Three-dimensional lithium-loving covalent organic framework with ether oxygen side chain, preparation method and application of three-dimensional lithium-loving covalent organic framework
By combining a three-dimensional lithiophilic covalent organic framework with ether oxygen side chains with a lithium cobalt oxide cathode, the interface problem caused by lithium deintercalation and intercalation at high voltage in the lithium cobalt oxide cathode is solved, achieving efficient lithium-ion transport and excellent cycle stability, thus improving the performance of lithium metal batteries.
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
- 2026-05-26
Smart Images
Figure CN122080346A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of covalent organic framework compound technology, and relates to a three-dimensional lithiophilic covalent organic framework with ether oxygen side chains, its preparation method and its application in lithium metal batteries. Background Technology
[0002] The performance degradation of lithium cobalt oxide cathodes at high voltages stems from the coupling of multiple failure mechanisms. Lithium deintercalation induces particle cracks, and the newly exposed surface exacerbates electrolyte decomposition and generates an unstable interface layer, leading to increased interfacial impedance. This is accompanied by side reactions such as irreversible phase transitions on the surface, oxygen evolution, and cobalt dissolution, ultimately deteriorating the battery's cycle and rate performance.
[0003] Adding surface coatings is considered one of the simplest and most effective methods for modifying the interface of lithium cobalt oxide cathodes. Encapsulating a stable protective layer around the cathode particles can effectively mitigate interfacial side reactions caused by solvent co-intercalation and transition metal dissolution, thus improving the structural stability of the cathode material under high voltage. However, traditional coating techniques still have certain limitations. Most coatings prevent direct contact between the electrode and the electrolyte, but these coating structures often contain gaps. The size of these gaps is larger than that of solvated lithium ions, thus preventing the effective stripping of the solvation shell during lithium ion intercalation to allow solvent molecules to reach the cathode particle surface. Secondly, most coating processes are complex, time-consuming, energy-intensive, and involve liquid-phase processing. Furthermore, some steps are costly and may cause side reactions due to solvent contact, damaging or adversely affecting the structure of the cathode material. In addition, while the introduction of a coating can prevent direct contact between the cathode material and the electrolyte, this interface also hinders lithium ion transport between the electrode and electrolyte. Therefore, developing a novel coating material that combines high ion conductivity, precise size sieving, and good interfacial stability is of great significance for promoting the practical application of lithium cobalt oxide in lithium metal batteries.
[0004] Covalent organic frameworks (COFs) are a class of porous organic materials composed of organic structural units linked by covalent bonds. They possess characteristics such as high porosity, large specific surface area, light weight, pre-designable structure, and high stability, making them promising lithium-ion conductors. By designing structurally sound COF materials and utilizing their framework characteristics and appropriate composite techniques, composite cathode materials with stable structure, thermodynamics, and electrochemical properties can be obtained. However, current reports on this topic are relatively limited. Summary of the Invention
[0005] One objective of this invention is to provide a covalent organic framework with ether oxygen side chains. The three-dimensional lithiophilic covalent organic framework with ether oxygen side chains is a topological structure synthesized from 2,5-bis(2-(2-methoxyethoxy)ethoxy)terephthalohydrazide and tetra(4-aldehydephenyl)methane.
[0006] Prepared by the following steps:
[0007] Diethyl 2,5-dihydroxyterephthalate, 1-bromo-2-(2-methoxyethoxy)ethane, and potassium carbonate were added to Shrek flasks. Anhydrous acetonitrile was added under argon protection, and the mixture was heated and stirred at 90°C for 48 hours. After the reaction was complete, the mixture was cooled, filtered, extracted, and dried overnight with anhydrous sodium sulfate. The crude product was then obtained by rotary evaporation after filtration, and purified by column chromatography to give a white intermediate, DGTH-CH2CH3. This intermediate was dissolved in anhydrous ethanol, and hydrazine hydrate was added. The mixture was heated and stirred at 90°C for 12 hours. Recrystallization yielded a white solid product, 2,5-bis(2-(2-methoxyethoxy)ethoxy)terephthalohydrazide (DGTH-NHNH2).
[0008] The second objective of this invention is to provide a method for preparing the above-mentioned three-dimensional lithiophilic covalent organic framework (3D-EO-COF) with ether oxygen side chains, comprising the following steps:
[0009] In a glass ampoule, tetra(4-aldehydephenyl)methane, DGTH-NHNH2, and a mixed solvent of mesitylene / 1,4-dioxane (v / v = 3:1) were added sequentially, and the mixture was ultrasonically treated to ensure uniform dispersion. Subsequently, a 6 mol / L aqueous acetic acid solution was added as a catalyst, and the mixture was again treated in an ultrasonic bath to obtain a uniformly dispersed reaction solution. The solution was frozen in a liquid nitrogen bath, and after three cycles of vacuum-thawing, it was vacuum-sealed and placed in a 120°C oven for 6 days to obtain a yellowish-white solid. The crude product was thoroughly washed with methanol, filtered, and dried in a freeze dryer for 12 hours to finally obtain a white powdery 3D-EO-COF.
[0010] Preferably, the liquid nitrogen freezing, vacuuming, and degassing processes are performed at least three times.
[0011] Preferably, the concentration of the acetic acid solution is 6 mol / L.
[0012] Preferably, the thorough washing solvent is methanol.
[0013] Preferably, the freeze-drying time is 12 hours.
[0014] A third objective of this invention is to provide a composite material based on the above-mentioned three-dimensional lithiophilic covalent organic framework with ether oxygen side chains and a lithium cobalt oxide cathode, which is prepared through the following steps:
[0015] A three-dimensional lithiophilic covalent organic framework with ether oxygen side chains was dispersed by ball milling in anhydrous acetonitrile solution, then mixed with a lithium cobalt oxide cathode and milled at a low speed of 200 rpm for 2 hours using a planetary ball mill. Afterwards, it was centrifuged and dried to load the framework onto the lithium cobalt oxide surface.
[0016] Preferably, the planetary ball mill rotates at a speed of 200 rpm.
[0017] Preferably, the low-speed mixing and grinding is carried out for 2 hours.
[0018] In a specific embodiment of the present invention, the three-dimensional lithiophilic covalent organic framework accounts for 0.3 wt% of the total mass of the lithium cobalt oxide cathode.
[0019] The fourth objective of this invention is to provide the application of the composite cathode material with the above-mentioned three-dimensional lithiophilic covalent organic framework having ether oxygen side chains in lithium metal batteries.
[0020] Compared with the prior art, the present invention has the following advantages:
[0021] This invention synthesizes a three-dimensional covalent organic framework material (3D-EO-COF) with high porosity and abundant lithiophilic sites, and constructs a modified cathode material by low-speed ball milling and compositing it with lithium cobalt oxide. The composite cathode material of this invention exhibits good Li⁺ diffusion coefficient and stability. The three-dimensional framework material acts as a physical barrier, effectively suppressing interfacial side reactions such as transition metal dissolution. Its rigid structure also buffers volumetric stress during cycling, improving interfacial compatibility with gel electrolytes and demonstrating excellent cycling stability. For example, at 3-4.5V, the capacity retention is 95.2% after 150 cycles at 2C rate.
[0022] 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
[0023] 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:
[0024] Figure 1 PXRD pattern of 3D-EO-COF, tetra(4-aldehydephenyl)methane (TFPM), 2,5-bis(2-(2-methoxyethoxy)ethoxy)terephthalohydrazide (DGTH-NHNH2);
[0025] Figure 2 Infrared spectrum of 3D-EO-COF, tetra(4-aldehydephenyl)methane (TFPM), 2,5-bis(2-(2-methoxyethoxy)ethoxy)terephthalohydrazide (DGTH-NHNH2);
[0026] Figure 3 TGA diagram of 3D-EO-COF;
[0027] Figure 4 PXRD plot of 3D-EO-LCO, LCO;
[0028] Figure 5 Infrared images of 3D-EO-LCO and LCO;
[0029] Figure 6 SEM image of LCO;
[0030] Figure 7 SEM image of 3D-EO-LCO;
[0031] Figure 8 The graph shows the long-cycle performance of 3D-EO-LCO and LCO at a 2C rate.
[0032] Figure 9 The structure is a three-dimensional lithiophilic covalent organic framework with ether oxygen side chains;
[0033] Figure 10 The structural formula is tetra(4-aldehydephenyl)methane (TFPM);
[0034] Figure 11 The structural formula is 2,5-bis(2-(2-methoxyethoxy)ethoxy)terephthalohydrazide (DGTH-NHNH2);
[0035] Figure 12 This is a schematic diagram of the synthesis route of DGTH-NHNH2;
[0036] Figure 13 This is a schematic diagram of the 3D-EO-COF synthesis. Detailed Implementation
[0037] 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.
[0038] The following description, with reference to the accompanying drawings, details the three-dimensional lithiophilic covalent organic framework with ether oxygen side chains disclosed in this invention, its preparation method, and its applications.
[0039] like Figure 1 , Figure 2 , Figure 3 , Figure 4 , Figure 5 , Figure 6 , Figure 7 , Figure 8 , Figure 9 , Figure 10, Figure 11 , Figure 12 and Figure 13 As shown.
[0040] The tetra(4-aldehydephenyl)methane used in the following examples was commercially available.
[0041] 2,5-Bis(2-(2-methoxyethoxy)ethoxy)terephthalohydrazide was prepared in-house; the specific synthetic route is as follows: Figure 12 As shown.
[0042] Diethyl 2,5-dihydroxyterephthalate (2.04 g, 8 mmol), 1-bromo-2-(2-methoxyethoxy)ethane (4.39 g, 24 mmol), and potassium carbonate (4.42 g, 32 mmol) were added to Shrek flasks. Under argon protection, 80 mL of anhydrous acetonitrile was added, and the mixture was heated and stirred at 90 °C for 48 hours. After the reaction was complete, the mixture was cooled, filtered, extracted, and dried overnight with anhydrous sodium sulfate. The crude product was then obtained by rotary evaporation after filtration, and purified by column chromatography to obtain a white intermediate DGTH-CH2CH3 (3.89 g, 85% yield). This intermediate (2.00 g, 4.36 mmol) was dissolved in 40 mL of anhydrous ethanol, and hydrazine hydrate (4 mL) was added. The mixture was heated and stirred at 90 °C for 12 hours. Recrystallization yielded a white solid product DGTH-NHNH2 (1.59 g, 85% yield).
[0043] Example
[0044] The three-dimensional lithiophilic covalent organic framework (3D-EO-COF) with ether oxygen side chains is an organic framework structure formed by the Schiff base reaction of tetra(4-aldehydephenyl)methane and 2,5-bis(2-(2-methoxyethoxy)ethoxy)terephthalohydrazide, and its structure is as follows: Figure 9 As shown.
[0045] The specific steps are as follows:
[0046] In a glass ampoule, tetra(4-aldehydephenyl)methane (21 mg, 0.05 mmol), DGTH-NHNH2 (45.7 mg, 0.10 mmol), and 2 mL of a mixed solvent of mesitylene / 1,4-dioxane (v / v = 3:1) were added sequentially, and the mixture was ultrasonically treated for 15 min to ensure uniform dispersion. Subsequently, 0.20 mL of a 6 mol / L acetic acid aqueous solution was added as a catalyst, and the mixture was again ultrasonically treated for 5 min to obtain a uniformly dispersed reaction solution. The solution was frozen in a liquid nitrogen bath, and after three cycles of vacuum-thawing, it was vacuum-sealed and reacted in a 120°C oven for 6 days to obtain a yellowish-white solid. The crude product was thoroughly washed with methanol, filtered, and dried in a freeze dryer for 12 h to finally obtain a white powdery 3D-EO-COF with a yield of 83%. Figure 13 As shown.
[0047] 3D-EO-COF-LCO Synthesis:
[0048] 0.3 wt% of 3D-EO-COF was dispersed by ball milling in anhydrous acetonitrile solution, and then mixed with lithium cobalt oxide cathode material. The mixture was then ground using a planetary ball mill at a low speed of 200 rpm for 2 hours. Afterward, the mixture was centrifuged and dried to load 3D-EO-COF onto the surface of lithium cobalt oxide, yielding 3D-EO-LCO.
[0049] Preparation of composite cathode:
[0050] A uniform slurry was prepared by mixing 3D-EO-LCO / Super-P / PVDF5180 at a mass ratio of 70:20:10 and coated onto an aluminum foil current collector. The resulting electrode was vacuum dried at 80°C for 12 hours to finally obtain the 3D-EO-LCO positive electrode.
[0051] The entire preparation process was carried out in an argon-atmospheric glove box to eliminate interference from moisture and oxygen. The surface loading of the active material in the prepared positive electrode was approximately 2-3 mg / cm³. -2 To assemble button cells, the electrode sheets are stamped into round pieces with a diameter of 10mm.
[0052] Battery assembly:
[0053] 3D-EO-LCO cathode, lithium foil, and PVDF gel electrolyte were used as the positive electrode, negative electrode, and electrolyte membrane, respectively. The electrolyte consisted of a hot-pressed PVDF spun membrane immersed in a solution of 1 M LiPF6, 0.15 M LiDFOB, DMC, FEC, and HFE (v / v / v = 1:1:1). Before battery assembly, the electrodes were pretreated by adding 5 μL of the above electrolyte solution followed by negative pressure wetting. Finally, the electrodes were assembled in the order of 3D-EO-LCO, PVDFGPE, and lithium foil to obtain a 3D-EO-LCO|PVDFGPE|Li battery, with 1C = 274 mAh g⁻¹. -1 .
[0054] Comparative Example
[0055] This comparative example is basically the same as the example, except that lithium cobalt oxide is used in the preparation of the positive electrode and the assembly of the battery. Specifically:
[0056] A uniform slurry was prepared by mixing LCO, Super-P, and PVDF5180 at a mass ratio of 70:20:10 and coated onto an aluminum foil current collector. The resulting electrode was then vacuum-dried at 80°C for 12 hours to finally obtain LCO.
[0057] The entire preparation process was carried out in an argon-atmospheric glove box to eliminate interference from moisture and oxygen. The surface loading of the active material in the prepared positive electrode was approximately 2-3 mg / cm³. -2 To assemble button cells, the electrode sheets are stamped into round pieces with a diameter of 10mm.
[0058] Battery assembly:
[0059] LCO, lithium foil, and PVDF gel electrolyte were used as the positive electrode, negative electrode, and electrolyte membrane, respectively. The electrolyte consisted of a hot-pressed PVDF spun membrane immersed in a solution of 1 M LiPF6, 0.15 M LiDFOB, DMC, FEC, and HFE (v / v / v = 1:1:1). Before battery assembly, the electrodes were pretreated by adding 5 μL of the above electrolyte solution followed by negative pressure wetting. Finally, the electrodes were assembled in the order of LCO, PVDFGPE, and lithium foil to obtain an LCO|PVDFGPE|Li battery, where 1C = 274 mAh g⁻¹. -1 .
[0060] Figure 1The PXRD pattern of 3D-EO-COF, tetrakis(4-aldehydephenyl)methane (TFPM), and 2,5-bis(2-(2-methoxyethoxy)ethoxy)terephthalohydrazide (DGTH-NHNH2) shows that 3D-EO-COF exhibits distinct diffraction peaks, with a particularly high intensity and sharp peak at 4.94°. Simultaneously, the characteristic peaks of its corresponding monomers, DGTH-NHNH2 and TFPM, disappear, indicating the successful synthesis of 3D-EO-COF.
[0061] Figure 2 The infrared spectrum of 3D-EO-COF, tetrakis(4-aldehydephenyl)methane (TFPM), and 2,5-bis(2-(2-methoxyethoxy)ethoxy)terephthalohydrazide (DGTH-NHNH2) shows that 3D-EO-COF is at 1537 cm⁻¹. -1 A C=N stretching vibration peak appeared at 1689 cm⁻¹, and the TFPM monomer was located at 1689 cm⁻¹. -1 The C=O characteristic peak has completely disappeared. The DGTH-NHNH2 monomer at 3272 cm⁻¹... -1 The weakening intensity of the -NH2 characteristic peak at the point indicates a reduction in the number of NH bonds, further proving the formation of -C=N-, which also demonstrates the successful synthesis of 3D-EO-COF.
[0062] Figure 3 The TGA curve of 3D-EO-COF shows that its thermal decomposition onset temperature is about 330°C, indicating good thermal stability.
[0063] Figure 4 The PXRD patterns of 3D-EO-LCO and LCO show that the diffraction peaks of 3D-EO-LCO and LCO completely overlap, with no other impurity peaks and no peak shift. This indicates that the crystal structure of lithium cobalt oxide was not changed during the low-speed ball milling composite process.
[0064] Figure 5 The infrared image of 3D-EO-LCO and LCO shows that at 3267cm... -1 A characteristic -NH2 peak appears at 1686 cm⁻¹. -1 The characteristic peak of C=O appears at 1532 cm⁻¹. -1 The characteristic peak of C=N appeared at 500-700 cm⁻¹. All three characteristic peaks mentioned above originate from 3D-EO-COF. -1 The characteristic peaks originate from the CoO6 octahedral structure of lithium cobalt oxide. This indicates the successful composite of 3D-EO-COF and lithium cobalt oxide, and the successful construction of the 3D-EO-COF physical interface layer.
[0065] Figure 6 The SEM image of LCO shows that the LCO particles have a smooth surface.
[0066] Figure 7 The image shows a SEM image of 3D-EO-LCO. It can be seen that the surface of 3D-EO-LCO prepared by low-energy ball milling becomes rough due to the adhesion of 3D-EO-COF.
[0067] Figure 8 The graph shows the long-term cycling performance of 3D-EO-LCO and LCO at 2C rate. It can be seen that long-term cycling performance tests were conducted on 3D-EO-LCO and LCO at 25℃, 3-4.5V, and 2C rate. 3D-EO-LCO exhibits superior cycling stability; after 150 cycles, its capacity showed almost no decay, retaining 95.2% of its capacity and still maintaining 161.6 mAh g⁻¹. -1 Discharge specific capacity
[0068] In summary, this invention synthesizes a three-dimensional covalent organic framework material (3D-EO-COF) with high porosity and abundant lithiophilic sites, and constructs a modified cathode material by low-speed ball milling and compositing it with lithium cobalt oxide. The composite cathode material of this invention exhibits good Li... ﹢ Diffusion coefficient and stability. The three-dimensional framework material acts as a physical barrier, effectively suppressing interfacial side reactions such as transition metal dissolution. Its rigid structure can also buffer volumetric stress during cycling, improving interfacial compatibility with gel electrolytes and exhibiting excellent cycling stability.
[0069] 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. A three-dimensional lithiophilic covalent organic framework with ether oxygen side chains, characterized in that, The structural formula is as follows:
2. The three-dimensional lithiophilic covalent organic framework with ether oxygen side chains as described in claim 1, characterized in that, Its preparation method includes the following steps: Tetra(4-aldehydephenyl)methane and 2,5-bis(2-(2-methoxyethoxy)ethoxy)terephthalohydrazide in a molar ratio of 1:2 were added to a solvent composed of 1,4-dioxane and mesitylene in a volume ratio of 1:
3. The mixture was ultrasonically dispersed, and acetic acid solution was added. The mixture was then subjected to liquid nitrogen freezing, vacuuming, and degassing in sequence. The tube was sealed with a flame gun, and the reaction was carried out at 120±10℃ for more than 144 h to obtain a crude product. The crude product was washed with methanol, filtered, and freeze-dried to obtain a covalent organic framework modified with ether oxygen side chains.
3. The three-dimensional lithiophilic covalent organic framework with ether oxygen side chains as described in claim 2, characterized in that, The 2,5-bis(2-(2-methoxyethoxy)ethoxy)terephthalohydrazide is prepared by the following steps: Diethyl 2,5-dihydroxyterephthalate, 1-bromo-2-(2-methoxyethoxy)ethane, and potassium carbonate were respectively placed into Shrek flasks; Anhydrous acetonitrile was added under argon protection, and the mixture was heated and stirred at 90°C for 48 hours. After the reaction is complete, cool and filter, extract, and dry with anhydrous sodium sulfate; The crude product was then obtained by filtration and rotary evaporation, and purified by chromatographic column to obtain the white intermediate DGTH-CH2CH3; The intermediate was dissolved in anhydrous ethanol, hydrazine hydrate was added, and the mixture was heated and stirred at 90°C for 12 hours. Recrystallization yielded a white solid product, 2,5-bis(2-(2-methoxyethoxy)ethoxy)terephthalohydrazide.
4. The three-dimensional lithiophilic covalent organic framework with ether oxygen side chains as described in claim 2, characterized in that, The liquid nitrogen freezing, vacuuming, and degassing processes are performed at least three times.
5. The three-dimensional lithiophilic covalent organic framework with ether oxygen side chains as described in claim 2, characterized in that, The concentration of the acetic acid solution is 6 mol / L.
6. The three-dimensional lithiophilic covalent organic framework with ether oxygen side chains as described in claim 2, characterized in that, The solvent used for filtration and washing is methanol.
7. The three-dimensional lithiophilic covalent organic framework with ether oxygen side chains as described in claim 2, characterized in that, The freeze-drying time is 12 hours.
8. The three-dimensional lithiophilic covalent organic framework with ether oxygen side chains as described in claim 1, characterized in that, The three-dimensional lithiophilic covalent organic framework with ether oxygen side chains is composited with a lithium cobalt oxide cathode via a low-energy ball milling method, including the following steps: A three-dimensional lithiophilic covalent organic framework with ether oxygen side chains was dispersed by ball milling in anhydrous acetonitrile solution, then mixed with lithium cobalt oxide cathode, and mixed and ground at a low speed of 200 rpm for 2 hours using a planetary ball mill, followed by centrifugal drying to load it onto the surface of lithium cobalt oxide.
9. The three-dimensional lithiophilic covalent organic framework with ether oxygen side chains as described in claim 8, characterized in that, The three-dimensional lithiophilic covalent organic framework, comprising 0.3 wt% of the total mass of lithium cobalt oxide, was mixed and ground for 2 hours using a planetary ball mill at a speed of 200 rpm.
10. The three-dimensional lithiophilic covalent organic framework with ether oxygen side chains as described in claim 8, characterized in that, The application of the aforementioned three-dimensional lithiophilic covalent organic framework in lithium metal batteries.