Double donor-acceptor linked covalent organic framework-based solid electrolyte as well as preparation method and application thereof

Abstract

The invention discloses a double donor-acceptor linked covalent organic framework-based solid electrolyte as well as a preparation method and application thereof, and relates to the technical field of solid electrolytes. The preparation method comprises the following steps: dissolving an electron double donor methyl benzidine and an electron acceptor aldehyde phenol in a mixed solvent of mesitylene and dioxane; adding acetic acid as a catalyst after complete dissolution; freezing the mixed solution with liquid nitrogen, vacuumizing a reaction tube after freezing, and carrying out sealed reaction to obtain a reactant; filtering or centrifugally separating reactants to obtain orange powder, washing the orange powder with acetone and tetrahydrofuran, and drying the washed orange powder to obtain a double donor-acceptor linked covalent organic framework material; and mixing the covalent organic framework material with a lithium salt to obtain the solid electrolyte. Through the donor and the acceptor, mutual static electricity between anions and cations is effectively weakened, dissociation of lithium ions is promoted, the ionic conductivity and the ionic transference number are improved, uniform deposition of the lithium ions is induced, growth of lithium dendrites is inhibited, and the cycling stability of the battery is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of solid electrolytes, and in particular, to a double donor-acceptor linked covalent organic framework-based solid electrolyte, a preparation method thereof, and an application thereof. Background Art

[0002] Due to serious safety hazards, liquid lithium-ion batteries can no longer meet the large demand for energy. Solid-state batteries using solid electrolytes instead of electrolytes and separators have high safety and significantly improved battery energy density, making them the best choice for power electric vehicles and large-scale energy storage systems. Therefore, the development of solid electrolytes is particularly important.

[0003] Typical solid electrolytes are divided into sulfides, oxides, halides, and polymers. Polymers have the characteristics of flexibility, good stability, and easy functionalization, and have become the focus of research. Covalent organic framework materials are formed by different units to form covalent bonds to synthesize crystalline and ordered macromolecules. Due to their excellent properties, they are increasingly used in polymer electrolytes. However, the ionic conductivity and ion transference number of polymer electrolytes are usually low. The main reason is that the strong coordination between lithium ions and anions makes it difficult for lithium ions to dissociate and migrate, ultimately resulting in an unsatisfactory battery capacity retention rate for such electrolytes. Summary of the Invention

[0004] The purpose of the present invention is to provide a double donor-acceptor linked covalent organic framework-based solid electrolyte, a preparation method thereof, and an application thereof, to solve the problem that the electrolytes prepared by the prior art have low ionic conductivity and ion transference number, resulting in an unsatisfactory battery capacity retention rate.

[0005] To solve the above technical problems, the present invention adopts the following technical solutions: A preparation method of a double donor-acceptor linked covalent organic framework-based solid electrolyte, characterized by comprising the following steps:

[0006] S1. Dissolve electron double donor methylbenzidine and electron acceptor aldehyde phenol in a mixed solvent of mesitylene and dioxane;

[0007] S2. After complete dissolution, add acetic acid as a catalyst to obtain a mixed solution;

[0008] S3. Freeze the mixed solution in step S2 with liquid nitrogen. After freezing, evacuate the reaction tube and seal the reaction tube by flame sealing, and react at a certain temperature to obtain a reactant;

[0009] S4. After filtering or centrifuging the reactant, an orange powder is obtained, which is washed with acetone and tetrahydrofuran. The washed powder is dried to obtain a double donor-acceptor linked covalent organic framework material;

[0010] S5. Mix the covalent organic framework material and the lithium salt to obtain a solid electrolyte.

[0011] A further technical solution is that in the step S1, the electron double donor is 3,3'-dimethylbenzidine, the electron acceptor is 1,3,5-triformylphloroglucinol, and the molar ratio of the electron double donor to the electron acceptor is 3:2.

[0012] A further technical solution is that in the step S1, the dioxane is 1,4-dioxane, and the volume ratio of mesitylene to 1,4-dioxane in the mixed solvent is 1:1.

[0013] A further technical solution is that in the step S2, the concentration of the acetic acid solution is 6 mol / L, and the volume ratio of its dosage to the volume of the mixed solvent is 1:20.

[0014] A further technical solution is that in the step S1, after the electron double donor and the electron acceptor are added to the mixed solvent, they are mixed under ultrasonic for 10 min, and in the step S3, the reaction is carried out at 120 °C for 72 h.

[0015] A further technical solution is that in the step S4, acetone and tetrahydrofuran are alternately washed, 5 times each, 50 mL each time.

[0016] A further technical solution is that in the step S5, the lithium salt is LiTFSI. The covalent organic framework material and the lithium salt with a mass ratio of 1:0.5 are mixed, ethanol is added, and stirred at room temperature for 12 hours, and finally vacuum dried at 100 °C to obtain the electrolyte.

[0017] A further technical solution is to compound the solid electrolyte and the PTFE dispersion by roll pressing to obtain an electrolyte membrane, then soak the electrolyte membrane in a lithium salt solvent for activation and drying, and use the electrolyte membrane to prepare a button battery or a solid battery.

[0018] A further technical solution is that the concentration of PTFE in the PTFE dispersion is 60%, and the dosage of the PTFE dispersion is 1% of the mass of the solid electrolyte; the lithium salt solvent is LiTFSI dissolved in propylene carbonate with a lithium salt concentration of 1 mol / L; the activation time is 12 h.

[0019] A further technical solution is that the drying temperature is 100 °C and the drying time is 12 h.

[0020] Reaction mechanism:

[0021] The electron donor selected is 3,3′-dimethylbenzidine with a strong electron-donating group methyl as a special modified functional group and two reaction sites, and the electron acceptor selected is phloroglucinol trialdehyde with three reaction sites and a strong electron-withdrawing C=O. The synthesized covalent organic framework material CH3-COF with double donor-acceptor linkage has the following two-dimensional hexagonal network structure.

[0022]

[0023] The electron donor is selected as methylbenzidine, and the methylbenzidine molecule has a large number of lone pairs of electrons. The electron acceptor is selected as phloroglucinol trialdehyde. The strong electron-donating group methyl enhances its electronegativity and accelerates the transfer of electrons to the strong electron-withdrawing C=O double bond.

[0024] This makes the pores of the prepared COF material electron-rich, thus effectively weakening the electrostatic interaction between lithium ions and anions, resulting in an increased degree of lithium ion dissociation, improving the ionic conductivity and ion transference number. Moreover, COF (covalent organic framework) provides a large number of one-dimensional ion channels, promoting the uniform deposition of lithium ions on the electrode and inhibiting the generation of dead lithium or lithium dendrites; the two-dimensional flexible extended structure increases the contact between the COF-based electrolyte and the electrode, reducing the interfacial impedance; the fluorine-containing sites form a special interfacial passivation layer LiF with lithium ions, improving the interfacial stability and the cycle stability of the battery.

[0025] Compared with the prior art, the beneficial effects of the present invention are:

[0026] By constructing a polymer electrolyte with double donor-acceptor linkage using electron donor methylbenzidine and electron acceptor phloroglucinol trialdehyde, it is possible to significantly regulate the electronic structure through the intermolecular interaction between the donor and the acceptor, making the COF pores electron-rich, effectively weakening the electrostatic interaction between cations and anions, thereby promoting the dissociation of lithium ions and improving the ionic conductivity and ion transference number.

[0027] At the same time, the COF material prepared by this method has a highly ordered structure, with a large number of one-dimensional nanoion channels inside, inducing the uniform deposition of lithium ions, significantly inhibiting the formation and growth of lithium dendrites, promoting the formation of a stable interface layer, and improving the cycle stability of the lithium iron phosphate solid-state battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is the infrared spectrum of the COF-based electrolyte described in Example 2;

[0029] Figure 2 It is the solid-state nuclear magnetic carbon spectrum of the COF-based electrolyte described in Example 2;

[0030] Figure 3 It is the scanning electron micrograph of the COF-based electrolyte described in Example 2;

[0031] Figure 4 Nitrogen adsorption - desorption curve of the COF - based electrolyte described in Example 2;

[0032] Figure 5 Ionic conductivity diagram of the COF - based electrolyte described in Example 2;

[0033] Figure 6 Electrochemical window diagram of the COF - based electrolyte described in Example 2;

[0034] Figure 7 Ionic transference number diagram of the COF - based electrolyte described in Example 2;

[0035] Figure 8 Cycling performance of the lithium symmetric battery prepared with the COF - based electrolyte described in Example 2;

[0036] Figure 9 Cycling performance of the solid - state battery prepared by matching the COF - based electrolyte described in Example 2 with a lithium iron phosphate cathode;

[0037] Figure 10 Charge - discharge curves of the solid - state battery prepared by matching the COF - based electrolyte described in Example 2 with a lithium iron phosphate cathode at different cycles. Detailed implementation manners

[0038] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the following further details the invention in combination with examples and drawings. It should be understood that the specific examples described herein are only used to explain the present invention and are not used to limit the present invention.

[0039] Example 1

[0040] A method for preparing a donor - acceptor linked covalent organic framework - based solid electrolyte includes the following steps:

[0041] S1. Dissolve the electron double - donor 3,3′ - dimethylbenzidine and the electron acceptor 1,3,5 - triformylphloroglucinol in a mixed solvent of mesitylene and 1,4 - dioxane at a molar ratio of 3:2. The volume ratio of mesitylene to 1,4 - dioxane in the mixed solvent is 1:1, and it is optimal that the mixed solvent can cover the electron double - donor and the electron acceptor;

[0042] S2. Ultrasonic the mixture in step S1 for 10 min. After complete dissolution, add acetic acid with a concentration of 6 mol / L as a catalyst to obtain a mixed solution. The dosage of acetic acid is in a volume ratio of 1:20 to the volume of the mixed solvent;

[0043] S3. Freeze the mixed solution in step S2 with liquid nitrogen. After freezing, evacuate the reaction tube and seal the reaction tube by flame sealing. React at 120 °C for 72 h to obtain the reactant.

[0044] S4. The reactant is obtained as an orange powder by filtration or centrifugation, and is alternately washed with acetone and tetrahydrofuran. The washed powder is dried to obtain a double donor-acceptor linked covalent organic framework material; acetone and tetrahydrofuran are each washed 5 times, 50 mL each time.

[0045] S5. Mix the covalent organic framework material and a lithium salt to obtain a solid electrolyte. The lithium salt is LiTFSI. Mix the covalent organic framework and the lithium salt in a mass ratio of 2:1, add ethanol, stir at room temperature for 12 hours, and finally vacuum dry at 100 °C to obtain the solid electrolyte.

[0046] S6. Compound the solid electrolyte and the PTFE dispersion by roll pressing to obtain an electrolyte membrane, and then soak the electrolyte membrane in a lithium salt solvent for activation and drying. The concentration of PTFE in the PTFE dispersion is 60%, and the amount of the PTFE dispersion used is 1% of the mass of the solid electrolyte; the lithium salt solvent is LiTFSI dissolved in propylene carbonate with a concentration of 1 mol / L; the activation time is 12 h. The drying temperature is 100 °C and the drying time is 12 h.

[0047] S7. The electrolyte membrane is used to prepare a button battery or a solid-state battery.

[0048] Example 2

[0049] Add 95.5 mg of methylbenzidine (3,3'-dimethylbenzidine) and 63 mg of 1,3,5-triformylphloroglucinol to 3 mL of a mixed solvent of mesitylene and 1,4-dioxane (1.5 mL each of mesitylene and 1,4-dioxane), and ultrasonically treat for 10 min.

[0050] Add 0.2 mL of acetic acid solution with a concentration of 6 mol / L to the ultrasonically treated solution, freeze the reaction tube with liquid nitrogen, evacuate, and seal the tube by flame sealing. The sealed tube is reacted at 120 °C for 72 h.

[0051] Break the tube, collect the solid powder by filtration or centrifugation, and alternately wash with acetone and tetrahydrofuran. Acetone and tetrahydrofuran are each washed 5 times, 50 mL each time. Then dry at 100 °C for 12 h to obtain a double donor-acceptor linked covalent organic framework material. As Figure 1 and Figure 2 shown, the peak at a wavenumber of 1250 in the infrared spectrum and the peak at a chemical shift of about 145 in the solid-state nuclear magnetic carbon spectrum are C-N bonds, indicating that this method for preparing COF materials (i.e., covalent organic framework materials) is feasible.

[0052] Mix the covalent organic framework material and lithium salt to obtain a solid electrolyte. The lithium salt is LiTFSI. Mix the covalent organic framework and lithium salt with a mass ratio of 2:1, add ethanol, stir at room temperature for 12 hours, and finally dry under vacuum at 100 °C to obtain the solid electrolyte.

[0053] Compound the solid electrolyte and PTFE dispersion by roll pressing to obtain an electrolyte membrane, and then soak the electrolyte membrane in a lithium salt solvent for activation and drying. The concentration of PTFE in the PTFE dispersion is 60%, and the amount of PTFE dispersion used is 1% of the mass of the solid electrolyte; the lithium salt solvent is LiTFSI dissolved in propylene carbonate with a concentration of 1 mol / L, and the activation time is 12 h. The drying temperature is 100 °C, and the drying time is 12 h.

[0054] As Figure 3 shown, the SEM of this electrolyte membrane proves that the surface is flat, which is beneficial to interface contact. As Figure 4 shown, the nitrogen adsorption and desorption curve of the COF-based electrolyte shows a specific surface area of 530.7511 m 2 / g, which is beneficial to the adsorption and migration of lithium ions.

[0055] Perform impedance testing on the double donor-acceptor linked COF electrolyte. As Figure 5 shown, the ionic conductivity of this electrolyte is calculated according to the ionic conductivity calculation formula based on the impedance value. The ionic conductivity of the donor-acceptor electrolyte is 6.7×10 -4 S / cm, which has a high ionic conductivity. As Figure 6 shown in the electrochemical window test of this electrolyte, the voltage window is 5.63 V, which has a high antioxidant capacity. As Figure 7 shown, the transference number of this electrolyte is 0.6, which has a high transference number and selectivity. The donor-donor-acceptor regulated COF-based solid electrolyte significantly improves the ionic conductivity, transference number and broadens the electrochemical reaction window, promoting the development of high-performance solid-state batteries.

[0056] Test Example 1

[0057] Use the COF-based electrolyte membrane obtained in Example 2 to assemble a lithium-lithium symmetric button battery and perform a constant current charge-discharge stability cycle test.

[0058] The preferred assembly method for the symmetric battery is 0.5 mm steel sheet, followed by lithium sheet, electrolyte membrane, lithium sheet and steel sheet, and a pressure of 10 MPa is applied to press into a symmetric battery. The battery is tested for constant current charge and discharge under the conditions of 0.2 mA / cm 2 and 0.2 mAh / cm 2 conditions. As Figure 8As shown, the symmetric battery remains stable after 1200 h of cycling, demonstrating long cycling stability of lithium ion insertion / extraction and effectiveness in suppressing lithium dendrites at the interface.

[0059] Test Example 2

[0060] The COF-based electrolyte membrane obtained in Example 2 was used in a solid-state battery. The process of assembling the lithium iron phosphate solid-state battery: the positive lithium iron phosphate electrode sheet, with a loading preferably of 3 mg / cm 2 , followed by the COF-based solid electrolyte membrane, and finally a lithium sheet. A pressure of 10 MPa was applied to press them into a solid-state battery. The battery was tested for galvanostatic charge and discharge at a high current density of 1C. As Figure 9 shown, the initial discharge specific capacity of the battery at 1C was 160 mAh / g, and the capacity retention rate could still reach 90% after 450 cycles, showing high capacity retention, and the discharge specific capacity was 144 mAh / g. As Figure 10 shown, the charge and discharge curves of the solid-state battery at different cycles, and the battery Coulomb efficiency was high and the capacity remained stable.

[0061] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. What is described in the above embodiments and the specification only illustrates the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of the present invention claimed is defined by the appended claims and their equivalents.

Claims

1. A preparation method of a double donor-acceptor linked covalent organic framework-based solid electrolyte, characterized in that, It includes the following steps: S1. Dissolve the electron double-donor methylbenzidine and the electron acceptor aldehyde group phenol in a mixed solvent of mesitylene and 1,4-dioxane; S2. After complete dissolution, add acetic acid as a catalyst to obtain a mixed solution; S3. Freeze the mixed solution in step S2 with liquid nitrogen. After freezing, evacuate the reaction tube and seal the reaction tube by flame sealing. React at a certain temperature to obtain a reactant; S4. After filtering or centrifuging the reactant, an orange powder is obtained, which is washed with acetone and tetrahydrofuran. The washed powder is dried to obtain a double-donor-acceptor linked covalent organic framework material; S5. Mix the covalent organic framework material and a lithium salt to obtain a solid electrolyte.

2. The preparation method according to claim 1, characterized in that: In step S1, the electron double-donor is 3,3′-dimethylbenzidine, the electron acceptor is 1,3,5-trihydroxybenzene tricarboxaldehyde, and the molar ratio of the electron double-donor to the electron acceptor is 3:

2.

3. The preparation method according to claim 1, characterized in that: In step S1, the 1,4-dioxane is 1,4-dioxane, and the volume ratio of mesitylene to 1,4-dioxane in the mixed solvent is 1:

1.

4. The preparation method according to claim 1, wherein: In step S2, the concentration of the acetic acid solution is 6 mol / L, and the dosage ratio to the volume of the mixed solvent is 1:

20.

5. The preparation method according to claim 1, characterized in that: In step S1, the electron double-donor and the electron acceptor are mixed under ultrasonic for 10 min after being added to the mixed solvent. In step S3, the reaction is carried out at 120 °C for 72 h.

6. The preparation method according to claim 1, characterized in that: In step S4, acetone and tetrahydrofuran are used for alternating washing, 5 times each, 50 mL each time.

7. The preparation method according to claim 1, characterized in that: In step S5, the lithium salt is LiTFSI. The covalent organic framework material and the lithium salt with a mass ratio of 1:0.5 are mixed, ethanol is added, and stirred at room temperature for 12 hours. Finally, it is vacuum dried at 100 °C to obtain the electrolyte.

8. The preparation method according to any one of claims 1 to 7, characterized in that: Compound the solid electrolyte and the PTFE dispersion by rolling to obtain an electrolyte membrane. Then soak the electrolyte membrane in a lithium salt solvent for activation and drying. The electrolyte membrane is used to prepare a button battery or a solid-state battery.

9. The preparation method according to claim 8, characterized in that: In the PTFE dispersion, the concentration of PTFE is 60%, and the dosage of the PTFE dispersion is 1% of the mass of the solid electrolyte; the lithium salt solvent is LiTFSI dissolved in propylene carbonate with a lithium salt concentration of 1 mol / L; the activation time is 12 h.

10. The preparation method according to claim 8, characterized in that: The drying temperature is 100 °C and the drying time is 12 h.

Images