Quasi-solid composite electrolytes containing ion-exchange treated covalent organic frameworks tp pa-so3h, methods of making and use thereof

Abstract

This invention discloses a quasi-solid-state composite electrolyte containing a covalent organic framework TpPa-SO3H treated with ion exchange, its preparation method, and its applications. This invention treats the covalent organic framework TpPa-SO3H via ion exchange, removing H+ from the sulfonic acid groups. + Replace with Li + This process forms an efficient lithium-ion conduction pathway, resulting in a solid-state composite electrolyte. When assembled with positive and negative electrodes, the resulting quasi-solid-state lithium-ion battery possesses advantages such as high thermal stability, excellent electrochemical performance, good cycle stability, and effective suppression of lithium dendrites, making it a promising candidate for applications in the lithium battery field.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, specifically a quasi-solid-state composite electrolyte containing a covalent organic framework TpPa-SO3H with ion exchange treatment, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries are widely used in energy storage systems due to their high energy density and wide operating voltage window, but their safety issues urgently need to be addressed. All-solid-state lithium metal batteries have attracted considerable attention due to their high safety and large energy density. However, the brittleness of traditional solid-state electrolytes, their low room-temperature ionic conductivity, and the battery failure caused by lithium dendrite growth limit their application.

[0003] In recent years, covalent organic framework (COF) materials have been widely studied for the preparation of solid electrolytes due to their unique pore structure and chemical stability. In particular, the covalent organic framework TpPa-SO3H is considered a promising quasi-solid electrolyte material due to its excellent ion conductivity and good chemical stability. Reference 1 reports the application of the modified covalent organic framework TpPa-SO3H in catalysis, showing good catalytic performance (C. Jin, N. Li, E. Lin, et al, Enzyme immobilization in porphyrinic covalent organic frameworks for photoenzymatic asymmetric catalysis, ACS Catal. 12(14)(2022)8259-8268.). Reference 2 further explores the safety and efficiency of the covalent organic framework TpPa-SO3H in energy storage (Y.He,N.An,C.Meng,etal,Highdensity active site COFs with a flower-like morphology for energy storage applications,J.Mater.Chem.10(20)(2022)11030-11038). Summary of the Invention

[0004] The purpose of this invention is to provide a quasi-solid-state composite electrolyte containing ion-exchange treated covalent organic framework TpPa-SO3H, its preparation method, and its application in lithium-ion batteries. This invention prepares a novel quasi-solid-state composite electrolyte by treating the covalent organic framework TpPa-SO3H with ion exchange, which not only improves the crystallinity and stability of COFs but also enhances the performance of Li-ion batteries. +The improved conductivity increases the transference number of lithium dendrites, resulting in high thermal stability, excellent electrochemical performance, good cycle stability, and effective suppression of lithium dendrites. This solves the problems of high brittleness, low room-temperature ionic conductivity, and battery failure caused by lithium dendrite growth in traditional solid-state electrolytes. Lithium-ion batteries assembled with this quasi-solid-state composite electrolyte exhibit high thermal stability and excellent electrochemical performance over a wide temperature range, effectively suppressing lithium dendrite growth and demonstrating good cycle stability.

[0005] The technical solution for achieving the objective of this invention is as follows:

[0006] A method for preparing a quasi-solid-state composite electrolyte containing an ion-exchange treated covalent organic framework TpPa-SO3H includes the following steps:

[0007] (1) Dissolve lithium salt in an organic solvent to prepare a lithium salt electrolyte;

[0008] (2) The lithium salt electrolyte and the covalent organic framework TpPa-SO3H powder were mixed and ground at a mass ratio of 2-3:8-7 to obtain a mixed powder.

[0009] (3) Use a mold to press the mixed powder into a sheet to obtain a quasi-solid composite electrolyte.

[0010] Furthermore, in step (1), the lithium salt is a lithium salt commonly used in the field of lithium batteries, including but not limited to lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium hexafluorophosphate, and lithium perchlorate. In a specific embodiment of the present invention, LiTFSI is taken as an example.

[0011] Furthermore, in step (1), the organic solvent is a conventionally used organic solvent in the lithium battery field, including but not limited to polyethylene glycol (PEG), propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate. In a specific embodiment of the present invention, PEG is taken as an example.

[0012] Furthermore, in step (2), the grinding time is 10 to 12 minutes.

[0013] This invention provides a quasi-solid-state composite electrolyte containing an ion-exchange treated covalent organic framework TpPa-SO3H, prepared by the above method.

[0014] Furthermore, the present invention provides the application of the above-mentioned quasi-solid-state composite electrolyte containing the ion-exchange treated covalent organic framework TpPa-SO3H in lithium-ion batteries.

[0015] Furthermore, in the lithium-ion battery, the aforementioned quasi-solid-state composite electrolyte containing the ion-exchange treated covalent organic framework TpPa-SO3H is a solid-state electrolyte, lithium iron phosphate is the positive electrode, and lithium sheet is the negative electrode.

[0016] Compared with the prior art, the present invention has the following advantages:

[0017] (1) This invention removes the H from the sulfonic acid group through ion exchange treatment. + Replace with Li + This forms an efficient lithium-ion conduction pathway, thereby increasing the lithium-ion transference number (tLi). + The efficiency of lithium-ion conduction was improved by increasing the value from 0.12 to 0.32.

[0018] (2) This invention transforms COFs from an unstable enol-imine structure to a stable ketone-enamine structure through ion exchange treatment, which helps to improve the electrochemical stability of the material and make it exhibit excellent stability in the voltage range of 0V to 4.5V. It also increases the oxidation decomposition initiation voltage from 4.0V to 5V, thereby improving the overall stability of the ion battery.

[0019] (3) The TpPa-SO3H treated by ion exchange in this invention exhibits higher stability during thermal decomposition, wherein the weight loss rate in the initial weight loss stage is reduced from 6% to 4%, at 0.1 mA / cm 2 Under these conditions, the cycle life is extended from 200 hours to 1000 hours, significantly improving the battery's lifespan. Furthermore, the pore structure in the covalent organic framework after ion exchange treatment is stable, effectively suppressing the growth of lithium dendrites, thereby improving the battery's safety and stability. Ion exchange treatment does not damage the framework structure of the covalent organic framework, and XRD testing shows that the crystallization peak intensity is similar to that of the untreated sample, indicating that ion exchange treatment can maintain the crystallinity of the material. Therefore, the lithium-ion battery prepared by the above method has the advantages of good cycle stability and effective suppression of lithium dendrites. Attached Figure Description

[0020] Figure 1 This is a diagram showing the thermal decomposition stages of TpPa-SO3H.

[0021] Figure 2 The infrared spectra of the covalent organic framework TpPa-SO3H and the ion-exchanged covalent organic framework TpPa-SO3H are shown.

[0022] Figure 3 The BET analysis diagrams for the covalent organic framework TpPa-SO3H are shown, where (a) is the adsorption-desorption curve, (b) is the pore size distribution, and (c) is the Langmuir isotherm adsorption curve.

[0023] Figure 4For LSV testing of the battery;

[0024] Figure 5 The diagram shows the constant current charge-discharge test results for the full battery, where (b) is a magnified view of a portion of (a).

[0025] Figure 6 The graph shows the long-cycle voltammetry test results for a Li-Li symmetric cell.

[0026] Figure 7 For battery Li + Ion transport number, where (a) is the impedance diagram and (b) is the current-time relationship diagram. Detailed Implementation

[0027] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments and accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] The covalent organic framework TpPa-SO3H of the present invention was prepared according to references 1 [Zhang, H., et al. "Highly Conductive Covalent Organic Frameworks for All-Solid-State Lithium Batteries." Journal of the American Chemical Society, 2019, 141(43): 17654-1766] and 2 [Li, Y., et al. "Polymer-COF Composite Electrolytes for Quasi-Solid-State Lithium Metal Batteries." Advanced Functional Materials, 2020, 30(18): 1905781.].

[0029] Example 1

[0030] 1. Preparation of quasi-solid-state composite electrolytes containing ion-exchange treated covalent organic framework TpPa-SO3H:

[0031] (1) The covalent organic framework material TpPa-SO3H powder was placed in a vacuum drying oven and heated at 100°C for 12 hours. Subsequently, the covalent organic framework material TpPa-SO3H powder was transferred to a heating table and dried in a glove box at 110°C for 3 days to eliminate the influence of water or solvent.

[0032] (2) PEG and LiTFSI were mixed at a [O] / [Li] molar ratio of 16:1 and stirred at 100℃ for 24 h. Then, the electrolyte was transferred to a glove box and heated at 25℃ for 24 h to prepare Li. + -PEG electrolyte.

[0033] (3) According to the mass ratio of covalent organic framework TpPa-SO3H powder to LiTFSI of 7:3, mix the covalent organic framework TpPa-SO3H powder and Li... + - The PEG electrolyte was mixed and ground for 10 minutes. The COF powder has large and strong pores, allowing the electrolyte to be easily locked in. Finally, the mixture was pressed for 10 minutes using a 5mm standard mold under 0.2 MPa pressure to obtain a quasi-solid-state composite electrolyte. All preparation steps were performed in an Ar atmosphere glove box with O2 and H2O contents less than 0.5 ppm.

[0034] 2. Sample Testing

[0035] (1) The synthesized quasi-solid-state composite electrolyte was characterized using Fourier transform infrared spectroscopy (FT-IR, Vertex 70), solid-state nuclear magnetic resonance (C13NMR), and X-ray diffraction (XRD, Smartlab). Performance analysis was performed using differential scanning calorimetry (DSC), thermogravimetric analysis (TAG), linear sweep voltammetry (LSV), electrochemical electrochemical impedance spectroscopy (AC impedence), dynamic rheometer (DHR), and ion transport number.

[0036] 3. Material Characterization

[0037] (1) To further determine the structure of the quasi-solid-state composite electrolyte containing the ion-exchange treated covalent organic framework TpPa-SO3H, Fourier transform infrared spectroscopy was used to analyze the sample. The results are as follows: Figure 2 As shown, 3400cm -1 and 1575cm -1 The absorption peaks at 1240 cm⁻¹ correspond to the NH stretching vibration and NH- bending vibration of the secondary amine, respectively. -1 The absorption peak at 3100 cm⁻¹ corresponds to the CN stretching vibration, demonstrating the transformation from the unstable enol-imine structure to the stable ketone-enamine structure. -1 The characteristic peak of the stretching vibration of sulfonate OH was weakened after PEG treatment.

[0038] (2) The sample was tested using X-ray diffraction (XRD) with a copper target and an incident wavelength of [wavelength missing]. When testing the powder sample, the scanning range was 2–15°, and the scanning speed was 10° / min. The results showed that the sample had a very strong peak at around 2°, indicating strong crystal plane reflection at this angle. Simultaneously, a weaker peak appeared at 2θ = 4.7°, corresponding to the (100) crystal plane of the sample. This indicates that the synthesized sample has good crystallinity.

[0039] (3) To determine the thermal stability of the samples, the samples were tested using TG at 50℃ and 800℃ with a heating rate of 5℃ / s. The results are as follows: Figure 1 As shown, the thermal decomposition of TpPa-SO3H mainly involves two stages: first, at 55℃-91℃, a weight loss of 4% occurs, which is likely due to the structural breakage of COFs, gradually decomposing into smaller molecules; then, at 290℃-400℃, a second weight loss stage occurs, with a weight loss of 22%. This is likely due to the continued decomposition of the sample's smaller molecules.

[0040] (4) The pore structure of the material was analyzed using the BET adsorption method. The results are as follows: Figure 3 As shown, the material exhibits a typical adsorption curve, indicating that it is a microporous material with a specific surface area of ​​51.09 m². 2 / g. The pore size distribution was calculated using the NLDFT method, and the material pore size is approximately 0.28 nm.

[0041] 4. Performance Testing

[0042] (1) The lithium iron phosphate cathode, quasi-solid-state composite electrolyte, and lithium sheet were sequentially placed into a 2032 coin cell, and excess space was filled with spacers and springs. After assembly, the cells were sealed using a coin cell packaging machine. The resulting cells underwent LSV testing, and the results are as follows: Figure 4 As shown, the current increases rapidly above 5V, indicating that the electrolyte is oxidized and decomposed; within the voltage range of 0V to 4.5V, the current remains at a low level, which can be considered as the electrochemical stability of the material, indicating that the material treated with PEG can be used with most commercial electrodes.

[0043] (2) At 60℃ and 0.1mA / cm 2 Under these conditions, a constant current charge-discharge test was performed on the sample symmetrical battery to obtain the voltage-time relationship curve. The results are as follows: Figure 5 As shown, the polarization voltage during the first charge-discharge cycle is 0.074V, which decreases briefly and then gradually increases, reaching 0.079V after 1000 hours of cycling.

[0044] (3) The performance of the electrolyte was investigated through long-cycle voltammetry testing. The symmetrical cell was tested at 25℃ under 0.05-0.3 mA / cm² conditions. -2The test was performed using five different current densities, with each current density cycled 10 times. The results are as follows: Figure 6 As shown, no short circuit occurred during the cycle, and the voltage fluctuation was small. Furthermore, when the current density suddenly decreased to 0.05 mA cm⁻¹... -2 The time potential level is similar to the initial level.

[0045] (4) Lithium-ion transference number is crucial for evaluating the performance of solid-state electrolytes, as it determines the role of lithium ions in current conduction. To test the transference number of the battery, a 10mV DC polarization voltage was applied across the battery terminals. The current decreased continuously over time, stabilizing after 3000s. The results are as follows: Figure 7 As shown. The initial current I0 (mA) was 17.73 μA and the steady-state current Is was 11.64 μA obtained by the chronoamperometry method. The initial internal resistance R0 was 167.82 Ω and the steady-state internal resistance Rs was 153.86 Ω before and after the voltage was applied, respectively, by EIS testing. The lithium-ion transport number tLi was calculated according to formula (1). + It is 0.32.

[0046]

[0047] In summary, ion exchange treatment of this covalent organic framework (TpPa-SO3H-ST) effectively improves the electrochemical performance of COFs. The results show that ion exchange treatment transforms the COF material from an unstable enol-imine structure to a stable ketone-enamine structure, thereby improving its stability. Furthermore, battery performance tests demonstrate that the ion-exchange-treated COFs exhibit stable lithium plating / stripping behavior. This method also improves Lithium plating performance without altering the original crystallinity of the COFs. + The conduction efficiency transfer number (tLi) + The interface is relatively stable, which helps to suppress lithium dendrite formation and exhibits good stability (0.1 mA / cm). 2 1000h).

[0048] Comparative Example 1

[0049] 1. Quasi-solid-state composite electrolyte of covalent organic framework TpPa-SO3H without ion exchange treatment:

[0050] To further verify the effect of ion exchange treatment on the electrochemical performance improvement of the sulfonic acid-modified covalent organic framework material (TpPa-SO3H), a comparative experiment was designed. In the comparative experiment, TpPa-SO3H was not subjected to ion exchange treatment, and the remaining experimental steps were consistent with those in the example.

[0051] 2. Structural characterization comparison

[0052] (1) FT-IR analysis: 3100 cm⁻¹ in the comparative example -1 The OH peak of the sulfonate group did not decrease, indicating that Li+ did not occur. + Replacement H + Ion exchange.

[0053] (2) Keto-enamine characteristic peak (1575 cm⁻¹) -1 The strength is lower than that of the example, indicating poor structural stability.

[0054] (3)XRD: The intensity of the crystallization peaks (2θ = 2° and 4.7°) is similar to that of the example, proving that the ion exchange did not destroy the COF framework.

[0055] (4) TG analysis: The weight loss rate only started to increase at 300℃, indicating that the covalent organic framework material has high thermal stability.

[0056] 3. Performance Test Results

[0057] (1) Lithium-ion transference number (tLi) + ): Comparative example tLi + Only 0.12 (significantly lower than the 0.32 of the example), due to the lack of Li + Transmission path.

[0058] (2) Cycle stability: Symmetric cells at 0.1 mA / cm 2 The polarization voltage increased sharply (0.15V) after 200 hours of cycling, much shorter than the 1000 hours in the previous example.

[0059] (3) LSV test: The oxidative decomposition initiation voltage dropped to 4.0V (5V in the example), and the electrolyte stability decreased.

[0060] The above comparative examples show that the untreated covalent organic framework TpPa-SO3H powder material, due to the lack of interaction between the sulfonic acid groups and Li, exhibits poor performance. + This combination leads to low lithium-ion conductivity (tLi). + The ion exchange process reduces the lithium dendrite growth rate by 60%, leading to increased interfacial impedance, which significantly degrades the structural thermal stability and electrochemical window, and fails to effectively suppress lithium dendrite growth, resulting in a drastically shortened cycle life. Therefore, the comparison of experimental results between Example 1 and Comparative Example 1 shows that the TpPa-SO3H without ion exchange treatment is inferior to the sample with ion exchange treatment in terms of structural stability, thermal stability, electrochemical stability, cycle stability, and lithium-ion conduction efficiency. This further proves the significant improvement effect of ion exchange treatment on the electrochemical performance of TpPa-SO3H, and verifies the effectiveness and superiority of the ion exchange treatment method in the examples.

[0061] Comparative Example 2

[0062] This comparative example is largely the same as Example 1, except that the mass ratio of lithium salt to covalent organic framework TpPa-SO3H powder is 1:1. Under this ratio, Li... + - PEG electrolyte and TpPa-SO3H powder are mixed according to the formula mass ratio, ground to obtain a mixed powder, and then pressed using a 5mm standard mold at a pressure of 0.2-0.5MPa for 10-15 minutes to prepare a quasi-solid-state composite electrolyte. At this time, Li + - An excessively high proportion of PEG electrolyte can lead to excessive fluidity, which can affect the ion conduction performance and mechanical strength of the quasi-solid composite electrolyte.

[0063] Comparative Example 3

[0064] This comparative example is largely the same as Example 1, except that the mass ratio of lithium salt to covalent organic framework TpPa-SO3H powder is 1:9. Under this ratio, Li... + - PEG electrolyte and TpPa-SO3H powder are mixed according to the formula mass ratio, ground to obtain a mixed powder, and then pressed using a 5mm standard mold at a pressure of 0.2-0.5MPa for 10-15 minutes to prepare a quasi-solid-state composite electrolyte. At this time, Li + - If the proportion of PEG electrolyte is too low, it will result in too high impedance and too low efficiency.

Claims

1. Process for the preparation of a quasi-solid composite electrolyte containing ion-exchange treated covalent organic frameworks TpPa-SO3H, characterized in that, Includes the following steps: (1) Dissolve lithium salt in an organic solvent to prepare lithium salt electrolyte. The lithium salt is lithium bis(trifluoromethanesulfonyl)imide and the organic solvent is polyethylene glycol. (2) The lithium salt electrolyte and the covalent organic framework TpPa-SO3H powder were mixed and ground according to the mass ratio of lithium salt to covalent organic framework TpPa-SO3H powder of 2~3:8~7 to obtain mixed powder; (3) Use a mold to press the mixed powder into a sheet to obtain a quasi-solid composite electrolyte.

2. The preparation method according to claim 1, characterized in that, In step (2), the grinding time is 10~12 min.

3. A quasi-solid-state composite electrolyte containing an ion-exchange treated covalent organic framework TpPa-SO3H, prepared by any one of the preparation methods described in claims 1 to 2.

4. The application of the quasi-solid-state composite electrolyte containing the ion-exchange treated covalent organic framework TpPa-SO3H as described in claim 3 in lithium-ion batteries.

5. The application according to claim 4, characterized in that, The quasi-solid-state composite electrolyte containing the ion-exchange treated covalent organic framework TpPa-SO3H is a solid electrolyte, with lithium iron phosphate as the positive electrode and lithium foil as the negative electrode.

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