Modified PEO electrolyte membrane and preparation method thereof

Abstract

The invention relates to the technical field of electrolyte membranes, in particular to a modified PEO electrolyte membrane and a preparation method thereof. The preparation method comprises the following steps: by taking polyethylene oxide as a matrix, dissolving PEO and a lithium salt in acetonitrile to form a polymer electrolyte solution, and adding two-dimensional reticular polyethylene glycol prepared from a polyethylene glycol reversed-phase suspension to obtain organic modified electrolyte slurry; and adding lithium lanthanum zirconium tantalum oxide nanoparticles, and carrying out ultrasonic treatment and drying to obtain the modified PEO electrolyte membrane. Through synergistic modification of the two-dimensional reticular polyethylene glycol and the inorganic nanoparticles, the ion transmission performance and the interface stability of the electrolyte membrane are improved.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of electrolyte membranes, in particular to a modified PEO electrolyte membrane and a preparation method thereof. BACKGROUND

[0002] With the rapid development of electric vehicles, consumer electronics and smart grids, the market demands high energy density, rechargeable and safe batteries. At present, although the traditional liquid lithium ion battery (LIBs) is the mainstream technology in the energy storage field, the organic liquid electrolyte used by the traditional liquid lithium ion battery has significant defects, including environmental unfriendliness, corrosiveness, flammability and thermal instability, which may cause serious safety hazards. In comparison, the solid-state battery technology using solid-state electrolyte instead of liquid electrolyte can not only significantly improve the safety performance of the battery, but also simplify the overall structure of the battery. Among them, the solid polymer electrolyte (SPEs) has broad application prospects in rechargeable batteries, fuel cells and supercapacitors and other electrochemical energy storage devices. The solid-state electrolyte is a new type of electrolyte material formed by introducing lithium salt into the traditional polymer electrolyte system. This type of electrolyte has elasticity, plasticity and mechanical stability, and can be processed without solvent, and the preparation process is simple and easy to realize the close interface contact of the electrode / electrolyte. Its flexible geometric shape adaptability, wide temperature range operability and high energy density characteristics further make it have significant potential in special application scenarios such as flexible batteries and wearable electronic devices, and provide an innovative path for the development of high-safety solid-state lithium batteries. Among them, the electrolyte system taking polyethylene oxide (PEO) as the matrix is a typical representative of polymer solid-state electrolyte. The polymer-based electrolyte has unique mechanical advantages and can effectively adapt to the volume change of the electrode material in the charging and discharging process through elastic deformation and plastic deformation. However, the conductivity of the pure PEO-based electrolyte is usually only 10 -7 S / cm order of magnitude at room temperature, which is difficult to meet the needs of actual battery applications. SUMMARY

[0003] In view of the deficiencies of the prior art, the application provides a modified PEO electrolyte membrane and a preparation method thereof. PEO is used as the matrix, lithium bis-trifluoromethylsulfonylimide (LiTFSI) is added, and two-dimensional network polyethylene glycol and lithium lanthanum zirconium tantalum oxide (LLZTO) nanoparticles are added for modification to obtain the modified PEO electrolyte membrane, so that the electrochemical window is improved to adapt to high-voltage electrodes and prolong the cycle life, the lithium ion migration number and transport rate are improved, and the interface stability with the electrode is improved.

[0004] To achieve the above purpose, the application adopts the following technical solutions:

[0005] In a first aspect, this application provides a modified PEO electrolyte membrane, wherein the modified PEO electrolyte membrane is prepared from a composite electrolytic slurry, the composite electrolytic slurry comprising an organic modified electrolyte slurry and inorganic nanoparticles; the inorganic nanoparticles are LLZTO nanoparticles; the organic modified electrolyte slurry is obtained by reacting a polymer electrolyte solution with a two-dimensional network polyethylene glycol; the polymer electrolyte solution comprises polyethylene oxide (PEO), lithium salt, and acetonitrile; the two-dimensional network polyethylene glycol is prepared from a polyethylene glycol (PEG) reverse suspension; the PEG reverse suspension is obtained by reacting hollow SiO2 microspheres, PEG, an emulsifier, and cyclohexane.

[0006] In one feasible implementation, the PEO includes an ethylene oxide unit (EO), and the EO and lithium ions (Li) in the lithium salt... + The molar ratio of PEO to acetonitrile is (10-20):1; the mass ratio of PEO to acetonitrile is 1:(14-20); the amount of two-dimensional network PEG is 5wt%-10wt% of PEO; the amount of inorganic nanoparticles added is 5wt%-10wt% of PEO; the mass-volume ratio of hollow SiO2 microspheres, PEG, emulsifier and cyclohexane is (3-3.5)g:(10-11.2)g:(0.55-0.62)g:(60-64)mL.

[0007] In one feasible implementation, the molecular weight of the PEO is 600,000, the molecular weight of the EO is 44; the lithium salt is lithium bis(trifluoromethanesulfonyl)imide; the particle size of the two-dimensional network PEG is 150-300 μm; the particle size of the hollow SiO2 microspheres is 2-5 μm; the molecular weight of the PEG is 1000 (i.e., PEG-1000); the emulsifier is polyethylene glycol 400 monostearate; and the thickness of the modified PEO electrolyte membrane is 180-240 μm.

[0008] Secondly, this application provides a method for preparing a modified PEO electrolyte membrane, comprising the following steps:

[0009] S1. Hollow SiO2 microspheres are activated to obtain pretreated hollow SiO2 microspheres; PEG is melted at a first set temperature, and an emulsifier is added and mixed to obtain a PEG mixture; cyclohexane is heated to a second set temperature and the PEG mixture is added dropwise, and a first ultrasonic treatment is performed. The pretreated hollow SiO2 microspheres are added and a first stirring is performed to obtain a PEG reverse suspension.

[0010] S2, the PEG reverse suspension is placed in a gradient temperature for freezing while second stirring is carried out, a frozen sample is obtained, the frozen sample is freeze-dried to obtain a freeze-dried product, the freeze-dried product is soaked in an alkaline solution for treatment, washed to neutral, dried and ground to obtain a two-dimensional network PEG;

[0011] S3, PEO and lithium salt are dissolved in acetonitrile to obtain a polymer electrolyte solution; the two-dimensional network PEG is added to the polymer electrolyte solution, and third stirring is carried out to obtain an organic modified electrolyte slurry;

[0012] S4, inorganic nanoparticles are added to the organic modified electrolyte slurry, and second ultrasonic treatment is carried out to obtain a composite electrolyte slurry, and the composite electrolyte slurry is dried to obtain the modified PEO electrolyte film.

[0013] Cyclohexane is a poor solvent of PEG-1000, as a continuous phase, receiving PEG mixed solution, molten PEG-1000 as a dispersed phase, in this system, emulsification is provided by polyethylene glycol 400 monostearate, the long-chain alkyl of stearic acid in the molecule of polyethylene glycol 400 monostearate serves as a hydrophobic chain, anchoring cyclohexane, the hydrophilic PEG segment is compatible with PEG-1000, under the action of ultrasonic, PEG-1000 forms micron-sized uniform droplets. The reverse phase system avoids the dissolution of PEG-1000; the pre-processed hollow SiO2 microspheres have a density close to that of cyclohexane, and are uniformly dispersed in the interstitial space of the droplets to form a double dispersion system. A vertical temperature gradient of “top -20℃→ bottom 0℃” is used to drive the directional crystallization of cyclohexane (freezing point 6.5℃): ice crystals grow directionally from the low-temperature zone (top) to the high-temperature zone (bottom) to form parallelly arranged flaky ice crystal templates, PEG-1000 droplets are squeezed into the interstitial space of the ice crystals and directionally stacked with the growth of the ice crystals to form a continuous network structure; magnetic stirring inhibits the sedimentation of SiO2 microspheres, so that they are uniformly embedded in the PEG-1000 network to provide templates for subsequent secondary pores; during the freeze-drying process, the cyclohexane ice crystals sublimate, leaving a network of pores to constitute the main framework of the two-dimensional structure; at this time, the hollow SiO2 microspheres form a physical occupation in the network, and after etching with a 5% NaOH solution (SiO2+2NaOH=Na2SiO3+H2O), pores are left through the network structure to form a porous network; freeze-drying at -45℃ avoids the softening of PEG-1000 and maintains the network skeleton; the network block after freeze-drying forms a rigid skeleton due to the intermolecular forces of PEG-1000, and after grinding, 0.15-0.3mm particles are retained, which completely retain the network porous characteristics.

[0014] PEO and LiTFSI (lithium bis(trifluoromethylsulfonyl)imide) are dissolved in acetonitrile, the ether oxygen bond (-O-) of PEO and the lithium ion of LiTFSI form a coordination bond, and the coordination bond provides a high ionic conductivity for the electrolyte. +The coordination forms a solvated sheath, the high polarity of acetonitrile promotes the dissociation of lithium salt, forming a uniform polymer-ion system, after adding two-dimensional network PEG, the ether chain of PEG interacts with the PEO main chain through hydrogen bond, the porous network of two-dimensional network structure provides Li + Additional transmission channels are provided while inhibiting the crystallization of PEO; after ultrasonic treatment, LLZTO nanoparticles are uniformly dispersed, and the high dielectric constant of LLZTO can weaken the coordination between PEO and Li + , promoting the dissociation of Li + ; meanwhile, the oxygen vacancies on the surface of LLZTO can act as Li + transport sites, constructing a transmission path, after vacuum drying of the slurry, a continuous film structure is formed, the flexible chain of PEO forms mechanical interlocking with two-dimensional network PEG and LLZTO nanoparticles, improving the mechanical strength of the film, and the porous structure and inorganic particles together improve the Li + conductivity.

[0015] In a feasible implementation scenario, the activation treatment in S1 comprises: mixing the hollow SiO2 microspheres with anhydrous ethanol at a solid-liquid ratio of 1:15, ultrasonic dispersing at 280-300 W for 25-35 min, and vacuum drying to obtain pretreated hollow SiO2 microspheres.

[0016] The polarity of ethanol forms hydrogen bonds with the SiO2 surface hydroxyl groups, breaking the microsphere agglomeration and improving the dispersibility.

[0017] In a feasible implementation scenario, the first set temperature in S1 is 60-65°C, the second set temperature is 40-45°C, the dropping speed is 1-1.5 mL / min, the first ultrasonic treatment power is 400-450 W, the time is 18-22 min, and the first stirring time is 25-35 min.

[0018] In a feasible implementation scenario, the gradient temperature in S2 is -20°C to 0°C, the second stirring speed is 50-80 rpm, and the freezing time is 40-60 min.

[0019] In a feasible implementation scenario, the freeze-drying parameters in S2 are -45°C, 0.08 mbar, and the freeze-drying time is 22-24 h; the alkaline solution is 5% NaOH solution; and the soaking time is 1.5-2 h.

[0020] In a feasible implementation scenario, the third stirring time in S3 is 12-24 h.

[0021] In a feasible implementation scenario, the second ultrasonic treatment time in S4 is 1-1.5 h.

[0022] Beneficial technical effects:

[0023] The application takes PEO matrix as a solid electrolyte base polymer, uses LLZTO nanoparticle inorganic filler and two-dimensional network PEG to modify PEG, provides more Li + transmission path, thereby shortening the Li + transmission path, making the flux uniform, reducing the risk of lithium dendrite puncture, and achieving the effect of prolonging the cycle life of the electrolyte film. At the same time, due to the increase of the conduction path and the shortening of the conduction path, the ionic conductivity of the electrolyte is improved, and the electrolyte impedance is reduced. On the other hand, the two-dimensional network PEG reduces the HOMO and LUMO energy levels of the PEG electrolyte, so that Li+ has a lower transport energy barrier, and the transport rate of lithium ions is improved. At the same time, the polymer electrolyte with low HOMO and LUMO energy levels can form a stable SEI interface with the high-voltage cathode electrode, thereby improving the electrochemical stability of the modified PEO electrolyte film. The modified PEO electrolyte film of the application provides a path for lithium ion transmission of the electrolyte film through the synergistic effect of two-dimensional network PEG, LLZTO, PEO, increases the ionic conductivity, widens the electrochemical window of the solid-state battery, and improves the lithium ion migration number. The prepared electrolyte film has high ionic conductivity, cycle stability and a wider electrochemical stability window, is suitable for the design and production of flexible batteries, and is beneficial to improve the safety performance of lithium ion batteries. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 A physical map of the modified PEO electrolyte film prepared in Example 1.

[0025] Figure 2 A 200 mu m scanning electron microscope image of the surface of the modified PEO electrolyte film prepared in Example 1.

[0026] Figure 3 A 10 mu m scanning electron microscope image of the surface of the modified PEO electrolyte film prepared in Example 1.

[0027] Figure 4 A 200 mu m scanning electron microscope image of the surface of the modified PEO electrolyte film prepared in Comparative Example 1.

[0028] Figure 5 A 200 mu m scanning electron microscope image of the surface of the modified PEO electrolyte film prepared in Comparative Example 3.

[0029] Figure 6 A 200 mu m scanning electron microscope image of the cross section of the modified PEO electrolyte film prepared in Example 1.

[0030] Figure 7 A polarization curve graph of the modified PEO electrolyte film prepared in Example 1.

[0031] Figure 8 Comparison of impedance curves of modified PEO electrolyte film prepared for Example 1 before polarization and after polarization.

[0032] Figure 9 Impedance graph of modified PEO electrolyte film prepared for Example 1 at different temperatures.

[0033] Figure 10 Voltage-time specific capacity graph of modified PEO electrolyte film prepared for Example 1.

[0034] Figure 11 Comparison of conductivity test of modified PEO electrolyte film prepared for Example 1, Comparative Example 1 and Comparative Example 2.

[0035] Figure 12 Comparison of electrochemical window test of modified PEO electrolyte film prepared for Example 1, Comparative Example 1 and Comparative Example 2.

[0036] Figure 13 XRD spectrum of modified PEO electrolyte film prepared for Example 1, Comparative Example 1, Comparative Example 2 and Comparative Example 3.

[0037] Figure 14 1mm scanning electron microscope graph of two-dimensional network PEG prepared in Example 1. DETAILED DESCRIPTION

[0038] In order to make the technical problems, technical solutions and beneficial effects to be solved in the present application more clear and explicit, the present application will be further described in detail below in conjunction with embodiments. However, this should not be understood as limiting the scope of the present application to the following examples. Without departing from the method idea of the present application, all other embodiments obtained by those skilled in the art without making creative labor, belong to the scope of protection of the present application.

[0039] In the present application, the terms used in the present application are merely for the purpose of describing specific embodiments, and are not intended to limit the present application.

[0040] In the present application, the singular forms "is", "or", "a", "any" and "the" are intended to include the plural forms, unless the context clearly indicates otherwise.

[0041] In addition, if the terms "first", "second" appear, they are only for the purpose of description, and cannot be understood as indicating or implying relative importance.

[0042] The following will specifically describe a modified PEO electrolyte film and a preparation method thereof provided by the present application in conjunction with different embodiments.

[0043] LLZTO nanoparticles used in the examples are Li 6.4 La3Zr 1.4 Ta 0.6 O 12 .

[0044] Example 1

[0045] A method for preparing a modified PEO electrolyte film, comprising the following steps:

[0046] 1. Mix 3 g of hollow SiO2 microspheres with anhydrous ethanol at a solid-liquid ratio of 1:15, ultrasonically disperse for 35 min at 280 W, and vacuum dry at 60°C for 2 h to obtain pretreated hollow SiO2 microspheres; melt 10 g of PEG-1000 in a water bath at 60°C, add 0.55 g of polyethylene glycol 400 monostearate, and stir to dissolve to obtain a PEG mixture; preheat 60 mL of cyclohexane to 40°C, pour it into a three-necked flask, and drop the PEG mixture into the three-necked flask at a rate of 1 mL / min, then ultrasonically treat for 22 min at 400 W, and then add the pretreated SiO2 microspheres to the three-necked flask, and continue to stir for 25 min to obtain a PEG reverse-phase suspension;

[0047] 2. Pour the PEG reverse-phase suspension into a cylindrical mold with a diameter of 5 cm and a height of 12 cm, the bottom of the mold is a copper plate, the bottom is immersed in an ice water bath, the stainless steel cover plate at the top of the mold is in contact with an aluminum plate containing a dry ice-ethanol mixture (-20°C), the mold is wrapped with a 5 mm thick polyurethane foam around the four sides, a temperature gradient of top -20°C to bottom 0°C is formed, a magnetic stir bar is placed at the bottom of the mold, and stirring is performed at 50 rpm, and a frozen sample is obtained after 40 min of freezing, the frozen sample is transferred to a freeze dryer, and freeze-drying is performed at -45°C and 0.08 mbar for 22 h to obtain a freeze-dried product, the freeze-dried product is soaked in a 5% NaOH solution for 1.5 h, washed with deionized water until neutral, and then dried, ground, and sieved to obtain a two-dimensional network PEG with a particle size of 150-300 μm;

[0048] 3. Mix PEO with a molecular weight of 600000, LiTFSI, and acetonitrile, the molar ratio of EO to LiTFSI is 14:1, and the mass ratio of PEO to acetonitrile is 1:19, stir until completely dissolved to obtain a polymer electrolyte solution; add two-dimensional network PEG to the polymer electrolyte solution, the mass of the two-dimensional network PEG is 7 wt% of the mass of PEO, and stir for 24 h to obtain an organic modified electrolyte slurry;

[0049] 4. Add LLZTO nanoparticles to the organic modified electrolyte slurry, the mass of the LLZTO nanoparticles is 5 wt% of the mass of PEO, and ultrasonically treat for 1 h to obtain a composite electrolyte slurry; cast the composite electrolyte slurry into a polytetrafluoroethylene mold, and vacuum dry at 60°C for 24 h to obtain a composite electrolyte film as shown in Figure 1The modified PEO electrolyte film shown has a thickness of 220 μm.

[0050] Example 2

[0051] A method for preparing a modified PEO electrolyte film, comprising the following steps:

[0052] 1. Mix 3.5 g of hollow SiO2 microspheres with anhydrous ethanol at a solid-liquid ratio of 1:15, ultrasonically disperse for 25 min at 300 W, and vacuum dry at 60°C for 2 h to obtain pretreated hollow SiO2 microspheres; melt 11.2 g of PEG-1000 in a water bath at 65°C, add 0.62 g of polyethylene glycol 400 monostearate, and stir to dissolve to obtain a PEG mixture; preheat 64 mL of cyclohexane to 45°C, pour it into a three-necked flask, and drop the PEG mixture into the three-necked flask at a drop rate of 1.5 mL / min, then ultrasonically stir for 18 min at 450 W, add the pretreated SiO2 microspheres to the three-necked flask, and continue to stir for 35 min to obtain a PEG inverse suspension;

[0053] 2. Pour the PEG inverse suspension into a cylindrical mold with a diameter of 5 cm and a height of 12 cm, the bottom of the mold is a red copper plate, the bottom is immersed in an ice water bath, the stainless steel cover plate at the top of the mold is in contact with an aluminum plate containing a dry ice-ethanol mixture (-20°C), the mold is wrapped with a 5 mm thick polyurethane foam around the four sides, a temperature gradient of top -20°C to bottom 0°C is formed, a magnetic stir bar is placed at the bottom of the mold, and stirring is performed at 80 rpm, and a frozen sample is obtained after 60 min of freezing; the frozen sample is transferred to a freeze dryer, and freeze-drying is performed at -45°C and 0.08 mbar for 24 h to obtain a freeze-dried product; the freeze-dried product is soaked in a 5% NaOH solution for 1.5 h, washed with deionized water until neutral, and then dried; after grinding, a two-dimensional network PEG with a particle size of 150-300 μm is sieved out;

[0054] 3. Mix PEO with a molecular weight of 600000, LiTFSI, and acetonitrile, the molar ratio of EO to LiTFSI is 10:1, and the mass ratio of PEO to acetonitrile is 1:20, stir until completely dissolved to obtain a polymer electrolyte solution; add two-dimensional network PEG to the polymer electrolyte solution, the mass of the two-dimensional network PEG is 5 wt% of the mass of PEO, and stir for 12 h to obtain an organic modified electrolyte slurry;

[0055] 4. Add LLZTO nanoparticles to the organic modified electrolyte slurry, the mass of the LLZTO nanoparticles is 7 wt% of the mass of PEO, and ultrasonically treat for 1.5 h to obtain a composite electrolyte slurry; cast the composite electrolyte slurry into a polytetrafluoroethylene mold, and vacuum dry at 60°C for 24 h to obtain a modified PEO electrolyte film with a thickness of 180 μm.

[0056] Example 3

[0057] A method for preparing a modified PEO electrolyte film, comprising the following steps:

[0058] 1. 3.2 g hollow SiO2 microspheres were mixed with anhydrous ethanol at a solid-liquid ratio of 1:15, ultrasonically dispersed at 290 W for 30 min, and vacuum dried at 60°C for 2 h to obtain pretreated hollow SiO2 microspheres; 10.6 g of PEG-1000 was melted in a water bath at 65°C, 0.58 g of polyethylene glycol 400 monostearate was added, and stirring was performed to obtain a PEG mixed solution; 62 mL of cyclohexane was preheated to 40°C and poured into a three-necked flask, the PEG mixed solution was added dropwise into the three-necked flask at a dropwise speed of 1.5 mL / min, ultrasonic stirring was performed at 450 W for 20 min, and then the pretreated SiO2 microspheres were added into the three-necked flask, and stirring was continued for 30 min to obtain a PEG reverse suspension;

[0059] 2. The PEG reverse suspension was injected into a cylindrical mold with a diameter of 5 cm and a height of 12 cm, the bottom of the mold was a red copper plate, the bottom was immersed in an ice water bath, the stainless steel cover plate at the top of the mold was in contact with an aluminum plate containing a dry ice-ethanol mixture (-20°C), the mold was wrapped with a 5 mm thick polyurethane foam around the four walls, a temperature gradient of top -20°C to bottom 0°C was formed, a magnetic stir bar was placed at the bottom of the mold, and stirring was performed at 60 rpm, and a frozen sample was obtained after 50 min of freezing, the frozen sample was transferred to a freeze dryer, and freeze drying was performed at -45°C and 0.08 mbar for 23 h to obtain a freeze-dried product, the freeze-dried product was soaked in a 5% NaOH solution for 2 h, washed with deionized water until neutral, and then dried, ground and sieved to obtain two-dimensional network PEG with a particle size of 150-300 μm;

[0060] 3. PEO with a molecular weight of 600000, LiTFSI and acetonitrile were mixed, the molar ratio of EO to LiTFSI was 18:1, and the mass ratio of PEO to acetonitrile was 1:15, stirring was performed until complete dissolution to obtain a polymer electrolyte solution; two-dimensional network PEG was added to the polymer electrolyte solution, the mass of the two-dimensional network PEG was 7 wt% of the mass of PEO, stirring was performed for 18 h to obtain an organic modified electrolyte slurry;

[0061] 4. LLZTO nanoparticles were added to the organic modified electrolyte slurry, the mass of the LLZTO nanoparticles was 10 wt% of the mass of PEO, ultrasonic treatment was performed for 1 h to obtain a composite electrolyte slurry; the composite electrolyte slurry was cast into a polytetrafluoroethylene mold, vacuum drying was performed at 60°C for 24 h to obtain a modified PEO electrolyte film with a thickness of 230 μm.

[0062] Example 4

[0063] A method for preparing a modified PEO electrolyte film, comprising the following steps:

[0064] 1. 3 g hollow SiO2 microspheres were mixed with anhydrous ethanol at a solid-liquid ratio of 1:15, dispersed by ultrasonic at 300 W for 35 min, and dried at 60 °C under vacuum for 2 h to obtain pretreated hollow SiO2 microspheres; 10 g of PEG-1000 was melted in a water bath at 60 °C, 0.55 g of polyethylene glycol 400 monostearate was added, and stirred to dissolve to obtain a PEG mixture; 60 mL of cyclohexane was preheated to 45 °C and poured into a three-necked flask, the PEG mixture was added dropwise into the three-necked flask at a rate of 1 mL / min, and after ultrasonic at 450 W for 22 min, the pretreated SiO2 microspheres were added into the three-necked flask, and stirring was continued for 30 min to obtain a PEG inverse suspension;

[0065] 2. The PEG inverse suspension was injected into a cylindrical mold with a diameter of 5 cm and a height of 12 cm, the bottom of the mold was a copper plate, the bottom was immersed in an ice water bath, the stainless steel cover plate at the top of the mold was in contact with an aluminum plate containing dry ice-ethanol mixture (-20 °C), the mold was wrapped with 5 mm thick polyurethane foam around the four walls, forming a temperature gradient of top -20 °C to bottom 0 °C, a magnetic stir bar was placed at the bottom of the mold, and stirring was carried out at 70 rpm, the frozen sample was obtained after freezing for 60 min, the frozen sample was transferred to a freeze dryer, and freeze-drying was carried out at -45 °C and 0.08 mbar for 24 h to obtain a freeze-dried product, the freeze-dried product was soaked in 5% NaOH solution for 2 h, washed with deionized water until neutral, dried, ground, and sieved to obtain two-dimensional network PEG with a particle size of 150-300 μm;

[0066] 3. PEO with a molecular weight of 600000, LiTFSI and acetonitrile were mixed, the molar ratio of EO:LiTFSI was 20:1, and the mass ratio of PEO to acetonitrile was 1:14, stirring until completely dissolved to obtain a polymer electrolyte solution; two-dimensional network PEG was added to the polymer electrolyte solution, the mass of the two-dimensional network PEG was 10 wt% of the mass of PEO, and stirring was carried out for 24 h to obtain an organic modified electrolyte slurry;

[0067] 4. LLZTO nanoparticles were added to the organic modified electrolyte slurry, the mass of the LLZTO nanoparticles was 10 wt% of the mass of PEO, and ultrasonic treatment was carried out for 1 h to obtain a composite electrolyte slurry; the composite electrolyte slurry was cast into a polytetrafluoroethylene mold, and vacuum drying was carried out at 60 °C for 24 h to obtain a modified PEO electrolyte film with a thickness of 240 μm.

[0068] Comparative Example 1

[0069] A method for preparing a modified PEO electrolyte film, the implementation steps and parameters are the same as those of Example 1, the difference is that two-dimensional network PEG is not used, and LLZTO nanoparticles are directly added to the polymer electrolyte solution after ultrasonic treatment for 1 h to obtain a composite electrolyte slurry.

[0070] Comparative Example 2

[0071] A method for preparing a modified PEO electrolyte film, the implementation steps and parameters are the same as those of Example 1, the difference is that no LLZTO nanoparticles are added, and the organic modified electrolyte slurry is directly cast into a polytetrafluoroethylene mold to dry, to obtain a modified PEO electrolyte film.

[0072] Comparative Example 3

[0073] A method for preparing a modified PEO electrolyte film, the implementation steps and parameters are the same as those of Example 1, the difference is that no LLZTO nanoparticles and two-dimensional network PEG are added, and the PEO-LiTFSI solution is directly cast into a polytetrafluoroethylene mold to dry, to obtain a modified PEO electrolyte film.

[0074] Performance test:

[0075] The modified PEO electrolyte films prepared in Examples 1-4 and Comparative Examples 1-3 were tested for the following performance:

[0076] Ion conductivity test:

[0077] Electrochemical impedance spectroscopy (EIS) is a test method for applying a small amplitude sinusoidal voltage (or current) disturbance signal to the system. Since the amplitude of the electrical signal disturbance applied to the system is very small, it has little effect on the system, so it is widely used in electrochemical research. The present application uses EIS test to obtain the bulk impedance value of the modified PEO electrolyte film, and then calculates the ion conductivity of the modified PEO electrolyte film. The sample is clamped between two stainless steel blocking electrodes, a small amplitude sinusoidal alternating voltage with varying frequency is applied to it, and the change process of the response current with the input voltage is measured, that is, the process of the impedance value of the modified PEO electrolyte film changing with the frequency is obtained.

[0078] The calculation formula of ion conductivity σ is:

[0079] σ = L / (R·S)

[0080] Where L is the thickness of the modified PEO electrolyte film, measured by a screw micrometer, in cm; R is the bulk impedance value of the modified PEO electrolyte film, in this experiment, the horizontal coordinate impedance value at the intersection of the high frequency region and the straight line in the EIS spectrum is taken as the bulk impedance value R of the modified PEO electrolyte film, in Ω; S is the area of the modified PEO electrolyte film, in cm 2 .

[0081] After the assembly of the double stainless steel (SS) blocking electrode, it was placed in a 60°C oven for 24 h and then at room temperature for 24 h to ensure good contact of the solid electrolyte film with the electrode and reduce the influence of the interface impedance on the test results. The test temperature range was 30-80°C, with a temperature rise of 10°C, and each temperature stage was maintained for at least 1 h. The voltage frequency range was 0.1-10 6 Hz, and the voltage amplitude was 10 mV.

[0082] Electrochemical window test:

[0083] The electrochemical stability window (ESW) refers to the stable voltage interval corresponding to the reaction-free process of the solid-state electrolyte during charging and discharging. The test process was to scan from the open circuit potential to 6 V, with a scan rate of 0.01 mV·s -1 .

[0084] Table 1 Performance test results of modified PEO electrolyte films

[0085] Ionic conductivity (S / cm) Electrochemical window (V) Example 1 6.737 x 10 -5 ]] 5.01 Example 2 6.521 x 10 -5 ]] 4.95 Example 3 6.604 x 10 -5 ]]> 4.89 Example 4 6.597 x 10 -5 ]]> 4.96 Comparative Example 1 1.230 x 10 -5 ]]> 4.53 Comparative Example 2 2.328 x 10 -5 ]]> 4.84 Comparative Example 3 8.624 x 10 -7 ]]> 3.98

[0086] As shown in Table 1, the ionic conductivity of the modified PEO electrolyte films prepared in Examples 1-4 was 6.521×10 -5 -6.737×10 -5 S / cm, and the electrochemical window was 4.89-5.01 V, with stability. The ionic conductivity of the modified PEO electrolyte films prepared in Comparative Examples 1-3 was 8.624×10 -7 -2.328×10 -5 S / cm, and the electrochemical window was 3.98-4.84 V, which was significantly lower than that of the examples.

[0087] Comparative Example 1 did not use two-dimensional network PEG, and the ionic conductivity was only 1.230×10 -5 S / cm, and the electrochemical window decreased to 4.53 V. Two-dimensional network PEG has a high dielectric constant, which can weaken the coordination between PEO and Li + through electrostatic interaction, promote the dissociation of LiTFSI, and its porous structure is the key path for fast migration of Li + Without addition, the PEO molecular chain is tightly packed, and Li + can only migrate through the ether oxygen bond (-O-) of the amorphous region of PEO, and the transmission path is less and tortuous, resulting in a significant decrease in conductivity. At the same time, two-dimensional network PEG interacts with PEO through intermolecular hydrogen bonds, which can inhibit PEO crystallization, and the crystallinity of PEO in Comparative Example 1 increases, and the proportion of amorphous region decreases, hindering the migration of Li +Migration. On the other hand, the network structure of two-dimensional PEG can buffer the stress at the electrode / electrolyte interface. Without its addition, side reactions are prone to occur at the interface, leading to a narrowing of the electrochemical window.

[0088] Comparative Example 2, without the addition of LLZTO nanoparticles, directly cast and dried the organic-modified electrolyte slurry to obtain a modified PEO electrolyte membrane with an ionic conductivity of 2.328 × 10⁻⁶. -5 With an S / cm ratio and an electrochemical window of 4.84 V, the oxygen vacancies on the surface of LLZTO nanoparticles can act as Li... + Temporary adsorption / desorption sites form a cooperative transport network; without addition, Li + Strong coordination with PEO leads to a decrease in free ion concentration and a decrease in conductivity, and Li + Migration relies solely on PEO chain segment movement, resulting in an increased migration energy barrier: LLZTO nanoparticles can inhibit the oxidative decomposition of PEO at high voltages. Without the addition, the electrolyte membrane is prone to oxidation above 4.8V, leading to a narrowing of the electrochemical window.

[0089] Comparative Example 3, without the addition of two-dimensional network PEG and LLZTO nanoparticles, had an ionic conductivity of 8.624 × 10⁻⁶. -7 The S / cm electrochemical window is 3.98V, which is significantly narrowed. In the pure PEO-LiTFSI system, the PEO molecular chains easily form ordered crystalline regions, and Li... + It can only migrate in a small number of amorphous regions, lacking both the porous channels of two-dimensional network PEG and the inorganic transport sites of LLZTO. + Migration relies entirely on the thermal motion of PEO segments, resulting in extremely low efficiency and conductivity close to the intrinsic value of pure PEO-based electrolytes.

[0090] like Figures 2-5 As shown in the comparison of SEM images of the modified PEO electrolyte membranes prepared in Example 1, Comparative Example 1, and Comparative Example 3, it can be seen that under a 200 μm SEM, the surface of the electrolyte membrane in Comparative Example 3 is uneven and exhibits a certain degree of crystallization. This is because PEO has the characteristic of being prone to crystallization, while the ion insertion and extraction of the electrolyte mainly occur in the non-crystalline region. This crystallization phenomenon is also the reason for the low room temperature conductivity of pure PEO solid electrolyte. In contrast, the surface smoothness of the modified PEO electrolyte membrane prepared in Comparative Example 1 is improved compared to Comparative Example 3 under a 200 μm SEM, with LLZTO nanoparticles evenly and randomly distributed within it, which is beneficial for interfacial contact with the electrodes. However, its surface is still uneven. After adding two-dimensional network PEG in Example 1, the membrane has a higher degree of smoothness, which is conducive to better ion exchange with the positive and negative electrodes.

[0091] like Figure 6The SEM cross-section of the modified PEO electrolyte film prepared in Example 1 shows that the modified PEO electrolyte film prepared in Example 1 also has high flatness inside.

[0092] As shown in Figure 7 , Figure 8 , the polarization curve diagram of the modified PEO electrolyte film prepared in Example 1 and the impedance curve before and after polarization show that the number of lithium ion migration of the button cell prepared from the modified PEO electrolyte film is 0.626, which is much higher than the number of lithium ion migration of the conventional PEO-based solid electrolyte (the number of lithium ion migration of the PEO-based solid electrolyte cell without modification is about 0.16).

[0093] As shown in Figure 9 , the impedance diagram of the modified PEO electrolyte film prepared in Example 1 at different temperatures shows that the solid-state battery prepared from the modified PEO electrolyte film prepared in Example 1 has excellent conductivity at 30°C-80°C, and the conductivity can reach 6 x 10 -4 S / cm 2 at 60°C.

[0094] As shown in Figure 10 , the specific capacity voltage curve diagram of the modified PEO electrolyte film prepared in Example 1 shows that in the electrochemical test with the charge cut-off voltage of 4.2V, the first charge capacity is 156.81mAh / g, the discharge capacity is 156.67mAh / g, and the charge-discharge efficiency is 99.91%. After 20 cycles, the discharge capacity is 146.93mAh / g, and the charge-discharge efficiency is 99.61%, which shows excellent cycle performance. After 50 cycles, the discharge capacity is 130.01mAh / g, and the charge-discharge efficiency is 98.75%. This shows that the introduction of two-dimensional network PEG effectively improves the cycle performance of the modified PEO electrolyte film.

[0095] As shown in Figure 11 , the ion conductivity diagram of the modified PEO electrolyte film prepared in Example 1, Comparative Example 1 and Comparative Example 2 shows that the ion conductivity increases with the increase of temperature, and the modified PEO electrolyte film has temperature dependence. Compared with Comparative Example 1 which is simply doped with LLZTO, the button cells assembled from the electrolyte film modified by two-dimensional network PEG in Comparative Example 2 and the electrolyte film modified by LLZTO and two-dimensional network PEG in Example 1 all show obviously improved ion conductivity, and the ion conductivity of the button cell assembled from the modified PEO electrolyte film in Example 1 is the highest.

[0096] As shown in Figure 12As shown, the electrochemical window of the modified PEO electrolyte film prepared in Example 1 of the present application can reach 5.01V, the electrochemical window of Comparative Example 1 can reach 4.5V, and the electrochemical window of the two-dimensional network PEG alone can reach 4.8V. The electrochemical window refers to the stable voltage interval corresponding to the non-reaction of the solid-state electrolyte in the charging and discharging process. As shown in the figure, the present application can greatly improve the electrochemical stability of the PEO-based solid-state electrolyte, and provides the possibility for matching high-voltage cathodes in the future.

[0097] As Figure 13 shown, the XRD spectrum of the modified PEO electrolyte film prepared in Example 1, Comparative Example 1, Comparative Example 2 and Comparative Example 3 of the present application shows that, compared with the comparative examples, the intensity of the PEO crystallization characteristic peak at 19.5° and 23.7° is obviously reduced after the addition of LLZTO and two-dimensional network PEG in Example 1. According to the characterization results, the peak intensity of Example 1 is lower, which shows that the effect of LLZTO and two-dimensional network PEG on the reduction of the crystallinity of the PEO-based solid-state electrolyte can be synergistically improved.

[0098] As Figure 14 shown, the two-dimensional network PEG prepared in Example 1 of the present application has a clear porous network structure.

[0099] In summary, the modified PEO electrolyte film prepared in the present application has high ionic conductivity, chemical stability, and a wider electrochemical stability window, and is suitable for the design and production of flexible batteries, which is beneficial to improve the electrochemical performance and safety performance of lithium ion batteries.

[0100] The above results show and describe the basic principles and main features of the present application and the advantages of the present application.

[0101] It should be understood by those skilled in the art that the present application is not limited by the above examples, and the above examples and descriptions in the specification are only to illustrate the principles of the present application. Without departing from the spirit and scope of the present application, various changes and improvements can be made to the present application, and these changes and improvements all fall within the scope of the claimed present application. The scope of protection claimed by the present application is defined by the equivalents of the appended claims.

Claims

1. A modified PEO electrolyte membrane, characterized by, The modified PEO electrolyte film is prepared from a composite electrolyte slurry, the composite electrolyte slurry comprises an organic modified electrolyte slurry and inorganic nanoparticles; the inorganic nanoparticles are lithium lanthanum zirconium tantalum oxide nanoparticles; the organic modified electrolyte slurry is obtained by reacting a polymer electrolyte solution and two-dimensional reticular polyethylene glycol; the polymer electrolyte solution comprises polyethylene oxide, lithium salt and acetonitrile; the two-dimensional reticular polyethylene glycol is prepared from polyethylene glycol inverse suspension; the polyethylene glycol inverse suspension is obtained by reacting hollow SiO2 microspheres, polyethylene glycol, emulsifier and cyclohexane.

2. The modified PEO electrolyte membrane according to claim 1, wherein, The polyethylene oxide comprises ethylene oxide units, and the molar ratio of the ethylene oxide units to lithium ions in the lithium salt is (10-20):1; the mass ratio of the polyethylene oxide to acetonitrile is 1:(14-20); the amount of the two-dimensional reticular polyethylene glycol is 5wt%-10wt% of the polyethylene oxide; the amount of the inorganic nanoparticles added is 5wt%-10wt% of the polyethylene oxide; the mass-volume ratio of the hollow SiO2 microspheres, polyethylene glycol, emulsifier and cyclohexane is (3-3.5)g:(10-11.2)g:(0.55-0.62)g:(60-64)mL.

3. The modified PEO electrolyte membrane according to claim 2, wherein, The molecular weight of the polyethylene oxide is 600000, and the molecular weight of the ethylene oxide units is 44; the lithium salt is lithium bistrifluoromethylsulfonylimide; the particle size of the two-dimensional reticular polyethylene glycol is 150-300μm; the particle size of the hollow SiO2 microspheres is 2-5μm; the molecular weight of the polyethylene glycol is 1000, and the emulsifier is polyethylene glycol 400 monostearate; the thickness of the modified PEO electrolyte film is 180-240μm.

4. A method for producing the modified PEO electrolyte membrane according to any one of claims 1 to 3, characterized by, The method comprises the following steps: S1, the hollow SiO2 microspheres are activated to obtain pretreated hollow SiO2 microspheres; the polyethylene glycol is melted at a first set temperature, the emulsifier is added and mixed to obtain a polyethylene glycol mixture; the cyclohexane is heated to a second set temperature, the polyethylene glycol mixture is added dropwise, first ultrasonic treatment is performed, the pretreated hollow SiO2 microspheres are added, first stirring is performed, and a polyethylene glycol inverse suspension is obtained; S2, the polyethylene glycol inverse suspension is placed in a gradient temperature for freezing, second stirring is performed at the same time, a frozen sample is obtained, the frozen sample is freeze-dried to obtain a freeze-dried product, the freeze-dried product is soaked in an alkaline solution for treatment, washed to neutral, dried and ground to obtain two-dimensional reticular polyethylene glycol; S3, the polyethylene oxide and the lithium salt are dissolved in acetonitrile to obtain a polymer electrolyte solution; the two-dimensional reticular polyethylene glycol is added to the polymer electrolyte solution, and third stirring is performed to obtain an organic modified electrolyte slurry; S4, the inorganic nanoparticles are added to the organic modified electrolyte slurry, second ultrasonic treatment is performed, a composite electrolyte slurry is obtained, and the composite electrolyte slurry is dried to obtain the modified PEO electrolyte film.

5. The method for preparing a modified PEO electrolyte membrane according to claim 4, characterized in that, The activation treatment of S1 comprises mixing the hollow SiO2 microspheres with anhydrous ethanol at a solid-liquid ratio of 1:15, ultrasonic dispersion at 280-300 W for 25-35 min, and vacuum drying to obtain pretreated hollow SiO2 microspheres.

6. The method for preparing a modified PEO electrolyte membrane according to claim 4, characterized in that, The first set temperature of S1 is 60-65 ℃, the second set temperature is 40-45 ℃, the dropping speed is 1-1.5 mL / min, the power of the first ultrasonic treatment is 400-450 W, the time is 18-22 min, and the first stirring time is 25-35 min.

7. The method for preparing a modified PEO electrolyte membrane according to claim 4, characterized in that, The gradient temperature of S2 is -20 ℃ to 0 ℃, the second stirring speed is 50-80 rpm, and the freezing time is 40-60 min.

8. The method for preparing a modified PEO electrolyte membrane according to claim 4, characterized in that, The parameters of the freeze-drying of S2 are -45 ℃, 0.08 mbar, the freeze-drying time is 22-24 h, the alkaline solution is 5% NaOH solution, and the soaking time is 1.5-2 h.

9. The method for preparing a modified PEO electrolyte membrane according to claim 4, characterized in that, The third stirring time of S3 is 12-24 h.

10. The method for preparing a modified PEO electrolyte membrane according to claim 4, characterized in that, The second ultrasonic treatment time of S4 is 1-1.5 h.

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