Preparation method and application of composite solid electrolyte based on acylhydrazone-based covalent organic framework

Abstract

The invention discloses a preparation method and application of a composite solid electrolyte based on an acylhydrazone-based covalent organic framework, and belongs to the technical field of solid electrolyte materials of lithium metal batteries. According to the invention, an acylhydrazone-based covalent organic framework (H-COF) is used as a structural template, hydrogen-bond interaction between a hydrazone bond of the structural template and acrylamide is used as an anchor point, and nano confinement polymerization of polyethylene glycol diacrylate (PEGDA) in an H-COF pore channel is realized through an in-situ photocuring process. The prepared H-COF / PEGDA composite solid electrolyte has good room temperature ionic conductivity and a broadened electrochemical stability window. The high-nickel positive electrode / lithium metal battery assembled based on the electrolyte can stably operate under the cut-off voltage of 4.5 V, shows excellent high-voltage compatibility and cycling stability, and has a wide application prospect.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium metal battery solid-state electrolyte materials, and particularly relates to a preparation method and application of a high-pressure-resistant composite solid-state electrolyte based on an acylhydrazone-based covalent organic framework. BACKGROUND

[0002] With the rapid development of electric vehicles and large-scale energy storage technologies, the market demand for high-energy-density and high-safety secondary batteries is increasingly urgent. Solid-state lithium metal batteries, with a theoretical capacity of 3860 mAh g -1 , are considered an important development direction of the next-generation high-energy-density energy storage system due to their intrinsic safety characteristics provided by solid-state electrolytes. Especially when matched with high-voltage positive electrode materials such as high-nickel ternary positive electrodes and lithium-rich manganese-based positive electrodes with working voltages exceeding 4.3 V, the system can significantly improve the energy density of the battery.

[0003] Although the currently widely studied polyether-based solid-state electrolytes have good flexibility and film-forming properties, the ether oxygen bonds in their molecular structures are prone to irreversible oxidation and rupture when the voltage is higher than 3.8 V (3.8 V vs. Li + / Li), which leads to continuous decomposition of the electrolyte at the high-voltage positive electrode interface, causing the interface impedance to rise, the capacity to decay, and the battery to fail more severely. This inherent electrochemical instability limits the actual electrochemical window of polyether-based electrolytes to below 4.0 V, making it difficult to adapt to current mainstream high-voltage positive electrodes, which seriously restricts its practical application in high-energy-density lithium metal battery systems and becomes a key bottleneck for its practicalization.

[0004] In recent years, covalent organic framework materials (COFs) with regular pore structures and functionalizable pore walls have provided a new idea for the design of high-voltage composite electrolytes. By rationally designing the COF skeleton and composite strategy, the electronic distribution of the ether oxygen bonds in the polyether chain segment can be effectively regulated through molecular-level interactions, consuming its lone pair of electrons, thereby enhancing the stability of the electrolyte in a strong oxidative environment, and providing a solid material foundation for the construction of a 4.5 V ultra-high-voltage operating lithium metal battery system. SUMMARY

[0005] The technical problem to be solved by the present application is to provide a preparation method and application of a composite solid-state electrolyte based on an acylhydrazone-based covalent organic framework.

[0006] The present application provides a preparation method of a composite solid-state electrolyte based on an acylhydrazone-based covalent organic framework, comprising the following steps: Step S1: acylhydrazone-based covalent organic framework (H-COF) is ground with acrylamide (AAm) in a mortar, polyethylene glycol diacrylate (PEGDA) and a small amount of solvent are added thereto, ultrasonic is performed, stirring is performed, and mother liquor A is obtained; Step S2: lithium salt is added to the mother liquor A, stirring is performed, and mother liquor B is obtained; Step S3: a photoinitiator is added to the mother liquor B, stirring is performed in the dark, and mother liquor C, i.e., a composite solid electrolyte precursor solution, is obtained; Step S4: the mother liquor C is poured on a polytetrafluoroethylene substrate and an anode material, and then ultraviolet light curing is performed, and the composite solid electrolyte is obtained.

[0007] A lithium metal battery, wherein a composite polymer solid electrolyte is used as a solid electrolyte material, metal lithium is used as a negative electrode material, and a high-voltage anode composite material is used as a positive electrode material.

[0008] The present application has the following beneficial effects: The present application uses H-COF as a structural template, uses the hydrogen bond interaction between the hydrazone bond and AAm as an anchor point, and realizes nano-limiting polymerization of PEGDA in the H-COF channel through an in-situ photopolymerization process. -4 S cm -1 The prepared optimal ratio composite solid electrolyte has good room temperature ionic conductivity (1.2*10 BRIEF DESCRIPTION OF DRAWINGS

[0009] Figure 1 It is a preparation flow chart of the composite solid electrolyte of the present application.

[0010] Figure 2 It is the chemical structure and infrared spectrum of H-COF-EO4 of the present application.

[0011] Figure 3 It is the optical photograph and infrared spectrum of HPEG-1 electrolyte before and after polymerization of the present application.

[0012] Figure 4 It is the optical photograph and scanning electron microscope image of HPEG-1 electrolyte of the present application.

[0013] Figure 5 It is the electrochemical impedance spectrogram of PEGDA, HPEG-1, HPEG-2, HPEG-3 electrolyte at room temperature of the present application.

[0014] Figure 6 Linear sweep voltammetry test diagram of PEGDA, HPEG-3 electrolyte of the application.

[0015] Figure 7 Cycle performance diagram of Li / NCM811 battery assembled by PEGDA, HPEG-3 electrolyte of the application in 2.8~4.5 V voltage range. DETAILED DESCRIPTION

[0016] The application will be further described below in connection with specific embodiments. It should be understood that these embodiments are only used to illustrate the application and not used to limit the scope of the application. In addition, it should be understood that after reading the content taught by the application, those skilled in the art can make various modifications or changes to the application, and these equivalent forms also fall within the scope defined by the appended claims of the application.

[0017] The application provides a high-pressure-resistant composite solid electrolyte based on an acylhydrazone-based covalent organic framework, and the high-pressure-resistant composite solid electrolyte component comprises an acylhydrazone-based covalent organic framework, AAm, PEGDA, and a lithium salt.

[0018] Further, the acylhydrazone-based covalent organic framework comprises: .

[0019] As shown in Figure 1 , a preparation method of the composite solid electrolyte based on the acylhydrazone-based covalent organic framework comprises the following steps: Step S1: The acylhydrazone-based covalent organic framework (H-COF) is ground with acrylamide (AAm) in a mortar, polyethylene glycol diacrylate (PEGDA) and a small amount of solvent are added thereto, and ultrasonic stirring is performed to obtain mother liquor A.

[0020] The preparation process of the acylhydrazone-based covalent organic framework is as follows: the aldehyde group and the hydrazine monomer are dissolved in an organic solvent, an acid catalyst is added, ultrasonic dispersion is performed until uniform, a solvothermal reaction is performed under an inert gas atmosphere, and the acylhydrazone-based covalent organic framework powder is obtained after washing and drying.

[0021] The aldehyde monomer is one of 4,4',4''-(1,3,5-triazine-2,4,6-triyl)triphenylaldehyde, 4,4',4''-(pyridine-2,4,6-triyl)triphenylaldehyde, 1,3,5-tris(p-formylphenyl)benzene, 4',4'',4'''(1,3,5-triazine-2,4,6-triyl)tris(([1,1'-biphenyl]-4-carboxaldehyde)), 5''-(4'-formyl-[1,1'-biphenyl]-4-yl)-[1,1':4',1'':3'',1''':4''',1''':4''-quaterphenyl]-4,4''-dicarboxaldehyde, 2',4',6'-trifluoro-5'-(4-formylphenyl)-[1,1':3',1''-terphenyl]-4,4''-dicarboxaldehyde.

[0022] The hydrazine monomer is one of 2,5-dimethoxyterephthalic dihydrazide, 2,5-diethoxyterephthalic dihydrazide, 2,5-bis(2-(2-methoxyethoxy)ethoxy)terephthalic dihydrazide, 2,5-bis(2-(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)terephthalic dihydrazide.

[0023] The organic solvent is one or more of 1,3,5-trimethylbenzene, 1,2-dichlorobenzene, n-butanol, 1,4-dioxane.

[0024] The acid catalyst is aqueous acetic acid.

[0025] The solvothermal reaction system is placed in a Schlenk tube, evacuated and filled with inert gas 3 times under liquid nitrogen freezing state, and then placed at 120 °C for 72-120 h after thawing; the washing is: sequentially washed with tetrahydrofuran, dichloromethane, n-hexane until the filtrate is colorless and transparent; the vacuum drying temperature is 50-100 °C, and the vacuum drying time is 24-48 h.

[0026] The mass percentage of acylhydrazone-based covalent organic framework in PEGDA is 1wt%-10wt%; the mass ratio of AAm to PEGDA is (0.1-1):1; the mass ratio of solvent to PEGDA is (0.1-1):1; the ultrasonic time in step S1 is 12-24 h, and the stirring time is 12-24 h.

[0027] The average molecular weight of PEGDA is one of 200, 400, 600, 800, 1000, 2000.

[0028] The solvent is one of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide.

[0029] Step S2: lithium salt is added to the mother liquor A, and stirred to obtain mother liquor B.

[0030] The mass ratio of polymer to lithium salt is 1:(0.5~1); the stirring time is 12~24 h.

[0031] The lithium salt is at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium trifluoromethanesulfonate, lithium bis(trifluoromethanesulfonyl)imide, and lithium bis(oxalato)borate.

[0032] Step S3: Add photoinitiator to mother liquor B, stir in the dark to obtain mother liquor C, which is the composite solid electrolyte precursor solution.

[0033] The photoinitiator has a mass percentage concentration of 0.01~0.1wt% in the polymer; the stirring time in the dark is 12~24 h.

[0034] The photoinitiator is one of 2-hydroxy-2-methyl-1-phenylpropanone, 1-hydroxycyclohexylbenzophenone, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, and benzophenone.

[0035] Step S4: Pour the mother liquor C onto the polytetrafluoroethylene plate and the positive electrode material and coat it, then cure it with ultraviolet light to obtain the composite solid electrolyte.

[0036] The cathode material is a high-voltage cathode composite material, including one of lithium iron phosphate cathode, lithium manganese iron phosphate cathode, lithium cobalt oxide cathode, and nickel cobalt manganese 811 cathode.

[0037] The coating thickness of mother liquor C is 100~200 μm; the UV curing time is 1~5 min; after curing, the thickness of the composite solid electrolyte membrane is 70~110 μm.

[0038] A lithium metal battery uses a composite polymer solid electrolyte as the solid electrolyte material; lithium metal as the negative electrode material; and a high-voltage positive electrode composite material as the positive electrode material.

[0039] Example 1: This example provides a method for preparing a high-voltage resistant composite solid electrolyte based on an acylhydrazone covalent organic framework, comprising the following steps: Step S1 : 4,4',4''-(Pyridine-2,4,6-triyl)triphenylaldehyde (BDPDT, 12 mg, 0.03 mmol), 2,5-bis(2-(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)terephthalohydrazide (EO4TH, 24 mg, 0.045 mmol) and acetic acid (100 μL, 6 mol / L) were added into a 10 mL Schlenk tube containing 1,4-dioxane / 1,3,5-trimethylbenzene mixed solvent (1 / 1 mL). The mixture was sonicated for 30 min to form solid aggregates, rapidly frozen at 77 K (liquid nitrogen bath), and degassed by three freeze-pump-thaw cycles. After being pumped to 10 -3 bar, the glass tube was sealed and heated at 120 °C for 3 days. The obtained light yellow powder-like precipitate was washed thoroughly with tetrahydrofuran, dichloromethane, n-hexane, and collected by filtration. Finally, the powder was dried in a regular oven at 100 °C for 24 h to obtain the acylhydrazone-based covalent organic framework (H-COF-EO4). The chemical structure of H-COF-EO4 is shown in Figure 2 (a) and its infrared spectrum is shown in Figure 2 (b), which proves the successful synthesis of the structure.

[0040] Step S2: 18 mg H-COF-EO4 was ground with 300 mg AAm in a mortar for 30 min, 600 mg PEGDA, 0.6 mL N-methylpyrrolidone were added thereto, and sonicated for 24 h, stirred for 24 h.

[0041] Step S3: 300 mg lithium bistrifluoromethanesulfonimide was added to the dispersion of step S2, and stirred for 12 h.

[0042] Step S4: 20 mg 2,4,6-trimethylbenzoyldiphenylphosphine oxide was added to the dispersion of step S3, and stirred in the dark for 12 h.

[0043] Step S5: The mother liquor in step S4 was poured onto a polytetrafluoroethylene substrate and a nickel cobalt manganese 811 positive electrode material, and a 120 μm film-forming doctor blade was used to evenly spread it, and a UV light curing lamp was used to irradiate it for 3 min to polymerize, and the optical photographs before and after the mother liquor polymerization are shown in Figure 3 (a) and its infrared spectrum is shown in Figure 3 (b), which proves the occurrence of the polymerization reaction. After the film was formed, it was peeled off from the substrate, cut into 16 mm original pieces, to obtain a H-COF-EO4 / PEGDA-based composite solid-state electrolyte, denoted as HPEG-1. The composite solid-state electrolyte / positive electrode in situ cured on the nickel cobalt manganese 811 positive electrode material was denoted as HPEG-1@NCM811.

[0044] The optical photograph and micro-morphology of HPEG-1 obtained in the example are shown in Figure 4 Figure 4 (a) is an optical photograph of the HPEG-1 electrolyte of the application, and (b) is a scanning electron microscope image of the cross-section at a size of 200 μm. H-COF-EO4 is uniformly dispersed in the polymer and forms a dense film morphology, which is conducive to the continuous and uniform transmission of lithium ions. Figure 4

[0045] Example 2: The present example provides a high-pressure-resistant composite solid-state electrolyte based on acylhydrazone-based covalent organic frameworks, which is prepared by the same method as in Example 1, except that the amount of H-COF-EO4 added in step S2 is 30 mg, and is denoted as HPEG-2 and HPEG-2@NCM811, respectively.

[0046] Example 3: The present example provides a high-pressure-resistant composite solid-state electrolyte based on acylhydrazone-based covalent organic frameworks, which is prepared by the same method as in Example 1, except that the amount of H-COF-EO4 added in step S2 is 42 mg, and is denoted as HPEG-3 and HPEG-3@NCM811, respectively.

[0047] Comparative Example 1: The present comparative example provides a composite solid-state electrolyte, which is prepared by the same method as in Example 1, except that no H-COF-EO4 is added in step S2, and is denoted as PEGDA and PEGDA@NCM811, respectively.

[0048] Application Example 1: Electrochemical impedance performance test of the composite solid-state electrolytes obtained in all examples and comparative examples: 1. In an argon atmosphere glove box, CR2032 button-type half-batteries were assembled in the order of negative electrode shell-stainless steel sheet-solid-state electrolyte film-stainless steel sheet-elastic sheet-positive electrode shell.

[0049] 2. The obtained batteries were subjected to electrochemical impedance performance test, and the test frequency range was 1 Hz-1 MHz. The test results are shown in Figure 5 Compared with the comparative example, Example 3 has a lower room temperature electrochemical impedance, indicating that the composite solid-state electrolyte in Example 3 has a stronger ion conduction ability at room temperature.

[0050] Application Example 2: Linear sweep voltammetry test of the composite solid-state electrolytes obtained in Example 3 and Comparative Example 1: 1. In an argon atmosphere glove box, CR2032 button-type half-batteries were assembled in the order of negative electrode shell-lithium metal-solid-state electrolyte film-stainless steel sheet-elastic sheet-positive electrode shell. ​​

[0051] 2. Perform linear sweep voltammetry on the obtained battery, with a test voltage of 2-6 V. The test results are as follows: Figure 6 As shown, compared to the comparative example in Figure (a), Example 3 in Figure (b) has a widened electrochemical stability window, indicating that the composite solid electrolyte in Example 3 has better antioxidant capacity and can better match the high-voltage cathode material.

[0052] Performance testing of Example 3 and Comparative Example 1 as electrolytes for high-voltage lithium metal batteries: 1. Using a two-electrode system, with lithium metal as the negative electrode, the composite solid electrolyte / positive electrode material obtained in Example 3 or Comparative Example 1 is used as an integrated electrolyte / positive electrode. The CR2032 coin cell is assembled in a glove box under an argon atmosphere.

[0053] 2. The obtained battery was subjected to constant current charge-discharge testing. The test conditions were as follows: potential range of 2.8~4.4V and 2.8~4.5V, current density of 0.2C (1C = 200 mAh g). -1 All charge / discharge performance tests were conducted at a constant temperature of 30 °C. Test results are as follows: Figure 7 As shown, the lithium metal battery assembled with the electrolyte in Example 3 can stably cycle for over 160 cycles within a voltage range of 2.8–4.5 V and a rate of 0.2 C, while the lithium metal battery assembled with the electrolyte in the comparative example experiences a continuous capacity decrease at high cutoff voltage until battery failure. This result demonstrates that the lithium metal battery applied in Example 3 exhibits higher high-voltage tolerance and stability.

[0054] The above description is merely a preferred embodiment of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method of preparing a composite solid-state electrolyte based on acylhydrazone-based covalent organic frameworks, characterized in that Comprising the following steps: Step S1: The acylhydrazone-based covalent organic framework is ground with acrylamide in a mortar, polyethylene glycol diacrylate, a small amount of solvent is added, ultrasonic, stirring, to obtain mother liquor A; Step S2: Lithium salt is added to mother liquor A, and stirred to obtain mother liquor B; Step S3: Photoinitiator is added to mother liquor B, and stirred in the dark to obtain mother liquor C, i.e. composite solid electrolyte precursor solution; Step S4: Pour mother liquor C on the polytetrafluoroethylene substrate and positive material, then perform ultraviolet curing to obtain the composite solid electrolyte.

2. The method of claim 1, wherein The preparation process of the acylhydrazone-based covalent organic framework in step S1 is as follows: the aldehyde group and hydrazine monomer are dissolved in an organic solvent, an acid catalyst is added, ultrasonic dispersion is performed until uniform, a solvothermal reaction is performed under an inert gas atmosphere, and the acylhydrazone-based covalent organic framework powder is obtained after washing and vacuum drying.

3. The method of claim 2, wherein The aldehyde group monomer is at least one of 4,4',4''-(1,3,5-triazine-2,4,6-triyl)triphenylaldehyde, 4,4',4''-(pyridine-2,4,6-triyl)triphenylaldehyde, 1,3,5-tris(p-formylphenyl)benzene, 4',4'',4''-(1,3,5-triazine-2,4,6-triyl)tris(([1,1'-biphenyl]-4-carboxaldehyde)), 5''-(4'-formyl-[1,1'-biphenyl]-4-yl)-[1,1':4',1'':3'',1''':4''',1''''-quaterphenyl]-4,4''''-dicarboxaldehyde, 2',4',6'-trifluoro-5'-(4-formylphenyl)-[1,1':3',1''-terphenyl]-4,4''-dicarboxaldehyde; The hydrazine monomer is at least one of 2,5-dimethoxyterephthalic dihydrazide, 2,5-diethoxyterephthalic dihydrazide, 2,5-bis(2-(2-methoxyethoxy)ethoxy)terephthalic dihydrazide, and 2,5-bis(2-(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)terephthalic dihydrazide; The organic solvent is one or more of mesitylene, 1,2-dichlorobenzene, n-butanol, and 1,4-dioxane; The acid catalyst is an aqueous acetic acid solution.

4. The method of claim 2, wherein The solvothermal reaction system is placed in a Schlenk tube, evacuated and filled with inert gas 3 times under liquid nitrogen freezing state, and then placed at 120 °C for 72-120 h after thawing; the washing is performed by sequentially washing with tetrahydrofuran, dichloromethane, and n-hexane until the filtrate is colorless and transparent; the vacuum drying temperature is 50-100 °C, and the vacuum drying time is 24-48 h.

5. The method of claim 1, wherein The mass percentage of the acylhydrazone-based covalent organic framework in polyethylene glycol diacrylate in step S1 is 1wt%-10wt%; the mass ratio of acrylamide to polyethylene glycol diacrylate is (0.1-1):1; the mass ratio of solvent to polyethylene glycol diacrylate is (0.1-1):1; the ultrasonic time in step S1 is 12-24 h, and the stirring time is 12-24 h; The average molecular weight of the polyethylene glycol diacrylate is at least one of 200, 400, 600, 800, 1000, 2000; The solvent is at least one of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide.

6. The method of claim 1, wherein the composite solid-state electrolyte is prepared by a process comprising: The mass ratio of the polymer to the lithium salt in the step S2 is 1:(0.5-1); the stirring time is 12-24 h; The lithium salt is at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium triflate, lithium bis-trifluoromethanesulfonimide, lithium bis(oxalato)borate.

7. The method for preparing the composite solid electrolyte according to claim 1, characterized in that, The mass percentage concentration of the photoinitiator in the polymer in the step S3 is 0.01-0.1wt%; the light-shielded stirring time is 12-24 h; The photoinitiator is at least one of 2-hydroxy-2-methyl-1-phenylpropanone, 1-hydroxycyclohexyl phenyl ketone, 2,4,6-trimethylbenzoyl diphenyl phosphine oxide, benzophenone.

8. The method for preparing the composite solid electrolyte according to claim 1, characterized in that, The positive electrode material in the step S4 is a high-voltage positive electrode composite material, including at least one of lithium iron phosphate positive electrode, lithium iron manganese phosphate positive electrode, lithium cobaltate positive electrode, nickel cobalt manganese 811 positive electrode; The scraping thickness of the mother liquor C is 100-200 μm; The ultraviolet light curing time is 1-5 min; after curing, the thickness of the composite solid electrolyte film is 70-110 μm.

9. A composite solid electrolyte obtained by the preparation method of any one of claims 1-8 is applied in a lithium metal battery.

10. A lithium metal battery, characterized in that, The composite solid electrolyte obtained by the preparation method of any one of claims 1-8 is used as a solid electrolyte material; metal lithium is used as a negative electrode material; and a high-voltage positive electrode composite material is used as a positive electrode material.

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