Preparation method and application of lithium metal negative electrode interface layer modified by thiourea-based covalent organic framework

Abstract

The invention discloses a preparation method and application of a lithium metal negative electrode interface layer modified by a thiourea-based covalent organic framework, and the preparation method comprises the following steps: S1, adding a monomer and thiourea into a reaction tube, then adding a reaction solvent to obtain a mixture, uniformly dispersing the mixture, and removing air in the reaction tube; heating and standing the reaction tube, filtering and separating a solid product after a reaction product is cooled, and washing and drying the solid product to obtain the thiourea-based covalent organic framework material (TUCOF); s2, adding the TUCOF obtained in the step S1 and an adhesive into N-methyl pyrrolidone, and uniformly stirring to obtain a uniform suspension; and S3, contacting the suspension obtained in the step S2 with lithium metal, and drying to obtain the lithium metal negative electrode interface layer modified by the thiourea-based covalent organic framework. The synthesized TUCOF material has a rich pore channel structure, uniform lithium ion flux distribution and rapid lithium ion migration are promoted along a porous channel, the lithium ion migration number is increased, and the growth of lithium dendrites is inhibited by an artificial solid electrolyte interface (SEI) layer based on a covalent organic framework material.

Description

Technical Field

[0001] The present invention belongs to the field of all-solid-state lithium metal batteries, and specifically relates to a preparation method and application of a lithium metal negative electrode interface layer modified by a thiourea-based covalent organic framework. Background Art

[0002] Lithium metal batteries (LMBs) have a high theoretical capacity (3860 mAh g -1 ), low reduction potential (-3.04 V vs. SHE) and low weight density (0.53 g cm -3 ) and presents significant application potential. However, due to the inevitable lithium dendrites and serious side reactions, LMBs using flammable liquid electrolytes face serious safety hazards, which hinders the practical application of LMBs. All-solid-state lithium metal batteries (ASSLMBs) achieve higher safety by adopting 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 lithium metal anode (LMA) and the electrolyte spontaneously form a solid electrolyte interface (SEI). The instability of the spontaneously formed SEI layer will lead to accelerated lithium dendrite growth, which in turn causes safety problems such as short circuit and thermal runaway. At the same time, the rupture and reconstruction of the SEI film will increase the internal resistance, lead to capacity decay, and reduce the cycle life and efficiency. In addition, the unstable SEI layer may also trigger side reactions, reducing the overall performance and safety of the battery. Therefore, the instability of the SEI is still the main obstacle to the large-scale application of LMA.

[0003] In the past few decades, there are two main strategies to enhance SEI: one is to modify the electrolyte system by changing the electrolyte composition (including solvents, lithium salts and additives) to design a stable SEI in situ; the other is to construct an artificial SEI with specific components by ex situ methods. Compared with electrolyte modification, the construction of artificial SEI has certain advantages due to its high controllability, passivation of lithium metal surface without consuming limited electrolyte and excellent mechanical properties. Covalent organic frameworks (COFs) are a class of organic porous crystalline materials connected by covalent bonds, with the advantages of regular pore structure, large specific surface area, light weight and controllable structure. Utilizing these characteristics, COFs can construct stable lithium ion transmission channels, increase the lithium ion migration number, provide more redox sites, and improve the mechanical properties of materials.

[0004] Although COFs are widely used in the interfacial modification of lithium metal negative electrodes, significantly improving the performance and stability of batteries, they still cannot meet the needs of practical applications. For example, He et al. (J. Mater. Chem. A, 2023, 11, 10155) mixed polythiourea and lithium salt as an artificial interface layer, which can reduce the decomposition of lithium salts, inhibit the growth of lithium dendrites, and form a stable SEI layer, thereby effectively improving the cycle performance of the battery. However, linear polythiourea does not have a regular pore structure and abundant deposition sites, which limits the rapid migration of lithium ions at the interface. Summary of the invention

[0005] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a preparation method and application of a thiourea-based covalent organic framework modified lithium metal negative electrode interface layer, by synthesizing TUCOF with strong lithiophilic functional groups (C=O and C=S) as the artificial interface layer of the lithium metal negative electrode; the S atoms in TUCOF can be adsorbed on the surface of lithium metal, and the lithiophilic functional groups (C=O and C=S) can effectively regulate the lithium ion flux distribution, and the TUCOF pore structure is regular and the pore size is appropriate, which promotes uniform lithium ion flux distribution and rapid lithium ion migration, thereby inhibiting the growth of lithium dendrites.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] The present invention provides a method for preparing a lithium metal negative electrode interface layer modified by a thiourea-based covalent organic framework, comprising the following steps:

[0008] S1, adding monomers and thiourea to a reaction tube, and then adding a reaction solvent to obtain a mixture, dispersing the mixture evenly, and removing the air in the reaction tube; heating the reaction tube and allowing it to stand, and after the reaction product is cooled, filtering and separating the solid product, and washing and drying the solid product to obtain a thiourea-based covalent organic framework material (TUCOF);

[0009] S2, adding the thiourea-based covalent organic framework material (TUCOF) and the adhesive obtained in step S1 into N-methylpyrrolidone (NMP), stirring evenly to obtain a uniform suspension;

[0010] S3, contacting the suspension obtained in step S2 with lithium metal, and obtaining the thiourea-based covalent organic framework-modified lithium metal negative electrode interface layer (TUCOF@Li) after drying.

[0011] In the preparation method as described above, in step S1, the monomer is one or more of trimesaldehyde, 2-hydroxy-1,3,5-benzenetricarbaldehyde, 2,4-dihydroxy-1,3,5-benzenetricarbaldehyde, and trialdehyde phloroglucinol.

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

[0013] In the preparation method as 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 as described above, in step S1, ultrasound is used to disperse the mixture uniformly, and the ultrasonic treatment time is 30 to 60 minutes, preferably 30 minutes.

[0015] In the preparation method as described above, in step S1, the mixture is subjected to a freeze-pump-thaw cycle, the air in the reaction tube is removed, and the reaction tube is sealed under nitrogen.

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

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

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

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

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

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

[0022] In the preparation method as described above, in step S3, vacuum drying is adopted, the drying temperature is 35 to 50° C., preferably 40° C., and the drying time is 12 to 48 hours, preferably 24 hours.

[0023] The present invention also provides the use of the thiourea-based covalent organic framework-modified lithium metal negative electrode interface layer in a lithium metal battery.

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

[0025] The present invention provides a preparation method and application of a thiourea-based covalent organic framework-modified lithium metal negative electrode interface layer. The synthesized TUCOF material has a regular pore structure and an appropriate pore size. The artificial interface layer provides abundant lithium-philic sites and forms a strong and stable framework structure, which promotes rapid lithium ion migration and uniform lithium ion flux distribution, thereby inhibiting the growth of lithium dendrites.

[0026] The present invention utilizes the high adsorption energy of S atoms contained in thiourea molecules for Li, so that they can be tightly combined with the Li surface. This close contact can effectively reduce the direct interaction between the electrode and the electrolyte. In addition, the high adsorption energy of S atoms for Li can maintain close contact with the Li surface and stabilize the electrode electrolyte interface.

[0027] The TUCOF material synthesized in the present invention has a rich pore structure, which promotes uniform lithium ion flux distribution and rapid lithium ion migration along the porous channels, increases the lithium ion migration number, and the artificial solid electrolyte interface (SEI) layer based on the covalent organic framework material inhibits the growth of lithium dendrites. Therefore, based on these advantages, the TUCOF-modified lithium metal anode has excellent cycle stability and rate performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a flow chart for the preparation of the thiourea-based covalent organic framework material (TUCOF) prepared in Example 1.

[0029] Figure 2 This is a Fourier transform infrared spectrum (FITR) of the thiourea-based covalent organic framework material prepared in Example 1, thiourea, and trialdehyde phloroglucinol.

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

[0031] Figure 4 These are the SEM images and mapping images of the thiourea-based covalent organic framework material prepared in Example 1.

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

[0033] Figure 6 The temperature-dependent impedance diagram of the Li-Li symmetric battery assembled for Application Example 1.

[0034] Figure 7 This is the temperature-dependent impedance diagram of the Li-Li symmetric battery assembled in Application Example 2.

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

[0036] Fig. 9 Arrhenius curve of the Li-Li symmetric battery assembled in Application Examples 1-3.

[0037] Fig.10 Cycling performance diagram of Li-Li symmetric batteries assembled for Application Examples 1 and 4.

[0038] Fig.11 The cycling performance diagram of the LFP-Li full battery assembled for Application Example 1 and Application Example 4.

[0039] Fig.12 This is the rate performance diagram of the LFP-Li full battery assembled for Application Example 1 and Application Example 4. DETAILED DESCRIPTION

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

[0041] Example 1

[0042] A method for preparing a lithium metal negative electrode artificial interface layer of a thiourea-based covalent organic framework material comprises the following steps:

[0043] S1, trialdehyde phloroglucinol (0.14mmol, 30mg) and thiourea (0.21mmol, 22.3mg) are added to the reaction tube. Then, reaction solvent 1,4-dioxane (0.9mL), mesitylene (0.9mL) and water (0.048mL) are added to obtain a mixture, and the above mixture is evenly dispersed with ultrasound, and then glacial acetic acid (0.052mL) is added dropwise, and the reaction mixture is subjected to a freeze-pump-thaw cycle and sealed under nitrogen. Then, the reaction tube is left to stand in a 120°C heating oven for 3 days. The reaction tube is cooled at room temperature. The solid is 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 were stirred and mixed in N-methylpyrrolidone (9 mL) at a mass ratio of 9:1 until a uniform TUCOF@NMP suspension with a concentration of 1 mg / mL was obtained.

[0045] S3. Drop the uniform suspension (30 μL) obtained in step S2 onto the lithium metal surface (φ=12 mm) and dry it in 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 a lithium metal negative electrode artificial interface layer of a thiourea-based covalent organic framework material comprises the following steps:

[0048] S1, trialdehyde phloroglucinol (0.14mmol, 30mg) and thiourea (0.21mmol, 22.3mg) are added to the reaction tube. Then, reaction solvent 1,4-dioxane (0.9mL), mesitylene (0.9mL) and water (0.048mL) are added to obtain a mixture, and the above mixture is evenly dispersed with ultrasound, and then glacial acetic acid (0.052mL) is added dropwise, and the reaction mixture is subjected to a freeze-pump-thaw cycle and sealed under nitrogen. Then, the reaction tube is left to stand in a 120°C heating oven for 3 days. The reaction tube is cooled at room temperature. The solid is 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 were stirred and mixed in N-methylpyrrolidone (18 mL) at a mass ratio of 9:1 until a uniform TUCOF@NMP suspension with a concentration of 0.5 mg / mL was obtained.

[0050] S3. Drop the uniform suspension (30 μL) obtained in step S2 onto the lithium metal surface (φ=12 mm) and dry it in 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 a lithium metal negative electrode artificial interface layer of a thiourea-based covalent organic framework material comprises the following steps:

[0053] S1, trialdehyde phloroglucinol (0.14mmol, 30mg) and thiourea (0.21mmol, 22.3mg) are added to the reaction tube. Then, reaction solvent 1,4-dioxane (0.9mL), mesitylene (0.9mL) and water (0.048mL) are added to obtain a mixture, and the above mixture is evenly dispersed with ultrasound, and then glacial acetic acid (0.052mL) is added dropwise, and the reaction mixture is subjected to a freeze-pump-thaw cycle and sealed under nitrogen. Then, the reaction tube is left to stand in a 120°C heating oven for 3 days. The reaction tube is cooled at room temperature. The solid is 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 were stirred and mixed in N-methylpyrrolidone (6 mL) at a mass ratio of 9:1 until a uniform TUCOF@NMP suspension with a concentration of 1.5 mg / mL was obtained.

[0055] S3. Drop the uniform suspension (30 μL) obtained in step S2 onto the lithium metal surface (φ=12 mm) and dry it in 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 recorded 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, and the electrolyte was an all-solid polyethylene oxide (PEO) film (EO:Li + =16:1).

[0060] The metal lithium sheet based on the covalent organic framework TUCOF prepared in Example 1 was used as the negative electrode, and a commercial lithium iron phosphate sheet was used as the positive electrode (φ=10 mm) to assemble the LFP-Li full battery. The electrolyte was an all-solid polyethylene oxide (PEO) film (EO:Li + =16:1), and its assembly process is prior art.

[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, and the electrolyte was an all-solid polyethylene oxide (PEO) film (EO:Li + =16:1), and its assembly process is prior art.

[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, and the electrolyte was an all-solid polyethylene oxide (PEO) film (EO:Li + =16:1), and its assembly process is prior art.

[0065] Application Example 4

[0066] Take the metal lithium sheet Bare Li in Comparative Example 1, assemble a Li-Li symmetric battery, and the electrolyte is a solid polyethylene oxide (PEO) film (EO:Li+ =16:1).

[0067] The metal lithium sheet Bare Li in Comparative Example 1 was used as the negative electrode, and a commercial lithium iron phosphate sheet (φ=10 mm) was used as the positive electrode to assemble the LFP-Li full battery. The electrolyte was a solid polyethylene oxide (PEO) film (EO:Li + =16:1), and its assembly process is prior art.

[0068] Figure 1 This is a flow chart of the preparation of Example 1 of the present invention. It can be seen 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 spectra (FITR) of the thiourea-based covalent organic framework material, thiourea, and trialdehyde phloroglucinol prepared in Example 1 of the present invention are shown in Table 1. By comparison, the 1636 cm -1 and 2886cm -1 The aldehyde peak at 1625 cm -1 and 1589cm -1 New peaks were found at , which were attributed to the formation of keto group and carbon-carbon double bond, proving the successful synthesis of TUCOF.

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

[0071] Figure 4 The SEM and EDS images of the thiourea-based covalent organic framework material prepared in Example 1 show that the TUCOF exhibits a nanorod-like morphology, and the energy dispersive spectroscopy (EDS) spectrum 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. The nitrogen adsorption isotherm diagram proves that the specific surface area of ​​TUCOF is 63.41 m 2 g -1 The pore size distribution diagram shows that the pore sizes are all mesopores, mainly distributed in 1.26nm and 2.73nm.

[0073] Figures 6 to 8The temperature-dependent impedance diagrams of the Li-Li symmetric batteries assembled for Application Examples 1 to 3 respectively show that the impedance decreases with increasing temperature and has the smallest impedance at the highest temperature of 70°C.

[0074] Fig. 9 The Arrhenius curve of the Li-Li symmetric battery assembled in Application Example 1-3 was obtained by substituting the variable temperature impedance value into the Arrhenius formula, and the SEI layer migration energy barrier of the Li-Li symmetric battery assembled in Application Example 1-3 was obtained. Among them, the SEI layer migration energy barrier of the symmetric battery assembled with a TUCOF@NMP suspension with a concentration of 1 mg / mL was the lowest, proving that 1 mg / mL is the optimal coating concentration of the artificial interface layer.

[0075] Fig.10 The cycling performance diagram of the Li-Li symmetric battery assembled in Application Example 1 and Application Example 4. The results show that after 400 hours of cycling, the polarization voltage of the symmetric battery assembled in Application Example 4 is significantly reduced, mainly due to the continuous growth of lithium dendrites, which pierce the electrolyte membrane and cause battery short circuit failure. The symmetric battery assembled in Application Example 1 remains stable after 1000 hours of cycling. The results show that the artificial interface layer provides abundant lithium-philic sites while forming a strong and stable framework structure, thereby inhibiting the growth of lithium dendrites.

[0076] Fig.11 The cycle performance diagram of the LFP-Li full battery assembled for Application Example 1 and Application Example 4 shows the discharge specific capacity and coulombic efficiency after 100 charge and discharge cycles at 60°C and 0.1C. The initial discharge specific capacity of the full battery of Application Example 1 is 166 mAh g -1 After 100 cycles, the discharge capacity remains at 160 mAh g -1 . The calculated capacity retention rate is 96%, which is much higher than the full battery in Application Example 4 (72%). This is mainly due to the fact that the artificial interface layer provides abundant lithium-philic sites, promotes rapid lithium ion migration and uniform lithium ion flux distribution, and reduces the generation of dead lithium.

[0077] Fig.12 The rate performance diagram of the LFP-Li full battery assembled in Application Example 1 and Application Example 4. The discharge specific capacity of the full battery 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 with the full battery in Application Example 4, when the rate is restored to 0.1C, the discharge capacity is restored to 166 mAh g -1 , indicating that the full battery assembled with lithium metal modified by 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 above examples. For ordinary technicians in this field, improvements or changes can be made based on the above description. All these improvements and changes should fall within the scope of protection of the claims attached to the present invention.

Claims

1. A method for preparing a lithium metal negative electrode interface layer modified by a thiourea-based covalent organic framework, characterized in that: The following steps are involved: S1, adding monomers and thiourea to a reaction tube, and then adding a reaction solvent to obtain a mixture, dispersing the mixture evenly, and removing the air in the reaction tube; heating the reaction tube and allowing it to stand, and after the reaction product is cooled, filtering and separating the solid product, and washing and drying the solid product to obtain a thiourea-based covalent organic framework material (TUCOF); S2, adding the thiourea-based covalent organic framework material (TUCOF) and the adhesive obtained in step S1 into NMP, stirring evenly to obtain a uniform suspension; S3, contacting the suspension obtained in step S2 with lithium metal, and obtaining the thiourea-based covalent organic framework-modified lithium metal negative electrode interface layer (TUCOF@Li) after drying.

2. The method for preparing the lithium metal negative electrode interface layer according to claim 1, characterized in that: In step S1, the monomer is one or more of trimesaldehyde, 2-hydroxy-1,3,5-benzenetricarbaldehyde, 2,4-dihydroxy-1,3,5-benzenetricarbaldehyde, and trialdehyde phloroglucinol.

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

3.

4. The method for preparing the lithium metal negative electrode 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.

5. The method for preparing the lithium metal negative electrode interface layer according to claim 1, characterized in that: In step S1, the mixture is subjected to a freeze-pump-thaw cycle, and the air in the reaction tube is removed and sealed under nitrogen.

6. The method for preparing the lithium metal negative electrode interface layer according to claim 1, characterized in that: In step S1, the reaction tube is placed in a heating oven for standing, the oven temperature is 100-150° C., and the standing time is 1-6 days.

7. The method for preparing the lithium metal negative electrode 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 to 12:

1.

8. The method for preparing the lithium metal negative electrode interface layer according to claim 7, characterized in that: In step S2, the binder is one or more of polyvinylidene fluoride, polyimide and styrene-butadiene rubber.

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

10. Use of the lithium metal negative electrode interface layer modified with the thiourea-based covalent organic framework according to any one of claims 1 to 9 in a lithium metal battery.

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