Atomically dispersed catalyst / nitrogen-doped carbon nanotube-modified glass fiber separator for lithium-sulfur batteries, preparation method, and application thereof

Abstract

The present invention belongs to the technical field of battery materials and discloses an atomically dispersed catalyst / nitrogen-doped carbon nanotube modified glass fiber diaphragm for lithium-sulfur batteries and its preparation method and application. The preparation method comprises the following steps: using glass fiber membrane, metal salt, ammonium chloride and ammonia water as raw materials, obtaining a precursor diaphragm of in-situ growth of metal silicate on glass fiber by a hydrothermal method; placing a nitrogen-containing carbon source and the precursor diaphragm of in-situ growth of metal silicate on glass fiber upstream and downstream of a tube furnace airflow, and in an inert gas atmosphere, subjecting the carbon source to high-temperature pyrolysis to release volatile gases containing cyanide by chemical vapor deposition to obtain a modified diaphragm with a hierarchical three-dimensional network structure; immersing the modified diaphragm in a dilute acid solution to etch away excess metal, retaining the atomically dispersed M-N in the nitrogen-doped carbon nanotubes. x active sites, and finally obtained an atomically dispersed catalyst / nitrogen-doped carbon nanotube-modified glass fiber separator for lithium-sulfur batteries.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery materials, and in particular relates to an atomically dispersed catalyst / nitrogen-doped carbon nanotube-modified glass fiber separator for lithium-sulfur batteries, and a preparation method and application thereof. Background Art

[0002] The Celgard series of composite porous separators (primarily composed of polypropylene and polyethylene) currently used in lithium-sulfur batteries suffer from issues such as virtually no restriction on the diffusion of lithium polysulfides, poor thermal stability, extreme flammability, and a high contribution to the heat of combustion. Therefore, the development of new functional separators with high thermal stability and low flammability is of great scientific and practical significance for achieving safe, high-performance lithium-sulfur batteries. Numerous studies have demonstrated that modifying Celgard separators with atomically dispersed catalyst / carbon composites can effectively enhance the electrochemical performance of lithium-sulfur batteries by regulating the adsorption-catalytic conversion of lithium polysulfides in lithium-sulfur batteries. The introduction of carbon materials reduces the interfacial resistance between the electrode and separator, while their porous structure limits the volume change of sulfur and allows for physical adsorption of fixed sulfur. Furthermore, the atomically dispersed catalysts, with their theoretical 100% atomic utilization, provide abundant surface active sites for the catalytic conversion of lithium polysulfides. This not only effectively chemically adsorbs and fixes polysulfides, suppressing the shuttle effect, but also accelerates the conversion of polysulfides to lithium sulfide or sulfur, enhancing the electrochemical kinetics of sulfur. To address safety issues, heat-resistant materials (glass fiber, polyamide, polyimide, polyethylene terephthalate, etc.) are directly used to prepare battery separators that are resistant to higher temperatures. The separators are made of heat-resistant polymer materials to prevent the separators from shrinking and deforming due to heat during use, causing short circuits between the positive and negative electrodes, and instantly releasing more heat, which is the fundamental way to cause combustion and explosion. Summary of the Invention

[0003] In order to overcome the shortcomings and deficiencies of the above-mentioned prior art and develop heat-resistant functionalized diaphragm materials to meet the growing demand for high-performance diaphragm materials for lithium-sulfur batteries, the primary purpose of the present invention is to provide a method for preparing an atomically dispersed catalyst / nitrogen-doped carbon nanotube modified glass fiber diaphragm for lithium-sulfur batteries; the method is to in situ grow a metal silicate precursor diaphragm (GF-MSiO) on a glass fiber by a hydrothermal method. x ), and then formed into GF / MN by chemical vapor deposition and pickling. x @NCNTs membrane has a simple preparation process and exhibits good mechanical properties and thermal stability.

[0004] Another object of the present invention is to provide an atomically dispersed catalyst / nitrogen-doped carbon nanotube modified glass fiber separator for lithium-sulfur batteries prepared by the above preparation method.

[0005] Another object of the present invention is to provide an application of the above-mentioned atomically dispersed catalyst / nitrogen-doped carbon nanotube modified glass fiber separator for lithium-sulfur batteries.

[0006] The purpose of the present invention is achieved through the following technical solutions:

[0007] A method for preparing an atomically dispersed catalyst / nitrogen-doped carbon nanotube modified glass fiber separator for lithium-sulfur batteries comprises the following steps:

[0008] (1) Glass fiber membrane, metal salt, ammonium chloride and ammonia water were used as raw materials to obtain a precursor membrane of in situ grown metal silicate on glass fiber (GF-MSiO) by hydrothermal method. x ); the metal salt is a chloride, nitrate or acetate of metal M;

[0009] (2) placing a nitrogen-containing carbon source upstream of the tube furnace gas flow, placing a precursor membrane of metal silicate in situ grown on the glass fiber obtained in step (1) downstream of the tube furnace gas flow, and subjecting the carbon source to high-temperature pyrolysis in an inert gas atmosphere to chemical vapor deposition of volatile gases containing cyanide groups to obtain a modified membrane having a hierarchical three-dimensional network structure composed of metal@nitrogen-doped carbon nanotubes and glass fiber membranes;

[0010] (3) Soaking the modified diaphragm obtained in step (2) in a dilute acid solution to etch excess metal and retain the atomically dispersed MN in the nitrogen-doped carbon nanotubes x Active sites, and finally obtained atomically dispersed catalyst / nitrogen-doped carbon nanotube modified glass fiber separator for lithium-sulfur batteries, namely GF / MN x @NCNTs diaphragm.

[0011] The M metal in step (1) is nickel, cobalt or copper; the process parameters of the hydrothermal method are: reaction temperature 90-140° C., reaction time 8-12 h.

[0012] In step (2), the nitrogen-containing carbon source is dicyandiamide or melamine; the inert gas is nitrogen or argon; and the high-temperature pyrolysis is carried out at a temperature of 700 to 900° C. for 1 to 3 hours.

[0013] In step (1), the amount of the metal salt is 0.5-2 mmol, the amount of ammonium chloride is 10-30 mmol, and the amount of ammonia water is 1-3 ml; and in step (2), the amount of the nitrogen-containing carbon source is 0.5-2 g.

[0014] The dilute acid solution in step (3) is dilute hydrochloric acid or dilute sulfuric acid with a concentration of 0.5-2 mol / L.

[0015] An atomically dispersed catalyst / nitrogen-doped carbon nanotube modified glass fiber separator for lithium-sulfur batteries prepared by the above preparation method.

[0016] The above-mentioned original lithium-sulfur battery atomically dispersed catalyst / nitrogen-doped carbon nanotube modified glass fiber separator is used in lithium-sulfur batteries.

[0017] Compared with the prior art, the present invention has the following advantages:

[0018] (1) During the preparation process of the diaphragm of the present invention, after the metal silicate is reduced to metal atoms and silicon dioxide at high temperature, the silicon dioxide and the chemical vapor deposition-like carbon nanotube growth process provide a dual in-situ confinement effect, which effectively prevents the metal atoms from migrating and aggregating into nanoparticles during the preparation process, thereby avoiding the inability to fully exert their efficient catalytic ability due to the reduction in the number of active sites.

[0019] (2) The nitrogen-doped carbon nanotubes produced during the preparation of the diaphragm of the present invention construct a three-dimensional conductive network in the positive electrode region, which can not only serve as an upper current collector to reduce the interfacial resistance on the sulfur positive electrode side to ensure rapid electron transmission, but also have the function of physical barrier and chemical adsorption of lithium polysulfide, thereby improving the rate performance of the sulfur positive electrode and delaying the diffusion of lithium polysulfide to the negative electrode.

[0020] (3) The atomically dispersed metal catalyst used in the preparation process of the diaphragm of the present invention should have more exposed active sites than nanoparticles, and has a stronger adsorption and anchoring effect on lithium polysulfide and a more efficient catalytic conversion ability; from the perspective of the preparation process, the direct in-situ growth of nanofunctional materials on the diaphragm substrate can simplify the tedious production process of preparing the modified diaphragm by conventional slurry coating and vacuum filtration methods. Since there is no need to add additional binders and conductive agents, the "dead weight" caused by these inactive ingredients can be avoided to reduce the energy density of the lithium-sulfur battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The glass fiber membrane pretreated in Example 1 of the present invention and the precursor membrane with in-situ growth of nickel silicate (GF-MSiO x ) and GF / MN x SEM images of @NCNTs membranes, where a is a pretreated glass fiber membrane; b is a precursor membrane with in-situ growth of nickel silicate; c and d are GF / MN x @NCNTs diaphragm.

[0022] Figure 2 PP diaphragm and GF / Ni-N x @Comparison of thermal stability of NCNTs separators.

[0023] Figure 3 PP diaphragm and GF / Ni-N x Comparison of electrochemical performance of @NCNTs, a is cycle stability; b is rate performance. DETAILED DESCRIPTION

[0024] The present invention will be described in further detail below with reference to the embodiments and drawings, but the embodiments of the present invention are not limited thereto.

[0025] Example 1

[0026] The glass fiber membrane was pretreated as follows: rinsing with acetone to remove impurities and drying; then 1 mmol of nickel acetate and 20 mmol of ammonium chloride were weighed and completely dissolved in 100 ml of deionized water, and 2 ml of ammonia water (25-28 wt%) was added to obtain a mixed solution; then a piece of the pretreated glass fiber membrane was placed in the mixed solution obtained above, transferred to a reactor and hydrothermally reacted at 95° for 10 hours to obtain a precursor membrane with in situ growth of nickel silicate (GF-NiSiO x ); 1.5g of dicyandiamide and the aforementioned in-situ grown precursor membrane with metal silicate (GF-NiSiO x ) were placed in the upstream and downstream of the tube furnace gas flow, and heat treated at 800 ° C for 2 h in a nitrogen atmosphere to obtain a modified membrane with a hierarchical three-dimensional network structure composed of metal@nitrogen-doped carbon nanotubes and glass fiber membrane; the modified membrane obtained above was immersed in 1 mol / L dilute hydrochloric acid to etch away excess metal, retaining the atomically dispersed Ni-N in the nitrogen-doped carbon nanotubes. x active sites, and finally GF / Ni-N x @NCNTs diaphragm.

[0027] The scanning electron microscope image of the product obtained in this Example 1 is as follows Figure 1 As shown, the product is a modified diaphragm with a hierarchical three-dimensional network structure of metal@nitrogen-doped carbon nanotubes grown on a glass fiber diaphragm, which greatly improves the thermal stability and mechanical properties of the diaphragm. Figure 1 a shows the typical microscopic morphology of glass fiber separator, and the surface of micron-sized glass fiber is smooth. Figure 1 In b, we can see that the originally smooth surface of the glass fiber has been completely covered by nickel silicate nanosheets. Figure 1 The CD shows that after chemical vapor deposition and acid washing, a large number of carbon nanotubes are in situ grown on the glass fiber. Figure 2 a and b show that the PP diaphragm has curled and shrunk after heat treatment at 150 ° C, while the GF / Ni-N obtained in Example 1 x NCNTs are resistant to high temperatures, and their shape remains unchanged, ensuring that the diaphragm does not shrink excessively when heated, thus avoiding exposure of the electrodes and causing short circuits. Figure 3 PP diaphragm and GF / Ni-N obtained in Example 1 xComparing the electrochemical performance of the GF / Ni-Nx@NCNTs separator, the cycle stability and rate performance of the lithium-sulfur battery using GF / Ni-Nx@NCNTs as the separator are significantly better than those using the PP separator.

[0028] Example 2

[0029] The glass fiber membrane was pretreated as follows: rinsing with acetone to remove impurities and drying; then 1 mmol of copper chloride and 20 mmol of ammonium chloride were weighed and completely dissolved in 100 ml of deionized water, and 2 ml of ammonia (25-28 wt%) was added to obtain a mixed solution; then a piece of the pretreated glass fiber membrane was placed in the mixed solution, transferred to a reactor and hydrothermally reacted at 140° for 10 hours to obtain an in situ grown metal silicate precursor membrane (GF-CuSiO x ); 1.5g dicyandiamide and the aforementioned in situ grown metal silicate precursor membrane (GF-CuSiO x ) were placed in the upstream and downstream of the tube furnace gas flow, respectively, and a chemical vapor deposition method was used to react at 800 ° C in a nitrogen atmosphere for 2 h to obtain a modified membrane with a hierarchical three-dimensional network structure composed of metal@nitrogen-doped carbon nanotubes and glass fiber membranes; the modified membrane obtained above was immersed in 1 mol / L dilute hydrochloric acid to etch away excess metal, retaining the atomically dispersed Cu-N in the nitrogen-doped carbon nanotubes. x active sites, and finally GF / Cu-N x @NCNTs diaphragm.

[0030] Example 3

[0031] The glass fiber membrane was pretreated as follows: it was rinsed with acetone to remove impurities and dried; 1 mmol of cobalt nitrate and 20 mmol of ammonium chloride were weighed and completely dissolved in 100 ml of deionized water, and 2 ml of ammonia water (25-28 wt%) was added to obtain a mixed solution; a piece of the pretreated glass fiber membrane was placed in the mixed solution, transferred to a reactor and hydrothermally reacted at 120° for 10 hours to obtain a precursor membrane with in situ growth of metal silicate (GF-CoSiO x ); 1.5 g of dicyandiamide and the aforementioned in-situ grown precursor membrane with metal silicate (GF-CoSiO x ) were placed in the upstream and downstream of the tube furnace gas flow, respectively, and a chemical vapor deposition method was used to react at 800 ° C in a nitrogen atmosphere for 2 h to obtain a modified membrane with a hierarchical three-dimensional network structure composed of metal@nitrogen-doped carbon nanotubes and glass fiber membranes; the modified membrane obtained above was immersed in 1 mol / L dilute hydrochloric acid to etch away excess metal, retaining the atomically dispersed Co-N in the nitrogen-doped carbon nanotubes. x active sites, and finally GF / Co-Nx @NCNTs diaphragm.

[0032] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A method for preparing an atomically dispersed catalyst / nitrogen-doped carbon nanotube modified glass fiber separator for lithium-sulfur batteries, characterized in that The following steps are included: (1) Using glass fiber membrane, metal salt, ammonium chloride and ammonia water as raw materials, a precursor membrane of in-situ growth of metal silicate on glass fiber is obtained by a hydrothermal method; the metal salt is a chloride, nitrate or acetate of metal M; (2) placing a nitrogen-containing carbon source upstream of the tube furnace gas flow, placing a precursor membrane of metal silicate in situ grown on the glass fiber obtained in step (1) downstream of the tube furnace gas flow, and subjecting the carbon source to high-temperature pyrolysis in an inert gas atmosphere to chemical vapor deposition of volatile gases containing cyanide groups to obtain a modified membrane having a hierarchical three-dimensional network structure composed of metal@nitrogen-doped carbon nanotubes and glass fiber membranes; (3) Soaking the modified diaphragm obtained in step (2) in a dilute acid solution to etch excess metal and retain the atomically dispersed MN in the nitrogen-doped carbon nanotubes x Active sites, and finally obtained atomically dispersed catalyst / nitrogen-doped carbon nanotube modified glass fiber separator for lithium-sulfur batteries, namely GF / MN x @NCNTs diaphragm.

2. The method for preparing an atomically dispersed catalyst / nitrogen-doped carbon nanotube modified glass fiber separator for lithium-sulfur batteries according to claim 1, characterized in that: The M metal in step (1) is nickel, cobalt or copper; the process parameters of the hydrothermal method are: reaction temperature 90-140° C., reaction time 8-12 h.

3. The method for preparing an atomically dispersed catalyst / nitrogen-doped carbon nanotube modified glass fiber separator for lithium-sulfur batteries according to claim 1, characterized in that: In step (2), the nitrogen-containing carbon source is dicyandiamide or melamine; the inert gas is nitrogen or argon; and the high-temperature pyrolysis is carried out at a temperature of 700 to 900° C. for 1 to 3 hours.

4. The method for preparing an atomically dispersed catalyst / nitrogen-doped carbon nanotube modified glass fiber separator for lithium-sulfur batteries according to claim 1, characterized in that: In step (1), the amount of the metal salt is 0.5-2 mmol, the amount of ammonium chloride is 10-30 mmol, and the amount of ammonia water is 1-3 ml; and in step (2), the amount of the nitrogen-containing carbon source is 0.5-2 g.

5. The method for preparing an atomically dispersed catalyst / nitrogen-doped carbon nanotube modified glass fiber separator for lithium-sulfur batteries according to claim 1, characterized in that: The dilute acid solution in step (3) is dilute hydrochloric acid or dilute sulfuric acid with a concentration of 0.5-2 mol / L.

6. An atomically dispersed catalyst / nitrogen-doped carbon nanotube modified glass fiber separator for lithium-sulfur batteries prepared by the preparation method according to any one of claims 1 to 5.

7. Use of the atomically dispersed catalyst / nitrogen-doped carbon nanotube-modified glass fiber separator for lithium-sulfur batteries according to claim 6 in lithium-sulfur batteries.

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