A polymer electrolyte based on a double in-situ polymerization strategy, and a preparation method and application thereof

Abstract

The application discloses a kind of polymer electrolyte based on double in-situ polymerization strategy and preparation method and application thereof.The polymer electrolyte includes polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) base film and crosslinked polymer network formed in the polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) base film inside and surface by double in-situ polymerization reaction.The base film is immersed in crosslinked polymer precursor solution, heated to carry out double in-situ polymerization to obtain the polymer electrolyte.The crosslinked network structure of the application penetrates PVDF-HFP spherical skeleton, reduces the crystallinity of polymer electrolyte, builds continuous lithium ion transmission channel, improves electrode / electrolyte interface stability, effectively inhibits lithium dendrite growth.Lithium metal battery using the polymer electrolyte has excellent cycle stability.

Description

Technical Field

[0001] This invention belongs to the field of lithium metal battery technology, specifically, it relates to a polymer electrolyte based on a dual in-situ polymerization strategy, its preparation method, and its application. Background Technology

[0002] Lithium metal batteries possess a high theoretical specific capacity (3860 mAh•g). -1 With its low reduction potential (-3.04 V vs. standard hydrogen electrode), lithium metal batteries are considered one of the most promising next-generation high-energy-density energy storage devices. The lithium-ion transport capacity of the electrolyte and the compatibility of the electrode / electrolyte interface are key factors determining the electrochemical performance of lithium metal batteries. Traditional carbonate-based liquid electrolytes are prone to decomposition during charge and discharge, posing safety hazards such as leakage and explosion. Therefore, using polymer electrolytes to partially or completely replace liquid electrolytes is considered one of the most feasible ways to achieve safe applications of lithium metal batteries.

[0003] Polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) has become a research hotspot in polymer electrolyte matrix materials in recent years due to its high dielectric constant, good thermal stability, and electrochemical stability. Introducing inorganic fillers can improve the ionic conductivity of PVDF-HFP-based electrolytes and suppress lithium dendrite growth. However, PVDF-HFP electrolyte membranes prepared by conventional methods (such as high-boiling-point solvent evaporation) have an inherent spherical framework structure with large internal voids, resulting in discontinuous lithium-ion transport channels and sluggish ion migration kinetics, especially leading to poor cycle performance in nickel-rich cathode systems. Furthermore, existing composite polymer electrolytes still face problems such as poor interfacial contact and low ionic conductivity.

[0004] Therefore, developing a polymer electrolyte that can construct continuous lithium-ion transport channels, improve ion migration kinetics, and form a stable electrode / electrolyte interface is of great significance for the development of high-energy-density lithium metal batteries. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a polymer electrolyte based on a dual in-situ polymerization strategy, its preparation method and application, which at least improves the lithium-ion transport capacity, interface stability and electrochemical performance of the polymer electrolyte, thereby improving the cycle stability of lithium metal batteries.

[0006] To address the above technical problems, according to one aspect of the present invention, a cross-linked polymer electrolyte network based on a dual in-situ polymerization strategy is provided, comprising a polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) base film and a cross-linked polymer network formed within and on the surface of the PVDF-HFP base film via a dual in-situ polymerization reaction; the cross-linked polymer network is generated by free radical polymerization and ring-opening polymerization of glycidyl methacrylate (GMA) and acrylonitrile (AN) in the presence of an initiator and a lithium salt.

[0007] In a preferred embodiment, the mass ratio of glycidyl methacrylate (GMA) to acrylonitrile (AN) is 1:(0.5-2).

[0008] In a preferred embodiment, the initiator is azobisisobutyronitrile (AIBN), and its addition amount is 0.5-2 wt.% of the total mass of glycidyl methacrylate (GMA) and acrylonitrile (AN).

[0009] In a preferred embodiment, the lithium salt is lithium difluorooxalate borate (LiDFOB), provided in the form of a liquid electrolyte, wherein the liquid electrolyte is a ethylene carbonate / dimethyl carbonate solution of lithium difluorooxalate borate (LiDFOB).

[0010] According to another aspect of the present invention, the present invention provides a method for preparing a cross-linked network polymer electrolyte based on a dual in-situ polymerization strategy, comprising: Step 1: Completely dissolve polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) in N,N-dimethylformamide (DMF) to obtain a casting solution; pour the casting solution into a mold and vacuum dry to obtain a polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) base film; Step 2: Glycidyl methacrylate (GMA) and acrylonitrile (AN) are dissolved in a lithium-containing liquid electrolyte, and then an initiator is added to obtain a crosslinked polymer precursor solution; Step 3: Immerse the polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) base membrane obtained in Step 1 into the crosslinked polymer precursor solution obtained in Step 2, allowing the crosslinked polymer precursor solution to fully penetrate into the interior of the PVDF-HFP base membrane; then heat and polymerize at 50-70°C for 6-24 hours. Through a dual reaction of free radical polymerization and lithium salt-induced ring-opening polymerization, a crosslinked polymer network is formed in situ inside and on the surface of the PVDF-HFP base membrane, resulting in the crosslinked network polymer electrolyte.

[0011] In a preferred embodiment, in step one, the mass-to-volume ratio of polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) to N,N-dimethylformamide (DMF) is 1 g / (8-12) mL.

[0012] In a preferred embodiment, in step one, polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) is added to N,N-dimethylformamide (DMF) and stirred at 55-65°C until completely dissolved.

[0013] In a preferred embodiment, in step three, the heating polymerization temperature is 60°C and the polymerization time is 12 hours.

[0014] According to another aspect of the present invention, the present invention provides the application of cross-linked network polymer electrolytes based on a dual in-situ polymerization strategy in the preparation of lithium metal batteries.

[0015] According to another aspect of the present invention, the present invention provides a lithium metal battery comprising a positive electrode, a negative electrode, and a cross-linked network polymer electrolyte based on a dual in-situ polymerization strategy located between the positive electrode and the negative electrode.

[0016] Compared with existing technologies, the polymer electrolyte based on a dual in-situ polymerization strategy provided by this invention, in addition to possessing the basic ion conduction function of general polymer electrolytes, also forms a continuous lithium-ion transport channel, significantly improving lithium-ion migration kinetics, thereby substantially increasing the free lithium-ion concentration and ionic conductivity. The polymer electrolyte provided by this invention can significantly improve the cycle stability of lithium metal batteries and has important practical application value. Attached Figure Description

[0017] Figure 1 Scanning electron microscope image of the polymer electrolyte PGAP based on the dual in-situ polymerization strategy prepared in Example 1; Figure 2 The image shows a scanning electron microscope (SEM) image of the polymer electrolyte pH prepared in Comparative Example 1 without undergoing dual in-situ polymerization. Figure 3 Cross-sectional scanning electron microscope image of the polymer electrolyte PGAP prepared in Example 1 based on a dual in-situ polymerization strategy; Figure 4 A cross-sectional scanning electron microscope image of the polymer electrolyte pH prepared in Comparative Example 1 without undergoing dual in-situ polymerization; Figure 5 A polarizing microscope image of the polymer electrolyte PGAP prepared in Example 1 based on a dual in-situ polymerization strategy; Figure 6 A polarizing microscope image of the polymer electrolyte pH prepared in Comparative Example 1 without undergoing double in-situ polymerization. Figure 7 Electrochemical impedance spectroscopy diagrams of CR2032 coin cells assembled in Example 1 and Comparative Example 1; Figure 8 The graph shows the cycle performance of the CR2032 coin cells assembled in Example 1 and Comparative Example 1. Detailed Implementation

[0018] The overall concept of this invention is to construct a through-linked network structure in the PVDF-HFP matrix through a dual reaction of free radical polymerization and lithium salt-induced ring-opening polymerization, thereby improving the lithium-ion transport capacity, interfacial stability and electrochemical performance of the polymer electrolyte, and thus improving the capacity, rate performance and cycle stability of lithium metal batteries.

[0019] Based on the above concept, a typical embodiment of the present invention provides a cross-linked network polymer electrolyte based on a dual in-situ polymerization strategy, comprising a polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) base film and a cross-linked polymer network formed inside and on the surface of the PVDF-HFP base film through a dual in-situ polymerization reaction; the cross-linked polymer network is generated by glycidyl methacrylate (GMA) and acrylonitrile (AN) through free radical polymerization and ring-opening polymerization reactions in the presence of an initiator and a lithium salt.

[0020] The cross-linked network structure runs through the spherical skeleton of PVDF-HFP, reducing the crystallinity of the polymer electrolyte, constructing a continuous lithium-ion transport channel, improving the stability of the electrode / electrolyte interface, and effectively suppressing lithium dendrite growth.

[0021] Another typical embodiment of the present invention provides a method for preparing the cross-linked network polymer electrolyte based on the dual in-situ polymerization strategy.

[0022] Step 1: Preparation of PVDF-HFP base film Polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) was completely dissolved in N,N-dimethylformamide (DMF) to obtain a casting solution; the casting solution was poured into a flat-bottomed polytetrafluoroethylene mold and dried under vacuum to obtain a polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) base film.

[0023] For example, the polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) base film is cut into circular pieces with a diameter of 19 mm for later use.

[0024] The mass-to-volume ratio of the polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) to N,N-dimethylformamide (DMF) is 1 g / (8-12) mL, for example: 1 g / 8 mL, 1 g / 10 mL, 1 g / 12 mL, etc., with the preferred mass-to-volume ratio being 1 g / 10 mL.

[0025] Polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) is added to N,N-dimethylformamide (DMF) and stirred at 55-65°C until completely dissolved. Exemplarily, the stirring temperature can be 55°C, 60°C, 65°C, etc., with 60°C being preferred. The stirring time is 10-14 hours, for example: 10 hours, 12 hours, 14 hours, etc., with 12 hours being preferred.

[0026] The vacuum drying temperature is 55-65°C, for example: 55°C, 60°C, 65°C, etc., with 60°C being the preferred drying temperature; the drying time is 10-14 hours, for example: 10 hours, 12 hours, 14 hours, etc., with 12 hours being the preferred drying time.

[0027] Step 2: Prepare the crosslinking polymer precursor solution In an argon-protected glove box, glycidyl methacrylate (GMA) and acrylonitrile (AN) were dissolved in a lithium-containing liquid electrolyte, and then an initiator was added to obtain a crosslinked polymer precursor solution.

[0028] The mass ratio of glycidyl methacrylate (GMA) to acrylonitrile (AN) is 1:(0.5-2). Exemplary examples include mass ratios of GMA to AN of 1:0.5, 1:0.8, 1:1, 1:1.5, 1:2, etc., with a preferred mass ratio of 1:1.

[0029] The initiator is azobisisobutyronitrile (AIBN), and its addition amount is 0.5-2 wt.% of the total mass of glycidyl methacrylate (GMA) and acrylonitrile (AN). For example, the addition amount of AIBN is 0.5 wt.%, 0.8 wt.%, 1.0 wt.%, 1.5 wt.%, 2 wt.%, etc., of the total mass of GMA and AN, preferably 1 wt.%.

[0030] The lithium salt is lithium difluorooxalate borate (LiDFOB), provided in the form of a liquid electrolyte, which is an ethylene carbonate (EC) / dimethyl carbonate (DMC) solution of lithium difluorooxalate borate (LiDFOB).

[0031] Preferably, the liquid electrolyte is a 1 M LiDFOB EC / DMC solution with a volume ratio of EC / DMC of 1:1.

[0032] Step 3, Dual In-Situ Polymerization The polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) base membrane obtained in step one is immersed in the crosslinked polymer precursor solution obtained in step two, allowing the crosslinked polymer precursor solution to fully penetrate into the interior of the PVDF-HFP base membrane. Then, it is heated for polymerization, and through a dual reaction of free radical polymerization and lithium salt-induced ring-opening polymerization, a crosslinked polymer network is formed in situ inside and on the surface of the PVDF-HFP base membrane, resulting in the crosslinked network polymer electrolyte.

[0033] The heating polymerization temperature is 50-70°C, such as 50°C, 55°C, 60°C, 65°C, 70°C, etc., with a preferred heating polymerization temperature of 60°C; the heating polymerization time is 6-24 hours, such as 6 hours, 7 hours, 10 hours, 12 hours, 18 hours, 24 hours, etc., with a preferred heating polymerization time of 12 hours.

[0034] More specifically, in an argon-protected glove box, the PVDF-HFP base film obtained in step one is placed in a button cell housing, and the crosslinked polymer precursor solution obtained in step two is dropped onto both sides of the PVDF-HFP base film to allow the precursor solution to fully penetrate into the interior of the PVDF-HFP base film.

[0035] The battery casing is then assembled, and the assembled battery is placed on a heating stage for polymerization. During this process, GMA and AN in the crosslinking polymer precursor solution generate copolymer segments through free radical polymerization, while the epoxy groups in GMA undergo ring-opening polymerization under the induction of LiDFOB, forming a crosslinked network structure that runs through the PVDF-HFP matrix.

[0036] The polymer electrolyte of the dual in-situ polymerization strategy provided in the above embodiments is matched with the lithium iron phosphate (LFP) positive electrode to assemble a lithium metal battery, with the negative electrode being metallic lithium.

[0037] The technical solutions claimed in this invention will be further described below through some embodiments. However, the embodiments and comparative examples are for explaining the implementation schemes of this invention and do not exceed the scope of the subject matter of this invention. The scope of protection of this invention is not limited by the embodiments. Unless otherwise specified, the materials and reagents used in this invention can be obtained from commercially available products in the art.

[0038] Example 1 1.0 g of polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) was dissolved in 10 mL of N,N-dimethylformamide (DMF) and stirred continuously at 60°C for 12 hours. The resulting casting solution was poured into a flat-bottomed polytetrafluoroethylene mold and dried overnight in a vacuum oven at 60°C to obtain a PVDF-HFP base film, which was then cut into discs with a diameter of 19 mm for later use. Under argon protection, 0.5 g of glycidyl methacrylate (GMA) and 0.5 g of acrylonitrile (AN) were dissolved in 10 mL of liquid electrolyte (1 M LiDFOB EC / DMC solution, EC:DMC volume ratio 1:1), and stirred at room temperature for 1 hour. Then, 10 mg of azobisisobutyronitrile (AIBN, accounting for 1 wt.% of the total mass of GMA and AN) was added, and stirring was continued for 1 hour to obtain a crosslinked polymer precursor solution. In an argon-protected glove box, the PVDF-HFP base film was placed in the coin cell casing, and 20 μL of crosslinked polymer precursor solution was dropped onto each side of the base film to allow the precursor solution to fully penetrate into the base film. The assembled battery was then placed on a 60°C heating stage and heated for 12 hours for polymerization. Through a dual reaction of free radical polymerization and lithium salt-induced ring-opening polymerization, a crosslinked network polymer electrolyte, denoted as PGAP, was formed in situ inside the PVDF-HFP matrix.

[0039] Comparative Example 1 The difference from Example 1 is that: no double in-situ polymerization is performed, and only pure PVDF-HFP base film is used as electrolyte.

[0040] 1.0 g of PVDF-HFP was dissolved in 10 mL of DMF and stirred at 60°C for 12 hours. The casting solution was poured into a flat-bottomed PTFE mold and dried overnight in a vacuum oven at 60°C to obtain the PVDF-HFP electrolyte membrane, denoted as PH. The PH membrane was cut into discs with a diameter of 19 mm and used directly for battery assembly without in-situ polymerization.

[0041] Comparative Example 2 The difference from Example 1 is that acetonitrile (ACN) is used as the solvent in this comparative example.

[0042] 1.0 g of polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) was dissolved in 10 mL of acetonitrile (ACN), and stirred continuously at 60°C for 12 hours. The resulting casting solution was poured into a flat-bottomed polytetrafluoroethylene mold and dried overnight in a vacuum oven at 60°C to obtain a PVDF-HFP base film, which was then cut into discs with a diameter of 19 mm for later use. Under argon protection, 0.5 g of glycidyl methacrylate (GMA) and 0.5 g of acrylonitrile (AN) were dissolved in 10 mL of liquid electrolyte (1 M LiDFOB EC / DMC solution, EC:DMC volume ratio 1:1), and stirred at room temperature for 1 hour. Then, 10 mg of azobisisobutyronitrile (AIBN, accounting for 1 wt.% of the total mass of GMA and AN) was added, and stirring was continued for 1 hour to obtain a crosslinked polymer precursor solution. In an argon-protected glove box, the PVDF-HFP base film was placed in the coin cell housing, and 20 μL of crosslinked polymer precursor solution was dropped onto each side of the base film to allow the precursor solution to fully penetrate into the base film. The assembled battery was then placed on a 60°C heating stage and heated for 12 hours for polymerization. Through a dual reaction of free radical polymerization and lithium salt-induced ring-opening polymerization, a crosslinked network polymer electrolyte was formed in situ inside the PVDF-HFP matrix.

[0043] Comparative Example 3 The difference from Example 1 is that tetrahydrofuran (THF) is used as the solvent in this comparative example.

[0044] 1.0 g of polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) was dissolved in 10 mL of tetrahydrofuran (THF) and stirred continuously at 60°C for 12 hours. The resulting casting solution was poured into a flat-bottomed PTFE mold and dried overnight in a vacuum oven at 60°C to obtain a PVDF-HFP base film, which was then cut into discs with a diameter of 19 mm for later use. Under argon protection, 0.5 g of glycidyl methacrylate (GMA) and 0.5 g of acrylonitrile (AN) were dissolved in 10 mL of liquid electrolyte (1 M LiDFOB EC / DMC solution, EC:DMC volume ratio 1:1), and stirred at room temperature for 1 hour. Then, 10 mg of azobisisobutyronitrile (AIBN, accounting for 1 wt.% of the total mass of GMA and AN) was added, and stirring was continued for 1 hour to obtain a crosslinked polymer precursor solution. In an argon-protected glove box, the PVDF-HFP base film was placed in the coin cell housing, and 20 μL of crosslinked polymer precursor solution was dropped onto each side of the base film to allow the precursor solution to fully penetrate into the base film. The assembled battery was then placed on a 60°C heating stage and heated for 12 hours for polymerization. Through a dual reaction of free radical polymerization and lithium salt-induced ring-opening polymerization, a crosslinked network polymer electrolyte was formed in situ inside the PVDF-HFP matrix.

[0045] Comparative Example 4 The difference from Example 1 is that N-methylpyrrolidone (NMP) is used as the solvent in this comparative example.

[0046] 1.0 g of polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) was dissolved in 10 mL of N-methylpyrrolidone (NMP) and stirred continuously at 60°C for 12 hours. The resulting casting solution was poured into a flat-bottomed polytetrafluoroethylene mold and dried overnight in a vacuum oven at 60°C to obtain a PVDF-HFP base film, which was then cut into 19 mm diameter discs for later use. Under argon protection, 0.5 g of glycidyl methacrylate (GMA) and 0.5 g of acrylonitrile (AN) were dissolved in 10 mL of liquid electrolyte (1 M LiDFOB EC / DMC solution, EC to DMC volume ratio 1:1) and stirred at room temperature for 1 hour. Then, 10 mg of azobisisobutyronitrile (AIBN, accounting for 1 wt.% of the total mass of GMA and AN) was added, and stirring was continued for 1 hour to obtain a crosslinking polymer precursor solution. In an argon-protected glove box, the PVDF-HFP base film was placed in a coin cell casing, and 20 mg of [unspecified substance] was dropped onto each side of the base film. A μL crosslinked polymer precursor solution was prepared to allow the precursor solution to fully penetrate into the base membrane. The assembled battery was then placed on a 60°C heating stage and heated for 12 hours to polymerize. Through a dual reaction of free radical polymerization and lithium salt-induced ring-opening polymerization, a crosslinked network polymer electrolyte was formed in situ inside the PVDF-HFP matrix.

[0047] Comparative Example 5 The difference from Example 1 is that this comparative example uses methyl methacrylate (MMA) and acrylonitrile (AN) monomers.

[0048] 1.0 g of polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) was dissolved in 10 mL of tetrahydrofuran (THF) and stirred continuously at 60°C for 12 hours. The resulting casting solution was poured into a flat-bottomed PTFE mold and dried overnight in a vacuum oven at 60°C to obtain a PVDF-HFP base film, which was then cut into 19 mm diameter discs for later use. Under argon protection, 0.5 g of methyl methacrylate (MMA) and 0.5 g of acrylonitrile (AN) were dissolved in 10 mL of liquid electrolyte (1 M LiDFOB EC / DMC solution, EC to DMC volume ratio 1:1), and stirred at room temperature for 1 hour. Then, 10 mg of azobisisobutyronitrile (AIBN, accounting for 1 wt.% of the total mass of GMA and AN) was added, and stirring was continued for 1 hour to obtain a crosslinking polymer precursor solution. In an argon-protected glove box, the PVDF-HFP base film was placed in a coin cell casing, and 20 mg of [unspecified substance] was dropped onto each side of the base film. A μL crosslinked polymer precursor solution was prepared to allow the precursor solution to fully penetrate into the base membrane. The assembled battery was then placed on a 60°C heating stage and heated for 12 hours to polymerize. Through a dual reaction of free radical polymerization and lithium salt-induced ring-opening polymerization, a crosslinked network polymer electrolyte was formed in situ inside the PVDF-HFP matrix.

[0049] Comparative Example 6 The difference from Example 1 is that this comparative example uses polyethylene glycol diacrylate (PEGDA) and acrylonitrile (AN) monomers.

[0050] 1.0 g of polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) was dissolved in 10 mL of tetrahydrofuran (THF) and stirred continuously at 60°C for 12 hours. The resulting casting solution was poured into a flat-bottomed PTFE mold and dried overnight in a vacuum oven at 60°C to obtain a PVDF-HFP base film, which was then cut into 19 mm diameter discs for later use. Under argon protection, 0.5 g of polyethylene glycol diacrylate (PEGDA) and 0.5 g of acrylonitrile (AN) were dissolved in 10 mL of liquid electrolyte (1 M LiDFOB EC / DMC solution, EC to DMC volume ratio 1:1), and stirred at room temperature for 1 hour. Then, 10 mg of azobisisobutyronitrile (AIBN, accounting for 1 wt.% of the total mass of GMA and AN) was added, and stirring was continued for 1 hour to obtain a crosslinking polymer precursor solution. In an argon-protected glove box, the PVDF-HFP base film was placed in a coin cell casing, and 20 mg of [unspecified substance] was dropped onto each side of the base film. A μL crosslinked polymer precursor solution was prepared to allow the precursor solution to fully penetrate into the base membrane. The assembled battery was then placed on a 60°C heating stage and heated for 12 hours to polymerize. Through a dual reaction of free radical polymerization and lithium salt-induced ring-opening polymerization, a crosslinked network polymer electrolyte was formed in situ inside the PVDF-HFP matrix.

[0051] Comparative Example 7 The difference from Example 1 is that this comparative example uses glycidyl methacrylate (GMA) and ethoxylated trimethylolpropane triacrylate (ETPTA) monomers.

[0052] 1.0 g of polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) was dissolved in 10 mL of tetrahydrofuran (THF) and stirred continuously at 60°C for 12 hours. The resulting casting solution was poured into a flat-bottomed PTFE mold and dried overnight in a vacuum oven at 60°C to obtain a PVDF-HFP base film, which was then cut into discs with a diameter of 19 mm for later use. Under argon protection, 0.5 g of glycidyl methacrylate (GMA) and 0.5 g of ethoxylated trimethylolpropane triacrylate (ETPTA) were dissolved in 10 mL of liquid electrolyte (1 M LiDFOB EC / DMC solution, EC:DMC volume ratio 1:1), and stirred at room temperature for 1 hour. Then, 10 mg of azobisisobutyronitrile (AIBN, accounting for 1% of the total mass of GMA and AIBN) was added. (wt.%), continue stirring for 1 hour to obtain a crosslinked polymer precursor solution; in an argon-protected glove box, place the PVDF-HFP base film in the coin cell housing, and add 20 μL of crosslinked polymer precursor solution to each side of the base film to allow the precursor solution to fully penetrate into the base film. Then, place the assembled battery on a 60°C heating stage and heat for polymerization for 12 hours. Through the dual reactions of free radical polymerization and lithium salt-induced ring-opening polymerization, a crosslinked network polymer electrolyte is formed in situ inside the PVDF-HFP matrix.

[0053] Comparative Example 8 The difference from Example 1 is that this comparative example uses glycidyl methacrylate (GMA) and 2,2,2-trifluoroethanol (TFEA) monomers.

[0054] 1.0 g of polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) was dissolved in 10 mL of tetrahydrofuran (THF) and stirred continuously at 60°C for 12 hours. The resulting casting solution was poured into a flat-bottomed PTFE mold and dried overnight in a vacuum oven at 60°C to obtain a PVDF-HFP base film, which was then cut into discs with a diameter of 19 mm for later use. Under argon protection, 0.5 g of glycidyl methacrylate (GMA) and 0.5 g of 2,2,2-trifluoroethanol (TFEA) were dissolved in 10 mL of liquid electrolyte (1 M LiDFOB EC / DMC solution, EC:DMC volume ratio 1:1), and stirred at room temperature for 1 hour. Then, 10 mg of azobisisobutyronitrile (AIBN, accounting for 1% of the total mass of GMA and AIBN) was added. (wt.%), continue stirring for 1 hour to obtain a crosslinked polymer precursor solution; in an argon-protected glove box, place the PVDF-HFP base film in the coin cell housing, and add 20 μL of crosslinked polymer precursor solution to each side of the base film to allow the precursor solution to fully penetrate into the base film. Then, place the assembled battery on a 60°C heating stage and heat for polymerization for 12 hours. Through the dual reactions of free radical polymerization and lithium salt-induced ring-opening polymerization, a crosslinked network polymer electrolyte is formed in situ inside the PVDF-HFP matrix.

[0055] Comparative Example 9 The difference from Example 1 is that this comparative example uses glycidyl methacrylate (GMA) and triethylene glycol dimethacrylate (TEGDMA) monomers.

[0056] 1.0 g of polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) was dissolved in 10 mL of tetrahydrofuran (THF) and stirred continuously at 60°C for 12 hours. The resulting casting solution was poured into a flat-bottomed PTFE mold and dried overnight in a vacuum oven at 60°C to obtain a PVDF-HFP base film, which was then cut into discs with a diameter of 19 mm for later use. Under argon protection, 0.5 g of glycidyl methacrylate (GMA) and 0.5 g of triethylene glycol dimethacrylate (TEGDMA) were dissolved in 10 mL of liquid electrolyte (1 M LiDFOB EC / DMC solution, EC to DMC volume ratio 1:1), and stirred at room temperature for 1 hour. Then, 10 mg of azobisisobutyronitrile (AIBN, accounting for 1% of the total mass of GMA and AIBN) was added. (wt.%), continue stirring for 1 hour to obtain a crosslinked polymer precursor solution; in an argon-protected glove box, place the PVDF-HFP base film in the coin cell housing, and add 20 μL of crosslinked polymer precursor solution to each side of the base film to allow the precursor solution to fully penetrate into the base film. Then, place the assembled battery on a 60°C heating stage and heat for polymerization for 12 hours. Through the dual reactions of free radical polymerization and lithium salt-induced ring-opening polymerization, a crosslinked network polymer electrolyte is formed in situ inside the PVDF-HFP matrix.

[0057] The electrolytes prepared in the examples and comparative examples were used to assemble CR2032 coin cells, and the corresponding battery performance was tested. The battery structure included placing a negative electrode shell, a lithium sheet, a separator (PVDF-HFP base film), a positive electrode sheet, and a positive electrode shell in sequence in the coin cell. Precursor solutions were injected on both sides of the separator, and then the mixture was heated to polymerize. For Comparative Example 1, a pH membrane was directly used as the electrolyte to assemble the battery.

[0058] The batteries of the examples and comparative examples were assembled and tested to detect their performance. The results are shown in Table 1.

[0059] Table 1 Electrochemical performance of each example and comparative example

[0060] By comparing Example 1 with Comparative Examples 1-9, Example 1 has a higher first-cycle discharge specific capacity and a higher 30-cycle discharge specific capacity.

[0061] pass Figure 1-2It can be observed that the PGAP polymer electrolyte prepared using Example 1 of this invention exhibits a relatively dense surface morphology, with the cross-linked network structure uniformly distributed in the polymer matrix and no obvious phase separation phenomenon, indicating that the GMA-AN cross-linked network has good compatibility with the PVDF-HFP matrix. In contrast, the PH polymer electrolyte prepared in Comparative Example 1 shows a distributed porous structure. Such pores may lead to structural instability, rapid capacity decay, and shortened cycle life during battery cycling.

[0062] pass Figure 3-4 It can be observed that the PGAP polymer electrolyte of Example 1 of the present invention is thinner, at 90 μm, which is beneficial for shortening the lithium ion transport path; while the PH polymer electrolyte of Comparative Example 1 is thicker, at 100 μm, which is not conducive to the rapid migration of lithium ions.

[0063] pass Figure 5-6 It can be observed that the PGAP polymer electrolyte of Example 1 of the present invention exhibits a darker field of view and negligible extinction phenomenon under a polarizing microscope, indicating that the introduction of the cross-linked GMA-AN network disrupts the ordered arrangement of polymer molecules. In contrast, the PH polymer electrolyte exhibits a brighter surface morphology and obvious extinction phenomenon under a polarizing microscope, indicating its high crystallinity.

[0064] pass Figure 7 As can be seen, the intrinsic impedance of the PGAP polymer electrolyte in Example 1 of this invention is 2.5 Ω, while the intrinsic impedance of the PH polymer electrolyte in Comparative Example 1 is 5.4 Ω. This indicates that the PGAP polymer electrolyte is beneficial for the rapid transport of lithium ions inside the battery.

[0065] pass Figure 8 It can be seen that the Li / PGAP / LFP battery of Example 1 of the present invention can still maintain a high discharge specific capacity of 136.2 mAh g after 30 cycles at 1 C rate. -1 In contrast, the Li / PH / LFP battery of Comparative Example 1 exhibited a significantly lower discharge specific capacity of 120.8 mAh g after 30 cycles. -1 This indicates that the Li / PGAP / LFP battery has superior electrochemical performance.

[0066] In summary, the polymer electrolyte PGAP based on the dual in-situ polymerization strategy provided in this application has better performance and significantly improves the cycle stability of lithium metal batteries.

Claims

1. A cross-linked network polymer electrolyte based on a dual in-situ polymerization strategy, characterized in that: It includes a polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) base film and a cross-linked polymer network formed inside and on the surface of the PVDF-HFP base film by a dual in-situ polymerization reaction; the cross-linked polymer network is generated by glycidyl methacrylate (GMA) and acrylonitrile (AN) in the presence of an initiator and a lithium salt via free radical polymerization and ring-opening polymerization.

2. The cross-linked network polymer electrolyte according to claim 1, characterized in that: The mass ratio of glycidyl methacrylate (GMA) to acrylonitrile (AN) is 1:(0.5-2).

3. The cross-linked network polymer electrolyte according to claim 1, characterized in that: The initiator is azobisisobutyronitrile (AIBN), and its addition amount is 0.5-2 wt.% of the total mass of glycidyl methacrylate (GMA) and acrylonitrile (AN).

4. The cross-linked network polymer electrolyte according to claim 1, characterized in that: The lithium salt is lithium difluorooxalate borate (LiDFOB), provided in the form of a liquid electrolyte, which is a ethylene carbonate / dimethyl carbonate solution of lithium difluorooxalate borate (LiDFOB).

5. The method for preparing the cross-linked network polymer electrolyte based on a dual in-situ polymerization strategy according to any one of claims 1-4, characterized in that, include: Step 1: Completely dissolve polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) in N,N-dimethylformamide (DMF) to obtain a casting solution; pour the casting solution into a mold and vacuum dry to obtain a polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) base film; Step 2: Glycidyl methacrylate (GMA) and acrylonitrile (AN) are dissolved in a lithium-containing liquid electrolyte, and then an initiator is added to obtain a crosslinked polymer precursor solution; Step 3: Immerse the polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) base membrane obtained in Step 1 into the crosslinked polymer precursor solution obtained in Step 2, allowing the crosslinked polymer precursor solution to fully penetrate into the interior of the PVDF-HFP base membrane; then heat and polymerize at 50-70°C for 6-24 hours. Through a dual reaction of free radical polymerization and lithium salt-induced ring-opening polymerization, a crosslinked polymer network is formed in situ inside and on the surface of the PVDF-HFP base membrane, resulting in the crosslinked network polymer electrolyte.

6. The preparation method according to claim 5, characterized in that: In step one, the mass-to-volume ratio of polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) to N,N-dimethylformamide (DMF) is 1 g / (8-12) mL.

7. The preparation method according to claim 5 or 6, characterized in that: In step one, polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) is added to N,N-dimethylformamide (DMF) and stirred at 55-65°C until completely dissolved.

8. The preparation method according to claim 7, characterized in that: In step three, the heating polymerization temperature is 60°C and the polymerization time is 12 hours.

9. The application of the cross-linked network polymer electrolyte based on the dual in-situ polymerization strategy according to any one of claims 1-4 in the preparation of lithium metal batteries.

10. A lithium metal battery, comprising a positive electrode and a negative electrode, characterized in that, It also includes the cross-linked network polymer electrolyte based on a dual in-situ polymerization strategy as described in any one of claims 1-4, located between the positive and negative electrodes.

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