High-performance blended polymer lithium ion solid-state electrolyte, preparation method and application thereof

Abstract

The application relates to a high-performance blended polymer lithium ion solid electrolyte as well as a preparation method and application thereof, and comprises the following steps: step-by-step stirring and dissolving lithium salt, polyvinylidene fluoride and polyethylene oxide in N-methylpyrrolidone and anhydrous acetonitrile to obtain a copolymer mixture solution; uniformly laying the copolymer mixture solution in an open container, drying in an atmospheric environment, and then drying in a vacuum environment to obtain the high-performance blended polymer lithium ion solid electrolyte. The obtained solid electrolyte is little affected by air humidity, has good thermal stability, high ionic conductivity and good mechanical properties, and simultaneously has the technical effect that when the solid electrolyte is applied to a battery, the battery has a long cycle life.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion solid-state battery technology, and particularly relates to a high-performance blended polymer lithium-ion solid electrolyte, its preparation method, and its application. Background Technology

[0002] Polymer solid electrolytes are a common type of solid electrolyte, typically referring to electrolytes containing polymer materials and capable of ion migration. They consist of three main parts: a polymer matrix, a lithium salt, and additives. The polymer matrix provides the supporting framework and ion transport medium, requiring good solubility for the lithium salt, easy dissociation of the lithium salt, and easy diffusion of the dissociated ions. The lithium salt provides lithium ions; to improve the lithium ion concentration and migration ability in the polymer system, lithium salts with low lattice energy, high anion charge delocalization, high dispersion constant, and good stability are usually selected.

[0003] Research on solid polymer electrolytes began in 1973 when Wright et al. discovered the conductivity of polyoxyethylene (PEO) complexes with alkali metal ions. This discovery laid the foundation for the research of polymer solid electrolytes. Since then, with the continuous deepening of research and the development of technology, polymer solid electrolytes have gradually become a new type of electrolyte material with broad application prospects.

[0004] Polymer solid electrolytes have advantages such as light weight, good film-forming properties, good viscoelasticity and stability. In the field of lithium-ion batteries and fuel cells, the application of polymer solid electrolytes will help improve the safety, stability and energy density of batteries, thereby meeting the demand for high-performance batteries in electric vehicles, mobile devices and other fields.

[0005] However, polymer solid electrolytes made from single components are susceptible to problems such as moisture and temperature, which hinder their production and application.

[0006] In summary, exploring a simple and feasible method and technology for preparing solid polymer films is of great significance for the research and development of solid electrolytes for lithium batteries. Summary of the Invention

[0007] In view of the problems existing in the prior art, the present invention provides a high-performance blended polymer lithium-ion solid electrolyte, its preparation method and application, which prepares a solid electrolyte membrane with a smooth and flat surface and no internal bubbles. The solid electrolyte membrane is less affected by air humidity, has good thermal stability, high ionic conductivity and good mechanical properties. At the same time, its application in batteries has technical effects such as long cycle life.

[0008] Specifically, the present invention provides the following technical solution:

[0009] A method for preparing a high-performance blended polymer lithium-ion solid electrolyte includes the following steps:

[0010] S1) Dissolve lithium salt in N-methylpyrrolidone to obtain a lithium salt solution;

[0011] S2) Under stirring conditions, the ground polyvinylidene fluoride and polyethylene oxide are dissolved in the lithium salt solution and anhydrous acetonitrile, respectively, to obtain a lithium salt-polyvinylidene fluoride mixed solution and a polyethylene oxide solution, respectively.

[0012] S3) Under stirring conditions, the polyethylene oxide solution is added dropwise to the lithium salt-polyvinylidene fluoride mixed solution to obtain a copolymer mixture solution;

[0013] S4) The copolymer mixture solution is evenly spread in an open container, dried at 45-60°C for 1-2 hours under normal pressure, and then dried at 45-55°C for 20-30 hours under vacuum to obtain the high-performance blended polymer lithium-ion solid electrolyte.

[0014] Specifically, the material is first dried in an atmospheric pressure environment for a certain period of time, and then dried in a vacuum environment for a certain period of time. The purpose is to remove some acetonitrile in advance to avoid excessive acetonitrile in the copolymer mixture solution, which would lead to excessive absorption of acetonitrile during film formation. Ultimately, excessive acetonitrile in the solid electrolyte would come into contact with moisture in the air, causing the solid electrolyte to absorb water too quickly and become too wet. This would result in the undesirable effect of being easily affected by moisture, leading to a decline in performance.

[0015] Preferably, the product is dried at 60°C for 2 hours under normal pressure or at 50°C for 24 hours under vacuum.

[0016] Further, the lithium salt is LiClO4, LiFSI, or LiTFSI (C2F6LiNO4S2); preferably C2F6LiNO4S2.

[0017] Furthermore, the molecular weight of the polyvinylidene fluoride is 80-120W, preferably 100W; and the molecular weight of the polyethylene oxide is 50-70W, preferably 60W.

[0018] Furthermore, the grinding specifically refers to grinding until fine and free of large particles.

[0019] Furthermore, the mass ratio of the polyethylene oxide to the polyvinylidene fluoride is 1:9-3:7, that is, the polyethylene oxide accounts for 10%-30% of the total mass of the polyethylene oxide and the polyvinylidene fluoride.

[0020] Specifically, an excessively high proportion of polyethylene oxide can lead to adverse effects such as rough solid electrolyte surface, decreased ionic conductivity, and reduced battery cycle life.

[0021] Preferably, the mass ratio of the polyethylene oxide to the polyvinylidene fluoride is 2:8.

[0022] Furthermore, the total mass ratio of the lithium salt to the polyvinylidene fluoride and the polyethylene oxide is 3:10-5:10.

[0023] Preferably, the total mass ratio of the lithium salt to the polyvinylidene fluoride and the polyethylene oxide is 4.5:10.

[0024] Furthermore, the mass-to-volume ratio of the polyvinylidene fluoride to the N-methylpyrrolidone is 1:9-13 g / mL.

[0025] Specifically, too little N-methylpyrrolidone will result in incomplete dissolution of the polyvinylidene fluoride, while too much N-methylpyrrolidone will cause the polyvinylidene fluoride solution to be too dilute or to overflow (separate layering).

[0026] Preferably, the mass-to-volume ratio of the polyvinylidene fluoride to the N-methylpyrrolidone is 1:10 g / mL.

[0027] Furthermore, the mass-to-volume ratio of the polyethylene oxide to the anhydrous acetonitrile is 1:8-12 g / mL.

[0028] Specifically, too little anhydrous acetonitrile will result in incomplete dissolution of the polyethylene oxide, while too much anhydrous acetonitrile will cause the polyethylene oxide solution to be too dilute or to overflow (separate layering).

[0029] Preferably, the mass-to-volume ratio of the polyethylene oxide to the anhydrous acetonitrile is 1:10 g / mL.

[0030] Furthermore, in step S2), the stirring time is 6-10 hours.

[0031] Furthermore, in step S3), the stirring time is 1-3 hours.

[0032] Furthermore, in steps S2) and S3), the stirring speed is 500-800 r / min.

[0033] Specifically, in steps S2) and S3), the stirring time should not be too long, especially in step S3). If the stirring time is too long, the acetonitrile will evaporate, which will cause the original lithium salt to be adsorbed on the inner wall and cause agglomeration. After the film is poured, the film will be obviously rough.

[0034] Preferably, in step S2), the stirring time is 6 hours; in step S3), the stirring time is 2 hours.

[0035] The present invention also provides a high-performance blended polymer lithium-ion solid electrolyte membrane prepared by the above preparation method.

[0036] The present invention also provides an application of the above-mentioned high-performance blended polymer lithium-ion solid electrolyte in a battery.

[0037] Furthermore, the high-performance blended polymer lithium-ion solid electrolyte replaces the electrolyte and separator in the lithium-ion battery.

[0038] Beneficial effects:

[0039] 1. This invention utilizes N-methylpyrrolidone (NMP) and anhydrous acetonitrile to dissolve polyvinylidene fluoride (PVDF) and polyethylene oxide (PEO), respectively. By taking advantage of the different evaporation points of N-methylpyrrolidone and anhydrous acetonitrile, the PVDF and PEO are mixed uniformly and channels that facilitate the passage of lithium ions are formed, thus preparing a polymer solid electrolyte membrane with a smooth and flat surface and no internal bubbles.

[0040] 2. This invention further controls various parameters in the solid electrolyte preparation process. For example, the dissolution and stirring time should not be too long, especially in step S3). If the stirring time is too long, acetonitrile will volatilize, causing the original lithium salt to be adsorbed on the inner wall and resulting in agglomeration. The film formed after casting will be noticeably rough. Drying in a normal pressure environment for a certain period of time, followed by drying in a vacuum environment for a certain period of time, aims to remove some acetonitrile in advance, avoiding excessive acetonitrile in the copolymer solution. This would lead to excessive acetonitrile absorption during film formation, ultimately causing the solid electrolyte to absorb water too quickly due to excessive acetonitrile in contact with moisture in the air, resulting in an overly wet phenomenon. This means the solid electrolyte is easily affected by moisture, leading to a decline in performance.

[0041] 3. Furthermore, this invention controls the ratio of polyvinylidene fluoride and polyethylene oxide in a completely dissolved state, and the resulting solid electrolyte membrane not only has a smooth and flat surface and no internal bubbles, but is also less affected by air humidity, has good thermal stability, high ionic conductivity and good mechanical properties. At the same time, its application in batteries has technical effects such as long cycle life. Attached Figure Description

[0042] Figure 1 The diagram shows the solution state and final solid electrolyte (membrane) of the copolymer mixtures of Examples 1-3 and Comparative Example 1 of the present invention;

[0043] Figure 2 The diagram shows the solution state and final solid electrolyte (membrane) of the copolymer mixture in Comparative Example 3 of this invention;

[0044] Figure 3 These are scanning electron microscope (SEM) images of the final solid electrolyte (membrane) of Examples 1-3 and Comparative Example 1 of the present invention.

[0045] Figure 4 The following are DSC diagrams of the final solid electrolyte (membrane) of Examples 1-3 and Comparative Examples 1-2 of the present invention;

[0046] Figure 5 The graph shows the conductivity changes of the final solid electrolyte (membrane) of Examples 1-3 and Comparative Examples 1-2 of the present invention as a function of temperature.

[0047] Figure 6 The tensile properties test diagrams are of the final solid electrolyte (membrane) of Examples 1-3 and Comparative Examples 1-2 of the present invention.

[0048] Figure 7 The graphs show the cycle performance of the final solid electrolyte (membrane) of Examples 1-3 and Comparative Examples 1-2 after they are made into batteries. Detailed Implementation

[0049] The technical solutions provided by the present invention will be described more clearly below with reference to the embodiments and accompanying drawings, but the scope of protection claimed by the present invention is not limited to the following embodiments.

[0050] Example 1:

[0051] A method for preparing a high-performance blended polymer lithium-ion solid electrolyte:

[0052] Weigh 0.45g of lithium bis(trifluoromethanesulfonylimide) (C2F6LiNO4S2), wherein the C2F6LiNO4S2 is a sample that has been dried in a drying oven at 60°C for 24 hours and then cooled to room temperature in the oven.

[0053] Weigh 0.9g of PVDF with a molecular weight of 100W and 0.1g of PEO with a molecular weight of 60W, and grind them separately in an agate grinding bowl to make them finer and free of large particles.

[0054] Lithium salt C2F6LiNO4S2 was dissolved in 9 mL of NMP to obtain a lithium salt solution. While stirring, ground PVDF was added to the lithium salt solution and stirred at 600 r / min for 6 h to obtain a lithium salt-PVDF mixed solution. While stirring, ground PEO was added to 1 mL of anhydrous acetonitrile and stirred at 600 r / min for 6 h to obtain a PEO solution.

[0055] While stirring, the PEO solution was added dropwise to the lithium salt-PVDF mixed solution, and the mixture was stirred at 600 r / min for 2 h to obtain a copolymer mixture solution;

[0056] The copolymer mixture solution was evenly spread in a petri dish, then dried in an oven at 60°C for 2 hours, and then dried in a vacuum drying oven at 50°C for 24 hours to obtain the high-performance blended polymer lithium-ion solid electrolyte (membrane).

[0057] Example 2:

[0058] The only difference from Example 1 is that: PVDF is 0.8g, NMP is 8mL; PEO is 0.2g, and anhydrous acetonitrile is 2mL.

[0059] Example 3:

[0060] The only difference from Example 1 is that: PVDF is 0.7g, NMP is 7mL; PEO is 0.3g, and anhydrous acetonitrile is 3mL.

[0061] Comparative Example 1:

[0062] The only difference from Example 1 is that: PVDF is 0.6g, NMP is 6mL; PEO is 0.4g, and anhydrous acetonitrile is 4mL.

[0063] Comparative Example 2:

[0064] The only difference from Example 1 is that: PVDF is 1g, NMP is 10mL; PEO is 0g, and anhydrous acetonitrile is 0mL.

[0065] Comparative Example 3:

[0066] The only difference from Example 2 is that the PEO solution was added dropwise to the lithium salt-PVDF mixed solution while stirring, and the mixture was stirred for 4 hours to obtain a copolymer mixture solution.

[0067] Results analysis:

[0068] like Figure 1 As shown, from left to right, the copolymer mixture solution states and final solid electrolyte (membrane) diagrams of Examples 1, 2, 3, and Comparative Example 1 are presented. Among them, compared with Examples 1-3, the copolymer mixture solution of Comparative Example 1 has the lowest transparency, and the membrane formed is rough and uneven with agglomeration, indicating that the compatibility between PVDF and PEO has deteriorated. Excessive PEO is lost to the membrane surface or membrane pores during the film formation process, resulting in a loose internal structure of the membrane.

[0069] like Figure 2 As shown, Figure 2 The left-hand figure shows the state of the copolymer mixture solution in Comparative Example 3. Compared with Example 2, the acetonitrile evaporated due to the excessive stirring time, which caused the original lithium salt to be adsorbed on the inner wall and resulted in agglomeration. Figure 2 The right side of the figure shows the final solid electrolyte (membrane) of Comparative Example 3. Compared with Example 2, its film formation is significantly rougher.

[0070] like Figure 3As shown, from left to right, are the surface scanning electron microscope (SEM) images of the final solid electrolyte (membrane) of Example 1, Example 2, Example 3, and Comparative Example 1. Among them, the membrane surface of Example 2 is the smoothest, with almost no aggregation, while the membrane surface of Comparative Example 1 has the worst smoothness and more aggregation.

[0071] like Figure 4 As shown, PVDF has a melting point of 160℃. After blending with PEO, the melting point shifts to the right, and the thermal stability is improved.

[0072] like Figure 5 As shown, compared to Comparative Example 2, at the same temperature, Examples 1-3 exhibit higher electrical conductivity, with the conductivity of Examples 1-3 increasing more significantly with increasing temperature. Conversely, the conductivity of Comparative Example 1 decreases.

[0073] like Figure 6 As shown, compared to Comparative Example 2, Examples 1-3 all obtained higher tensile strain at break and tensile strength values. Comparative Example 1, however, only obtained a better tensile strain at break, with almost no improvement in its tensile strength. Therefore, Examples 1-3 of the present invention achieved excellent mechanical properties.

[0074] The dried solid electrolytes of Examples 1-3 and Comparative Examples 1-2 were cut into sheets using a battery die-cutting machine. The cut solid electrolyte (membrane) sheets were then assembled into lithium-ion button cells in a glove box. The assembly sequence for a symmetrical cell was: positive electrode shell, lithium sheet, solid electrolyte (membrane), lithium sheet, spacer, spring contact, and negative electrode shell. The assembled cells were left to stand at room temperature for 24 hours, followed by performance testing at room temperature. The final results are as follows: Figure 7 As shown, compared to Comparative Example 1, Example 2 has the longest cycle life, followed by Example 3 and Example 1, while Comparative Example 2 is relatively poor.

[0075] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A method for preparing a high-performance blended polymer lithium-ion solid electrolyte, characterized in that, Includes the following steps: S1) Dissolve lithium salt in N-methylpyrrolidone to obtain a lithium salt solution; S2) Under stirring conditions, the ground polyvinylidene fluoride and polyethylene oxide are respectively placed in the lithium salt solution and anhydrous acetonitrile and stirred to dissolve, respectively, to obtain lithium salt-polyvinylidene fluoride mixed solution and polyethylene oxide solution; S3) Under stirring conditions, the polyethylene oxide solution is added dropwise to the lithium salt-polyvinylidene fluoride mixed solution to obtain a copolymer mixture solution; S4) The copolymer mixture solution is evenly spread in an open container, dried at 45-60°C for 1-2 hours under normal pressure, and then dried at 45-55°C for 20-30 hours under vacuum to obtain the high-performance blended polymer lithium-ion solid electrolyte. The mass ratio of the polyethylene oxide to the polyvinylidene fluoride is 1:9-3:7; The total mass ratio of the lithium salt to the polyvinylidene fluoride and the polyethylene oxide is 3:10-5:10; The mass-to-volume ratio of the polyvinylidene fluoride to the N-methylpyrrolidone is 1:9-13 g / mL; The mass-to-volume ratio of the polyethylene oxide to the anhydrous acetonitrile is 1:8-12 g / mL.

2. The preparation method according to claim 1, characterized in that, In step S2), the stirring time is 6-10 hours.

3. The preparation method according to claim 1, characterized in that, In step S3), the stirring time is 1-3 hours.

4. A high-performance blended polymer lithium-ion solid electrolyte prepared by the preparation method according to any one of claims 1-3.

5. The application of the high-performance blended polymer lithium-ion solid electrolyte according to claim 4 in batteries.

6. The application according to claim 5, characterized in that, The high-performance blended polymer lithium-ion solid electrolyte replaces the electrolyte and separator in lithium-ion batteries.

Images