Oxygen vacancy manganese dioxide / graphene oxide aqueous zinc ion positive electrode material and preparation method thereof

Abstract

The application discloses an oxygen vacancy manganese dioxide / graphene oxide aqueous zinc ion positive electrode material and a preparation method thereof, and comprises the following steps: 1, preparing a graphene oxide dispersion liquid; 2, adding potassium permanganate and ammonium chloride into the graphene oxide dispersion liquid, and obtaining a mixed solution after ultrasonic treatment; 3, carrying out hydrothermal reaction on the mixed solution, continuously stirring in the process, collecting the obtained precipitate, washing the precipitate with deionized water for three times, and drying to obtain a powder-shaped oxygen vacancy manganese dioxide / graphene oxide composite material; 4, dissolving the oxygen vacancy manganese dioxide / graphene oxide composite material, a conductive agent and a binder in N-N dimethylformamide, grinding in a mortar, coating the mixed slurry on a current collector, drying under vacuum condition, and pressing by a punching machine to obtain the positive electrode material. The prepared positive electrode material has high reversible electrochemical capacity and high cycle performance, and can improve the electrochemical performance of manganese dioxide.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of zinc ion positive electrode materials, and particularly relates to an oxygen vacancy manganese dioxide / graphene oxide aqueous zinc ion positive electrode material and a preparation method thereof. BACKGROUND

[0002] With the increasing attention to the global energy crisis, greenhouse effect and air pollution, the global range has started to change from using fossil fuel energy to using sustainable clean energy. Clean energy such as solar energy and wind energy needs large-scale energy storage devices, which greatly promotes the research of new large-scale storage systems with high efficiency, reliability and low cost. Aqueous zinc ion battery has the characteristics of high safety, rich zinc reserves, low cost, simple preparation process, low anode potential (-0.763V vs. SHE), high zinc theoretical capacity (820mA h g-1), and is expected to become a green energy storage device in the new generation of large-scale energy storage systems.

[0003] However, the aqueous zinc ion battery still faces a series of challenges. The development of high-performance positive electrode materials is one of the focuses of attention. In particular, manganese-based oxides have attracted great interest from researchers due to their large storage on earth, no pollution and high discharge voltage. However, the Jahn-Teller effect of Mn itself further destabilizes the host lattice framework, leading to irreversible dissolution of manganese oxides, showing poor kinetics and continuous capacity decay.

[0004] The existing patent (CN110729518A) further improves the dissolution problem of active material by preparing a fibrous aqueous rechargeable zinc ion battery based on manganese dioxide / graphene, but has not achieved high electrochemical capacity.

[0005] The existing patent of a vertical graphene / manganese dioxide composite material and a preparation method thereof, first obtains graphene by microwave plasma chemical vapor deposition method, and then obtains the final composite material by hydrothermal method to realize high specific capacity, high rate performance and high cycle life, but the preparation process is relatively complex and the energy consumption is high. SUMMARY

[0006] In order to overcome the shortcomings of the above technology, the purpose of the present application is to provide an oxygen vacancy manganese dioxide / graphene oxide aqueous zinc ion positive electrode material and a preparation method thereof. The prepared positive electrode material has high reversible electrochemical capacity and high cycle performance, and can improve the electrochemical performance of manganese dioxide.

[0007] In order to achieve the above purpose, the technical scheme adopted by the present application is:

[0008] An oxygen vacancy manganese dioxide / graphene oxide aqueous zinc ion positive electrode material. Manganese dioxide and graphene oxide are in situ composited through a hydrothermal reaction to successfully introduce oxygen vacancies. The resulting positive electrode material has a nanoscroll structure with a high specific surface area, thus exhibiting excellent electrochemical performance.

[0009] A method for preparing an oxygen vacancy manganese dioxide / graphene oxide aqueous zinc ion positive electrode material comprises the following steps:

[0010] Step 1: preparing a graphene oxide dispersion;

[0011] Step 2: adding potassium permanganate and ammonium chloride to the graphene oxide dispersion obtained in step 1, and obtaining a mixed solution after ultrasonic treatment;

[0012] Step 3: The mixed solution obtained in step 2 is transferred to a polytetrafluoroethylene-lined high-pressure hydrothermal autoclave, and a hydrothermal reaction is carried out at a certain temperature with continuous stirring during the process. The resulting precipitate is collected, washed three times with deionized water, and dried to obtain a powdered oxygen vacancy manganese dioxide / graphene oxide composite material;

[0013] Step 4: dissolve the oxygen vacancy manganese dioxide / graphene oxide composite material obtained in step 3, the conductive agent, and the binder in NN dimethyl pyrrolidone, grind them in a mortar, apply the mixed slurry on the current collector, dry it under vacuum conditions, and press it into a sheet punch to obtain the positive electrode material.

[0014] The specific steps of step 1 include:

[0015] a. Natural graphite and potassium permanganate were added in a mass ratio of 1:5 to 98% sulfuric acid, and then stirred in an ice bath at a stirring speed of 300 r / min~400 r / min for 1h~2h to obtain a mixture A;

[0016] b. The mixture A was heated to 35 ° C, and then kept at a temperature of 35 ° C for 1h, deionized water was added to the mixture A, and then the mixture with deionized water was heated to 90 ° C ~ 95 ° C, and then kept at a temperature of 90 ° C ~ 95 ° C to obtain a mixture B;

[0017] c. The mixture B was naturally cooled to room temperature, and then a 35% mass fraction of H2O2 solution was added to the mixture B, and the mixture was reacted at room temperature at a stirring speed of 100 r / min to 300 r / min for 10 minutes to obtain a graphene oxide solution;

[0018] d. The graphene oxide solution obtained in step c was washed several times with deionized water until neutral and set aside;

[0019] e. Disperse 5-18 ml of graphite oxide of a certain mass density in an appropriate amount of deionized water and ultrasonicate for 30 minutes to form a uniformly dispersed graphene oxide dispersion.

[0020] In step 2, potassium permanganate and ammonium chloride are added to the graphene oxide dispersion at a molar ratio of 1:(0.25-0.5), and ultrasonicated for 15 minutes.

[0021] The density of the graphene oxide used in step 1 and step 2 is 0.5-1.0 g / ml.

[0022] In step 3, the volume of the mixed solution is 50-70 ml, the hydrothermal temperature is 120-160° C., the duration is 24-60 h, and the stirring speed is 2000-4000 r / min.

[0023] The drying method in step 3 is forced air drying at a temperature of 60-80° C. for 10-12 hours.

[0024] In the oxygen vacancy manganese dioxide / graphene oxide in step 3, the mass fraction of graphene oxide is 5%-15%.

[0025] In step 4, the oxygen vacancy manganese dioxide / graphene oxide composite material, the conductive agent, and the binder are dissolved in NN dimethyl pyrrolidone in a mass ratio of 8:1:1, and continuously ground in a mortar for more than 30 minutes. The mixed slurry is coated on the current collector, dried at 60-100°C under vacuum conditions for 8-12 hours, and then pressed by a sheet punching machine to obtain a positive electrode material with a diameter of 12 mm.

[0026] The current collector in step 4 is any one of titanium foil, stainless steel foil, stainless steel mesh, and carbon paper.

[0027] The positive electrode material is applied to a battery, the negative electrode of the battery is a commercial zinc foil, the electrolyte is a mixed aqueous solution of zinc sulfate and manganese sulfate, the battery shell is a CR2032 button-type battery shell, and the separator is a glass fiber material. The battery assembled with the above materials is tested for the negative electrode material within a voltage range of 0.8-1.85V.

[0028] The electrolyte is a mixed aqueous solution formed by 1M zinc sulfate and 0.1M, 0.2M or 0.3M manganese sulfate.

[0029] Beneficial effects of the present invention:

[0030] Oxygen vacancy manganese dioxide / graphene oxide nanoscroll composites were synthesized through a simple hydrothermal reaction. Manganese dioxide was converted into a nanoscroll structure with a higher specific surface area, which increased the active sites of the material. The introduction of a large number of oxygen vacancies played a vital role in promoting the transfer of ions and protons, effectively adjusting the local electronic structure of the transition metal element Mn, which can greatly improve the electrochemical performance. The in-situ composite of manganese dioxide and graphene oxide, on the one hand, increased the conductivity of the material, and on the other hand, was beneficial to the structural stability of manganese dioxide, which inhibited the Mn 2+ Therefore, the manganese dioxide / graphene oxide cathode with oxygen vacancies shows excellent specific capacity, cycle stability and rate performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is the XRD pattern of the oxygen vacancy manganese dioxide / graphene oxide nanoscroll composite material prepared in Example 1 of the present invention.

[0032] Figure 2 TEM image of the oxygen vacancy manganese dioxide / graphene oxide nanoscroll composite material prepared in Example 1 of the present invention.

[0033] Figure 3 This is a high-resolution TEM image of the oxygen vacancy manganese dioxide / graphene oxide nanoscroll composite material prepared in Example 1 of the present invention.

[0034] Figure 4 This is a magnification diagram of the oxygen vacancy manganese dioxide / graphene oxide nanoscroll composite material prepared in Example 1 of the present invention when used as a nanoscroll composite material.

[0035] Figure 5 This is an impedance diagram of the oxygen vacancy manganese dioxide / graphene oxide nanoscroll composite material prepared in Example 1 of the present invention when used as a nanoscroll composite material. DETAILED DESCRIPTION

[0036] The present invention will be further described in detail below with reference to the embodiments.

[0037] Example 1

[0038] (1) 6 ml of graphene oxide with a mass density of 1 mg / ml was dispersed in 60 ml of deionized water, and after ultrasonication for 30 min, a graphene oxide dispersion was obtained. 0.2528 g of potassium permanganate and 0.0855 g of ammonium chloride were added to the graphene oxide dispersion, and ultrasonication was performed for 15 min.

[0039] (2) The mixed solution obtained in step (1) was transferred to a 100 ml polytetrafluoroethylene-lined high-pressure hydrothermal autoclave, placed in a 120° C. oil bath, and reacted continuously for 24 h with continuous stirring at a speed of 2000 / min. The resulting precipitate was collected, washed three times with deionized water, and dried to obtain a powdered oxygen vacancy manganese dioxide / graphene oxide composite.

[0040] Figure 1 (XRD spectrum) It can be seen that the characteristic peaks of the obtained oxygen vacancy manganese dioxide / graphene oxide nanoscroll composite material at 12.7° (110) crystal plane, 18.1° (200) crystal plane, 28.8° (310) crystal plane, and 37.5° (211) crystal plane all match well with the α-MnO2 standard card (JCPDS No.44-0141), which also shows that the introduction of graphene does not significantly destroy the phase structure of MnO2. Figure 2 and Figure 3 The TEM image of the obtained material shows that the lattice spacing of the sample is 0.70nm, corresponding to the (110) crystal plane of α-MnO2.

[0041] (3) Take 80 mg of the oxygen vacancy manganese dioxide / graphene oxide composite material obtained in step (2), 10 mg of Ketjen black, and 10 mg of polyvinylidene fluoride, mix them, add an appropriate amount of NN dimethyl pyrrolidone, and grind them in a mortar for more than 30 minutes. The mixed slurry is coated on carbon paper, dried at 60°C for 12 hours under vacuum conditions, and pressed by a punching machine to obtain a positive electrode material with a diameter of 12 mm. The negative electrode is commercial zinc foil, and a mixed aqueous solution of 1M zinc sulfate and 0.1M manganese sulfate is used as the electrolyte. The battery shell uses a CR2032 button-type battery shell, and the diaphragm uses a glass fiber material. The battery assembled with the above materials is tested for the negative electrode material in the voltage range of 0.8-1.85V. The rate performance at different current densities is as follows. Figure 3 As shown in the figure, the specific capacities of the MnO2 electrode at current densities of 0.2C, 0.5C, 1C, 2C, 3C, and 4C are 171, 166, 144, 121, 94, and 52 mAh / g, respectively. While those of the MnO2 / rGO electrode are 221, 203, 165, 136, 116, and 104 mAh / g, which are significantly better than the rate performance of the MnO2 electrode.

[0042] Figure 5 In order to investigate the comparison of electrode conductivity of MnO2 / rGO electrodes, electrochemical impedance spectroscopy tests were performed. The Nyquist plots of MnO2 and MnO2 / rGO electrodes and the corresponding equivalent circuit diagrams ( Figure 4-5). where Rs is the bulk solution resistance, Rct is the interfacial charge transfer resistance, CPE represents the constant phase element accounting for the double-layer capacitance, and Zw is the Warburg impedance. The results show that the semicircle diameter in the high-frequency region is related to the Rct value, while the slope in the low-frequency region is positively correlated with the diffusion rate. Fitting revealed that the Rct value of the Zn||MnO2 battery with the MnO2 / rGO electrode was 40Ω, lower than the Rct value of the pure MnO2 electrode (60Ω), indicating that the introduction of graphene oxide enhances the electrode's conductivity.

[0043] Example 2

[0044] (1) Disperse 12 ml of graphene oxide with a mass density of 1 mg / ml into 50 ml of deionized water, ultrasonicate for 30 min to obtain a graphene oxide dispersion, add 0.2528 g of potassium permanganate and 0.0855 g of ammonium chloride into the graphene oxide dispersion, and ultrasonicate for 15 min;

[0045] (2) The mixed solution obtained in step (1) was transferred to a 100 ml polytetrafluoroethylene-lined high-pressure hydrothermal autoclave, placed in a 150° C. oil bath, and reacted continuously for 48 h with continuous stirring at a speed of 3000 / min. The resulting precipitate was collected, washed three times with deionized water, and dried to obtain a powdered oxygen vacancy manganese dioxide / graphene oxide composite material;

[0046] (3) 80 mg of the oxygen vacancy manganese dioxide / graphene oxide composite material obtained in step (2), 10 mg of acetylene black, and 10 mg of polyvinylidene fluoride were mixed, an appropriate amount of NN dimethyl pyrrolidone was added, and the mixture was continuously ground in a mortar for more than 30 minutes. The mixed slurry was coated on titanium foil, dried at 80°C under vacuum conditions for 10 hours, and then pressed using a sheet punching machine to obtain a positive electrode material with a diameter of 12 mm. The negative electrode was commercial zinc foil, a mixed aqueous solution of 1M zinc sulfate and 0.2M manganese sulfate was used as the electrolyte, the battery shell was a CR2032 button-type battery shell, and the separator was a glass fiber material. The battery assembled with the above materials was tested in the voltage range of 0.8-1.85V.

[0047] Example 3

[0048] (1) Disperse 12 ml of graphene oxide with a mass density of 1 mg / ml into 70 ml of deionized water, and ultrasonicate for 30 min to obtain a graphene oxide dispersion. Add 0.2528 g of potassium permanganate and 0.1710 g of ammonium chloride into the graphene oxide dispersion, and ultrasonicate for 15 min.

[0049] (2) The mixed solution obtained in step (1) was transferred to a 100 ml polytetrafluoroethylene-lined high-pressure hydrothermal autoclave, placed in a 150° C. oil bath, and reacted continuously for 60 h with continuous stirring at a speed of 4000 / min. The resulting precipitate was collected, washed three times with deionized water, and dried to obtain a powdered oxygen vacancy manganese dioxide / graphene oxide composite material;

[0050] (3) 80 mg of the oxygen vacancy manganese dioxide / graphene oxide composite material obtained in step (2), 10 mg of carbon nanotubes, and 10 mg of polyvinylidene fluoride were mixed, an appropriate amount of NN dimethyl pyrrolidone was added, and the mixture was continuously ground in a mortar for more than 30 minutes. The mixed slurry was coated on a stainless steel mesh, dried at 100°C under vacuum for 8 hours, and then pressed using a sheet punching machine to obtain a positive electrode material with a diameter of 12 mm. The negative electrode was commercial zinc foil, a mixed aqueous solution of 1M zinc sulfate and 0.3M manganese sulfate was used as the electrolyte, the battery shell was a CR2032 button-type battery shell, and the separator was a glass fiber material. The battery assembled with the above materials was tested in the voltage range of 0.8-1.85V.

Claims

1. A method for preparing an oxygen vacancy manganese dioxide / graphene oxide aqueous zinc ion positive electrode material, characterized in that: The following steps are included: Step 1: preparing a graphene oxide dispersion; Step 2: adding potassium permanganate and ammonium chloride to the graphene oxide dispersion obtained in step 1, and obtaining a mixed solution after ultrasonic treatment; Step 3: The mixed solution obtained in step 2 is transferred to a polytetrafluoroethylene-lined high-pressure hydrothermal autoclave, and a hydrothermal reaction is carried out at a certain temperature with continuous stirring during the process. The resulting precipitate is collected, washed three times with deionized water, and dried to obtain a powdered oxygen vacancy manganese dioxide / graphene oxide composite material; Step 4: dissolving the oxygen vacancy manganese dioxide / graphene oxide composite material obtained in step 3, a conductive agent, and a binder in NN dimethyl pyrrolidone, grinding them in a mortar, coating the mixed slurry on a current collector, drying under vacuum conditions, and pressing with a sheet punch to obtain a positive electrode material; An oxygen-vacancy manganese dioxide / graphene oxide aqueous zinc ion cathode material. The in-situ compounding of manganese dioxide and graphene oxide via a hydrothermal reaction successfully introduces a large number of oxygen vacancies. The resulting cathode material has a nanoscroll structure with a high specific surface area, thus exhibiting excellent electrochemical performance. In step 2, 0.2528 g of potassium permanganate and 0.0855 g of ammonium chloride were added to the graphene oxide dispersion and ultrasonicated for 15 minutes; The density of the graphene oxide used in step 1 and step 2 is 0.5-1.0 g / ml; The hydrothermal temperature in step 3 is 120-160°C.

2. The method for preparing an oxygen vacancy manganese dioxide / graphene oxide aqueous zinc ion positive electrode material according to claim 1, wherein: The specific steps of step 1 include: a. Natural graphite and potassium permanganate were added to 98% sulfuric acid in a mass ratio of 1:5, and then stirred in an ice bath at a stirring speed of 300 r / min~400 r / min for 1h~2h to obtain a mixture A; b. Mixture A was heated to 35 ° C, and then kept at a temperature of 35 ° C for 1h, deionized water was added to the mixture A, and then the mixture with deionized water was heated to 90 ° C ~ 95 ° C, and then kept at a temperature of 90 ° C ~ 95 ° C to obtain a mixture B; c. The mixture B was naturally cooled to room temperature, and then a 35% mass fraction of H2O2 solution was added to the mixture B. The mixture was stirred at room temperature at a speed of 100 r / min~300 r / min for 10 min to obtain a graphene oxide solution; d. The graphene oxide solution obtained in step c was washed several times with deionized water until neutral and set aside; e. Disperse 5-18 ml of graphite oxide of a certain mass density in an appropriate amount of deionized water and ultrasonicate for 30 minutes to form a uniformly dispersed graphene oxide dispersion.

3. The method for preparing an oxygen vacancy manganese dioxide / graphene oxide aqueous zinc ion positive electrode material according to claim 1, wherein: In step 3, the volume of the mixed solution is 50-70 ml, the hydrothermal temperature is 120-160° C., the duration is 24-60 h, and the stirring speed is 2000-4000 r / min.

4. The method for preparing an oxygen vacancy manganese dioxide / graphene oxide aqueous zinc ion positive electrode material according to claim 1, wherein: The drying method in step 3 is forced air drying at a temperature of 60-80°C for 10-12 hours; In the oxygen vacancy manganese dioxide / graphene oxide in step 3, the mass fraction of graphene oxide is 5%-15%.

5. The method for preparing an oxygen vacancy manganese dioxide / graphene oxide aqueous zinc ion positive electrode material according to claim 1, wherein: In step 4, the oxygen vacancy manganese dioxide / graphene oxide composite material, the conductive agent, and the binder are dissolved in NN dimethyl pyrrolidone in a mass ratio of 8:1:1, and the mixture is continuously ground in a mortar for more than 30 minutes. The mixed slurry is coated on the current collector, dried at 60-100° C. under vacuum conditions for 8-12 hours, and then pressed by a sheet punching machine to obtain a positive electrode material with a diameter of 12 mm; The current collector in step 4 is any one of titanium foil, stainless steel foil, stainless steel mesh, and carbon paper.

6. The oxygen vacancy manganese dioxide / graphene oxide aqueous zinc ion positive electrode material according to any one of claims 1 to 5, characterized in that: The positive electrode material is applied to a battery, wherein the negative electrode of the battery is a commercial zinc foil, the electrolyte is a mixed aqueous solution of zinc sulfate and manganese sulfate, the battery shell is a CR2032 button-type battery shell, and the separator is a glass fiber material. The battery assembled with the above materials is tested for the positive electrode material within a voltage range of 0.8-1.85V.

7. The positive electrode material according to claim 6 is used in a battery, characterized in that: The electrolyte is a mixed aqueous solution formed by 1M zinc sulfate and 0.1M, 0.2M or 0.3M manganese sulfate.

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