High-efficiency low-surface-energy composite material as well as preparation method and application thereof

Abstract

The invention discloses a high-efficiency low-surface-energy composite material as well as a preparation method and application thereof, and relates to a composite material as well as a preparation method and application thereof. The invention provides a high-efficiency and low-surface-energy composite material aiming at the problem of adjusting the internal mechanism of a lithium-sulfur battery by a d-band center, the high-efficiency and low-surface-energy composite material is formed by vertically anchoring nitrogen-doped carbon nanotubes embedded with cobalt nanoparticles on a Ti3C2 nanosheet and has a one-dimensional and two-dimensional three-dimensional composite structure, the diameter of each carbon nanotube is 10-30nm, each carbon nanotube is terminated by a cobalt nanoparticle cluster, and the diameter of each carbon nanotube is 10-30nm. The Ti3C2 nanosheets are wrapped by the carbon nanotubes and are gathered and uniformly distributed on the surface of Ti3C2, the transverse unfolding size of the Ti3C2 nanosheets is not less than 30 mu m < 2 >, and the thickness of the Ti3C2 nanosheets is less than 5 nm; after the Co-coated NCNT and the Ti3C2 in the composite material are combined, the centers of d bands of the two assemblies move upwards, and adsorption and catalytic conversion of the lithium-sulfur polymer electrolyte are facilitated.

Description

TECHNICAL FIELD

[0001] The present application relates to a composite material and a preparation method and application thereof. BACKGROUND

[0002] The d-band center theory provides a powerful framework for understanding the interaction between catalysts and adsorbates, and adjusting the d-band center has become a core strategy for designing efficient low surface energy materials. Although a large number of studies have shown certain results, most of the mechanistic insights are heavily dependent on density functional theory calculations, and direct experimental evidence about the modulation of the d-band center (especially under operating conditions) is still very scarce. Filling this gap is crucial for validating theoretical models and guiding rational material design. In particular, metal-nitrogen-carbon structures have shown strong catalytic activity for lithium polysulfide (LiPSs) conversion due to their tunable electronic structure and rich active sites. These characteristics make them an attractive building block for constructing synergistic heterostructures with MXene properties, but this integration aspect is still in its infancy and has not been fully explored. Importantly, by adjusting the position of the d-band center, its surface activity can be significantly enhanced. This center determines the binding strength of the adsorbate and the energy barrier of the intermediate reaction.

[0003] There are some studies that have effectively combined the high conductivity of carbon nanotubes with the catalytic ability of Ti3C2 by combining carbon nanotube structures with Ti3C2, although this design not only effectively prevents the stacking of MXene sheets, but also creates a three-dimensional continuous conductive network throughout the material system. However, the synthesis methods are different. For example, the team of Zhao Cezhou (CN 113140410 A) of Xiamen University used ultrasonic to physically composite nitrogen-doped carbon nanosheets with Ti3C2, but such a synthesis method is difficult to mix uniformly at the nanoscale, which is not conducive to the formation of a uniform catalytic surface. The team of Hou Linrui (Jinan University, CN 114300668 A) used carbon sources to form agglomerated carbon nanotubes through gas phase deposition at high temperature, but such a method forms nanotubes with a particularly large difference in diameter. Moreover, carbon nanotubes are grown based on transition metals such as cobalt, which is not conducive to the exposure of metal active sites. Therefore, in order to obtain a composite material with more excellent catalytic function, it is necessary to seek a uniform synthesis method for carbon nanotubes and MXene. SUMMARY

[0004] The present application is aimed at the problem of adjusting the d-band center of lithium-sulfur batteries, and provides a high-efficiency low-surface-energy composite material and a preparation method and application thereof.

[0005] The application discloses a high-efficiency low-surface-energy composite material, which is a nitrogen-doped carbon nanotube embedded with cobalt nanoparticles and vertically anchored on a Ti3C2 nanosheet, and has a one-dimensional and two-dimensional three-dimensional composite structure, wherein the carbon nanotube has a diameter of 10-30 nm and is terminated by a cobalt nanoparticle cluster, the Ti3C2 nanosheet is wrapped by the carbon nanotube and is uniformly distributed on the surface of the Ti3C2, and the lateral development size of the Ti3C2 nanosheet is not less than 30 mu m 2 The thickness is less than 5 nm; after combination of the Co@NCNT and the Ti3C2 in the composite material, the d-band centers of the two components are both moved upward, which is beneficial to adsorption and catalytic conversion of a lithium-sulfur polymer electrolyte.

[0006] The application discloses a preparation method of a high-efficiency low-surface-energy composite material, and specifically discloses the following steps.

[0007] I. Preparation of Ti3C2 aerogel

[0008] 1. LiF is dissolved in hydrochloric acid and stirred until mixed uniformly to obtain an etching solution;

[0009] 2. Ti3AlC2 powder is added to the etching solution, heated and stirred for a period of time to obtain a reaction product; the reaction product is washed with LiCl solution and hydrochloric acid in sequence, and then repeatedly washed with ultrapure water until the reaction product is 6-7, to obtain a precipitate; the precipitate is dispersed in deionized water and centrifuged to obtain a dark green Ti3C2 suspension, which is concentrated and ultrasonically treated, and finally freeze-dried to obtain the Ti3C2 aerogel;

[0010] II. Preparation of Co@NCNT / Ti3C2

[0011] 1. The unidirectional Ti3C2 aerogel is added to methanol and stirred uniformly to obtain a uniform Ti3C2 aerogel suspension;

[0012] 2. Cobalt nitrate hexahydrate is added to the uniform Ti3C2 aerogel suspension to obtain solution A;

[0013] 3. 2-methyl imidazole is added to the uniform Ti3C2 aerogel suspension to obtain solution B;

[0014] 4. Solution B is poured into solution A under the condition of vigorous stirring at room temperature, and is gently stirred for a period of time and then left to react; after the reaction is completed, the precipitate is collected to obtain a ZIF-67 / Ti3C2 composite;

[0015] 5. Annealing the ZIF-67 / Ti3C2 composite at 400-500 DEG C under the protection of H2 / Ar mixed gas atmosphere for a period of time, cooling to room temperature, the nitrogen-doped carbon nanotube embedded with cobalt nanoparticles is vertically anchored on the Ti3C2 nanosheet, to obtain a Co@NCNT / Ti3C2 composite, which is a high-efficiency low-surface-energy composite material.

[0016] The high-efficiency low-surface-energy composite material is used as a diaphragm of a lithium-sulfur battery or a positive electrode of a lithium-sulfur battery.

[0017] Effects of the present application:

[0018] 1. The composite material obtained by the present application, i.e. the Co@NCNT / Ti3C2 composite, in which the nitrogen-doped carbon nanotube embedded with cobalt nanoparticles is vertically anchored on the Ti3C2 nanosheet, has a one-dimensional and two-dimensional three-dimensional composite structure, which is beneficial to the penetration of electrolyte and the rapid transmission of ions.

[0019] 2. In the composite material obtained by the present application, i.e. the Co@NCNT / Ti3C2 composite, in which the nitrogen-doped carbon nanotube embedded with cobalt nanoparticles is vertically anchored on the Ti3C2 nanosheet, the diameter of the nitrogen-doped carbon nanotube is 10-30 nm, and each is terminated with a cobalt nanoparticle cluster; the nitrogen-doped carbon nanotube uniformly wraps the Ti3C2, which is aggregated and uniformly distributed on the surface of the Ti3C2, which is beneficial to the rapid conduction of electrons.

[0020] 3. In the composite material obtained by the present application, i.e. the Co@NCNT / Ti3C2 composite, in which the nitrogen-doped carbon nanotube embedded with cobalt nanoparticles is vertically anchored on the Ti3C2 nanosheet, the lateral development size of the Ti3C2 nanosheet is not less than 30 mu m 2 , and the thickness is less than 5 nm; the Co@NCNT / Ti3C2 composite has abundant heterojunction interfaces, which can provide more active sites when used as a catalyst, and is beneficial to the improvement of catalytic activity and performance.

[0021] 4. The composite material obtained by the present application, i.e. the Co@NCNT / Ti3C2 composite, in which the nitrogen-doped carbon nanotube embedded with cobalt nanoparticles is vertically anchored on the Ti3C2 nanosheet, has abundant heterojunction interfaces; since the d-band center and Fermi level of Co@NCNT and Ti3C2 are not the same, the d-band center of the two components is moved upward after being combined, which is beneficial to the adsorption and catalytic conversion of lithium-sulfur polymer electrolyte.

[0022] Five, the composite material obtained by the present application, that is, Co@NCNT / Ti3C2 composite, in which nitrogen-doped carbon nanotubes embedded with cobalt nanoparticles are vertically anchored on Ti3C2 nanosheets, has abundant hetero-interfaces; when used in lithium-sulfur batteries, lithium forms reversible intercalation / deintercalation with polysulfide species, has strong adsorption effect on polysulfides, creates conditions for better anchoring of lithium polysulfide dissolved in electrolyte, and is conducive to inhibiting the shuttle effect;

[0023] Six, the composite material obtained by the present application, that is, Co@NCNT / Ti3C2 composite, in which nitrogen-doped carbon nanotubes embedded with cobalt nanoparticles are vertically anchored on Ti3C2 nanosheets, has abundant hetero-interfaces; when used in lithium metal batteries, the built-in electric field formed at the interface between the two can attract lithium ions, uniformize lithium ion flux, and improve the stability of the lithium negative electrode;

[0024] Seven, the composite material obtained by the present application, that is, Co@NCNT / Ti3C2 composite, in which nitrogen-doped carbon nanotubes embedded with cobalt nanoparticles are vertically anchored on Ti3C2 nanosheets, has abundant hetero-interfaces; when used in lithium-sulfur batteries, Co@NCNT and Ti3C2 synergistically act on sulfur species through selective catalysis by adjusting the d-band center, that is, slowing down the conversion of elemental sulfur to long-chain polysulfides and accelerating the conversion of long-chain polysulfides to lithium sulfide, thereby reducing the accumulation of polysulfides in the electrolyte, effectively inhibiting the polysulfide shuttle, and providing a theoretical basis and technical support for the research and practical application of lithium-sulfur batteries;

[0025] Eight, the composite material obtained by the present application, that is, Co@NCNT / Ti3C2 composite, in which nitrogen-doped carbon nanotubes embedded with cobalt nanoparticles are vertically anchored on Ti3C2 nanosheets, has abundant hetero-interfaces; when used in lithium-sulfur batteries, due to the nitrogen defects on the carbon nanotubes, Li + will be embedded in the defects and combined with soluble polysulfides, thereby promoting the conversion of lithium polysulfide, weakening the shuttle effect, ultimately improving the loss of active material and the decay of capacity, and enhancing the performance of lithium-sulfur batteries;

[0026] Nine, the composite material obtained by the present application, that is, Co@NCNT / Ti3C2 composite, in which nitrogen-doped carbon nanotubes embedded with cobalt nanoparticles are vertically anchored on Ti3C2 nanosheets, has abundant hetero-interfaces; when used in lithium-sulfur batteries, the Co@NCNT / Ti3C2 composite has a three-dimensional network structure combining one-dimensional and two-dimensional structures, can produce a physical barrier effect on lithium polysulfide dissolved in electrolyte, effectively slowing down the shuttle effect; the carbon nanotubes act as a conductive framework, forming a network structure that is conducive to the infiltration of electrolyte and the rapid conduction of ions / electrons, while promoting the three-dimensional precipitation of Li2S, thereby obtaining better electrochemical performance;

[0027] 10. The present invention provides a composite material in which nitrogen-doped carbon nanotubes embedded with cobalt nanoparticles are vertically anchored on Ti3C2 nanosheets, namely Co@NCNT / Ti3C2 composite. The process is ingenious, the processing equipment is inexpensive, the procedure and method are simple, the cost is low, and it is conducive to large-scale industrial production.

[0028] XI. The composite material obtained by this invention, namely Co@NCNT / Ti3C2 composite, in which nitrogen-doped carbon nanotubes embedded with cobalt nanoparticles are vertically anchored on Ti3C2 nanosheets, has a loading amount of 0.1~5 mg / cm³ when used to modify polypropylene separators for lithium-sulfur batteries. 2 This effectively suppressed the shuttle effect, resulting in an improved specific capacity (1241 mAh g⁻¹ at 0.1C) compared to commercial polypropylene membranes. -1 Commercial polypropylene separators have a capacity of 890 mAh / g. -1 Rate performance (5C, 559.2mAh g) -1 And cycle stability (at 1C, the decay rate per 700 cycles is 0.051%).

[0029] 12. The present invention provides a composite material, namely Co@NCNT / Ti3C2 composite, in which nitrogen-doped carbon nanotubes embedded with cobalt nanoparticles are vertically anchored on Ti3C2 nanosheets. This composite material can be used in the separator and cathode of lithium-sulfur batteries. At the same time, because the composite material has good electrocatalytic activity, it also has broad application prospects in the fields of solar cells, supercapacitors, lithium-ion batteries, photocatalysis or electrocatalysis, electrostatic shielding, and nanobiomedicine. Attached Figure Description

[0030] Figure 1 The X-ray diffraction pattern of the Co@NCNT / Ti3C2 composite prepared in Example 1;

[0031] Figure 2 This is a low-magnification scanning electron microscope image of the Co@NCNT / Ti3C2 composite prepared in Example 1;

[0032] Figure 3 Here is a high-magnification scanning electron microscope image of the Co@NCNT / Ti3C2 composite prepared in Example 1;

[0033] Figure 4 This is a low-magnification transmission electron microscope image of the Co@NCNT / Ti3C2 composite heterojunction prepared in Example 1;

[0034] Figure 5 This is a high-magnification transmission electron microscope image of the Co@NCNT / Ti3C2 composite heterojunction prepared in Example 1;

[0035] Figure 6 Digital images of Li2S6, Ti3C2 and Li2S6, Co@NCNT and Li2S6, Co@NCNT / Ti3C2 and Li2S6 solutions after standing for 24 hours;

[0036] Figure 7 Charge-discharge curves of lithium-sulfur batteries with PP, Ti3C2-PP, Co@NCNT-PP, Co@NCNT / Ti3C2-PP as separators at 0.1C;

[0037] Figure 8 CV curves of lithium-sulfur batteries with Ti3C2-PP, Co@NCNT-PP, Co@NCNT / Ti3C2-PP as separators;

[0038] Figure 9 Tafel slope plots of lithium-sulfur batteries with Ti3C2-PP, Co@NCNT-PP, Co@NCNT / Ti3C2-PP as separators at different conversion processes (according to Figure 8 fitting);

[0039] Figure 10 Activation energy plots of lithium-sulfur batteries with Ti3C2-PP, Co@NCNT-PP, Co@NCNT / Ti3C2-PP as separators at different conversion processes (according to Figure 9 derivation);

[0040] Figure 11 Rate capability of lithium-sulfur batteries with Ti3C2-PP, Co@NCNT-PP, Co@NCNT / Ti3C2-PP as separators;

[0041] Figure 12 Cycle performance of lithium-sulfur batteries with Co@NCNT / Ti3C2-PP as separators;

[0042] Figure 13 High sulfur loading and low liquid sulfur ratio performance of lithium-sulfur batteries with Co@NCNT / Ti3C2-PP as separators;

[0043] Figure 14 In-situ Raman spectra of lithium-sulfur batteries with Co@NCNT / Ti3C2-PP as separators;

[0044] Figure 15 Different element X-ray photoelectron spectroscopy of lithium-sulfur batteries with Co@NCNT / Ti3C2-PP as separators after disassembling after discharging and charging;

[0045] Figure 16The photoelectron energy spectrum and the ultraviolet photoelectron spectrum of Co@NCNT-PP, Ti3C2-PP and Co@NCNT / Ti3C2, respectively;

[0046] Figure 17 The photoelectron energy spectrum and the ultraviolet photoelectron spectrum of Co@NCNT / Ti3C2 after discharging and charging, respectively;

[0047] Figure 18 The calculated and experimental d-band center of Co@NCNT, Ti3C2, Co@NCNT / Ti3C2 and Co@NCNT / Ti3C2 after discharging and charging, respectively;

[0048] Figure 19 The covalent orbital hybridization of Co@NCNT / Ti3C2-PP in the process of Li2S insertion and extraction in lithium-sulfur batteries, respectively;

[0049] Figure 20 The state density diagram of Co@NCNT / Ti3C2-PP in the process of Li2S insertion and extraction in lithium-sulfur batteries, respectively. DETAILED DESCRIPTION

[0050] Specific embodiment one: the high-efficiency low-surface-energy composite material of the embodiment is a nitrogen-doped carbon nanotube embedded with cobalt nanoparticles vertically anchored on Ti3C2 nanosheets, and has a one-dimensional and two-dimensional three-dimensional composite structure, wherein the carbon nanotube has a diameter of 10-30 nm, each is terminated with a cobalt nanoparticle cluster, the Ti3C2 nanosheet is wrapped by the carbon nanotube, and is aggregated and uniformly distributed on the surface of the Ti3C2, and the lateral development size of the Ti3C2 nanosheet is not less than 30 μm 2 , and the thickness is less than 5 nm; after the combination of Co@NCNT and Ti3C2 in the composite material, the d-band centers of the two components are both moved upward, which is beneficial to the adsorption and catalytic conversion of lithium-sulfur polymer electrolyte.

[0051] Specific embodiment two: the preparation method of the high-efficiency low-surface-energy composite material of the embodiment is completed according to the following steps:

[0052] I. Preparation of Ti3C2 aerogel:

[0053] ①, dissolve LiF in hydrochloric acid and stir until mixed evenly to obtain an etching solution;

[0054] ②, the Ti3AlC2 powder is added into the etching solution, heated and stirred for a period of time to obtain a reaction product; the reaction product is washed with LiCl solution and hydrochloric acid in sequence, and then repeatedly washed with ultrapure water until 6-7 to obtain a precipitate; the precipitate is dispersed in deionized water and centrifuged to obtain a dark green Ti3C2 suspension, which is concentrated and ultrasonicated, and finally freeze-dried to obtain the Ti3C2 aerogel;

[0055] II. Preparation of Co@NCNT / Ti3C2:

[0056] ①, the unidirectional Ti3C2 aerogel is added into methanol and stirred uniformly to obtain a uniform Ti3C2 aerogel suspension;

[0057] ②, the cobalt nitrate hexahydrate is added into the uniform Ti3C2 aerogel suspension to obtain solution A;

[0058] ③, 2-methylimidazole is added into the uniform Ti3C2 aerogel suspension to obtain solution B;

[0059] ④, at room temperature, solution B is poured into solution A under vigorous stirring, and stirred gently for a period of time, and then left to react, after the reaction is completed, the precipitate is collected to obtain a ZIF-67 / Ti3C2 composite;

[0060] ⑤, under the protection of H2 / Ar mixed gas atmosphere, the ZIF-67 / Ti3C2 composite is annealed at 400℃-500℃ for a period of time, and cooled to room temperature, the cobalt nanoparticle-embedded nitrogen-doped carbon nanotube is vertically anchored on the Ti3C2 nanosheet to obtain a Co@NCNT / Ti3C2 composite, which is a high-efficiency low-surface-energy composite material.

[0061] Specific embodiment three: the difference between this embodiment and one of the specific embodiments one or two is that the mass of LiF and the volume of hydrochloric acid in the etching solution in step one ① is (1.5g-1.6g):20 mL; the mass fraction of hydrochloric acid in step one ① is 30%-38%. The other steps are the same as those in specific embodiments one or two.

[0062] Specific embodiment four: the difference between this embodiment and one of the specific embodiments one to three is that the mass of Ti3AlC2 powder and the volume of etching solution in step one ② is 1g:(18 mL-22 mL); the heating and stirring temperature in step one ② is 35℃-40℃, and the heating and stirring time is 40h-50h. The other steps are the same as those in specific embodiments one to three.

[0063] Embodiment five: the difference between this embodiment and one of embodiments one to four is that in step one ②, the Ti3AlC2 powder is added to the etching solution, heated and stirred for a period of time to obtain a reaction product; the reaction product is first washed 2-4 times using a LiCl solution with a concentration of 1-2 mol / L, then washed 2-4 times using hydrochloric acid with a concentration of 1-2 mol / L, and then repeatedly washed with ultrapure water until 6-7 times to obtain a precipitate; the precipitate is dispersed in deionized water and centrifuged to obtain a dark green Ti3C2 suspension, which is concentrated to 20-25 mg / mL -1 ~25mgmL -1 and ultrasonic for 20-40 min, and finally freeze-dried at -80℃ and 10 Pa for 40-50 h to obtain a unidirectional Ti3C2 aerogel. The other steps are the same as embodiments one to four.

[0064] Embodiment six: the difference between this embodiment and one of embodiments one to five is that in step two ①, the mass to volume ratio of the unidirectional Ti3C2 aerogel to methanol is (50-70 mg):100 mL; in step two ②, the mass to volume ratio of the cobalt nitrate hexahydrate to the uniform Ti3C2 aerogel suspension is (2-3 g):50 mL. The other steps are the same as embodiments one to five.

[0065] Embodiment seven: the difference between this embodiment and one of embodiments one to six is that in step two ③, the mass to volume ratio of the 2-methylimidazole to the uniform Ti3C2 aerogel suspension is (2-3 g):50 mL. The other steps are the same as embodiments one to six.

[0066] Embodiment eight: the difference between this embodiment and one of embodiments one to seven is that in step two ④, the speed of the vigorous stirring is 1000-2000 r / min; in step two ④, the speed of the gentle stirring is 100-200 r / min, and the time of the gentle stirring is 10-20 min; in step two ④, the time of the standing reaction is 10-12 h. The other steps are the same as embodiments one to seven.

[0067] Embodiment nine: the difference between this embodiment and one of embodiments one to eight is that in step two ⑤, the time of the annealing is 4-5 h; in step two ⑤, the volume ratio of H2 to Ar in the H2 / Ar mixed gas is 19:1. The other steps are the same as embodiments one to eight.

[0068] Embodiment ten: this embodiment is a high-efficiency low-surface-energy composite material used as a separator of a lithium-sulfur battery or a positive electrode of a lithium-sulfur battery.

[0069] The beneficial effects of the present application are verified by the following examples:

[0070] Example 1: A preparation method of a high-efficiency low-surface-energy composite material, which is completed according to the following steps:

[0071] I. Preparation of Ti3C2 aerogel:

[0072] ①, 1.56 g of LiF was dissolved in 20 mL of hydrochloric acid and stirred until mixed evenly to obtain an etching solution;

[0073] The mass fraction of hydrochloric acid in step one ① is 36%;

[0074] ②, 1 g of Ti3AlC2 powder was added to the etching solution obtained in step one ①, heated and stirred at 38℃ for 48 h to obtain a reaction product; first washed with 1 mol / L LiCl solution for 3 times, then washed with 1 mol / L hydrochloric acid for 3 times, and then repeatedly washed with ultrapure water until 6 to obtain a precipitate; the precipitate was dispersed in deionized water and centrifuged to obtain a dark green Ti3C2 suspension, which was concentrated to 20 mg / mL -1 and ultrasonic for 30 min, and finally freeze-dried at -80℃ and 10 Pa for 48 h to obtain a unidirectional Ti3C2 aerogel;

[0075] II. Preparation of Co@NCNT / Ti3C2:

[0076] ①, 60 mg of unidirectional Ti3C2 aerogel was added to 100 mL of methanol and stirred evenly to obtain a uniform Ti3C2 aerogel suspension;

[0077] ②, 2.34 g of cobalt nitrate hexahydrate was added to 50 mL of uniform Ti3C2 aerogel suspension to obtain solution A;

[0078] ③, 2.63 g of 2-methylimidazole was added to 50 mL of uniform Ti3C2 aerogel suspension to obtain solution B;

[0079] ④, under the conditions of 26℃ and vigorous stirring, solution B was poured into solution A, and gently stirred for a period of time, and then reacted for 12 h. After the reaction was completed, the mixture was phase separated, and the precipitate was collected to obtain a ZIF-67 / Ti3C2 composite;

[0080] The speed of vigorous stirring in step two ④ is 1500 r / min;

[0081] The speed of gentle stirring in step two ④ is 150 r / min, and the gentle stirring time is 15 min;

[0082] ⑤ Under the protection of H2 / Ar mixed gas atmosphere, the ZIF-67 / Ti3C2 composite was annealed at 435℃ for 4.5h and cooled to room temperature. Nitrogen-doped carbon nanotubes embedded with cobalt nanoparticles were vertically anchored on Ti3C2 nanosheets to obtain Co@NCNT / Ti3C2 composite, which is a high-efficiency low surface energy composite material.

[0083] In step 2⑤, the volume ratio of H2 to Ar in the H2 / Ar mixed gas is 19:1.

[0084] Comparative Example 1: The preparation method of Co@NCNT was carried out according to the following steps:

[0085] ① Add 2.34 g of cobalt nitrate hexahydrate to 50 mL of a uniform Ti3C2 aerogel suspension to obtain solution A;

[0086] ② Add 2.63g of 2-methylimidazole to 50mL of a homogeneous Ti3C2 aerogel suspension to obtain solution B;

[0087] ③ Pour solution B into solution A at 26℃ and with vigorous stirring. Stir gently for a period of time, then let it stand for 12 hours. After the reaction is complete, the resulting mixture undergoes phase separation. Collect the precipitate to obtain ZIF-67.

[0088] The vigorous stirring speed mentioned in step 2③ is 1500 r / min;

[0089] The gentle stirring speed described in step 2③ is 150 r / min, and the gentle stirring time is 15 min;

[0090] ④ Under the protection of H2 / Ar mixed gas atmosphere, ZIF-67 was annealed at 435℃ for 4.5h and cooled to room temperature to obtain nitrogen-doped carbon nanotubes with cobalt nanoparticles embedded vertically on Ti3C2 nanosheets, which is a high-efficiency low surface energy composite material.

[0091] In step 2④, the volume ratio of H2 to Ar in the H2 / Ar mixed gas is 19:1.

[0092] Figure 1 The X-ray diffraction pattern of the Co@NCNT / Ti3C2 composite prepared in Example 1;

[0093] Figure 1 The diffraction peaks all belong to Co@NCNT and Ti3C2, indicating that the product synthesized in Example 1 is a Co@NCNT / Ti3C2 complex.

[0094] Figure 2Low magnification scanning electron microscopy image of Co@NCNT / Ti3C2 composite prepared for Example 1;

[0095] It can be seen from Figure 2 that the product synthesized in Example 1 is based on Ti3C2.

[0096] Figure 3 High magnification scanning electron microscopy image of Co@NCNT / Ti3C2 composite prepared for Example 1;

[0097] It can be seen from Figure 3 that a large number of Co@NCNTs approximately form a regular dodecahedron structure, with a rough surface.

[0098] Figure 4 Low magnification transmission electron microscopy image of Co@NCNT / Ti3C2 composite heterojunction prepared for Example 1;

[0099] Figure 5 High magnification transmission electron microscopy image of Co@NCNT / Ti3C2 composite heterojunction prepared for Example 1;

[0100] It can be seen from Figure 5 that the tip of Co@NCNT is a Co particle, and the interplanar spacing is 0.234 nm and 0.249 nm, corresponding to the (111) and (200) crystal planes of Co, respectively, proving the presence of Co.

[0101] Visible adsorption test:

[0102] A Li2S6 solution (5 mM) was prepared by dissolving lithium sulfide (Li2S) and sulfur in a 1:5 molar ratio in a mixed solution of 1,3-dioxolane (DOL) and 1,2-dimethoxyethane (DME) (volume ratio 1:1) at 60°C for 24 h, then 10 mg of Co@NCNT, Ti3C2, Co@NCNT / Ti3C2 were added to 5 mL of Li2S6 solution respectively under Ar atmosphere, and then left to stand for 24 h. The state of the solution was observed, as shown in Figure 6

[0103] Figure 6 Digital images of Li2S6, Ti3C2 and Li2S6, Co@NCNT and Li2S6, Co@NCNT / Ti3C2 and Li2S6 solutions after standing for 24 hours;

[0104] It can be seen from Figure 6 ​It can be seen that the color of Li2S6 solution added with Co@NCNT, Ti3C2, Co@NCNT / Ti3C2 has been basically changed from brownish yellow to transparent, which indicates that they all have strong adsorption capacity for polysulfides and can greatly promote the conversion process of polysulfides in the next step.

[0105] Application Examples:

[0106] Assembly and electrochemical test of lithium-sulfur battery:

[0107] (1) Preparation of C / S positive electrode:

[0108] After the uniformly mixed C / S (mass ratio of 3:7) was filled with argon as a protective gas and put into a reaction kettle, a melting method was used to heat at 155°C for 12h. After cooling to room temperature, the obtained C / S mixture was uniformly ground with conductive carbon black and PVDF at a mass ratio of 8:1:1, and NMP was used as a solvent for ultrasonic treatment for 1 hour (the total mass of C / S mixture, conductive carbon black and PVDF to the volume of NMP was 1g:5mL), and then an automatic coating machine was used to coat the mixed slurry on an aluminum foil as a positive electrode. The prepared electrode was dried in a vacuum oven at 60°C for 12h, and finally the electrode sheet was cut into a diameter of 13mm, and the sulfur loading was 1 mg / cm 2 , to obtain a C / S positive electrode;

[0109] (2) Preparation of Co@NCNT / Ti3C2 modified composite separator:

[0110] The Co@NCNT / Ti3C2 composite powder prepared in Example 1 and the PVDF binder were uniformly mixed at a mass ratio of 9:1, and a certain amount of N-methyl pyrrolidone (NMP) was added to form a suspension (the total mass of Co@NCNT / Ti3C2 composite powder and PVDF binder to the volume of NMP was 1g:20mL), and the suspension was ultrasonically treated for 1h. Then the uniformly dispersed suspension was vacuum filtered onto a commercial polypropylene (PP) separator (Celgard 2400), and the obtained Co@NCNT / Ti3C2 separator was vacuum dried at 50°C for 2h, and then punched into a diameter of 19mm, and the loading of the modified material on the separator was 0.8mgcm -2 ; As a comparison, the Co@NCNT or Ti3C2 separator was prepared using the same process, and Co@NCNT or Ti3C2 powder was added when uniformly mixed with the PVDF binder.

[0111] (3) Assembly of lithium-sulfur battery:

[0112] The electrochemical performance was tested using a battery model 2025, which was assembled in an argon-filled glove box; the C / S positive electrode prepared in step (1) was used as the positive electrode, lithium sheet as the negative electrode, and the separator was Co@NCNT / Ti3C2 composite separator, Co@NCNT / Ti3C2-PP composite separator, and commercial PP separator (Celgard 2400), respectively; the electrolyte used was 1.0 M lithium bis(trifluoromethane) sulfonimide (LiTFSI) in a DOL / DME (volume ratio 1:1) mixed solution containing 2wt% LiNO3. The amount ratio of electrolyte to sulfur was 20 μL mg -1 ;

[0113] (4) Electrochemical test:

[0114] The cyclic voltammetry (CV) curve of the lithium-sulfur battery was tested on a VMP3 electrochemical workstation (France BioLogic) at a scan rate of 0.1 mV / s and a voltage range of 1.7-2.8 V; the charge and discharge performance test was performed on a LAND battery test system (CT2001A, Wuhan, China) at room temperature and a voltage range of 1.7-2.8 V. The specific capacity was measured at 0.1C, 0.2C, 0.5C, 1C, 2C, and 5C (1 C=1675 mA / g) under constant current charge and discharge.

[0115] Figure 7 The charge and discharge curves of the lithium-sulfur batteries with PP, Ti3C2-PP, Co@NCNT-PP, and Co@NCNT / Ti3C2-PP separators at 0.1C;

[0116] The lithium-sulfur battery using the Co@NCNT / Ti3C2 composite modified separator showed a specific capacity of 1241 mAhg -1 at 0.1C, the lithium-sulfur battery using the Co@NCNT modified separator showed a specific capacity of 1165 mAhg -1 , the lithium-sulfur battery using the Ti3C2 modified separator showed a specific capacity of 953 mAhg -1 , and the lithium-sulfur battery using the commercial polypropylene separator had a specific capacity of 890 mAhg -1 . It can also be seen that the lithium-sulfur battery using the Co@NCNT / Ti3C2 modified separator had a relatively small potential within the dashed line and the potential of the process of oxidizing Li2S to lithium polysulfide and converting lithium polysulfide to Li2S, showing better reaction kinetics than the other two batteries.

[0117] Figure 8 The CV curves of the lithium-sulfur batteries with Ti3C2-PP, Co@NCNT-PP, and Co@NCNT / Ti3C2-PP separators;

[0118] from Figure 8 As can be seen from the data, at 0.1 mV / s, the lithium-sulfur battery with a separator modified by the Co@NCNT / Ti3C2 composite has a larger CV curve area, and the cathode and anode peaks show obvious inward shift. This indicates that the lithium-sulfur battery with a separator modified by the Co@NCNT / Ti3C2 has lower electrochemical polarization and faster redox kinetics, suggesting that the Co@NCNT / Ti3C2 composite can effectively anchor lithium polysulfides, reduce the shuttle effect, and improve battery performance.

[0119] Figure 9 Tafel slope diagrams for different conversion processes in lithium-sulfur batteries with separators of Ti3C2-PP, Co@NCNT-PP, and Co@NCNT / Ti3C2-PP (based on...) Figure 8 (derived from fitting)

[0120] from Figure 9 As can be seen, the lithium-sulfur battery with a separator modified by the Co@NCNT / Ti3C2 composite has a smaller Tafel slope, both during the discharge and charging processes. This indicates that the Co@NCNT / Ti3C2 composite can effectively slow down the formation of lithium polysulfides and reduce their accumulation in the electrolyte.

[0121] Figure 10 Activation energy diagrams of different conversion processes in lithium-sulfur batteries with separators of Ti3C2-PP, Co@NCNT-PP, and Co@NCNT / Ti3C2-PP (based on...) Figure 9 (derived)

[0122] from Figure 10 As can be seen from the data, the activation energy of the lithium-sulfur battery with the membrane modified by the Co@NCNT / Ti3C2 composite is the lowest in all processes, indicating that Co@NCNT / Ti3C2 has a bidirectional catalytic effect on sulfur conversion and can better suppress the shuttle effect from the source.

[0123] Figure 11 Rate characteristics of lithium-sulfur batteries with separators of Ti3C2-PP, Co@NCNT-PP, and Co@NCNT / Ti3C2-PP respectively;

[0124] from Figure 11 As can be seen from the data, at 5C, the lithium-sulfur battery with a separator modified using the Co@NCNT / Ti3C2 composite exhibits a capacity of 559 mAh / g. -1The specific capacity is higher than that of lithium-sulfur batteries using Co@NCNT or Ti3C2 modified separators, and the voltage curve platform remains flat, while Co@NCNT and Ti3C2 alone show obvious polarization, indicating that lithium-sulfur batteries with Co@NCNT / Ti3C2 composite modified separators have better rate performance.

[0125] Figure 12 Cycle performance of lithium-sulfur batteries with Co@NCNT / Ti3C2-PP separators;

[0126] From Figure 12 , it can be seen that the attenuation rate of lithium-sulfur batteries using Co@NCNT / Ti3C2 composite modified separators is 0.051% per cycle at 1C, and the retention rate is more than 60% after 700 cycles, so Co@NCNT / Ti3C2 composite can well improve the cycle performance of lithium-sulfur batteries.

[0127] Figure 13 High sulfur loading and low liquid sulfur ratio performance of lithium-sulfur batteries with Co@NCNT / Ti3C2-PP separators;

[0128] From Figure 13 , it can be seen that even under the conditions of actual sulfur loading (4.52 mg cm -2 ) and dilute electrolyte (5 μL mg -1 ), an area capacity of 3.85 mAh cm -2 can still be achieved, which shows that Co@NCNT / Ti3C2 composite can be beneficial to the operation of lithium-sulfur batteries under harsh conditions.

[0129] Figure 14 In-situ Raman spectrum of lithium-sulfur batteries with Co@NCNT / Ti3C2-PP separators;

[0130] From Figure 14 , it can be seen that a in-situ Raman cell structure is constructed using Co@NCNT / Ti3C2 composite modified separators to monitor the real-time changes of S chemistry. During the initial discharge process, three characteristic Raman bands corresponding to S8 appear at 150.6, 219.4 and 473.9 cm -1 . As the reaction proceeds, these peaks completely disappear, and signals at 232.1, 399.9 and 461.6 cm -1 appear, which are attributed to Li2S8, Li2S6 and Li2S4, respectively. At about 370 cm -1No obvious Li2S Raman signature was observed, which is due to the Li2S intercalation into the nitrogen-defect sites of the NCNT scaffold, which can disturb the lattice vibration of Li2S and suppress its spectral visibility. During the subsequent charging process, the Li2S6 and Li2S4 peaks reappeared and intensified at the early stage, followed by the appearance of the Li2S8 signal at the charging plateau. These intermediates were eventually oxidized back to S8, completing a reversible sulfur redox cycle. No residual LiPSs peaks were observed after charging, which confirms the efficient and complete regeneration of the active S species.

[0131] Figure 15 Different elemental X-ray photoelectron spectroscopy of the Co@NCNT / Ti3C2-PP separator for lithium-sulfur batteries after discharging and charging;

[0132] From Figure 15 It is known from the Co 2p spectra that the valence state of cobalt increases after discharging, indicating that electrons are provided outward, promoting the reduction of sulfur species. During charging, the valence state of cobalt decreases, indicating that electrons flow back to the cobalt center, thus promoting the oxidation of LiPSs to S8. This redox response behavior highlights the role of cobalt as a dynamic electron mediator, which can bidirectionally maintain the transformation of sulfur. The intercalation mechanism is further elucidated in the N 1s spectra. After discharging, the relative intensity of pyridinic nitrogen and pyrrolic nitrogen decreases, while the oxidized nitrogen species increases. This trend indicates that Li2S may intercalate into nitrogen-doped defect sites, changing the local coordination environment and temporarily passivating active nitrogen centers. During charging, the release (delithiation) of Li2S restores the configuration of nitrogen, thus enabling subsequent catalytic cycles. This reversible lithium ion intercalation / deintercalation on nitrogen-defect carbon introduces a dynamic site coupling mechanism, supporting stable cycling. The changes in the C 1s spectrum further confirm this conclusion. After charging, the proportion of high-binding-energy C components increases significantly, which is attributed to the strong interaction between exposed NCNT defect sites and LiTFSI electrolyte species. Conversely, after discharging, these sites may be occupied by Li2S and blocked or adjusted, thus weakening the adsorption of the electrolyte. Consistent with these trends, the binding energy is shown to decrease in the Li 1s spectrum after discharging, reflecting that lithium is in a more reduced state after gaining electrons (similar to Li 0 ). After charging, lithium returns to a higher oxidation state, which is consistent with the loss of electrons during oxidation. This reversible lithium ion redox adjustment at the interlayer-electrolyte interface further demonstrates that the Co@NCNT / Ti3C2 layer not only promotes electron transfer and anchoring of LiPSs, but also serves as a dynamic host for lithium ion intercalation, thus stabilizing the sulfur redox reaction.

[0133] Figure 16Inverse photoelectron and ultraviolet photoelectron spectra of Co@NCNT-PP, Ti3C2-PP, Co@NCNT / Ti3C2, respectively;

[0134] From Figure 16 it can be seen that the d-band center of Ti3C2 is located at -5.91 eV, while that of Co@NCNT is located at -4.97 eV. During the mixing process, the d-band center of Co@NCNT / Ti3C2 is shifted significantly upwards to -3.82 eV, close to the Fermi level, which indicates that the availability of electrons is enhanced. More notably, the half-width of the d-band of Co@NCNT, 21.49 eV, and Ti3C2, 4.53 eV, is specifically narrowed to only 2.80 eV in the composite, which indicates that the electron population for redox reactions is more concentrated and available.

[0135] Figure 17 Inverse photoelectron and ultraviolet photoelectron spectra of Co@NCNT / Ti3C2 after discharging and charging, respectively;

[0136] From Figure 17 it can be seen that the d-band center of Co@NCNT / Ti3C2 material is shifted from -5.97 eV in the discharged state to -6.23 eV in the charged state, which is a direct spectroscopic evidence that the insertion of lithium ions is accompanied by the upward shift of the d-band, while the extraction of lithium ions during the charging process lowers the energy of the d-band.

[0137] Figure 18 Calculated and experimental d-band center of Co@NCNT, Ti3C2, Co@NCNT / Ti3C2, and Co@NCNT / Ti3C2 after discharging and charging, respectively;

[0138] From Figure 18 it can be seen that the d-band center of these catalysts is calculated, and its trend is similar to that of the IPES / UPS results, which proves that the IPES / UPS spectroscopic technique is an effective way to track and make the d-band modulation of the orbital energy level visible.

[0139] Figure 19 Covalent orbital hybridization of Co@NCNT / Ti3C2-PP during the insertion and extraction of Li2S in lithium-sulfur batteries, respectively;

[0140] From Figure 19As can be seen from Table 1, the density functional theory simulation shows that Li2S is more inclined to be combined at the C-N defect, and the binding energy thereof is -1925.08 eV, which is slightly higher than the binding energy on Ti3C2 (-1927.42 eV). The projected density of states (PDOS) shows that the embedding of Li2S can increase the cobalt-sulfur hybridization, and the removal of Li2S can weaken the hybridization, which confirms the reversible electronic interaction between Li2S and the active cobalt site, thereby realizing the bidirectional catalysis.

[0141] Figure 20 The density of states diagram of the Li2S insertion and removal processes in the lithium-sulfur battery of Co@NCNT / Ti3C2-PP, respectively;

[0142] From Figure 20 As can be seen from Table 1, the density functional theory simulation shows that Li2S is more inclined to be combined at the C-N defect, and the binding energy thereof is -1925.08 eV, which is slightly higher than the binding energy on Ti3C2 (-1927.42 eV). The projected density of states (PDOS) shows that the embedding of Li2S can increase the cobalt-sulfur hybridization, and the removal of Li2S can weaken the hybridization, which confirms the reversible electronic interaction between Li2S and the active cobalt site, thereby realizing the bidirectional catalysis.

[0143] The above merely describes preferred embodiments of the present application but is not intended to limit the present application. The present application can have various modifications and changes for those skilled in the art. Any modification, equivalent replacement, improvement, etc. within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A high-efficiency, low-surface-energy composite material, characterized in that... The composite material consists of nitrogen-doped carbon nanotubes embedded with cobalt nanoparticles vertically anchored on Ti3C2 nanosheets, exhibiting both one-dimensional and two-dimensional three-dimensional composite structures. The carbon nanotubes have a diameter of 10–30 nm, each terminated by a cluster of cobalt nanoparticles. The Ti3C2 nanosheets are encapsulated by the carbon nanotubes, aggregated and uniformly distributed on the surface of Ti3C2, with a lateral unfolded dimension of not less than 30 μm. 2 Meanwhile, the thickness is less than 5nm; after Co@NCNT and Ti3C2 are combined in the composite material, the d-band centers of the two components move upward, which is beneficial to the adsorption and catalytic conversion of lithium-sulfur polymer electrolyte.

2. The method for preparing a high-efficiency low surface energy composite material as described in claim 1, characterized in that... The preparation method is specifically carried out according to the following steps: I. Preparation of Ti3C2 aerogel: ① Dissolve LiF in hydrochloric acid and stir until homogeneous to obtain an etching solution; ② Add Ti3AlC2 powder to the etching solution, heat and stir for a period of time to obtain the reaction product; wash the reaction product with LiCl solution and hydrochloric acid in sequence, and then wash the reaction product repeatedly with ultrapure water until 6~7 to obtain the precipitate; disperse the precipitate in deionized water and centrifuge to obtain a dark green Ti3C2 suspension, concentrate it and sonicate it, and finally freeze dry it to obtain Ti3C2 aerogel; II. Preparation of Co@NCNT / Ti3C2: ① Add the unidirectional Ti3C2 aerogel to methanol and stir until homogeneous to obtain a uniform Ti3C2 aerogel suspension; ② Add cobalt nitrate hexahydrate to a uniform Ti3C2 aerogel suspension to obtain solution A; ③ Add 2-methylimidazole to a uniform Ti3C2 aerogel suspension to obtain solution B; ④ At room temperature, under vigorous stirring, pour solution B into solution A, stir gently for a period of time, and then let it stand to react. After the reaction is complete, collect the precipitate to obtain the ZIF-67 / Ti3C2 complex. ⑤ Under the protection of H2 / Ar mixed gas atmosphere, the ZIF-67 / Ti3C2 composite is annealed at 400℃~500℃ for a period of time and cooled to room temperature. Nitrogen-doped carbon nanotubes embedded with cobalt nanoparticles are vertically anchored on Ti3C2 nanosheets to obtain Co@NCNT / Ti3C2 composite, which is a high-efficiency low surface energy composite material.

3. The method for preparing a high-efficiency low surface energy composite material according to claim 1, characterized in that... In step 1①, the mass ratio of LiF to hydrochloric acid in the etching solution is (1.5g~1.6g):20 mL; the mass fraction of hydrochloric acid in step 1① is 30%~38%.

4. The method for preparing a high-efficiency low surface energy composite material according to claim 1, characterized in that... The mass ratio of Ti3AlC2 powder to etching solution in step 1 and 2 is 1 g:(18 mL~22 mL); the heating and stirring temperature in step 1 and 2 is 35℃~40℃, and the heating and stirring time is 40h~50h.

5. The method for preparing a high-efficiency low surface energy composite material according to claim 1, characterized in that... In step 1②, Ti3AlC2 powder is added to the etching solution and heated and stirred for a period of time to obtain the reaction product. First, the product is washed 2-4 times with a 1-2 mol / L LiCl solution, then washed 2-4 times with a 1-2 mol / L hydrochloric acid solution, and finally rinsed repeatedly with ultrapure water until a precipitate is obtained. The precipitate is dispersed in deionized water and centrifuged to obtain a dark green Ti3C2 suspension, which is then concentrated to 20 mg / mL. -1 ~25mg / mL -1 The aerogel was sonicated for 20-40 minutes and then freeze-dried at -80℃ and 10Pa for 40-50 hours to obtain a unidirectional Ti3C2 aerogel.

6. The method for preparing a high-efficiency low surface energy composite material according to claim 1, characterized in that... In step 2①, the mass ratio of the unidirectional Ti3C2 aerogel to the volume ratio of methanol is (50mg~70mg):100mL; in step 2②, the mass ratio of cobalt nitrate hexahydrate to the volume ratio of the homogeneous Ti3C2 aerogel suspension is (2g~3g):50mL.

7. The method for preparing a high-efficiency low surface energy composite material according to claim 1, characterized in that... The mass ratio of 2-methylimidazole to the volume ratio of the uniform Ti3C2 aerogel suspension in step 2③ is (2g~3g):50mL.

8. The method for preparing a high-efficiency low surface energy composite material according to claim 1, characterized in that... The speed of vigorous stirring in step 2④ is 1000r / min to 2000r / min; the speed of gentle stirring in step 2④ is 100r / min to 200r / min, and the time for gentle stirring is 10min to 20min; the time for standing reaction in step 2④ is 10h to 12h.

9. The method for preparing a high-efficiency low surface energy composite material according to claim 1, characterized in that... The annealing time mentioned in step 2.5 is 4h~5h; the volume ratio of H2 to Ar in the H2 / Ar mixed gas mentioned in step 2.5 is 19:

1.

10. The application of a high-efficiency, low-surface-energy composite material prepared by the preparation method according to claim 1, characterized in that... A high-efficiency, low-surface-energy composite material is used as a separator or positive electrode in lithium-sulfur batteries.

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