A hollow multi-shell cobalt selenide modified separator for lithium-sulfur batteries and a preparation method thereof

Abstract

The application discloses a hollow multi-shell layer cobalt selenide modified diaphragm for lithium-sulfur batteries and a preparation method thereof. Ammonium metavanadate is heated in a water bath to form a light yellow clear solution, then cobalt chloride hexahydrate and hexamethylenetetramine are added, and after stirring, washing and drying, the obtained product is dispersed in ethylene glycol with sodium selenite, and hydrazine hydrate is added to carry out hydrothermal reaction to prepare hollow multi-shell layer cobalt selenide. The hollow multi-shell layer cobalt selenide is dissolved in an organic solvent with a conductive agent and a binder, and the mixture is uniformly attached to the diaphragm of the lithium-sulfur battery by vacuum filtration to obtain the hollow multi-shell layer cobalt selenide modified diaphragm for lithium-sulfur batteries. The hollow multi-shell layer cobalt selenide has strong adsorption and catalytic capacity, can effectively inhibit the shuttle effect of polysulfides, accelerate the redox kinetic process and improve the utilization rate of active substances, so that the lithium-sulfur battery prepared by using the hollow multi-shell layer cobalt selenide has excellent discharge specific capacity, good cycle stability and excellent rate performance.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium-sulfur batteries, and particularly relates to a hollow multi-shell cobalt selenide modified separator for a lithium-sulfur battery and a preparation method thereof. BACKGROUND

[0002] Compared with other energy storage systems such as lead-acid batteries, nickel-hydrogen batteries and lithium-ion batteries, lithium-sulfur batteries have the advantages of high theoretical specific capacity (1675 mAh g −1 ), high energy density (2600 Wh kg −1 ), environmental friendliness and low cost, and are favored by researchers. Therefore, lithium-sulfur batteries are considered as a promising alternative to commercial lithium-ion batteries. However, the commercialization process of lithium-sulfur batteries is still hindered by the following problems: (1) the almost insulating properties of S8 and the discharge product Li2S, which lead to slow redox kinetics at the positive electrode of the battery; (2) the shuttle effect of polysulfides (LiPSs) will deposit a layer of Li2S2 and Li2S solid on the surface of the lithium metal negative electrode, resulting in problems such as reduced coulombic efficiency, poor cycle performance and high self-discharge of the lithium-sulfur battery; (3) due to the difference in density between S8 and Li2S, significant volume expansion will occur during the cycle process of the battery, which will destroy the structure of the positive electrode material and seriously reduce the capacity of the battery; (4) due to the uneven deposition of Li + on the negative electrode during the charge and discharge process of the battery, lithium dendrite growth may occur on the surface of the lithium metal negative electrode, which is easy to pierce the separator, which will bring serious safety hazards.

[0003] To solve the above problems, researchers have studied the positive electrode, negative electrode, separator and electrolyte of lithium-sulfur batteries. The research results show that coating a separator modification material on the separator of the positive electrode side of the lithium-sulfur battery can effectively alleviate the LiPSs shuttle effect caused by the large pores of the polyolefin separator. Researchers have also tried to use carbon materials, polymer materials and transition metal oxides as separator modification materials to modify the commercial polyolefin separator. Among them, transition metal selenides have good electrical conductivity, and have higher catalytic activity for the redox kinetics process of LiPSs. In addition, the structure and morphology of the material also affect its electrochemical performance. The hollow structure of the hollow multi-shell structure material can provide more adsorption and catalytic sites, and the multi-shell structure can also inhibit the shuttle of polysulfides through a physical barrier. Based on the above advantages, using a hollow multi-shell cobalt selenide modified separator as a lithium-sulfur battery separator modification layer can greatly improve the electrochemical performance of the battery. SUMMARY

[0004] In order to solve the problem that the polyolefin separator of lithium-sulfur battery cannot well solve the polysulfide shuttle effect due to large pores, the application provides a hollow multi-shell cobalt selenide modified separator for lithium-sulfur battery and a preparation method thereof. The hollow multi-shell cobalt selenide is used to modify the lithium-sulfur battery separator based on a commercial polyolefin separator, so as to inhibit the polysulfide shuttle effect, accelerate the redox kinetics process, and improve the utilization rate of active substances.

[0005] In order to achieve the above-mentioned purpose, the application adopts the following technical solutions:

[0006] A hollow multi-shell cobalt selenide modified separator for lithium-sulfur battery, the preparation method comprises the following steps:

[0007] (1) ammonium metavanadate is added to deionized water, heated in a water bath to form a light yellow clear solution, then cobalt chloride hexahydrate and hexamethylenetetramine are added in sequence, and continue to stir under water bath condition to make them uniform, then cooled to room temperature, washed with deionized water and anhydrous ethanol for multiple times, and dried;

[0008] (2) the dried product obtained in step (1) and sodium selenite are added to ethylene glycol, magnetically stirred and dispersed, then hydrazine hydrate is added for hydrothermal reaction, cooled to room temperature after reaction, washed with deionized water and anhydrous ethanol for multiple times, dried, and hollow multi-shell cobalt selenide is obtained;

[0009] (3) the hollow multi-shell cobalt selenide obtained in step (2) is mixed with a conductive agent and a binder and dissolved in an organic solvent, ultrasonically dispersed uniformly, then the above mixture is filtered by using a lithium-sulfur battery separator as a filter membrane, and then dried and cut to prepare the hollow multi-shell cobalt selenide modified separator for lithium-sulfur battery.

[0010] Further, the mass ratio of ammonium metavanadate, cobalt chloride hexahydrate and hexamethylenetetramine used in step (1) is (0.1-1):(0.02-0.2):(1-2).

[0011] Further, the temperature of the water bath heating in step (1) is 50-90 ℃.

[0012] Further, the stirring time in step (1) is 1-5 h.

[0013] Further, the amount ratio of the dried product, sodium selenite, ethylene glycol and hydrazine hydrate used in step (2) is 0.01 g-0.1 g:0.1 g-1 g:10 mL-40 mL:0.1 mL-2 mL.

[0014] Further, the temperature of the hydrothermal reaction in step (2) is 100-200 ℃, and the time is 1-5 h.

[0015] Further, the mass ratio of the hollow multi-shell cobalt selenide to the conductive agent and the binder used in step (3) is (1-5):(0.1-1):(1-2); wherein the conductive agent is Ketjen black, and the binder is polyvinylidene fluoride.

[0016] Further, the organic solvent in step (3) is 1-methyl-2-pyrrolidone.

[0017] Further, the lithium-sulfur battery separator in step (3) is made of polypropylene or polyethylene.

[0018] The present application has the following advantages:

[0019] (1) The present application modifies the positive side of the lithium-sulfur battery separator with hollow multi-shell cobalt selenide, which effectively alleviates the shuttle effect of polysulfides.

[0020] (2) The present application uses hollow multi-shell cobalt selenide as a separator modification material for lithium-sulfur batteries. Transition metal selenides can effectively adsorb polysulfides, reduce the reaction barrier of polysulfides, accelerate the redox kinetics of polysulfides, and effectively inhibit the shuttle effect of polysulfides. The hollow structure can provide more adsorption and catalytic sites, and the multi-shell structure can also inhibit the shuttle of polysulfides through physical barriers. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 X-ray diffraction analysis spectrum of the hollow multi-shell cobalt selenide prepared in Example 1.

[0022] Figure 2 Transmission electron microscope image of the hollow multi-shell cobalt selenide prepared in Example 1. As can be seen from the figure, the obtained cobalt selenide has a hollow multi-shell capsule structure.

[0023] Figure 3 The cyclic voltammetry (CV) curves of the batteries assembled with the hollow multi-shell cobalt selenide modified polypropylene (PP) separator and the unmodified polypropylene (PP) separator prepared in Example 1, respectively, at a scan rate of 0.1 mV s -1 From the comparison of polarization degree and peak current in the figure, it can be seen that the electrochemical performance of the hollow multi-shell cobalt selenide modified separator is better than that of the unmodified PP separator.

[0024] Figure 4 The cyclic performance curves of the batteries assembled with the hollow multi-shell cobalt selenide modified polypropylene (PP) separator and the unmodified polypropylene (PP) separator prepared in Example 1, respectively, at a current density of 0.2 C. As can be seen from the figure, the battery assembled with the hollow multi-shell cobalt selenide modified separator has higher initial discharge capacity and more excellent cycle performance. DETAILED DESCRIPTION

[0025] A hollow multi-shell cobalt selenide modified separator for lithium-sulfur batteries, a preparation method thereof comprises the following steps:

[0026] (1) 0.1-1 g of ammonium metavanadate is dissolved in 20-60 mL of 50-90 ℃ deionized water, and continuously stirred at this temperature until a light yellow solution is formed, then 0.02-0.2 g of cobalt chloride hexahydrate and 1-2 g of hexamethylenetetramine are sequentially added, continuously stirred at 50-90 ℃ for 1-5 h, cooled to room temperature, centrifuged, and the orange yellow precipitate is collected, then washed several times with deionized water and anhydrous ethanol, and finally dried to obtain a powder product;

[0027] (2) 0.1-1 g of Na2SeO3 and 0.01-0.1 g of the powder product dried in step (1) are dispersed in 10-40 mL of ethylene glycol by magnetic stirring, 0.1-2 mL of hydrazine hydrate is added after stirring uniformly, and stirring is continued until uniform; then it is transferred to a reaction kettle, reacted in an oven at 100-200 ℃ for 1-5 h, cooled to room temperature, washed several times with deionized water and ethanol, and finally dried to obtain a hollow multi-shell cobalt selenide powder;

[0028] (3) 1-5 mg of the hollow multi-shell cobalt selenide powder obtained in step (2), 1-2 mg of polyvinylidene fluoride and 0.1-1 mg of Ketjen black are uniformly dispersed in 5-40 mL of 1-methyl-2-pyrrolidone by ultrasonic, then the mixture is uniformly coated on a polypropylene or polyethylene separator by vacuum filtration, and the large piece of separator coated with the modified layer is cut after vacuum drying treatment to obtain a hollow multi-shell cobalt selenide modified separator.

[0029] In order to make the content of the application more convenient to understand, the technical solutions of the application will be further described below in combination with specific embodiments, but the application is not limited thereto.

[0030] Example 1

[0031] A hollow multi-shell cobalt selenide modified separator for lithium-sulfur batteries, a preparation method thereof comprises the following steps:

[0032] (1) 0.1 g of ammonium metavanadate is dissolved in 50 mL of 60 ℃ deionized water, and continuously stirred at this temperature until a light yellow solution is formed, then 0.02 g of cobalt chloride hexahydrate and 1 g of hexamethylenetetramine are sequentially added, continuously stirred at 60 ℃ for 2 h, cooled to room temperature, centrifuged, and the orange yellow precipitate is collected, then washed several times with deionized water and anhydrous ethanol, and finally dried to obtain a powder product;

[0033] (2) Take 0.1 g of Na2SeO3 and 0.01 g of the powder product dried in step (1), disperse in 40 mL of ethylene glycol by magnetic stirring, after stirring evenly, add 0.3 mL of hydrazine hydrate, and continue to stir evenly; then, transfer it to the reaction kettle, react in the oven at 100 ℃ for 1 h, after cooling to room temperature, wash with deionized water and ethanol for several times, and finally dry to obtain a hollow multi-shell cobalt selenide powder;

[0034] (3) Take 1 mg of the hollow multi-shell cobalt selenide powder obtained in step (2), 1 mg of polyvinylidene fluoride and 0.1 mg of ketchen black, disperse uniformly in 5 mL of 1-methyl-2-pyrrolidone by ultrasonic, then coat the above mixture uniformly on a polypropylene or polyethylene separator by vacuum filtration method, then cut the large piece of separator coated with the modification layer after vacuum drying treatment to obtain a hollow multi-shell cobalt selenide modified separator.

[0035] Example 2

[0036] A hollow multi-shell cobalt selenide modified separator for lithium-sulfur battery, the preparation method comprising the following steps:

[0037] (1) Take 0.5 g of ammonium metavanadate and dissolve it in 50 mL of 50 ℃ deionized water, and continuously stir at this temperature until a light yellow solution is formed, then add 0.15 g of cobalt chloride hexahydrate and 2 g of hexamethylenetetramine in sequence, continuously stir at 50 ℃ for 3 h, after cooling to room temperature, centrifugal separation is carried out, the orange yellow precipitate is collected, then washed with deionized water and anhydrous ethanol for several times, and finally dried to obtain a powder product;

[0038] (2) Take 0.8 g of Na2SeO3 and 0.03 g of the powder product dried in step (1), disperse in 40 mL of ethylene glycol by magnetic stirring, after stirring evenly, add 0.3 mL of hydrazine hydrate, and continue to stir evenly; then, transfer it to the reaction kettle, react in the oven at 120 ℃ for 4 h, after cooling to room temperature, wash with deionized water and ethanol for several times, and finally dry to obtain a hollow multi-shell cobalt selenide powder;

[0039] (3) Take 3 mg of the hollow multi-shell cobalt selenide powder obtained in step (2), 1.3 mg of polyvinylidene fluoride and 0.8 mg of ketchen black, disperse uniformly in 25 mL of 1-methyl-2-pyrrolidone by ultrasonic, then coat the above mixture uniformly on a polypropylene or polyethylene separator by vacuum filtration method, then cut the large piece of separator coated with the modification layer after vacuum drying treatment to obtain a hollow multi-shell cobalt selenide modified separator.

[0040] Example 3

[0041] A hollow multi-shell cobalt selenide modified separator for lithium-sulfur batteries, a preparation method thereof comprises the following steps:

[0042] (1) 1 g of ammonium metavanadate is weighed and dissolved in 60 mL of 90 DEG C deionized water, and continuously stirred at this temperature until a light yellow solution is formed, then 0.1 g of cobalt chloride hexahydrate and 1.5 g of hexamethylenetetramine are added in sequence, continuously stirred at 90 DEG C for 5 h, and after cooling to room temperature, centrifugal separation is carried out, the orange yellow precipitate is collected, then washed with deionized water and anhydrous ethanol for several times, and finally dried to obtain a powder product;

[0043] (2) 1 g of Na2SeO3 and 0.1 g of the powder product dried in step (1) are weighed and dispersed in 40 mL of ethylene glycol by magnetic stirring, then 1.5 mL of hydrazine hydrate is added and continuously stirred until uniform; then, it is transferred to a reaction kettle and reacted in a 200 DEG C oven for 5 h, after cooling to room temperature, it is washed with deionized water and ethanol for several times, and finally dried to obtain a powder of hollow multi-shell cobalt selenide;

[0044] (3) 5 mg of the hollow multi-shell cobalt selenide powder obtained in step (2), 1.1 mg of polyvinylidene fluoride and 1 mg of ketjen black are uniformly dispersed in 30 mL of 1-methyl-2-pyrrolidone by ultrasonic, then the mixture is uniformly coated on a polypropylene or polyethylene separator by vacuum filtration, and then the large piece of separator coated with the modified layer is cut after vacuum drying treatment to obtain a hollow multi-shell cobalt selenide modified separator.

[0045] Electrochemical performance test

[0046] Battery assembly: the hollow multi-shell cobalt selenide modified separator obtained in the example is cut into a circular piece with a diameter of 19 mm, a sulfur positive electrode, a lithium negative electrode and a lithium-sulfur battery electrolyte are used to assemble a CR 2032 button cell in a glove box, and the electrochemical performance thereof is tested by a blue electricity test system.

[0047] The results show that the capacity of the battery assembled by using the hollow multi-shell cobalt selenide modified separator obtained in examples 1, 2 and 3 is 1050, 1008 and 998 mAh / g respectively under a current density of 1 C, wherein the electrochemical performance of example 1 is the best.

[0048] The hollow multi-shell cobalt selenide with strong adsorption and catalytic capacity for LiPSs is introduced as a modified material, which not only relieves the shuttle effect of polysulfides, but also accelerates the reaction kinetics process, and the lithium-sulfur battery using the hollow multi-shell cobalt selenide modified separator shows excellent discharge specific capacity, good cycle stability and excellent rate performance.

[0049] The above merely describes preferred embodiments of the present application, and any equivalent changes and modifications made within the scope of the present application should be included in the scope of the present application.

Claims

1. A method for preparing a hollow multi-shell cobalt selenide modified separator for lithium-sulfur batteries, characterized in that, The method comprises the following steps: (1) adding ammonium metavanadate into deionized water, heating in a water bath to form a light yellow clear solution, then adding cobalt chloride hexahydrate and hexamethylenetetramine in sequence, and continuing to stir under water bath condition to make them uniform, then cooling to room temperature, washing with deionized water and anhydrous ethanol for multiple times, and drying; (2) adding the dried product obtained in step (1) and sodium selenite into ethylene glycol, dispersing by magnetic stirring, then adding hydrazine hydrate to perform hydrothermal reaction, cooling to room temperature after reaction, washing with deionized water and anhydrous ethanol for multiple times, drying, and obtaining the hollow multi-shell selenium cobalt; (3) dissolving the hollow multi-shell selenium cobalt obtained in step (2) and a conductive agent and a binder in an organic solvent, uniformly dispersing by ultrasonic, then performing suction filtration on the mixed solution by using a lithium-sulfur battery separator as a filter membrane, and then drying and cutting to obtain the hollow multi-shell selenium cobalt modified separator for lithium-sulfur batteries.

2. The preparation method of the hollow multi-shell cobalt selenide modified separator for lithium-sulfur batteries according to claim 1, characterized in that: The mass ratio of ammonium metavanadate, cobalt chloride hexahydrate and hexamethylenetetramine used in step (1) is (0.1-1):(0.02-0.2):(1-2).

3. The method for preparing the hollow multi-shell cobalt selenide modified separator for lithium-sulfur batteries according to claim 1, characterized in that: The temperature of the water bath heating in step (1) is 50-90 ℃.

4. The preparation method of hollow multi-shell cobalt selenide modified separator for lithium-sulfur battery according to claim 1, characterized in that: The stirring time in step (1) is 1-5 h.

5. The method for preparing the hollow multi-shell cobalt selenide modified separator for lithium-sulfur batteries according to claim 1, characterized in that: The amount ratio of the dried product, sodium selenite, ethylene glycol and hydrazine hydrate used in step (2) is 0.01 g-0.1 g:0.1 g-1 g:10 mL-40 mL:0.1 mL-2 mL.

6. The method for preparing the hollow multi-shell cobalt selenide modified separator for lithium-sulfur batteries according to claim 1, characterized in that: The temperature of the hydrothermal reaction in step (2) is 100-200 ℃, and the time is 1-5 h.

7. The method for preparing the hollow multi-shell cobalt selenide modified separator for lithium-sulfur batteries according to claim 1, characterized in that: The mass ratio of the hollow multi-shell selenium cobalt, the conductive agent and the binder used in step (3) is (1-5):(0.1-1):(1-2); The conductive agent is Ketjen black, and the binder is polyvinylidene fluoride.

8. The method for preparing the hollow multi-shell cobalt selenide modified separator for lithium-sulfur batteries according to claim 1, characterized in that: The organic solvent in step (3) is 1-methyl-2-pyrrolidone.

9. The method for preparing the hollow multi-shell cobalt selenide modified separator for lithium-sulfur batteries according to claim 1, characterized in that: The lithium-sulfur battery separator in step (3) is polypropylene or polyethylene material.

10. A hollow multi-shell selenium cobalt modified separator for lithium-sulfur batteries prepared by the method in claim 1.

Images