A single-layer porous amorphous carbon film and preparation method, a lithium-ion battery modified diaphragm and preparation method

Abstract

The present invention discloses a single-layer porous amorphous carbon film and a preparation method thereof, a lithium-ion battery modified diaphragm and a preparation method thereof. The preparation method of the single-layer porous amorphous carbon film comprises the following steps: preparing an amphiphilic condensed-ring aromatic hydrocarbon monomer Tpy-large; assembling the Tpy-large condensed-ring aromatic hydrocarbon as a monomer into a film at a water-air interface by a Langmuir film-forming method and transferring the film to be pyrolyzed; this method can solve the contradiction between the amount of carbon source and the number of growth cores mentioned above, each condensed-ring aromatic hydrocarbon molecule is a nucleation core, and the low volatility of condensed-ring aromatic hydrocarbon molecules also ensures that there are sufficient carbon source molecules during the film growth process, and the single-layer porous amorphous carbon film is successfully prepared; at the same time, the Langmuir film preparation technology can reasonably regulate the interface pressure, adjust the distance between amphiphilic condensed-ring aromatic hydrocarbon molecules, further reduce the amount of carbon source, and thus regulate the film thickness; the method is used for lithium-ion battery modified diaphragms to regulate Li + transport, deposition and inhibiting the growth of lithium dendrites.

Description

Technical Field

[0001] The present invention belongs to the technical field of functional materials and relates to porous amorphous carbon film materials, in particular to a single-layer porous amorphous carbon film and a preparation method thereof, and a lithium-ion battery modified diaphragm and a preparation method thereof. Background Art

[0002] Carbon is one of the most versatile elements in the periodic table. It can react with almost all elements in the form of sp, sp 2 and sp 3 Two-dimensional (2D) carbon materials, composed of conjugated networks, possess unique π-electron systems and exceptional carrier transport properties. By varying the periodicity of the hybridized carbon atom network, the physical and chemical properties of 2D carbon materials, particularly their band gap, can be tuned. These 2D carbon materials have a wide range of applications in transistors, energy storage devices, and superconductors.

[0003] Many two-dimensional material membranes, such as graphene, do not inherently possess nanopores. Nanopores can be introduced into two-dimensional material membranes through physical methods such as electron beam irradiation, plasma etching, and ion bombardment. However, these methods suffer from poor control over the chemical functionality of the pores, elusive process scalability, and high process costs. While bottom-up fabrication of two-dimensional nanoporous membranes could address these issues, the lack of reliable methods to produce high-quality, large-scale nanoporous two-dimensional membranes remains technically challenging.

[0004] At present, the preparation of single-layer nanoporous amorphous carbon films is difficult. First, there is a contradiction between the amount of carbon source and the number of growth cores in the growth of single-layer amorphous carbon films. According to the Arrhenius equation, the growth of single-layer amorphous carbon films requires as many growth nucleation cores as possible. The methods for preparing amorphous carbon films reported in existing literature are mainly chemical vapor deposition methods. In chemical vapor deposition methods, the growth nucleation core requirements can usually be met by providing a large amount of carbon source (for example, increasing the methane flow rate and ratio). However, at the same time, a large amount of carbon source will accelerate the growth of the carbon film into a multilayer structure instead of staying in a single layer, and it is difficult to obtain a large-area single-layer amorphous carbon film with this method.

[0005] Langmuir-Blodgett (LB) film technology is a single-molecule film deposition technique invented by Langmuir and Blodgett. The so-called LB film refers to a single-layer or multi-layer molecular film obtained by depositing one or more molecular films spread on the surface of a liquid onto a substrate using a certain pulling method. LB films have many advantages over other systems: (1) They are ultra-thin and have precisely controlled thickness, with film thicknesses as low as nanometers; (2) The molecular arrangement in the film is highly ordered and anisotropic, which is controllable at the molecular level, allowing for the design and realization of different-level structures as needed; and (3) The film-making conditions are mild and the operation is simple.

[0006] Lithium metal has a high theoretical energy density (3860 mAh g -1 ), the lowest electrochemical redox potential (-3.04 V vs. standard hydrogen electrode) and low density (0.534 g cm -3 ), is considered to be the ultimate material that can replace graphite negative electrodes in high-energy-density batteries. However, despite the many advantages of lithium metal batteries, their application still faces some problems: due to the continuous side reactions between the highly reactive metallic lithium and the organic electrolyte during the battery cycle, the coulombic efficiency (CE) decreases. In addition, during the battery cycle, the uneven lithium precipitation on the surface of the metallic lithium negative electrode is prone to form needle-shaped, mossy or branch-like lithium dendrites. The continuous growth of lithium dendrites will cause the repeated rupture and growth of the solid electrolyte interphase (SEI), resulting in the attenuation of the battery cycle performance, further piercing the diaphragm to reach the positive electrode, causing an internal short circuit, and ultimately causing the battery to catch fire and explode, posing a huge safety hazard.

[0007] In liquid-based lithium metal batteries, the separator is a key component. On the one hand, it acts as a barrier to isolate the positive and negative electrodes and prevent electron tunneling between the electrodes and internal short circuits. On the other hand, it also acts as a barrier between the positive and negative electrodes. + The diaphragm affects the mass transfer (diffusion) of lithium ions on the electrode, thereby affecting the growth of lithium dendrites. However, the role of the diaphragm in the growth of lithium dendrites has not received much attention. Currently, polyolefin diaphragms are widely used, but the pore size range of this diaphragm is large and the distribution is uneven, so uneven Li ions are formed during the deposition process. + flux, it is precisely because of the uneven Li + The flux distribution caused the local excessive growth of lithium dendrites and the uneven deposition of lithium. + To solve the problem of uneven distribution, the development of advanced separators with uniform pore distribution or coatings with special structural arrangements can promote the formation of uniform Li + flux, thereby achieving excellent deposition cycle stability of the metallic lithium anode.

[0008] The work on membrane modification to suppress lithium dendrites mainly focuses on using materials such as graphene, h-BN, and ceramic films to coat the surface of commercial membranes. However, these materials are highly polycrystalline and have many grain boundaries, which are mechanically weak points and may eventually contribute to the growth of lithium dendrites. The ideal membrane must be designed to achieve Li + The uniform distribution of Li +flux, preventing the formation of a negative electrode nucleus of lithium metal with a thermodynamic radius higher than the critical thermodynamic radius. At the same time, the thickness of the diaphragm is also an influencing factor. When the thickness of the diaphragm is thicker, it will increase the Li + Resistance to flow. Summary of the Invention

[0009] In view of the shortcomings of the prior art, the present invention aims to provide a single-layer porous amorphous carbon film and its preparation method, a lithium-ion battery modified diaphragm and its preparation method, and a large-area single-layer porous amorphous carbon film is prepared by a "bottom-up" Langmuir film formation-pyrolysis two-step method of organic small molecules, which effectively reduces the amount of carbon source and thus regulates the film thickness. The single-layer porous amorphous carbon film is used to prepare a lithium-ion battery modified diaphragm, which can effectively regulate Li + deposition and inhibit the growth of lithium dendrites.

[0010] In order to achieve the above object, the present invention adopts the following technical solutions:

[0011] A method for preparing a single-layer porous amorphous carbon film comprises the following steps:

[0012] Step 1, preparing the amphiphilic condensed ring aromatic hydrocarbon monomer Tpy-large;

[0013] Step 2: Dissolve the amphiphilic fused ring aromatic hydrocarbon monomer Tpy-large prepared in step 1 in chloroform to prepare a 1 mg / L solution, and drop 20 μL of the solution onto a 50 cm 2 The water-air interface;

[0014] Step 3: After the chloroform is completely evaporated, the baffle of the Langmuir thin film preparation instrument is slowly pushed to maintain the interface pressure of the condensed aromatic hydrocarbon molecular interface assembled film at 5 to 20 mN / m, and the assembled film is transferred to the substrate by a vertical deposition method;

[0015] Step 4: Transfer the substrate with the assembled film prepared in step 3 to a rapid thermal processing tube furnace, and pyrolyze it at 800-900° C. in an argon atmosphere at normal pressure for 1 min to obtain a single-layer porous amorphous carbon film.

[0016] Preferably, the preparation method of the amphiphilic fused-ring aromatic hydrocarbon monomer Tpy-large described in step 1 comprises:

[0017] S1. Under a nitrogen atmosphere, dissolve 26.7 g of hexaphenylbenzene in 250 mL of 0.1 M sodium carbonate solution. Add 40 mL of liquid bromine dropwise while stirring. Stir at room temperature overnight. Filter the resulting precipitate and wash it with 10% sodium bicarbonate to obtain hexaphenylbenzene bromide, which is recorded as substance 2.

[0018] S2. To 20 mL of acetic acid solution containing 365 mg of ammonium acetate was added 500 mg of 4'-(4-bromophenyl)-2,2':6',2"-isopyridine, and the mixture was stirred for 8 hours. The resulting precipitate was filtered and recrystallized from ethanol. The recrystallized product was dissolved in 5 mL of DMSO with 32 mg of Pd(dppf)Cl2, 379 mg of potassium acetate, and 344 mg of diboronic acid pinacol ester. The mixture was frozen and deoxygenated three times, and then heated to 80°C under nitrogen protection for 12 hours. After the reaction, the reaction solution was extracted with chloroform, the extract was dried over magnesium sulfate, and the solvent was evaporated. The resulting solid was recrystallized from ethanol to obtain pure substance 3.

[0019] S3. Substance 2 and substance 3 are subjected to classic Suzuki coupling to obtain the amphiphilic fused ring aromatic hydrocarbon monomer Tpy-large.

[0020] Preferably, the waiting time for the chloroform in step 3 to completely evaporate is 5 to 15 minutes.

[0021] Preferably, the substrate in step three comprises a copper sheet, a silicon sheet or a glass sheet.

[0022] A single-layer porous amorphous carbon film prepared by the method described above.

[0023] A method for preparing a modified lithium-ion battery diaphragm comprises the following steps:

[0024] Step 1: transferring the single-layer porous amorphous carbon film according to claim 4 onto a hydrophilic single-layer polypropylene separator by a PMMA method;

[0025] Step 2: The single-layer porous amorphous carbon film prepared in step 1 was transferred to a hydrophilic single-layer polypropylene separator by immersing in acetone for 10 minutes to remove polymethyl methacrylate to obtain a lithium-ion battery modified separator.

[0026] A modified lithium ion battery diaphragm prepared by the method described above.

[0027] Compared with the prior art, the present invention has the following technical effects:

[0028] The present invention proposes for the first time a method for preparing a large-area single-layer porous amorphous carbon film from organic small molecules "bottom-up" through a two-step Langmuir film formation-pyrolysis method, that is, a method for preparing an amorphous carbon film by assembling a Ty-large condensed-ring aromatic hydrocarbon at a water-air interface using a Langmuir film formation method and transferring pyrolysis. This method can solve the contradiction between the amount of carbon source and the number of growth cores mentioned above. Each condensed-ring aromatic hydrocarbon molecule is a nucleation core. The low volatility of condensed-ring aromatic hydrocarbon molecules also ensures that there are sufficient carbon source molecules during the film growth process, and a single-layer porous amorphous carbon film is successfully prepared. At the same time, the Langmuir film preparation technology can reasonably control the interfacial pressure and adjust the distance between amphiphilic condensed-ring aromatic hydrocarbon molecules, further reducing the amount of carbon source and thus controlling the film thickness. The amorphous carbon film has good mechanical support. At the same time, the amorphous carbon film itself has nanopores and is a porous amorphous carbon film. The surface of the film is evenly distributed with Li + nanopores through which

[0029] The present invention combines a porous amorphous carbon film prepared by the Langmuir film-forming-pyrolysis method with a hydrophilic single-layer polypropylene membrane to prepare a lithium-ion battery modified membrane. Compared with the unmodified membrane, the membrane modified with the amorphous carbon membrane can regulate the Li + concentration distribution, improve the deposition behavior of lithium, and thus regulate the Li + The transfer and deposition of lithium metals can be enhanced and the growth of lithium dendrites can be suppressed, providing a feasible and effective way to improve the cycle stability of lithium metal batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a schematic diagram of the preparation process of amphiphilic condensed ring aromatic hydrocarbons;

[0031] Figure 2 Schematic diagram of the process for preparing single-layer porous amorphous carbon membrane from amphiphilic condensed-ring aromatic hydrocarbons;

[0032] Figure 3 SEM image (10.0 μm) of the single-layer porous amorphous carbon film prepared in Example 1;

[0033] Figure 4 SEM image (100.0 μm) of the single-layer porous amorphous carbon film prepared in Example 1;

[0034] Figure 5 This is the single-layer porous amorphous carbon film transferred onto the silicon wafer in Example 1 (dark color);

[0035] Figure 6 This is a test diagram for ion transmembrane transport;

[0036] Figure 7 Comparison of time-voltage curves of Li|Li symmetric batteries (0.5 mA cm -2; 1mAh cm -2 );

[0037] Figure 8 This is a comparison chart of LiFePO4|Li battery rate performance. DETAILED DESCRIPTION

[0038] The specific contents of the present invention are further explained in detail below with reference to the embodiments.

[0039] Example 1

[0040] This embodiment provides a method for preparing a single-layer porous amorphous carbon film, comprising the following steps:

[0041] Step 1, preparing the amphiphilic condensed ring aromatic hydrocarbon monomer Tpy-large;

[0042] S1. Under a nitrogen atmosphere, dissolve 26.7 g of hexaphenylbenzene in 250 mL of 0.1 M sodium carbonate solution. Add 40 mL of liquid bromine dropwise while stirring. Stir at room temperature overnight. Filter the resulting precipitate and wash it with 10% sodium bicarbonate to obtain hexaphenylbenzene bromide, which is recorded as substance 2.

[0043] S2. To 20 mL of acetic acid solution containing 365 mg of ammonium acetate was added 500 mg of 4'-(4-bromophenyl)-2,2':6',2"-isopyridine, and the mixture was stirred for 8 hours. The resulting precipitate was filtered and recrystallized from ethanol. The recrystallized product was dissolved in 5 mL of DMSO with 32 mg of Pd(dppf)Cl2, 379 mg of potassium acetate, and 344 mg of diboronic acid pinacol ester. The mixture was frozen and deoxygenated three times, and then heated to 80°C under nitrogen protection for 12 hours. After the reaction, the reaction solution was extracted with chloroform, the extract was dried over magnesium sulfate, and the solvent was evaporated. The resulting solid was recrystallized from ethanol to obtain pure substance 3.

[0044] S3, substance 2 and substance 3 are subjected to classic Suzuki coupling to obtain the amphiphilic fused ring aromatic hydrocarbon monomer Tpy-large;

[0045] Step 2: Dissolve the amphiphilic fused ring aromatic hydrocarbon monomer Tpy-large prepared in step 1 in chloroform to prepare a 1 mg / L solution, and drop 20 μL of the solution onto a 50 cm 2 The water-air interface;

[0046] Step 3: After waiting for 15 minutes for the chloroform to completely evaporate, the Langmuir thin film preparation instrument baffle is slowly pushed to maintain the interface pressure of the polycyclic aromatic hydrocarbon molecular interface assembly film at 20 mN / m, and the assembled film is transferred to the silicon wafer substrate by a vertical deposition method;

[0047] Step 4: Transfer the substrate with the assembled film prepared in step 3 to a rapid thermal processing tube furnace, and pyrolyze it at 900° C. under an argon atmosphere and normal pressure for 1 min to obtain a single-layer porous amorphous carbon film.

[0048] The single-layer amorphous carbon film was transferred onto a SiN chip with a 500 nm diameter opening by the PMMA method, and the chip was placed in a dual-chamber flow cell, and LiCl solution or KCl solution (concentrations varied from 1 M to 1 mM) was placed on both sides. + or K + and Cl - The volume mobility of the ions is similar, and the liquid junction potential can be ignored. Measure the current value at different voltages and calculate its resistance.

[0049] A method for preparing a modified lithium-ion battery diaphragm comprises the following steps:

[0050] Step 1: treating a single-layer polypropylene membrane with oxygen plasma for 5 seconds to obtain a hydrophilic surface, and transferring the single-layer porous amorphous carbon film according to claim 4 to the hydrophilic single-layer polypropylene membrane by a PMMA method;

[0051] The specific steps of the PMMA method include: applying 950PMMAA4 solution (PMMA is polymethyl methacrylate) to the surface of the amorphous carbon film with a substrate through a coating machine, and then immersing the substrate in an etching solution after drying. The etching solution is selected according to the selected substrate and can be a strong base, a strong acid, or a strong oxidant. After the substrate is completely dissolved, the film floating on the surface of the solution is washed three times with deionized water;

[0052] Step 2: The single-layer porous amorphous carbon film prepared in step 1 was transferred to a hydrophilic single-layer polypropylene separator by immersing in acetone for 10 minutes, and the polymethyl methacrylate protective layer was removed to obtain a modified separator for a lithium-ion battery.

[0053] In an argon-filled glove box (O₂ <0.1 ppm, H₂O <0.1 ppm), 2032-type coin cell cases were used with amorphous carbon film-modified separators and Celgard 2325 as separators. Symmetric lithium cells, lithium-copper cells, and lithium metal full cells were assembled and subjected to corresponding electrochemical tests. To observe the morphology of lithium deposition on copper foil and measure Coulombic efficiency, copper foil was used as the working electrode in the lithium-copper cell. For the LiFePO₄ full cell, the electrode sheet was prepared by mixing battery-grade LiFePO₄ with conductive carbon and polyvinylidene fluoride binder in a weight ratio of 70:20:10 in N-methyl-2-pyrrolidone solvent. The resulting slurry was coated on aluminum foil and vacuum-dried at 90°C for 12 hours. 60 μL of 1 M LiPF₆ and EC / DEC (1:1 by volume) electrolyte was added to the symmetric lithium cells and lithium-copper cells.

[0054] Figure 1 This is a schematic diagram of the preparation process of amphiphilic condensed ring aromatic hydrocarbons;

[0055] Figure 2 Schematic diagram of the process for preparing single-layer porous amorphous carbon membrane from amphiphilic condensed-ring aromatic hydrocarbons;

[0056] Figure 3 SEM image (10.0 μm) of the single-layer porous amorphous carbon film prepared in Example 1; Figure 4 The SEM image (100.0 μm) of the single-layer porous amorphous carbon film prepared in Example 1; Figure 3 and Figure 4 It can be seen that the membrane can be stably laid flat on the porous substrate and has good mechanical support;

[0057] Figure 5 A single-layer porous amorphous carbon film (dark color) transferred onto a silicon wafer in Example 1;

[0058] Figure 6 This is a test diagram of ion transport across the porous amorphous carbon membrane prepared in Example 1. Figure 6 It can be seen that the membrane surface is evenly distributed with nanopores for Li+ to pass through;

[0059] Figure 7 Comparison of time-voltage curves of Li|Li symmetric batteries (0.5 mA cm -2 ; 1mAh cm -2 ); Figure 8 This is a comparison chart of LiFePO4|Li battery rate performance, from Figure 7 and Figure 8 It can be seen that the addition of the modified membrane can regulate the Li2+ in the nanochannel compared with the unmodified membrane. + The concentration distribution of lithium metal batteries can be improved by improving the deposition behavior of lithium, which can provide a feasible and effective way to improve the cycle stability of lithium metal batteries.

[0060] Example 2

[0061] This embodiment provides a method for preparing a single-layer porous amorphous carbon film, comprising the following steps:

[0062] Step 1, preparing the amphiphilic condensed ring aromatic hydrocarbon monomer Tpy-large;

[0063] S1. Under a nitrogen atmosphere, dissolve 26.7 g of hexaphenylbenzene in 250 mL of 0.1 M sodium carbonate solution. Add 40 mL of liquid bromine dropwise while stirring. Stir at room temperature overnight. Filter the resulting precipitate and wash it with 10% sodium bicarbonate to obtain hexaphenylbenzene bromide, which is recorded as substance 2.

[0064] S2. To 20 mL of acetic acid solution containing 365 mg of ammonium acetate was added 500 mg of 4'-(4-bromophenyl)-2,2':6',2"-isopyridine, and the mixture was stirred for 8 hours. The resulting precipitate was filtered and recrystallized from ethanol. The recrystallized product was dissolved in 5 mL of DMSO with 32 mg of Pd(dppf)Cl2, 379 mg of potassium acetate, and 344 mg of diboronic acid pinacol ester. The mixture was frozen and deoxygenated three times, and then heated to 80°C under nitrogen protection for 12 hours. After the reaction, the reaction solution was extracted with chloroform, the extract was dried over magnesium sulfate, and the solvent was evaporated. The resulting solid was recrystallized from ethanol to obtain pure substance 3.

[0065] S3, substance 2 and substance 3 are subjected to classic Suzuki coupling to obtain the amphiphilic fused ring aromatic hydrocarbon monomer Tpy-large;

[0066] Step 2: Dissolve the amphiphilic fused ring aromatic hydrocarbon monomer Tpy-large prepared in step 1 in chloroform to prepare a 1 mg / L solution, and drop 20 μL of the solution onto a 50 cm 2 The water-air interface;

[0067] Step 3: After waiting for 5 minutes for the chloroform to completely evaporate, the Langmuir thin film preparation instrument baffle is slowly pushed to maintain the interface pressure of the polycyclic aromatic hydrocarbon molecular interface assembled film at 5 mN / m, and the assembled film is transferred to the copper substrate by a vertical deposition method;

[0068] Step 4: Transfer the substrate with the assembled film prepared in step 3 to a rapid thermal processing tube furnace, and pyrolyze it at 800° C. under an argon atmosphere and normal pressure for 1 min to obtain a single-layer porous amorphous carbon film.

[0069] Example 3

[0070] This embodiment provides a method for preparing a single-layer porous amorphous carbon film, comprising the following steps:

[0071] Step 1, preparing the amphiphilic condensed ring aromatic hydrocarbon monomer Tpy-large;

[0072] S1. Under a nitrogen atmosphere, dissolve 26.7 g of hexaphenylbenzene in 250 mL of 0.1 M sodium carbonate solution. Add 40 mL of liquid bromine dropwise while stirring. Stir at room temperature overnight. Filter the resulting precipitate and wash it with 10% sodium bicarbonate to obtain hexaphenylbenzene bromide, which is recorded as substance 2.

[0073] S2. To 20 mL of acetic acid solution containing 365 mg of ammonium acetate was added 500 mg of 4'-(4-bromophenyl)-2,2':6',2"-isopyridine, and the mixture was stirred for 8 hours. The resulting precipitate was filtered and recrystallized from ethanol. The recrystallized product was dissolved in 5 mL of DMSO with 32 mg of Pd(dppf)Cl2, 379 mg of potassium acetate, and 344 mg of diboronic acid pinacol ester. The mixture was frozen and deoxygenated three times, and then heated to 80°C under nitrogen protection for 12 hours. After the reaction, the reaction solution was extracted with chloroform, the extract was dried over magnesium sulfate, and the solvent was evaporated. The resulting solid was recrystallized from ethanol to obtain pure substance 3.

[0074] S3, substance 2 and substance 3 are subjected to classic Suzuki coupling to obtain the amphiphilic fused ring aromatic hydrocarbon monomer Tpy-large;

[0075] Step 2: Dissolve the amphiphilic fused ring aromatic hydrocarbon monomer Tpy-large prepared in step 1 in chloroform to prepare a 1 mg / L solution, and drop 20 μL of the solution onto a 50 cm 2 The water-air interface;

[0076] Step 3: After waiting for 10 minutes for the chloroform to completely evaporate, the Langmuir thin film preparation instrument baffle is slowly pushed to maintain the interfacial pressure of the polycyclic aromatic hydrocarbon molecular interface assembled film at 15 mN / m, and the assembled film is transferred to the glass substrate by vertical deposition method;

[0077] Step 4: Transfer the substrate with the assembled film prepared in step 3 to a rapid thermal processing tube furnace, and pyrolyze it at 850° C. under an argon atmosphere and normal pressure for 1 min to obtain a single-layer porous amorphous carbon film.

[0078] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the present invention.

Claims

1. A method for preparing a single-layer porous amorphous carbon film, characterized in that: The following steps are involved: Step 1, preparing the amphiphilic condensed ring aromatic hydrocarbon monomer Tpy-large; Step 2: Dissolve the amphiphilic fused ring aromatic hydrocarbon monomer Tpy-large prepared in step 1 in chloroform to prepare a 1 mg / L solution, and drop 20 μL of the solution onto a 50 cm 2 The water-air interface; Step 3: After the chloroform is completely evaporated, the baffle of the Langmuir thin film preparation instrument is slowly pushed to maintain the interface pressure of the condensed aromatic hydrocarbon molecular interface assembled film at 5 to 20 mN / m, and the assembled film is transferred to the substrate by a vertical deposition method; Step 4: Transfer the substrate with the assembled film prepared in step 3 to a rapid thermal processing tube furnace, and pyrolyze it at 800-900° C. in an argon atmosphere at normal pressure for 1 min to obtain a single-layer porous amorphous carbon film.

2. The method for preparing a single-layer porous amorphous carbon film according to claim 1, wherein: The preparation method of the amphiphilic fused-ring aromatic hydrocarbon monomer Tpy-large described in step 1 comprises: S1. Under a nitrogen atmosphere, dissolve 26.7 g of hexaphenylbenzene in 250 mL of 0.1 M sodium carbonate solution. Add 40 mL of liquid bromine dropwise while stirring. Stir at room temperature overnight. Filter the resulting precipitate and wash it with 10% sodium bicarbonate to obtain hexaphenylbenzene bromide, which is recorded as substance 2. S2. To 20 mL of acetic acid solution containing 365 mg of ammonium acetate was added 500 mg of 4'-(4-bromophenyl)-2,2':6',2"-isopyridine, and the mixture was stirred for 8 hours. The resulting precipitate was filtered and recrystallized from ethanol. The recrystallized product was dissolved in 5 mL of DMSO with 32 mg of Pd(dppf)Cl2, 379 mg of potassium acetate, and 344 mg of diboronic acid pinacol ester. The mixture was frozen and deoxygenated three times, and then heated to 80°C under nitrogen protection for 12 hours. After the reaction, the reaction solution was extracted with chloroform, the extract was dried over magnesium sulfate, and the solvent was evaporated. The resulting solid was recrystallized from ethanol to obtain pure substance 3. S3. Substance 2 and substance 3 are subjected to classic Suzuki coupling to obtain the amphiphilic fused ring aromatic hydrocarbon monomer Tpy-large.

3. The method for preparing a single-layer porous amorphous carbon film according to claim 1, wherein: The waiting time for the chloroform described in step 3 to completely evaporate is 5 to 15 minutes.

4. The method for preparing a single-layer porous amorphous carbon film according to claim 1, wherein: The substrate described in step three includes a copper sheet, a silicon sheet or a glass sheet.

5. A single-layer porous amorphous carbon film prepared by the method according to any one of claims 1 to 4.

6. A method for preparing a modified lithium ion battery diaphragm, characterized in that: The following steps are involved: Step 1: transferring the single-layer amorphous carbon film according to claim 5 onto a hydrophilic single-layer polypropylene membrane by a PMMA method; Step 2: The single-layer amorphous carbon film prepared in step 1 was transferred to a hydrophilic single-layer polypropylene separator by immersing in acetone for 10 minutes to remove the polymethyl methacrylate to obtain a modified separator for a lithium-ion battery.

7. A modified lithium ion battery separator prepared by the method according to claim 6.

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