PEO-based solid electrolyte with high ionic conductivity and preparation method thereof

Abstract

The invention discloses a PEO-based solid electrolyte with high ionic conductivity and a preparation method of the PEO-based solid electrolyte, and belongs to the technical field of lithium-sulfur batteries. The electrolyte is composed of a PEO matrix, amorphous MOF (aMOF), a free radical polymer and a lithium salt. The aMOF is synthesized through a solvothermal method, the vacancy concentration is regulated and controlled through calcination or reducing agent treatment, lithium ion transmission can be promoted, and polysulfide can be chemically adsorbed; the free radical polymer can be used as an electron mediator for improving the ion transference number and the mechanical strength and synergistically inhibiting the growth of lithium dendrites. The room temperature ionic conductivity of the electrolyte is greater than or equal to 1.2 * 10 <-4 > S cm <-1 >, and the coulombic efficiency is gt; the cycle life of the lithium-sulfur battery is gt; in addition, the stability is kept in a wide temperature range of-20 to 80 DEG C, and the method is suitable for high-energy density (gt; 500 Wh / kg) energy storage system.

Description

Technical Field

[0001] The present invention belongs to the field of lithium-sulfur batteries, and particularly relates to a PEO-based solid electrolyte with high ionic conductivity and a preparation method thereof. Background Art

[0002] Lithium-sulfur (Li-S) batteries are considered important candidates for the next generation of high-performance energy storage systems due to their high energy density (theoretical specific capacity of 1675 mAh g -1 -1) and low cost advantages. However, traditional liquid electrolyte Li-S batteries face problems such as polysulfide shuttle effect, lithium dendrite growth, and electrolyte volatilization, which limit their commercial progress.

[0003] Currently, common lithium-sulfur batteries use liquid electrolytes, but they are prone to side reactions. The dissolution and diffusion of polysulfides will lead to the loss of active substances and reduce the Coulomb efficiency. In addition, lithium metal anodes are prone to form lithium dendrites during cycling, posing a short-circuit risk and seriously affecting the battery life and safety. Therefore, developing a solid electrolyte with high safety and high stability is the key to solving this problem.

[0004] Solid polymer electrolytes (SPEs) have become a research hotspot due to their excellent safety, good interfacial compatibility, and processability. Among them, PEO-based SPEs have good flexibility and lithium ion transport ability, but they have problems such as low ionic conductivity (<10 -5 S cm -1 -1 at room temperature), weak lithium dendrite inhibition ability, and low polysulfide solubility, which limit their application in Li-S batteries. In addition, the mechanical strength of pure PEO electrolytes is relatively low, making it difficult to effectively prevent the penetration of lithium dendrites, thus affecting the long-term stability of the battery.

[0005] To solve these problems, researchers have proposed various modification strategies, such as introducing inorganic fillers (such as oxides, sulfides), adding ionic liquids or cross-linking agents, etc. However, these methods still have problems such as poor interfacial compatibility and limited ion migration. Therefore, exploring new functional fillers to improve the ionic conductivity, mechanical properties, and lithium dendrite inhibition ability of PEO-based SPEs has important research and application value. Summary of the Invention

[0006] The present invention provides a novel solid electrolyte, which synergistically modifies PEO through amorphous MOF (aMOF), including but not limited to metal-organic frameworks (MOFs) and their derivatives and radical polymers, to improve the lithium ion transport efficiency, stabilize the interface, and inhibit the growth of lithium dendrites, thereby enhancing the cycle life and rate performance of lithium-sulfur batteries.

[0007] In a first aspect, a PEO-based solid electrolyte with high ionic conductivity and its application in lithium-sulfur batteries, the electrolyte comprising:

[0008] 40 - 80 wt.% of a poly(ethylene oxide) (PEO) matrix;

[0009] 1 - 20 wt.% of an amorphous metal-organic framework (aMOF), the aMOF containing oxygen vacancies, metal vacancies, sulfur vacancies or nitrogen vacancies, for promoting lithium ion transport and adsorbing polysulfides;

[0010] 1 - 20 wt.% of a radical polymer, the radical polymer being poly(2,2,6,6-tetramethylpiperidinyl methacrylate) (PTPA) or a 2,2,6,6-tetramethylpiperidinyloxy (TEMPO) derivative, which can act as an electron mediator for increasing the ion transference number and enhancing the mechanical strength;

[0011] 5 - 40 wt.% of a lithium salt (LiTFSI or LiFSI), providing lithium ion transport.

[0012] Wherein, the mass ratio of aMOF to the radical polymer is 1:1 to 1:2, and the ionic conductivity of the electrolyte at room temperature (25 °C) is ≥ 1.2×10 -4 S cm -1 , and the lithium ion transference number is ≥ 0.75.

[0013] Preferably, the aMOF is synthesized by a solvothermal method, and the precursor is selected from the reaction products of zirconium-based, aluminum-based or zinc-based metal salts and organic ligands (such as terephthalic acid, trimellitic acid), and the vacancy concentration is regulated by calcination temperature (300 - 500 °C) or treatment with a reducing agent (such as NaBH4).

[0014] In a second aspect, a method for preparing a solid electrolyte, comprising the following steps: dissolving PEO, lithium salt and aMOF in an anhydrous solvent and dispersing by ultrasonic treatment; adding the radical polymer, stirring evenly, and stirring at 60 °C for 4 - 8 hours; forming a film by spin coating or casting, and drying in a vacuum environment for 12 - 24 hours; performing heat treatment at 90 - 120 °C to enhance the film stability.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0016] 1. Synergistically improving the ion transport efficiency and transference number: The oxygen / metal / sulfur / nitrogen vacancies in the amorphous MOF (aMOF) can serve as fast lithium ion channels, significantly increasing the room temperature ionic conductivity of the electrolyte (> 10 -4 S cm -1) Radical polymers (such as PTPA) promote the dissociation of lithium salts through their redox-active groups, increase the lithium ion transference number to above 0.8, reduce concentration polarization, and enhance rate performance.

[0017] 2. Dual inhibition of polysulfide shuttling and lithium dendrite growth: aMOF chemisorbs polysulfides (such as Li2S6) through vacancy defects, reduces their dissolution and diffusion, and inhibits the shuttling effect (coulombic efficiency increased to >99%); the radical polymer forms a network structure with high mechanical strength (modulus >500 MPa), physically blocks the penetration of lithium dendrites, and at the same time its radical groups can passivate the lithium metal interface, reduce side reactions, and extend the battery cycle life (>1000 times).

[0018] 3. Enhancement of interfacial stability and structural integration: Through spin coating / casting film combined with heat treatment at 90 - 120 °C, uniform composite of aMOF and PEO matrix and crosslinking and curing of the radical polymer are achieved, forming a dense structure without interfacial impedance (porosity <5%), maintaining dimensional stability at high temperatures (thermal decomposition temperature >300 °C), and being suitable for wide temperature range applications (-20 - 80 °C) of high energy density lithium-sulfur batteries (>500 Wh / kg). Description of the Drawings

[0019] Figure 1 It is a cycle diagram of a lithium-sulfur battery. Detailed Embodiments

[0020] To facilitate the understanding of the present invention, the present invention will be described more comprehensively and meticulously below in conjunction with the specification drawings and preferred experimental examples, but the protection scope of the present invention is not limited to the following specific embodiments.

[0021] Unless otherwise defined, all professional terms used hereinafter have the same meaning as commonly understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the protection scope of the present invention.

[0022] Unless otherwise specifically stated, various raw materials, reagents, instruments, and equipment used in the present invention can be obtained through market purchases or can be prepared by existing methods.

[0023] Example 1

[0024] In this example, the composition of the solid electrolyte includes: 60 wt.% of polyethylene oxide (PEO, molecular weight 6 million), 15 wt.% of zirconium-based amorphous metal-organic framework (aMOF, with oxygen vacancies), 15 wt.% of the radical polymer poly(2,2,6,6-tetramethylpiperidine-1-oxyl acrylate) (PTPA), and 10 wt.% of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). Among them, the mass ratio of aMOF to PTPA is 1:1. The zirconium-based aMOF is prepared by the solvothermal method: Dissolve zirconium nitrate (4.5 g) and terephthalic acid (2.1 g) in N,N-dimethylformamide (DMF, 80 mL), react at 120 °C for 24 hours, after centrifugation and ethanol washing, calcine at 500 °C for 3 hours to obtain an amorphous structure (no characteristic peaks in XRD). During preparation, first dissolve PEO and LiTFSI in anhydrous acetonitrile (50 mL), add the zirconium-based aMOF powder, and ultrasonically disperse for 30 minutes; then add PTPA, and magnetically stir at 60 °C for 6 hours to form a homogeneous slurry, and form a film by the casting method (thickness 100 μm), vacuum dry for 18 hours and then perform heat treatment at 110 °C for 1 hour. Performance tests show that the ionic conductivity of this electrolyte at room temperature (25 °C) reaches 1.8×10 -4 S cm -1 (EIS test), the lithium ion transference number is 0.82 (LSV method), and the elastic modulus is 620 MPa (nanoindentation). Apply it to a lithium-sulfur battery (sulfur loading 2 mg cm -2 ), and the capacity retention rate is 77% after 200 cycles at 0.5C rate (as Figure 1 shown).

[0025] Example 2

[0026] In this example, an aluminum-based aMOF (containing metal vacancies) and a TEMPO derivative are used for blending modification. The specific composition is: 50 wt.% PEO, 20 wt.% aluminum-based aMOF, 20 wt.% TEMPO-acrylic acid copolymer, 10 wt.% lithium bis(fluorosulfonyl)imide (LiFSI), and the mass ratio of aMOF to the radical polymer is 1:2. The synthesis of the aluminum-based aMOF uses aluminum chloride (3.0 g) and trimesic acid (1.8 g) as precursors, reacts in an ethanol solvent at 100 °C for 12 hours, and introduces metal vacancies through reduction treatment with NaBH4 (0.5 g) for 2 hours. During the preparation process, dissolve PEO and LiFSI in anhydrous dimethyl sulfoxide (DMSO, 40 mL), add the aluminum-based aMOF and ultrasonically disperse for 40 minutes, then add the TEMPO derivative, stir at 60 °C for 8 hours, and form a film by the spin coating method (3000 rpm, thickness 80 μm), vacuum dry for 24 hours and then perform heat treatment at 90 °C for 2 hours. The test results show that the tensile strength of the electrolyte is 12 MPa (2 MPa for pure PEO), and the ionic conductivity at room temperature is 5×10 -4 S cm-1 , the ionic conductivity at 60 °C is 5×10 -3 S cm -1 , and the symmetric lithium battery has not short-circuited after cycling for 2000 hours at 0.5 mA cm -2 (SEM shows no dendrites on the surface of the lithium negative electrode). Thermogravimetric analysis (TGA) shows that its thermal decomposition temperature reaches 320 °C, and the thermal shrinkage rate at 80 °C is only 1.5%, which is suitable for battery applications in high-temperature environments.

[0027] Example 3

[0028] In this example, an electrolyte suitable for a wide temperature range of -20 to 80 °C was designed, containing 70 wt.% PEO, 10 wt.% zinc-based aMOF (with sulfur vacancies), 10 wt.% mixed radical polymer (mass ratio of PTPA to TEMPO is 1:1), and 10 wt.% LiTFSI, and the mass ratio of aMOF to the radical polymer is 1:1.5. The zinc-based aMOF was synthesized by reacting zinc acetate (3.3 g) with 2-mercaptobenzoic acid (1.5 g) in methanol at 80 °C for 10 hours, and the sulfur vacancy concentration was 3.2×10 20 cm -3 after calcination at 400 °C. During preparation, PEO and LiTFSI were dissolved in tetrahydrofuran (THF, 60 mL), zinc-based aMOF was added and ultrasonically dispersed for 50 minutes, then the mixture of PTPA and TEMPO was added, and stirred at 60 °C for 4 hours. After casting into a film (thickness 120 μm), it was heat-treated at 120 °C for 1.5 hours. Performance tests show that the ionic conductivities of this electrolyte at -20 °C, 25 °C, and 80 °C are 3.2×10 -5 S cm -1 , 1.4×10 -4 S cm -1 and 2.1×10 -3 S cm -1 respectively; the discharge capacity of the low-temperature (-20 °C) lithium-sulfur battery is 1200 mAh g -1 (0.1 C), and the capacity retention rate after 200 cycles at high temperature (80 °C) is 89%. XPS analysis shows that a Li3N protective layer is formed on the surface of the lithium negative electrode after cycling (derived from the nitrogen active sites of TEMPO), effectively inhibiting the decomposition of the electrolyte.

Claims

1. A PEO-based solid electrolyte with high ionic conductivity, characterized in that, The electrolyte comprises: 40 - 80 wt.% of a polyethylene oxide matrix; 1 - 20 wt.% of an amorphous metal-organic framework containing oxygen vacancies, metal vacancies, sulfur vacancies or nitrogen vacancies for promoting lithium ion transport and adsorbing polysulfides; 1 - 20 wt.% of a radical polymer, which is poly(2,2,6,6-tetramethylpiperidinyl oxylate acrylate) or a 2,2,6,6-tetramethylpiperidinyloxy derivative, as an electron mediator for increasing the ion transference number and enhancing the mechanical strength; 5 - 40 wt.% of a lithium salt for providing lithium ion transport.

2. The PEO-based solid electrolyte with high ionic conductivity according to claim 1, characterized in that, The mass ratio of aMOF to the radical polymer is from 1:1 to 1:2, and the ionic conductivity of the electrolyte at room temperature is ≥ 1.2×10 -4 S cm -1 , and the lithium ion transference number is ≥ 0.

75.

3. The PEO-based solid electrolyte with high ionic conductivity according to claim 1, characterized in that, The aMOF is synthesized by a solvothermal method, the precursor is selected from the reaction product of a zirconium-based, aluminum-based or zinc-based metal salt and an organic ligand, and the vacancy concentration is regulated by the calcination temperature or treatment with a reducing agent.

4. A PEO-based solid electrolyte with high ionic conductivity according to claim 1, characterized in that, The lithium salt is LiTFSI or LiFSI.

5. The PEO-based solid electrolyte with high ionic conductivity according to claim 3, characterized in that, The calcination temperature is 300 - 500 °C.

6. The PEO-based solid electrolyte with high ionic conductivity according to claim 3, characterized in that, The reducing agent is NaBH4; The organic ligand is terephthalic acid or trimesic acid.

7. A method for preparing a PEO-based solid electrolyte according to any one of claims 1 to 6, comprising the following steps: In dissolve the polyethylene oxide matrix, the lithium salt and the amorphous metal-organic framework in an anhydrous solvent and disperse them by ultrasonic treatment; add the radical polymer, stir evenly, and stir at 60 °C for 4 - 8 hours; form a film by spin coating or casting method and dry it in a vacuum environment for 12 - 24 hours; perform heat treatment at 90 - 120 °C to enhance the stability of the film.

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