CN116284632A

CN116284632A - PEG chain grafted covalent organic framework material, preparation method and application thereof

Info

Publication number: CN116284632A
Application number: CN202310312399.6A
Authority: CN
Inventors: 许冰清; 何柏颖; 张根; 钟原; 刘涛
Original assignee: Nanjing University of Science and Technology
Current assignee: Nanjing University of Science and Technology
Priority date: 2023-03-28
Filing date: 2023-03-28
Publication date: 2023-06-23

Abstract

The invention discloses a covalent organic framework material grafted by PEG chains, a preparation method and application thereof. The covalent organic framework is prepared by taking PEG chain grafted amino compound and trialdehyde phloroglucinol as raw materials, taking mesitylene/1, 4-dioxane solution as a solvent and acetic acid as a catalyst and carrying out hydrothermal reaction. After the PEG chain grafted covalent organic framework material is mixed with PEO, lithium salt and LAGP ceramic powder, a self-supporting ultrathin organic-inorganic composite ultrathin solid electrolyte membrane can be formed, and the self-supporting ultrathin organic-inorganic composite ultrathin solid electrolyte membrane can be applied to a solid lithium battery, so that the problems of dendrite growth behavior, side reaction and the like of the battery in the circulation process can be effectively reduced, and the safety and long-circulation performance of the solid lithium battery are improved.

Description

PEG chain grafted covalent organic framework material, preparation method and application thereof

Technical Field

The invention belongs to the field of covalent organic framework compounds, and relates to a PEG chain grafted covalent organic framework material, a preparation method and application thereof in solid-state lithium batteries.

Background

Compared with the traditional flammable and volatile liquid electrolyte, the solid electrolyte has excellent mechanical property, better mechanical strength and electrochemical property, and can effectively inhibit the growth of lithium dendrites and interface side reaction problems in the electrochemical cycle process, thereby improving the safety and stability of the battery; and secondly, the solid electrolyte is adopted to match the lithium metal cathode with the high-voltage anode, so that a wide voltage window can be realized, and the problem of energy density limitation caused by liquid electrolyte is avoided. Among them, polymer electrolytes are of great interest. Polyethylene oxide (PEO) contains a large amount of ether oxygen groups, lithium ions undergo a process of complexing-decomplexing-re-complexing on the groups, PEO molecular chains are entangled with each other, and a single chain segment can also move, so Li ⁺ Can move along with the movement of the chain segments. The high molecular weight PEO flocculates and a gel Solid electrolyte (Junying Yin, et al, high Ionic Conductivity PEO-Based Electrolyte with, D Framework for Dendrite-Free Solid-State Lithium Metal Batteries at Ambient Temperature, chemical Engineering journal 2021) is obtained at the PEO melting point temperature. Meanwhile, ceramic particles are used as Solid electrolytes for lithium Batteries (Faruk Okur et al. Intermediate-Stage Sintered LLZO Scaffolds for Li-gas Solid-State Batteries, adv. Energy mate. 2023.) because of their excellent ion conducting properties, excellent mechanical properties and good safety. The use of a suitable ceramic electrolyte in which lithium ions are preferentially transported through the ceramic phase rather than through the PEO-ceramic interface or PEO pathway has proven to be a viable approach as an electrolyte by blending with PEO in combination with previous studies (Jin Zheng et al, lithium Ion Pathway within Li ₇ La ₃ Zr ₂ O ₁₂ Polyethylene Oxide Composite Electrolytes, angel. Chem. Int. Ed. 2016.). However, during the battery cycle, the ceramic powder particles may find a side reaction, taking Lithium Aluminum Germanium Phosphate (LAGP) as an example, the valence state of Ge element is obviously reduced after the cycle, and the reaction is carried out from Ge ⁴⁺ Reduction to Ge ²⁺ And Ge (Ge) ⁰ Li and Ge form amorphous formsThe internal crystal structure of the alloy becomes complex, leading to non-uniform Li ⁺ Deposition occurs to make the electrolyte more susceptible to dendrite destruction (Andrea Paolella, et al Understanding the Reactivity of a Thin Li) _1.5 Al _0.5 Ge _1.5 (PO ₄ ) ₃ Solid-State Electrolyte toward Metallic Lithium Anode, adv. Energy mater.2020.) and the LAGP material undergoes anisotropic volume changes during cycling, which may create localized stresses within the material that cause cracks within the material. It is therefore also an important consideration to find suitable materials for doping or coating to stabilize the structure of ceramic particles.

The covalent organic framework (Covalent Organic Framework, COF) is an organic polymeric framework porous structure polymer material. The light atoms (hydrogen, boron, carbon, nitrogen and the like) are subjected to chemical reaction, covalent bonds are used as connecting bridges to form a two-dimensional structure or a three-dimensional topological structure which is ordered and is stacked between layers, and the orientation is consistent. The material has a highly periodic crystalline porous rigid structure, large specific surface area, excellent thermal weight stability, ordered pore canal arrangement, and potential application prospect in catalysis, battery, ion conduction, gas storage, compound separation and the like. COF incorporating PEG segments can assist Li ⁺ Is prepared by dissolving PEG chain COF in THF solution containing lithium salt, drying and pressing to obtain solid electrolyte, wherein soft PEG chain is dissolved in Li ⁺ Plays a key role in rapid transport in the dissolution of (a). The obtained electrolyte has good lithium ion conductivity, thermal stability and mechanical stability (Zhang G, et al, acquisition of glass Poly (ethylene oxide)) Anchored in a Covalent Organic Framework as a Solid-State Li ⁺ Electrolyte,Journal of the American Chemical Society.2019.)。

Disclosure of Invention

The invention aims to provide a covalent organic framework material grafted by PEG chains, a preparation method and application thereof in solid-state lithium batteries. The PEG chain grafted COFs material combines the frame characteristics of COFs and the characteristics of the composite solid electrolyte, and improves the overall structural stability and electrochemical performance of the modified electrolyte.

The technical scheme for realizing the purpose of the invention is as follows:

covalent organic framework materials grafted with PEG chains ([ COF-PEG-n (n=1, 2))]) Is an amino compound ([ PEG-n-NHNH) grafted by three aldehyde groups in three aldehyde groups phloroglucinol and PEG chains ₂ (n＝1,2)]) Is connected to form a hexagonal topological structure synthesized by-C=N-NH covalent bond, and has the following structural formula:

the structural formula of the PEG chain grafted amino compound is as follows:

the structural formula of the trialdehyde phloroglucinol is as follows:

the preparation method of the PEG chain grafted covalent organic framework material comprises the following steps:

adding a tri-aldehyde phloroglucinol and PEG chain grafted amino compound with a molar ratio of 2:3 into a mesitylene/1, 4-dioxane solution with a volume ratio of 1:7-7:1, carrying out ultrasonic dissolution, adding acetic acid, carrying out ultrasonic dissolution again to disperse the solution into a suspension, carrying out liquid nitrogen freezing, vacuumizing and degassing treatment on the suspension, carrying out tube sealing operation by using a flame gun in a vacuum state, reacting for 48-168 h at 120+/-20 ℃ to obtain a crude product, washing the crude product with dichloromethane, ethyl acetate, methanol and acetone in sequence, carrying out suction filtration, carrying out Soxhlet extraction by using tetrahydrofuran and chloroform, and carrying out vacuum drying to obtain a covalent organic framework material grafted by the PEG chain ([ COF-PEG-n (n=1, 2) ].

Preferably, the number of freezing, evacuating, and degassing treatments of liquid nitrogen is at least 3.

Preferably, the volume ratio of mesitylene to 1, 4-dioxane in the mesitylene/1, 4-dioxane solution is 1:3.

Preferably, the concentration of the trialdehyde phloroglucinol is 0.02 to 0.6mol/L.

Preferably, the concentration of PEG chain grafted amine based compound is 0.01 to 0.3mol/L.

Preferably, the acetic acid concentration is 3 to 12mol/L, more preferably 6mol/L.

Preferably, the reaction temperature is 120 ℃.

Preferably, the reaction time is 72h.

Preferably, the vacuum drying temperature is 80 ℃ and the vacuum drying time is 12h

The preparation method of the ultrathin solid electrolyte based on the covalent organic framework material grafted by PEG chains comprises the following steps:

step 1, dispersing LAGP powder, PEO and lithium salt in acetonitrile at 60+/-5 ℃ under stirring, uniformly mixing, pouring an electrolyte solution into a Teflon mold, drying under inert atmosphere, and cutting to obtain an original PEO-LiFSI-LAGP (PLL) electrolyte film;

and 2, dispersing COF-PEG-n powder, PEO and lithium salt in acetonitrile at 60+/-5 ℃ under stirring, pouring the mixed solution on the surface of an original PEO-LiFSI-LAGP (PLL) electrolyte film, drying in inert atmosphere, and cutting to obtain the COF-PEG-n/PLL electrolyte film.

The lithium salt according to the present invention is a conventionally used lithium salt in battery electrolytes, such as lithium hexafluorophosphate (LiPF) ₆ ) Lithium bis (trifluoromethanesulfonyl imide) (LiTFSI), lithium bis (fluorosulfonyl) imide (LiFSI), and the like.

Preferably, in

step

1 or 2, the molar ratio of PEO to lithium salt is from 8:1 to 18:1, more preferably 10:1.

Preferably, in step 1, the mass ratio of the LAGP powder to the PEO/lithium salt mixture is 2:8-8: 2, more preferably 4:6.

Preferably, in step 2, the mass ratio of COF-PEG-n powder to PEO/lithium salt mixture is 0.01:0.99 to 0.02:0.98, more preferably 0.015:0.995.

Preferably, in

step

1 or 2, the drying time is 24 to 48 hours.

The invention provides the ultrathin solid electrolyte based on the covalent organic framework material grafted by the PEG chain, which is prepared by the preparation method.

Further, the invention provides the application of the ultrathin solid electrolyte based on the covalent organic framework material grafted by PEG chains in a solid lithium battery.

The solid-state lithium battery of the invention can be a lithium ion battery or a lithium metal battery.

Compared with the prior art, the invention has the following advantages:

(1) According to the invention, PEG chains are grafted in the holes of the covalent organic framework, so that the covalent organic framework can better transmit lithium ions, meanwhile, the structural stability and the mechanical strength of the covalent organic framework can be improved, the severe volume change generated in the working process of the lithium ion battery can be effectively buffered, and the side reaction of ceramic particles is reduced. Meanwhile, the lithium salt and polyethylene glycol in the polymer electrolyte can improve the cycle stability and rate capability of the lithium battery.

(2) The ultrathin polymer solid electrolyte based on the covalent organic framework material grafted by PEG chains has good lithium battery cycle performance, for example, an integrated battery of a Li|COF-PEG-2-PLL|Li battery with a COF-PEG-2/PLL being an electrolyte membrane can stably circulate for more than 85 hours. The ultrathin solid electrolyte membrane adopted by the solid lithium battery can effectively reduce the overall thickness of the battery and improve the overall volume energy density of the battery, and meanwhile, the integration of the diaphragm and the electrolyte can simplify the preparation process of the lithium battery, so that the ultrathin solid electrolyte membrane can be used for preparing the safe and high-energy-density solid lithium battery.

Drawings

FIG. 1 is an X-ray diffraction pattern of (a) COF-PEG-1 and (b) COF-PEG-1;

FIG. 2 is a Fourier transform infrared spectrum of COF-PEG-1 and COF-PEG-2;

FIG. 3 is a TGA curve of COF-PEG-1 and COF-PEG-1;

FIG. 4 is a nitrogen adsorption and desorption curve of COF-PEG-1;

FIG. 5 is a scanning electron microscope image of COF-PEG-1;

FIG. 6 is a voltage versus time plot of Li|PEO-LiFSI-LAGP|Li;

FIG. 7 is a voltage versus time plot of Li|COF-PEG-n/PEO-LiWSI-LAGP|Li;

Detailed Description

The present invention will be further described in detail below with reference to examples, which are provided to illustrate the objects, technical solutions and advantages of the present invention. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention. To make several variants and improvements, all falling within the scope of protection of the present invention.

PEG-n-NHNH according to the invention ₂ (n=1, 2) is commercially available and can also be referred to (Zhang G, et al acquisition of glass Poly (ethylene oxide) Anchored in a Covalent Organic Framework as a Solid-State Li) ⁺ Electroyte, journal of the American Chemical society, 2019.) prepared by itself as PEG-2-NHNH ₂ For example, the specific synthetic route is as follows:

the method comprises the following specific steps:

(1) Compound 2c: compound 1a (1.02 g,4 mmol), potassium carbonate (1.21 g,8.8 mmol) were added to a schlenk flask, after three nitrogen additions under vacuum, compound 2b (2.0 g,8.8 mmol) and 50ml of ultra-dry acetonitrile were injected through a needle tube, after reaction at 90 ℃ for 48h, cooled to room temperature, concentrated in vacuo, then extracted with water and dichloromethane, the organic phase was washed with saturated brine, dried over anhydrous sodium sulfate, and chromatographed on a column of silica gel (petroleum ether: ethyl acetate=1:1) to give a pure solid (2.01 g, 91%).

(2)PEG-2-NHNH ₂ And (3) synthesis: 2ml of NH-NH was added to Compound 2c (1.12 g,3 mmol) ₂ 20ml of absolute ethanol solution is reacted for 24 hours at 90 ℃,washing with petroleum ether after finishing to obtain the target product, namely white solid PEG-2-NHNH ₂ (1000mg,77％)。

Example 1

The covalent organic framework (COF-PEG-2) grafted by PEG chain is prepared from trialdehyde phloroglucinol and PEG-2-NHNH ₂ The organic framework structure formed by Schiff base reaction has the following structure:

PEG-2-NHNH ₂ the structure of (2) is as follows:

the preparation method of the COF-PEG-2 comprises the following specific steps:

glass ampoule (volume about 20mL, length 18cm, neck length 9 cm) was filled with trialdehyde phloroglucinol (21.0 mg,0.1 mmol), PEG-2-NHNH ₂ (64.57 mg,0.15 mmol) and mesitylene/1, 4-dioxane (3:1, 4mL by volume). Then, the ampoule is immersed in an ultrasonic bath for 5 minutes; subsequently, 0.4mL of 6.0mol/L aqueous acetic acid was added, and the ampoule was immersed in an ultrasonic bath for 2 minutes. The mixture was sonicated for 2 minutes to obtain a uniform dispersion. The tube was then flash frozen at 77K with a liquid nitrogen bath and degassed by three freeze pump-thaw cycles, sealed under vacuum, and heated at 120 ℃ for 3 days. Breaking ampoule bottle neck, centrifuging to separate yellow gel product, washing crude product with dichloromethane, ethyl acetate, methanol and acetone sequentially, suction filtering, extracting with tetrahydrofuran and chloroform Soxhlet, and vacuum drying at 80deg.C for 12 hr to obtain COF-PEG-2 as brown yellow powder with yield of 85%. The reaction formula is as follows:

example 2

The implementation isExamples are essentially the same as example 1, the only difference being that the monomer is PEG-1-NHNH ₂ The method specifically comprises the following steps:

trialdehydo phloroglucinol (21.00 mg,0.10 mmol) and PEG-1-NH were weighed out ₂ (51.35 mg,0.15 mmol) was placed in an ampoule glass (volume: about 20mL, length of 18cm, neck length: 9 cm). After adding 3ml of mesitylene, 1ml of 1,4 dioxane and 6mol/L HAc 0.4ml, sonicated for 3min, the ampoule was then flash frozen and evacuated under liquid nitrogen and the tube sealed with a flame gun. Standing to room temperature, heating at 120deg.C for 72h, taking out solid after reaction, washing crude product with dichloromethane, ethyl acetate, methanol and acetone, suction filtering, soxhlet extracting with tetrahydrofuran and chloroform, and vacuum drying at 80deg.C for 12h to obtain brown yellow COF-PEG-1 with yield of 80%.

Example 3

0.343g of polyethylene oxide (PEO, mw-600,000) and 0.14g of lithium bis-fluorosulfonyl imide (LiFSI) are dissolved in 7.5mL of acetonitrile, and 0.1932g of lithium aluminum germanium phosphate (Li) _1.5 Al _0.5 Ge _1.5 P ₃ O ₁₂ LAGP) powder. And stirring the obtained mixture for 24 hours at 60 ℃ under anhydrous and anaerobic conditions until the mixture is uniformly mixed to obtain the PEO-LiWSI-LAGP electrolyte solution.

10mg of COF-PEG-1, 0.343g of polyethylene oxide (PEO, mw-600,000) and 0.14g of lithium bis-fluorosulfonyl imide (LiFSI) are dissolved in 12.5mL of acetonitrile, and the obtained mixture is stirred for 24 hours at 60 ℃ under the condition of no water and no oxygen until the mixture is uniformly mixed to obtain a COF-PEG-1 electrolyte solution.

10mg of COF-PEG-2, 0.343g of polyethylene oxide (PEO, mw-600,000) and 0.14g of lithium bis-fluorosulfonyl imide (LiFSI) are dissolved in 12.5mL of acetonitrile, and the obtained mixture is stirred for 24 hours at 60 ℃ under the condition of no water and no oxygen until the mixture is uniformly mixed to obtain a COF-PEG-2 electrolyte solution.

Example 4

The PEO-LiFSI-LAGP mixed solution in example 3 is poured into a Teflon mold, the mass is 1.0g, the mixture is dried for 24 to 48 hours under inert atmosphere, and the mixture is cut to obtain the original PEO-LiFSI-LAGP (PLL) electrolyte film.

Example 5

The COF-PEG-1 mixed solution of example 3 was cast on the surface of the original PEO-LiFSI-LAGP (PLL) electrolyte film of example 4, dried under an inert atmosphere, and cut to obtain the COF-PEG-1/PLL electrolyte film.

The COF-PEG-2 mixture of example 3 was cast on the surface of the original PEO-LiFSI-LAGP (PLL) electrolyte film of example 4, dried under an inert atmosphere, and cut to obtain COF-PEG-2/PLL electrolyte film.

Comparative example 1

The PEO-LiFSI-LAGP electrolyte film of example 4 was used as an electrolyte separator for a lithium battery, and the assembled lithium battery was completed in a glove box with two end lithium sheets having diameters of 14mm and 8mm, respectively. At 0.1mA/cm ² The charging and discharging curves of the battery are tested under the current density of the battery, and the specific experimental method is as follows: PLL electrolyte membranes and lithium sheets of 14mm and 8mm were assembled in a glove box with a water oxygen content below 0.5 ppm. After the temperature is kept at 60 ℃ for 12 hours, a blue electric system is used for 0.1mA/cm under the same temperature condition ² And a current density of 0.1mAh/cm ² The voltage versus time curve of the cell was measured at the deposition density of (c).

Example 6

The COF-PEG-n/PPL electrolyte film of example 5 was used as an electrolyte separator for a lithium battery, and the assembled lithium battery was completed in a glove box with two end lithium sheets having diameters of 14mm and 8mm, respectively. At 0.1mA/cm ² The charging and discharging curves of the battery are tested under the current density of the battery, and the specific experimental method is as follows: the PPL electrolyte membrane and the lithium sheets of 14mm and 8mm were assembled in a glove box with a water oxygen content of less than 0.5 ppm. After the temperature is kept at 60 ℃ for 12 hours, a blue electric system is used for 0.1mA/cm under the same temperature condition ² And a current density of 0.1mAh/cm ² The voltage versus time curve of the cell was measured at the deposition density of (c).

FIG. 1 is an XRD pattern of a) COF-PEG-1, b) COF-PEG-2, demonstrating the crystallinity of PEG-linked-branched covalent organic framework materials.

FIG. 2 is an infrared ray of COF-PEG-1 and COF-PEG-2As can be seen, COF-PEG-1 and COF-PEG-2 are at 1226cm ^-1 And 1675cm ^-1 The formation of c=n bonds can be confirmed by the infrared absorption peak of (a).

FIG. 3 shows the TGA curves of a) COF-PEG-1 and b) COF-PEG-2, wherein the two materials are subjected to thermal decomposition reaction at a temperature close to 400 ℃, and the materials are good in thermal stability.

FIG. 4 is N of COF-PEG-2 ₂ The adsorption and desorption curve graph shows that the adsorption type of the material is an I-type adsorption curve according to comparison with a model, and shows that the micropore characteristic of the material has the BET specific surface area of 148.95m ² ·g ^-1 。

FIG. 5 is an SEM image of COF-PEG-1, and b) is a partial magnified image of a), and it can be observed that the microstructure of COF-PEG-1 is in the form of pellets, each pellet having a diameter of 1 to 3. Mu.m.

Fig. 6 is a graph of voltage versus time for a li symmetric battery with PEO-LiFSI-LAGP as the solid electrolyte membrane, wherein both the positive and negative electrodes of the battery are lithium sheets, making up a coin cell. The figure shows that the battery can stably circulate for more than 80 hours, but the first-turn voltage reaches 0.598V, and the battery polarization voltage is larger and exceeds 0.45V in the subsequent circulation process, which indicates that the polarization in the battery is serious, so that the battery is not fully charged, and the charging time is prolonged.

Fig. 7 is a graph of Li symmetric cell voltage versus time with COF-PEG-n/PPL as solid electrolyte separator, b) is an enlarged view of a) the first 6 hours of li|cof-PEG-1/pll|li (d) is an enlarged view of c) the first 6 hours of li|cof-PEG-2/pll|li. The graph shows that the battery using the COF-PEG-n/PPL ultrathin solid electrolyte membrane has good cycling stability, the first-turn voltage is respectively 0.212V and 0.343V, the battery terminal voltage is smaller than that of a lithium-lithium symmetrical battery using a PPL electrolyte membrane in the subsequent cycle, the voltage fluctuation is small, no obvious polarization exists in the battery, and the introduction of the COF-PEG-n can improve the capacity and cycling performance of the solid lithium metal battery.

Claims

A covalent organic framework material grafted by a PEG chain, characterized in that a hexagonal topological structure synthesized by connecting three aldehyde groups in a trialdehyde phloroglucinol with two amine groups of an amine compound grafted by the PEG chain to form a-c=n-NH covalent bond has the following structural formula:
2. the method of preparing a PEG chain grafted covalent organic framework material according to claim 1, comprising the steps of:

adding a tri-aldehyde phloroglucinol and PEG chain grafted amino compound with a molar ratio of 2:3 into a mesitylene/1, 4-dioxane solution with a volume ratio of 1:7-7:1, carrying out ultrasonic dissolution, adding acetic acid, carrying out ultrasonic dissolution again to disperse into a suspension, carrying out liquid nitrogen freezing, vacuumizing and degassing treatment on the suspension, carrying out tube sealing operation by using a flame gun in a vacuum state, reacting for 48-168 h at 120+/-20 ℃ to obtain a crude product, washing the crude product with dichloromethane, ethyl acetate, methanol and acetone in sequence, carrying out suction filtration, carrying out Soxhlet extraction by using tetrahydrofuran and chloroform, and carrying out vacuum drying to obtain a covalent organic framework material grafted by the PEG chain;

the structural formula of the PEG chain grafted amino compound is as follows:

the structural formula of the trialdehyde phloroglucinol is as follows:
3. the method according to claim 2, wherein the number of freezing, evacuating and degassing treatments with liquid nitrogen is at least 3; in the trimethylbenzene/1, 4-dioxane solution, the volume ratio of the mesitylene to the 1, 4-dioxane is 1:3; the concentration of the trialdehyde phloroglucinol is 0.02-0.6 mol/L; the concentration of the PEG chain grafted amino compound is 0.01-0.3 mol/L; acetic acid concentration is 3 to 12mol/L, more preferably 6mol/L; the reaction temperature is 120 ℃; the reaction time is 72h; the vacuum drying temperature is 80 ℃ and the vacuum drying time is 12h.
4. A method for preparing an ultrathin solid electrolyte based on a covalent organic framework material grafted with PEG chains according to claim 1, characterized in that it comprises the following steps:

step 1, dispersing LAGP powder, PEO and lithium salt in acetonitrile at 60+/-5 ℃ under stirring, uniformly mixing, pouring the solution in a Teflon mold, drying in inert atmosphere, and cutting to obtain an original PEO-LiFSI-LAGP electrolyte film;

and 2, dispersing COF-PEG-n powder, PEO and lithium salt in acetonitrile at 60+/-5 ℃ under stirring, uniformly mixing, pouring the solution on the surface of an original PEO-LiFSI-LAGP electrolyte film, drying under inert atmosphere, and cutting to obtain the COF-PEG-n/PLL electrolyte film.
5. The method according to claim 4, wherein in step 1 or 2, the lithium salt is lithium hexafluorophosphate, lithium bistrifluoro-methane-sulfonyl imide or lithium bistrifluoro-sulfonyl imide; the molar ratio of PEO to lithium salt is 8:1 to 18:1, more preferably 10:1; the drying time is 24-48 h.
6. The method according to claim 4, wherein in step 1 the mass ratio of LAGP powder to PEO/lithium salt mixture is 2:8 to 8:2, more preferably 4:6.
7. The method according to claim 4, wherein in step 2, the mass ratio of the COF-PEG-n powder to the PEO/lithium salt mixture is 0.01:0.99-0.02:0.98, more preferably 0.015:0.995.
8. An ultrathin solid electrolyte of covalent organic framework material based on PEG chain grafting, prepared according to the preparation method of any one of claims 4-7.
9. Use of an ultra-thin solid electrolyte based on a covalent organic framework material grafted with PEG chains according to claim 8 in solid-state lithium batteries.
10. The use according to claim 9, wherein the solid state lithium battery is a lithium ion battery or a lithium metal battery.