Preparation method of surface modified aramid nanofiber and application thereof in all-solid-state polymer electrolyte and lithium battery

Abstract

The application provides a preparation method of surface modified aramid nanofiber and application of the aramid nanofiber in a full solid-state polymer electrolyte and a lithium battery. The application adopts a surface modified aramid nanofiber synthesis strategy relying on a high-activity ring-opening polymerization process, uses polyethylene glycol to modify the surface of the aramid nanofiber, enhances the compatibility of the aramid nanofiber and the solid-state polymer electrolyte, and applies the prepared material to a composite structure solid-state polymer electrolyte. Inspection shows that the surface modified aramid nanofiber prepared by the application significantly enhances the mechanical performance of the solid-state polymer electrolyte. The strategy combines the ring-opening polymerization process and the construction of the composite structure solid-state polymer electrolyte, and realizes the improvement of the electrochemical performance and the cycle stability of the full solid-state lithium metal battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of polymer electrolyte, and particularly to a preparation method of surface modified aramid nanofiber and application thereof in all-solid-state polymer electrolyte and lithium battery. BACKGROUND

[0002] With the increasing global concern for environmental protection and the intensification of energy crisis, the rapid development of renewable energy technology is promoted, among which, the electrochemical energy storage system as a key technology for energy conversion and storage plays a vital role. In the electrochemical energy storage system, the all-solid-state lithium battery has broad development prospects due to its superior safety performance and stability. The all-solid-state lithium battery uses a solid-state electrolyte to replace the traditional liquid electrolyte, which not only can significantly improve the safety of the battery, prevent electrolyte leakage and volatilization, but also has the characteristics of high energy density. In addition, the excellent performance of the solid-state electrolyte in chemical and thermal stability further promotes the development of all-solid-state lithium battery technology.

[0003] As one of the core components of all-solid-state lithium battery, the solid-state polymer electrolyte has attracted widespread attention due to its good film-forming property, flexibility and processing convenience. However, the solid-state polymer electrolyte currently faces many challenges in practical application, including poor high-pressure stability, poor mechanical strength and high interfacial impedance, which seriously affect the electrochemical performance and safety of the battery. One of the effective ways to improve the above problems is to blend fillers with polymer matrix to prepare composite structure solid-state polymer electrolyte, which has become a research hotspot. Among many filler systems, aramid nanofiber has a broad application prospect in the field of energy storage batteries due to its high strength, high modulus, high temperature resistance and flame retardance, as well as its unique properties such as high aspect ratio and large specific surface area. When it is applied as a filler in composite structure solid-state polymer electrolyte, it exhibits good cycle stability. However, due to the highly rigid structure of aramid nanofiber and the weak interaction between PEO polymer backbone, the interface compatibility with the electrolyte is poor, which reduces the electrochemical performance of the battery. Therefore, it is necessary to provide a solution to improve the interface compatibility of aramid nanofiber with solid-state polymer electrolyte to overcome the above problems. SUMMARY

[0004] The purpose of the present application is to overcome the shortcomings and deficiencies of the prior art, and to provide a preparation method of surface modified aramid nanofiber and application thereof in all-solid-state polymer electrolyte and lithium battery. The technical solutions adopted by the present application are as follows:

[0005] In a first aspect, a preparation method of surface modified aramid nanofiber is provided, which comprises the following steps:

[0006] (1) adding a certain molecular weight polyethylene glycol and a small amount of catalyst in an appropriate amount of tetrahydrofuran, stirring for 15 min under argon atmosphere, adding a monomer containing an epoxy group, and reacting the mixture at room temperature for 24 h. Subsequently, after rotary evaporation, washing, and drying, an epoxy polyethylene glycol is prepared;

[0007] (2) mixing aramid nanofibers and the product obtained in step (1) in an appropriate ratio, reacting the mixture at high temperature for 12 h under an argon protective atmosphere, and obtaining a surface-modified aramid nanofiber dispersion after multiple suction filtration.

[0008] Further, the polyethylene glycol in step (1) has a molecular weight of 200-10000.

[0009] Further, the catalyst in step (1) is selected from one or more of sodium hydride, benzyl triethyl ammonium chloride, and triphenylphosphine.

[0010] Further, the monomer containing an epoxy group in step (1) is selected from one of epoxy bromopropane, epoxy chloropropane, and epoxy bromobutane.

[0011] Further, the mixing ratio of aramid nanofibers to epoxy polyethylene glycol in step (2) is one of molar ratios of 1:1, 1:1.3, 1:2, and 1:3.

[0012] Further, the high temperature in step (2) ranges from 60 to 100 o C.

[0013] In a second aspect, the surface-modified aramid nanofiber prepared by the above method for preparing a surface-modified aramid nanofiber is also within the protection scope of the present application, and the application of the surface-modified aramid nanofiber in a solid-state polymer electrolyte and in a full-solid-state lithium metal battery is also within the protection scope of the present application. The application of the surface-modified aramid nanofiber can effectively improve the electrochemical performance of the battery.

[0014] As a preferred, the method for preparing a solid-state polymer electrolyte comprises:

[0015] (1) dissolving different proportions of surface-modified aramid nanofibers and lithium salt in acetonitrile, and adding polyethylene oxide (PEO) to obtain a uniform mixture liquid by stirring;

[0016] (2) pouring the mixture liquid obtained in step (1) into a polytetrafluoroethylene mold in batches, naturally drying, vacuum drying, and then preparing a surface-modified aramid nanofiber solid-state polymer electrolyte with a gradient structure through a hot pressing process.

[0017] Further, the proportion of the surface-modified aramid nanofiber in step (1) accounts for 1%-20% of the mass ratio of the added PEO.

[0018] Further, the lithium salt in step (1) is selected from one or more of LiTFSI, LiPF6, LiFSI and LiBOB.

[0019] The present application has the following advantages: the present application provides a preparation method of surface-modified aramid nanofiber, the surface-modified aramid nanofiber prepared by the method is applied to a full-solid-state polymer electrolyte, which not only improves the interface compatibility but also enhances the mechanical strength; the composite solid-state polymer electrolyte is applied to a full-solid-state lithium metal battery, the full-solid-state lithium metal battery exhibits good electrochemical performance and cycle stability, and has a wide application prospect. BRIEF DESCRIPTION OF DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and for those skilled in the art, other drawings can be obtained according to these drawings without creative labor.

[0021] Figure 1 X-ray photoelectron spectroscopy (XPS) diagram of aramid nanofiber before and after surface modification of Example 1;

[0022] Figure 2 Tensile stress-strain curve of surface-modified aramid nanofiber of Example 1;

[0023] Figure 3 Rate discharge performance of lithium cobalt oxide full-solid-state battery assembled by full-solid-state polymer electrolyte of Example 1 at 65 ℃ and long cycle performance curve at 0.5 C rate. DETAILED DESCRIPTION

[0024] In order to make the objects, technical solutions and advantages of the present application clearer, the following will further describe the present application in detail with reference to the drawings.

[0025] Example 1

[0026] (1) Preparation of epoxy polyethylene glycol: first, 5 g of polyethylene glycol (molecular weight 200) and 0.4 g of sodium hydride were dissolved in an appropriate amount of tetrahydrofuran, and the mixture was stirred under argon atmosphere for 15 min to ensure the inert conditions of the reaction system; next, 1.03 g of epoxy bromopropane was slowly added to the reaction mixture, and the reaction was continued at room temperature for 24 h to promote the complete epoxy reaction.

[0027] After the reaction is completed, most of the tetrahydrofuran is removed by rotary evaporation, and then an appropriate amount of n-hexane is added for washing to remove unreacted residues and byproducts. Finally, the resulting product is dried at 60 ℃ for 12 h to obtain epoxy polyethylene glycol.

[0028] (2) Preparation of surface-modified aramid nanofiber: First, aramid nanofiber and epoxy polyethylene glycol are added in a three-necked flask in a molar ratio of 1:1.3; in order to achieve precise control of the pH value of the solution, concentrated hydrochloric acid and ammonia are then introduced to adjust the pH of the solution to the target range; during the entire reaction process, the container is placed in an argon protective atmosphere, and the temperature of the reaction mixture is maintained at 80 ℃, while continuous stirring is maintained for 12 h to promote the reaction; after the reaction is completed, repeated filtration is performed using deionized water and anhydrous ethanol to remove unreacted raw materials and byproducts, and finally a surface-modified aramid nanofiber dispersion is obtained.

[0029] (3) Preparation of gradient composite solid-state polymer electrolyte membrane: First, 1% and 5% of the surface-modified aramid nanofiber by mass of PEO are weighed and added to acetonitrile with 0.25 g of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) to prepare two different concentrations of surface-modified aramid nanofiber dispersion.

[0030] Next, the above dispersion is transferred to an anhydrous oxygen-free glove box, and then 0.92 g of PEO is added to each dispersion and continuously stirred for 12 hours to ensure thorough mixing; then, the dispersion containing 5% surface-modified aramid nanofiber is cast on a polytetrafluoroethylene mold, and most of the acetonitrile is removed by natural evaporation; next, the dispersion containing 1% surface-modified aramid nanofiber is added to the mold, and after volatilization at room temperature for 12 h, the acetonitrile is completely removed by vacuum drying at 50-70 ℃ for 24 h.

[0031] Finally, the resulting gradient solid-state polymer electrolyte membrane is hot-pressed at 60-100 ℃ and 8-12 MPa for 2-10 min using a flat hot press and cooled to room temperature to prepare a circular membrane with a thickness of 70-80 μm and a diameter of 16.5 mm. When assembling a lithium metal battery, the gradient composite solid-state polymer electrolyte is matched with the lithium negative electrode on the high-concentration side.

[0032] Example 2

[0033] The molecular weight of the polyethylene glycol is changed to 500, and the rest of the operations are the same as in Example 1.

[0034] Example 3

[0035] The molecular weight of the polyethylene glycol is changed to 5000, and the rest of the operations are the same as in Example 1.

[0036] Example 4

[0037] Benzyl triethyl ammonium chloride was used instead of sodium hydride as catalyst and the rest of the procedure was same as example 1.

[0038] Example 5

[0039] Triphenyl phosphine was used instead of sodium hydride as catalyst and the rest of the procedure was same as example 1.

[0040] Example 6

[0041] Epichlorohydrin was used instead of epibromohydrin as epoxy group and the rest of the procedure was same as example 1.

[0042] Example 7

[0043] Epibromobutane was used instead of epibromohydrin as epoxy group and the rest of the procedure was same as example 1.

[0044] Example 8

[0045] Molar ratio of aramid nanofiber and epoxy polyethylene glycol was adjusted to 1 : 1 and the rest of the procedure was same as example 1.

[0046] Example 9

[0047] Molar ratio of aramid nanofiber and epoxy polyethylene glycol was adjusted to 1 : 2 and the rest of the procedure was same as example 1.

[0048] Example 10

[0049] Molar ratio of aramid nanofiber and epoxy polyethylene glycol was adjusted to 1 : 3 and the rest of the procedure was same as example 1.

[0050] Example 11

[0051] 2% surface modified aramid nanofiber dispersion was used instead of 1% surface modified aramid nanofiber dispersion and the rest of the procedure was same as example 1.

[0052] Example 12

[0053] 10% surface modified aramid nanofiber dispersion was used instead of 5% surface modified aramid nanofiber dispersion and the rest of the procedure was same as example 1.

[0054] Example 13

[0055] 10% surface modified aramid nanofiber dispersion was used instead of 5% surface modified aramid nanofiber dispersion, 2% surface modified aramid nanofiber dispersion was used instead of 1% surface modified aramid nanofiber dispersion and the rest of the procedure was same as example 1.

[0056] Example 14

[0057] LiPF6 is used instead of LiTFSI as lithium salt, and the rest of the operations are the same as in Example 1.

[0058] Example 15

[0059] LiFSI is used instead of LiTFSI as lithium salt, and the rest of the operations are the same as in Example 1.

[0060] Example 16

[0061] LiBOB is used instead of LiTFSI as lithium salt, and the rest of the operations are the same as in Example 1.

[0062] Example 17

[0063] A flat plate hot press is used to prepare a composite solid-state polymer electrolyte with a thickness of 40 μm, and the rest of the operations are the same as in Example 1.

[0064] Example 18

[0065] A gradient composite solid-state polymer electrolyte is used to match the lithium negative electrode on the low concentration side, and the rest of the operations are the same as in Example 1.

[0066] Comparative Example 1

[0067] No surface-modified aramid nanofiber is added in the PEO-based solid-state polymer electrolyte film, and the rest of the operations are the same as in Example 1.

[0068] Comparative Example 2

[0069] No aramid nanofiber is added in the PEO-based solid-state polymer electrolyte film, and the rest of the operations are the same as in Example 1.

[0070] As can be seen from Table 1, the all-solid-state polymer electrolyte prepared by using the surface-modified aramid nanofiber according to the present application has a higher capacity, better capacity retention rate and better coulombic efficiency for the assembled lithium cobaltate solid-state full cell than the comparative examples.

[0071]

[0072] The above disclosure is only the preferred embodiments of the present application, and of course cannot limit the scope of the rights of the present application, so the equivalent changes made according to the claims of the present application still fall within the scope of the present application.

Claims

1. An all-solid-state polymer electrolyte comprising surface-modified aramid nanofibers, characterized in that, The preparation method of the surface-modified aramid nanofibers includes the following steps: (1) Epoxy polyethylene glycol is prepared by adding polyethylene glycol, catalyst and monomer containing epoxy group to tetrahydrofuran; (2) Mix the aramid nanofibers with the product obtained in step (1) and react them at high temperature to obtain surface-modified aramid nanofibers.

2. The all-solid-state polymer electrolyte according to claim 1, characterized in that: The polyethylene glycol has a molecular weight of 200 to 10,000.

3. The all-solid-state polymer electrolyte according to claim 1, characterized in that: In step (1), the catalyst is selected from one or more of sodium hydride, benzyltriethylammonium chloride, and triphenylphosphine, and the monomer containing the epoxy group is selected from one of epichlorohydrin, epichlorohydrin, and epichlorobutane.

4. The all-solid-state polymer electrolyte according to claim 1, characterized in that: In step (2), the aramid nanofibers and epoxy polyethylene glycol are mixed in a molar ratio of 1:1, 1:1.3, 1:2, or 1:3; the high temperature range is 60~100℃.

5. The all-solid-state polymer electrolyte according to claim 1, characterized in that, Its preparation methods include: ① Add surface-modified aramid nanofibers, lithium salt and polyethylene oxide to acetonitrile and stir to obtain a uniform mixture; ② The mixture obtained in step ① is poured into polytetrafluoroethylene molds in batches, and after natural evaporation, vacuum drying and hot pressing, a surface-modified aramid nanofiber polymer electrolyte with a gradient structure is obtained.

6. The all-solid-state polymer electrolyte according to claim 5, characterized in that: The surface-modified aramid nanofibers in step ① account for 1% to 20% of the mass of polyethylene oxide.

7. The all-solid-state polymer electrolyte according to claim 5, characterized in that: In step ①, the lithium salt is selected from one or more of LiTFSI, LiPF6, LiFSI and LiBOB.

8. A lithium battery comprising the all-solid-state polymer electrolyte as described in claim 1.

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