Preparation method of TPU coated Al2O3 porous polymer electrolyte membrane, electrolyte membrane and application thereof

Abstract

The invention discloses a preparation method of a TPU coated Al2O3 porous polymer electrolyte membrane, an electrolyte membrane and application thereof, and the preparation method comprises the following steps: S1, adding TPU into a solvent, and violently stirring for 12 hours to obtain a TPU solution; s2, adding nano aluminum oxide into the TPU solution, and violently stirring for 12 hours to obtain a TPU-coated AlO solution; and S3, sucking the TPU-coated AlO solution onto a glass plate, removing bubbles in vacuum, transferring the TPU-coated AlO solution into water, standing for 2 hours, stripping an obtained electrolyte membrane from the glass plate after the solvent and the water are completely replaced, taking out the electrolyte membrane, and drying the electrolyte membrane to obtain the TPU-coated AlO porous polymer electrolyte membrane. According to the preparation method of the TPU coated Al2O3 porous polymer electrolyte membrane, the electrolyte membrane and the application of the electrolyte membrane, an organic-inorganic composite porous polymer membrane is prepared through a physical mixing and phase transfer method, and the electrolyte membrane not only has relatively thin thickness and relatively light weight, but also has certain lithium dendrite resisting capability and can improve the safety of liquid absorption capability; the requirement of quick charging can be met, and the safety and performance of the battery are improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery material preparation, and specifically relates to a preparation method of a TPU@Al2O3 porous polymer electrolyte membrane, a TPU@Al2O3 porous polymer electrolyte membrane, and an application of the TPU@Al2O3 porous polymer electrolyte membrane in a battery. Background Art

[0002] In today's new energy era, energy storage devices are crucial for the efficient storage and utilization of energy. While numerous energy storage devices, such as supercapacitors and solar cells, each have their own unique characteristics, lithium-ion batteries, with their significant advantages such as high energy density, long cycle life, and low self-discharge, have emerged as one of the most widely used energy storage devices. They are widely used in electric vehicles, portable electronic devices, and other fields, significantly promoting the development of the new energy industry.

[0003] However, lithium-ion batteries are not without flaws. Traditionally, they use liquid electrolytes, which, while offering high ionic conductivity, carry the risk of thermal runaway. Under abnormal conditions such as high temperature, overcharging, and short circuits, the liquid electrolyte can combust or even explode, causing serious safety issues. This not only limits the application of lithium-ion batteries in safety-critical applications but also poses a potential threat to user safety and property.

[0004] To address the safety issues of liquid electrolytes, solid-state electrolytes have emerged. Solid-state electrolytes possess excellent thermal stability and mechanical properties, effectively preventing thermal runaway. However, their development is limited by several factors. For example, their relatively low ionic conductivity results in low battery charge and discharge efficiency; the high interfacial impedance between the solid electrolyte and the electrodes affects battery performance and lifespan; and the complex and costly preparation process for solid-state electrolytes limits their large-scale application.

[0005] Semi-solid electrolytes, a class intermediate between liquid and solid electrolytes, have attracted widespread attention from researchers. Combining the advantages of both liquid and solid electrolytes, these electrolytes mitigate safety risks and reduce the risk of thermal runaway. Furthermore, they offer excellent processability and improved ionic conductivity. Through rational design and fabrication, semi-solid electrolytes can achieve a favorable balance between safety and performance.

[0006] Celgard, a porous material widely used in commercial lithium-ion batteries, is the separator. This porous structure allows Celgard separators to effectively absorb electrolyte, providing the necessary medium for lithium ion transport. Furthermore, lithium ions can be transported through its pores, ensuring the normal charge and discharge process of the battery. However, commercial Celgard separators also have some shortcomings. To maintain a certain level of toughness, their pores are not distributed continuously and densely, which to some extent limits the lithium ion transport rate. Furthermore, to maintain good contact and wettability with the electrodes, commercial separators are very thin. While this thin structure reduces interfacial impedance and improves ionic conductivity, it also results in poor resistance to dendrite formation. At high current densities and voltages, lithium dendrites grow rapidly and are more likely to pierce the separator, causing a battery short circuit. Furthermore, at high temperatures, the separator shrinks and melts, ceasing to function, seriously compromising battery safety and stability.

[0007] Therefore, designing a safe porous polymer membrane that is thinner, lighter, has a certain ability to resist lithium dendrites, and can improve liquid absorption capacity to meet the needs of fast charging has become a research hotspot in the current lithium-ion battery field and a development direction expected by the public. Summary of the Invention

[0008] Purpose of the invention: In order to overcome the above shortcomings, the purpose of the present invention is to provide a method for preparing a TPU@Al2O3 porous polymer electrolyte membrane, an electrolyte membrane and its application. The design is reasonable. Through physical mixing and phase transfer method, an organic-inorganic composite porous polymer membrane is prepared. It has a thinner thickness and lighter weight, and has a certain ability to resist lithium dendrites, as well as the safety of improving liquid absorption capacity. It can meet the needs of fast charging, improve the safety and performance of the battery, and has broad application prospects.

[0009] The purpose of the present invention is achieved through the following technical solutions: A method for preparing a TPU@Al2O3 porous polymer electrolyte membrane comprises the following steps: S1: Add TPU to the solvent and stir vigorously at 45-80°C for 8-12 hours to obtain a TPU solution; S2: Add nano-alumina to the above TPU solution and stir vigorously at 45-80°C for 8-12 hours to obtain TPU@Al2O3 solution; S3: Using the phase transfer method, the above TPU@Al2O3 solution was pipetted onto a smooth and clean glass plate. After vacuum removal of bubbles, the solution was transferred to water and allowed to stand for 0.1-1 h. After the solvent and water were completely replaced, the obtained electrolyte membrane was peeled off from the glass plate. After removal, it was dried in an oven at 45-80°C for 8-12 h to obtain a TPU@Al2O3 porous polymer electrolyte membrane.

[0010] The TPU@Al2O3 porous polymer electrolyte membrane described in the present invention is prepared from a thermoplastic polyurethane elastomer (TPU) and nano-alumina (Al2O3) by physical mixing and phase transfer. TPU can not only effectively transmit lithium ions but also maintain good thermal stability and has good toughness. It is also abundant, readily available, and inexpensive. The hydrophilic hydroxyl groups on the surface of Al2O3 can improve the liquid absorption capacity of the polymer membrane and its wettability with electrodes after being composited with TPU to form a membrane. The addition of Al2O3 improves the ionic conductivity of the TPU-based semi-solid electrolyte, improves the mechanical strength of the polymer membrane, and enhances the liquid absorption capacity of the polymer membrane. The increased lithium salt concentration can better resist lithium dendrites, and the nano-alumina can mitigate the growth of lithium dendrites.

[0011] The TPU@Al2O3 porous polymer electrolyte membrane of the present invention has a three-dimensional porous structure that creates a dedicated lithium ion channel, and the pores are filled with Al2O3.

[0012] Furthermore, in the preparation method of the above-mentioned TPU@Al2O3 porous polymer electrolyte membrane, in S1, the solvent is a mixture of one or more of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, formamide, acetonitrile, toluene, xylene, and dichloromethane; the mass fraction of the TPU solution is 10~45%; and the mixture is vigorously stirred at 70°C for 12h.

[0013] Preferably, in S1, the solvent is N-methylpyrrolidone (NMP); the mass fraction of the TPU solution is 15%, which can ensure the stability and uniformity of the solution in the subsequent preparation process and is conducive to forming a good porous structure.

[0014] Furthermore, in the above-mentioned method for preparing the TPU@Al2O3 porous polymer electrolyte membrane, in S2, the particle size of the nano-alumina is 200~800nm, and the addition amount of the nano-alumina is 15~45wt% of the TPU solution; and the mixture is vigorously stirred at 70°C for 12h.

[0015] Preferably, in S2, the particle size of the nano-alumina is 400 nm, and the added amount of the nano-alumina is 30 wt % of the TPU solution.

[0016] Furthermore, in the above-mentioned method for preparing the TPU@Al2O3 porous polymer electrolyte membrane, in S3, the mixture is allowed to stand for 2 hours and then dried in an oven at 70°C for 12 hours.

[0017] In the phase transfer method, the replacement time of solvent NMP and is 2h, which can ensure that NMP is fully replaced by water, thereby forming a stable porous structure; the drying temperature is 70°C and the drying time is 12h, which can ensure the removal of moisture without destroying the structure and performance of the porous polymer membrane.

[0018] Furthermore, in the above-mentioned method for preparing the TPU@Al2O3 porous polymer electrolyte membrane, in S3, the TPU@Al2O3 porous polymer electrolyte membrane is punched into discs with a diameter of 8-16 mm and transferred to a glove box for standby use.

[0019] Preferably, the TPU@Al2O3 porous polymer electrolyte membrane is punched into discs with a diameter of 10 mm and transferred to a glove box for standby use.

[0020] The present invention also relates to an electrolyte membrane, which is prepared according to the above-mentioned method for preparing the TPU@Al2O3 porous polymer electrolyte membrane.

[0021] The present invention also relates to the application of the TPU@Al2O3 porous polymer electrolyte membrane, which is applied to lithium-ion batteries and has better safety performance and stability.

[0022] Furthermore, the above-mentioned TPU@Al2O3 porous polymer electrolyte membrane is applied to a symmetrical battery, and the symmetrical battery is assembled from a metal lithium sheet, a stainless steel sheet and a TPU@Al2O3 porous polymer electrolyte membrane.

[0023] Metal lithium was punched into a 10 mm diameter lithium sheet, pressed onto a stainless steel sheet, and assembled with a TPU@Al2O3 porous polymer electrolyte into a symmetrical battery.

[0024] Furthermore, the above-mentioned TPU@Al2O3 porous polymer electrolyte membrane is applied to a half-cell, and the half-cell is assembled by a lithium iron phosphate positive electrode sheet, a stainless steel sheet and a TPU@Al2O3 porous polymer electrolyte membrane.

[0025] The lithium iron phosphate positive electrode was punched into a lithium iron phosphate positive electrode sheet with a diameter of 8 mm and pressed onto a stainless steel sheet, and assembled with the TPU@Al2O3 porous polymer electrolyte into a half-cell.

[0026] Furthermore, the application of the above-mentioned TPU@Al2O3 porous polymer electrolyte membrane and the method for preparing the lithium iron phosphate positive electrode sheet include the following steps: (1) Weigh lithium iron phosphate, conductive carbon black, and polyvinylidene fluoride, wherein the mass ratio of lithium iron phosphate, conductive carbon black, and polyvinylidene fluoride is 90:5:5; grind lithium iron phosphate and polyvinylidene fluoride in a mortar for 5 to 20 minutes, add conductive carbon black after mixing, and continue grinding for 5 to 20 minutes. After the three are uniform in color and mixed evenly, add organic solvent and continue grinding for 5 to 20 minutes until a uniform black and bright positive electrode slurry is obtained; (2) Place the rough surface of a clean aluminum foil on a smooth glass plate, wipe the aluminum foil with anhydrous ethanol or deionized water and make the aluminum foil stick to the glass plate; transfer the positive electrode slurry prepared above to one end of the aluminum foil and roll it with a 100-200 μm applicator; transfer the coated positive electrode slurry to a sodium lamp to dry the organic solvent on the surface, and finally transfer it to a vacuum oven at 100-150 ° C for 10-20 hours to obtain a lithium iron phosphate positive electrode; (3) Use a punch to punch the dried lithium iron phosphate positive electrode into a lithium iron phosphate positive electrode sheet and transfer it to the glove box for standby use.

[0027] Preferably, the conductive carbon black is Super P.

[0028] Preferably, the solvent is NMP.

[0029] Preferably, lithium iron phosphate (LiFePO4, LFP) and polyvinylidene fluoride (PVDF) are first ground in a mortar for 10 minutes, and after being evenly mixed, conductive carbon black Super P is added and ground for another 10 minutes. After the three are uniform in color and evenly mixed, solvent NMP is added dropwise and ground for another 10 minutes until a uniform black and shiny positive electrode slurry is obtained.

[0030] Preferably, a 120 μm applicator roller is used.

[0031] Preferably, the mixture is dried in a vacuum oven at 110° C. for 12 h.

[0032] Preferably, a punch is used to punch the dried lithium iron phosphate positive electrode into a lithium iron phosphate positive electrode sheet with a diameter of 8 mm, and then the mass of each lithium iron phosphate positive electrode sheet is weighed. After removing the mass of the aluminum foil, the mass of the lithium iron phosphate active material is calculated according to the initial ratio, and finally the obtained lithium iron phosphate positive electrode sheet is transferred to a glove box for standby use.

[0033] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention discloses a method for preparing a TPU@Al2O3 porous polymer electrolyte membrane. By physical mixing and phase transfer, an organic-inorganic composite TPU@Al2O3 porous polymer membrane is prepared. The porous structure creates a special lithium ion channel, which accelerates the transmission of lithium ions in the electrolyte. Compared with a non-porous membrane, the porous membrane can allow lithium ions to shuttle between the positive and negative electrodes more efficiently, thereby achieving rapid charging of the battery. The porous structure also increases the specific surface area of the membrane, allowing the membrane to absorb more electrolyte, further enhancing the liquid absorption capacity. (2) The TPU@Al2O3 porous polymer electrolyte membrane disclosed in the present invention adopts TPU as the polymer matrix. TPU has good lithium ion transmission ability, good thermal stability, good toughness, abundant production and low price. The hydrophilic hydroxyl groups on the surface of nano-alumina can greatly improve the liquid absorption capacity of the polymer membrane and the wettability with the electrode after being compounded with TPU to form a membrane. The membrane with good liquid absorption capacity and wettability can reduce the internal resistance of the battery and improve the charge and discharge efficiency. After the nano-alumina is compounded with TPU, the microstructure of the electrolyte is changed, making the lithium ions more It is easy to move in it. At the same time, the porous structure also provides more channels for the transmission of lithium ions. The two work together to significantly improve the ionic conductivity. Nano-alumina, as an inorganic filler, can enhance the structural stability of the TPU matrix and make the diaphragm more durable. The electrolyte filled in the porous structure can increase the concentration of lithium salt. High concentration of lithium salt can better resist the growth of lithium dendrites. Nano-alumina filled in the pores can alleviate the growth of lithium dendrites. Nano-alumina can interact with lithium dendrites to hinder their further growth, thereby protecting the integrity of the diaphragm. (3) The application of the TPU@Al2O3 porous polymer electrolyte membrane disclosed in the present invention is applied in lithium-ion batteries. Compared with existing separators, the TPU@Al2O3 porous polymer electrolyte membrane has advantages in pore structure, dendrite resistance, and thermal stability. It can meet the needs of fast charging, improve the safety and performance of lithium-ion batteries, and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 XRD test patterns of the electrolyte membranes of Example 1, Comparative Example 1, and Comparative Example 2 of the present invention; Figure 2 SEM images of the electrolyte membrane (a, b) of Example 1 of the present invention and a commercial Celgard membrane (c); Figure 3 This is a graph showing thermal stability testing of the electrolyte membrane of Example 1 of the present invention and a commercial Celgard membrane; Figure 4 This is an impedance test diagram of the electrolyte membrane of Example 1 of the present invention; Figure 5 Graphs showing constant current charge and discharge tests at room temperature for the symmetrical batteries of Comparative Example 6 (a), Comparative Example 4 (b), and Example 8 (c) of the present invention; Figure 6 This is a diagram showing a constant current charge and discharge test of a symmetrical battery in Example 2 of the present invention at room temperature; Figure 7 This is a rate performance test diagram of the symmetrical battery of Example 2 of the present invention; Figure 8 This is a graph showing the number of cycles versus discharge specific capacity / coulombic efficiency of a half-cell of Example 3 of the present invention subjected to a constant current charge and discharge performance test at a charge and discharge rate of 1 C at room temperature; Figure 9 10, 50, 100, and 110 cycles of constant current charge and discharge performance testing of the half-cell of Example 3 of the present invention at room temperature at a charge and discharge rate of 1 C. DETAILED DESCRIPTION

[0035] The following is a summary of Example 1, Comparative Examples 1 to 3, Examples 2 to 3, Comparative Examples 4 to 9 in conjunction with the attached Figure 1 、 2 , 3, 4, 5, 6, 7, 8, 9 and specific experimental data clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work shall fall within the scope of protection of the present invention.

[0036] The TPU model in the following examples of the present invention is German Bayer 385A. Unless otherwise specified, the materials, methods and equipment used in the examples of the present invention are conventional materials, methods and equipment in this technical field.

[0037] The following Example 1 and Comparative Examples 1 to 3 provide an electrolyte membrane and a preparation method thereof.

[0038] Example 1 Example 1 is a TPU@Al2O3 porous polymer electrolyte membrane, the preparation of which includes the following steps: S1: Add a certain amount of TPU into a certain amount of NMP and stir vigorously at 70°C for 12 hours to prepare a TPU solution with a mass fraction of 15%; S2: Weigh a certain mass of the above TPU solution, calculate the mass of nano-alumina according to the 30% addition amount, weigh it and add it to the weighed TPU solution, and stir vigorously at 70°C for 12 hours to prepare TPU@Al2O3 solution; S3: Phase transfer method is used; first, a certain amount of evenly mixed TPU@Al2O3 solution is pipetted onto a smooth and clean glass plate. After vacuum removal of bubbles, the solution is transferred to deionized water and allowed to stand for 2 hours. After the NMP and water are completely replaced, the obtained electrolyte membrane is peeled off from the glass plate, taken out, and dried in a 70°C oven for 12 hours. The membrane is then punched into 10 mm diameter discs and transferred to a glove box for standby use, thereby obtaining a TPU@Al2O3 porous polymer electrolyte membrane.

[0039] Comparative Example 1 Comparative Example 1 is a TPU@Al2O3 non-porous polymer electrolyte membrane, the preparation of which includes the following steps: S1: Add a certain amount of TPU into a certain amount of NMP and stir vigorously at 70°C for 12 hours to prepare a TPU solution with a mass fraction of 15%; S2: Weigh a certain mass of the above TPU solution, calculate the mass of nano-alumina according to the 30% addition amount, weigh it and add it to the weighed TPU solution, and stir vigorously at 70°C for 12 hours to prepare TPU@Al2O3 solution; S3: Using the solution casting method; first, a certain amount of evenly mixed TPU@Al2O3 solution is pipetted into a polytetrafluoroethylene or battery shell mold. After removing bubbles, the solution is transferred to a vacuum drying oven at 70°C for 12 hours. After drying, the solution is peeled off from the mold, punched into 14 mm diameter discs, and transferred to a glove box for standby use to obtain a TPU@Al2O3 non-porous polymer electrolyte membrane.

[0040] Comparative Example 2 Comparative Example 2 is a TPU non-porous polymer electrolyte membrane, the preparation of which includes the following: S1: Add a certain amount of TPU into a certain amount of NMP and stir vigorously at 70°C for 12 hours to prepare a TPU solution with a mass fraction of 15%; S2: Use solution casting method; first, absorb a certain amount of evenly mixed TPU solution into a polytetrafluoroethylene or battery shell mold, remove bubbles, transfer to a vacuum drying oven at 70°C for 12 hours, peel off from the mold after drying, and then punch into 14 mm diameter discs and transfer to a glove box for standby use to obtain a TPU non-porous polymer electrolyte membrane.

[0041] Comparative Example 3 Comparative Example 3 is a TPU porous polymer electrolyte membrane, the preparation of which includes the following: S1: Add a certain amount of TPU into a certain amount of NMP and stir vigorously at 70°C for 12 hours to prepare a TPU solution with a mass fraction of 15%; S2: Phase transfer method was used; first, a certain amount of evenly mixed TPU solution was pipetted onto a smooth and clean glass plate. After vacuum removal of bubbles, the solution was transferred to deionized water and allowed to stand for 2 hours. After the NMP and water were completely replaced, the obtained electrolyte membrane was peeled off from the glass plate, taken out, and dried in a 70°C oven for 12 hours. The membrane was then punched into discs with a diameter of 10 mm and transferred to a glove box for later use, thereby obtaining a TPU porous polymer electrolyte membrane.

[0042] The following Example 2, Example 3, and Comparative Examples 4 to 9 provide a lithium-ion battery.

[0043] Example 2 The symmetrical battery of Example 2 uses the TPU@Al2O3 porous polymer electrolyte membrane of Example 1. Its preparation includes the following steps: bright and fresh metallic lithium is punched into lithium sheets with a diameter of 10 mm, pressed onto a stainless steel sheet, and assembled with the TPU@Al2O3 porous polymer electrolyte membrane of Example 1 into a symmetrical battery.

[0044] Example 3 The half-cell of Example 3 uses the TPU@Al2O3 porous polymer electrolyte membrane of Example 1, and its preparation includes the following: pressing a lithium iron phosphate positive electrode sheet onto a stainless steel sheet and assembling it with the TPU@Al2O3 porous polymer electrolyte membrane of Example 1 into a half-cell.

[0045] Among them, the preparation of lithium iron phosphate positive electrode sheets includes the following: (1) Lithium iron phosphate (LFP), conductive carbon black (Super P) and polyvinylidene fluoride (PVDF) were weighed, where the mass ratio of LFP, Super P and PVDF was 18:1:1; LFP and PVDF were first ground in a mortar for 10 minutes, and after they were evenly mixed, conductive carbon black was added and continued to be ground for 10 minutes. After the three were uniform in color and evenly mixed, an organic solvent was added and continued to be ground for 10 minutes until a uniform black and shiny positive electrode slurry was obtained; (2) Place the rough surface of a clean aluminum foil on a smooth glass plate, wipe the aluminum foil with anhydrous ethanol or deionized water and keep the aluminum foil close to the glass plate to prevent bubbles and wrinkles from affecting the performance of the positive electrode coating; transfer the positive electrode slurry prepared above to one end of the aluminum foil and roll it with a 120μm applicator; transfer the coated positive electrode slurry to a sodium lamp to dry the organic solvent on the surface, and finally transfer it to a vacuum oven at 110℃ for 12h to obtain a lithium iron phosphate positive electrode; (3) Use a punch to punch the dried lithium iron phosphate positive electrode into lithium iron phosphate positive electrode sheets with a diameter of 8 mm. Then weigh the mass of each lithium iron phosphate positive electrode sheet. After removing the mass of the aluminum foil, calculate the mass of the lithium iron phosphate active material according to the initial ratio. Finally, transfer the obtained lithium iron phosphate positive electrode sheets to the glove box for later use.

[0046] Comparative Example 4 The symmetrical battery of Comparative Example 4 uses the TPU@Al2O3 non-porous polymer electrolyte membrane of Comparative Example 1, and its preparation includes the following steps: bright and fresh metallic lithium is punched into lithium sheets with a diameter of 10 mm and pressed onto a stainless steel sheet, and then assembled with the TPU@Al2O3 non-porous polymer electrolyte membrane of Comparative Example 1 into a symmetrical battery.

[0047] Comparative Example 5 The half-cell of Comparative Example 5 uses the TPU@Al2O3 non-porous polymer electrolyte membrane of Comparative Example 1, and its preparation includes the following: pressing the lithium iron phosphate positive electrode sheet on a stainless steel sheet and assembling it with the TPU@Al2O3 non-porous polymer electrolyte membrane of Comparative Example 1 into a half-cell.

[0048] The preparation of the lithium iron phosphate positive electrode sheet is the same as that in Example 3.

[0049] Comparative Example 6 The symmetrical battery of Comparative Example 6 uses the TPU non-porous polymer electrolyte membrane of Comparative Example 2, and its preparation includes the following steps: punching bright and fresh metallic lithium into lithium sheets with a diameter of 10 mm and pressing them on a stainless steel sheet, and assembling them with the TPU non-porous polymer electrolyte membrane of Comparative Example 2 into a symmetrical battery.

[0050] Comparative Example 7 The half-cell of Comparative Example 7 uses the TPU non-porous polymer electrolyte membrane of Comparative Example 2, and its preparation includes the following: pressing the lithium iron phosphate positive electrode sheet on a stainless steel sheet and assembling it with the TPU non-porous polymer electrolyte membrane of Comparative Example 2 into a half-cell.

[0051] The preparation of the lithium iron phosphate positive electrode sheet is the same as that in Example 3.

[0052] Comparative Example 8 The symmetrical battery of Comparative Example 8 uses the TPU porous polymer electrolyte membrane of Comparative Example 3, and its preparation includes the following steps: punching bright and fresh metallic lithium into lithium sheets with a diameter of 10 mm and pressing them on a stainless steel sheet, and assembling them with the TPU porous polymer electrolyte membrane of Comparative Example 3 into a symmetrical battery.

[0053] Comparative Example 9 The half-cell of Comparative Example 9 uses the TPU porous polymer electrolyte membrane of Comparative Example 3, and its preparation includes the following: pressing the lithium iron phosphate positive electrode sheet on a stainless steel sheet and assembling it with the TPU porous polymer electrolyte membrane of Comparative Example 3 into a half-cell.

[0054] The preparation of the lithium iron phosphate positive electrode sheet is the same as that in Example 3.

[0055] Effect verification The electrolyte membranes of Example 1, Comparative Example 1 and Comparative Example 2 of the present invention were subjected to XRD test. The test results are as follows: Figure 1 shown.

[0056] Depend on Figure 1 It can be seen that the electrolyte membrane of Comparative Example 2 ( Figure 1 The intensity of the main peak at 20.3° is still very high. After adding nano-alumina, the electrolyte membrane of Example 1 ( Figure 1 The electrolyte membrane of comparative example 1 ( Figure 1 The intensity of the main peak at 20.3° for the non-porous TPU@Al2O3 (labeled as non-porous TPU@Al2O3) decreases, and the two curves overlap. Compared to the electrolyte membrane of Comparative Example 2, the addition of nano-alumina reduces the crystallinity of the TPU and increases the amorphous region of the composite polymer separator, which facilitates lithium ion transport. Furthermore, the characteristic peaks of nano-alumina are also present in the electrolyte membranes of Example 1 and Comparative Example 1, indicating that the porous structure is successfully doped with nano-alumina and that it is not separated during the phase transfer process.

[0057] The electrolyte membrane of Example 1 of the present invention and the commercial Celgard membrane were subjected to SEM testing. The test results are as follows: Figure 2 shown.

[0058] Depend on Figure 2 It can be seen that: Example 1 ( Figure 2 The surface of the electrolyte membrane of a and b) is distributed with uniform pores of basically the same size. The pores are three-dimensionally distributed and stacked layer by layer. Nano-aluminum oxide exists in the pores, and nano-aluminum oxide particles are also evenly distributed in the TPU polymer matrix. This structure, on the one hand, opens up the channel for lithium ion transmission, and on the other hand, reduces the crystallinity of the TPU polymer matrix skeleton, and lithium ions can also be better transmitted in the TPU matrix. The three-dimensional distribution of pores stacked layer by layer can inhibit the growth of "lithium dendrites" on the surface of metallic lithium, making it difficult to directly pierce the diaphragm and cause battery short circuit. Compared with the commercial Celgard diaphragm ( Figure 2 c), it can be seen that its pore distribution is discontinuous. Such a structure provides fewer lithium ion transmission channels, slowing down the transmission speed of lithium ions.

[0059] Thermal stability tests were conducted on the electrolyte membrane of Example 1 of the present invention and the commercial Celgard membrane. The test results are as follows: Figure 3 shown.

[0060] Depend on Figure 3 Available: Place a layer of aluminum foil on the heating table and place the commercial Celgard membrane ( Figure 3 Celgard) and the electrolyte membrane of Example 1 ( Figure 3The commercial Celgard membrane (labeled as porous TPU@Al2O3) was punched into a 19mm diameter disc and placed on a heating table. Photos were taken at room temperature for comparison. The temperature was then raised from 80°C, maintaining the temperature for 5 minutes at 20°C intervals. When heated to 120°C, the commercial Celgard membrane began to deform. At 140°C, the commercial Celgard membrane was in a semi-twisted state until it completely melted at 160°C. The electrolyte membrane of Example 1 maintained its shape without any change, indicating that the electrolyte membrane of Example 1 has excellent thermal stability and is highly safe for use in lithium-ion batteries.

[0061] The electrolyte membranes of Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3 of the present invention and the commercial Celgard membrane were tested for liquid absorption rate, porosity, and ionic conductivity. The test results are shown in Table 1. The calculation method is as follows: Porosity calculation: The electrolyte membrane was punched into a circle with a diameter of 16 mm, its thickness was measured, and the initial mass Ma was weighed. It was then immersed in n-butanol until saturated. After being taken out and the surface solvent was wiped off, the total mass Mb was weighed. The porosity of the electrolyte membrane was calculated using the formula η = (M-M0) / M0.

[0062] Liquid absorption rate calculation: Weigh the initial mass M0 of the electrolyte membrane, then soak the electrolyte membrane in the electrolyte until saturated. After removing it, gently wipe off the surface solution, and then weigh the total mass M. The liquid absorption rate of the electrolyte membrane is calculated according to the formula η = (Mb-Ma) / ρV, where ρ is the density of n-butanol and V is the volume of the electrolyte membrane.

[0063] Ionic conductivity test: The electrolyte membrane was punched into a circle with a diameter of 10 mm, and the thickness and diameter were measured. Then, the membrane was placed between two stainless steel sheets (SS) to assemble an SS / electrolyte membrane / SS symmetrical cell. The ionic conductivity of the electrolyte membrane was tested by AC impedance in an electrochemical workstation at a test frequency range of 1 Hz to 10 6 Hz. According to the formula б=d / (R b S) to calculate the ionic conductivity, d is the thickness of the electrolyte membrane, Rb is the test impedance, and S is the area of the electrolyte membrane. In addition, the impedance diagram of the porous TPU@Al2O3 (i.e., the electrolyte membrane of Example 1) in the assembled SS / porous TPU@Al2O3 (i.e., the electrolyte membrane of Example 1) / SS symmetric cell is shown in the figure: Figure 4 shown.

[0064] Table 1 Liquid absorption, porosity, and ionic conductivity of the electrolyte membranes of Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3 of the present invention and the commercial Celgard membrane Combined with Table 1, Figure 4It can be seen that porosity and liquid absorption are directly proportional. The electrolyte membrane of Example 1 has the highest porosity and liquid absorption, and the highest ionic conductivity. Although the electrolyte membranes of Comparative Examples 1 and 2 have no pores, the polymer swells in response to liquid and also has a certain liquid absorption rate.

[0065] The symmetrical batteries of Comparative Examples 4, 6 and 8 of the present invention were subjected to constant current charge and discharge tests at room temperature. The test results are as follows: Figure 5 The symmetrical battery of Example 2 of the present invention was subjected to constant current charge and discharge tests at room temperature. The test results are shown in FIG. Figure 6 shown.

[0066] Depend on Figure 5 、 6 It can be seen that the symmetrical cells assembled with the electrolyte membranes of Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3, i.e., the symmetrical cells of Example 2, Comparative Example 4, Comparative Example 6, and Comparative Example 8, have a high sensitivity of 1 mA / cm 2 The test was conducted by constant current charge and discharge for 1 h each. Figure 5 As shown, the symmetrical battery of Comparative Example 6 ( Figure 5 a, and marked as Li / non-porous TPU / Li) can only be stably cycled for 100 h, with a stable polarization voltage of 50 Mv. The symmetrical battery of Example 8 ( Figure 5 The symmetrical battery of Example 4 ( Figure 5 b, and marked as Li / non-porous TPU@Al2O3 / Li) stably cycled for 750 h with a polarization voltage of 70 mV. Therefore, the porous separator has better cycling stability than the non-porous separator, and the cycling stability is even better when nano-alumina is added. Figure 6 As shown, the symmetrical battery of Example 2 ( Figure 6 The three-dimensional porous structure provides a lithium ion transmission channel, and the lithium ions can be transmitted in the TPU skeleton. Therefore, the battery can be stably cycled for 2000 h with very small polarization and no dendrite growth.

[0067] The rate performance of the symmetrical battery of Example 2 of the present invention was tested, and the test results are as follows: Figure 7 shown.

[0068] Depend on Figure 7 It can be seen that the symmetrical battery of Example 2 ( Figure 7 Marked as Li / porous TPU@Al2O3 / Li), at 1mA / cm 2At a current density of 2 mA / cm, the polarization voltage is 25 mV. When the current density increases to 2 mA / cm 2 When the polarization voltage increases to 50 mV, the current density increases to 5 mA / cm 2 When the polarization voltage increases to 130 mV, the current density increases to 10 mA / cm 2 When the polarization voltage increases to 220 mV, the current density returns to 1 mA / cm 2 When the polarization voltage is 10 mA / cm2, the polarization voltage will also drop to 22 mV, and then the cycle will be stable for 300 h. This shows that the porous TPU@Al2O3 electrolyte membrane can withstand 10 mA / cm2 2 The current density, high current charge and discharge without direct short circuit, and the excellent rate performance of the porous TPU@Al2O3 electrolyte membrane, as well as its strong ability to suppress lithium dendrites, also show that the porous TPU@Al2O3 electrolyte membrane has excellent cycle stability and is stable enough to withstand high current cycles, which has the potential to achieve fast charging.

[0069] The half-cell of Example 3 of the present invention was subjected to constant current charge and discharge performance test at room temperature, wherein the test voltage window range was 2 to 4.2 V and the charge and discharge rate was 1 C. The test results are as follows: Figure 8 、 9 shown.

[0070] Figure 8 For the half-cell of Example 3 ( Figure 8 The number of cycles (marked as Li / porous TPU@Al2O3 / Li) - discharge capacity / Coulombic efficiency is given by Figure 8 As shown in the figure: the first ten cycles are a battery activation process, so the coulombic efficiency of the first ten cycles is relatively low. The discharge capacity of the half-cell of Example 3 in the first cycle is 159.9 mAh / g, and the coulombic efficiency is 20.97%; the discharge capacity of the 11th cycle after stabilization is 147.6 mAh / g, and the coulombic efficiency is 96.01%; after 110 cycles, the discharge capacity is 154.5 mAh / g, and the coulombic efficiency is 98.79%; after 110 cycles, the capacity retention rate is 96.6%, and the coulombic efficiency has almost no change.

[0071] Figure 9 For the half-cell of Example 3 ( Figure 8 The capacity-voltage curves of the 10th, 50th, 100th, and 110th cycles of the porous TPU@Al2O3 / Li are shown in Fig. Figure 9 As shown in the figure, as the cycle of the half-cell of Example 3 stabilizes, the voltage polarization becomes smaller and smaller, and the charge and discharge voltage platforms at the 110th cycle are 3.56 and 3.28 V, respectively. This shows that the half-cell of Example 3 has good cycle performance.

[0072] In summary, the present invention prepares an organic-inorganic composite porous polymer membrane through physical mixing and phase transfer method. It has a thinner thickness and lighter weight, and has a certain ability to resist lithium dendrites. It can also improve the safety of liquid absorption capacity, meet the needs of fast charging, and improve the safety and performance of lithium-ion batteries.

[0073] The present invention has many specific application paths, and the above is only a preferred embodiment of the present invention. It should be noted that the above embodiments are only used to illustrate the present invention and are not intended to limit the scope of protection of the present invention. For those skilled in the art, several improvements can be made without departing from the principles of the present invention, and these improvements should also be considered as the scope of protection of the present invention.

Claims

1. A method for preparing a TPU@Al2O3 porous polymer electrolyte membrane, characterized in that: The steps include: S1: Add TPU to the solvent and stir vigorously at 45-80°C for 8-12 hours to obtain a TPU solution; S2: Add nano-alumina to the above TPU solution and stir vigorously at 45-80°C for 8-12 hours to obtain TPU@Al2O3 solution; S3: Using the phase transfer method, the above TPU@Al2O3 solution was pipetted onto a smooth and clean glass plate. After vacuum removal of bubbles, the solution was transferred to water and allowed to stand for 0.1-1 h. After the solvent and water were completely replaced, the obtained electrolyte membrane was peeled off from the glass plate. After removal, it was dried in an oven at 45-80°C for 8-12 h to obtain a TPU@Al2O3 porous polymer electrolyte membrane.

2. The method for preparing the TPU@Al2O3 porous polymer electrolyte membrane according to claim 1, characterized in that: In S1, the solvent is one or a mixture of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, formamide, acetonitrile, toluene, xylene, and dichloromethane; the mass fraction of the TPU solution is 10-45%; and the mixture is vigorously stirred at 70°C for 12 hours.

3. The method for preparing the TPU@Al2O3 porous polymer electrolyte membrane according to claim 1, characterized in that: In the S2, the particle size of the nano-alumina is 200-800 nm, and the amount of the nano-alumina added is 15-45 wt % of the TPU solution; the mixture is vigorously stirred at 70° C. for 12 h.

4. The method for preparing the TPU@Al2O3 porous polymer electrolyte membrane according to claim 1, wherein: In the above-mentioned S3, the mixture was allowed to stand for 2 hours and then dried in an oven at 70° C. for 12 hours.

5. The method for preparing the TPU@Al2O3 porous polymer electrolyte membrane according to claim 1, characterized in that: In S3, the TPU@Al2O3 porous polymer electrolyte membrane is punched into discs with a diameter of 8-16 mm and transferred to a glove box for standby use.

6. An electrolyte membrane, characterized in that The TPU@Al2O3 porous polymer electrolyte membrane is prepared according to the preparation method of any one of claims 1 to 5.

7. The use of the electrolyte membrane according to claim 6, characterized in that: The TPU@Al2O3 porous polymer electrolyte membrane is applied to lithium-ion batteries.

8. The use of the electrolyte membrane according to claim 7, characterized in that: The TPU@Al2O3 porous polymer electrolyte membrane is applied to a symmetrical battery, which is assembled from a metal lithium sheet, a stainless steel sheet, and the TPU@Al2O3 porous polymer electrolyte membrane.

9. The use of the electrolyte membrane according to claim 7, characterized in that: The TPU@Al2O3 porous polymer electrolyte membrane is applied to a half-cell, which is assembled from a lithium iron phosphate positive electrode sheet, a stainless steel sheet, and the TPU@Al2O3 porous polymer electrolyte membrane.

10. Use of the electrolyte membrane according to claim 9, characterized in that: The method for preparing the lithium iron phosphate positive electrode sheet comprises the following steps: (1) Weigh lithium iron phosphate, conductive carbon black, and polyvinylidene fluoride, wherein the mass ratio of lithium iron phosphate, conductive carbon black, and polyvinylidene fluoride is 90:5:5; grind lithium iron phosphate and polyvinylidene fluoride in a mortar for 5 to 20 minutes, add conductive carbon black after mixing, and continue grinding for 5 to 20 minutes. After the three are uniform in color and mixed evenly, add organic solvent and continue grinding for 5 to 20 minutes until a uniform black and bright positive electrode slurry is obtained; (2) Place the rough surface of a clean aluminum foil on a smooth glass plate, wipe the aluminum foil with anhydrous ethanol or deionized water and make the aluminum foil stick to the glass plate; transfer the positive electrode slurry prepared above to one end of the aluminum foil and roll it with a 100-200 μm applicator; transfer the coated positive electrode slurry to a sodium lamp to dry the organic solvent on the surface, and finally transfer it to a vacuum oven at 100-150 ° C for 10-20 hours to obtain a lithium iron phosphate positive electrode; (3) Use a punch to punch the dried lithium iron phosphate positive electrode into a lithium iron phosphate positive electrode sheet and transfer it to the glove box for standby use.

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