High-pressure-resistant in-situ polymerization quasi-solid electrolyte membrane as well as preparation method and application thereof

Abstract

The invention relates to the technical field of lithium battery polymer solid electrolyte materials, and discloses a high-pressure-resistant in-situ polymerization quasi-solid electrolyte membrane as well as a preparation method and application thereof. The preparation method comprises the following steps: carrying out esterification reaction on bacterial cellulose and 2-bromoisobutyryl bromide to obtain bromine-modified bacterial cellulose, grafting a double-block polymer side chain on the surface of the bromine-modified bacterial cellulose to obtain a one-dimensional polymer brush, and preparing a one-dimensional polymer brush film; a one-dimensional polymer brush film is used as a supporting film, an in-situ polymerization precursor solution is dropwise added to the surface of the supporting film, and the high-pressure-resistant in-situ polymerization quasi-solid electrolyte film is obtained through in-situ ring opening polymerization. The prepared high-pressure-resistant in-situ polymerization quasi-solid-state electrolyte membrane has excellent mechanical performance, the thickness of polymer electrolyte can be reduced, and growth of lithium dendrites can be inhibited; the rich pore structure is beneficial to rapid transmission of lithium ions; and the block in the side chain is beneficial to lithium ion transmission and lithium metal uniform deposition, and improves the stability of the electrolyte membrane in a high-voltage environment.

Description

Technical Field

[0001] This application relates to the technical field of lithium battery polymer solid electrolyte materials, and particularly relates to a high-voltage-resistant in-situ polymerization quasi-solid electrolyte membrane, its preparation method and application. Background Art

[0002] Currently, with the increasing demand for long-distance driving in electric vehicles and long-time use in portable electronic devices, higher requirements are put forward for the new generation of rechargeable batteries, which need to have high safety, high energy density and long life to meet the needs.

[0003] To improve the energy density of the battery, researchers have replaced the negative electrode with lithium metal with ultra-high theoretical capacity (3860 mAh g -1 ) and extremely low reduction potential (-3.04 V vs. NHE), and paired high-voltage positive electrodes (such as: LiCoO 2 and LiNi 0.8 Co 0.1 Mn 0.1 O 2 ) with lithium metal negative electrodes and other methods to increase the output voltage of the battery, and then improve the energy density of the lithium metal battery. However, in liquid lithium metal batteries, high voltage (>4.3 V) will cause the continuous decomposition of electrolyte solvent molecules at the electrode / electrolyte interface, and the electrolyte solvent molecules will react with highly reactive lithium metal to form an uneven SEI, resulting in a rapid attenuation of the battery capacity. Based on this, there is still no single-component liquid electrolyte suitable for high-voltage lithium metal battery systems. In addition, due to the flammability and explosiveness of liquid electrolytes, liquid lithium metal batteries have serious safety hazards.

[0004] To develop safe and long-lasting high-energy density lithium metal batteries, a new strategy is to replace liquid electrolytes with solid electrolytes to avoid the problems that occur in liquid electrolytes in batteries. Among various solid electrolytes, polymer electrolytes have attracted much attention due to their excellent flexibility and processability. Quasi-solid polymer electrolytes (QSPEs) obtained by in-situ polymerization have high ionic conductivity and excellent electrode / electrolyte interface compatibility, so they are considered to be one of the electrolytes with great application potential. Currently, many monomers have been used to prepare in-situ polymerization QSPEs, such as 1,3-dioxolane, polyethylene glycol methacrylate and tetrahydrofuran, etc. However, these liquid monomers often cannot be completely converted into polymer electrolytes, and the residual monomers are prone to decomposition under high-voltage conditions, resulting in poor cycle stability. In addition, the mechanical strength of in-situ prepared QSPEs is poor, so the film thickness of QSPEs will inevitably increase in practical applications, which seriously reduces the energy density of the battery.

[0005] Introducing fluorine-containing groups into the above liquid monomers has been proven to be an effective strategy to improve the antioxidant properties of QSPEs. However, the thickness of QSPEs under this strategy is still close to 100 μm, which hinders their application in high-energy-density lithium metal batteries. Using thin films with good mechanical properties (such as polyolefin separators and polyvinylidene fluoride-hexafluoropropylene thin films) as the supporting membranes of QSPEs can greatly improve the mechanical strength of QSPEs, thus significantly reducing the thickness of QSPEs. However, the antioxidant properties of such QSPEs are still not ideal.

[0006] Therefore, developing QSPEs with excellent mechanical strength and oxidation stability to prepare high-voltage and long-cycle lithium metal batteries remains a huge challenge. Summary of the Invention

[0007] This application provides a high-voltage-resistant in-situ polymerization quasi-solid-state electrolyte membrane, its preparation method and application, aiming to solve the problem that existing quasi-solid-state electrolyte thin films cannot have both high mechanical properties and high oxidation resistance.

[0008] To achieve the above object, this application adopts the following technical solutions.

[0009] In the first aspect of this application, a preparation method of a high-voltage-resistant in-situ polymerization quasi-solid-state electrolyte membrane is provided, including:

[0010] S1, reacting bacterial cellulose with 2-bromo-2-methylpropionyl bromide through an esterification reaction to obtain bromine-modified bacterial cellulose;

[0011] S2, respectively carrying out polymerization reactions of the bromine-modified bacterial cellulose with a lithium single-ion conductor-based polymer monomer and a polymer monomer containing a fluorinated alkane group to graft diblock polymer side chains on the surface of the bromine-modified bacterial cellulose to obtain a one-dimensional polymer brush; dispersing it in a solvent and forming a membrane by suction filtration, and drying to obtain a one-dimensional polymer brush thin film;

[0012] S3, using the one-dimensional polymer brush thin film as a supporting membrane, dropping an in-situ polymerization precursor solution on its surface, and carrying out in-situ ring-opening polymerization to obtain a high-voltage-resistant in-situ polymerization quasi-solid-state electrolyte membrane.

[0013] Preferably, the in-situ polymerization precursor solution in S3 includes a lithium salt, an initiator, and an organic solvent;

[0014] The lithium salt includes at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium bis(oxalato)borate, or lithium difluoro(oxalato)borate;

[0015] The initiator is at least one of magnesium bis(trifluoromethanesulfonyl)imide, zinc bis(trifluoromethanesulfonyl)imide, lithium hexafluorophosphate, aluminum trifluoromethanesulfonate, or stannous fluoride;

[0016] The organic solvent is a mixture of 1,3-dioxolane and a carbonate, and the carbonate includes at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate or methyl ethyl carbonate.

[0017] Further preferably, the concentration of the lithium salt in the in-situ polymerization precursor solution is 1-2 mol / L, and the concentration of the initiator is 0.2-0.5 mol / L;

[0018] The volume ratio of the 1,3-dioxolane to the carbonate is 3:2.

[0019] Preferably, step S1 is specifically as follows:

[0020] Disperse bacterial cellulose in N,N-dimethylformamide, add 4-dimethylaminopyridine and triethylamine, and mix evenly;

[0021] Drop 2-bromoisobutyryl bromide into the above mixture at 0 °C under an inert atmosphere, raise the temperature to 30 °C and stir for 24 h, quench the reaction with ethanol, collect the solid product, wash and dry to obtain bromine-modified bacterial cellulose,

[0022] Among them, the mass-volume ratio of the bacterial cellulose to N,N-dimethylformamide is 1 mg / 0.4 mL; the mass ratio of the bacterial cellulose to 4-dimethylaminopyridine is 1 mg / 1.75 mg; the mass-volume ratio of the bacterial cellulose to triethylamine is 1 mg / 26.3 μL; the mass-volume ratio of the bacterial cellulose to 2-bromoisobutyryl bromide is 1 mg / 30 μL.

[0023] Preferably, step S2 specifically includes:

[0024] Disperse the bromine-modified bacterial cellulose in N,N-dimethylformamide, add a lithium single-ion conductor-based polymer monomer, tris(2-pyridylmethyl)amine, copper bromide and vitamin C, raise the temperature to 60-70 °C, and seal and react under an inert atmosphere, collect the solid product, wash to obtain an intermediate product;

[0025] Disperse the intermediate product in N,N-dimethylformamide, add a fluorinated alkane group-containing polymer monomer, tris(2-pyridylmethyl)amine, copper bromide and vitamin C, raise the temperature to 60-70 °C, and seal and react under an inert atmosphere, collect the solid product, wash to obtain a one-dimensional polymer brush with a double-block polymer grafted on the surface;

[0026] Disperse the one-dimensional polymer brush in N,N-dimethylformamide, vacuum filter and dry to obtain a one-dimensional polymer brush film.

[0027] Further preferably, the lithium single-ion conductor polymer monomer includes any one or a mixture of two or more of lithium p-styrenesulfonate, lithium p-styrene trifluoromethanesulfonimide, lithium 3-sulfopropyl methacrylate, or 1-[3-(methacryloyloxy)propylsulfonyl]-1-(trifluoromethanesulfonyl)imide;

[0028] The fluorinated alkane group-containing polymer monomer includes any one or a mixture of two or more of trifluoroethyl methacrylate, 2-(perfluoropentyl)ethyl methacrylate, 2-(perfluorobutyl)ethyl methacrylate, or ethyl 2-(perfluorohexyl)methacrylate.

[0029] Further preferably, the mass-volume ratio of the bromine-modified bacterial cellulose to N,N-dimethylformamide is 1 mg / 0.1 mL;

[0030] The mass ratio of the bromine-modified bacterial cellulose, lithium single-ion conductor polymer monomer, tris(2-pyridylmethyl)amine, copper bromide, and vitamin C is 1:20:0.75:0.075:0.275;

[0031] The mass-volume ratio of the intermediate product to N,N-dimethylformamide is 1 mg / 0.1 mL; the mass-volume ratio of the intermediate product to the fluorinated alkane group-containing polymer monomer is 1 mg / 10 μL;

[0032] The mass ratio of the intermediate product, tris(2-pyridylmethyl)amine, copper bromide, and vitamin C is 1:0.75:0.075:0.275;

[0033] The dispersion concentration of the one-dimensional polymer brush in N,N-dimethylformamide is 2 mg / mL.

[0034] In the second aspect of the present application, a high-voltage-resistant in-situ polymerization quasi-solid electrolyte membrane prepared by the above preparation method is provided.

[0035] In the third aspect of the present application, the application of the high-voltage-resistant in-situ polymerization quasi-solid electrolyte membrane in a lithium metal battery is provided.

[0036] In the fourth aspect of the present application, a lithium metal battery is provided, which includes a positive electrode, a negative electrode, and a quasi-solid electrolyte; the quasi-solid electrolyte is the above high-voltage-resistant in-situ polymerization quasi-solid electrolyte membrane;

[0037] The positive electrode includes any one of lithium iron phosphate, lithium nickel cobalt manganese oxide, or lithium cobalt oxide; the negative electrode is a lithium metal.

[0038] Compared with the prior art, the beneficial effects of the present application are:

[0039] In this application, a one-dimensional polymer brush thin film is prepared by grafting side chains of diblock polymers with specific functions onto the surface of bromine-modified bacterial cellulose. Then, a precursor solution containing 1,3-dioxolane polymerization is dropped into the one-dimensional polymer brush thin film to undergo in-situ ring-opening polymerization in the film, obtaining a high-pressure-resistant in-situ polymerization quasi-solid electrolyte membrane. The high-pressure-resistant in-situ polymerization quasi-solid electrolyte membrane prepared in this application uses bacterial cellulose as the skeleton, which can significantly improve the mechanical properties of the polymer electrolyte, reduce the thickness of the polymer electrolyte, and help inhibit the growth of lithium dendrites. Among them, the one-dimensional molecular brushes overlap with each other to form a rich pore structure, which helps to uniformly absorb more in-situ polymerization precursor solutions and ensure the rapid transport of lithium ions. The lithium single-ion conductor block in its side chain can increase the ionic conductivity and lithium ion transference number, which is beneficial to the transport of lithium ions and the uniform deposition of lithium metal. The block containing fluorinated alkane groups can improve the antioxidant property of the electrolyte membrane and is beneficial to improving the stability of the electrolyte membrane in a high-voltage environment.

[0040] The high-pressure-resistant in-situ polymerization quasi-solid electrolyte membrane prepared in this application has excellent mechanical properties, relatively high room-temperature ionic conductivity, and excellent high-voltage stability, and can be used to prepare high-capacity high-voltage lithium metal batteries. The high-voltage lithium metal battery assembled with it has excellent electrochemical performance. Brief Description of the Drawings

[0041] In order to more clearly illustrate the technical solutions of the embodiments of this application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments recorded in this application. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0042] Figure 1 Scanning electron micrographs of the surface of bacterial cellulose and one-dimensional polymer brush thin film provided in Example 1;

[0043] Figure 2 Scanning electron micrographs of the cross-section of bacterial cellulose and one-dimensional polymer brush thin film provided in Example 1;

[0044] Figure 3 Atomic force microscopy Young's modulus distribution diagrams of the one-dimensional polymer brush film provided in Example 1, the bacterial cellulose film of Comparative Example 3, and the polypropylene separator of Comparative Example 4;

[0045] Figure 4 Impedance spectrum diagram and ionic conductivity-temperature relationship curve diagram of the steel sheet|steel sheet symmetric battery assembled with the electrolyte membrane of this application;

[0046] Figure 5Electrochemical floating test result diagrams of the Li|NCM811 full cells assembled with the electrolyte membranes provided in Example 1, Comparative Example 3, and Comparative Example 4;

[0047] Figure 6 Electrochemical floating test result diagrams of the Li|NCM811 full cells assembled with the electrolyte membranes provided in Comparative Example 1 and Comparative Example 2;

[0048] Figure 7 Cycling performance test result diagrams of the Li|NCM811 full cells assembled with the electrolyte membranes provided in Example 1, Comparative Example 3, and Comparative Example 4;

[0049] Figure 8 Critical current density test result diagrams of the Li|Li symmetric cells assembled with the electrolyte membranes provided in Example 1, Comparative Example 3, and Comparative Example 4;

[0050] Figure 9 Cycling performance test diagrams of the Li|Li symmetric cells assembled with the electrolyte membranes provided in Example 1, Comparative Example 3, and Comparative Example 4. Detailed implementation manners

[0051] Next, the technical solutions in the embodiments of the present application will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present application.

[0052] In the following description of this embodiment, the terms "include", "comprise", "have", "contain", etc. are all open-ended terms, that is, they are meant to include but not be limited to.

[0053] In the following description of this embodiment, the term "and / or" is used to describe the association relationship of associated objects, indicating that three relationships can exist. For example, A and / or B can represent: A exists alone, B exists alone, and both A and B exist simultaneously. Where A and B can be singular or plural. The character " / " generally represents an "or" relationship between the associated objects before and after.

[0054] In the following description of this embodiment, the term "at least one" means one or more, and "a plurality" means two or more. "At least one of the following (items)" or its similar expressions refer to any combination of these items, including any combination of single (item) or plural items (items). For example, "at least one of a, b, or c", or, "at least one of a, b, and c" can both represent: a, b, c, a - b (that is, a and b), a - c, b - c, or a - b - c, where a, b, and c can be single or plural respectively.

[0055] The terms used in the embodiments of the present application are for the purpose of describing specific embodiments only and are not intended to limit the present application. The singular forms "a" and "the" used in the embodiments of the present application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0056] Those skilled in the art should understand that in the following description of the embodiments of the present application, the sequence numbers do not mean the order of execution, and some or all steps can be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation to the implementation process of the embodiments of the present application.

[0057] Those skilled in the art should understand that the numerical ranges in the embodiments of the present application should be understood as specifically disclosing each intermediate value between the upper and lower limits of the range. The intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, are also included in the present application. The upper and lower limits of these smaller ranges can be independently included or excluded from the range.

[0058] Unless otherwise specified, the technical / scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present application pertains. Although the present application only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the implementation or testing of the present application. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0059] In a first aspect, the present application provides a method for preparing a high-voltage-resistant in-situ polymerization quasi-solid electrolyte membrane, including:

[0060] S1, reacting bacterial cellulose with 2-bromo isobutyryl bromide through an esterification reaction to obtain bromine-modified bacterial cellulose;

[0061] S2, respectively carrying out a polymerization reaction on the bromine-modified bacterial cellulose with a lithium single-ion conductor-based polymer monomer and a polymer monomer containing a fluorinated alkane group, grafting a diblock polymer side chain on the surface of the bromine-modified bacterial cellulose to obtain a one-dimensional polymer brush; dispersing it in a solvent, and forming a membrane by suction filtration, and drying to obtain a one-dimensional polymer brush thin film;

[0062] Specifically, using the Br group on the bromine-modified bacterial cellulose as an active grafting site, and using surface-initiated atom transfer radical polymerization technology to graft a diblock polymer side chain with specific functions on the surface of the bromine-modified bacterial cellulose to prepare a one-dimensional polymer brush.

[0063] S3. Using the one-dimensional polymer brush thin film as a support film, drop an in-situ polymerization precursor solution on its surface, and obtain a high-pressure-resistant in-situ polymerization quasi-solid electrolyte film through in-situ ring-opening polymerization.

[0064] In this application, step S1 is specifically as follows:

[0065] Disperse bacterial cellulose in N,N-dimethylformamide, and add 4-dimethylaminopyridine and triethylamine, and mix evenly. Among them, the mass-volume ratio of bacterial cellulose to N,N-dimethylformamide is 1 mg / 0.4 mL; the mass ratio of bacterial cellulose to 4-dimethylaminopyridine is 1 mg / 1.75 mg; the mass-volume ratio of bacterial cellulose to triethylamine is 1 mg / 26.3 μL.

[0066] Drop 2-bromoisobutyryl bromide into the above-mentioned mixed solution at 0 °C under an inert atmosphere condition, raise the temperature to 30 °C and stir for reaction for 24 h, add ethanol to quench the reaction, collect the solid-phase product, wash, and dry to obtain bromine-modified bacterial cellulose. Among them, the mass-volume ratio of bacterial cellulose to 2-bromoisobutyryl bromide is 1 mg / 30 μL.

[0067] In this application, step S2 specifically includes:

[0068] Disperse the bromine-modified bacterial cellulose in N,N-dimethylformamide, add a lithium single-ion conductor polymer monomer, tris(2-pyridylmethyl)amine, copper bromide, and vitamin C, raise the temperature to 60-70 °C, and seal and react under an inert atmosphere, collect the solid-phase product, wash, and obtain an intermediate product; among them, the mass-volume ratio of the bromine-modified bacterial cellulose to N,N-dimethylformamide is 1 mg / 0.1 mL; the mass ratio of the bromine-modified bacterial cellulose, the lithium single-ion conductor polymer monomer, tris(2-pyridylmethyl)amine, copper bromide, and vitamin C is 1:20:0.75:0.075:0.275;

[0069] Disperse the intermediate product in N,N-dimethylformamide, add a fluorinated alkane group-containing polymer monomer, tris(2-pyridylmethyl)amine, copper bromide, and vitamin C, raise the temperature to 60-70 °C, and seal and react under an inert atmosphere, collect the solid-phase product, wash, and obtain a one-dimensional polymer brush grafted with a diblock polymer on the surface. Among them, the mass-volume ratio of the intermediate product to N,N-dimethylformamide is 1 mg / 0.1 mL; the mass-volume ratio of the intermediate product to the fluorinated alkane group-containing polymer monomer is 1 mg / 10 μL; the mass ratio of the intermediate product, tris(2-pyridylmethyl)amine, copper bromide, and vitamin C is 1:0.75:0.075:0.275.

[0070] Disperse the one-dimensional polymer brush in N,N-dimethylformamide, perform vacuum filtration, and dry it in a vacuum oven at 35 - 45 °C for 24 h to obtain a one-dimensional polymer brush film. Among them, the dispersion concentration of the one-dimensional polymer brush in N,N-dimethylformamide is 2 mg / mL.

[0071] In this application, the lithium single-ion conductor polymer monomers include any one or a mixture of two or more of lithium p-styrenesulfonate, lithium p-styrene trifluoromethanesulfonimide, lithium 3-sulfopropyl methacrylate, or 1-[3-(methacryloyloxy)propylsulfonyl]-1-(trifluoromethanesulfonyl)imide lithium; the polymer monomers containing fluorinated alkane groups include any one or a mixture of two or more of trifluoroethyl methacrylate, 2-(perfluoropentyl)ethyl methacrylate, 2-(perfluorobutyl)ethyl methacrylate, 2-(perfluorohexyl)ethyl methacrylate.

[0072] In this application, the in-situ polymerization precursor solution in step S3 includes a lithium salt, an initiator, and an organic solvent; among them, the concentration of the lithium salt in the in-situ polymerization precursor solution is 1 - 2 mol / L, and the initiator concentration is 0.2 - 0.5 mol / L.

[0073] The lithium salt includes at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium bis(oxalato)borate, or lithium difluoro(oxalato)borate;

[0074] The initiator is at least one of magnesium bis(trifluoromethanesulfonyl)imide, zinc bis(trifluoromethanesulfonyl)imide, lithium hexafluorophosphate, aluminum trifluoromethanesulfonate, or stannous fluoride;

[0075] The organic solvent is a mixture of 1,3-dioxolane and a carbonate, and the carbonate includes at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, or methyl ethyl carbonate; among them, the volume ratio of 1,3-dioxolane to the carbonate is 3:2.

[0076] In this application, bromine-modified bacterial cellulose (BC-Br) is first synthesized through an esterification reaction, and then, using the Br group on BC-Br as an active grafting site, a polymer side chain with specific functions is grafted onto the BC surface by surface-initiated atom transfer radical polymerization (SI-ATRP) technology to prepare a one-dimensional polymer brush, and then a one-dimensional polymer brush film is obtained; during the process of assembling the battery, an in-situ polymerization precursor solution containing 1,3-dioxolane is dropped into the one-dimensional polymer brush film, so that 1,3-dioxolane undergoes in-situ ring-opening polymerization in the film, and then a high-voltage-resistant in-situ polymerization quasi-solid electrolyte film is obtained.

[0077] The high-voltage resistant in-situ polymerization quasi-solid electrolyte membrane prepared in this application uses bacterial cellulose as the backbone, which can significantly improve the mechanical properties of the polymer electrolyte, reduce the thickness of the polymer electrolyte, and help inhibit the growth of lithium dendrites. Among them, one-dimensional molecular brushes overlap with each other to form a rich pore structure, which helps to uniformly absorb more in-situ polymerization precursor solutions and ensure the rapid transport of lithium ions. The lithium single-ion conductor block in its side chain can increase the ionic conductivity and lithium ion transference number, which is beneficial to the transport of lithium ions and the uniform deposition of lithium metal. The block containing fluorinated alkane groups can improve the antioxidant property of the electrolyte membrane and is beneficial to improving the stability of the electrolyte membrane in a high-voltage environment.

[0078] The high-voltage resistant in-situ polymerization quasi-solid electrolyte membrane prepared in this application has excellent mechanical properties, relatively high room-temperature ionic conductivity, and excellent high-voltage stability. It can be used as a quasi-solid electrolyte for lithium metal batteries, especially for high-capacity and high-voltage lithium metal batteries. The high-voltage lithium metal battery containing the high-voltage resistant in-situ polymerization quasi-solid electrolyte membrane of this application has excellent electrochemical performance.

[0079] This application also provides a lithium metal battery, which includes a positive electrode, a negative electrode, and a quasi-solid electrolyte. The quasi-solid electrolyte is the above-mentioned high-voltage resistant in-situ polymerization quasi-solid electrolyte membrane, which has excellent electrochemical performance. For the lithium metal battery of this application, the positive electrode can be any one of lithium iron phosphate, lithium nickel cobalt manganese oxide, or lithium cobalt oxide, and the negative electrode is lithium metal.

[0080] The following further illustrates this application through examples.

[0081] Example 1

[0082] This example provides a preparation method of a high-voltage resistant in-situ polymerization quasi-solid electrolyte membrane, including:

[0083] S1, After uniformly mixing 500 mg of bacterial cellulose, 0.8772 g of 4-dimethylaminopyridine, 13.15 mL of anhydrous triethylamine, and 200 mL of anhydrous N,N-dimethylformamide, add 15 mL of 2-bromoisobutyryl bromide at 0 °C under a nitrogen atmosphere, and then raise the temperature to 30 °C and react for 24 h. Centrifuge and separate the solid phase, and wash it three times by centrifugation with ethanol and water respectively to obtain bromine-modified bacterial cellulose, denoted as BC.

[0084] S2. After uniformly mixing 200 mg of bromine-modified bacterial cellulose, 4 g of 1-[3-(methacryloyloxy)propylsulfonyl]-1-(trifluoromethanesulfonyl)imide lithium, 150 mg of tris(2-pyridylmethyl)amine, 15 mg of copper bromide, and 20 mL of N,N-dimethylformamide, 55 mg of ascorbic acid was added under a nitrogen atmosphere, and then the temperature was raised to 65 °C for reaction for 24 h. The solid phase was separated by centrifugation and centrifugally washed three times with N,N-dimethylformamide to obtain an intermediate product;

[0085] After uniformly mixing 200 mg of the intermediate product, 2 mL of 2-(perfluorohexyl)ethyl methacrylate, 150 mg of tris(2-pyridylmethyl)amine, 15 mg of copper bromide, and 20 mL of N,N-dimethylformamide, 55 mg of ascorbic acid was added under a nitrogen atmosphere, and then the temperature was raised to 65 °C for reaction for 24 h. The solid phase was separated by centrifugation and centrifugally washed three times with N,N-dimethylformamide to obtain a one-dimensional polymer brush;

[0086] After uniformly mixing 20 mg of the one-dimensional polymer brush and 10 mL of N,N-dimethylformamide, vacuum filtration was used, and then it was dried in a vacuum oven at 40 °C for 24 h to obtain a one-dimensional polymer brush film with a radius of 2.1 cm.

[0087] S3. Using the one-dimensional polymer brush film as a support film, 15 μL of the in-situ polymerization precursor solution was dropped on both sides of the film during battery assembly, and after standing at 30 °C for 24 h, an electrolyte membrane was obtained, denoted as BPMF-QSPE.

[0088] Among them, the preparation method of the precursor solution is as follows: Lithium hexafluorophosphate and lithium bis(trifluoromethanesulfonyl)imide are dissolved in a mixed solvent of 1,3-dioxolane and ethyl methyl carbonate, the volume ratio of 1,3-dioxolane to ethyl methyl carbonate is 3:2, the concentration of lithium hexafluorophosphate is 0.5 mol / L, and the concentration of lithium bis(trifluoromethanesulfonyl)imide is 1 mol / L.

[0089] Example 2

[0090] The difference between Example 2 and Example 1 is that in step S3, the concentration of lithium hexafluorophosphate is 0.2 mol / L, and the concentration of lithium bis(trifluoromethanesulfonyl)imide is 2 mol / L, and the rest are the same as in Example 1.

[0091] Comparative Example 1

[0092] S1 is the same as in Example 1;

[0093] S2. After uniformly mixing 200 mg of bromine-modified bacterial cellulose, 4 g of 1-[3-(methacryloyloxy)propylsulfonyl]-1-(trifluoromethanesulfonyl)imide lithium, 150 mg of tris(2-pyridylmethyl)amine, 15 mg of copper bromide, and 20 mL of N,N-dimethylformamide, 55 mg of ascorbic acid was added under a nitrogen atmosphere. Subsequently, the temperature was raised to 65 °C and reacted for 24 h. The solid phase was separated by centrifugation and washed three times by centrifugation with N,N-dimethylformamide to obtain an intermediate product.

[0094] After uniformly mixing 20 mg of the intermediate product and 10 mL of N,N-dimethylformamide, vacuum filtration was used, and then it was dried in a vacuum oven at 40 °C for 24 h to obtain a one-dimensional polymer brush film with a radius of 2.1 cm.

[0095] S3. The same as in Example 1. The electrolyte membrane prepared in Comparative Example 1 is denoted as BPM-QSPE.

[0096] Comparative Example 2

[0097] S1. The same as in Example 1;

[0098] S2. After uniformly mixing 200 mg of bromine-modified bacterial cellulose, 2 mL of 2-(perfluorohexyl)ethyl methacrylate, 150 mg of tris(2-pyridylmethyl)amine, 15 mg of copper bromide, and 20 mL of N,N-dimethylformamide, 55 mg of ascorbic acid was added under a nitrogen atmosphere. Subsequently, the temperature was raised to 65 °C and reacted for 24 h. The solid phase was separated by centrifugation and washed three times by centrifugation with N,N-dimethylformamide to obtain a one-dimensional polymer brush.

[0099] After uniformly mixing 20 mg of the one-dimensional polymer brush and 10 mL of N,N-dimethylformamide, vacuum filtration was used, and then it was dried in a vacuum oven at 40 °C for 24 h to obtain a one-dimensional polymer brush film with a radius of 2.1 cm.

[0100] S3. The same as in Example 1. The electrolyte membrane prepared in Comparative Example 2 is denoted as BPF-QSPE.

[0101] Comparative Example 3

[0102] S1. After uniformly mixing 20 mg of bacterial cellulose and 10 mL of N,N-dimethylformamide, vacuum filtration was used, and then it was dried in a vacuum oven at 40 °C for 24 h to obtain a bacterial cellulose film with a radius of 2.1 cm.

[0103] S3. Using the bacterial cellulose film as a support membrane, 15 μL of the in-situ polymerization precursor solution was dropped on both sides of the film during battery assembly, and after standing at 30 °C for 24 h, an electrolyte membrane was obtained, denoted as BC-QSPE. Among them, the preparation method of the precursor solution is the same as that in Example 1.

[0104] Comparative Example 4

[0105] Using a polypropylene separator as the support membrane, 15 μL of the in-situ polymerization precursor solution was dropped on both sides of the thin film during battery assembly. After being placed at 30 °C for 24 h, an electrolyte membrane was obtained, denoted as PP-QSPE. Among them, the preparation method of the precursor solution was the same as that in Example 1.

[0106] The raw material bacterial cellulose and the one-dimensional polymer brush thin film of Example 1 were evaluated for their morphology, and the microscopic morphology of the surface and cross-section was observed.

[0107] The scanning electron microscope images of the surface of the bacterial cellulose and the one-dimensional polymer brush thin film are as Figure 1 shown, where (a) is the bacterial cellulose and (b) is the one-dimensional polymer brush thin film. From Figure 1 it can be seen that after grafting the polymer side chains, the bacterial cellulose became significantly thicker, indicating successful side chain grafting and the retention of a rich pore structure after grafting.

[0108] The scanning electron microscope images of the cross-section of the bacterial cellulose and the one-dimensional polymer brush thin film are as Figure 2 shown, where (a) is the bacterial cellulose and (b) is the one-dimensional polymer brush thin film. Figure 2 It can be seen that after grafting the polymer side chains, the thickness of the thin film increased from 17 μm to 19 μm.

[0109] The one-dimensional polymer brush thin film prepared in Example 1, the bacterial cellulose thin film of Comparative Example 3, and the polypropylene separator of Comparative Example 4 were tested for the Young's modulus distribution using an atomic force microscope, and the test results are as Figure 3 shown. Among them, Figure 3 in a is the Young's modulus distribution diagram of the polypropylene separator, b is the Young's modulus distribution diagram of the bacterial cellulose thin film, and c is the Young's modulus distribution diagram of the one-dimensional polymer brush thin film.

[0110] From Figure 3 it can be seen that due to the good mechanical properties of bacterial cellulose, the Young's modulus (2.1 GPa) of the bacterial cellulose (BC) thin film is higher than that of the polypropylene (PP) separator (675 MPa); although the Young's modulus of the BC film (BC-g-PLiMTFSI-b-PPFEMA) after grafting the polymer side chains, that is, the one-dimensional polymer brush thin film, decreased, its Young's modulus still reached 1.9 GPa, exceeding the PP separator.

[0111] The high-voltage-resistant in-situ polymerization quasi-solid electrolyte membrane prepared in Example 1 was assembled into a steel sheet|steel sheet symmetric battery, specifically as follows:

[0112] Using a steel sheet with a diameter of 15.6 mm and a thickness of 1.5 mm as the positive and negative electrodes, and the electrolyte membrane BPMF-QSPE of Example 1 as the electrolyte, a steel sheet|steel sheet symmetric cell was assembled in a glove box under an argon atmosphere, where the contents of moisture and oxygen in the glove box were less than 0.1 ppm. By the same method, steel sheet|steel sheet symmetric cells were assembled using the electrolyte membranes prepared in Comparative Examples 1-4 respectively.

[0113] The impedance spectra of the steel sheet|steel sheet symmetric cells assembled with the above electrolyte membranes were respectively tested using a CHI760E electrochemical workstation, and the test frequency range was 106 Hz to 0.1 Hz. The impedance spectra of the electrolyte membrane BPMF-QSPE of Example 1 and the electrolyte membranes of Comparative Examples 1-4 are respectively as Figure 4 shown in a-e below.

[0114] Using a CHI760E electrochemical workstation, the impedance spectra of the steel sheet|steel sheet symmetric cells assembled with the above electrolyte membranes were tested at different temperatures (30 - 80 °C), and the corresponding ionic conductivities were calculated using Equation (1);

[0115]

[0116] where σ, L, Rb, and AS are respectively the ionic conductivity of the electrolyte membrane, the thickness of the electrolyte membrane, the area of the steel sheet, and the bulk resistance of the electrolyte membrane obtained by testing;

[0117] Finally, a graph with 1000 / T as the abscissa and logσ as the ordinate was plotted to obtain the ionic conductivity-temperature relationship graph. The ionic conductivity-temperature relationship graphs of the electrolyte membrane BPMF-QSPE of Example 1 and the electrolyte membranes of Comparative Examples 1-4 are as Figure 4 shown in f below.

[0118] The impedance data and room temperature ionic conductivity data of the electrolyte membrane BPMF-QSPE of Example 1 and the electrolyte membranes of Comparative Examples 1-4 are specifically shown in Table 1.

[0119] Table 1 Impedance and room temperature ionic conductivity data of the electrolyte membrane

[0120] Sample Name Impedance (Ω) Room Temperature Ionic Conductivity (S / cm) Example 1 BPMF-QSPE 3.44 <![CDATA[4.45×10 -4 > Comparative Example 1 BPM-QSPE 3.70 <![CDATA[4.14×10 -4 > Comparative Example 2 BPF-QSPE 6.89 <![CDATA[2.00×10 -4 > Comparative Example 3 BC-QSPE 11.87 <![CDATA[1.12×10 -4 > Comparative Example 4 PP-QSPE 9.66 <![CDATA[1.53×10 -4 >

[0121] From Figure 4As can be seen from Table 1, for the electrolyte membranes of Example 1, Comparative Example 1, and Comparative Example 2, their impedance and room-temperature ionic conductivity are higher than those of the bacterial cellulose-based electrolyte membrane of Comparative Example 3 and the PP separator-based electrolyte membrane of Comparative Example 4. Among them, the electrolyte membranes of Example 1 and Comparative Example 1 with lithium single-ion conductor blocks have higher room-temperature ionic conductivity and lower impedance, indicating that the lithium single-ion conductor blocks can promote the dissociation of lithium salts and are beneficial to lithium-ion transport. The electrolyte membrane of Example 1 has a double-block polymer side chain with a lithium single-ion conductor block and a fluorine-containing group block, and it has the highest room-temperature ionic conductivity and the lowest impedance. From Figure 4 As can be seen from f in it, the electrolyte membrane of Example 1 has the lowest ion transport energy barrier, which is beneficial to the rapid transport of lithium ions, further verifying the above conclusion.

[0122] The high-voltage resistant in-situ polymerization quasi-solid-state electrolyte membrane prepared in Example 1 was assembled into a lithium metal battery as follows:

[0123] Using a lithium sheet with a diameter of 15.6 mm and a thickness of 0.45 mm as the negative electrode, LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811) electrode sheet as the positive electrode, and the electrolyte membrane BPMF-QSPE of Example 1 as the electrolyte, a Li|NCM811 full cell was assembled in a glove box under an argon atmosphere, and the contents of moisture and oxygen in the glove box were less than 0.1 ppm. Among them, the NCM811 loading of the NCM811 electrode sheet is 7.5 mg cm -2 , and the diameter of the electrode sheet is 12 mm. By the same method, Li|NCM811 full cells were assembled using the electrolyte membranes prepared in Comparative Examples 1-4 respectively. The above Li|NCM811 full cells were respectively used for battery cycle performance testing and electrochemical floating testing.

[0124] Among them, the specific method of the electrochemical floating test is as follows: First, charge the Li|NCM811 full cell to 4.0 V, and then charge the battery in a constant voltage charging mode and gradually increase the charging voltage by 0.1 V each time, and each voltage is maintained for 5 hours. When a significant increase in the measured response current is obtained, it indicates that the electrolyte membrane starts to decompose at this voltage. The results of the electrochemical floating test are as Figure 5 and Figure 6 shown.

[0125] From Figure 5 and Figure 6It can be seen that the current of the Li|NCM811 full cell assembled with the electrolyte membrane BPMF-QSPE of Example 1 and the electrolyte membrane BPF-QSPE of Comparative Example 2 still did not increase significantly at 5.0 V, indicating that these two electrolyte membranes remained stable at 5.0 V; while the current of the Li|NCM811 full cells assembled with the electrolyte membrane BPM-QSPE of Comparative Example 1, the electrolyte membrane BC-QSPE of Comparative Example 3, and the electrolyte membrane PP-QSPE of Comparative Example 4 increased significantly at 4.7 V, indicating that the corresponding electrolyte membranes decomposed at 4.7 V. The above results show that the block containing fluorinated alkane groups has good antioxidant properties. Therefore, the electrolyte membranes BPM-QSPE of Example 1 and BPF-QSPE of Comparative Example 2 remained stable at 5 V, meeting the requirements of high-voltage lithium metal batteries.

[0126] The Li|NCM811 full cells assembled with the electrolyte membranes prepared in Example 1 and Comparative Examples 3-4 were subjected to cyclic performance tests under the following conditions: temperature was 30 °C, charge-discharge voltage range was 2.7-4.5 V, current density was 1C, and the NCM811 loading was 7.5 mg cm -2 ; The test results are as Figure 7 shown.

[0127] From Figure 7 it can be seen that the initial discharge specific capacity of the Li|NCM811 full cell based on the electrolyte membrane BPMF-QSPE of Example 1 was 206.4 mAh g -1 , and it still maintained 71.2% of the specific capacity after 370 cycles, which was significantly better than the Li|NCM811 full cells assembled with the electrolyte membranes of Comparative Example 3 and Comparative Example 4, indicating that the electrolyte membrane BPMF-QSPE prepared in Example 1 could significantly improve the cyclic performance of the high-voltage and high-loading Li|NCM811 full cell.

[0128] The high-voltage-resistant in-situ polymerization quasi-solid electrolyte membrane prepared in Example 1 was used to assemble a Li|Li symmetric battery as follows:

[0129] A lithium sheet with a diameter of 15.6 mm and a thickness of 0.45 mm was used as the negative electrode, a lithium sheet with a diameter of 11.0 mm and a thickness of 0.45 mm was used as the positive electrode, and the high-voltage-resistant in-situ polymerization quasi-solid electrolyte membrane of Example 1 was used as the electrolyte. The Li|Li symmetric battery was assembled in a glove box under an argon atmosphere, and the contents of water and oxygen in the glove box were less than 0.1 ppm. By the same method, Li|Li symmetric batteries were assembled with the electrolyte membranes prepared in Comparative Examples 3-4 respectively. The assembled Li|Li symmetric batteries were used for the limiting current density test and the lithium deposition / stripping cycle test.

[0130] Among them, the test method for the limiting current density is as follows: The corresponding Li|Li symmetric battery is subjected to lithium deposition / stripping cycle tests under the condition that the current density gradually increases, starting from 0.1 mA cm -2 and increasing by 0.05 mA cm -2 for each cycle, and each cycle lasts for 1 hour. The test results are as shown in Figure 8 .

[0131] As can be seen from Figure 8 , due to the good lithium conduction performance of the lithium single-ion conductor block, the electrolyte membrane BPM-QSPE of Example 1 has a relatively high critical current density. Even when the current density reaches 5.6 mA cm -2 , there is still no significant voltage fluctuation or short-circuit behavior. In sharp contrast, the electrolyte membrane BC-QSPE of Comparative Example 3 and the electrolyte membrane PP-QSPE of Comparative Example 4 show obvious voltage increase or even short-circuit behavior at current densities of 2.0 mA cm -2 and 2.6 mA cm -2 respectively. The above results show that the high-voltage in-situ polymerization quasi-solid electrolyte membrane of Example 1 has a relatively high critical current density, meeting the requirements of high cathode loading lithium metal batteries.

[0132] Among them, the conditions for the lithium deposition / stripping cycle test are: the current density is 0.2 mA cm -2 , and the areal capacity is 0.2 mAh cm -2 ; the test results are as shown in Figure 9 .

[0133] As can be known from Figure 9 , the voltage plateau of the Li|Li symmetric battery based on the electrolyte membrane BPM-QSPE of Example 1 is still very stable after cycling for 1046 h; in contrast, the cycling performance of the Li|Li symmetric batteries based on the electrolyte membrane BC-QSPE of Comparative Example 3 and the electrolyte membrane PP-QSPE of Comparative Example 4 is poor. The voltage plateau increases rapidly after only about 500 h of cycling, and the battery fails within 600 h.

[0134] Although the present application has been described in detail with general descriptions and specific embodiments in this specification, on the basis of the present application, some modifications or improvements can be made, which are obvious to those skilled in the art. Therefore, these modifications or improvements made without departing from the spirit of the present application all fall within the scope of protection required by the present application.

Claims

1. A method for preparing a high-voltage resistant in-situ polymerized quasi-solid electrolyte membrane, characterized in that: include: S1, esterifying bacterial cellulose with 2-bromoisobutyryl bromide to obtain bromine-modified bacterial cellulose; S2, polymerizing the bromine-modified bacterial cellulose with a lithium single ion conductor polymer monomer and a fluorinated alkane group-containing polymer monomer, respectively, to graft diblock polymer side chains onto the surface of the bromine-modified bacterial cellulose to obtain a one-dimensional polymer brush; dispersing the brush in a solvent, forming a film by suction filtration, and drying to obtain a one-dimensional polymer brush film; S3, using the one-dimensional polymer brush film as a support film, dripping an in-situ polymerization precursor solution on the surface thereof, and obtaining a high-voltage resistant in-situ polymerization quasi-solid electrolyte membrane through in-situ ring-opening polymerization.

2. The preparation method according to claim 1, characterized in that: The in-situ polymerization precursor solution in S3 includes a lithium salt, an initiator and an organic solvent; The lithium salt includes at least one of bis(trifluoromethanesulfonyl imide) lithium, bis(fluorosulfonyl imide) lithium, lithium bis(oxalatoborate) or lithium difluorooxalatoborate; The initiator is at least one of bis(trifluoromethanesulfonyl imide) magnesium, bis(trifluoromethanesulfonyl imide) zinc, lithium hexafluorophosphate, aluminum trifluoromethanesulfonate or stannous fluoride; The organic solvent is a mixture of 1,3-dioxolane and carbonate, and the carbonate includes at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate or ethyl methyl carbonate.

3. The preparation method according to claim 2, characterized in that: The concentration of lithium salt in the in-situ polymerization precursor solution is 1-2 mol / L, and the concentration of initiator is 0.2-0.5 mol / L; The volume ratio of the 1,3-dioxolane to the carbonate is 3:

2.

4. The preparation method according to claim 1, characterized in that: Step S1 is specifically as follows: Dispersing bacterial cellulose in N,N-dimethylformamide, adding 4-dimethylaminopyridine and triethylamine, and mixing well; 2-Bromoisobutyryl bromide was added dropwise to the mixed solution at 0°C under an inert atmosphere, the temperature was raised to 30°C and stirred for reaction for 24 hours, ethanol was added to quench the reaction, the solid phase product was collected, washed, and dried to obtain bromine-modified bacterial cellulose; Among them, the mass volume ratio of bacterial cellulose to N,N-dimethylformamide is 1 mg / 0.4 mL; the mass volume ratio of bacterial cellulose to 4-dimethylaminopyridine is 1 mg / 1.75 mg; the mass volume ratio of bacterial cellulose to triethylamine is 1 mg / 26.3 μL; the mass volume ratio of bacterial cellulose to 2-bromoisobutyryl bromide is 1 mg / 30 μL.

5. The preparation method according to claim 1, characterized in that: Step S2 specifically includes: The bromine-modified bacterial cellulose is dispersed in N,N-dimethylformamide, and a lithium single ion conductor polymer monomer, tri(2-pyridylmethyl)amine, copper bromide and vitamin C are added, the temperature is raised to 60-70° C., the reaction is sealed under an inert atmosphere, and the solid phase product is collected and washed to obtain an intermediate product; The intermediate product is dispersed in N, N-dimethylformamide, and a polymer monomer containing a fluorinated alkane group, tris(2-pyridylmethyl)amine, copper bromide and vitamin C are added, the temperature is raised to 60-70° C., and the reaction is sealed under an inert atmosphere, and the solid phase product is collected and washed to obtain a one-dimensional polymer brush with a diblock polymer grafted on the surface; The one-dimensional polymer brush is dispersed in N,N-dimethylformamide, vacuum filtered and dried to obtain a one-dimensional polymer brush film.

6. The preparation method according to claim 5, characterized in that: The lithium single ion conductor polymer monomer includes any one of p-styrene sulfonate, p-styrene trifluoromethylsulfonyl lithium imide, 3-sulfonate propyl methacrylate lithium or 1-[3-(methacryloyloxy)propyl sulfonyl]-1-(trifluoromethylsulfonyl) imide lithium or a mixture of two or more thereof; The high molecular monomer containing fluorinated alkane groups includes any one of trifluoroethyl methacrylate, 2-(perfluoropentyl)ethyl methacrylate, 2-(perfluorobutyl)ethyl methacrylate, and 2-(perfluorohexyl)ethyl methacrylate, or a mixture of two or more thereof.

7. The preparation method according to claim 5, characterized in that: The mass volume ratio of the bromine-modified bacterial cellulose to N,N-dimethylformamide is 1 mg / 0.1 mL; The mass ratio of bromine-modified bacterial cellulose, lithium single ion conductor polymer monomer, tris(2-pyridylmethyl)amine, copper bromide, and vitamin C is 1:20:0.75:0.075:0.275; The mass volume ratio of the intermediate product to N,N-dimethylformamide is 1 mg / 0.1 mL; the mass volume ratio of the intermediate product to the fluorinated alkane group-containing polymer monomer is 1 mg / 10 μL; The mass ratio of the intermediate product, tris(2-pyridylmethyl)amine, copper bromide, and vitamin C is 1:0.75:0.075:0.275; The dispersion concentration of the one-dimensional polymer brush in N,N-dimethylformamide is 2 mg / mL.

8. A high-voltage resistant in-situ polymerized quasi-solid electrolyte membrane prepared by the preparation method according to any one of claims 1 to 7.

9. Use of the high-voltage resistant in-situ polymerized quasi-solid electrolyte membrane according to claim 8 in lithium metal batteries.

10. A lithium metal battery, characterized in that: It includes a positive electrode, a negative electrode and a quasi-solid electrolyte; The quasi-solid electrolyte is the high-voltage resistant in-situ polymerized quasi-solid electrolyte membrane according to claim 8; The positive electrode includes any one of lithium iron phosphate, lithium nickel cobalt manganese oxide or lithium cobalt oxide; The negative electrode is lithium metal.

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