A solid-state electrolyte membrane based on polymer grafting cross-linking and a preparation method and application thereof

Abstract

This invention belongs to the field of lithium battery technology and discloses a solid electrolyte membrane based on polymer graft crosslinking, its preparation method, and its application. A lithium salt is dissolved in a high dielectric constant solvent to obtain solution a; a polymer matrix, a functional group donor, and azobisisobutyronitrile are added to a polar solvent and reacted at 60-120℃ for 3-5 h to obtain solution b; wherein the polymer matrix includes any one of fluorinated polymers, polyacrylonitrile polymers, and polyether polymers, and the functional group donor is a fluorinated ether group, an ether oxygen group, or a carbonyl group compound monomer or oligomer; solution c, obtained by mixing solution a and solution b, is subjected to degassing, coating, drying, and annealing to obtain the solid electrolyte membrane. The solid electrolyte membrane of this invention is simple to prepare, can be mass-produced, and is suitable for high-energy-density lithium metal batteries, drones, energy storage systems, and other fields.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery technology, and particularly relates to a method for preparing a solid electrolyte membrane. Background Technology

[0002] With the continued growth in demand for high-energy-density and high-safety energy storage systems, solid-state lithium metal batteries have attracted widespread attention due to their potential high energy density and intrinsic safety. Among them, the electrolyte material, as the core component coupling lithium-ion transport and electrode reaction, directly determines the overall performance and lifespan of the battery due to its structural stability, ion conductivity, and interfacial compatibility.

[0003] Compared to inorganic solid electrolytes, polymer solid electrolytes possess advantages such as good flexibility, excellent film-forming properties, and tight interfacial contact, giving them a natural advantage in reducing interfacial impedance and adapting to complex electrode structures. However, existing polymer solid electrolyte systems generally face the technical bottleneck of "difficulty in simultaneously achieving ion conductivity, mechanical stability, and electrochemical stability window," limiting their application in high-voltage, high-energy-density lithium metal batteries.

[0004] Currently, the most researched and applied polymer solid electrolytes mainly include polyethylene oxide (PEO) and polyvinylidene fluoride (PVDF) systems. PEO-based electrolytes rely on the coordination between ether oxygen groups and lithium salts to achieve lithium-ion migration. Although they possess some salt-dissolving ability, they have high crystallinity, low mechanical modulus, and are prone to oxidative decomposition at high operating voltages, making them unsuitable for high-voltage cathode materials. In contrast, PVDF and its copolymers are widely used in electrode binders and composite electrolytes due to their high dielectric constant, excellent thermal stability, and chemical stability. However, their molecular backbone lacks effective lithium-ion coordinating groups, and ion transport mainly relies on non-directional random migration, resulting in limited room-temperature ionic conductivity and lithium-ion transference number.

[0005] To improve the ion transport performance of PVDF-based polymers, existing technologies typically increase the dielectric constant or reduce the lithium salt dissociation energy by introducing inorganic fillers, constructing multiphase composite systems, or physically blending the polymers. However, these methods often rely on fillers or phase interface effects to achieve performance improvements, which can easily lead to problems such as insufficient interfacial bonding, discontinuous phase structures, and localized stress concentrations. Furthermore, they struggle to maintain stable ion transport channels under long-term cycling or high-current conditions, and exhibit poor processing consistency and structural controllability.

[0006] Therefore, existing technologies still lack a design strategy that can simultaneously ensure the stability of the polymer skeleton and the efficient migration of lithium ions at the molecular structure level, especially without relying on a large amount of inorganic fillers, to achieve the regulation of the internal polar structure of the polymer and the construction of a continuous ion transport network, thereby meeting the comprehensive requirements of high-energy-density solid-state lithium metal batteries for electrolyte materials in terms of safety, stability and electrochemical performance. Summary of the Invention

[0007] To address the problems of insufficient lithium-ion transport pathways, low lithium salt dissociation efficiency, and high electrode / electrolyte interface impedance in existing fluoropolymer solid electrolytes, this invention proposes a polymer-grafted crosslinked solid electrolyte membrane, its preparation method, and its applications. By constructing a dual-network structure through the synergistic effect of chemical grafting and physical hydrogen bonding, a balance between high ionic conductivity and excellent mechanical stability is achieved, overcoming the limitations of traditional polymer electrolytes.

[0008] To achieve the above objectives, the technical solution of the present invention is as follows:

[0009] A method for preparing a solid electrolyte membrane based on polymer graft crosslinking, comprising the following steps:

[0010] (1) Dry all the glassware required for the experiment in vacuum at 80℃ for 6 hours; dry the polymer matrix and functional group donors in vacuum at 40-80℃ for 4-12 hours;

[0011] (2) Dissolve the lithium salt in a high dielectric constant solvent to obtain solution a. Add the polymer matrix, functional group donor, and azobisisobutyronitrile (AIBN) to a polar solvent and react at 60-120℃ for 3-5 h under inert gas protection to obtain solution b. The polymer matrix is ​​a polymeric material constituting the continuous film-forming phase of the solid electrolyte membrane, including any one of fluoropolymers, polyacrylonitrile polymers, and polyether polymers. The functional group donor is a reactive component that does not constitute the film-forming phase of the electrolyte membrane but contains functional groups that can undergo grafting and crosslinking reactions with the polymer matrix. The functional group donor is a monomer or oligomer of a compound containing a fluorinated ether group, an etheroxy group, or a carbonyl group, and the polymer matrix and the functional group donor are not the same (i.e., two different materials are used). Further, the functional group donor is any one of polyethylene oxide, polyethylene glycol monomethyl ether, propylene carbonate, dimethyl carbonate, and perfluoroethylene oxide.

[0012] (3) Mix solution a and solution b to obtain solution c; degas solution c, then cast it on a glass or PTFE substrate by casting method, and scrape it with a suitable scale; then dry the film and anneal it at high temperature to improve the β phase content and structural uniformity to obtain a solid electrolyte membrane.

[0013] In step (2) above, the lithium salt is at least one of inorganic lithium salt, inorganic lithium salt and organic-inorganic composite lithium salt, and the high dielectric constant solvent is at least one of carbonate, ether, dimethyl sulfoxide (DMSO) and amide; the concentration of lithium salt in solution a is 0.3-1 M.

[0014] More preferably, the inorganic lithium salt includes at least one of lithium tetrafluoroborate, lithium hexafluorophosphate, and lithium hexafluoroarsenate; the organic lithium salt includes at least one of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(oxalateborate)borate (LiBOB), and lithium bis(fluorooxalateborate)borate (LiDFOB); the carbonate solvent includes at least one of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate; the ether solvent is a monomethyl ether, such as ethylene glycol methyl ether and diethylene glycol methyl ether; and the amides include N-methylpyrrolidone (NMP) and N,N-dimethylformamide (DMF).

[0015] In step (2) above, the polar solution is any one of amines, ketones, amides and polar aprotic solvents containing sulfoxide groups; the mass ratio of polymer matrix, functional group donor, lithium salt and azobisisobutyronitrile is 1:0.1-0.65:0.015-0.2:0.001-0.05.

[0016] Furthermore, the amide solvents include at least one of N,N-dimethylformamide (DMF) and N-methylpyrrolidone (NMP); the ketone solvents include one or more of 2-butanone, acetone and cyclohexanone in any proportion; and the polar aprotic solvent containing a sulfoxide group is dimethyl sulfoxide (DMSO).

[0017] More specifically, the aforementioned fluoropolymers are at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), and polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP); the polyacrylonitrile polymers are one or both of polyacrylonitrile (PAN) or polyvinyl acrylonitrile (PVN); and the polyether polymers are any one of polypropylene oxide (PPO), fluorinated polyethers (such as perfluoropolyether (PFPE) and perfluoroethylene oxide (PFA)), polyethylene oxide (PEO), polyethylene glycol monomethyl ether (mPEG), polyethylene glycol methacrylate (PEGMA), polymethyl methacrylate (PMMA), and polypropylene glycol (PPG). The relative molecular mass of the fluoropolymers, polyacrylonitrile polymers, and polyether polymers is 10,000-800,000.

[0018] In step (3) above, drying refers to drying at 40-100℃ for 2-12 h and drying at 60-120℃ for 4-12 h in sequence; the annealing conditions are: annealing at 70-120℃ and vacuum of -0.5~-1Mpa for 1-6 h.

[0019] Solid electrolyte membrane prepared using the above preparation method.

[0020] The above-mentioned solid electrolyte membranes are used in lithium metal batteries, drones, or energy storage systems.

[0021] The beneficial effects of this invention are:

[0022] (1) This invention introduces a polymer grafting and crosslinking structural design method, which, while maintaining the mechanical stability of the fluoropolymer backbone, constructs continuous lithium-ion coordination and migration channels at the molecular level. This method effectively avoids the problem of limited electrochemical performance caused by the lack of lithium-conducting groups in a single fluoropolymer system, and overcomes the shortcomings of traditional PEO-based polymer electrolytes in terms of membrane stability and film formation consistency, providing a method for preparing a polymer solid electrolyte membrane with controllable structure and stable performance.

[0023] (2) This invention uses fluoropolymers and functional groups as the composite polymer matrix. Under the action of an initiator, chemical cross-linking reactions occur between chain segments. Fluoropolymers and polyether segments preferentially undergo grafting connections under initiation conditions. The resulting grafted structures further serve as building nodes for the cross-linking network, thereby forming a three-dimensional network structure in the polymer system with the fluorinated backbone as the skeleton and the functional group segments as flexible transport units. Subsequently, a cross-linked polymer electrolyte membrane is prepared using a casting process. Among them, the fluorinated backbone provides the electrolyte membrane with excellent mechanical strength, thermal stability, and high voltage withstand capability, while the ether oxygen groups rich in the PEO segments provide effective coordination and dissociation sites for the lithium salt. By fixing the PEO segments in the PVDF backbone network through the cross-linking structure, the structural instability under high voltage conditions is avoided while suppressing PEO crystallization and excessive chain segment movement.

[0024] (3) The electrolyte membrane prepared by blending-grafting-curing in this invention has high room temperature ionic conductivity and significantly improved lithium-ion transference number (t). Li⁺ The assembled lithium-symmetric cell exhibits a wide electrochemical stability window (approximately 0.85 V) and a wide electrochemical stability window (approximately 5 V). The value of the assembled lithium-symmetric cell is approximately 0.2 mA·cm⁻¹. -2 With over 1500 hours of stable cycling, lithium iron phosphate batteries exhibit excellent rate performance and cycle stability. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 Digital photographs of the solid electrolyte membranes prepared in Examples 1(a), 5(b), and 8(c).

[0027] Figure 2 SEM images of the solid electrolyte membranes prepared in Examples 2(a), 3(b), and 8(c), respectively.

[0028] Figure 3 This is a comparison diagram of the film thickness of the solid electrolyte membranes prepared in the examples and comparative examples.

[0029] Figure 4 The AC impedance spectra of the polymer solid electrolyte membranes of Examples 1-5 applied to stainless steel symmetric cells are shown.

[0030] Figure 5 Ion mobility diagrams for the solid electrolyte membranes prepared in Examples 2(a) and 7(b).

[0031] Figure 6 This is a comparison chart of the ion mobility of the solid electrolyte membranes prepared in Examples 2 and 7 and Comparative Example 1.

[0032] Figure 7 The graph shows the rate performance of batteries assembled using the polymer electrolyte membranes prepared in Examples 2, 5, and 7. Detailed Implementation

[0033] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] Unless otherwise specified, all raw materials used in the following examples are common commercially available products that can be directly purchased in the art. For example, polyvinylidene fluoride was purchased from Beijing Innocare Technology Co., Ltd.; ultra-dry acetonitrile was purchased from Tianjin Kemeio Chemical Reagent Co., Ltd.; and polypropylene oxide and ethylene carbonate were purchased from Shanghai Titan Technology Co., Ltd.

[0035] Example 1

[0036] The preparation method of the solid electrolyte membrane based on polymer graft crosslinking in this embodiment includes the following steps:

[0037] (1) The polymer matrix PVDF (Mw≈6×10) 5 The functional group donor PEO (terminally hydroxylated, Mw≈1×10) was vacuum dried at 80℃ for 12 h. 5 Dry under vacuum at 50°C for 6 hours.

[0038] (2) Take 2 g PVDF and 20 mg AIBN and add them to 100 mL N-methylpyrrolidone. Stir at 60 °C for 6 h until completely dissolved. Add 1 g PEO and continue stirring until homogeneous. Heat to 120 °C and react under argon protection for 5 h to achieve graft crosslinking of PVDF segments with PEO ether oxygen. After cooling to room temperature, add 500 µL of 0.5 M LiTFSI solution (solvent is N-methylpyrrolidone), stir for 1 h, and cast into a film. Then dry at 60 °C for 6 h, vacuum dry at 100 °C for 12 h, and finally anneal at 90 °C for 2 h to obtain a solid electrolyte membrane (thickness 20 μm) based on polymer graft crosslinking. The obtained polymer membrane has high flexibility and an ionic conductivity of 0.27 mS / cm.

[0039] Example 2

[0040] The preparation method of the solid electrolyte membrane based on polymer graft crosslinking in this embodiment includes the following steps:

[0041] (1) The polymer matrix PVDF (Mw≈8×10) 5 The product was vacuum dried at 80℃ for 12 h, and the functional group donor polyethylene glycol monomethyl ether (Mw≈2000) was vacuum dried at 50℃ for 6 h.

[0042] (2) Take 2 g of PVDF and 20 mg of AIBN and add them to 100 mL of N,N-dimethylformamide. Stir at 60 °C for 6 h until completely dissolved. Add 1 g of polyethylene glycol monomethyl ether and continue stirring until homogeneous. Heat to 120 °C and react under argon protection for 4 h to achieve graft crosslinking of PVDF segments with ether oxygen. After cooling to room temperature, add 700 µL of 0.3 M LiFSI solution (solvent is N,N-dimethylformamide), stir for 4 h, and cast into a film. Then dry at 40 °C for 6 h, vacuum dry at 100 °C for 12 h, and finally anneal at 90 °C for 4 h to obtain a solid electrolyte membrane based on polymer graft crosslinking. The obtained polymer membrane has a thickness of 27 μm and a dense and smooth surface.

[0043] Example 3

[0044] The preparation method of the solid electrolyte membrane based on polymer graft crosslinking in this embodiment includes the following steps:

[0045] (1) The polymer matrix PVDF-HFP (Mw≈6×10) 5 ), propylene carbonate (functional group donor) was vacuum dried at 50°C for 6 h.

[0046] (2) Take 2 g of PVDF-HFP and 7 mg of AIBN and add them to 100 mL of N-methylpyrrolidone. Stir at 60 °C for 2 h until completely dissolved. Add 270 µL of propylene carbonate and continue stirring until homogeneous. Heat to 80 °C and react under argon protection for 3 h to achieve graft crosslinking of PVDF segments and carbonyl groups. After cooling to room temperature, add 500 µL of a 0.7 M mixed solution of LiTFSI and LiBOB in a molar ratio of 1:1 (solvent is N-methylpyrrolidone), stir for 1 h, and cast into a film. Then dry at 40 °C for 4 h, vacuum dry at 80 °C for 12 h, and finally anneal at 90 °C for 2 h to obtain a solid electrolyte membrane based on polymer graft crosslinking (thickness of about 25 μm). The obtained membrane has a uniform structure and an electrochemical stability window of 4.77 V.

[0047] Example 4

[0048] The preparation method of the solid electrolyte membrane based on polymer graft crosslinking in this embodiment includes the following steps:

[0049] (1) The polymer matrix PVDF (Mw≈2×10) 5 ), functional group donor PEO (Mw≈1×10 5 Dry in vacuum at 80℃ for 4 h.

[0050] (2) Take 1 g PVDF and 40 mg AIBN and add them to 100 mL dimethyl sulfoxide. Stir at 60 °C for 6 h until completely dissolved. Add 0.5 g PEO and continue stirring until homogeneous. Heat to 80 °C and react under argon protection for 4 h to achieve graft crosslinking of PVDF segments with PEO ether oxygen. After cooling to room temperature, add 500 µL of a 1 M mixed solution of LiTFSI and LiBOB in a molar ratio of 1:1 (solvent is dimethyl sulfoxide), stir for 1 h, and cast into a film. Then dry at 40 °C for 8 h, vacuum dry at 80 °C for 10 h, and finally anneal at 90 °C for 3 h to obtain a solid electrolyte membrane based on polymer graft crosslinking (thickness of about 23 μm). The obtained membrane has good thermal stability and an ionic conductivity of 0.29 mS / cm.

[0051] Example 5

[0052] The preparation method of the solid electrolyte membrane based on polymer graft crosslinking in this embodiment includes the following steps:

[0053] (1) The polymer matrix PAN (Mw≈1×10) 5 ), functional group donor mPEG (Mw≈2×10), 4 Dry under vacuum at 40℃ for 6 hours.

[0054] (2) Take 2 g PAN and 5 mg AIBN and add them to 100 mL N-methylpyrrolidone. Stir at 60 °C for 2 h until completely dissolved. Add 0.5 g mPEG and continue stirring until homogeneous. Heat to 80 °C and react under argon protection for 4 h to achieve graft crosslinking of PVDF segments with ether oxygen. After cooling to room temperature, add 600 µL of 1 M LiBOB solution (solvent is N-methylpyrrolidone), stir for 2 h, and cast into a film. Then dry at 40 °C for 8 h, vacuum dry at 80 °C for 6 h, and finally anneal at 85 °C for 2 h to obtain a solid electrolyte membrane based on polymer graft crosslinking (thickness of about 24 μm). The obtained membrane is thin and flexible, with an ionic conductivity of 0.32 mS / cm.

[0055] Example 6

[0056] The preparation method of the solid electrolyte membrane based on polymer graft crosslinking in this embodiment includes the following steps:

[0057] (1) The polymer matrix PVN (Mw≈1×10 5 ), functional group donor PEO (Mw≈1×10 5 Dry under vacuum at 40℃ for 6 hours.

[0058] (2) Take 2 g PVN and 20 mg AIBN and add them to 100 mL N-methylpyrrolidone. Stir at 60 °C for 2 h until completely dissolved. Add 0.5 g PEO and continue stirring until homogeneous. Heat to 80 °C and react under argon protection for 4 h to achieve graft crosslinking of PVDF segments with ether oxygen. After cooling to room temperature, add 500 µL of a 1 M mixed solution of LiTFSI and LiBOB in a molar ratio of 1:1 (solvent is N-methylpyrrolidone), stir for 1 h, and cast into a film. Then dry at 40 °C for 8 h, vacuum dry at 80 °C for 6 h, and finally anneal at 85 °C for 2 h to obtain a solid electrolyte membrane based on polymer graft crosslinking (thickness of about 27 μm). The obtained membrane has high flexibility and an elongation at break increased by 129%.

[0059] Example 7

[0060] The preparation method of the solid electrolyte membrane based on polymer graft crosslinking in this embodiment includes the following steps:

[0061] (1) The polymer matrix PEO (Mw≈4×10)5 The functional group donor dimethyl carbonate (DMC) was vacuum dried at 40 °C for 8 h.

[0062] (2) Take 2 g PEO and 10 mg AIBN and add them to 100 mL N,N-dimethylformamide. Stir at 70 °C for 2 h until completely dissolved. Add 1 mL DMC and continue stirring until homogeneous. Heat to 80 °C and react under argon protection for 4 h to achieve graft crosslinking of PEO segments and carbonyl groups. After cooling to room temperature, add 500 µL of 0.7 M LiDFOB solution (solvent: N,N-dimethylformamide), stir for 2 h, and cast into a film. Then dry at 40 °C for 4 h, vacuum dry at 60 °C for 10 h, and finally anneal at 80 °C for 2 h to obtain a solid electrolyte membrane based on polymer graft crosslinking (thickness approximately 22 μm). The obtained membrane has an ionic conductivity of 0.43 mS / cm and a transport number of 0.64.

[0063] Example 8

[0064] The preparation method of the solid electrolyte membrane based on polymer graft crosslinking in this embodiment includes the following steps:

[0065] (1) The polymer matrix PPO (Mw≈2×10) 5 ), functional group donor PFA (Mw≈1×10 5 Dry under vacuum at 45°C for 6 hours.

[0066] (2) Take 2 g PPO and 20 mg AIBN and add them to 100 mL N-methylpyrrolidone. Stir at 90 °C for 4 h until completely dissolved. Add 0.7 g PFA and continue stirring until homogeneous. Heat to 90 °C and react under argon protection for 4 h to achieve graft crosslinking of PPO segments with fluoroether groups. After cooling to room temperature, add 500 µL of a 0.7 M mixed solution of LiTFSI and LiDFOB in a molar ratio of 7:3 (solvent is N-methylpyrrolidone), stir for 4 h, and cast into a film. Then dry at 40 °C for 2 h, vacuum dry at 60 °C for 12 h, and finally anneal at 80 °C for 4 h to obtain a solid electrolyte membrane based on polymer graft crosslinking (thickness of about 21 μm). The obtained membrane has high thermal stability and is suitable for high-temperature solid-state battery systems.

[0067] Example 9

[0068] The preparation method of the solid electrolyte membrane based on polymer graft crosslinking in this embodiment includes the following steps:

[0069] (1) The polymer matrix PVDF (Mw≈6×10) 5 The functional group donor PEO (terminally hydroxylated, Mw≈1×10) was vacuum dried at 80℃ for 4 h.5 Dry under vacuum at 50°C for 12 h.

[0070] (2) Take 2 g PVDF and 100 mg AIBN and add them to 100 mL N-methylpyrrolidone. Stir at 60 °C for 6 h until completely dissolved. Add 1.3 g PEO and continue stirring until homogeneous. Heat to 120 °C and react under argon protection for 5 h to achieve graft crosslinking of PVDF segments with PEO ether oxygen. After cooling to room temperature, add 348 µL of 0.5 M LiTFSI solution (solvent is N-methylpyrrolidone), stir for 1 h, and cast into a film. Then dry at 40 °C for 12 h, then vacuum dry at 120 °C for 4 h, and finally anneal at 70 °C for 6 h to obtain a solid electrolyte membrane based on polymer graft crosslinking.

[0071] Example 10

[0072] The preparation method of the solid electrolyte membrane based on polymer graft crosslinking in this embodiment includes the following steps:

[0073] (1) The polymer matrix PVDF (Mw≈6×10) 5 The functional group donor PEO (terminally hydroxylated, Mw≈1×10) was vacuum dried at 80℃ for 12 h. 5 Dry under vacuum at 50°C for 6 hours.

[0074] (2) Take 2 g PVDF and 20 mg AIBN and add them to 100 mL N-methylpyrrolidone. Stir at 60 °C for 6 h until completely dissolved. Add 0.2 g PEO and continue stirring until homogeneous. Heat to 120 °C and react under argon protection for 5 h to achieve graft crosslinking of PVDF segments with PEO ether oxygen. After cooling to room temperature, add 500 µL of 0.5 M LiTFSI solution (solvent is N-methylpyrrolidone), stir for 1 h, and cast into a film. Then dry at 60 °C for 6 h, vacuum dry at 100 °C for 12 h, and finally anneal at 120 °C for 1 h to obtain a solid electrolyte membrane based on polymer graft crosslinking.

[0075] Comparative Example 1

[0076] The preparation method of the solid electrolyte membrane in this comparative example differs from that in Example 1 in that it does not include the functional group donor PEO. The specific steps are as follows:

[0077] (1) The polymer matrix PVDF (Mw≈6×10) 5 Dry under vacuum at 80℃ for 12 h.

[0078] (2) Take 2 g PVDF and 20 mg AIBN and add them to 100 mL N-methylpyrrolidone. Stir at 60 °C for 6 h until completely dissolved. After cooling to room temperature, add 500 µL of 0.5 M LiTFSI solution (solvent: N-methylpyrrolidone), stir for 1 h, and cast into a film. Dry at 60 °C for 6 h, then vacuum dry at 100 °C for 12 h, and finally anneal at 90 °C for 2 h to obtain a solid electrolyte membrane (thickness 74 μm). In this comparative example, the ionic conductivity of the electrolyte is 1.1 × 10⁻⁶. -4 mS / cm.

[0079] Comparative Example 2

[0080] The preparation method of the solid electrolyte membrane in this comparative example differs from that in Example 1 in that azobisisobutyronitrile is not added. The specific steps are as follows:

[0081] (1) The polymer matrix PVDF (Mw≈6×10) 5 The functional group donor PEO (terminally hydroxylated, Mw≈1×10) was vacuum dried at 80℃ for 12 h. 5 Dry under vacuum at 50°C for 6 hours.

[0082] (2) 2 g of PVDF was added to 100 mL of N-methylpyrrolidone and stirred at 60 °C for 6 h until completely dissolved; 1 g of PEO was added and stirring continued until homogeneous. The temperature was raised to 120 °C and reacted under nitrogen protection for 5 h. After cooling to room temperature, 500 µL of 0.5 M LiTFSI solution (solvent: N-methylpyrrolidone) was added, and the mixture was stirred for 1 h. The mixture was then cast into a film (approximately 76 μm thick), dried at 60 °C for 6 h, vacuum dried at 100 °C for 12 h, and finally annealed at 90 °C for 2 h to obtain a solid electrolyte membrane. In this comparative example, the electrolyte microphases were separated, and the polymer and lithium salt alternating between light and dark regions. The ionic conductivity of the electrolyte was 1.3 × 10⁻⁶. -4 mS / cm.

[0083] Comparative Example 3

[0084] The preparation method of the solid electrolyte membrane in this comparative example differs from that in Example 1 in that it uses a different grafting method. The steps are as follows:

[0085] (1) The polymer matrix PVDF, functional group donor PEO, sulfur, and triallyl isocyanurate (TAIC) were added to a planetary vacuum mixer in a ratio of 46:46:7:1. The mixing temperature of the mixer was 170℃, the running speed was 80rpm, and the mixing time was 10 hours to obtain PEO / PVDF.

[0086] (2) 2 g of PEO / PVDF and LiTFSI were dissolved in acetonitrile and stirred. The lithium salt was 25% of the polymer matrix by mass. The stirring temperature was 60℃, the stirring speed was 500 rpm, and the stirring time was 10 hours to obtain a uniformly dispersed slurry. The slurry was cast into a film, left to stand in a drying oven for 12 hours, and then dried in a vacuum drying oven at 40℃ for 6 hours to obtain a solid electrolyte membrane (approximately 107 μm thick). In this comparative example, the ionic conductivity of the electrolyte was 0.78 × 10⁻⁶. -4 The polymer electrolyte membrane thickness increased significantly with mS / cm, and the capacity retention rate at 0.5C cycle decreased to 67.1%.

[0087] Figure 1 The images show digital photographs of polymer solid electrolyte membranes prepared using three different polymer matrices, as described in Examples 1, 5, and 8. The images show that the electrolyte membrane surface is smooth and has a certain degree of light transmittance.

[0088] Figure 2 The images show SEM images of polymer solid electrolyte membranes prepared with two different functional group donors, as shown in Examples 2, 3, and 8. The images demonstrate the influence of different functional groups on the polymer crystallization behavior.

[0089] Figure 3 The figures show a comparison of the thickness of the polymer solid electrolyte membranes obtained in Examples 1-8. It can be seen from the figures that the type of polymer matrix affects the thickness of the electrolyte membrane.

[0090] Application examples

[0091] (1) The polymer solid electrolyte membranes of Examples 1-5 and Comparative Examples 1-3 were applied to stainless steel symmetric cells, and AC impedance spectra were tested at room temperature using an electrochemical workstation. The test conditions were an amplitude of 10 mV and a frequency range of 1 MHz to 0.1 Hz. Figure 4 As shown in Table 1, the test results were calculated according to formula (1). In the formula, σ is the ionic conductivity (mS / cm), where L is the thickness of the solid electrolyte membrane (cm), R is the bulk resistance value read from the AC impedance spectrum (Ω), and S is the contact area between the solid electrolyte membrane and the stainless steel electrode (cm²). 2 ).

[0092] Formula (1)

[0093] (2) The electrolyte membranes of Examples 2, 7 and Comparative Example 1 were applied to lithium symmetric batteries, and chronovoltammetry and AC impedance spectroscopy were tested. The ion transport number was calculated according to formula (2), where I o and I ss These are the initial current and the steady-state current, respectively. V is the applied polarization voltage (10 mV), R o and R ss These are the initial resistance and the steady-state resistance, respectively.

[0094] Formula (2)

[0095] from Figure 5 and Figure 6 The data shows that the ion transference numbers of the conventional SPE (Comparative Example 1), Examples 2 and 7 are 0.24, 0.85 and 0.64, respectively, indicating that the introduction of functional groups can increase the ion transference number.

[0096] (3) The electrolyte membranes of Examples 1-5, Comparative Examples 1, 3, and 5 were applied to stainless steel / lithium metal batteries for electrochemical window testing. Linear scan curves were recorded using an electrochemical workstation at a scan rate of 0.5 mV / s and a voltage range from open-circuit voltage to 7 V. The electrochemical stability windows of different solid electrolyte membranes were read based on the current rise. As shown in Table 1, the maximum electrochemical stability windows of Examples 1-5 were all higher than 4.5 V.

[0097] Table 1

[0098]

[0099] Depend on Figures 4-6 As shown in Table 1, the prepared solid polymer film has a higher electrochemical stability voltage window and ionic conductivity, which proves that the electrochemical performance of the examples is better than that of the comparative examples.

[0100] (4) The rate performance of the assembled LFP / / Li batteries was measured at different current densities using Examples 2, 5, and 7. Examples 2, 5, and 7 demonstrated excellent rate performance, with charge / discharge specific capacities of 127.9, 126.8, and 128.4 mAh / g at 2 C, respectively. Figure 7 ).

[0101] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a solid electrolyte membrane based on polymer graft crosslinking, characterized in that, The steps are as follows: (1) Dissolve the lithium salt in a solvent with a high dielectric constant to obtain solution a; (2) Add the polymer matrix, functional group donor and azobisisobutyronitrile to a polar solvent and react at 60-120℃ for 3-5 h to obtain solution b; wherein, the polymer matrix includes any one of fluoropolymers, polyacrylonitrile polymers and polyether polymers, and the functional group donor is a fluoroether group, an ether oxygen group or a carbonyl group compound monomer or oligomer; (3) The solution c obtained by mixing solution a and solution b is degassed, coated, dried and annealed to obtain a solid electrolyte membrane.

2. The method for preparing a solid electrolyte membrane based on polymer graft crosslinking according to claim 1, characterized in that, In step (1), the high dielectric constant solvent is at least one of carbonates, ethers, dimethyl sulfoxides, and amides.

3. The method for preparing a solid electrolyte membrane based on polymer graft crosslinking according to claim 2, characterized in that, In step (1), the concentration of lithium salt in solution a is 0.3-1 M.

4. The method for preparing a solid electrolyte membrane based on polymer graft crosslinking according to claim 3, characterized in that, In step (2), the polar solvent is any one of amines, ketones, amides, and polar aprotic solvents containing sulfoxide groups.

5. The method for preparing a solid electrolyte membrane based on polymer graft crosslinking according to claim 4, characterized in that, In step (2), the mass ratio of polymer matrix, functional group donor, lithium salt and azobisisobutyronitrile in solution c is 1:0.1-0.65:0.015-0.2:0.001-0.

05.

6. The method for preparing a solid electrolyte membrane based on polymer graft crosslinking according to claim 5, characterized in that, The fluoropolymer is at least one of polyvinylidene fluoride, polytetrafluoroethylene, and polyvinylidene fluoride-hexafluoropropylene copolymer; the polyacrylonitrile polymer is one or both of polyacrylonitrile or polyvinyl acrylonitrile; and the polyether polymer is any one of polypropylene oxide, fluorinated polyether, polyethylene oxide, polyethylene glycol monomethyl ether, polyethylene glycol methacrylate, polymethyl methacrylate, and polypropylene glycol.

7. The method for preparing a solid electrolyte membrane based on polymer graft crosslinking according to claim 1, characterized in that, The functional group donor is any one of polyethylene oxide, polyethylene glycol monomethyl ether, propylene carbonate, dimethyl carbonate, and perfluoroethylene oxide.

8. The method for preparing a solid electrolyte membrane based on polymer graft crosslinking according to claim 7, characterized in that, In step (3), drying refers to drying at 40-100℃ for 2-12 h and drying at 60-120℃ for 4-12 h in sequence; the annealing conditions are: treatment at 70-120℃ for 1-6 h.

9. A solid electrolyte membrane prepared by the preparation method according to any one of claims 1-8.

10. The application of the solid electrolyte membrane of claim 9 in lithium metal batteries, drones, or energy storage systems.

Images