Preparation method and application of Fe3O4-doped bicontinuous carbon spheres

Abstract

The present invention discloses an Fe3O4-doped bicontinuous structure carbon sphere, its preparation method and application. The preparation method includes the following steps: Step S1: Mix an aqueous solution of cubic phase polymer colloidal particles (PC), an aqueous solution of epigallocatechin gallate, and an aqueous solution of ferric chloride hexahydrate (FeCl3·6H2O), stir, and adjust the pH value to 6.8 - 7.4 to obtain a pyrolysis precursor MPN@PC (MPN is a metal polyphenol network) complex; Step S2: Calcinate the pyrolysis precursor MPN@PC complex to obtain SP-Fe3O4-C cubic phase carbon microspheres. In this application, the construction of three-dimensional ordered pores (~30 nm) on the mesoscopic scale (2 - 50 nm) is achieved in the carbon spheres; using the Fe3O4-doped bicontinuous structure carbon spheres of this application as the sulfur cathode host can realize the construction of a lithium-sulfur battery with high capacity, high rate and long cycle life.

Description

Technical Field

[0001] The present invention relates to the field of batteries, and in particular to a method for preparing Fe3O4-doped bicontinuous carbon spheres and applications thereof in the field of lithium-sulfur batteries. Background Art

[0002] Lithium-sulfur batteries have a high theoretical specific energy (2567Wh kg -1 ) and theoretical specific capacity (1675 mAh g -1 ). And the active material is natural sulfur, which is abundant in resources and cheap. Therefore, lithium-sulfur batteries are the most promising alternative to traditional lithium-ion batteries. However, the insulating properties of sulfur and its discharge products lead to slow electrochemical reaction kinetics and low utilization of active materials. And the dissolution and shuttle effect of polysulfides (Li2S4-Li2S8) in the electrolyte seriously reduce the coulombic efficiency and cycle stability of the battery. Therefore, lithium-sulfur batteries face problems such as low utilization of active sulfur, small actual capacity, low coulombic efficiency, short cycle life and poor rate performance.

[0003] In response to the above problems, researchers have developed many functionalized sulfur host materials to improve the performance of lithium-sulfur batteries. Among the many sulfur host materials (carbon materials, polymers, and metal oxides / nitrides / sulfides, etc.), porous carbon particles are considered to be the most promising host materials for high-performance lithium-sulfur batteries. The main reasons are as follows: 1. Carbon-based materials have high conductivity, which can increase the conductivity of the electrode and improve the rate performance of sulfur cathode materials; 2. Porous carbon materials have a large specific surface area, which can increase the sulfur loading; 3. The pore structure can act as a physical barrier to alleviate the dissolution and migration of polysulfides during circulation and inhibit the shuttle effect; 4. Porous carbon materials have good mechanical and chemical stability, which can effectively alleviate the large volume changes of the sulfur cathode during battery cycling; 5. Carbon-based materials have excellent structural adjustability and are easy to introduce polar substances and metal-based nanoparticles, which can further achieve chemical anchoring or catalytic conversion of polysulfides.

[0004] For example, Jin Zhong et al. introduced CeO2 into mesoporous nitrogen-doped carbon nanospheres by post-loading as a sulfur cathode host material to effectively fix and catalyze the conversion of lithium polysulfide (see Figure 1 The designed lithium-sulfur battery has a high reversible capacity (1066 mAh g -1 ,0.2C), high rate (737mAh g -1,2.0C) and long cycle life (after 1000 cycles at 2.0C, the capacity decay per cycle is 0.024%) (ACSNano 2017,11,7274.). In 2019, Zisheng Zhang's team used polymethyl methacrylate (PMMA) nanospheres as templates and prepared porous CNT / Fe3O4 microspheres with a three-dimensional structure by spray drying and calcination, which were used as sulfur cathode host materials in lithium-sulfur batteries. Although this material has a porous structure left after PMMA is calcined and removed, it is not a completely continuous pore in the three-dimensional direction, and the pores are not connected, making it difficult for active substances such as electrolytes to enter deep into the material, limiting the utilization rate of the material and material transport. In addition, the preparation of CNT / Fe3O4 microspheres is to load Fe3O4 particles on CNT by post-loading iron. The preparation process is complicated, time-consuming and costly. When this material is used as the positive electrode of a lithium-sulfur battery, it has a high sulfur loading (77%), but only achieves mediocre performance: a capacity of 1270 mAh g at 0.2C. -1 ; At 3C rate, the performance is only 602mAh g -1 After 300 cycles at 1C, the capacity decay per cycle reaches 0.084%. (Mater.Lett.2019,255,126529.) Summary of the invention

[0005] In view of the above-mentioned defects of the prior art, the technical problem to be solved by the present invention is to provide a preparation method and application of Fe3O4-doped bicontinuous structure carbon spheres. The Fe3O4-doped bicontinuous structure carbon spheres prepared by the method of the present invention have a three-dimensional through-ordered pore structure, low cost and simple steps. Lithium-sulfur batteries using it as the positive sulfur host material can achieve high capacity, high rate and long cycle effects.

[0006] The present invention provides a method for preparing Fe3O4-doped bicontinuous carbon spheres, which comprises the following steps:

[0007] Step S1: Mixing and stirring a cubic polymer colloidal particle (PC) aqueous solution, an epigallocatechin gallate (EGCG) aqueous solution, and a FeCl3·6H2O aqueous solution, and adjusting the pH value to 6.8-7.4; obtaining a pyrolysis precursor MPN@PC composite;

[0008] Step S2: calcining the pyrolysis precursor MPN@PC composite to obtain SP-Fe3O4-C cubic carbon microspheres.

[0009] In the present invention, the preparation method of the cubic polymer colloidal particle aqueous solution can be conventional in the art, for example, by synthesizing PS by atom transfer radical polymerization. 241 -b-PEO45 The block copolymer (wherein the PS segment length can be between 200 and 300) is then prepared by solution self-assembly.

[0010] In the present invention, in step S1, the concentration of the cubic polymer colloidal particle aqueous solution is preferably 1 mg mL -1 .

[0011] In the present invention, in step S1, the concentration of the EGCG aqueous solution is preferably 30 mM.

[0012] In the present invention, in step S1, the FeCl3·6H2O aqueous solution is preferably 30 mM.

[0013] In the present invention, in step S1, the volume ratio of the cubic polymer colloidal particle aqueous solution, the FeCl3·6H2O aqueous solution and the EGCG aqueous solution is preferably 20:0.5:1 to 20:2.1:1.

[0014] In the present invention, in step S1, the pH value is preferably adjusted using 3-(N-morpholino)propanesulfonic acid (MOPS) buffer.

[0015] In the present invention, in step S1, after adjusting the pH value, the process may further include secondary stirring for 0 to 30 minutes, centrifugation, washing and drying.

[0016] In the present invention, in step S2, the calcination step preferably includes heating, an intermediate insulation stage and a final insulation stage in sequence.

[0017] Wherein, the heating rate is preferably 0 to 5°C / min, excluding 0.

[0018] The temperature of the intermediate insulation section is preferably 350-400° C., and the insulation time is preferably 1-2 hours.

[0019] The temperature of the final insulation section is preferably 750-850° C., and the insulation time is preferably 2-3 hours.

[0020] The present invention also provides a Fe3O4-doped bicontinuous carbon sphere, which is prepared by the above preparation method. The average mesopore size of the Fe3O4-doped bicontinuous carbon sphere is 30 nm.

[0021] The present invention also provides an application of Fe3O4-doped bicontinuous structure carbon spheres as positive electrode materials in batteries.

[0022] Beneficial effects of the present invention:

[0023] 1) This application uses low-cost natural plant polyphenols and Fe 3+The formed metal polyphenol network acts as a carbon source, enabling the in-situ doping of Fe3O4 into the carbon framework, avoiding the tedious and time-consuming post-loading step.

[0024] 2) This application realizes the construction of three-dimensional ordered pores (~30nm) on a mesoscopic scale (2-50nm) in carbon spheres;

[0025] 3) Using the Fe3O4-doped carbon material with a bicontinuous structure of the present application as a sulfur positive electrode host can realize the construction of a lithium-sulfur battery with high capacity, high rate and long cycle; BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Schematic diagram of CeO2 / mesoporous nitrogen-doped carbon nanospheres in the literature.

[0027] Figure 2 This is a schematic diagram of the invention principle of this application.

[0028] Figure 3 The structure of the SP-Fe3O4-C cubic carbon microspheres in the embodiment is demonstrated: (a, b) are scanning electron microscope images: Figure a clearly shows the ordered porous structure of SP-Fe3O4-C; Figure b shows the uniform doping of Fe3O4 particles in the SP-Fe3O4-C carbon skeleton; Figure c is a small angle X-ray diffraction;

[0029] Figure 4 The cycle performance of the lithium-sulfur battery based on the SP-Fe3O4-C structure in the embodiment at a rate of 0.2C;

[0030] Figure 5 It is the rate performance of the lithium-sulfur battery based on the SP-Fe3O4-C structure in the embodiment. DETAILED DESCRIPTION

[0031] The following describes several preferred embodiments of the present invention with reference to the drawings in the specification, so that the technical content is clearer and easier to understand. The present invention can be embodied in many different forms of embodiments, and the protection scope of the present invention is not limited to the embodiments mentioned in the text.

[0032] Example

[0033] This patent reports a cubic polymer colloidal particle (PC) with a double-hole structure assembled by block copolymer (PS-b-PEO) as a template, and the material components are easily available and inexpensive (-)-epigallocatechin gallate (EGCG) and Fe 3+The derived metal polyphenol network (MPN) is a carbonization precursor and metal source. Based on the hydrogen bonding between the hydroxyl groups in EGCG and the PEO segments in the template, the EGCG small molecules can be adsorbed inside the template pores, and further through the coordination interaction between metal ions and EGCG, the formation of the MPN network in the template is realized. The polymer particle template is first removed by high-temperature pyrolysis under N2 atmosphere, and then the temperature is increased to convert the MPN precursor into a continuous carbon network. During this process, Fe3O4 is in-situ doped in the carbon network skeleton, and finally a dual-continuous structure carbon sphere (SP-Fe3O4-C) is obtained, such as Figure 2 As shown in the invention principle diagram. The obtained SP-Fe3O4-C has a set of three-dimensional continuous carbon skeletons and a set of three-dimensional continuous mesopores. The rich continuous mesoporous channel structure gives it a high specific surface area and a large pore volume, which provides conditions for rapid ion transport and high sulfur loading. Therefore, the lithium-sulfur battery based on the SP-Fe3O4-C host material exhibits excellent performance. The specific preparation process is as follows:

[0034] (1) Preparation of cubic polymer colloidal particle template (PC): PS was first synthesized by atom transfer radical polymerization. 241 -b-PEO 45 Block copolymers, PC was prepared by co-solvent method. Experimental operation process: 20mg PS 241 -b-PEO 45 Dissolved in 2 mL of dioxane / N,N-dimethylformamide (v / v 92:8); stirred at 200 rpm and stirred at 1 mL h -1 2 mL of water was added to the polymer solution at a rate of . After assembly, the organic solvent was removed by dialysis, and then the PC template was obtained by centrifugation at 3000 rpm for 3 min.

[0035] (2) Preparation of pyrolysis precursor MPN@PC composite: EGCG aqueous solution (30 mM, 1 mL) and FeCl3·6H2O (30 mM, 1.3 mL) were added to 20 mL PC aqueous solution (1 mg mL -1 ) in; the suspension was stirred at 500 rpm for 2 h to ensure that EGCG and Fe 3+ Completely diffuse into the pores of the PC template; then add 25mL of 3-(N-morpholino)propanesulfonic acid (MOPS) buffer (pH=7.4) to adjust the pH value of the suspension to 6.8-7.4; then, continue to stir the reactants for another 20 minutes, collect the products by centrifugation, and wash them several times with water and ethanol respectively until the supernatant is colorless and transparent; finally, dry the collected products to obtain the MPN@PC composite.

[0036] (3) Preparation of SP-Fe3O4-C cubic carbon microspheres: The obtained MPN@PC composite was placed in an alumina ceramic boat and heated in a tube furnace at 2°C min-1 under a nitrogen atmosphere. -1 The temperature was raised at a heating rate of 350 ° C for 2 h to completely remove the template, and then calcined at 800 ° C for 2 h to ensure sufficient carbonization of the skeleton and in-situ doping of Fe3O4. The morphology is as follows Figure 3 As shown, the mesopore size is about 30nm and has a three-dimensional ordered pore structure (Figure a clearly shows the ordered porous structure of SP-Fe3O4-C; Figure b shows the uniform doping of Fe3O4 particles in the SP-Fe3O4-C carbon skeleton; Figure c is small-angle X-ray diffraction, which further proves the orderliness of the SP-Fe3O4-C structure from a statistically macroscopic perspective).

[0037] (4) Preparation of lithium-sulfur battery: The SP-Fe3O4-C prepared as above is used as the sulfur positive electrode host material of the lithium-sulfur battery. After loading sulfur, SP-Fe3O4-C / S is obtained as the positive electrode, lithium metal foil is used as the negative electrode, polypropylene (PP) is used as the separator, and the electrolyte solution is composed of 1M lithium bistrifluoromethanesulfonimide salt (LiTFSI) in a solvent of dioxolane (DOL) / dimethyl ether (DME) (volume ratio = 1:1), wherein 1wt% lithium nitrate (LiNO3) is used as an additive, and 50 μl of electrolyte is added to each battery.

[0038] (5) Electrochemical test: The electrochemical performance test was conducted on the LAND battery test system with a voltage window of 1.7-2.8V. Figure 4 As shown in the figure, the battery made of SP-Fe3O4-C as the sulfur cathode host material of the lithium-sulfur battery has a capacity decay of only 0.027% per cycle after 1200 cycles. Figure 5 As shown in Figure 2, the battery made with SP-Fe3O4-C as the sulfur cathode host material for lithium-sulfur batteries has excellent rate performance and high capacity at all rates: at 0.2, 0.5, 1.0, 2.0, 3.0, 4.0 and 5.0C, the capacities are 1303.4, 1197.0, 1093.9, 911.0, 837.4, 788.8 and 691.8 mAh g, respectively. -1 .

[0039] The preferred specific embodiments of the present invention are described in detail above. It should be understood that ordinary technicians in the field can make many modifications and changes based on the concept of the present invention without creative work. Therefore, all technical solutions that can be obtained by technicians in the technical field based on the concept of the present invention through logical analysis, reasoning or limited experiments on the basis of the prior art should be within the scope of protection determined by the claims.

Claims

1. A method for preparing Fe3O4-doped bicontinuous carbon spheres, characterized in that: It includes the following steps: Step S1: Mixing and stirring the cubic polymer colloidal particle aqueous solution, the epigallocatechin gallate aqueous solution and the FeCl3·6H2O aqueous solution, and adjusting the pH value to 6.8-7.4; obtaining a pyrolysis precursor metal polyphenol network@cubic polymer colloidal particle complex; Step S2: calcining the pyrolysis precursor metal polyphenol network@cubic polymer colloidal particle complex to obtain SP-Fe3O4-C cubic carbon microspheres.

2. The preparation method according to claim 1, characterized in that In step S1, the concentration of the cubic polymer colloidal particle aqueous solution is 1 mg mL -1 ; In step S1, the concentration of the epigallocatechin gallate aqueous solution is 30 mM; In step S1, the FeCl3·6H2O aqueous solution is 30 mM.

3. The preparation method according to claim 1, characterized in that: In step S1, the volume ratio of the cubic polymer colloidal particle aqueous solution, the FeCl3·6H2O aqueous solution and the epigallocatechin gallate aqueous solution is 20:0.5:1 to 20:2.1:

1.

4. The preparation method according to claim 1, characterized in that: In step S1, the pH value is adjusted using 3-(N-morpholinyl)propanesulfonic acid buffer; In step S1, after adjusting the pH value, the process further includes secondary stirring for 0 to 30 minutes, centrifugation, washing and drying.

5. The preparation method according to claim 1, characterized in that: In step S2, the calcination steps sequentially include heating, an intermediate insulation stage and a final insulation stage.

6. The preparation method according to claim 5, characterized in that: The heating rate is 0-5°C / min, excluding 0.

7. The preparation method according to claim 5, characterized in that: The temperature of the intermediate insulation section is 350° C. to 400° C., and the insulation time is 1 to 2 hours.

8. The preparation method according to claim 5, characterized in that: The temperature of the final insulation section is 750-850° C., and the insulation time is 2-3 hours.

9. A Fe3O4-doped bicontinuous carbon sphere, characterized in that: It is prepared by the preparation method according to any one of claims 1 to 8, and the average mesopore size of the Fe3O4-doped bicontinuous carbon sphere is 30nm.

10. Use of the Fe3O4-doped bicontinuous carbon spheres as claimed in claim 9 as positive electrode materials in batteries.

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