V4C3Tx MXene-porous carbon OPC composite coating and synthesis method thereof

Abstract

The invention discloses a V4C3Tx MXene (at) porous carbon OPC composite coating and a synthesis method, the V4C3Tx MXene (at) porous carbon OPC composite coating is prepared by the following steps: firstly, etching V4C3Tx MXene by using HCl and LiF through a wet chemical etching method to prepare nano Mo2V2C3Tx powder, then forming a metal organic framework MOF through coordination of Zr < 4 + > and H2ATA, generating a Zr-MOF precursor after hydrothermal reaction, carbonizing the precursor at 800 DEG C in an argon atmosphere, and carbonizing at high temperature to convert the MOF into a porous carbon skeleton OPC, thereby obtaining the V4C3Tx MXene (at) porous carbon OPC composite coating. Meanwhile, ZrO2 is removed through subsequent acid pickling. Then V4C3TxMXene, OPC and a PVDF binder are mixed according to the mass ratio of 7: 2: 1, an NMP solvent is added dropwise, grinding is performed to form a uniform coating, the viscosity of the coating is 2000-3000 cP, and the battery diaphragm can be uniformly coated with the coating. According to the V4C3Tx MXene-porous carbon OPC composite coating prepared by the preparation method disclosed by the invention, the electrocatalytic activity, the conductivity and the polysulfide fixing capacity are remarkably improved through a material synergistic effect, uniform deposition of lithium ions is promoted, and meanwhile, the V4C3Tx MXene-porous carbon OPC composite coating has mechanical stability and industrialization potential.

Description

Technical Field

[0001] The present invention relates to the technical field of coating material preparation, and particularly to a V4C3T x MXene@porous carbon OPC composite coating and a synthesis method thereof. Background Art

[0002] The research on the functional modification of lithium-sulfur battery separators is focusing on three core issues: the suppression of polysulfide shuttle effect, the synergistic failure of catalytic interfaces and conductive skeletons, and the contradiction between kinetic performance and structural stability. The main manifestations are as follows: (1) Although traditional carbon-based coatings can provide a conductive network of 120 S / cm, their physical adsorption energy for long-chain polysulfides is only 0.4 - 0.6 eV, and coating exfoliation occurs due to volume expansion during cycling, resulting in a 380% increase in the interfacial contact resistance after 500 cycles. In recent years, the emerging MXene-based modification schemes (such as Ti3C2T x / CNTs hybrid coatings) have increased the adsorption energy to 1.2 eV through the Lewis acid-base interaction of surface end groups. However, the problem of anisotropic ion transport caused by MXene sheet stacking is prominent, and the lithium-ion diffusion coefficient drops sharply to 2.3×10 -10 cm² / s at a high sulfur loading of 5 mg / cm², resulting in a concentration polarization overpotential as high as 270 mV.

[0003] (2) The synergistic failure mechanism of catalytic interfaces and conductive skeletons is also a major technical barrier in the functional modification of lithium-sulfur battery separators. Although metal-organic framework-derived carbon materials have a mesoporous structure of 3.2 nm that can improve the polysulfide confinement ability, there is a lattice mismatch of ~1.8% at the heterojunction with MXene, and microcracks are generated under charge-discharge stress, reducing the exposure rate of catalytic active sites from the initial 82% to 31% after 300 cycles.

[0004] (3) The contradiction between kinetic performance and structural stability is also a major technical barrier in the functional modification of lithium-sulfur battery separators: The current optimal MoS2@rGO catalytic layer can achieve a specific capacity of 832 mAh / g at a rate of 0.5C. However, its two-dimensional planar structure causes the vertical deposition thickness of Li2S to exceed 50 nm, leading to local stress concentration and a coating crack propagation rate of 1.2 μm / cycle. Although the emerging liquid metal modification strategy reduces the Li2S nucleation overpotential to 80 mV through an adaptive interface, the electromigration effect of metal droplets at a high current density (3C) results in uneven distribution of active substances, causing the capacity retention rate to plummet to 41% after 100 cycles. These multi-dimensional performance conflicts lead to a fundamental bottleneck in the industrial application of existing modified separators - when the sulfur surface amount is increased to 8 mg / cm², the battery volume energy density is always difficult to exceed 700 Wh / L, and the 1C cycle life is generally less than 400 times, severely restricting the practical application of high-energy lithium-sulfur batteries. Summary of the Invention

[0005] The embodiments of the present application provide a V4C3T x MXene@porous carbon OPC composite coating and its synthesis method, which solve the technical problems of suppressing the polysulfide shuttle effect, the synergistic failure of the catalytic interface and the conductive skeleton, and the contradiction between kinetic performance and structural stability in the functional modification coating of lithium-sulfur battery separators in the prior art. Through the material synergistic effect, the electrocatalytic activity, conductivity and polysulfide fixation ability are significantly improved, and the uniform deposition of lithium ions is promoted.

[0006] The embodiments of the present application provide a V4C3T x MXene@porous carbon OPC composite coating synthesis method, comprising the following steps: Step 1: Preparation of Mo2V2C3T x nanosheet powder Mix HCl solution and LiF to obtain mixed solution A, then add Mo2V2AlC3 powder to mixed solution A, and etch at 45 - 55 °C for 48 - 72 h to obtain Mo2V2C3T x suspension; then centrifuge the Mo2V2C3T x suspension, collect the precipitate and wash it to neutral, and dry it to obtain Mo2V2C3T x nanosheet powder; Step 2: Preparation of octahedral nanoporous carbon OPC ① Dissolve ZrCl4 and H2ATA in a mixed solution of DMF and acetic acid, stir and sonicate until transparent, then transfer to a polytetrafluoroethylene tank for hydrothermal reaction. After heating in an oven, transfer the product to a centrifuge tube, wash repeatedly with methanol until the impurity components are removed, and finally transfer to a vacuum drying oven for drying. Grind the obtained dry particles into powder; ② Place the powder in a tube furnace at 800 °C for carbonization for 150 min. The carbonization atmosphere is a special gas, and the heating rate is a constant linear rate to obtain a black powder product; ③ Add the black powder to 30 wt% hydrofluoric acid, stir at room temperature for 8 h. After the reaction, centrifuge the black powder with deionized water until the supernatant is neutral. Finally, transfer the product to a vacuum drying oven and heat it at 80 °C to obtain octahedral nanoporous carbon OPC; Step 3: V4C3T x Synthesis of MXene @ nanoporous carbon OPC composite coating The V4C3T x MXene prepared in Step 1, the OPC prepared in Step 2, and the binder are mixed in a ratio of 7:2:1, and after sufficient grinding for 30 min, then dropwise add N-methylpyrrolidone (NMP) solution and continue grinding to form a uniform coating, that is, V4C3T x MXene @ nanoporous carbon OPC composite coating is prepared.

[0007] Preferably, in Step 1, the HCl concentration is 12 mol / L, and the mass ratio of HCl to LiF and Mo2V2AlC3 is 5.48 - 10.95:1:0.625 - 1.25.

[0008] Preferably, in Step 2, both the stirring and sonication are 15 min.

[0009] Preferably, in Step 2, the carbonization atmosphere is argon, and the heating rate is 5 °C min -1

[0010] Preferably, in Step 3, the coating viscosity is 2000 - 3000 cP.

[0011] The embodiment of the present invention also provides a V4C3T x MXene @ nanoporous carbon OPC composite coating, and the composite coating is prepared by any of the above methods.

[0012] The embodiment of the present invention also provides an application of a V4C3T x MXene @ nanoporous carbon OPC composite coating. The composite coating is used as a functional coating and coated on the separator for lithium batteries, and the thickness of the composite coating is 5 - 10 μm.

[0013] One technical solution provided in the embodiments of the present application has at least the following technical effects: 1. Since MXene, OPC, and PVDF binder are mixed in a mass ratio of 7:2:1, a high proportion of MXene provides catalytic activity, OPC enhances conductivity and adsorption capacity, and PVDF ensures coating adhesion. NMP solvent is added dropwise and ground to form a uniform coating. The coating viscosity is 2000 - 3000 cP, with excellent viscosity, effectively solving the technical problems of suppressing the polysulfide shuttle effect in the functionalized modified coating of the lithium-sulfur battery separator, the synergistic failure of the catalytic interface and the conductive framework, and the contradiction between kinetic performance and structural stability. Through the material synergistic effect, the electrocatalytic activity, conductivity, and polysulfide fixation ability are significantly improved, promoting the uniform deposition of lithium ions, and at the same time having mechanical stability and industrialization potential.

[0014] 2. V4C3T in the embodiments of the present invention x The MXene@porous carbon OPC composite coating is coated on the battery separator, and the battery separator is applied to the battery. The test comparison results show that the separator has a strong ability to enhance the redox reaction kinetics of polysulfide lithium compared with before coating, and can reduce the initial overpotential of Li2S nucleation, thereby promoting the rapid nucleation and growth kinetics of Li2S. Description of the Drawings

[0015] Figure 1 Scanning electron microscope (SEM) images of V4C3T x MXene and OPC materials prepared in Example 1 of the present application.

[0016] Figure 2 Scanning electron microscope (SEM) images of V4C3T x MXene@OPC-PP separator bending and folding test images prepared in Example 2 of the present application.

[0017] Figure 3 Cyclic voltammograms of Li2S6-containing electrolytes of three different types of separators prepared in Example 3 of the present application.

[0018] Figure 4 Li2S nucleation test results of three different types of separators prepared in Example 3 of the present application.

[0019] Figure 5 Rate cycling performance graphs of three different types of separators prepared in Example 3 of the present application. Detailed Embodiments

[0020] The embodiments of the present application provide a V4C3T xMXene@Porous Carbon OPC Composite Coating and Synthesis Method, which solve the technical problems in the prior art of the suppression of the polysulfide shuttle effect by the functionalized modification coating of the lithium-sulfur battery separator, the synergistic failure of the catalytic interface and the conductive framework, and the contradiction between the kinetic performance and the structural stability. Through the material synergistic effect, the electrocatalytic activity, conductivity and polysulfide fixation ability are significantly improved, and the uniform deposition of lithium ions is promoted.

[0021] The technical solutions in the embodiments of the present application to solve the above problems have the following general ideas: First, V4C3T is etched by the wet chemical etching method x MXene to obtain nanoscale Mo2V2C3T x powder, and then through Zr 4+ coordinates with H2ATA (aminotrimethylphosphonic acid) to form a metal-organic framework MOF, reacts at 120 °C for 48 hours to generate a Zr-MOF precursor, and the precursor is carbonized at 800 °C in an argon atmosphere. The high-temperature carbonization converts the MOF into a porous carbon framework OPC, and at the same time, ZrO2 is removed by subsequent pickling. Then, MXene, OPC and PVDF binder are mixed in a mass ratio of 7:2:1. The high proportion of MXene provides catalytic activity, OPC enhances conductivity and adsorption capacity, and PVDF ensures the adhesion of the coating. Dropwise add NMP solvent and grind to form a uniform coating. The coating viscosity is 2000-3000 cP, which can be uniformly coated on the battery separator. After being coated and modified with V4C3T x MXene@Porous Carbon OPC composite coating on the battery separator is applied to the battery. The test comparison results show that the current response is the strongest at 0.41 V (oxidation peak) and -0.37 V (reduction peak), indicating that it significantly accelerates the LiPS conversion; the Li2S deposition capacity reaches 277.78 mAh / g, which is better than the control group (164.61 and 145.42 mAh / g); at a high rate of 5 C, the capacity remains 433.47 mAh / g, and at 0.2 C, it recovers to 1039.46 mAh / g, proving that V4C3T x MXene@Porous Carbon OPC composite coating on the battery separator has excellent kinetic performance. The test results verify that V4C3T x MXene@Porous Carbon OPC composite coating significantly improves the electrocatalytic activity, conductivity and polysulfide fixation ability through the material synergistic effect, promotes the uniform deposition of lithium ions, and at the same time has mechanical stability and industrialization potential.

[0022] In order to better understand the above technical solutions, the above technical solutions will be described in detail below in conjunction with the accompanying drawings of the specification and specific implementation manners. Example 1

[0023] Step 1: Preparation of Mo2V2C3T x Preparation of nano-sheet powder (1) Mix 20 - 40 mL of 12 M HCl solution and 1.6 g of LiF to obtain a mixed solution. Add 1 - 2 g of Mo2V2AlC3 powder to the mixed solution and etch at 45 - 55 °C for 48 - 72 h to obtain Mo2V2C3T x suspension.

[0024] (2) After centrifuging the Mo2V2C3T x suspension, collect the precipitate and wash it until neutral. After drying, obtain Mo2V2C3T x nano-sheet powder (V4C3T x MXene).

[0025] Step 2: Preparation of octahedral nano-porous carbon OPC (1) Dissolve 0.396 g of ZrCl4 and 0.306 g of H2ATA in a mixed solution of 45 mL of DMF and 5 mL of acetic acid, stir for 15 min, and then sonicate for 15 min. Transfer the obtained transparent solution to a 100 mL polytetrafluoroethylene autoclave for hydrothermal reaction. After heating in an oven at 120 °C for 48 h, transfer the product to a centrifuge tube and wash it repeatedly with methanol 6 times. Finally, transfer it to a vacuum drying oven and heat it at 90 °C for 3 h, and grind the obtained dry particles into powder.

[0026] (2) Place 0.3 g of the powder in a tube furnace at 800 °C for carbonization for 150 min, the carbonization atmosphere is argon, and the heating rate is 5 °C min -1 . Finally, obtain a black powder product.

[0027] (3) Add 0.4 g of the black powder to 30 mL of hydrofluoric acid (30 wt%) and stir at room temperature for 8 h. After the reaction, centrifuge the black powder with deionized water until the supernatant is neutral. Finally, transfer the product to a vacuum drying oven and heat it at 80 °C for 12 h to obtain octahedral nano-porous carbon (OPC).

[0028] Step 3: Synthesis of V4C3T x MXene @ porous carbon OPC composite coating Mix the V4C3T x MXene prepared in Step 1, the porous carbon OPC prepared in Step 2, and the binder PVDF in a ratio of 7:2:1. After thorough grinding for 30 min, then add N-methylpyrrolidone (NMP) solution dropwise and continue grinding to form a uniform coating, that is, obtain V4C3Tx MXene@porous carbon OPC composite coating. Embodiment 2

[0029] The coating was coated on a commercial PP separator and dried in a vacuum oven at 60 °C for 12 h to obtain the modified V4C3T x MXene@OPC-PP separator.

[0030] Please refer to Figure 2 ,V4C3T x The MXene@OPC coating has good adhesion to the commercial separator, and no obvious powdering occurs after multiple folding, indicating that V4C3T x The MXene@porous carbon OPC composite coating has excellent adhesive properties. Embodiment 3

[0031] The V4C3T obtained in Example 2 x The MXene@OPC-PP separator was assembled into a button-type battery in the order of sulfur / porous carbon cathode → electrolyte → separator → electrolyte → metal lithium anode. During the assembly process, 25 μL of electrolyte was added to each side of the positive and negative electrodes. The assembled battery was then left to stand for 24 h, followed by the corresponding electrochemical test.

[0032] Please refer to Figures 3 - 5 ,exist Figure 3 In the cyclic voltammetry curve test, an electrolyte containing Li2S6 was used; Figure 4 In the Li2S nucleation test in , the electrolyte containing Li2S8 was used on the cathode side, while the normal electrolyte was used on the anode side; Figure 5 In the rate cycling performance diagram, normal electrolyte is used.

[0033] Test results such as Figure 3 As shown, during the polarization process, Li2S6 is converted into high-order and low-order polysulfides at the anode and cathode, respectively. x The cell with MXene@OPC-PP separator showed the largest peak area and the highest peak current response (0.41 V and −0.37 V), indicating its strong ability to enhance the redox reaction kinetics of lithium polysulfide.

[0034] Please refer to Figure 4 , Figure 4 The results of the constant potential nucleation experiment reveal the regulatory effect of different separators on solid-state Li2S. According to Faraday's law, Figure 4 The specific capacities of Li2S deposited on the cathode with the three separators were calculated to be 277.78, 164.61, and 145.42 mAh g-1 This result means that V4C3T x The MXene@OPC-PP separator reduces the initial overpotential of Li2S nucleation, thus promoting the rapid nucleation and growth kinetics of Li2S.

[0035] Please refer to Figure 5 , at a current density of 5 C, the specific capacity remains at 433.47 mAh g -1 , when the current density is reset to 0.2 C, the discharge capacity recovers to 1039.46 mAh g -1 . The excellent rate performance of the optimized battery confirms the improvement of the polysulfide conversion kinetic capacity, which is attributed to V4C3T x The synergistic enhancement effect of MXene and porous carbon OPC.

[0036] The technical solutions in the embodiments of the present application described above have at least the following technical effects: 1. Since MXene, porous carbon OPC and PVDF binder are mixed in a mass ratio of 7:2:1, the high proportion of MXene provides catalytic activity, OPC enhances conductivity and adsorption capacity, and PVDF ensures coating adhesion. NMP solvent is added drop by drop and ground to form a uniform coating with a coating viscosity of 2000 - 3000 cP and excellent viscosity, effectively solving the technical problems of inhibiting the polysulfide shuttle effect of the functionalized modified coating of the lithium-sulfur battery separator, the synergistic failure of the catalytic interface and the conductive skeleton, and the contradiction between kinetic performance and structural stability. The electrocatalytic activity, conductivity and polysulfide fixation ability are significantly improved through the material synergistic effect, promoting the uniform deposition of lithium ions, and at the same time having mechanical stability and industrialization potential.

[0037] 2. The V4C3T x MXene@porous carbon OPC composite coating is coated on the battery separator. After testing, the separator has a strong ability to enhance the redox reaction kinetics of polysulfide compared with before coating, and can reduce the initial overpotential of Li2S nucleation, thus promoting the rapid nucleation and growth kinetics of Li2S.

[0038] Although the preferred embodiments of the present invention have been described, those skilled in the art can make additional changes and modifications once they know the basic creative concept. Therefore, the appended claims are intended to be construed to include the preferred embodiments and all changes and modifications falling within the scope of the present invention.

[0039] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the present invention The spirit and scope of the invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention is also intended to include these changes and variations.

Claims

1. A V4C3T x Synthesis method of MXene @ porous carbon OPC composite coating, characterized in that It includes the following steps: Step 1: Mo2V2C3T x Preparation of nano-sheet powder Prepare a mixed solution A by mixing an HCl solution and LiF, and then add Mo2V2AlC3 powder to the mixed solution A. Etch at 45 - 55 °C for 48 - 72 h to obtain Mo2V2C3T x suspension; then centrifuge the Mo2V2C3T x suspension, collect the precipitate and wash it until neutral, and dry it to obtain Mo2V2C3T x nanosheet powder; Step 2: Preparation of octahedral nanoporous carbon OPC ① Dissolve ZrCl4 and H2ATA in a mixed solution of DMF and acetic acid, stir and ultrasonicate until transparent, then transfer to a polytetrafluoroethylene tank for hydrothermal reaction. After heating in an oven, transfer the product to a centrifuge tube, wash repeatedly with methanol until the impurity components are removed, and finally transfer to a vacuum drying oven for drying. Grind the obtained dried particles into powder; ② Place the powder in a tubular furnace at 800 °C for carbonization for 150 min. The carbonization atmosphere is a special gas, and the heating rate is a constant linear rate to obtain a black powder product; ③ Add the black powder to 30 wt% hydrofluoric acid, stir at room temperature for 8 h. After the reaction, centrifuge the black powder with deionized water until the supernatant is neutral. Finally, transfer the product to a vacuum drying oven and heat it at 80 °C to obtain octahedral nanoporous carbon OPC; Step 3: V4C3T x Synthesis of MXene @ Porous Carbon OPC Composite Coating The V4C3T prepared in Step 1 x After mixing the MXene prepared in Step 1, the OPC prepared in Step 2 and the binder in a ratio of 7:2:1, and thoroughly grinding for 30 min, then the N-methylpyrrolidone solution is added dropwise and grinding is continued to form a uniform coating, thus obtaining the V4C3T x MXene@porous carbon OPC composite coating.

2. The synthesis method according to claim 1, wherein In the first step, the concentration of HCl is 12 mol / L, and the mass ratio of HCl to LiF and Mo2V2AlC3 is 5.48 - 10.95:1:0.625 - 1.

25.

3. The synthesis method according to claim 1, characterized in that, Both the stirring and ultrasonication in the second step are 15 min.

4. The synthesis method according to claim 1, wherein The carbonization atmosphere in the second step is argon, and the heating rate is 5 °C / min -1 .

5. The synthesis method according to claim 1, wherein The viscosity of the coating in the third step is 2000 - 3000 cP.

6. A V4C3T x MXene@porous carbon OPC composite coating, characterized in that The composite coating is prepared by any of the methods described in claims 1 - 4.

7. A V4C3Tx MXene @ porous carbon OPC composite coating, characterized in that, The composite coating is used as a functional coating and coated on the separator for lithium batteries, and the thickness of the composite coating is 5 - 10 μm.

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