CN109888178B

CN109888178B - Flexible self-supporting lithium-sulfur battery composite positive electrode material and preparation method thereof

Info

Publication number: CN109888178B
Application number: CN201910177840.8A
Authority: CN
Inventors: 周永宁; 陈东; 岳昕阳; 李璕琭
Original assignee: Fudan University
Current assignee: Fudan University
Priority date: 2019-03-10
Filing date: 2019-03-10
Publication date: 2021-09-17
Anticipated expiration: 2039-03-10
Also published as: CN109888178A

Abstract

The invention belongs to the technical field of electrochemistry, and particularly relates to a flexible self-supporting lithium-sulfur battery composite positive electrode material and a preparation method thereof. The composite cathode material of the lithium-sulfur battery is a bendable composite flexible membrane consisting of elemental sulfur, fibrous molybdenum trioxide and a multi-walled carbon nanotube and is marked as MoO₃-MCNT @ S having a self-supporting structure without additional current collector and with a polysulfide barrier layer. The material is prepared by a hydrothermal method and a suction filtration method. The composite material has excellent charge and discharge performance, and has higher reversible capacity and good cycle performance within the voltage range of 1.5-2.8V and the current density of 0.1-2C; under the current density of 0.5C, the specific capacity can still be maintained at 600-800 mAh g after 350 circles⁻¹. The electrode material has the comprehensive advantages of high specific capacity, good rate capability, long cycle life, simple preparation method, low raw material price and the like.

Description

Flexible self-supporting lithium-sulfur battery composite positive electrode material and preparation method thereof

Technical Field

The invention belongs to the technical field of electrochemistry, and particularly relates to a positive electrode material capable of being used for a lithium-sulfur battery and a preparation method thereof.

Background

In recent years, with the rapid development of new energy science and technology, the performance requirements of people on secondary batteries are continuously increased. However, the theoretical specific capacity of the lithium ion battery which is commercially mature at presentAnd the specific energy is lower, and the living needs of people can not be met any more. In addition, the cost of the conventional lithium ion battery is also high. Therefore, the development of a novel high-energy-density, safe and cheap battery system is a research hotspot in the field of energy storage at present. Compared with the traditional lithium ion battery, the theoretical specific capacity of the lithium-sulfur battery has very obvious advantages (the theoretical specific capacity of the sulfur anode in the lithium-sulfur battery is 1675 mAh.g)⁻¹Energy density was 2600 Wh.kg⁻¹Tens times of the anode material of the traditional lithium ion battery). And the elemental sulfur has the advantages of low price, abundant resources, environmental friendliness and the like, so that the lithium sulfur battery is considered as the most promising next-generation high-energy-density secondary battery. However, lithium-sulfur batteries also face a number of problems that need to be solved: 1. the sulfur simple substance has poor conductivity, so that the electrode has poor reaction kinetics; 2. the lithium-sulfur battery can generate a series of polysulfide reaction intermediates in the discharging process, and the polysulfide reaction intermediates are easy to dissolve in electrolyte, so that a shuttle effect between a positive electrode and a negative electrode is caused, the active substance sulfur of the positive electrode is continuously lost, and the battery capacity is greatly attenuated; 3. under the action of the shuttle effect, the discharge products of lithium sulfide and lithium oversulfide formed at the negative electrode of the battery can greatly influence the reaction interface activity of the electrode. In addition, the large volume change of the sulfur positive electrode in the charging and discharging process can cause the active material sulfur to be separated, so that the battery structure is damaged, and the irreversible attenuation of the battery capacity is caused. The key point for solving the problems is to design a composite cathode material with excellent pertinence, which can effectively improve the dissolution and shuttling of polysulfide in electrolyte and the corrosion to a lithium cathode and reduce the volume change in the charging and discharging processes.

The invention prepares a novel composite sulfur positive electrode material (MoO) of a lithium-sulfur battery by combining a hydrothermal method with a suction filtration method₃MCNT @ S), a flexible electrode material with a self-supporting structure, and a novel positive electrode material for lithium-sulfur batteries with high specific capacity and good cycle performance.

Disclosure of Invention

The invention aims to provide a novel flexible self-supporting composite positive electrode material with good performance for a lithium-sulfur battery and a preparation method thereof.

The invention provides a positive electrode material for a lithium-sulfur battery, which is a bendable composite flexible film consisting of elemental sulfur, fibrous molybdenum trioxide and a multi-walled carbon nanotube and is marked as MoO₃-MCNT @ S having a self-supporting structure without additional current collector and with a polysulfide barrier layer. Research shows that the material has good electrochemical performance and can be used as a positive electrode material of a lithium-sulfur battery. There has been no report of the application of a flexible self-supporting material containing molybdenum trioxide to a lithium sulfur battery.

The invention provides a composite flexible membrane MoO₃/MCNT @ S, the thickness of which is 40-120 μm.

The invention provides a preparation method of a composite cathode material for a lithium-sulfur battery, which comprises the following specific steps:

(1) firstly, nano-scale MoO is added₃Adding the particles into deionized water, stirring uniformly, then dropwise adding hydrogen peroxide under magnetic stirring, and heating the mixed solution in an oil bath kettle to obtain transparent MoO₃Solution, and hydrothermal reaction of MoO₃Preparation of the solution into fibrous MoO₃An emulsion;

(2) the fibrous MoO prepared in the step (1) is put into₃Adding the emulsion, MCNT and SDS dispersant into deionized water and uniformly stirring to obtain solution A; carrying out suction filtration, washing and drying on the solution to obtain MoO with a self-supporting structure₃Compounding film;

(3) the fibrous MoO prepared in the step (1) is put into₃Adding the emulsion, MCNT, S powder and SDS dispersant into deionized water and uniformly stirring to obtain solution B; the MoO prepared in the step (2) is added₃Placing the composite membrane serving as a filter membrane in a sand core funnel, carrying out suction filtration on the solution B, washing with water, and drying to obtain the flexible self-supporting sulfur composite cathode material with a double-layer membrane structure, and marking as MoO₃/MCNT@S。

In step (1) of the present invention, fibrous MoO is prepared₃The emulsion conditions were: the concentration of hydrogen peroxide is 20-50%, the oil bath temperature of the oil bath pot is 70-100 ℃, the hydro-thermal reaction temperature is 100-300 ℃, and the reaction is carried outThe time is 0.5-1.5 h.

In step (2) of the present invention, MoO is prepared₃The solution A conditions of the composite membrane are as follows: MoO₃The mass ratio of the emulsion to the MCNT is 2: 1-3: 1, and the mass ratio of the MCNT to the SDS dispersant is 1: 8-1: 10.

In step (3) of the present invention, MoO is prepared₃Solution B conditions of/MCNT @ S were: MoO₃The mass ratio of the emulsion to MCNT @ S is 2: 1-3: 1, wherein the mass ratio of S to MCNT is 5: 4-8: 1, and the mass ratio of MCNT @ S to SDS dispersant is 1: 8-1: 10.

In the invention, the filter membrane used for suction filtration is an aqueous organic mixed nylon new sub-filter membrane (the aperture is 0.22 mu m), and the size of the aperture of the sand core funnel is 200-400 meshes.

According to the invention, the drying material is dried in a vacuum manner at the temperature of 30-70 ℃ for 6-24 h.

In the present invention, MoO₃The morphology of/MCNT @ S is obtained by a scanning electron microscope and is a film-like structure formed by interlacing fiber rods.

In the present invention, MoO₃the/MCNT @ S composite material can be directly used as an electrode of a lithium-sulfur battery. The prepared sample is dried and cut into a circular electrode slice with the diameter of 12mm, and an additional current collector is not needed.

In the present invention, MoO₃The electrochemical performance test of the/MCNT @ S composite material adopts a lithium-sulfur battery system consisting of double electrodes. Wherein, MoO₃the/MCNT @ S composite material is used as a working electrode, and the high-purity lithium sheet is used as a counter electrode and a reference electrode at the same time. The electrolyte is 1M LiTFSI/DOL-DME (the volume ratio of DOL to DME is 1:1) and 2-4 wt.% LiNO₃The septum is Celgard2400, 2320 and 2300. The cell was assembled in a glove box filled with argon. The charge and discharge experiments of the lithium sulfur battery were performed on a blue (Land) battery test system.

In the present invention, the MoO is synthesized₃the/MCNT @ S composite material has excellent charge and discharge performance, and has higher reversible capacity and good cycle performance within the voltage range of 1.5-2.8V and the current density of 0.1-2C. Under the current density of 0.5C, the specific capacity can still be maintained at 600-800 mAh g after 350 circles⁻¹. The electrode material hasHigh specific capacity, good rate capability, long cycle life, simple preparation method, low price of raw materials and the like.

The performances show that the flexible self-supporting MoO prepared by the hydrothermal method and the suction filtration method₃the/MCNT @ S composite cathode material is a novel cathode material with excellent performance, and can be applied to lithium-sulfur batteries, especially flexible batteries.

Drawings

FIG. 1 is MoO₃Appearance pictures and flexible pictures of the/MCNT @ S composite cathode material.

FIG. 2 shows MoO₃The cyclic discharge capacity curve at 0.5C current density for/MCNT @ S.

Detailed Description

Example 1

First 0.5g of MoO₃Adding the particles into 50mL of deionized water, stirring for 30min, dropwise adding 10mL of 30% hydrogen peroxide, heating the mixed solution in an oil bath kettle at 80 ℃ for 1h, transferring the mixed solution into a 100mL hydrothermal kettle, and keeping the temperature at 180 ℃ for 30min to obtain a product after hydrothermal reaction, namely MoO₃An emulsion. 2mL of MoO₃The emulsion, 10mg MCNT and 0.1g SDS dispersant were added to 50mL deionized water and stirred well to give solution A. Carrying out suction filtration, washing and drying on the solution to obtain MoO with a self-supporting structure₃A composite membrane. 3mL of MoO₃The emulsion, 15mg MCNT @ S (where S: MCNT = 7:2, wt.%) and 0.2g SDS dispersant were dissolved in 50mL deionized water and stirred well to give solution B. The MoO prepared previously is added₃Placing the composite membrane as a filter membrane in a sand core funnel, carrying out suction filtration on the solution B, washing with water, and carrying out vacuum drying at 60 ℃ for 12h to obtain a flexible self-supporting sulfur positive electrode material (MoO) with a double-layer membrane structure and a thickness of 62 mu m₃/MCNT@S)。

The characterization result of a scanning electron microscope shows that the flexible self-supporting sulfur anode material with the double-layer film is in a film structure formed by fiber rods in a staggered mode. The material is used as a working electrode, and a high-purity lithium sheet is used as a counter electrode to assemble a simulation battery. Wherein the electrolyte is 1M LiTFSI/DOL-DME (volume ratio of DOL to DME is 1:1) +2wt.% LiNO₃The diaphragm is CThe battery assembly was carried out in an oven filled with argon. The charge and discharge test result shows that the capacity of the material is kept at 666 mAh g after the material is cycled for 350 circles under the current density of 0.5C⁻¹。

Example 2

First 0.5g of MoO₃Adding the particles into 50mL of deionized water, stirring for 30min, dropwise adding 10mL of 30% hydrogen peroxide, heating the mixed solution in an oil bath kettle at 80 ℃ for 1h, transferring the mixed solution into a 100mL hydrothermal kettle, and keeping the temperature at 180 ℃ for 30min to obtain a product after hydrothermal reaction, namely MoO₃An emulsion. 4mL of MoO₃The emulsion, 20mg MCNT and 0.2g SDS dispersant were added to 50mL deionized water and stirred well to give solution A. Carrying out suction filtration, washing and drying on the solution to obtain MoO with a self-supporting structure₃A composite membrane. 6mL of MoO₃The emulsion, 30mg MCNT @ S (where S: MCNT = 7:2, wt.%) and 0.4g SDS dispersant were dissolved in 50mL deionized water and stirred well to give solution B. The MoO prepared previously is added₃Placing the composite membrane as a filter membrane in a sand core funnel, carrying out suction filtration on the solution B, washing with water, and carrying out vacuum drying at 60 ℃ for 12h to obtain a flexible self-supporting sulfur positive electrode material (MoO) with a thickness of 101 mu m and a double-layer membrane structure₃/MCNT@S)。

The characterization result of a scanning electron microscope shows that the flexible self-supporting sulfur anode material with the double-layer film is in a film structure formed by fiber rods in a staggered mode. The material is used as a working electrode, and a high-purity lithium sheet is used as a counter electrode to assemble a simulation battery. Wherein the electrolyte is 1M LiTFSI/DOL-DME (volume ratio of DOL to DME is 1:1) +2wt.% LiNO₃The separator was Celgard2400, and the cell assembly was carried out in an argon-filled dry box. The charge and discharge test result shows that the capacity of the material is about 880 mAh g after the material is cycled for 200 circles under the current density of 0.2C⁻¹。

Claims

1. The preparation method of the flexible self-supporting composite positive electrode material for the lithium-sulfur battery is characterized in that the positive electrode material is a bendable composite flexible film composed of elemental sulfur, fibrous molybdenum trioxide and a multi-walled carbon nanotube and is marked as MoO₃MCNT @ S, which has a self-supporting structure without additional current collectors, and is self-bearing with a polysulfide barrier layer;

the method comprises the following specific steps:

(2) the fibrous MoO prepared in the step (1) is put into₃Adding the emulsion, MCNT and SDS dispersant into deionized water and uniformly stirring to obtain solution A; carrying out suction filtration, washing and drying on the solution to obtain MoO with a self-supporting structure₃Compounding film; MCNT is multi-walled carbon nano-tube, SDS is sodium dodecyl sulfate;

2. The preparation method according to claim 1, wherein in the step (1), the concentration of the hydrogen peroxide is 20-50%, the temperature of the oil bath is 70-100 ℃, the temperature of the hydrothermal reaction is 100-300 ℃, and the reaction time is 0.5-1.5 h.

3. The method according to claim 1, wherein in the step (2), MoO₃The mass ratio of the emulsion to the MCNT is 2: 1-3: 1, and the mass ratio of the MCNT to the SDS dispersant is 1: 8-1: 10.

4. The method according to claim 1, wherein in the step (3), MoO₃The mass ratio of the emulsion to MCNT @ S is 2: 1-3: 1, wherein the mass ratio of S to MCNT is 5:4And (3) 1:8, wherein the mass ratio of MCNT @ S to SDS dispersant is 1: 8-1: 10.

5. The preparation method according to claim 1, wherein the filtration membrane for suction filtration is an aqueous organic mixed nylon neonanofiltration membrane, the pore diameter is 0.22 μm, and the sand core funnel is 200-400 mesh.

6. The preparation method according to claim 1, wherein the drying is performed in a vacuum drying mode at a temperature of 30-70 ℃ for 6-24 hours.