TiO2 / Co-coated NC composite material as well as preparation method and application thereof

Abstract

The invention discloses a TiO2 / Co-NC composite material as well as a preparation method and application thereof, and belongs to the technical field of energy storage materials. The preparation method of the TiO2 / Co-NC composite material comprises the following steps: mixing polyacrylonitrile powder and carbon nanotubes in an amide organic solvent to obtain a first mixed solution; preparing the first mixed solution into a PAN / CNT electrospinning fiber membrane through an electrostatic spinning method; uniformly mixing a cobalt source and 2-methylimidazole in water, and adding the mixture into the PAN / CNT electrospinning fiber membrane to obtain an impregnated PAN / CNT electrospinning fiber membrane; carrying out annealing treatment and carbonization treatment on the Co-coated NC film to obtain a Co-coated NC film; and putting the Co-coated NC film into an atomic layer deposition chamber to obtain the TiO2 / Co-coated NC composite material. The TiO2 / Co-coated NC composite material can realize high-capacity electrochemical performance by utilizing photo-assistance, and keeps excellent specific capacity and long-term cycle performance under the condition of high sulfur load.

Description

Technical Field

[0001] This invention relates to the field of energy storage materials technology, and more specifically to TiO2 / Co@NC composite materials, their preparation methods, and applications. Background Technology

[0002] With the escalating energy crisis, developing high-energy-density energy storage systems is a key task in addressing the ever-increasing energy demand. Solar energy, due to its low cost, renewability, and environmental friendliness, is widely considered an ideal alternative or supplement to traditional energy sources. Currently, solar cells are used for energy conversion, while energy storage batteries are used for energy storage. Integrating solar cells and energy storage batteries directly enables the conversion and storage of solar energy. Based on voltage matching principles, lithium-ion batteries have a relatively high charging voltage (3.0V–4.2V), making them unsuitable for integration with solar cells. Conversely, lithium-sulfur batteries have a lower charging voltage (1.6V–2.8V), making them more suitable for integration with solar cells. Furthermore, as a replacement for commercial lithium-ion batteries, lithium-sulfur batteries have attracted significant attention due to their ultra-high theoretical energy density, low cost, and environmental friendliness.

[0003] However, the shuttle effect caused by soluble polysulfides and the slow redox kinetics in lithium-sulfur batteries result in poor electrochemical performance, thus limiting their applications. Therefore, the ingenious design of advanced photo-assisted lithium-sulfur batteries utilizing solar energy is urgently needed. Summary of the Invention

[0004] To address the above problems, this invention provides TiO2 / Co@NC composite materials, their preparation methods, and applications. The TiO2 / Co@NC composite materials can achieve high-capacity electrochemical performance using photo-assisted methods, and maintain excellent specific capacity and long-term cycling performance under high sulfur loading.

[0005] The first objective of this invention is to provide a method for preparing TiO2 / Co@NC composite materials, comprising the following steps: Polyacrylonitrile powder and carbon nanotubes were mixed in an amide-based organic solvent to obtain a first mixture; the first mixture was then used to prepare a PAN / CNT electrospun fiber membrane by electrospinning. After uniformly mixing cobalt source and 2-methylimidazole in water, the mixture is added to a PAN / CNT electrospun fiber membrane and allowed to stand to undergo a coordination reaction, resulting in an impregnated PAN / CNT electrospun fiber membrane. In this step, cobalt salt and 2-methylimidazole are mixed in an aqueous solvent using a solvent method. Cobalt ions and imidazole groups form a metal-organic framework through coordination, gradually forming a three-dimensional plate-like crystal structure as the reaction proceeds.

[0006] The impregnated PAN / CNT electrospun fiber membrane was annealed in air at 200℃~300℃, and then carbonized in argon at 750℃~800℃ to obtain the Co@NC membrane.

[0007] TiO2 was deposited on Co@NC film using a titanium source as a precursor and atomic layer deposition was used to form TiO2, thus obtaining TiO2 / Co@NC composite material.

[0008] In the preparation of this invention, carbon nanotubes are introduced into the electrospinning solution system. The core purpose is to construct a continuous and efficient three-dimensional conductive network, fundamentally solving the bottleneck problem of insufficient conductivity of traditional polymer fibers, thereby laying the material foundation for their application in high-performance electronic devices.

[0009] Then, when preparing impregnated PAN / CNT electrospun fiber membranes using a cobalt source and 2-methylimidazole, the core advantage of introducing a cobalt source alone to form ZIF-67 lies in the ability to utilize the unique physicochemical properties of cobalt to achieve performance superior to other materials in specific applications. Specifically, ZIF-67 is composed of cobalt ions and 2-methylimidazole ligands. Compared to ZIF-8, which is composed of zinc and has been studied more extensively, the choice of ZIF-67, i.e., the choice of a cobalt source, is mainly based on the following advantages:

[0010] 1. Enhanced catalytic activity. This is the most important and common reason: cobalt is an excellent catalytic active center, especially in many important chemical reactions.

[0011] 2. Enhanced electrochemical stability. Especially in aqueous solutions or electrochemical environments, ZIF-67 exhibits greater resistance to structural collapse. This means that the synthesized ZIF-67 nanosheets maintain a longer lifespan and more stable performance during application, a significant technological advantage.

[0012] 3. Unique value as a precursor or template. When ZIF-67 is calcined in an inert atmosphere, it transforms into a composite material consisting of cobalt nanoparticles embedded in a nitrogen-doped carbon matrix. This material combines the high catalytic activity of cobalt with the high conductivity and large specific surface area of ​​carbon materials, making it a top-tier electrocatalyst.

[0013] The three-dimensional sheet-like crystalline structure on the impregnated PAN / CNT electrospun fiber membrane creates a highly active interface and mass transport channels, achieving a perfect synergistic effect with the conductive fiber substrate. The three-dimensional sheet-like structure has an extremely high specific surface area, meaning that a huge number of cobalt active sites can be exposed per unit mass of material. Simultaneously, due to the thinness of the sheet-like structure itself, coupled with the three-dimensional wrinkled morphology, almost all active sites are exposed on or near the surface, allowing reactants to easily access them and greatly improving the accessibility of the active sites.

[0014] During carbonization, a series of complex chemical reactions are driven by high temperature in an oxygen-deficient environment to transform precursors such as organic ligands and polymers into highly graphitized carbon, while simultaneously reducing and reconstructing metal species into highly active nanoparticles. The argon atmosphere serves to prevent the material from being oxidized and ablated at high temperatures.

[0015] In a preferred embodiment of the present invention, the electrospinning voltage is 20kV to 25kV, the distance between the nozzle and the collector is 15cm to 20cm, and the injection speed is 0.8mL / h to 0.9mL / h. Within this parameter range, a uniform PAN / CNT electrospun fiber membrane is obtained.

[0016] In a preferred embodiment of the present invention, the molar ratio of cobalt source to 2-methylimidazole is 1:8 to 9.

[0017] In a preferred embodiment of the present invention, the settling time is 4 to 4.5 hours. This settling time allows sufficient time for the coordination reaction to form cobalt nanosheets on the PAN / CNT electrospun fiber membrane.

[0018] In a preferred embodiment of the present invention, the annealing time is 1 hour to 1.5 hours.

[0019] In a preferred embodiment of the present invention, the carbonization treatment time is 1.5h to 2h.

[0020] In a preferred embodiment of the present invention, the atomic deposition method uses a deposition temperature of 80°C to 100°C and a deposition cycle of 13 to 15 times. Under these process conditions, a uniform TiO2 coating is formed.

[0021] The second objective of this invention is to provide a TiO2 / Co@NC composite material prepared by the above-described preparation method.

[0022] A third objective of this invention is to provide the application of the aforementioned TiO2 / Co@NC composite material as a cathode in a photo-assisted lithium-sulfur battery. Specifically, the TiO2 / Co@NC composite material can be used in photo-assisted lithium-sulfur batteries and flexible photo-assisted lithium-sulfur batteries.

[0023] More preferably, in application, the TiO2 / Co@NC composite material is used as the cathode of the photo-assisted lithium-sulfur battery, and the lithium sheet is used as the anode. Under high sulfur load and illumination conditions, it can stably supply power to LED lights. Specifically, the TiO2 / Co@NC composite material is used as the positive electrode of the lithium-sulfur battery, the lithium sheet is used as the negative electrode, lithium-sulfur electrolyte is added, and a windowed button cell battery case of model 2032 is used. The photo-assisted lithium-sulfur battery is assembled in a MIKROUNA glove box filled with argon gas, with moisture and oxygen content below 1.0 ppm. Celgard 2400 is used as the separator, and lithium foil is used as the counter electrode.

[0024] Compared with the prior art, the present invention has the following beneficial effects: This invention uses a prepared PAN / CNT electrospun fiber membrane as a matrix, adds a cobalt source and 2-methylimidazole to form a metal-organic framework ZIF-67, and then obtains a Co@NC membrane through annealing and carbonization. Introducing polar molecules, such as TiO2, onto the Co@NC membrane, the resulting TiO2 / Co@NC composite material effectively improves the adsorption capacity for polysulfides. The metal-organic framework ZIF-67 has a large specific surface area and porous structure, while TiO2, as a polar molecule, participates, and the synergistic effect of the two promotes the adsorption capacity for polysulfides. TiO2 and Co3O4 form a Schottky heterojunction, and their synergistic effect, with the built-in electric field at the Schottky heterojunction interface, promotes the separation of photogenerated carriers. Excited photogenerated electrons and residual holes participate in the charging and discharging processes, respectively, promoting the redox reaction of polysulfides and improving the catalytic ability of the polysulfide conversion process. Using the TiO2 / Co@NC composite material prepared in this invention as the cathode of a photo-assisted lithium-sulfur battery, the capacity and energy density of the lithium-sulfur battery are significantly improved by introducing a light field. Under photoexcitation, the cobalt nanoparticles generate a large number of highly active hot electrons and heat through localized surface plasmon resonance, converting photoelectrons into hot electrons and reducing energy loss.

[0025] With a conventional sulfur loading of 2 mg·cm⁻¹ -2 Under these conditions, the specific capacity of the photovoltaic cell reaches its highest level of 1429.5 mAh·g after activation. -1 Furthermore, under illumination, the capacity retention of TiO2 / Co@NC remained at 94.3% after approximately 180 cycles. Simultaneously, the corresponding coulombic efficiency was also close to 99%. In contrast, the specific capacity under dark conditions was significantly lower than that under illumination. In practical applications, long-cycle tests with high sulfur loading were also conducted, at a sulfur loading of 6 mg·cm⁻¹. -2 Furthermore, under a discharge rate of 1C, the specific capacity under illumination still reaches 613.6 mAh·g after 200 cycles. -1This further demonstrates the stability and reliability of the TiO2 / Co@NC composite material under high load conditions, providing a promising path for combining optoelectronic-assisted strategies with Li-S cells. Attached Figure Description

[0026] Figure 1 This is a schematic diagram illustrating the PALSB design concept and working mechanism of the TiO2 / Co@NC photocathode of this invention.

[0027] Figure 2 The figures show the synthesis, morphology, and crystallinity characterization of TiO2 / Co@NC in Example 1 of this invention. a is a schematic diagram of the synthesis of TiO2 / Co@NC; b is a SEM image of TiO2 / Co@NC at 3 kV and 10 k magnification; c is a SEM image of TiO2 / Co@NC at 15 kV and 8 k magnification; d is a TEM image of TiO2 / Co@NC, with the inset in d being an HRTEM image of TiO2 / Co@NC. e is an XRD pattern; f is the Co2p XPS spectrum of TiO2 / Co@NC and Co@NC; and g is the Ti2p XPS spectrum of TiO2 / Co@NC.

[0028] Figure 3 Raman comparison images of TiO2 / Co@NC prepared in Example 1 and Co@NC prepared in Comparative Example 1.

[0029] Figure 4 In the diagram, a is the electric field distribution of cobalt under illumination as shown by the finite-difference time-domain method; b is the electric field distribution of cobalt and titanium dioxide under illumination as shown by the finite-difference time-domain method; c is the ultraviolet-visible absorption spectrum, and the inset in c is the Dock curve converted from the ultraviolet-visible spectrum; d is the Mott-Schottky test diagram of TiO2 / Co@NC; e is the schematic diagram of the Mott-Schottky contact before and after contact of TiO2 / Co@NC; f is the photoresponse current diagram of TiO2 / Co@NC and Co@NC; and g is the PL emission spectrum of TiO2 / Co@NC and Co@NC.

[0030] Figure 5 The figures show a comparison of the performance of the TiO2 / Co@NC battery under light and dark conditions. a) shows the UV-Vis absorption spectra of the Li2S6 solution contained in the TiO2 / Co@NC and Co@NC synthetic samples under light and dark conditions; b) is a schematic diagram of the structure of the light-assisted Li-S battery; c) shows the performance of different materials at 5 mV·s. -1 CV test graphs under illumination and no illumination conditions, where d represents TiO2 / Co@NC at 0.1 mV·s. -1 CV curves under both illuminated and dark conditions. e represents the voltage drop across the curve. Figure 5The linear scan voltammetry curve and corresponding Tafel plot are obtained from d, f is the CV curve of TiO2 / Co@NC cathode at different scan rates, and g is the Li corresponding to the CV curve. + The diffusion coefficient histogram is shown. h is the constant potential discharge curve of Li2S8 under illumination, and i is the dimensionless current-time transient graph of Li2S nucleation process in TiO2 / Co@NC battery under illumination and without illumination.

[0031] Figure 6 The following are the test graphs for the charge and discharge performance of the TiO2 / Co@NC battery of this invention: a is the EIS graph, b is the initial charge and discharge curve, c is the GCD curve under illumination and without illumination, d is the bar chart of ∆E and Q2 / Q1, e is the rate performance graph, and f is the long cycle performance at 2C.

[0032] Figure 7 The specific capacity diagrams of TiO2 / Co@NC prepared in Example 1 and Co@NC prepared in Comparative Example 1 at a discharge rate of 1C are shown.

[0033] Figure 8 In the figure, (a) is the Raman diagram of TiO2 / Co@NC under illumination, and (b) is the Raman diagram under illumination at 0.2 mA·s. -1 The charge-discharge curves of TiO2 / Co@NC at different current densities are shown in Figures 1-3. (c) is the contour plot of the Raman spectrum change of the photocathode under illumination; (d) is the Raman spectrum of the TiO2 / Co@NC battery under dark conditions; and (e) is the Raman spectrum of the TiO2 / Co@NC battery under dark conditions at 0.2 mA·s⁻¹. -1 (f) shows the charge-discharge curves of TiO2 / Co@NC at current density; (f) shows the contour plot of the Raman spectrum change of the photocathode under dark conditions.

[0034] Figure 9 This is a scan image of TiO2 / Co@NC prepared in Example 2 of the present invention.

[0035] Figure 10 This is a scan image of TiO2 / Co@NC prepared in Example 3 of the present invention. Detailed Implementation

[0036] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0037] To address the problems in the background technology, this invention provides a method for using ZIF-67-derived Co nanoparticles in combination with the typical semiconductor material TiO2. By leveraging the plasmon resonance effect of the non-noble metal nanoparticles Co and its combination with the photoelectric effect of the semiconductor TiO2, this method can be applied to the field of secondary battery energy storage, represented by lithium-sulfur batteries. In terms of material selection, this invention chooses ZIF-67-derived Co nanoparticles and the typical semiconductor material TiO2 to reveal the objective laws of the non-noble metal resonance effect and its application potential in synergistic effects with semiconductor photoelectric technology.

[0038] The polyacrylonitrile used in this invention was commercially available and had a molecular weight of 15w. The multi-walled carbon nanotubes used were purchased from Jiangsu Xianfeng Nanomaterials Technology Co., Ltd., and the product name was hydroxylated multi-walled carbon nanotubes (length) 4-6nm, with the product number 102702.

[0039] Example 1 S1. Dissolve 1g of polyacrylonitrile powder and 0.12g of multi-walled carbon nanotubes in 12mL of N,N-dimethylformamide solvent and stir continuously overnight to obtain the first mixture.

[0040] The electrospinning voltage was set to 20kV, the distance between the nozzle and the collector to 15cm, and the injection speed to 0.8mL per hour. The mixture was prepared into PAN / CNT electrospun fiber membranes, cut into 2cm×5cm pieces with a mass of 0.03g, and set aside for later use.

[0041] S2. Add Co(NO3)2·6H2O to water to obtain a 0.05 mol / L aqueous solution of cobalt nitrate.

[0042] 2-Methylimidazole was added to water to obtain a 0.4 mol / L aqueous solution of 2-methylimidazole.

[0043] 60 mL of cobalt nitrate aqueous solution was quickly poured into 60 mL of 2-methylimidazole aqueous solution and added to the PAN / CNT electrospun fiber membrane cut from S1. The membrane was left to stand in a constant temperature oven at 25°C for 4 h, then washed with deionized water and left to dry in a vacuum oven at 45°C for 12 h to obtain the impregnated PAN / CNT electrospun fiber membrane.

[0044] S3. The impregnated PAN / CNT electrospun fiber membrane is annealed in air at 250°C for 1 hour at a heating rate of 5°C / min, and then carbonized in argon at 800°C for 90 minutes at a heating rate of 5°C / min to obtain the Co@NC membrane.

[0045] S4: The Co@NC membrane prepared in S3 was placed in an atomic layer deposition chamber. At 80°C, the first precursor TiCl4 was introduced into the reaction chamber at a rate of 50 sccm and adsorbed onto the surface of ZIF-67 for 0.2 s. Then, N2 was introduced at a rate of 200 sccm to purge and remove excess TiCl4 adsorbed on the ZIF-67 surface for 1 s. The second precursor H2O reacted with the TiCl4-based molecular layer adsorbed on the ZIF-67 surface to form TiO2 and HCl gas for 0.1 s. N2 was introduced again at a rate of 200 sccm to purge the remaining H2O and generated HCl gas for 1 s. The first precursor TiCl4 and the second precursor H2O were used alternately. After 13 cycles, the thickness of TiO2 was 1 nm, and a TiO2 / Co@NC fiber membrane was obtained, denoted as TiO2 / Co@NC.

[0046] Example 2 S1. Dissolve 1g of polyacrylonitrile powder and 0.12g of multi-walled carbon nanotubes in 12mL of N,N-dimethylformamide solvent and stir continuously overnight to obtain the first mixture.

[0047] The electrospinning voltage was set to 22kV, the distance between the nozzle and the collector to 18cm, and the injection speed was set to 0.85mL per hour. The mixture was prepared into PAN / CNT electrospun fiber membranes, cut into 2cm×5cm pieces with a mass of 0.03g, and set aside for later use.

[0048] S2. Add Co(NO3)2·6H2O to water to obtain a 0.05 mol / L aqueous solution of cobalt nitrate.

[0049] 2-Methylimidazole was added to water to obtain a 0.4 mol / L aqueous solution of 2-methylimidazole.

[0050] 60 mL of cobalt nitrate aqueous solution was quickly poured into 67.5 mL of 2-methylimidazole aqueous solution and added to the PAN / CNT electrospun fiber membrane cut from S1. The membrane was left to stand in a constant temperature oven at 25°C for 4.5 h, then washed with deionized water and left to dry in a vacuum oven at 45°C for 12 h to obtain the impregnated PAN / CNT electrospun fiber membrane.

[0051] S3. The impregnated PAN / CNT electrospun fiber membrane is annealed in air at 280°C for 90 min at a heating rate of 5°C / min, and then carbonized in argon at 780°C for 100 min at a heating rate of 5°C / min to obtain the Co@NC membrane.

[0052] S4: The Co@NC membrane prepared in S3 was placed in an atomic layer deposition chamber. At 90°C, the first precursor TiCl4 was introduced into the reaction chamber at a rate of 50 sccm and adsorbed onto the surface of ZIF-67 for 0.2 s. Then, N2 was introduced at a rate of 200 sccm to purge and remove excess TiCl4 adsorbed on the ZIF-67 surface for 1 s. The second precursor H2O reacted with the TiCl4-based molecular layer adsorbed on the ZIF-67 surface to form TiO2 and HCl gas for 0.1 s. N2 was introduced again at a rate of 200 sccm to purge the remaining H2O and generated HCl gas for 1 s. The first precursor TiCl4 and the second precursor H2O were used alternately. After 14 cycles, the thickness of TiO2 was 1 nm, and the TiO2 / Co@NC fiber membrane was obtained.

[0053] Example 3 S1. Dissolve 1g of polyacrylonitrile powder and 0.12g of multi-walled carbon nanotubes in 12mL of N,N-dimethylformamide solvent and stir continuously overnight to obtain the first mixture.

[0054] The electrospinning voltage was set to 25kV, the distance between the nozzle and the collector to 20cm, and the injection speed was set to 0.9mL per hour. The mixture was prepared into PAN / CNT electrospun fiber membranes, cut into 2cm×5cm pieces with a mass of 0.03g, and set aside for later use.

[0055] S2. Add Co(NO3)2·6H2O to water to obtain a 0.05 mol / L aqueous solution of cobalt nitrate.

[0056] 2-Methylimidazole was added to water to obtain a 0.4 mol / L aqueous solution of 2-methylimidazole.

[0057] 60 mL of cobalt nitrate aqueous solution was quickly poured into 64 mL of 2-methylimidazole aqueous solution and added to the PAN / CNT electrospun fiber membrane cut from S1. The membrane was left to stand in a constant temperature oven at 25°C for 4.3 h, then washed with deionized water and left to dry in a vacuum oven at 45°C for 12 h to obtain the impregnated PAN / CNT electrospun fiber membrane.

[0058] S3. The impregnated PAN / CNT electrospun fiber membrane is annealed in air at 300°C for 80 min at a heating rate of 5°C / min, and then carbonized in argon at 700°C for 2 h at a heating rate of 5°C / min to obtain the Co@NC membrane.

[0059] S4: The Co@NC membrane prepared in S3 was placed in an atomic layer deposition chamber. At 60°C, the first precursor TiCl4 was introduced into the reaction chamber at a rate of 50 sccm and adsorbed onto the surface of ZIF-67 for 0.2 s. Then, N2 was introduced at a rate of 200 sccm to purge and remove excess TiCl4 adsorbed on the ZIF-67 surface for 1 s. The second precursor H2O reacted with the TiCl4-based molecular layer adsorbed on the ZIF-67 surface to form TiO2 and HCl gas for 0.1 s. N2 was introduced again at a rate of 200 sccm to purge the remaining H2O and generated HCl gas for 1 s. The first precursor TiCl4 and the second precursor H2O were used alternately for 15 cycles to obtain the TiO2 / Co@NC fiber membrane.

[0060] Comparative Example 1 S1. Dissolve 1g of polyacrylonitrile powder and 0.12g of multi-walled carbon nanotubes in 12mL of N,N-dimethylformamide solvent and stir continuously overnight to obtain the first mixture.

[0061] The electrospinning voltage was set to 20kV, the distance between the nozzle and the collector to 15cm, and the injection speed to 0.8mL per hour. The mixture was then prepared into a PAN / CNT electrospun fiber membrane, cut into 1.95cm×5.05cm pieces with a mass of 0.0292g, and set aside for later use.

[0062] S2. Add Co(NO3)2·6H2O to water to obtain a 0.05 mol / L aqueous solution of cobalt nitrate.

[0063] 2-Methylimidazole was added to water to obtain a 0.4 mol / L aqueous solution of 2-methylimidazole.

[0064] 60 mL of cobalt nitrate aqueous solution was quickly poured into 60 mL of 2-methylimidazole aqueous solution and added to the PAN / CNT electrospun fiber membrane cut from S1. The membrane was left to stand in a constant temperature oven at 25°C for 4 h, then washed with deionized water and left to dry in a vacuum oven at 45°C for 12 h to obtain the impregnated PAN / CNT electrospun fiber membrane.

[0065] S3. The impregnated PAN / CNT electrospun fiber membrane is annealed in air at 250°C for 1 hour at a heating rate of 5°C / min, and then carbonized in argon at 800°C for 90 minutes at a heating rate of 5°C / min to obtain a Co@NC membrane, denoted as Co@NC.

[0066] Figure 1This diagram illustrates the design concept and working mechanism of a light-assisted lithium-sulfur battery utilizing a TiO2 / Co@NC photocathode. Under light irradiation, photogenerated electrons in the semiconductor TiO2 are excited, leaving holes in the valence band and generating electron-hole pairs.

[0067] Figure 2 The term 'a' in the diagram represents the synthesis route of the TiO2 / Co@NC photocathode. This hierarchical structure was constructed through a synergistic process of electrospinning, solvothermal growth, and atomic layer deposition (ALD). The specific steps are as follows: First, a nanofiber substrate was prepared by electrospinning a composite material of polyacrylonitrile and multi-walled carbon nanotubes. Then, cobalt-based zeolite imidazolium ester framework crystals were grown in situ under controlled solvothermal conditions to achieve functionalization modification. After obtaining the Co@NC structure through pyrolysis, a precisely controlled ALD process was used for 13 cycles at 100°C to deposit a uniform TiO2 coating on the fiber surface.

[0068] from Figure 2 As can be seen from b, it exhibits the morphology of leaf-like nanosheets on a single fiber. These tightly wrapped cobalt nanosheets have a large specific surface area.

[0069] Figure 2 In the image, 'c' represents the scan image of TiO2 / Co@NC, and the bright spots in the image represent small cobalt particles.

[0070] Figure 2 In the figure, d is the TEM image of TiO2 / Co@NC. By matching the TEM lattice fringe spacing with the crystal diffraction database of the xrd image, it is shown that the obtained crystal corresponds to cobalt crystal.

[0071] Figure 2 X-ray diffraction was used to analyze the crystal phase of the metallic cobalt phase. The characteristic diffraction peak at 44.3° corresponds to the (200) crystal plane of face-centered cubic cobalt, which corresponds to JCPDS No. 41-0943, confirming the successful formation of metallic cobalt. The decrease in diffraction intensity of TiO2 / Co@NC compared to the original Co@NC indicates that the TiO2 coating is effective.

[0072] Figure 3 Raman comparison images of TiO2 / Co@NC prepared in Example 1 and Co@NC prepared in Comparative Example 1. The Raman spectra show the characteristic peak of Co at 1379 cm⁻¹. -1 D-band at 1610cm -1 The G-band vibration peak at I is a characteristic peak of carbon materials. D / I G It can reflect the electrical conductivity of a material. D / I G The smaller the value, the better the conductivity. Figure 3Raman spectroscopy analysis revealed the evolution of the carbon matrix and metal-semiconductor heterostructure. Under 532 nm laser excitation, both TiO2 / Co@NC and Co@NC composites exhibited a typical 1379 cm⁻¹. -1 D-band at 1610cm -1 The G-band vibration peaks at these locations correspond to disordered carbon and graphitized regions, respectively.

[0073] In the quantitative analysis of TiO2 / Co@NC, I D / I G The value is 1.0045, and the I of Co@NC is... D / I G The value is 0.9928, indicating that the strength ratio of TiO2 / Co@NC is higher than that of Co@NC. This change is due to the adhesion of TiO2.

[0074] Figure 2 f to g in the image show high-resolution XPS spectra of Co and Ti, respectively. Figure 2 As can be seen from f, compared to Co@NC, the characteristic peak of zero-valent cobalt confirms the presence of metallic cobalt, and the negative shift of the characteristic peak of the Co2p orbital in the composite layer indicates an increase in surface electron concentration, successfully constructing the TiO2 / Co@NC heterostructure. From Figure 2 The g-values ​​show that the characteristic peaks of Ti2p1 / 2 and 2p3 / 2 further verify the modification of TiO2.

[0075] from Figure 4 In the diagram, 'a' and 'b' represent the electric field distributions of cobalt and cobalt and titanium dioxide under illumination, as shown by the finite-difference time-domain method. Figure 4 As can be seen from 'a' in the diagram, cobalt can absorb sunlight under illumination, causing the electric field distribution on the cobalt side to radiate outwards from the center. Figure 4 As can be seen from Figure b, when cobalt and titanium dioxide come into contact to form a Schottky heterojunction, the titanium dioxide side also exhibits an enhanced electric field distribution, except for the cobalt side. This indicates that titanium dioxide also has a photoelectric response. Furthermore, the electric field strength generated when titanium dioxide comes into contact with cobalt is stronger than that generated when only the cobalt side is present. This suggests that the photogenerated electrons generated by titanium dioxide flow to the cobalt side, effectively enhancing the electric field strength on the cobalt surface.

[0076] from Figure 4 As shown in 'c', the UV-Vis absorption spectra reveal the band structure information of TiO2 / Co@NC and Co@NC. The absorption edge of TiO2 / Co@NC is 409 nm, indicating that its photoresponse range is wider.

[0077] from Figure 4 As can be seen from d and e, under illumination, the temperature of the entire battery increases, which is beneficial to improving the reaction kinetics of the Li-S battery and accelerating the redox reaction.

[0078] from Figure 4 As can be seen from f in the figure, the positive slope of the Mott-Schottky diagram indicates that TiO2 exhibits N-type semiconductor characteristics with electrons as the primary charge carriers. The flat band potential is 1.84V, which suggests that the conduction band potential of TiO2 / Co@NC is approximately 1.94V.

[0079] from Figure 4 As can be seen from g, this is the photoluminescence emission spectrum of the semiconductor. The emission intensity of TiO2 / Co@NC is much lower than that of Co@NC, indicating that the introduction of the Schottky heterojunction can reduce the recombination rate of photogenerated carriers. Specifically, photogenerated electrons are captured by Co, and photogenerated holes are captured by TiO2.

[0080] The TiO2 / Co@NC battery prepared in Example 1 of this invention was then used to characterize its performance. The characterization results are shown below. Figures 5-8 The electrolyte used in the photo-assisted lithium-sulfur battery of this invention is prepared according to the following steps:

[0081] 0.1603 g of sulfur powder and 0.045 g of lithium sulfide were dissolved in 2 mL of lithium-sulfur electrolyte at a molar ratio of sulfur powder to lithium sulfide of 5:1. The solution was then stirred vigorously at 60°C for 24 hours to obtain a Li₂S₆ solution with a concentration of 5 mol / L. The lithium-sulfur electrolyte was purchased from Dongguan Kelude New Energy Technology Co., Ltd., model KLD-S02.

[0082] Battery assembly was performed in a MIKROUNA glove box filled with argon gas, with moisture and oxygen content below 1.0 ppm. Celgard 2400 was used as the separator, and lithium foil was used as the anode. The cathode was the product prepared in Example 1 or Comparative Example 1. A 5 mm diameter window was opened on one side of the cathode box, and both sides were sealed with PET tape. 26 µL of the prepared Li₂S₆ solution was added to a container containing 2 mg·cm⁻¹ of argon gas. -2 In the sample, the E / S ratio of each cell was 10 μL mg. -1 After assembly, the battery was left to stand for 4 hours to ensure complete electrolyte penetration. This invention uses a power of 50 mW·cm⁻¹. -2 A 500W xenon lamp solar simulator and a 300nm–800nm ​​filter are used to prevent overheating. The electrode material of the light-assisted lithium-S button cell has a size of 1×1cm. 2 .

[0083] from Figure 5As shown in Figure 'a', TiO2 / Co@NC exhibits significantly better adsorption performance for LiPSs than Co@NC. This is because the presence of polar TiO2 molecules enhances the adsorption of LiPSs. Furthermore, in the dark, the TiO2 / Co@NC sample immersed in the solution appears slightly yellow, while after illumination, the solution becomes colorless and transparent. This indicates that illumination promotes the adsorption of polysulfide LiPSs by TiO2 / Co@NC. Simultaneously, after contact with a photocathode under illumination, the characteristic peak corresponding to Li2S6 in the UV-Vis spectrum is significantly weakened. This suggests that TiO2 / Co@NC has a stronger affinity for polysulfide compounds under illumination, which is more conducive to inhibiting the shuttle movement of polysulfide compounds.

[0084] from Figure 5 As shown in b, the engineering structure of the photo-assisted lithium-sulfur battery is as follows. Unlike traditional Li-S battery structures, the developed coin cell integrates a precisely designed optical window Φ=5mm within the cathode casing, at a concentration of 2mg / cm³. 2 Under sulfur loading conditions, the active region of the photocathode is strategically aligned with that of the TiO2 / Co@NC photocathode. The multilayer encapsulation structure ensures good light transmittance while maintaining the interface integrity between the lithium metal anode and the organic electrolyte system.

[0085] Figure 5 In the 'c' section, 'no Li2S6' means that no Li2S6 is added to the electrolyte, and the cathode is the product prepared in Example 1.

[0086] from Figure 5 As can be seen from 'c', the electrocatalytic polysulfide conversion kinetics were systematically studied under controlled illumination conditions using symmetrical cell cyclic voltammetry. Cyclic voltammetry was employed within a potential window of -1.0 V to 1.0 V relative to the lithium metal reference electrode, at a rate of 5 mV·s⁻¹. -1 The scan rate was used for testing. Cyclic scan results revealed fundamental differences in electrochemical behavior: the coin cell containing a blank electrolyte exhibited negligible current density, while both the Co@NC and TiO2 / Co@NC configurations showed significantly enhanced redox activity. Specifically, at 500 W / m², 2 Under sunlight irradiation, the polarization voltage of the TiO2 / Co@NC photocathode decreases, the peak current density increases, and a redox couple appears at 0.20 / 0.41V, corresponding to the cathode Li2S4 / Li2S2 and the anode L... i2 S8 / S8 phase transition. These characteristic potential pairs indicate that the redox kinetics of sulfur are improved through a dual-pathway catalysis combining plasmonic hot-electron Co nanoparticles and photogenerated carrier TiO2. It should be noted that... Figure 5In the 'c' section, TiO2 / Co@NC-L refers to data under illumination conditions, while TiO2 / Co@NC-D and Co@NC-D refer to data under darkness conditions.

[0087] from Figure 5 As can be seen from d in the figure, the TiO2 / Co@NC electrode operates within a voltage range of 1.6V to 2.8V and a voltage of 0.1mV·s. -1 CV images of Li-S coin cells under both light and dark conditions at a scan rate of [missing value].

[0088] During the cathode scan, the two reduction peaks near 2.28 V and 1.95 V are attributed to the reduction of sulfur to form long-chain polysulfides LiPSs, where n ranges from 4 to 8, and the further conversion to short-chain polysulfides LiPSs, respectively. n At this point, n is less than 4. Correspondingly, during the anodic scan, the oxidation peak near 2.50V is attributed to the conversion of Li2S / Li2S2 to long-chain LiPS. Furthermore, the negative shift of the oxidation peak and the positive shift of the reduction peak of TiO2 / Co@NC under illumination indicate that its polarization is minimal, and the reversibility during charge-discharge processes is improved.

[0089] from Figure 5 As can be seen from 'e', ​​by processing the CV curve, the linear scanning voltammetric curves and corresponding Tafel slope curves of the cathode and anode scanning processes were obtained.

[0090] During the cathode scanning process, the Tafel slope of the TiO2 / Co@NC cell under illumination was 118.09 mV·dec. -1 Under dark conditions, the Tafel slope is 162.33 mV·dec -1 During the anodic scanning process, the Tafel slope of the TiO2 / Co@NC cell under illumination was 133.05 mV·dec. -1 Under dark conditions, the Tafel slope is 214.67 mV·dec. -1 The results indicate that illumination conditions may improve the inherent electrocatalytic activity and conversion rate of polysulfides, and enhance reaction kinetics.

[0091] from Figure 5 As can be seen from f in the figure, the value is between 0.1 and 0.5 mV·s. -1 The corresponding CV curves at different scan rates were obtained. These curves were linearly fitted by the relationship between scan rate and peak current to study the effect of light on the electrochemical kinetics of Li-S cells.

[0092] The slope of the TiO2 / Co@NC curve under illumination is much greater than that of the Co@NC curve under darkness, indicating that photogenerated carriers enhance the efficiency of Li.+ The diffusion capability is enhanced. Therefore, it can be concluded that the thermal effect of localized surface plasmon resonance generated by Co particles and the photoconductive effect of TiO2 photogenerated carriers are improved.

[0093] from Figure 5 As can be seen from the 'h' value, Li₂S precipitation experiments were conducted under illumination to evaluate the catalytic conversion activity of the Li-S battery for S. Under illumination, the lithium battery achieved a nucleation capacity of 548.95 mAh·g⁻¹ within a minimum response time of 1361 seconds. -1 This indicates that the kinetics of liquid transformation are faster under light conditions, and the formation of Li2S is also faster.

[0094] Figure 5 The transient plot of dimensionless current 'i' reveals the Li₂S deposition mode under and without illumination. Under dark conditions, a two-dimensional progressive nucleation mode of Li₂S deposition is observed, while under illumination, Li₂S deposition conforms to a three-dimensional transient nucleation mode. This is attributed to the increased conductivity and surface charge concentration of the cathode under illumination, leading to closer contact between TiO₂ / Co@NC, polysulfides, and lithium ions. Therefore, hot electrons and photogenerated electrons greatly promote the dissolution of soluble polysulfides into Li₂S, thereby significantly promoting Li₂S deposition.

[0095] Figure 6 In the diagram, 'a' represents the impedance and equivalent circuit diagram of the battery under both light and dark conditions. Compared to the impedance under dark conditions, TiO2 / Co@NC exhibits the lowest impedance under light, a reduction of 13Ω. This indicates that the photoconductive effect of photogenerated carriers under light can reduce interfacial impedance and improve electrode surface dynamics.

[0096] Figure 6 In section b, the initial discharge capacity of the battery under illumination is 1281 mAh·g. -1 The polarization voltage difference (144 mV) between the first charge and second discharge plateau under illumination, compared to 181 mV under dark conditions, is denoted by ΔE. Under illumination, battery polarization is attributed to lithium-ion diffusion, which kinetically accelerates the redox conversion of lithium-ion batteries. The discharge curve of a lithium-ion battery consists of two discharge plateaus, with the high-voltage and low-voltage plateaus associated with the conversion of S8 to soluble lithium polysulfides and subsequent reduction to insoluble Li2S. Therefore, in lithium batteries based on polyphenylene sulfide (PPS) membranes, the ratio of the low-voltage plateau capacity to the high-voltage plateau capacity in the discharge curve is positively correlated with the electrocatalytic redox activity of the catalyst supported on the PPS substrate. This ratio can serve as a key indicator for evaluating the catalytic efficiency of the catalyst in the lithium polysulfide conversion reaction. The ratio of the low-voltage plateau capacity to the high-voltage plateau capacity is denoted as Q2 / Q1.

[0097] Figure 6 In the figure, 'c' represents the charge-discharge potential and time curves under illumination and darkness conditions. The discharge voltage plateau under illumination was 2.09 V. After removing the light source, the discharge voltage plateau dropped to 2.04 V, a decrease of approximately 50 mV, thus reducing the emission capability. These findings indicate that the hot electrons and photoelectrons generated by TiO2 / Co@NC lower the energy barrier of the sulfur redox reaction under illumination. After a 50-hour constant current charge-discharge test under illumination, the illumination-induced charge-discharge voltage change persisted, suggesting that the TiO2 / Co@NC cathode can stably improve the electrochemical kinetics of Li-S batteries.

[0098] Figure 6 In the figure, the Q2 / Q1 value of the battery under illumination highlights the strong redox catalytic activity of LiPSs, which is higher than the Q2 / Q1 value of 1.55 under dark conditions.

[0099] from Figure 6 As can be seen from the 'e', ​​this product has good application potential; direct light irradiation for 12 hours is sufficient to achieve the photocharging process. During the subsequent discharge process, the specific capacity of the photo-assisted lithium-sulfur battery reached 260 mAh·g. -1 .

[0100] Figure 6 In this figure, f represents the cycling performance of the TiO2 / Co@NC battery at a high current of 2C under light and dark conditions. The standard sulfur loading is 2 mg·cm⁻¹. -2 Under these conditions, the specific capacity reaches its highest level of 1429.5 mAh·g after activation. -1 Under illumination, the capacity retention of TiO2 / Co@NC remained at 94.3% after approximately 180 cycles. Simultaneously, the corresponding coulombic efficiency was close to 99%. In contrast, the specific capacity under dark conditions was significantly lower than that under illumination. In practical applications, long-cycle tests with high sulfur loadings were also conducted, such as... Figure 7 As shown. At a sulfur loading of 6 mg·cm⁻¹ -2 Furthermore, under a discharge rate of 1C, the specific capacity under illumination still reaches 613.6 mAh·g after 200 cycles. -1 This further demonstrates the stability and reliability of the TiO2 / Co@NC photocathode under high load conditions.

[0101] Figure 8 (a) and Figure 8 Figure (d) shows that during the discharge process under light irradiation, S8 2- At 153cm -1 217cm -1 and 471cm -1The Raman characteristic peak intensity gradually decreases at this point, a phenomenon corresponding to... Figure 8 (a) and Figure 8 The discharge process in (d) of the middle. Simultaneously, at 400cm... -1 and 452cm -1 S4 appeared within the range 2- and S3 2- The Raman characteristic peaks indicate the formation of long-chain and intermediate-chain polysulfides. As the discharge process progresses, these polysulfides are further reduced to insoluble Li₂S and deposited on the electrode, leading to a gradual decrease in long-chain and intermediate-chain polysulfides during the subsequent low-voltage plateau phase. This change corresponds to... Figure 8 (a) and Figure 8 The discharge process in (d) of the middle.

[0102] During the subsequent light-induced charging process, i.e. Figure 8 (a) and Figure 8 In the charging process shown in (d), the oxidation process of polysulfides can be clearly observed, which is essentially a solid-liquid transformation process of polysulfides. Compared with light-assisted lithium-sulfur batteries, although similar Raman phenomena have been observed in the charge-discharge cycles of conventional lithium-sulfur batteries, the Raman signal intensity is significantly stronger under no-light conditions. Specific data are as follows: Figure 8 (b) and Figure 8 As shown in (e) in the diagram.

[0103] It should be noted that, Figure 8 (c) in the middle is Figure 8 Another representation of (a) is obtained by drawing contour lines. Figure 8 In the diagram, (c) indicates the strength of the peak. Similarly, Figure 8 (f) in the middle is Figure 8 Another representation of (d) is obtained by drawing contour lines. Figure 8 In the figure, (f) indicates the strength of the peak.

[0104] These experimental results corroborate the aforementioned XPS analysis, fully demonstrating that hot electrons and photo-excited electrons can participate in the photo-assisted discharge process based on TiO2 / Co@NC materials, effectively promoting the reduction and conversion of S8 to polysulfides. Simultaneously, photo-excited holes can promote the oxidation process of polysulfides to S8. Therefore, the improved battery specific capacity and enhanced energy storage performance indicate that the underlying mechanism is that the TiO2 / Co@NC material promotes the redox reaction kinetics of key polysulfide intermediates such as Li2S6 and Li2S4.

[0105] Figure 9 and Figure 10The scan images of TiO2 / Co@NC prepared in Examples 2 and 3 show the morphology of leaf-like nanosheets on a single fiber. These tightly wrapped cobalt nanosheets have a large specific surface area.

[0106] In the TiO2 / Co@NC prepared by this invention, Co@NC converts photoelectrons into thermionic electrons through the plasma resonance effect of the material itself and the photothermal effect as detailed in (i) below; TiO2 participates in the charging and discharging process through the photoelectric effect mechanism described in (ii) below, promotes the redox reaction of polysulfides, and at the same time, as a polar molecule, exhibits good adsorption performance for polysulfides.

[0107] (i) Under photoexcitation, the local surface plasmon resonance of cobalt nanoparticles should generate a large number of highly active hot electrons and heat. The highly active hot electrons can directly participate in the redox reaction, and the heat can promote the continuous self-heating of the battery and promote the kinetics of polysulfide conversion reaction.

[0108] (ii) Under light irradiation, semiconductor TiO2 generates electron-hole pairs. Under the influence of the built-in electric field constructed by TiO2 and Co nanoparticles, photogenerated electrons are excited to the conduction band, while holes remain in the valence band. The photogenerated electrons and holes will participate in the charging and discharging processes, respectively, thereby promoting the redox reaction of polysulfides.

[0109] (iii) The metal-organic framework ZIF-67 possesses a large specific surface area, while TiO2, as a polar molecule, can synergistically increase the effective adsorption of polysulfides. Furthermore, in-situ Raman spectroscopy clearly demonstrates that the synergistic photoelectrocatalytic process plays a crucial role in the liquid-solid reaction stage of polysulfides. Thanks to the superior performance of the photoelectrocatalytic synergistic reaction, the photo-assisted Li-S battery exhibits a high efficiency of 1429.5 mAh·g⁻¹ under 2C conditions. -1 The study demonstrates a high discharge specific capacity and an ultra-long lifetime of approximately 180 cycles. This research offers a promising path for combining photoelectric-assisted strategies with Li-S batteries.

[0110] Quantitative analysis showed that the strength ratio of TiO2 / Co@NC was I. D / I G =1.0045, Co@NC has ID / IG=0.9928, and the strength ratio of TiO2 / Co@NC is higher than that of Co@NC. This change is due to the adhesion of TiO2. Conduction band potential: 1.94 eV, Valence band potential: 3.07 eV The temperature is 2°C, and the typical sulfur loading is 2 mg·cm³. -2 Under these conditions, the specific capacity reaches its highest level after activation, at 1429.5 mAh·g. -1Under illumination, the capacity retention of TiO2 / Co@NC remains at 94.3% after approximately 180 cycles. Simultaneously, the corresponding coulombic efficiency is close to 99%.

[0111] Sulfur loading is 6 mg·cm -2 Furthermore, at a temperature of 1°C, the specific capacity under illumination still reaches 613.6 mAh·g after 200 cycles. -1 .

[0112] Optical charging can be achieved by direct light exposure for 12 hours. During the subsequent discharge process, the specific capacity of the light-assisted lithium button battery reached 260 mAh·g. -1 .

[0113] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0114] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for preparing a TiO2 / Co@NC composite material, characterized in that, Includes the following steps: Polyacrylonitrile powder and carbon nanotubes were mixed in an amide-based organic solvent to obtain a first mixture; the first mixture was then used to prepare a PAN / CNT electrospun fiber membrane by electrospinning. After the cobalt source and 2-methylimidazole were mixed evenly in water, they were added to the PAN / CNT electrospun fiber membrane and allowed to stand to undergo a coordination reaction, thus obtaining the impregnated PAN / CNT electrospun fiber membrane. The impregnated PAN / CNT electrospun fiber membrane was annealed in air at 200℃~300℃, and then carbonized in argon at 750℃~800℃ to obtain Co@NC membrane; Using titanium as a precursor, TiO2 was deposited on Co@NC film by atomic layer deposition to obtain TiO2 / Co@NC composite material.

2. The method for preparing a TiO2 / Co@NC composite material according to claim 1, characterized in that, In the electrospinning method, the electrospinning voltage is 20kV to 25kV, the distance between the nozzle and the collector is 15cm to 20cm, and the injection speed is 0.8mL / h to 0.9mL / h.

3. The method for preparing a TiO2 / Co@NC composite material according to claim 1, characterized in that, The molar ratio of cobalt source to 2-methylimidazole is 1:8 to 9.

4. The method for preparing a TiO2 / Co@NC composite material according to claim 1, characterized in that, The settling time is 4 to 4.5 hours.

5. The method for preparing a TiO2 / Co@NC composite material according to claim 1, characterized in that, The annealing time is 1 hour to 1.5 hours.

6. The method for preparing a TiO2 / Co@NC composite material according to claim 1, characterized in that, The carbonization process takes 1.5 to 2 hours.

7. The method for preparing a TiO2 / Co@NC composite material according to claim 1, characterized in that, In atomic layer deposition, the deposition temperature is 60℃~90℃, and the deposition cycle is 13 to 15 times.

8. A TiO2 / Co@NC composite material prepared by the preparation method according to any one of claims 1 to 7.

9. The application of the TiO2 / Co@NC composite material of claim 8 as a cathode in a photo-assisted lithium-sulfur battery.

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