Preparation method of PDOL-based in-situ polymerization gel electrolyte of lithium-sulfur battery

Abstract

The invention belongs to the field of chemical power sources, and particularly relates to a preparation method of a PDOL-based in-situ polymerization gel electrolyte of a lithium-sulfur battery. According to the method, in-situ polymerization of 1, 3-dioxolame (DOL) at normal temperature and normal pressure is promoted by utilizing a defective metal organic framework (MOFs), and a polymer electrolyte layer with functional groups is formed. The polymer electrolyte layer not only effectively inhibits the shuttle effect of polysulfide, but also reduces the formation of lithium dendrites by homogenizing lithium ion flow, thereby protecting the negative electrode. In addition, the active center of the metal organic framework provides more binding sites for lithium ions, and the ionic conductivity and the ionic mobility of the gel electrolyte are remarkably improved. The preparation method disclosed by the invention has the advantages of low cost, simplicity in operation and the like, an assembled soft package battery is subjected to a charge-discharge test in a voltage range of 1.8-2.5 V, the reversible discharge specific capacity reaches 1415.5 mAh / g at 0.1 C, the reversible discharge specific capacity is 693.2 mAh / g after 50 cycles, and the average efficiency reaches 93.04%.

Description

Technical Field

[0001] The present invention belongs to the field of chemical power sources, and particularly relates to a preparation method of a PDOL-based in-situ polymerization gel electrolyte for lithium-sulfur batteries. Technical Background

[0002] Lithium-sulfur batteries have a high theoretical specific capacity (1675 mAh g -1 ) and energy density (2600 Wh kg -1 ), and are low in cost, low in toxicity and environmentally friendly. In the future, they are expected to be used in fields such as electric vehicles, rail transit, large-scale energy storage systems, aerospace, etc. to meet the various needs of national defense, military and civilian use.

[0003] However, polysulfides (Li 2 S n ) intermediates generated at the positive electrode of lithium-sulfur batteries and slow redox kinetics lead to the shuttle effect, ultimately causing irreversible loss of active substances, low Coulomb efficiency, attenuation of battery cycle life, and growth of lithium dendrites on the surface of the lithium negative electrode and other adverse effects. In order to suppress the shuttle effect, people mostly adopt physical barrier, chemical adsorption and catalytic schemes to inhibit the shuttle of polysulfide ions. However, a single scheme strategy has little effect on suppressing the shuttle of polysulfide ions.

[0004] By constructing a modified layer on the separator on the positive electrode side to solve the above problems, the process is simple, the processability is strong, the cost is low, and it is conducive to the commercialization of lithium-sulfur batteries. Traditional commercial separators are mostly made of polypropylene (PP), polyethylene (PE) or PP / PE / PP composites. Although their processes are mature and the costs are low, they have micron-sized holes on their surfaces and poor wettability to electrolytes, and cannot inhibit the diffusion of polysulfides in the electrolyte, resulting in low utilization rate of active substances and low Coulomb efficiency.

[0005] Therefore, it is necessary to propose a preparation method of a PDOL-based in-situ polymerization gel electrolyte for lithium-sulfur batteries from the perspective of electrolytes to solve the above problems. Summary of the Invention

[0006] The purpose of the present invention is to solve the problems of low Coulomb efficiency, poor cycle stability and potential safety hazards caused by the shuttle effect and lithium dendrite growth in lithium-sulfur batteries.

[0007] The concept of the present invention lies in realizing the in-situ ring-opening polymerization of DOL by virtue of the Lewis acidity of defective metal-organic frameworks, and fixing the ether-based electrolyte and metal-organic frameworks in the gel phase through the polymer skeleton synthesized by in-situ polymerization. And the sulfonic acid group helps to catalyze the decomposition of lithium nitrate into Li 3N is used to construct a better-performing SEI layer. In addition, the in-situ polymerization method can effectively improve the interfacial compatibility between the positive electrode, negative electrode, and electrolyte. The presence of lithium nitrate and metal-organic frameworks can effectively enhance the battery cycle and electrochemical performance.

[0008] To achieve the above object, the present invention adopts the following technical solutions:

[0009] In a first aspect, the present invention provides an in-situ preparation method for a novel PDOL-based solid polymer electrolyte, comprising the following steps:

[0010] S1: Under a protective atmosphere, dissolve a lithium salt in a solvent composed of a mixture of DOL and a linear ether organic compound to obtain an electrolyte solution;

[0011] In the solvent, the volume ratio of DOL to the linear ether organic compound is 7:3 to 3:7; the total concentration of the lithium salt in the electrolyte solution is 1 to 3 mol / L;

[0012] S2: Dissolve an organic ligand and an aluminum salt in an organic solvent, add a monocarboxylic acid to the mixed solution to obtain a precursor solution; transfer the prepared precursor solution to hydrothermal synthesize at 150 - 200 °C for 12 - 24 h; after sufficient reaction, cool to room temperature, filter and collect the solid product and wash the solid product until it is clean, and dry the washed solid product to obtain a defective metal-organic framework;

[0013] The organic ligand is any one of terephthalic acid, amino terephthalic acid, and sulfonic acid group terephthalic acid;

[0014] The ratio of the organic ligand to the aluminum salt is a molar ratio of 2:1 to 1:2; the addition amount of the monocarboxylic acid in the mixed solution is 10 - 50% of the molar amount of the organic ligand;

[0015] S3: Under a protective atmosphere, add the defective metal-organic framework obtained in step S2 to the electrolyte solution obtained in step S1, and the mass concentration fraction of the defective metal-organic framework is 1 - 5 wt%; after uniform dispersion, place the electrolyte solution containing the defective metal-organic framework at room temperature and wait for the in-situ polymerization of DOL to obtain a quasi-solid polymer electrolyte.

[0016] Preferably, the linear ether organic compound in step S1 is any one or a mixture of two or more of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

[0017] Preferably, the lithium salt in step S1 is any one or a mixture of two or more of lithium bis(trifluoromethanesulfonyl)imide LiTFSI, lithium bis(fluorosulfonyl)imide LiFSI, lithium hexafluorophosphate LiPF 6 , lithium tetrafluoroborate LiBF 4 in the mixture.

[0018] Preferably, the organic solvent in step S2 is any one of N,N-dimethylformamide, dichloromethane, and N-methylpyrrolidone.

[0019] Preferably, the monocarboxylic acid in step S2 is any one of trifluoroacetic acid, formic acid, acetic acid, and propionic acid.

[0020] Further, in step S2, the addition amount of the monocarboxylic acid in the mixed solution is 0.1 - 1.0 mol / L.

[0021] Preferably, the aluminum salt in step S2 is any one of aluminum nitrate, aluminum chloride, aluminum sulfate, aluminum acetate, and aluminum hydroxide.

[0022] In a second aspect, the present invention provides a lithium-sulfur battery with a PDOL-based in-situ polymerization gel electrolyte, which is prepared by using the in-situ preparation method of the novel quasi-solid polymer electrolyte described in the first aspect. The lithium-sulfur battery can inhibit the shuttle effect of polysulfides in the lithium-sulfur battery.

[0023] Preferably, the negative electrode of the lithium-sulfur battery is any one of metallic lithium and lithium alloy; the positive electrode is a sulfur-carbon material; the separator is any one of PP and PE separators.

[0024] Preferably, after the defective metal-organic framework is dissolved in the electrolyte obtained in step S1, the quasi-solid polymer electrolyte is injected into the battery to be filled with the positive electrode, negative electrode, and separator installed, and then wait for the in-situ polymerization of DOL at room temperature to complete the assembly.

[0025] Compared with the prior art, the significant advantages brought by the present invention are as follows:

[0026] (1) The polymerization reaction of the monomer at the electrode / electrolyte interface in-situ generates a gel polymer electrolyte layer on the surface of the lithium negative electrode, improving the interfacial compatibility.

[0027] (2) The defective metal-organic framework has uncoordinated aluminum centers and other active sites, which can form strong chemical adsorption with sulfur atoms in polysulfides, thus effectively fixing polysulfides and preventing their migration.

[0028] (3) There are uncoordinated aluminum centers and open pore structures in the defective metal-organic framework, which can form more ion conduction channels in cooperation with the PDOL network after forming the polymer electrolyte, thereby improving the ionic conductivity of the overall electrolyte.

[0029] (3) The uncoordinated aluminum centers in the defective metal-organic framework can homogenize the lithium ion flow, which is beneficial to the uniform deposition of lithium ions to inhibit dendrite growth.

[0030] Starting from improving the problems of polysulfide shuttle, lithium dendrite growth and safety in lithium-sulfur batteries, this method uses defective metal-organic frameworks to initiate the in-situ polymerization of DOL, constructing a simple and feasible in-situ gel electrolyte with high safety performance, providing a technical approach for lithium-sulfur batteries to obtain higher energy density and better cycle stability. Description of the Drawings

[0031] Figure 1 Schematic diagram of the defective metal-organic framework structure described in the present invention;

[0032] Figure 2 Schematic diagram of the principle of ring-opening polymerization of DOL initiated by defective metal-organic frameworks

[0033] Figure 3 Optical image of the PDOL-based in-situ polymerization gel electrolyte of the lithium-sulfur battery prepared in Example 1

[0034] Figure 4 Cycling performance graph of the lithium-sulfur soft-pack battery in Example 2

[0035] In the figure: the current density is 0.1C, where 1C = 1000 mAh / g;

[0036] The abscissa is the number of cycles, with the unit of n, and the ordinate is the discharge specific capacity, with the unit of mAh / g; the right ordinate is the Coulombic efficiency, with the unit of %. Detailed Description of the Invention

[0037] To facilitate the understanding of the present invention, the present invention will be described more comprehensively and in detail below in conjunction with the drawings of the specification and preferred experimental examples, but the protection scope of the present invention is not limited to the following specific examples.

[0038] Unless otherwise defined, all the technical terms used hereinafter have the same meaning as commonly understood by those skilled in the art. The technical 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.

[0039] Unless otherwise specifically stated, various raw materials, reagents, instruments and equipment used in the present invention can be obtained through market purchase or can be prepared by existing methods.

[0040] Example 1

[0041] Dissolve 1.0 M LiTFSI in a solvent composed of a 1:1 volume ratio mixture of 1,3-dioxolane (DOL) and dimethoxyethane (DME); stir at room temperature at a rotation speed of 150 r / min for 3 h under a protective atmosphere of argon to completely dissolve the lithium salt, obtaining an electrolyte solution.

[0042] Terephthalic acid and aluminum nitrate were mixed in N,N-dimethylformamide (DMF) at a molar ratio of 1:1, stirred at 600 r / min for 1 h, and according to the content of the organic ligand, 30% of trifluoroacetic acid based on the content of the organic ligand was added, and stirring was continued at 500 r / min for 2 h. The mixed solution was transferred to a reaction kettle lined with polytetrafluoroethylene and hydrothermally synthesized at 180 °C for 20 h. After the reaction was completed, it was cooled to room temperature, and the solid product was filtered and collected in a fume hood and washed repeatedly with ethanol. The washed precipitate was transferred to a drying oven at 70 °C and dried to a constant weight.

[0043] The prepared defective metal-organic framework was added to the prepared electrolyte at a mass ratio of 3 wt% under a protective atmosphere of argon, and stirred at 100 r / min at room temperature for 2 h under a protective atmosphere of argon. After continuing to be placed in a room temperature environment for 12 h, the gel electrolyte could be gelated.

[0044] Figure 3 It is the optical image of the finally obtained PDOL-based in-situ polymerization gel electrolyte for lithium-sulfur batteries, and it can be seen that the gel reaction is obvious and in good condition.

[0045] Example 2

[0046] A mixed lithium salt with a total concentration of 1 M LiTFSI and LiBF 4 was dissolved in a solvent composed of 1,3-dioxolane (DOL) and ethylene glycol dimethyl ether (DME) with a volume ratio of 1:1; stirred at 150 r / min at room temperature for 12 h under a protective atmosphere of argon to completely dissolve the lithium salt.

[0047] Sulfonic acid group terephthalic acid and aluminum chloride were mixed in N,N-dimethylformamide (DMF) at a molar ratio of 1:1, stirred at 400 r / min for 3 h, and according to the content of the organic ligand, 50% of trifluoroacetic acid based on the content of the organic ligand was added, and stirring was continued at 500 r / min for 2 h. The mixed solution was transferred to a reaction kettle lined with polytetrafluoroethylene and hydrothermally synthesized at 180 °C for 16 h. After the reaction was completed, it was cooled to room temperature, and the solid product was filtered and collected in a fume hood and washed repeatedly with ethanol. The washed precipitate was transferred to a drying oven at 80 °C and dried to a constant weight.

[0048] The prepared defective metal-organic framework was added to the prepared electrolyte at a mass ratio of 1 wt% under a protective atmosphere of argon, and stirred at 150 r / min at room temperature for 3 h under a protective atmosphere of argon. Then the obtained electrolyte was injected into the soft-pack battery to be filled with liquid and left standing at room temperature for 12 h. The positive electrode material of the battery was a carbon-sulfur composite positive electrode, the negative electrode material was lithium metal, and the separator was a PP separator. Figure 4Figure for the cycling performance of the lithium-sulfur soft-pack battery prepared based on the method of Example 2 of the present invention. In the voltage range of 1.8 - 2.5 V and at a current density of 0.1 C (1 C = 1000 mA / g), the initial discharge specific capacity is 1415.5 mAh / g. After 50 cycles, the reversible capacity is 693.2 mAh / g, and the average Coulombic efficiency is 93.04%. It can be seen from this that the lithium-sulfur battery prepared by the method of the present invention exhibits a high specific capacity and excellent cycling stability.

[0049] Example 3

[0050] A mixed lithium salt with a total concentration of 1 M LiFSI and LiPF 6 is dissolved in a solvent composed of 1,3-dioxolane (DOL) and dimethoxyethane (DME) mixed in a volume ratio of 1:1; under a protective atmosphere of argon, it is stirred at a room temperature rotation speed of 150 r / min for 12 h to completely dissolve the lithium salt.

[0051] Aminoterephthalic acid and aluminum nitrate are mixed in N,N-dimethylformamide (DMF) at a molar ratio of 1:1 and stirred at a rotation speed of 400 r / min for 3 h. According to the content of the organic ligand, 25% of trifluoroacetic acid based on the content of the organic ligand is added, and stirring is continued at a rotation speed of 600 r / min for 3 h. The mixed solution is transferred to a reaction kettle lined with polytetrafluoroethylene and hydrothermally synthesized at 180 °C for 16 h. After the reaction is completed, it is cooled to room temperature, and the solid product is collected by filtration in a fume hood and washed repeatedly with ethanol. The washed precipitate is transferred to an 80 °C drying oven and dried to a constant weight.

[0052] Under a protective atmosphere of argon, the prepared defective metal-organic framework is added to the prepared electrolyte at a mass ratio of 1 wt%, and stirred at a room temperature rotation speed of 150 r / min for 3 h under a protective atmosphere of argon. Then, the obtained electrolyte is injected into the soft-pack battery to be filled with liquid and left to stand at room temperature for 12 h. The positive electrode material of the battery is a carbon-sulfur composite positive electrode, the negative electrode material is lithium metal, and the separator is a PP separator.

[0053] Safety performance of the lithium-sulfur soft-pack battery prepared based on the method of Example 3 of the present invention. Under the condition of puncturing with a steel needle with a diameter of 3 mm and maintaining for 10 s, there is no phenomenon of electrolyte leakage and no phenomenon of battery deflagration. The soft-pack battery of the lithium-sulfur battery prepared by the method of the present invention exhibits excellent safety performance.

Claims

1. An in-situ preparation method of a PDOL reference solid polymer electrolyte, characterized in that: The following steps are involved: S1: Under a protective atmosphere, dissolving lithium salt in a solvent mixed with DOL and linear ether organic matter to obtain an electrolyte; In the solvent, the volume ratio of DOL to the linear ether organic matter is 7:3 to 3:7; the total concentration of lithium salt in the electrolyte is 1 to 3 mol / L; S2: dissolving the organic ligand and aluminum salt in an organic solvent, adding a monocarboxylic acid to the mixed solution to obtain a precursor solution; subjecting the prepared precursor solution to hydrothermal synthesis at 150-200°C for 12-24 hours; after sufficient reaction, cooling to room temperature, filtering and collecting the solid product, washing the solid product until clean, and drying the washed solid product to obtain a defective metal organic framework; The organic ligand is any one of terephthalic acid, aminoterephthalic acid, and sulfonateterephthalic acid; The molar ratio of the organic ligand to the aluminum salt is 2:1 to 1:2; the amount of the monocarboxylic acid added to the mixed solution is 10 to 50% of the molar amount of the organic ligand; S3: Under a protective atmosphere, the defective metal organic framework obtained in step S2 is added to the electrolyte obtained in step S1, and the mass concentration fraction of the defective metal organic framework is 1 to 5wt%; after uniform dispersion, the electrolyte containing the defective metal organic framework is placed at room temperature to wait for DOL in situ polymerization to obtain a quasi-solid polymer electrolyte.

2. The in-situ preparation method of the PDOL reference solid polymer electrolyte according to claim 1, characterized in that: The linear ether organic compound in step S1 is any one of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether, or a mixture of two or more thereof.

3. The in-situ preparation method of the PDOL reference solid polymer electrolyte according to claim 1, characterized in that: The lithium salt in step S1 is any one of lithium bis(trifluoromethanesulfonyl)imide LiTFSI, lithium bis(fluorosulfonyl)imide LiFSI, lithium hexafluorophosphate LiPF6, and lithium tetrafluoroborate LiBF4, or a mixture of two or more thereof.

4. The in-situ preparation method of the PDOL reference solid polymer electrolyte according to claim 1, characterized in that: The organic solvent in step S2 is any one of N,N-dimethylformamide, dichloromethane and N-methylpyrrolidone.

5. The in-situ preparation method of the PDOL reference solid polymer electrolyte according to claim 1, characterized in that: The monocarboxylic acid in step S2 is any one of trifluoroacetic acid, formic acid, acetic acid and propionic acid.

6. The in-situ preparation method of the PDOL reference solid polymer electrolyte according to claim 5, characterized in that: In the step S2, the amount of monocarboxylic acid added to the mixed solution is 0.1-1.0 mol / L.

7. The in-situ preparation method of the PDOL reference solid polymer electrolyte according to claim 1, characterized in that: The aluminum salt in step S2 is any one of aluminum nitrate, aluminum chloride, aluminum sulfate, aluminum acetate, and aluminum oxychloride.

8. A lithium-sulfur battery with a PDOL-based in-situ polymerized gel electrolyte, prepared by the in-situ preparation method of the novel quasi-solid polymer electrolyte according to any one of claims 1 to 7.

9. The lithium-sulfur battery with PDOL-based in-situ polymerized gel electrolyte according to claim 8, characterized in that: The negative electrode of the lithium-sulfur battery is any one of metallic lithium or lithium alloy; the positive electrode is sulfur-carbon material; and the diaphragm is any one of PP and PE diaphragms.

10. The lithium-sulfur battery with PDOL-based in-situ polymerized gel electrolyte according to claim 8, characterized in that: The quasi-solid polymer electrolyte is dissolved in the electrolyte obtained in step S1 through the defective metal organic framework and then injected into the battery to be filled with the positive electrode, the negative electrode and the separator installed, and the assembly is completed after waiting for the DOL to polymerize in situ at room temperature.

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