A preparation method of a fluorine-doped NiCo2O4 bimetallic oxide positive electrode material for a lithium-sulfur battery, a preparation method of a positive electrode for a lithium-sulfur battery, and a lithium-sulfur battery

Abstract

This invention discloses a method for preparing fluorine-doped NiCo2O4 bimetallic oxide cathode material for lithium-sulfur batteries. By using fluorine doping to modify the bimetallic oxide nickel cobalt oxide, fluorine doping can induce lattice distortion through its electronegativity difference, generating a large number of oxygen vacancies and regulating the electronic state of metal ions to enhance the interaction between the cathode material and polysulfides. This invention also applies the prepared fluorine-doped NiCo2O4 bimetallic oxide cathode material for lithium-sulfur batteries to the preparation of cathodes for lithium-sulfur batteries and lithium-sulfur batteries, exhibiting good energy storage performance and electrochemical reversibility under low temperature, room temperature and high temperature conditions.

Description

Technical Field

[0001] This invention relates to the field of lithium-sulfur battery technology, specifically to a method for preparing a fluorine-doped NiCo2O4 bimetallic oxide cathode material for lithium-sulfur batteries, a method for preparing a cathode for lithium-sulfur batteries, and a lithium-sulfur battery. Background Technology

[0002] Lithium-sulfur batteries have become a research hotspot in the energy storage field due to their ultra-high theoretical specific capacity (1675 mAh / g), energy density (approximately 2500 Wh / kg), and resource and environmental advantages. Their applications in electric vehicles, portable electronic devices, and grid-scale energy storage are highly attractive. However, the development of lithium-sulfur batteries still faces many challenges, including the poor conductivity of sulfur, the shuttle effect of lithium polysulfides, and the volume expansion of electrodes during charging and discharging. Furthermore, in extreme environments, such as low temperatures, the battery's specific capacity decays and its cycle stability is significantly reduced, while high temperatures exacerbate the shuttle effect, leading to an exponential increase in the rate of irreversible loss of active materials. In addition, high temperatures can induce uncontrolled side reactions at the electrode-electrolyte interface, repeated rupture and reconstruction of the SEI film, accelerated corrosion and pulverization of the lithium metal anode, and ultimately, thermal runaway of the battery.

[0003] To overcome these challenges, various strategies have been proposed in recent decades, including membrane modification, binder selection, electrolyte optimization, and anode protection. These methods have improved the performance of lithium-sulfur batteries to some extent. However, most current work focuses on improving performance under single conditions (low or high temperature), failing to achieve good operation across the entire temperature range from -40°C to 60°C or even wider. As humanity continues to explore the world, the ability of energy systems to operate effectively over a wide temperature range is a critical issue.

[0004] In lithium-sulfur batteries, single-metal oxides are fundamental electrocatalytic systems for regulating LiPSs (lithium polysulfides) conversion and mitigating the shuttle effect due to their well-defined active sites and controllable chemical reactions. They can efficiently anchor LiPSs through metal-sulfur coordination bonds. Furthermore, they are low-cost and have mature processes, making them potential for large-scale application. However, their inherent limitations make it difficult to satisfy the SRR (Solution-Reduction Ratio) requirement. SRR is an electrochemical process occurring on the positive electrode side of a lithium-sulfur battery, involving a series of reactions from the reduction of ring S8 to various polysulfide intermediates, and the final reaction to form Li2S, with the overall chemical formula S8 + 16e⁻. - +16Li +→8Li2S) synergistic requirements of "strong adsorption-fast catalysis-high stability": single metal sites are prone to adsorption-catalytic performance imbalance. At the same time, its intrinsic band gap is wide, its conductivity is poor, and its electron transfer efficiency is low, which makes it unable to accelerate the conversion of key intermediates and suppress the accumulation of polysulfides, which seriously limits the wide temperature range application of lithium-sulfur batteries.

[0005] Compared to single-metal oxides as electrocatalysts in lithium-sulfur batteries, bimetallic oxides possess more core advantages, resulting in significantly superior overall performance when used as lithium-sulfur battery support materials. Among them, spinel-type nickel cobalt oxide (NiCo2O4), with its unique mixed valence structure and synergistic effect, has become a preferred material for cathode supports in lithium-sulfur batteries at room temperature. However, traditional nickel cobalt oxide materials struggle to meet the core requirements of high-performance batteries under extreme temperatures, particularly regarding catalytic performance and shuttle effect suppression. Therefore, developing a cathode material for lithium-sulfur batteries with excellent performance over a wide temperature range is of great significance.

[0006] In view of this, the inventor of this case conducted in-depth research, which led to the creation of this case. Summary of the Invention

[0007] The purpose of this invention is to provide a method for preparing fluorine-doped NiCo2O4 bimetallic oxide cathode material for lithium-sulfur batteries, and to apply the prepared fluorine-doped NiCo2O4 bimetallic oxide cathode material for lithium-sulfur batteries to prepare cathodes for lithium-sulfur batteries and lithium-sulfur batteries. It exhibits good energy storage performance and electrochemical reversibility under low temperature, room temperature and high temperature conditions.

[0008] To achieve the above objectives, the solution of the present invention is: A method for preparing a fluorine-doped NiCo2O4 bimetallic oxide cathode material for lithium-sulfur batteries includes the following steps: Step 1: First, add 1.2~3.6 mmol Co(NO3)2·6H2O and 0.6~1.8 mmol Ni(NO3)2·6H2O to 50~150 mL of deionized water and stir for 20 min to disperse evenly. Then add 0.72 g of urea and heat in an oil bath at 80℃ for 15 min. Then add 1.5 g of solid ammonium fluoride and continue heating and stirring at 80℃ for 12 h to obtain the precursor solution. The ratio of Co(NO3)2·6H2O : Ni(NO3)2·6H2O : deionized water : urea : ammonium fluoride is 1.2 mmol : 0.6 mmol : 50 mL : 0.24 g : 0.5 g. Step 2: Then, the obtained precursor solution is transferred to a 200mL polytetrafluoroethylene reactor and hydrothermally reacted at 120℃ for 12h. The product is then washed and dried. Step 3: Finally, place the dried product in a tube furnace and heat it to 350°C at a heating rate of 2°C / min under air atmosphere, and calcine for 8 h to obtain the black fluorine-doped NiCo2O4 bimetallic oxide cathode material for lithium-sulfur batteries, denoted as F-NiCo2O. 4-x Material.

[0009] In step 2, the product is washed with deionized water 3 to 5 times and dried by vacuum drying at a temperature of 60 to 80°C for 10 to 12 hours.

[0010] The fluorine-doped NiCo2O4 bimetallic oxide cathode material used in the lithium-sulfur battery has a bowl-shaped stacked structure.

[0011] The fluorine-doped NiCo2O4 bimetallic oxide cathode material used in the lithium-sulfur battery has a particle size of 4~5μm.

[0012] A method for preparing a positive electrode for lithium-sulfur batteries includes the following steps: Step 1: First, F-NiCo2O 4-x The material and sublimed sulfur were ground evenly at a mass ratio of 1:3, placed in a weighing bottle, put into a forced-air drying oven, and heat-treated at 155℃ for 6 hours. After cooling, the sulfur-loaded composite material was obtained. Step 2, then 15 wt A % aqueous dispersion of acrylonitrile multi-component copolymer (model LA-132) was diluted to 4%. wt %~6 wt An aqueous dispersion of % acrylonitrile multi-component copolymer was sealed and stirred continuously for 10-14 h to obtain a milky white viscous binder dispersion. Step 3: Then, the sulfur-loaded composite material, conductive carbon black and the prepared binder dispersion are dissolved in a mixture of water and ethanol in proportion, and stirred in a ball mill for 10-12 hours to obtain a uniformly mixed slurry. Step 4: Then, the prepared slurry is coated onto aluminum foil, placed in a vacuum drying oven, and dried at 55~68℃ for 10~15 hours. Finally, it is cut to obtain the positive electrode for lithium-sulfur batteries.

[0013] In step 3, the mass ratio of the binder in the sulfur-loaded composite material, conductive carbon black, and binder dispersion is 6.5~7.5 : 1.7~2.3 : 1.

[0014] In step 3, the volume ratio of water to ethanol is 1:3. The amount of the mixture is determined based on the total volume of the sulfur-loaded composite material and the conductive carbon black. The volume ratio of the mixture to the total volume of the sulfur-loaded composite material and the conductive carbon black is 0.8~1:1~1.2.

[0015] The sulfur loading of the positive electrode used in the lithium-sulfur battery is 1.2~15 mg / cm³. 2 .

[0016] A lithium-sulfur battery includes a positive electrode, a positive electrode shell, a lithium-sulfur electrolyte, a polypropylene separator, and a negative electrode shell. The positive electrode, positive electrode shell, lithium-sulfur electrolyte, polypropylene separator, and negative electrode shell are assembled to form the lithium-sulfur battery. The positive electrode is a positive electrode for lithium-sulfur batteries, and the amount of lithium-sulfur electrolyte added is 35~70 μL.

[0017] By adopting the above technical solution, the present invention provides a method for preparing a fluorine-doped NiCo2O4 bimetallic oxide cathode material for lithium-sulfur batteries. By using fluorine-doped nickel cobalt oxide, fluorine doping can induce lattice distortion through its electronegativity difference, resulting in the generation of a large number of oxygen vacancies and regulating the electronic state of metal ions, thereby strengthening the interaction between the cathode material and polysulfides. In addition, the unique bowl-shaped stacked spherical structure of the material and the LiF-CEI film generated in situ on the cathode side during battery operation after fluorine doping can effectively alleviate volume expansion while suppressing the shuttle effect and optimizing electron transport efficiency, thereby effectively improving the adaptability of the cathode material in a wide temperature range.

[0018] The lithium-sulfur battery uses a fluorine-doped NiCo2O4 bimetallic oxide cathode material (F-NiCo2O4). 4-x The material is used to prepare the positive electrode for lithium-sulfur batteries and lithium-sulfur batteries, and has the following advantages: 1. Stable operation of lithium-sulfur batteries in extreme low-temperature environments was achieved. Even at -40℃, the battery maintained stable cycling, and after 100 cycles at a current density of 0.2 C, the reversible specific capacity remained at 349.7 mAh g. -1 ; 2. F-NiCo2O 4-x The material possesses excellent polysulfide confinement capability and rapid redox reaction kinetics, which can effectively suppress the shuttle effect exacerbated under high-temperature conditions. As a host material for sulfur in lithium-sulfur batteries, it retains a performance of 1161.31 mAh g⁻¹ after 100 cycles under high temperature of 60℃ and high current density of 2C. - ¹ High reversible specific capacity with a capacity decay rate as low as 0.011% per cycle; 3. F-NiCo2O 4-x The material achieves ultra-high sulfur utilization and excellent long-cycle stability at room temperature. When used as the positive electrode host material for lithium-sulfur batteries, it retains a 587.58 mAh g⁻¹ after 600 cycles at a high current density of 5 C. -¹ Stable specific capacity with a capacity decay rate as low as 0.016% per revolution; 4. F-NiCo2O 4-x The material exhibits excellent high sulfur loading capacity, making it suitable as a cathode host material for lithium-sulfur batteries at 10 mg / cm³. -1 Under high sulfur load, it can still maintain 530.27 mAh g⁻¹ after 100 cycles at a current density of 0.5 C. -1 Specific capacity.

[0019] Therefore, the fluorine-doped NiCo2O4 bimetallic oxide cathode material prepared by this invention exhibits good energy storage performance and electrochemical reversibility when applied to lithium-sulfur batteries under low temperature, room temperature and high temperature conditions. Attached Figure Description

[0020] Figure 1 F-NiCo2O 4-x A diagram illustrating the intrinsic reaction mechanism of the material as the cathode in a lithium-sulfur battery. Figure 2 The F-NiCo2O prepared in Example 1 4-x Electron microscopy (EM) images of the material, where a, b, and c are SEM images at different magnifications; d is the EDS image corresponding to b; e is the TEM image; and f is the total stress, Exx, Eyy, and stress diagrams in the Exy direction obtained from GPA stress analysis. Figure 3 The F-NiCo2O prepared in Example 1 4-x Characterization diagrams of the materials and the NiCo2O4 material prepared in Comparative Example 1, where a is an XRD comparison diagram, b is an EPR comparison diagram, c is an XPS comparison diagram corresponding to Co 2p, and d is an XPS comparison diagram corresponding to Ni 2p. Figure 4 To the F-NiCo2O prepared in Example 1 4-x The figure shows the results of DFT calculations performed on the NiCo2O4 material prepared in Comparative Example 1, where a represents F-NiCo2O 4-x The optimized adsorption configuration of the material for lithium polysulfides, b and c are the Li2S6-to-F-NiCo2O adsorption configurations obtained from Bader charge calculations. 4-x A graph showing the number of electrons transferred on the surface of NiCo2O4 material; Figure 5 To evaluate the F-NiCo2O prepared in Example 1 4-xThe following are experimental graphs showing the adsorption capacities of the materials, the NiCo2O4 material prepared in Comparative Example 1, and conductive carbon black for polysulfides. In graph a, UV absorption spectra of the solutions after adsorption in Li2S6 are shown, with the inset in graph a being an optical photograph after adsorption. Graph b shows the adsorption capacities of different polysulfides in F-NiCo2O4. 4-x Figure 1 shows the DFT calculation results of the adsorption energy on the surface of NiCo2O4 material. Figure 2 shows the in-situ Raman diagram of the lithium-sulfur battery in Application Example 1 on the lithium anode separator side, and Figure 3 shows the in-situ Raman diagram of the lithium-sulfur battery in Application Example 3 on the lithium anode separator side. Figure 6 The following are the non-in-situ XPS spectra of lithium-sulfur batteries in Application Examples 1, 3, and 5: a is the O 1s spectrum of the lithium-sulfur battery in Application Example 1, b is the O 1s spectrum of the lithium-sulfur battery in Application Example 3, c is the Li 1s spectrum of the lithium-sulfur battery in Application Example 1, d is the F 1s spectrum of the lithium-sulfur battery in Application Example 1, and e is the F 1s spectrum of the lithium-sulfur battery in Application Example 5. Figure 7 SEM images of the positive electrode of lithium-sulfur batteries in Application Examples 1, 3, and 5 after 100 cycles at a current density of 1C, where a corresponds to Application Example 1, b corresponds to Application Example 3, and c corresponds to Application Example 5. Figure 8 F-NiCo2O 4-x A schematic diagram illustrating the mechanism by which a battery assembled from these materials protects the positive electrode during operation. Figure 9 A comparison graph of the cycle performance of lithium-sulfur batteries in Application Examples 1, 3 and 5 at 1C current density; Figure 10 The graph shows the long-cycle performance of the lithium-sulfur battery in Application Example 1 at a current density of 5 C. Figure 11 The lithium-sulfur batteries used in Application Examples 2 and 4 were tested at high sulfur loading (10 mg / cm³). -2 Cyclic performance at 0.5 C current density; Figure 12 The graph shows the cycle performance of the lithium-sulfur battery in Application Example 1 at a low temperature of -40°C and a current density of 0.2 C. Figure 13 The graph shows the long-cycle performance of lithium-sulfur batteries in Application Examples 1, 3, and 5 at a high temperature of 60°C and a current density of 2C. Detailed Implementation

[0021] To further explain the technical solution of the present invention, the present invention will be described in detail below through specific embodiments.

[0022] I. Preparation of cathode materials Example 1 A method for preparing a fluorine-doped NiCo2O4 bimetallic oxide cathode material for lithium-sulfur batteries includes the following steps: Step 1: First, add 1.047g Co(NO3)2·6H2O and 0.524g Ni(NO3)2·6H2O to 150mL of deionized water and stir for 20min to disperse them evenly. Then, add 0.72g of urea and heat in an oil bath at 80℃ for 15min. Then, add 1.5g of ammonium fluoride solid and continue to heat and stir at 80℃ for 12h to obtain the precursor solution. Step 2: Then, the obtained precursor solution was transferred to a 200 mL polytetrafluoroethylene reactor and hydrothermally reacted at 120 °C for 12 h. The product was then washed three times with deionized water and vacuum dried at 60 °C for 10 h. Step 3: Finally, place the dried product in a tube furnace and heat it to 350°C at a heating rate of 2°C / min under air atmosphere, and calcine for 8 h to obtain a black fluorine-doped NiCo2O4 bimetallic oxide cathode material for lithium-sulfur batteries, denoted as F-NiCo2O. 4-x Material.

[0023] Example 2 A method for preparing a positive electrode for lithium-sulfur batteries includes the following steps: Step 1: First, take the F-NiCo2O prepared in Example 1... 4-x The material and sublimed sulfur were ground evenly at a mass ratio of 1:3, placed in a weighing bottle, put into a forced-air drying oven, and heat-treated at 155℃ for 6 hours. After cooling, the sulfur-loaded composite material was obtained. Step 2, then 15 wt A 5% aqueous dispersion of acrylonitrile multi-component copolymer (model LA-132) was diluted to 5%. wt An aqueous dispersion of % acrylonitrile multi-component copolymer was sealed and stirred continuously for 12 h to obtain a milky white viscous binder dispersion. Step 3: Then, the sulfur-loaded composite material, conductive carbon black, and the prepared binder dispersion are dissolved in a mixture of water and ethanol (volume ratio 1:3) at a ratio of 7:2:1 (where the mass of the binder dispersion is based on the mass of the remaining acrylonitrile copolymer binder after the positive electrode is dried). The mixture is then placed in a ball mill and stirred for 12 hours to obtain a uniformly mixed slurry. The volume ratio of the mixture to the total volume of the sulfur-loaded composite material and conductive carbon black is 0.8:1. Step 4: The prepared slurry is then coated onto aluminum foil and placed in a vacuum drying oven at 60°C for 12 hours. Finally, it is cut using a slicing machine to obtain the positive electrode for lithium-sulfur batteries, with a diameter of 16 mm and a sulfur loading of approximately 1.5 mg / cm³. 2 .

[0024] Example 3 A method for preparing a positive electrode for lithium-sulfur batteries includes the following steps: Step 1: First, take the F-NiCo2O prepared in Example 1... 4-x The material and sublimed sulfur were ground evenly at a mass ratio of 1:3, placed in a weighing bottle, and placed in a forced-air drying oven. The mixture was then heat-treated at 155℃ for 6 hours and cooled to obtain the sulfur-loaded composite material. Step 2, then 15 wt A 5% aqueous dispersion of acrylonitrile multi-component copolymer (model LA-132) was diluted to 5%. wt An aqueous dispersion of % acrylonitrile multi-component copolymer was sealed and stirred continuously for 12 h to obtain a milky white viscous binder dispersion. Step 3: Then, the sulfur-loaded composite material, conductive carbon black, and the prepared binder dispersion are dissolved in a mixture of water and ethanol (volume ratio 1:3) at a ratio of 7:2:1 (where the mass of the binder dispersion is based on the mass of the remaining acrylonitrile copolymer binder after the positive electrode is dried). The mixture is then placed in a ball mill and stirred for 12 hours to obtain a uniformly mixed slurry. The volume ratio of the mixture to the total volume of the sulfur-loaded composite material and conductive carbon black is 0.8:1. Step 4: The prepared slurry is then coated onto aluminum foil and placed in a vacuum drying oven at 60°C for 12 hours. Finally, it is cut using a slicing machine to obtain the positive electrode for lithium-sulfur batteries, with a diameter of 16 mm and a sulfur loading of approximately 10 mg / cm³. 2 .

[0025] Comparative Example 1 A method for preparing a NiCo2O4 bimetallic oxide cathode material for lithium-sulfur batteries includes the following steps: Step 1: First, add 1.047g Co(NO3)2·6H2O and 0.524g Ni(NO3)2·6H2O to 150mL of deionized water and stir for 20min to disperse it evenly. Then add 0.72g of urea and heat in an oil bath at 80℃ for 12h to obtain the precursor solution. Step 2: Then, the obtained precursor solution was transferred to a 200 mL polytetrafluoroethylene reactor and hydrothermally reacted at 120 °C for 12 h. The product was then washed three times with deionized water and dried under vacuum at 60 °C. Step 3: Finally, place the dried product in a tube furnace and heat it to 350°C at a heating rate of 2°C / min in air atmosphere. Calcine for 8 hours to obtain the black NiCo2O4 bimetallic oxide cathode material for lithium-sulfur batteries, denoted as NiCo2O4 material.

[0026] Comparative Example 2 A method for preparing a positive electrode for lithium-sulfur batteries includes the following steps: Step 1: First, grind the NiCo2O4 material prepared in Comparative Example 1 with sublimed sulfur at a mass ratio of 1:3, place it in a weighing bottle, put it in a forced-air drying oven, heat-treat it at 155℃ for 6 hours, and obtain the sulfur-loaded composite material after cooling. Step 2, then 15 wt A 5% aqueous dispersion of acrylonitrile multi-component copolymer (model LA-132) was diluted to 5%. wt An aqueous dispersion of % acrylonitrile multi-component copolymer was sealed and stirred continuously for 12 h to obtain a milky white viscous binder dispersion. Step 3: Then, the sulfur-loaded composite material, conductive carbon black, and the prepared binder dispersion are dissolved in a mixture of water and ethanol (volume ratio 1:3) at a ratio of 7:2:1 (where the mass of the binder dispersion is based on the mass of the remaining acrylonitrile copolymer binder after the positive electrode is dried). The mixture is then placed in a ball mill and stirred for 12 hours to obtain a uniformly mixed slurry. The volume ratio of the mixture to the total volume of the sulfur-loaded composite material and conductive carbon black is 0.8:1. Step 4: The prepared slurry is then coated onto aluminum foil and placed in a vacuum drying oven at 60°C for 12 hours. Finally, it is cut using a slicing machine to obtain the positive electrode for lithium-sulfur batteries, with a diameter of 16 mm and a sulfur loading of approximately 1.5 mg / cm³. 2 .

[0027] Comparative Example 3 A method for preparing a positive electrode for lithium-sulfur batteries includes the following steps: Step 1: First, grind the NiCo2O4 material prepared in Comparative Example 1 with sublimed sulfur at a mass ratio of 1:3, place it in a weighing bottle, put it in a forced-air drying oven, heat-treat it at 155℃ for 6 hours, and obtain the sulfur-loaded composite material after cooling. Step 2, then 15 wt A 5% aqueous dispersion of acrylonitrile multi-component copolymer (model LA-132) was diluted to 5%. wt An aqueous dispersion of % acrylonitrile multi-component copolymer was sealed and stirred continuously for 12 h to obtain a milky white viscous binder dispersion. Step 3: Then, the sulfur-loaded composite material, conductive carbon black, and the prepared binder dispersion are dissolved in a mixture of water and ethanol (volume ratio 1:3) at a ratio of 7:2:1 (where the mass of the binder dispersion is based on the mass of the remaining acrylonitrile copolymer binder after the positive electrode is dried). The mixture is then placed in a ball mill and stirred for 12 hours to obtain a uniformly mixed slurry. The volume ratio of the mixture to the total volume of the sulfur-loaded composite material and conductive carbon black is 0.8:1. Step 4: The prepared slurry is then coated onto aluminum foil and placed in a vacuum drying oven at 60°C for 12 hours. Finally, it is cut using a slicing machine to obtain the positive electrode for lithium-sulfur batteries, with a diameter of 16 mm and a sulfur loading of approximately 10 mg / cm³. 2 .

[0028] II. Application of Cathode Materials Application Example 1 The positive electrode of the lithium-sulfur battery prepared in Example 2 was used as the positive electrode sheet. It was then assembled with a positive electrode shell, a lithium-sulfur electrolyte, a polypropylene separator, and a negative electrode shell to form a lithium-sulfur battery. The amount of lithium-sulfur electrolyte added was 35 μL. The lithium-sulfur electrolyte was designated LP001, and its composition was a 1:1 volume ratio of DOL and DME, with a lithium salt content of 0.5 mol / L. -1 LiCF3SO3 and 0.5 mol L -1 LiNO3.

[0029] Application Example 2 The positive electrode of the lithium-sulfur battery prepared in Example 3 was used as the positive electrode sheet. It was then assembled with a positive electrode shell, a lithium-sulfur electrolyte, a polypropylene separator, and a negative electrode shell to form a lithium-sulfur battery. The amount of lithium-sulfur electrolyte added was 70 μL. The lithium-sulfur electrolyte was designated LP001, and its composition consisted of DOL and DME in a volume ratio of 1:1, with a lithium salt content of 0.5 mol / L. -1 LiCF3SO3 and 0.5 mol L -1 LiNO3.

[0030] Application Example 3 The positive electrode used in Comparative Example 2 was a lithium-sulfur battery. This positive electrode was assembled with a positive electrode shell, a lithium-sulfur electrolyte, a polypropylene separator, and a negative electrode shell. The amount of lithium-sulfur electrolyte added was 35 μL. The lithium-sulfur electrolyte was designated LP001 and consisted of DOL and DME in a 1:1 volume ratio. The lithium salt content was 0.5 mol / L. -1 LiCF3SO3 and 0.5 mol L -1 LiNO3.

[0031] Application Example 4 The positive electrode used in Comparative Example 3 was a positive electrode sheet. This positive electrode was assembled with a positive electrode shell, a lithium-sulfur electrolyte, a polypropylene separator, and a negative electrode shell to form a lithium-sulfur battery. The amount of lithium-sulfur electrolyte added was 70 μL. The lithium-sulfur electrolyte was designated LP001, and its composition was a 1:1 volume ratio of DOL and DME, with a lithium salt content of 0.5 mol / L. -1 LiCF3SO3 and 0.5 mol L -1 LiNO3.

[0032] Application Example 5 A lithium-sulfur battery was assembled using conductive carbon black as the positive electrode, along with a positive electrode shell, lithium-sulfur electrolyte, polypropylene separator, and negative electrode shell. The amount of lithium-sulfur electrolyte added was 35 μL, and the electrolyte type was LP001. The electrolyte composition was DOL and DME in a 1:1 volume ratio, with 0.5 mol / L lithium salt. -1 LiCF3SO3 and 0.5 mol L -1 LiNO3.

[0033] This application example serves as a blank test object.

[0034] III. Reaction Mechanism Figure 1 F-NiCo2O 4-x The intrinsic reaction mechanism of the material as the cathode in lithium-sulfur batteries is as follows: fluorine doping introduces abundant oxygen vacancies, enhancing its adsorption and catalytic conversion capabilities for polysulfides. Simultaneously, during battery cycling, a LiF-rich CEI film is generated in situ, physically confining the polysulfides. These two components, along with F-NiCo2O... 4-x The unique bowl-shaped stacked structure, combined with the "fluorine doping-induced oxygen vacancies-in-situ generation of LiF-CEI film-unique microstructure" synergistic system, improves the performance of lithium-sulfur batteries in a wide temperature range.

[0035] IV. Material Characterization and Analysis 1. Figure 2 The F-NiCo2O prepared in Example 1 4-x Electron micrographs of the material. Figure 2 F-NiCo2O is clearly shown in a, b, c, and d. 4-x The material is uniformly stacked in a bowl-like cross-shape to form a spherical structure, and the elements are evenly distributed. Figure 2 The TEM image of e shows that after fluorine doping, F-NiCo2O 4-x The lattice spacing of the material is slightly expanded compared to the (310) crystal plane of standard NiCo2O4. Figure 2 GPA stress analysis of f shows that the stress in the material is concentrated in the Exx and Eyy directions, which is due to the F doping after fluorine doping. - Replaced the O in the material 2- This leads to lattice expansion in the material, triggering lattice relaxation and tensile stress, proving that F... - Successful doping.

[0036] 2. Figure 3 a is the F-NiCo2O prepared in Example 1. 4-x The XRD patterns of the materials and the NiCo2O4 material prepared in Comparative Example 1 confirm that F-NiCo2O4-x The main components of the material are NiCo2O4 and F-NiCo2O. 4-x The diffraction peaks are shifted by about 0.1° to a smaller angle compared to the standard card, which is due to the lattice expansion caused by oxygen vacancies induced by fluorine doping. Figure 3 b is the F-NiCo2O prepared in Example 1. 4-x The EPR comparison images of the materials and the NiCo2O4 material prepared in Comparative Example 1 show that F-NiCo2O 4-x The resonance signal of the material at g=2.003 (the characteristic signal of oxygen vacancies) is much stronger than that of NiCo2O4, confirming that fluorine doping can induce the generation of abundant oxygen vacancies in NiCo2O4. Figure 3 c. Figure 3 XPS results for d show that after F doping, the characteristic peaks of Co 2p and Ni 2p both shift to higher binding energies. This is due to the influence of F. - This is due to the strong electronegativity of the material, and also because of the Co content. 3+ / Co 2+ and Ni 3+ / Ni 2+ The ratio of [variable] increases significantly, and the increase in the metal valence state helps to improve the conductivity of the material.

[0037] 3. Figure 4 To the F-NiCo2O prepared in Example 1 4-x The results of DFT calculations on the materials and the NiCo2O4 material prepared in Comparative Example 1 are shown in the figure. Figure 4 The Bader charge calculations in b and 4c show that Li2S6 is oriented towards F-NiCo2O 4-x The number of transferred electrons is 0.634e. - It is much higher than the 0.441e of NiCo2O4. - This indicates that F-NiCo2O 4-x It has more frequent electron exchange with polysulfides, its redox reaction is more intense, and it has a stronger interfacial anchoring ability and electrocatalytic activity for polysulfides. Figure 4 The projected density of states results for the Co sites at e and 4g show that, after fluorine doping, F-NiCo2O 4-x The d-band center shifted from -1.565 eV in NiCo2O4 to -1.511 eV, closer to the Fermi capability. This indicates that fluorine doping can modulate the electronic state of the d orbitals of the material, lower the energy barrier for electronic excitation, and promote the participation of electrons in redox reactions.

[0038] 4. Figure 5 To evaluate the F-NiCo2O prepared in Example 1 4-xThe figures show various experimental results regarding the adsorption capacity of NiCo2O4 material prepared in Comparative Example 1 and conductive carbon black for polysulfides. Figure 5 The UV-Vis absorption spectrum of F-NiCo2O after Li2S6 adsorption shows that 4-x The intensity of the characteristic peaks in the Li₂S₆ solution decreased significantly after adsorption, indicating that F-NiCo₂O 4-x It has a stronger adsorption capacity for Li2S6; Figure 5 DFT calculation of F-NiCo2O 4-x The binding energy results of NiCo2O4 material for S8 and a series of polysulfides show that F-NiCo2O 4-x The material exhibits a higher binding energy for polysulfides, indicating a stronger adsorption capacity for polysulfides. Figure 5 The conclusions obtained are highly consistent, further confirming that F-NiCo2O 4-x It has a stronger adsorption capacity for polysulfides; Figure 5 In-situ Raman results for c and 5d show that for F-NiCo2O 4-x The lithium anode-side separator of the battery exhibits only a small number of Li2S8 characteristic peaks during initial discharge and upon completion of charging, and these peaks rapidly diminish as discharge progresses. The Li2S6 characteristic peak appears only as a weak peak upon completion of charging, and no short-chain polysulfide (Li2S4) characteristic peaks appear throughout the entire charging and discharging process. This is because a small amount of long-chain polysulfides temporarily diffuses to the lithium anode side due to the shuttle effect, but this is mitigated by F-NiCo2O. 4-x The ability to strongly anchor polysulfides and rapidly catalyze their conversion is due to the NiCo2O4 battery. In contrast, although the intensity of the Li2S8 characteristic peak gradually decreases with discharge, the characteristic peaks of Li2S6 and Li2S4 gradually increase with charging. This indicates that NiCo2O4 has a certain effect on anchoring and catalyzing polysulfides. However, a large number of long-chain polysulfides will still penetrate the separator through the shuttle effect and react irreversibly with the lithium anode to generate short-chain polysulfides that are deposited on the lithium anode side, resulting in the irreversible loss of active materials.

[0039] 5. Figure 6 These are the in-situ XPS images of lithium-sulfur batteries from Application Examples 1, 3, and 5. Figure 6 The in-situ XPS 1s spectra of F-NiCo2O in a and 6b indicate that F-NiCo2O 4-x The battery still maintains a considerable number of oxygen vacancies after 50 cycles at a current density of 0.5C, which indicates that oxygen vacancies induced by fluorine doping can exist stably. Figure 6 The in-situ XPS Li 1s and F1s spectra of c, 6d, and 6e show that in F-NiCo2O4-x During battery cycling, the Li 1s characteristic peak at 55.8 eV and the F 1s characteristic peak at around 685 eV, belonging to LiF, remain stable. Furthermore, the intensity of the F 1s characteristic peak at around 685 eV gradually increases with discharge, while the intensity of the F 1s characteristic peak at around 685 eV in the corresponding conductive carbon black battery is almost non-existent. This indicates that during battery cycling, F-NiCo2O… 4-x A LiF-rich CEI film was generated in situ on the positive electrode side of the battery, which physically confined the polysulfides and mitigated the shuttle effect.

[0040] 6. Figure 7 The images are SEM images of the positive electrode of the lithium-sulfur batteries used in Application Examples 1, 3, and 5 after 100 cycles at a 1C current density. Figure 7 As can be observed in a, after 100 charge-discharge cycles at a current density of 1C, F-NiCo2O 4-x The electrode structure is intact, with no obvious cracks or holes, which is far superior to the comparative example. Figure 7 b) and conductive carbon black ( Figure 7 c), the resulting pores and cracks are marked with red circles, thus proving that F-NiCo2O 4-x The material exhibits excellent electrode stability, F-NiCo2O 4-x The mechanism for protecting the positive electrode during operation of a battery assembled from materials, such as... Figure 8 As shown, during the charging and discharging process, a LiF-rich CEI film is generated in situ on the positive electrode side, which physically confines the polysulfides and suppresses their shuttle effect. Combined with its own special bowl-shaped stacked structure, it protects the positive electrode structure.

[0041] V. Performance Testing of Cathode Materials 1. Figure 9 Application Examples 1, 3, and 5 (corresponding to F-NiCo2O respectively) 4-x A comparison of the cycling performance of lithium-sulfur batteries (using F-NiCo2O4 material and conductive carbon black as the positive electrode) at 1C current density. The figure shows that F-NiCo2O4... 4-x The material exhibits the best cycle stability and the highest reversible capacity when applied to lithium-sulfur batteries.

[0042] 2. Figure 10 For the lithium-sulfur battery of Application Example 1 (corresponding to F-NiCo2O) 4-x The graph shows the long-cycle performance of the material (used as a positive electrode) at a current density of 5 C. As can be seen from the graph, the material can still provide 587.58 mAh g⁻¹ after 600 cycles. -1 The reversible capacity, with a capacity decay rate of less than 0.016% per cycle, indicates that this F-NiCo2O exhibits good reversibility. 4-xThe material has good long-cycle performance.

[0043] 3. Figure 11 Application Examples 2 and 4 (corresponding to F-NiCo2O respectively) 4-x High sulfur loading (10 mg / cm³) in lithium-sulfur batteries (using NiCo2O4 as the cathode material). 2 The charge-discharge cycle performance diagram at a current density of 0.5 C shows that, due to F-NiCo2O 4-x The material's excellent properties enable the battery to achieve a sulfur loading of 10 mg / cm³. 2 It still maintains a capacity of 530.27 mAh after 100 cycles. -1 The specific capacity demonstrates its adaptability to high sulfur loading.

[0044] 4. Figure 12 For the lithium-sulfur battery of Application Example 1 (corresponding to F-NiCo2O) 4-x The graph shows the charge-discharge cycle performance of the material (used as the positive electrode) at a current density of 0.2C at -40°C. Even after 100 cycles in the extreme low-temperature environment of -40°C, this lithium-sulfur battery still maintains a capacity of 349.7 mAh g⁻¹. -1 The specific capacity confirms its excellent low-temperature adaptability.

[0045] 5. Figure 13 The graph shows the long-cycle performance of lithium-sulfur batteries in Application Examples 1, 3, and 5 at 60°C with 2C current density. The graph shows the lithium-sulfur battery in Application Example 1 (corresponding to F-NiCo2O). 4-x (Using the material as the positive electrode) After 100 cycles at 60℃ and 2C, the specific capacity remained at 1161.31 mAh g⁻¹. -1 In application example 3, the specific capacity decreased from the initial 1201.51 mAh g after 100 cycles. -1 Sharply reduced to 549.09 mAh g -1 Application Example 5 starts from an initial 913.77 mAh g -1 Reduced to 673.63mAh g -1 This strongly confirms that F-NiCo2O 4-x The material exhibits excellent high-temperature adaptability as a cathode material in the field of lithium-sulfur batteries.

[0046] It should be noted that the specific capacity of lithium-sulfur batteries under cycling conditions at 60℃ and 2C current density (…) Figure 13 ) Specific capacity higher than that under normal temperature and 1C current density cycling performance ( Figure 9 This is due to the accelerated electrochemical reaction kinetics at high temperatures, and is a normal phenomenon.

[0047] Therefore, the present invention provides an F-NiCo2O cathode for lithium-sulfur batteries. 4-x The material improves the long-cycle stability of the battery; lithium-sulfur batteries based on this material have excellent adaptability over a wide temperature range, with stable performance at 60°C, and can still work normally even in low-temperature environments of -40°C.

[0048] The above embodiments and figures are not intended to limit the product form and style of the present invention. Any appropriate changes or modifications made by those skilled in the art should be considered as not departing from the patent scope of the present invention.

Claims

1. A method for preparing a fluorine-doped NiCo2O4 bimetallic oxide cathode material for lithium-sulfur batteries, characterized in that: Includes the following steps: Step 1: First, add 1.2~3.6 mmol Co(NO3)2·6H2O and 0.6~1.8 mmol Ni(NO3)2·6H2O to 50~150 mL of deionized water and stir for 20 min to disperse evenly. Then, add 0.24~0.72 g of urea and heat in an oil bath at 80℃ for 15 min. Then, add 0.5~1.5 g of solid ammonium fluoride and continue heating and stirring at 80℃ for 12 h to obtain the precursor solution. The ratio of Co(NO3)2·6H2O : Ni(NO3)2·6H2O : deionized water : urea : ammonium fluoride is 1.2 mmol : 0.6 mmol : 50 mL : 0.24 g : 0.5 g. Step 2: Then, the obtained precursor solution is transferred to a 200 mL polytetrafluoroethylene reactor and hydrothermally reacted at 120 °C for 12 h. The product is then washed and dried. Step 3: Finally, place the dried product in a tube furnace and heat it to 350°C at a heating rate of 2°C / min under air atmosphere, and calcine for 8 h to obtain the black fluorine-doped NiCo2O4 bimetallic oxide cathode material for lithium-sulfur batteries, denoted as F-NiCo2O. 4-x Material.

2. The method for preparing a fluorine-doped NiCo2O4 bimetallic oxide cathode material for lithium-sulfur batteries according to claim 1, characterized in that: In step 2, the product is washed with deionized water 3 to 5 times and dried by vacuum drying at a temperature of 60 to 80°C for 10 to 12 hours.

3. The method for preparing a fluorine-doped NiCo2O4 bimetallic oxide cathode material for lithium-sulfur batteries according to claim 1, characterized in that: The fluorine-doped NiCo2O4 bimetallic oxide cathode material used in the lithium-sulfur battery has a bowl-shaped stacked structure.

4. The method for preparing a fluorine-doped NiCo2O4 bimetallic oxide cathode material for lithium-sulfur batteries according to claim 1, characterized in that: The fluorine-doped NiCo2O4 bimetallic oxide cathode material used in the lithium-sulfur battery has a particle size of 4~5μm.

5. A method for preparing a positive electrode for lithium-sulfur batteries, characterized in that: Includes the following steps: Step 1: First, take the F-NiCo2O as described in claim 1... 4-x The material and sublimed sulfur were ground evenly at a mass ratio of 1:3, placed in a weighing bottle, put into a forced-air drying oven, and heat-treated at 155℃ for 6 hours. After cooling, the sulfur-loaded composite material was obtained. Step 2, then 15 wt The aqueous dispersion of % acrylonitrile multi-component copolymer was diluted to 4%. wt %~6 wt An aqueous dispersion of % acrylonitrile multi-component copolymer was sealed and stirred continuously for 10-14 h to obtain a milky white viscous binder dispersion. Step 3: Then, the sulfur-loaded composite material, conductive carbon black and the prepared binder dispersion are dissolved in a mixture of water and ethanol in proportion, and stirred in a ball mill for 10-12 hours to obtain a uniformly mixed slurry. Step 4: Then, the prepared slurry is coated onto aluminum foil, placed in a vacuum drying oven, and dried at 55~68℃ for 10~15 hours. Finally, it is cut to obtain the positive electrode for lithium-sulfur batteries.

6. The method for preparing a positive electrode for a lithium-sulfur battery according to claim 5, characterized in that: In step 3, the mass ratio of the binder in the sulfur-loaded composite material, conductive carbon black, and binder dispersion is 6.5~7.5 : 1.7~2.3 :

1.

7. The method for preparing a positive electrode for a lithium-sulfur battery according to claim 5, characterized in that: In step 3, the volume ratio of water to ethanol is 1:

3. The amount of the mixture is determined based on the total volume of the sulfur-loaded composite material and the conductive carbon black. The volume ratio of the mixture to the total volume of the sulfur-loaded composite material and the conductive carbon black is 0.8~1:1~1.

2.

8. The method for preparing a positive electrode for a lithium-sulfur battery according to claim 5, characterized in that: The sulfur loading of the positive electrode used in the lithium-sulfur battery is 1.2~15 mg / cm³. 2 .

9. A lithium-sulfur battery, comprising a positive electrode, a positive electrode shell, a lithium-sulfur electrolyte, a polypropylene separator, and a negative electrode shell, wherein the positive electrode, the positive electrode shell, the lithium-sulfur electrolyte, the polypropylene separator, and the negative electrode shell are assembled to form the lithium-sulfur battery, wherein the positive electrode is the positive electrode for a lithium-sulfur battery as described in claim 5, and the amount of lithium-sulfur electrolyte added is 35~70 μL.

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