Method for preparing polymer solid electrolyte by roll-to-roll continuous film preparation process

Abstract

The invention relates to a method for preparing a polymer solid electrolyte by a roll-to-roll continuous film preparation process. According to the method, ethylene carbonate monomers and olefin monomers are subjected to photo-initiated free radical polymerization and then subjected to thermal-initiated free radical polymerization, and then the solid electrolyte thin film is prepared through a double-roller film pressing machine. The preparation method is simple and controllable in process and has high ionic conductivity and cycling stability, the ionic conductivity of the obtained solid electrolyte film can reach 1.03 * 10 <-5 > S cm <-1 >-1.28 * 10 <-4 > S cm <-1 >, and the film obtained by a double-roller film pressing machine is uniform in surface and can be widely applied to industrial large-scale production.

Description

Technical Field

[0001] The present invention relates to the field of solid electrolytes, and more particularly to a method for preparing a polymer solid electrolyte using a roll-to-roll continuous film-making process. Background Art

[0002] With the increasing development of electric vehicles and the rapid growth in demand for portable electronic devices and energy storage, people's attention to lithium batteries continues to increase. At present, the future development of the lithium battery industry shows a positive trend. Lithium-ion batteries have high energy density (250-400Wh kg -1 ), long cycle life, good rate performance, low cost, etc. However, commercial lithium-ion batteries currently have problems such as flammable organic electrolytes and the easy generation of lithium dendrites. Once a short circuit occurs in the battery, a large amount of heat will be released immediately inside, causing the organic electrolyte to burn and causing serious safety hazards.

[0003] Compared with liquid batteries, solid-state batteries do not use flammable organic electrolytes, which can fundamentally prevent such combustion accidents. The electrolytes of solid-state lithium batteries can be divided into three categories: inorganic solid electrolytes (ISE), polymer solid electrolytes (SPE) and composite polymer electrolytes (CPE). Solid electrolyte membrane (SEF) is a solid ion conductor and electronic insulating material, mainly used in batteries as electrolytes and separators. This membrane allows lithium ions to move freely between the positive and negative electrodes of the battery while preventing the flow of electrons, thereby improving the safety and energy density of the battery.

[0004] Organic composite solid electrolytes play a supporting role through the composite of polymer electrolyte and organic skeleton, thereby improving the strength of electrolyte membrane. Most polymers themselves are crystalline, which is the reason why the ionic conductivity of polymer solid electrolytes is low. By blending or copolymerization, the crystalline structure of the polymer itself can be effectively destroyed, so that the amorphous area increases and the ionic conductivity is improved. Polymer solid electrolytes need to be polymerized from monomers. Depending on the type of monomer, the polymerization mechanism is also different, which can be divided into: cationic polymerization, anionic polymerization, and free radical polymerization. Free radical synthesized polymers can achieve high ionic conductivity by adjusting the reaction conditions and the structure of the polymer, which is crucial to the performance of the battery. Among the common matrix materials of free radical polymers, polyolefin-based materials and polyvinyl carbonate-based materials occupy an important position. The ester group in the polymer can effectively coordinate with lithium ions, and its skeleton or side chain has good flexibility. In particular, polyvinyl carbonate-based polymer electrolytes not only exhibit excellent ionic conductivity, but also maintain sufficient thermal stability. This is due to the strong interaction between the ester group and the oxygen atom, which further promotes the migration of ions in the polymer electrolyte, thereby enhancing its conductive performance.

[0005] The roll-to-roll film making process using a double-roll laminator is an efficient and continuous film preparation technology that is widely used in many fields. Its main process is: during the film making process, the material is fed into the double-roll laminator, which is a key equipment in the roll-to-roll film making process. The double-roll laminator precisely controls the pressure, temperature, and spacing between the rollers to evenly distribute the film material, complete the film forming and quality control, and ensure the efficient production, stable quality, and reliable performance of the roll-to-roll film. CN202410658630.1 discloses a pre-oxidized and sulfurized MOF-based solid electrolyte for lithium-ion batteries and a preparation method thereof. The process activates the MOF material, grinds it, and then applies it on one side of the PP diaphragm with a scraper to dry and form a film. The coating process will result in uneven film thickness; CN202310972967.5 provides a preparation method and application of an in-situ polymerized self-supporting solid electrolyte membrane. The patent extrude the precursor slurry through a twin-screw extruder. Film making using this method will result in flow marks, bubbles and other problems, and the production cost is high; CN202410638900.2 provides a solid electrolyte membrane and a preparation device, preparation method and battery thereof. The patent adopts a roll-to-roll production process integrating slurry coating to prepare a solid electrolyte film. After slurry coating, it needs to be dried. For thick films or materials with strict drying conditions, the drying process takes a long time, which limits the production speed and reduces production efficiency. Summary of the invention

[0006] In view of the low ionic conductivity and complicated preparation process of current solid electrolytes, the present invention has developed a roll-to-roll continuous film-making process for preparing polymer solid electrolytes. The method uses two types of reactive monomers to initiate free radical polymerization by light and then initiate free radical polymerization by heat, and then obtains a new type of solid electrolyte film by a double-roll film pressing machine. The process of the present invention is simple and controllable, and has high ionic conductivity and cycle stability. The ionic conductivity of the obtained solid electrolyte film can reach 1.03×10 -5 Scm -1 ~1.28×10 -4 S cm -1 .

[0007] The technical solution of the present invention is:

[0008] A method for preparing a polymer solid electrolyte by a roll-to-roll continuous film-making process, the method comprising the following steps:

[0009] (1) Weighing two monomers, adding a photoinitiator and a thermal initiator, and mixing and stirring to obtain a mixed solution;

[0010] The two monomers are ethylene carbonate monomers and olefin monomers; the molar ratio is ethylene carbonate:olefin = 1:3 to 2:3;

[0011] The mass of the photoinitiator is 0.2-1.5wt% of the two monomers, and the mass of the thermal initiator is 0.2-0.8wt% of the two monomers;

[0012] (2) placing the mixed solution under a UV lamp and irradiating the mixture under UV light for 2-3 minutes to obtain a precursor solution;

[0013] (3) The precursor solution is poured into a double-roll film press at a uniform speed to form a film, and the obtained film is then subjected to free radical thermal polymerization at 80-120° C. for 24-36 hours to obtain a solid electrolyte film.

[0014] In the step (1), the ethylene carbonate monomer is selected from one or both of vinyl ethylene carbonate and ethylene carbonate; the olefin monomer is selected from one or more of 1-[(3-methacryloyloxy)propyl]-3-methylimidazolium bis(trifluoromethanesulfonyl)amide, 1-methyl-3-propylimidazolium-N-[3-(methacryloyloxy)propylsulfonyl]-N-(trifluoromethanesulfonyl)amide, 2,2,3,3,4,4,5,5-octafluoro-1,6-hexanediol diacrylate, and ditrimethylolpropane acrylate.

[0015] The photoinitiator is specifically 2,4,6-trimethylbenzoyldiphenylphosphine oxide (TPO);

[0016] The thermal initiator is specifically azobisisobutyronitrile (AIBN);

[0017] The speed required for mixing and stirring in step (1) is 200-400 rpm -1 , stirring treatment time is 12-24h;

[0018] The wavelength of ultraviolet light irradiation in step (2) is 365nm;

[0019] The obtained solid polymer film has a thickness of 40 to 150 μm;

[0020] The film drawing process is as follows:

[0021] The polymerized precursor solution is poured into the rollers of a double-roll film press. After the rollers rotate, the precursor solution enters between a pair of rollers rotating in opposite directions. After the film is drawn, a solid electrolyte film is obtained.

[0022] Among them, the wheel speed of the double-roll film laminating machine is 1-20rmp, the film drawing speed is 20-100mm / min, the precursor flow rate is 1-10ml / min; the speed ratio of the front roller to the rear roller is 1.2:1.

[0023] The essential features of the present invention are:

[0024] The present invention uses a roll-to-roll film-making process of a double-roll film press to make a film from a precursor solution obtained by two traditional free radical polymerization methods. The method uses a photo-initiated free radical polymerization and then a thermally initiated free radical polymerization of two types of reaction monomers, and then a new solid electrolyte film is obtained by a double-roll film press. The photo-initiated free polymerization can control the generation amount and reaction rate by adjusting factors such as light intensity and light irradiation time; the combination of the two free radical polymerizations can combine olefin monomers with ethylene carbonate monomers, enrich the ion transmission pathway and thus optimize the ion conduction performance. The strong cross-linked structure formed by chemical bonds, the polymer solid electrolyte prepared by polymerization shows excellent thermal stability; the solution is made into a film by a roll-to-roll film-making process. This method can quickly and significantly shorten the drying time, thereby improving production efficiency. Secondly, the double-roll design ensures uniform contact of the material on the entire working surface. This uniformity not only improves the quality of the coating, but also reduces the tensile stress of the material during processing, thereby reducing the risk of damage. This film-making process can be industrialized for production.

[0025] The beneficial effects of the present invention are:

[0026] The present invention has the advantages of uniform thickness and high production efficiency, and has good electrochemical and mechanical properties. The ionic conductivity of the solid electrolyte film prepared by this method is as high as 1.03×10 -5 S cm -1 ~1.28×10 -4 Scm -1After 100 cycles, the battery capacity can reach 730.5 mAh g -1 ~1106.7mAh g -1 , the tensile strength reaches 3.47~4.25MPa. Therefore, the solid electrolyte membrane obtained by this method has the advantages of high ionic conductivity, high cycle stability and good mechanical properties, and the film prepared by a double-roll film pressing machine can be mass-produced industrially. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 A physical picture of the solid electrolyte film in the present invention;

[0028] Figure 2 is the ionic conductivity diagram of the solid electrolyte film obtained in Example 1;

[0029] Figure 3 is the ionic conductivity diagram of the solid electrolyte film obtained in Example 2;

[0030] Figure 4 is the ionic conductivity diagram of the solid electrolyte film obtained in Example 3;

[0031] Figure 5 The mechanical properties of the solid electrolyte membranes of the three embodiments are characterized in FIG.

[0032] Figure 6 This is a comparison chart of the cycling performance of LiFePO4 / EM / Li batteries assembled with solid electrolytes from three embodiments at 0.2C. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific implementation described herein is only used to explain the present invention and is not intended to limit the present invention.

[0034] The polymer solid electrolyte of the present invention is a polymer solid electrolyte with excellent performance synthesized by polymer monomers through light-induced free radical polymerization and heat-induced free radical polymerization. The precursor solution is film-formed by a double-roll film press to obtain a solid electrolyte film with uniform material and can be widely used in industrial production.

[0035] Solid electrolytes are mainly used in the manufacture of batteries, generators and capacitors. Solid electrolytes have good electrical properties, excellent electrical conductivity, good anti-oxidation and can improve the stability and discharge capacity of batteries, which can help improve the discharge capacity, stability and cycle performance of batteries.

[0036] As shown in the following reaction formula, ethylene carbonate monomers and olefin monomers undergo free radical initiated polymerization, and the synthesized polymer serves as a solid electrolyte.

[0037]

[0038] The following example is a novel method for preparing a polymer electrolyte.

[0039] Example 1

[0040] Preparation of polymer electrolyte precursor: 2.28 g (0.02 mol) of ethylene carbonate, 14.67 g (0.03 mol) of 1-[(3-methacryloyloxy)propyl]-3-methylimidazolium bis(trifluoromethanesulfonyl)amide, 0.084 g of AIBN initiator, and 0.034 g of TPO were added. The solution was placed in a glass bottle and stirred thoroughly with a magnetic stirrer (speed of 300 rmin). -1 ) for 12 hours to obtain a solution. Irradiate with an ultraviolet lamp (wavelength 365nm) for 2 minutes (irradiation distance 5cm, irradiation power 5W) to obtain a precursor solution.

[0041] The precursor solution was poured into the middle of the roller of the double-roll film press (Beidou Precision Instrument Co., Ltd., PT-506B). After the rollers rotated (the speed ratio of the front roller to the rear roller was 1.2:1), the precursor solution entered between a pair of rollers rotating in opposite directions. When drawing the film, the film was slowly pulled out (roller speed 5rmp, film drawing speed 40mm / min, precursor flow rate 5ml / min), and the film was transferred to a blast drying oven and heated at 80°C for polymerization for 24h to obtain a solid polymer film (thickness 80μm).

[0042] Example 2

[0043] The specific implementation steps are the same as those in Example 1, except that the polymerization monomer and the amount of the polymerization monomer are changed from 2.28 g of vinyl ethylene carbonate to 1.72 g of vinylene carbonate, and from 14.67 g of 1-[(3-methacryloyloxy)propyl]-3-methylimidazolium bis(trifluoromethanesulfonyl)amide to 13.90 g of 1-methyl-3-propylimidazolium-N-[3-(methacryloyloxy)propylsulfonyl]-N-(trifluoromethanesulfonyl)amide.

[0044] Example 3

[0045] The specific implementation steps are the same as those in Example 1, except that the polymerization monomer and the amount of the polymerization monomer are changed from 14.67 g of 1-[(3-methacryloyloxy)propyl]-3-methylimidazolium bis(trifluoromethanesulfonyl)amide to 11.1 g of 2,2,3,3,4,4,5,5-octafluoro-1,6-hexanediol diacrylate.

[0046] Comparative Example 1

[0047] The ionic conductivity test of the solid electrolyte film in Example 1 includes the following steps:

[0048] Ionic conductivity is a physical quantity that characterizes the ionic conductivity of solid electrolyte films. At 25°C, the solid electrolyte membrane is tested in a stainless steel sheet / solid electrolyte membrane / stainless steel sheet test structure with a frequency range of 10 -2 Hz-10 5 The AC impedance test is performed under the condition of Hz. First, a solid electrolyte film with a specification of 2cm×2cm is taken, and two stainless steel (SS) gaskets with a diameter of 16mm are used as electrodes to construct a SS / electrolyte / SS structure for EIS test. The amplitude of the applied sinusoidal signal is 20mV.

[0049] The calculation formula of ionic conductivity (σ) is:

[0050]

[0051] Where l is the thickness of the electrolyte film, S is the effective area of ​​contact between the electrolyte and the SS electrode, and R is the resistance of the electrolyte film in the EIS test results.

[0052] The ionic conductivity with temperature was measured between 25℃ and 80℃, and the equilibrium time for each test temperature was 60min. Each temperature was tested three times in parallel. The impedance of the film gradually decreased with the increase of temperature, and the ionic conductivity gradually increased. Figure 2 As shown, the temperature is 80℃, and the maximum ionic conductivity is 6.55×10 -5 S cm -1 .

[0053] Comparative Example 2

[0054] The ionic conductivity test of the solid electrolyte film in Example 2 includes the following steps:

[0055] Ionic conductivity is a critical property for electrolytes. First, a solid electrolyte film with a size of 2cm×2cm is taken and placed between two stainless steel sheets to form a sandwich structure (SS / EM / SS). Each temperature is tested three times in parallel. The impedance of the film decreases gradually with the increase of temperature, and the ionic conductivity increases gradually. Figure 3 As shown in the figure, the ambient temperature is 80℃ and the maximum ionic conductivity is 1.28×10 -4 S cm -1 .

[0056] Comparative Example 3

[0057] The ionic conductivity test of the solid electrolyte film in Example 3 includes the following steps:

[0058] Ionic conductivity is the core performance indicator of electrolyte materials. First, prepare a solid electrolyte film sample with a standard size of 2cm×2cm. Then, the film is precisely placed between two pieces of stainless steel (SS) to form a sandwich structure of SS / EM / SS to ensure the stability and accuracy of the test environment. In order to obtain reliable data, three parallel test operations are performed for each preset temperature point to ensure the repeatability and accuracy of the results. As the test temperature gradually increased, it was observed that the impedance of the film showed a significant decrease, and the ionic conductivity formed a steady upward trend. At the specific temperature of 80°C, the solid electrolyte film exhibited excellent ion conductivity properties such as Figure 4 As shown, its ionic conductivity is 3.8×10 -5 S cm -1 .

[0059] like Figure 1 The figure shows a real solid electrolyte of the present invention, and the surface of the electrolyte film is flat and uniform without holes.

[0060] Mechanical properties test

[0061] The mechanical properties of the sample film were measured at a tensile rate of 30 mm min -1 .like Figure 5 As shown, the three embodiments all have good mechanical properties, and the tensile strengths are 3.47 MPa, 4.25 MPa, and 4.12 MPa, respectively.

[0062] Cycle performance test:

[0063] Lithium metal is used as the electrode and the electrolyte membrane (EM) is placed between the lithium metals to form a Li / EM / Li battery. The battery cycle performance is tested at a current density of 0.2C. Figure 6 As shown, the specific capacity of the battery in Example 1 can reach 946.7 mAh g after 100 cycles at 0.2C discharge. -1 Example 2: The specific capacity of the battery can reach 1106.7 mAh g after 100 cycles at 0.2C discharge. -1 Example 3 The specific capacity of the battery can reach 730.5 mAh g after 100 cycles at 0.2C discharge. -1 This shows that the three batteries have good interface stability and long-term battery cycle performance.

[0064] Through the above examples, we can see that the solid electrolyte obtained by first light-initiated free radical polymerization and then heat-initiated free radical polymerization has excellent ionic conductivity and cycle stability. The introduction of vinyl carbonate during the polymerization process ensures that the solid electrolyte film has higher oxidative stability; the introduction of olefins improves the mechanical strength and interfacial compatibility of the solid electrolyte film. As can be seen from the examples, the solid electrolyte film obtained by this preparation method has good electrical conductivity, long-term battery cycle performance and can be industrially produced.

[0065] The above are only several preferred embodiments of the present invention, but the present invention is not limited to the above several specific implementations. The above specific implementations are illustrative, not restrictive, and researchers in the field can make improvements and perfections under the guidance of the present invention and in accordance with the spirit and principles of the present invention, which are all within the protection scope of the present invention.

[0066] Matters not covered by the present invention are known technologies.

Claims

1. A method for preparing a polymer solid electrolyte by a roll-to-roll continuous film-making process, characterized in that: The method comprises the following steps: (1) Weighing two monomers, adding a photoinitiator and a thermal initiator, and stirring to obtain a mixed solution; The two monomers are ethylene carbonate monomers and olefin monomers; the molar ratio is ethylene carbonate:olefin = 1:3 to 2:3; The mass of the photoinitiator is 0.2-1.5wt% of the two monomers, and the mass of the thermal initiator is 0.2-0.8wt% of the two monomers; (2) placing the mixed solution under a UV lamp and irradiating the mixture under UV light for 2-3 minutes to obtain a precursor solution; (3) The precursor solution is poured into a double-roll film press at a uniform speed to form a film, and the obtained film is then subjected to free radical thermal polymerization at 80-120° C. for 24-36 hours to obtain a solid electrolyte film.

2. The method for preparing a polymer solid electrolyte by a roll-to-roll continuous film-making process according to claim 1, characterized in that: In the step (1), the ethylene carbonate monomer is selected from one or both of vinyl ethylene carbonate and ethylene carbonate, and the olefin monomer is selected from one or more of 1-[(3-methacryloyloxy)propyl]-3-methylimidazolium bis(trifluoromethanesulfonyl)amide, 1-methyl-3-propylimidazolium-N-[3-(methacryloyloxy)propylsulfonyl]-N-(trifluoromethanesulfonyl)amide, 2,2,3,3,4,4,5,5-octafluoro-1,6-hexanediol diacrylate, and ditrimethylolpropane acrylate.

3. The method for preparing a polymer solid electrolyte by a roll-to-roll continuous film-making process according to claim 1, wherein the photoinitiator is specifically 2,4,6-trimethylbenzoyldiphenylphosphine oxide (TPO); The thermal initiator is specifically azobisisobutyronitrile (AIBN).

4. The method for preparing a polymer solid electrolyte by a roll-to-roll continuous film-making process according to claim 1, characterized in that: The speed required for mixing and stirring in step (1) is 200-400 rpm -1 The stirring time is 12-24h.

5. The method for preparing a polymer solid electrolyte by a roll-to-roll continuous film-making process according to claim 1, characterized in that: The wavelength of ultraviolet light irradiation in step (2) is 365nm.

6. The method for preparing a polymer solid electrolyte by a roll-to-roll continuous film-making process according to claim 1, characterized in that: The film drawing method is as follows: The precursor solution after polymerization is poured into the roller of the double-roll film press. After the roller rotates, the precursor solution enters between a pair of rollers rotating in opposite directions. After the film is drawn, a solid electrolyte film is obtained. Among them, the wheel speed of the double-roll film laminating machine is 1-20rmp, the film drawing speed is 20-100mm / min, the precursor flow rate is 1-10ml / min; the speed ratio of the front roller to the rear roller is 1.2:

1.

7. The method for preparing a polymer solid electrolyte by a roll-to-roll continuous film-making process according to claim 1, characterized in that: The obtained solid polymer film has a thickness of 40 to 150 μm.

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