A positive electrode host material, its preparation method and application

Abstract

This invention provides a cathode host material, its preparation method, and its application. The cathode host material comprises hollow porous microspheres and Fe3O4-FeTe heterostructured nanoparticles supported on the hollow porous microspheres. This invention constructs a sulfur host material by supporting Fe3O4-FeTe heterostructured nanoparticles on porous hollow carbon microspheres. This material possesses both a robust structure and abundant catalytic sites, effectively addressing the issues of sulfur loading and catalytic conversion. The porous hollow structure effectively stores sulfur, while the internally loaded nanoparticles with an internal electric field can perform bidirectional catalytic conversion of sulfur. Simultaneously, the porous outer shell serves as a conductive substrate, continuously providing electrons to accelerate the conversion.

Description

Technical Field

[0001] This invention belongs to the field of battery materials technology, and relates to a positive electrode host material, its preparation method and application. Background Technology

[0002] Currently, commercially available lithium cobalt oxide or lithium iron phosphate cathode lithium-ion batteries have relatively low energy densities (200-300 Wh·kg). -1 Furthermore, there are safety concerns. Therefore, developing rechargeable batteries with high energy density and high reliability is an urgent priority. The conversion reaction based on the reduction of sulfur to lithium sulfide (Li₂S) can produce 1675 mAh·g. -1 (S8+16Li + The high theoretical capacity of 8Li₂S is significantly higher than that of intercalation cathode materials (such as lithium cobalt oxide and lithium iron phosphate), which have capacities below 200 mAh·g. -1 An electron charge transfer reaction operating at approximately 2.2V enables lithium-sulfur batteries to achieve a specific energy density of 2600 Wh·kg⁻¹. -1 With optimal configuration, the actual energy density can reach 500-600 Wh·kg. -1 Furthermore, sulfur has advantages such as abundant resources, safety, and environmental friendliness. Breakthroughs in lithium-sulfur batteries will promote the development and application of renewable energy.

[0003] Despite the enormous potential of lithium-sulfur batteries to replace lithium-ion batteries, they still face several key challenges. The most significant of these is the slow conversion kinetics of the sulfur reduction reaction (SRR) during discharge, due to sulfur's low conductivity and complex electron conversion processes. The sulfur reduction reaction involves a series of phase transitions, reducing solid sulfur to various soluble intermediates, and then further reducing it to the final insoluble Li₂S₂ / Li₂S products. This slow kinetics leads to incomplete sulfur reduction during discharge, thus reducing the specific capacity and rate capability of lithium-sulfur batteries. Another challenge is the reduction of lithium polysulfide intermediates (Li₂S₂ / Li₂S₂). n (3≤n≤8) Dissolution and diffusion from the cathode into the electrolyte. The conversion reaction between sulfur and lithium produces various Li₂S that are soluble in common organic electrolytes. n This troublesome phenomenon has two harmful effects: 1) it leads to lithium anode passivation due to the deposition of an inactive Li2S2 / Li2S layer on the lithium surface; 2) it causes the accumulation of short-chain Li2S on the passivated lithium anode. n-x These short-chain polysulfides can diffuse back to the positive electrode and then react with long-chain Li2S. n A reaction occurs. This repetitive process creates a shuttle effect, leading to rapid capacity decay and reduced coulombic efficiency in lithium-sulfur batteries. Furthermore, lithium metal anodes face significant challenges, such as severe side reactions and harmful lithium dendrite growth.

[0004] Generally, insufficient sulfur utilization due to slow SRR kinetics exacerbates polysulfide shuttle. Significant efforts have been made over the past few decades to overcome these challenges. Introducing mesoporous carbon (CMK-3) as a host material into the sulfur cathode effectively restricts sulfur diffusion and provides a channel for the high reactivity of lithium ions with sulfur. This restriction ensures sufficient redox reactions and improves sulfur utilization. However, this confinement strategy does not fundamentally solve the problems of slow redox reactions and shuttle effects, because confined polysulfides accumulate in the cathode region due to the concentration gradient in the electrolyte and inevitably diffuse towards the anode side. Therefore, accelerating the conversion kinetics of SRR is considered a feasible strategy for achieving full utilization of the sulfur cathode. Catalyst materials that can promote charge transfer and lower the reaction energy barrier of the sulfur cathode have shown great advantages in improving SRR kinetics. Thus, the polysulfide shuttle problem can be effectively solved. However, despite considerable progress in recent years, the fundamental conversion mechanism of polysulfide shuttle remains elusive, and the underlying conversion mechanism, involving multiple electron transfer reactions, remains difficult to elucidate. From both experimental and theoretical perspectives, further clarification is needed regarding the catalytic role of SRR in enhancing conversion kinetics. Furthermore, accurate analysis of the structural evolution of sulfur species and catalytic activity during the SRR process is essential.

[0005] Therefore, preparing host materials that can simultaneously address polysulfide shuttle, stepwise catalytic conversion, and effectively accommodate sulfur still presents significant challenges. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a positive electrode host material, its preparation method, and its applications. This invention constructs a porous hollow carbon microsphere-supported Fe3O4-FeTe heterostructure nanoparticle catalyst as a sulfur host material. This material possesses both a robust structure and abundant catalytic sites, effectively solving the problems of sulfur loading and catalytic conversion. The porous hollow structure effectively stores sulfur, while the internally loaded nanoparticles with an internal electric field can perform bidirectional catalytic conversion of sulfur. Simultaneously, the porous outer shell serves as a conductive substrate, continuously providing electrons to accelerate the conversion.

[0007] To achieve this objective, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides a positive electrode host material, the positive electrode host material comprising hollow porous microspheres and Fe3O4-FeTe heterostructure nanoparticles loaded on the hollow porous microspheres.

[0009] This invention utilizes a porous hollow carbon microsphere-supported Fe3O4-FeTe heterostructure nanoparticle catalyst as a sulfur host material. This catalyst possesses both a robust structure and abundant catalytic sites, effectively addressing the challenges of sulfur loading and catalytic conversion. The porous hollow structure effectively stores sulfur, while the internally supported Fe3O4-FeTe heterostructure nanoparticles with their built-in electric field enable bidirectional catalytic conversion of sulfur. Simultaneously, the porous outer shell serves as a conductive substrate, continuously providing electrons to accelerate the conversion.

[0010] As a preferred embodiment of the present invention, the hollow porous microspheres are made of carbon.

[0011] Preferably, the diameter of the hollow porous microspheres is 30-35 μm, for example, it can be 30 μm, 31 μm, 32 μm, 33 μm, 34 μm or 35 μm, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0012] Preferably, the wall thickness of the hollow porous microspheres is 1.5-2μm, for example, it can be 1.5μm, 1.6μm, 1.7μm, 1.8μm, 1.9μm or 2μm, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0013] As a preferred technical solution of the present invention, the particle size of the Fe3O4-FeTe heterostructure nanoparticles is 15-22nm, for example, it can be 15nm, 16nm, 17nm, 18nm, 19nm, 20nm, 21nm or 22nm, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0014] In a second aspect, the present invention provides a method for preparing the positive electrode host material described in the first aspect, the method comprising:

[0015] (1) Fe3O4 nanoparticles were dispersed in n-hexane, and then hollow porous microsphere precursors were added for adsorption to obtain adsorption products;

[0016] (2) The adsorption product and the Te source are calcined to obtain the positive electrode host material.

[0017] It should be noted that the adsorption product is a hollow porous microsphere precursor with adsorbed Fe3O4 nanoparticles.

[0018] This invention employs a high-temperature calcination tellurization method to prepare a sulfur host material with heterostructured nanoparticles loaded on hollow porous carbon microspheres by controlling the loading amount of nanoparticles, the amount of tellurium source, and the tellurization temperature. Since some oleic acid is retained on the surface of Fe3O4 nanoparticles, it can be well loaded on the inner wall of the microspheres after carbonization during calcination, thus obtaining a host material with high dispersion and high loading amount.

[0019] This method has a simple process flow and is highly controllable.

[0020] As a preferred embodiment of the present invention, the surface of the Fe3O4 nanoparticles is coated with oleic acid.

[0021] In this invention, since some oleic acid is retained on the surface of Fe3O4 nanoparticles, it can be well loaded onto the inner wall of the microspheres after carbonization during calcination, thereby obtaining a host material with high dispersion and high loading capacity.

[0022] Preferably, the method for preparing the Fe3O4 nanoparticles includes:

[0023] (a) Ferric chloride tetrahydrate, sodium oleate and solvent are mixed and reacted to obtain ferric oleate;

[0024] (b) The ferric oleate, oleic acid and octadecene are mixed and reacted to obtain Fe3O4 nanoparticles.

[0025] In this invention, Fe3O4 nanoparticles coated with oleic acid can be obtained by using the above method.

[0026] As a preferred technical solution of the present invention, the solvent in step (a) includes n-hexane, water and ethanol;

[0027] Preferably, the mass ratio of ferric chloride tetrahydrate, sodium oleate, and solvent in step (a) is (18-25):(28-35):500, wherein the range of ferric chloride tetrahydrate “18-25” can be, for example, 18, 19, 20, 21, 22, 23, 24, or 25, and the range of sodium oleate “28-35” can be, for example, 28, 29, 30, 31, 32, 33, 34, or 35, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0028] Preferably, the reaction temperature in step (a) is 70-75°C, for example, it can be 70°C, 71°C, 72°C, 73°C, 74°C or 75°C, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0029] Preferably, the reaction time in step (a) is 3.5-4.5 h, for example, it can be 3.5 h, 3.6 h, 3.7 h, 3.8 h, 3.9 h, 4 h, 4.2 h, 4.4 h or 4.5 h, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0030] Preferably, in step (a), after the reaction, the steps of separation, rotary evaporation and drying are performed sequentially.

[0031] Preferably, the temperature of the rotary evaporation is 75-85℃, for example, it can be 75℃, 76℃, 78℃, 80℃, 82℃, 84℃ or 85℃, etc., but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0032] In this invention, by precisely controlling the temperature of rotary evaporation, ferric oleate with suitable viscosity can be obtained.

[0033] Preferably, the mass ratio of ferric oleate, oleic acid, and octadecene in step (b) is (118-125):(2-5):1000, wherein the range of ferric oleate "118-125" can be, for example, 118, 119, 120, 121, 122, 123, 124, or 125, and the range of oleic acid can be, for example, 2, 3, 4, or 5, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0034] Preferably, the reaction temperature in step (b) is 314-320°C, for example, it can be 314°C, 315°C, 316°C, 317°C, 318°C, 319°C or 320°C, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0035] In this invention, Fe3O4 nanoparticles of different nanoscale sizes can be obtained by adjusting the reaction temperature in step (b). If the reaction temperature in step (b) is too low, the nanoparticles will have difficulty nucleating; if the reaction temperature in step (b) is too high, the nanoparticles may grow too large or cross-linking may occur.

[0036] Preferably, the reaction time in step (b) is 1.8-2.2 h, for example, it can be 1.8 h, 1.9 h, 2 h, 2.1 h or 2.2 h, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0037] As a preferred embodiment of the present invention, the Te source includes Te powder.

[0038] Preferably, the solid-liquid ratio of the Fe3O4 nanoparticles to the n-hexane is (45-50) mg:(25-35) mL, wherein the range of Fe3O4 nanoparticles "(45-50) mg" can be, for example, 45 mg, 46 mg, 47 mg, 48 mg, 49 mg, 50 mg, etc., and the range of n-hexane "(25-35) mL" can be, for example, 25 mL, 26 mL, 27 mL, 28 mL, 30 mL, 32 mL, 34 mL, or 35 mL, etc. However, it is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0039] In this invention, by adjusting the solid-liquid ratio of Fe3O4 nanoparticles to n-hexane, the uniform loading of nanoparticles within the porous cavity of the hollow porous microsphere precursor can be controlled. If the solid-liquid ratio of Fe3O4 nanoparticles to n-hexane is too small, the concentration of nanoparticles will be too low, resulting in a smaller amount of adsorbable particles and a reduction in the amount of catalytically active substances. If the solid-liquid ratio of Fe3O4 nanoparticles to n-hexane is too large, the nanoparticles will be unevenly dispersed, resulting in poor dispersion of the adsorbed particles and agglomeration.

[0040] Preferably, the hollow porous microsphere precursor is made of a polymer, wherein the polymer includes P(MMA-GMA). P(MMA-GMA) is a copolymer of methyl methacrylate and glycidyl methacrylate.

[0041] Preferably, the preparation method of the hollow porous microsphere precursor includes a two-step emulsion solidification method.

[0042] Preferably, the two-step emulsion solidification method includes the following steps: dissolving P(MMA-GMA) as a framework material in ethyl acetate, dissolving the hydrophilic stabilizer PVA-217 in the external aqueous phase, and simultaneously dissolving NaCl in the aqueous phases (W1 and W2) to adjust the osmotic pressure. This method is a double emulsion method: a method of introducing the aqueous phase into the oil droplet. The inner aqueous phase (i.e., W1) is dispersed in the polymer solution (i.e., O) to prepare a W1 / O primary emulsion. Then, the primary emulsion is further dispersed in the outer aqueous phase (i.e., W2) to prepare a W1 / O / W2 double emulsion. Finally, the organic solvent that dissolves the polymer is removed, and the solvent removal process is controlled so that the inner aqueous phases fuse together to form through pores during the solvent removal process, ultimately obtaining ultra-large porous microspheres.

[0043] Preferably, the calcination temperature is 780-820℃, for example, it can be 780℃, 790℃, 800℃, 810℃ or 820℃, etc. However, it is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0044] In this invention, if the calcination temperature is too low, the phase transformation of the nanoparticles will be incomplete; if the calcination temperature is too high, the outer shell of the microspheres will be destroyed due to the catalytic effect of Fe, resulting in structural breakage.

[0045] Preferably, the calcination time is 1-2.2h, for example, it can be 1h, 1.2h, 1.5h, 1.8h, 2h or 2.2h, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0046] In this invention, high-purity heterostructure materials can be obtained by controlling the calcination temperature and calcination time.

[0047] As a preferred technical solution of the present invention, the preparation method specifically includes:

[0048] (I) Ferric chloride tetrahydrate, sodium oleate and solvent are mixed and reacted at 70-75℃ for 3.5-4.5h under stirring. Then, the steps of separation, rotary evaporation and drying are carried out in sequence to obtain ferric oleate.

[0049] The mass ratio of ferric chloride tetrahydrate, sodium oleate and solvent is (18-25):(28-35):500, and the rotary evaporation temperature is 75-85℃.

[0050] (II) The ferric oleate, oleic acid and octadecene are mixed and reacted at 314-320℃ for 1.8-2.2h to obtain Fe3O4 nanoparticles;

[0051] The mass ratio of ferric oleate, oleic acid and octadecene is (118-125):(2-5):1000;

[0052] (III) Fe3O4 nanoparticles were dispersed in n-hexane, and then hollow porous microsphere precursors were added for ultrasonic dispersion and adsorption to obtain adsorption products.

[0053] The solid-liquid ratio of Fe3O4 nanoparticles to n-hexane is (45-50) mg:(25-35) mL.

[0054] (IV) The adsorption product and Te powder are calcined in an argon-hydrogen mixed atmosphere at a temperature of 780℃-820℃ for 1-2.2h to obtain the positive electrode host material.

[0055] Thirdly, the present invention provides a cathode material, which is obtained by calcining a cathode host material as described in the first aspect with sulfur.

[0056] Fourthly, the present invention provides a lithium-sulfur battery, wherein the positive electrode of the lithium-sulfur battery includes the positive electrode material described in the third aspect.

[0057] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0058] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0059] (1) This invention constructs a porous hollow carbon microsphere-supported Fe3O4-FeTe heterostructure nanoparticle catalyst as a sulfur host material. It possesses both a robust structure and abundant catalytic sites, effectively addressing the issues of sulfur loading and catalytic conversion. The porous hollow structure can effectively store sulfur, while the internally supported Fe3O4-FeTe heterostructure nanoparticles with an internal electric field can perform bidirectional catalytic conversion of sulfur. Simultaneously, the porous outer shell can serve as a conductive substrate, continuously providing electrons to accelerate the conversion.

[0060] (2) This invention employs a high-temperature calcination tellurization method to prepare a sulfur-containing host material with heterostructured nanoparticles loaded on hollow porous carbon microspheres by controlling the loading amount of nanoparticles, the amount of tellurium source, and the tellurization temperature. Since some oleic acid is retained on the surface of the nanoparticles, it can be well loaded onto the inner wall of the microspheres after carbonization during calcination, thus obtaining a host material with high dispersion and high loading capacity. This method has a simple process flow and strong controllability. Attached Figure Description

[0061] Figure 1 Transmission electron microscopy (TEM) image of Fe3O4 nanoparticles prepared in Example 1 of this invention.

[0062] Figure 2 Scanning electron microscope image of the hollow porous microsphere precursor provided in Embodiment 2 of the present invention.

[0063] Figure 3 This is a scanning electron microscope image of Fe3O4-FeTe@MCM prepared in Example 3 of the present invention.

[0064] Figure 4 This is a macroscopic transmission electron microscope image of Fe3O4-FeTe@MCM prepared in Example 3 of the present invention.

[0065] Figure 5 This is a magnified transmission electron microscope image of Fe3O4-FeTe@MCM prepared in Example 3 of the present invention.

[0066] Figure 6 This is a cycle performance diagram of the battery assembled in Embodiment 1 of the present invention. Detailed Implementation

[0067] The technical solution of the present invention will be further illustrated below through specific embodiments.

[0068] Example 1

[0069] This embodiment provides a positive electrode host material, which includes hollow porous microspheres and Fe3O4-FeTe heterostructured nanoparticles loaded on the hollow porous microspheres, denoted as Fe3O4-FeTe@MCM;

[0070] The hollow porous microspheres are made of carbon; the diameter of the hollow porous microspheres is 30 μm, the wall thickness of the hollow porous microspheres is 2 μm, and the particle size of the Fe3O4-FeTe heterostructure nanoparticles is 20 nm.

[0071] This embodiment also provides a method for preparing the above-mentioned positive electrode host material, the method comprising the following steps:

[0072] (1) Ferric chloride tetrahydrate, sodium oleate, n-hexane, deionized water and ethanol were placed in a 500 mL round-bottom flask and reacted at 70 °C and 400 rpm for 4 h using a magnetic stirrer. Then the products were separated using warm water (60 °C, volume greater than 1500 mL, washed 4 times) and a separatory funnel. The lower layer in the separatory funnel was water and the upper layer was an oily substance. The collected oily substance was poured into a 50 mL round-bottom flask and connected to an anti-backflow connector. Then the product was evaporated using a rotary evaporator at 80 °C. The resulting liquid was evaporated in several batches. The evaporated product was collected in a beaker and dried in a vacuum drying oven at 80 °C for 8 h to obtain ferric oleate.

[0073] The mass ratio of ferric chloride tetrahydrate, sodium oleate, and solvent (n-hexane, deionized water, and ethanol) is 20:30:500.

[0074] (2) The ferric oleate, oleic acid and octadecene were mixed in a 50 mL three-necked flask and reacted at 317 °C for 2 h. The resulting liquid was washed three times with acetone and n-hexane and then dried to obtain Fe3O4 nanoparticles.

[0075] The mass ratio of ferric oleate, oleic acid and octadecene is 123:3:1000.

[0076] (3) Fe3O4 nanoparticles were dispersed in n-hexane, and then hollow porous microsphere precursors were added for ultrasonic dispersion and adsorption to obtain adsorption products.

[0077] The solid-liquid ratio of Fe3O4 nanoparticles to n-hexane is 50 mg: 25 mL; the hollow porous microsphere precursor is made of P(MMA-GMA).

[0078] (4) After drying the adsorption product, the Te powder is heated to 800°C for 2 hours in an argon-hydrogen mixed atmosphere at a heating rate of 2°C / min to obtain the positive electrode host material, namely Fe3O4-FeTe@MCM.

[0079] Figure 1 The image shows a transmission electron microscope image of the Fe3O4 nanoparticles prepared in this embodiment. As can be seen from the image, uniform Fe3O4 nanoparticles with a diameter of about 20 nm were prepared in this embodiment.

[0080] Example 2

[0081] This embodiment provides a positive electrode host material, which includes hollow porous microspheres and Fe3O4-FeTe heterostructured nanoparticles loaded on the hollow porous microspheres, denoted as Fe3O4-FeTe@MCM;

[0082] The hollow porous microspheres are made of carbon; the diameter of the hollow porous microspheres is 32 micrometers, the wall thickness of the hollow porous microspheres is 1.5 micrometers, and the particle size of the Fe3O4-FeTe heterostructure nanoparticles is 18 nanometers.

[0083] This embodiment also provides a method for preparing the above-mentioned positive electrode host material, the method comprising the following steps:

[0084] (1) Ferric chloride tetrahydrate, sodium oleate, n-hexane, deionized water and ethanol were placed in a 500 mL round-bottom flask and reacted at 70 °C and 400 rpm for 4 h using a magnetic stirrer. Then the products were separated using warm water (60 °C, volume greater than 1500 mL, washed 4 times) and a separatory funnel. The lower layer in the separatory funnel was water and the upper layer was an oily substance. The collected oily substance was poured into a 50 mL round-bottom flask and connected to an anti-backflow connector. Then the product was evaporated using a rotary evaporator at 80 °C. The resulting liquid was evaporated in several batches. The evaporated product was collected in a beaker and dried in a vacuum drying oven at 80 °C for 8 h to obtain ferric oleate.

[0085] The mass ratio of ferric chloride tetrahydrate, sodium oleate, and solvent (n-hexane, deionized water, and ethanol) is 25:35:500.

[0086] (2) The ferric oleate, oleic acid and octadecene were mixed in a 50 mL three-necked flask and reacted at 317 °C for 2 h. The resulting liquid was washed three times with acetone and n-hexane and then dried to obtain Fe3O4 nanoparticles.

[0087] The mass ratio of ferric oleate, oleic acid and octadecene is 125:5:1000.

[0088] (3) Fe3O4 nanoparticles were dispersed in n-hexane, and then hollow porous microsphere precursors were added for ultrasonic dispersion and adsorption to obtain adsorption products.

[0089] The solid-liquid ratio of Fe3O4 nanoparticles to n-hexane is 50 mg: 30 mL; the hollow porous microsphere precursor is made of P(MMA-GMA).

[0090] (4) After drying the adsorption product, the Te powder is heated to 800°C for 2 hours in an argon-hydrogen mixed atmosphere at a heating rate of 2°C / min to obtain the positive electrode host material, namely Fe3O4-FeTe@MCM.

[0091] Figure 2 The scanning electron microscope (SEM) images of the hollow porous microsphere precursor provided in this embodiment show that the pore size and diameter of the hollow porous microsphere precursor are uniform.

[0092] Example 3

[0093] This embodiment provides a positive electrode host material, which includes hollow porous microspheres and Fe3O4-FeTe heterostructured nanoparticles loaded on the hollow porous microspheres, denoted as Fe3O4-FeTe@MCM;

[0094] The hollow porous microspheres are made of carbon; the diameter of the hollow porous microspheres is 35 μm, the wall thickness of the hollow porous microspheres is 1.8 μm, and the particle size of the Fe3O4-FeTe heterostructure nanoparticles is 22 nm.

[0095] This embodiment also provides a method for preparing the above-mentioned positive electrode host material, the method comprising the following steps:

[0096] (1) Ferric chloride tetrahydrate, sodium oleate, n-hexane, deionized water and ethanol were placed in a 500 mL round-bottom flask and reacted at 70 °C and 400 rpm for 4 h using a magnetic stirrer. Then the products were separated using warm water (60 °C, volume greater than 1500 mL, washed 4 times) and a separatory funnel. The lower layer in the separatory funnel was water and the upper layer was an oily substance. The collected oily substance was poured into a 50 mL round-bottom flask and connected to an anti-backflow connector. Then the product was evaporated using a rotary evaporator at 80 °C. The resulting liquid was evaporated in several batches. The evaporated product was collected in a beaker and dried in a vacuum drying oven at 80 °C for 8 h to obtain ferric oleate.

[0097] The mass ratio of ferric chloride tetrahydrate, sodium oleate, and solvent (n-hexane, deionized water, and ethanol) is 18:28:500.

[0098] (2) The ferric oleate, oleic acid and octadecene were mixed in a 50 mL three-necked flask and reacted at 317 °C for 2 h. The resulting liquid was washed three times with acetone and n-hexane and then dried to obtain Fe3O4 nanoparticles.

[0099] The mass ratio of ferric oleate, oleic acid and octadecene is 118:2:1000.

[0100] (3) Fe3O4 nanoparticles were dispersed in n-hexane, and then hollow porous microsphere precursors were added for ultrasonic dispersion and adsorption to obtain adsorption products.

[0101] The solid-liquid ratio of Fe3O4 nanoparticles to n-hexane is 50 mg: 35 mL; the hollow porous microsphere precursor is made of P(MMA-GMA).

[0102] (4) After drying the adsorption product, the Te powder is heated to 800°C for 2 hours in an argon-hydrogen mixed atmosphere at a heating rate of 2°C / min to obtain the positive electrode host material, namely Fe3O4-FeTe@MCM.

[0103] Figure 3 The image shows a scanning electron microscope (SEM) image of the cathode host material (Fe3O4-FeTe@MCM) prepared in this embodiment. As can be seen from the image, a carbonized structure material with a complete morphology can still be obtained after loading Fe3O4 nanoparticles inside the polymer hollow porous microsphere precursor and performing tellurization calcination.

[0104] Figure 4 and Figure 5 Macroscopic transmission electron microscopy (TEM) images and magnified TEM images of the Fe3O4-FeTe@MCM prepared in this embodiment are shown respectively. Figure 3 It can be seen that Fe3O4-FeTe nanoparticles are dispersed and loaded on the inner wall of the hollow porous microspheres.

[0105] Example 4

[0106] The difference between this embodiment and embodiment 1 is that the reaction temperature in step (2) is 300°C.

[0107] The remaining preparation methods and parameters are consistent with those in Example 1.

[0108] Example 5

[0109] The difference between this embodiment and embodiment 1 is that the reaction temperature in step (2) is 350°C.

[0110] The remaining preparation methods and parameters are consistent with those in Example 1.

[0111] Example 6

[0112] The difference between this embodiment and embodiment 1 is that the solid-liquid ratio of Fe3O4 nanoparticles and n-hexane in step (3) is 30mg:50mL.

[0113] The remaining preparation methods and parameters are consistent with those in Example 1.

[0114] Example 7

[0115] The difference between this embodiment and embodiment 1 is that the solid-liquid ratio of Fe3O4 nanoparticles and n-hexane in step (3) is 60mg:25mL.

[0116] The remaining preparation methods and parameters are consistent with those in Example 1.

[0117] Example 8

[0118] The difference between this embodiment and embodiment 1 is that the calcination temperature in step (4) is 700°C.

[0119] The remaining preparation methods and parameters are consistent with those in Example 1.

[0120] Example 9

[0121] The difference between this embodiment and embodiment 1 is that the calcination temperature in step (4) is 900°C.

[0122] The remaining preparation methods and parameters are consistent with those in Example 1.

[0123] Comparative Example 1

[0124] The difference between this embodiment and embodiment 1 is that step (4) is omitted.

[0125] The remaining preparation methods and parameters are consistent with those in Example 1.

[0126] Performance testing

[0127] The positive electrode host material and sulfur powder prepared according to the above embodiments and comparative examples were ground and mixed at a mass ratio of 7:2:1. The mixed powder was placed in a ceramic boat and calcined at 155°C for 6 hours under an argon atmosphere. The resulting black blocky powder is the S@Fe3O4-FeTe@MCM positive electrode active material. The prepared positive electrode active material, Ketjen black, and binder (PVDF) were mixed at a mass ratio of 8:1:1 to form a slurry. This slurry was then coated onto aluminum foil and dried in a vacuum oven at 50°C for 6 hours. After that, it was cut using a Φ=12mm cutting machine for assembly to obtain button batteries, and capacity performance testing was performed.

[0128] The test conditions were: 5C charge-discharge, 500 cycles.

[0129] Figure 6The cycle performance of the battery assembled in Example 1 is shown, which still exhibits 570 mAh·g after 500 cycles at a high current of 5C. -1 It has a high discharge capacity and a capacity decay rate of only 0.05% per cycle, exhibiting excellent cycle stability.

[0130] The test results for the batteries assembled in the above embodiments and comparative examples are shown in Table 1.

[0131] Table 1

[0132]

[0133]

[0134] analyze:

[0135] As shown in Examples 1-3, the button battery prepared by this invention can still retain 570 mAh·g after 500 cycles at a high current of 5C. -1 The discharge capacity and capacity retention rate are both high. Therefore, using S@Fe3O4-FeTe@MCM prepared in this invention as the host material for lithium-sulfur batteries can significantly improve the catalytic conversion and cycle stability of lithium-sulfur batteries.

[0136] The data from Examples 1 and 4-5 show that if the reaction temperature in step (b) is too low, the nanoparticles are difficult to nucleate, resulting in a low yield and defects that greatly affect the catalytic effect in the battery. If the reaction temperature in step (b) is too high, the nanoparticles are too large or even agglomerate, which reduces the exposed active sites and affects the catalytic effect in the battery.

[0137] The data from Examples 1 and 6-7 show that if the solid-liquid ratio of Fe3O4 nanoparticles to n-hexane is too small, the loading will be reduced and the amount of catalytic active material will be too small to meet the loading requirements for long-cycle battery operation. If the solid-liquid ratio of Fe3O4 nanoparticles to n-hexane is too large, the loading will be too large, resulting in a reduction in the exposed active sites and affecting the long-cycle performance of the battery.

[0138] The data from Examples 1 and 8-9 show that if the calcination temperature is too low, the carbonization degree of the shell is insufficient, the conductivity is poor, and the rate of electron migration during recycling is affected, resulting in poor performance. If the calcination temperature is too high, the carbon shell will break at excessively high temperatures due to the catalytic effect of Fe, resulting in an incomplete structure that cannot effectively confine the active material during recycling, leading to poor performance.

[0139] As can be seen from the data results of Example 1 and Comparative Example 1, if the Te powder is not calcined, the heterostructure material cannot be formed due to the absence of tellurium, and therefore there is no built-in electric field to regulate the adsorption and catalytic intensity, resulting in poor battery cycle performance.

[0140] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A positive electrode host material for lithium-sulfur batteries, characterized in that, The positive electrode host material includes hollow porous microspheres and Fe3O4-FeTe heterostructure nanoparticles loaded on the hollow porous microspheres.

2. The positive electrode host material according to claim 1, characterized in that, The hollow porous microspheres are made of carbon.

3. The positive electrode host material according to claim 1, characterized in that, The diameter of the hollow porous microspheres is 30-35 μm.

4. The positive electrode host material according to claim 1, characterized in that, The hollow porous microspheres have a wall thickness of 1.5-2 μm.

5. The positive electrode host material according to claim 1, characterized in that, The Fe3O4-FeTe heterostructure nanoparticles have a particle size of 15-22 nm.

6. A method for preparing the positive electrode host material according to any one of claims 1-5, characterized in that, The preparation method includes: (1) Fe3O4 nanoparticles were dispersed in n-hexane, and then hollow porous microsphere precursors were added for adsorption to obtain the adsorption product; (2) The adsorption product and the Te source are calcined to obtain the positive electrode host material.

7. The preparation method according to claim 6, characterized in that, The surface of the Fe3O4 nanoparticles is coated with oleic acid. The preparation method of the Fe3O4 nanoparticles includes: (a) Ferric chloride tetrahydrate, sodium oleate and solvent are mixed and reacted to obtain ferric oleate; the solvent in step (a) includes n-hexane, water and ethanol; (b) The ferric oleate, oleic acid and octadecene are mixed and reacted to obtain Fe3O4 nanoparticles.

8. The preparation method according to claim 7, characterized in that, The mass ratio of ferric chloride tetrahydrate, sodium oleate, and solvent in step (a) is (18-25):(28-35):

500.

9. The preparation method according to claim 7, characterized in that, The reaction temperature in step (a) is 70-75°C; The reaction time in step (a) is 3.5-4.5 h.

10. The preparation method according to claim 7, characterized in that, In step (a), after the reaction, the steps of separation, rotary evaporation and drying are performed sequentially; The temperature of the rotary evaporation is 75-85℃.

11. The preparation method according to claim 7, characterized in that, In step (b), the mass ratio of ferric oleate, oleic acid, and octadecene is (118-125):(2-5):1000.

12. The preparation method according to claim 7, characterized in that, The reaction temperature in step (b) is 314-320℃; The reaction time in step (b) is 1.8-2.2 h.

13. The preparation method according to claim 6, characterized in that, The Te source includes Te powder.

14. The preparation method according to claim 6, characterized in that, The solid-liquid ratio of the Fe3O4 nanoparticles to the n-hexane is (45-50) mg:(25-35) mL.

15. The preparation method according to claim 6, characterized in that, The hollow porous microsphere precursor is made of a polymer, and the polymer includes P(MMA-GMA).

16. The preparation method according to claim 6, characterized in that, The calcination temperature is 780-820℃; The calcination time is 1-2.2 hours.

17. The preparation method according to claim 6, characterized in that, The preparation method specifically includes: (I) Ferric chloride tetrahydrate, sodium oleate and solvent are mixed and reacted at 70-75℃ for 3.5-4.5 h with stirring. Then, the steps of separation, rotary evaporation and drying are carried out in sequence to obtain ferric oleate. The mass ratio of ferric chloride tetrahydrate, sodium oleate, and solvent is (18-25):(28-35):500, and the rotary evaporation temperature is 75-85℃; the solvent in step (a) includes n-hexane, water, and ethanol. (II) The ferric oleate, oleic acid and octadecene are mixed and reacted at 314-320℃ for 1.8-2.2h to obtain Fe3O4 nanoparticles; The mass ratio of ferric oleate, oleic acid and octadecene is (118-125):(2-5):1000; (III) Fe3O4 nanoparticles were dispersed in n-hexane, and then hollow porous microsphere precursors were added for ultrasonic dispersion and adsorption to obtain the adsorption product. The solid-liquid ratio of Fe3O4 nanoparticles to n-hexane is (45-50) mg:(25-35) mL. (IV) The adsorption product and Te powder are calcined in an argon-hydrogen mixed atmosphere at a temperature of 780-820°C for 1-2.2 h to obtain the positive electrode host material.

18. A positive electrode material, characterized in that, The cathode material is obtained by calcining a mixture of the cathode host material as described in any one of claims 1-5 and sulfur.

19. A lithium-sulfur battery, characterized in that, The positive electrode of the lithium-sulfur battery includes the positive electrode material as described in claim 18.

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