A modified sepiolite fiber and its preparation method and a composite polymer solid electrolyte membrane and its preparation method and application

Abstract

The present invention provides a modified sepiolite fiber and a preparation method thereof, and a composite polymer solid electrolyte membrane and a preparation method and application thereof, and relates to the technical field of lithium ion batteries. The present invention provides a modified sepiolite fiber, comprising a sepiolite fiber and a ZIF‑8 metal organic framework material coating the surface of the sepiolite fiber. The modified sepiolite fiber provided by the present invention can give full play to the fiber reinforcement effect of sepiolite and the energy storage advantage of the ZIF‑8 metal organic framework material. The ionic conductivity and mechanical properties of the polyethylene oxide composite polymer solid electrolyte membrane obtained by the modified sepiolite fiber and polyethylene oxide are significantly improved, and its ionic conductivity can reach up to 2.04×10 <supgt;‑5< / supgt;S·cm<supgt;‑1< / supgt;。

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to a modified sepiolite fiber and a preparation method thereof, and a composite polymer solid electrolyte membrane and a preparation method and application thereof. Background Art

[0002] The electrolytes of traditional lithium-ion batteries are all liquid. These liquid electrolytes are flammable, easy to leak, and have poor mechanical properties, which makes lithium-ion batteries have many potential risks. Therefore, it is of great significance to develop solid-state batteries assembled with solid electrolytes with high ionic conductivity, which can also greatly improve the safety performance of batteries.

[0003] Polymer solid electrolytes are one of the common solid electrolytes. Polyethylene oxide (PEO) is the most widely used matrix of polymer electrolytes. Its high crystallinity limits the transmission of lithium ions, resulting in generally low ionic conductivity of solid-state lithium batteries. The use of sepiolite fibers to form amorphous regions in polymer electrolyte PEO, enhance the interaction between inorganic fillers and polymers, and reduce crystallinity is an effective method. At the same time, fibrous sepiolite has a large aspect ratio and modulus, which can improve the mechanical properties of polymers. However, simply modifying PEO with sepiolite fibers has weak interfacial interactions, and the effect of improving PEO ionic conductivity is not very obvious. Summary of the invention

[0004] In view of this, the present invention aims to provide a modified sepiolite fiber and a preparation method thereof, and a composite polymer solid electrolyte membrane and a preparation method and application thereof. The PEO polymer solid electrolyte membrane obtained by using the modified sepiolite fiber provided by the present invention has a high ionic conductivity.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The invention provides a modified sepiolite fiber, comprising the sepiolite fiber and a ZIF-8 metal organic framework material coating the surface of the sepiolite fiber.

[0007] The present invention provides a method for preparing the modified sepiolite fiber described in the above technical solution, comprising the following steps:

[0008] The sepiolite fiber, the silane coupling agent and the alcohol-water solvent are mixed for pre-modification to obtain the pre-modified sepiolite fiber;

[0009] The pre-modified sepiolite fiber, 2-methylimidazole, zinc acetate and an alcohol solvent are mixed to carry out a homogeneous precipitation reaction to obtain the modified sepiolite fiber.

[0010] Preferably, the silane coupling agent includes one or more of KH560, KH570 and KH550; the mass ratio of the sepiolite fiber to the silane coupling agent is (0.5-1):(0.4-0.8).

[0011] Preferably, the pre-modification temperature is 70-80° C. and the time is 8-10 hours.

[0012] Preferably, the mass ratio of the pre-modified sepiolite fiber, 2-methylimidazole and zinc acetate is (0.5-1):(12.3-24.6):(8.9-17.8).

[0013] Preferably, the temperature of the homogeneous precipitation reaction is 35-45° C. and the time is 4-10 hours.

[0014] The present invention provides a composite polymer solid electrolyte membrane, comprising polyethylene oxide, lithium salt and modified sepiolite fiber, wherein the modified sepiolite fiber is the modified sepiolite fiber described in the above technical scheme or the modified sepiolite fiber prepared by the preparation method described in the above technical scheme, the mass of the modified sepiolite fiber is 1-10% of the mass of polyethylene oxide, and the mass of the lithium salt is 32-38% of the mass of polyethylene oxide.

[0015] Preferably, the lithium salt includes one or more of lithium bis(trifluoromethanesulfonyl imide), lithium bis(difluorosulfonyl imide) and lithium perchlorate.

[0016] The present invention provides a method for preparing the composite polymer solid electrolyte membrane described in the above technical solution, comprising the following steps:

[0017] Mixing the modified sepiolite fiber, polyethylene oxide, lithium salt and an organic solvent to obtain a mixed solution;

[0018] The mixed solution is coated into a film to obtain the composite polymer solid electrolyte membrane.

[0019] The present invention provides the use of the composite polymer solid electrolyte membrane described in the above technical solution or the composite polymer solid electrolyte membrane prepared by the preparation method described in the above technical solution in a lithium ion battery.

[0020] The present invention provides a modified sepiolite fiber, comprising a sepiolite fiber and a ZIF-8 metal organic framework material coating the surface of the sepiolite fiber. The modified sepiolite fiber provided by the present invention gives full play to the fiber reinforcement effect of sepiolite and the energy storage advantage of the ZIF-8 metal organic framework material, and the ionic conductivity and mechanical properties of the polyethylene oxide composite polymer electrolyte membrane obtained by using the modified sepiolite fiber are significantly improved, and the ionic conductivity can reach up to 2.04×10 -5 S cm -1 .

[0021] The present invention provides a method for preparing the modified sepiolite fiber described in the above technical solution. The present invention uses a silane coupling agent to organically modify the sepiolite fiber, and then uses 2-methylimidazole as an organic linker and zinc acetate as a Zn source to prepare the ZIF-8 coated sepiolite fiber. The preparation method provided by the present invention has a simple process, is easy to operate, and is convenient for large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The scanning electron microscope images of ZIF-8 prepared in Example 1 at different scales;

[0023] Figure 2 IR spectra of pure sepiolite fiber (SEP), ZIF-8 in Example 1, and ZIF-8@SEP in Example 3;

[0024] Figure 3 XRD diffraction patterns of pure sepiolite fiber (SEP), ZIF-8 in Example 1, and ZIF-8@SEP in Example 3;

[0025] Figure 4 are SEM images of pure sepiolite fiber (SEP), ZIF-8 in Example 1, and ZIF-8@SEP in Example 3;

[0026] Figure 5 is an elemental analysis diagram of ZIF-8@SEP in Example 3;

[0027] Figure 6 The electrochemical impedance spectra of the polymer electrolyte membranes prepared in Examples 6 to 9 and Comparative Example 1 are shown;

[0028] Figure 7 The stress-strain curves of the polymer electrolyte membranes prepared in Examples 6 to 9 and Comparative Example 1 at a tensile rate of 2 mm / min;

[0029] Figure 8 The SEM images of the PEO / LITFSI electrolyte membrane prepared in Comparative Example 1 and the PEO / LITFSI / ZIP-8@SEP7 electrolyte membrane prepared in Example 9 are shown in FIG. Figure 8 (a) is the SEM photo of PEO / LITFSI electrolyte membrane, (b) is the SEM photo of PEO / LITFSI / ZIP-8@SEP7 electrolyte membrane; (c) is the cross-sectional photo of PEO / LITFSI / ZIP-8@SEP7 electrolyte membrane. DETAILED DESCRIPTION

[0030] The invention provides a modified sepiolite fiber, comprising the sepiolite fiber and a ZIF-8 metal organic framework material coating the surface of the sepiolite fiber.

[0031] In the present invention, the ZIF-8 metal organic framework material (also referred to as ZIF-8 zeolite imidazole skeleton structure material) combines the advantages of MOFs materials and zeolite materials, and has a porous structure, a high specific surface area and excellent electrical conductivity while having structural and functional adjustability, and is a novel porous material with great research potential. The present invention uses sepiolite fiber as a raw material, and ZIF-8 is coated on the sepiolite fiber, wherein the ZIF-8 metal organic framework compound has a large specific surface area to prevent large-scale crystallization of the polymer and form a fast ion transmission channel, thereby improving the ionic conductivity of the polymer electrolyte. The present invention gives full play to the excellent performance of sepiolite fiber and ZIF-8 metal organic framework material, constructs ZIF-8 modified sepiolite fiber, synergistically improves the electrochemical (high ionic conductivity) and mechanical properties of PEO, provides new ideas for inorganic fillers of composite polymer electrolyte membranes, and opens up new ways for the development of all-solid-state lithium-ion batteries.

[0032] The present invention provides a method for preparing the modified sepiolite fiber described in the above technical solution, comprising the following steps:

[0033] The sepiolite fiber, the silane coupling agent and the alcohol-water solvent are mixed for pre-modification to obtain the pre-modified sepiolite fiber;

[0034] The pre-modified sepiolite fiber, 2-methylimidazole, zinc acetate and an alcohol solvent are mixed to carry out a homogeneous precipitation reaction to obtain the modified sepiolite fiber.

[0035] In the present invention, unless otherwise specified, the raw materials involved are commercially available products well known to those skilled in the art.

[0036] The present invention mixes sepiolite fiber, silane coupling agent and alcohol-water solvent for pre-modification to obtain pre-modified sepiolite fiber. In the present invention, the silane coupling agent preferably includes one or more of KH560, KH570 and KH550, and more preferably KH560; the mass ratio of the sepiolite fiber and the silane coupling agent is preferably (0.5-1):(0.4-0.8), and more preferably 1:(0.4-0.8); the alcohol-water solvent is preferably a mixed solvent of ethanol and water, and the volume ratio of ethanol and water is preferably 3:1. In the present invention, the pre-modification temperature is preferably 70-80°C, and more preferably 75°C, and the time is preferably 8-10h, and more preferably 8-9h. In the present invention, the specific operation of the pre-modification is preferably: mixing the silane coupling agent with an alcohol-water solvent to obtain a silane coupling agent solution; adding sepiolite fiber to the silane coupling agent solution for ultrasonication, and then pre-modifying the obtained mixed solution under stirring; the ultrasonication time is preferably 15 to 30 minutes. In the present invention, after the pre-modification, the obtained product is preferably washed with ethanol, vacuum dried and ground in sequence to obtain pre-modified sepiolite fiber; the vacuum drying temperature is preferably 50 to 70°C, and the time is preferably 20 to 24 hours. The present invention uses a silane coupling agent to organically modify sepiolite fiber, which is conducive to the smooth progress of the in-situ reaction and allows ZIF-8 to be better coated on the surface of sepiolite.

[0037] After obtaining the pre-modified sepiolite fiber, the present invention mixes the pre-modified sepiolite fiber, 2-methylimidazole, zinc acetate and an alcohol solvent for homogeneous precipitation reaction to obtain the modified sepiolite fiber. In the present invention, the mass ratio of the pre-modified sepiolite fiber, 2-methylimidazole and zinc acetate is preferably (0.5-1):(12.3-24.6):(8.9-17.8), more preferably (0.5-1):(18-24.6):(15-17.8); the alcohol solvent is preferably methanol, and the present invention has no special requirements for the amount of the alcohol solvent, as long as it is fully dissolved. In the present invention, the mixing method is preferably: dissolving the modified sepiolite fiber and 2-methylimidazole in an alcohol solvent respectively to obtain a modified sepiolite fiber dispersion and a 2-methylimidazole solution; ultrasonically mixing the modified sepiolite fiber dispersion and the 2-methylimidazole solution to obtain a modified sepiolite fiber-2-methylimidazole mixed solution; dissolving zinc acetate in an alcohol solvent, and dripping the obtained zinc acetate solution drop by drop into the modified sepiolite fiber-2-methylimidazole mixed solution. In the present invention, the ultrasonic mixing time is preferably 25 minutes, and after the ultrasonic mixing, 2-methylimidazole is adsorbed on the surface of the sepiolite fiber. In the present invention, the temperature of the homogeneous precipitation reaction is preferably 35 to 45°C, more preferably 35 to 40°C, and the time is preferably 4 to 10 hours, more preferably 4 to 5 hours; the homogeneous precipitation reaction is preferably carried out under stirring conditions, and the time of the homogeneous precipitation reaction is calculated from the completion of the dropwise addition of the zinc acetate solution. During the homogeneous precipitation reaction, 2-methylimidazole is deprotonated under the action of heating and alcohol solvent, and reacts with zinc ions to form ZIF-8 crystal nuclei that are coated on the surface of sepiolite fibers. After the homogeneous precipitation reaction, the obtained reaction solution is preferably centrifuged, solid-phase dried and ground in sequence to obtain the modified sepiolite fibers; the solid-phase drying temperature is preferably 50 to 70° C., and the time is preferably 20 to 24 hours.

[0038] The present invention provides a composite polymer solid electrolyte membrane, comprising polyethylene oxide, lithium salt and modified sepiolite fiber, wherein the modified sepiolite fiber is the modified sepiolite fiber described in the above technical solution or the modified sepiolite fiber prepared by the preparation method described in the above technical solution. In the present invention, the molecular weight of the polyethylene oxide is preferably 200,000 to 500,000; the lithium salt preferably includes one or more of lithium bistrifluoromethanesulfonyl imide, lithium bisdifluorosulfonyl imide and lithium perchlorate, and more preferably lithium bistrifluoromethanesulfonyl imide (LITFSI). In the present invention, the mass of the modified sepiolite fiber is 1 to 10 of the mass of polyethylene oxide, preferably 1 to 7%, specifically 1%, 3%, 5% and 7%, and the mass of the lithium salt is 32 to 38% of the mass of polyethylene oxide, preferably 32 to 35%. The ionic conductivity and mechanical properties of the polyethylene oxide composite polymer electrolyte membrane obtained by the modified sepiolite fiber of the present invention are significantly improved, and its ionic conductivity can reach up to 2.04×10 -5 S cm -1 .

[0039] The present invention provides a method for preparing the composite polymer solid electrolyte membrane described in the above technical solution, comprising the following steps:

[0040] Mixing the modified sepiolite fiber, polyethylene oxide, lithium salt and an organic solvent to obtain a mixed solution;

[0041] The mixed solution is coated into a film to obtain the composite polymer solid electrolyte membrane.

[0042] In the present invention, the organic solvent is preferably acetonitrile. The present invention has no special requirements for the amount of the organic solvent, as long as it can be fully dissolved. In the present invention, the method of mixing the modified sepiolite fiber, polyethylene oxide, lithium salt and organic solvent is preferably: the modified sepiolite fiber is first mixed with the organic solvent; polyethylene oxide and lithium salt are then added to the obtained first mixed solution in sequence for second mixing; the first mixing preferably includes ultrasonic mixing and stirring mixing in sequence, the ultrasonic mixing time is preferably 15 to 20 minutes, and the stirring mixing time is preferably 1 to 3 hours; the second mixing is preferably stirring mixing, and the stirring mixing time is preferably 20 to 24 hours. In the present invention, the coating film forming method is preferably a doctor blade method; the thickness of the composite polymer solid electrolyte membrane is preferably 70 to 80 μm.

[0043] The present invention provides the use of the composite polymer solid electrolyte membrane described in the above technical solution or the composite polymer solid electrolyte membrane prepared by the preparation method described in the above technical solution in a lithium ion battery. The present invention has no special requirements for the application method, and the application method familiar to those skilled in the art can be used.

[0044] The modified sepiolite fiber and its preparation method and the composite polymer solid electrolyte membrane and its preparation method and application provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be understood as limiting the scope of protection of the present invention.

[0045] Example 1

[0046] 4.46 g of zinc acetate and 6.16 g of 2-methylimidazole were dissolved in 50 mL of methanol, respectively, stirred for 10 min each, then mixed and stirred for 8 h, centrifuged, dried for 24 h, and ground to obtain the ZIF-8 finished product.

[0047] The method is a solvent thermal synthesis method, in which zinc ions and 2-methylimidazole are dissolved in an organic solvent. Under the action of the solvent, 2-methylimidazole is deprotonated and reacts with zinc ions to form ZIF-8 crystal nuclei. Then, excess neutral 2-methylimidazole is adsorbed on the positively charged surface of ZIF-8 nanocrystals to finally obtain ZIF-8 metal organic framework materials.

[0048] The prepared ZIF-8 was subjected to SEM test, and the results were as follows Figure 1 As shown, the morphological characteristics of ZIF-8 can be clearly seen, and its size is 80-100nm.

[0049] Example 2

[0050] 3.35 g of zinc acetate and 5.24 g of 2-methylimidazole were dissolved in 45 mL of methanol, respectively, stirred for 20 min each, then mixed and stirred for 10 h, centrifuged, dried for 20 h, and ground to obtain the ZIF-8 finished product.

[0051] Example 3

[0052] Preparation of modified sepiolite fiber, i.e. ZIF-8 coated sepiolite fiber:

[0053] 2 g of silane coupling agent KH560 was mixed with 200 mL of a mixed solvent of ethanol and water (the volume ratio of ethanol to water was 3:1), 2.5 g of washed sepiolite fiber was added, ultrasonicated for 15 min, heated and stirred in a 75°C water bath for 8 h, washed once with ethanol, centrifuged, dried in a vacuum drying oven for 24 h, and ground to obtain pre-modified sepiolite fiber;

[0054] 0.25 g of pre-modified sepiolite fiber and 6.16 g of 2-methylimidazole were dissolved in 50 mL of methanol respectively, mixed and ultrasonicated for 25 min, then 4.46 g of zinc acetate was dissolved in 50 mL of methanol and added dropwise into the mixed solution, followed by magnetic stirring at 35 °C for 4 h, centrifuged, and dried in a vacuum drying oven for 24 h. ZIF-8-coated sepiolite fibers were obtained by grinding, denoted as ZIF-8@SEP.

[0055] Figure 2 The infrared spectra of pure sepiolite fiber (SEP), ZIF-8 in Example 1 and ZIF-8@SEP in Example 3 are shown in FIG. Figure 2 It can be seen that pure sepiolite fiber is at 3673cm -1 The stretching vibration peak of sepiolite hydroxyl (-OH) appears; 900cm -1 ~1100cm -1 1030cm of the spectrum -1 、972cm -1 、930cm -1 The asymmetric stretching diffraction peak of Si-O-Si bond appears at 765cm -1 With 798cm -1 Symmetrical stretching vibration of Si-O-Si bond appears. ZIF-8 at 3138cm -1 and 2800cm -1 The absorption peaks at 1581cm -1 The absorption peaks appearing around are the stretching vibration peaks of C=N; at 1145cm -1 and 990cm -1 The stretching vibration peak of CN appears at 140°, while some stretching vibration peaks of sepiolite and ZIF-8 appear at ZIF-8@SEP, indicating successful encapsulation.

[0056] Figure 3 The XRD diffraction patterns of pure sepiolite fiber (SEP), ZIF-8 in Example 1, and ZIF-8@SEP in Example 3 are shown in Table 1. Figure 3 It can be seen that the positions of 2θ=19.7°, 26.4°, 30.5° are the main components of SEP, Mg 4 Si 6 O 15 (OH) 2 6H 2 O diffraction peak. 7.3°, 12.6°, 14.6°, 16.4° and 17.9° are typical diffraction peaks of ZIF-8, while the peak of ZIF-8@SEP in the range of 7° to 20° is weakened, but still exists, and the peak between 25° and 35° is enhanced, indicating that ZIF-8 has been successfully coated on SEP.

[0057] Figure 4This is a SEM test analysis of pure sepiolite fiber (SEP), ZIF-8 in Example 1, and ZIF-8@SEP in Example 3. From the SEM photos, it can be observed that ZIF-8 is a tetrahedron with sharp edges and corners, with a size of about 100nm, while SEP is a needle-like structure with a smooth surface. In ZIF-8@SEP, ZIF-8 particles with a size of about 100nm appear on the surface of SEP. From the analysis of the SEM images, it can be concluded that ZIF-8 has been successfully coated on SEP.

[0058] Figure 5 This is an elemental analysis test of ZIF-8@SEP in Example 3. Through element scanning, four elements, Si, Mg, Zn and N, were found in ZIF-8@SEP, among which Si has the highest content, which is 53%.

[0059] Example 4

[0060] Preparation of modified sepiolite fiber, i.e. ZIF-8 coated sepiolite fiber:

[0061] 1 g of silane coupling agent KH560 was mixed with 100 mL of a mixed solvent of ethanol and water (the volume ratio of ethanol to water was 3:1), 2.5 g of washed sepiolite fiber was added, ultrasonicated for 15 min, heated and stirred in a 75°C water bath for 8 h, washed once with ethanol, centrifuged, dried in a vacuum drying oven for 24 h, and ground to obtain pre-modified sepiolite fiber;

[0062] 0.14 g of pre-modified sepiolite fiber and 5.16 g of 2-methylimidazole were dissolved in 50 mL of methanol respectively, mixed and ultrasonicated for 25 min, then 4.46 g of zinc acetate was dissolved in 50 mL of methanol and added dropwise into the mixed solution, followed by magnetic stirring at 35 °C for 4 h, centrifuged, dried in a vacuum drying oven for 24 h, and ground to obtain ZIF-8-coated sepiolite.

[0063] Example 5

[0064] Preparation of modified sepiolite fiber, i.e. ZIF-8 coated sepiolite fiber:

[0065] 2 g of silane coupling agent KH560 was mixed with 200 mL of a mixed solvent of ethanol and water (the volume ratio of ethanol to water was 3:1), 2.5 g of washed sepiolite fiber was added, ultrasonicated for 15 min, heated and stirred in a 75°C water bath for 8 h, washed once with ethanol, centrifuged, dried in a vacuum drying oven for 24 h, and ground to obtain pre-modified sepiolite fiber;

[0066] 0.14 g of pre-modified sepiolite fiber and 5.16 g of 2-methylimidazole were dissolved in 50 mL of methanol respectively, mixed and ultrasonicated for 25 min, then 4.46 g of zinc acetate was dissolved in 50 mL of methanol and added dropwise into the mixed solution, then magnetically stirred at 35 °C for 4 h, centrifuged, dried in a vacuum drying oven for 24 h, and ground to obtain ZIF-8-coated sepiolite.

[0067] Example 6

[0068] Preparation of composite polymer electrolyte membrane:

[0069] Weigh 0.005g of ZIF-8@SEP prepared in Example 3, add 20mL of acetonitrile to dissolve, ultrasonicate for 15min, and stir for 1h; then weigh 0.5g of polyethylene oxide and 0.16g of lithium bis(trifluoromethanesulfonyl)imide (LITFSI) and slowly add them in sequence, stir for 24h to mix evenly, then scrape the mixture into a composite electrolyte membrane with a thickness of about 70μm and place it in a glove box for standby use. The obtained composite polymer electrolyte membrane is recorded as PEO / LITFSI / ZIF-8@SEP1, and its mechanical properties, ionic conductivity, etc. are characterized.

[0070] Example 7

[0071] Preparation of composite polymer electrolyte membrane:

[0072] Weigh 0.015g of ZIF-8@SEP prepared in Example 3, add 20mL of acetonitrile to dissolve, ultrasonicate for 15min, and stir for 1h; then weigh 0.5g of polyethylene oxide and 0.16g of lithium bis(trifluoromethanesulfonyl)imide (LITFSI) and slowly add them in sequence, stir for 24h to mix evenly, then scrape the mixture into a composite electrolyte membrane with a thickness of about 70μm and place it in a glove box for standby use. The obtained composite polymer electrolyte membrane is recorded as PEO / LITFSI / ZIF-8@SEP3, and its mechanical properties, ionic conductivity, etc. are characterized.

[0073] Example 8

[0074] Preparation of composite polymer electrolyte membrane:

[0075] Weigh 0.025g of ZIF-8@SEP prepared in Example 3, add 20mL of acetonitrile to dissolve, ultrasonicate for 15min, stir for 1h, then weigh 0.5g of polyethylene oxide and 0.16g of lithium bis(trifluoromethanesulfonyl)imide (LITFSI) and slowly add them in sequence, stir for 24h to mix evenly, then scrape the mixture into a composite electrolyte membrane with a thickness of about 70μm, and place it in a glove box for standby use. The obtained composite polymer electrolyte membrane is recorded as PEO / LITFSI / ZIF-8@SEP5, and its mechanical properties, ionic conductivity, etc. are characterized.

[0076] Example 9

[0077] Preparation of composite polymer electrolyte membrane:

[0078] Weigh 0.035g of ZIF-8@SEP prepared in Example 3, add 20mL of acetonitrile to dissolve, ultrasonicate for 15min, stir for 1h, then weigh 0.5g of polyethylene oxide and 0.16g of lithium bis(trifluoromethanesulfonyl)imide (LITFSI) and slowly add them in sequence, stir for 24h to mix evenly, then scrape the mixture into a composite electrolyte membrane with a thickness of about 70μm, and place it in a glove box for standby use. The obtained composite polymer electrolyte membrane is recorded as PEO / LITFSI / ZIF-8@SEP7, and its mechanical properties, ionic conductivity, etc. are characterized.

[0079] Comparative Example 1

[0080] 0.5 g of polyethylene oxide and 0.16 g of lithium bis(trifluoromethanesulfonyl)imide were weighed and slowly added to 20 mL of acetonitrile to dissolve, and ultrasonicated for 15 min. The mixture was stirred for 24 h to mix evenly, and then the mixture was scraped into a composite electrolyte membrane with a thickness of about 70 μm, further vacuum dried, and placed in a glove box for use. The obtained polymer electrolyte membrane was recorded as PEO / LITFSI, and its mechanical properties, ionic conductivity, etc. were characterized.

[0081] Figure 6 The electrochemical impedance spectra of the polymer electrolyte membranes prepared in Examples 6 to 9 and Comparative Example 1 are shown in Table 1. The impedance and ionic conductivity of the polymer electrolyte membranes prepared in Examples 6 to 9 and Comparative Example 1 are shown in Table 1:

[0082] Table 1 Impedance and ionic conductivity of polymer electrolyte membranes of Examples 6 to 9 and Comparative Example 1 (measured at 60°C)

[0083]

[0084] Depend on Figure 6As can be seen from Table 1, the impedance values ​​of the blocked batteries of Comparative Example 1 and Examples 6 to 9 measured at 60°C are 163Ω, 65.1Ω, 62.6Ω, 68.5Ω and 111Ω, respectively, and the corresponding ionic conductivities are 0.78×10 -5 (S cm -1 ), 1.99×10 -5 (S cm -1 ), 2.04×10 -5 (S cm -1 ), 1.94×10 -5 (S cm -1 ) and 1.17×10 -5 (S cm -1 ). It shows that the impedance of the blocked battery after adding different contents of ZIF-8@SEP has a tendency to decrease within a certain range, thereby increasing the ionic conductivity. By comparing with Comparative Example 1, it can be seen that the addition of ZIP-8@SEP effectively improves the ionic conductivity of the composite electrolyte film. It shows that increasing the ZIF-8@SEP content within a certain range is beneficial to reducing the impedance of the composite electrolyte membrane, thereby improving the ionic conductivity, effectively reducing the resistance of lithium ion transmission in the electrolyte, and reducing the internal resistance of the battery.

[0085] Figure 7 The stress-strain curves of the polymer electrolyte membranes prepared in Examples 6 to 9 and Comparative Example 1 at a tensile rate of 2 mm / min. Figure 7 It can be seen that PEO / LITFSI exhibits flexibility, with a yield strain of about 10%; the addition of ZIP-8@SEP gives the PEO chain segment a certain rigidity, causing the ZIP-8@SEP composite film to have a lower yield point deformation. Specifically, the yield strain of PEO / LITFSI / ZIP-8@SEP7 (Example 9) is 7%, and its stress value is higher than that of PEO / LITFSI. When the ZIP-8@SEP content is increased to 5wt% (Example 8), the yield strain of the composite film reaches 9%, and the stress is maximum, which improves the modulus and strength of the composite film to the greatest extent. The improvement in the stretchability of the PEO / LITFSI / ZIP-8@SEP composite electrolyte membrane can be attributed to the introduction of ZIP-8@SEP, which increases the physical cross-linking sites and promotes the mobility of the PEO chain.

[0086] Figure 8 The SEM images of the PEO / LITFSI electrolyte membrane prepared in Comparative Example 1 and the PEO / LITFSI / ZIP-8@SEP7 electrolyte membrane prepared in Example 9 are shown in FIG. Figure 8(a) is a SEM photo of PEO / LITFSI electrolyte membrane, (b) is a SEM photo of PEO / LITFSI / ZIP-8@SEP7 electrolyte membrane; (c) is a cross-sectional photo of PEO / LITFSI / ZIP-8@SEP7 electrolyte membrane. Figure 8 As can be seen from (a) and (b), the surface of the PEO / LITFSI electrolyte membrane is smooth and relatively uniform. After adding 7% ZIP-8@SEP, fibrous ZIP-8@SEP appears on the surface of the electrolyte membrane, and the distribution is relatively uniform, and it also presents a relatively uniform and flat surface. At the same time, Figure 8 As can be seen in (c), the thickness of the prepared electrolyte membrane is about 70 μm.

[0087] It can be seen from the above examples that the polyethylene oxide composite polymer solid electrolyte membrane obtained by using the modified sepiolite fiber (ZIF-8 coated sepiolite fiber) provided by the present invention has significantly improved ionic conductivity and mechanical properties.

[0088] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A composite polymer solid electrolyte membrane, It is characterized in that The invention comprises polyethylene oxide, lithium salt and modified sepiolite fiber, wherein the mass of the modified sepiolite fiber is 1-7% of the mass of polyethylene oxide, and the mass of the lithium salt is 32-38% of the mass of polyethylene oxide; the modified sepiolite fiber comprises sepiolite fiber and ZIF-8 metal organic framework material coating the surface of the sepiolite fiber; The preparation method of the modified sepiolite fiber comprises the following steps: The sepiolite fiber, the silane coupling agent and the alcohol-water solvent are mixed for pre-modification to obtain the pre-modified sepiolite fiber; The pre-modified sepiolite fiber, 2-methylimidazole, zinc acetate and an alcohol solvent are mixed to perform a homogeneous precipitation reaction to obtain the modified sepiolite fiber; The mass ratio of the pre-modified sepiolite fiber, 2-methylimidazole and zinc acetate is (0.5-1):(12.3-24.6):(8.9-17.8).

2. The composite polymer solid electrolyte membrane according to claim 1, It is characterized in that The silane coupling agent includes one or more of KH560, KH570 and KH550; the mass ratio of the sepiolite fiber to the silane coupling agent is (0.5-1):(0.4-0.8).

3. The composite polymer solid electrolyte membrane according to claim 1 or 2, It is characterized in that The pre-modification temperature is 70-80° C. and the time is 8-10 hours.

4. The composite polymer solid electrolyte membrane according to claim 1, It is characterized in that The temperature of the homogeneous precipitation reaction is 35-45° C. and the time is 4-10 hours.

5. The composite polymer solid electrolyte membrane according to claim 1, It is characterized in that The lithium salt includes one or more of lithium bis(trifluoromethanesulfonyl imide), lithium bis(difluorosulfonyl imide) and lithium perchlorate.

6. A method for preparing a composite polymer solid electrolyte membrane according to any one of claims 1 to 5, It is characterized in that The following steps are involved: Mixing the modified sepiolite fiber, polyethylene oxide, lithium salt and an organic solvent to obtain a mixed solution; The mixed solution is coated into a film to obtain the composite polymer solid electrolyte membrane.

7. Use of the composite polymer solid electrolyte membrane according to any one of claims 1 to 5 or the composite polymer solid electrolyte membrane prepared by the preparation method according to claim 6 in lithium ion batteries.

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