CN112054153A

CN112054153A - Modified diaphragm for lithium-sulfur battery and preparation method thereof

Info

Publication number: CN112054153A
Application number: CN202011124450.3A
Authority: CN
Inventors: 张燕
Original assignee: Guangzhou Haoyue New Energy Equipment Co ltd
Current assignee: Guangzhou Haoyue New Energy Equipment Co ltd
Priority date: 2020-10-20
Filing date: 2020-10-20
Publication date: 2020-12-08

Abstract

The invention relates to a modified diaphragm for a lithium-sulfur battery, and belongs to the technical field of electrochemical energy storage. The utility model provides an intermediate level combined material has abundant porous structure, including porous graphene and porous sponge structure's skeleton, has avoided among the prior art because the block ion transmission route that lamellar structure such as graphite alkene caused. Cobalt titanium oxide is produced in the pore channel structure of the porous framework through in-situ reaction, and a large amount of lithium polyoxide adsorption sites are provided by the uniformly dispersed oxide nanocrystals. The sulfonated polyether ether ketone is introduced, the interface resistance of the electrode is reduced, and negatively charged groups can repel the transmission of negatively charged polysulfide ions, so that the shuttle of lithium polyoxide is blocked. The present application realizes a lithium sulfur secondary battery with high cycle stability.

Description

Modified diaphragm for lithium-sulfur battery and preparation method thereof

Technical Field

The application relates to a preparation method of a modified diaphragm for a lithium-sulfur battery and a preparation method of an interlayer material, belonging to the field of battery materials.

Background

The commercial application of lithium ion batteries was successfully realized by the company sony, japan, 1992, and then the development of lithium ion batteries was rapid. However, the theoretical specific capacity and energy density of lithium ion batteries limit further development, and therefore, the development of novel electrochemical energy storage devices with high energy density, long cycle life and low cost is urgently needed. The lithium-sulfur battery has the advantages of high theoretical specific capacity, high energy density, rich resources and the like, and has strong competitiveness in a plurality of new-generation energy storage systems. However, the current lithium-sulfur batteries also have some fatal disadvantages: sulfur and discharge products have low conductivity, so that the utilization rate of active substances is low and the polarization resistance is large; secondly, the intermediate product in the charging and discharging process is dissolved in the electrolyte and shuttled between the positive electrode and the negative electrode, so that the utilization rate of the positive electrode material is low, and the cycle life is short; and the volume of the sulfur anode can be greatly changed in the charging and discharging process. Other disadvantages include potential safety hazards such as lithium cathode corrosion and lithium dendrites.

In order to solve these problems, on the one hand, the conductive skeleton material is introduced into the positive electrode, so that the conductivity of the positive electrode is increased, and meanwhile, the polyoxide is captured, and the volume expansion is relieved. On the other hand, with respect to electrolyte additives and lithium negative electrode protection. Meanwhile, the research on interlayer materials has attracted much attention. The concept of the 'intermediate layer' is firstly proposed in 2012 by the Manthiram topic group, a porous carbon paper is introduced between the positive electrode and the diaphragm to serve as the intermediate layer, a conductive network is constructed in the positive electrode area, and the shuttle effect of polyoxide is inhibited, so that the utilization rate of active substances is improved, and the electrochemical performance of the lithium-sulfur battery is improved.

The charge and discharge processes of the intermediate layer lithium sulfur battery are complex redox reactions that undergo multiple phase changes, multiple steps. During discharging, the cyclic S8 molecule can carry out ring opening reaction, and is combined with lithium ions and electrons to form soluble intermediate product lithium polyoxide, and finally converted into insoluble Li2S2/Li2S, and the charging process is just the reverse. The middle layer mainly realizes the inhibition of the transmembrane diffusion of the polyoxide through two action modes of physical separation and chemical adsorption.

The physical barrier inhibits the diffusion of the polyoxide, namely, the intermediate layer is used as a barrier layer between the positive electrode and the diaphragm to block the migration of the polyoxide to the negative electrode, and the physical barrier is generally realized by increasing the migration path of the polyoxide, porous adsorption, electrostatic repulsion and the like. At present, carbon materials such as carbon nanotubes and graphene are mainly used as an interlayer material. Physical barrier effects can inhibit the diffusion of polyoxides to some extent, but have limited barrier effects. Chemisorption, i.e., sulfur fixation by chemical bonding of polar materials and polyoxides. The lithium ion conductive material mainly comprises a doped carbon material with lithium-philic and sulfur-philic characteristics, a metal compound, a conductive polymer and the like, and the material is specifically selected according to the lithium ion conductive performance, so that the polyoxide diffusion is balanced and inhibited, and the lithium ion transmission is ensured.

The diaphragm is one of the important components of the lithium-sulfur battery, plays a role in isolating electrons and conducting ions, and the performance of the diaphragm can directly influence the overall performance of the battery. At present, the lithium-sulfur battery diaphragm is usually a non-polar film such as polypropylene, polyethylene (PP/PE) and the like, and the diaphragm cannot prevent the shuttle of polyoxide dissolved in electrolyte between a positive electrode and a negative electrode. Most of the currently researched and developed composite diaphragms limit the shuttle of polysulfide ions in the charging and discharging process based on the principle of physical and/or chemical adsorption, and have limited effect on improving the overall performance of the battery. Therefore, it is necessary to develop a composite separator with excellent performance to effectively inhibit the shuttle effect of the polyoxide and improve the electrochemical performance of the lithium-sulfur battery.

Disclosure of Invention

The invention aims to overcome the defects of the prior art, and provides an efficient modified diaphragm which can efficiently block shuttling of lithium polyoxide and has high electron conduction efficiency and ion shuttling speed.

In order to achieve the above purpose, the invention provides the following technical scheme:

a modified diaphragm for a lithium-sulfur battery comprises a porous substrate; and an interlayer material coating disposed on a surface of the substrate; wherein the interlayer material coating comprises sulfonated polyether ether ketone, porous graphene, titanium cobalt oxide and a porous carbon material.

In a preferred embodiment of the present invention, the porous carbon material is a carbon sponge.

As a preferred technical scheme of the invention, the porous substrate is a PP/PE diaphragm.

The invention also provides a preparation method of the modified diaphragm for the lithium-sulfur battery, which comprises the following steps:

(1) preparation of porous carbon material:

cleaning melamine sponge, carbonizing the melamine sponge under a protective atmosphere, and cooling to obtain carbon sponge;

(2) preparing porous graphene oxide:

adding graphene oxide into an alkali solution for ultrasonic dispersion, and then performing reflux treatment at 100 ℃; washing the obtained sample with anhydrous ethanol and deionized water, filtering for 3 times, and drying the sample;

(3) preparing a cobalt titanium oxide/porous graphene/porous carbon composite material:

preparing a mixed solution of titanium salt and cobalt salt with a certain concentration; dispersing the porous carbon in the step (1) and the porous graphene oxide in the step (2) in the mixed solution, carrying out hydrothermal reaction, filtering, drying to obtain a first precursor material, and then annealing in an inert atmosphere to obtain a cobalt titanium oxide/porous graphene/porous carbon composite material;

(4) preparing a modified diaphragm:

adding the cobalt titanium oxide/porous graphene/porous carbon material into sulfonated polyether ether ketone and isopropanol, stirring to prepare uniformly dispersed slurry, coating the slurry on a porous substrate to prepare a uniform interlayer coating, and performing vacuum drying.

As a preferred technical scheme of the invention, the carbonization step in the step (1) is carried out at the temperature of 400-900 ℃, preferably 800-900 ℃ for 4-6 h.

As a preferred technical scheme of the invention, the alkali solution in the step (2) is more than one of sodium hydroxide and potassium hydroxide, and the concentration of the alkali solution is 5-20M; the reflux treatment time is 1-20 h.

As a preferable technical scheme of the invention, the molar ratio of titanium to cobalt in the mixed solution in the step (3) is 1:1-10, and the titanium salt is titanium tetrachloride; the cobalt salt is cobalt acetate.

As a preferred technical scheme of the invention, the temperature of the hydrothermal reaction in the step (3) is 100-200 ℃, the reaction time is 6-12 h, the temperature of the annealing treatment is 400-800 ℃, and the reaction time is 1-5 h.

As a preferable embodiment of the present invention, cobalt titanium oxide: porous graphene: the mass ratio of the porous carbon is (0.01-1): (5-10); (5-10).

In a preferred embodiment of the present invention, the intermediate layer contains sulfonated polyether ether ketone in an amount of 1 to 10% by mass.

Compared with the prior art, the beneficial effects of the invention are embodied in the following aspects:

(1) the conventional graphene material is of a lamellar structure, and the aggregate of the graphene material inhibits the shuttle of lithium polyoxide and also seriously hinders the transmission of lithium ions, so that the rate performance of the battery is not facilitated. The utility model provides an intermediate level combined material has abundant porous structure, including porous graphene and porous sponge structure's skeleton, has avoided among the prior art because the block ion transmission route that lamellar structure such as graphite alkene caused, therefore has improved ion transmission efficiency.

(2) Through in-situ reaction, cobalt titanium oxide is produced in the pore channel structure of the porous framework, and a large number of lithium polyoxide adsorption sites are provided by the uniformly dispersed oxide nanocrystals, so that the diffusion of the lithium polyoxide to the negative electrode side and the accumulation of the lithium polyoxide on the surface of the intermediate layer are hindered.

(3) The sulfonated polyether ether ketone is also introduced, and the polymer can firmly bond the middle layer material on the diaphragm and reduce the interface resistance of the electrode. Meanwhile, sulfonated polyether ether ketone is a negatively charged group, so that the transmission of lithium ions can be promoted, and the transmission of negative polysulfide ions is rejected, so that the shuttle of lithium polyoxide is blocked.

Through the synergistic effect of the substances in the structure of the lithium-sulfur battery, the lithium-sulfur battery has longer cycle life and excellent rate performance.

Drawings

FIG. 1 is TEM image of cobalt titanium oxide/porous graphene/porous carbon composite material in example 1

FIG. 2 is a graph of the cycle performance of example 1 and comparative example 1

Detailed Description

The present invention will be described in further detail with reference to the following detailed description and the accompanying drawings, which are not intended to limit the invention to the embodiments shown herein.

Example 1

(1) preparation of porous carbon material:

washing 10g of melamine sponge by using absolute ethyl alcohol and deionized water, drying, carbonizing the melamine sponge at 500 ℃ for 6 hours under the protection of nitrogen, and cooling to obtain carbon sponge;

(2) preparing porous graphene oxide:

adding graphene oxide into a 10M sodium hydroxide solution for ultrasonic dispersion, and then carrying out reflux treatment at 100 ℃ for 10 hours; washing the obtained sample with anhydrous ethanol and deionized water, filtering for 3 times, and drying the sample;

preparing 2mol/L mixed solution of titanium salt and cobalt salt, wherein the titanium salt is titanium tetrachloride, the cobalt salt is cobalt acetate, and the molar ratio of titanium to cobalt is 1: 1. Adding 2ml of the solution into 100ml of deionized water to form a mixture, dispersing 5g of the porous carbon obtained in the step (1) and 5g of the porous graphene oxide obtained in the step (2) in the mixed solution, carrying out hydrothermal reaction at 140 ℃ for 6h, filtering and drying to obtain a precursor material, and then carrying out annealing treatment at 500 ℃ for 2h in a nitrogen atmosphere to obtain a cobalt titanium oxide/porous graphene/porous carbon composite material;

(4) preparing a modified diaphragm:

adding 5g of cobalt titanium oxide/porous graphene/porous carbon material and 0.2g of sulfonated polyether ether ketone into 50ml of isopropanol, stirring to prepare uniformly dispersed slurry, coating the slurry on a PP/PE porous substrate to prepare a uniform interlayer coating, and drying in vacuum.

To test the performance of the materials, lithium sulfur batteries were prepared.

The sulfur/active carbon composite material is used as a positive electrode, a metal lithium sheet is used as a negative electrode, and LiPF₆The 1, 3-dioxolane and 1, 2-dimethoxyethane solution is used as an electrolyte to prepare the lithium-sulfur secondary battery. One side of the modified diaphragm loaded with the interlayer material faces the positive electrode. Initial capacity of battery at 0.1C charge-discharge rateReach 1250mAh/g, and the battery capacity is 1076mAh/g after 100 circles.

Example 2

(1) preparation of porous carbon material:

(2) preparing porous graphene oxide:

adding graphene oxide into a sodium hydroxide solution with the concentration of 15M for ultrasonic dispersion, and then carrying out reflux treatment for 10 hours at 100 ℃; washing the obtained sample with anhydrous ethanol and deionized water, filtering for 3 times, and drying the sample;

preparing 2mol/L mixed solution of titanium salt and cobalt salt, wherein the titanium salt is titanium tetrachloride, the cobalt salt is cobalt acetate, and the molar ratio of titanium to cobalt is 1: 1. Adding 3ml of the solution into 100ml of deionized water to form a mixture, dispersing 10g of the porous carbon obtained in the step (1) and 5g of the porous graphene oxide obtained in the step (2) in the mixed solution, carrying out hydrothermal reaction at 180 ℃ for 1h, filtering, drying to obtain a precursor material, and then carrying out annealing treatment at 800 ℃ for 1h in a nitrogen atmosphere to obtain a cobalt titanium oxide/porous graphene/porous carbon composite material;

(4) preparing a modified diaphragm:

adding 9g of cobalt titanium oxide/porous graphene/porous carbon material and 1g of sulfonated polyether ether ketone into 50ml of isopropanol, stirring to prepare uniformly dispersed slurry, coating the slurry on a PP/PE porous substrate to prepare a uniform interlayer coating, and drying in vacuum.

Comparative example 1

The sulfur/active carbon composite material is used as a positive electrode, a metal lithium sheet is used as a negative electrode, and LiPF₆The 1, 3-dioxolane and 1, 2-dimethoxyethane solution is used as an electrolyte to prepare the lithium-sulfur secondary battery. PP/PE separator as lithium-sulfur separatorAnd (3) a membrane. Under the charge and discharge rate of 0.1C, the initial capacity of the battery reaches 1175mAh/g, and the capacity of the battery after 100 circles is 534 mAh/g.

The cycle performance of example 1 and comparative example 1 is shown in fig. 2, with curve 1 representing example 1 and curve 2 representing comparative example 1. As can be seen from the results of the above examples and comparative example 1, the present application achieved excellent cycle performance of the lithium sulfur battery.

Variations and modifications to the above-described embodiments may occur to those skilled in the art based upon the disclosure and teachings of the above specification. Therefore, the present application is not limited to the specific embodiments disclosed and described above, and some modifications and variations of the present application should fall within the scope of the claims of the present application. In addition, although specific terms are used herein, they are used in a descriptive sense only and not for purposes of limitation.

Claims

1. A modified diaphragm for a lithium-sulfur battery is characterized by comprising the following components:

a porous substrate; and

a coating of interlayer material disposed on a surface of the substrate;

wherein the interlayer material coating comprises sulfonated polyether ether ketone, porous graphene, titanium cobalt oxide and a porous carbon material.

2. The modified separator according to claim 1, wherein the porous carbon material is a carbon sponge.

3. The modified separator according to claim 1 or 2, wherein the porous substrate is a PP/PE separator.

4. A method for preparing a modified separator for a lithium-sulfur battery according to any one of claims 1 to 3, further characterized by comprising the steps of:

(1) preparation of porous carbon material:

(2) preparing porous graphene oxide:

(4) preparing a modified diaphragm:

5. The method according to claim 4, wherein the carbonization step in step (1) is carried out at a temperature of 400 to 900 ℃, preferably 800 to 900 ℃, for a time of 4 to 6 hours.

6. The preparation method according to claim 4 or 5, wherein the alkali solution in the step (2) is more than one of sodium hydroxide and potassium hydroxide, and the concentration of the alkali solution is 5-20M; the reflux treatment time is 1-20 h.

7. The production method according to any one of claims 4 to 6, wherein the molar ratio of titanium to cobalt in the mixed solution in the step (3) is 1:1 to 10, and the titanium salt is titanium tetrachloride; the cobalt salt is cobalt acetate.

8. The method as claimed in any one of claims 4 to 6, wherein the hydrothermal reaction in step (3) is performed at a temperature of 100 to 200 ℃ for 6 to 12 hours, the annealing treatment is performed at a temperature of 400 ℃ and 800 ℃ for 1 to 5 hours.

9. The production method according to any one of claims 4 to 6, wherein the ratio of cobalt titanium oxide: porous graphene: the mass ratio of the porous carbon is (0.01-1): (5-10); (5-10).

10. The production method according to any one of claims 4 to 6, wherein the sulfonated polyether ether ketone is contained in the intermediate layer in an amount of 1 to 10% by mass.