Carbon-coated nano-microsphere, metal oxide and elemental sulfur (CNS (at) MOx (at) S) composite material, and preparation method and application of carbon-coated nano-microsphere, metal oxide and elemental sulfur (CNS (at) MOx (at) S) composite material

Abstract

The invention discloses a carbon-coated nano-microsphere, metal oxide and elemental sulfur (CS (at) MOx (at) S) composite material and a preparation method and application thereof, and relates to the technical field of electrode materials. The method comprises the following steps: preparing carbon-coated SiO2 nano microspheres; the preparation method comprises the following steps: by taking carbon-coated SiO2 nano microspheres and a metal oxide precursor as raw materials and deionized water or absolute ethyl alcohol as a solvent, carrying out reaction, and embedding metal oxide into the carbon-coated SiO2 nano microspheres to obtain composite microspheres; and grinding the composite microspheres and elemental sulfur, and reacting at 150-160 DEG C in an argon atmosphere for 10-20 hours to obtain the carbon-coated nano-microsphere, metal oxide and elemental sulfur composite material. The CNS (at) MOx (at) S composite material is used as the composite cathode material to be applied to the lithium ion battery, so that the problems of low reaction activity and low initial discharge capacity of the current cathode material at ultralow temperature can be effectively solved.

Description

Technical Field

[0001] This invention relates to the field of electrode materials technology, specifically to a carbon-coated nanosphere@metal oxide@sulfur (CNS@MO) material. x @S) Composite materials, their preparation methods, and applications. Background Technology

[0002] Lithium-ion batteries, as the most widely used commercial energy storage device today, effectively solve the energy storage problem by utilizing their unique electrochemical energy storage performance. With the rapid development of lithium-ion battery technology, they are widely used in various portable electronic devices, such as mobile phones, watches, and computers, greatly facilitating their use. Currently, in the rapidly developing electric vehicle industry, lithium-ion batteries have become the largest energy source. As technology continues to advance, the application scenarios for lithium-ion batteries are constantly being explored. Deep space and deep-sea exploration, aviation and aerospace technology, extreme weather conditions, and environments inaccessible to humans can all utilize lithium-ion batteries as an energy source for valuable scientific research. However, current lithium-ion batteries cannot fully meet current usage demands. There is a need for lithium-ion batteries with larger capacity, better cycle performance, higher safety, better low-temperature performance, and greater reliability to meet the needs of daily life and production. Furthermore, the performance and range of lithium-ion batteries currently used in electric vehicles are significantly reduced at low temperatures, especially in environments such as deep space and extreme weather where temperatures can drop to tens of degrees below zero. Therefore, there is an urgent need to find a composite cathode material with high electrochemical activity at low temperatures, and a matching electrolyte with low freezing point and viscosity, to adapt to the application of lithium-ion batteries at low and ultra-low temperatures.

[0003] Currently, graphite remains the most widely used cathode material in the lithium-ion battery market. However, at low temperatures, the slow lithium-ion insertion process and low lithium-ion diffusion coefficient hinder the rapid charge and discharge of lithium-ion batteries at low temperatures. Furthermore, graphite cathodes exhibit significant capacity loss (capacity at -20℃ is only 12% of that at room temperature). Sulfur-containing composite cathode materials, as a new generation of cathode materials for lithium batteries, possess high charge storage capacity (1672 mAh g⁻¹). -1 Due to its low cost and the widespread availability of sulfur, lithium-ion batteries have become the most promising low-cost, high-capacity energy storage material. However, sulfur-containing lithium batteries still face many challenges. At low temperatures, the cathode and anode reaction kinetics are slow, and the conductivity is poor, resulting in slow electrochemical reaction rates, low capacity, and poor cycle performance. Furthermore, soluble lithium polysulfides (Li₂S₃)... x 2< xThe shuttle effect of ≤8) causes battery self-discharge, resulting in a sharp drop in battery capacity. The insulation between elemental sulfur and insoluble sulfides (Li2S2 and Li2S) prevents the active materials of the battery from being fully activated. The drastic volume changes during charging and discharging also have a huge impact on the electrochemical performance of the battery, which seriously restricts its commercial development. Summary of the Invention

[0004] To address the shortcomings of the aforementioned background technology, the main technical problem solved by this invention is as follows: In existing technologies, when sulfur is used as a cathode material for lithium-ion batteries under ultra-low temperature conditions, sulfur suffers from poor conductivity, low initial charge-discharge efficiency, poor cycle stability, large volume expansion rate, and rapid capacity decay, severely restricting its widespread application in lithium-ion batteries. This invention provides a carbon-coated nanosphere@metal oxide@sulfur (CNS@MO) material. x @S) composite materials, their preparation methods, and applications. This method mainly involves carbon-coated SiO2 nanospheres (CNS) and metal oxides (MO). x Based on ) and elemental sulfur (S), CNS@MO was prepared. x @S composite material effectively solves the problems of poor conductivity and volume expansion effect of sulfur-containing materials, and constructs an excellent adsorption network to improve cycle stability and further enhance the comprehensive performance of the cathode electrode in ultra-low temperature environment.

[0005] The first objective of this invention is to provide a method for preparing a carbon-coated nanosphere@metal oxide@sulfur composite material, comprising the following steps: Preparation of carbon-coated SiO2 nanospheres; Using carbon-coated SiO2 nanospheres and metal oxide precursors as raw materials, and deionized water or anhydrous ethanol as solvent, the metal oxides are embedded into the carbon-coated SiO2 nanospheres through a reaction to obtain composite microspheres; wherein the metal oxide is one of MgO, TiO2, MnO2, and ZrO2. After grinding the composite microspheres and elemental sulfur, the mixture was reacted at 150-160℃ for 10-20 hours under an argon atmosphere to obtain a carbon-coated nanosphere@metal oxide@sulfur composite material. The mass ratio of the composite microspheres to elemental sulfur is 1:(0.25~2).

[0006] Preferably, the carbon-coated SiO2 nanospheres are prepared according to the following steps: Dendritic silica nanospheres were uniformly dispersed in Tris-HCl buffer solution, followed by the addition of dopamine hydrochloride. After reacting for 16-26 hours, the mixture was centrifuged and washed with water and ethanol until the supernatant was clear. The supernatant was then dried and carbonized at 750-850℃ for 4-8 hours under an argon atmosphere to obtain carbon-coated SiO2 nanospheres. The dendritic silica nanospheres were prepared according to the following steps: Using triethanolamine, hexadecyltrimethylammonium bromide, sodium salicylate, and tetraethyl orthosilicate as raw materials, and deionized water as solvent, the raw materials are uniformly dispersed in the solvent and reacted at 20-30℃ for 5-9 h. Subsequently, the reaction is carried out in air at 600-900℃ for 5-9 h to obtain dendritic silica nanospheres. The mass ratio of triethanolamine, hexadecyltrimethylammonium bromide, sodium salicylate, and tetraethyl orthosilicate is 1:(5~9):(2~5):(58~65).

[0007] Preferably, when the metal oxide in the composite microspheres is MgO, the composite microspheres are prepared according to the following steps: using carbon-coated SiO2 nanospheres, magnesium chloride, and ammonia as raw materials, and deionized water as solvent, the raw materials are uniformly dispersed in the solvent, stirred in a water bath, and then calcined under an argon atmosphere to obtain the composite microspheres; wherein, the mass ratio of the carbon-coated SiO2 nanospheres, magnesium chloride, and ammonia is 2: (1.18~4.73): (2.00~8.00).

[0008] Preferably, when the metal oxide in the composite microspheres is TiO2, the composite microspheres are prepared according to the following steps: Using carbon-coated SiO2 nanospheres, tetrabutyl titanate, and ammonia as raw materials, and anhydrous ethanol as solvent, the raw materials are uniformly dispersed in the solvent and stirred in an oil bath under nitrogen protection to obtain composite microspheres. The mass ratio of carbon-coated SiO2 nanospheres, tetrabutyl titanate, and ammonia is 2: (3.00~12.00): (6.00~30.00).

[0009] Preferably, when the metal oxide in the composite microspheres is MnO2, the composite microspheres are prepared according to the following steps: Using carbon-coated SiO2 nanospheres, manganese sulfate, and potassium permanganate as raw materials, and deionized water as solvent, the raw materials are uniformly dispersed in the solvent, stirred in an oil bath, and then calcined under an argon atmosphere to obtain composite microspheres. The mass ratio of the carbon-coated SiO2 nanospheres, manganese sulfate, and potassium permanganate is 2: (1.05~4.19):(0.73~2.91).

[0010] Preferably, when the metal oxide in the composite microspheres is ZrO2, the composite microspheres are prepared according to the following steps: Using carbon-coated SiO2 nanospheres, zirconium oxychloride, and ammonia as raw materials, and deionized water as solvent, the raw materials are uniformly dispersed in the solvent and subjected to hydrothermal reaction to obtain composite microspheres. The mass ratio of carbon-coated SiO2 nanospheres, zirconium oxychloride, and ammonia is 2: (2.01~8.03):(3.75~15.00).

[0011] The second objective of this invention is to provide a carbon-coated nanosphere@metal oxide@sulfur composite material, which includes carbon-coated SiO2 nanospheres and metal oxides and sulfur embedded in the carbon-coated SiO2 nanospheres; The metal oxides are loaded into the pores of carbon-coated SiO2 nanospheres by in-situ growth; elemental sulfur is loaded into the carbon-coated SiO2 nanospheres by tubular furnace melting.

[0012] The mass ratio of the carbon-coated SiO2 nanospheres to the metal oxide and elemental sulfur is 1: (0.25~1): (0.25~2); The particle size of the carbon-coated SiO2 nanospheres is 250~300nm.

[0013] The third objective of this invention is to provide an application of the carbon-coated nanospheres@metal oxides@sulfur composite material as described in claim 7 in lithium-ion batteries.

[0014] The fourth objective of this invention is to provide a cathode material prepared from a carbon-coated nanosphere@metal oxide@sulfur composite material, the preparation method of which includes: The electrode precursor solution was prepared by mixing carbon-coated nanospheres@metal oxides@sulfur composite material, conductive carbon fiber and polyvinylidene fluoride and stirring evenly. The electrode precursor solution was coated onto the substrate and dried under vacuum to obtain the cathode material; The mass ratio of the carbon-coated nanospheres@metal oxides@sulfur composite material, conductive carbon fiber, and polyvinylidene fluoride is (7~8): (1~2): 1. The cathode material is in sheet form with a thickness of 150~170μm.

[0015] The fifth objective of this invention is to provide a lithium-ion battery in which the cathode uses the aforementioned cathode material.

[0016] Compared with the prior art, the beneficial effects of the present invention are: This invention provides a carbon-coated nanosphere@metal oxide@sulfur (CNS@MO) x @S) composite materials, their preparation methods, and applications. This invention addresses the limitations of existing technologies where cathode electrodes still suffer from poor conductivity, low initial charge-discharge efficiency, poor cycle stability, short battery life, and insufficient cycle performance under ultra-low temperature conditions. It proposes a CNS@MO composite material.x @S composite material. This composite material has the advantages of high electrical conductivity, high initial charge-discharge efficiency, and good cycle performance and stability under ultra-low temperature conditions.

[0017] The CNS@MO provided by this invention x @S composite material is obtained by in-situ growth of metal oxides onto carbon-coated nanospheres (CNS) to obtain CNS@MO. x Nanospheres were used to load elemental sulfur onto CNS@MO via tube furnace melting. x CNS@MO was fabricated on nanospheres. x @S composite material. This material can improve the first charge-discharge efficiency under ultra-low temperature conditions by taking advantage of the high electrochemical reactivity of elemental sulfur under ultra-low temperature conditions, low cost, non-toxicity and environmental friendliness, and the metal oxide suppressing the shuttle effect of lithium polysulfides. It also has good structural stability and long cycle life.

[0018] The present invention provides CNS@MO x The lithium-ion battery cathode material based on CNS (carbon nanotubes) effectively addresses the low conductivity and volume expansion issues of elemental sulfur in batteries by combining CNS with metal oxides and elemental sulfur, and then modifying it with doping. The CNS provides electron and ion transport channels. Simultaneously, the combination with metal oxides effectively mitigates the shuttle effect of lithium polysulfides generated during the charge-discharge process of elemental sulfur, reducing capacity loss during charge-discharge at ultra-low temperatures. This improves the electrochemical activity and cycle stability of the composite cathode material, and the preparation method is simple and easy to implement.

[0019] Compared with existing lithium-ion batteries, the CNS@MO prepared using this invention... x Lithium-ion batteries assembled with @S composite cathode materials exhibit higher initial discharge capacity, better stability, and superior electrochemical performance under ultra-low temperature conditions. Specifically, the higher initial discharge capacity is demonstrated by the cathode material achieving 300-400 mAh g⁻¹ during initial discharge at -40°C. -1 The CNS exhibits a high discharge specific capacity and maintains excellent charge-discharge performance even after 100 cycles. This indicates that the porous structure and conductive carbon layer of CNS not only mitigate the volume expansion effect of elemental sulfur during charge-discharge, preventing cathode material breakage and maintaining internal structural stability, but also construct a better electron transport network, compensating for the insufficient conductivity of elemental sulfur. The in-situ grown metal oxide can effectively adsorb soluble lithium polysulfides generated during charge-discharge using its good hydrophilic interaction, effectively suppressing the shuttle effect and improving the battery's cycle stability. The superior electrochemical performance is reflected in the CNS@MO provided by this invention. xA lithium-ion battery assembled using @S composite material as the cathode material exhibits a short-cycle performance of 0.1 A·g at -40°C. -1 At low current densities, the discharge specific capacity remained relatively stable, achieving a first-time 307.97 mAh g⁻¹. -1 The discharge specific capacity remained at 53.24 mAh g after 100 cycles. -1 It has a high discharge specific capacity and good capacity retention.

[0020] This invention provides a CNS@MO x @S composite material can be used to prepare cathode electrodes, and further applied to the preparation of lithium-ion batteries for use in ultra-low temperature environments. Attached Figure Description

[0021] Figure 1 CNS@MgO provided for Example 5 and Comparative Example 1 (0.25~1) @S (1.5) and CNS@S (1.5) Composite cathode material at -40℃ and 0.1A g -1 Short-cycle performance under certain conditions.

[0022] Figure 2 CNS@MgO provided in Examples 1 and 6 (0.75) @S (0.5) and CNS@MgO (0.75) @S (0.25~2) Composite cathode material at -40℃ and 0.1A g -1 Short-cycle performance under certain conditions.

[0023] Figure 3 CNS@TiO2 was provided for Example 7 and Comparative Example 1. (0.25~1) @S (1.5) and CNS@S (1.5) Composite cathode material at -40℃ and 0.1A g -1 Short-cycle performance under certain conditions.

[0024] Figure 4 CNS@TiO2 provided for Examples 2 and 8 (1) @S (1.5) and CNS@TiO2 (1) @S (0.25~2) Composite cathode material at -40℃ and 0.1A g -1 Short-cycle performance under certain conditions.

[0025] Figure 5 CNS@MnO2 provided for Example 9 and Comparative Example 1 (0.25~1) @S (1.5) and CNS@S (1.5)The composite cathode material prepared from composite materials is suitable for use at -40℃ and 0.1A g. -1 Short-cycle performance under certain conditions.

[0026] Figure 6 CNS@MnO2 provided for Examples 3 and 10 (0.5) @S (0.5) and CNS@MnO2 (0.5) @S (0.25~2) Composite cathode material at -40℃ and 0.1A g -1 Short-cycle performance under certain conditions.

[0027] Figure 7 CNS@ZrO2 provided for Example 11 and Comparative Example 1 (0.25~1) @S (1.5) and CNS@S (1.5) Composite cathode material at -40℃ and 0.1A g -1 Short-cycle performance under certain conditions.

[0028] Figure 8 CNS@ZrO2 provided for Examples 4 and 12 (0.5) @S (0.25) and CNS@ZrO2 (0.5) @S (0.5~2) Composite cathode material at -40℃ and 0.1A g -1 Short-cycle performance under certain conditions.

[0029] Figure 9 (a) CNS and (b) CNS@MgO provided in Examples 1-4 (0.75) @S (0.5) (c)CNS@TiO2 (1) @S (1.5) (d) CNS@ZrO2 (0.5) @S (0.25) Transmission electron microscope (TEM) images and EDS elemental scanning images of the composite material.

[0030] Figure 10 (a) CNS@MgO provided in Examples 1-4 (0.75) @S (0.5) (b)CNS@TiO2 (1) @S (1.5) (c)CNS@MnO2 (0.5) @S (0.5) (d) CNS@ZrO2 (0.5) @S (0.25) X-ray photoelectron spectra of composite materials.

[0031] Figure 11X-ray diffraction patterns of the composite materials provided in Examples 1-4 and Examples 6, 8, 10, and 12.

[0032] Figure 12 It is the (a) CNS@MgO provided in Example 13 (0.75) @S (0.5) (b)CNS@TiO2 (1) @S (1.5) (c)CNS@MnO2 (0.5) @S (0.5) (d) CNS@ZrO2 (0.5) @S (0.25) Cyclic voltammetry curves of a battery assembled with composite cathode material at -40°C, where 1 is the test performed before short cycles and 2 is the test performed after short cycles.

[0033] Figure 13 It is the (a) CNS@MgO provided in Example 13 (0.75) @S (0.5) (b)CNS@TiO2 (1) @S (1.5) (c)CNS@MnO2 (0.5) @S (0.5) (d) CNS@ZrO2 (0.5) @S (0.25) The battery assembled with composite cathode material at 100 mA g -1 Capacity-voltage curves for the first three cycles under short-cycle conditions at -40℃.

[0034] Figure 14 It is the (a) CNS@MgO provided in Example 13 (0.75) @S (0.5) (b)CNS@TiO2 (1) @S (1.5) (c)CNS@MnO2 (0.5) @S (0.5) (d) CNS@ZrO2 (0.5) @S (0.25) Rate performance curve of a battery assembled with composite cathode material at -40℃.

[0035] Figure 15 It is the (a) CNS@MgO provided in Example 13 (0.75) @S (0.5) (b)CNS@TiO2 (1) @S (1.5) (c)CNS@MnO2 (0.5) @S (0.5) (d) CNS@ZrO2 (0.5) @S (0.25)Electrochemical impedance spectroscopy of a battery assembled with composite cathode material at -40℃, where 1 is the impedance spectrum before cycling and 2 is the impedance spectrum after cycling.

[0036] Figure 16 It is the CNS@MgO provided in Example 13 (0.75) @S (0.5) CNS@TiO2 (1) @S (1.5) CNS@MnO2 (0.5) @S (0.5) CNS@ZrO2 (0.5) @S (0.25) Composite cathode materials and CNS@S (0.5) A battery assembled from composite cathode materials and nanospheres (CNS) at 100 mA g -1 Comparison chart of short-cycle performance under -40℃ conditions. Detailed Implementation

[0037] To enable those skilled in the art to better understand and implement the technical solutions of the present invention, the present invention will be further described below in conjunction with specific embodiments and accompanying drawings. However, the embodiments described are not intended to limit the present invention.

[0038] This invention is based on the fact that elemental sulfur has a theoretically high energy density (1675 Wh / kg). -1 With its characteristics of limited toxicity, good environmental compatibility, abundant reserves, low cost, and excellent low-temperature electrochemical performance, sulfur is a highly promising and attractive cathode material for ultra-low temperature lithium-ion batteries. Therefore, this invention develops a novel ultra-low temperature lithium-ion battery composite cathode material based on elemental sulfur, carbon nanotube conductive networks, and metal oxides, characterized by high energy storage, fast charging and discharging, safety, stability, and environmental friendliness: CNS@MO, which boasts high current density and excellent long-cycle performance. x @S lithium-ion battery composite cathode material can effectively solve the problems of poor discharge performance and low cycle life of current cathode materials under ultra-low temperature conditions. It can also solve the problems of volume expansion effect of elemental sulfur and large loss of active material under ultra-low temperature conditions, thus constructing an excellent Li-ion battery cathode. + The transmission channel enhances long-term cycling stability and further improves the overall performance of sulfur-containing composite cathode electrodes at ultra-low temperatures.

[0039] The purpose of this invention is to prepare CNS@MO based on elemental sulfur, carbon nanotube conductive networks, and metal oxide nanoparticles. x @S composite materials are used as composite cathode materials in lithium-ion batteries. Specifically, metal oxide nanoparticles are grown in situ into carbon-coated nanospheres (CNS) to obtain carbon-coated nanospheres (CNS@MO) that support metal oxides as an excellent carrier for elemental sulfur. xThe carbon nanotube conductive network enhances the conductivity of the system and further activates the poorly conductive elemental sulfur. Simultaneously, the in-situ grown metal oxides can effectively adsorb lithium polysulfides, a readily soluble substance in the electrolyte, through their hydrophilic interactions with polysulfides. This improves the cycle life of the battery in ultra-low temperature environments, making high-performance lithium-ion batteries capable of operating in ultra-low temperature conditions possible and demonstrating significant application potential. Therefore, this invention develops a CNS@MO battery with high current density and stable cycle performance in ultra-low temperature environments. x @S composite materials and their preparation methods, as well as composite cathode materials and applications in lithium-ion batteries under ultra-low temperature environments.

[0040] To achieve the above objectives, the first aspect of the present invention provides a method for preparing a carbon-coated nanosphere@metal oxide@sulfur composite material, comprising the following steps: Preparation of carbon-coated SiO2 nanospheres; Using carbon-coated SiO2 nanospheres and metal oxide precursors as raw materials, and deionized water or anhydrous ethanol as solvent, the metal oxides are embedded into the carbon-coated SiO2 nanospheres through a reaction to obtain composite microspheres; wherein the metal oxide is one of MgO, TiO2, MnO2, and ZrO2. After grinding the composite microspheres and elemental sulfur, the mixture was reacted at 150–160 °C for 10–20 h under an argon atmosphere to obtain a carbon-coated nanosphere@metal oxide@sulfur composite material (CNS@MO). x @S); The mass ratio of the composite microspheres to elemental sulfur is 1:(0.25~2).

[0041] The unique porous network structure of the carbon-coated SiO2 nanospheres (CNS) prepared in this invention provides ample habitat for elemental sulfur, effectively supporting its volume expansion during charge-discharge at ultra-low temperatures and preventing irreversible damage to the cathode material. Simultaneously, the carbon nanotube conductive network significantly improves the system's conductivity, activating unreacted elemental sulfur and effective polysulfides deposited in the electrolyte. Furthermore, the in-situ grown metal oxides effectively adsorb readily soluble lithium polysulfides in the electrolyte, preventing significant loss and degradation of these effective substances. This system effectively addresses the issues of effective substance loss and low reactivity of elemental sulfur during ultra-low temperature charge-discharge processes.

[0042] It should be noted that the carbon-coated nanospheres@metal oxides@sulfur composite material (CNS@MO) x @S), MO xThe metal oxide is represented by one of MgO, TiO2, MnO2, and ZrO2, and the composite materials are represented by CNS@MgO@S, CNS@TiO2@S, CNS@MnO2@S, and CNS@ZrO2@S, respectively.

[0043] The carbon-coated SiO2 nanospheres were prepared according to the following steps: Dendritic silica nanospheres were uniformly dispersed in Tris-HCl buffer solution, followed by the addition of dopamine hydrochloride. After reacting for 16-26 hours, the mixture was centrifuged and washed with water and ethanol until the supernatant was clear. The supernatant was then dried and carbonized at 750-850℃ for 4-8 hours under an argon atmosphere to obtain carbon-coated SiO2 nanospheres. The dendritic silica nanospheres were prepared according to the following steps: Using triethanolamine, hexadecyltrimethylammonium bromide, sodium salicylate, and tetraethyl orthosilicate as raw materials, and deionized water as solvent, the raw materials are uniformly dispersed in the solvent and reacted at 20-30℃ for 5-9 h. Subsequently, the reaction is carried out in air at 600-900℃ for 5-9 h to obtain dendritic silica nanospheres. The mass ratio of triethanolamine, hexadecyltrimethylammonium bromide, sodium salicylate, and tetraethyl orthosilicate is 1:(5~9):(2~5):(58~65).

[0044] An exemplary method for preparing carbon-coated SiO2 nanospheres (CNS) includes: Dendritic silica nanospheres were prepared at a concentration of 2 mg / mL. -1 The dendritic silica nanospheres were added to 350 mL of Tris-HCl buffer solution and sonicated for 1 h to uniformly disperse them. The mixture was then stirred at 30 °C for 0.5 h to enhance dispersibility. Dopamine hydrochloride (DA), in equal mass to silica, was added every 0.5 h for a total of 3 additions. After reacting for 24 h, the mixture was centrifuged (8000 rpm, 10 min), washed with water and ethanol until the supernatant was clear, and then dried in a forced-air drying oven at 60 °C for 24 h. After complete drying, the nanospheres were carbonized at 800 °C under an argon atmosphere for 6 h to obtain carbon-coated SiO2 nanospheres (CNS). The Tris-HCl buffer solution is a tris(hydroxymethyl)aminomethane-hydrochloric acid solution with a concentration of 5 mg·mL⁻¹. -1 .

[0045] Dendritic silica nanospheres (SiO2) are prepared according to the following steps: Triethanolamine (TEA, 544 mg), the structure-directing agent hexadecyltrimethylammonium bromide (CTAB, 3.04 g), and sodium salicylate (NaSal, 1.680 g) were dissolved in 200 mL of ultrapure water and stirred at 1000 rpm for 1 h at 80 °C. Then, the silicon source—tetraethyl silicate (TEOS, 32 mL)—was added, and the reaction was allowed to proceed for 12 h. The mixture was then centrifuged (8000 rpm, 10 min) to obtain silica microspheres. The silica microspheres were dried in a 60 °C oven for 24 h and then thoroughly ground. The ground silica microsphere powder was placed in a ceramic boat and calcined in a tube furnace at 600 °C for 8 h in air to remove the organic molecular template, yielding dendritic silica nanospheres.

[0046] In this invention, composite microspheres (CNS@MO) x Metal oxides (MO) in ) x When the MgO is used, the composite microspheres are prepared according to the following steps: using carbon-coated SiO2 nanospheres, magnesium chloride, and ammonia as raw materials, and deionized water as solvent, the raw materials are uniformly dispersed in the solvent, stirred in a water bath, and then calcined under an argon atmosphere to obtain composite microspheres; wherein, the mass ratio of the carbon-coated SiO2 nanospheres, magnesium chloride, and ammonia is 2: (1.18~4.73): (2.00~8.00).

[0047] For example, the composite microspheres obtained by embedding MgO into carbon-coated SiO2 nanospheres are prepared by: using carbon-coated nanospheres (CNS), magnesium chloride, and ammonia as raw materials, and deionized water as solvent, uniformly dispersing the raw materials in the solvent, stirring in a water bath at 50°C for 2 hours, and then calcining at 600°C for 4 hours under an argon atmosphere to obtain CNS@MgO composite microspheres.

[0048] In this invention, when the metal oxide in the composite microspheres is TiO2, the composite microspheres are prepared according to the following steps: Using carbon-coated SiO2 nanospheres, tetrabutyl titanate, and ammonia as raw materials, and anhydrous ethanol as solvent, the raw materials are uniformly dispersed in the solvent and stirred in an oil bath under nitrogen protection to obtain composite microspheres. The mass ratio of carbon-coated SiO2 nanospheres, tetrabutyl titanate, and ammonia is 2: (3.00~12.00): (6.00~30.00).

[0049] For example, the composite microspheres obtained by embedding TiO2 into carbon-coated SiO2 nanospheres are prepared by: using carbon-coated nanospheres (CNS), tetrabutyl titanate, and ammonia as raw materials, and anhydrous ethanol as solvent, uniformly dispersing the raw materials in the solvent, and stirring in an oil bath at 80°C for 12 h under nitrogen protection to obtain CNS@TiO2 composite microspheres.

[0050] In this invention, when the metal oxide in the composite microspheres is MnO2, the composite microspheres are prepared according to the following steps: Using carbon-coated SiO2 nanospheres, manganese sulfate, and potassium permanganate as raw materials, and deionized water as solvent, the raw materials are uniformly dispersed in the solvent, stirred in an oil bath, and then calcined under an argon atmosphere to obtain composite microspheres. The mass ratio of the carbon-coated SiO2 nanospheres, manganese sulfate, and potassium permanganate is 2: (1.05~4.19):(0.73~2.91).

[0051] For example, the composite microspheres obtained by embedding MnO2 into carbon-coated SiO2 nanospheres are prepared by: using carbon-coated nanospheres (CNS), manganese sulfate, and potassium permanganate as raw materials, and deionized water as solvent, uniformly dispersing the raw materials in the solvent, stirring in an oil bath at 90°C for 5 hours, and then calcining at 280°C for 2 hours under an argon atmosphere to obtain CNS@MnO2 composite microspheres.

[0052] In this invention, when the metal oxide in the composite microspheres is ZrO2, the composite microspheres are prepared according to the following steps: Using carbon-coated SiO2 nanospheres, zirconium oxychloride, and ammonia as raw materials, and deionized water as solvent, the raw materials are uniformly dispersed in the solvent and subjected to hydrothermal reaction to obtain composite microspheres. The mass ratio of carbon-coated SiO2 nanospheres, zirconium oxychloride, and ammonia is 2: (2.01~8.03):(3.75~15.00).

[0053] For example, the composite microspheres obtained by embedding ZrO2 into carbon-coated SiO2 nanospheres are prepared by: using carbon-coated nanospheres (CNS), zirconium oxychloride, and ammonia as raw materials, and deionized water as solvent, uniformly dispersing the raw materials in the solvent, and hydrothermally reacting at 180°C for 18 hours to obtain CNS@ZrO2 composite microspheres.

[0054] A second aspect of the present invention provides a carbon-coated nanosphere@metal oxide@sulfur composite material, the composite material comprising carbon-coated SiO2 nanospheres, and metal oxides and sulfur embedded in the carbon-coated SiO2 nanospheres; The metal oxides are loaded into the pores of carbon-coated SiO2 nanospheres by in-situ growth; elemental sulfur is loaded into the carbon-coated SiO2 nanospheres by tubular furnace melting.

[0055] The mass ratio of the carbon-coated SiO2 nanospheres to the metal oxide and elemental sulfur is 1: (0.25~1): (0.25~2); The particle size of the carbon-coated SiO2 nanospheres is 250~300nm.

[0056] A third aspect of this invention provides the application of a carbon-coated nanosphere@metal oxide@sulfur composite material in lithium-ion batteries.

[0057] A fourth aspect of the present invention provides a cathode material, which is prepared using the above-mentioned carbon-coated nanospheres@metal oxides@sulfur composite material, and the preparation method includes: The electrode precursor solution was prepared by mixing carbon-coated nanospheres@metal oxides@sulfur composite material, conductive carbon fiber and polyvinylidene fluoride and stirring evenly. The electrode precursor solution was coated onto the substrate and dried under vacuum to obtain the cathode material; The mass ratio of the carbon-coated nanospheres@metal oxides@sulfur composite material, conductive carbon fiber, and polyvinylidene fluoride is (7~8): (1~2): 1. The cathode material is in sheet form with a thickness of 150~170μm.

[0058] It should be noted that conductive carbon fiber has good conductivity, which can reduce the internal resistance of the battery. Moreover, conductive carbon fiber has high purity and uniform quality, which can avoid harmful side reactions caused by impurities in the battery. At the same time, it can enhance the adhesion of the electrode precursor liquid to the current collector and prevent it from falling off. Polyvinylidene fluoride has good conductivity and chemical stability, and can effectively improve the contact between the electrode and the electrolyte.

[0059] The fifth aspect of the present invention provides a lithium-ion battery, wherein the cathode of the lithium-ion battery uses the cathode material described above.

[0060] It should be noted that, unless otherwise specified, the experimental methods used in this invention are all conventional methods; and the reagents and materials used, unless otherwise specified, are all commercially available.

[0061] The following examples illustrate the preparation of CNS@MO-based materials. x The tests for @S composite materials, cathode materials, and lithium-ion batteries were obtained using the following methods.

[0062] The sheet-shaped cathode material is cut into small round pieces with a diameter of 14 mm using a cutting machine. The thickness of the sheet-shaped cathode material is 150~170 μm.

[0063] The electrochemical performance of the prepared cathode material in an ultra-low temperature environment was determined using a lithium-ion battery.

[0064] The battery assembly steps are as follows: First, the sheet-like CNS@MO... xAfter drying, the @S composite cathode material was placed in a glove box to thoroughly remove oxygen and moisture. The required water and oxygen content in the glove box was: H2O < 0.1 ppm, O2 < 0.1 ppm. Next, the following components were arranged in the glove box from top to bottom: gasket, lithium sheet, separator, and active electrode, with an appropriate amount of electrolyte injected, and the negative electrode shell was then placed on top. Finally, the battery was encapsulated and allowed to stand for 12 hours before electrochemical performance testing was conducted at an ultra-low temperature of -40℃. The counter electrode used in the battery assembly process was a lithium metal sheet, the electrolyte was a commercial electrolyte (1M lithium bis(trifluoromethanesulfonyl)imide in a 1:1 volume ratio of 1,3-dioxypentane and 1,2-dimethoxyethane, with 2% lithium nitrate as an additive), the battery separator was a polypropylene film (Celgard 2500), and the battery casing model was CR2016.

[0065] Cyclic voltammetry (CVT) measures the potential at which redox processes occur in a material, plotted on the x-axis (voltage) and y-axis (current). It is crucial for analyzing the electrochemical reaction mechanisms occurring during the electrochemical processes of materials. The CVT testing conditions are: voltage window of 0.01–2.8 V, negative scan direction, and scan rate of 0.2 mV / s. -1 .

[0066] Constant current charge-discharge performance testing involves measuring the electrochemical performance of materials under constant current to analyze basic parameters such as initial charge-discharge specific capacity, cycle stability, reversible specific capacity, and charge-discharge plateau.

[0067] Rate performance studies involve testing at different current densities to investigate how the tested sample adapts to different current densities, and to determine the capacity recovery and electrochemical stability of the material at high rates.

[0068] AC impedance testing can analyze the electrochemical mechanism of materials during cycling. By fitting the impedance using Zview software, the specific values ​​of the impedance of each part in the electrochemical process can be obtained, thereby analyzing the influence of impedance on electrochemical performance and testing the kinetics and electrode interface characteristics of lithium-ion batteries.

[0069] Example 1 A method for preparing CNS@MgO@S composite material and CNS@MgO@S composite cathode material includes the following steps: Step 1: Preparation of CNS@MgO@S composite material.

[0070] Weigh 354.8 mg of solid MgCl2 and 200 mg of CNS, add them to 100 mL of deionized water, sonicate for 30 min, and after uniform dispersion, stir in a 50°C water bath for 30 min (500 rpm). Then add 0.6 mL of ammonia water, continue stirring in a 50°C water bath for 2 h (500 rpm), centrifuge for 10 min (8000 rpm), wash three times each with deionized water and anhydrous ethanol, collect the sediment and dry it in a 60°C forced-air drying oven for 24 h. Remove it, grind it thoroughly with a quartz mortar, transfer the obtained powder to an alumina ceramic boat, place it in a tube furnace, and calcine it at 600°C for 4 h under an Ar atmosphere to obtain carbon-coated magnesium oxide nanospheres. The mass ratio of CNS to in-situ generated magnesium oxide should be 1:0.75, denoted as CNS@MgO. (0.75) .

[0071] CNS@MgO (0.75) The carbon-coated nanospheres@magnesium oxide@sulfur (CNS@MgO@S) composite material was obtained by thoroughly grinding the carbon nanospheres and magnesium oxide in a mortar and reacting them at 155°C under an argon atmosphere for 12 hours. The CNS@MgO composite material was further processed into a composite material containing elemental sulfur. (0.75) The mass ratio of sulfur to elemental sulfur is 1:0.5, denoted as CNS@MgO. (0.75) @S (0.5) Its appearance is as shown in the attached image. Figure 9 As shown in (b).

[0072] The SiO2 nanoparticles were obtained by the following preparation method: Triethanolamine (TEA, 544 mg), the structure-directing agent hexadecyltrimethylammonium bromide (CTAB, 3.04 g), and sodium salicylate (NaSal, 1.680 g) were dissolved in 200 mL of ultrapure water and stirred at 1000 rpm for 1 h at 80 °C. Then, the silicon source—tetraethyl silicate (TEOS, 32 mL)—was added, and the reaction was allowed to proceed for 12 h. After the reaction was complete, unreacted substances and solvents were removed by centrifugation (8000 rpm, 10 min) to obtain silica microspheres. The silica microspheres were dried in a forced-air drying oven at 60 °C for 24 h and then thoroughly ground. The ground silica microsphere powder was placed in a ceramic boat and calcined in a tube furnace at 600 °C for 8 h in air atmosphere to obtain dendritic silica nanospheres.

[0073] The carbon-coated SiO2 nanospheres (CNS) were obtained by the following preparation method: Dendritic silica nanospheres were prepared at a concentration of 2 mg / mL. -1The dendritic silica nanospheres were added to 350 mL of Tris-HCl buffer solution and sonicated for 1 h to uniformly disperse them. The mixture was then stirred at 30 °C for 0.5 h to enhance dispersibility. Dopamine hydrochloride (DA), in equal mass to silica, was added every 0.5 h for a total of 3 additions. After reacting for 24 h, the mixture was centrifuged (8000 rpm, 10 min), washed with water and ethanol until the supernatant was clear, and then dried in a forced-air drying oven at 60 °C for 24 h. After complete drying, the nanospheres were carbonized at 800 °C under an argon atmosphere for 6 h to obtain carbon-coated nanospheres (CNS), the morphology of which is shown in the attached figure. Figure 9 As shown in (a).

[0074] Step 2: Preparation of CNS@MgO@S composite cathode material.

[0075] CNS@MgO (0.75) @S (0.5) Composite materials, conductive carbon fiber, and polyvinylidene fluoride were mixed in a mass ratio of 7:2:1 and stirred for at least 12 hours. The mixture was then coated onto aluminum foil using a 150 μm film scraper. The mixture was dried at 60°C for 12 hours, followed by vacuum drying at 60°C for at least 24 hours to obtain the CNS@MgO@S composite cathode material, which is a sheet-like lithium-ion battery cathode material. This cathode material was then cut into electrode sheets with a diameter of 14 mm using a die-cutting machine.

[0076] The prepared CNS@MgO@S composite cathode material is in thin film form with a thickness of 158 μm.

[0077] Example 2 The preparation method of a CNS@TiO2@S composite material and a CNS@TiO2@S composite cathode material is the same as that in Example 1, except that: In step one, 1200 mg of tetrabutyl titanate was weighed and added to 120 mL of anhydrous ethanol to prepare a 10 mg / mL solution. -1 Anhydrous ethanol solution of tetrabutyl titanate was prepared. 200 mg of CNS was weighed and added to 100 mL of anhydrous ethanol, sonicated for 30 min, and then stirred for 30 min under N2 protection. The tetrabutyl titanate anhydrous ethanol solution was added dropwise to the well-dispersed CNS anhydrous ethanol dispersion using a constant pressure dropping funnel. Then, 12 mL of ammonia water was added, and the mixture was reacted at 80 °C in an oil bath for 12 h under N2 atmosphere. After centrifugation for 10 min (8000 rpm), the mixture was washed 6 times with anhydrous ethanol, and the deposit was collected and dried in a 60 °C forced-air drying oven for 24 h. The product was then removed, thoroughly ground, and carbon-coated titanium dioxide nanospheres were obtained. The mass ratio of CNS to in-situ generated titanium dioxide should be 1:1, denoted as CNS@TiO2. (1) .

[0078] CNS@TiO2 in carbon-coated nanospheres@titanium dioxide@sulfur (CNS@TiO2@S) composite material (1) The mass ratio of sulfur to elemental sulfur is 1:1.5, denoted as CNS@TiO2. (1) @S (1.5) Its appearance is as shown in the attached image. Figure 9 As shown in (c).

[0079] In step two, CNS@TiO2 is used. (1) @S (1.5) A CNS@TiO2@S composite cathode material was prepared. The prepared CNS@TiO2@S composite cathode material was in the form of a thin film with a thickness of 161 μm.

[0080] Example 3 The preparation method of a CNS@MnO2@S composite material and a CNS@MnO2@S cathode material is the same as that in Example 1, except that: In step one, 209.25 mg of MnSO4 was weighed and added to 100 mL of deionized water. After stirring for 1 hour (700 rpm), 200 mg of CNS was added and stirred for 12 hours (700 rpm) to obtain a CNS-MnSO4 dispersion. Then, 145.5 mg of KMnO4 was weighed and dissolved in 100 mL of deionized water to prepare a potassium permanganate solution. The potassium permanganate solution was added to the CNS-MnSO4 dispersion, and the mixture was continuously stirred in a 90°C oil bath for 5 hours (700 rpm). After centrifugation for 10 minutes (8000 rpm), the mixture was washed three times each with deionized water and anhydrous ethanol. The precipitate was collected and dried in a 60°C oven for 24 hours. The precipitate was then removed, thoroughly ground, and transferred to an alumina ceramic boat. The boat was placed in a tube furnace and calcined at 280°C for 2 hours under an Ar atmosphere to obtain carbon-coated manganese dioxide nanospheres. The mass ratio of CNS to in-situ generated manganese dioxide should be 1:0.5, denoted as CNS@MnO2. (0.5) .

[0081] CNS@MnO2 in carbon-coated nanospheres@manganese dioxide@sulfur (CNS@MnO2@S) composite material (0.5) The mass ratio of sulfur to elemental sulfur is 1:0.5, denoted as CNS@MnO2. (0.5) @S (0.5) .

[0082] In step two, CNS@MnO2 is used. (0.5) @S (0.5) A CNS@MnO2@S composite cathode material was prepared. The prepared CNS@MnO2@S composite cathode material was in the form of a thin film with a thickness of 168 μm.

[0083] Example 4 A method for preparing a CNS@ZrO2@S composite material and a cathode material is the same as in Example 1, except that: In step one, 200 mg of CNS was weighed and added to 60 mL of deionized water. The mixture was ultrasonically dispersed for 30 min, then stirred for 15 min (500 rpm). Next, 401.5 mg of ZrOCl2 was added and stirred for 2 h (500 rpm). Then, 0.75 mL of NH3·H2O was added and stirred for 1 h (500 rpm). The mixture was then added to a 100 mL polytetrafluoroethylene reactor and hydrothermally reacted at 180 °C for 18 h. After centrifugation for 10 min (8000 rpm), the mixture was washed three times each with deionized water and anhydrous ethanol. The precipitate was collected and dried in a 60 °C oven for 24 h. The precipitate was then removed and thoroughly ground in a quartz mortar to obtain carbon-coated zirconium dioxide nanospheres. The mass ratio of CNS to in-situ generated zirconium dioxide should be 1:0.5, denoted as CNS@ZrO2. (0.5) .

[0084] CNS@ZrO2 in carbon-coated nanospheres@zirconia@sulfur (CNS@ZrO2@S) composite material (0.5) The mass ratio of sulfur to elemental sulfur is 1:0.25, denoted as CNS@ZrO2. (0.5) @S (0.25) Its appearance is as shown in the attached image. Figure 9 As shown in (d).

[0085] In step two, CNS@ZrO2 is used. (0.5) @S (0.25) A CNS@ZrO2@S composite cathode material was prepared. The prepared CNS@ZrO2@S composite cathode material was in the form of a thin film with a thickness of 165 μm.

[0086] Example 5 is the same as Example 1, except that the mass ratios of CNS to MgO and S are 1:0.25:1.5; 1:0.5:1.5; 1:0.75:1.5; and 1:1:1.5, respectively, with corresponding ammonia amounts of 0.2, 0.4, 0.6, and 0.8 mL, respectively, denoted as CNS@MgO. (0.25) @S (1.5) CNS@MgO (0.5) @S (1.5) CNS@MgO (0.75) @S (1.5) CNS@MgO (1) @S (1.5) Composite materials and composite cathode materials with thicknesses of 155 μm, 159 μm, 157 μm, and 160 μm, respectively.

[0087] Example 6 is the same as Example 1, except that the mass ratios of CNS to MgO and S are 1:0.75:0.25; 1:0.75:0.75; 1:0.75:1; 1:0.75:1.5; and 1:0.75:2, respectively, and are denoted as CNS@MgO. (0.75) @S (0.25) CNS@MgO (0.75) @S (0.75) CNS@MgO (0.75) @S (1) CNS@MgO (0.75) @S (1.5) CNS@MgO (0.75) @S (2) Composite materials and composite cathode materials with thicknesses of 158 μm, 161 μm, 160 μm, 160 μm, and 163 μm, respectively.

[0088] Example 7 is the same as Example 1, except that the mass ratios of CNS to TiO2 and S are 1:0.25:1.5; 1:0.5:1.5; 1:0.75:1.5; and 1:1:1.5, respectively, with corresponding ammonia amounts of 3, 6, 9, and 12 mL, respectively, denoted as CNS@TiO2. (0.25) @S (1.5) CNS@TiO2 (0.5) @S (1.5) CNS@TiO2 (0.75) @S (1.5) CNS@TiO2 (1) @S (1.5) Composite materials and composite cathode materials have thicknesses of 158 μm, 163 μm, 160 μm, and 165 μm, respectively.

[0089] Example 8 is the same as Example 1, except that the mass ratios of CNS to TiO2 and S are 1:1:0.25; 1:1:0.5; 1:1:0.75; 1:1:1; and 1:1:2, respectively, and are denoted as CNS@TiO2. (1) @S (0.25) CNS@TiO2 (1) @S (0.5) CNS@TiO2 (1) @S (0.75) CNS@TiO2 (1) @S (1) CNS@TiO2 (1) @S (2) Composite materials and composite cathode materials with thicknesses of 161 μm, 159 μm, 163 μm, 162 μm, and 164 μm, respectively.

[0090] Example 9 is the same as Example 1, except that the mass ratios of CNS to MnO2 and S are 1:0.25:1.5; 1:0.5:1.5; 1:0.75:1.5; and 1:1:1.5, respectively. The corresponding amounts of KMnO4 used are 72.75, 145.5, 218.25, and 291 mg, respectively, and are denoted as CNS@MnO2. (0.25) @S (1.5) CNS@MnO2 (0.5) @S (1.5) CNS@MnO2 (0.75) @S (1.5) CNS@MnO2 (1) @S (1.5) Composite materials and composite cathode materials have thicknesses of 156 μm, 159 μm, 158 μm, and 163 μm, respectively.

[0091] Example 10 is the same as Example 1, except that the mass ratios of CNS to TiO2 and S are 1:0.5:0.25; 1:0.5:0.75; 1:0.5:1; 1:0.5:1.5; and 1:1:2, respectively, and are denoted as CNS@MnO2. (0.5) @S 0.25) CNS@MnO2 (0.5) @S (0.75) CNS@MnO2 (0.5) @S (0.5) CNS@MnO2 (0.5) @S (1.5) CNS@MnO2 (0.5) @S (2) Composite materials and composite cathode materials with thicknesses of 159 μm, 163 μm, 161 μm, 165 μm, and 164 μm, respectively.

[0092] Example 11 is the same as Example 1, except that the mass ratios of CNS to ZrO2 and S are 1:0.25:1.5; 1:0.5:1.5; 1:0.75:1.5; and 1:1:1.5, respectively, with corresponding ammonia amounts of 0.375, 0.75, 1.125, and 1.5 mL, respectively, and are denoted as CNS@ZrO2. (0.25) @S (1.5) CNS@ZrO2 (0.5) @S (1.5) CNS@ZrO2 (0.75) @S (1.5) CNS@ZrO2 (1) @S (1.5)Composite materials and composite cathode materials have thicknesses of 161 μm, 160 μm, 163 μm, and 167 μm, respectively.

[0093] Example 12 is the same as Example 1, except that the mass ratios of CNS to TiO2 and S are 1:0.5:0.5; 1:0.5:0.75; 1:0.5:1; 1:0.5:1.5; and 1:1:2, respectively, and are denoted as CNS@ZrO2. (0.5) @S (0.5) CNS@ZrO2 (0.5) @S (0.75) CNS@ZrO2 (0.5) @S (1) CNS@ZrO2 (0.5) @S (1.5) CNS@ZrO2 (0.5) @S (2) Composite materials and composite cathode materials with thicknesses of 159 μm, 164 μm, 167 μm, 166 μm, and 168 μm, respectively.

[0094] Comparative Example 1 is the same as Example 1, except that, In step one, CNS and sulfur were added to a quartz mortar and ground thoroughly. Then, the mixture was added to an alumina ceramic boat and placed in a tube furnace. Under a closed Ar atmosphere, the mixture was reacted at 155°C for 12 hours to obtain a carbon-coated nanosphere@sulfur composite material. The mass ratios of CNS and S were 1:1.5 and 1:0.5, respectively. This is denoted as CNS@S. (1.5) and CNS@S (0.5) The composite material and the composite cathode material have thicknesses of 159 μm and 157 μm, respectively.

[0095] Example 13 A type of CNS@MO x The specific steps for assembling a lithium-ion battery using the @S composite cathode material are as follows: The CNS@MO provided in Examples 1-12 and Comparative Example 1 x @S composite cathode material and CNS@S (1.5) With CNS@S (0.5)A 14mm diameter electrode sheet made of composite cathode material was placed in a glove box to thoroughly remove oxygen and moisture. The required water and oxygen content in the glove box was: H2O < 0.1ppm, O2 < 0.1ppm. Next, the following layers were arranged in the glove box from top to bottom: gasket, lithium sheet, separator, and active electrode, with an appropriate amount of electrolyte injected, and the negative electrode shell was then placed on top. Finally, the battery was sealed and allowed to stand for 12 hours before electrochemical performance testing. The counter electrode used in the battery assembly process was a lithium metal sheet, the electrolyte was a commercial electrolyte (1M lithium bis(trifluoromethanesulfonyl)imide in a 1:1 volume ratio of 1,3-dioxypentane and 1,2-dimethoxyethane, with 2% lithium nitrate as an additive), the battery separator was a polypropylene film (Celgard 2500), and the battery casing model was CR2016.

[0096] To illustrate the CNS@MO prepared by the method provided in this invention x The relevant properties of the CNS@MO composite material are described in conjunction with the accompanying drawings, highlighting the CNS@MO prepared in the examples and comparative examples. x @S composite materials, CNS@S (1.5) With CNS@S (0.5) The morphology and structure of the composite materials were characterized. Lithium-ion batteries were assembled, and their cycle performance, electrochemical reaction mechanism, and rate performance under ultra-low temperature conditions were measured.

[0097] Figure 1 CNS@MgO provided for Example 5 and Comparative Example 1 (0.25~1) @S (1.5) and CNS@S (1.5) Composite cathode material at -40℃ and 0.1A g -1 The short-cycle performance under the given conditions is shown in Table 1. Table 1 shows the discharge specific capacity data for the corresponding number of cycles.

[0098] Table 1

[0099] Figure 2 CNS@MgO provided for Examples 1 and 6 (0.75) @S (0.5) and CNS@MgO (0.75) @S (0.25~2) Composite cathode material at -40℃ and 0.1A g -1 The short-cycle performance diagram under the given conditions is shown in Table 2, which contains the corresponding discharge specific capacity data for the relevant number of cycles.

[0100] Table 2

[0101] Comparison of the data shows that, under ultra-low temperature conditions of -40℃, the CNS@MgO in situ supported on MgO in Example 5... (0.25~1) @S (1.5) Comparison of composite cathode materials: Unloaded CNS@S in Example 1 (1.5) Better cycling performance. The performance was optimal when the CNS to MgO mass ratio was 1:0.75, and remained superior throughout the first forty cycles. Compared to Example 1 and Example 6, when CNS@MgO... (0.75) When the mass ratio of CNS to sulfur is 1:0.5, the CNS@MgO in Example 1 (0.75) @S (0.5) The composite cathode material exhibits a high overall discharge specific capacity and slow decay, resulting in stable cycling. This indicates that when the MgO metal oxide reaches a certain optimal loading, it fully leverages the advantages of the porous structure of the CNS to accommodate volume expansion and enhance the system's conductivity. Simultaneously, the hydrophilic interaction between the conductive carbon layer of the CNS and MgO also plays a beneficial role, suppressing the shuttle effect of lithium polysulfides to some extent and improving the cryogenic cycling performance of the composite cathode material in Example 1.

[0102] Figure 3 CNS@TiO2 was provided for Example 7 and Comparative Example 1. (0.25~1) @S (1.5) and CNS@S (1.5) Composite cathode material at -40℃ and 0.1A g -1 The short-cycle performance diagram under the given conditions is shown in Table 3, which contains the corresponding discharge specific capacity data for the relevant number of cycles.

[0103] Table 3

[0104] Figure 4 CNS@TiO2 provided for Examples 2 and 8 (1) @S (1.5) and CNS@TiO2 (1) @S (0.25~2) Composite cathode material at -40℃ and 0.1A g -1 The short-cycle performance diagram under the given conditions is shown in Table 4, which contains the discharge specific capacity data for the corresponding number of cycles.

[0105] Table 4

[0106] It can be seen that the CNS@TiO2 loaded with TiO2 in Example 7 (0.25~1) @S (1.5) The first-cycle discharge specific capacity of the composite cathode material system compared to CNS@S (1.5)The significant improvement indicates that TiO2 may enhance the electronic conductivity of the system, enabling it to fully activate the supported elemental sulfur in the initial stage. Specifically, when the mass ratio of CNS to TiO2 is 1:1, CNS@TiO2... (1) @S (1.5) Superior cycling performance was observed in all 100 cycles. However, the sulfur loading significantly affected the first-cycle discharge specific capacity of the cathode material. Example 2's CNS@TiO2 (1) @S (1.5) Compared to other cathode materials in Example 8, such as CNS@TiO2, the composite cathode material is a better choice. (1) @S (0.25) The initial discharge specific capacity of the former is 1.31 times that of the latter, demonstrating better electrochemical performance.

[0107] Figure 5 CNS@MnO2 provided for Example 9 and Comparative Example 1 (0.25~1) @S (1.5) and CNS@S (1.5) The composite cathode material prepared from composite materials is suitable for use at -40℃ and 0.1A g. -1 The short-cycle performance diagram under the given conditions is shown in Table 5, which contains the discharge specific capacity data for the corresponding number of cycles.

[0108] Table 5

[0109] Figure 6 CNS@MnO2 provided for Examples 3 and 10 (0.5) @S (0.5) and CNS@MnO2 (0.5) @S (0.25~2) Composite cathode material at -40℃ and 0.1A g -1 The short-cycle performance diagram under the given conditions is shown in Table 6, which contains the corresponding discharge specific capacity data for the relevant number of cycles.

[0110] Table 6

[0111] It can be observed that the composite cathode material CNS@MnO2 loaded with MnO2 in Example 9 (0.25~1) @S (1.5) The first-cycle discharge specific capacity compared to CNS@S in Comparative Example 1 (1.5) There is a significant improvement. When the mass ratio of CNS to MnO2 is 1:0.5, it shows relatively good cycling performance in 100 cycles, demonstrating good adsorption and electrochemical catalysis.

[0112] The composite cathode materials provided in Examples 3 and 10 both exhibited good cycling stability after 100 cycles at an ultra-low temperature of -40°C. The CNS@MnO2 provided in Example 3... (0.5) @S (0.5) The composite cathode material exhibits superior cycle performance compared to that in Example 10. This indicates that under ultra-low temperature conditions of -40℃, the metal oxide MnO2 and elemental sulfur achieve the optimal ratio, maximizing the hydrophilic interaction and electrocatalytic effect of MnO2 on the polysulfides generated during charge and discharge. This results in the best suppression of the shuttle effect in this system, making CNS@MnO2... (0.5) @S (0.5) Composite cathode materials achieve optimal electrochemical performance.

[0113] Figure 7 CNS@ZrO2 provided for Example 11 and Comparative Example 1 (0.25~1) @S (1.5) and CNS@S (1.5) Composite cathode material at -40℃ and 0.1A g -1 The short-cycle performance diagram under the given conditions is shown in Table 7, which contains the corresponding discharge specific capacity data for the relevant number of cycles.

[0114] Table 7

[0115] Figure 8 CNS@ZrO2 provided for Examples 4 and 12 (0.5) @S (0.25) and CNS@ZrO2 (0.5) @S (0.5~2) Composite cathode material at -40℃ and 0.1A g -1 The short-cycle performance diagram under the given conditions is shown in Table 8, which contains the corresponding discharge specific capacity data for the relevant number of cycles.

[0116] Table 8

[0117] It can be seen that when the mass ratio of CNS to ZrO2 in Example 11 is 1:0.5, CNS@ZrO2 (0.5) @S (1.5) Composite cathode materials have the highest initial discharge specific capacity and also exhibit certain advantages over 100 cycles.

[0118] CNS@ZrO2 provided in Example 4 (0.5) @S (0.25) The composite cathode material compared to the CNS@ZrO2 provided in Example 12 (0.5) @S (0.5~2)The composite cathode material exhibits better charge-discharge performance, better cycle performance, and better cycle stability. This indicates that at this ratio, the electrochemical performance of CNS, ZrO2, and elemental sulfur can be fully utilized. However, the shuttle effect is not well suppressed, and the discharge specific capacity becomes extremely low almost after the 10th cycle.

[0119] Figure 9 (a) CNS and (b) CNS@MgO provided in Examples 1-4 (0.75) @S (0.5) (c)CNS@TiO2 (1) @S (1.5) (d)CNS@ZrO2 (0.5) @S (0.25) Transmission electron microscopy (TEM) images and EDS elemental scanning images of the composite material. It can be seen that CNS exhibits a good spherical morphology and abundant porous structure. CNS@MO x The CNS composite materials all exhibited good microporous structure and spherical morphology. The elemental distributions all coincided with the dark-field morphology, indicating that elemental sulfur and various metal oxides were uniformly distributed within the CNS pores, allowing them to play a better role during charge and discharge.

[0120] Figure 10 The (a) CNS@MgO provided in Examples 1-4 (0.75) @S (0.5) (b)CNS@TiO2 (1) @S (1.5) (c)CNS@MnO2 (0.5) @S (0.5) (d) CNS@ZrO2 (0.5) @S (0.25) X-ray photoelectron spectra of the composite materials are shown, where (1) is the full-resolution spectrum, (2) is the C 1s high-resolution spectrum, (3) is the Si 1s high-resolution spectrum, (b)-4 is the Ti 2p high-resolution spectrum, (c)-4 is the Mn 2p high-resolution spectrum, and (d)-4 is the Zr 3d high-resolution spectrum. It can be seen that the main characteristic peaks of C are the C-C bond at 288.6 eV and the CO bond at 284.8 eV. The characteristic peak of Si 2p is 103.7 eV, indicating that Si exists in amorphous SiO2 form. Characteristic peaks of Ti=O, Mn=O, and Zr=O appear at 458.2 eV and 464.0 eV for Ti, 641.8 eV and 653.0 eV for Mn, and 182.5 eV and 184.9 eV for Zr, indicating that metal oxides were loaded onto carbon-coated nanospheres through in-situ growth.

[0121] Figure 11The (a) CNS@MgO provided in Examples 1-4 (0.75) @S、(b) CNS@TiO2 (1) @S、(c) CNS@MnO2 (0.5) @S、(d) CNS@ZrO2 (0.5) @S composite materials and CNS@MgO provided in Examples 6, 8, 10, and 12 (0.75) @S (0.25~2) CNS@TiO2 (1) @S (0.25~2) CNS@MnO2 (0.5) @S (0.25~2) CNS@ZrO2 (0.5) @S (0.5~2) X-ray diffraction pattern of composite materials.

[0122] It can be seen that in composite cathode materials with high sulfur content, CNS@TiO2... (1) @S (1.5) CNS@TiO2 (1) @S (2) and CNS@MnO2 (0.5) @S (2) A sulfur crystal peak appeared in the X-rays. Other sulfur-loaded composite cathode materials showed shifted, fragmented, and amorphous peaks. This could be because, with low sulfur content, the sulfur almost completely penetrates the CNS pores during melting, preventing X-rays from reaching the sulfur and forming its characteristic peaks. Alternatively, the sulfur crystal structure may change during melting, transforming from a regular crystal structure to an amorphous state, resulting in amorphous peaks. The peak fragmentation and shift could be due to the influence of the loaded metal oxide on the electron distribution of the crystal, or the introduction of new defect energy levels. As the sulfur crystal structure changes and becomes less regular, it may increase the reactivity at ultra-low temperatures, enhancing the electrochemical performance of the composite cathode material.

[0123] Figure 12 It is the (a) CNS@MgO provided in Example 13 (0.75) @S (0.5) (b) CNS@TiO2 (1) @S (1.5) (c)CNS@MnO2 (0.5) @S (0.5) (d) CNS@ZrO2 (0.5) @S (0.25) Cyclic voltammograms of the battery assembled with composite cathode materials were tested at -40°C, where 1 represents the test before short-cycle testing and 2 represents the test after short-cycle testing. It can be seen that the four CNS@MO...x The cyclic voltammetry curves of the @S composite cathode material showed relatively clear redox peaks before short-cycle cycling. After short-cycle cycling, both redox potentials decreased significantly. This is likely because the electrolyte viscosity increased during cycling at ultra-low temperatures, reducing ion migration rates and electrochemical reaction rates, resulting in weaker redox potentials.

[0124] Figure 13 It is the (a) CNS@MgO provided in Example 13 (0.75) @S (0.5) (b)CNS@TiO2 (1) @S (1.5) (c)CNS@MnO2 (0.5) @S (0.5) (d) CNS@ZrO2 (0.5) @S (0.25) The battery assembled with composite cathode material at 100 mA g -1 Capacity-voltage curves for the first three cycles under short-cycle conditions at -40℃. It can be seen that the four CNS@MO... x The @S composite cathode materials exhibit a relatively stable discharge plateau during the first cycle at -40℃ ultra-low temperature, with high initial discharge specific capacity. This stable capacity-voltage curve ensures voltage stability during charge and discharge, increasing the practicality of the composite cathode material. CNS@TiO2 (1) @S (1.5) and CNS@ZrO2 (0.5) @S (0.25) The high discharge specific capacity observed in the first three cycles indicates that the loading of TiO2 and ZrO2 can increase the electronic conductivity of the system and activate elemental sulfur. (CNS@MgO) (0.75) @S (0.5) and CNS@MnO2 (0.5) @S (0.5) The significant differences may be due to a low amount of elemental sulfur, or increased viscosity of the electrolyte under ultra-low temperature conditions, which reduces the reaction rate and prevents sulfur from fully participating in the charge-discharge reaction.

[0125] Figure 14 It is the (a) CNS@MgO provided in Example 13 (0.75) @S (0.5) (b)CNS@TiO2 (1) @S (1.5) (c)CNS@MnO2 (0.5) @S (0.5) (d) CNS@ZrO2 (0.5) @S (0.25) Rate performance curves of batteries assembled with composite cathode materials at -40℃. It can be seen that the four CNS@MO materials...x @S composite cathode materials exhibit certain rate performance even in cryogenic environments. After cycling at high current densities, they can recover a portion of their initial discharge specific capacity at low current densities. This demonstrates the effectiveness of CNS@MO in cryogenic environments. x The @S composite cathode material was not damaged under high current conditions.

[0126] Figure 15 It is the (a) CNS@MgO provided in Example 13 (0.75) @S (0.5) (b)CNS@TiO2 (1) @S (1.5) (c)CNS@MnO2 (0.5) @S (0.5) (d) CNS@ZrO2 (0.5) @S (0.25) Electrochemical impedance spectroscopy of the battery assembled with composite cathode material at -40℃, where 1 is the impedance spectrum before cycling and 2 is the impedance spectrum after cycling. Table 9 shows the corresponding fitted impedance data.

[0127] Table 9

[0128] R1 represents the resistance of the components themselves, including the electrode shell and gaskets, which doesn't change significantly before and after cycling. R2 represents the resistance encountered when charge enters the battery system. It can be seen that the resistance of these four composite cathode materials increased several times after cycling compared to before cycling, indicating that CNS@MO... x A thick solid electrolyte film forms on the surface of the @S composite cathode material, hindering charge transfer. Simultaneously, the shuttle effect generated by the sulfur-containing electrode during charging and discharging causes a significant portion of solid, insoluble, and poorly conductive lithium polysulfides to accumulate on the surface of the composite cathode material, severely impeding charge transfer. Furthermore, under ultra-low temperature conditions, the viscosity of the electrolyte continuously increases. These factors contribute the majority of the impedance.

[0129] Figure 16 It is the CNS@MgO provided in Example 13 (0.75) @S (0.5) CNS@TiO2 (1) @S (1.5) CNS@MnO2 (0.5) @S (0.5) CNS@ZrO2 (0.5) @S (0.25) Composite cathode material and CNS@S provided in Comparative Example 1 (0.5) A battery assembled from composite cathode materials and nanospheres (CNS) at 100 mA g -1A comparison chart of short-cycle performance at -40℃ is shown in Table 10, which contains discharge specific capacity data for the corresponding number of cycles.

[0130] Table 10

[0131] It can be seen that CNS@S in Comparative Example 1 (0.5) Compared to unmodified carbon-coated nanospheres (CNS), the short-cycle performance was improved, and the initial discharge specific capacity was significantly increased. Even after 100 cycles, a certain discharge specific capacity was maintained, indicating that elemental sulfur can, to some extent, enhance the ultra-low temperature electrochemical performance of carbon-coated nanospheres. In-situ growth of MgO and MnO2 in CNS@MgO (0.75) @S (0.5) and CNS@MnO2 (0.5) @S (0.5) Compared to CNS and CNS@S (0.5) The short-cycle performance is significantly improved, indicating that the metal oxides MgO and MnO2 can enhance the electrochemical performance of the composite cathode material at low temperatures to a certain extent. CNS@TiO2, loaded with metal oxides TiO2 and ZrO2, exhibits good short-cycle performance. (1) @S (1.5) and CNS@ZrO2 (0.5) @S (0.25) Compared with other materials, composite cathode materials have a higher initial discharge specific capacity, indicating that they may be able to enhance the electronic conductivity of cathode materials to a certain extent, activate more elemental sulfur, and improve the initial discharge specific capacity of composite cathode materials at ultra-low temperatures.

[0132] In summary, this invention provides a carbon-coated nanospheres@metal oxides (MgO, TiO2, MnO2, ZrO2)@sulfur composite material (CNS@MO). x The invention relates to CNS@MO, its preparation method, and its application. The composite material comprises porous carbon-coated nanospheres and metal oxides and elemental sulfur embedded within the porous carbon-coated nanospheres. The metal oxides (MgO, TiO2, MnO2, ZrO2) are loaded into the pores of the porous carbon-coated nanospheres via in-situ growth, while elemental sulfur is loaded into the pores of the carbon-coated nanospheres via tubular furnace melting. This invention primarily uses carbon-coated nanospheres, metal oxides, and elemental sulfur as a basis to prepare CNS@MO. x @S composite material. This invention uses CNS@MO composite material. x@S composite material, when used as a composite cathode material in lithium-ion batteries, can effectively solve the problems of low reactivity and low initial discharge capacity of current cathode materials at ultra-low temperatures. It can also construct a porous carbon structure and load metal oxides, effectively improving the problems of sulfur volume expansion, poor conductivity and shuttle effect, and further improving the overall performance of lithium batteries at ultra-low temperatures.

[0133] Although embodiments of the present invention have been shown and described above, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a carbon-coated nanosphere@metal oxide@sulfur composite material, characterized in that, Includes the following steps: Preparation of carbon-coated SiO2 nanospheres; Using carbon-coated SiO2 nanospheres and metal oxide precursors as raw materials, and deionized water or anhydrous ethanol as solvent, the metal oxides are embedded into the carbon-coated SiO2 nanospheres through a reaction to obtain composite microspheres; wherein the metal oxide is one of MgO, TiO2, MnO2, and ZrO2. After grinding the composite microspheres and elemental sulfur, the mixture was reacted at 150-160℃ for 10-20 hours under an argon atmosphere to obtain a carbon-coated nanosphere@metal oxide@sulfur composite material. The mass ratio of the composite microspheres to elemental sulfur is 1:(0.25~2).

2. The preparation method of the carbon-coated nanospheres@metal oxides@sulfur composite material according to claim 1, characterized in that, Carbon-coated SiO2 nanospheres were prepared according to the following steps: Dendritic silica nanospheres were uniformly dispersed in Tris-HCl buffer solution, followed by the addition of dopamine hydrochloride. After reacting for 16-26 hours, the mixture was centrifuged and washed with water and ethanol until the supernatant was clear. The supernatant was then dried and carbonized at 750-850℃ for 4-8 hours under an argon atmosphere to obtain carbon-coated SiO2 nanospheres. The dendritic silica nanospheres were prepared according to the following steps: Using triethanolamine, hexadecyltrimethylammonium bromide, sodium salicylate, and tetraethyl orthosilicate as raw materials, and deionized water as solvent, the raw materials are uniformly dispersed in the solvent and reacted at 20-30℃ for 5-9 h. Subsequently, the reaction is carried out in air at 600-900℃ for 5-9 h to obtain dendritic silica nanospheres. The mass ratio of triethanolamine, hexadecyltrimethylammonium bromide, sodium salicylate, and tetraethyl orthosilicate is 1:(5~9):(2~5):(58~65).

3. The method for preparing the carbon-coated nanospheres@metal oxides@sulfur composite material according to claim 1, characterized in that, When the metal oxide in the composite microspheres is MgO, the composite microspheres are prepared according to the following steps: using carbon-coated SiO2 nanospheres, magnesium chloride, and ammonia as raw materials, and deionized water as solvent, the raw materials are uniformly dispersed in the solvent, stirred in a water bath, and then calcined under an argon atmosphere to obtain composite microspheres; wherein, the mass ratio of the carbon-coated SiO2 nanospheres, magnesium chloride, and ammonia is 2: (1.18~4.73): (2.00~8.00).

4. The method for preparing the carbon-coated nanospheres@metal oxides@sulfur composite material according to claim 1, characterized in that, When the metal oxide in the composite microspheres is TiO2, the composite microspheres are prepared according to the following steps: Using carbon-coated SiO2 nanospheres, tetrabutyl titanate, and ammonia as raw materials, and anhydrous ethanol as solvent, the raw materials are uniformly dispersed in the solvent and stirred in an oil bath under nitrogen protection to obtain composite microspheres. The mass ratio of carbon-coated SiO2 nanospheres, tetrabutyl titanate, and ammonia is 2: (3.00~12.00): (6.00~30.00).

5. The method for preparing the carbon-coated nanospheres@metal oxides@sulfur composite material according to claim 1, characterized in that, When the metal oxide in the composite microspheres is MnO2, the composite microspheres are prepared according to the following steps: Using carbon-coated SiO2 nanospheres, manganese sulfate, and potassium permanganate as raw materials, and deionized water as solvent, the raw materials are uniformly dispersed in the solvent, stirred in an oil bath, and then calcined under an argon atmosphere to obtain composite microspheres. The mass ratio of the carbon-coated SiO2 nanospheres, manganese sulfate, and potassium permanganate is 2: (1.05~4.19): (0.73~2.91).

6. The method for preparing the carbon-coated nanospheres@metal oxides@sulfur composite material according to claim 1, characterized in that, When the metal oxide in the composite microspheres is ZrO2, the composite microspheres are prepared according to the following steps: Using carbon-coated SiO2 nanospheres, zirconium oxychloride, and ammonia as raw materials, and deionized water as solvent, the raw materials are uniformly dispersed in the solvent and subjected to hydrothermal reaction to obtain composite microspheres. The mass ratio of carbon-coated SiO2 nanospheres, zirconium oxychloride, and ammonia is 2: (2.01~8.03): (3.75~15.00).

7. A carbon-coated nanospheres@metal oxides@sulfur composite material prepared by the method according to any one of claims 1 to 6, characterized in that, The composite material includes carbon-coated SiO2 nanospheres, and metal oxides and elemental sulfur embedded in the carbon-coated SiO2 nanospheres; The metal oxides are loaded into the pores of carbon-coated SiO2 nanospheres by in-situ growth; elemental sulfur is loaded into the carbon-coated SiO2 nanospheres by tubular furnace melting. The mass ratio of the carbon-coated SiO2 nanospheres to the metal oxide and elemental sulfur is 1: (0.25~1): (0.25~2); The particle size of the carbon-coated SiO2 nanospheres is 250~300nm.

8. The application of the carbon-coated nanospheres@metal oxides@sulfur composite material as described in claim 7 in lithium-ion batteries.

9. A cathode material, characterized in that, The cathode material is prepared using the carbon-coated nanospheres@metal oxides@sulfur composite material as described in claim 7, and its preparation method includes: A carbon-coated nanosphere@metal oxide@sulfur composite material, conductive carbon fiber and polyvinylidene fluoride were mixed and stirred evenly to prepare an electrode precursor solution; the electrode precursor solution was coated on a substrate and dried under vacuum to obtain the cathode material. The mass ratio of the carbon-coated nanospheres@metal oxides@sulfur composite material, conductive carbon fiber and polyvinylidene fluoride is (7~8):(1~2):1; the cathode material is sheet-shaped and has a thickness of 150~170μm.

10. A lithium-ion battery, characterized in that, The cathode in the lithium-ion battery uses the cathode material described in claim 9.

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