A method for preparing carbon-coated titanium dioxide nanocatalysts, cathode sheets, and lithium-sulfur batteries.

Abstract

This invention relates to the field of lithium-sulfur battery preparation technology, and discloses a surface oxidation technique for improving the adsorption performance of lithium-sulfur batteries. The technique includes the following steps: isopropyl titanate and ethanol are mixed and stirred, polyacrylonitrile is added, and after stirring to dissolve, the solution is freeze-dried to obtain a precursor. The precursor is calcined under an inert atmosphere for 4-8 hours to obtain carbon-coated titanium dioxide nanoparticles; subsequently, the carbon-coated titanium dioxide nanoparticles are etched under ozone for 30-90 minutes to finally obtain oxidized carbon-coated titanium dioxide nanoparticles. This invention provides a surface oxidation technique for improving the adsorption performance of lithium-sulfur batteries, effectively increasing the porosity and specific surface area of ​​carbon-coated nanomaterials, enhancing the adsorption capacity for polysulfides, and improving the cycle stability of lithium-sulfur batteries. This method is simple to operate and easy to synthesize.

Description

Technical Field

[0001] This invention relates to the field of lithium-sulfur battery preparation technology, and in particular to an oxidized carbon-coated titanium dioxide nanocatalyst, a positive electrode, and a method for preparing lithium-sulfur batteries. Background Technology

[0002] With the rapid development of the new energy industry and the rise of portable electronic devices, the demand for batteries with high energy density and long cycle life is increasing. Among technologies that "surpass lithium-ion batteries," lithium-sulfur batteries stand out due to their low cost and high theoretical capacity (1675 mAh g⁻¹). -1 ) and high energy density (2600 Wh kg) -1 Lithium-sulfur batteries stand out due to their advantages, making them one of the most promising candidate batteries. However, the commercial viability of lithium-sulfur batteries is severely hampered by problems such as poor conductivity of sulfur and severe shuttle and slow conversion kinetics of soluble polysulfides.

[0003] Among them, the back-and-forth movement of polysulfides between the positive and negative electrodes is one of the important reasons for the rapid capacity decay and poor cycle stability of lithium-sulfur batteries. To solve the above problems, the main approach currently adopted is to load or incorporate catalyst materials into lithium-sulfur batteries, such as membrane modification and functionalization of sulfur host materials, to promote the adsorption and conversion of polysulfides and improve the cycle life of the battery. Carbon-coated materials, as one of the catalyst materials for lithium-sulfur batteries, play a huge role in lithium-sulfur batteries, thanks to the following characteristics of the material: (1) The surface carbon layer can serve as a stable interface, protecting the internal active material from direct contact with the electrolyte, thereby reducing potential adverse reactions on the particle surface and helping to improve cycle stability and battery life. (2) The carbon layer surrounding the active material forms a continuous conductive network, promoting the rapid transfer of electrons inside the electrode material and significantly improving the overall conductivity of the composite material, thereby improving the charge and discharge performance of the battery. (3) The surface carbon layer can provide a buffer for the active material, reducing the volume expansion and contraction of the active material during charge and discharge, helping to maintain the integrity of the material structure, thereby improving the cycle performance of the battery. However, some carbon-coated materials cannot maximize their catalytic performance due to problems such as dense particle distribution, small carbon layer spacing, and the shielding of active sites. Summary of the Invention

[0004] To address the technical problems mentioned in the background section, this invention provides a titanium dioxide nanoparticle catalyst coated with a carbon oxide layer, a positive electrode, and a method for preparing a lithium-sulfur battery.

[0005] This invention provides a catalyst material surface oxidation technology that increases the porosity and specific surface area of ​​the material. While preserving the original structure of the carbon-coated material, it introduces more CO active sites to enhance the adsorption of polysulfides. Furthermore, by replacing conductive carbon black with this material in the positive electrode of lithium-sulfur batteries, it accelerates the conversion kinetics of polysulfides while ensuring efficient electron transport in the lithium-sulfur battery. The catalyst battery treated with this technology not only exhibits significant adsorption performance but also good cycle stability and rate performance.

[0006] This invention is achieved using the following technical solution: a method for preparing titanium dioxide nanoparticles coated with a carbon oxide layer, comprising the following steps:

[0007] Isopropyl titanate and ethanol were stirred and mixed, then polyacrylonitrile was added and stirred to dissolve, thus obtaining a precursor solution.

[0008] The precursor material was then obtained by freeze-drying, and the dried material was then calcined in an inert atmosphere for 4-8 hours to obtain carbon-coated titanium dioxide nanoparticles.

[0009] The carbon-coated titanium dioxide nanoparticles were etched under ozone for 30-90 min to finally obtain titanium dioxide nanoparticles coated with an oxide layer.

[0010] Preferably, the precursor solution contains 1.0-3.0 wt% isopropyl titanate, 6.0-10.0 wt% polyacrylonitrile, and 10-40 mL of ethanol; the solution is stirred for 4-8 h; and the freeze-drying time is 36-48 h.

[0011] Preferably, the precursor material is transferred to a tube furnace for calcination, and then calcined at 600-800℃ for 4-8 hours under an argon atmosphere with an argon flow rate of 20-50 mL min-1, followed by annealing and cooling.

[0012] Preferably, the ozone purity is 20-40% and the treatment time is 30-90 min.

[0013] The present invention proposes a titanium dioxide nanocatalyst coated with an oxide layer, which is prepared by the above method.

[0014] This invention proposes a method for preparing a positive electrode sheet, comprising the following steps: melting sulfur and multi-walled carbon nanotubes in a certain proportion to obtain negative sulfur carbon nanotubes, then mixing negative sulfur carbon nanotubes, conductive carbon black, titanium dioxide nanocatalyst coated with carbon oxide layer and binder in a certain proportion to prepare a slurry, uniformly coating the obtained slurry on a current collector, drying and cutting to obtain a battery positive electrode sheet.

[0015] Titanium dioxide nanocatalyst coated with carbon oxide layer is mixed with binder in appropriate ratio, and the resulting slurry is uniformly coated on current collector, dried and cut to obtain symmetrical battery electrode.

[0016] Furthermore, the ratio of sulfur to multi-walled carbon nanotubes is 3:2, and the ratio of negative sulfur carbon nanotubes to conductive carbon black to catalyst to binder is 8:1:1:1.

[0017] Furthermore, the ratio of sulfur to multi-walled carbon nanotubes is 7:3, and the ratio of negative sulfur carbon nanotubes to conductive carbon black to catalyst to binder is 7:2:1:1.

[0018] Preferably, the electrode drying temperature is 40~60℃, and the drying time is 6~8 h.

[0019] This invention conducts a visual adsorption experiment, as detailed below:

[0020] In an anhydrous and oxygen-free glove box, sublimed sulfur and lithium sulfide were dissolved in a 5:1 molar ratio in a mixed solvent of 1,3-dioxolane (DOL) and ethylene glycol dimethyl ether (DME) (volume ratio 1:1). The mixture was heated and stirred for 48 h to obtain a 0.05 M Li₂S₆ solution. The obtained solution was then diluted to a certain concentration with DOL / DME (volume ratio 1:1), and appropriate amounts of catalyst were added to a certain amount of the diluent, shaken well, and allowed to stand for 10 h. The color change of the solution was recorded. Subsequently, a small amount of the supernatant after adsorption was taken, diluted with anhydrous ethanol, and subjected to UV-Vis spectroscopy.

[0021] This invention proposes a method for assembling a lithium-sulfur battery, comprising the following steps: in an anhydrous and oxygen-free glove box, the positive electrode shell, the aforementioned positive electrode sheet, electrolyte, separator, lithium sheet, gasket, and negative electrode shell are assembled in sequence, and then pressed with a packaging machine to obtain a button-type lithium-sulfur battery.

[0022] In an anhydrous and oxygen-free glove box, the positive electrode shell, electrode, electrolyte, separator, electrolyte, electrode, gasket, and negative electrode shell are assembled in sequence, and then pressed together with a packaging machine to obtain a symmetrical battery.

[0023] Compared to the unoxidized catalyst, the catalyst treated with the present invention exhibits significantly enhanced adsorption of polysulfides. Symmetrical cell test results also demonstrate that this technology can improve the conversion kinetics between the catalyst and polysulfides. Furthermore, compared to batteries with unoxidized catalysts, the batteries assembled using the present invention show significantly improved cycle stability and rate performance.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] 1. This invention provides a method for preparing titanium dioxide nanomaterials coated with a carbon oxide layer. A precursor material is obtained through simple chemical synthesis, followed by a one-step calcination to obtain the carbon-coated nanomaterial. This method is simple to operate and easy to synthesize.

[0026] 2. This invention provides a simple surface oxidation technique that can increase the specific surface area of ​​materials, enhance the adsorption and conversion performance of polysulfides, and accelerate the polysulfide conversion kinetics. Carbon-coated nanomaterials treated with oxygen are used to prepare lithium-sulfur battery cathodes. During the multi-step conversion of sulfur, intermediate polysulfides are rapidly adsorbed and converted, which helps improve the cycle stability of lithium-sulfur batteries.

[0027] 3. This invention provides a method for preparing a lithium-sulfur battery cathode by applying a catalyst to a sulfur cathode to form a cathode sheet, which not only ensures the electron transport efficiency but also effectively suppresses the back-and-forth movement of polysulfides. Attached Figure Description

[0028] Figure 1 These are X-ray diffraction (XRD) patterns of the carbon-coated titanium dioxide nanoparticle catalyst prepared in this invention before and after oxidation treatment.

[0029] Figure 2 These are transmission electron microscope (TEM) images of the carbon-coated titanium dioxide nanoparticle catalyst prepared in this invention before and after oxidation treatment.

[0030] Figure 3 These are high-resolution transmission electron microscopy (HR-TEM) images of the carbon-coated titanium dioxide nanoparticle catalyst prepared in this invention before and after oxidation treatment.

[0031] Figure 4 These are the adsorption-desorption curves and pore size distribution diagrams of the carbon-coated titanium dioxide nanoparticle catalyst prepared in this invention before and after oxidation treatment.

[0032] Figure 5 This is the infrared (IR) spectrum of the carbon-coated titanium dioxide nanoparticle catalyst prepared in this invention before and after oxidation treatment.

[0033] Figure 6 This is the UV-Vis absorption spectrum of the carbon-coated titanium dioxide nanoparticle catalyst prepared in this invention before and after oxidation treatment, showing the adsorption of Li2S6.

[0034] Figure 7 The figures show the symmetrical cyclic voltammetry (CV) curves and Tafel slope curves of the carbon-coated titanium dioxide nanoparticle catalyst prepared in this invention before and after oxidation treatment.

[0035] Figure 8This is a charge-discharge curve of a lithium-sulfur battery assembled before and after oxidation treatment of the carbon-coated titanium dioxide nanoparticle catalyst prepared in this invention at 0.1C.

[0036] Figure 9 This is a cyclic voltammetry (CV) curve of a lithium-sulfur battery assembled before and after oxidation treatment with the carbon-coated titanium dioxide nanoparticle catalyst prepared in this invention, at 0.1 mV s⁻¹.

[0037] Figure 10 This is a graph showing the cycling performance of lithium-sulfur batteries assembled before and after oxidation treatment using the carbon-coated titanium dioxide nanoparticle catalyst prepared in this invention, at a 1C rate.

[0038] Figure 11 This is a graph showing the rate performance of lithium-sulfur batteries assembled before and after oxidation treatment using the carbon-coated titanium dioxide nanoparticle catalyst prepared in this invention, at 0.2C~5C. Detailed Implementation

[0039] The present invention will now be further described in conjunction with the accompanying drawings and specific embodiments. It should be noted that, without conflict, the various embodiments or technical features described below can be arbitrarily combined to form new embodiments.

[0040] All chemical reagents used in this invention are analytical grade isopropyl titanate, ethanol, and polyacrylonitrile. Sublimed sulfur was purchased from Sinopharm Chemical Reagent Co., Ltd., and multi-walled carbon nanotubes were purchased from Shenzhen Suiheng Technology Co., Ltd. The electrolyte and diaphragm used in step 4 were purchased from Suzhou Duoduo Chemical Technology Co., Ltd.

[0041] Example 1:

[0042] Catalyst preparation: 300 μL of isopropyl titanate was added to 20 mL of anhydrous ethanol and stirred for 5 min. 1.8 g of polyacrylonitrile was added and stirred for 6 h to obtain a precursor solution. The solution was then freeze-dried in a freeze dryer for 36 h. Subsequently, the precursor material was freeze-dried at 5 ℃ for 3 min under an argon atmosphere. -1 The temperature was increased to 600 °C in a tube furnace and annealed for 4 h. The resulting material was then treated with 30% ozone for 60 min to oxidize the surface, yielding oxygen-treated carbon-coated titanium dioxide nanoparticles.

[0043] Example 2: Preparation of the electrode: (1) Sublimed sulfur and multi-walled carbon nanotubes were mixed in a ratio of 7:3 and then melted at 155°C for 12 h to obtain negative sulfur carbon nanotubes. Then, negative sulfur carbon nanotubes, conductive carbon black, catalyst and binder were mixed in a ratio of 7:2:1:1 (where the binder was polyvinylidene fluoride), and an appropriate amount of N-methylpyrrolidone solvent was added. The mixture was ground and prepared into a uniform slurry, which was then coated onto a current collector (the current collector was carbon-coated aluminum foil). After vacuum drying at 60°C for 8 h, the mixture was cut into round pieces with a diameter of 12 mm to obtain the positive electrode of the battery. (2) The catalyst and binder were mixed in a suitable ratio to obtain a uniform slurry, which was then coated onto a current collector. After vacuum drying at 60°C for 8 h, the mixture was cut into round pieces with a diameter of 12 mm to obtain the symmetrical battery electrode.

[0044] Example 3: Assembly of lithium-sulfur battery: (1) The lithium-sulfur battery was assembled in a glove box filled with argon gas, with a water content of less than 0.01 ppm and an oxygen content of less than 0.2 ppm. First, the positive electrode containing the catalyst was placed in a CR2016 positive electrode shell, and 20 μL of lithium-sulfur battery electrolyte (a mixed solution of 1,3-dioxolane (DOL) and ethylene glycol dimethyl ether (DME) containing 1 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and 1% lithium nitrate (LiNO3) in a volume ratio of 1:1) was added. Then, a Celgard 2500 separator, a 14 mm commercial lithium sheet, a stainless steel gasket, and a negative electrode shell were added in sequence to obtain a coin-type lithium-sulfur battery. The battery electrochemical performance was tested by first forming the battery at a rate of 0.1 C, and then cycling it at 1 C. The test voltage range was 1.7~2.8 V. (2) With other conditions unchanged, the positive and negative electrodes are replaced with the symmetrical battery electrodes prepared in step 2. 20 μL of the 0.05 M Li₂S₆ prepared in step 2 is added to the positive electrode side, and 20 μL of the above lithium-sulfur battery electrolyte is added to the negative electrode side. The electrodes are assembled sequentially in the order of positive electrode shell, electrode, electrolyte, separator, electrolyte, electrode, gasket, and negative electrode shell, and then packaged to obtain the symmetrical battery. The cyclic voltammetry test voltage range for the symmetrical battery is -1 to 1 V, and the scan rate is 1 mV s. -1 .

[0045] Experimental Example: Implementation of the Visual Adsorption Experiment: In an anhydrous and oxygen-free glove box, 80 mg of sublimed sulfur and 23 mg of lithium sulfide were dissolved in 10 mL of a mixed solvent of 1,3-dioxolane (DOL) and ethylene glycol dimethyl ether (DME) (volume ratio 1:1). The mixture was heated and stirred for 48 h to obtain a 0.05 M Li₂S₆ solution. The prepared solution was then diluted 20 times with DOL / DME (volume ratio 1:1), and 15 mg of catalyst was added to 2 mL of the diluted solution, shaken well, and allowed to stand for 10 h. The color change of the solution was recorded. Subsequently, a small amount of the supernatant after adsorption was taken and diluted 100 times with anhydrous ethanol for UV-Vis spectroscopy.

[0046] Comparative Example 1:

[0047] Comparative Example 1 provides a method for preparing a catalyst material, with other conditions being the same as in Example 1, except that in step 1 of Example 1, the material is not subjected to ozone treatment after annealing.

[0048] Results analysis:

[0049] As attached Figure 1 As shown, the X-ray diffraction peaks of the catalyst before and after oxygen treatment did not shift, indicating that the oxygen treatment of the material does not change the phase structure of the catalyst material, which remains anatase phase.

[0050] As attached Figure 2 The TEM images show that there are more porous pores between the oxygen-treated catalyst particles.

[0051] As attached Figure 3 As shown, the lattice spacing of the catalyst before and after oxygen treatment is 0.362 nm and 0.361 nm, respectively, belonging to the (101) crystal plane of the anatase phase. The lattice stripes of the catalyst after oxygen treatment are more obvious, indicating that the technology does not change the phase of the material, but can expose more catalyst active sites.

[0052] As attached Figure 4 As shown, the oxygen-treated catalyst exhibits increased porosity and a significantly improved BET specific surface area, nearly six times that of the untreated catalyst. (See attached figure.) Figure 2 Analysis suggests that this is because after the catalyst undergoes surface oxidation treatment, some of the carbon layer peels off, thereby exposing more pores and increasing the specific surface area of ​​the material.

[0053] As attached Figure 5As shown in the infrared spectral curves before and after oxygen treatment, the intensity of the CO stretching vibration peak in the example indicates an increase in the number of carbon-oxygen binding sites on the catalyst. This suggests that after ozone is introduced, some carbon on the catalyst surface is converted, providing more pores. In addition, some carbon binds with oxygen, enhancing the oxidation activity of the catalyst material and facilitating the adsorption and conversion of polysulfides by the catalyst.

[0054] As attached Figure 6 Visualization of polysulfide adsorption experiments showed that after 10 hours, the Li₂S₆ solution in the example had become completely transparent, while the color of the comparative solution remained almost unchanged compared to the original solution. Furthermore, UV-Vis absorption spectroscopy of the supernatant from each solution revealed that the example solution exhibited the lowest absorbance. These results indicate that surface oxidation treatment can effectively improve the adsorption and conversion of polysulfides.

[0055] As attached Figure 7 As shown, the CV curve results of the symmetrical battery indicate that the lithium-sulfur battery of the embodiment has a higher response current, and the Tafel fitting curve results show that the redox current density of the embodiment is higher. These results indicate that surface oxidation treatment of the material accelerates the redox conversion kinetics of polysulfides, which helps to suppress the shuttle movement of polysulfides and improve the cycle stability of the lithium-sulfur battery.

[0056] As attached Figure 8 As shown in the first charge-discharge curve of the battery at 0.1C, it can be seen that compared with the comparative battery, the discharge specific capacity (1110.11 mAh g) is significantly lower. -1 The example battery exhibits a higher discharge specific capacity, reaching 1212.17 mAhg. -1 This indicates that the catalytic performance of the material is significantly increased after oxidation treatment.

[0057] As attached Figure 9 As shown, the lithium-sulfur battery at 0.1 mV s -1 The CV curves below show that the embodiment has a higher response current and a larger integral area compared to the comparative example, which indicates that the redox conversion kinetics of the battery in the embodiment is faster and can provide higher battery capacity.

[0058] As attached Figure 10 As shown in the figure, the cycle curve of the lithium-sulfur battery after 600 cycles at 1C rate is shown. The results show that the embodiment has better cycle capacity and cycle stability. After 600 cycles, the capacity retention rate of the embodiment is 77.24%, with an average capacity decay of 0.037% per cycle, while the average capacity decay of the comparative embodiment is 0.043% per cycle. This indicates that the material can promote the conversion of polysulfides and reduce the capacity decay caused by polysulfide shuttle.

[0059] As attached Figure 11 As shown in the cycle rate diagram of the lithium-sulfur battery at different rates, the discharge specific capacity of the example at 0.2C, 0.5C, 1C, 2C, and 5C is 829.04 mAh g. -1 655.22 mAh g -1 594.93 mAh g -1 518.13mAh g -1 412.95 mAh g -1 Furthermore, the capacity remained stable even after cycling at high rates and returning to low rates. Moreover, compared to the comparative example, the embodiment maintained higher capacity stability under high-rate conditions.

[0060] Therefore, the experimental results show that the catalyst material treated with oxygen can enhance the adsorption and conversion performance of lithium-sulfur batteries, accelerate the redox conversion kinetics of lithium-sulfur batteries, and improve the battery's discharge specific capacity, cycle stability, and rate performance.

[0061] This invention provides a surface oxidation technology that can effectively increase the specific surface area of ​​materials, enhance their adsorption capacity for polysulfides, promote the conversion between sulfur species, and accelerate the reaction kinetics of lithium-sulfur batteries. Furthermore, this method is simple to operate, low in cost, and conducive to the large-scale synthesis and preparation of materials. This invention provides a new solution to the problems of poor adsorption performance and low conversion efficiency of carbon-coated catalyst materials for lithium-sulfur batteries.

[0062] The above embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention shall fall within the scope of protection claimed by the present invention.

Claims

1. A method for preparing a titanium dioxide nanocatalyst coated with a carbon oxide layer, characterized in that, Includes the following steps: Isopropyl titanate and ethanol were stirred and mixed, polyacrylonitrile was added and stirred to dissolve, and a precursor solution was obtained. The precursor material was then obtained by freeze-drying. The dried material was then calcined in an inert atmosphere for 4-8 h to obtain carbon-coated titanium dioxide nanoparticles. The carbon-coated titanium dioxide nanoparticles were then etched under ozone for 30-90 minutes to finally obtain titanium dioxide nanoparticles coated with carbon oxide layer. The precursor solution contains 1.0–3.0 wt% isopropyl titanate, 6.0–10.0 wt% polyacrylonitrile, and 10–40 mL of ethanol; the solution is stirred for 4–8 h; and the freeze-drying time is 36–48 h. The precursor was transferred to a tube furnace for calcination, followed by argon gas flow at a rate of 20–50 mL / min. -1 Calcine at 600-800℃ for 4-8 hours, then anneal and cool down.

2. The method for preparing a titanium dioxide nanocatalyst coated with a carbon oxide layer as described in claim 1, characterized in that, The ozone purity is 20-40%, and the treatment time is 30-90 minutes.

3. A titanium dioxide nanocatalyst coated with a carbon oxide layer, characterized in that, It is prepared by the method described in any one of claims 1-2.

4. A method for preparing a positive electrode sheet, characterized in that, The process includes the following steps: melting sulfur and multi-walled carbon nanotubes in a certain proportion to obtain negative sulfur carbon nanotubes; then mixing negative sulfur carbon nanotubes, conductive carbon black, titanium dioxide nanocatalyst coated with carbon oxide layer as described in claim 3, and binder in a certain proportion to prepare a slurry; uniformly coating the obtained slurry onto the current collector, drying and cutting to obtain the battery positive electrode sheet. Titanium dioxide nanocatalyst coated with carbon oxide layer is mixed with binder in appropriate ratio, and the resulting slurry is uniformly coated on current collector, dried and cut to obtain symmetrical battery electrode.

5. The method for preparing a positive electrode sheet as described in claim 4, characterized in that, The ratio of sulfur to multi-walled carbon nanotubes is 3:2, and the ratio of negative sulfur carbon nanotubes to conductive carbon black to catalyst to binder is 8:1:1:

1.

6. The method for preparing a positive electrode sheet as described in claim 4, characterized in that, The ratio of sulfur to multi-walled carbon nanotubes is 7:3, and the ratio of negative sulfur carbon nanotubes to conductive carbon black to catalyst to binder is 7:2:1:

1.

7. The method for preparing a positive electrode sheet as described in claim 4, characterized in that, The electrode drying temperature is 40~60℃, and the drying time is 6~8 h.

8. A method for assembling a lithium-sulfur battery, characterized in that, The process includes the following steps: In an anhydrous and oxygen-free glove box, the positive electrode shell, the positive electrode sheet prepared by any of the methods described in claims 4-7, the electrolyte, the separator, the lithium sheet, the gasket, and the negative electrode shell are assembled in sequence, and then pressed together with a packaging machine to obtain a coin-type lithium-sulfur battery. In an anhydrous and oxygen-free glove box, the positive electrode shell, electrode, electrolyte, separator, electrolyte, electrode, gasket, and negative electrode shell are assembled in sequence, and then pressed together with a packaging machine to obtain a symmetrical battery.

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