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

Abstract

The invention relates to a high-performance blended polymer lithium ion solid electrolyte and a preparation method and application thereof, and the preparation method comprises the following steps: dissolving a lithium salt, polyvinylidene fluoride and polyoxyethylene in N-methyl pyrrolidone and anhydrous acetonitrile step by step, stirring and dissolving, and then carrying out mixing treatment to obtain a copolymerization mixture solution; and uniformly spreading the copolymerization mixture solution in an open container, drying in a normal pressure environment, and drying in a vacuum environment to obtain the high-performance blended polymer lithium ion solid electrolyte. The obtained solid electrolyte is slightly influenced by air humidity, has good thermal stability, high ionic conductivity and good mechanical properties, and has the technical effects of long cycle life and the like when being applied to a battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium - ion solid - state batteries, and particularly relates to a high - performance blended polymer lithium - ion solid - state electrolyte, a preparation method thereof, and an application thereof. Background Art

[0002] Polymer solid - state electrolytes are one of the common solid - state electrolytes, which generally refer to electrolytes containing polymer materials and capable of ion migration. It consists of three main parts: a polymer matrix, a lithium salt, and an additive. The polymer matrix provides a support framework and an ion - transfer medium, and it is required to have good solubility for the lithium salt, in which the lithium salt is easily dissociated and the dissociated ions are easily diffused. The lithium salt can provide lithium ions. To increase the lithium - ion concentration and migration ability in the polymer system, lithium salts with low lattice energy, high anion - charge delocalization degree, high dissociation constant, and good stability are usually selected.

[0003] The research on solid polymer electrolytes began in 1973. Wright et al. discovered the conductivity of the complex of polyethylene oxide (PEO) and alkali - metal ions. This discovery laid the foundation for the research on polymer solid - state electrolytes. Since then, with the continuous in - depth research and technological development, polymer solid - state electrolytes have gradually become a new type of electrolyte material with broad application prospects.

[0004] Polymer solid - state electrolytes have the advantages of light weight, good film - forming property, good visco - elasticity and stability. In the fields of lithium - ion batteries and fuel cells, the application of polymer solid - state electrolytes will help improve the safety, stability and energy density of batteries, so as to meet the requirements for high - performance batteries in fields such as electric vehicles and mobile devices.

[0005] However, the polymer solid - state electrolytes prepared from single components have problems such as being affected by moisture and temperature, which hinder their production and application.

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

[0007] In view of the problems existing in the above - mentioned prior art, the present invention provides a high - performance blended polymer lithium - ion solid - state electrolyte, a preparation method thereof, and an application thereof, and prepares a solid - state electrolyte membrane with a smooth and flat surface and no bubbles inside. This solid - state electrolyte membrane is less affected by air humidity, has good thermal stability, high ionic conductivity and good mechanical properties. At the same time, when it is applied to a battery, it has technical effects such as a long cycle life.

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

[0009] A preparation method of a high - performance blended polymer lithium - ion solid - state electrolyte, comprising the following steps:

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

[0011] S2) Under stirring conditions, place the ground polyvinylidene fluoride and polyethylene oxide into the lithium salt solution and anhydrous acetonitrile respectively to dissolve, and obtain a lithium salt-polyvinylidene fluoride mixed solution and a polyethylene oxide solution respectively;

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

[0013] S4) Spread the copolymer mixture solution evenly in an open container, dry it at 45-60 °C for 1-2 hours in an atmospheric environment, and then place it in a vacuum environment and dry it at 45-55 °C for 20-30 hours to obtain the high-performance blended polymer lithium ion solid electrolyte.

[0014] Specifically, first dry it for a certain time in an atmospheric environment, and then dry it for a certain time in a vacuum environment. The purpose is to remove part of the acetonitrile in advance to avoid too much acetonitrile in the copolymer mixture solution, resulting in excessive absorption of acetonitrile during film formation, and finally too much acetonitrile in the solid electrolyte contacts with the moisture in the air, causing the solid electrolyte to absorb water too quickly and showing an overly wet phenomenon, that is, showing a bad result of being easily affected by moisture and resulting in performance degradation.

[0015] Preferably, dry it at 60 °C for 2 hours in an atmospheric environment and dry it at 50 °C for 24 hours in a vacuum environment.

[0016] Further, the lithium salt is LiClO 4 or LiFSI or LiTFSI (C 2 F 6 LiNO 4 S 2 ); preferably C 2 F 6 LiNO 4 S 2 .

[0017] Further, the molecular weight of the polyvinylidene fluoride is 800,000-1,200,000, preferably 1,000,000; the molecular weight of the polyethylene oxide is 500,000-700,000, preferably 600,000.

[0018] Further, the grinding is specifically to grind until it is fine and without large particles.

[0019] Further, 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, if the proportion of polyethylene oxide is too high, it will lead to adverse consequences such as rough surface of the solid electrolyte, decreased ionic conductivity, and decreased battery cycle life.

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

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

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

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

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

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

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

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

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

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

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

[0032] Further, 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 volatilize, which will cause the original lithium salt to be adsorbed on the inner wall and cause agglomeration, and the film - forming state will be significantly rough after casting the film.

[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 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. The present invention uses N-methylpyrrolidone (NMP) and anhydrous acetonitrile to dissolve polyvinylidene fluoride (PVDF) and polyethylene oxide (PEO) respectively. By using the different evaporation points of N-methylpyrrolidone and anhydrous acetonitrile, the polyvinylidene fluoride and polyethylene oxide are evenly mixed inside and form channels conducive to the passage of lithium ions, and a polymer solid electrolyte membrane with a smooth and flat surface and no bubbles inside is prepared.

[0040] 2. The present invention further controls various parameters in the preparation process of the solid electrolyte. For example, the dissolution stirring time should not be too long. Especially in step S3), if the stirring time is too long, acetonitrile will volatilize, which will drive the original lithium salt to adsorb on the inner wall and cause agglomeration. After pouring the film, the film formation state is significantly rough. For example, first dry in an atmospheric environment for a certain time, and then dry in a vacuum environment for a certain time. The purpose is to remove part of the acetonitrile in advance to avoid too much acetonitrile in the copolymer mixture solution, resulting in too much acetonitrile being absorbed during film formation. Eventually, too much acetonitrile in the solid electrolyte contacts with the moisture in the air, causing the solid electrolyte to absorb water too quickly and showing an overly wet phenomenon, that is, showing a bad result of being easily affected by moisture and resulting in performance degradation.

[0041] 3. The present invention further controls the proportional relationship between polyvinylidene fluoride and polyethylene oxide in the state where both polyvinylidene fluoride and polyethylene oxide are completely dissolved. The finally prepared solid electrolyte membrane is not only smooth and flat on the surface and has no bubbles inside, but also has little influence from air humidity, good thermal stability, high ionic conductivity and good mechanical properties. At the same time, when it is applied to a battery, it has technical effects such as a long cycle life. Description of the drawings

[0042] Figure 1 It is a diagram of the copolymer mixture solution state and the final solid electrolyte (membrane) of Examples 1-3 and Comparative Example 1 of the present invention;

[0043] Figure 2Figure of the copolymer mixture solution state and the final solid-state electrolyte (membrane) of Comparative Example 3 of the present invention;

[0044] Figure 3 Scanning electron microscope images of the surfaces of the final solid-state electrolytes (membranes) of Examples 1-3 and Comparative Example 1 of the present invention;

[0045] Figure 4 DSC diagrams of the final solid-state electrolytes (membranes) of Examples 1-3 and Comparative Examples 1-2 of the present invention;

[0046] Figure 5 Graph of the change in conductivity with temperature of the final solid-state electrolytes (membranes) of Examples 1-3 and Comparative Examples 1-2 of the present invention;

[0047] Figure 6 Tensile property test diagrams of the final solid-state electrolytes (membranes) of Examples 1-3 and Comparative Examples 1-2 of the present invention;

[0048] Figure 7 Cycling performance diagrams of the final solid-state electrolytes (membranes) of Examples 1-3 and Comparative Examples 1-2 of the present invention after being made into batteries. Detailed implementation manners

[0049] The technical solutions provided by the present invention will be described more clearly below in conjunction with the examples and the drawings. However, the scope of protection required by the present invention is not limited to the following examples only.

[0050] Example 1:

[0051] A preparation method of a high-performance blended polymer lithium-ion solid-state electrolyte:

[0052] Weigh 0.45 g of lithium bis(trifluoromethanesulfonyl)imide (C 2 F 6 LiNO 4 S 2 ), where the C 2 F 6 LiNO 4 S 2 is a sample that has been dried in an oven at 60 °C for 24 h and then cooled to room temperature with the furnace;

[0053] Weigh 0.9 g of PVDF with a molecular weight of 100W and 0.1 g of PEO with a molecular weight of 60W, and grind them respectively in an agate mortar to make them finer and without large particles;

[0054] Mix the lithium salt C 2 F 6 LiNO 4 S 2Dissolve it in 9 mL of NMP to obtain a lithium salt solution. While stirring, add the ground PVDF to the above lithium salt solution and stir at 600 r / min for 6 h to obtain a lithium salt-PVDF mixed solution. While stirring, add the ground PEO to 1 mL of anhydrous acetonitrile and stir at 600 r / min for 6 h to obtain a PEO solution.

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

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

[0057] Example 2:

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

[0059] Example 3:

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

[0061] Comparative Example 1:

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

[0063] Comparative Example 2:

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

[0065] Comparative Example 3:

[0066] The difference from Example 2 is only that: While stirring, add the PEO solution dropwise to the lithium salt-PVDF mixed solution and stir for 4 h to obtain a copolymer mixture solution.

[0067] Result analysis:

[0068] As Figure 1As shown, from left to right are the solution states of the copolymer mixtures of Example 1, Example 2, Example 3 and Comparative Example 1 and the final solid electrolyte (membrane) diagrams. Among them, compared with Examples 1-3, the copolymer mixture solution of Comparative Example 1 has the lowest transparency, the formed membrane is rough and uneven, and there is agglomeration, indicating that the compatibility between PVDF and PEO becomes worse, and too much 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] As Figure 2 shown, Figure 2 In the left figure, it is the state of the copolymer mixture solution in Comparative Example 3. Compared with Example 2, due to the too long stirring time, acetonitrile volatilizes, driving the original lithium salt to adsorb on the inner wall and causing agglomeration; Figure 2 In the right figure, it is the final solid electrolyte (membrane) of Comparative Example 3. Compared with Example 2, its film-forming state is significantly rough.

[0070] As Figure 3 shown, from left to right are the surface scanning electron microscope diagrams of the final solid electrolytes (membranes) of Example 1, Example 2, Example 3 and Comparative Example 1. Among them, the surface of the membrane in Example 2 is the flattest and almost no agglomeration occurs. Correspondingly, the surface flatness of the membrane in Comparative Example 1 is the worst and more agglomeration appears.

[0071] As Figure 4 shown, the melting point of PVDF is 160 °C. After adding PEO for blending, the melting point shifts to the right and the thermal stability is improved.

[0072] As Figure 5 shown, compared with Comparative Example 2, at the same temperature, Examples 1-3 have higher conductivity, and as the temperature increases, the conductivity of Examples 1-3 increases more. On the contrary, the conductivity of Comparative Example 1 decreases instead.

[0073] As Figure 6 shown, compared with Comparative Example 2, Examples 1-3 all obtain higher fracture tensile strain values and tensile strength values. While Comparative Example 1 only obtains a better fracture tensile strain value and its tensile strength value hardly increases. Therefore, Examples 1-3 of the present invention obtain excellent mechanical properties.

[0074] The solid electrolytes of Examples 1-3 and Comparative Examples 1-2 after drying are cut into pieces using a battery punching machine. The cut solid electrolyte (membrane) is assembled into a lithium battery button battery in a glove box. Among them, the order of assembling into a symmetric battery is: positive electrode shell, lithium sheet, solid electrolyte (membrane), lithium sheet, gasket, spring piece, negative electrode shell; the assembled battery is left standing at room temperature for 24 h and then the performance test is carried out at room temperature. The final results are as Figure 7As shown, compared with Comparative Example 1, Example 2 has the longest cycle life, followed by Example 3 and Example 1, and Comparative Example 2 is relatively poor.

[0075] The above-described embodiments merely represent several implementation manners of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention.

Claims

1. A method for preparing a high-performance blended polymer lithium ion solid electrolyte, characterized in that: The steps include: S1) dissolving a lithium salt in N-methylpyrrolidone to obtain a lithium salt solution; S2) placing the ground polyvinylidene fluoride and polyethylene oxide in the lithium salt solution and anhydrous acetonitrile respectively under stirring to dissolve, to obtain a lithium salt-polyvinylidene fluoride mixed solution and a polyethylene oxide solution respectively; S3) adding the polyethylene oxide solution dropwise to the lithium salt-polyvinylidene fluoride mixed solution under stirring to obtain a copolymer mixture solution; S4) the copolymer mixture solution is evenly spread in an open container, dried at 45-60° C. in a normal pressure environment for 1-2 hours, and then placed in a vacuum environment and dried at 45-55° C. for 20-30 hours to obtain the high-performance blended polymer lithium ion solid electrolyte.

2. The preparation method according to claim 1, characterized in that: The mass ratio of the polyethylene oxide to the polyvinylidene fluoride is 1:9-3:

7.

3. The preparation method according to claim 1, characterized in that: The total mass ratio of the lithium salt to the polyvinylidene fluoride and the polyethylene oxide is 3:10-5:

10.

4. The preparation method according to claim 1, characterized in that: The mass volume ratio of the polyvinylidene fluoride to the N-methylpyrrolidone is 1:9-13 g / mL.

5. The preparation method according to claim 1, characterized in that: The mass volume ratio of the polyethylene oxide to the anhydrous acetonitrile is 1:8-12 g / mL.

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

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

8. A high-performance blended polymer lithium ion solid electrolyte prepared according to the preparation method according to any one of claims 1 to 7.

9. Use of the high-performance blended polymer lithium-ion solid electrolyte according to claim 8 in a battery.

10. The use according to claim 9, characterized in that: The high-performance blended polymer lithium-ion solid electrolyte replaces the electrolyte and the separator in the lithium-ion battery.

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