A dense positive electrode material for lithium-sulfur batteries and a preparation method thereof, and a lithium-sulfur battery

Abstract

The application discloses a lithium-sulfur battery dense positive material and a preparation method and lithium-sulfur battery thereof, and the lithium-sulfur battery dense positive material is a Ni / Co-MOF@MXene-NH2 / S@RGO lithium-sulfur battery dense positive material; the Ni / Co-MOF@MXene-NH2 / S@RGO lithium-sulfur battery dense positive material is first formed by melting and compounding Ni / Co-MOF@MXene-NH2 heterojunction material and sulfur in a vacuum environment to form a Ni / Co-MOF@MXene-NH2 / S sulfur positive material, and then is compounded with RGO suspension under hydrothermal conditions to form the Ni / Co-MOF@MXene-NH2 / S@RGO lithium-sulfur battery dense positive material. The application can effectively solve the technical problems of the existing lithium-sulfur battery, such as shuttle effect, slow kinetics, serious volume expansion, poor conductivity and poor cycle stability.

Description

Technical Field

[0001] This invention belongs to the technical field of batteries, and particularly relates to a dense cathode material for lithium-sulfur batteries, its preparation method, and lithium-sulfur batteries. Background Technology

[0002] Lithium-sulfur batteries (LSBs) are known for their high theoretical specific capacity (~1675 mAh g). -1 High theoretical mass energy density (~2600Wh kg) -1 Lithium-sulfur batteries have attracted much attention in electrochemical energy storage systems due to their advantages such as low cost (<150 USD / ton). The theoretical capacity and energy density of lithium-ion batteries are higher than those of current commercial lithium-ion batteries, while their price is far lower.

[0003] Despite the promising commercial prospects of lithium-sulfur batteries, their commercial application still faces some significant challenges, primarily including: 1) active sulfur (conductivity 5×10⁻⁶). -30 S cm -1 ) and the final discharge product (Li2S2 / Li2S, with a conductivity of 10) -13 Sm -1 (1) near-insulating properties; (2) long-chain lithium polysulfide (Li2S) x (3) The volume expansion caused by complex electrochemical reaction processes (≈80% expansion rate) will damage the electrode structure and shorten its lifespan; (4) The redox kinetics of lithium-sulfur batteries are slow during charging and discharging. The above four challenges greatly reduce the cycle stability and energy density of lithium-sulfur batteries, which seriously limits their commercial application. In order to solve these challenges, the main approach at present is to combine elemental sulfur with various conductive carbon-based materials through chemical or physical interactions, thereby solving the problem of poor conductivity. However, the interaction between the nonpolar surface of these conductive carbon materials and the polar polysulfide ions is weak, which makes it impossible for them to effectively anchor soluble lithium polysulfides, resulting in a large amount of lithium polysulfides shuttling to the negative electrode through the separator, thereby greatly reducing the effective utilization rate of elemental sulfur. Some studies have found that using polar materials (e.g., oxides, sulfides, selenides) to form strong chemisorption with lithium polysulfides can effectively solve the shuttle effect of lithium polysulfides. However, most polar materials have poor conductivity, which can severely hinder the ion / electron transfer rate.

[0004] Therefore, solving the problems of poor conductivity, shuttle effect, severe volume expansion, and slow kinetics of lithium-sulfur batteries in the prior art has become a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a dense cathode material for lithium-sulfur batteries, a method for preparing the same, and a lithium-sulfur battery.

[0006] A dense cathode material for lithium-sulfur batteries, wherein the dense cathode material for lithium-sulfur batteries is a Ni / Co-MOF@MXene-NH2 / S@RGO dense cathode material for lithium-sulfur batteries;

[0007] The Ni / Co-MOF@MXene-NH2 / S@RGO lithium-sulfur battery dense cathode material is first formed by melting and combining Ni / Co-MOF@MXene-NH2 heterojunction material with sulfur in a vacuum environment to form Ni / Co-MOF@MXene-NH2 / S sulfur cathode material. Then, the Ni / Co-MOF@MXene-NH2 / S sulfur cathode material is combined with RGO suspension under hydrothermal conditions to form Ni / Co-MOF@MXene-NH2 / S@RGO lithium-sulfur battery dense cathode material. The Ni / Co-MOF@MXene-NH2 heterojunction material is a heterojunction nanosheet formed by in-situ growth of Ni / Co-MOF on the surface of aminated MXene-NH2 material.

[0008] The Ni / Co-MOF@MXene-NH2 heterojunction material has a sheet diameter of 10 nm to 2 μm and a thickness of 5 to 20 nm.

[0009] A method for preparing a dense cathode material for lithium-sulfur batteries includes the following steps:

[0010] Step 1: Add an amination reagent to the MXene nanosheet suspension and stir magnetically to form aminated MXene-NH2; after the cobalt salt and nickel salt are stirred evenly with the MXene-NH2 solution, they are added to a mixed solution composed of 1,4-dicarboxybenzene (PTA) solution and polyvinylpyrrolidone (PVP), and then a strongly alkaline solution is added to the mixed solution. A hydrothermal reaction is carried out under high temperature and high pressure to obtain Ni / Co-MOF@MXene-NH2 heterojunction material. The amination reagent is 3-aminopropyltriethoxysilane.

[0011] Step 2: Mix and grind the Ni / Co-MOF@MXene-NH2 heterojunction material with elemental sulfur to obtain a mixture, and then carry out a melt diffusion reaction under vacuum to obtain Ni / Co-MOF@MXene-NH2 / S sulfur cathode material;

[0012] Step 3: The Ni / Co-MOF@MXene-NH2 / S sulfur cathode material is subjected to a hydrothermal reaction with an RGO suspension to obtain a dense Ni / Co-MOF@MXene-NH2 / S@RGO lithium-sulfur battery cathode material with an electrode density of 1.3-2.0 g / cm³. 3 .

[0013] In step one, the aminated MXene-NH2 is selected from Ti3C2-NH2, V2C-NH2, Nb2C-NH2 or Mo2C-NH2.

[0014] In step one, the cobalt salt is C4H6CoO4·4H2O or Co(NO3)2·6H2O; the nickel salt is Ni(CH3COO)2·4H2O or Ni(NO3)2·6H2O; and the molar ratio of cobalt salt to nickel salt is 1:(0.1~10).

[0015] In step one, the strongly alkaline solution is NaOH or KOH.

[0016] In step two, the content of elemental sulfur in the mixture is 60-85 wt%, and the temperature is maintained at 160-185°C for 12-18 hours during the melt diffusion reaction.

[0017] In step three, the temperature of the hydrothermal reaction is 100–180°C; the time of the hydrothermal reaction is 36–54 h; and the pressure of the hydrothermal reaction is 1.5–2.5 MPa.

[0018] In step three, the mass of the RGO suspension is 12 to 25 wt% of the Ni / Co-MOF@MXene-NH2 / S sulfur cathode material.

[0019] A lithium-sulfur battery, wherein the negative electrode of the lithium-sulfur battery is a lithium sheet, and the positive electrode of the lithium-sulfur battery comprises a dense positive electrode material for lithium-sulfur batteries prepared by the above-described preparation method.

[0020] Compared with the prior art, the present invention has the following beneficial technical effects:

[0021] 1. Compared with ordinary composite materials, the Ni / Co-MOF@MXene-NH2 heterojunction structure material has a stronger bond and a more uniform dispersion. Ni / Co-MOF and aminated MXene-NH2 are bonded by covalent bonds. Specifically, the -NH2 functional groups on the surface of MXene-NH2 are bonded to nickel or cobalt in Ni / Co-MOF to form Ti-N-Ni or Ti-N-Co structures. Therefore, the heterojunction structure of this application has a more stable chemical structure than traditional composite materials.

[0022] 2. Ni / Co-MOF@MXene-NH2 combines with sulfur to provide excellent physicochemical and catalytic effects on lithium polysulfides. This application achieves excellent sulfur fixation through the combination of nickel or cobalt atoms with the sulfur element in lithium polysulfides, forming S-Ni or S-Co bonds. This fundamentally suppresses the "shuttle effect" and improves the electrochemical performance of lithium-sulfur batteries.

[0023] Furthermore, the dense Ni / Co-MOF@MXene-NH2 / S@RGO cathode material formed by combining Ni / Co-MOF@MXene-NH2 / S sulfur cathode material with RGO in this application possesses a three-dimensional conductive network structure formed by the cross-linking of three two-dimensional materials: Ni / Co-MOF, MXene-NH2, and RGO. This three-dimensional conductive network can effectively alleviate the volume expansion problem of lithium-sulfur batteries during charge and discharge, thereby improving the capacity stability and lifespan of the sulfur cathode. Moreover, this conductive network is more conducive to the transport of electrons and ions, which greatly improves the redox kinetics during the charge and discharge process of lithium-sulfur batteries, thus optimizing the rate performance of lithium-sulfur batteries. Attached Figure Description

[0024] Figure 1 This is a scanning electron microscope (SEM) image of the Ni / Co-MOF@MXene-NH2 heterojunction structure material in Example 1 of this application;

[0025] Figure 2 XPS full spectrum of Ni / Co-MOF@MXene-NH2 heterojunction structure material provided in the embodiments of this application;

[0026] Figure 3 XRD pattern of Ni / Co-MOF@MXene-NH2 heterojunction structure material provided in the embodiments of this application;

[0027] Figure 4 Transmission electron microscope (TEM) image of the Ni / Co-MOF@MXene-NH2 heterojunction structure material provided in the embodiments of this application;

[0028] Figure 5 These are before-and-after comparison photos of the dense Ni / Co-MOF@MXene-NH2 / S@RGO cathode material provided in this embodiment of the invention, showing its wrinkling process. Figure 5 It can be seen that the bulk density of the dense Ni / Co-MOF@MXene-NH2 / S@RGO cathode is approximately 1.86 g / cm³. 3 ;

[0029] Figure 6The CV curves of the Ni / Co-MOF@MXene-NH2 heterojunction structure material, Ni / Co-MOF material, and MXene-NH2 material, respectively assembled into symmetrical cells according to embodiments of the present invention, are compared to their catalytic conversion capabilities for lithium polysulfides. Figure 6 Comparing the intensities of the redox characteristic peaks corresponding to the three materials, it can be seen that the Ni / Co-MOF@MXene-NH2 heterojunction structure material has the best catalytic conversion effect on lithium polysulfides.

[0030] Figure 7 A 100-cycle curve of the Ni / Co-MOF@MXene-NH2 / S@RGO lithium-sulfur battery provided in the embodiments of this application. Detailed Implementation

[0031] To further understand the features, technical means, and specific objectives and functions achieved by the present invention, the present invention will be described in further detail below with reference to the accompanying drawings and specific embodiments.

[0032] This application provides a lithium-sulfur battery cathode material and its preparation method, which addresses the technical defects of existing lithium-sulfur batteries, such as shuttle effect, severe volume expansion, poor conductivity, cycle stability, and safety performance.

[0033] All raw materials used in the following examples are either commercially available or self-made.

[0034] Example 1

[0035] A dense cathode material for lithium-sulfur batteries, the specific preparation method of which is as follows:

[0036] 1. Preparation of Ni / Co-MOF@MXene-NH2 heterojunction structure material:

[0037] 1.1 MXene (Ti3AlC2) precursor was etched in a mixed solution of lithium fluoride and 9 mol / L hydrochloric acid at 36.5 °C for 24 h to obtain MXene (Ti3C2) suspension. 3-aminopropyltriethoxysilane and NH2(CH2)3Si(OC2H5)3 were added to the MXene (Ti3C2) nanosheet suspension and magnetically stirred to form aminated MXene-NH2. 3-aminopropyltriethoxysilane acted as an amination reagent.

[0038] 1.2 After thoroughly mixing cobalt salt, nickel salt, and MXene-NH2 solution, the mixture was added to a mixed solution consisting of 1,4-dicarboxybenzene (PTA) solution and polyvinylpyrrolidone (PVP), with a cobalt:nickel molar ratio of 1:1. Then, NaOH solution was added to the mixed solution, and the mixture was subjected to a hydrothermal reaction at 120℃ for 36 hours. The reacted material was then repeatedly washed with alternating amounts of alcohol and deionized water and centrifuged until the solution was neutral. The precipitate obtained by centrifugation was freeze-dried to obtain Ni / Co-MOF@MXene-NH2 heterojunction material. The Ni / Co-MOF@MXene-NH2 heterojunction material had a sheet diameter of 100 nm and a thickness of 5 nm.

[0039] 2. Preparation of Ni / Co-MOF@MXene-NH2 / S cathode material: Ni / Co-MOF@MXene-NH2 heterojunction material and elemental sulfur were mixed and ground at a mass ratio of 1:4 to obtain a mixture. The sulfur content in the mixture was made up to 80%. The mixture was placed in a sealed tube, and the temperature was controlled at 160℃ for 12 hours. The air in the tube was removed to form a vacuum, so that the elemental sulfur was uniformly melted in the Ni / Co-MOF@MXene-NH2 heterojunction material, and finally the Ni / Co-MOF@MXene-NH2 / S cathode material was obtained.

[0040] 3. The Ni / Co-MOF@MXene-NH2 / S cathode material and RGO suspension were mixed and stirred at a mass ratio of 8.5:1.5, and then subjected to a hydrothermal reaction at 200℃ for 20 h to obtain Ni / Co-MOF@MXene-NH2 / S@RGO columnar hydrogel. The Ni / Co-MOF@MXene-NH2 / S@RGO columnar hydrogel was then kept in an oven at 45℃ for 48 h to obtain a dense Ni / Co-MOF@MXene-NH2 / S@RGO lithium-sulfur battery cathode material with an electrode density of 1.86 g / cm³. 3 .

[0041] 4. The dense cathode material of Ni / Co-MOF@MXene-NH2 / S@RGO lithium-sulfur battery is used to prepare Ni / Co-MOF@MXene-NH2 / S@RGO lithium-sulfur battery according to existing conventional methods.

[0042] 5. The performance of the Ni / Co-MOF@MXene-NH2 heterojunction material and the Ni / Co-MOF@MXene-NH2 / S@RGO lithium-sulfur battery prepared above was tested. The results are as follows: Figures 1 to 7 As shown.

[0043] Figure 2The XPS full spectrum of the Ni / Co-MOF@MXene-NH2 heterojunction material provided in the embodiments of this application shows that carbon, titanium, nitrogen, nickel and cobalt are all present in the sample, which proves that the Ni / Co-MOF@MXene-NH2 heterojunction material was successfully synthesized.

[0044] Figure 3 The XRD pattern of the Ni / Co-MOF@MXene-NH2 heterojunction structure material provided in the embodiments of this application is from... Figure 3 It can be seen that the obtained Ni / Co-MOF@MXene-NH2 heterojunction structure basically corresponds to the MOF mp:1758489 crystal plane. Simultaneously, a strong peak appears at approximately 2θ = 7.3°, corresponding to the (002) crystal plane of MXene-NH2, but the peak position is slightly offset relative to the standard card. This is because the formation of the heterojunction affects the MXene lattice to some extent, causing a slight distortion in the MXene lattice. Furthermore, TEM observation shows that Ni / Co-MOF and MXene-NH2 form a heterojunction interface (see...). Figure 4 Therefore, XRD and TEM confirmed the successful synthesis of Ni / Co-MOF@MXene-NH2 heterojunction materials.

[0045] Figure 5 These are before-and-after comparison photos of the Ni / Co-MOF@MXene-NH2 / S@RGO lithium-sulfur battery dense cathode material provided in the embodiments of this application, created by... Figure 5 It can be seen that the volume of the hydrogel material before shrinkage is approximately 3.32 cm³. 3 The volume after natural air drying is only 0.24 cm³. 3 The electronic balance measured a mass of 446.4 mg, therefore its density is approximately 1.86 g / cm³. 3 .

[0046] Figure 6 The Ni-MOF@MXene-NH2 heterojunction, Co-MOF@MXene-NH2 heterojunction, and Ni / Co-MOF@MXene-NH2 heterojunction materials provided in this application embodiment were respectively assembled into symmetrical cells. The CV curves of their catalytic conversion capabilities for lithium polysulfides were compared. Figure 6 Comparing the intensities of the redox characteristic peaks corresponding to the three materials, it can be seen that the Ni / Co-MOF@MXene-NH2 heterojunction material has the best catalytic conversion effect on lithium polysulfides.

[0047] Figure 7 The cycling curve of the Ni / Co-MOF@MXene-NH2 / S@RGO lithium-sulfur battery provided in the embodiments of this application is obtained from... Figure 7 It can be seen that the specific capacity of the Ni / Co-MOF@MXene-NH2 / S@RGO heterojunction material is 1220mAh / g in the first cycle, and the specific capacity remains at about 965mAh / g after 100 cycles. At a discharge rate of 0.2C, the capacity loss per cycle is about 0.21%.

[0048] Example 2

[0049] A dense cathode material for lithium-sulfur batteries, the specific preparation method of which is as follows:

[0050] 1. Preparation of Ni / Co-MOF@MXene-NH2 heterojunction structure material:

[0051] 1.1. MXene precursor (Ti3AlC2) was etched in a mixed solution of lithium fluoride and 9 mol / L hydrochloric acid at 36.5 °C for 24 h to obtain MXene (Ti3C2) suspension. 3-aminopropyltriethoxysilane was added to the MXene (Ti3C2) nanosheet suspension and magnetically stirred to form aminated MXene-NH2.

[0052] 1.2 After thoroughly mixing cobalt salt, nickel salt, and MXene-NH2 solution, add them to a mixed solution consisting of 1,4-dicarboxybenzene (PTA) solution / polyvinylpyrrolidone (PVP), with a cobalt:nickel molar ratio of 1:2. Then, add NaOH solution to the above mixed solution and carry out a hydrothermal reaction at 150℃ for 32 hours. After the reaction is complete, wash the material repeatedly with alcohol and deionized water alternately and centrifuge until the solution is neutral. Freeze-dry the precipitate obtained by centrifugation to obtain Ni / Co-MOF@MXene-NH2 heterojunction material; the Ni / Co-MOF@MXene-NH2 heterojunction material has a sheet diameter of 150 nm and a thickness of 8-12 nm.

[0053] 2. Preparation of Ni / Co-MOF@MXene-NH2 / S cathode material: Ni / Co-MOF@MXene-NH2 material and elemental sulfur were mixed and ground at a mass ratio of 1:3 to obtain a mixture. The sulfur content in the mixture was made up to 75%. The mixture was placed in a sealed tube, and the temperature was controlled at 155℃ for 14 hours. The air in the tube was removed to form a vacuum, so that the elemental sulfur was uniformly melted in the Ni / Co-MOF@MXene-NH2 heterojunction material, and finally the Ni / Co-MOF@MXene-NH2 / S cathode material was obtained.

[0054] 3. The Ni / Co-MOF@MXene-NH2 / S cathode material and RGO suspension were mixed and stirred at a mass ratio of 8:2, and then subjected to a hydrothermal reaction at 180℃ for 24 h to obtain Ni / Co-MOF@MXene-NH2 / S@RGO columnar hydrogel. The Ni / Co-MOF@MXene-NH2 / S@RGO columnar hydrogel was then kept in an oven at 60℃ for 48 h to obtain a dense Ni / Co-MOF@MXene-NH2 / S@RGO lithium-sulfur battery cathode material with an electrode density of 1.92 g / cm³. 3 .

[0055] 4. The dense cathode material of Ni / Co-MOF@MXene-NH2 / S@RGO lithium-sulfur battery is used to prepare Ni / Co-MOF@MXene-NH2 / S@RGO lithium-sulfur battery according to existing conventional methods.

[0056] 5. The Ni / Co-MOF@MXene-NH2 / S@RGO lithium-sulfur battery prepared above was subjected to performance testing. The initial discharge specific capacity reached approximately 1280 mAh / g, and after 100 cycles, its discharge specific capacity was approximately 1050 mAh / g.

[0057] Example 3

[0058] A dense cathode material for lithium-sulfur batteries, the specific preparation method of which is as follows:

[0059] 1. Preparation of Ni / Co-MOF@MXene-NH2 heterojunction structure material:

[0060] 1.1. MXene (Ti3AlC2) precursor was etched in a mixed solution of lithium fluoride and 12 mol / L hydrochloric acid at 36.5 °C for 24 h to obtain MXene (Ti3C2) suspension. 3-aminopropyltriethoxysilane was added to the MXene (Ti3C2) nanosheet suspension and magnetically stirred to form aminated MXene-NH2.

[0061] 1.2. Cobalt salt, nickel salt, and MXene-NH2 solution were stirred evenly and then added to a mixed solution of 1,4-dicarboxybenzene (PTA) solution / polyvinylpyrrolidone (PVP), with a cobalt:nickel molar ratio of 2:1. NaOH solution was then added to the mixed solution, and a hydrothermal reaction was carried out at 180℃ for 36 hours. The reacted material was then washed repeatedly with alternating alcohol and deionized water and centrifuged until the solution was neutral. The precipitate obtained by centrifugation was freeze-dried to obtain Ni / Co-MOF@MXene-NH2 heterojunction material. The Ni / Co-MOF@MXene-NH2 heterojunction material had a sheet diameter of 150-300 nm and a thickness of 10-20 nm.

[0062] 2. Preparation of Ni / Co-MOF@MXene-NH2 / S cathode material: Ni / Co-MOF@MXene-NH2 material and elemental sulfur were mixed and ground at a mass ratio of 1:9 to obtain a mixture. The sulfur content in the mixture was made up to 90%. The mixture was placed in a sealed tube, and the temperature was controlled at 155℃ for 12 hours. The air in the tube was removed to allow the elemental sulfur to be uniformly melted in the Ni / Co-MOF@MXene-NH2 heterojunction structure material, and finally, Ni / Co-MOF@MXene-NH2 / S cathode material was obtained.

[0063] 3. The Ni / Co-MOF@MXene-NH2 / S cathode material and RGO suspension were mixed and stirred at a mass ratio of 8.2:1.8, and then subjected to a hydrothermal reaction at 180℃ for 28 h to obtain Ni / Co-MOF@MXene-NH2 / S@RGO columnar hydrogel. The Ni / Co-MOF@MXene-NH2 / S@RGO columnar hydrogel was then kept in an oven at 55℃ for 48 h to obtain a dense Ni / Co-MOF@MXene-NH2 / S@RGO lithium-sulfur battery cathode material with an electrode density of 1.90 g / cm³. 3 .

[0064] 4. The dense cathode material of lithium-sulfur batteries is used to prepare Ni / Co-MOF@MXene-NH2 / S@RGO lithium-sulfur batteries using existing conventional methods.

[0065] 5. The Ni / Co-MOF@MXene-NH2 / S@RGO lithium-sulfur battery prepared above was subjected to performance testing. The initial discharge specific capacity reached approximately 1086 mAh / g, and after 100 cycles, its discharge specific capacity was approximately 780 mAh / g.

[0066] Example 4

[0067] A dense cathode material for lithium-sulfur batteries, the specific preparation method of which is as follows:

[0068] 1. Preparation of Ni / Co-MOF@MXene-NH2 heterojunction structure material:

[0069] 1.1. MXene (Ti3AlC2) precursor was etched in a mixed solution of lithium fluoride and 12 mol / L hydrochloric acid at 36.5 °C for 24 h to obtain MXene (Ti3C2) suspension. 3-aminopropyltriethoxysilane was added to the MXene (Ti3C2) nanosheet suspension and magnetically stirred to form aminated MXene-NH2.

[0070] 1.2 After thoroughly mixing cobalt salt, nickel salt, and MXene-NH2 solution, add the mixture to a mixed solution consisting of 1,4-dicarboxybenzene (PTA) solution and polyvinylpyrrolidone (PVP), with a cobalt:nickel molar ratio of 4:1. Then, add NaOH solution to the mixed solution and perform a hydrothermal reaction at 200℃ for 48 hours. After the reaction is complete, wash the material repeatedly with alternating alcohol and deionized water and centrifuge until the solution is neutral. Freeze-dry the precipitate obtained by centrifugation to obtain Ni / Co-MOF@MXene-NH2 heterojunction material. The Ni / Co-MOF@MXene-NH2 heterojunction material has a sheet diameter of 200-400 nm and a thickness of 20-40 nm.

[0071] 2. Preparation of Ni / Co-MOF@MXene-NH2 / S cathode material: Ni / Co-MOF@MXene-NH2 heterojunction material and elemental sulfur were mixed and ground at a mass ratio of 3:7 to obtain a mixture. The sulfur content in the mixture was made up to 70%. The mixture was placed in a sealed tube, and the temperature was controlled at 160℃ for 15 hours. The air in the tube was removed to allow the elemental sulfur to be uniformly melted in the Ni / Co-MOF@MXene-NH2 heterojunction material, and finally the Ni / Co-MOF@MXene-NH2 / S cathode material was obtained.

[0072] 3. The Ni / Co-MOF@MXene-NH2 / S cathode material and RGO suspension were mixed and stirred at a mass ratio of 8.8:1.2, and then subjected to a hydrothermal reaction at 200℃ for 18 h to obtain Ni / Co-MOF@MXene-NH2 / S@RGO columnar hydrogel. The Ni / Co-MOF@MXene-NH2 / S@RGO columnar hydrogel was then kept in an oven at 55℃ for 60 h to obtain a dense Ni / Co-MOF@MXene-NH2 / S@RGO lithium-sulfur battery cathode material with an electrode density of 1.72 g / cm³. 3 .

[0073] 4. The dense cathode material of Ni / Co-MOF@MXene-NH2 / S@RGO lithium-sulfur battery is used to prepare Ni / Co-MOF@MXene-NH2 / S@RGO lithium-sulfur battery according to existing conventional methods.

[0074] 5. The Ni / Co-MOF@MXene-NH2 / S@RGO heterojunction lithium-sulfur battery prepared above was subjected to performance testing. The initial discharge specific capacity reached approximately 1320 mAh / g, and after 100 cycles, its discharge specific capacity was approximately 1180 mAh / g.

[0075] Example 5

[0076] A dense cathode material for lithium-sulfur batteries, the specific preparation method of which is as follows:

[0077] 1. Preparation of Ni / Co-MOF@MXene-NH2 heterojunction structure material:

[0078] 1.1. MXene (Ti3AlC2) precursor was etched in a mixed solution of lithium fluoride and 12 mol / L hydrochloric acid at 36.5 °C for 24 h to obtain MXene (Ti3C2) suspension. 3-aminopropyltriethoxysilane was added to the MXene (Ti3C2) nanosheet suspension and magnetically stirred to form aminated MXene-NH2.

[0079] 1.2 After thoroughly mixing cobalt salt, nickel salt, and MXene-NH2 solution, add the mixture to a mixed solution consisting of 1,4-dicarboxybenzene (PTA) solution and polyvinylpyrrolidone (PVP), with a cobalt:nickel molar ratio of 1:4. Then, add NaOH solution to the mixed solution and perform a hydrothermal reaction at 200℃ for 36 hours. After the reaction is complete, wash the material repeatedly with alternating alcohol and deionized water and centrifuge until the solution is neutral. Freeze-dry the precipitate obtained by centrifugation to obtain Ni / Co-MOF@MXene-NH2 heterojunction material. The Ni / Co-MOF@MXene-NH2 heterojunction material has a sheet diameter of 120-200 nm and a thickness of 5-15 nm.

[0080] 2. Preparation of Ni / Co-MOF@MXene-NH2 / S cathode material: Ni / Co-MOF@MXene-NH2 heterojunction material and elemental sulfur were mixed and ground at a mass ratio of 4:6 to obtain a mixture. The sulfur content in the mixture was made up to 60%. The mixture was placed in a sealed tube, and the temperature was controlled at 165℃ for 12 hours. The air in the tube was removed to allow the elemental sulfur to be uniformly melted in the Ni / Co-MOF@MXene-NH2 heterojunction material, and finally, Ni / Co-MOF@MXene-NH2 / S cathode material was obtained.

[0081] 3. The Ni / Co-MOF@MXene-NH2 / S cathode material and RGO suspension were mixed and stirred at a mass ratio of 8.6:1.4, and then subjected to a hydrothermal reaction at 200℃ for 16 h to obtain Ni / Co-MOF@MXene-NH2 / S@RGO columnar hydrogel. The Ni / Co-MOF@MXene-NH2 / S@RGO columnar hydrogel was then kept in an oven at 60℃ for 48 h to obtain a dense Ni / Co-MOF@MXene-NH2 / S@RGO lithium-sulfur battery cathode material with an electrode density of 1.78 g / cm³. 3 .

[0082] 4. The dense cathode material of Ni / Co-MOF@MXene-NH2 / S@RGO lithium-sulfur battery is used to prepare Ni / Co-MOF@MXene-NH2 / S@RGO lithium-sulfur battery according to existing conventional methods.

[0083] 5. The Ni / Co-MOF@MXene-NH2 / S@RGO lithium-sulfur battery prepared above was subjected to performance testing. The initial discharge specific capacity reached approximately 1340 mAh / g, and after 100 cycles, its discharge specific capacity was approximately 1176 mAh / g.

[0084] As can be seen from the above embodiments, this application discovers that Ni / Co-MOF can be grown in situ on the surface of MXene-NH2, thereby forming a Ni / Co-MOF@MXene-NH2 nanosheet heterostructure nanomaterial. The Ni and Co atoms in Ni / Co-MOF / MXene-NH2 can serve as active sites for adsorbing lithium polysulfides. These Ni / Co active sites interact with the S atoms in the lithium polysulfides. 2- The combination of Ni / Co-MOF@MXene-NH2 / S and RGO forms Ni-S or Co-S bonds, which effectively reduces the dissolution of mid-discharge products during charge and discharge. It also catalyzes the rapid conversion of lithium polysulfides into low-sulfide lithium, which is insoluble in the electrolyte, thereby suppressing the polysulfide ion "shuttle effect." Simultaneously, the dense Ni / Co-MOF@MXene-NH2 / S@RGO cathode material formed by combining Ni / Co-MOF@MXene-NH2 / S with RGO possesses a three-dimensional conductive network structure resulting from the cross-linking of three two-dimensional materials: Ni / Co-MOF, MXene-NH2, and RGO. This three-dimensional conductive network effectively alleviates the volume expansion problem of lithium-sulfur batteries during charge and discharge, and also facilitates electron and ion transport. This results in the Ni / Co-MOF@MXene-NH2 / S@RGO dense cathode material exhibiting excellent specific capacity and cycle performance during charge and discharge.

[0085] It should be noted that the above description is not intended to limit the present invention. Any obvious substitutions without departing from the inventive concept of the present invention are within the protection scope of the present invention.

Claims

1. A lithium sulfur battery compact cathode material, characterized by, The lithium-sulfur battery dense positive material is a Ni / Co-MOF@MXene-NH2 / S@RGO lithium-sulfur battery dense positive material. The Ni / Co-MOF@MXene-NH2 / S@RGO lithium-sulfur battery dense positive material is formed by first melting and compounding Ni / Co-MOF@MXene-NH2 heterojunction material and sulfur in a vacuum environment to form a Ni / Co-MOF@MXene-NH2 / S sulfur positive material, and then compounding the Ni / Co-MOF@MXene-NH2 / S sulfur positive material and RGO suspension under hydrothermal conditions to form the Ni / Co-MOF@MXene-NH2 / S@RGO lithium-sulfur battery dense positive material; wherein the Ni / Co-MOF@MXene-NH2 heterojunction material is a heterojunction nanosheet formed by in-situ growth of Ni / Co-MOF on the surface of the aminated MXene-NH2 material.

2. The lithium-sulfur battery compact cathode material of claim 1, wherein, The flake diameter of the Ni / Co-MOF@MXene-NH2 heterojunction material is 10 nm to 2 μm, and the thickness of the Ni / Co-MOF@MXene-NH2 heterojunction material is 5 to 20 nm.

3. A method of producing a dense positive electrode material for lithium-sulfur batteries according to claim 1 or 2, characterized in that, The method comprises the following steps: Step one: adding an amination reagent to a MXene nanosheet suspension and magnetically stirring to form aminated MXene-NH2; after uniformly stirring cobalt salt, nickel salt and the MXene-NH2 solution, adding the mixture solution composed of 1,4-dicarboxybenzene (PTA) solution and polyvinylpyrrolidone (PVP) into a strong alkaline solution, and performing a hydrothermal reaction under high temperature and high pressure to obtain the Ni / Co-MOF@MXene-NH2 heterojunction material; the amination reagent is 3-aminopropyltriethoxysilane; Step two: mixing and grinding the Ni / Co-MOF@MXene-NH2 heterojunction material with elemental sulfur to obtain a mixture, and performing a melt diffusion reaction under vacuum to obtain the Ni / Co-MOF@MXene-NH2 / S sulfur positive material; Step three, hydrothermal reaction of the Ni / Co-MOF@MXene-NH2 / S sulfur positive electrode material and RGO suspension is carried out to obtain a Ni / Co-MOF@MXene-NH2 / S@RGO lithium-sulfur battery dense positive electrode material, and the electrode density is 1.3-2.0 g / cm 3 .

4. The production method according to claim 3, characterized by, In step one, the aminated MXene-NH2 is selected from Ti3C2-NH2, V2C-NH2, Nb2C-NH2 or Mo2C-NH2.

5. The preparation method according to claim 3, characterized in that, In step one, the cobalt salt is C4H6CoO4·4H2O or Co(NO3)2·6H2O; the nickel salt is Ni(CH3COO)2·4H2O or Ni(NO3)2·6H2O; and the molar ratio of the cobalt salt to the nickel salt is 1:(0.1-10).

6. The preparation method according to claim 3, characterized in that, In step one, the strong alkaline solution is NaOH or KOH.

7. The preparation method according to claim 3, characterized in that, In step two, the content of the elemental sulfur in the mixture is 60-85 wt%, and the temperature is maintained at 160-185 ℃ during the melt diffusion reaction, and the time is 12-18 h.

8. The preparation method according to claim 3, characterized in that, In step three, the temperature of the hydrothermal reaction is 100-180 ℃; the time of the hydrothermal reaction is 36-54 h; and the pressure of the hydrothermal reaction is 1.5-2.5 MPa.

9. The preparation method according to claim 3, characterized in that, In step three, the mass of the RGO suspension is 12-25 wt% of the mass of the Ni / Co-MOF@MXene-NH2 / S sulfur positive electrode material.

10. A lithium-sulfur battery, characterized by, The negative electrode of the lithium-sulfur battery is a lithium sheet, and the positive electrode of the lithium-sulfur battery comprises the lithium-sulfur battery dense positive electrode material of claim 1 or 2 or the lithium-sulfur battery dense positive electrode material prepared by the preparation method of any one of claims 3 to 9.

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