Quasi-solid-state composite electrolyte containing covalent organic framework TpPa-SO3H subjected to ion exchange treatment as well as preparation method and application of quasi-solid-state composite electrolyte

Abstract

The invention discloses a quasi-solid-state composite electrolyte containing a covalent organic framework TpPa-SO3H subjected to ion exchange treatment as well as a preparation method and application of the quasi-solid-state composite electrolyte. The covalent organic framework TpPa-SO3H is treated through an ion exchange method, H < + > in a sulfonic acid group is replaced with Li < + >, an efficient lithium ion conduction path is formed, and the solid-state composite electrolyte is prepared and assembled with a positive electrode and a negative electrode to form the quasi-solid-state lithium ion battery. The lithium ion battery has the advantages of high thermal stability, excellent electrochemical performance, good cycle stability and effective inhibition on lithium dendrites, and has a wide application prospect in the field of lithium batteries.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries, and specifically relates to a quasi-solid composite electrolyte containing ion-exchanged covalent organic framework TpPa-SO 3 H, and its preparation method and application. Background Art

[0002] Lithium-ion batteries are widely used in energy storage systems due to their high energy density and wide working voltage window, but their safety issues need to be urgently solved. All-solid-state lithium-metal batteries have attracted much attention due to their high safety and large energy density. However, problems such as the brittleness of traditional solid electrolytes, low room-temperature ionic conductivity, and the growth of lithium dendrites leading to battery failure limit their applications.

[0003] In recent years, covalent organic framework (COF) materials have been widely studied for the preparation of solid electrolytes due to their unique pore structures and chemical stabilities. In particular, the covalent organic framework TpPa-SO 3 H, due to its excellent ionic conductivity and good chemical stability, is considered a promising quasi-solid electrolyte material. Literature 1 reported the application of modified covalent organic framework TpPa-SO 3 H 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.). Literature 2 further explored the safety and efficiency of covalent organic framework TpPa-SO 3 H in energy storage (Y. He, N. An, C. Meng, et al, High density 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 object of the present invention is to provide a quasi-solid composite electrolyte containing ion-exchanged covalent organic framework TpPa-SO 3 H, and its preparation method and application in lithium-ion batteries. The present invention processes the covalent organic framework TpPa-SO by an ion exchange method 3H, a novel quasi-solid composite electrolyte was prepared, which not only improved the crystallinity and stability of COFs, but also enhanced the conduction efficiency of Li + , increased its transference number, and had the advantages of high thermal stability, excellent electrochemical performance, good cycle stability, and effective inhibition of lithium dendrites, solving the problems of large brittleness, low room temperature ionic conductivity of traditional solid electrolytes, and battery failure caused by lithium dendrite growth. The lithium-ion battery assembled with this quasi-solid composite electrolyte has high thermal stability and excellent electrochemical performance in a wide temperature range, can effectively inhibit the growth of lithium dendrites, and exhibits good cycle stability.

[0005] The technical solutions to achieve the object of the present invention are as follows:

[0006] A preparation method of a quasi-solid composite electrolyte containing ion-exchanged covalent organic framework TpPa-SO 3 H, comprising the following steps:

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

[0008] (2) According to the mass ratio of the lithium salt to the covalent organic framework TpPa-SO 3 H powder being 2-3:8-7, mix the lithium salt electrolyte solution with the covalent organic framework TpPa-SO 3 H powder, and grind to obtain a mixed powder;

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

[0010] Further, 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, lithium perchlorate, etc. In the specific implementation manner of the present invention, LiTFSI is taken as an example.

[0011] Further, in step (1), the organic solvent is an organic solvent commonly used in the field of lithium batteries, including but not limited to polyethylene glycol (PEG), propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate, etc. In the specific implementation manner of the present invention, PEG is taken as an example.

[0012] Further, in step (2), the grinding time is 10-12 min.

[0013] The present invention provides a quasi-solid composite electrolyte containing ion-exchanged covalent organic framework TpPa-SO 3 H prepared by the above preparation method.

[0014] Further, the present invention provides the above-mentioned covalent organic framework TpPa-SO containing ion-exchanged treatment3 Application of quasi-solid composite electrolyte of H in lithium-ion batteries.

[0015] Furthermore, in the lithium-ion battery, the above-mentioned covalent organic framework TpPa-SO with ion exchange treatment 3 The quasi-solid composite electrolyte of H is a solid electrolyte, lithium iron phosphate is the positive electrode, and lithium foil is the negative electrode.

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

[0017] (1) Through ion exchange treatment, the present invention replaces H in the sulfonic acid group + with Li + , forming an efficient lithium-ion conduction path, thereby increasing the lithium-ion transference number (tLi + ) from 0.12 to 0.32, improving the conduction efficiency of lithium ions.

[0018] (2) Through ion exchange treatment, the present invention transforms the COFs from an enol-imino unstable structure into a keto-enamine stable structure, which helps to improve the electrochemical stability of the material, enabling it to exhibit excellent stability in the voltage range of 0V to 4.5V, increasing the initial oxidation decomposition voltage from 4.0V to 5V, and enhancing the overall stability of the ion battery.

[0019] (3) TpPa-SO 3 H after ion exchange treatment by the present invention shows higher stability during the thermal decomposition process. Among them, the weight loss rate in the initial weight loss stage decreases from 6% to 4%. Under the condition of 0.1mA / cm 2 , the cycle life is extended from 200 hours to 1000 hours, greatly improving the service life of the battery. Moreover, the pore structure in the covalent organic framework after ion exchange treatment is stable, which can effectively inhibit the growth of lithium dendrites, thereby improving the safety and stability of the battery. The ion exchange treatment does not damage the framework structure of the covalent organic framework, and XRD tests show that the intensity of the crystallization peak is similar to that of the untreated sample, indicating that the 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 inhibition of lithium dendrites. Description of the Drawings

[0020] Figure 1 It is a thermal decomposition stage diagram of TpPa-SO 3 H;

[0021] Figure 2 It is an infrared spectrum diagram of the covalent organic framework TpPa-SO 3 H and the covalent organic framework TpPa-SO 3 H after ion exchange;

[0022] Figure 3 For the BET analysis diagram of covalent organic framework TpPa-SO 3 H, where (a) is the adsorption-desorption curve, (b) is the pore size distribution, and (c) is the Langmuir isothermal adsorption curve;

[0023] Figure 4 For the LSV test diagram of the battery;

[0024] Figure 5 For the constant current charge-discharge test diagram of the full battery, where the (b) diagram is the partial enlarged view of the (a) diagram;

[0025] Figure 6 For the long cyclic voltammetry test diagram of the Li-Li symmetric battery;

[0026] Figure 7 For the battery Li + ion transference number, where (a) is the impedance diagram and (b) is the current-time relationship diagram. Specific implementation manners

[0027] The technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments and the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0028] The covalent organic framework TpPa-SO of the present invention 3 H is prepared with reference to Reference 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 Reference 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. Covalent organic framework TpPa-SO with ion exchange treatment3 Preparation of quasi-solid composite electrolyte of H

[0031] (1) Put the covalent organic framework material TpPa-SO 3 H powder into a vacuum drying oven and heat it at 100 °C for 12 h. Subsequently, transfer the covalent organic framework material TpPa-SO 3 H powder to a heating stage and dry it in a glove box at 110 °C for 3 days to exclude the influence of water or solvent.

[0032] (2) Mix PEG and LiTFSI at a molar ratio of [O] / [Li] of 16:1, stir at 100 °C for 24 h, then transfer the electrolyte to a glove box and heat it at 25 °C for 24 h to prepare Li + -PEG electrolyte.

[0033] (3) According to the mass ratio of the covalent organic framework TpPa-SO 3 H powder and LiTFSI of 7:3, mix and grind the covalent organic framework TpPa-SO 3 H powder and Li + -PEG electrolyte for 10 minutes. The pores of the COF are large and strong, so the electrolyte is easily locked by the COF powder. Finally, press the mixture under a pressure of 0.2 Mpa for 10 min through a 5 mm standard mold to obtain the quasi-solid composite electrolyte. All preparation steps are completed in a glove box under an Ar atmosphere, and the O 2 and H 2 O content is less than 0.5 ppm.

[0034] 2. Sample testing

[0035] (1) Use Fourier transform infrared spectroscopy (FT-IR, Vertex 70), solid nuclear magnetic resonance (C13NMR), and X-ray diffractometer (XRD, Smartlab) to characterize the synthesized quasi-solid composite electrolyte. Perform performance analysis through differential scanning calorimeter (DSC), thermogravimetric analysis (TAG), linear sweep voltammetry (LSV), electrochemical impedance spectroscopy (AC impedence), dynamic rheometer (DHR), and ion transference number.

[0036] 3. Material characterization

[0037] (1) To further determine the structure of the quasi-solid composite electrolyte containing ion-exchanged covalent organic framework TpPa-SO 3 H, use Fourier transform infrared to test the sample, and the results are as Figure 2 shown, 3400 cm -1 and 1575 cm -1The absorption peaks at [specific location] correspond to the N-H stretching vibration and NH-bending vibration of secondary amines respectively, and 1240 cm -1 The absorption peak at [specific location] corresponds to the C-N stretching vibration, proving the transformation from the unstable enol-imine structure to the stable keto-enamine structure. 3100 cm -1 The characteristic peak of the O-H stretching vibration of the sulfonate group at [specific location] weakens after PEG treatment.

[0038] (2) The samples were tested by X-ray diffraction (XRD). The target used was a copper target, and the incident wavelength was When testing the powder samples, the scanning range was 2 - 15°, and the scanning speed was 10° / min. The results showed that there was a very strong peak at about 2°, indicating strong crystal plane reflection of the sample at this angle. At the same time, a peak with weaker intensity appeared at 2θ = 4.7°, which corresponded to the (100) crystal plane of the sample. This indicated that the synthesized sample had good crystallinity.

[0039] (3) To determine the thermal stability of the samples, the obtained samples were tested by TG from 50 °C to 800 °C at a heating rate of 5 °C / s. The results are as Figure 1 shown, indicating that TpPa-SO 3 H has two main stages of thermal decomposition: First, from 55 °C to 91 °C, with a weight loss of 4%. It is analyzed that the structure of the COFs may break and gradually decompose into small molecules; then, the second weight loss stage occurs from 290 °C to 400 °C, with a weight loss of 22%. It is analyzed that the small molecules of the sample may continue to decompose.

[0040] (4) The BET method was used for adsorption experiments to analyze the pore structure of the materials. The results are as Figure 3 shown, indicating that the materials showed a typical adsorption curve, indicating that the materials belonged to microporous materials, and the specific surface area was 51.09 m 2 / g. The pore size distribution was calculated by the NLDFT method, and the pore size of the materials was about 0.28 nm.

[0041] 4. Performance Testing

[0042] (1) The lithium iron phosphate cathode sheet, quasi-solid composite electrolyte, and lithium sheet were sequentially placed into a 2032 coin cell, and the excess space was filled with gaskets and spring sheets. After assembly, it was sealed with a coin cell encapsulation machine. The prepared cells were subjected to LSV testing. The results are as Figure 4 shown, indicating that when the voltage is above 5V, the current increases rapidly, indicating that the electrolyte is oxidized and decomposed; in the voltage range of 0V - 4.5V, the current remains at a low level, and it can be considered that the material is electrochemically stable, indicating that the material after PEG treatment can be used in combination with most commercial electrodes.

[0043] (2) At 60 °C, 0.1 mA / cm2 Under the condition of Figure 5 as shown in the figure, it shows that the polarization voltage during the first charge and discharge is 0.074 V, which gradually increases after a short decrease and increases to 0.079 V after 1000 h of cycling.

[0044] (3) Through long-term cyclic voltammetry tests, the performance of the electrolyte was explored. At 25 °C, the symmetric cell was cycled at 0.05 - 0.3 mA cm -2 divided into 5 stepped current densities for cyclic testing, and each step was cycled 10 times for charge and discharge. The results are as Figure 6 shown. During the cycling process, no short-circuit phenomenon occurred and the voltage fluctuation was small. And when the current density suddenly decreased to 0.05 mA cm -2 the potential level was similar to the initial one.

[0045] (4) The lithium-ion transference number is the key to evaluating the performance of solid electrolytes, which can determine the role of lithium ions in current conduction. For the battery test of the transference number, a 10 mV DC polarization voltage was applied across the battery, and the current decayed continuously with time and basically stabilized after 3000 s. The results are as Figure 7 shown. The initial current I 0 (mA) obtained by chronoamperometry was 17.73 μA and the steady-state current Is was 11.64 μA. The initial internal resistance R 0 was 167.82 Ω and the steady-state internal resistance Rs was 153.86 Ω were obtained by EIS tests before and after applying the voltage. According to formula (1), the lithium-ion transference number tLi + was calculated to be 0.32.

[0046]

[0047] In summary, treating this covalent organic framework (TpPa-SO 3 H-ST) by ion exchange can effectively improve the electrochemical performance of COFs. The results show that treating by ion exchange can transform the COF material from an enol-imine unstable structure to a keto-enamine stable structure, thereby improving its stability. At the same time, the battery performance test results show that the COFs treated by ion exchange have stable lithium plating / stripping behavior. At the same time, this method improves the conduction efficiency transference number of Li + (tLi + is 0.32) without changing the original crystallinity of COFs. The interface is relatively stable, which plays a certain inhibitory role on lithium dendrites and has good stability (0.1 mA / cm 2 1000 h).

[0048] Comparative Example 1

[0049] 1. Covalent organic framework TpPa-SO without ion exchange treatment 3 H quasi-solid composite electrolyte:

[0050] In order to further verify the improvement effect of ion exchange treatment on the electrochemical performance of sulfonic acid group-modified covalent organic framework material (TpPa-SO 3 H), a comparative experiment was designed. In the comparative experiment, TpPa-SO 3 H was not subjected to ion exchange treatment, and the remaining experimental steps were the same as those in the examples.

[0051] 2. Comparison of structural characterizations

[0052] (1) FT-IR analysis: The O-H peak of sulfonate at 3100 cm -1 in the comparative example did not weaken, indicating that no ion exchange of Li + replacing H + occurred.

[0053] (2) The intensity of the keto-enamine characteristic peak (1575 cm -1 ) was lower than that in the example, indicating poorer structural stability.

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

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

[0056] 3. Performance test results

[0057] (1) Lithium ion transference number (tLi + ): In the comparative example, tLi + was only 0.12 (significantly lower than 0.32 in the example), due to the lack of Li + conduction path.

[0058] (2) Cycling stability: The symmetric cell showed a sharp increase in polarization voltage (0.15 V) after cycling for 200 hours at 0.1 mA / cm 2 , much shorter than 1000 hours in the example.

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

[0060] The above comparative examples show that the covalent organic framework TpPa-SO 3 H powder material without ion exchange treatment has sulfonic acid groups that do not react with Li +Combination will lead to low lithium-ion conduction efficiency (tLi + decreases by 60%), resulting in an increase in interfacial impedance, significantly deteriorating the structural thermal stability and electrochemical window, and being unable to effectively inhibit the growth of lithium dendrites, greatly shortening the cycle life. Therefore, the experimental results of Example 1 and Comparative Example 1 show that TpPa-SO without ion exchange treatment 3 H is inferior to the ion-exchanged sample 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 TpPa-SO 3 H's electrochemical performance and can verify the effectiveness and superiority of the ion exchange treatment method in the examples.

[0061] Comparative Example 2

[0062] This comparative example is roughly the same as Example 1, except that the mass ratio of the lithium salt to the covalent organic framework TpPa-SO 3 H powder is 1:1. At this ratio, after mixing the Li + -PEG electrolyte with the TpPa-SO 3 H powder according to the formulated mass ratio, grinding to obtain a mixed powder, and then using a 5 mm standard mold to press the mixed powder at a pressure of 0.2 - 0.5 MPa for 10 - 15 minutes to prepare a quasi-solid composite electrolyte. At this time, the excessive proportion of the Li + -PEG electrolyte will lead to too high fluidity, which will affect the ion conduction performance and mechanical strength of the quasi-solid composite electrolyte.

[0063] Comparative Example 3

[0064] This comparative example is roughly the same as Example 1, except that the mass ratio of the lithium salt to the covalent organic framework TpPa-SO 3 H powder is 1:9. At this ratio, after mixing the Li + -PEG electrolyte with the TpPa-SO 3 H powder according to the formulated mass ratio, grinding to obtain a mixed powder, and then using a 5 mm standard mold to press the mixed powder at a pressure of 0.2 - 0.5 MPa for 10 - 15 minutes to prepare a quasi-solid composite electrolyte. At this time, the too low proportion of the Li + -PEG electrolyte will lead to too large impedance and too low efficiency.

Claims

1. A method for preparing a quasi-solid composite electrolyte containing a covalent organic framework TpPa-SO3H treated with ion exchange, characterized in that: The following steps are involved: (1) Dissolving lithium salt in an organic solvent to prepare a lithium salt electrolyte; (2) mixing the lithium salt electrolyte and the covalent organic framework TpPa-SO3H powder in a mass ratio of 2-3:8-7, and grinding to obtain a mixed powder; (3) The mixed powder is pressed into tablets using a mold to produce a quasi-solid composite electrolyte.

2. The preparation method according to claim 1, characterized in that: In step (1), the lithium salt is lithium bis(trifluoromethanesulfonyl)imide, lithium hexafluorophosphate or lithium perchlorate.

3. The preparation method according to claim 1, characterized in that: In step (1), the organic solvent is polyethylene glycol, propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate or ethyl methyl carbonate.

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

5. A quasi-solid composite electrolyte containing a covalent organic framework TpPa-SO3H treated with ion exchange, obtained according to the preparation method described in any one of claims 1 to 4.

6. Use of the quasi-solid composite electrolyte containing the ion-exchange treated covalent organic framework TpPa-SO3H according to claim 5 in lithium-ion batteries.

7. The use according to claim 6, characterized in that: The quasi-solid composite electrolyte containing the covalent organic framework TpPa-SO3H treated with ion exchange is the solid electrolyte, lithium iron phosphate is the positive electrode, and the lithium sheet is the negative electrode.

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