Manganese-based high-performance composite positive electrode material coated with polydopamine and grown on MXene material in situ and preparation method of manganese-based high-performance composite positive electrode material

Abstract

The invention discloses a manganese-based high-performance composite positive electrode material coated with polydopamine and grown on an MXene material in situ and a preparation method of the manganese-based high-performance composite positive electrode material. The preparation method comprises the following steps: (1) preparing Ni-gamma-MnO2 / MXene; and (2) preparation of the Ni-gamma-MnO2 / MXene (at) PDA. According to the technical scheme, nickel and manganese dioxide are promoted to realize in-situ growth on an MXene substrate by virtue of a hydrothermal synthesis method, so that a composite material with a specific structure is constructed, then, an active material containing the composite structure is uniformly dispersed in a tris buffer solution environment, and on the basis, oxygen is used as an initiator to trigger a self-polymerization reaction, so that the nickel-manganese dioxide composite material is obtained. According to the present invention, the surface of the active material can be tightly coated with the polydopamine in the highly uniform manner, the preparation process is simple, the raw material is cheap, and the coating of the polydopamine can reduce the effective contact degree between the aqueous electrolyte and MnO2, reduce the dissolution of MnOOH, and further make the structure more stable.

Description

Technical Field

[0001] The present invention relates to the field of manganese-based composite cathode materials, and in particular to a manganese-based high-performance composite cathode material coated with polydopamine and grown in situ on a MXene material and a preparation method thereof. Background Art

[0002] With the development of new energy, energy storage has become a crucial focus. In view of the development demand for 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 frontier technologies for positive electrode materials. Aqueous zinc-ion batteries (ZIBs) are a promising low-cost, risk-free, high-performance secondary battery, thanks to their abundant Zn sources, Zn 2+ The low redox potential (-0.76 V vs. SHE) and high theoretical capacity (819 mAh g -1 ), aqueous zinc-ion batteries are expected to become a potential alternative to commercial lithium-ion batteries (LIBs), but aqueous zinc-ion batteries on the market are not currently used on a large scale. The main challenges currently faced by aqueous zinc-ion batteries are: achieving dendrite-free zinc deposition at the negative electrode interface. Considering the strong electrostatic interaction between zinc ions and the host material, finding a suitable positive electrode material with high capacity and long service life is also a great challenge.

[0003] At present, the positive electrode materials of aqueous zinc-ion batteries mainly include vanadium-based materials, Prussian blue analogs, manganese-based materials and phosphate materials. Among them, manganese dioxide has a higher specific capacity of 308mAh g -1 , with abundant natural reserves, high energy density and high power density, it has become the most promising candidate material and has received widespread attention. Common MnO2 crystal structures have the following forms: 1. Tunnel structure, such as α-MnO2, β-MnO2, γ-MnO2, etc.; 2. Layered structure, such as δ-MnO2; 3. Three-dimensional (3D) spinel structure, such as λ-MnO2. Under the condition of weakly acidic electrolyte, electrochemical reaction occurs, H + and Zn 2+ Inserted into manganese dioxide, two discharge products are generated: MnOOH and According to relevant literature reports, MnOOH is easily soluble in aqueous electrolytes. Due to the Jahn-Teller effect, its crystal structure collapses, so manganese dioxide is very likely to dissolve active substances during the charge and discharge cycle, resulting in rapid capacity decay. In addition, the conductivity of manganese dioxide is poor, only 10 -8 —10 -5 S / cm, resulting in its electron transfer rate being limited by the slow electron transfer kinetics of the system. Summary of the invention

[0004] In order to solve the above-mentioned technical problems, the purpose of the present invention is to provide a polydopamine-coated manganese-based high-performance composite positive electrode material grown in situ on a MXene material and a preparation method thereof. The manganese-based high-performance composite positive electrode material has a stable structure, good conductivity and the active substance is not easily dissolved.

[0005] In order to achieve the above-mentioned purpose, the present invention adopts the following technical solutions:

[0006] A method for preparing a polydopamine-coated manganese-based high-performance composite positive electrode material grown in situ on a MXene material, comprising the following steps:

[0007] (1) Preparation of Ni-γ-MnO2 / MXene: Manganese chloride tetrahydrate and nickel nitrate hexahydrate are dissolved in a MXene aqueous dispersion and fully dissolved under vigorous stirring for standby use. Potassium permanganate solution is dropped into the liquid and stirred vigorously. After the potassium permanganate solution is added, stirring is continued. Then, the mixed solution is transferred to a polytetrafluoroethylene reactor and heated. The initial product after the reaction is centrifuged, washed, vacuum dried, ground into powder, and finally heated in a muffle furnace to obtain a Ni-γ-MnO2 / MXene composite material.

[0008] (2) Preparation of Ni-γ-MnO2 / MXene@PDA: The Ni-γ-MnO2 / MXene composite material prepared in step (1) was added to a tris buffer solution, ultrasonically dispersed, stirred, and dopamine was continuously added and stirred. Then, under the initiation of oxygen, dopamine self-polymerized to coat the surface of the Ni-γ-MnO2 / MXene composite material with a dopamine film, thereby obtaining a polydopamine-coated Ni-γ-MnO2 / MXene composite material.

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

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

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

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

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

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

[0015] Preferably, the method for preparing MXene comprises the following steps:

[0016] LiF and Ti3AlC2 are used as raw materials, heated and stirred in a hydrochloric acid solution. After the reaction is completed, multilayer MXene is obtained by centrifugation, washing and drying. The multilayer MXene product is dissolved in pure water, centrifuged, and the supernatant is poured off to obtain a few-layer MXene dispersion.

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

[0018] The present invention has the following beneficial effects due to the adoption of the above technical solution:

[0019] 1. In this scheme, 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. Subsequently, 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 the self-polymerization reaction, so that polydopamine can be tightly wrapped on the surface of the active material in a highly uniform manner. The preparation process is simple, the raw materials are cheap, and the coating of polydopamine can reduce the effective contact between the aqueous electrolyte and MnO2, and can also reduce the side reactions occurring at the electrode / electrolyte interface. Similarly, the chemical interaction between MnO2 and the surface coating can reduce the dissolution of MnOOH, thereby making the structure more stable;

[0020] 2. Various hydrophilic groups on polydopamine can make it easier to capture H in solution. + , thereby enhancing the battery's cycle performance under high current and enhancing the electrolyte's infiltration into the electrode sheet, allowing the battery capacity to be fully released; a flexible buffer surface layer is constructed between the electrolyte and the electrode through polydopamine, which reduces the contact between the electrolyte and MnO2, reduces side reactions, stabilizes the structure and enhances high current cycle performance, slowly releases capacity and thereby tolerates the volume change that occurs when ions are inserted / extracted; however, due to the two-dimensional layered structure of MXene, excessive polydopamine coating will cause the ion transport channel to be blocked, thereby causing MXene failure. The performance is best when the mass ratio of dopamine to Ni-γ-MnO2 / MXene composite material is 1:6;

[0021] 4. The introduction of MXene materials 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 provides a platform for manganese dioxide to anchor, enhances the conductivity of the active material, and provides an orderly channel for ion insertion and extraction for manganese dioxide in the charge and discharge cycle with its layered structure; MXene as a substrate can also play a stress buffering role, inhibiting the volume expansion of the active material during the recycling process;

[0022] 5. The doping of Ni metal distorts the lattice of manganese dioxide, increasing the lattice spacing of manganese dioxide, thereby providing a wider transmission channel for the diffusion of ions. The diffusion barrier of ions is reduced, and the nickel ion doping will interact with the manganese oxygen bond, enhance the stability of the structure, inhibit the phase transition of the manganese dioxide nanosheet structure to the spinel structure, and reduce the impact of its Jahn-Teller effect, thereby improving the cycle stability of the material;

[0023] 6. In the present invention, oxygen-rich water is used as a solvent to prepare a tris buffer solution, so that when dopamine is coated, dopamine can be quickly coated in an oxygen-rich environment and the corresponding coating time can be shortened, thereby weakening the blocking of the MXene empty layer by dopamine. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0025] Figure 2 The electrochemical impedance spectroscopy diagram of Ni-γ-MnO2 / MXene@PDA at 30°C;

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

[0027] Figure 4 For the assembled Ni-γ-MnO2 / MXene@PDA│GF / A│Zn and γ-MnO2│GF / A│Zn batteries at 0.5Ag -1 Comparison of cycling stability at current density of ;

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

[0029] The present invention is further described below by detailed examples to make the technical solutions and advantages of the present invention clearer. However, the following examples are exemplary and intended to be used to explain the present invention, and should not be construed as limiting the present invention.

[0030] Embodiment 1:

[0031] (1) Preparation of MXene substrate

[0032] 1) Prepare 40 ml of 9M hydrochloric acid solution and pour it into a 100 ml polytetrafluoroethylene reactor. Add 2 g of LiF into the solution at room temperature and stir at 530 rpm for 30 min until it is fully dissolved.

[0033] 2) Weigh 2 g of MAX material (Ti3AlC2) and slowly add the MAX material into the above reactor in batches within 10 min. Adjust the reaction temperature to 35°C and continue stirring for 24 h.

[0034] 3) After the reaction is completed, the reaction liquid is centrifuged at 5000 rpm for 10 minutes. After the centrifugation is completed, the supernatant is poured out, about 40 ml of pure water is added and shaken evenly, and then placed in an ultrasonic cleaning machine for ultrasonic cleaning for 10 minutes. After the ultrasonic cleaning is completed, the reaction liquid is placed in a centrifuge for further centrifugation. The above operation is repeated until the centrifugation cannot completely separate the solid and the liquid, the supernatant is black, and the bottom precipitate expands explosively. At this time, when the pH of the supernatant is measured at 5, the operation is terminated.

[0035] 4) Add 40 ml of ethanol to the centrifuge tube and ultrasonicate for 1 hour. After the ultrasonication is completed, centrifuge at 10,000 rpm for 60 minutes, collect the lower layer of precipitate, put it into a vacuum drying oven, and dry it at 60°C for 12 hours to obtain multilayer MXene.

[0036] 5) Take the multilayer MXene product, add an appropriate amount of pure water, ultrasonicate for 20 minutes, and centrifuge at 5000 rpm for 3 minutes. Pour out the supernatant to obtain a dispersion of few-layer MXene in water. The concentration of the dispersion can be obtained by filtration and weighing.

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

[0038] 1) In a 100 ml three-necked flask, weigh 75 mmol of manganese chloride tetrahydrate and 20 mmol of nickel nitrate hexahydrate and dissolve them in 30 ml of 6.4 mg / ml MXene aqueous dispersion and stir vigorously until fully dissolved for later use.

[0039] 2) Weigh 25 mmol of potassium permanganate and dissolve it in 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 to stir for 30 min, transfer it to a 100 ml polytetrafluoroethylene reactor, heat it from room temperature to 160 ° C and keep it for 1 h, take out the liner after the oven is cooled to room temperature, pour it into two 50 ml centrifuge tubes, centrifuge at 8000 rpm for 5 min, wash it with ultrapure water five times, wash it with anhydrous ethanol for the last time, and vacuum dry it at 80 ° C for 16 h.

[0040] 3) Take out the dried sample, grind the block sample into powder with an agate mortar, transfer it to a porcelain boat, cover it with a lid and put it into a muffle furnace, heat it from room temperature to 200°C at a rate of 5°C / min and keep it for 36 hours, cool it down to room temperature with the furnace and take it out 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 nickel-doped manganese dioxide / MXene composite material sample and add it to 200 ml of 0.1 mol / l tris buffer, the tris buffer is prepared with oxygen-enriched water, start stirring after ultrasonic dispersion, weigh 40 mg of dopamine and add it to 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 initiator oxygen, dopamine begins to self-polymerize, and a layer of polydopamine film is coated 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) In a 100 ml three-necked flask, weigh 75 mmol of manganese chloride tetrahydrate and dissolve it in 30 ml of ultrapure water until fully dissolved and set aside.

[0046] 2) Weigh 25 mmol of potassium permanganate and dissolve it in 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. Stir. After the potassium permanganate solution is added, continue stirring for 30 min. Transfer it to a 100 ml polytetrafluoroethylene reactor, heat it from room temperature to 160 ° C and keep it for 1 h. After the oven is cooled to room temperature, take out the liner, pour it into two 50 ml centrifuge tubes, centrifuge at 8000 rpm for 5 min, wash it with ultrapure water five times, wash it with anhydrous ethanol for the last time, and vacuum dry it at 80 ° C for 16 h.

[0047] 3) Take out the dried sample, grind the block sample into powder with an agate mortar, transfer it to a porcelain boat, cover it with a lid and put it into a muffle furnace, heat it from room temperature to 200°C at a rate of 5°C / min and keep it for 36 hours, cool it down to room temperature with the furnace and take it out to obtain a γ-MnO2 composite material.

[0048] Preparation of electrode materials

[0049] Preparation of positive electrode sheet: The composite material prepared in Example 1 and Comparative Example 1, acetylene black and binder (PVDF) were uniformly mixed in N-methylpyrrolidone (NMP) according to the optimal weight ratio of 7:2:1. Use a 120μm thick scraper to evenly coat it on a 500mes stainless steel mesh. Finally, place it in a vacuum drying oven at 80°C and dry it for 12h. Use a 14mm caliber punching machine to punch the sheet and place it in a dryer for use. The active material loading is controlled at 1.3mg cm -1 .

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

[0051] Battery Assembly:

[0052] Aqueous zinc ion batteries: Figure 5 As shown, the positive electrode shell, positive electrode sheet, GF / A separator, zinc sheet, stainless steel spring sheet, gasket and negative electrode shell are assembled into a button battery in sequence, and then assembled into an aqueous zinc ion battery under a nominal pressure of 50 kPa;

[0053] Test instruments and methods:

[0054] Physical characterization: A scanning electron microscope (SEM, SU8100, HITACHI, Japan) was used to detect the morphology and surface element distribution of the Ni-γ-MnO2 / MXene@PDA composite material sample prepared in Example 1.

[0055] The SEM test results are as follows Figure 1 As shown, the layered structure of the MXene material is very obvious, with sizes ranging from 5-15μm. On the surface of the layered MXene material, manganese dioxide nanosheets can be found uniformly grown on its surface and between layers.

[0056] Electrochemical characterization: Electrochemical impedance spectroscopy (EIS) was measured by assembling Ni-γ-MnO2 / MXene@PDA│GF / A│Zn full cells at a nominal pressure of 50 kPa. Test conditions: 30 °C, 10 -2 Hz~10 5 Hz; Cyclic voltammetry was used to determine the redox peak position of the positive electrode material and the insertion and extraction potentials of different ions. The test conditions were: within the voltage range of 0.8-1.8V; 0.1mV s-1 The scanning 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 Electric Test System CT2001A instrument in the voltage range of 0.8~1.8V and the current density of 0.5A. -1 , Cycling performance at 30°C. During the electrochemical testing, the battery was not subjected to additional stress.

[0058] Test results such as Figures 2 to 4 As shown, specifically, Figure 2 This is the electrochemical impedance spectrum of the R / MX@PDA full battery at 30°C. s 1.34Ω, compared with the γ-MnO2 full battery R s The electrode interface resistance of the R / MX@PDA full battery is significantly reduced, indicating that MXene plays a role in establishing a conductive pathway, reducing the solution resistance of the battery and alleviating the electrode polarization. Figure 3 It is the charge and discharge curve during the cycle process. A relatively obvious voltage platform can be found near 1.4-1.6V, and as the number of cycles increases, the position and shape of the platform do not change much, which is more beneficial to the practical application of the battery. Figure 4 The charge and discharge cycle curves of the two batteries show that the initial capacity of the γ-MnO2 full battery is 202 mAh g -1 After 50 cycles, the capacity retention rate is about 41.09%, while the initial capacity of the R / MX@PDA full battery is 93 mAh g -1 After cycling, the capacity can reach up to 278 mAh g -1 , after 400 cycles, the capacity retention rate is 73.02%. Therefore, on the whole, the RMX@PDA battery performs better in charge and discharge cycle performance. It has a higher capacity retention rate and more stable coulombic efficiency during long-term cycles, which is crucial for battery life and performance stability in practical applications. In contrast, although the γ-MnO2 full battery has a higher initial specific capacity, its capacity decays faster during the cycle, and the coulombic efficiency fluctuates greatly, and its reliability in long-term use may be relatively low.

[0059] All features described in the description, the attached claims and the drawings are essential features for the invention both individually and in any combination.

Claims

1. A method for preparing a polydopamine-coated manganese-based high-performance composite cathode material grown in situ on a MXene material, characterized in that: The following steps are involved: (1) Preparation of Ni-γ-MnO2 / MXene: Manganese chloride tetrahydrate and nickel nitrate hexahydrate are dissolved in a MXene aqueous dispersion and fully dissolved under vigorous stirring for standby use. Potassium permanganate solution is dropped into the liquid and stirred vigorously. After the potassium permanganate solution is added, stirring is continued. Then, the mixed solution is transferred to a polytetrafluoroethylene reactor and heated. The initial product after the reaction is centrifuged, washed, vacuum dried, ground into powder, and finally heated in a muffle furnace to obtain a Ni-γ-MnO2 / MXene composite material. (2) Preparation of Ni-γ-MnO2 / MXene@PDA: The Ni-γ-MnO2 / MXene composite material prepared in step (1) was added to a tris buffer solution, ultrasonically dispersed, stirred, and dopamine was continuously added and stirred. Then, under the initiation of oxygen, dopamine self-polymerized to coat the surface of the Ni-γ-MnO2 / MXene composite material with a dopamine film, thereby obtaining a polydopamine-coated Ni-γ-MnO2 / MXene composite material.

2. The method for preparing a polydopamine-coated manganese-based high-performance composite positive electrode material 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, MXene accounts for 30% of the total mass of the Ni-γ-MnO2 / MXene composite material; and the molar ratio of Ni to Mn is 1:

5.

3. The method for preparing a polydopamine-coated manganese-based high-performance composite positive electrode material grown in situ on a MXene material according to claim 1, characterized in that: In step (1), the heating temperature in the polytetrafluoroethylene reactor is 160° C. and the heating time is 1 h.

4. The method for preparing a polydopamine-coated manganese-based high-performance composite positive electrode material grown in situ on a MXene material according to claim 1, characterized in that: In step (1), the initial product after the reaction is centrifuged at 8000 rpm for 5 min, washed with ultrapure water five times, washed with anhydrous ethanol for the last time, and vacuum dried at 80° C. for 16 h.

5. The method for preparing a polydopamine-coated manganese-based high-performance composite positive electrode material grown in situ on a MXene material according to claim 1, characterized in that: In step (1), the temperature is increased to 200° C. at a rate of 5° C. / min in a muffle furnace and maintained for 36 h.

6. The method for preparing a polydopamine-coated manganese-based high-performance composite positive electrode material grown in situ on a MXene material according to claim 1, characterized in that: In step (2), the mass ratio of dopamine and Ni-γ-MnO2 / MXene composite material is 1:

6.

7. The method for preparing a polydopamine-coated manganese-based high-performance composite positive electrode material grown in situ on a MXene material according to claim 1, characterized in that: Tris buffer was prepared using oxygen-enriched water as solvent.

8. The method for preparing a polydopamine-coated manganese-based high-performance composite positive electrode material grown in situ on a MXene material according to claim 1, characterized in that: The preparation method of MXene includes the following steps: LiF and Ti3AlC2 are used as raw materials, heated and stirred in a hydrochloric acid solution. After the reaction is completed, multilayer MXene is obtained by centrifugation, washing and drying. The multilayer MXene product is dissolved in pure water, centrifuged, and the supernatant is poured off to obtain a few-layer MXene dispersion.

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

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