Preparation method of a thioureyl covalent organic framework modified lithium metal negative electrode interface layer and application thereof

Abstract

This invention discloses a method for preparing a lithium metal anode interface layer modified with a thiourea-based covalent organic framework and its application, comprising the following steps: S1, adding monomers and thiourea to a reaction tube, followed by the addition of a reaction solvent to obtain a mixture; dispersing the mixture evenly and removing air from the reaction tube; heating the reaction tube and allowing it to stand until the reaction product cools; filtering to separate the solid product; washing and drying the solid product to obtain a thiourea-based covalent organic framework material (TUCOF); S2, adding the TUCOF obtained in step S1 and a binder to N-methylpyrrolidone and stirring evenly to obtain a uniform suspension; S3, contacting the suspension obtained in step S2 with lithium metal and drying to obtain the lithium metal anode interface layer modified with the thiourea-based covalent organic framework. The TUCOF material synthesized by this invention has a rich porous structure, which promotes uniform lithium-ion flux distribution and rapid lithium-ion migration along the porous channels, increasing the lithium-ion transference number; and the artificial solid electrolyte interface (SEI) layer based on the covalent organic framework material inhibits lithium dendrite growth.

Description

Technical Field

[0001] This invention belongs to the field of all-solid-state lithium metal batteries, specifically relating to a method for preparing a lithium metal anode interface layer modified with a thiourea-based covalent organic framework and its application. Background Technology

[0002] Lithium metal batteries (LMBs) benefit from the high theoretical capacity (3860 mAh g) of lithium metal anodes. -1 It has a low reduction potential (-3.04V vs. SHE) and a low weight density (0.53g / cm³). -3 While exhibiting significant application potential, lithium metal batteries (LMBs) using flammable liquid electrolytes face serious safety hazards due to unavoidable lithium dendrite formation and severe side reactions, hindering their practical application. All-solid-state lithium metal batteries (ASSLMBs) achieve higher safety by employing inherently non-flammable solid polymer electrolytes (SPEs). In particular, polyethylene oxide (PEO)-based electrolytes have become attractive SPEs due to their good mechanical properties, processability, and compatibility with electrodes. However, the spontaneous formation of a solid electrolyte interface (SEI) between the lithium metal anode (LMA) and the electrolyte, and the instability of this spontaneously formed SEI layer, can accelerate lithium dendrite growth, leading to safety issues such as short circuits and thermal runaway. Simultaneously, the rupture and rebuilding of the SEI film increases internal resistance, causing capacity decay and reducing cycle life and efficiency. Furthermore, an unstable SEI layer can also trigger side reactions, reducing the overall performance and safety of the battery. Therefore, the instability of the SEI remains a major obstacle limiting the large-scale application of LMAs.

[0003] Over the past few decades, two main strategies have been employed to enhance the SEI (Sediment Injection): one involves altering the electrolyte system by changing the electrolyte composition (including solvents, lithium salts, and additives) to design a stable SEI in situ; the other is the construction of artificial SEIs with specific components using non-situ methods. Compared to electrolyte modification, the construction of artificial SEIs offers certain advantages due to their high controllability, passivation of the lithium metal surface without consuming limited electrolyte, and excellent mechanical properties. Covalent organic frameworks (COFs) are a class of porous organic crystalline materials linked by covalent bonds, possessing advantages such as regular pore structures, large specific surface areas, lightweight, and controllable structures. Utilizing these properties, COFs can construct stable lithium-ion transport channels, increase lithium-ion transference numbers, provide more redox sites, and improve the mechanical properties of materials.

[0004] Although COFs are widely used for interface modification of lithium metal anodes, significantly improving battery performance and stability, they still cannot meet the needs of practical applications. For example, He et al. (J. Mater. Chem. A, 2023, 11, 10155) used a mixture of polythiourea and lithium salt as an artificial interface layer, which can reduce lithium salt decomposition, inhibit lithium dendrite growth, and form a stable SEI layer, thereby effectively improving the cycle performance of the battery. However, linear polythiourea lacks a regular pore structure and abundant deposition sites, limiting the rapid migration of lithium ions at the interface. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a method for preparing a lithium metal anode interface layer modified with a thiourea-based covalent organic framework and its application. This method involves synthesizing TUCOF with strong lithiophilic functional groups (C=O and C=S) as an artificial interface layer for lithium metal anodes. The S atoms in TUCOF can be adsorbed onto the lithium metal surface, and the lithiophilic functional groups (C=O and C=S) can effectively regulate the lithium-ion flux distribution. Furthermore, the regular pore structure and suitable pore size of TUCOF promote uniform lithium-ion flux distribution and rapid lithium-ion migration, thereby inhibiting the growth of lithium dendrites.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] This invention provides a method for preparing a lithium metal anode interface layer modified with a thiourea-based covalent organic framework, comprising the following steps:

[0008] S1. Add the monomer and thiourea to the reaction tube, then add the reaction solvent to obtain a mixture. Disperse the mixture evenly and remove the air from the reaction tube. Heat the reaction tube and let it stand. After the reaction product cools down, filter to separate the solid product. After washing and drying the solid product, obtain the thiourea-based covalent organic framework material (TUCOF).

[0009] S2. Add the thiourea-based covalent organic framework material (TUCOF) and adhesive obtained in step S1 to N-methylpyrrolidone (NMP), stir until homogeneous, and obtain a uniform suspension.

[0010] S3. The suspension obtained in step S2 is contacted with lithium metal and dried to obtain the lithium metal anode interface layer (TUCOF@Li) modified with the thiourea-based covalent organic framework.

[0011] In the preparation method described above, in step S1, the monomer is one or more of the following: pyromellitic methyl ether, 2-hydroxy-1,3,5-phenyltricarboxaldehyde, 2,4-dihydroxy-1,3,5-pyromellitic methyl ether, and trialdehyde-resorcinol.

[0012] In the preparation method described above, in step S1, the molar ratio of the monomer to thiourea is 1 to 3:3.

[0013] In the preparation method described above, in step S1, the reaction solvent is one or more of mesitylene, water, 1,4-dioxane, and glacial acetic acid.

[0014] In the preparation method described above, in step S1, the mixture is dispersed evenly using ultrasound, and the ultrasound treatment time is 30-60 min, preferably 30 min.

[0015] In the preparation method described above, in step S1, the mixture undergoes a freezing-pumping-thawing cycle to remove air from the reaction tube and is sealed under nitrogen.

[0016] In the preparation method described above, in step S1, the reaction tube is placed in a heated oven for standing at a temperature of 100-150°C for 1-6 days.

[0017] In the preparation method described above, in step S1, the washing solvent is one or more of methanol, tetrahydrofuran, and acetone, and the number of washing cycles is 3 to 6, preferably 3.

[0018] In the preparation method described above, in step S2, the mass ratio of the thiourea-based covalent organic framework material to the binder is 6–12:1.

[0019] In the preparation method described above, in step S2, the binder is one or more of polyvinylidene fluoride, polyimide, and styrene-butadiene rubber.

[0020] In the preparation method described above, in step S2, the thiourea-based covalent organic framework material and binder are dispersed in NMP and stirred for 10–60 min to form a uniform suspension.

[0021] In the preparation method described above, in step S3, the suspension is dropped onto the surface of lithium metal, the volume of the suspension is preferably 10-60 μL, and the diameter of the lithium metal sheet is preferably 6-30 mm.

[0022] In the preparation method described above, in step S3, vacuum drying is used, the drying temperature is 35-50℃, preferably 40℃, and the drying time is 12-48h, preferably 24h.

[0023] The present invention also provides the application of the lithium metal anode interface layer modified by the thiourea-based covalent organic framework in lithium metal batteries.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] This invention provides a method for preparing a lithium metal anode interface layer modified with a thiourea-based covalent organic framework and its application. The synthesized TUCOF material has a regular pore structure and an appropriate pore size. This artificial interface layer provides abundant lithiophilic sites while forming a robust and stable framework structure, which promotes rapid lithium ion migration and uniform lithium ion flux distribution, thereby inhibiting the growth of lithium dendrites.

[0026] This invention utilizes the high adsorption energy of the S atoms in the thiourea molecule for Li, which allows it to bind tightly to the Li surface. This tight contact effectively reduces the direct interaction between the electrode and the electrolyte. In addition, the high adsorption energy of the S atoms for Li can maintain tight contact with the Li surface and stabilize the electrode-electrolyte interface.

[0027] The TUCOF material synthesized in this invention possesses a rich porous structure, which promotes uniform lithium-ion flux distribution and rapid lithium-ion migration along the porous channels, thereby increasing the lithium-ion transference number. Furthermore, the artificial solid electrolyte interface (SEI) layer based on a covalent organic framework material suppresses lithium dendrite growth. Therefore, based on these advantages, the TUCOF-modified lithium metal anode exhibits excellent cycle stability and rate performance. Attached Figure Description

[0028] Figure 1 This is a flowchart illustrating the preparation process of the thiourea-based covalent organic framework material (TUCOF) obtained in Example 1.

[0029] Figure 2 The Fourier transform infrared (FITR) spectra of the thiourea-based covalent organic framework material prepared in Example 1, along with thiourea and trialdehyde-based phloroglucinol.

[0030] Figure 3 The image shows the powder X-ray diffraction (PXRD) pattern of the thiourea-based covalent organic framework material prepared in Example 1.

[0031] Figure 4 The images show the SEM image and mapping diagram of the thiourea-based covalent organic framework material prepared in Example 1.

[0032] Figure 5 The nitrogen adsorption isotherm and pore size distribution diagram are shown for the thiourea-based covalent organic framework material prepared in Example 1.

[0033] Figure 6 The temperature impedance diagram is shown for the Li-Li symmetric cell assembled in Application Example 1.

[0034] Figure 7 The temperature impedance diagram is for the Li-Li symmetric cell assembled in Application Example 2.

[0035] Figure 8The temperature-dependent impedance diagram of the Li-Li symmetric cell assembled in Application Example 3 is shown.

[0036] Figure 9 Arrhenius curves for the Li-Li symmetric cells assembled in Application Examples 1-3.

[0037] Figure 10 The cycling performance diagrams are for the Li-Li symmetric cells assembled in Application Examples 1 and 4.

[0038] Figure 11 The cycling performance of the LFP-Li full cells assembled for Application Examples 1 and 4 is shown in the figure.

[0039] Figure 12 The rate performance of the LFP-Li full cells assembled for Application Examples 1 and 4 is shown in the figure. Detailed Implementation

[0040] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. These embodiments are only used to illustrate the present invention and do not limit the scope of protection of the present invention.

[0041] Example 1

[0042] A method for preparing an artificial interface layer for a lithium metal anode using a thiourea-based covalent organic framework material includes the following steps:

[0043] S1. Trialdehyde-based phloroglucinol (0.14 mmol, 30 mg) and thiourea (0.21 mmol, 22.3 mg) were added to the reaction tube. Immediately afterwards, 1,4-dioxane (0.9 mL), mesitylene (0.9 mL), and water (0.048 mL) were added to obtain a mixture. The mixture was ultrasonically dispersed, and then glacial acetic acid (0.052 mL) was added dropwise. The reaction mixture was subjected to a freeze-pump-thaw cycle and sealed under nitrogen. The reaction tube was then placed in a 120°C oven for 3 days. The reaction tube was then cooled to room temperature. The solid was separated by filtration and washed with excess methanol, tetrahydrofuran, and acetone, and then dried to obtain the thiourea-based covalent organic framework material TUCOF.

[0044] S2. The thiourea-based covalent organic framework material (9 mg) and polyvinylidene fluoride (1 mg) obtained in step S1 are mixed in N-methylpyrrolidone (9 mL) at a mass ratio of 9:1 until a homogeneous TUCOF@NMP suspension with a concentration of 1 mg / mL is obtained.

[0045] S3. The uniform suspension (30 μL) obtained in step S2 is dropped onto the lithium metal surface (φ = 12 mm) and dried under vacuum at 40 °C for 24 h to obtain a lithium metal sheet based on the covalent organic framework TUCOF.

[0046] Example 2

[0047] A method for preparing an artificial interface layer for a lithium metal anode using a thiourea-based covalent organic framework material includes the following steps:

[0048] S1. Trialdehyde-based phloroglucinol (0.14 mmol, 30 mg) and thiourea (0.21 mmol, 22.3 mg) were added to the reaction tube. Immediately afterwards, 1,4-dioxane (0.9 mL), mesitylene (0.9 mL), and water (0.048 mL) were added to obtain a mixture. The mixture was ultrasonically dispersed, and then glacial acetic acid (0.052 mL) was added dropwise. The reaction mixture was subjected to a freeze-pump-thaw cycle and sealed under nitrogen. The reaction tube was then placed in a 120°C oven for 3 days. The reaction tube was then cooled to room temperature. The solid was separated by filtration and washed with excess methanol, tetrahydrofuran, and acetone, and then dried to obtain the thiourea-based covalent organic framework material TUCOF.

[0049] S2. The thiourea-based covalent organic framework material (9 mg) and polyvinylidene fluoride (1 mg) obtained in step S1 are mixed in N-methylpyrrolidone (18 mL) at a mass ratio of 9:1 until a homogeneous TUCOF@NMP suspension with a concentration of 0.5 mg / mL is obtained.

[0050] S3. The uniform suspension (30 μL) obtained in step S2 is dropped onto the lithium metal surface (φ = 12 mm) and dried under vacuum at 40 °C for 24 h to obtain a lithium metal sheet based on the covalent organic framework TUCOF.

[0051] Example 3

[0052] A method for preparing an artificial interface layer for a lithium metal anode using a thiourea-based covalent organic framework material includes the following steps:

[0053] S1. Trialdehyde-based phloroglucinol (0.14 mmol, 30 mg) and thiourea (0.21 mmol, 22.3 mg) were added to the reaction tube. Immediately afterwards, 1,4-dioxane (0.9 mL), mesitylene (0.9 mL), and water (0.048 mL) were added to obtain a mixture. The mixture was ultrasonically dispersed, and then glacial acetic acid (0.052 mL) was added dropwise. The reaction mixture was subjected to a freeze-pump-thaw cycle and sealed under nitrogen. The reaction tube was then placed in a 120°C oven for 3 days. The reaction tube was then cooled to room temperature. The solid was separated by filtration and washed with excess methanol, tetrahydrofuran, and acetone, and then dried to obtain the thiourea-based covalent organic framework material TUCOF.

[0054] S2. The thiourea-based covalent organic framework material (9 mg) and polyvinylidene fluoride (1 mg) obtained in step S1 are mixed in N-methylpyrrolidone (6 mL) at a mass ratio of 9:1 until a homogeneous TUCOF@NMP suspension with a concentration of 1.5 mg / mL is obtained.

[0055] S3. The uniform suspension (30 μL) obtained in step S2 is dropped onto the lithium metal surface (φ = 12 mm) and dried under vacuum at 40 °C for 24 h to obtain a lithium metal sheet based on the covalent organic framework TUCOF.

[0056] Comparative Example 1

[0057] The difference between Comparative Example 1 and Example 1 is that the metallic lithium in Comparative Example 1 is not treated in any way and is referred to as Bare Li.

[0058] Application Example 1

[0059] The lithium metal sheet based on the covalent organic framework TUCOF prepared in Example 1 was used to assemble a Li-Li symmetric battery. The electrolyte was an all-solid-state polyethylene oxide (PEO) thin film (EO:Li). + =16:1).

[0060] Using the lithium metal sheet based on the covalent organic framework TUCOF prepared in Example 1 as the negative electrode and a commercially available lithium iron phosphate sheet (φ = 10 mm) as the positive electrode, an LFP-Li full cell was assembled. The electrolyte was an all-solid-state polyethylene oxide (PEO) thin film (EO:Li). + =16:1), and its assembly process is existing technology.

[0061] Application Example 2

[0062] The lithium metal sheet based on the covalent organic framework TUCOF prepared in Example 2 was used to assemble a Li-Li symmetric battery. The electrolyte was an all-solid-state polyethylene oxide (PEO) thin film (EO:Li). + =16:1), and its assembly process is existing technology.

[0063] Application Example 3

[0064] The lithium metal sheet based on the covalent organic framework TUCOF prepared in Example 3 was used to assemble a Li-Li symmetric battery. The electrolyte was an all-solid-state polyethylene oxide (PEO) thin film (EO:Li). + =16:1), and its assembly process is existing technology.

[0065] Application Example 4

[0066] Using the lithium metal sheet Bare Li from Comparative Example 1, a Li-Li symmetric cell was assembled, with the electrolyte being an all-solid-state polyethylene oxide (PEO) thin film (EO:Li).+ =16:1).

[0067] Using the metallic lithium sheet Bare Li from Comparative Example 1 as the negative electrode and a commercially available lithium iron phosphate sheet (φ = 10 mm) as the positive electrode, an LFP-Li full cell was assembled. The electrolyte was an all-solid-state polyethylene oxide (PEO) thin film (EO:Li). + =16:1), and its assembly process is existing technology.

[0068] Figure 1 The flowchart of Example 1 of this invention shows that the synthesized TUCOF covalent organic framework contains lithiophilic functional groups (C=O and C=S), which promotes rapid lithium-ion migration and uniform lithium-ion flux distribution.

[0069] Figure 2 The Fourier transform infrared (FITR) spectra of the thiourea-based covalent organic framework material, thiourea, and trialdehyde-based phloroglucinol prepared in Example 1 of this invention are shown below. Comparison revealed that the 1636 cm⁻¹ spectrum belongs to trialdehyde-based phloroglucinol. -1 and 2886cm -1 The aldehyde peak disappears at 1625 cm⁻¹. -1 and 1589cm -1 The discovery of new peaks at the two peaks, attributed to the formation of ketone groups and carbon-carbon double bonds, confirms the successful synthesis of TUCOF.

[0070] Figure 3 The powder X-ray diffraction (XRD) pattern of the thiourea-based covalent organic framework material prepared in Example 1 shows prominent peaks at 5.82° and 10.14°, which belong to the (100) and (110) planes of TUCOF, respectively, indicating that the TUCOF material has high crystallinity.

[0071] Figure 4 The images show the SEM and EDS images of the thiourea-based covalent organic framework material prepared in Example 1. The SEM image shows that TUCOF exhibits a nano-short rod morphology, and the energy dispersive spectroscopy (EDS) image shows that the elements C, N, O and S are uniformly distributed in the synthesized COF.

[0072] Figure 5 The nitrogen adsorption isotherm and pore size distribution diagram of the thiourea-based covalent organic framework material prepared in Example 1 are shown. The nitrogen adsorption isotherm confirms that the specific surface area of ​​TUCOF is 63.41 m². 2 g -1 The pore size distribution diagram shows that all pores are mesopores, mainly distributed at 1.26 nm and 2.73 nm.

[0073] Figures 6-8The figures show the temperature-dependent impedance diagrams of the Li-Li symmetric cells assembled in Examples 1 to 3. The impedance decreases as the temperature increases, and the impedance is minimized at the highest temperature of 70°C.

[0074] Figure 9 To obtain the Arrhenius curves of the Li-Li symmetric cells assembled in Examples 1-3, the temperature-dependent impedance values ​​were substituted into the Arrhenius formula to calculate the SEI layer migration barrier of the Li-Li symmetric cells assembled in Examples 1-3. The symmetric cells assembled with TUCOF@NMP suspension at a concentration of 1 mg / mL had the lowest SEI layer migration barrier, proving that 1 mg / mL is the optimal coating concentration for the artificial interface layer.

[0075] Figure 10 The figures show the cycling performance of the Li-Li symmetric cells assembled in Application Examples 1 and 4. The results indicate that after 400 hours of cycling, the polarization voltage of the symmetric cell assembled in Application Example 4 significantly decreased, mainly due to the continuous growth of lithium dendrites. These dendrites pierced the electrolyte membrane, leading to a short circuit. In contrast, the symmetric cell assembled in Application Example 1 remained stable after 1000 hours of cycling. These results demonstrate that the artificial interface layer provides abundant lithiophilic sites while simultaneously forming a robust and stable framework structure, thereby suppressing lithium dendrite growth.

[0076] Figure 11 Cyclic performance graphs of the LFP-Li full cells assembled for Application Examples 1 and 4 show the discharge specific capacity and coulombic efficiency after 100 charge-discharge cycles at 60°C and 0.1C. The initial discharge specific capacity of the full cell in Application Example 1 was 166 mAh g⁻¹. -1 After 100 cycles, the discharge specific capacity remained at 160 mAh g. -1 Calculations showed that the capacity retention was 96%, significantly higher than the full cell in Application Example 4 (72%). This is mainly due to the abundance of lithiophilic sites provided by the artificial interface layer, which facilitates rapid lithium-ion migration and uniform lithium-ion flux distribution, reducing the formation of dead lithium.

[0077] Figure 12 The figures show the rate performance of the LFP-Li full cells assembled in Application Examples 1 and 4. The discharge specific capacities of the full cell in Application Example 1 at current densities of 0.1, 0.2, 0.3, 0.5, and 1C are 167, 166, 165, 163, and 156 mAh g, respectively. -1 Compared to the full cell in Application Example 4, when the rate is restored to 0.1C, the discharge specific capacity is restored to 166 mAh g. -1 This indicates that the lithium metal assembled with the artificial interface layer has excellent rate performance.

[0078] It should be understood that the application of the present invention is not limited to the examples above. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A method for preparing a lithium metal anode interface layer modified with a thiourea-based covalent organic framework, characterized in that, Includes the following steps: S1. Add the monomer and thiourea to the reaction tube, then add the reaction solvent to obtain a mixture. Disperse the mixture evenly and remove the air from the reaction tube. Heat the reaction tube and let it stand. After the reaction product cools, filter to separate the solid product. After washing and drying the solid product, obtain the thiourea-based covalent organic framework material (TUCOF). S2. Add the thiourea-based covalent organic framework material (TUCOF) and adhesive obtained in step S1 to NMP, stir until homogeneous, and obtain a uniform suspension. S3. The suspension obtained in step S2 is contacted with lithium metal and dried to obtain the lithium metal anode interface layer modified by the thiourea-based covalent organic framework (TUCOF@Li). In step S1, the monomer is one or more of the following: pyromellitic pyromellitic aldehyde, 2-hydroxy-1,3,5-phenyltricarboxaldehyde, 2,4-dihydroxy-1,3,5-pyromellitic pyromellitic aldehyde, and trialdehyde-resorcinol. In step S1, the reaction tube is placed in a heated oven for standing at a temperature of 100~150℃ for 1~6 days.

2. The method for preparing the lithium metal anode interface layer according to claim 1, characterized in that, In step S1, the molar ratio of the monomer to thiourea is 1~3:

3.

3. The method for preparing the lithium metal anode interface layer according to claim 1, characterized in that, In step S1, the reaction solvent is one or more of mesitylene, water, 1,4-dioxane and glacial acetic acid.

4. The method for preparing the lithium metal anode interface layer according to claim 1, characterized in that, In step S1, the mixture is subjected to a freezing-pumping-thawing cycle to remove air from the reaction tube and is then sealed under nitrogen.

5. The method for preparing the lithium metal anode interface layer according to claim 1, characterized in that, In step S2, the mass ratio of the thiourea-based covalent organic framework material to the binder is 6~12:

1.

6. The method for preparing the lithium metal anode interface layer according to claim 5, characterized in that, In step S2, the adhesive is one or more of polyvinylidene fluoride, polyimide, and styrene-butadiene rubber.

7. The method for preparing the lithium metal anode interface layer according to claim 1, characterized in that, In step S3, a suspension is dropped onto the surface of lithium metal. The volume of the suspension is 10~60μL and the diameter of the lithium metal sheet is 6~30mm.

8. The application of the lithium metal anode interface layer modified with the thiourea-based covalent organic framework according to any one of claims 1 to 7 in lithium metal batteries.

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