Semi-solid electrolyte composite material and preparation method thereof

Abstract

The invention discloses a zirconium-based metal organic framework (Zr-MOF) composite semi-solid electrolyte material prepared based on an electrostatic spinning technology and application of the zirconium-based metal organic framework (Zr-MOF) composite semi-solid electrolyte material. The material is composed of a three-dimensional polymer fiber network, surface-coated Zr-MOF nanoparticles and an organic liquid electrolyte solution, a polymer matrix provides mechanical support, and Zr-MOF micropores and a liquid electrolyte form a multistage ion transmission channel. The preparation method comprises the processes of electrostatic spinning forming, in-situ Zr-MOF synthesis and gradient pressure electrolyte infiltration. The ionic conductivity of the material at 25 DEG C reaches 1.2 * 10 S / cm, the lithium ion transference number is 0.65, the capacity retention ratio after 500 cycles is greater than or equal to 90%, and the material is suitable for high-energy-density lithium ion batteries and flexible energy storage devices through acupuncture safety tests.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries and relates to a semi-solid electrolyte composite material and a preparation method thereof, and specifically relates to a zirconium-based metal-organic framework (Zr-MOF) composite semi-solid electrolyte prepared based on electrospinning technology and a preparation method thereof, which is suitable for high-safety, high-energy-density energy storage devices. Background Art

[0002] Lithium-ion batteries, as a mainstream electrochemical energy storage device, rely heavily on their electrolyte system for performance. Traditional liquid electrolytes, composed of lithium salts (such as LiPF6) dissolved in carbonate organic solvents (e.g., EC and DMC), offer high ionic conductivity (approximately 10⁻² S / cm) and good electrode wettability, but they suffer from inherent drawbacks: 1) Organic solvents are flammable and volatile, leading to a high risk of thermal runaway (thermal decomposition temperature <200°C), potentially leading to safety hazards such as battery fire and explosion; 2) Liquid electrolytes are poorly compatible with highly active lithium metal anodes, easily inducing dendrite growth that pierces the separator (dendrite length >50 μm after 100 cycles); 3) They have a limited electrochemical window (<4.3 V vs. Li⁺ / Li), making them difficult to pair with high-voltage cathode materials (e.g., LiCoO2 and NCM811). Although additives (e.g., FEC and VC) can partially improve interfacial stability, they cannot fundamentally address leakage and thermal safety issues, severely hindering the development of high-energy-density batteries.

[0003] To improve safety, all-solid-state electrolytes (including inorganic ceramics such as LLZO, sulfide-based electrolytes such as LGPS, and polymer-based electrolytes such as PEO-based electrolytes) have become a research hotspot. However, these materials face multiple technical barriers: 1) Inorganic solid electrolytes have poor rigid interface contact, with electrode / electrolyte interface impedance as high as 10³ Ω·cm², and are brittle and difficult to process on a large scale; 2) Polymer electrolytes have low room temperature ionic conductivity (PEO-based electrolytes <10⁻ 4 S / cm at 25°C), requiring high-temperature operation (>60°C). 3) Although composite solid-state electrolytes attempt to combine porous materials with polymer matrices, their MOFs are unevenly dispersed and their pore structures are disordered, resulting in discontinuous ion transport channels (effective ion conduction paths account for <40%). Furthermore, physical defects in the contact between the solid electrolyte and the electrodes can easily lead to localized current density unevenness, accelerating battery failure.

[0004] In recent years, semi-solid electrolytes (solid-liquid hybrid electrolytes) have been considered a compromise between safety and ion transport efficiency. These achieve a synergistic effect of "solid flame retardancy + liquid ion conductivity" by confining a liquid electrolyte within a porous solid framework. However, existing technologies still have drawbacks. In most solutions, the solid framework has a single pore size, making it impossible to construct multi-scale ion-conducting channels; the liquid electrolyte is not fully infiltrated, resulting in insufficient interfacial stability. Furthermore, the lack of precise design of the solid-liquid synergistic mechanism makes it difficult to meet the ion transport efficiency and cycle life requirements of practical applications. Summary of the Invention

[0005] The embodiments of the present application provide a semi-solid electrolyte composite material and a preparation method thereof, aiming to resolve the technical contradictions of the flammability and leakage of traditional liquid electrolytes and the large interface impedance of all-solid electrolytes. By constructing a multi-level ion-conducting network of "polymer three-dimensional skeleton + Zr-MOF micropores + liquid electrolyte", high ionic conductivity, dendrite suppression and improved thermal stability are simultaneously achieved, and a gradient pressure infiltration process that can be scalably produced is developed to meet the needs of high-safety and long-life lithium-ion batteries.

[0006] In order to solve the above technical problems, the technical solution proposed in this application is: The present invention provides A semi-solid electrolyte composite material comprising an integrated ion-conducting network of the following components: a) polymer matrix network: a three-dimensional porous framework composed of continuous polymer fibers prepared by electrospinning, wherein the polymer is selected from at least one of polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), and polyacrylonitrile (PAN); b) a zirconium-based metal-organic framework material (Zr-MOF) functional unit, uniformly coating the surface of the polymer fiber in the form of nanoparticles, selected from at least one of UiO-66, UiO-67, and MOF-808, with a loading of 5-40 wt%; c) Organic liquid electrolyte solution: Filled in the gaps between the polymer fibers and the microporous channels of the Zr-MOF, comprising a lithium salt and an organic solvent, wherein the lithium salt is at least one of lithium bistrifluoromethanesulfonyl imide (LiTFSI), lithium hexafluorophosphate (LiPF6), or lithium perchlorate (LiClO4), and the organic solvent is a mixed solvent of at least two of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC).

[0007] Preferably, the fiber diameter of the polymer matrix network is 100-500 nm and the porosity is 70-85%; The microporous channel diameter of the Zr-MOF is 0.5-3 nm, and the BET specific surface area is 800-1500 m² / g.

[0008] Preferably, the volume of the organic liquid electrolyte solution accounts for 30-60% of the total volume of the composite material, and contains 1-5 wt % of an additive, fluoroethylene carbonate (FEC).

[0009] Preferably, the composite material has an ionic conductivity of ≥1×10⁻³ S / cm at 25°C, a lithium ion transference number ≥0.6, and a capacity retention rate of ≥90% after 500 cycles at a 0.5C rate.

[0010] On the other hand, the present application claims protection for a method for preparing the semi-solid electrolyte composite material as described in any of the foregoing items, comprising the following steps: a) preparing an electrospinning solution: dispersing the polymer and Zr-MOF metal ligand in a mixed solvent and ultrasonically treating the mixture to form a uniform suspension; b) Electrospinning: Coaxial electrospinning is used, with the inner layer being a pure polymer and the outer layer being a polymer mixed with metal ligands. The spinning voltage is controlled at 15-30 kV, the receiving distance is 10-25 cm, the solution flow rate is 0.5-2 mL / h, and the ambient humidity is ≤40%; c) In situ growth of MOF: The fiber membrane was immersed in a methanol solution containing organic ligands for 12 h to allow the MOF to grow in situ on the fiber surface; d) Post-treatment: The fiber membrane is heat-treated at 60-120°C for 1-5 hours and then soaked in an organic liquid electrolyte solution.

[0011] Preferably, the zirconium salt in step a) is zirconium tetrachloride (ZrCl4) or zirconium oxychloride octahydrate (ZrOCl2·8H2O), the organic ligand is terephthalic acid, 2-aminoterephthalic acid or trimesic acid, and the solvent is N,N-dimethylformamide (DMF) or N-methylpyrrolidone (NMP).

[0012] Preferably, the infiltration treatment in step d) adopts a gradient pressure method, comprising: The first stage: immersion for 1-3 hours at a vacuum degree of ≤1×10⁻³ Pa; The second stage: pressure treatment at 5-10 MPa for 20-60 minutes.

[0013] Compared with the prior art, the semi-solid electrolyte composite material and the preparation method thereof of the present invention have achieved the following beneficial technical effects: The present invention significantly improves the comprehensive performance of the electrolyte through multi-level pore structure design and solid-liquid synergistic mechanism. Its three-dimensional polymer skeleton provides stable mechanical support, effectively inhibits the growth of lithium dendrites, and enhances battery safety; the Zr-MOF microporous network optimizes the ion transmission path, combined with the interfacial wettability of the liquid electrolyte, to achieve efficient ion conduction and low interfacial impedance. The material combines the flame retardant properties of the solid system with the high conductivity advantages of the liquid system, maintaining stable working performance over a wide temperature range. The gradient pressure infiltration process ensures uniform distribution of the electrolyte, improves production yield, and provides a reliable solution for high energy density and long cycle life lithium-ion batteries. DETAILED DESCRIPTION

[0014] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0015] The present invention provides a composite semi-solid electrolyte material, specifically a Zr-MOF composite semi-solid electrolyte material, comprising the following components: Polymer matrix network: A three-dimensional porous fiber skeleton is formed by electrospinning, and the material is selected from polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP) or polyacrylonitrile (PAN); Zr-MOF functional units: Uniformly coated on the surface of polymer fibers in the form of nanoparticles, selected from UiO-66, UiO-67 or MOF-808, with a loading of 5-40 wt%. Its microporous channels (pore size 0.5-3 nm) provide nanoscale ion transport pathways; Organic liquid electrolyte: Filled in the fiber gaps and MOF pores, containing lithium salts (LiTFSI, LiPF6 or LiClO4) and carbonate solvents (EC, DMC, EMC).

[0016] The innovation of the present invention is: Multi-level pore structure design: polymer fiber gaps (micrometer level) and MOF micropores (nanometer level) form continuous ion channels; In situ MOF growth: MOF grows in situ on the surface of polymer fibers, achieving uniform distribution of MOF in the electrolyte and increasing MOF loading. At the same time, MOF wraps and protects the polymer fibers to prevent side reactions.

[0017] Gradient infiltration process: vacuum pressure combined method achieves efficient electrolyte filling (pore filling rate > 95%).

[0018] The present invention will be further described below in conjunction with the embodiments: Example 1: Preparation of basic Zr-MOF composite electrolyte Example 1: In-situ growth of UiO-66 by coaxial spinning (in-situ time 12 h) 1. Coaxial Spinning Solution Preparation Inner layer solution: 15 wt% PVDF-HFP dissolved in DMF / acetone (volume ratio 7:3), without MOF precursor Outer layer solution: 12 wt% PVDF-HFP + 0.2 M ZrCl4 dissolved in DMF / acetone (volume ratio 7:3) Dispersion process: Ultrasonic dispersion of the outer layer solution for 30 minutes to ensure that ZrCl4 is completely dissolved 2. Coaxial electrospinning Equipment parameters: Inner layer flow rate: 0.5 mL / h, outer layer flow rate: 1.0 mL / h Voltage: 22 kV, Receiving distance: 15 cm, Humidity: 35% Fiber membrane characteristics: Core-shell structure (inner layer pure PVDF-HFP, outer layer containing Zr²⁺) Fiber diameter: 300±50 nm, porosity: 75% 3. In situ MOF Growth Soaking solution: 0.15 M terephthalic acid methanol solution (pH=4, adjusted with acetic acid) In-situ conditions: 12 hours of immersion at room temperature, Zr²⁺ reacts with terephthalic acid to form UiO-66 Loading calculation: Zr element content was detected by EDX, and the MOF loading was converted to 18 wt% Particle size characterization: SEM shows that the MOF particles on the fiber surface have a particle size of 80-120 nm 4. Electrolyte infiltration Electrolyte: 1 M LiPF6 in EC / DMC / EMC (1:1:1) + 3 wt% FEC Gradient pressure method: vacuum degree 5×10⁻ 4 Pa / 2h → 6 MPa / 30min Electrolyte volume share: 42%.

[0019] Performance testing:

[0020] Example 2: In-situ growth of MOF-808 by coaxial spinning (in-situ time 24 h) 1. Coaxial Spinning Solution Preparation Inner layer solution: 12 wt% PAN dissolved in DMF Outer layer solution: 10 wt% PAN + 0.3 M ZrOCl2・8H2O dissolved in DMF Dispersion process: The outer layer solution is magnetically stirred for 2 hours until it becomes clear 2. Coaxial electrospinning Equipment parameters: Inner layer flow rate: 0.8 mL / h, outer layer flow rate: 1.2 mL / h Voltage: 25 kV, Receiving distance: 18 cm, Humidity: 30% Fiber membrane characteristics: Core-shell structure (inner layer PAN, outer layer PAN+Zr 4 ⁺) Fiber diameter: 250±30 nm, porosity: 78% 3. In situ MOF Growth Soaking solution: 0.2 M trimesic acid ethanol solution (containing 5% HF) In-situ conditions: immersion at 60°C for 24 hours (accelerated reaction) Loading calculation: MOF loading was 32 wt% as measured by thermogravimetric analysis (TGA). Particle size characterization: TEM shows that the MOF particles on the fiber surface are 150-200 nm in size (the particle size increases with time) 4. Electrolyte infiltration Electrolyte: 1.2 M LiTFSI in EC / EMC (2:1) + 2 wt% FEC Gradient pressure method: vacuum degree 8×10⁻ 4 Pa / 3h → 8 MPa / 20min Electrolyte volume ratio: 50%.

[0021] Performance testing:

[0022] Example 3: In-situ growth of UiO-66 by coaxial spinning (in-situ time comparison) 1. Spinning and in-situ conditions Inner layer solution: 10 wt% PVDF dissolved in DMF / acetone (6:4) Outer layer solution: 8 wt% PVDF + 0.15 M ZrCl4 In situ time: Control group A: 6 hours of immersion, loading 10 wt%, particle size 50-80 nm Example 3: Soaking for 18 hours, loading amount 25 wt%, particle size 100-150 nm.

[0023]

[0024] Comparative analysis and mechanism description of examples 1. Relationship between load and in-situ time The in situ growth time was extended from 6 h to 24 h, and the MOF loading increased from 10 wt% to 32 wt%, indicating that prolonging the reaction time can promote the full coordination of Zr²⁺ with the ligand and form a denser MOF coating.

[0025] However, too long a time (>24h) may cause excessive growth of MOF particles, blocking the fiber pores and reducing the electrolyte infiltration efficiency (for example, the ionic conductivity decreases when the loading amount is >35%).

[0026] 2. Relationship between particle size and ion conduction Short-term in-situ growth (6-12h) forms nanoscale MOF particles (<100 nm), providing high-density microporous channels suitable for high-frequency ion transport; Long-term in-situ growth (18-24h) forms larger MOF particles (100-200 nm). Although it slightly reduces the pore density, it enhances the physical confinement ability of the electrolyte and improves the cycle stability.

[0027] 3. Advantages of coaxial spinning The inner layer of pure polymer provides mechanical support, and the outer layer of polymer containing zirconium salt serves as the MOF growth substrate, avoiding the needle clogging and uneven dispersion problems caused by the traditional "MOF synthesis and then spinning" method (for example, in Example 1, the outer layer of ZrCl4 solution spins smoothly without particle agglomeration).

[0028] The core-shell structure enables MOF to grow only on the fiber surface, forming an optimized structure of "conductive channel-mechanical support" separation. Compared with traditional blended spinning, the effective utilization rate of MOF is increased by more than 40%.

[0029] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A semi-solid electrolyte composite material, characterized in that: The integrated ion-conducting network is composed of the following components: a) polymer matrix network: a three-dimensional porous framework composed of continuous polymer fibers prepared by electrospinning, wherein the polymer is selected from at least one of polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), and polyacrylonitrile (PAN); b) a zirconium-based metal-organic framework material (Zr-MOF) functional unit, uniformly coating the surface of the polymer fiber in the form of nanoparticles, selected from at least one of UiO-66, UiO-67, and MOF-808, with a loading of 5-40 wt%; c) Organic liquid electrolyte solution: Filled in the gaps between the polymer fibers and the microporous channels of the Zr-MOF, comprising a lithium salt and an organic solvent, wherein the lithium salt is at least one of lithium bistrifluoromethanesulfonyl imide (LiTFSI), lithium hexafluorophosphate (LiPF6), or lithium perchlorate (LiClO4), and the organic solvent is a mixed solvent of at least two of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC).

2. The composite material according to claim 1, wherein: The polymer matrix network has a fiber diameter of 100-500 nm and a porosity of 70-85%; The microporous channel diameter of the Zr-MOF is 0.5-3 nm, and the BET specific surface area is 800-1500 m² / g.

3. The composite material according to claim 1, wherein: The volume of the organic liquid electrolyte solution accounts for 30-60% of the total volume of the composite material, and contains 1-5 wt% of an additive, fluoroethylene carbonate (FEC).

4. The composite material according to claim 1, wherein: The composite material has an ionic conductivity of ≥1×10⁻³ S / cm at 25°C, a lithium ion migration number ≥0.6, and a capacity retention rate of ≥90% after 500 cycles at a 0.5C rate.

5. A method for preparing the semi-solid electrolyte composite material according to any one of claims 1 to 4, characterized in that: The following steps are involved: a) preparing an electrospinning solution: dispersing the polymer and Zr-MOF metal ligand in a mixed solvent and ultrasonically treating the mixture to form a uniform suspension; b) Electrospinning: Coaxial electrospinning is used, with the inner layer being a pure polymer and the outer layer being a polymer mixed with metal ligands. The spinning voltage is controlled at 15-30 kV, the receiving distance is 10-25 cm, the solution flow rate is 0.5-2 mL / h, and the ambient humidity is ≤40%; c) In situ growth of MOF: The fiber membrane was immersed in a methanol solution containing organic ligands for 12 h to allow the MOF to grow in situ on the fiber surface; d) Post-treatment: The fiber membrane is heat-treated at 60-120°C for 1-5 hours and then soaked in an organic liquid electrolyte solution.

6. The method according to claim 5, wherein: In step a), the zirconium salt is zirconium tetrachloride (ZrCl4) or zirconium oxychloride octahydrate (ZrOCl2·8H2O), the organic ligand is terephthalic acid, 2-aminoterephthalic acid or trimesic acid, and the solvent is N,N-dimethylformamide (DMF) or N-methylpyrrolidone (NMP).

7. The method according to claim 5, wherein: The infiltration treatment in step d) adopts a gradient pressure method, comprising: The first stage: immersion for 1-3 hours at a vacuum degree of ≤1×10⁻³ Pa; The second stage: pressure treatment at 5-10 MPa for 20-60 minutes.

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