A manganese-based high-performance composite cathode material coated with polydopamine and grown in situ on a MXene material and a preparation method thereof

Abstract

The application discloses a kind of polydopamine-coated manganese-based high-performance composite positive electrode materials and its preparation method, which is in-situ grown on MXene material, comprising the following steps: (1) preparation of Ni-gamma-MnO2 / MXene;(2) preparation of Ni-gamma-MnO2 / MXene@PDA.This technical solution promotes in-situ growth of nickel and manganese dioxide on MXene substrate by means of hydrothermal synthesis method, to construct a composite material with a specific structure, then, active material containing the above composite structure is uniformly dispersed in tris buffer solution environment, on this basis, oxygen is used as initiator to trigger the polymerization reaction, so that polydopamine can tightly wrap the surface of active material in a highly uniform manner, the preparation process is simple, raw materials are cheap, and the coating of polydopamine can reduce the effective contact degree between aqueous electrolyte and MnO2, reduce the dissolution of MnOOH, and make the structure more stable.

Description

TECHNICAL FIELD

[0001] The application relates to the field of manganese-based composite positive electrode materials, in particular to a manganese-based high-performance composite positive electrode material coated with polydopamine and in-situ grown on a MXene material and a preparation method thereof. BACKGROUND

[0002] With the development of new energy, energy storage has become a crucial focus. In view of the development demand of high-capacity and long-life aqueous zinc-ion secondary batteries in the field of new chemical energy storage technology, it is urgent to develop reliable positive electrode material frontier technology. Aqueous zinc-ion batteries (ZIBs) are a promising low-cost, risk-free and high-performance secondary battery, which is attributed to the abundant Zn source, low redox potential (-0.76 V vs. SHE) and high Zn theoretical capacity (819 mAh g 2+ ) of Zn -1 / Zn pair. Aqueous zinc-ion batteries are expected to become potential substitutes for commercial lithium-ion batteries (LIBs), but they have not been widely used in the market. The main challenge of aqueous zinc-ion batteries is to achieve dendrite-free zinc deposition at the negative electrode interface. Considering the strong electrostatic interaction between zinc ions and the host material, it is also a great challenge to find a suitable positive electrode material with high capacity and long service life.

[0003] At present, the positive electrode materials of aqueous zinc-ion batteries mainly include vanadium-based materials, prussian blue analog materials, manganese-based materials and phosphate materials. Among them, manganese dioxide has a high specific capacity of 308 mAh g -1 , abundant natural reserves, high energy density and high power density, and thus becomes the most promising candidate material and attracts widespread attention. Common MnO2 crystal structures have the following forms: 1, tunnel structure, for example, alpha-MnO2, beta-MnO2, gamma-MnO2 and the like; 2, layered structure, for example, delta-MnO2; 3, three-dimensional (3D) spinel structure, for example, lambda-MnO2. Under the condition of weak acidic electrolyte, electrochemical reaction occurs, H + and Zn 2+ insert into manganese dioxide to generate two discharge products MnOOH and According to the relevant literature, MnOOH is easily soluble in aqueous electrolyte, and its crystal structure collapses due to the Jahn-Teller effect, so manganese dioxide is prone to active substance dissolution during the charge and discharge cycle, thereby causing rapid capacity decay. In addition, the conductivity of manganese dioxide is poor, only 10 -8 -10 -5 S / cm, so that the electron transport rate is limited by the slow electron transport kinetics of the system. SUMMARY

[0004] To solve the above technical problems, the purpose of the present application is to provide a manganese-based high-performance composite cathode material coated with polydopamine and grown in situ on MXene material and a preparation method thereof, which has stable structure, good conductivity and is not easy to dissolve active substances.

[0005] To achieve the above purpose, the present application adopts the following technical solutions:

[0006] A preparation method of a manganese-based high-performance composite cathode material coated with polydopamine and grown in situ on MXene material, comprising the following steps:

[0007] (1) Preparation of Ni-γ-MnO2 / MXene: Dissolve manganese chloride tetrahydrate and nickel nitrate hexahydrate in MXene aqueous dispersion, fully dissolve under vigorous stirring, add potassium permanganate solution dropwise and stir vigorously, continue stirring after the addition of potassium permanganate solution is completed, then transfer the mixed solution to a polytetrafluoroethylene reactor for heating, centrifuge the initial product after reaction, wash, vacuum dry, grind into powder, and finally heat in a muffle furnace to obtain Ni-γ-MnO2 / MXene composite material;

[0008] (2) Preparation of Ni-γ-MnO2 / MXene@PDA: Add the Ni-γ-MnO2 / MXene composite material prepared in step (1) to tris buffer solution, ultrasonic dispersion, stirring, continue to add dopamine, stir, then under the initiation of oxygen, dopamine self-polymerization, and a dopamine film is coated on the surface of the Ni-γ-MnO2 / MXene composite material to obtain a polydopamine-coated Ni-γ-MnO2 / MXene composite material.

[0009] Preferably, in step (1), the concentration of MXene aqueous dispersion is 6.4 mg / ml, and MXene accounts for 30% of the total mass of Ni-γ-MnO2 / MXene composite material; the molar ratio of Ni to MnO2 is 1:5.

[0010] Preferably, in step (1), the heating temperature in the polytetrafluoroethylene reactor is 160℃, and the heating time is 1h.

[0011] Preferably, in step (1), the initial product after reaction is centrifuged at a speed of 8000 rpm for 5 min, washed with ultrapure water five times, then washed with anhydrous ethanol for the last time, and vacuum dried at 80℃ for 16h.

[0012] Preferably, in step (1), the temperature is raised to 200℃ at a rate of 5℃ / min in the muffle furnace and maintained for 36h.

[0013] Preferably, in step (2), the mass ratio of dopamine and Ni-γ-MnO2 / MXene composite material is 1:6.

[0014] Preferably, the tris buffer solution is prepared using oxygen-rich water as a solvent.

[0015] Preferably, the preparation method of MXene comprises the following steps:

[0016] LiF and Ti3AlC2 are used as raw materials, heated and stirred in a hydrochloric acid solution, centrifuged, washed and dried after the reaction is completed to obtain multi-layer MXene, and the multi-layer MXene product is dissolved in pure water, centrifuged, and the supernatant is discarded to obtain a few-layer MXene dispersion.

[0017] A manganese-based high-performance composite positive electrode material coated with polydopamine prepared by the above preparation method is grown in situ on the MXene material.

[0018] The present application has the following beneficial effects due to the use of the above technical solutions:

[0019] 1. In the present application, the hydrothermal synthesis method is used to promote the in-situ growth of nickel and manganese dioxide on the MXene substrate to construct a composite material with a specific structure. Then, the active material containing the above composite structure is uniformly dispersed in a tris buffer solution environment. On this basis, oxygen is used as an initiator to trigger a self-polymerization reaction, so that polydopamine can tightly wrap the surface of the active material in a highly uniform manner. The preparation process is simple, the raw materials are inexpensive, and the coating of polydopamine can reduce the effective contact between the aqueous electrolyte and MnO2, and also reduce the side reactions occurring at the electrode / electrolyte interface. Similarly, the chemical external interaction between MnO2 and the surface coating can reduce the dissolution of MnOOH, thereby making the structure more stable.

[0020] 2. The various hydrophilic groups on the polydopamine can make it easier to capture H + , thereby enhancing the cycle performance of the battery under large current and enhancing the electrolyte's infiltration of the electrode sheet, allowing the battery capacity to be fully released. By constructing a flexible buffer surface layer between the electrolyte and the electrode using polydopamine, the contact between the electrolyte and MnO2 is reduced, the side reactions are reduced, the structure is stabilized, and the large current cycle performance is enhanced, slowly releasing capacity and resisting volume changes that occur when ions are inserted / extracted. However, since MXene has a two-dimensional layered structure, if the polydopamine coating is excessive, it will block the ion transport channel, causing MXene to fail. The mass ratio of dopamine and Ni-γ-MnO2 / MXene composite material is 1:6, which has the best performance.

[0021] 4、The introduction of MXene material can reduce the contact resistance between the electrode active material and the current collector, thereby improving the charge and discharge performance of the device; moreover, the introduction of MXene makes the manganese dioxide have an anchoring platform, and enhances the conductivity of the active material, and provides an ordered channel for ion intercalation and deintercalation for the layered structure of manganese dioxide in the charge and discharge cycle; using MXene as the substrate can also play a stress buffering role and inhibit the volume expansion of the active material in the recycling process;

[0022] 5、The doping of Ni metal causes the lattice of manganese dioxide to be distorted, so that the lattice spacing of manganese dioxide is increased, thereby providing a wider transmission channel for ion diffusion. The diffusion potential barrier of ions is reduced, and the nickel ion doping interacts with the manganese-oxygen bond, enhances the stability of the structure, inhibits the phase change of the nanosheet structure of manganese dioxide to the spinel structure, reduces the influence of the Jahn-Teller effect, and thereby improves the cycle stability of the material;

[0023] 6、In the present application, oxygen-rich water is used as a solvent to configure a tris buffer, so that when dopamine is coated, dopamine is quickly coated in an oxygen-rich environment, and the corresponding coating time is shortened, thereby weakening the blockage of dopamine to the MXene empty layer. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 It is a scanning electron microscope image of Ni-γ-MnO2 / MXene@PDA;

[0025] Figure 2 It is an electrochemical impedance diagram of Ni-γ-MnO2 / MXene@PDA at 30 DEG C;

[0026] Figure 3 It is a charge and discharge curve diagram of Ni-γ-MnO2 / MXene@PDA│GF / A│Zn battery;

[0027] Figure 4 It is a cycle stability comparison diagram of assembled Ni-γ-MnO2 / MXene@PDA│GF / A│Zn and γ-MnO2│GF / A│Zn batteries at a current density of 0.5 Ag -1

[0028] Figure 5 It is a schematic diagram of the assembly of the aqueous zinc ion battery. DETAILED DESCRIPTION

[0029] The present application will be further described below by means of specific examples, so that the technical scheme and advantages of the present application are more clear. However, the following examples are exemplary and are intended to explain the present application, and cannot be understood as a limitation of the present application. ​

[0030] Example 1:

[0031] (1) Preparation of MXene substrate

[0032] 1) A 40ml solution of 9M hydrochloric acid was prepared and poured into a 100ml polytetrafluoroethylene reaction kettle. 2g of LiF was added to the solution at room temperature and stirred at 530rpm for 30min until it was fully dissolved.

[0033] 2) 2g of MAX material (Ti3AlC2) was weighed and slowly added to the above reaction kettle in batches within 10min. The reaction temperature was adjusted to 35°C and stirring was continued for 24h.

[0034] 3) The reaction liquid after the reaction was centrifuged at 5000rpm for 10min. After centrifugation, the supernatant was discarded, about 40ml of pure water was added and shaken evenly, then put into an ultrasonic cleaning machine for ultrasonic cleaning for 10min. After ultrasonic cleaning, it was put into a centrifuge for continuous centrifugation. The above operation was repeated until the solid and liquid could not be completely separated by centrifugation. The supernatant was black and the bottom precipitate expanded explosively. At this time, the pH of the supernatant was measured to be 5, and the operation was ended.

[0035] 4) 40ml of ethanol was added to the centrifuge tube and ultrasonic cleaning was carried out for 1h. After ultrasonic cleaning, centrifugation was carried out at 10000rpm for 60min. The lower precipitate was collected and put into a vacuum drying oven for drying at 60°C for 12h. Multilayer MXene was obtained.

[0036] 5) The multilayer MXene product was taken and an appropriate amount of pure water was added. After ultrasonic cleaning for 20min, centrifugation was carried out at 5000rpm for 3min. The supernatant was poured out to obtain a few-layer MXene dispersion in water. The concentration of the dispersion was obtained by weighing after suction filtration.

[0037] (2) Preparation of Ni-γ-MnO2 / MXene (R / MX)

[0038] 1) 75mmol of manganese chloride tetrahydrate and 20mmol of nickel nitrate hexahydrate were weighed in a 100ml three-necked flask and dissolved in 30ml of 6.4mg / ml MXene water dispersion under vigorous stirring. It was ready for use after being fully dissolved.

[0039] 2) Weigh 25 mmol of potassium permanganate into 40 ml of ultrapure water, pour it into a 50 ml constant pressure dropping funnel, and drop the potassium permanganate solution into the three-necked flask at a rate of 5 s / drop, and stir vigorously. After the potassium permanganate solution is added, continue stirring for 30 min. Transfer to a 100 ml polytetrafluoroethylene reactor, heat from room temperature to 160°C and keep for 1 h. After the oven cools to room temperature, remove the liner, pour it into two 50 ml centrifuge tubes, centrifuge at 8000 rpm for 5 min, wash with ultrapure water five times, then use anhydrous ethanol for the last time, and vacuum dry at 80°C for 16 h.

[0040] 3) Take out the dried sample, grind the blocky sample into powder with a agate mortar, transfer it to a porcelain boat, cover it with a lid and put it into a muffle furnace to heat from room temperature to 200°C at a rate of 5°C / min and keep for 36 hours. After the oven cools to room temperature, remove it to obtain a nickel-doped manganese dioxide / MXene composite material.

[0041] (3) Preparation of Ni-γ-MnO2 / MXene@PDA (R / MX@PDA)

[0042] 1) Weigh 240 mg of the above nickel-doped manganese dioxide / MXene composite material into 200 ml of 0.1 mol / l tris buffer, and use oxygen-rich water to prepare the tris buffer. After ultrasonic dispersion, start stirring. Weigh 40 mg of dopamine into the buffer and continue stirring at a stirring rate of 840 rpm / min. The reaction is best carried out in a fume hood. Under the initiation of the initiator oxygen, dopamine begins to self-polymerize, coating a layer of polydopamine film on the surface of the material to obtain a polydopamine-coated Ni-γ-MnO2 / MXene composite material.

[0043] Comparative Example 1:

[0044] (1) Preparation of γ-MnO2

[0045] 1) Weigh 75 mmol of manganese chloride tetrahydrate into 30 ml of ultrapure water in a 100 ml three-necked flask and dissolve thoroughly.

[0046] 2) Weigh 25 mmol of potassium permanganate into 40 ml of ultrapure water, pour it into a 50 ml constant pressure dropping funnel, and drop the potassium permanganate solution into the three-necked flask at a rate of 5 s / drop, and stir. After the potassium permanganate solution is added, continue stirring for 30 min. Transfer to a 100 ml polytetrafluoroethylene reactor, heat from room temperature to 160°C and keep for 1 h. After the oven cools to room temperature, remove the liner, pour it into two 50 ml centrifuge tubes, centrifuge at 8000 rpm for 5 min, wash with ultrapure water five times, then use anhydrous ethanol for the last time, and vacuum dry at 80°C for 16 h.

[0047] 3) After drying, the sample was taken out, and the blocky sample was ground into powder with a maroon mortar, transferred to a porcelain boat, covered with a lid, and placed in a muffle furnace to be heated at a rate of 5 ℃ / min from room temperature to 200 ℃ and kept for 36 hours. After the furnace was cooled to room temperature, it was taken out to obtain the γ-MnO2 composite material.

[0048] Preparation of electrode material

[0049] Preparation of positive sheet: The composite material prepared in Example 1 and Comparative Example 1, acetylene black and binder (PVDF) were uniformly mixed in N-methyl pyrrolidone (NMP) according to the optimal weight ratio of 7:2:1. A doctor blade with a thickness of 120 μm was used for uniform coating on a 500 mes stainless steel mesh. Finally, it was placed in a vacuum drying oven at 80 ℃ for drying for 12 h. A 14 mm diameter sheet puncher was used to punch the sheet, which was placed in a desiccator for standby. The active material loading was controlled at 1.3 mg cm-2. -1 .

[0050] Zinc sheet negative electrode: purchased directly from Corund.

[0051] Battery assembly:

[0052] Aqueous zinc ion battery: As shown in Figure 5 , the positive shell, positive sheet, GF / A separator, zinc sheet, stainless steel spring, gasket and negative shell were assembled in order to form a button cell, and the aqueous zinc ion battery was assembled under a nominal pressure of 50 kpa;

[0053] Test instrument and method:

[0054] Physical characterization: The morphology and surface element distribution of the Ni-γ-MnO2 / MXene@PDA composite material sample prepared in Example 1 were detected by a scanning electron microscope (SEM, SU8100, Japan HITACHI company).

[0055] The SEM detection results are shown in Figure 1 , the layered structure of the MXene material is very obvious, and the size is different between 5-15 μm. On the surface of the layered MXene material, manganese dioxide nanosheets were found to be uniformly grown on the surface and interlayer.

[0056] Electrochemical characterization: The Ni-γ-MnO2 / MXene@PDA│GF / A│Zn full cell was assembled under a nominal pressure of 50 kpa to measure the electrochemical impedance (EIS), and the test conditions were: 30 ℃, 10 -2 Hz-10 5 Hz; the redox peak position of the positive material and the insertion and extraction potential of different ions were determined by cyclic voltammetry, and the test conditions were: in the voltage range of 0.8-1.8 V; 0.1 mV s-1 the scan rate.

[0057] The assembled Ni-γ-MnO2 / MXene@PDA│GF / A│Zn and γ-MnO2│GF / A│Zn batteries were tested on the Wuhan Blue Electronic Test System CT2001A instrument for the cycle performance at a voltage range of 0.8-1.8 V, a current density of 0.5 Ag -1 , and a temperature of 30℃. During the electrochemical test, the battery was not subjected to additional pressure.

[0058] The test results are shown in Figures 2 to 4 , specifically, Figure 2 is the electrochemical impedance spectrum of the R / MX@PDA full battery at 30℃, and it can be seen that R s is 1.34Ω, and compared with the R s of the γ-MnO2 full battery, which is 2.03Ω, the electrode interface resistance of the R / MX@PDA full battery is obviously reduced, indicating that MXene plays a role in establishing a conductive path, reducing the solution resistance of the battery and alleviating the electrode polarization effect. Figure 3 is the charge-discharge curve during the cycle process, and a relatively obvious voltage platform can be found near 1.4-1.6V, and the position and shape of the platform change little with the increase of the cycle number, which is relatively favorable for the practical application of the battery. Figure 4 is the charge-discharge cycle curve of the two batteries, and it can be found that the initial capacity of the γ-MnO2 full battery is 202mAh g -1 , and the capacity retention rate is about 41.09% after 50 cycles, while the initial capacity of the R / MX@PDA full battery is 93mAh g -1 , and the capacity can reach up to 278mAh g -1 after the cycle, and the capacity retention rate is 73.02% after 400 cycles. Therefore, in summary, the RMX@PDA battery performs better in terms of charge-discharge cycle performance, and it has a higher capacity retention rate and more stable coulomb efficiency in the long-term cycle process, which is crucial for the battery life and performance stability in practical applications. In contrast, although the initial specific capacity of the γ-MnO2 full battery is higher, the capacity decays faster during the cycle process, and the coulomb efficiency fluctuates greatly, and the reliability in long-term use may be relatively low.

[0059] All the features described in the specification, the attached claims, and the drawings, whether alone or in any combination thereof, are important features of the present application.

Claims

1. A method for preparing a manganese-based high-performance composite cathode material coated with polydopamine in situ grown on a MXene material, characterized in that, The method comprises the following steps: (1) Preparation of Ni-γ-MnO2 / MXene: Dissolve manganese chloride tetrahydrate and nickel nitrate hexahydrate in a MXene aqueous dispersion, fully dissolve under vigorous stirring, drop potassium permanganate solution into the liquid and stir vigorously, continue stirring after the dropwise addition of potassium permanganate solution is completed, then transfer the mixed solution to a polytetrafluoroethylene reactor for heating, centrifuge the initial product after reaction, wash, vacuum dry, grind into powder, and finally heat in a muffle furnace to obtain a Ni-γ-MnO2 / MXene composite material; (2) Preparation of Ni-γ-MnO2 / MXene@PDA: Add the Ni-γ-MnO2 / MXene composite material prepared in step (1) into a tris buffer solution, ultrasonic dispersion, stirring, continue to add dopamine, stir, then under the initiation of oxygen, dopamine self-polymerizes to coat a dopamine film on the surface of the Ni-γ-MnO2 / MXene composite material, to obtain a polydopamine-coated Ni-γ-MnO2 / MXene composite material.

2. The preparation method of a manganese-based high-performance composite cathode material coated with polydopamine and grown in situ on a MXene material according to claim 1, characterized in that, In step (1), the concentration of the MXene aqueous dispersion is 6.4 mg / ml, and MXene accounts for 30% of the total mass of the Ni-γ-MnO2 / MXene composite material; the molar ratio of Ni to Mn is 1:

5.

3. The method of claim 1, wherein the method is characterized by: In step (1), the heating temperature in the polytetrafluoroethylene reactor is 160℃, and the heating time is 1h.

4. The method of claim 1, wherein the method is characterized by: In step (1), the initial product after reaction is centrifuged at a speed of 8000 rpm for 5 min, washed with ultrapure water five times, then washed with anhydrous ethanol for the last time, and vacuum dried at 80℃ for 16h.

5. The method of claim 1, wherein the method is characterized by: In step (1), the temperature in the muffle furnace is increased to 200℃ at a rate of 5℃ / min and maintained for 36h.

6. The method of claim 1, wherein the method is characterized by: In step (2), the mass ratio of dopamine to Ni-γ-MnO2 / MXene composite material is 1:

6.

7. The method of claim 1, wherein the method is characterized by: The tris buffer solution is prepared using oxygen-enriched water as the solvent.

8. The method of claim 1, wherein the method is characterized by: The method for preparing MXene comprises the following steps: Using LiF and Ti3AlC2 as raw materials, heating and stirring in a hydrochloric acid solution, after the reaction is completed, centrifuging, washing, and drying to obtain multi-layer MXene, dissolving the multi-layer MXene product in pure water, centrifuging, and discarding the supernatant to obtain a few-layer MXene dispersion.

9. A manganese-based high-performance composite cathode material coated with polydopamine and grown in situ on MXene material, prepared by the method according to any one of claims 1-8.

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