Na < + > pre-embedded delta-MnO2 electrode material and preparation method and application thereof

Abstract

The invention discloses a Na < + > pre-embedded delta-MnO2 electrode material and a preparation method and application thereof, and the method comprises the following steps: a, adding Mn (NO3) 2 into a NaOH solution mixed with H2O2, and reacting to generate a MnO (OH) precursor; b, dispersing the precursor in a NaOH solution, and carrying out a hydrothermal reaction; and washing the reaction product, and drying to obtain the Na < + > pre-embedded layered delta-MnO2. The method is simple and controllable in process and good in repeatability; na < + > is pre-embedded into a stable structure and the conductivity is improved; the performance of the capacitor is broken through, a wide voltage window and high energy density are achieved, and the capacitor is suitable for high-frequency and high-power demand scenes.

Description

Technical Field

[0001] The present invention relates to the field of electrochemical energy storage, and particularly to a Na + pre-embedded δ-MnO2 electrode material, a preparation method thereof, and an application thereof. Background Art

[0002] An aqueous ammonium ion (NH4 + ) energy storage system is a technology that has emerged in recent years. It utilizes abundant electrode resources and the fast diffusion kinetics characteristics of NH4 + to achieve excellent rate performance at low cost. Compared with metal ion charge carriers (Li + , Na + , K + , Zn 2+ , Mg 2+ ), the non-metal NH4 + ion is sustainable and rich in resources on the earth. In addition, NH4 + has a small hydrated ion size (3.31 Å) and a light molar mass (18 g mol ⁻1 ), which helps to improve its ion diffusion kinetics performance in aqueous batteries. Compared with acidic electrolytes, NH4 + aqueous solution has lower corrosivity and a lower hydrogen evolution reaction (HER) potential. In addition, ammonium salts have a highly dissociative property, which can provide better ionic conductivity.

[0003] Due to multi-valent redox reactions, high redox potentials, and double-electron transfer characteristics, manganese-based electrode materials can achieve high specific capacity and high energy density, thus attracting extensive attention in aqueous ammonium ion energy storage systems. In addition, low cost and low toxicity make manganese-based materials an ideal choice for large-scale practical applications, but their poor electronic conductivity will lead to slow kinetics performance. Despite the breakthrough progress in electrode materials, aqueous ammonium ion storage still faces challenges such as low energy density and limited working potential window. Summary of the Invention

[0004] In view of the above-mentioned defects or deficiencies in the prior art, it is desirable to provide a preparation method and an application of a Na + pre-embedded δ-MnO2 electrode material to solve the above technical problems.

[0005] A preparation method of a Na + pre-embedded δ-MnO2 electrode material includes the following steps: a. Adding Mn(NO3)2 to a NaOH solution mixed with H2O2 to react to form a MnO(OH) precursor; b. Disperse the MnO(OH) precursor in the NaOH solution and conduct a hydrothermal reaction; after washing the reaction product, dry it to obtain Na + pre-embedded layered δ-MnO2.

[0006] Furthermore, in step a, the molar ratio of H2O2 to NaOH in the H2O2 and NaOH mixed solution is 2:1.

[0007] Furthermore, the hydrothermal reaction control parameters in step b are: reaction temperature 160 - 180 °C, reaction duration 16 - 24 h.

[0008] Even further, provide a Na + pre-embedded δ-MnO2 electrode material, prepared by the above method, the material is a layered structure, the length of the nanosheets is more than 1 micron, the width is more than 100 nanometers, the thickness is more than 10 nanometers, and the interlayer spacing is 0.711 nm.

[0009] Even further, provide an ammonium ion capacitor, comprising: Positive electrode: including the Na + pre-embedded δ-MnO2 electrode material described in claim 4; Negative electrode: including expanded graphite; Electrolyte: NH4AC aqueous solution.

[0010] Furthermore, the preparation method of the positive electrode includes: mixing the Na + pre-embedded δ-MnO2 electrode material, superconducting carbon black, and polyvinylidene fluoride in a mass ratio of 75:15:10, fully grinding them, adding an appropriate amount of N-methylpyrrolidone to wet them, grinding again, and then uniformly coating the obtained slurry on the surface of the hydrophilic carbon paper, drying it to obtain the positive electrode of the ammonium ion capacitor.

[0011] Furthermore, the preparation method of the expanded graphite includes: a. Mix natural graphite flakes and sodium nitrate in a mass ratio of 1:1, and add sulfuric acid to the mixture under ice bath conditions, the mass of concentrated sulfuric acid is 20 - 50 times that of graphite; b. Slowly add potassium permanganate to the mixed solution in the ice bath and heat it; c. Then add water and stir at 90 °C. After the reaction ends, add hydrogen peroxide to remove the excess KMnO4. Finally, collect the yellow precipitate by centrifugation and vacuum dry it at room temperature to obtain graphite oxide; d. Heat the tubular furnace to 1000 °C, then push the graphite oxide powder into the heating zone under an argon atmosphere and process it for 10 seconds, and quickly take it out to obtain expanded graphite.

[0012] Further, the preparation method of the negative electrode includes: thoroughly grinding expanded graphite and polyvinylidene fluoride in a mass ratio of 9:1, adding an appropriate amount of N-methylpyrrolidone for wetting, grinding again, and then uniformly coating the obtained slurry on the surface of hydrophilic carbon paper and drying to obtain the negative electrode of the ammonium ion hybrid capacitor.

[0013] Further, the mass ratio of the positive electrode to the negative electrode is 1:1.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: 1) Hydrothermal method is used to prepare Na + pre-embedded in layered MnO2. The method is simple, highly repeatable, and has good controllability. A uniform precursor is formed by reacting a specific ratio of H2O2 / NaOH mixed solution with Mn(NO3)2, and combined with the hydrothermal reaction parameters, Na + is efficiently embedded in layered δ-MnO2, and the process is simple and the product structure is stable; 2) The pre-embedding of cations can stabilize the structure of MnO2 by coordinating with adjacent host atoms. In addition, the pre-embedded ions can effectively enhance the electronic conductivity, activate more active sites, and promote the diffusion kinetics, thereby significantly improving the capacitance and stability of the capacitor; 3) The preparation method of expanded graphite realizes a high specific surface area and improves the NH4⁺ adsorption capacity through ice bath oxidation to control the structural integrity, high-temperature instantaneous expansion to form a porous conductive network, and purification with hydrogen peroxide to remove impurities; it improves the fast charge storage ability and has a stable structure.

[0015] 4) Using the cation pre-embedded interlayer MnO2 material as the positive electrode and expanded graphite as the negative electrode to assemble an ammonium ion hybrid supercapacitor can broaden the working voltage, thereby improving the energy density and power density of the device. After matching the Na-MnO2 positive electrode with the expanded graphite negative electrode, the working voltage is extended to 2.1 V, and the energy density reaches 80.8 Wh kg -1 and the capacity retention rate is ≥90% after 1000 cycles.

[0016] 5) It is used for high-voltage ammonium ion hybrid capacitors to solve the problem of the limited working potential window of existing ammonium ion energy storage systems. In scenarios such as new energy vehicles and high-speed rail energy storage, the wide voltage window and high power density can suppress voltage fluctuations and achieve instantaneous high-power output.

[0017] It should be understood that the content described in the invention content part is not intended to limit the key or important features of the embodiments of the present invention, nor to limit the scope of the present invention. Other features of the present invention will become easily understood through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments read in conjunction with the accompanying drawings: Figure 1 Scanning electron microscope image of Na-MnO2 for Example 1; Figure 2 Cyclic voltammograms at different scanning rates and galvanostatic charge-discharge curves at different current densities of Example 1 in 1 M NH4Ac electrolyte solution; Figure 3 Scanning electron microscope image of H-MnO2 for Comparative Example 1; Figure 4 Scanning electron microscope image of Mg-MnO2 for Comparative Example 2; Figure 5 XRD patterns of Na-MnO2, H-MnO2, and Mg-MnO2; Figure 6 Schematic diagram of the assembly of Na-MnO2 / / expanded graphite; Figure 7 Cyclic voltammograms of Na-MnO2 / / expanded graphite at upper cutoff potentials from 1.8 V to 2.2 V; Figure 8 Cyclic voltammograms and galvanostatic charge-discharge curves of Na-MnO2 / / expanded graphite in the voltage range of 0 - 2.1 V. Detailed Description of the Specific Embodiment

[0019] The present invention will be further described in detail below with reference to the accompanying drawings and examples. It can be understood that the specific embodiments described herein are only for explaining the related invention and not for limiting the invention. Additionally, it should be noted that for the sake of description, only the parts related to the invention are shown in the drawings.

[0020] It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the drawings and examples.

[0021] Example 1 (1) Na + Pre-embed layered MnO2, and the preparation method is as follows: a. Dissolve 0.12 mol of NaOH in 180 mL of deionized water, and then add 20 mL of 30 wt.% H2O2 aqueous solution to the NaOH solution.

[0022] b. Then, quickly inject 100 mL of 0.3 mol L -1 Mn(NO3)2 solution into the above mixture. After slowly stirring for 30 minutes, filter to remove the excess liquid.

[0023] c. Redisperse the residue with 30 mL of 2 mol / L -1 NaOH solution, seal it in a stainless-steel autoclave with a polytetrafluoroethylene inner lining, and carry out hydrothermal reaction at 160 °C for 16 hours.

[0024] d. After washing the reaction product, dry it at 80 °C for 24 hours to obtain Na + pre-embedded layered MnO2 (Na-MnO2).

[0025] Figure 1 Figure [Figure number not provided in the original] is the scanning electron microscopy image of the prepared Na-MnO2, showing nanosheets with a length of several micrometers, a width of several hundred nanometers, a thickness of about dozens of nanometers, irregular edges, and accompanied by the mutual stacking between the sheets.

[0026] (II) Applications 1. Preparation of the electrode material for ammonium ion capacitor: After thoroughly grinding 75 mg of Na-MnO2, 15 mg of superconducting carbon black, and 10 mg of polyvinylidene fluoride, add an appropriate amount of N-methylpyrrolidone to moisten it. After grinding again, uniformly coat the obtained slurry on the surface of hydrophilic carbon paper and dry it to obtain the positive electrode of the ammonium ion capacitor.

[0027] 2. Electrochemical analysis results: Method: At normal temperature and pressure, assemble a three-electrode system with the Na-MnO2-coated electrode as the working electrode, a platinum wire as the counter electrode, and a saturated calomel electrode as the reference electrode. The electrolyte is 1 M NH4AC aqueous solution. In the potential range of 0 - 0.8 V, perform cyclic voltammetry scanning tests and constant current charge-discharge tests on the Na-MnO2 electrode material to study its specific capacitance and energy storage rate performance.

[0028] Figure 2 Figure [Figure number not provided in the original] is the cyclic voltammogram curve of the Na-MnO2 prepared in Example 1 at a scanning rate from 1 - 10 mV / s -1 and the constant current charge-discharge curve at a current density from 0.5 - 5 A / g -1 These cyclic voltammograms have two pairs of oxidation / reduction peaks at 0.4 - 0.6 V and 0.2 - 0.4 V, corresponding to the Faradaic pseudocapacitance process of H + / NH4 + intercalation / deintercalation in the Na-MnO2 host. All the constant current charge-discharge curves have almost equal charge and discharge times, indicating a high Coulombic efficiency. These curves have a weak discharge platform, confirming that Na-MnO2 does not follow the double-layer capacitance energy storage mechanism. According to the discharge curves, the specific capacitances of Na-MnO2 at 0.5, 1, 2, 3, and 5 A / g are calculated -1The specific capacitances are up to 368, 300, 220, 176, and 131 F g in sequence -1 .

[0029] Comparative Example 1 The Na-MnO2 prepared in Example 1 was redispersed in 1 L of 1 mol L -1 HNO3 and magnetically stirred for 1 day. After suction filtration, the filter cake was redispersed into 1 L of 1 mol L -1 HNO3 exchange solution. This ion exchange process was repeated more than five times to achieve a complete phase transition from sodium birnessite to hydro birnessite. Subsequently, the product was washed and dried at 80 °C for 24 h to finally obtain H-MnO2.

[0030] Using H-MnO2 as the active material, the positive electrode material of the ammonium ion capacitor was prepared, and its electrochemistry was analyzed. The preparation method and test method were the same as those in Example 1. Comparative Example 2 The difference between Comparative Example 2 and Comparative Example 1 was only that the 1 L of 1 mol L -1 HNO3 exchange solution was replaced with 1 L of 1 mol L - 1 MgCl2, and the others were the same as in Comparative Example 1, to achieve a complete phase transition from sodium birnessite to magnesium buserite. Subsequently, the product was washed and dried at 80 °C for 24 h to finally obtain Mg-MnO2.

[0031] Using Mg-MnO2 as the active material, the positive electrode material of the ammonium ion capacitor was prepared, and its electrochemistry was analyzed. The preparation method and test method were the same as those in Example 1. The scanning electron micrographs of H-MnO2 and Mg-MnO2 prepared in Comparative Examples 1 and 2 are as Figure 3 and Figure 4 shown, both showing a layered morphology similar to that of Na-MnO2. In the structure of Mg-MnO2, a small amount of ribbon-like crystals formed by the splitting of nanosheets could be observed.

[0032] The XRD patterns of Example 1 and Comparative Examples 1-2 are as Figure 5 shown. It can be seen from the figure that all the diffraction peaks of Na-MnO2 can be attributed to δ-MnO2 with a layered structure (standard card JCPDS No. 42-1317). The three characteristic peaks located at 12.6°, 25.3°, and 36.9° correspond to the diffraction of the (001), (002), and (100) crystal planes respectively. The H-MnO2 and Mg-MnO2 samples both showed similar diffraction characteristic peaks. However, due to Mg 2+With a larger ionic diameter, the (001) peak of Mg-MnO2 shifts towards a lower angle, corresponding to an enlarged interlayer spacing.

[0033] Example 2 (I) Preparation of expanded graphite as the anode material for ammonium ion capacitors, the method is as follows a. Mix natural graphite flakes (2 g, 99.8%, from Alfa Aesar Chemical Reagent Company) with sodium nitrate (NaNO3, 2 g), and add sulfuric acid (H2SO4, 46 mL) to the mixture under ice bath conditions.

[0034] b. Slowly add potassium permanganate (KMnO4, 6 g) to the mixed solution in the ice bath, and heat at 35 °C for 90 minutes.

[0035] c. Subsequently, add water (120 mL) and stir at 90 °C for 20 minutes. After the reaction, add hydrogen peroxide (H2O2, 30 wt%, 6 mL) to remove the excess KMnO4. Finally, collect the yellow precipitate by centrifugation and vacuum dry it at room temperature to obtain graphite oxide GO.

[0036] d. Heat the tube furnace to 1000 °C, then push the GO powder into the heating zone under an argon atmosphere for 10 seconds, and quickly take it out to obtain expanded graphite.

[0037] (II) Application 1. Preparation of the electrode material for ammonium ion capacitors: After thoroughly grinding 45 mg of expanded graphite and 5 mg of polyvinylidene fluoride, add an appropriate amount of N-methylpyrrolidone to moisten it, and grind it again. Then, evenly coat the obtained slurry on the surface of hydrophilic carbon paper and dry it to obtain the anode of the ammonium ion hybrid capacitor.

[0038] 2. Electrochemical analysis results: Method: An expanded graphite electrode was used as the working electrode, a platinum wire as the counter electrode, and a saturated calomel electrode as the reference electrode to assemble a three-electrode system. The electrolyte was 1 M NH4AC aqueous solution. The test potential range was -0.8 to 0.2 V. Cyclic voltammetry scanning tests and constant current charge-discharge tests were carried out on the expanded graphite electrode material to study its specific capacitance and energy storage rate performance. The cyclic voltammograms of expanded graphite at different scanning rates all maintained a nearly symmetric rectangular shape. As the scanning rate increased, the area enclosed by the curve increased correspondingly, confirming the capacitive characteristics of the electrode. Even at a high scanning rate of 500 mV·s⁻¹, a complete rectangular profile could still be clearly observed, indicating its excellent rate performance. The constant current charge-discharge curves at different current densities all showed capacitive linear ramp characteristics. The specific capacitance values were calculated to be 253, 217, 156, 130, 126, and 109 F·g⁻¹ at current densities of 1.5, 3, 5, 8, 10, and 15 A·g⁻¹, respectively. Example 3 (1) Preparation of the Na-MnO2 / / expanded graphite ammonium ion capacitor, the method is as follows a. The Na-MnO2 electrode in Example 1 was used as the positive electrode, and the expanded graphite electrode in Example 2 was used as the negative electrode. The masses of the two electrodes were close.

[0039] b. 1M NH4AC was used as the electrolyte. The battery was assembled in the order of positive electrode battery cover - steel sheet - positive electrode sheet - separator - electrolyte - negative electrode sheet - steel sheet - elastic sheet - negative electrode battery cover, and was successively encapsulated in a CR2032 battery case and compacted with a tablet press to assemble an ammonium ion hybrid capacitor.

[0040] The structure of the Na-MnO2 / / expanded graphite ammonium ion hybrid capacitor is as Figure 6 shown, and NH4 + ions act as charge carriers and are reversibly transported between the expanded graphite negative electrode and the Na-MnO2 positive electrode. Based on the independent potential windows of 0 - 0.8 V for the positive electrode material and -0.8 - 0.2 V for the negative electrode material, a working voltage of 1.6 V can theoretically be achieved. Figure 7 The CV curves of Na-MnO2 / / expanded graphite at different cut-off voltages (1.8 V to 2.2 V) are shown. Among them, 2.1 V is the optimal working voltage range. After exceeding this threshold, different degrees of water electrolysis phenomena will occur inside the device, triggering irreversible charge-discharge reactions.

[0041] Figure 8The left figure shows that Na-MnO2 / / expanded graphite operates stably in a wide voltage window of 0-2.1 V, and no obvious oxygen evolution characteristics are observed at different scan rates. These CV curves all show ideal rectangular profiles, indicating that a good kinetic balance is achieved between the two electrodes. The constant current charge and discharge curves at different currents in the right figure show symmetrical triangular profiles, confirming that the electrochemical kinetic processes of the positive and negative electrode materials have excellent matching. According to the charge and discharge curves at different current densities, the total mass of all materials based on the positive and negative electrodes is calculated. The system can obtain a maximum energy density of 80.8Wh·kg⁻¹ at a power density of 630 W·kg⁻¹, and a maximum power density of 21 kW·kg⁻¹ at an energy density of 23.2 Wh·kg⁻¹.

[0042] Comparative Example 3 Preparation of EGN / / EGN Ammonium Ion Capacitor The EGN electrodes were used as positive and negative electrodes, respectively, to assemble a capacitor and test its electrochemical performance. The preparation method and test method were the same as those in Example 3. The working voltage of the EGN / / EGN ammonium ion capacitor was 0-1.6 V, and there would be an obvious oxygen evolution signal peak when the voltage exceeded 1.6 V.

[0043] In the description of this specification, the description of the terms "one embodiment", "some embodiments", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0044] The above are only preferred embodiments of the present application and are not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A Na + The method for preparing a pre-embedded δ-MnO2 electrode material is characterized in that: The following steps are involved: a. Add Mn(NO3)2 to a NaOH solution mixed with H2O2 to react and generate a MnO(OH) precursor; b. Dispersing the MnO(OH) precursor in a NaOH solution and performing a hydrothermal reaction; washing the reaction product and drying it to obtain Na + Pre-intercalated layered δ-MnO2.

2. The preparation method according to claim 1, characterized in that The molar ratio of H2O2 to NaOH in the mixed solution of H2O2 and NaOH in step a is 2:

1.

3. The preparation method according to claim 1 or 2, characterized in that: The hydrothermal reaction control parameters in step b are: reaction temperature 160~180°C, reaction time 16~24h.

4. A Na + The pre-embedded δ-MnO2 electrode material is prepared by the method according to any one of claims 1 to 3, characterized in that: The material is a layered structure, the nanosheet has a length of more than 1 micron, a width of more than 100 nanometers, a thickness of more than 10 nanometers, and an interlayer distance of 0.711 nm.

5. An ammonium ion capacitor, characterized in that: include: Positive electrode: comprising the Na + Pre-embedded δ-MnO2 electrode material; Negative electrode: including expanded graphite; Electrolyte: NH4AC aqueous solution.

6. The ammonium ion capacitor according to claim 5, characterized in that The preparation method of the positive electrode comprises: + The pre-embedded δ-MnO2 electrode material, superconducting carbon black and polyvinylidene fluoride were fully ground in a mass ratio of 75:15:10, and then an appropriate amount of N-methylpyrrolidone was added for wetting. After grinding again, the obtained slurry was evenly applied to the surface of the hydrophilic carbon paper and dried to obtain the positive electrode of the ammonium ion capacitor.

7. The ammonium ion capacitor according to claim 5 or 6, characterized in that: The preparation method of the expanded graphite comprises: a. Mix natural graphite flakes and sodium nitrate in a mass ratio of 1:1, add sulfuric acid to the mixture under ice bath conditions, and the mass of concentrated sulfuric acid is 20-50 times that of graphite; b. Slowly add potassium permanganate to the mixture in an ice bath and heat; c. Then water was added and stirred at 90 ° C. After the reaction was completed, hydrogen peroxide was added to remove excess KMnO4, and finally the yellow precipitate was collected by centrifugation and dried in vacuum at room temperature to obtain graphite oxide; d. The tube furnace was heated to 1000 ° C, and then the graphite oxide powder was pushed into the heating zone under an argon atmosphere for 10 seconds and quickly taken out to obtain expanded graphite.

8. The ammonium ion capacitor according to claim 5 or 6, characterized in that: The preparation method of the negative electrode comprises: fully grinding expanded graphite and polyvinylidene fluoride according to a mass ratio of 9:1, adding an appropriate amount of N-methylpyrrolidone for wetting, grinding again, evenly applying the obtained slurry to the surface of hydrophilic carbon paper, and drying to obtain the negative electrode of the ammonium ion hybrid capacitor.

9. The ammonium ion capacitor according to claim 5 or 6, characterized in that: The mass ratio of the positive electrode to the negative electrode is 1:1.

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