Ultrathin films with both lithium conductivity and strong mechanical properties, their preparation methods and applications
By combining PEG-TGCl-COF with ANF, an ultrathin film with both lithium conductivity and strong mechanical properties was prepared, which solved the challenges of existing electrolyte films in terms of mechanical strength and lithium dendrite suppression, and achieved high ion transport and stable interfacial contact.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- NANJING UNIV OF SCI & TECH
- Filing Date
- 2026-03-10
- Publication Date
- 2026-06-02
Smart Images
Figure CN122136571A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of advanced functional membrane materials, specifically relating to an ultrathin film that combines lithium conductivity with strong mechanical properties, its preparation method and application, especially its application as a high-performance electrolyte membrane framework material. Background Technology
[0002] High-energy-density batteries place higher demands on electrolyte membranes, requiring not only excellent ion transport performance but also minimizing thickness to increase energy density. However, reducing membrane thickness presents significant challenges to its mechanical strength and ability to suppress lithium dendrites. Traditional polymer electrolyte membranes often struggle to achieve a balance between ionic conductivity, mechanical strength, and lithium dendrite suppression.
[0003] In existing technologies, covalent organic frameworks (COFs) have shown potential in ion transport due to their regular pore structure and tunable chemical properties. Aramid nanofibers (ANFs), on the other hand, are widely used to reinforce composite materials due to their excellent mechanical strength and high specific surface area. However, effectively combining the ion transport advantages of COFs with the mechanical strength advantages of ANFs to prepare ultrathin films with both lithium conductivity and strong mechanical properties, while simultaneously addressing the lack of lithium conductivity in COF frameworks, the limited mechanical properties of single COF films, and the interface problems that may arise from the introduction of fillers, remains a significant challenge. Summary of the Invention
[0004] The purpose of this invention is to provide an ultrathin film that combines lithium conductivity with strong mechanical properties, aiming to solve the multiple challenges of existing functional film materials in terms of ion transport, mechanical strength and ultrathinness.
[0005] The PEG-TGCl-COF used in this invention is synthesized from triaminoguanidine hydrochloride (TGCl) and an aldehyde monomer (PEG2-CHO) containing a PEG side chain.
[0006] Ultrathin films are prepared by the following steps:
[0007] Kevlar fibers were dissolved in DMSO solution, and excess potassium hydroxide solid was added. The mixture was stirred to obtain an ANF dispersion. The synthesized PEG-TGCl-COF was placed in a ball mill jar, and a prepared 1,4-dioxane-water mixture and agate milling beads were added. After milling, a COF nanosheet solution was obtained. The ANF dispersion was taken, and DMSO solution and an appropriate amount of water were added to prepare ANF / COF mixtures with different COF contents. The ANF / COF mixtures were then poured into a vacuum filtration apparatus and filtered using a vacuum membrane. After complete filtration, an ultrathin ANF / COF composite membrane was obtained through water washing and wetting separation, and then freeze-dried.
[0008] Preferably, the volume ratio of the 1,4-dioxane to water mixed solution is 2:0.6.
[0009] Preferably, the volume ratio of DMSO to aqueous solution is 9:1.
[0010] Preferably, the filtration membrane is a nylon membrane.
[0011] The second objective of this invention is to provide an ultrathin solid electrolyte based on the above-mentioned ANF / COF composite membrane, which is prepared through the following steps:
[0012] The ANF / COF composite membrane was cut into circular slices. 1M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and 1M lithium difluorooxalate borate (LiDFOB) were added to a mixed solution of 1,3-dioxolane (DOL) / fluoroethylene carbonate (FEC). After stirring until a homogeneous solution was formed, the solution was added dropwise to both sides of the ANF / COF membrane. The membrane was then allowed to stand on a hot plate at 30°C for 48 hours to obtain the composite electrolyte membrane through in-situ polymerization.
[0013] Preferably, the volume ratio of DOL to FEC solution is 7:3.
[0014] The third objective of this invention is to provide the application of the above-mentioned ultrathin solid electrolyte based on ANF / COF composite film in lithium metal solid batteries.
[0015] Compared with the prior art, the present invention has the following advantages:
[0016] This invention utilizes PEG-TGCl-COF with polyethylene glycol (PEG) chains on its backbone to prepare COF nanosheet solutions via ball milling. Its regular pore structure and cationic backbone effectively immobilize anions in the electrolyte through strong electrostatic forces, while the lithiophilic PEG side chains can induce Li-... + The directional conduction of lithium ions significantly improves the lithium-ion transference number. Aramid nanofibers (ANF), with their excellent mechanical strength, are used to construct a tough porous three-dimensional network framework. This not only provides excellent mechanical support for the ultrathin electrolyte membrane, but the abundant amide groups in ANF also enable hydrogen bonding with COF. This stable three-dimensional framework effectively inhibits lithium dendrite penetration and decouples mechanical strength from thickness. Subsequently, polymer PDOL is introduced into the ANF / COF composite framework through in-situ polymerization, ensuring continuous and tight interfacial contact between the electrolyte and the electrode, effectively reducing interfacial resistance. The organic combination of these three components enables the composite electrolyte membrane to synergistically achieve multiple functions, including mechanical enhancement, ion-selective transport, promotion of lithium salt dissociation, and optimization of interfacial contact.
[0017] Additional features and advantages of this invention will be set forth in the description which follows, or may be learned by practicing the invention. Attached Figure Description
[0018] The technical solution and beneficial effects of the present invention will become apparent and readily understood from the following description in conjunction with the accompanying drawings, wherein:
[0019] Figure 1 Fourier transform infrared spectra of TGCI, PEG2-CHO, and PEG-TGCl-COF;
[0020] Figure 2 The 1H liquid NMR spectra of polymers PDOL and DOL are shown.
[0021] Figure 3 Impedance diagrams of four electrolytes, PE, KM, KCM-12.5%, and KCM-25%, at 25°C;
[0022] Figure 4 Scanning electron microscope image at KCM-12.5%;
[0023] Figure 5 KCM-12.5% electrolyte at 0.2 mAcm −2 The graph shows the long-cycle performance test results at current density.
[0024] Figure 6 The graph shows the full-cell cycle performance of KCM-12.5% electrolyte at 1C and 25℃.
[0025] Figure 7 This is the structural formula of the product of the present invention;
[0026] Figure 8 The structural formula is that of triaminoguanidine hydrochloride (TGCI);
[0027] Figure 9 The structural formula of the aldehyde monomer PEG2-CHO;
[0028] Figure 10 This is a schematic diagram of the synthesis route;
[0029] Figure 11 This is a schematic diagram of the reaction. Detailed Implementation
[0030] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.
[0031] The triaminoguanidine hydrochloride (TGCl) and PEG2-CHO used in the following examples were prepared in-house.
[0032] like Figure 7The diagram shows the structural formula of the product of this invention;
[0033] like Figure 8 The image shows the structural formula of triaminoguanidine hydrochloride (TGCI);
[0034] like Figure 9 The figure shows the structural formula of the aldehyde monomer PEG2-CHO.
[0035] The specific synthetic route of TGCI and PEG2-CHO is as follows: Figure 10 As shown.
[0036] (a) Compound TGCI:
[0037] 1.91 g of guanidine hydrochloride was slowly added to 10 mL of 1,4-dioxane under constant stirring, followed by the addition of 3.41 g of hydrazine hydrate.
[0038] After the mixture was refluxed for 3 hours and cooled to room temperature, the product was filtered and washed with 1,4-dioxane to remove the remaining hydrazine hydrate. Finally, it was dried in a vacuum oven to obtain TGCl with a yield of 92%.
[0039] (b) Compound 1a:
[0040] Under an argon atmosphere, 4 mmol of 2,5-dibromohydroquinone (1.07 g) and 20 mmol of K2CO3 (2.76 g) were dissolved in 20 mL of anhydrous acetonitrile, and then 8.75 mmol of 1-bromo-2-(2-methoxyethoxy)ethane (1.2 mL) were added. The reaction was stirred at 90 °C for 12 hours.
[0041] The mixture obtained by filtration was concentrated using a rotary evaporator.
[0042] Finally, the product was collected by silica gel column chromatography (petroleum ether: ethyl acetate = 1:1) and filtered to obtain ammonia monomer 1a (yield: 72%).
[0043] (c) Compound PEG2-CHO:
[0044] 5 mmol of 1a (2.36 g), 15 mmol of 4-formylphenylboronic acid (2.26 g), 340 mg of Pd(PPh3)4 and 15 mmol of K2CO3 (2.07 g) were dissolved in a mixture of 100 mL of anhydrous tetrahydrofuran and 20 mL of deoxygenated water.
[0045] The reactants were placed in an oil bath and stirred overnight at 80°C.
[0046] After cooling to room temperature, the solvent was concentrated under vacuum using a rotary evaporator, then extracted with dichloromethane, washed with H2O, separated, dried with Na2SO4, filtered, and concentrated.
[0047] The crude product was purified by column chromatography (petroleum ether / ethyl acetate: 1 / 1) to obtain a pale yellow powder of PEG2-CHO (yield: 70%).
[0048] Example 1
[0049] The cationic covalent organic framework with PEG side chains (PEG-TGCl-COF) is an organic framework structure formed by the Schiff base reaction of triaminoguanidine hydrochloride (TGCl) and PEG2-CHO. The synthetic steps are as follows:
[0050] Place 0.1 mmol of triaminoguanidine hydrochloride (14 mg) and 0.15 mmol of PEG2-CHO (78.4 mg) in a long-necked Pyrex tube (18 cm long, 9 cm neck, approximately 20 mL in volume).
[0051] Mix 2 mL of 1,4-dioxane with 0.6 mL of deionized water and add the mixture to a Pyrex tube. Sonicate the mixture until the monomer dissolves. Then add 6 mol L⁻¹ acetic acid solution (130 μL) as a catalyst and sonicate the Pyrex tube for 30 minutes until the solution forms a gel.
[0052] The gel inside the tube was then rapidly frozen with liquid nitrogen and subjected to vacuum treatment. The neck of the tube was then sealed with a flame torch. After cooling to room temperature, the tube was placed in a 120°C oven for 72 hours to obtain a gel-like product.
[0053] COF was activated by Soxhlet extraction with tetrahydrofuran, followed by freeze-drying to obtain a yellow solid with a yield of 80%. The reaction formula is as follows. Figure 11 As shown.
[0054] The synthesized PEG-TGCl-COF was placed in a ball mill jar, and a prepared solution (1,4-dioxane:water = 2:0.6) and agate milling beads were added. After the ball mill was run at 500 rpm for 24 hours, COF nanosheets were obtained. The obtained high-concentration COF nanosheet solution was diluted to a solution of 1 mg / mL.
[0055] 0.2 mg of Kevlar fiber was dissolved in 100 mL of DMSO solution, excess potassium hydroxide solid was added, and the mixture was stirred at 60 °C for 5 days to obtain an ANF dispersion with a concentration of 2 mg / mL.
[0056] Take 4 mL of LANF dispersion and add it to DMSO and aqueous solution to prepare ANF / COF mixtures with COF contents of 0%, 12.5%, and 25%.
[0057] Pour the prepared ANF / COF mixed solution into a vacuum filtration device, select a nylon membrane as the filter membrane, and obtain an ultra-thin ANF / COF composite membrane after the solution has been completely filtered.
[0058] Experiment Example 2
[0059] The ultrathin film with ANF and COF content of 12.5% prepared in Example 1 was cut into 16 mm round slices for later use. Then, 1 M LiTFSI and 1 M LiDFOB were dissolved in DOL / FEC (volume ratio 7:3) to prepare a 1 mL solution.
[0060] By adding 15 μL of solution to each side of the ultrathin film and allowing it to stand on a hot plate at 30 °C for 48 hours, PDOL electrolyte is introduced through in-situ polymerization to obtain the high-performance composite electrolyte membrane KCM-12.5.
[0061] Comparative Example 1
[0062] This comparative example is basically the same as Example 2, except that the COF content is not added. Specifically:
[0063] The ultrathin film with ANF and COF content of 0 prepared in Example 1 was cut into 16 mm round slices for later use. Then, 1 M LiTFSI and 1 M LiDFOB were dissolved in DOL / FEC (volume ratio 7:3) to prepare a 1 mL solution.
[0064] 15 μL of solution was added to each side of the ultrathin film, and after standing on a hot stage at 30 °C for 48 hours, PDOL electrolyte was introduced by in-situ polymerization to obtain the composite electrolyte membrane KM.
[0065] Comparative Example 2
[0066] This comparative example is basically the same as Example 2, except that the COF content is increased to 25%, specifically:
[0067] The ultrathin film with 25% ANF and COF content prepared in Example 1 was cut into 16 mm round slices for later use. Then, 1 M LiTFSI and 1 M LiDFOB were dissolved in DOL / FEC (volume ratio 7:3) to prepare a 1 mL solution.
[0068] By adding 15 μL of solution to each side of the ultrathin film and allowing it to stand on a 30°C hot plate for 48 hours, PDOL electrolyte is introduced through in-situ polymerization to obtain the high-performance composite electrolyte membrane KCM-25.
[0069] Comparative Example 3
[0070] This comparative example is basically the same as Example 2, the only difference being the use of commercially available PE diaphragm membrane, specifically:
[0071] Commercial PE membrane was cut into 16mm discs for later use. 1M LiTFSI and 1M LiDFOB were dissolved in DOL / FEC (volume ratio 7:3) to prepare a 1mL solution. 15μL of the solution was added dropwise to each side of the ultrafilm. After standing on a 30℃ hot plate for 48 hours, PDOL electrolyte was introduced through in-situ polymerization to obtain the high-performance composite electrolyte membrane PM.
[0072] Figure 1 The Fourier transform infrared (FTIR) spectra of PEG-TGCl-COF and its monomers show that, in PEG-TGCl-COF, the N–H stretching vibration of triaminoguanidine hydrochloride (3320 cm⁻¹) is present. −1 and 3191cm −1 The C=O stretching vibration (1687 cm⁻¹) of the aldehyde monomer PEG2-CHO. −1 ) disappeared at 1610cm −1 The presence of an imine C=N stretching vibration signal peak nearby indicates that imine condensation has occurred, proving the successful synthesis of COF.
[0073] Figure 2 The liquid NMR spectra of polymers PDOL and DOL show a significant decrease in the characteristic peaks (a and b) corresponding to the monomer DOL, indicating a transformation of DOL during polymerization. Simultaneously, new peaks (c and d) appear, attributed to repeating units in the PDOL polymer chain, confirming the formation of the PDOL electrolyte. The conversion rate of DOL monomer in different electrolyte systems was quantitatively analyzed by integrating peaks b and d in the 1H NMR spectra. After standing for 48 hours, the DOL monomer conversion rate of the PDOL electrolyte was 88.9%.
[0074] Figure 3 Impedance plots of four electrolytes (PE, KM, KCM-12.5%, and KCM-25%) at 25℃ are presented. The thicknesses of the four electrolytes were measured using a micrometer at 7μm, 5μm, 6μm, and 6μm, respectively. The conductivity was calculated using the formula: .
[0075] The calculated values are 5.16 × 10 −5 Scm −1 5.33×10 −5 Scm −1 5.19×10 −5 Scm −1 and 2.6×10 − 5Scm −1 KCM-12.5% exhibits high ionic conductivity.
[0076] Figure 4 The scanning electron microscope image of KCM-12.5% shows that the prepared electrolyte membrane has a layered stacked structure.
[0077] Figure 5 KCM-12.5% electrolyte at 0.2 mAcm −2 Long-cycle performance tests at current densities showed stable lithium deposition / stripping behavior.
[0078] Figure 6 The graph shows the full-cell cycle performance of the KCM-12.5% electrolyte at 1C and 25℃. The assembled lithium iron phosphate full cell retains 98% of its capacity after more than 400 cycles at 1C, demonstrating excellent electrochemical performance.
[0079] In summary, the present invention has the following advantages:
[0080] This invention utilizes PEG-TGCl-COF with polyethylene glycol (PEG) chains on its framework to prepare COF nanosheet solutions via ball milling. Its regular pore structure and cationic framework effectively immobilize anions in the electrolyte through strong electrostatic interactions. The lithiophilic PEG side chains induce directional Li+ transport, significantly increasing the lithium-ion transference number. Aramid nanofibers (ANF), with their excellent mechanical strength, are used to construct a robust porous three-dimensional network framework, providing excellent mechanical support for the ultrathin electrolyte membrane. The abundant amide groups in ANF facilitate hydrogen bonding with COF, and this stable three-dimensional framework effectively inhibits lithium dendrite penetration and decouples mechanical strength from thickness. Subsequently, PDOL polymer is introduced into the ANF / COF composite framework through in-situ polymerization, ensuring continuous and tight interfacial contact between the electrolyte and electrode, effectively reducing interfacial resistance. The organic combination of these three components enables the composite electrolyte membrane to synergistically achieve multiple functions, including mechanical enhancement, ion-selective transport, promotion of lithium salt dissociation, and optimization of interfacial contact.
[0081] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.
Claims
1. An ultrathin film possessing both lithium conductivity and strong mechanical properties, characterized in that, The ultrafilm is constructed from a cationic covalent organic framework and aramid nanofibers. The COF is PEG-TGCl-COF with polyethylene glycol chains on the backbone, and its structural formula is as follows:
2. The ultrathin film with both lithium conductivity and strong mechanical properties as described in claim 1, characterized in that, Its preparation method includes the following steps: Preparation of cationic covalent organic framework nanosheet solution with lithium-conducting side chains: PEG-TGCl-COF was synthesized from triaminoguanidine hydrochloride and PEG2-CHO by solvothermal method, and then COF nanosheet solution was prepared by ball milling; Then, aramid nanofibers were dissolved in dimethyl sulfoxide solution, potassium hydroxide solid was added, and the mixture was stirred to obtain an ANF dispersion; Finally, the ANF dispersion, the COF nanosheet solution, the DMSO solution, and water were mixed, and the ANF / COF composite ultrathin film was prepared by vacuum-assisted self-packing and then freeze-dried.
3. The ultrathin film with both lithium conductivity and strong mechanical properties as described in claim 1, characterized in that, The thickness of the ultrathin film, which combines lithium conductivity with strong mechanical properties, is less than 10 μm.
4. The ultrathin film with both lithium conductivity and strong mechanical properties as described in claim 1, characterized in that, The triaminoguanidine hydrochloride and the PEG2-CHO were dissolved in a mixed solvent of 1,4-dioxane and deionized water at a concentration of 6 mol / L. −1 Acetic acid solution was used as a catalyst, and the reaction was carried out at 120°C for 72 hours.
5. The ultrathin film with both lithium conductivity and strong mechanical properties as described in claim 1, characterized in that, The COF content in the ANF / COF mixed solution is 12.5%.
6. The ultrathin film with both lithium conductivity and strong mechanical properties as described in claim 1, characterized in that, The ultrathin composite membrane serves as a framework and is composited with the polymer electrolyte PDOL.
7. The ultrathin film with both lithium conductivity and strong mechanical properties as described in claim 1, characterized in that, The solid-state lithium battery is either a lithium iron phosphate full battery or a nickel-cobalt-manganese lithium full battery.