Montmorillonite-doped composite solid polymer electrolyte as well as preparation method and application thereof

Abstract

The invention discloses a montmorillonite-doped composite solid polymer electrolyte as well as a preparation method and application thereof. According to the preparation method, a commercial silane coupling agent taking amino as a main functional group reacts with montmorillonite to prepare amino-functionalized modified montmorillonite. The modified montmorillonite is then compounded with polyoxyethylene and a lithium salt to form a solid electrolyte material. The preparation method provided by the invention has the characteristics of simple operation and high safety, and is suitable for large-scale industrial continuous production. The prepared composite solid polymer electrolyte has the characteristics of excellent ionic conductivity, wide electrochemical stability window and excellent compatibility with an electrode material, and the safety of the lithium ion battery is effectively improved through the combined action of the characteristics. Besides, the composite solid polymer electrolyte prepared by the method disclosed by the invention is particularly suitable for development and production of flexible batteries due to high mechanical strength and good chemical stability.

Description

Technical Field

[0001] The present invention relates to the technical field of solid polymer electrolyte materials, and particularly relates to a composite solid polymer electrolyte doped with montmorillonite, a preparation method thereof, and an application thereof. Background Art

[0002] In the technical field of lithium-ion battery, the development of electrolyte materials is of crucial importance. It must possess excellent ion transport performance, and key functional characteristics such as interfacial properties, electrochemical stability, thermal stability, safety, and mechanical properties need to be comprehensively considered. Currently, the commonly used LiPF 6 carbonate-based electrolytes, although providing high ionic conductivity and excellent wetting properties, are flammable, volatile, and have insufficient antioxidant ability, which limits the further development of lithium-ion batteries in terms of safety and energy density. In contrast, solid electrolyte materials contain almost no or only a very small amount of liquid components, providing new possibilities for completely solving the battery safety problem and promising to fundamentally improve the battery safety.

[0003] In the technical field of lithium-ion battery, the development of organic-inorganic composite solid electrolytes is an important technological advancement. Such electrolytes are made by introducing inorganic particles into traditional polymer electrolytes, aiming to improve the comprehensive performance of the electrolytes. The elastic and plastic deformation capabilities of polymer-based electrolytes can adapt to the volume changes (expansion and contraction) of the electrodes during the charge and discharge processes of the battery, while the addition of inorganic particles can effectively prevent the crystallization of the polymer matrix, improve the interaction between the polymer and lithium ions, and thus significantly improve the ion transport efficiency, interfacial properties, and mechanical properties of the electrolyte. Nevertheless, the compatibility between the inorganic filler and the polymer matrix remains a technical challenge, because the aggregation tendency of the filler in the matrix may have an adverse effect on the performance of the electrolyte. Summary of the Invention

[0004] Aiming at the technical problem of poor compatibility between the inorganic filler and the polymer matrix in the existing organic-inorganic composite solid electrolytes, the present invention provides a composite solid polymer electrolyte doped with montmorillonite, a preparation method thereof, and an application thereof. In the present invention, the modified montmorillonite is used as a filler, which not only exhibits excellent dispersibility, but also significantly improves the compatibility with polyethylene oxide, and at the same time has excellent dissociation ability for lithium salts. The preparation method of the present invention has the characteristics of simple operation and low cost, and is suitable for large-scale industrial production. The composite solid polymer electrolyte material prepared by the method of the present invention is particularly suitable for preparing lithium-ion batteries, including flexible batteries, and exhibits high ionic conductivity and excellent mechanical properties, providing new possibilities for the development of battery technology.

[0005] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] A composite solid polymer electrolyte modified montmorillonite, its composition by mass percentage includes: montmorillonite nanoparticles 3% - 4%, lithium salt 27% - 28%, polyethylene oxide 68% - 69%. The modified montmorillonite nanoparticles have significant dispersibility, which enables them to form good compatibility with polyethylene oxide with lithium ion conduction ability, while an appropriate amount of lithium salt provides excellent dissociation ability for the electrolyte.

[0007] Furthermore, the montmorillonite nanoparticles are modified montmorillonite nanoparticles. The introduction of montmorillonite nanoparticles can significantly improve the performance of the electrolyte, and after modifying the montmorillonite nanoparticles, the performance of the electrolyte can be further improved.

[0008] The preparation method of the above-mentioned composite solid polymer electrolyte doped with montmorillonite includes the following steps:

[0009] Step 1: Disperse montmorillonite nanoparticles or modified montmorillonite nanoparticles into a solvent to form a mixed solution with a mass percentage concentration of 0.3% - 0.5% (preferably 0.4%), and add a lithium salt.

[0010] Step 2: Dissolve polyethylene oxide in the mixed solution obtained in Step 1, stir evenly, and then cast into a film. After the solvent evaporates, a composite solid polymer electrolyte doped with montmorillonite nanoparticles is obtained.

[0011] Furthermore, in Step 1, the solvent is selected from one or a combination of several of acetonitrile, acetone, N,N-dimethylformamide (DMF), N-methylpyrrolidone (NMP), or water.

[0012] Furthermore, in Step 1, the lithium salt is selected from one or a combination of several of the following compounds: lithium perchlorate (LiClO 4 ), lithium hexafluoroarsenate (LiAsF 6 ), lithium tetrafluoroborate (LiBF 4 ), lithium hexafluorophosphate (LiPF 6 ), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium trifluoromethanesulfonate (LiCF 3 SO 3 ), lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LiODFB), lithium chloride (LiCl).

[0013] Furthermore, in Step 2, the thickness of the film after film formation is between 100 - 200 μm.

[0014] The above-mentioned modified montmorillonite nanoparticles are prepared by the following method:

[0015] S1. Disperse montmorillonite particles into a solvent so that the mass fraction of montmorillonite in the solvent is 5.5% - 6.5% (preferably 5.9% - 6.1%), and disperse evenly by magnetic stirring;

[0016] S2. Add an acetic acid solution of an amino-containing silane coupling agent to the dispersion system of the montmorillonite particles obtained in step S1;

[0017] S3. After completing the addition step, react the reaction system at 60 - 100 °C for 6 - 10 hours, filter and separate, wash with absolute ethanol, and then dry to finally obtain modified montmorillonite nanoparticles, which have organic cation exchange properties.

[0018] Further, in S1, the solvent is selected from one or a combination of acetone, absolute ethanol, toluene, xylene, acetic acid, etc. to achieve uniform dispersion of montmorillonite particles.

[0019] Further, in S2, the amino-containing silane coupling agent is γ-aminopropyltriethoxysilane (KH550) to achieve modification of montmorillonite particles.

[0020] Further, in S3, the filtration method is specifically to perform filtration and separation by vacuum filtration method, and then perform washing and drying with absolute ethanol to obtain modified montmorillonite nanoparticles.

[0021] The ionic conductivity of the obtained composite solid polymer electrolyte membrane at 30 °C is 2.75×10 -5 S / cm.

[0022] The above-mentioned composite solid polymer electrolyte doped with montmorillonite is suitable for the preparation of lithium-ion batteries, including flexible batteries.

[0023] The present invention relates to a preparation method of a composite solid polymer electrolyte. A commercial silane coupling agent with amino as the main functional group is used to react with montmorillonite to prepare amino-functionalized modified montmorillonite. This modified montmorillonite is then compounded with polyethylene oxide and a lithium salt to form a solid electrolyte material. Since the modified montmorillonite particles exhibit strong dispersibility in weakly polar solvents, this helps to enhance the ion dissociation ability, dispersibility and compatibility of the material in polyethylene oxide. This method is characterized by simple operation and high safety, and is suitable for large-scale industrial continuous production. The prepared solid polymer electrolyte has the following characteristics: excellent ionic conductivity, wide electrochemical stability window, and good compatibility with electrode materials. These characteristics work together to effectively improve the safety of lithium-ion batteries. In addition, the solid polymer electrolyte membrane prepared by the method of the present invention, due to its high mechanical strength and good chemical stability, is particularly suitable for the development and production of flexible batteries.

[0024] The beneficial effects of the present invention are mainly reflected in the following aspects:

[0025] 1. The modified montmorillonite particles of the present invention are prepared by the coupling reaction of montmorillonite and an amino-silane coupling agent (KH550), and have good dispersibility in weakly polar solvents, further promoting the dissociation of lithium salts and enhancing the ionic conductivity of solid polymer electrolytes.

[0026] 2. The modified montmorillonite particles of the present invention effectively solve the problems of nanoparticle aggregation and poor compatibility with polymer substrates through the coupling reaction, realizing the uniform distribution of particles in the matrix.

[0027] 3. The polymer film prepared by the method of the present invention shows, through the electrochemical tests after battery assembly, that the ionic conductivity of this solid polymer electrolyte is significantly better than that of the composite polymer electrolyte doped with unmodified montmorillonite particles, improving by two orders of magnitude and being able to meet the actual application requirements of lithium-ion batteries. Description of the Drawings

[0028] Figure 1 is the infrared comparison diagram of MMT and MMT(KH550) in Example 1 of the present invention, where MMT represents unmodified montmorillonite nanoparticles MMT, and MMT(KH550) represents modified montmorillonite nanoparticles.

[0029] Figure 2 is the thermogravimetric comparison diagram of PEO obtained in Example 2, PEO-MMT obtained in Example 3, and PEO-MMT(KH550) obtained in Example 4.

[0030] Figure 3 is the electrochemical window diagram of PEO obtained in Example 2, PEO-MMT obtained in Example 3, and PEO-MMT(KH550) obtained in Example 4 of the present invention.

[0031] Figure 4 is the electrochemical impedance comparison diagram of PEO obtained in Example 2, PEO-MMT obtained in Example 3, and PEO-MMT(KH550) obtained in Example 4 of the present invention.

[0032] Figure 5 is the conductivity comparison diagram of PEO obtained in Example 2, PEO-MMT obtained in Example 3, and PEO-MMT(KH550) obtained in Example 4 of the present invention. Detailed Embodiments

[0033] The following further elaborates on the present invention in detail with reference to the drawings and specific embodiments, but the present invention is not limited thereto.

[0034] Example 1

[0035] The nano-montmorillonite particles modified with amino-silane coupling agent were prepared according to the following steps: 10 g of amino-silane coupling agent (KH550) was dissolved in 50 mL of absolute ethanol solution, and 50 mL of glacial acetic acid solution was added dropwise under stirring to obtain the glacial acetic acid solution of silane coupling agent. 5.0 g of montmorillonite particles (KH550) and the glacial acetic acid solution of 4.68 mmol of silane coupling agent were accurately weighed, and they were uniformly dispersed in 100 mL of absolute ethanol solution by magnetic stirring, and refluxed at 80 °C for 8 hours. After filtration separation and washing with absolute ethanol three times, they were dried and ground to obtain the modified montmorillonite nano-particles, denoted as MMT(KH550). As Figure 1 shown, the infrared spectra of MMT and MMT(KH550) are shown. It can be seen from the figure that the absorption peaks at 2960 and 2870 cm -1 are attributed to the stretching vibrations of ─CH 3 and ─CH 2 bonds. The absorption peak at 2365 cm - corresponds to the ─OH functional group, and the absorption peak at 1423 cm -1 corresponds to the characteristic absorption peak of ammonium salt. Figure 2 is the thermogravimetric diagram of PEO, PEO-MMT and PEO-MMT(KH550). PEO starts to lose weight at 213 °C and the mass no longer decreases after 520 °C. PEO-MMT and PEO-MMT(KH550) start to lose weight at 368 °C and the mass no longer decreases at 500 °C. The addition of the filler enables the solid electrolyte to withstand a high temperature of at least 350 °C, effectively improving the mechanical strength of the PEO-based.

[0036] Example 2

[0037] In an argon glove box, polyethylene oxide (PEO) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) with a mass ratio of 20:8 were fully dissolved in acetonitrile, and after stirring for 24 hours, a uniform viscous solution was obtained. Then the electrolyte mixture was cast on a polytetrafluoroethylene plate to evaporate the solvent, and then dried in a vacuum drying oven at 80 °C for 36 hours. The thickness of the prepared solid polymer electrolyte membrane (denoted as PEO) was about 130 - 140 μm, the electrochemical window was 4.15 V, and the ionic conductivity at 30 °C was 3.16×10 -7 S / cm.

[0038] Example 3

[0039] In an argon glove box, polyethylene oxide (PEO), unmodified montmorillonite nanoparticles (MMT), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) with a mass ratio of 20:1:8 were fully dissolved in acetonitrile. After stirring for 24 hours, a homogeneous viscous solution was obtained. Then, the electrolyte mixture was cast on a polytetrafluoroethylene plate, the solvent was evaporated, and then dried in a vacuum drying oven at 80 °C for 36 hours. The prepared solid polymer electrolyte membrane doped with nanoparticles (denoted as PEO-MMT) had a thickness of about 150 - 160 μm, an electrochemical window of 4.52 V, and an ionic conductivity of 2.08×10 -5 S / cm.

[0040] Example 4

[0041] In an argon glove box, polyethylene oxide (PEO), montmorillonite nanoparticles modified with amino silane coupling agent prepared in Example 1 (MMT(KH550)), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) with a mass ratio of 20:1:8 were fully dissolved in acetonitrile. After stirring for 24 hours, a homogeneous viscous solution was obtained. Then, the electrolyte mixture was cast on a polytetrafluoroethylene plate, the solvent was evaporated, and then dried in a vacuum drying oven at 80 °C for 36 hours. The prepared solid polymer electrolyte membrane with modified nanoparticles (PEO-MMT(KH550)) had a thickness of about 150 - 160 μm. The electrochemical window was 4.75 V, and the ionic conductivity was 2.75×10 -5 S / cm.

[0042] Figure 3 As shown, the electrochemical windows of PEO, PEO-MMT, and PEO-MMT(KH550) are presented. It can be seen that the electrochemical window of PEO is 4.15 V, which can be broadened to 4.52 V after adding nanoparticles. When the modified MMT is used as a filler and added to the PEO electrolyte, the electrochemical window is further increased to 4.75 V, indicating that the filler effectively improves the narrow electrochemical window of the PEO-based solid electrolyte. Figure 4 As shown, the impedance diagrams of PEO, PEO-MMT, and PEO-MMT(KH550) at 60 °C are presented. It can be seen that the impedance value of PEO is 184.01 ohm. The addition of MMT reduces the impedance value to 17.36 ohm, and the addition of modified MMT further reduces the impedance value to 6.36 ohm. Figure 5 As shown, the ionic conductivities of the three solid electrolytes from 30 - 80 °C are presented. The addition of the filler significantly increases the ionic conductivity, and the addition of the modified MMT particles further improves the conductivity. It shows that the addition of the filler reduces the crystallinity of the PEO-based material, expands the amorphous region, and the modified MMT promotes the migration of lithium ions, thus improving the ionic conductivity.

Claims

1. A composite solid polymer electrolyte doped with montmorillonite, characterized in that: The electrolyte comprises, by mass percentage, 3% to 4% of montmorillonite nanoparticles, 27% to 28% of lithium salt, and 68% to 69% of polyethylene oxide.

2. The composite solid polymer electrolyte doped with montmorillonite according to claim 1, characterized in that: The montmorillonite nanoparticles are modified montmorillonite nanoparticles.

3. The method for preparing the composite solid polymer electrolyte doped with montmorillonite according to claim 1 or 2, characterized in that: The steps include: Step 1: dispersing montmorillonite nanoparticles or modified montmorillonite nanoparticles in a solvent to form a mixed solution with a mass percentage concentration of 0.3% to 0.5%, and adding lithium salt; Step 2: dissolving polyethylene oxide in the mixed solution obtained in step 1, stirring and mixing evenly, and then casting into a film, and after the solvent evaporates, obtaining a composite solid polymer electrolyte doped with montmorillonite.

4. The preparation method according to claim 3, characterized in that: In step 1, the solvent is selected from one or a combination of acetonitrile, acetone, N,N-dimethylformamide, N-methylpyrrolidone or deionized water.

5. The preparation method according to claim 3, characterized in that: In step 1, the lithium salt is selected from one or a combination of the following compounds: lithium perchlorate, lithium hexafluoroarsenate, lithium tetrafluoroborate, lithium hexafluorophosphate, lithium bis(trifluoromethylsulfonyl imide), lithium bis(fluorosulfonyl imide), lithium trifluoromethylsulfonate, lithium bis(oxalatoborate), lithium difluorooxalatoborate, and lithium chloride.

6. The preparation method according to claim 3, characterized in that: In step 2, the thickness of the film after film formation is between 100-200 μm.

7. The preparation method according to claim 3, characterized in that: The modified montmorillonite nanoparticles are prepared by the following preparation method: S1. dispersing montmorillonite particles into a solvent so that the mass fraction of montmorillonite in the solvent is 5.5% to 6.5%, and uniformly dispersing the particles by magnetic stirring; S2. Adding a glacial acetic acid solution of an amino-containing silane coupling agent to the dispersion of montmorillonite particles obtained in step S1; S3. After the addition step is completed, the reaction system is reacted at 60-100° C. for 6-10 h, separated by filtration and washed with anhydrous ethanol, and then dried to finally obtain modified montmorillonite nanoparticles.

8. The preparation method according to claim 7, characterized in that: In S1, the solvent is selected from one or a combination of acetone, anhydrous ethanol, toluene, xylene, and glacial acetic acid.

9. The preparation method according to claim 3, characterized in that: In S2, the amino-containing silane coupling agent is γ-aminopropyltriethoxysilane.

10. Use of the composite solid polymer electrolyte according to any one of claims 1 to 2 or the composite solid polymer electrolyte obtained by the preparation method according to any one of claims 3 to 9 in the preparation of lithium ion batteries.

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