Single atom loaded porous carbon-nano iron oxide core-shell material, and preparation and use thereof

Abstract

Disclosed in the present invention are a single atom loaded porous carbon-nano iron oxide core-shell material, and preparation and use thereof. Nano iron oxide is used as a hard template, and a polymer is used for self-assembly reaction of iron oxide to form polymer-coated nano iron oxide particles (PM@Fe2O3) each having a core-shell structure; and then metal atoms in a phthalocyanine salt and polymer functional groups on the surfaces of the nano iron oxide particles form strong π-π interactions, thereby obtaining single metal element doped polymer coated nano iron oxide particles, and high-temperature treatment is carried out in an argon gas atmosphere to obtain the single atom loaded porous carbon-nano iron oxide core-shell material. The material can be applied to a lithium-sulfur battery. The single atom loaded porous carbon-nano iron oxide core-shell material prepared in the present invention has the high catalytic activity of single atoms and the strong polarity effect of the oxide, the reaction kinetics of the lithium-sulfur battery is remarkably improved, and stable cycling of the battery is achieved in a wide temperature interval.

Description

Single-atom-loaded porous carbon-nano-iron oxide core-shell materials and their preparation and application Technical Field

[0001] The present invention belongs to the field of battery technology, and in particular relates to a single-atom loaded porous carbon-nano iron oxide core-shell material and its preparation and application. Background Art

[0002] Lithium-sulfur batteries have the advantages of high theoretical specific capacity, environmental friendliness and abundant resources, and are electrochemical energy storage systems with great application prospects. Sulfur is the element that makes lithium-sulfur batteries have high energy density (1675mAh g -1 and 2600Wh kg -1 ), but the sulfur positive electrode has the problems of weak intrinsic conductivity and low self-utilization rate, and cannot meet the long-term recycling requirements within a wide temperature range.

[0003] Three-dimensional porous carbon cages are low-cost, easy to prepare, highly graphitized, and well coupled with elemental sulfur. As a carrier material, they can significantly improve the conductivity of the sulfur cathode. At the same time, constructing functional sites on three-dimensional porous carbon cages to regulate the electrochemical behavior of the sulfur cathode is the most effective strategy. Studies have shown that iron-based oxides have strong polarity and can serve as polar functional sites to promote the full reduction of solid-phase lithium sulfide and improve the utilization rate of the sulfur cathode. Based on this, Professor Manthiram's research group designed a Yolk-Shell structure of Fe3O4 coupled porous carbon cages for sulfur storage, distributing elemental sulfur around the Fe3O4 nanoboxes and encapsulating them inside the porous carbon cages. The Fe3O4 core serves as a functional site for electrochemical reactions, utilizing its strong polarity to adsorb non-polar solid-phase lithium polysulfides (Li2S2 / Li2S). This effectively inhibits the aggregation of the surrounding Li2S2 / Li2S during long cycles, promoting the full reduction of the lithiation reaction at the low-potential platform of the sulfur cathode (Adv. Mater. 2017, 29 1702707). Unfortunately, during long cycles over a wide temperature range, the composite electrode undergoes severe dissolution and aggregation in the electrolyte, leading to irreversible loss of elemental sulfur at the high-potential platform and inadequate reduction at the low-potential platform, causing rapid capacity decay.

[0004] Summary of the Invention

[0005] To address the aforementioned shortcomings of the existing technology, the present invention provides a single-atom-loaded porous carbon-nano-iron oxide core-shell material, its preparation, and application. The single-atom-loaded porous carbon-nano-iron oxide core-shell material prepared by the present invention combines the high catalytic activity of single atoms with the strong polarity of oxides, significantly improving the reaction kinetics of lithium-sulfur batteries and achieving stable battery cycling over a wide temperature range. Furthermore, the preparation method offers the advantages of low cost, simplicity, and wide applicability.

[0006] The technical solution of the present invention is:

[0007] The present invention relates to a method for preparing a single-atom loaded porous carbon-nano iron oxide core-shell material, comprising the following steps:

[0008] 1) Dispersing nano-iron oxide particles in an aqueous solution of tris(hydroxymethylaminomethane), adding dopamine hydrochloride, stirring at 500-1000 rpm / min for a period of time, centrifuging, washing, and drying to obtain polymer-coated nano-iron oxide particles, denoted as PM@Fe2O3;

[0009] 2) Using N,N-dimethylformamide as a solvent, a phthalocyanine metal salt M-Ph solution is prepared, and the solution is added dropwise to an aqueous solution of PM@Fe2O3 dispersion. The mixture is stirred for a period of time, centrifuged, and the precipitate is dried to obtain a single metal element-doped polymer-coated nano-iron oxide core-shell material;

[0010] 3) In a nitrogen atmosphere, the product obtained in step 2) is treated at 500-1100° C. for 0.5-15 h, and then immersed in a hydrochloric acid solution to obtain a single-atom-loaded porous carbon-nano-iron oxide core-shell material.

[0011] Preferably, the preparation method of the nano iron oxide particles is: dissolving sodium dihydrogen phosphate and ferric chloride hexahydrate in deionized water, and reacting them in a hydrothermal environment of 70-120° C. for not less than 10 hours.

[0012] Preferably, the molar ratio of sodium dihydrogen phosphate to ferric chloride hexahydrate is 1:50 to 1:5.

[0013] Preferably, in step 1), the concentration of the aqueous solution of tris(hydroxymethyl)aminomethane is 0.1-10 g / L, the mass ratio of iron oxide to tris(hydroxymethyl)aminomethane is in the range of 1:1-1:10, and the mass ratio of iron oxide to dopamine hydrochloride is in the range of 0.1:1-3:1; and the stirring time is 4-12 h.

[0014] Preferably, in step 2), the phthalocyanine metal salt is any one of metal Mg-Ph, Co-Ph, Ni-Ph, Cu-Ph, Zn-Ph, Fe-Ph, Mn-Ph and Al-Ph.

[0015] Preferably, in step 2), the concentration of the phthalocyanine metal salt M-Ph solution is 0.1 to 150 g / L, the concentration of the PM@Fe2O3 dispersed aqueous solution is 1 to 100 g / L, and the volume ratio of the phthalocyanine metal salt M-Ph solution to the PM@Fe2O3 dispersed aqueous solution is 1:10 to 1:1000; the stirring time is 0.5 to 8 h.

[0016] Preferably, in step 3), the heating rate to 500-1100° C. is 2-30° C. / min.

[0017] Preferably, in step 3), the concentration of the hydrochloric acid solution is 0.1 to 10 mol / L, and the soaking time is 0.1 to 10 h.

[0018] The present invention also relates to a single-atom loaded porous carbon-nano iron oxide core-shell material, which is prepared by the above-mentioned preparation method and is denoted as M S -PC@Fe2O3, where PC is porous carbon, M S The present invention uses nano-iron oxide as a hard template and utilizes a high molecular weight polymer to self-polymerize on the iron oxide to form polymer-coated nano-iron oxide particles (PM@Fe2O3) with a core-shell structure. Then, the metal atoms in the phthalocyanine salts are used to form a strong π-π interaction with the polymer functional groups on the surface of the nano-iron oxide particles, thereby obtaining single metal element doped polymer-coated nano-iron oxide particles. The nano-iron oxide particles are then subjected to high temperature treatment under an argon gas atmosphere to obtain a single-atom-loaded porous carbon-nano-iron oxide core-shell material (PM@Fe2O3). S -PC@Fe2O3)

[0019] Preferably, M S is any one of the metal elements Mg, Co, Ni, Cu, Zn, Mn, Fe, Mn and Al. The mass of iron oxide is S -PC@Fe2O3 total mass percentage is 5% to 65%, total M S The number of moles of the element accounts for M S -0.01% to 10% of the total molar number of all elements in PC@Fe2O3.

[0020] The present invention also relates to the application of single-atom loaded porous carbon-nano iron oxide core-shell material in lithium-sulfur batteries with a wide temperature range of -20 to 55°C.

[0021] The beneficial effects of the present invention are:

[0022] (1) The single-atom-loaded porous carbon-nano-iron oxide core-shell material prepared by the present invention has both the high catalytic activity of single atoms and the strong polarity of oxides, which helps to significantly improve the reaction kinetics of lithium-sulfur batteries and give full play to the ultra-stable cycle and wide temperature range performance of the battery; using the single-atom-loaded porous carbon-nano-iron oxide core-shell material as the sulfur storage positive electrode, it can stably cycle for at least 100 cycles in a wide temperature range of -20°C to 55°C.

[0023] (2) The present invention modifies atomic-level metal MN on a nitrogen-doped carbon cage matrix. x site, and utilize the dual functions of sulfur fixation and catalysis of this site to improve the irreversible loss of sulfur. On the one hand, the atomic-level MNx The sites have a strong sulfur-fixing effect on liquid-phase lithium polysulfide, which can inhibit the dissolution of lithium polysulfide in the electrolyte; on the other hand, the catalytic function of the sites can accelerate the conversion kinetics of liquid-phase lithium polysulfide, reduce the relaxation time of the intermediate phase lithium polysulfide conversion, and synergistically improve the loss in the sulfur positive electrode lithiation reaction. The present invention maximizes the dual functions of sulfur fixation and catalysis at the atomic scale, significantly improving the long-term stable cycle of the battery in a wide temperature range (-20 to 55°C), showing excellent cycle performance and rate performance in a wide temperature range, providing experience for similar future research on lithium-sulfur battery positive electrode carrier materials, and helping to promote practical research in the field of lithium-sulfur batteries.

[0024] (3) The present invention utilizes iron oxide and single atomic level sites to collaboratively modify nitrogen-doped porous carbon cages (M S -PC@Fe2O3), optimizes the site distribution, composition and structure at the surface interface of porous carbon cages through hierarchical site engineering, and improves the electrical conductivity of the carbon matrix by doping with heteroelements, overcoming the weak intrinsic conductivity of sulfur. The porous carbon matrix gives the sulfur storage carrier a high specific surface area and porous structure, which inhibits the structural collapse caused by volume expansion during complete lithiation of sulfur. The active sites enhance the electrochemical reaction kinetics and alleviate the irreversible loss of active substances under high and low temperature test conditions.

[0025] (4) The preparation method of the present invention has the advantages of low cost, simplicity, environmental protection, and wide application range. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0027] FIG1 is an XRD pattern of the single-atom-supported porous carbon-nano iron oxide core-shell material prepared in Example 1;

[0028] FIG2 is the SEM morphology of the single-atom loaded porous carbon-nano iron oxide core-shell material prepared in Example 2;

[0029] FIG3 is a TEM image of a single-atom-loaded porous carbon-nano iron oxide core-shell material prepared in Example 3;

[0030] FIG4 is a high-resolution TEM image of the single-atom-supported porous carbon-nano-iron oxide core-shell material prepared in Example 4;

[0031] FIG5 is a HAADF image and a high-resolution TEM image of the single-atom-loaded porous carbon-nano-iron oxide core-shell material prepared in Example 5;

[0032] FIG6 is a cyclic voltammetry curve of the single-atom supported porous carbon-nano iron oxide core-shell material prepared in Example 6;

[0033] FIG7 is a performance curve of the single-atom-supported porous carbon-nano iron oxide core-shell material prepared in Example 7 in a long cycle at -20°C and 55°C;

[0034] FIG8 is an XRD pattern of the manganese metal oxide-supported porous carbon-nano iron oxide core-shell material prepared in Comparative Example 1. DETAILED DESCRIPTION

[0035] To make the objectives, technical solutions, and advantages of the present invention more clearly understood, the present invention will be further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings. It should be understood that these descriptions are merely exemplary and are not intended to limit the scope of the present invention. In addition, in the following description, descriptions of well-known structures and technologies are omitted to avoid unnecessary confusion of the concepts of the present invention.

[0036] The solvent N,N-dimethylformamide used in the following examples is of chromatographic grade, sodium dihydrogen phosphate contains two crystal waters, and the purity is required to be ≥99%, and the remaining reagents are of analytical grade.

[0037] Example 1

[0038] A method for preparing a single-atom loaded porous carbon-nano iron oxide core-shell material:

[0039] 1) Dissolving 0.01 mol of sodium dihydrogen phosphate and 0.15 mol of ferric chloride hexahydrate in 100 mL of deionized water, reacting the mixture in a hydrothermal environment at 80° C. for 60 h, followed by centrifugation and drying to prepare Fe2O3 nanoparticles with an ellipsoidal morphology;

[0040] 0.2 g of nano-iron oxide particles were redispersed in 200 mL of a 3 g / L aqueous solution of tris(hydroxymethyl)aminomethane. Dopamine hydrochloride was added to the above solution at a mass ratio of iron oxide to dopamine hydrochloride of 0.1:1. The mixture was stirred at 675 rpm / min at room temperature for 8 h, then centrifuged, washed, and dried to obtain polymer-coated nano-iron oxide (PM@Fe2O3).

[0041] 2) A 1.5 g / L phthalocyanine Mg-Ph solution was prepared in N,N-dimethylformamide as a solvent; 10 μL of the solution was added dropwise to 10 mL of a 60 g / L PM@Fe2O3 suspension in water. The mixture was stirred at room temperature for 6 h, centrifuged, and dried in a vacuum oven at 60°C for 10 h to obtain a single metal element-doped polymer-coated nano-iron oxide core-shell material (Mg-PM@Fe2O3).

[0042] 3) The powder obtained in step 2) was placed in an agate mortar and ground for 10 minutes, placed in a corundum crucible, and then placed in a tube furnace. In a nitrogen atmosphere, the temperature was increased at a rate of 6°C / min and kept at 550°C for 5 hours. After cooling to room temperature, it was first dispersed in 36 mL of 0.5 mol / L hydrochloric acid solution and soaked for 0.5 hours. Then, it was fully centrifuged and washed and dried to prepare a single-atom-loaded porous carbon-nano iron oxide core-shell material (Mg SA -PC@Fe2O3).

[0043] After analysis, the XRD pattern of the single-atom-supported porous carbon-nano-iron oxide prepared in this example is shown in Figure 1. It can be seen that the prepared powder has obvious characteristic peaks of iron oxide and graphitized carbon. In addition, no diffraction peaks of magnesium-related compounds are observed.

[0044] Example 2

[0045] A method for preparing a single-atom loaded porous carbon-nano iron oxide core-shell material:

[0046] 1) Dissolving 0.015 mol of sodium dihydrogen phosphate and 0.3 mol of ferric chloride hexahydrate in 80 mL of deionized water, reacting the mixture in a hydrothermal environment at 110° C. for 30 h, followed by centrifugation and drying to prepare Fe2O3 nanoparticles with an ellipsoidal morphology;

[0047] 0.15 g of nano-iron oxide particles were redispersed in 160 mL of a 5 g / L aqueous solution of tris(hydroxymethyl)aminomethane. Dopamine hydrochloride was added to the above solution at a mass ratio of iron oxide to dopamine hydrochloride of 0.2:1. The mixture was stirred at 805 rpm / min at room temperature for 6 h, and then centrifuged, washed, and dried to obtain polymer-coated nano-iron oxide (PM@Fe2O3).

[0048] 2) A 2.5 g / L phthalocyanine Co-Ph solution was prepared in N,N-dimethylformamide as a solvent; 15 μL of the solution was added dropwise to 12 mL of a 55 g / L PM@Fe2O3 suspension solution. The mixture was stirred at room temperature for 5 h, centrifuged, and dried in a vacuum oven at 60°C for 10 h to obtain a single metal element-doped polymer-coated nano-iron oxide core-shell material (Co-PM@Fe2O3).

[0049] 3) The powder obtained in step 2) was placed in an agate mortar and ground for 10 minutes, placed in a corundum crucible, and then placed in a tube furnace. In a nitrogen atmosphere, the temperature was increased at a rate of 6°C / min and kept at 550°C for 5 hours. After cooling to room temperature, it was first dispersed in 22 mL of 0.5 mol / L hydrochloric acid solution and soaked for 0.5 hours. Then, it was fully centrifuged and washed and dried to prepare a single-atom-loaded porous carbon-nano iron oxide core-shell material (Co SA -PC@Fe2O3).

[0050] After analysis: The scanning electron microscope image of the single-atom-supported porous carbon-nano-iron oxide prepared in this embodiment is shown in Figure 2. It can be seen that the prepared powder particles have a regular nano-ellipsoidal morphology when observed under SEM.

[0051] Example 3

[0052] A method for preparing a single-atom loaded porous carbon-nano iron oxide core-shell material:

[0053] 1) Dissolving 0.02 mol of sodium dihydrogen phosphate and 0.16 mol of ferric chloride hexahydrate in 105 mL of deionized water, reacting the mixture in a hydrothermal environment at 100° C. for 30 h, followed by centrifugation and drying to prepare Fe2O3 nanoparticles with an ellipsoidal morphology;

[0054] 0.25 g of nano-iron oxide particles were redispersed in 220 mL of a 3.5 g / L aqueous solution of tris(hydroxymethyl)aminomethane. Dopamine hydrochloride was added to the above solution at a mass ratio of iron oxide to dopamine hydrochloride of 0.5:1. The solution was stirred at 650 rpm / min at room temperature for 6 h, and then centrifuged, washed, and dried to obtain polymer-coated nano-iron oxide (PM@Fe2O3).

[0055] 2) A 5 g / L phthalocyanine metal salt Ni-Ph solution was prepared in N,N-dimethylformamide as a solvent; 25 μL of the above solution was added dropwise to 13 mL of a 60 g / L PM@Fe2O3 suspension aqueous solution. The mixture was stirred at room temperature for 6 h, and the resulting precipitate was centrifuged and dried in a vacuum oven at 60°C for 10 h to obtain a single metal element-doped polymer-coated nano-iron oxide core-shell material (Ni-PM@Fe2O3).

[0056] 3) The powder obtained in step 2) was placed in an agate mortar and ground for 10 minutes, placed in a corundum crucible, and then placed in a tube furnace. In a nitrogen atmosphere, the temperature was increased at a rate of 10 ° C / min, and kept at 750 ° C for 4 hours. After cooling to room temperature, it was first dispersed in 19 mL of 0.5 mol / L hydrochloric acid solution and soaked for 1 hour, then fully centrifuged and washed and dried to prepare a single atom-loaded porous carbon-nano iron oxide core-shell material (NiSA -PC@Fe2O3).

[0057] After analysis: the transmission electron microscopy of the single-atom-supported porous carbon-nano-iron oxide prepared in this example is shown in Figure 3. It can be seen that the prepared powder particles have a core-shell structure when observed under TEM.

[0058] Example 4

[0059] A method for preparing a single-atom loaded porous carbon-nano iron oxide core-shell material:

[0060] 1) Dissolving 0.012 mol of sodium dihydrogen phosphate and 0.12 mol of ferric chloride hexahydrate in 110 mL of deionized water, reacting the mixture in a hydrothermal environment at 95° C. for 45 hours, and then centrifuging and drying the mixture to prepare Fe2O3 nanoparticles having an ellipsoidal morphology;

[0061] 0.22 g of nano-iron oxide particles were redispersed in 260 mL of a 5.5 g / L aqueous solution of tris(hydroxymethylaminomethane), and dopamine hydrochloride was added to the above solution at a mass ratio of 1:1 between iron oxide and dopamine hydrochloride. The mixture was stirred at 700 rpm / min at room temperature for 6 h, and then centrifuged, washed, and dried to obtain polymer-coated nano-iron oxide (PM@Fe2O3).

[0062] 2) A 10 g / L Cu-Ph phthalocyanine solution was prepared in N,N-dimethylformamide as a solvent; 45 μL of the solution was added dropwise to 15 mL of a 50 g / L PM@Fe2O3 suspension solution. The mixture was stirred at room temperature for 4 h, centrifuged, and dried in a vacuum oven at 60°C for 10 h to obtain a single metal element-doped polymer-coated nano-iron oxide core-shell material (Cu-PM@Fe2O3).

[0063] 3) The powder obtained in step 2) was placed in an agate mortar and ground for 10 minutes, placed in a corundum crucible, and then placed in a tube furnace. In a nitrogen atmosphere, the temperature was increased at a rate of 5°C / min and kept at 700°C for 6 hours. After cooling to room temperature, it was first dispersed in 26 mL of 0.5 mol / L hydrochloric acid solution and soaked for 2 hours. Then, it was fully centrifuged and washed and dried to prepare a single-atom-loaded porous carbon-nano iron oxide core-shell material (Cu SA -PC@Fe2O3).

[0064] After analysis: The high-resolution transmission electron microscopy of the single-atom-supported porous carbon-nano-iron oxide prepared in this example is shown in Figure 4. It can be seen that the prepared powder particles are observed as lattice fringes of iron oxide under TEM.

[0065] Example 5

[0066] A method for preparing a single-atom loaded porous carbon-nano iron oxide core-shell material:

[0067] 1) Dissolving 0.03 mol of sodium dihydrogen phosphate and 0.6 mol of ferric chloride hexahydrate in 130 mL of deionized water, reacting the mixture in a hydrothermal environment at 110° C. for 55 hours, and then centrifuging and drying the mixture to prepare Fe2O3 nanoparticles having an ellipsoidal morphology;

[0068] 0.3 g of nano-iron oxide particles were redispersed in 300 mL of a 5 g / L aqueous solution of tris(hydroxymethyl)aminomethane, and dopamine hydrochloride was added to the above solution at a mass ratio of iron oxide to dopamine hydrochloride of 1.5:1. The mixture was stirred at 800 rpm / min at room temperature for 7 h, and then centrifuged, washed, and dried to obtain polymer-coated nano-iron oxide (PM@Fe2O3).

[0069] 2) A 35 g / L phthalocyanine Mn-Ph solution was prepared in N,N-dimethylformamide as a solvent; 45 μL of the above solution was added dropwise to 11 mL of a 75 g / L PM@Fe2O3 aqueous suspension. The mixture was stirred at room temperature for 8 h, centrifuged, and dried in a vacuum oven at 60°C for 10 h to obtain a single metal element-doped polymer-coated nano-iron oxide core-shell material (Mn-PM@Fe2O3).

[0070] 3) The powder obtained in step 2) was placed in an agate mortar and ground for 10 minutes, placed in a corundum crucible, and then placed in a tube furnace. In a nitrogen atmosphere, the temperature was increased at a rate of 10°C / min and kept at 750°C for 4 hours. After cooling to room temperature, it was first dispersed in 26 mL of 0.5 mol / L hydrochloric acid solution and soaked for 1 hour. Then, it was fully centrifuged and washed and dried to prepare a single-atom-loaded porous carbon-nano iron oxide core-shell material (Mn SA -PC@Fe2O3).

[0071] Analysis shows that the high-angle annular dark field image and scanning transmission electron image of the single-atom-loaded porous carbon-nano-iron oxide prepared in this example under a transmission electron microscope are shown in Figure 5. As can be seen, the prepared powder particles exhibit a typical core-shell structure under TEM, with no lattice fringes in the outermost carbon layer.

[0072] Example 6

[0073] A method for preparing a single-atom loaded porous carbon-nano iron oxide core-shell material:

[0074] 1) Dissolving 0.02 mol of sodium dihydrogen phosphate and 0.18 mol of ferric chloride hexahydrate in 125 mL of deionized water, reacting the mixture in a hydrothermal environment at 95° C. for 45 hours, and then centrifuging and drying the mixture to prepare Fe2O3 nanoparticles having an ellipsoidal morphology;

[0075] 0.5 g of nano-iron oxide particles were redispersed in 200 mL of a 5 g / L aqueous solution of tris(hydroxymethyl)aminomethane. Dopamine hydrochloride was added to the above solution at a mass ratio of iron oxide to dopamine hydrochloride of 1.5:1. The mixture was stirred at 800 rpm / min at room temperature for 7 h, then centrifuged, washed, and dried to obtain polymer-coated nano-iron oxide (PM@Fe2O3).

[0076] 2) A 50 g / L Fe-Ph phthalocyanine solution was prepared in N,N-dimethylformamide as a solvent; 100 μL of the solution was added dropwise to 12 mL of an 80 g / L PM@Fe2O3 aqueous suspension. The mixture was stirred at room temperature for 8 h, centrifuged, and dried in a vacuum oven at 60°C for 10 h to obtain a single metal element-doped polymer-coated nano-iron oxide core-shell material (Fe-PM@Fe2O3).

[0077] 3) The powder obtained in step 2) was placed in an agate mortar and ground for 10 minutes, placed in a corundum crucible, and then placed in a tube furnace. In a nitrogen atmosphere, the temperature was increased at a rate of 2°C / min and kept at 800°C for 6 hours. After cooling to room temperature, it was first dispersed in 32 mL of 0.5 mol / L hydrochloric acid solution and soaked for 1 hour. Then, it was fully centrifuged and washed and dried to prepare a single-atom-loaded porous carbon-nano iron oxide core-shell material (Fe SA -PC@Fe2O3).

[0078] After analysis, the single-atom loaded porous carbon-nano iron oxide core-shell material prepared in this embodiment was subjected to melt sulfurization at 155°C to obtain the sulfur storage cathode material Fe SA -PC@Fe2O3-S. The cyclic voltammetry curve of the assembled button cell is shown in Figure 6. Two obvious reduction peaks appear in the discharge platform. At 2.41V, the sulfur element S8 begins to dissolve gradually in the electrolyte and transforms into long-chain lithium polysulfide S8→Li2S x (4≤x≤8), and then the long-chain lithium polysulfide is further lithiated at 2.11V and transformed into a short-chain lithium polysulfide: Li2S x (4≤x≤8)→Li2S x (1≤x≤3). Correspondingly, an obvious oxidation peak also appears on the charging platform and splits into a main peak and a secondary peak. At 2.19V, the solid phase lithium sulfide begins to delithiate and gradually transform into sulfur: Li2Sx (4≤x≤8)→S8.

[0079] Example 7

[0080] A method for preparing a single-atom loaded porous carbon-nano iron oxide core-shell material:

[0081] 1) Dissolving 0.02 mol of sodium dihydrogen phosphate and 0.18 mol of ferric chloride hexahydrate in 90 mL of deionized water, reacting the mixture in a hydrothermal environment at 95°C for 45 hours, followed by centrifugation and drying to prepare Fe2O3 nanoparticles with ellipsoidal morphology;

[0082] 0.16 g of nano-iron oxide particles were redispersed in 160 mL of a 5 g / L aqueous solution of tris(hydroxymethyl)aminomethane. Dopamine hydrochloride was added to the above solution at a mass ratio of iron oxide to dopamine hydrochloride of 1.5:1. The mixture was stirred at 800 rpm / min at room temperature for 7 h, and then centrifuged, washed, and dried to obtain polymer-coated nano-iron oxide (PM@Fe2O3).

[0083] 2) A 50 g / L phthalocyanine Zn-Ph solution was prepared in N,N-dimethylformamide as a solvent; 100 μL of the above solution was added dropwise to 21 mL of an 80 g / L PM@Fe2O3 aqueous suspension. The mixture was stirred at room temperature for 8 hours, centrifuged, and dried in a vacuum oven at 60°C for 10 hours to obtain a single metal element-doped polymer-coated nano-iron oxide core-shell material (Zn-PM@Fe2O3).

[0084] 3) The powder obtained in step 2) was placed in an agate mortar and ground for 10 minutes, placed in a corundum crucible, and then placed in a tube furnace. In a nitrogen atmosphere, the temperature was increased at a rate of 2°C / min and kept at 800°C for 6 hours. After cooling to room temperature, it was first dispersed in 26 mL of 0.5 mol / L hydrochloric acid solution and soaked for 1 hour. Then, it was fully centrifuged and washed and dried to prepare a single-atom-loaded porous carbon-nano iron oxide core-shell material (Zn SA -PC@Fe2O3).

[0085] After analysis, the bimetallic atom-loaded porous carbon prepared in this embodiment was subjected to melt sulfurization at 155°C to obtain the sulfur storage cathode material Zn SA -PC@Fe2O3-S, the long cycle performance of the assembled button battery is shown in Figure 7. When it can be stably cycled for more than 100 cycles at a current density of 0.2C at 55°C, Zn SA -PC@Fe2O3-S composite electrode can release 1269mAh g -1The first discharge capacity of the battery is 982 mAh g after 100 cycles. -1 , the average coulombic efficiency is above 99.2%, and the capacity decay rate of each cycle is only 0.2%. When the test temperature of the button battery is reduced to -20℃, it can be stably cycled for more than 100 cycles at a current density of 1C. SA -PC@Fe2O3-S composite electrode can release 769mAh g -1 The first discharge capacity of the battery is 622 mAh g after 100 cycles. -1 The average Coulombic efficiency is above 98.6%, and the capacity decay rate of each cycle is only 0.19%.

[0086] Comparative Example 1

[0087] A method for preparing a single-atom loaded porous carbon-nano iron oxide core-shell material:

[0088] 1) Dissolving 0.02 mol of sodium dihydrogen phosphate and 0.18 mol of ferric chloride hexahydrate in an equal amount of 120 mL of deionized water, reacting in a hydrothermal environment at 95°C for 45 hours, followed by centrifugation and drying to prepare Fe2O3 nanoparticles with ellipsoidal morphology;

[0089] 0.12 g of nano-iron oxide particles were redispersed in 120 mL of a 5 g / L aqueous solution of tris(hydroxymethyl)aminomethane. Dopamine hydrochloride was added to the above solution at a mass ratio of iron oxide to dopamine hydrochloride of 1.5:1. The mixture was stirred at 800 rpm / min at room temperature for 7 h, and then centrifuged, washed, and dried to obtain polymer-coated nano-iron oxide (PM@Fe2O3).

[0090] 2) A 45 g / L phthalocyanine Mn-Ph solution was prepared using ethanol as the solvent; 90 μL of the solution was added dropwise to 20 mL of a 90 g / L PM@Fe2O3 aqueous suspension. The mixture was stirred at room temperature for 8 h, centrifuged, and dried in a vacuum oven at 60°C for 10 h to obtain a single metal element-doped polymer-coated nano-iron oxide core-shell material (Mn-PM@Fe2O3).

[0091] 3) The powder obtained in step 2) was placed in an agate mortar and ground for 10 minutes, loaded into a corundum crucible, and then placed in a tube furnace. In a nitrogen atmosphere, the temperature was increased at a rate of 6°C / min and kept at 750°C for 6 hours. After cooling to room temperature, it was first dispersed in 27 mL of 0.5 mol / L hydrochloric acid solution and soaked for 1 hour, then fully centrifuged and washed and dried to prepare a core-shell material.

[0092] Analysis revealed that the surface of the prepared porous carbon-based composite material contained numerous metal oxide particles, not single metal atoms. This is evident in the XRD spectrum in Figure 8, which shows characteristic peaks not only for iron oxide but also for manganese oxide. Because the solubility and dispersibility of phthalocyanine metal salts in ethanol are much lower than in N,N-dimethylformamide, the prepared powder is not a porous carbon material loaded with bimetallic atoms, but rather a porous carbon-based material loaded with metal particles.

[0093] It should be understood that the above-described specific embodiments of the present invention are merely illustrative or illustrative of the principles of the present invention and do not constitute limitations of the present invention. Therefore, any modifications, equivalent substitutions, improvements, etc. made without departing from the spirit and scope of the present invention should be included within the scope of protection of the present invention. In addition, the appended claims are intended to cover all variations and modifications that fall within the scope and metes and bounds of the appended claims, or equivalents thereof.

Claims

1. A method for preparing a single-atom loaded porous carbon-nano iron oxide core-shell material, characterized in that: The following steps are involved: 1) dispersing nano iron oxide particles in an aqueous solution of tris(hydroxymethyl)aminomethane, adding dopamine hydrochloride, stirring at 500-1000 rpm / min for a period of time, centrifugation washing, and drying to obtain polymer-coated nano iron oxide particles, which are recorded as PM@Fe2O3; 2) using N,N-dimethylformamide as solvent, preparing a phthalocyanine metal salt M-Ph solution, adding the solution dropwise to the PM@Fe2O3 dispersed aqueous solution, stirring for a period of time, centrifuging, and drying the precipitate to obtain a single metal element doped polymer-coated nano iron oxide particle core-shell material; 3) In a nitrogen atmosphere, the product obtained in step 2) is treated at 500-1100° C. for 0.5-15 h, and immersed in a hydrochloric acid solution to obtain a single-atom-loaded porous carbon-nano iron oxide core-shell material.

2. The preparation method according to claim 1, characterized in that: The preparation method of nano iron oxide particles is as follows: dissolving sodium dihydrogen phosphate and ferric chloride hexahydrate in deionized water, and reacting them in a hydrothermal environment of 70-120° C. for not less than 10 hours.

3. The preparation method according to claim 2, characterized in that: The molar ratio of sodium dihydrogen phosphate to ferric chloride hexahydrate is 1:50 to 1:

5.

4. The preparation method according to claim 1, characterized in that: In step 1), the concentration of the aqueous solution of tris(hydroxymethyl)aminomethane is 0.1-10 g / L, the mass ratio of iron oxide to tris(hydroxymethyl)aminomethane is in the range of 1:1-1:10, and the mass ratio of iron oxide to dopamine hydrochloride is in the range of 0.1:1-3:1; and the stirring time is 4-12 h.

5. The preparation method according to claim 1, characterized in that: In step 2), the phthalocyanine metal salt is any one of metal Mg-Ph, Co-Ph, Ni-Ph, Cu-Ph, Zn-Ph, Fe-Ph, Mn-Ph and Al-Ph.

6. The preparation method according to claim 1, characterized in that: In step 2), the concentration of the phthalocyanine metal salt M-Ph solution is 0.1-150 g / L, the concentration of the PM@Fe2O3 dispersed aqueous solution is 1-100 g / L, and the volume ratio of the phthalocyanine metal salt M-Ph solution to the PM@Fe2O3 dispersed aqueous solution is 1:10-1:1000; the stirring time is 0.5-8 h.

7. The preparation method according to claim 1, characterized in that: In step 3), the heating rate to 500-1100° C. is 2-30° C. / min.

8. The preparation method according to claim 1, characterized in that: In step 3), the concentration of the hydrochloric acid solution is 0.1 to 10 mol / L, and the soaking time is 0.1 to 10 h.

9. A single atom-loaded porous carbon-nano iron oxide core-shell material, characterized in that: The method is prepared by the method according to any one of claims 1 to 8.

10. Use of the single-atom-loaded porous carbon-nano iron oxide core-shell material according to claim 9 in a lithium-sulfur battery with a wide temperature range, wherein the wide temperature range is -20 to 55°C.

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