CN115663138A - Nitrogen-doped carbon film-wrapped manganese monoxide nanowire lithium battery material and preparation method thereof - Google Patents

Abstract

The invention discloses a nitrogen-doped carbon film-wrapped manganese monoxide nanowire lithium battery material and a preparation method thereof, and the preparation method comprises the following steps: firstly, preparing a manganese dioxide nanowire precursor by using a hydrothermal synthesis mode; then mixing the manganese dioxide nanowire precursor with dopamine hydrochloride in a water and ethanol solution dropwise added with ammonia water, and continuously magnetically stirring to prepare the manganese dioxide nanowire wrapped by the polydopamine film; and finally, annealing the manganese dioxide nanowire wrapped by the polydopamine film in an inert atmosphere to obtain the target product manganese monoxide nanowire (N-C @ MnO) wrapped by the N-doped C film. The preparation method is simple and mature, has low cost, can realize mass production, and the obtained material has good chemical stability, high speed performance, excellent cycle stability and excellent coulombic efficiency.

Description

Manganese monoxide nanowire lithium battery material wrapped by nitrogen-doped carbon film and its preparation method

technical field

The invention relates to a manganese monoxide nanowire lithium battery material wrapped by a nitrogen-doped carbon film and a preparation method thereof, belonging to the technical field of nanometer materials.

Background technique

Manganese oxide nanomaterials (MnOx, including MnO ₂ , MnO, Mn ₂ O ₃ , Mn ₃ O ₄ ) and their derivatives, due to their tunable structure and morphology, unique physical and chemical properties, abundant resources, environmental Due to its friendliness and good biological safety, it has received extensive attention in the fields of biomedicine, lithium batteries, supercapacitors, electrocatalytic hydrogen evolution, environmental treatment, zinc batteries, and photocatalysis. Especially in the field of lithium batteries, manganese oxides have a high theoretical specific capacity (the theoretical specific capacities of MnO ₂ , Mn ₂ O ₃ , MnO and Mn ₃ O ₄ in lithium-ion batteries are 1233, 1018, 756 and 937 mAh g, respectively. ^-1 ), is a very promising alternative anode material. However, under normal circumstances, pure manganese oxides are not directly used as battery electrode materials. On the one hand, this type of material has poor electrical conductivity; The performance is significantly reduced, and the cycle stability is poor; in addition, industrial production also limits the use of this type of material. In order to solve the first two types of problems, some work has proposed to improve the conductivity, cycle stability and service life of such materials by improving the structure of manganese oxides, such as layered porous MnO/carbon microsphere materials, δ-MnO ₂ porous composites and _{porous Mn2O3} nanocubic materials encapsulated in carbon shells.

Contents of the invention

Based on the problems existing in the above-mentioned prior art, the present invention provides a nitrogen-doped carbon film-wrapped manganese monoxide nanowire lithium battery material with high chemical stability, good rate performance, excellent cycle stability and coulombic efficiency, and a preparation method thereof .

The present invention adopts following technical scheme for realizing the purpose:

A method for preparing a manganese monoxide nanowire lithium battery material wrapped by a nitrogen-doped carbon film, which is characterized in that: firstly, a manganese dioxide nanowire precursor is prepared by hydrothermal synthesis; and then the manganese dioxide nanowire precursor is mixed with hydrochloric acid The dopamine is mixed in the water and ethanol solution dripped with ammonia water, and the magnetic stirring is continued to prepare the manganese dioxide nanowires wrapped by the polydopamine film; finally, the manganese dioxide nanowires wrapped by the polydopamine film are annealed under an inert atmosphere, that is The target product N-doped C film-wrapped manganese monoxide nanowires was obtained, denoted as N-C@MnO. Specifically include the following steps:

(1) Add 0.39-0.50g KMnO ₄ and 0.5mL hydrochloric acid with a mass concentration of 36-38% into 45-60mL deionized water, stir with a glass rod to form a homogeneous solution, pour it into a hydrothermal reaction kettle and seal it, Then transfer it to a constant temperature blower box, raise the temperature to 160°C, keep it warm for 10 hours, and cool it down to room temperature naturally; the reaction product is centrifuged with deionized water and acetone, collected, and dried to obtain the _MnO2 nanowire precursor;

(2) Disperse 0.12 g of the MnO _nanowire precursor obtained in step (1) and 0.13-0.26 g of dopamine hydrochloride in a mixed solution of 150 mL of deionized water and ethanol, and add 0.1-0.5 mL of ammonia water with a mass concentration of 25-28% , magnetic stirring for 5-12h, make dopamine hydrochloride use MnO ₂ nanowires as a template, polymerize into a polydopamine film and wrap it outside the MnO ₂ nanowires, obtain MnO ₂ nanowires wrapped in a polydopamine film, centrifuge with acetone, collect, and dry ;

(3) In a CVD tube furnace, under an inert atmosphere (nitrogen or argon), anneal the _MnO2 nanowires wrapped by the polydopamine film obtained in step (2) at 600-700° C. for 2-3 hours, and then open the tube furnace. The lid is cooled rapidly, and the target product, manganese monoxide nanowires wrapped in N-doped carbon film, is obtained.

Further, the hydrothermal reaction kettle used in step (1) is a polytetrafluoroethylene substrate with a volume of 100 mL.

Further, in step (1) and step (2), the centrifugal force of the centrifugation is 4000×g～6000×g, the single centrifugation time is 5 min, and the centrifugation is not less than 3 times.

Further, in step (3), the heating rate of the CVD tube furnace is 10-20° C./min.

The beneficial effects of the present invention are:

1. The method for preparing N-C@MnO nanowire material of the present invention is simple and mature, with low cost, and the obtained material has good chemical stability, high energy density, excellent cycle stability and coulombic efficiency.

2. The N-C@MnO nanowire lithium battery material synthesized by the present invention improves the service life and cycle stability of the MnO material. The carbon film protects and supports the manganese monoxide and facilitates the charge transport. During the charging and discharging process of the lithium battery prepared by using the negative electrode material obtained in the present invention, the transport of Li ions is outside the carbon film, between the nanowires, and does not contact with the manganese oxide. The movement of lithium ions has no effect on the structure of manganese oxide. The volume expansion and fragmentation of MnO occurs inside the carbon film, without collapsing into a pile like pure MnO. The doping of nitrogen in the carbon film improves the conductivity of the material. A three-dimensional porous structure is formed between the nanowires, providing a transport path for lithium ions while improving electrical conductivity.

3. The advantages of the nanowires obtained in the present invention are: the MnO nanowire material wrapped by the nitrogen-doped carbon film has a stable structure and good conductivity, and has excellent cycle stability, rate performance and Coulombic efficiency as a lithium battery material, and can be quantified production (yield rate up to 79%), suitable for industrialized production.

Description of drawings

Fig. 1 is the MnO of embodiment ₁ gained Nanowire, polydopamine membrane wrap MnO Nanowire SEM picture, wherein: (a) is MnO _Nanowire SEM picture; (b) _is polydopamine membrane wraps MnO _Nanowire SEM picture.

Figure 2 is a TEM picture of the N-doped carbon film wrapped MnO nanowire obtained in Example 1, wherein (a) and (b) are both pictures of the N-doped carbon film wrapped MnO nanowire, and (b) is a part of (a) Zoom in on the graph.

Fig. 3 is the polydopamine film wrapped MnO nanowire and the XRD spectrum of the N-doped carbon film wrapped MnO nanowire of embodiment ₁ gained, wherein: ₍ a) is the polydopamine film wrapped MnO Nanowire XRD collection; (b) is XRD pattern of N-doped carbon film wrapped MnO nanowires.

Fig. 4 is the TEM and element mapping diagram of the N-doped carbon film wrapped MnO nanowire obtained in Example 1, wherein: (a), (b) are respectively the TEM and the mapping diagram of the N-doped carbon film wrapped MnO nanowire; c)-(f) are elemental analysis diagrams of Mn, O, C, and N, respectively.

Figure 5 is the XPS spectrum of the N-doped carbon film wrapped MnO nanowire obtained in Example 1, wherein: (a) corresponds to the Mn2p spectrum peak of the nanowire; (b) corresponds to the spectrum peak of the nanowire C1s; (c) corresponds to the nanowire The O1s peak of the nanowire; (d) corresponds to the N1s peak of the nanowire.

Fig. 6 is the lithium battery performance test of the N-doped carbon film wrapped MnO nanowire obtained in Example 1, wherein: (a) is a cyclic voltammetry curve (CV) figure; (b) is a rate performance figure; (c) is a constant Steady current charge and discharge (GCD) diagram; (d) is the cycle stability test diagram, specifically the charge and discharge capacitance and Coulombic efficiency diagram during 1000 charge and discharge processes.

7 is the AC impedance (EIS) of the N-doped carbon film wrapped MnO nanowire obtained in Example 1.

Detailed ways

The above objects, features and advantages of the present invention will be described below in conjunction with specific embodiments and accompanying drawings. This embodiment is carried out on the premise of the above-mentioned technical solution of the invention, specifically including detailed implementation and operation process. The technical connotation of the present invention includes but not limited to this embodiment, and the present invention can be implemented with a variety of materials different from the present invention, and those skilled in the art can make similar improvements without violating the connotation of the present invention, so the present invention does not Limited by the specific implementation disclosed below.

Example 1

In this example, N-C@MnO nanowires were prepared according to the following steps:

(1) Preparation of MnO ₂ nanowires

Add 0.39g of KMnO ₄ solid and 0.5mL of hydrochloric acid with a mass concentration of 36-38% into 45mL of deionized water, stir with a glass rod to form a homogeneous solution, pour it into a hydrothermal reaction kettle and cover it. Then transfer it to a constant temperature blower box, raise the temperature to 160°C at a heating rate of 5°C/min, keep it warm for 10h, and cool down to room temperature naturally. The reaction product is attached to the wall and bottom of the reaction kettle, the aqueous solution is sucked off, and while the product is scooped off with a medicine spoon, deionized water is added dropwise to form a suspension. Finally, it was collected by centrifugation with deionized water and acetone (centrifugation force 4000xg, centrifugation time 5min, centrifugation 3 times, first centrifugation with deionized water once, then centrifugation with acetone twice), and then dried in a constant temperature drying oven at 60°C for 5h to obtain MnO ₂ nanowire precursors.

(2) _MnO2 nanowires wrapped in polydopamine membrane

Disperse 0.12g and 0.26g of dopamine hydrochloride _MnO2 nanowire precursor obtained in step (1) in a mixed solution of 150mL deionized water and ethanol (water: ethanol volume ratio is 2:1), add 0.2mL mass concentration of 25 ~ 28% ammoniacal liquor, magnetic stirring 12h, make dopamine hydrochloride take MnO ₂ nanowires as a template, polymerize into polydopamine film, be wrapped in MnO ₂ nanowires, obtain the MnO ₂ nanowires that polydopamine film wraps, extract with acetone (centrifugal force 4000xg, centrifugation time 5min, centrifugation 3 times), centrifugation, and then dried in a constant temperature drying oven at 60°C for 5h.

(3) Preparation of N-C@MnO nanowires

Anneal the _MnO2 nanowires wrapped by the polydopamine film obtained in step (2) with a CVD tube furnace: first place the _MnO2 nanowires wrapped by the polydopamine film in a quartz boat and place it in the center of the quartz tube. First pass 300 sccm of nitrogen gas, and scrub for 10 minutes. Then, under the nitrogen condition of 150 sccm, the temperature was raised to 700° C. at a heating rate of 15° C./min, and kept at 700° C. for 2.5 hours, and then the cover of the tube furnace was opened, and the temperature was rapidly lowered. That is, the target product NC@MnO nanowires was obtained.

Fig. 1 is the SEM figure of the _MnO nanowire (Fig. 1 (a)) and the _MnO nanowire (Fig. 1 (b)) wrapped by the polydopamine film obtained in this example, it can be seen that the final product has obvious nanometer Linear shape, relatively uniform size, rough surface, which is conducive to the adsorption of reactants.

Figure 2 is a TEM image of the NC@MnO nanowires obtained in this example, and it can be clearly seen that the manganese oxide nanowires are wrapped with a layer of carbon film. Due to the removal of some O elements in MnO ₂ during the annealing process (or the removal of carbon oxides with C), the surface of the nanowires is uneven. In Fig. 2(a), some spherical nanoparticles at the edge are carbon spheres, which are formed by annealing polydopamine spheres formed by excess dopamine hydrochloride in an alkaline environment and magnetic stirring. These carbon spheres can improve the conductivity of NC@MnO nanowires.

Fig. 3 is the XRD spectrum of polydopamine film wrapping MnO _nanowire and N-doped carbon film wrapping MnO nanowire obtained in this embodiment, wherein: (a) is polydopamine film wrapping _MnO nanowire and standard PDF card 44-0141 (b) is the MnO _XRD comparison spectrum of N-doped carbon film-wrapped MnO nanowires and the standard PDF card 71-1177. It can be clearly seen that the _XRD characteristic peaks 2θ=18.107, 28.841, 37.522, 39.010, 49.864, 56.372 of MnO nanowires are consistent with the standard spectrum, and the XRD characteristic peaks 2θ=34.840, 40.492, 58.618, 70.091, 73.664 of MnO nanowires Consistent with the standard spectrum, it can be proved to be _MnO2 and MnO materials, respectively.

Figure 4 is the TEM element mapping diagram of the N-C@MnO nanowire obtained in this embodiment, wherein: (a) is the TEM of the N-C@MnO nanowire; (b) is the surface scanning mapping diagram of all elements; (c)-(f ) are the Mn, O, C, and N element mapping diagrams of N-C@MnO nanowires, respectively. From the element mapping diagram in Figure 4, it can be clearly seen that the Mn, O, C, and N elements in the N-C@MnO nanowires are evenly distributed.

Figure 5 is the XPS spectrum of the NC@MnO nanowires obtained in this example. (a) is the Mn2p orbital characteristic peak of Mn element, in which 653.8eV and 642.3eV are Mn2p _1/2 and Mn2p _3/2 spectral peaks respectively; 646.4eV is the vibration excitation peak of MnO, which is consistent with the data in the literature. Combined with the characterization of XRD, it also shows that the final product is MnO nanowires. (b) is the peak spectrum of C element, in which 284.8eV, 286.9eV, and 288.3eV correspond to CC, COC/CO, and OC=O peaks, respectively, which are consistent with the XPS characteristic peaks of carbon materials in the literature. (c) is the O element peak spectrum, in which 531.1eV and 533.3eV correspond to the peaks of metal oxides and carbon nitrogen oxides, respectively, indicating that oxygen exists in the form of manganese oxide and carbon nitrogen oxides. (d) is the N element peak spectrum, in which 398.4eV, 400.7eV, and 403.5eV correspond to the characteristic peaks of nitrides. Since the N element comes from dopamine hydrochloride, in dopamine hydrochloride, the nitrogen element is formed between the carbon element and the hydrogen element. Bond, so after annealing, there are still some nitrides.

Figure 6 shows the lithium battery performance test of the NC@MnO nanowires obtained in this example. The battery preparation process is as follows, the NC@MnO sample is mixed with a conductive agent (acetylene black) and a binder (polyvinylidene fluoride) in a certain ratio (7:2:1wt%), dispersed in n-methylpyrrolidone (NMP) Made into a slurry. The above slurry was uniformly coated on the copper foil, dried in a vacuum oven for 10 h, and then cut into small discs (with an area of 1.13 cm ² ) to prepare working electrode sheets. Coin-type (LIR 2032) cells based on this material were fabricated as half-cells in an argon-filled glove box. Celgard 2400 and a lithium metal disk were used as the separator and reference/counter electrode, and the electrolyte was _LiPF6 at a concentration of 1M. Rate performance and cycle stability were performed on a battery test system (CT-3008a, NEWARE, Shenzhen), and the test range was 0.01-3.00V. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were tested on a CHI 760E electrochemical workstation. (a) is the CV diagram, in which oxidation peaks and reduction peaks can be seen, corresponding to the oxidation and reduction processes of MnO, respectively. (b) is the rate performance diagram, charge and discharge performance at different currents (0.1-5.0Ag ^-1 ). It can be seen from the figure that as the current increases, the specific capacitance gradually decreases; but at the same current, the specific capacitance is more stable; and after returning to the current of 0.1A g ^-1 again, the specific capacitance is relatively improved, indicating that as Lithium battery anode material NC@MnO nanowire has better rate performance. (c) is a constant current charge-discharge (GCD) diagram. The first discharge process has a longer platform, and the platform of the subsequent charge-discharge curves is almost constant. It can be seen that the stability and reversibility of the material are good. (d) is the cycle stability test diagram, specifically the charge and discharge capacitance and Coulomb efficiency diagram during 1000 charge and discharge processes. In the 1000-time cycle test, the current is 2A·g ^-1 , and the specific capacitance fluctuates around 350mA·g ^-1 , which shows that it has good cycle stability and reversibility. The Coulombic efficiency is greater than or close to 100% in 1000 cycles, and the specific capacitance after 1000 cycles is 300mA·g ^-1 , compared with the initial maximum value of 375mA·g ^-1 during the cycle, 80% of the specific capacitance is retained, indicating that the material It has good reversibility and long cycle life.

The present invention analyzes the AC impedance (EIS) of the N-C@MnO nanowire material, as shown in Figure 7, it is obvious that the cycle performance test has a smaller impedance, which is beneficial to the transport of carriers and improves the conductivity.

This embodiment is carried out under the conditions of the claims of the present invention, and the technical content contained in the present invention includes but is not limited to the above-mentioned embodiments. Therefore, this embodiment is exemplary, not restrictive. Other oxide/non-oxide nanowire materials in the field, and nitrogen-doped carbon film-wrapped oxide/non-oxide nanowires prepared according to the technical requirements of the present invention should be included in the protection scope of the present invention.

Claims (7)

1. A method for preparing a manganese monoxide nanowire lithium battery material wrapped by a nitrogen-doped carbon film, characterized in that: firstly, a manganese dioxide nanowire precursor is prepared by hydrothermal synthesis; then the manganese dioxide nanowire precursor is Mix with dopamine hydrochloride in water and ethanol solution with ammonia water added dropwise, and continue magnetic stirring to prepare manganese dioxide nanowires wrapped by polydopamine film; finally, anneal the manganese dioxide nanowires wrapped by polydopamine film under inert atmosphere , that is, to obtain the target product N-doped C film-wrapped manganese monoxide nanowires, denoted as N-C@MnO. 2. The preparation method of the manganese monoxide nanowire lithium battery material wrapped by nitrogen-doped carbon film according to claim 1, is characterized in that, comprises the following steps: (1) Add 0.39-0.50g KMnO ₄ and 0.5mL hydrochloric acid with a mass concentration of 36-38% into 45-60mL deionized water, stir with a glass rod to form a homogeneous solution, pour it into a hydrothermal reaction kettle and seal it, Then transfer it to a constant temperature blower box, raise the temperature to 160°C, keep it warm for 10 hours, and cool it down to room temperature naturally; the reaction product is centrifuged with deionized water and acetone, collected, and dried to obtain the _MnO2 nanowire precursor; (2) Disperse 0.12 g of the MnO _nanowire precursor obtained in step (1) and 0.13-0.26 g of dopamine hydrochloride in a mixed solution of 150 mL of deionized water and ethanol, and add 0.1-0.5 mL of ammonia water with a mass concentration of 25-28% , magnetic stirring for 5-12h, make dopamine hydrochloride use MnO ₂ nanowires as a template, polymerize into a polydopamine film and wrap it outside the MnO ₂ nanowires, obtain MnO ₂ nanowires wrapped in a polydopamine film, centrifuge with acetone, collect, and dry ; (3) In a CVD tube furnace, under an inert atmosphere, anneal the _MnO nanowires wrapped by the polydopamine film obtained in step (2) at 600-700°C for 2-3 hours, then open the cover of the tube furnace, and cool down rapidly, that is The target product N-doped carbon film-wrapped manganese monoxide nanowires was obtained. 3. The preparation method of the manganese monoxide nanowire lithium battery material wrapped by nitrogen-doped carbon film according to claim 2, characterized in that: the hydrothermal reaction kettle used in step (1) is a polytetrafluoroethylene substrate with a volume of 100mL. 4. The preparation method of manganese monoxide nanowire lithium battery material wrapped by nitrogen-doped carbon film according to claim 2, characterized in that: in step (1) and step (2), the centrifugal force of the centrifugation is 4000× g～6000×g, the single centrifugation time is 5min, and the centrifugation time is not less than 3 times. 5. The preparation method of manganese monoxide nanowire lithium battery material wrapped by nitrogen-doped carbon film according to claim 2, characterized in that: in step (3), the heating rate of the CVD tube furnace is 10-20°C/ min. 6. The preparation method of manganese monoxide nanowire lithium battery material wrapped by nitrogen-doped carbon film according to claim 2, characterized in that: in step (3), the inert atmosphere is nitrogen or argon. 7. A manganese monoxide nanowire lithium battery material wrapped by a nitrogen-doped carbon film prepared by the preparation method described in any one of claims 1-6.

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