A method for preparing high-crystallinity two-dimensional lithium sulfide nanosheets

Abstract

The application discloses a preparation method of high-crystallinity two-dimensional lithium sulfide nanosheet, which comprises the following steps: adopting a composite material of carbon nanotubes and sulfur as a positive electrode, adopting polypropylene modified by a single-atom nickel catalyst supported by carbon tubes as a diaphragm, adopting lithium sheet as a negative electrode, adding an electrolyte to assemble a full battery, discharging to 1.7 V, and growing the high-crystallinity two-dimensional lithium sulfide nanosheet on the diaphragm uniformly. The lithium sulfide nanosheet is prepared by an electrochemical method. In the discharging process, the single-atom nickel catalyst supported by the carbon tubes and the modified layer can not only physically block the diffusion of polysulfide lithium to the negative electrode, but also quickly capture the dissolved polysulfide lithium, realizes in-situ catalytic conversion, and obtains the high-crystallinity two-dimensional sheet-shaped lithium sulfide nanosheet. The lithium sulfide is prepared by using a lithium-sulfur battery, a large amount of organic solvent is not needed, the reaction is easy to control, the generated lithium sulfide is in a two-dimensional sheet structure, the size can reach the micron level, the lithium sulfide is convenient for subsequent collection and purification, and the preparation process is simple.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of material synthesis, and particularly relates to a method for preparing lithium sulfide by using a lithium-sulfur battery in a green and efficient manner, which can be applied to the fields of lithium-sulfur batteries and all-solid-state batteries. BACKGROUND

[0002] Lithium-ion batteries have become an indispensable energy supply and a key component of most devices in today's modern society due to their high energy density, good cycle life, and excellent storage characteristics. As lithium-ion batteries are applied to large electric vehicles that pursue long endurance and fast charging and discharging capabilities, there is an urgent need for battery energy systems with long service life, large capacity, and high safety. All-solid-state lithium metal batteries are considered to be the most promising batteries because their anodes have an extremely high theoretical specific capacity of 3860 mAh g -1 and an extremely low reduction potential (-3.04 V relative to the standard hydrogen electrode). Replacing the highly flammable liquid electrolyte with a solid electrolyte is crucial for effectively suppressing the safety hazards of traditional lithium-ion batteries because the solid electrolyte has lower flammability and better compatibility with the lithium metal anode than the liquid electrolyte.

[0003] Lithium sulfide is an important material for developing all-solid-state lithium batteries based on sulfide solid electrolytes and can also be used as a positive electrode material for high-capacity lithium-sulfur batteries. The development and optimization of its production process have attracted widespread attention and attention. In previous studies on the synthesis of lithium sulfide, Fang et al. dissolved LiCl and Na2S in anhydrous ethanol, with a molar ratio of LiCl to Na2S of 2:1. After sufficient stirring and centrifugation, the byproduct NaCl and ethanol solvent were removed to obtain the product lithium sulfide powder (Greensynthesis of the battery material lithium sulfide via metathetic reactions, Chemical Communications, 2022). However, the organic solvent anhydrous ethanol is flammable and volatile, and is not easy to recover, which is dangerous and difficult to control in large-scale industrial production. SUMMARY

[0004] The application aims to provide a preparation method of high-crystallinity two-dimensional lithium sulfide nanosheets.

[0005] The application comprises the following steps: a preparation method of high-crystallinity two-dimensional lithium sulfide nanosheets, comprising the following steps:

[0006] The carbon nanotube and sulfur composite material is used as a positive electrode, the carbon tube loaded monatomic nickel catalyst modified polypropylene is used as a separator, lithium sheet is used as a negative electrode, and an electrolyte is added to assemble a full battery, and then the full battery is discharged at a certain rate to 1.7 V, so that high-crystallinity two-dimensional lithium sulfide nanosheets are obtained, which are uniformly grown on the separator.

[0007] Preferably, when the carbon tube loaded monatomic nickel catalyst modified polypropylene is used as the separator, the loading amount is 0.1 mg cm -2 to 1 mg cm -2 This is because the high catalytic activity monatomic nickel catalyst with the loading amount has high lithium sulfide preparation efficiency and high crystal quality, and the overuse of the catalyst can be avoided.

[0008] Preferably, the carbon nanotube and sulfur composite material is obtained by coating the carbon nanotube, sulfur, conductive agent Super P and binder La133 on a current collector after mixing, wherein the mass ratio of the carbon nanotube and the sulfur is 2:8, and the mass ratio of the carbon nanotube, the sulfur, the conductive agent Super P and the binder La133 is 8:1:1.

[0009] Preferably, the concentration of lithium bis(trifluoromethanesulfonyl)imide in the electrolyte is 1 mol / L -1 , the concentration of lithium nitrate is 1 wt%, the electrolyte uses a mixed solvent of 1,3-dioxolane and 1,2-dimethoxyethane in a volume ratio of 1:1, and the concentration of lithium nitrate is 1 wt%. The lithium sulfide prepared at the concentration has a sheet structure and high crystallinity.

[0010] Preferably, the discharge rate is 0.2 to 5 C to 1.7 V, preferably 0.5 C to 2 C. Under different discharge current rates, the modified separator can obtain uniformly grown lithium sulfide nanosheets with high crystallinity.

[0011] Compared with the prior art, the present application has the following advantages:

[0012] (1) The present application prepares lithium sulfide nanosheets by an electrochemical method. During the discharge process, the carbon tube loaded monatomic nickel catalyst modified layer which is tightly packed can not only physically block the diffusion of polysulfide lithium to the negative electrode, but also quickly capture the dissolved polysulfide lithium to realize in-situ catalytic conversion, so that high-crystallinity two-dimensional sheet-shaped lithium sulfide nanosheets are obtained.

[0013] (2) The present application uses a lithium-sulfur battery to prepare lithium sulfide, without using a large amount of organic solvent, and the reaction is easy to control. The generated lithium sulfide has a two-dimensional sheet structure and a micron-level size, which is convenient for subsequent collection and purification. The preparation process is simple, and the commercialization prospect is good. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1Scanning electron microscope image of high crystallinity two-dimensional lithium sulfide nanosheets prepared for Example 1, a is 5 μm, b is 1 μm.

[0015] Figure 2 Electrochemical rate performance graph of high crystallinity two-dimensional lithium sulfide nanosheets prepared for Example 1 applied to lithium-sulfur batteries.

[0016] Figure 3 Electrochemical cycle performance graph of high crystallinity two-dimensional lithium sulfide nanosheets prepared for Example 1 applied to lithium-sulfur batteries.

[0017] Figure 4 XRD spectrum of high crystallinity two-dimensional lithium sulfide nanosheets prepared for Example 1.

[0018] Figure 5 Scanning electron microscope image of high crystallinity two-dimensional lithium sulfide nanosheets prepared for Example 2.

[0019] Figure 6 Scanning electron microscope image of high crystallinity two-dimensional lithium sulfide nanosheets prepared for Example 3.

[0020] Figure 7 Scanning electron microscope image of carbon nanotube modified polypropylene separator after discharge for Comparative Example 1.

[0021] Figure 8 Electrochemical cycle performance graph of batteries for Comparative Example 1 and Example 1. DETAILED DESCRIPTION

[0022] The present application will be described in detail below with reference to the examples and the accompanying drawings.

[0023] The present application first prepared a composite material of carbon nanotubes and sulfur as a positive electrode sulfur source, with metal lithium as a lithium source, and used a carbon tube loaded monatomic nickel catalyst modified polypropylene as a lithium sulfide growth substrate. After assembling a battery using a lithium-sulfur electrolyte, discharging at a discharge rate of 0.2 to 5 C to 1.7 V, high crystallinity two-dimensional lithium sulfide nanosheets with a diameter of 0.5 ~ 1.5 μm and a thickness of 10 ~ 50 nm were obtained, which were uniformly grown on the modified polypropylene separator.

[0024] The positive electrode used in the following examples, i.e. the composite material of carbon nanotubes and sulfur, was self-prepared by mixing carbon nanotubes, sulfur, conductive agent Super P and binder La133, and then coating on a current collector to obtain, wherein the mass ratio of carbon nanotubes and sulfur was 2:8, and the mass ratio of carbon nanotubes, sulfur, conductive agent Super P and binder La133 was 8:1:1.

[0025] The carbon nanotube-supported single-atom nickel catalyst used in the polypropylene membrane modified with carbon nanotube-supported single-atom nickel catalyst in the following examples was prepared according to the "One-pot pyrolysis method to fabricate carbon nanotube supported Ni single-atom catalysts with ultrahigh loading. ACS Applied Energy Materials, 2018". The modified membrane was obtained by vacuum filtration and drying of polypropylene and the prepared catalyst solution.

[0026] Example 1

[0027] A composite material of carbon nanotubes and sulfur was used as the positive electrode, 0.1 mg cm⁻¹ -2 A polypropylene membrane modified with a single-atom nickel catalyst supported on carbon nanotubes was used as the separator, a lithium sheet was used as the negative electrode, and the electrolyte was 1 mol L⁻¹. -1 Lithium bis(trifluoromethanesulfonyl)imide was dissolved in a mixed solvent of 1,3-dioxolane and 1,2-dimethoxyethane in a volume ratio of 1:1, and 1 wt% lithium nitrate was added. A battery was assembled and discharged at a rate of 1C to 1.7 V to obtain highly crystalline two-dimensional lithium sulfide nanosheets with a diameter of 0.5 ~ 1.5 μm and a thickness of 10 ~ 50 nm, which were uniformly grown on a modified polypropylene separator.

[0028] Figure 1 The polypropylene separator modified with a carbon nanotube-supported single-atom nickel catalyst prepared in Example 1 was applied to a lithium-sulfur battery, and scanning electron microscope (SEM) images at different resolutions were obtained at 1.7 V. The images show that the separator surface is completely covered by an array of lithium sulfide nanosheets with a diameter of 0.5–1.5 μm and a thickness of 10–50 nm. Furthermore, the lithium sulfide nanosheet array grows uniformly towards the sulfur cathode, indicating that the polysulfides dissolved at the cathode are rapidly lithilated and deposited on the lithium sulfide surface.

[0029] Figure 2 The polypropylene separator modified with a carbon nanotube-supported single-atom nickel catalyst prepared in Example 1 was applied to a lithium-sulfur battery, and the constant current charge-discharge curves at different rates were obtained. As can be seen from the figures, the battery exhibited current densities of 1435, 1130, 1008, 893, 826, and 747 mAh g⁻¹ at 0.2, 0.5, 1, 2, 3, and 5C, respectively. -1 The specific capacity indicates that it has excellent rate performance. In addition, the constant current charge-discharge curve of this battery shows very weak polarization with increasing current density, which indicates the rapid conversion kinetics of polysulfides catalyzed by the active sites on the modified separator.

[0030] Figure 3 The carbon tube supported monatomic nickel catalyst modified polypropylene separator prepared in Example 1 was applied to a lithium-sulfur battery, and the long cycle performance of 500 cycles at 0.5C and 2C was tested. As can be seen from the figure, the reversible capacity of the battery after 500 cycles at 0.5C and 2C was 873 and 629 mAh g -1 , respectively, and the cycle decay rate per cycle was 0.047% and 0.060%, respectively, indicating the long cycle stability of the battery.

[0031] Figure 4 The carbon tube supported monatomic nickel catalyst modified polypropylene separator prepared in Example 1 was applied to a lithium-sulfur battery, and the XRD spectrum at discharge to 2.1V was tested. As can be seen from the figure, the carbon tube supported monatomic nickel catalyst modified polypropylene separator has obvious lithium sulfide (220) and (400) peaks at 2.1V, and the intensity ratio of the (400) peak to the (220) peak is enhanced compared with the lithium sulfide sample, indicating that the lithium sulfide crystal grows along the (100) direction.

[0032] Example 2

[0033] A composite material of carbon nanotubes and sulfur was used as the positive electrode, 1 mg cm -2 of carbon tube supported monatomic nickel catalyst modified polypropylene was used as the separator, lithium sheet was used as the negative electrode, and the electrolyte was 1 mol L -1 of lithium bis(trifluoromethanesulfonyl)imide dissolved in a mixed solvent of 1,3-dioxolane and 1,2-dimethoxyethane in a volume ratio of 1:1, and 1 wt% of lithium nitrate was added, and the battery was assembled, and discharged to 1.7 V at a rate of 1C, to obtain sheet high crystallinity two-dimensional lithium sulfide nanosheets with a diameter of 0.5 ~ 1.5 μm and a thickness of 10 ~ 50 nm, which were uniformly grown on the modified polypropylene separator.

[0034] Figure 5 The carbon tube supported monatomic nickel catalyst modified polypropylene separator prepared in Example 2 was applied to a lithium-sulfur battery, and the scanning electron microscope image at 1.7 V was tested. As can be seen from the figure, the surface of the separator uniformly grows high crystallinity two-dimensional lithium sulfide nanosheets with a diameter of 0.5 ~ 1.5 μm and a thickness of 10 ~ 50 nm, indicating that the positive electrode dissolved polysulfide is quickly lithiated and deposited on the surface of the modified separator.

[0035] Example 3

[0036] A composite material of carbon nanotubes and sulfur was used as the positive electrode, 1 mg cm -2 of carbon tube supported monatomic nickel catalyst modified polypropylene was used as the separator, lithium sheet was used as the negative electrode, and the electrolyte was 1 mol L -1The lithium bis(trifluoromethanesulfonyl)imide was dissolved in a mixed solvent of 1,3-dioxolane and 1,2-dimethoxyethane with a volume ratio of 1:1, and 1 wt% of lithium nitrate was added, a battery was assembled, and discharged at a rate of 2C to 1.7 V to obtain high-crystallinity two-dimensional lithium sulfide nanosheets with a diameter of 0.5~1.5 μm and a thickness of 10~50 nm, which were uniformly grown on the modified polypropylene separator.

[0037] Figure 6 The carbon nanotube-supported monatomic nickel catalyst-modified polypropylene separator prepared in Example 2 was applied to a lithium-sulfur battery, and scanning electron microscope images at different resolutions at 1.7 V were obtained. As can be seen from the images, lithium sulfide nanosheets with a diameter of 0.5~1.5 μm and a thickness of 10~50 nm were uniformly grown on the surface of the separator, indicating that the modified separator effectively catalyzed the conversion and deposition of polysulfides into sheet-shaped lithium sulfide.

[0038] Comparative Example 1

[0039] This comparative example used a carbon nanotube-modified polypropylene separator with a loading of 0.5 mg cm -2 , and the difference from Example 1 was that the material used to modify the separator was different.

[0040] Figure 7 Scanning electron microscope images of the carbon nanotube-modified polypropylene separator in a lithium-sulfur battery at (a) discharge state 2.1 V and (b) 1.7 V. As can be seen from the images, the carbon nanotube-modified polypropylene separator did not undergo significant changes in morphology during the discharge process, indicating that the carbon nanotubes, which had no catalytic activity, were unable to prepare micron-sized lithium sulfide nanosheets.

[0041] Figure 8 Electrochemical cycling performance chart of the batteries of Comparative Example 1 and Example 1. As can be seen from the chart, the carbon nanotube-modified polypropylene separator had a capacity of 724 mAh g -1 at 0.5C after 500 cycles, which rapidly decreased to 285 mAh g -1 , while the carbon nanotube-supported monatomic nickel catalyst-modified polypropylene separator had a reversible capacity of 723 mAh g -1 after 500 cycles at 1C, indicating the excellent rate performance and structural stability of the carbon nanotube-supported monatomic nickel catalyst-modified polypropylene separator.

Claims

1. A method for preparing two-dimensional lithium sulfide nanosheets, characterized in that, A composite material of carbon nanotubes and sulfur was used as the positive electrode, polypropylene modified with a single-atom nickel catalyst supported on carbon nanotubes was used as the separator, and lithium sheets were used as the negative electrode. An electrolyte was added to assemble a full cell, which was discharged at a certain rate to 1.7 V, and two-dimensional lithium sulfide nanosheets were uniformly grown on the separator. Among them, the composite material of carbon nanotubes and sulfur is obtained by coating a current collector with a mixture of carbon nanotubes, sulfur, conductive agent Super P and binder La133. The mass ratio of carbon nanotubes to sulfur is 2:8, and the mass ratio of carbon nanotubes to sulfur, conductive agent Super P and binder La133 is 8:1:

1. The concentration of lithium bis(trifluoromethanesulfonyl)imide in the electrolyte is 1 mol L. -1 The lithium nitrate concentration was 1 wt%, and the electrolyte was a mixed solvent of 1,3-dioxolane and 1,2-dimethoxyethane in a volume ratio of 1:

1.

2. The method as described in claim 1, characterized in that, When polypropylene modified with a carbon nanotube-supported single-atom nickel catalyst is used as a membrane, its loading is 0.1 mg cm⁻¹. -2 Up to 1 mg cm -2 .

3. The method as described in claim 1, characterized in that, Discharge to 1.7 V at a discharge rate of 0.2 to 5C.

4. The method as described in claim 1, characterized in that, Discharge to 1.7 V at a discharge rate of 0.5C to 2C.

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