Method for preparing solid polymer electrolyte by UV (ultraviolet) photo-initiated tandem cationic polymerization

Abstract

The invention relates to a method for preparing a solid polymer electrolyte by UV photo-initiated tandem cationic polymerization. The method comprises the following steps: mixing a free radical polymerization monomer, a cationic polymerization monomer, an initiator and a lithium salt, carrying out light free radical polymerization under ultraviolet irradiation to obtain a free radical polymerization prepolymer, carrying out extrusion primary shaping on the free radical polymerization prepolymer, and carrying out series cationic polymerization to prepare the solid electrolyte. The solid electrolyte has the characteristics of environment friendliness, good stability, safety in use and difficulty in liquid leakage, does not use redundant monomers and solvents, and can realize rapid and batch production of the solid electrolyte.

Description

Technical field:

[0001] The present invention relates to the field of lithium-ion batteries, and more particularly to a method for preparing a solid polymer electrolyte by UV-light-induced tandem cationic polymerization. Background technology:

[0002] With the continuous advancement of technology and the increasing demand for high energy density and safety performance in markets such as electric vehicles and portable electronic devices, solid-state batteries have gradually attracted widespread attention as a new battery technology. Compared with traditional liquid electrolyte batteries, solid-state batteries use solid electrolytes instead of liquid electrolytes and offer many significant advantages, such as higher energy density, improved safety, and longer service life. The research and application of solid-state electrolytes has become a key direction in the development of battery technology. Traditional lithium-ion batteries are widely used in various electronic products, and one of their core components is liquid electrolytes. While liquid electrolytes play an important role in these batteries, they also have certain shortcomings. For example, liquid electrolytes can cause internal short circuits in the battery, increasing the risk of fire and explosion. Furthermore, the chemical stability and ionic conductivity of liquid electrolytes decrease at high temperatures, limiting the battery's operating temperature range and energy density. By replacing traditional liquid electrolytes, solid-state electrolytes overcome many of the shortcomings of liquid electrolyte batteries. Solid-state electrolytes not only have higher chemical stability but also generally exhibit better thermal stability. This allows solid-state batteries to maintain high performance even at high temperatures and reduces the risk of thermal runaway. At the same time, the use of solid-state electrolytes can significantly improve the energy density of batteries, because solid-state electrolytes can allow the use of higher lithium metal negative electrodes, thereby increasing the energy storage capacity of the battery. Solid-state electrolytes have many advantages, but they also face some challenges in practical applications. First, the ionic conductivity of solid-state electrolytes is usually lower than that of liquid electrolytes, which limits the charge and discharge speed of the battery. Second, poor interface contact between solid-state electrolytes and electrode materials may lead to increased internal resistance, thereby affecting the overall performance of the battery. In addition, the manufacturing process of solid-state electrolytes is complex and the cost is high, which to some extent restricts their large-scale production and commercial application.

[0003] Electrolytes are an indispensable component of the battery industry. The use of solid-state electrolytes not only enables safer and more efficient power storage but also improves the user experience. Patent CN 119315124A synthesizes a cross-linked polyether-based solid electrolyte using free radical photopolymerization. However, its thickness is difficult to adjust during the synthesis process. Therefore, a solid-state electrolyte with easily adjustable electrolyte thickness, industrial production capability, excellent safety, and environmental friendliness is urgently needed. Summary of the invention:

[0004] To address the current challenges of high manufacturing costs, difficult manufacturing processes, and difficulty in industrial production of solid-state electrolytes, this invention proposes a method for preparing solid-state electrolytes using UV-light-induced tandem cationic polymerization. This method involves mixing free radical polymerization monomers, cationic polymerization monomers, an initiator, and a lithium salt, followed by photo-radical polymerization under UV light to produce a free radical polymerization prepolymer. The free radical polymerization prepolymer is then initially shaped and then subjected to tandem cationic polymerization to produce the solid-state electrolyte. The solid-state electrolyte prepared by this method is environmentally friendly, stable, safe, and leak-resistant. This method utilizes bulk polymerization, using photo-radical-polymerizable monomers such as acrylic acid and cationically polymerizable monomers such as glycerol methacrylate, to prepare the solid polymer electrolyte through UV-light-induced free radical polymerization and tandem cationic polymerization. This method first produces a prepolymer through photo-induced free radical polymerization of photo-radical-polymerizable monomers, followed by tandem cationic polymerization to introduce the epoxy group into the solid-state electrolyte. This method eliminates the use of excess monomers and solvents, enabling rapid, mass-produced production of solid-state electrolytes.

[0005] The technical solution of the present invention is:

[0006] A method for preparing a solid polymer electrolyte by UV light-initiated tandem cationic polymerization, the method comprising the following steps:

[0007] S1: mixing a photopolymerization monomer, a cationic polymerization monomer, a lithium salt, a photopolymerization initiator, and a cationic polymerization initiator, and magnetically stirring at 20-30° C. for 3-5 hours to obtain a mixed material;

[0008] Wherein, the photoinitiated polymerization monomer accounts for 20-60% of the mass of the mixed material; the cationic polymerization monomer accounts for 10-30% of the mass of the mixed material; and the lithium salt accounts for 15-30% of the mass of the mixed material;

[0009] The photopolymerization initiator accounts for 0.5-5% of the mass of the mixed material; the cationic polymerization initiator accounts for 10-20% of the mass of the mixed material;

[0010] The photoinitiated polymerization monomer is one or more of ethylene glycol diacrylate (BPA), methacryloyl glycidyl ester (GAM), 2-[[[(1,6-dihydro-4-methyl-6-oxo-2-pyrimidinyl)amino]carbonyl]amino]ethyl 2-methacrylate (UPyMA), ethylene glycol methyl ether acrylate (EGDMA), methyl methacrylate (MMA), vinyl pyrrolidone (VP), bisphenol A epoxy resin, and acrylic acid (AA);

[0011] The cationic polymerization monomer is one or more of hydroxybutyl vinyl ether (HBVE), 3,3-bis(chloromethyl)oxetane (BCMO), 1,3-dioxolane (DOL), trioxane (TXE), and ethylene glycol diglycidyl ether (EGDE);

[0012] The lithium salt is lithium bis(trifluoromethanesulfonyl)imide (LiTFSI);

[0013] The cationic polymerization initiator is lithium difluorooxalatoborate (LiDFOB);

[0014] The photopolymerization initiator is TPO.

[0015] S2: transferring the mixture obtained in step S1 into a reactor and reacting it under ultraviolet light for 10-300 seconds to obtain a photo-free radical polymerization prepolymer, i.e., a solid polymer electrolyte prepolymer;

[0016] The wavelength range of the ultraviolet light is 315-400 nm, and the distance between the ultraviolet lamp and the mixture is 3-20 cm.

[0017] S3: slowly extruding through a twin-roll extruder while dripping the photo-radical polymerization prepolymer obtained in step S2 to preliminarily shape the solid electrolyte membrane;

[0018] The gap thickness of the double-roll laminator is 0.1-1 mm;

[0019] Release paper of the release film;

[0020] The slow extrusion has an extrusion rate of 0.5-5 min -1 .

[0021] S2: cationic polymerization of the solid electrolyte membrane produced in step S1 in a vacuum oven at 40-100° C. for 18-30 hours to obtain a solid electrolyte membrane;

[0022] Application of UV light-initiated tandem cationic polymerization prepared by the method to prepare solid polymers for solid electrolyte materials in lithium-ion batteries;

[0023] In the lithium-ion battery, the positive electrode is sulfur and the negative electrode is a lithium sheet.

[0024] The essential features of the present invention are:

[0025] The present invention addresses the technical problems of solid electrolyte synthesis methods, optimizes traditional free radical polymerization methods, and proposes a new method for preparing solid electrolytes by UV light-initiated polymerization and cationic polymerization in series. The method comprises the following steps: using photo-free radical polymerization monomers and cationic polymerization monomers, firstly synthesizing a copolymer prepolymer of multiple monomers by ultraviolet light-initiated free radical polymerization, then drawing a film between two layers of release paper using a twin-roll extruder, and then subjecting the film to cationic polymerization to obtain a polymerized solid polymer electrolyte with high ionic conductivity, good stability, and mass production capability. Compared with traditional free radical polymerization solid electrolytes, the method does not use excess solvents, has good film-forming properties, and is highly environmentally friendly.

[0026] The beneficial effects of the present invention are:

[0027] The beneficial effect of the present invention is that free radical photopolymerizable monomers such as acrylic acid and glycidyl acrylate and cationic polymerizable monomers such as dioxolane and glycidyl acrylate can be polymerized in series to form random copolymers through a method of free radical photopolymerization in series with cationic polymerization. This method can achieve solvent-free and industrialized continuous production. 1,3-Dioxolane (DOL) as a cyclic ether small molecule solvent and reactive monomer has a high dielectric constant (ε=7.1), strong lithium salt dissociation and room temperature ion transport capabilities. Adding DOL can have higher room temperature ion conductivity, adjustable mechanical strength, reduced crystallization tendency and simplified preparation process flow; adding acrylic acid can improve the flexibility and mechanical properties of the solid electrolyte and improve the processability of the membrane; promote ion migration, enhance ionic conductivity, and have good compatibility with other polymers or electrolyte components, which helps to improve the overall performance. By optimizing the monomer content, the performance of the solid electrolyte is greatly improved; lithium difluorooxalatoborate can be used as an initiator to initiate cationic polymerization, and as a lithium salt additive, it can increase the conductivity of the electrolyte. The solid polymer electrolyte prepared by UV light-initiated polymerization and cationic polymerization can still maintain 90% of the original after 500 cycles, and the capacity can also be maintained at 80% of the original battery, which has a good effect on improving battery performance and is of great significance for the research and development of lithium batteries. Description of the drawings:

[0028] Figure 1 ionic conductivity-temperature diagrams of Examples 1-4 and Comparative Example 1;

[0029] Figure 2 The tension-deformation diagrams of Examples 1-3 and Comparative Example 1 are shown;

[0030] Figure 3 Specific capacity / Coulombic efficiency-cycle number diagram of the long cycle performance diagram of Example 1 and Comparative Example 1. Specific implementation methods:

[0031] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific implementations described herein are only used to explain the present invention and are not intended to limit the present invention.

[0032] The primary function of solid-state electrolytes is to act as ion conductors, providing pathways for ion conduction in batteries or fuel cells while simultaneously blocking the passage of electrons, thereby enabling electrochemical reactions. Their high ionic conductivity, excellent thermal stability, and mechanical strength enable improvements in energy density and safety, and are widely used in novel energy storage and conversion devices.

[0033] The present invention uses a photopolymerization and cationic polymerization method to synthesize a solid electrolyte with strong ionic conductivity and stable performance in a short period of time. This method improves ionic conductivity while also achieving solvent-free and industrially scalable continuous production.

[0034]

[0035] The twin-roll extruder was initially finalized;

[0036]

[0037] The reaction process of the present invention is shown in the figure above: 2-[[[(1,6-dihydro-4-methyl-6-oxo-2-pyrimidinyl)amino]carbonyl]amino]ethyl 2-methacrylate, vinyl pyrrolidone, acrylic acid and glycidyl methacrylate are used as free radical polymerization monomers to undergo free radical polymerization under the initiation of ultraviolet light to obtain a photo-free radical polymerization prepolymer obtained by photo-free radical polymerization. A twin-roll extruder is then used to preliminarily shape the obtained photo-free radical polymerization prepolymer, and then the prepolymer is placed in an oven for cationic polymerization to obtain a solid electrolyte. Methacryloyl glycidyl ester can be cationic polymerized with epoxy monomers such as trioxane and 1,3-dioxolane to obtain a solid electrolyte polymer.

[0038] The following example is a method for preparing a high-temperature rapid cross-linking polyhydroxyacrylate emulsion.

[0039] Example 1:

[0040] S1: Preparation of polymer precursor: 1.8 g vinyl pyrrolidone (VP), 2.84 g glycidyl methacrylate (GAM), 0.72 g acrylic acid (AA), 0.50 g 2-[[[(1,6-dihydro-4-methyl-6-oxo-2-pyrimidinyl)amino]carbonyl]amino]ethyl 2-methacrylate, 1.48 g 1,3-dioxolane (DOL), 0.9 g trioxane, 2.0 g lithium difluorooxalatoborate (LiDFOB), 2.5 g lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and 0.10 g photoinitiator (TPO) were magnetically stirred in a beaker for 3 h to allow the monomers to mix thoroughly. The monomer solution was obtained by stirring at 300 rpm. UV light (wavelength 365 nm) was then irradiated at a distance of 5 cm for 3 min to obtain a viscous photo-free radical polymerization prepolymer.

[0041] S2: Preparation of electrolyte film: drip a few drops of the precursor solution between two A4 size release films, and pass it through a twin-roll extruder at 1m min. -1 The polymerized electrolyte membrane was extruded at a speed of 1000 nm to obtain a uniform electrolyte membrane with a thickness of 0.5 mm between the two rollers. The membrane was then transferred to a blast drying oven, and the polymerized electrolyte membrane was subjected to a vacuum cationic polymerization reaction in a vacuum oven at 80°C for 24 hours.

[0042] S3: Preparation of test battery: Assemble the prepared solid electrolyte into a battery in the glove phase according to the 2032 model positive electrode shell - positive electrode material (sulfur element) - solid electrolyte - negative electrode material lithium sheet - gasket - spring sheet - 2032 model negative electrode shell.

[0043] Preparation of the ion conductivity test cell: The prepared solid electrolyte was assembled into a cell in a glove box according to the following steps: 2032 type positive electrode shell-stainless steel-solid electrolyte-stainless steel-spring sheet-2032 type negative electrode shell.

[0044] Example 2:

[0045] The other steps were the same as those in Example 1, except that 0.9 g of trioxane was replaced by 0.5 g of trioxane.

[0046] Example 3:

[0047] The other steps are the same as in Example 1, except that 2.84g of methacryloyl glycidyl ester (GAM) is replaced with 3.42g of methacryloyl glycidyl ester (GAM).

[0048] Example 4:

[0049] The other steps were the same as those in Example 1, except that 1.48 g of 1,3-dioxolane (DOL) was replaced by 2.96 g of 1,3-dioxolane (DOL).

[0050] Comparative Example 1

[0051] S1: Preparation of polymer precursor: 1.8g vinyl pyrrolidone (VP), 2.84g glycidyl methacrylate (GAM), 0.72g acrylic acid (AA), and 0.10g photoinitiator (TPO) were stirred in a beaker at 300 rpm to obtain a monomer solution. Irradiate with a UV lamp (wavelength 365nm) for 3 minutes to obtain a relatively viscous prepolymer.

[0052] S2: Preparation of electrolyte film: The precursor solution was dropped between two films and slowly extruded through a twin-roll extruder to obtain a uniform electrolyte membrane with a thickness of 0.5 mm between the twin rollers; the membrane was then transferred to a forced air drying oven and the polymerized electrolyte membrane was evacuated in a vacuum oven at 80°C for 24 hours.

[0053] S3: Preparation of test battery: Assemble the prepared solid electrolyte into a battery in the glove phase according to the 2032 model positive electrode shell - positive electrode material (sulfur element) - solid electrolyte - negative electrode material lithium sheet - gasket - spring sheet - 2032 model negative electrode shell.

[0054] Preparation of the ion conductivity test cell: The prepared solid electrolyte was assembled into a cell in a glove box according to the following steps: 2032 type positive electrode shell-stainless steel-solid electrolyte-stainless steel-spring sheet-2032 type negative electrode shell.

[0055] Analysis Parameter Example 1

[0056] Ionic conductivity of solid electrolyte membrane: It is a key indicator for evaluating its performance in batteries. Ionic conductivity (usually expressed in S cm -1 The unit of ion conductivity is the electrolyte membrane's ability to conduct ions, which directly affects the battery's charge and discharge efficiency and power density.

[0057] The ionic conductivity of the solid electrolyte membrane is calculated by the following formula:

[0058] σ=d / Re×S

[0059] Where d is the thickness of the sample under test (cm); Re is the body impedance of the sample under test (Ω), which can be obtained from the intersection of the semicircle and the oblique line in the Nyquist plot of electrochemical impedance spectroscopy; S is the effective area of ​​the electrode (cm 2 ).

[0060] Experimental steps for testing the ionic conductivity of solid electrolyte membranes: prepare or obtain a solid electrolyte membrane sample (2×2 cm), ensuring that the membrane thickness is uniform; use the four-probe method or other appropriate resistance measurement method to measure the membrane resistance (R); calculate the ionic conductivity using the above formula based on the membrane thickness (L) and cross-sectional area (A) and the measured resistance (R).

[0061] The ionic conductivity with temperature was measured between 30 and 80 °C, with a 60 min equilibration time for each test temperature. The average value was obtained by performing three parallel tests at each temperature. Figure 1 It can be seen that the impedance of the film gradually decreases with increasing temperature, and the ionic conductivity gradually increases. The embodiment is significantly higher than the comparative example 1.

[0062] Analysis Parameter Example 2

[0063] Mechanical properties of solid electrolyte membranes: These are key indicators for evaluating their performance in batteries. Tensile strength testing: Samples of standard size and shape are cut and tested multiple times using a universal tensile testing machine under standard temperature and humidity conditions, averaging the measured values. Dumbbell-shaped specimens are prepared, measuring 15 mm long and 4 mm wide, at a temperature of 25°C.

[0064] Figure 2 The tensile strengths of Example 1 and Comparative Example 1 are shown. It can be seen that the mechanical strength of the embodiment is higher.

[0065] Analysis Parameter Example 3

[0066] Cycling performance testing is the core link for solid-state electrolytes to move from the laboratory to commercial applications. By systematically evaluating their performance under actual working conditions, it can reveal intrinsic defects of the material (such as insufficient electrochemical window) or interface compatibility problems, thereby guiding component design, structural optimization and battery process improvement.

[0067] Constant current charge and discharge test: The battery's electrochemical performance, long cycle performance, and rate performance were tested using a Shenzhen Neware BTs-5V5mA multi-channel battery cycler. The test conditions were a constant room temperature of 25°C and an operating voltage of 1.7V-2.8V.

[0068] Figure 3 The figure shows the cycle performance of Example 1 and Comparative Example 1. It can be seen from the figure that the solid polymer electrolyte in Example 1 can still maintain 90% of the original capacity after 500 cycles, and the capacity can also be maintained at 80% of the original battery, which is significantly better than the solid electrolyte in the comparative example.

[0069] The above descriptions are only several preferred embodiments of the present invention, but the present invention is not limited to the above-mentioned specific embodiments. The above-mentioned specific embodiments are illustrative rather than restrictive. Under the guidance of the present invention and in accordance with the spirit and principles of the present invention, researchers in this field can also make improvements and perfections, all of which fall within the scope of protection of the present invention.

[0070] Matters not covered by the present invention are known technologies.

Claims

1. A method for preparing a solid polymer electrolyte by UV light-initiated tandem cationic polymerization, characterized in that: The method comprises the following steps: S1: mixing a photopolymerization monomer, a cationic polymerization monomer, a lithium salt, a photopolymerization initiator, and a cationic polymerization initiator, and magnetically stirring at 20-30° C. for 3-5 hours to obtain a mixed material; Wherein, the photoinitiated polymerization monomer accounts for 20-60% of the mass of the mixed material; the cationic polymerization monomer accounts for 10-30% of the mass of the mixed material; and the lithium salt accounts for 15-30% of the mass of the mixed material; The photopolymerization initiator accounts for 0.5-5% of the mass of the mixed material; the cationic polymerization initiator accounts for 10-20% of the mass of the mixed material; The photoinitiated polymerization monomer is one or more of ethylene glycol diacrylate (BPA), methacryloyl glycidyl ester (GAM), 2-[[[(1,6-dihydro-4-methyl-6-oxo-2-pyrimidinyl)amino]carbonyl]amino]ethyl 2-methacrylate (UPyMA), ethylene glycol methyl ether acrylate (EGDMA), methyl methacrylate (MMA), vinyl pyrrolidone (VP), bisphenol A epoxy resin, and acrylic acid (AA); The cationic polymerization monomer is one or more of hydroxybutyl vinyl ether (HBVE), 3,3-bis(chloromethyl)oxetane (BCMO), 1,3-dioxolane (DOL), trioxane (TXE), and ethylene glycol diglycidyl ether (EGDE); S2: transferring the mixture obtained in step S1 into a reactor and reacting it under ultraviolet light for 10-300 seconds to obtain a photo-free radical polymerization prepolymer, i.e., a solid polymer electrolyte prepolymer; The wavelength range of the ultraviolet light is 315-400 nm, and the distance between the ultraviolet lamp and the mixture is 3-20 cm; S3: dripping the photo-free radical polymerization prepolymer obtained in step S2 between two release papers in a double-roll laminating machine, and extruding it through a double-roll extruder to preliminarily shape the solid electrolyte membrane; The gap thickness of the double-roll laminator is 0.1-1 mm; S2: The solid electrolyte membrane produced in step S1 is subjected to cationic polymerization in a vacuum oven at 40-100° C. for 18-30 hours to obtain a solid electrolyte membrane.

2. The method for preparing a solid polymer electrolyte by UV light-initiated tandem cationic polymerization according to claim 1, characterized in that: The lithium salt is lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

3. The method for preparing a solid polymer electrolyte by UV light-initiated tandem cationic polymerization according to claim 1, wherein: The cationic polymerization initiator is lithium difluorooxalatoborate (LiDFOB).

4. The method for preparing a solid polymer electrolyte by UV light-initiated tandem cationic polymerization according to claim 1, wherein: The photopolymerization initiator is TPO.

5. Use of the solid polymer prepared by UV light-initiated tandem cationic polymerization as claimed in claim 1, characterized in that it is used as a solid electrolyte material in lithium-ion batteries; In the lithium-ion battery, the positive electrode is sulfur and the negative electrode is a lithium sheet.

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