Preparation method and application of a lithium negative electrode based on benzothiazole group covalent organic framework modification

Abstract

The application provides a preparation method and application of a lithium negative electrode based on a benzothiazole group covalent organic framework, and the benzothiazole group covalent organic framework material is applied to the construction of a lithium metal negative electrode interface protection layer, the polar thiazole group in the COF material molecule can promote the dissociation of lithium salt, and the ordered porous structure can provide a uniform ion transmission channel, so as to guide the uniform deposition of lithium ions on the surface of lithium metal and reduce the growth of dendrites. The preparation process of the covalent organic framework material is simple, the yield is high, the scraping coating process is matched, the major bottleneck of the stability of a lithium metal battery can be effectively solved, and the improved lithium metal symmetrical battery matched with a polyethylene oxide full solid electrolyte can realize the continuous stable deintercalation of lithium for more than 600 hours under a current density of 0.2 mA / cm2, and has a wide application prospect in the field of high-safety high-energy lithium metal batteries.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of synthesis and application of energy storage directional functional polymer materials, and in particular to a preparation method and application of a lithium negative electrode based on a benzothiazole group covalent organic framework modification. BACKGROUND

[0002] Under the background of global energy saving and emission reduction, electrochemical energy storage devices represented by high-performance lithium batteries have great development prospects in the development and wide application of new energy. Lithium metal batteries are considered to be the ultimate solution for high specific energy power batteries, which have the advantages of high energy density and low electrochemical potential, which makes them have wide application potential in the field of new energy vehicles, etc. However, compared with the urgent practical demand, there are more serious development bottlenecks in lithium metal batteries. Among them, the most notable is the problem of battery charge-discharge stability and safety caused by lithium dendrites. During the cycle charge-discharge process of lithium metal battery, irregular deposition on the lithium metal negative electrode side will produce more serious "dead lithium" accumulation, which will cause the charge-discharge stability of the battery to decrease significantly, and at the same time, the sharp lithium dendrites may pierce the separator or solid-state electrolyte membrane, causing short circuit of the battery and serious safety problems.

[0003] In order to overcome the above challenges, the electrolyte or electrolyte / electrode interface side optimization strategy can be used to suppress the generation of dendrites. Among them, the lithium metal negative electrode protection has more significant effect because it can regulate the lithium deposition behavior by active and passive strategies, so it has attracted more attention. In the active strategy, the specific group and structure of the negative electrode protection layer interact with lithium ions to regulate the lithium ion deposition nucleation process, and then guide the regular deposition of lithium metal; in the passive strategy, the dense negative electrode protection layer with high mechanical strength can physically resist the growth of dendrites and significantly reduce the probability of short circuit. However, the traditional negative electrode protection material has the following significant shortcomings: the structure and composition are difficult to control accurately, the compatibility with lithium metal is not strong, and it is difficult to form a self-supporting film. In addition, the lithium metal negative electrode often undergoes significant volume expansion and contraction during repeated deposition / stripping process. Therefore, how to improve the long cycle stability of the lithium metal negative electrode protection layer without affecting the ion conductivity will become the research focus of the future development and application of lithium metal. SUMMARY

[0004] The purpose of the present application is to overcome the shortcomings and deficiencies of the prior art, and to provide a preparation method and application of a lithium negative electrode based on a benzothiazole group covalent organic framework (COF) modification.

[0005] The technical scheme adopted by the present application is as follows: the first aspect of the present application provides a benzothiazole group modified lithium negative electrode modified benzothiazole group covalent organic framework material.

[0006] As a further arrangement, it is a covalent organic framework material formed by polymerization of benzobisthiazole group monomers and aldehyde group monomers.

[0007] As a further arrangement, the molar ratio of the benzobisthiazole group monomers and the aldehyde group monomers is (1-2):1.

[0008] As a further arrangement, the polymerization conditions are to dissolve the benzobisthiazole group monomers and the aldehyde group monomers in a system comprising solvent A, solvent B, and catalyst A, and to perform high-pressure polymerization at 150-200 DEG C for 60-85 h.

[0009] As a further arrangement, the solvent A comprises one or more of o-dichlorobenzene, p-dichlorobenzene, mesitylene; the solvent B comprises one or more of dimethylacetamide, dimethylformamide, dimethyl sulfoxide, N-methyl pyrrolidone; and the catalyst A comprises one or more of trifluoromethane sulfonic acid, scandium trifluoromethane sulfonate, aluminum trifluoromethane sulfonate, zinc trifluoromethane sulfonate, lithium trifluoromethane sulfonate.

[0010] As a further arrangement, the temperature of the high-temperature high-pressure polymerization is set to 150-200 DEG C, and the time is set to 60-85 h.

[0011] As a further arrangement, the high-temperature high-pressure polymerization reaction is performed in a thick-walled pressure-resistant tube, and argon is introduced to remove air in the tube before the polymerization reaction.

[0012] As a further arrangement, the aldehyde group monomer is selected from at least one of 1,3,5-tris(4-formylphenyl)triazine, 1,3,5-tris(4-formylphenyl)benzene, triformylphenylamine, 1,3,5-tris(3-formylphenyl)benzene, 1,3,5-triformylbenzene, and 1,3,5-triformyl-2,4,6-trimethylbenzene.

[0013] As a further arrangement, the benzobisthiazole group monomer is specifically 2,6-dimethylbenzo[1,2-d:4,5-d']bisthiazole (DBBT), and the preparation method is as follows:

[0014] 2,5-diamino-1,4-diphenylthiophenol dihydrochloride is suspended and dispersed in solvent D and an acid-binding agent is added dropwise to obtain a dispersion, the dispersion is added to a certain amount of a mixture of original acetic acid triethyl ester and a catalyst by a syringe, stirred at a specific temperature, then cooled and diluted. The crude product of the reaction is obtained by filtration and recrystallized by a specific purification solvent to obtain white needle-shaped monomer 2,6-ditolyl[1,2-d:4,5-d']bisthiazole (DBBT).

[0015] The above solvent D is selected from one or more of dimethylacetamide, dimethylformamide, dimethyl sulfoxide, N-methyl pyrrolidone; the above acid-binding agent is selected from one or more of pyridine, triethylamine, potassium carbonate; the above stirring temperature is controlled in the range of 30-80 degrees, and the stirring time is 1-2h; the above purification solvent is selected from one or more of dichloromethane, chloroform, n-hexane, cyclohexane, diethyl ether, tetrahydrofuran.

[0016] The second aspect of the present application provides a preparation method of a lithium negative electrode modified by a benzothiazole-based covalent organic framework material, the steps are as follows:

[0017] (1) dispersing the benzothiazole-based covalent organic framework material prepared by the above method, a binder and a lithium salt in solvent C to obtain a dispersion;

[0018] (2) coating the dispersion obtained in step (1) on the surface of lithium metal to form a film, and drying the lithium metal coated with the wet film of the dispersion to obtain a lithium negative electrode modified by a benzothiazole-based covalent organic framework material.

[0019] As a further setting, in step (1), the binder is selected from one or more of polyvinylidene fluoride, polyethylene oxide, poly(vinylidene fluoride-hexafluoropropylene),

[0020] The lithium salt is selected from one or more of lithium perchlorate, lithium tetrafluoroborate, lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonylimide.

[0021] As a further setting, the mass ratio of the benzothiazole-based covalent organic framework material, the binder and the lithium salt is 65-85:0-10:10-25.

[0022] The third aspect of the present application provides an application of a lithium negative electrode modified by a benzothiazole-based covalent organic framework material prepared by the above method in the field of lithium ion batteries.

[0023] The beneficial effects of the present application are as follows:

[0024] 1. The present application combines polymerization process, and obtains a highly structured benzothiazole-based covalent organic framework material under relatively mild conditions. The material has a special nanowire morphology and regular group arrangement, and can self-assemble and arrange on the surface of lithium metal to form a dense thin protective layer under low binder or no binder conditions. The inherent amino and benzothiazole groups of the framework structure can effectively promote the dissociation of lithium salt and guide the regular deposition of lithium metal, and the matching lithium symmetric and full battery system can realize the significant improvement of the charge-discharge stability under the premise of not sacrificing the ion conductivity performance of the system.

[0025] 2. The polar benzothiazole group in the COF material molecule can promote the dissociation of lithium salt, and the ordered porous structure can provide uniform ion transmission channels, thereby guiding the uniform deposition of lithium ions on the surface of lithium metal and reducing dendrite growth. The rigid structure of the COF material can provide mechanical support to resist the volume expansion of lithium metal during the charge-discharge process. The excellent electronic insulation and ionic conduction properties of the COF material can participate in the construction of the artificial SEI layer, avoid the influence of direct electron transfer through the electrolyte on the stability, and reduce the occurrence of electrochemical side reactions.

[0026] 3. Unlike the commonly used groups in the construction of traditional covalent organic framework materials, the benzothiazole group has a more rigid planar molecular configuration. Assembling it into a two-dimensional covalent organic framework is conducive to the ordered arrangement of molecules, which can then construct a more continuous lithium ion channel at the electrode / electrolyte interface, guide the uniform deposition of lithium ions, and promote efficient lithium ion conduction. In addition, the benzothiazole group is rich in S and N atoms, which can reversibly coordinate Li ions through controlled ion complexation and release, set binding sites on the inner wall of the continuous lithium ion channel, and realize synergistic lithium ion conduction. Thirdly, the intermolecular ordered packing formed by the benzothiazole conjugated system has stronger self-assembly mechanical properties, which has a significant effect on inhibiting the generation of lithium dendrites.

[0027] 4. The benzothiazole-based covalent organic framework material prepared by the method provided by the present application has a simple preparation process, high yield, and can be matched with a doctor blade coating process. It can effectively solve the major bottleneck of lithium metal battery stability, and the improved lithium metal symmetric battery matched with polyethylene oxide full solid electrolyte can realize continuous stable lithium extraction for more than 600 hours under a current density of 0.2 mA / cm2, and has a wide application prospect in the field of high-safety high-energy lithium metal batteries. BRIEF DESCRIPTION OF DRAWINGS

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed in the following embodiment or prior art description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and for those skilled in the art, other drawings obtained according to these drawings without creative labor still belong to the scope of the present application.

[0029] Figure 1 Chemical reaction formula for each embodiment of the present application;

[0030] Figure 2 Part of the benzothiazole COF material solid-state nuclear magnetic carbon spectrum characterization;

[0031] Figure 3 Part of the benzothiazole COF material TEM characterization;

[0032] Figure 4 Part of the embodiment and the comparative example match lithium metal symmetric battery cycle performance comparison. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical scheme and advantages of the present application clearer, the present application will be further described in detail below with reference to the drawings.

[0034] Example 1

[0035] Step S1, 2, 5-diamino-1, 4-diphenyl sulfide dihydrochloride (1.47 g, 6.0 mmol) was suspended and dispersed in 12 mL of dimethylacetamide, 12.5 mmol of pyridine was added dropwise to obtain dispersion A; dispersion A was added to a mixture of 18.0 mmol of triethyl orthoacetate and 0.3 mmol of scandium trifluoromethanesulfonate by a syringe, stirred at 50°C for 1.5 hours, then cooled to room temperature and diluted with water. The crude product of the reaction was obtained by filtration and recrystallized with a mixture of dichloromethane and n-hexane to obtain white needle-shaped monomer 2, 6-dimethylbenzo[1, 2-d: 4, 5-d'] bis (thiazole) (DBBT).

[0036] Step S2, the thick-walled pressure-resistant tube was pre-argon for 5 minutes to remove air, 0.3 mmol of DBBT, 0.2 mmol of 1, 3, 5-tri (4-formylphenyl) triazine, 7 mL of dimethylformamide, 3 mL of o-dichlorobenzene, 2 mL of trifluoromethanesulfonic acid were added to the pressure-resistant tube, and the product was fully dispersed by ultrasonic for ten minutes. The reaction tube was heated to 180°C under closed condition for three days. After the reaction was completed, the mixture was cooled to room temperature and neutralized with 0.1 mol L -1 ammonia. The precipitated product was collected and washed with methanol, tetrahydrofuran and dichloromethane in turn (50 mL of each solvent, repeated three times). The washed product was dried at 60°C under vacuum for 12 hours to obtain yellow COF-1 powder.

[0037] Step S3, 85 mg of COF-1 powder, 5 mg of polyvinylidene fluoride, 10 mg of lithium bis (trifluoromethanesulfonyl) imide were dissolved and dispersed in 3 mL of anhydrous N-methyl pyrrolidone to obtain a slurry, which was uniformly scraped on the surface of lithium metal, and the wet film thickness was controlled to be 300 μm.

[0038] The lithium metal coated with the wet film of the slurry is dried at room temperature and then dried at 60 degrees under vacuum overnight to obtain the surface-protected lithium metal anode.

[0039] Example 2

[0040] The difference between this embodiment and Example 1 is that in step S3, 75 mg of COF-1 powder, 5 mg of polyvinylidene fluoride, and 20 mg of lithium bis-trifluoromethanesulfonimide are dissolved and dispersed in 3 mL of anhydrous acetone to obtain a slurry, and the slurry is uniformly scraped onto the surface of the lithium metal with a wet film thickness of 300 μm.

[0041] The lithium metal coated with the wet film of the slurry is dried at room temperature and then dried at 60 degrees under vacuum overnight to obtain the surface-protected lithium metal anode.

[0042] Example 3

[0043] The difference between this embodiment and Example 1 is that in step S2, 1,3,5-tris(4-formylphenyl)benzene is used instead of 1,3,5-tris(4-formylphenyl)triazine, and the remaining process and process parameters are the same, and COF-2 powder is prepared, and in step S3, COF-2 powder is used instead of COF-1 powder.

[0044] Example 4

[0045] The difference between this embodiment and Example 1 is that in step S2, tri-formylphenylamine is used instead of 1,3,5-tris(4-formylphenyl)triazine, and the remaining process and process parameters are the same, and COF-3 powder is prepared, and in step S3, COF-3 powder is used instead of COF-1 powder.

[0046] Example 5

[0047] The difference between this embodiment and Example 1 is that in step S2, 1,3,5-tris(3-formylphenyl)benzene is used instead of 1,3,5-tris(4-formylphenyl)triazine, and the remaining process and process parameters are the same, and COF-4 powder is prepared, and in step S3, COF-4 powder is used instead of COF-1 powder.

[0048] Example 6

[0049] The difference between this embodiment and embodiment 1 is that in step S2, 1,3,5-tri(3-formylphenyl)benzene is used instead of 1,3,5-tri(4-formylphenyl) triazine, and the rest of the process and process parameters are the same, which will not be repeated here. COF-5 powder is prepared, and in step S3, COF-5 powder is used instead of COF-1 powder.

[0050] Example 7

[0051] The difference between this embodiment and embodiment 1 is that in step S2, 1,3,5-tri(3-formylphenyl)benzene is used instead of 1,3,5-tri(4-formylphenyl) triazine, and the rest of the process and process parameters are the same, which will not be repeated here. COF-5 powder is prepared, and in step S3, COF-5 powder is used instead of COF-1 powder.

[0052] Example 8

[0053] The difference between this embodiment and embodiment 3 is that in step S3, 80mg COF-2 powder, 20mg lithium bis(trifluoromethanesulfonyl)imide is dissolved and dispersed in 3mL anhydrous acetone to obtain a slurry, and the slurry is uniformly scraped on the surface of lithium metal, and the wet film thickness is controlled to be 300μm.

[0054] Example 9

[0055] The difference between this embodiment and embodiment 3 is that in step S3, 75mg COF-2 powder, 5mg poly(vinylidene fluoride-hexafluoropropylene), 20mg lithium bis(trifluoromethanesulfonyl)imide is dissolved and dispersed in 3mL anhydrous acetone to obtain a slurry, and the slurry is uniformly scraped on the surface of lithium metal, and the wet film thickness is controlled to be 300μm.

[0056] The lithium metal coated with the slurry wet film is dried at room temperature and then vacuum dried at 60 degrees overnight to finally obtain the surface-protected lithium metal anode.

[0057] Example 10

[0058] The difference between this embodiment and embodiment 4 is that in step S3, 75mg COF-3 powder, 5mg polyvinylidene fluoride, 20mg lithium bis(trifluoromethanesulfonyl)imide is dissolved and dispersed in 3mL anhydrous acetone to obtain a slurry, and the slurry is uniformly scraped on the surface of lithium metal, and the wet film thickness is controlled to be 300μm.

[0059] The lithium metal coated with the slurry wet film is dried at room temperature and then vacuum dried at 60 degrees overnight to finally obtain the surface-protected lithium metal anode.

[0060] Comparative Example 1

[0061] The comparative example selects unmodified lithium sheet without surface protection as the lithium metal negative electrode.

[0062] Comparative Example 2

[0063] Disperse 33 mg of polyvinylidene fluoride and 66 mg of lithium bis(trifluoromethanesulfonyl)imide in 3 mL of anhydrous N-methylpyrrolidone to obtain a slurry, uniformly scrape the slurry on the surface of lithium metal, and control the wet film thickness to be 300 μm.

[0064] After the lithium metal coated with the slurry wet film is dried at room temperature, it is vacuum dried at 80 degrees overnight, and finally the surface-protected lithium metal negative electrode is prepared.

[0065] Comparative Example 3

[0066] Disperse 100 mg of polyvinylidene fluoride in 3 mL of anhydrous N-methylpyrrolidone to obtain a slurry, uniformly scrape the slurry on the surface of lithium metal, and control the wet film thickness to be 300 μm.

[0067] After the lithium metal coated with the slurry wet film is dried at room temperature, it is vacuum dried at 80 degrees overnight, and finally the surface-protected lithium metal negative electrode is prepared.

[0068] Liquid nuclear magnetic hydrogen spectrum is used to analyze the group composition of the synthesized COF. The nuclear magnetic test results of some example samples are shown in Figure 2 .

[0069] Grind the above-prepared COF sample and disperse it in anhydrous ethanol under ultrasonic, prepare a sample for TEM characterization, and the nuclear magnetic test results of some example samples are shown in Figure 3 . As can be seen from the figure, different COF materials exhibit significantly different morphologies, among which COF-1 exhibits a special nanowire morphology, which gives it great potential for self-supporting film formation.

[0070] The above-prepared surface-protected lithium metal is matched with a polyethylene oxide-based all-solid-state polymer electrolyte (electrolyte composition: polyethylene oxide with a number average molecular weight of 1 million, lithium bis(trifluoromethanesulfonyl)imide, mass ratio of 0.69:0.25, film is prepared by acetonitrile solution casting method, film thickness is 100 μm), a Li||Li symmetric battery is assembled, and its lithium extraction and insertion cycle performance at 65°C and 0.1 mAh / cm2is tested, and the performance of some examples and comparative examples is shown in Figure 4 and Table 1. As can be seen from the figure, the COF material and negative electrode protection process designed in the present patent has a significant effect on guiding regular deposition of lithium metal, inhibiting the generation of dendrites, and improving the stability of lithium metal batteries.

[0071] Table 1 shows the cycle performance test of Li||Li symmetric batteries assembled by some examples and comparative examples of the all-solid-state electrolyte film

[0072]

[0073] As can be seen from the table, the lithium symmetric battery assembled using the benzothiazole-based covalent organic framework synthesized in this invention, combined with the lithium metal surface coating process, exhibits significantly improved interface compatibility and long-cycle stability compared to the comparative example. This can be attributed to the excellent lithium deposition guidance effect and dendrite suppression ability of the COF material.

[0074] The above description discloses only preferred embodiments of the present invention and should not be construed as limiting the scope of the present invention. Therefore, equivalent variations made in accordance with the claims of the present invention are still within the scope of the present invention.

Claims

1. A method for preparing a lithium anode based on a benzothiazole-based covalent organic framework material, characterized in that, The steps are as follows: (1) A dispersion was obtained by adding benzothiazolyl covalent organic framework material, binder and lithium salt to solvent C; (2) The dispersion obtained in step (1) is coated onto the surface of lithium metal to form a film. After the lithium metal coated with the wet film of dispersion is dried, a lithium anode modified with benzothiazolyl covalent organic framework material is obtained. The benzothiazole-based covalent organic framework material is a covalent organic framework material with benzothiazole groups formed by the polymerization of benzobisthiazole-based structural monomers and aldehyde-based structural monomers. The benzobisthiazolyl monomer is 2,6-dimethyl[1,2-] d :4,5- d Bis(thiazole), wherein the aldehyde monomer is selected from at least one of 1,3,5-tris(4-formylphenyl)triazine, 1,3,5-tris(4-formylphenyl)benzene, triformylphenylamine, 1,3,5-tris(3-formylphenyl)benzene, 1,3,5-triformylbenzene, and 1,3,5-triformyl-2,4,6-trimethylbenzene.

2. The method for preparing a lithium anode based on a benzothiazole-based covalent organic framework material as described in claim 1, characterized in that: The molar ratio of the benzobisthiazolyl monomer and the aldehyde monomer is (1-2):

1.

3. The method for preparing a lithium anode based on a benzothiazole-based covalent organic framework material according to claim 1, characterized in that: The polymerization conditions are as follows: the benzobisthiazolyl monomer and the aldehyde monomer are dissolved in a system containing solvent A, solvent B and catalyst A, and the polymerization reaction is carried out under high pressure at 150-200℃ for 60-85h.

4. The method for preparing a lithium anode based on a benzothiazole-based covalent organic framework material modified according to claim 3, characterized in that: Solvent A includes one or more of o-dichlorobenzene, p-dichlorobenzene, and mesitylene; solvent B includes one or more of dimethylacetamide, dimethylformamide, dimethyl sulfoxide, and N-methylpyrrolidone; catalyst A includes one or more of trifluoromethanesulfonic acid, scandium trifluoromethanesulfonate, aluminum trifluoromethanesulfonate, zinc trifluoromethanesulfonate, and lithium trifluoromethanesulfonate.

5. The method for preparing a lithium anode based on a benzothiazole-based covalent organic framework material according to claim 1, characterized in that: In step (1), the adhesive is selected from one or more of polyvinylidene fluoride, polyethylene oxide, and poly(vinylidene fluoride-hexafluoropropylene). The lithium salt is selected from one or more of lithium perchlorate, lithium tetrafluoroborate, lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, and lithium trifluoromethanesulfonylimide.

6. The method for preparing a lithium anode based on a benzothiazole-based covalent organic framework material modified according to claim 1, characterized in that: The mass ratio of the benzothiazole-based covalent organic framework material, the binder, and the lithium salt is 65-85:0-10:10-25, and the mass of the binder is not 0.

7. The application of the lithium anode based on benzothiazole-based covalent organic framework material modified by any one of claims 1-6 in the field of lithium-ion batteries.

Images