CN112993256A

CN112993256A - Application of covalent organic framework material in lithium metal negative electrode protection

Info

Publication number: CN112993256A
Application number: CN202110176056.2A
Authority: CN
Inventors: 张彦涛; 杨泽华; 王文搏; 刘佳; 张云瑞; 苏玉金; 曹雪普; 乔山林; 张向京
Original assignee: Hebei University of Science and Technology
Current assignee: Hebei University of Science and Technology
Priority date: 2021-02-09
Filing date: 2021-02-09
Publication date: 2021-06-18
Anticipated expiration: 2041-02-09
Also published as: CN112993256B

Abstract

The invention particularly discloses application of a covalent organic framework material in lithium metal negative electrode protection. The COFs material is prepared by a monomer 1 and a monomer 2 through Schiff base reaction, wherein the monomer 1 is one of 1,3, 5-tri (4-aminophenyl) benzene, 1,3, 5-tri (4' -aldehyde phenyl) benzene, 1,3, 5-triaminobenzene or trimesic aldehyde, and the monomer 2 is one of 2, 5-dimethoxy terephthalaldehyde, 2, 5-dihydroxy terephthalaldehyde, 2, 5-dimethoxy-p-phenylenediamine, 2, 5-dihydroxy-phenylenediamine, p-phenylenediamine or p-phenylenediamine. The COFs material provided by the invention is a large conjugated six-membered ring structure taking a C-N functional group as a node, and also contains a three-dimensional spherical structure with a regular one-dimensional pore channel structure, so that the growth of lithium dendrites can be effectively inhibited, the cycle performance and the safety performance of a lithium metal battery are obviously improved, and the COFs material has a wide application prospect in the field of lithium metal batteries.

Description

Application of covalent organic framework material in lithium metal negative electrode protection

Technical Field

The invention relates to the technical field of lithium batteries, in particular to application of a covalent organic framework material in lithium metal negative electrode protection.

Background

With the continuous development of the industrial level, the environmental pollution problem and the shortage of the traditional petrochemical energy are becoming more serious, so the reasonable development and utilization of new renewable energy sources (such as wind energy, solar energy and the like) have become the subject of the key research at present. However, the dispersivity and discontinuity of renewable new energy sources bring great difficulty to the centralized utilization of new energy sources. In recent years, the development of energy storage devices has been receiving more and more extensive attention, among them, lithium metal cathode materials have been developed because of their high 3860mAh g^-1The method has the advantages of high theoretical specific capacity, lowest oxidation-reduction potential (-3.04V vs SHE), low density, stable discharge, environmental friendliness and the like, and is focused on by research and development personnel.

However, the current battery devices using lithium metal as the negative electrode material cannot sufficiently satisfy the commercialization requirements, mainly because: firstly, the chemical property of the metal lithium is more active, and the metal lithium can easily generate irreversible chemical reaction with the organic electrolyte, so that the capacity is reduced; secondly, in the process of charging and discharging of the lithium battery, because local current density is too large or current distribution is not uniform, lithium metal dendrite is easy to form and the volume of the battery is changed, the lithium dendrite is easy to break to form dead lithium, the coulombic efficiency and the battery capacity of the battery are reduced, and besides, the lithium dendrite is easy to puncture a diaphragm. Causing internal short circuit of the battery, thermal failure of the battery or explosion, and causing safety problems in the use of the lithium battery.

At present, the main solutions to the above problems are: (1) the growth of lithium dendrites is inhibited by using an organic or inorganic solid electrolyte, however, this method has a problem of poor ionic conductivity; (2) a local high-concentration or ultrahigh-concentration organic electrolyte system is developed to effectively inhibit the growth of lithium dendrites, and then the use of the high-concentration organic electrolyte is determined to have high cost and unfriendly environment. The problems of lithium dendrite and volume change existing in the current lithium metal as a negative electrode material are not effectively solved. Therefore, finding a convenient and effective method to inhibit dendrite growth and improve the stability of lithium metal batteries is a key and hot spot in the development of lithium metal batteries.

Disclosure of Invention

Aiming at the problems of poor cycle performance and low coulombic efficiency of the cathode material in the conventional lithium ion battery, the invention provides an application of a covalent organic framework material in lithium metal cathode protection.

In order to solve the technical problems, the technical scheme provided by the invention is as follows:

the application of a covalent organic framework material in lithium metal negative electrode protection is characterized in that the covalent organic framework material is prepared by a monomer 1 and a monomer 2 through Schiff base reaction; the monomer 1 is one of 1,3, 5-tri (4-aminophenyl) benzene, 1,3, 5-tri (4' -aldehyde phenyl) benzene, 1,3, 5-triaminobenzene or trimesic aldehyde, and the monomer 2 is one of 2, 5-dimethoxy terephthalaldehyde, 2, 5-dihydroxy terephthalaldehyde, 2, 5-dimethoxy p-phenylenediamine, 2, 5-dihydroxy phenylenediamine, p-phenylenediamine or p-phenylenediamine.

Compared with the prior art, the Covalent Organic Frameworks (COFs) material with the three-dimensional spherical structure is prepared by using the monomers 1 and 2 through Schiff base reaction, and can be used as an artificial solid electrolyte interface film (SEI film) for protecting a lithium metal negative electrode. The formed COFs material is uniformly distributed with abundant C ═ N functional groups, and the C ═ N functional groups have strong binding energy to lithium ions, so that the lithium affinity of the material is improved, and the wetting of molten lithium is facilitated, thereby facilitating the uniform deposition of metal lithium and avoiding the formation of nucleation sites for the growth of lithium dendrites; meanwhile, the COFs material formed by the reaction of the monomer 1 and the monomer 2 contains a large conjugated structure taking a C-N functional group as a node, the existence of the unique conjugated structure is beneficial to enhancing the chemical stability of the material, the lithium metal cathode is continuously and effectively protected in a longer circulating process, the side reaction of the lithium cathode is reduced, the mechanical strength of an SEI film can be improved, and the volume expansion phenomenon in the deposition and de-intercalation processes of metal lithium is effectively reduced; moreover, the COFs material with the three-dimensional spherical structure also has a higher specific surface area, which is beneficial to reducing the local current density and further improving the deposition uniformity of the metal lithium in the matrix; in addition, the prepared COFs material also has a large number of regular one-dimensional pore channel structures which can be used as ion transmission channels to promote the uniform passing of lithium ions and homogenize lithium ion flow, and a carrier is also provided in the lithium deposition process to disperse the aggregation of lithium ions/electrons, so that the continuous growth of lithium dendrites is favorably relieved; the COFs material provided by the invention can act together from multiple aspects, thereby achieving the effects of effectively inhibiting lithium dendrites and buffering volume expansion.

Preferably, the preparation method of the covalent organic framework material comprises the following steps: adding the monomer 1 and the monomer 2 into a solvent, uniformly mixing, adding acetic acid, stirring at 20-30 ℃ for reaction for 6-72h, quenching the reaction, washing and drying to obtain the covalent organic framework material.

The specific monomer 1 and the specific monomer 2 defined by the invention can be used for preparing a three-dimensional solid spherical structure through Schiff base reaction, and the specific surface area and the chemical stability of the material are improved, so that the mechanical strength and the stability of the SEI film are improved, the growth of lithium dendrites is effectively inhibited, and the continuous long-term protection of a lithium metal cathode is realized.

Preferably, the molar ratio of the monomer 1 to the monomer 2 is 1: 1-2.

Preferably, the monomer 1 and CH in acetic acid₃The molar ratio of COOH was 1: 150-500.

Preferably, the concentration of the acetic acid is 3-17.5 mol/L.

More preferably, the acetic acid is glacial acetic acid.

Preferably, the solvent is anhydrous acetonitrile, and the volume mass ratio of the anhydrous acetonitrile to the monomer 1 is 0.7-3:1, wherein the volume unit is milliliter, and the mass unit is milligram.

Preferably, the organic solvent for quenching reaction is benzaldehyde, and the organic solvent for washing can be selected from ether solvents or alcohol solvents.

The preparation method of the COFs material provided by the invention is simple, the operation is simple and convenient, the raw materials are easy to obtain, the production cost is low, and the COFs material is green and pollution-free and is suitable for industrial production.

The invention also provides a protection method of the lithium metal negative electrode, which forms a protection layer on the surface of the lithium metal negative electrode and comprises the following specific steps:

a step of dispersing the covalent organic framework material described in any one of the above in an organic solvent to prepare a dispersion liquid,

or adding the covalent organic framework material and the binder into an organic solvent, and uniformly mixing to prepare slurry;

and b, coating the dispersion liquid or the slurry on the surface of the lithium metal cathode, and drying to obtain the lithium metal cathode.

The three-dimensional spherical COFs material provided by the invention has a larger gap structure, and molecules are connected by covalent bonds, so that the chemical stability of the material is obviously improved, and the COFs material contains abundant C-N and a regular one-dimensional pore channel structure, so that the homogenization of lithium electron flow is facilitated, and the electrodeposition of lithium metal on a negative electrode is more uniform; meanwhile, the existence of a large conjugated structure with stable chemical properties can also increase the mechanical strength of an SEI film, effectively inhibit the growth of lithium dendrites, and can keep the structural stability in a longer cycle time, and the SEI film is coated on the surface of a lithium metal negative electrode to be used as the SEI film of the lithium battery negative electrode, so that the formation of the lithium dendrites can be effectively inhibited, the occurrence of short circuit problems in the use process of the battery is avoided, the safety performance of the battery is improved, the coulombic efficiency and the stability of the lithium metal battery negative electrode can be greatly improved, and the service life of the battery is prolonged.

Alternatively, the dispersion of covalent organic framework material may be applied to the lithium metal surface by one or more of spray coating, spin coating, or drop coating.

Alternatively, the binder is a binder conventional in the art, such as polyvinylidene fluoride, and the specific amount can be adjusted by one skilled in the art.

Preferably, the mass ratio of the binder to the organic frame material is 1: 4.

Alternatively, the slurry may be uniformly drawn on the surface of the lithium metal negative electrode by means of a drawing method.

Preferably, in step a, the organic solvent comprises at least one of isopropanol, absolute ethanol, tetrahydrofuran, N-methylpyrrolidone or N, N-dimethylformamide.

The organic solvents are all conventional chemical pure reagents sold in the market, and in order to improve the safety of the test, anhydrous pure solvents are all adopted to prepare the dispersion liquid.

Preferably, in the step b, the concentration of the organic framework material in the dispersion is 1-2 wt%, and the coating amount of the organic framework material on the surface of the lithium metal is 15-40 muL-cm^-2。

Preferably, in the step b, the coating amount of the slurry on the surface of the lithium metal is 0.5-1.5 mg-cm^-2。

The invention also provides a lithium metal negative electrode which is treated by adopting any one of the protection methods of the lithium metal negative electrode.

The invention also provides a lithium metal-based battery, and the negative electrode of the lithium metal-based battery is the lithium metal negative electrode.

Optionally, the electrolyte of the lithium ion battery is an ether electrolyte or a carbonate electrolyte including a lithium salt.

Preferably, the lithium salt is one or more of lithium bistrifluoromethanesulfonylimide, lithium hexafluorophosphate, lithium nitrate, lithium perchlorate, lithium hexafluoroarsenate and lithium tetrafluoroborate; the solvent in the electrolyte is one or more of sulfones, ethers, carbonates, carboxylic acid esters and the like.

Optionally, the lithium metal-based battery is a secondary battery system using metal lithium as a negative electrode, such as a lithium ion battery, a lithium sulfur battery, a lithium oxygen battery, a lithium nitrogen battery, or a lithium carbon dioxide battery.

The three-dimensional spherical COFs material provided by the invention is used as an artificial SEI film to be coated on the surface of the lithium metal negative electrode, so that the problem of lithium dendrite occurring in the lithium metal circulation process can be solved, the volume expansion can be effectively relieved, and the lithium metal negative electrode has excellent circulation stability. The lithium ion battery with stable structure and excellent capacity and cycle performance can be obtained by applying the cathode in the lithium ion battery, and the preparation method of the COFs material has the advantages of wide raw material source, low price, simple and easy preparation process, capability of large-scale production, development of a new way for structural design and optimization of a safe lithium cathode material and wide application prospect.

Drawings

FIG. 1 is an XRD pattern of three-dimensional spherical COFs material prepared in example 1 of the present invention;

FIG. 2 is an SEM image of three-dimensional spherical COFs material prepared in example 1 of the present invention;

FIG. 3 is a TEM image of three-dimensional spherical COFs material prepared in example 1 of the present invention;

fig. 4 is a graph of the cycling stability performance of a lithium metal anode fabricated into a lithium-lithium symmetric cell, wherein (a): a lithium-lithium symmetric battery assembled from an unprotected lithium metal negative electrode, (b): the lithium-lithium symmetrical battery assembled by the lithium metal negative electrode protected by the three-dimensional spherical COFs material prepared in the embodiment 1 of the invention;

fig. 5 is a graph of the cycling stability performance of a lithium metal anode fabricated into a lithium-copper symmetric cell, wherein (a): a lithium-copper symmetric battery assembled by a lithium metal negative electrode protected by the three-dimensional spherical COFs material prepared in example 1 of the present invention, (b): the lithium-copper symmetrical battery assembled by the lithium metal negative electrode protected by the three-dimensional spherical COFs material prepared in the comparative example 1 is provided.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

In order to better illustrate the invention, the following examples are given by way of further illustration.

In the following examples, all reagents were commercially available unless otherwise specified, and the experimental procedures were carried out according to the conventional experimental procedures unless otherwise specified.

Example 1

A preparation method of a three-dimensional spherical covalent organic framework material comprises the following steps:

938.3mg of 1,3, 5-tris (4-aminophenyl) benzene and 776mg of 2, 5-dimethoxyterephthalaldehyde are weighed, added into 1000mL of acetonitrile (AR, 99.0 percent), uniformly mixed by ultrasonic, added with 50mL of glacial acetic acid (17.5M), stirred and reacted at room temperature of 25 ℃ for 12 hours, added with 40 mu L of benzaldehyde after the reaction is finished to quench the reaction, washed with acetonitrile after 1 hour, centrifuged to collect solid matters, washed with acetonitrile for three times, and dried at 120 ℃ overnight to obtain solid yellow powder, namely the three-dimensional spherical COFs material, wherein the specific reaction equation is as follows:

fig. 1 is an XRD chart of the three-dimensional spherical COFs material prepared, and it can be seen that the COFs material prepared in this example has high crystallinity, has a distinct peak at 2.74 °, and still has five diffraction peaks at 2 θ ═ 4.8 °, 5.6 °, 7.38 °, 9.71 ° and 25.2 °, corresponding to the (100), (110), (200), (210), (220) and (001) crystal planes, respectively.

The COFs material prepared in this example was subjected to Fourier transform infrared spectroscopy at 1617cm^-1The stretching vibration peak of the C ═ N group appears, indicating that the three-dimensional covalent organic framework material (N-COFs) contains the C ═ N group.

The COFs material prepared in the embodiment is subjected to a nitrogen adsorption and desorption experiment, and the specific surface area of the COFs material prepared in the embodiment is calculated to be 1217m according to a BET equation³(g) based on a non-local density functional theory model (Nonloc)al Density Functional Theory(NLDFT)]And calculating, wherein the pore diameter of the COFs material is intensively distributed at 3.2 nm. The larger pore size distribution is beneficial to uniform and rapid passing of lithium ions, and the pore channel structure of ordered accumulation can promote the uniform deposition of the lithium ions.

SEM and TEM images of the COFs prepared in this example are shown in FIG. 2 and FIG. 3, respectively, and it is obvious from the images that the COFs prepared in this example have a three-dimensional solid spherical structure.

Preparation of lithium metal negative electrode: mixing the COFs material with anhydrous N-methyl pyrrolidone uniformly to obtain 2 wt% dispersion, transferring 60 μ L with a liquid transfer gun, and dripping into a container with a diameter of three times

And drying the lithium sheet at room temperature under a vacuum condition to obtain the lithium metal negative electrode.

The battery assembling process comprises the following steps: the lithium metal negative electrode is assembled into a lithium-lithium symmetrical battery, a polypropylene diaphragm is adopted, an electrolyte is LiTFSI/DME-DOL (dimethyl ether (DME) and 1, 3-Dioxolane (DOL) form a mixed solution in a volume ratio of 1: 1), lithium bistrifluoromethanesulfonylimide (LiTFSI) is added into the mixed solution, the concentration of the LiTFSI in an electrolyte solution is 1.0M, anhydrous lithium nitrate is added into the electrolyte, and the concentration of the anhydrous lithium nitrate in the electrolyte solution is 2 wt%, so that a CR2032 button battery is assembled. And a blank lithium metal cathode which is not protected is arranged as a contrast, and the CR2032 button cell is assembled according to the method. And (3) standing the assembled battery device in a thermostat at 25 ℃ for 2h, and then carrying out constant current charge and discharge test on a blue test system.

At a current density of 0.5mA cm^-2The depth of discharge is 0.5mAh cm^-2The lithium-lithium battery protected with the COFs material prepared in example 1 was cycled for 2700h with a polarization potential of 12mV by performing a constant current charge-discharge test under the conditions. Lithium-lithium batteries without negative electrode protection were at 0.5mA cm^-2、0.5mAh·cm^-2The polarization potential was 50mV at 500h cycling.

At a current density of 1mA cm^-2Depth of discharge of 1mAh·cm^-2The constant current charge and discharge test was performed under the conditions, and the test results are shown in fig. 4. The lithium-lithium battery protected by the COFs material prepared in example 1 has the polarization potential of 32mV after 1000 hours of circulation, and has no polarization potential growth trend in circulation and stable performance. The lithium-lithium battery without the negative electrode protection showed a severe increase in polarization potential after 550 hours of charge-discharge cycling, with a polarization potential of 90 mV. The COFS material prepared by the embodiment is coated on the surface of a lithium metal negative electrode to construct an artificial SEI layer, so that the situation that the polarization potential of the battery is too large in the charging and discharging process can be effectively reduced, the growth of lithium dendrites can be effectively inhibited, the lithium metal negative electrode can be effectively protected, and the cycle performance of the lithium ion battery is remarkably improved.

Example 2

1300mg of 1,3, 5-tri (4' -aldehyde phenyl) benzene and 1009mg of 2, 5-dimethoxy p-phenylenediamine are weighed, mixed and added into 1500mL of acetonitrile (AR, 99.0 percent), the mixture is uniformly mixed by ultrasonic, 75mL of glacial acetic acid (17.5M) is added, the mixture is stirred and reacted for 36 hours at room temperature and 20 ℃, 40 mu L of benzaldehyde is added after the reaction is finished for quenching reaction, the mixture is washed by acetonitrile after 1 hour, solid substances are collected by centrifugation, the mixture is washed by acetonitrile for three times, and the mixture is dried overnight at 120 ℃ to obtain solid yellow powder, namely the three-dimensional spherical COFs material, wherein the specific reaction is as follows:

preparation of lithium metal negative electrode: weighing 4mg of the prepared COFs material and 1mg of polyvinylidene chloride serving as a binder (dried at 180 ℃ in advance) and adding the materials into 0.5mL of anhydrous N-methylpyrrolidone for uniform mixing to obtain slurry, uniformly dividing the slurry into four parts, and respectively and uniformly blade-coating the four parts until the diameter is equal to that of the slurry

The lithium sheets (4 sheets) were dried under vacuum at room temperature to obtain a lithium metal negative electrode.

At a current density of 0.5mA cm^-2The depth of discharge is 0.5mAh cm^-2A constant current charge-discharge test was carried out under the conditions that the lithium-lithium battery protected with the COFs material prepared in example 2 had a polarization potential of 10mV at 2500h cycles. Lithium-lithium batteries without negative electrode protection were at 0.5mA cm^-2、0.5mAh·cm^-2Next, the polarization potential was 58mV at 520h of cycling.

At a current density of 1mA cm^-2The depth of discharge is 1mAh cm^-2A constant current charge-discharge test was carried out under the conditions that the polarization potential of the lithium-lithium battery protected with the COFs material prepared in example 2 was 34mV at 1000 hours of cycling. The lithium-lithium battery without the negative electrode protection has a polarization potential of 90mV after 500 hours of charge-discharge cycle.

Example 3

weighing 350mg of terephthaldehyde and 200mg of 1,3, 5-triaminobenzene, adding the materials into 500mL of acetonitrile (AR, 99.0%), ultrasonically mixing uniformly, adding 25mL of glacial acetic acid (17.5M), stirring at room temperature of 30 ℃ for reaction for 72h, adding 20 mu L of benzaldehyde after the reaction is finished to quench the reaction, washing the materials sequentially through acetonitrile, tetrahydrofuran and absolute ethyl alcohol after 1h, centrifugally collecting solid substances, washing the materials sequentially through acetonitrile, tetrahydrofuran and absolute ethyl alcohol for three times, and drying the materials at 120 ℃ overnight, namely the three-dimensional spherical COFs material has the following specific reaction:

preparation of lithium metal negative electrode: adding the COFs material prepared above into anhydrous N-methyl pyrrolidone, mixing well to obtain a dispersion liquid with the concentration of the COFs material of 1 wt%, transferring 80 μ L by using a liquid transfer gun, and dripping the dispersion liquid to a diameter of four times

At a current density of 0.5mA cm^-2The depth of discharge is 0.5mAh cm^-2A constant current charge-discharge test was carried out under the conditions that the lithium-lithium battery protected with the COFs material prepared in example 3 had a polarization potential of 12mV at 2500h cycles. Lithium-lithium batteries without negative electrode protection were at 0.5mA cm^-2、0.5mAh·cm^-2Next, the polarization potential was 60mV at 520h cycling.

At a current density of 1mA cm^-2The depth of discharge is 1mAh cm^-2A constant current charge-discharge test was carried out under the conditions that the polarization potential of the lithium-lithium battery protected with the COFs material prepared in example 3 was 32mV at 1100 hours of cycling. Lithium-lithium battery charge-discharge cycle without negative electrode protectionThe polarization potential reached 95mV at 530 hours.

Example 4

702.9mg of 1,3, 5-tri (4-aminophenyl) benzene and 498mg of 2, 5-dihydroxy terephthalaldehyde are taken and added into 500mL of acetonitrile (AR, 99.0 percent) to be uniformly mixed by ultrasonic, 25mL of glacial acetic acid (17.5M) is added, the mixture is stirred and reacted for 6h at the room temperature of 25 ℃, 40 mu L of benzaldehyde is added after the reaction is finished to quench the reaction, the reaction is washed for 1h by acetonitrile, solid substances are collected by centrifugation, the solid substances are washed for three times by acetonitrile and dried for overnight at the temperature of 120 ℃, and solid yellow powder, namely the three-dimensional spherical COFs material is obtained, and the specific reaction is as follows:

preparation of lithium metal negative electrode: weighing 8mg of the prepared COFs material and 2mg of polyvinylidene chloride serving as a binder (dried at 180 ℃ in advance) and adding the materials into 1mL of anhydrous N-methylpyrrolidone to be uniformly mixed to obtain slurry, uniformly dividing the slurry into three parts, and respectively and uniformly blade-coating the three parts until the diameter is equal to that of the slurry

The lithium sheets (3 sheets) were dried under vacuum at room temperature to obtain a lithium metal negative electrode.

The battery assembling process comprises the following steps: the lithium metal negative electrode is assembled into a lithium-copper symmetrical battery and a lithium-lithium symmetrical electrode, a polypropylene diaphragm is adopted, an electrolyte is LiTFSI/DME-DOL (dimethyl ether (DME) and 1, 3-Dioxolane (DOL) form a mixed solution in a volume ratio of 1: 1), lithium bistrifluoromethanesulfonylimide (LiTFSI) is added into the mixed solution, the concentration of the LiTFSI in an electrolyte solution is 1.0M, anhydrous lithium nitrate is added into the electrolyte, and the concentration of the anhydrous lithium nitrate in the electrolyte solution is 2 wt%, so that the CR2032 button battery is assembled. And a blank lithium metal cathode which is not protected is arranged as a contrast, and the CR2032 button cell is assembled according to the method. And (3) standing the assembled battery device in a thermostat at 25 ℃ for 2h, and then carrying out constant current charge and discharge test on a blue test system.

At a current density of 0.5mA cm^-2The depth of discharge is 0.5mAh cm^-2A constant current charge-discharge test was carried out under the conditions that the lithium-lithium battery protected with the COFs material prepared in example 4 had a polarization potential of 10mV at 2500h cycles. Lithium-lithium batteries without negative electrode protection were at 0.5mA cm^-2、0.5mAh·cm^-2Next, the polarization potential was 60mV at 510h of cycling.

At a current density of 1mA cm^-2The depth of discharge is 1mAh cm^-2Constant current charge and discharge tests are carried out under the conditions, and the test results show that the 150-cycle coulombic efficiency of the lithium-copper battery protected by the COFs material prepared in example 4 can be maintained at 98.14%, and the polarization potential of the lithium-copper battery is 35mV after 1100 hours of cycle. The 50-cycle coulombic efficiency of the lithium-copper battery without the negative electrode protection is only 86 percent originally, and the polarization potential of the lithium-copper battery reaches 97mV after the lithium-copper battery is cycled for 550 hours.

Example 5

weighing 780.9mg of 1,3, 5-tris (4' -aldehyde phenyl) benzene and 324.4mg of p-phenylenediamine, adding the materials into 1000mL of acetonitrile (AR, 99.0%), uniformly mixing by ultrasonic wave, adding 50mL of glacial acetic acid (17.5M), stirring at room temperature of 25 ℃ for reacting for 36h, adding 40 mu L of benzaldehyde after the reaction is finished to quench the reaction, washing with acetonitrile after 1h, centrifuging to collect solid substances, washing with acetonitrile for three times, and drying at 120 ℃ overnight to obtain solid yellow powder, namely the three-dimensional spherical COFs material, wherein the specific reaction is as follows:

preparation of lithium metal negative electrode: adding the COFs material prepared above into anhydrous N-methyl pyrrolidone, mixing well to obtain a dispersion liquid with the concentration of the COFs material of 2 wt%, transferring 35 μ L by using a liquid transfer gun, and dripping the dispersion liquid to a diameter of three times

Lithium (ii) ofAnd drying the sheet at room temperature under a vacuum condition to obtain the lithium metal negative electrode.

At a current density of 0.5mA cm^-2The depth of discharge is 0.5mAh cm^-2A constant current charge-discharge test was performed under the conditions that the lithium-lithium battery protected with the COFs material prepared in example 5 had a polarization potential of 12mV at 2300h of cycling. Lithium-lithium batteries without negative electrode protection were at 0.5mA cm^-2、0.5mAh·cm^-2The polarization potential was 70mV at 500h cycling.

At a current density of 1mA cm^-2The depth of discharge is 1mAh cm^-2A constant current charge-discharge test was carried out under the conditions that the polarization potential was 30mV for 1100 hours of cycling of the lithium-lithium battery protected with the COFs material prepared in example 5. The lithium-lithium battery without the negative electrode protection had a polarization potential of 98mV after 560 hours of charge-discharge cycling.

Example 6

weighing 246.3mg of 1,3, 5-triaminobenzene and 498.4mg of 2, 5-dihydroxy terephthalaldehyde, adding into 500mL of acetonitrile (AR, 99.0%), uniformly mixing by ultrasonic wave, adding 25mL of glacial acetic acid (17.5M), stirring at room temperature of 25 ℃ for 24h, adding 40 mu L of benzaldehyde after the reaction is finished to quench the reaction, washing with acetonitrile after 1h, centrifuging to collect solid substances, washing with acetonitrile for three times, and drying at 120 ℃ overnight to obtain solid yellow powder, namely the three-dimensional spherical COFs material, wherein the specific reaction is as follows:

preparation of lithium metal negative electrode: adding the COFs material into anhydrous N-methyl pyrrolidone, mixing uniformly to obtain a dispersion liquid with the concentration of the COFs material being 2 wt%, transferring 60 mu L by using a liquid transfer gun, and dripping the dispersion liquid to a diameter of three times

At a current density of 0.5mA cm^-2The depth of discharge is 0.5mAh cm^-2A constant current charge-discharge test was carried out under the conditions that the lithium-lithium battery protected with the COFs material prepared in example 6 had a polarization potential of 10mV at 2500h cycles. Lithium-lithium batteries without negative electrode protection were at 0.5mA cm^-2、0.5mAh·cm^-2Next, the polarization potential was 75mV at 520h cycling.

At a current density of 1mA cm^-2The depth of discharge is 1mAh cm^-2Constant current charge and discharge tests were performed under the conditions that the lithium-lithium battery protected with the COFs material prepared in example 6 cycled 1200 hours with a polarization potential32 mV. The lithium-lithium battery without negative electrode protection reached a polarization potential of 94mV at 540 hours of charge-discharge cycling.

Example 7

weighing 324mg of trimesic aldehyde and 420.4mg of 2, 5-dihydroxy phenylenediamine, mixing and adding the mixture into 500mL of acetonitrile (AR, 99.0%), ultrasonically mixing uniformly, adding 25mL of glacial acetic acid (17.5M), stirring at room temperature of 25 ℃ for 48h, adding 40 mu L of benzaldehyde after the reaction is finished to quench the reaction, washing sequentially by acetonitrile, tetrahydrofuran and absolute ethyl alcohol after 1h, centrifuging to collect solid substances, washing sequentially by acetonitrile, tetrahydrofuran and absolute ethyl alcohol for three times, and drying at 120 ℃ overnight to obtain solid yellow powder, namely the three-dimensional spherical COFs material, wherein the specific reaction is as follows:

The battery assembling process comprises the following steps: the lithium metal negative electrode is assembled into a lithium-lithium symmetrical battery and a lithium-copper symmetrical battery, a polypropylene diaphragm is adopted, an electrolyte is LiTFSI/DME-DOL (dimethyl ether (DME) and 1, 3-Dioxolane (DOL) form a mixed solution in a volume ratio of 1: 1), lithium bistrifluoromethanesulfonylimide (LiTFSI) is added into the mixed solution, the concentration of the LiTFSI in an electrolyte solution is 1.0M, anhydrous lithium nitrate is added into the electrolyte, and the concentration of the anhydrous lithium nitrate in the electrolyte solution is 2 wt%, so that the CR2032 button battery is assembled. And a blank lithium metal cathode which is not protected is arranged as a contrast, and the CR2032 button cell is assembled according to the method. And (3) standing the assembled battery device in a thermostat at 25 ℃ for 2h, and then carrying out constant current charge and discharge test on a blue test system.

At a current density of 0.5mA cm^-2The depth of discharge is 0.5mAh cm^-2Constant current charge and discharge tests were performed under the conditions that a lithium-copper battery protected with the COFs material prepared in example 7 maintained a coulombic efficiency of 98% after 140 cycles, and the polarization potential of the lithium-lithium battery was 11mV at 2500h cycles. Lithium-copper battery without negative electrode protection at 0.5mA cm^-2、0.5mAh·cm^-2After 50 cycles, the coulombic efficiency can be kept at 86%, and the polarization potential of the lithium-lithium battery is 77mV at 520h of cycling.

At a current density of 1mA cm^-2The depth of discharge is 1mAh cm^-2A constant current charge-discharge test was carried out under the conditions that the polarization potential was 28mV for 1200 hours of cycling of the lithium-lithium battery protected with the COFs material prepared in example 7. The lithium-lithium battery without the negative electrode protection reached a polarization potential of 98mV after 540 hours of charge-discharge cycling.

Example 8

weighing 324.3mg of trimesic aldehyde and 505mg of 2, 5-dimethoxy p-phenylenediamine, adding the mixture into 500mL of acetonitrile (AR, 99.0%), carrying out ultrasonic mixing uniformly, adding 25mL of glacial acetic acid (17.5M), stirring at room temperature of 25 ℃ for 36h, adding 40 mu L of benzaldehyde after the reaction is finished to quench the reaction, washing the reaction product sequentially through acetonitrile, tetrahydrofuran and absolute ethyl alcohol after 1h, centrifuging to collect solid substances, washing the reaction product sequentially through acetonitrile, tetrahydrofuran and absolute ethyl alcohol for three times, and drying the reaction product at 120 ℃ overnight to obtain solid yellow powder, namely the three-dimensional spherical COFs material, wherein the specific reaction is as follows:

At a current density of 0.5mA cm^-2The depth of discharge is 0.5mAh cm^-2Constant current charge and discharge tests were performed under the conditions that the lithium-lithium battery protected with the COFs material prepared in example 8 had a polarization potential of 16mV at 2500h of cycling. The polarization potential of the lithium-lithium battery without the negative electrode protection is 68mV when the lithium-lithium battery is cycled for 500 hours.

At a current density of 1mA cm^-2The depth of discharge is 1mAh cm^-2A constant current charge-discharge test was carried out under the conditions that the lithium-lithium battery protected with the COFs material prepared in example 8 had a polarization potential of 30mV on a 1200 hour cycle. The lithium-lithium battery without negative electrode protection had a polarization potential of 100mV after 540 hours of charge-discharge cycling.

Comparative example 1

The present comparative example provides a method of preparing a covalent organic framework material:

weighing 218.94mg of 1,2,4, 5-tetraaminobenzene and 672mg of cyclohexadecanone, adding into 500mL of acetonitrile (AR, 99.0%), ultrasonically mixing uniformly, adding 50mL of glacial acetic acid (17.5M), stirring at room temperature of 25 ℃ for 12h, adding 40 mu L of benzaldehyde after the reaction is finished to quench the reaction, washing with acetonitrile and absolute ethyl alcohol in sequence after 1h, centrifuging to collect solid substances, washing with acetonitrile and absolute acetonitrile in sequence for three times, and drying at 120 ℃ overnight to obtain the COFs material, wherein the specific reactions are as follows:

preparation of lithium metal negative electrode: adding the COFs material prepared by the comparative example into anhydrous N-methyl pyrrolidone, uniformly mixing to prepare a dispersion liquid with the concentration of the COFs material of 2 wt%, transferring 60 mu L by using a liquid transfer gun, and dripping the dispersion liquid to a diameter of three times

A lithium-copper symmetrical battery is assembled by adopting the lithium metal cathode prepared in the way of example 1, the diaphragm and the electrolyte are all the same as example 1, and then a CR2032 button cell is assembled. And the lithium metal negative electrode protected by the three-dimensional spherical COFs material prepared in example 1 was also assembled into a lithium-copper battery according to the above method, and assembled into a CR2032 button cell.

And (3) standing the assembled battery device in a thermostat at 25 ℃ for 2h, and then carrying out constant current charge and discharge test on a blue test system.

At a current density of 1mA cm^-2The depth of discharge is 1mAh cm^-2The constant current charge and discharge test was performed under the conditions, and the test results are shown in fig. 5. As can be seen from the figure, the coulombic efficiency of the lithium-copper battery protected by the COFs material prepared in example 1 can be maintained at 98.17% after 140 cycles. After the lithium-copper battery protected by the COFs material prepared in the comparative example 1 is circulated for 40 circles, the coulombic efficiency can be kept at 81% originally, and after the lithium-copper battery is circulated for 60 circles, the coulombic efficiency is only 48% originally, which is far less than that of the lithium metal battery protected by the COFs material prepared in the example 1.

Except for COFs prepared by reacting the monomer 1 and the monomer 2 adopted in the embodiments 1 to 8, other COFs materials prepared by adopting the monomer 1 and the monomer 2 of the invention to be combined and through Schiff base reaction can achieve the technical effects basically equivalent to those of the embodiments 2 to 8, and the effects are slightly lower than those of the embodiment 1.

By replacing the molar ratio of the monomer 1 to the monomer 2 in examples 1 to 8 of the present invention with other ratios defined in the present invention, the technical effects equivalent to those of the corresponding examples can be achieved.

Acetic acid is a catalyst for Schiff base reaction of the monomer 1 and the monomer 2, and other acetic acid solutions with other concentrations defined in the present invention may be used in addition to glacial acetic acid used in the examples, as long as the body 1 and CH in acetic acid defined in the present invention are satisfied₃The molar ratio of COOH was 1:150-500, the effects comparable to those of the corresponding examples were achieved.

Acetonitrile is a solvent for Schiff base reaction of the monomer 1 and the monomer 2, and can achieve basically equivalent technical effects within the dosage range defined by the invention.

In the methods for manufacturing a lithium metal negative electrode in examples 1 to 8, the organic solvent in which the COFs material is dispersed may be at least one of anhydrous isopropyl alcohol, anhydrous ethanol, anhydrous tetrahydrofuran, and anhydrous N, N-dimethylformamide, in addition to the anhydrous N-methylpyrrolidone, and all the organic solvents may achieve technical effects equivalent to the anhydrous N-methylpyrrolidone.

In conclusion, the three-dimensional spherical COFs material prepared by the monomer 1 and the monomer 2 through the Schiff base reaction protects the lithium metal cathode, can effectively reduce the occurrence of side reactions on the surface of lithium metal, enables the appearance of lithium deposition to be smoother, and effectively inhibits the growth of lithium dendrites, thereby effectively improving the cycle performance of the lithium-based metal battery and remarkably reducing the polarization potential.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents or improvements made within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims

1. The application of the covalent organic framework material in lithium metal negative electrode protection is characterized in that the covalent organic framework material is prepared by reacting a monomer 1 and a monomer 2 through Schiff base; the monomer 1 is one of 1,3, 5-tri (4-aminophenyl) benzene, 1,3, 5-tri (4' -aldehyde phenyl) benzene, 1,3, 5-triaminobenzene or trimesic aldehyde, and the monomer 2 is one of 2, 5-dimethoxy terephthalaldehyde, 2, 5-dihydroxy terephthalaldehyde, 2, 5-dimethoxy p-phenylenediamine, 2, 5-dihydroxy phenylenediamine, p-phenylenediamine or p-phenylenediamine.

2. The use of a covalent organic framework material as claimed in claim 1 for lithium metal anode protection, wherein the preparation method of the covalent organic framework material comprises the following steps: adding the monomer 1 and the monomer 2 into a solvent, uniformly mixing, adding acetic acid, stirring at 20-30 ℃ for reaction for 6-72h, quenching the reaction, washing and drying to obtain the covalent organic framework material.

3. The use of a covalent organic framework material in the protection of lithium metal anodes according to claim 2, characterized in that the molar ratio of monomer 1 to monomer 2 is 1: 1-2; and/or

The monomer 1 and CH in acetic acid₃The molar ratio of COOH was 1: 150-500.

4. The use of a covalent organic framework material of claim 3 for lithium metal negative electrode protection, wherein the concentration of acetic acid is 3-17.5 mol/L.

5. The use of a covalent organic framework material in the protection of lithium metal anodes according to claim 2, characterized in that the solvent is anhydrous acetonitrile, the volume to mass ratio of anhydrous acetonitrile to monomer 1 is 0.7-3:1, wherein the volume is in ml and the mass is in mg.

6. A method for protecting a lithium metal negative electrode is characterized in that a protective layer is formed on the surface of the lithium metal negative electrode, and the method comprises the following specific steps:

step a of dispersing the covalent organic framework material as defined in any of claims 1 to 5 in an organic solvent to prepare a dispersion,

or adding the covalent organic framework material and the binder in any one of claims 1 to 5 into an organic solvent, and uniformly mixing to prepare slurry;

7. The method for protecting a lithium metal anode according to claim 6, wherein the organic solvent comprises at least one of isopropyl alcohol, absolute ethyl alcohol, tetrahydrofuran, N-methylpyrrolidone, or N, N-dimethylformamide in the step a.

8. The method for protecting a lithium metal negative electrode according to claim 6, wherein in the step b, the concentration of the organic framework material in the dispersion is 1 to 2 wt%, and the coating amount of the dispersion on the surface of the lithium metal is 15 to 40. mu.L-cm^-2；

In the step b, the coating weight of the slurry on the surface of the lithium metal is 0.5-1.5 mg-cm^-2。

9. A lithium metal negative electrode treated by the method for protecting a lithium metal negative electrode according to any one of claims 6 to 8.

10. A lithium metal-based battery, characterized in that the negative electrode is the lithium metal negative electrode according to claim 9.