Preparation method and application of two-dimensional porous carbon sheet composite metal sulfide

Abstract

The application discloses a preparation method and application of two-dimensional porous carbon sheet composite metal sulfide, and aims at the problems of poor internal conductivity and shuttle effect of a lithium-sulfur battery at present, wherein metal sulfide with uniform particles and good dispersity is compounded on the two-dimensional porous carbon sheet, the two-dimensional porous carbon sheet is used for modification of a lithium-sulfur battery diaphragm, the shuttle problem of polysulfide is relieved through physical confinement of the two-dimensional porous carbon sheet and chemical adsorption and catalysis of the metal sulfide, and the electrochemical performance of the battery is improved.

Description

Technical Field

[0001] This invention belongs to the field of inorganic synthesis technology, specifically relating to a method for preparing and applying two-dimensional porous carbon sheet composite metal sulfides. Background Technology

[0002] Lithium-sulfur batteries are considered a candidate material for next-generation energy storage systems due to their abundance, safety, and low cost. However, sulfur and its reaction products have poor conductivity, and severe volume expansion during charging and discharging can cause active materials to detach from the current collector. Furthermore, soluble lithium polysulfides diffuse from the positive electrode to the negative electrode during the battery reaction, creating a shuttle effect that leads to low coulombic efficiency and rapid capacity decay. Therefore, designing a reasonable battery structure to prevent polysulfides from shutting down to the negative electrode while improving the conductivity of the battery electrodes is a necessary means to solve the current problems of lithium-sulfur batteries.

[0003] The sulfur atoms in metal sulfides possess high electronegativity, enabling them to capture electrons from transition metals and act as stable reaction intermediates, thus exhibiting excellent adsorption and catalytic activity for active materials in lithium-sulfur batteries, enhancing battery reaction kinetics. Currently, methods for synthesizing metal sulfides include high-temperature solid-state methods and hydrothermal methods; however, the resulting products generally have large particle sizes and low purity, and the raw materials used in their synthesis pose certain environmental threats. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing and applying two-dimensional porous carbon sheets composite metal sulfides, in order to solve one or more of the aforementioned technical problems. This invention prepares a two-dimensional porous carbon sheet using cellulose diacetate as a carbon source, and uniformly composites a layer of metal sulfides onto its surface. This invention is used as a modifying material for lithium-sulfur battery separators. The two-dimensional porous carbon sheet can physically block polysulfides dissolved in the lithium-sulfur battery electrolyte, improving the utilization rate of active materials. The surface metal sulfides can act as active sites to catalyze and adsorb polysulfides, improving the conversion kinetics of polysulfides.

[0005] This invention is achieved using the following technical solution:

[0006] A method for preparing two-dimensional porous carbon sheet composite metal sulfides includes the following steps:

[0007] Weigh out cellulose diacetate and potassium hydroxide in a set mass ratio, grind and mix them thoroughly, sinter them under a nitrogen atmosphere, remove impurities by acid washing with hydrochloric acid, and then dry them to obtain two-dimensional porous carbon sheets.

[0008] Weigh out two-dimensional porous carbon sheets, metal acetate and urea according to the set mass ratio, add ethanol as solvent, and sonicate until the metal acetate is completely dissolved; after evaporating the ethanol, place it in a tube furnace and heat it under a nitrogen atmosphere. During this process, carbon reduces the metal salt ions to their corresponding elemental metal particles, thus obtaining two-dimensional porous carbon with elemental metal particles.

[0009] Two-dimensional porous carbon particles of elemental metal are ground until fluffy and placed in a magnetic boat. The magnetic boat is then placed in a tube furnace. A magnetic boat containing sublimed sulfur is placed upstream of the magnetic boat near the gas inlet. After heating, the sulfur vapor, carried by nitrogen gas, sulfides the metal particles on the surface of the two-dimensional carbon sheet, forming metal sulfides.

[0010] A further improvement of the present invention is that the mass ratio of cellulose diacetate to potassium hydroxide is 1:1 to 3.

[0011] A further improvement of the present invention is that 1 mmol of transition metal acetate and 100 mg of urea are added to every 100 mg of two-dimensional porous carbon sheet.

[0012] A further improvement of the present invention is that the metal acetate is iron acetate, cobalt acetate, or nickel acetate.

[0013] A further improvement of the present invention is that the amount of ethanol added is sufficient to completely dissolve the weighed metal acetate.

[0014] A further improvement of the present invention is that the heating temperature under a nitrogen atmosphere is 700-800°C.

[0015] A further improvement of this invention is that the nitrogen flow rate during heating in a nitrogen atmosphere is 100–200 mL / h. -1 .

[0016] A further improvement of the present invention is that the metal acetate is sonicated for 10 minutes until it is completely dissolved.

[0017] An application of a two-dimensional porous carbon sheet composite metal sulfide, which is prepared by the aforementioned preparation method, is used as a membrane modification material for lithium-sulfur batteries.

[0018] Compared with the prior art, the present invention has at least the following beneficial technical effects:

[0019] I. The carbon source of the two-dimensional porous carbon sheet in this invention is cellulose diacetate, and the activator is potassium hydroxide. The two-dimensional porous carbon material can be obtained by uniformly mixing the materials using the simplest mechanical mixing method and then treating them at high temperature. At the same time, it can ensure that the morphology of the prepared carbon material is uniform. The equipment used in the preparation process is simple, avoiding complex instruments and equipment, and the cost of raw materials is low.

[0020] Second, a certain proportion of urea is added along with the catalyst in this invention. The purpose is that urea can undergo a complexation reaction with metal ions, thereby avoiding the agglomeration of metal particles. After coating the material of this invention onto the separator, the uniformity of the catalytic site distribution is ensured, which is conducive to the more efficient catalytic conversion of polysulfides in lithium-sulfur batteries.

[0021] Third, this invention uses a two-step method to synthesize three different types of metal sulfides. In the first step, the metal source added during sintering is the corresponding metal acetate, and in the second step, the sulfur source for sulfidation is sublimed sulfur. The raw materials are simple, low-cost, and environmentally friendly. The prepared metal sulfides have high crystallinity, uniform particle size, and good dispersibility, which is beneficial for more efficient catalysis of polysulfide conversion in lithium-sulfur batteries and accelerates battery reaction kinetics.

[0022] IV. The structure of the composite metal sulfide on two-dimensional porous carbon prepared by the method of this invention can be used for membrane modification in lithium-sulfur batteries. The layered two-dimensional porous carbon is coated onto the membrane in a stacked manner, increasing the migration path of polysulfides as they shuttle towards the negative electrode. This provides a physical barrier to polysulfides dissolved in the lithium-sulfur battery electrolyte, improving the utilization rate of the active material. Simultaneously, the metal sulfides loaded onto the two-dimensional porous carbon sheets can improve the conductivity inside the battery, enhance reaction kinetics, and serve as catalytic sites for the reaction, adsorbing and catalyzing the conversion of polysulfides. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art are briefly introduced below; obviously, the drawings described below are some embodiments of the present invention, and those skilled in the art can obtain other drawings based on these drawings without creative effort.

[0024] Figure 1 These are the X-ray diffraction patterns of the materials prepared in Examples 1, 2, and 3 of this invention, wherein... Figure 1 a is the X-ray diffraction pattern of iron disulfide composite on a two-dimensional porous carbon sheet. Figure 1 b is the X-ray diffraction pattern of nickel disulfide composite on a two-dimensional porous carbon sheet. Figure 1 c is the X-ray diffraction pattern of cobalt disulfide composite on a two-dimensional porous carbon sheet;

[0025] Figure 2 These are scanning electron microscope (SEM) images of the materials prepared in Examples 1, 2, and 3 of this invention, wherein... Figure 2 Image a is a scanning electron microscope image of iron disulfide composite on a two-dimensional porous carbon sheet. Figure 2 b is a scanning electron microscope image of nickel disulfide composite on a two-dimensional porous carbon sheet. Figure 2c is a scanning electron microscope image of cobalt disulfide composite on a two-dimensional porous carbon sheet;

[0026] Figure 3 These are transmission electron microscope (TEM) images of the materials prepared in Examples 1, 2, and 3 of this invention, wherein... Figure 3 a and 3b are transmission electron microscopy (TEM) images of composite iron disulfide on a two-dimensional porous carbon sheet. Figure 3 Transmission electron microscopy (TEM) images of nickel disulfide composites on c and 3d two-dimensional porous carbon sheets. Figure 3 e and 3f are transmission electron micrographs of cobalt disulfide composite on a two-dimensional porous carbon sheet;

[0027] Figure 4 The cycle performance of the batteries with composite metal sulfide modified separators on two-dimensional porous carbon sheets prepared in Examples 1, 2, and 3 of this invention is shown.

[0028] Figure 5 The rate performance of the batteries with composite metal sulfide modified separators on two-dimensional porous carbon sheets prepared in Examples 1, 2, and 3 of this invention is shown. Detailed Implementation

[0029] To make the objectives, technical effects, and technical solutions of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely below; obviously, the described embodiments are only a part of the embodiments of the present invention. Other embodiments obtained by those skilled in the art based on the disclosed embodiments of the present invention without creative effort should all fall within the scope of protection of the present invention.

[0030] The specific preparation process of a two-dimensional porous carbon sheet composite metal sulfide according to an embodiment of the present invention is as follows:

[0031] Weigh out cellulose diacetate and potassium hydroxide in a mass ratio of 1:1 to 3, grind them thoroughly in a mortar, place the mixture in a nickel crucible, and put it into a tube furnace. Pour 100–200 ml of the mixture into a container and heat at a constant temperature. -1 Nitrogen gas was introduced into the tube furnace at a flow rate of 1% as a protective atmosphere. After sintering, impurities were removed by acid washing with 1M hydrochloric acid, and the carbon sheets were dried overnight to obtain two-dimensional porous carbon sheets.

[0032] Add 1 mmol of cobalt acetate hydrate (or nickel acetate hydrate or iron acetate hydrate) and 100 mg of urea to 100 mg of the above-mentioned two-dimensional porous carbon sheet (the mass of the two-dimensional carbon sheet can be changed while adding metal salt and urea in the above proportions). Add an appropriate amount of ethanol as a solvent and ultrasonically stir until homogeneous. After evaporating the ethanol to dryness at 80°C, heat it in a tube furnace under a nitrogen atmosphere. During this process, carbon reduces the metal salt ions to their corresponding elemental metal particles, thus obtaining two-dimensional porous carbon doped with iron, cobalt, or nickel. Grind the product obtained from the above sintering until fluffy and place it in a magnetic boat. Place the magnetic boat in a tube furnace and heat at 100–200 ml / h.-1 Nitrogen gas is introduced at a rate of 10°C / min as a protective atmosphere. A magnetic boat containing sublimated sulfur is placed upstream of the magnetic boat near the inlet. -1 The temperature was raised to 400℃ and held for 2 hours. Under the influence of nitrogen gas, sulfur vapor sulfided the metal particles on the surface of the two-dimensional carbon sheet, resulting in a two-dimensional porous carbon sheet composite metal sulfide material.

[0033] Example 1

[0034] This invention discloses a method for preparing a two-dimensional porous carbon sheet composite metal sulfide, the prepared product of which can be used for modifying lithium-sulfur battery separators. The specific steps include:

[0035] Weigh 1g of hydroxyethyl cellulose and 2g of potassium hydroxide and grind them thoroughly in a mortar. Place the mixture into a nickel crucible and heat it in a tube furnace at 5°C for 1 minute. -1 The temperature was raised to 500℃ and held for 2 hours. After acid washing and drying, two-dimensional porous carbon sheets were obtained. 100 mg of the two-dimensional porous carbon sheets, 1 mmol of cobalt acetate hydrate, and 100 mg of urea were weighed and dissolved in 20 ml of ethanol by ultrasonication. The ethanol was then evaporated to dryness at 80℃. The mixture was placed in a magnetic boat and heated in a tube furnace at 5℃ for 1 minute. -1 The temperature was raised to 800℃ and held for 2 hours to obtain two-dimensional carbon nanosheets doped with cobalt particles.

[0036] The sintered product obtained above is ground until fluffy and placed in a magnetic boat. The magnetic boat is then placed in a tube furnace at 200 ml / h. -1 Nitrogen gas is introduced at a rate of 10°C / min as a protective atmosphere. A magnetic boat containing sufficient sublimed sulfur is placed upstream of the magnetic boat near the inlet. -1 The temperature was raised to 400℃ and held for 2 hours. Under the influence of nitrogen gas, sulfur vapor sulfided the metal particles on the surface of the two-dimensional carbon sheet, resulting in a two-dimensional porous carbon sheet composite cobalt disulfide material.

[0037] Example 2

[0038] This invention discloses a method for preparing a two-dimensional porous carbon sheet composite metal sulfide, the prepared product of which can be used for modifying lithium-sulfur battery separators. The specific steps include:

[0039] Weigh 1g of hydroxyethyl cellulose and 2g of potassium hydroxide and grind them thoroughly in a mortar. Place the mixture into a nickel crucible and heat it in a tube furnace at 5°C for 1 minute. -1 The temperature was raised to 500℃ and held for 2 hours. After acid washing and drying, two-dimensional porous carbon sheets were obtained. 100 mg of the two-dimensional porous carbon sheets, 1 mmol of nickel acetate hydrate, and 100 mg of urea were weighed and dissolved in 20 ml of ethanol by ultrasonication. The ethanol was then evaporated to dryness at 80℃. The mixture was placed in a magnetic boat and heated in a tube furnace at 5℃ for 1 minute. -1The temperature was raised to 800℃ and held for 2 hours to obtain two-dimensional carbon nanosheets doped with nickel particles.

[0040] The sintered product obtained above is ground until fluffy and placed in a magnetic boat. The magnetic boat is then placed in a tube furnace at 200 ml / h. -1 Nitrogen gas is introduced at a rate of 10°C / min as a protective atmosphere. A magnetic boat containing sufficient sublimed sulfur is placed upstream of the magnetic boat near the inlet. -1 The temperature was raised to 400℃ and held for 2 hours. Under the influence of nitrogen gas, sulfur vapor sulfided the metal particles on the surface of the two-dimensional carbon sheet, resulting in a two-dimensional porous carbon sheet composite nickel disulfide material.

[0041] Example 3

[0042] This invention discloses a method for preparing a two-dimensional porous carbon sheet composite metal sulfide, the prepared product of which can be used for modifying lithium-sulfur battery separators. The specific steps include:

[0043] Weigh 1g of hydroxyethyl cellulose and 2g of potassium hydroxide and grind them thoroughly in a mortar. Place the mixture into a nickel crucible and heat it in a tube furnace at 5°C for 1 minute. -1 The temperature was raised to 500℃ and held for 2 hours. After acid washing and drying, two-dimensional porous carbon sheets were obtained. 100 mg of the two-dimensional porous carbon sheets, 1 mmol of ferric acetate hydrate, and 100 mg of urea were weighed and dissolved in 20 ml of ethanol by ultrasonication. The ethanol was then evaporated to dryness at 80℃. The mixture was placed in a magnetic boat and heated in a tube furnace at 5℃ for 1 minute. -1 The temperature was raised to 800℃ and held for 2 hours to obtain two-dimensional carbon nanosheets doped with iron particles.

[0044] The sintered product obtained above is ground until fluffy and placed in a magnetic boat. The magnetic boat is then placed in a tube furnace at 200 ml / h. -1 Nitrogen gas is introduced at a rate of 10°C / min as a protective atmosphere. A magnetic boat containing sufficient sublimed sulfur is placed upstream of the magnetic boat near the inlet. -1 The temperature was raised to 400℃ and held for 2 hours. Under the influence of nitrogen gas, sulfur vapor sulfided the metal particles on the surface of the two-dimensional carbon sheet, resulting in a two-dimensional porous carbon sheet composite iron disulfide material.

[0045] Example 4

[0046] The method for preparing a two-dimensional porous carbon sheet composite metal sulfide according to an embodiment of the present invention differs from that in Example 1 only in that 2g of potassium hydroxide is replaced with 1g of potassium hydroxide when activating cellulose diacetate; otherwise, it is exactly the same as that in Example 1.

[0047] Example 5

[0048] The method for preparing a two-dimensional porous carbon sheet composite metal sulfide according to an embodiment of the present invention differs from that in Example 1 only in that 2g of potassium hydroxide is replaced with 3g of potassium hydroxide when activating cellulose diacetate; otherwise, it is exactly the same as that in Example 1.

[0049] Example 6

[0050] The method for preparing a two-dimensional porous carbon sheet composite metal sulfide according to an embodiment of the present invention differs from that in Example 1 only in that the activation temperature during the preparation of the two-dimensional porous carbon sheet is changed from 500°C to 600°C; otherwise, it is exactly the same as that in Example 1.

[0051] Example 7

[0052] The method for preparing a two-dimensional porous carbon sheet composite metal sulfide according to an embodiment of the present invention differs from that in Example 1 only in that the activation temperature during the preparation of the two-dimensional porous carbon sheet is changed from 500°C to 700°C; otherwise, it is exactly the same as that in Example 1.

[0053] Example 8

[0054] The method for preparing a two-dimensional porous carbon sheet composite metal sulfide according to an embodiment of the present invention differs from that in Example 1 only in that the activation temperature during the preparation of the two-dimensional porous carbon sheet is changed from 500°C to 800°C; otherwise, it is exactly the same as that in Example 1.

[0055] This invention provides an application of a two-dimensional porous carbon sheet composite metal sulfide as a membrane modification material for lithium-sulfur batteries. The material of this invention was coated onto a polypropylene membrane, and assembled into a coin cell for performance testing. The battery with the modified membrane exhibited a first-cycle discharge specific capacity of 1568.84 mAh g⁻¹. -1 Furthermore, the battery exhibits excellent cycle stability, maintaining a capacity of 907.44 mAh g² after 200 charge-discharge cycles. -1 Its specific capacity and rate performance are also excellent. Under a high current of 2C, the battery can maintain stable charge and discharge, and the discharge specific capacity can reach 906.36 mAh g. -1 .

[0056] Matters not covered in this invention are common knowledge.

[0057] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing two-dimensional porous carbon sheet composite metal sulfides, characterized in that, Includes the following steps: Weigh out cellulose diacetate and potassium hydroxide in a predetermined mass ratio, grind and mix thoroughly, sinter under a nitrogen atmosphere, remove impurities by acid washing with hydrochloric acid, and dry to obtain two-dimensional porous carbon sheets; the mass ratio of cellulose diacetate and potassium hydroxide is 1:1 to 3. Weigh out two-dimensional porous carbon sheets, metal acetate, and urea according to the set mass ratio, add ethanol as a solvent, and sonicate for 10 minutes until the metal acetate is completely dissolved; after evaporating the ethanol to dryness, place it in a tube furnace and heat under a nitrogen atmosphere. During this process, carbon reduces the metal salt ions to their corresponding elemental metal particles, thus obtaining two-dimensional porous carbon with elemental metal particles; add 1 mmol of metal acetate and 100 mg of urea to every 100 mg of two-dimensional porous carbon sheets; the metal acetate is iron acetate, cobalt acetate, or nickel acetate; Two-dimensional porous carbon particles of elemental metal are ground until fluffy and placed in a magnetic boat. The magnetic boat is then placed in a tube furnace. A magnetic boat containing sublimed sulfur is placed upstream of the magnetic boat near the gas inlet. After heating, the sulfur vapor, carried by nitrogen gas, sulfides the metal particles on the surface of the two-dimensional carbon sheet, forming metal sulfides.

2. The method for preparing a two-dimensional porous carbon sheet composite metal sulfide according to claim 1, characterized in that, The amount of ethanol added is sufficient to completely dissolve the weighed metal acetate.

3. The method for preparing a two-dimensional porous carbon sheet composite metal sulfide according to claim 1, characterized in that, The temperature for heating under a nitrogen atmosphere is 700–800°C.

4. The method for preparing a two-dimensional porous carbon sheet composite metal sulfide according to claim 1, characterized in that, The nitrogen flow rate during heating under a nitrogen atmosphere is 100–200 mL / h. -1 .

5. An application of a two-dimensional porous carbon sheet composite metal sulfide, characterized in that, The two-dimensional porous carbon sheet composite metal sulfide is prepared by the preparation method of any one of claims 1 to 4, and it is used as a membrane modification material for lithium-sulfur batteries.

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