Preparation method of amorphous cobalt boride modified lithium-sulfur battery composite cathode material

Abstract

The application discloses a preparation method of an amorphous CoB modified lithium-sulfur battery composite positive electrode material, which comprises the following steps: firstly, synthesizing a ZnCo@TA precursor; then, preparing a Co-CoP@HNC carrier through calcination and phosphorization treatment; subsequently, forming an amorphous CoB modification layer on the surface of the carrier through boronization treatment; and finally, obtaining a final product through mixed calcination of the carrier and sulfur powder. The preparation method is simple, and a uniform amorphous CoB layer can be constructed on the surface of the Co-CoP heterojunction by accurately controlling an amorphization process. The modification layer not only provides abundant active sites, but also forms a gradient interface structure, thereby significantly enhancing the adsorption and catalytic conversion capacity of the material to polysulfides. The lithium-sulfur battery assembled by using the positive electrode material exhibits a high specific capacity of 1438.9 mAh·g ‑1 at a current density of 0.2 C, and the coulombic efficiency is as high as 95.5% after 100 cycles.

Description

Technical Field

[0001] This invention belongs to the field of novel energy storage materials technology, and relates to a method for preparing an amorphous CoB-modified lithium-sulfur battery composite cathode material. Background Technology

[0002] With the accelerated pace of global energy structure transformation, the development of novel energy storage systems with high energy density and long cycle life has become a current research hotspot. Among numerous energy storage technologies, lithium-sulfur batteries stand out due to their high energy density (up to 2675 Wh·kg⁻¹). -1 The theoretical energy density and 1675 mAh·g -1 The theoretical specific capacity of polysulfides has attracted much attention, but the shuttle effect and sluggish reaction kinetics of polysulfides severely limit their practical applications. In recent years, amorphous materials have shown great potential in solving these problems due to their unique structural properties.

[0003] Traditional crystalline materials, due to their inherent periodic structure, often exhibit rigidity during charge and discharge, making it difficult to adapt to the large volume changes (up to 80%) of sulfur cathodes. In contrast, amorphous materials offer the following significant advantages: First, their unique structure, characterized by long-range disorder and short-range order, provides abundant active sites, significantly enhancing their ability to anchor polysulfides. Second, their isotropic structure facilitates uniform stress distribution, effectively mitigating structural damage caused by volume expansion. Third, the continuous electronic state distribution promotes rapid charge transport. More importantly, the amorphous / grain boundary composite structure can form a gradient interface, maintaining structural stability while providing rapid ion transport channels.

[0004] However, the application of existing amorphous materials in lithium-sulfur batteries still faces key challenges: on the one hand, precisely controlling the amorphous phase content is difficult; too low a content fails to leverage its advantages, while too high a content leads to decreased conductivity and makes it difficult to effectively suppress the shuttle effect; on the other hand, current research mainly employs surface modification strategies to construct amorphous layers on crystalline materials, such as forming amorphous CoB on Co surfaces through NaBH4 solution treatment. Although this method is simple and effective, industrialization challenges remain in large-scale preparation, including batch consistency (requiring >98%) and cost control.

[0005] Based on this, the present invention constructs a uniform amorphous CoB modification layer on the surface of the Co-CoP heterojunction to enhance its adsorption and catalytic conversion capabilities for polysulfides, thereby ultimately improving the overall performance of lithium-sulfur batteries. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention aims to provide a method for preparing an amorphous CoB-modified lithium-sulfur battery composite cathode material. The method first synthesizes a ZnCo@TA precursor, then prepares a Co-CoP@HNC support through calcination and phosphating. Subsequently, an amorphous CoB modification layer is formed on the support surface through boronizing. Finally, the material is mixed with sulfur powder and calcined to obtain the final product. This invention offers a simple preparation method, enabling the precise control of the amorphization process to construct a uniform amorphous CoB layer on the surface of the Co-CoP heterojunction. This modification layer not only provides abundant active sites but also forms a gradient interface structure, significantly enhancing the material's adsorption and catalytic conversion capabilities for polysulfides. A lithium-sulfur battery assembled using this cathode material exhibits a current density of 1438.9 mAh·g at 0.2C. -1 It has a high specific capacity, and its coulombic efficiency reaches 95.5% after 100 cycles.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A method for preparing an amorphous CoB-modified lithium-sulfur battery composite cathode material comprises the following steps in sequence:

[0009] (1) Preparation of ZnCo@TA precursor

[0010] Zn(NO3)2·6H2O and Co(NO3)2·6H2O were dissolved in 50 mL of methanol at a molar ratio of 1:1. 2-methylimidazole solution was added, and the mixture was stirred at room temperature for 24 h. After centrifugation at 8000 rpm for 10 min, ZnCo-MOF was obtained. ZnCo-MOF was mixed with tannic acid and reacted for 10 min. After washing three times with ethanol, it was dried under vacuum at 60 °C for 12 h to obtain ZnCo@TA precursor.

[0011] (2) Preparation of Co-CoP@HNC carrier

[0012] ZnCo@TA precursor was calcined under an argon atmosphere to obtain Co@HNC; Co@HNC was mixed with NaH2PO2 and then subjected to phosphating treatment to obtain Co-CoP@HNC support;

[0013] (3) Preparation of amorphous CoB modified composite materials

[0014] 100 mg of Co-CoP@HNC carrier was immersed in 20 mL of 0.05-0.2 mol / L NaBH4 solution and reacted for 1 h. After washing twice with deionized water, it was dried under vacuum at 60 °C for 12 h to obtain CoB / Co-CoP@HNC composite material.

[0015] (4) Preparation of CoB / Co-CoP@HNC / S composite cathode material

[0016] CoB / Co-CoP@HNC and sulfur powder were mixed evenly at a mass ratio of 1:3 and then heat-treated at 150-160℃ for 12 hours to obtain CoB / Co-CoP@HNC / S composite cathode material.

[0017] As a limitation of the preparation method of the present invention, in step (1), the mass ratio of Co(NO3)2·6H2O to 2-methylimidazole solution is 1:(1-10).

[0018] In this invention, when the mass ratio of Co(NO3)2·6H2O to 2-methylimidazole solution is 1:(1-10), 2-methylimidazole can fully coordinate metal ions to form ZnCo-MOF with regular morphology and uniform pores, thereby ensuring the complete structure and stable performance of the precursor prepared subsequently. If the mass ratio is less than this, the metal ions are not fully coordinated, and amorphous impurities are easily generated, which leads to defects in the structure of the subsequent precursor and affects the performance of the carrier. If the mass ratio is greater than this, the formation of excessive metal Co will increase the proportion of crystalline state and affect the subsequent phosphating and borylation processes.

[0019] As another limitation of the preparation method of the present invention, in step (1), the 2-methylimidazole solution is obtained by dissolving 1.9g of 2-methylimidazole and 0.2g of cetyltrimethylammonium bromide (CTAB) in 50mL of methanol and sonicating for 10min.

[0020] As a third limitation of the preparation method of the present invention, in step (1), the mass ratio of ZnCo-MOF to tannic acid is 1:0.5.

[0021] As a fourth limitation of the preparation method of the present invention, in step (2), the heating rate during calcination is 5℃ / min, the temperature is 900℃, and the time is 2h.

[0022] As a fifth limitation of the preparation method of the present invention, in step (2), the mass ratio of Co@HNC to NaH2PO2 is 1:(3-5).

[0023] As a sixth limitation of the preparation method of the present invention, in step (2), the heating rate during the phosphating treatment is 5℃ / min, the temperature is 300-400℃, and the time is 2h.

[0024] In this invention, the heating rate, temperature, and time during phosphating treatment affect the formation quality and distribution uniformity of the Co-CoP heterojunction. When the calcination temperature is 300-400℃, NaH2PO2 can slowly decompose to produce PH3 gas, which reacts fully with Co@HNC, thus ensuring the stability of the formed Co-CoP heterojunction. If the temperature is below 300℃, NaH2PO2 decomposes incompletely, resulting in insufficient phosphating reaction and a low proportion of Co-CoP heterojunctions, leading to insufficient catalytic activity. If the temperature is above 400℃, the reaction will be too vigorous, easily causing the support structure to collapse, thus degrading the material properties. The 2-hour phosphating treatment ensures that phosphorus fully penetrates and reacts with Co, guaranteeing the formation of the Co-CoP heterojunction.

[0025] This invention successfully prepared an amorphous CoB-modified Co-CoP heterostructure (CoB / Co-CoP@HNC) with hollow nitrogen-doped carbon (HNC) as a support by combining MOF etching, in-situ phosphating, and low-temperature boronizing. This structure was then used as the host sulfur cathode material in lithium-sulfur batteries. The composite material serves as a highly efficient adsorption and catalytic medium for polysulfides, significantly improving battery performance.

[0026] Amorphous CoB exhibits superior polysulfide capture and catalytic capabilities compared to crystalline Co and CoP. By introducing amorphous CoB to construct an amorphous / grain boundary composite structure, a synergistic effect can be achieved, thereby enabling more efficient anchoring and conversion of polysulfides, effectively suppressing the shuttle effect, reducing the loss of active materials, and accelerating redox reaction kinetics.

[0027] The CoB / Co-CoP@HNC heterostructure, through the introduction of amorphous CoB, synergistically modulates the triple effects of the built-in electric field (BIEF), spin state, and dipole interaction: First, the amorphous CoB layer weakens the BIEF intensity at the Co-CoP interface (the surface potential decreases from 1.33V to 0.41V), promoting the bidirectional migration of polysulfides during charging and discharging; second, boron doping transforms the spin state of Co from medium spin (μeff = 2.08μB) to low spin (μeff = 1.49μB), enhancing d-electron localization, reducing the dp orbital bandgap to 0.42eV, and optimizing Co-S orbital hybridization; furthermore, CoB itself possesses a strong dipole moment (6.37 Debye, higher than CoP's 5.15 Debye), which, through Co… + δ→B - The directional arrangement of δ atoms generates electrostatic adsorption, with an adsorption energy of up to -3.22 eV for Li2S6.

[0028] First-principles calculations further elucidated the mechanism of performance enhancement at the electronic structure level. Calculations showed that modification with amorphous CoB shifted the d-band center of the Co atom by 0.35 eV, significantly enhancing its orbital hybridization with polysulfides. Specifically, in Li₂S₆ adsorption, the dp orbital band gap of the amorphous CoB system decreased to 0.42 eV, a 71.4% reduction compared to the crystalline CoP system (1.47 eV). Crystalline orbital Hamiltonian population (COHP) analysis revealed a 35% increase in the bonding state integral (-ICOHP) between amorphous CoB and Li₂S₆, indicating stronger Co-S covalent interactions. Bader charge analysis confirmed that the charge transfer at the amorphous CoB interface reached 1.56 e, a 19.1% increase compared to crystalline CoP (1.31 e). These results clearly reveal the electronic structure essence of how amorphous CoB improves polysulfide conversion efficiency. This multidimensional synergistic effect enables the battery to exhibit excellent electrochemical performance.

[0029] The above-mentioned technical solution of the present invention is a whole in which each step is closely related and mutually influential, and together they determine the morphological characteristics and performance of the product.

[0030] The above technical solution has the following advantages or beneficial effects:

[0031] 1. This invention constructs a high-density active adsorption-catalytic center on the surface of a Co-CoP heterojunction through a precisely controlled amorphous CoB modification layer. The unique long-range disorder of the amorphous structure generates abundant coordination unsaturated sites, which exhibit extremely strong chemisorption capacity for polysulfides (Li₂S₆ adsorption energy -3.22 eV). Simultaneously, the continuous distribution of electronic states in the amorphous phase promotes charge transfer during the catalytic process, significantly increasing the Li₂S deposition capacity to 180 mAh·g⁻¹. -1 This significantly improves the conversion efficiency of polysulfides;

[0032] 2. The amorphous CoB-modified lithium-sulfur battery composite cathode material prepared by this invention achieves a power density of 1438.9 mAh·g at 0.2C. -1 It exhibits high specific capacity, with a coulombic efficiency of 95.5% after 100 cycles, and at 7.9 mg·cm⁻¹ -2 It still maintains 7.024 mAh·cm³ even with high sulfur loading. -2 Area capacity;

[0033] 3. The preparation method of this invention is simple, the process is easy to control, and it is suitable for large-scale industrial production.

[0034] This invention is applicable to the preparation of amorphous CoB-modified lithium-sulfur battery composite cathode materials.

[0035] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. Attached Figure Description

[0036] Figure 1 This is a scanning electron microscope image of CoB / Co-CoP@HNC prepared in Example 1 of the present invention;

[0037] Figure 2 This is a transmission electron microscope image of CoB / Co-CoP@HNC prepared in Example 1 of the present invention;

[0038] Figure 3 The image shown is an HRTEM image of CoB / Co-CoP@HNC prepared in Example 1 of this invention.

[0039] Figure 4 X-ray diffraction patterns of CoB / Co-CoP@HNC, 1-CoB / Co-CoP@HNC, 2-CoB / Co-CoP@HNC, and Co-CoP@HNC / S materials prepared in Examples 1-3 and Comparative Example 1 of the present invention, respectively.

[0040] Figure 5 This is a high-resolution electron microscope image of the CoB / Co-CoP@HNC material prepared in Example 1 of this invention, with high-angle annular dark-field spherical aberration correction.

[0041] Figure 6 The EXAFS Fourier transform spectra of CoB / Co-CoP@HNC, Co, Co3O4, and CoO prepared in Example 1 of this invention are shown.

[0042] Figure 7 This is a potentiostatic lithium sulfide deposition curve of the CoB / Co-CoP@HNC material prepared in Example 1 of the present invention;

[0043] Figure 8 This is a potentiostatic lithium sulfide deposition curve of the Co-CoP@HNC material prepared in Comparative Example 1 of this invention;

[0044] Figure 9 The graphs show the cycle performance of lithium-sulfur batteries assembled using the cathode materials prepared in Examples 1-3 and Comparative Example 1 of the present invention, respectively.

[0045] Figure 10 The graphs show the rate performance of lithium-sulfur batteries assembled using the cathode materials prepared in Examples 1-3 and Comparative Example 1 of the present invention, respectively.

[0046] Figure 11 The images show the spectra of the cathode materials prepared in Example 1 and Comparative Example 1 of this invention in EPR.

[0047] Figure 12The graphs show the cycle performance of lithium-sulfur batteries assembled using the cathode materials prepared in Examples 1 and 4-5 of this invention, respectively.

[0048] Figure 13 The graphs show the cycle performance of lithium-sulfur batteries assembled using the cathode materials prepared in Examples 1 and 6-7 of this invention, respectively.

[0049] Figure 14 The high loading performance diagram of the CoB / Co-CoP@HNC / S cathode material prepared in Example 1 of this invention;

[0050] Figure 15 The CoB / Co-CoP@HNC / S cathode material prepared in Example 1 of this invention was tested at 12 mg·cm⁻¹. -2 Performance diagram of the assembled pouch cell;

[0051] Figure 16 The above are the CV electrochemical curves of the cathode materials prepared in Examples 1-3 of this invention at a scan rate of 0.1 mV / s. Detailed Implementation

[0052] The following embodiments are merely some, not all, of the embodiments of the present invention. Therefore, the detailed descriptions of the embodiments provided below are not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0053] In this invention, unless otherwise specified, all equipment and raw materials are commercially available or commonly used in the industry. The methods described in the following embodiments are conventional methods in the art, unless otherwise specified.

[0054] Example 1

[0055] This embodiment prepares an amorphous CoB-modified lithium-sulfur battery composite cathode material, and the preparation process and steps are as follows:

[0056] (1) Preparation of ZnCo@TA precursor

[0057] Zn(NO3)2·6H2O and Co(NO3)2·6H2O were dissolved in 50 mL of methanol at a molar ratio of 1:1. A 2-methylimidazole solution (obtained by dissolving 1.9 g of 2-methylimidazole and 0.2 g of CTAB in 50 mL of methanol and sonicating for 10 min) was added. The mass ratio of Co(NO3)2·6H2O to the 2-methylimidazole solution was 1:1. After stirring at room temperature for 24 h, the mixture was centrifuged at 8000 rpm for 10 min to obtain ZnCo-MOF. 1 g of ZnCo-MOF was mixed with 0.5 g of tannic acid and reacted for 10 min. After washing three times with ethanol, the mixture was dried under vacuum at 60 °C for 12 h to obtain the ZnCo@TA precursor.

[0058] (2) Preparation of Co-CoP@HNC carrier

[0059] The ZnCo@TA precursor was heated from room temperature to 900℃ at a heating rate of 5℃ / min under an argon atmosphere and held for 2h to obtain Co@HNC; 1g Co@HNC was mixed with 4g NaH2PO2 and heated from room temperature to 350℃ at a heating rate of 5℃ / min and phosphating was performed for 2h to obtain the Co-CoP@HNC support.

[0060] (3) Preparation of amorphous CoB modified composite materials

[0061] 100 mg Co-CoP@HNC was immersed in 20 mL of 0.1 mol / L NaBH4 solution and reacted for 1 h. After washing twice with deionized water, it was dried under vacuum at 60 °C for 12 h to obtain amorphous CoB modified CoB / Co-CoP@HNC composite material.

[0062] (4) Preparation of CoB / Co-CoP@HNC / S composite cathode material

[0063] CoB / Co-CoP@HNC and sulfur powder were mixed evenly at a mass ratio of 1:3 and then heat-treated at 155℃ for 12h to obtain CoB / Co-CoP@HNC / S composite cathode material.

[0064] Examples 2-7

[0065] Examples 2-7 describe the preparation of amorphous CoB-modified lithium-sulfur battery composite cathode materials. The preparation process is similar to that in Example 1, except that the technical parameters are different, as detailed below:

[0066] The composite cathode materials prepared in Examples 2-7 above are respectively designated as 1-CoB / Co-CoP@HNC / S, 2-CoB / Co-CoP@HNC / S, 3-CoB / Co-CoP@HNC / S, 4-CoB / Co-CoP@HNC / S, 5-CoB / Co-CoP@HNC / S, and 6-CoB / Co-CoP@HNC / S.

[0067] Comparative Example

[0068] To investigate the influence of different parameters during the preparation process of this invention on the performance of the product, the following comparative experiments were conducted. Different lithium-sulfur battery cathode materials were prepared according to the following comparative examples:

[0069] Comparative Example 1

[0070] This comparative example prepares a Co-CoP@HNC / S composite cathode material without amorphization treatment. The preparation process is similar to that of Example 1, except that step (3) is not performed, that is, the Co-CoP@HNC prepared in step (2) is directly mixed with sulfur powder.

[0071] The Co-CoP@HNC / S composite cathode material prepared in this comparative example was used to construct a lithium-sulfur battery, and its cycle performance was tested. The initial discharge specific capacity at a current density of 0.2C was 1227 mAh·g. -1 After 100 cycles, the discharge specific capacity is 753 mAh·g. -1 Therefore, excessively high BIEF is detrimental to the accelerated solid-liquid phase transition of LiPSs during charging, increases reaction polarization, and is detrimental to the stability of the cycling process.

[0072] Comparative Example 2

[0073] This comparative example prepares a CoB / Co-CoP@HNC / S composite cathode material. The preparation process is similar to that in Example 1, except that the concentration of NaBH4 solution in step (3) is 0.3 mol / L.

[0074] The CoB / Co-CoP@HNC / S composite cathode material prepared in this comparative example was used to construct a lithium-sulfur battery, and its cycle performance was tested. The initial discharge specific capacity at a current density of 0.2C was 1200 mAh·g. -1 After 100 cycles, the discharge specific capacity is 790 mAh·g. -1 Therefore, the strong spin effect caused by insufficient borylation is not conducive to suppressing the shuttle effect of LiPSs, reducing cycle stability and polysulfide conversion efficiency.

[0075] Comparative Example 3

[0076] This comparative example prepares a CoB / Co-CoP@HNC / S composite cathode material. The preparation process is similar to that in Example 1, except that in step (1), the mass ratio of Co(NO3)2·6H2O to 2-methylimidazole solution is 1:20.

[0077] The CoB / Co-CoP@HNC / S composite cathode material prepared in this comparative example was used to construct a lithium-sulfur battery, and its cycle performance was tested. The initial discharge specific capacity at a current density of 0.2C was 1270 mAh·g. -1 After 100 cycles, the discharge specific capacity is 750 mAh·g. -1 Therefore, insufficient transition metal coordination leads to a low amorphous content, which is detrimental to the stability of the structure during amorphous formation, the adsorption of LiPSs, and reduces cycle stability.

[0078] Comparative Example 4

[0079] This comparative example prepares a CoB / Co-CoP@HNC / S composite cathode material. The preparation process is similar to that in Example 1, except that in step (2), the phosphating process is as follows: the temperature is increased from room temperature to 250℃ at a heating rate of 5℃ / min, and the phosphating process is carried out for 2 hours.

[0080] The CoB / Co-CoP@HNC / S composite cathode material prepared in this comparative example was used to construct a lithium-sulfur battery, and its cycle performance was tested. The initial discharge specific capacity at a current density of 0.2C was 1300 mAh·g. -1 After 100 cycles, the discharge specific capacity is 800 mAh·g. -1 Therefore, the strong dipole interactions caused by a small amount of phosphating are detrimental to the reaction kinetics of polysulfides, which is not conducive to suppressing the shuttle effect of LiPSs and reducing cycle stability.

[0081] Morphology and performance testing

[0082] The composite cathode materials prepared in Examples 1-7 and Comparative Examples 1-4 of this invention were subjected to a series of morphology tests; and they were respectively assembled into lithium-sulfur batteries for electrochemical performance testing. The specific test results are as follows:

[0083] Figure 1 The image shows a scanning electron microscope (SEM) image of the CoB / Co-CoP@HNC prepared in Example 1 of this invention. As can be seen from the image, the cathode material has a distinct hollow structure, which is beneficial for sulfur loading.

[0084] Figure 2The image shows a transmission electron microscope (TEM) image of CoB / Co-CoP@HNC prepared in Example 1 of this invention. As can be seen from the image, the cathode material exhibits a polyhedral nanobox morphology with a diameter of approximately 150 nm and a wall thickness of approximately 10 nm.

[0085] Figure 3 The image shows an HRTEM image of CoB / Co-CoP@HNC prepared in Example 1 of this invention. The phase boundaries of the crystal structure of Co and the amorphous component can be clearly observed from the image.

[0086] Figure 4 The X-ray diffraction patterns of the CoB / Co-CoP@HNC, 1-CoB / Co-CoP@HNC / S, 2-CoB / Co-CoP@HNC, and Co-CoP@HNC materials prepared in Examples 1-3 and Comparative Example 1 of this invention are shown in the figures. As can be seen from the figures, by controlling the concentration of NaBH4, differentially borated Co-CoP materials were obtained. After NaBH4 boration treatment, the peak intensity of cobalt decreased slightly, which is due to the formation of amorphous CoB.

[0087] Figure 5 This is a high-resolution electron microscope (HRTEM) image of the CoB / Co-CoP@HNC material prepared in Example 1 of the present invention, with high-angle annular dark-field spherical aberration correction. As can be seen from the image, the nanostructure consists of amorphous CoB components and well-crystallized Co nanoparticles. The arrangement of crystalline atoms and the phase boundaries between crystalline and amorphous components can be clearly seen.

[0088] Figure 6 The Fourier transform plots of the EXAFS spectra of CoB / Co-CoP@HNC, Co, Co3O4, and CoO prepared in Example 1 of this invention are shown. The results indicate that... The FT peak at that location corresponds to three coordination environments: Co-B (2.41), Co-P (2.35), and Co-O (1.92), while The FT peak at this point comes from two coordination contributions: Co-Co (3.83) and Co-P (4.36), which together constitute the CoB / Co-CoP configuration.

[0089] Figure 7 This is a potentiostatic lithium sulfide deposition curve of the CoB / Co-CoP@HNC material prepared in Example 1 of the present invention. As can be seen from the figure, the CoB / Co-CoP@HNC material contributes 180 mAh·g of lithium sulfide during this deposition process. -1 The capacity indicates that the formation of amorphous CoB is beneficial to accelerating the conversion of LiPSs.

[0090] Figure 8This is a potentiostatic lithium sulfide deposition curve of the Co-CoP@HNC / S material prepared in Comparative Example 1 of this invention. As can be seen from the figure, lithium sulfide contributed 86 mAh·g during the deposition process of the Co-CoP@HNC / S material. -1 The capacity indicates that pure crystalline Co-CoP is not conducive to the deposition of Li2S6.

[0091] Figure 9 The graphs show the cycle performance of lithium-sulfur batteries assembled using the composite cathode materials prepared in Examples 1-3 and Comparative Example 1 of this invention. As can be seen from the graphs, CoB / Co-CoP@HNC / S (Example 1) exhibits the best performance at 0.2C (1C = 1675 mA·g). -1 The initial discharge specific capacity at the current density is 1438.9 mAh·g. -1 After 100 cycles, the discharge specific capacity is 934 mAh·g. -1 The initial discharge specific capacity of 1-CoB / Co-CoP@HNC / S (Example 2) at a current density of 0.2C is 1372 mAh·g. -1 After 100 cycles, the discharge specific capacity is 840 mAh·g. -1 The initial discharge specific capacity of 2-CoB / Co-CoP@HNC / S (Example 3) at a current density of 0.2C is 1337 mAh·g. -1 After 100 cycles, the discharge specific capacity is 810 mAh·g. -1 The initial discharge specific capacity of Co-CoP@HNC / S (Comparative Example 1) at a current density of 0.2C is 1227 mAh·g. -1 After 100 cycles, the discharge specific capacity is 753 mAh·g. -1 .

[0092] Figure 10 The rate performance diagrams of lithium-sulfur batteries assembled using the composite cathode materials prepared in Examples 1-3 and Comparative Example 1 of this invention are shown. The results indicate that the average discharge specific capacities of CoB / Co-CoP@HNC / S (Example 1) at current densities of 0.2C, 0.5C, 1C, 2C, and 5C are 1381.9, 1189.01, 1016.37, 862.98, and 749.04 mAh·g, respectively. -1 Returning to the 0.2C average discharge specific capacity, it is 1068.54 mAh·g. -1 The average discharge specific capacities of 1-CoB / Co-CoP@HNC / S (Example 2) at current densities of 0.2C, 0.5C, 1C, 2C, and 5C were 1312, 991, 837, 629, and 599 mAh·g, respectively. -1 Returning to the point where the average discharge specific capacity at 0.2C is 1003 mAh·g-1 The average discharge specific capacities of 2-CoB / Co-CoP@HNC / S (Example 3) at current densities of 0.2C, 0.5C, 1C, 2C, and 5C were 1270, 1070, 911, 750, and 608 mAh·g, respectively. -1 Returning to the point where the average discharge specific capacity at 0.2C is 1080 mAh·g -1 The average discharge specific capacities of Co-CoP@HNC / S (Comparative Example 1) at current densities of 0.2C, 0.5C, 1C, 2C, and 5C were 1240, 921, 792, 666, and 557 mAh·g, respectively. -1 Returning to the 0.2C average discharge specific capacity, it is 911 mAh·g. -1 .

[0093] Figure 11 The images show the spectra of the composite materials prepared in Example 1 and Comparative Example 1 in EPR. As can be seen from the images, CoB / Co-CoP@HNC does not have a distinct peak, while CoP treated with NaBH4 forms a peak (CoP...). 1-x @HNC) indicates that vacancies were generated, further indicating that the introduction of NaBH4 does not affect the CoP end in Co-CoP. Phosphating can regulate the relative content of elemental Co, ultimately affecting the formation ratio of amorphous materials.

[0094] Figure 12 The figures show the cycle performance of lithium-sulfur batteries assembled using the composite cathode materials prepared in Examples 1 and 4-5 of this invention, respectively. As can be seen from the figures, the 3-CoB / Co-CoP@HNC / S and 4-CoB / Co-CoP@HNC / S cathode materials prepared in Examples 4 and 5 exhibit the best performance at 0.2C (1C = 1675 mAh·g⁻¹). -1 The initial discharge specific capacities at current densities were 1328 and 1270 mAh·g, respectively. -1 After 100 cycles, the discharge specific capacities were 849 and 758 mAh·g, respectively. -1 .

[0095] Figure 13 The figures show the 0.2C cycle performance of lithium-sulfur batteries assembled using the composite cathode materials prepared in Examples 1 and 6-7 of this invention. As can be seen from the figures, the 5-CoB / Co-CoP@HNC / S and 6-CoB / Co-CoP@HNC / S cathode materials prepared in Examples 6 and 7 exhibit the best performance at 0.2C (1C = 1675 mAh·g⁻¹). -1 The initial discharge specific capacities at current densities were 1337 and 1254 mAh·g, respectively. -1 After 100 cycles, the discharge specific capacities were 835 and 770 mAh·g, respectively.-1 .

[0096] Figure 14 The CoB / Co-CoP@HNC / S cathode material prepared in Example 1 of this invention is subjected to a high sulfur loading (7.9 mg·cm³). -2 The high-capacity performance diagram shows that the CoB / Co-CoP@HNC / S cathode still achieves 877.98 mAh·g after 45 cycles at 1.3C. -1 (The surface loading of sulfur content is 7.024 mAh·g) -1 The initial capacity and 740.86 mAh·g -1 (The surface loading of sulfur content is 5.926 mAh·g) -1 ) retention rate.

[0097] Figure 15 The CoB / Co-CoP@HNC / S cathode material prepared in Example 1 of this invention was tested at 12 mg·cm⁻¹. -2 The performance graph of the assembled pouch cell is shown below. It can be seen from the graph that the CoB / Co-CoP@HNC / S cathode exhibits a capacity of 963 mAh·g at 0.05C. -1 The initial capacity.

[0098] Figure 16 The figure shows the CV electrochemical curves of the cathode materials prepared in Examples 1-3 of this invention at a scan rate of 0.1 mV / s. As can be seen from the figure, the cathode materials prepared in Examples 1-3 have polarization voltages of 0.274 V, 0.31 V, 0.315 V, and 0.316 V, indicating that appropriate amorphous CoB formation can reduce reaction polarization.

[0099] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing an amorphous CoB-modified lithium-sulfur battery composite cathode material, characterized in that, Follow these steps in sequence: (1) Preparation of ZnCo@TA precursor Zn(NO3)2·6H2O and Co(NO3)2·6H2O were dissolved in 50 mL of methanol at a molar ratio of 1:

1. 2-methylimidazole solution was added, and the mixture was stirred at room temperature for 24 h. After centrifugation at 8000 rpm for 10 min, ZnCo-MOF was obtained. ZnCo-MOF was mixed with tannic acid and reacted for 10 min. After washing three times with ethanol, it was dried under vacuum at 60 °C for 12 h to obtain the ZnCo@TA precursor. The mass ratio of Co(NO3)2·6H2O to 2-methylimidazole solution is 1:(1-10). (2) Preparation of Co-CoP@HNC vector ZnCo@TA precursor was calcined under an argon atmosphere to obtain Co@HNC; Co@HNC was mixed with NaH2PO2 and then subjected to phosphating treatment. The heating rate during the phosphating treatment was 5℃ / min, the temperature was 300-400℃, and the time was 2h to obtain Co-CoP@HNC carrier. (3) Preparation of amorphous CoB modified composite materials 100 mg of Co-CoP@HNC carrier was immersed in 20 mL of 0.05-0.2 mol / L NaBH4 solution and reacted for 1 h. After washing twice with deionized water, it was dried under vacuum at 60 °C for 12 h to obtain CoB / Co-CoP@HNC composite material. (4) Preparation of CoB / Co-CoP@HNC / S composite cathode material CoB / Co-CoP@HNC and sulfur powder were mixed evenly at a mass ratio of 1:3 and then heat-treated at 150-160℃ for 12 h to obtain CoB / Co-CoP@HNC / S composite cathode material.

2. The method for preparing an amorphous CoB-modified lithium-sulfur battery composite cathode material according to claim 1, characterized in that, In step (1), the 2-methylimidazole solution is obtained by dissolving 1.9 g of 2-methylimidazole and 0.2 g of cetyltrimethylammonium bromide in 50 mL of methanol and then sonicating for 10 min.

3. The method for preparing an amorphous CoB-modified lithium-sulfur battery composite cathode material according to claim 1, characterized in that, In step (1), the mass ratio of ZnCo-MOF to tannic acid is 1:0.

5.

4. The method for preparing an amorphous CoB-modified lithium-sulfur battery composite cathode material according to claim 1, characterized in that, In step (2), the heating rate during calcination is 5℃ / min, the temperature is 900℃, and the time is 2 h.

5. The method for preparing an amorphous CoB-modified lithium-sulfur battery composite cathode material according to claim 1, characterized in that, In step (2), the mass ratio of Co@HNC to NaH2PO2 is 1:(3-5).

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