Preparation and application of polyvinylidene fluoride electrolyte membrane containing fluorine MOF

Abstract

The invention provides a preparation method and application of a polyvinylidene fluoride electrolyte membrane containing fluorine MOF. The preparation method comprises the following steps: preparing CoNi-MOF with a fluorine-containing structure by adopting an ultrasonic technology, adding the prepared CoNi-MOF with the fluorine-containing structure, lithium bis (trifluoromethanesulfonimide) (LiTFSI), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) and succinonitrile (SN) into dimethylformamide (DMF), and fully stirring to obtain uniform mixed slurry; the complete electrolyte film is obtained through volatilization drying treatment, the obtained electrolyte film shows a wide electrochemical window, side reaction of nitrile compounds and lithium metal can be inhibited, and meanwhile the cycling stability of the PVDF-HFP-based polymer solid electrolyte battery is remarkably improved.

Description

Technical Field

[0001] The present invention relates to the preparation and application fields of solid electrolyte membranes, and in particular to the preparation and application of a polyvinylidene fluoride electrolyte membrane containing fluorine-containing MOF. Background Art

[0002] Among the numerous energy storage devices, lithium-ion batteries are widely used due to their high energy density and clean and environmentally friendly advantages. Traditional lithium batteries usually use flammable non-aqueous liquid electrolytes, which leads to serious safety issues during use. Solid-state lithium batteries are considered to be the fundamental solution to the safety issues of traditional batteries. Solid-state batteries have reliable electrochemical properties and good safety, and can also enable lithium metal to be directly applied to solid-state batteries, which will accelerate the arrival of the clean energy era.

[0003] Solid electrolytes mainly include sulfides, oxides and halides, as well as polymers. Inorganic solid electrolytes have excellent ionic conductivity and safety, but some problems still hinder their application, such as poor processing conditions and high interfacial impedance. Unfortunately, these shortcomings have not yet been completely resolved. Compared with inorganic materials, polymers have excellent elasticity and plasticity. This means good interfacial contact and processing properties, as well as certain mechanical properties. Polymer electrolytes are promising alternatives to liquid electrolytes, which usually choose non-ionic organic solvents with strong polarity. An environment with a high dielectric constant is conducive to the dissociation of lithium, and this strategy is also applicable to the selection of polymer electrolytes, especially in liquid-deficient all-solid electrolytes. The polarity of the polymer greatly affects the electrostatic force between ions. In this regard, PVDF has a high relative dielectric constant of 8.3, which can weaken the interaction between ion pairs and is more conducive to the dissociation of lithium.

[0004] Although the room temperature ionic conductivity of a single PVDF-HFP polymer electrolyte is much higher than that of polyethylene oxide, its room temperature ionic conductivity is still much lower than that of liquid electrolytes and cannot be used on a large scale. At present, an effective strategy to improve polymer electrolytes is to add inorganic fillers to polymer electrolytes to improve their ionic conductivity and electrochemical properties. However, unnecessary side reactions or phase separation between the inorganic / polymer interfaces of traditional fillers such as LLZTO and LATP will seriously affect the persistent ion transport and long-term stability. Metal organic frameworks (MOFs) with high porosity, stability, and active metal sites are used as fillers, which not only provide chemical cross-linking sites with polymers, but also promote the transport of lithium ions. Summary of the invention

[0005] In view of the problems of low ion conductivity and complex process of the above-mentioned polymer film electrolyte, the present invention provides a preparation and application of a polyvinylidene fluoride electrolyte membrane containing fluorine MOF, so as to overcome the problems of low ion conductivity of film electrolyte and poor battery cycle stability in the prior art.

[0006] In order to achieve the above-mentioned purpose, the technical solution adopted by the present invention is as follows: The present invention provides a fluorine-containing MOFs-based solid electrolyte membrane, wherein the electrolyte membrane components include MOFs materials, solvents, lithium salts, polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), and succinonitrile (SN).

[0007] Furthermore, the MOFs material is CoNi-MOF.

[0008] Furthermore, the solvent is any one or more of methyl pyrrolidone (NMP) or dimethylformamide (DMF), and the lithium salt is any one of LiFSI or LiTFSI.

[0009] The present invention also provides a method for preparing a fluorine-containing MOF PVDF-HFP electrolyte membrane, which specifically comprises the following steps:

[0010] (1) Preparation of MOFs materials;

[0011] (2) Preparation of MOFs-based solid electrolyte membrane: The product of step (1), lithium salt, PVDF-HFP and SN are stirred in DMF. After stirring, the slurry is injected into a mold and dried.

[0012] Furthermore, the method specifically includes the following steps:

[0013] (1) Preparation of fluorine-containing MOF: DMF, ethanol and water are mixed evenly. Then, organic ligands, CoCl2·6H2O and NiCl2·6H2O are dissolved in the mixed solution. Subsequently, triethylamine (TEA) is quickly injected into the solution. Then, the colloidal solution is ultrasonically treated, and finally centrifuged, washed, centrifuged and dried.

[0014] (2) Preparation of fluorine-containing MOF composite solid electrolyte membrane: Fluorine-containing CoNi-MOF, lithium salt, PVDF-HFP, and succinonitrile are stirred in DMF. After stirring, the slurry is injected into a mold and dried.

[0015] Furthermore, the method specifically includes the following steps:

[0016] (1) Preparation of fluorinated MOF: Preparation of fluorinated CoNi-MOF: 0.375mmol CoCl2·6H2O, 0.375mmol NiCl2·6H2O, 1.5mmol difluoroterephthalic acid or tetrafluoroterephthalic acid were mixed with 72mL of DMF / ethanol / deionized water mixed solution, the volume ratio of DMF, ethanol and water was 16:1:1, TEA (800mL) was added to the mixed solution, and ultrasonic treatment was performed for 8 hours. After centrifugation, DMF and anhydrous ethanol were used for centrifugal washing 3-5 times respectively, the centrifugal speed was 9000rpm, and the centrifugal washing time for each time was 7min. The washed product was moved to a vacuum oven at 60℃ and dried for 12h; after drying, the powder was collected;

[0017] (1) Preparation of PVDF-HFP electrolyte membrane containing fluorine MOF: PVDF-HFP, LiTFSI, SN and fluorine MOF in a weight ratio of 10:10:3:0.5 were added to 15 mL DMF and magnetically stirred at a stirring speed of 500-600 rpm for 12 h. After stirring, the slurry was injected into a mold and transferred to a vacuum drying device at 80°C for vacuum drying for 12 h, and then transferred to another vacuum drying device for vacuum drying for 24 h.

[0018] The present invention also provides an application of a fluorine-containing MOF PVDF-HFP electrolyte membrane in a solid-state battery.

[0019] Furthermore, the solid-state battery is a solid-state lithium-ion battery.

[0020] Compared with the prior art, the present invention has the following significant beneficial effects:

[0021] The electronegative functional groups at the Lewis acid sites on MOFs are attributed to chemical interactions. However, the effect of improving polymer electrolytes in terms of tunable structures and mechanisms is still unsatisfactory. PVDF-HFP has high chemical permeability and extended electrochemical window. However, the high intermolecular crystallinity in the α phase usually leads to low room temperature (RT) ionic conductivity. Interfacial fluorides or the introduction of inorganic fluorides can reduce crystallinity and weaken chemical reactivity, especially the transformation of the highly polarized β phase enhances the charge transfer ability. In the fluorinated CoNi-MOF of the present invention, the fluoride ion substituents enhance the p-phase stability and disordered oscillation of the PVDF-HFP chains through chemical complexation, optimizing the charge transfer in the electrolyte. In addition, the highly distributed F groups regulate the electron distribution on the porous channels and strengthen the TFSI - The invention can absorb anions and promote the transmission of lithium ions. The preparation process of the invention is simple and can improve the yield of the electrolyte membrane. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1XRD diagram of CoNi-MOF and F-CoNi-MOF in the embodiment

[0023] Figure 2 This is the EDS element distribution diagram of F-CoNi-MOF in the embodiment;

[0024] Figure 3 (a) is the SEM image of the PVDF-HFP-F-CoNi-MOF electrolyte film when the scale is 100 μm, (b) is the SEM image of the PVDF-HFP-F-CoNi-MOF electrolyte film when the scale is 30 μm;

[0025] Figure 4 This is the EIS test graph of the PVDF-HFP-F-CoNi-MOF electrolyte film at 30-80°C in the embodiment;

[0026] Figure 5 It is the Arrhenius diagram of the PVDF-HFP-F-CoNi-MOF electrolyte film in the embodiment;

[0027] Figure 6 It is the It test diagram of PVDF-HFP-F-CoNi-MOF electrolyte film in the embodiment, and the inset is the EIS test diagram before and after polarization;

[0028] Figure 7 It is the LSV diagram of PVDF-HFP-F-CoNi-MOF electrolyte film in the embodiment;

[0029] Figure 8 The graph is a cycle stability diagram of the PVDF-HFP-F-CoNi-MOF electrolyte film in the embodiment at 0.5C (1C=170mAh / g). The voltage condition is 2.3-3.8V. DETAILED DESCRIPTION

[0030] In order to make the purpose and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0031] The instruments, reagents, materials, etc. involved in the following examples, unless otherwise specified, are all conventional instruments, reagents, materials, etc. in the prior art and can be obtained through regular commercial channels. The experimental methods, detection methods, etc. involved in the following examples, unless otherwise specified, are all conventional experimental methods, detection methods, etc. in the prior art.

[0032] The preparation process of the fluorine-containing MOF composite solid electrolyte membrane of the present invention is as follows, and the specific synthesis steps of the embodiment of the present invention are as follows:

[0033] (1) Preparation of fluorinated MOF Preparation of fluorinated CoNi-MOF: 0.375mmol CoCl2·6H2O, 0.375mmol NiCl2·6H2O, 1.5mmol difluoroterephthalic acid and 72mL of DMF / ethanol / deionized water mixed solution were mixed, the volume ratio of DMF, ethanol and water was 16:1:1, TEA (800mL) was added to the mixed solution, and ultrasonic treatment was performed for 8 hours. After centrifugation, DMF and anhydrous ethanol were used for centrifugal washing 3-5 times respectively, the centrifugal speed was 9000rpm, and the centrifugal washing time for each time was 7min. The washed product was moved to a vacuum oven at 60℃ and dried for 12h; after drying, the powder was collected;

[0034] (2) Preparation of fluorine-containing MOF composite solid electrolyte membrane: PVDF-HFP, LiTFSI, succinonitrile and fluorine-containing MOF in a weight ratio of 1:1:0.3:0.05 were added to 15 mL of DMF and magnetically stirred at a speed of 500-600 rpm for 12 h. After stirring, the slurry was injected into a mold, moved to a vacuum drying equipment at 80°C and vacuum dried for 12 h, and then transferred to another vacuum drying equipment and vacuum dried for 24 h.

[0035] The products obtained in the above steps (1) and (2) were subjected to relevant tests respectively, and the test results are shown in Appendix 1-8.

[0036] The test results of this embodiment show that: Figure 1 The XRD diagrams of CoNi-MOF and F-CoNi-MOF show that the synthesized materials have the same crystal structure and good crystallinity. The XRD diffraction peak of F-CoNi-MOF shifts to the left, indicating that the introduction of CF bonds leads to an increase in the interplanar spacing, thereby having better compatibility with the polymer chain segment. Figure 2 This shows that the elements in the nanostructured MOF material are evenly distributed and have good uniformity. The structure and morphology of MOFs have not changed after F modification. This more intuitively shows that the crystal structure is not destroyed before and after modification, indicating that it has good stability. Figure 3 The SEM morphology of PVDF-HFP-F-CoNi-MOF shows that after adding F-modified MOF, the morphology of the polymer film becomes more compact, and smaller grains are observed in the 30μm image. The appearance of small grains makes the grain contact more compact, enhances the interfacial lithium ion transmission and makes the lithium ion flux uniform. Figure 4 It can be calculated that the ionic conductivity of PVDF-HFP-F-CoNi-MOF electrolyte film at 30 °C is 9.36×10 -4 S cm -1 Attached Figure 5The results show that the activation energy of the electrolyte membrane is 0.15 eV. Figure 6 The data in the calculation show that the electrolyte membrane ion migration number is 0.60. Figure 7 It can be seen that the potential window of the electrolyte membrane is 1.5-.4.8V. Figure 8 It shows that at 0.5C, the initial specific discharge capacity of PVDF-HFP-F-CoNi-MOF electrolyte film is 152 mA h g- 1 After 200 cycles, the discharge capacity can still reach 140.24 mA hg -1 , the capacity retention rate is 92.4%.

[0037] In summary, combined with the Figure 1-8 It can be seen that the preparation process of this embodiment is simple, which improves the yield and efficiency of the material. Since the F-CoNi-MOF of this embodiment has a stable structure, the electrolyte membrane prepared therefrom effectively improves the ionic conductivity of the solid electrolyte membrane, increases the number of lithium ion migration, improves the electrochemical window and other properties, and is relatively stable in long cycles.

[0038] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A polyvinylidene fluoride electrolyte membrane containing fluorine MOF, characterized in that: The electrolyte membrane components include fluorine-containing CoNi-MOF material, solvent, lithium salt, polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), and succinonitrile (SN).

2. A method according to claim 1, characterized in that : The solvent is methyl pyrrolidone (NMP) or dimethylformamide (DMF), and the lithium salt is lithium bis(fluorosulfonyl)imide (LiFSI) or lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

3. A method for preparing a PVDF-HFP electrolyte membrane containing fluorine MOF, characterized in that: The steps include: (1) Preparation of MOF materials; (2) Preparation of fluorine-containing MOF composite solid electrolyte membrane The product of step (1) is stirred with lithium salt, PVDF-HFP, and succinonitrile in DMF. After stirring, the slurry is injected into a mold and dried.

4. The method for preparing a PVDF-HFP electrolyte membrane containing fluorine MOF according to claim 3, characterized in that: The steps include: (1) DMF, ethanol and water are mixed uniformly. Then, the organic ligand, CoCl2·6H2O and NiCl2·6H2O are dissolved in the mixed solution. Subsequently, triethylamine (TEA) is rapidly injected into the solution. Then, the colloidal solution is ultrasonically treated, and finally centrifuged, recovered, washed, centrifuged and dried. (2) Preparation of fluorine-containing MOF composite solid electrolyte membrane: Fluorine-containing CoNi-MOF, lithium salt, PVDF-HFP, and succinonitrile are stirred in DMF. After stirring, the slurry is injected into a mold and dried.

5. The method for preparing a PVDF-HFP electrolyte membrane containing fluorine MOF according to claim 4, characterized in that: The organic linker is difluoroterephthalic acid or tetrafluoroterephthalic acid.

6. The method for preparing a PVDF-HFP electrolyte membrane containing fluorine MOF according to claim 4, characterized in that: The steps include: (1) Preparation of fluorinated CoNi-MOF: 0.375mmol CoCl2·6H2O, 0.375mmol NiCl2·6H2O, 1.5mmol organic linker and 72mL DMF / ethanol / deionized water mixed solution were mixed, the volume ratio of DMF, ethanol and water was 16:1:1, TEA (800μL) was added to the mixed solution, and ultrasonic treatment was performed for 8 hours. After centrifugation, DMF and anhydrous ethanol were centrifuged and washed 3-5 times respectively, the centrifugal speed was 9000rpm, and the centrifugal washing time was 7min each time. The washed product was moved to a vacuum oven at 60℃ and dried for 12h; (2) Preparation of fluorine-containing MOF composite solid electrolyte membrane: PVDF-HFP, LiTFSI, SN and fluorine-containing MOF in a weight ratio of 10:10:(1-5):0.5 were added to 15 mL of DMF and magnetically stirred at a speed of 500-600 rpm for 12 h. After stirring, the slurry was injected into a mold, moved to a vacuum drying equipment at 80°C for vacuum drying for 12 h, and then transferred to another vacuum drying equipment for vacuum drying for 24 h.

7. Use of the electrolyte membrane according to claim 1 in a solid-state battery.

8. The use of a fluorine-containing MOF PVDF-HFP electrolyte membrane in a solid-state battery according to claim 7, characterized in that: The solid-state battery is a solid-state lithium-ion battery.

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