity of the aqueous zinc-manganese battery are improved.

Description

Technical Field

[0001] The invention relates to the technical field of electrochemical energy storage, in particular to manganese dioxide containing oxygen vacancies and a preparation method thereof. Background Art

[0002] As traditional fuel resources become increasingly scarce and the environmental pollution caused by their consumption becomes increasingly serious, renewable energy (such as solar energy, wind energy, etc.) is gradually being applied to the energy market. Due to the intermittent and regional limitations of renewable energy, it is necessary to develop an energy storage system that is highly safe, low-cost, high-performance, and long-life. At present, aqueous zinc-manganese batteries have the characteristics of high safety, abundant zinc reserves, low cost, simple preparation process, and high theoretical zinc capacity. They are regarded as the most promising green energy storage devices in the next generation of large-scale energy storage systems.

[0003] Aqueous zinc-manganese batteries mainly use zinc as the negative electrode, manganese dioxide as the positive electrode, and a solution containing zinc ions as the electrolyte. The battery is charged and discharged through the reversible extraction and embedding of zinc ions in manganese dioxide. However, the manganese dioxide obtained by traditional preparation methods has problems such as poor conductivity, low specific capacity and poor cycle stability. Summary of the invention

[0004] In order to solve the problems of poor conductivity, low specific capacity and poor cycle stability of manganese dioxide in aqueous zinc-manganese batteries in the prior art, the present invention provides a manganese dioxide containing oxygen vacancies and a preparation method thereof, which improves the cycle stability, conductivity and specific capacity.

[0005] In order to achieve the above object, the specific scheme adopted by the present invention is: a method for preparing manganese dioxide containing oxygen vacancies, placing manganese dioxide under reducing conditions to undergo a reduction reaction to obtain manganese dioxide containing oxygen vacancies.

[0006] As an optimized solution of the above-mentioned manganese dioxide containing oxygen vacancies and its preparation method: the process of the reduction reaction of the manganese dioxide is that the manganese dioxide is calcined in a reducing atmosphere at a temperature of 200-400° C. for 0.5-8h to obtain manganese dioxide containing oxygen vacancies.

[0007] As another optimized solution of the above-mentioned manganese dioxide containing oxygen vacancies and its preparation method: the process of the reduction reaction of the manganese dioxide is to prepare a reducing agent solution with a concentration of 0.001-5 mol / L, place the manganese dioxide in the reducing agent solution for reaction for 15-30 minutes, and obtain the manganese dioxide containing oxygen vacancies.

[0008] As another optimized solution of the above-mentioned manganese dioxide containing oxygen vacancies and the preparation method thereof: the reducing agent solution is one or more of potassium borohydride solution, sodium borohydride solution, ascorbic acid solution, citric acid solution, and glucose solution.

[0009] As another optimized solution of the above-mentioned manganese dioxide containing oxygen vacancies and the preparation method thereof: the process of the reduction reaction of the manganese dioxide is as follows: the manganese dioxide material is dispersed in a solvent to obtain a manganese dioxide dispersion with a concentration of 0.01 to 1 g / mL, and the dispersion is dropped on a carbon-based current collector, and dried at 60 to 100° C. for 2 to 12 hours to obtain a manganese dioxide electrode material; the manganese dioxide electrode material is immersed in an electrolyte and a reduction voltage of -0.5V to -1.23V vs. Ag / AgCl is applied for electrochemical reduction treatment to obtain manganese dioxide containing oxygen vacancies.

[0010] As another optimization scheme for the above-mentioned manganese dioxide containing oxygen vacancies and the preparation method thereof: the electrolyte is at least one of sodium sulfate solution, potassium sulfate solution, sodium nitrate solution, potassium nitrate solution, sodium chloride solution, and potassium chloride solution.

[0011] As another optimized solution of the above-mentioned manganese dioxide containing oxygen vacancies and its preparation method: the process of the reduction reaction of the manganese dioxide is to ball mill the manganese dioxide at a rotation speed of 2000-10000 rpm for 1-24h to obtain the manganese dioxide containing oxygen vacancies.

[0012] A manganese dioxide containing oxygen vacancies is obtained by using the above method for preparing manganese dioxide containing oxygen vacancies.

[0013] The above-mentioned manganese dioxide containing oxygen vacancies is used in aqueous zinc-manganese batteries.

[0014] As an optimization scheme for the application of the above-mentioned manganese dioxide containing oxygen vacancies in aqueous zinc-manganese batteries: the manganese dioxide containing vacancies is mixed with a conductive agent and a binder in a mass ratio of 7:0.5 to 2:0.5 to 1 to obtain a mixture; the mixture is dissolved in a solvent to obtain a viscous slurry, and the viscous slurry is coated on a current collector, and dried at 50-80°C for 6-24h to obtain a positive electrode material for an aqueous zinc-manganese battery.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] 1. The present invention provides a method for preparing manganese dioxide containing oxygen vacancies. Manganese dioxide reduces Mn element to a state lower than +4 valence through a reduction reaction, that is, the valence state of Mn element changes to between 2 and 4. Under the premise of maintaining its stable structure, its conductivity is improved. Manganese dioxide containing vacancies is more likely to transmit electrons, which is beneficial to improving the rate performance and stability of the battery. Manganese dioxide containing vacancies increases the affinity of Zn 2+ and H +The storage space of the battery increases, thereby increasing its active sites and improving the specific capacity of the battery, thereby increasing the energy density of the zinc-manganese battery; the increase in active sites is conducive to reducing the storage pressure of the battery during the charge and discharge process, effectively avoiding the occurrence of side reactions and improving the cycle stability of the battery.

[0017] 2. In the present invention, manganese dioxide is ball-milled at a rotation speed of 2000-10000 rpm for 1-24h. During the ball-milling process, no reducing agent is needed to be added. Mechanical force causes the chemical bonds inside the manganese dioxide crystal to be distorted and deformed, especially the bonding between oxygen atoms and other atoms is affected. Among them, the atomic arrangement on the surface of the manganese dioxide crystal is disturbed, resulting in an increase in surface energy, making the surface atoms in an unstable state, and the oxygen atoms originally tightly bound in the lattice are separated from their original positions; secondly, the bond strength is weakened, and the oxygen atoms are more likely to move out of the lattice to form oxygen vacancies; at the same time, during the mechanical grinding process, defects such as dislocations and grain boundaries are formed inside the manganese dioxide. These defects provide channels and energy barrier regions for the diffusion of oxygen atoms. Oxygen atoms are more likely to move along these defect positions, so that oxygen vacancies are formed at certain positions. In summary, no reducing agent needs to be added during the ball-milling process of manganese dioxide, and oxygen vacancies can be formed. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Schematic diagram of the reaction mechanism of the zinc-manganese battery of the present invention;

[0019] Figure 2 is a cycle curve diagram of a zinc-manganese battery prepared in Example 13;

[0020] Figure 3 is a charge and discharge curve diagram of a zinc-manganese battery prepared in Example 13;

[0021] Figure 4 is a cycle curve diagram of a zinc-manganese battery prepared in Example 12;

[0022] Figure 5 is a charge and discharge curve diagram of a zinc-manganese battery prepared in Example 12;

[0023] Figure 6 is a cycle curve diagram of a zinc-manganese battery prepared in Example 14;

[0024] Figure 7 This is a charge and discharge curve diagram of the zinc-manganese battery prepared in Example 14. DETAILED DESCRIPTION

[0025] The technical solution of the present invention is further elaborated in detail below in conjunction with specific embodiments. The parts of the present invention that are not described and disclosed in detail in the following embodiments should be understood as the prior art known or should be known to those skilled in the art.

[0026] A method for preparing manganese dioxide containing oxygen vacancies, wherein manganese dioxide is placed under reducing conditions to undergo a reduction reaction to obtain manganese dioxide containing oxygen vacancies, which can be achieved by electrochemical reduction, reducing gas reduction, reducing agent reduction or mechanical grinding reduction. Under reducing conditions, manganese dioxide reduces the Mn element to a state lower than +4 valence through a reduction reaction, that is, the valence state of the Mn element changes to between 2 and 4, thereby improving its conductivity while maintaining its stable structure, and the manganese dioxide containing vacancies is more likely to transmit electrons, which is beneficial to improving the rate performance and stability of the battery; the manganese dioxide containing vacancies increases the affinity of the Zn 2+ and H + The storage space of the battery increases, thereby increasing its active sites and improving the specific capacity of the battery, thereby increasing the energy density of the zinc-manganese battery; the increase in active sites is conducive to reducing the storage pressure of the battery during the charge and discharge process, effectively avoiding the production of side reaction products, and improving the cycle stability of the battery.

[0027] Example 1

[0028] A method for preparing manganese dioxide containing oxygen vacancies, wherein the process of manganese dioxide undergoing reduction reaction is to prepare a reducing agent solution with a concentration of 0.001-5 mol / L, place the manganese dioxide in the reducing agent solution for reaction for 15-30 minutes, and obtain manganese dioxide containing oxygen vacancies. The reducing agent solution is one or more of potassium borohydride solution, sodium borohydride solution, ascorbic acid solution, citric acid solution, and glucose solution.

[0029] In this embodiment, the specific steps include: preparing an ascorbic acid solution with a concentration of 0.001 mol / L; placing 0.01 mol of manganese dioxide in a potassium borohydride solution and reacting for 30 minutes at room temperature to obtain manganese dioxide containing oxygen vacancies, and at the same time, introducing C doping into the manganese dioxide to further improve its conductivity and structural stability.

[0030] Example 2

[0031] A method for preparing manganese dioxide containing oxygen vacancies comprises the following specific steps: preparing a potassium borohydride solution with a concentration of 5 mol / L; placing 0.01 mol of manganese dioxide in the potassium borohydride solution and reacting for 15 minutes at room temperature to obtain manganese dioxide containing oxygen vacancies.

[0032] Example 3

[0033] A method for preparing manganese dioxide containing oxygen vacancies comprises the following specific steps: preparing a potassium borohydride solution with a concentration of 0.1 mol / L; placing 0.01 mol of manganese dioxide in the potassium borohydride solution and reacting for 20 minutes at room temperature to obtain manganese dioxide containing oxygen vacancies.

[0034] Example 4

[0035] A method for preparing manganese dioxide containing oxygen vacancies, wherein the process of manganese dioxide undergoing reduction reaction is that manganese dioxide is calcined for 0.5-8h at a temperature of 200-400°C in a reducing atmosphere to obtain manganese dioxide containing oxygen vacancies, wherein the reducing atmosphere is one or more of hydrogen, ammonia and carbon monoxide. Under the reducing atmosphere, manganese dioxide is in a pure atmosphere environment, and the preparation method does not destroy the morphology and distribution state of manganese dioxide, and maintains its high specific surface area and the integrity of the charge transfer channel. Under the reducing atmosphere, manganese dioxide will also undergo corresponding doping reactions, for example, C doping is introduced into manganese dioxide under a CO atmosphere, and in an NH atmosphere, C doping is introduced into manganese dioxide. 3 In the atmosphere, manganese dioxide was introduced into N doping. 2 Introducing H doping, C doping, N doping and H doping in the atmosphere changes the charge distribution state of manganese dioxide, which is beneficial to improve the storage of Zn in manganese dioxide containing oxygen vacancies. 2+ and H + space, further improving its specific capacity and stability.

[0036] In this embodiment, the specific steps include:

[0037] Manganese dioxide is calcined in a hydrogen atmosphere at a temperature of 200° C. for 8 h to obtain manganese dioxide containing oxygen vacancies.

[0038] Example 5

[0039] A method for preparing manganese dioxide containing oxygen vacancies comprises calcining manganese dioxide at a temperature of 400° C. for 0.5 h in a hydrogen atmosphere to obtain manganese dioxide containing oxygen vacancies.

[0040] Example 6

[0041] A method for preparing manganese dioxide containing oxygen vacancies comprises calcining manganese dioxide at a temperature of 300° C. for 2 hours in a hydrogen atmosphere to obtain manganese dioxide containing oxygen vacancies.

[0042] Example 7

[0043] A method for preparing manganese dioxide containing oxygen vacancies, wherein the process of the reduction reaction of manganese dioxide is as follows: the manganese dioxide material is dispersed in a solvent to obtain a manganese dioxide dispersion with a concentration of 0.01 to 1 g / mL, and the dispersion is dripped onto carbon paper, and dried at 80°C for 2 hours to obtain a manganese dioxide electrode material; the manganese dioxide electrode material is immersed in an electrolyte and a reduction voltage of -0.5V to -1.23V vs. Ag / AgCl is applied for electrochemical reduction treatment to obtain manganese dioxide containing oxygen vacancies, wherein the electrolyte is at least one of sodium sulfate solution, potassium sulfate solution, sodium nitrate solution, potassium nitrate solution, sodium chloride solution, and potassium chloride solution; and the reduction potential is a constant potential method or a linear sweep voltammetry method. Conventional methods mainly reduce manganese dioxide raw materials, and the raw materials need to be exposed to the air for a long time during the electrode preparation process, while the preparation method directly reduces the electrode, and the prepared finished electrode can be directly assembled into a battery to avoid oxidation of manganese dioxide.

[0044] In this embodiment, the specific steps include:

[0045] The manganese dioxide material is dispersed in a solvent to obtain a manganese dioxide dispersion with a concentration of 0.1 g / mL, and the dispersion is dropped onto carbon paper and dried at 80°C for 2 hours to obtain a manganese dioxide electrode material; the manganese dioxide electrode material is immersed in an electrolyte and a reduction voltage of -0.5V to -1.23V vs. Ag / AgCl is applied for electrochemical reduction treatment to obtain manganese dioxide containing oxygen vacancies, the electrolyte is a sodium sulfate solution; and the reduction potential is a constant potential method.

[0046] Example 8

[0047] A method for preparing manganese dioxide containing oxygen vacancies. The process of reducing the manganese dioxide is as follows: ball milling the manganese dioxide at a rotation speed of 2000 / min for 24 hours to obtain the manganese dioxide containing oxygen vacancies.

[0048] Example 9

[0049] A method for preparing manganese dioxide containing oxygen vacancies. The process of reducing the manganese dioxide is as follows: ball milling the manganese dioxide at a rotation speed of 10000 / min for 1 hour to obtain the manganese dioxide containing oxygen vacancies.

[0050] Example 10

[0051] A method for preparing manganese dioxide containing oxygen vacancies. The process of reducing the manganese dioxide is as follows: ball milling the manganese dioxide at a rotation speed of 5000 / min for 6 hours to obtain the manganese dioxide containing oxygen vacancies.

[0052] Embodiment 11

[0053] A manganese dioxide containing oxygen vacancies is obtained by the preparation method described in any one of the above embodiments 1-10.

[0054] Example 12

[0055] The application of manganese dioxide containing oxygen vacancies in aqueous zinc-manganese batteries is to mix the dried raw materials with a conductive agent and an adhesive at a mass ratio of 7:0.5 to 2:0.5 to 1 to obtain a mixture; the mixture is dissolved in a solvent to obtain a viscous slurry, and the viscous slurry is coated on a current collector, and dried at 50-80°C for 6-24 hours to obtain a positive electrode material for an aqueous zinc-manganese battery. The adhesive is one or more of polyvinylidene fluoride (PVDF), sodium carboxymethyl cellulose (CMC), polytetrafluoroethylene (PTFE), polyvinyl alcohol and polyethylene oxide; the conductive agent is porous carbon, activated carbon, carbon nanotubes, Ketjen black, carbon fiber; the solvent is 1-methyl-2-pyrrolidone, deionized water, acetonitrile, ethanol; the current collector is one or more of zinc foil, copper foil, tin foil, titanium foil, stainless steel foil, stainless steel mesh, carbon cloth and carbon felt.

[0056] In this embodiment, the manganese dioxide containing oxygen vacancies obtained in Example 3 is used as a raw material, and the specific steps include:

[0057] The prepared manganese dioxide containing oxygen vacancies (hereinafter referred to as raw material) was washed three times by alternating centrifugation with deionized water and ethanol, and the washed raw material was placed in a vacuum oven at 60° C. and dried for 12 h;

[0058] The dried raw materials were mixed with Ketjen black and PVDF in a mass ratio of 7:2:1 to obtain a mixture; the mixture was dispersed in a 1-methyl-2-pyrrolidone solvent to obtain a viscous slurry, and the viscous slurry was coated on a current collector, and dried at 50° C. for 24 hours to obtain a positive electrode material for an aqueous zinc-manganese battery, and the positive electrode material was cut into discs with a diameter of 12 mm as positive electrode sheets for button batteries;

[0059] The above positive electrode sheet, the zinc sheet negative electrode and the glass fiber separator are assembled into a button battery, wherein the electrolyte is:

[0060] 2MZnSO 4 +0.2MMnSO 4 +0.05MTPABr (TPABr is tetrapropylammonium bromide).

[0061] The electrochemical performance test of the button cell obtained above was carried out:

[0062] The cycle performance of the button battery was tested under the following conditions: the current density was 0.5A g -1 .like Figure 4 Shown are the cycle performance test results. Figure 5 The figure shows the charge and discharge curve. It can be seen from the data in the figure that the zinc-manganese battery has a charge and discharge rate of 0.5A g -1The specific capacity can reach 442 mAh g -1 , and the coulombic efficiency is 99.82%. The zinc-manganese battery assembled with the positive electrode sheet prepared by the manganese dioxide containing oxygen vacancies in Example 3 has a higher discharge specific capacity and good cycle stability.

[0063] Embodiment 13

[0064] In this embodiment, the manganese dioxide containing oxygen vacancies obtained in Example 6 is used as a raw material, and the specific steps include:

[0065] Manganese dioxide containing oxygen vacancies is mixed with Ketjen black and PVDF in a mass ratio of 7:2:1 to obtain a mixture; the mixture is dissolved in a 1-methyl-2-pyrrolidone solvent to obtain a viscous slurry, and the viscous slurry is coated on a current collector, and dried at 60° C. for 12 hours to obtain a positive electrode material for an aqueous zinc-manganese battery, and the positive electrode material is cut into discs with a diameter of 12 mm as positive electrode sheets for button batteries;

[0066] The above positive electrode sheet, the zinc sheet negative electrode and the glass fiber separator are assembled into a button battery, wherein the electrolyte is:

[0067] 2MZnSO 4 +0.2MMnSO 4 +0.05MTPABr.

[0068] The electrochemical performance test of the button cell obtained above was carried out:

[0069] The cycle performance of the zinc-manganese battery was tested at a current density of 0.5A g -1 .like Figure 2 The following are the results of the cycle performance test. Figure 3 The figure shows the charge and discharge curve. It can be seen from the data in the figure that the zinc-manganese battery has a charge and discharge rate of 0.5A g -1 The specific capacity can reach 592 mAh g -1 , compared with MnO 2 The theoretical capacity has been significantly improved, and the Coulomb efficiency is 99.69%.

[0070] Embodiment 14

[0071] In this embodiment, the manganese dioxide containing oxygen vacancies obtained in embodiment 10 is used as a raw material, and the specific steps include:

[0072] Manganese dioxide containing oxygen vacancies is mixed with Ketjen black and PVDF in a mass ratio of 7:2:1 to obtain a mixture; the mixture is dissolved in a 1-methyl-2-pyrrolidone solvent to obtain a viscous slurry, and the viscous slurry is coated on a current collector, and dried at 60° C. for 12 hours to obtain a positive electrode material for an aqueous zinc-manganese battery, and the positive electrode material is cut into discs with a diameter of 12 mm as positive electrode sheets for button batteries;

[0073] The above positive electrode sheet, the zinc sheet negative electrode and the glass fiber separator are assembled into a button battery, wherein the electrolyte is:

[0074] 2MZnSO 4 +0.2MMnSO 4 +0.05MTPABr.

[0075] The electrochemical performance test of the button cell obtained above was carried out:

[0076] The cycle performance of the zinc-manganese battery was tested at a current density of 0.5A g -1 .like Figure 6 The following are the results of the cycle performance test. Figure 7 The data in the figure show that the zinc-manganese battery assembled with the positive electrode active material prepared by the present invention has a charge and discharge curve of 0.5A g -1 The specific capacity can reach 608 mAh g at a current density of -1 , and the coulombic efficiency is 99.60%. And it can be clearly seen that a high voltage platform of about 1.7V appears, which further indicates that the ball milling method makes MnO 2 The lattice of the zinc-manganese battery is distorted to a certain extent, resulting in certain oxygen vacancies, which makes the zinc-manganese battery have a higher discharge specific capacity.

[0077] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing manganese dioxide containing oxygen vacancies, characterized in that: The manganese dioxide is placed under reducing conditions to undergo a reduction reaction to obtain manganese dioxide containing oxygen vacancies.

2. A method for preparing manganese dioxide containing oxygen vacancies as claimed in claim 1, characterized in that: The process of the reduction reaction of manganese dioxide is that the manganese dioxide is calcined in a reducing atmosphere at a temperature of 200-400° C. for 0.5-8 hours to obtain manganese dioxide containing oxygen vacancies.

3. The method for preparing manganese dioxide containing oxygen vacancies according to claim 1, characterized in that: The process of the reduction reaction of manganese dioxide is to prepare a reducing agent solution with a concentration of 0.001-5 mol / L, place the manganese dioxide in the reducing agent solution and react for 15-30 minutes to obtain manganese dioxide containing oxygen vacancies.

4. A method for preparing manganese dioxide containing oxygen vacancies as claimed in claim 3, characterized in that: The reducing agent solution is one or more of potassium borohydride solution, sodium borohydride solution, ascorbic acid solution, citric acid solution, and glucose solution.

5. The method for preparing manganese dioxide containing oxygen vacancies according to claim 1, characterized in that: The process of the reduction reaction of manganese dioxide is as follows: the manganese dioxide material is dispersed in a solvent to obtain a manganese dioxide dispersion with a concentration of 0.01 to 1 g / ml, and the dispersion is dropped on a carbon-based current collector, and dried at 60 to 100° C. for 2 to 12 hours to obtain a manganese dioxide electrode material; the manganese dioxide electrode material is immersed in an electrolyte and a reduction voltage of -0.5V to -1.23V vs. Ag / AgCl is applied for electrochemical reduction treatment to obtain manganese dioxide containing oxygen vacancies.

6. A method for preparing manganese dioxide containing oxygen vacancies as claimed in claim 5, characterized in that: The electrolyte is at least one of a sodium sulfate solution, a potassium sulfate solution, a sodium nitrate solution, a potassium nitrate solution, a sodium chloride solution, and a potassium chloride solution.

7. The method for preparing manganese dioxide containing oxygen vacancies according to claim 1, characterized in that: The process of the reduction reaction of manganese dioxide is to ball-mill the manganese dioxide at a rotation speed of 2000-10000 rpm for 1-24 hours to obtain manganese dioxide containing oxygen vacancies.

8. A manganese dioxide containing oxygen vacancies, characterized in that: The manganese dioxide containing oxygen vacancies is obtained by the method for preparing manganese dioxide containing oxygen vacancies according to any one of claims 1 to 7.

9. Use of the manganese dioxide containing oxygen vacancies as claimed in claim 8 in aqueous zinc-manganese batteries.

10. The use of manganese dioxide in aqueous zinc-manganese batteries according to claim 9, characterized in that: The manganese dioxide containing vacancies is mixed with a conductive agent and a binder in a mass ratio of 7:0.5 to 2:0.5 to 1 to obtain a mixture; the mixture is dispersed in a solvent to obtain a viscous slurry, and the viscous slurry is coated on a current collector, and dried at 50-80° C. for 6-24 hours to obtain a positive electrode material for an aqueous zinc-manganese battery.

Images