Preparation method of self-supporting composite sulfur positive electrode material and application thereof in lithium-sulfur battery

Abstract

The application relates to a preparation method and application of a self-supporting composite sulfur positive electrode material in a lithium-sulfur battery, and aims to solve the problems of poor catalytic activity and poor stability of the existing self-supporting positive electrode material of the lithium-sulfur battery. The method comprises the following steps: S1, preparing nanorod-shaped manganese-doped titanium dioxide; S2, loading the catalyst on a carbon source; and S3, loading active substances to obtain the self-supporting composite sulfur positive electrode material. The method does not use a binder, has good mechanical properties, provides a three-dimensional conductive network and a smooth ion migration channel, the rich macropores can effectively relieve the volume expansion before and after the positive electrode reaction, the nanorod-shaped TiO2-Mn has catalytic activity, can effectively catalyze the conversion of long-chain lithium polysulfide into short-chain lithium polysulfide, and can reduce the active substance loss in the charging and discharging process of the lithium-sulfur battery. The discharge specific capacity is 475.53 mAh / g under a large current density of 3C, and the method can be used in the field of lithium-sulfur batteries.

Description

Technical Field

[0001] This invention belongs to the field of lithium-sulfur battery technology, specifically relating to the preparation method and application of self-supporting cathode materials for lithium-sulfur batteries. Background Technology

[0002] With the rapid development of society and technology, people's demand for energy is also gradually increasing. In existing energy storage systems, the actual energy density of lithium-ion batteries has approached their theoretical value, limiting their development in the high-energy-density market. Among new energy storage devices, lithium-sulfur batteries have attracted widespread attention from researchers due to their high theoretical specific capacity (1675 mAh / g) and theoretical specific energy (2600 Wh / kg), low cost, and environmental friendliness, and are considered a promising next-generation battery system. However, lithium-sulfur batteries still face some technical challenges, such as the shuttle effect of polysulfides, the poor conductivity of sulfur, and volume expansion during charge and discharge. These problems affect the electrochemical performance of lithium-sulfur batteries and hinder their further development.

[0003] In recent years, the use of self-supporting substrates to prepare binder-free electrodes has attracted the attention of researchers. Traditional coated electrodes require the addition of binders, and the material loses capacity under uneven stress. Flexible self-supporting electrodes do not use organic solvents and binders, are environmentally friendly, have easily controllable product structures, can effectively suppress sulfur expansion and adsorb polysulfides, and their better mechanical properties can prevent energy storage devices from being damaged under external forces. Currently, research on self-supporting cathode materials for lithium-sulfur batteries focuses on carbonaceous frameworks with microporous and porous structures. Although current self-supporting cathode materials have greatly improved the physical confinement effect of polysulfides, the low chemical activity and nonpolarity of carbon itself limit its chemical effect on polysulfides. CN110438798A discloses a method for preparing lithium-sulfur battery cathode materials by electrospinning a mixed solution of polymethyl methacrylate and polyacrylonitrile. However, the electrospun fibers prepared by this method have insufficient mechanical strength and catalytic activity, and cannot effectively solve the problems of sulfur volume expansion during charge and discharge and poor cathode reaction kinetics. Summary of the Invention

[0004] This invention aims to address the problems of poor catalytic activity and stability in existing self-supporting cathode materials for lithium-sulfur batteries. It provides a self-supporting cathode material for lithium-sulfur batteries and its electrospinning preparation method. This method is simple, avoiding the cumbersome traditional grinding and coating processes, and also avoids the use of inactive materials (such as conductive agents and binders). Based on existing carbon self-supporting cathode materials, this invention introduces a novel manganese (Mn)-doped titanium dioxide (TiO2) catalyst to obtain the self-supporting cathode material TiO2-Mn@CNF / S for lithium-sulfur batteries. This improves the overall polarity of the electrode material, which is beneficial for the chemisorption of polysulfides, thereby enhancing the catalytic activity of the material, better limiting the shuttle effect of polysulfides, and thus improving the electrochemical performance of lithium-sulfur batteries.

[0005] The preparation method of the self-supporting composite sulfur cathode material of the present invention is carried out according to the following steps:

[0006] I. Preparation of manganese-doped titanium dioxide nanorods:

[0007] Titanium source and manganese salt are dissolved in solvent I and stirred until homogeneous to obtain a mixed solution; at the same time, spinning polymer template is dissolved in solution II and stirred until homogeneous to obtain a spinning polymer template solution; the mixed solution and the spinning polymer template solution are mixed and stirred at room temperature for 10-12 h to obtain an electrospinning solution;

[0008] The electrospinning solution was drawn into a syringe, and the distance between the receiver of the electrospinning device and the metal needle of the syringe was adjusted to 10~20 cm. Electrospinning was carried out under the conditions of DC voltage of 15~20 kV and injection rate of 0.6~1.5 mL / h. The solution was then vacuum dried to obtain a fiber membrane.

[0009] The fiber membrane is cut into pieces and placed in a tube furnace. It is first heated to 300-500℃ in air and calcined for 2-4 hours, and then heated to 600-800℃ and calcined for 2-4 hours to obtain the positive electrode catalyst, namely nanorod-shaped manganese-doped titanium dioxide.

[0010] II. Catalyst loading on carbon source:

[0011] Weigh out the positive electrode catalyst, carbon source, and solvent III; wherein the positive electrode catalyst accounts for 5% to 20% of the mass of the carbon source, and the solvent III accounts for 200% to 380% of the mass of the carbon source; first, add the positive electrode catalyst to solvent III and sonicate it for 10 to 30 minutes to facilitate dispersion; then add the carbon source to solvent III in which the positive electrode catalyst is dispersed, and stir at room temperature for 10 to 12 hours to obtain an electrospinning solution;

[0012] The electrospinning solution was drawn into a syringe, and the distance between the receiver of the electrospinning device and the metal needle of the syringe was adjusted to 10~20cm. Electrospinning was carried out under the conditions of DC voltage of 10~18kV and injection rate of 0.5~1.2mL / h. After vacuum drying, a porous polymer fiber membrane was obtained.

[0013] The porous polymer fiber membrane was placed in a muffle furnace and heated to 220-280℃ at a rate of 2-5℃ / min, and held for 1-3 h for pre-oxidation treatment. Then, in a tube furnace, under inert gas protection, the temperature was raised to 700-1000℃ at a rate of 2-5℃ / min and held for 2-4 h for carbonization treatment to obtain a self-supporting carbon skeleton membrane.

[0014] III. Loading of active substances:

[0015] The self-supporting carbon skeleton membrane prepared in step two is immersed in carbon disulfide solution, taken out and dried, and then placed in a furnace and heated to 120~155℃ for 10~12 h under an inert atmosphere for heat treatment to obtain the self-supporting composite sulfur cathode material.

[0016] Furthermore, the titanium source mentioned in step one is tetrabutyl titanate.

[0017] Furthermore, the manganese salt mentioned in step one is manganese acetate or manganese nitrate.

[0018] Furthermore, the solvent I mentioned in step one is a mixed solution of ethanol and acetic acid in a volume ratio of 1:(1~3).

[0019] Furthermore, solvent II mentioned in step one is N,N-dimethylpyrrolidone.

[0020] Furthermore, the spinning polymer template mentioned in step one is polyvinylpyrrolidone.

[0021] Furthermore, the carbon source mentioned in step two is one or more of polyacrylonitrile, polyvinylpyrrolidone, and polypropylene carbonate.

[0022] Furthermore, solvent III mentioned in step two is N,N-dimethylformamide.

[0023] Furthermore, the concentration of sulfur in the carbon disulfide solution described in step three is 30~100 mg / ml.

[0024] Furthermore, the inert gas mentioned in step three is argon or nitrogen.

[0025] The application of the self-supporting composite sulfur cathode material prepared by the above method is to use it in lithium-sulfur batteries.

[0026] Furthermore, the lithium-sulfur battery is assembled with a self-supporting composite sulfur cathode material as the cathode, along with a negative electrode, a separator, active material, and an ether electrolyte.

[0027] Furthermore, the method for preparing the ether electrolyte is as follows: LiNO3 is added as an additive at a mass percentage concentration of 2% to a 1.0 M LITFSI solution; wherein the solvent of the LITFSI solution is a mixture of dioxolane (DOL) and ethylene glycol dimethyl ether (DME) in a volume ratio of 1:1.

[0028] The self-supporting composite cathode material of the present invention is composed of a porous conductive carbon skeleton, a cathode reaction catalyst, and an active material; wherein the cathode reaction catalyst is formed by electrospinning followed by heat treatment; the catalyst loading is formed by co-spinning of the catalyst and a carbon source, wherein the mass of the catalyst is 5% to 20% of the carbon source, and the carbon source is one or more of polyacrylonitrile, polyvinylpyrrolidone, and polypropylene carbonate; the loading of the active material is achieved by solution impregnation.

[0029] The beneficial effects of this invention are as follows:

[0030] (1) The method of preparing self-supporting cathode material by electrospinning technology has the advantages of low cost, controllable morphology, easy adjustment of composition and stable structure. Based on the existing carbon self-supporting cathode material, a new catalyst of manganese (Mn) doped titanium dioxide (TiO2) is introduced. The activity of metal and non-metal centers of transition metal catalyst is improved by single doping, and the self-supporting cathode material TiO2-Mn@CNF for lithium-sulfur battery is obtained. This improves the overall polarity and catalytic activity of the electrode material, better restricts the shuttle effect of polysulfides, and thus improves the electrochemical performance of lithium-sulfur battery.

[0031] (2) The self-supporting composite cathode material prepared by this invention has certain flexibility and good strength, and can effectively suppress the problems of sulfur volume expansion and polysulfide shuttle effect during charging and discharging. At the microstructure level, the one-dimensional conductive network formed by the interwoven carbon nanofibers can effectively improve the transport efficiency of lithium ions and electrons, which can alleviate the problem of large volume strain during cycling. At the same time, the nanoscale TiO2-Mn loaded on the surface is conducive to the full exposure of the catalyst active sites, which improves the utilization rate of the catalyst, accelerates the cathode reaction kinetics, and reduces the dissolution of intermediate polysulfides. At the electronic structure level, Mn doping further activates the catalytic activity of the metal active site Ti, so that Mn-doped TiO2 has a stronger chemical binding effect on polysulfides, and produces a strong adsorption effect, which significantly enhances the catalytic activity of TiO2 catalyst, thereby enhancing the cathode reaction kinetics and further reducing the dissolution of intermediate polysulfides. Thanks to the ingeniously designed microstructure and optimized electronic structure of the cathode material, as well as the improved cathode reaction kinetics, the self-supporting cathode material of this invention enables the assembly of lithium-sulfur batteries with high specific capacity and high cycle stability, achieving stable operation under high loads and thus possessing greater practical application value. This lithium-sulfur battery exhibits a discharge specific capacity as high as 1183.21 mAh / g in the first cycle at a current density of 0.2 C, retains a discharge specific capacity of 1010.14 mAh / g after 100 stable cycles, and achieves a discharge specific capacity of 475.53 mAh / g at a current density of 3 C. Attached Figure Description

[0032] Figure 1 The images shown are scanning electron microscope (SEM) images of the fiber precursor and nanorod-shaped TiO2-Mn obtained in step one of Example 1.

[0033] Figure 2 The images show the physical diagram of the self-supporting electrode obtained in Example 1 and the contact angle test diagram of the electrolyte on the self-supporting electrode.

[0034] Figure 3 This is a cycle performance test of the TiO2-Mn@CNF / S self-supporting cathode in Example 1 at a current density of 0.2C.

[0035] Figure 4 Cyclic voltammetry test of the TiO2-Mn@CNF / S self-supporting cathode in Example 1.

[0036] Figure 5 This is a test of the catalytic ability of the TiO2-Mn@CNF support material for Li2S deposition in Example 1.

[0037] Figure 6 The CV test of the TiO2-Mn@CNF support material in Example 1 is shown.

[0038] Figure 7 The image shows the cycling diagram of the TiO2-Mn@CNF / S self-supporting cathode prepared in Example 1 at a 3C current density.

[0039] Figure 8 This is a cycling diagram of a lithium-sulfur battery assembled with the self-supporting electrode prepared in Example 2.

[0040] Figure 9 This is a cycling diagram of a lithium-sulfur battery assembled with the self-supporting electrode prepared in Example 3. Detailed Implementation

[0041] The beneficial effects of the present invention will be verified using the following examples.

[0042] Example 1: The preparation method of the self-supporting composite sulfur cathode material in this example is carried out according to the following steps:

[0043] I. Preparation of manganese-doped titanium dioxide nanorods:

[0044] 1.70 g of tetrabutyl titanate and 0.41 g of manganese acetate were dissolved in a mixed solution of 3 mL acetic acid and 2 mL ethanol and stirred for 3 h to obtain a mixed solution; at the same time, 2.0 g of polyvinylpyrrolidone (PVP) was directly dissolved in 20 mL of N,N-dimethylformamide and stirred for 3 h to obtain a spinning polymer template solution; the mixed solution and the spinning polymer template solution were mixed and stirred at room temperature for 12 h to obtain a uniform and transparent electrospinning solution;

[0045] The electrospinning solution was drawn into a 10 mL syringe. The distance between the receiver of the electrospinning device and the metal needle of the syringe was adjusted to 15 cm. Electrospinning was carried out under the conditions of DC voltage of 18 kV and injection rate of 1.2 mL / h. The solution was then vacuum dried to obtain a fiber membrane.

[0046] The fiber membrane was cut into pieces and placed in a ceramic boat. The ceramic boat was then placed in a tube furnace and calcined in air at a heating rate of 5℃ / min to 500℃ for 2 hours. Then, it was calcined at the same heating rate to 700℃ for 2 hours to obtain nanorod-shaped manganese-doped titanium dioxide (TiO2-Mn) catalyst.

[0047] II. Catalyst loading on carbon source:

[0048] Weigh 0.26 g of TiO2-Mn catalyst, 3.0 g of polyacrylonitrile and 30 mL of N,N-dimethylformamide; first add TiO2-Mn catalyst to N,N-dimethylformamide and sonicate for 30 min to facilitate dispersion; then add polyacrylonitrile and stir at room temperature for 12 h to dissolve evenly to obtain electrospinning solution.

[0049] The electrospinning solution was drawn into a 5mL syringe. The distance between the receiver of the electrospinning device and the metal needle of the syringe was adjusted to 15cm. Electrospinning was carried out under the conditions of DC voltage of 16kV and injection rate of 0.8mL / h. After vacuum drying, a porous polymer fiber membrane was obtained.

[0050] The porous polymer fiber membrane was placed in a muffle furnace and heated to 280°C at a rate of 2°C / min, and held at that temperature for 2 hours for pre-oxidation treatment. Then, in a tube furnace, under nitrogen protection, the temperature was increased to 900°C at a rate of 5°C / min and held at that temperature for 2 hours for carbonization treatment, to obtain a self-supporting carbon skeleton membrane, denoted as TiO2-Mn@CNF.

[0051] III. Loading of active substances:

[0052] The self-supporting carbon skeleton membrane prepared in step two was cut into circular pieces with a diameter of 12 mm, then immersed in a carbon disulfide solution with a sulfur concentration of 100 mg / mL, dried, and then placed in a furnace and heated to 155 °C under a nitrogen atmosphere for 12 h for heat treatment to obtain the self-supporting composite sulfur cathode material, denoted as TiO2-Mn@CNF / S.

[0053] Using the self-supporting composite sulfur cathode material prepared in Example 1 as the cathode, the cathode, separator, electrolyte, and lithium metal anode were placed inside the battery casing. The separator was Celgard 2500, and the electrolyte was formed by adding LiNO3 as an additive at a mass concentration of 2% to a 1.0 M LITFSI solution. The LITFSI solution was a mixture of DOL and DME with a volume ratio of 1:1 as the solvent. After the battery was packaged, it was left to stand for 20 h to obtain a lithium-sulfur battery.

[0054] In step three of this embodiment, the masses of the self-supporting carbon skeleton membrane before and after impregnation are recorded as m. o The loading of active substance S is calculated using m' and m'.

[0055]

[0056] The loading of active material S in the self-supported composite sulfur cathode material obtained in Example 1 is 1.0~1.1 mg / cm³. 2 .

[0057] Figure 1 These are scanning electron microscope (SEM) images of the fiber membrane obtained in step one of Example 1 and the nanorod-shaped manganese-doped titanium dioxide (TiO2-Mn) catalyst, where a is the fiber membrane and b is the TiO2-Mn catalyst. Figure 1 It can be seen that the obtained TiO2-Mn catalyst has a nanorod morphology with a certain porosity structure.

[0058] Figure 2 These are physical images of the self-supporting composite sulfur cathode material obtained in Example 1 and contact angle test results of the electrolyte on the self-supporting electrode. Image a is the physical image, and image b is the contact angle test result. Image a shows that the self-supporting electrode has good flexibility and mechanical strength. Image b shows that the contact angle between the self-supporting electrode and the electrolyte is 5.5°, indicating that the self-supporting electrode has good wettability to the electrolyte.

[0059] The lithium-sulfur battery assembled in Example 1 was tested for its cycle performance by constant current charge and discharge. The constant current charge and discharge test conditions were: room temperature (25°C) and the charge and discharge test voltage window was 1.7~2.8V. Figure 3 Cycling performance of the TiO2-Mn@CNF / S self-supporting electrode was tested at a current density of 0.2C. The lithium-sulfur battery exhibited a first-cycle discharge specific capacity of 1183.21 mAh / g and a discharge specific capacity of 1010.14 mAh / g after 100 cycles, demonstrating good long-term cycling stability. Furthermore, calculations showed that the battery's average coulombic efficiency per cycle was 99%, indicating excellent cycling stability.

[0060] Figure 4 Cyclic voltammetry tests were performed on the lithium-sulfur battery assembled with the TiO2-Mn@CNF / S self-supporting electrode obtained in Example 1 at 0.1 mV / s. The analysis showed that the oxidation peak potential was 2.39 V and the peak current was 3.46 mA; the first reduction peak potential was 2.29 V and the peak current was 0.80 mA; and the second reduction peak potential was 2.05 V and the peak current was 1.57 mA. Calculations showed that the oxidation peak area and the reduction peak area were basically equal, indicating that the redox reaction at the cathode has good reversibility.

[0061] The catalytic ability of the self-supporting support for Li₂S deposition was tested using a constant voltage method. The constant voltage discharge test conditions were as follows: at room temperature (25°C), the lithium-sulfur battery was first discharged at a constant current to 2.05V, and then discharged at a constant voltage (1.95~2.06V) until the current stabilized (i ≤ 0.01mA). The deposition capacity of lithium sulfide (Li₂S) was evaluated by comparing the peak position and peak area with their corresponding values. Figure 5 This is a graph showing the catalytic deposition capability of the TiO2-Mn@CNF / S self-supporting electrode obtained in Example 1 for Li2S. From... Figure 5 It can be seen that the deposition peak of the TiO2-Mn@CNF / S self-supporting electrode appears at about 180s, which is relatively early and has a large peak area. The calculated lithium sulfide deposition capacity is 343.29 mAh / g, indicating that the cathode has good catalytic conversion ability for Li2S deposition.

[0062] The strength of the redox reaction at the positive electrode was evaluated by cyclic voltammetry (CV) testing using a symmetrical cell assembly. Both the positive and negative electrodes of the symmetrical cell were 1.13 cm⁻¹. 2 The self-supporting carbon framework film TiO2-Mn@CNF prepared in step two of Example 1 used 40 μL of 0.2 M Li2S6 electrolyte. The electrolyte was prepared by adding sulfur powder and Li2S powder to 10 mL of lithium-sulfur electrolyte in a glove box at a molar ratio of 5:1, heating and stirring at 40°C until completely dissolved, yielding a brownish-yellow solution. The CV testing conditions were: room temperature (25°C), voltage range of -0.8 to 0.8 V, and scan rate of 10 mV / s. Evaluation was performed by comparing redox currents. Figure 6 CV testing of a symmetric cell based on the self-supporting carbon framework film TiO2-Mn@CNF prepared in Example 1. Figure 6 It can be seen that when the scan rate is 10 mV / s, the redox current of TiO2-Mn@CNF is 58.1 mA. The large redox current indicates that the self-supporting electrode pair has good electrochemical activity, thereby promoting the positive electrode reaction kinetics.

[0063] Figure 7 The graph shows the cycling performance of the TiO2-Mn@CNF / S self-supporting composite sulfur cathode prepared in Example 1 at 3C current density. Figure 7 It can be seen that the discharge specific capacity is 475.53 mAh / g in the first cycle at a current density of 3 C, and 324.65 mAh / g after 100 cycles, demonstrating good high-rate performance and cycle stability.

[0064] Example 2: The preparation method of the self-supporting composite sulfur cathode material in this example is carried out according to the following steps:

[0065] I. Preparation of manganese-doped titanium dioxide nanorods:

[0066] 1.70 g tetrabutyl titanate and 0.61 g manganese acetate were dissolved in a mixed solution of 3 mL acetic acid and 2 mL ethanol and stirred for 3 h to obtain a mixed solution; at the same time, 2.0 g polyvinylpyrrolidone (PVP) was directly dissolved in 20 mL N,N-dimethylformamide and stirred for 3 h to obtain a spinning polymer template solution; the mixed solution and the spinning polymer template solution were mixed and stirred at room temperature for 12 h to obtain a uniform and transparent electrospinning solution;

[0067] The electrospinning solution was drawn into a 10 mL syringe. The distance between the receiver of the electrospinning device and the metal needle of the syringe was adjusted to 15 cm. Electrospinning was carried out under the conditions of DC voltage of 18 kV and injection rate of 1.2 mL / h. The solution was then vacuum dried to obtain a fiber membrane.

[0068] The fiber membrane was cut into small pieces and placed inside a ceramic boat. The ceramic boat was then placed in a tube furnace and heated in air at 5°C for 1 minute. -1 The temperature was increased to 500℃ and calcined for 2 hours at the same heating rate, and then increased to 700℃ and calcined for 2 hours at the same heating rate to obtain nanorod-shaped manganese-doped titanium dioxide (TiO2-Mn) catalyst.

[0069] II. Catalyst loading on carbon source:

[0070] Weigh 0.26 g of TiO2-Mn catalyst, 3.0 g of polyacrylonitrile and 30 mL of N,N-dimethylformamide; first add TiO2-Mn catalyst to N,N-dimethylformamide and sonicate for 30 min to facilitate dispersion; then add polyacrylonitrile and stir at room temperature for 12 h to dissolve evenly to obtain electrospinning solution.

[0071] The electrospinning solution was drawn into a 5mL syringe. The distance between the receiver of the electrospinning device and the metal needle of the syringe was adjusted to 15cm. Electrospinning was carried out under the conditions of DC voltage of 16kV and injection rate of 0.8mL / h. After vacuum drying, a porous polymer fiber membrane was obtained.

[0072] The porous polymer fiber membrane was placed in a muffle furnace and heated to 280°C at a rate of 2°C / min and held for 2 hours for pre-oxidation treatment. Then, in a tube furnace, under nitrogen protection, the temperature was raised to 900°C at a rate of 5°C / min and held for 2 hours for carbonization treatment to obtain a self-supporting carbon skeleton membrane.

[0073] III. Loading of active substances:

[0074] The self-supporting carbon skeleton membrane prepared in step two was cut into circular pieces with a diameter of 12 mm, then immersed in a carbon disulfide solution with a sulfur concentration of 100 mg / mL, dried, and then placed in a furnace and heated to 155 °C under a nitrogen atmosphere for 12 h for heat treatment to obtain the self-supporting composite sulfur cathode material, denoted as TiO2-Mn@CNF / S.

[0075] The active material S loading of the self-supporting composite sulfur cathode material obtained in Example 2 was 1.0~1.1 mg / cm³. 2 .

[0076] Lithium-sulfur batteries were prepared using the same method as in Example 1, and cycle tests were performed. The cycle diagram of the TiO2-Mn@CNF / S prepared in Example 2 at a current density of 0.5 C is shown below. Figure 8 As shown, from Figure 8It can be seen that the discharge specific capacity is 1008.62 mAh / g in the first cycle at a current density of 0.5 C, and 790.61 mAh / g after 100 cycles.

[0077] Example 3: The preparation method of the self-supporting composite sulfur cathode material in this example is carried out according to the following steps:

[0078] I. Preparation of manganese-doped titanium dioxide nanorods:

[0079] 1.70 g tetrabutyl titanate and 1.22 g manganese acetate were dissolved in a mixed solution of 3 mL acetic acid and 2 mL ethanol and stirred for 3 h to obtain a mixed solution; at the same time, 1.0 g polyvinylpyrrolidone (PVP) was directly dissolved in 10 mL N,N-dimethylformamide and stirred for 3 h to obtain a spinning polymer template solution; the mixed solution and the spinning polymer template solution were mixed and stirred at room temperature for 12 h to obtain a uniform and transparent electrospinning solution;

[0080] The electrospinning solution was drawn into a 10 mL syringe. The distance between the receiver of the electrospinning device and the metal needle of the syringe was adjusted to 15 cm. Electrospinning was carried out under the conditions of DC voltage of 18 kV and injection rate of 1.2 mL / h. The solution was then vacuum dried to obtain a fiber membrane.

[0081] The fiber membrane was cut into small pieces and placed inside a ceramic boat. The ceramic boat was then placed in a tube furnace and heated in air at 5°C for 1 minute. -1 The temperature was increased to 500℃ and calcined for 2 hours at the same heating rate, and then increased to 700℃ and calcined for 2 hours at the same heating rate to obtain nanorod-shaped manganese-doped titanium dioxide (TiO2-Mn) catalyst.

[0082] II. Catalyst loading on carbon source:

[0083] Weigh 0.26 g of TiO2-Mn catalyst, 3.0 g of polyacrylonitrile and 30 mL of N,N-dimethylformamide; first add TiO2-Mn catalyst to N,N-dimethylformamide and sonicate for 30 min to facilitate dispersion; then add polyacrylonitrile, heat to 60℃ and stir for 12 h to dissolve evenly to obtain electrospinning solution;

[0084] The electrospinning solution was drawn into a 5mL syringe. The distance between the receiver of the electrospinning device and the metal needle of the syringe was adjusted to 15cm. Electrospinning was carried out under the conditions of DC voltage of 16kV and injection rate of 0.8mL / h. After vacuum drying, a porous polymer fiber membrane was obtained.

[0085] The porous polymer fiber membrane was placed in a muffle furnace and heated to 280°C at a rate of 2°C / min and held for 2 hours for pre-oxidation treatment. Then, in a tube furnace, under nitrogen protection, the temperature was raised to 900°C at a rate of 5°C / min and held for 2 hours for carbonization treatment to obtain a self-supporting carbon skeleton membrane.

[0086] III. Active substance loading:

[0087] The self-supporting carbon skeleton membrane prepared in step two was cut into circular pieces with a diameter of 12 mm, then immersed in a carbon disulfide solution with a sulfur concentration of 100 mg / mL, dried, and then placed in a furnace and heated to 155 °C under a nitrogen atmosphere for 12 h for heat treatment to obtain the self-supporting composite sulfur cathode material, denoted as TiO2-Mn@CNF / S.

[0088] The loading of active material S in the self-supported composite sulfur cathode material of Example 3 is 1.0~1.1 mg / cm³. 2 .

[0089] Lithium-sulfur batteries were prepared using the same method as in Example 1, and cycle tests were performed. Figure 9 The image shows the cycling curve of TiO2-Mn@CNF / S prepared in Example 3 at a current density of 0.5 C. Figure 9 It can be seen that the discharge specific capacity is 901.61 mAh / g in the first cycle at a current density of 0.5 C, and 572.39 mAh / g after 100 cycles.

[0090] This invention employs electrospinning and subsequent heat treatment processes to construct a three-dimensional ordered self-supporting composite sulfur cathode material. The self-supporting cathode material prepared by this method does not require a binder, possesses excellent mechanical properties, and provides a three-dimensional conductive network and smooth ion migration channels. Its abundant macropores effectively increase sulfur loading, and the nanorod-shaped TiO2-Mn exhibits catalytic activity, effectively catalyzing the conversion of long-chain lithium polysulfides to short-chain lithium polysulfides, reducing active material loss during lithium-sulfur battery charging and discharging. The self-supporting composite sulfur cathode material synthesized by this invention has a stable structure, a simple process, and effectively improves the electrochemical performance of lithium-sulfur batteries.

Claims

1. A method for preparing a self-supporting composite sulfur cathode material, characterized in that, This method is performed in the following steps: I. Preparation of manganese-doped titanium dioxide nanorods: Titanium source and manganese salt are dissolved in solvent I and stirred until homogeneous to obtain a mixed solution; at the same time, spinning polymer template is dissolved in solvent II and stirred until homogeneous to obtain a spinning polymer template solution; the mixed solution and the spinning polymer template solution are mixed and stirred at room temperature for 10-12 h to obtain an electrospinning solution; wherein the titanium source is tetrabutyl titanate and the manganese salt is manganese acetate or manganese nitrate. The electrospinning solution was drawn into a syringe, and the distance between the receiver of the electrospinning device and the metal needle of the syringe was adjusted to 10~20 cm. Electrospinning was carried out under the conditions of DC voltage of 15~20 kV and injection rate of 0.6~1.5 mL / h. The solution was then vacuum dried to obtain a fiber membrane. The fiber membrane is cut into pieces and placed in a tube furnace. It is first heated to 300-500℃ in air and calcined for 2-4 hours, and then heated to 600-800℃ and calcined for 2-4 hours to obtain the positive electrode catalyst, namely nanorod-shaped manganese-doped titanium dioxide. II. Catalyst loading on carbon source: Weigh out the positive electrode catalyst, carbon source, and solvent III; wherein the positive electrode catalyst accounts for 5% to 20% of the mass of the carbon source, and the solvent III accounts for 200% to 380% of the mass of the carbon source; first, add the positive electrode catalyst to solvent III and sonicate it for 10 to 30 minutes to facilitate dispersion; then add the carbon source to solvent III in which the positive electrode catalyst is dispersed, and stir at room temperature for 10 to 12 hours to obtain an electrospinning solution; The electrospinning solution was drawn into a syringe, and the distance between the receiver of the electrospinning device and the metal needle of the syringe was adjusted to 10~20cm. Electrospinning was carried out under the conditions of DC voltage of 10~18kV and injection rate of 0.5~1.2mL / h. After vacuum drying, a porous polymer fiber membrane was obtained. The porous polymer fiber membrane was placed in a muffle furnace and heated to 220-280℃ at a rate of 2-5℃ / min, and held for 1-3 hours for pre-oxidation treatment. Then, in a tube furnace, under inert gas protection, the temperature was raised to 700-1000℃ at a rate of 2-5℃ / min and held for 2-4 hours for carbonization treatment to obtain a self-supporting carbon skeleton membrane. III. Loading of active substances: The self-supporting carbon skeleton membrane prepared in step two is immersed in a sulfur / carbon disulfide solution, removed and dried, and then placed in a furnace and heated to 120~155℃ under an inert atmosphere for 10~12 h for heat treatment to obtain a self-supporting composite sulfur cathode material.

2. The method for preparing a self-supporting composite sulfur cathode material according to claim 1, characterized in that, Solvent I mentioned in step one is a mixed solution of ethanol and acetic acid in a volume ratio of 1:(1~3).

3. The method for preparing a self-supporting composite sulfur cathode material according to claim 1, characterized in that, Solvent II mentioned in step one is N,N-dimethylpyrrolidone.

4. The method for preparing a self-supporting composite sulfur cathode material according to claim 1, characterized in that, The spinning polymer template mentioned in step one is polyvinylpyrrolidone.

5. The method for preparing a self-supporting composite sulfur cathode material according to claim 1, characterized in that, The carbon source mentioned in step two is one or more of polyacrylonitrile, polyvinylpyrrolidone, and polypropylene carbonate.

6. The method for preparing a self-supporting composite sulfur cathode material according to claim 1, characterized in that, Solvent Ⅲ mentioned in step 2 is N,N-dimethylformamide.

7. The application of the self-supporting composite sulfur cathode material prepared by the method of claim 1, characterized in that, This application involves using self-supporting composite sulfur cathode materials in lithium-sulfur batteries.

8. The application of the self-supporting composite sulfur cathode material according to claim 7, characterized in that, The lithium-sulfur battery is assembled with a self-supporting composite sulfur cathode material as the cathode, and a negative electrode, a separator, and an ether electrolyte.

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