Preparation method of high-crystallinity two-dimensional lithium sulfide nanosheet

Abstract

The invention discloses a preparation method of a high-crystallinity two-dimensional lithium sulfide nanosheet, which comprises the following steps: by taking a composite material of a carbon nanotube and sulfur as a positive electrode, polypropylene modified by a carbon tube loaded monatomic nickel catalyst as a diaphragm and a lithium sheet as a negative electrode, adding an electrolyte to assemble a total battery, discharging to 1.7 V, and uniformly growing two-dimensional lithium sulfide nanosheets with high crystallinity on the diaphragm. The lithium sulfide nanosheet is prepared through an electrochemical method, in the discharging process, the closely-packed carbon tube loaded monatomic nickel catalyst modification layer can physically block diffusion of lithium polysulfide to a negative electrode and can rapidly capture dissolved lithium polysulfide, in-situ catalytic conversion is achieved, and the obtained high-crystallinity two-dimensional sheet-shaped lithium sulfide nanosheet has the advantages of being high in crystallinity and good in electrochemical performance. The lithium sulfide is prepared by using the lithium-sulfur battery, a large amount of organic solvent is not needed, the reaction is easy to control, the generated lithium sulfide is of a two-dimensional sheet structure, the size can reach the micron order, subsequent collection and purification are facilitated, and the preparation process method is simple.

Description

Technical Field

[0001] The present invention belongs to the field of material synthesis, and specifically relates to a method for green and efficient preparation of lithium sulfide using a lithium-sulfur battery, which can be applied to the fields of lithium-sulfur batteries and all-solid-state batteries. Background Art

[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 used in large electric vehicles that pursue long driving range and fast charging and discharging capabilities, people are in urgent need of battery energy systems with long life, large capacity and high safety. All-solid-state lithium metal batteries are considered to be the most promising batteries because their anodes have a high energy density of 3860mAh g -1 The extremely high theoretical specific capacity and extremely low reduction potential (-3.04 V relative to the standard hydrogen electrode) of solid electrolytes are crucial to effectively suppress the safety hazards of traditional lithium-ion batteries, because solid electrolytes are less flammable and more compatible with lithium metal anodes than liquid electrolytes.

[0003] Lithium sulfide is an important material for the development of all-solid-state lithium batteries based on sulfide solid electrolytes. It can also be used as a positive electrode material for high-capacity lithium-sulfur batteries. Its production process development and optimization are increasingly receiving widespread attention and attention. In previous studies on the synthesis of lithium sulfide, Fang et al. dissolved LiCl and Na2S in anhydrous ethanol, respectively, where the molar ratio of LiCl and Na2S raw materials was 2:1, stirred thoroughly and centrifuged, and the by-product NaCl and ethanol solvent were removed to obtain the product lithium sulfide powder (Green synthesis of the battery material lithium sulfide via metathetic reactions, Chemical Communications, 2022). However, the organic solvent anhydrous ethanol is flammable, volatile, and difficult to recycle. It is highly dangerous and difficult to control when used for large-scale industrial production. Summary of the invention

[0004] The purpose of the present invention is to provide a method for preparing two-dimensional lithium sulfide nanosheets with high crystallinity.

[0005] The present invention comprises the following steps: A method for preparing a high-crystallinity two-dimensional lithium sulfide nanosheet comprises the following steps:

[0006] A composite material of carbon nanotubes and sulfur is used as the positive electrode, polypropylene modified with single-atom nickel catalyst loaded with carbon nanotubes is used as the separator, and a lithium sheet is used as the negative electrode. An electrolyte is added to assemble a full battery, which is discharged to 1.7 V at a certain rate to obtain highly crystalline two-dimensional lithium sulfide nanosheets that grow evenly on the separator.

[0007] Preferably, when the carbon tube-supported single-atom nickel catalyst modified polypropylene is used as a diaphragm, its loading is 0.1 mgcm -2 to 1 mg cm -2 This is because the efficiency and crystal quality of preparing lithium sulfide using this loaded single-atom nickel catalyst with high catalytic activity are high, while overuse of the catalyst can be avoided.

[0008] Preferably, the composite material of carbon nanotubes and sulfur is obtained by mixing carbon nanotubes, sulfur, conductive agent Super P and binder La133 and then coating the mixture on a current collector, wherein 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.

[0009] Preferably, the concentration of lithium bis(trifluoromethanesulfonyl)imide in the electrolyte is 1 mol L -1 The concentration of lithium nitrate is 1wt%, 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 this concentration has a flaky structure and high crystallinity.

[0010] Preferably, the modified diaphragm is discharged to 1.7 V at a discharge rate of 0.2 to 5C, preferably 0.5C to 2C. Under different discharge current rates, uniformly grown flat lithium sulfide nanosheets can be obtained on the modified diaphragm, and the crystals have a high degree of crystallinity.

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

[0012] (1) The present invention prepares lithium sulfide nanosheets by an electrochemical method. During the discharge process, the tightly stacked carbon tube-supported single-atom nickel catalyst modification layer can not only physically block the diffusion of lithium polysulfide to the negative electrode, but also quickly capture the dissolved lithium polysulfide, achieving in-situ catalytic conversion, and obtaining highly crystalline two-dimensional sheet-like lithium sulfide nanosheets.

[0013] (2) The present invention utilizes lithium-sulfur batteries to prepare lithium sulfide, which does not require the use of large amounts of organic solvents. The reaction is easy to control, and the generated lithium sulfide is a two-dimensional sheet structure with a size of up to micrometers, which is convenient for subsequent collection and purification. The preparation process is simple and has good commercial prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1This is a scanning electron microscope image of the high-crystallinity two-dimensional lithium sulfide nanosheet prepared in Example 1, a is 5 μm, and b is 1 μm.

[0015] Figure 2 This is the electrochemical rate performance diagram of the high-crystallinity two-dimensional lithium sulfide nanosheets prepared in Example 1 applied to lithium-sulfur batteries.

[0016] Figure 3 This is a diagram of the electrochemical cycle performance of the high-crystallinity two-dimensional lithium sulfide nanosheets prepared in Example 1 and applied to lithium-sulfur batteries.

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

[0018] Figure 5 This is a scanning electron microscope image of the high-crystallinity two-dimensional lithium sulfide nanosheets prepared in Example 2.

[0019] Figure 6 This is a scanning electron microscope image of the high-crystallinity two-dimensional lithium sulfide nanosheets prepared in Example 3.

[0020] Figure 7 This is a scanning electron microscope image of the carbon nanotube-modified polypropylene membrane after discharge in Comparative Example 1.

[0021] Figure 8 It is the electrochemical cycle performance diagram of the battery of comparative example 1 and embodiment 1. DETAILED DESCRIPTION

[0022] The present invention is described in detail below in conjunction with embodiments and drawings.

[0023] The present invention firstly prepares a composite material of carbon nanotubes and sulfur as a positive electrode sulfur source, uses metallic lithium as a lithium source, and uses polypropylene modified with a single-atom nickel catalyst supported by carbon nanotubes as a lithium sulfide growth substrate. After assembling the battery using a lithium-sulfur electrolyte, the battery is discharged to 1.7 V at a discharge rate of 0.2 to 5C, and a high-crystallinity two-dimensional lithium sulfide nanosheet with a diameter of 0.5 to 1.5 μm and a thickness of 10 to 50 nm can be obtained, which is uniformly grown on a modified polypropylene diaphragm.

[0024] The positive electrode used in the following embodiments, i.e., the composite material of carbon nanotubes and sulfur, is self-made, and is obtained by mixing carbon nanotubes, sulfur, conductive agent Super P and binder La133 and then coating the mixture on a current collector, wherein 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.

[0025] The carbon tube-supported single-atom nickel catalyst in the polypropylene membrane modified with the carbon nanotube-supported single-atom nickel catalyst used in the following examples is prepared according to (One-pot pyrolysis method to fabricate carbon nanotube supported Ni single-atom catalysts with ultrahigh loading. ACS Applied Energy Materials, 2018). The polypropylene and the prepared catalyst solution are vacuum filtered and dried to obtain a modified membrane.

[0026] Example 1

[0027] The composite material of carbon nanotubes and sulfur was used as the positive electrode, 0.1 mg cm -2 The polypropylene diaphragm modified with single-atom nickel catalyst supported by carbon tubes was used as the diaphragm, the lithium sheet was used as the negative electrode, and the electrolyte was 1 mol L -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. The battery was assembled and discharged to 1.7 V at a rate of 1C 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 the modified polypropylene separator.

[0028] Figure 1 The carbon tube-supported single-atom nickel catalyst modified polypropylene diaphragm prepared in Example 1 is applied to lithium-sulfur batteries, and the scanning electron microscope images at different resolutions at 1.7 V. It can be seen from the figure that the surface of the diaphragm is completely covered by the lithium sulfide nanosheet array with a diameter of 0.5 ~ 1.5μm and a thickness of 10 ~ 50nm, and the lithium sulfide nanosheet array grows uniformly toward the sulfur positive electrode, indicating that the polysulfide dissolved in the positive electrode is rapidly lithiated and deposited on the lithium sulfide surface.

[0029] Figure 2 The carbon tube-supported single-atom nickel catalyst modified polypropylene diaphragm prepared in Example 1 is applied to lithium-sulfur batteries, and the constant current charge-discharge curves at different rates are shown in the figure. It can be seen from the figure that the battery exhibits 1435, 1130, 1008, 893, 826 and 747 mAh g at current densities of 0.2, 0.5, 1, 2, 3 and 5C, respectively. -1 The specific capacity of the battery shows excellent rate performance. In addition, the constant current charge-discharge curve of the battery shows very weak polarization with the increase of current density, which indicates the rapid conversion kinetics of polysulfide under the catalysis of active sites on the modified separator.

[0030] Figure 3 The carbon tube-supported single-atom nickel catalyst modified polypropylene diaphragm prepared in Example 1 is applied to lithium-sulfur batteries, and has long cycle performance of 500 cycles at 0.5C and 2C. It can be seen from the figure that after 500 cycles at 0.5 and 2C, the reversible capacity of the battery is 873 and 629 mAh g, respectively. -1 The cycle attenuation rates of each cycle are 0.047% and 0.060%, respectively, indicating the long-cycle stability of the battery.

[0031] Figure 4 The carbon tube-supported single-atom nickel catalyst-modified polypropylene diaphragm prepared in Example 1 was applied to a lithium-sulfur battery, and the XRD spectrum when discharged to 2.1 V. It can be seen from the figure that the carbon tube-supported single-atom nickel catalyst-modified polypropylene diaphragm has obvious lithium sulfide (220) and (400) peaks at 2.1 V, 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 crystals grow preferentially along the (100) direction.

[0032] Example 2

[0033] The composite material of carbon nanotubes and sulfur is used as the positive electrode, 1 mg cm -2 The carbon tube-supported single-atom nickel catalyst modified polypropylene was used as the separator, the lithium sheet was used as the negative electrode, and the electrolyte was 1 mol L -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. The 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 the modified polypropylene separator.

[0034] Figure 5 The carbon tube-supported single-atom nickel catalyst modified polypropylene diaphragm prepared in Example 2 is applied to lithium-sulfur batteries, and the scanning electron microscope image at 1.7 V. It can be seen from the figure that high-crystallinity two-dimensional lithium sulfide nanosheets with a diameter of 0.5 to 1.5 μm and a thickness of 10 to 50 nm are uniformly grown on the surface of the diaphragm, indicating that the polysulfide dissolved in the positive electrode is rapidly lithiated and deposited on the surface of the modified diaphragm.

[0035] Example 3

[0036] The composite material of carbon nanotubes and sulfur was used as the positive electrode, 1 mg cm -2 The carbon tube-supported single-atom nickel catalyst modified polypropylene membrane was used as the separator, the lithium sheet was used as the negative electrode, and the electrolyte was 1 mol L -1Lithium 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. The battery was assembled and discharged at a rate of 2C 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 the modified polypropylene separator.

[0037] Figure 6 The carbon tube-supported single-atom nickel catalyst modified polypropylene diaphragm prepared in Example 2 is applied to lithium-sulfur batteries, and the scanning electron microscope images at different resolutions at 1.7 V. It can be seen from the figure that lithium sulfide nanoparticles with a diameter of 0.5 to 1.5 μm and a thickness of 10 to 50 nm are uniformly grown on the surface of the diaphragm, indicating that the modified diaphragm effectively catalyzes the conversion and deposition of polysulfide into flaky lithium sulfide.

[0038] Comparative Example 1

[0039] This comparative example uses a loading of 0.5 mg cm -2 The carbon nanotube-modified polypropylene membrane of Example 1 is different from that of Example 1 in that the materials used to modify the membrane are different.

[0040] Figure 7 The scanning electron micrographs of the carbon nanotube-modified polypropylene separator in the lithium-sulfur battery at (a) discharge state 2.1 V and (b) 1.7 V. As can be seen from the figure, the carbon nanotube-modified polypropylene separator did not undergo obvious morphological changes during the discharge process, indicating that carbon nanotubes without catalytic activity cannot prepare micron-sized lithium sulfide nanosheets.

[0041] Figure 8 The electrochemical cycle performance diagram of the battery of Comparative Example 1 and Example 1 shows that the capacity of the carbon nanotube-modified polypropylene separator increased from 724 mAh g to 1.5 mAh g after 500 cycles at 0.5 C. -1 Quickly drops to 285 mAh g -1 The reversible capacity of the polypropylene separator modified by the single-atom nickel catalyst supported by carbon nanotubes was 723 mAh g after 500 cycles at 1C. -1 , demonstrating the excellent rate performance and structural stability of the polypropylene diaphragm modified with carbon tube-supported single-atom nickel catalyst.

Claims

1. A method for preparing high-crystallinity two-dimensional lithium sulfide nanosheets, characterized in that: A composite material of carbon nanotubes and sulfur is used as the positive electrode, polypropylene modified with a single-atom nickel catalyst loaded with carbon nanotubes is used as the separator, and a lithium sheet is used as the negative electrode. An electrolyte is added to assemble a full battery, which is discharged to 1.7 V at a certain rate, and highly crystalline two-dimensional lithium sulfide nanosheets are uniformly grown on the separator.

2. The method according to claim 1, characterized in that When the carbon nanotube-supported single-atom nickel catalyst modified polypropylene is used as a separator, the loading amount is 0.1 mg cm -2 to 1 mg cm -2 .

3. The method according to claim 1, characterized in that The composite material of carbon nanotubes and sulfur is obtained by mixing carbon nanotubes, sulfur, conductive agent Super P and binder La133 and then coating the mixture on a current collector, wherein 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.

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

1.

5. The method according to claim 1, wherein Discharge to 1.7 V at a discharge rate of 0.2 to 5C.

6. The method according to claim 1, wherein: Discharge to 1.7 V at a discharge rate of 0.5C to 2C.

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