A cubic phase cobalt nickel sulfide and few-layer Ti3C2T for room temperature sodium-sulfur batteries x Preparation method of MXene nanosheet composite material

Abstract

The present invention discloses a cubic phase cobalt nickel sulfide and few-layer Ti3C2T3 for room temperature sodium-sulfur battery. x Preparation method of MXene nanosheet composite material. The invention content is: a cubic phase cobalt-nickel bimetallic sulfide supported on a few-layer Ti3C2T x MXene nanosheets as highly active catalytic materials ((Co 0.5 Ni 0.5 )9S8@Ti3C2T x ), can be used as an effective sulfur host material for room temperature sodium-sulfur batteries, showing excellent sodium storage performance. The specific preparation method is: first, Ti3C2T is obtained by LiF / HCl etching and stripping method. x MXene nanosheet substrate; then compound it with cobalt nickel metal salt solution to form a uniform solution; then add hydrazine hydrate reducing agent to react to generate Co 0.5 Ni 0.5 @Ti3C2T x Precursor; then generates cubic phase (Co 0.5 Ni 0.5 )9S8; washing and freeze-drying to obtain a composite catalytic material; the present invention adjusts the ratio of cobalt and nickel, and the ratio is 1:1 when the cubic phase (Co 0.5 Ni 0.5 )9S8 and Ti3C2T x MXene composite materials have the best catalytic performance. When used in room-temperature sodium-sulfur batteries, they can promote the rapid conversion of soluble sodium polysulfide to insoluble Na2S, thereby improving the specific capacity and cycle life of room-temperature sodium-sulfur batteries.

Description

Technical Field

[0001] The present invention relates to the field of electrochemical energy storage, in particular to a cubic phase cobalt nickel sulfide and few-layer Ti3C2T3O3 composite for room temperature sodium-sulfur batteries. x Preparation method of MXene nanosheet composite material. Background Art

[0002] Rechargeable batteries, as an important class of recyclable electrochemical energy storage devices, have attracted considerable attention with the development of human society. Among currently commercialized battery systems, lithium-ion batteries dominate. However, the limited capacity of their cathode materials and the high cost resulting from the limited and uneven distribution of lithium and cobalt resources make it difficult to meet the large-scale demand for high-energy-density rechargeable batteries. Therefore, rechargeable room-temperature sodium-sulfur batteries, with their high theoretical capacity and low cost, have attracted researchers' attention.

[0003] Room-temperature sodium-sulfur batteries are considered the most promising electrochemical energy storage devices due to their high energy density, low cost, and high safety. Elemental sulfur as a cathode material is far superior to other electrode materials in terms of reserves, cost, and environmental friendliness, and its capacity is superior to other materials due to its sixteen-electron reaction mechanism. Despite these advantages, sulfur faces significant challenges in terms of cycle life and rate capacity due to its shortcomings, such as poor conductivity, severe volume expansion, the shuttle effect of intermediate phase polysulfides, and low utilization of active materials. To address these issues, current research is primarily focused on the design and synthesis of catalytic materials for room-temperature sodium-sulfur batteries. Effective catalytic materials can adsorb sodium polysulfide, prevent the shuttle effect, and accelerate its conversion to short-chain Na2S, thereby improving the cycle life and rate capacity of room-temperature sodium-sulfur batteries.

[0004] Transition metal sulfides exhibit excellent chemical adsorption capabilities due to their unique electronic structure, effectively preventing the shuttling effect of polysulfides while also exhibiting high sodium storage capacity. However, current research indicates that monometallic sulfides have limited adsorption sites and tend to agglomerate during the synthesis process, reducing the contact area with polysulfides and hindering their full adsorption catalytic performance.

[0005] Therefore, in view of the technical defects of the prior art, the present invention proposes a technical solution to overcome the problems of the prior art. That is, by designing a highly dispersed cubic phase cobalt-nickel bimetallic sulfide and a few-layer conductive Ti3C2T x MXene catalytic materials increase the contact area with sodium polysulfide, increase adsorption sites, and effectively promote the rapid conversion of long-chain sodium polysulfide to short-chain Na2S, thereby improving the specific energy and cycle life of room-temperature sodium-sulfur batteries. Summary of the Invention

[0006] The purpose of the present invention is to prepare a cubic phase (Co 0.5 Ni 0.5 )9S8 nanobowls dispersed in a few layers of highly conductive Ti3C2T x The composite material on MXene nanosheets is used as the host catalytic material for the sulfur positive electrode of room-temperature sodium-sulfur batteries. The composite based on the three-dimensional open bowl structure and the two-dimensional highly conductive MXene sheet can improve the conductivity, increase the loading amount and utilization rate of active sulfur, increase the adsorption sites of polysulfides, effectively prevent the shuttle effect of sodium polysulfide and thus catalyze the conversion of sodium polysulfide, thereby improving the specific energy and cycle life of room-temperature sodium-sulfur batteries.

[0007] Another object of the present invention is to provide a room temperature sodium-sulfur battery composite positive electrode material with high capacity and long cycle life.

[0008] In order to achieve the purpose of the above invention, the specific technical solutions of the present invention are as follows:

[0009] Step 1: Take 5 or 10 mL of 12M hydrochloric acid solution and 15 or 30 mL of deionized water to make a 9M hydrochloric acid solution, add 1 or 2 g of LiF powder, seal and stir for a certain period of time, then slowly add 1 or 2 g of Ti3AlC2 MAX powder, and stir the reaction system in a sealed state at a temperature range of 24-40 ° C for 24-40 hours. The obtained solution is centrifuged and repeatedly washed with deionized water to obtain a precipitate; the obtained precipitate is dispersed in 50 mL of deionized water, shaken on a shaker for 5 minutes, and then dispersed into 125 or 250 mL of solution. Ultrasonication is carried out under Ar atmosphere for one hour, and the upper black solution is centrifuged to obtain Ti3C2T x The MXene aqueous solution was stored in a refrigerator at about 3°C ​​until use.

[0010] Step 2: Dissolve the metal salts of CoCl2·6H2O and NiCl2·6H2O in a molar ratio of 1:1 in a three-necked flask containing 100 mL of ethylene glycol solvent and stir with a strong magnetic stirrer to form a uniform cobalt-nickel salt solution; take an appropriate volume of the black suspension obtained in step 1 and mix it evenly with a small amount of the above nickel salt solution, centrifuge and disperse it with ethylene glycol to obtain Ti3C2T x MXene ethylene glycol solution; at the same time, 300 mg of PVP surface modifier was dissolved in a three-necked flask and mixed with Ti3C2T x After the MXene glycol solution is mixed evenly, it is transferred to an oil bath at 160-180°C and reacted for 5 minutes. Then, 2 mL of 80 wt% hydrazine hydrate solution is added thereto and the reduction reaction is carried out for 1-2 hours to obtain Co 0.5 Ni 0.5 Nanoparticles deposited on Ti3C2T xComposite precursors on MXene sheets.

[0011] Step 3: 533 mg of thiourea powder was dissolved in 40 mL of ethylene glycol solvent, and the obtained uniform transparent solution was slowly added dropwise to the reaction system of step 2, and reacted at 160-180 ° C for 2-3 hours, cooled naturally to room temperature, centrifuged and washed 6 times with deionized water and alcohol, and freeze-dried to obtain (Co 0.5 Ni 0.5 )9S8@Ti3C2T x Composite materials.

[0012] Step 4: In order to study the effect of different cobalt-nickel ratios on the performance of room-temperature sodium-sulfur batteries, cobalt-nickel metal sulfides (Co 0.8 Ni 0.2 )9S8@Ti3C2T x and (Co 0.3 Ni 0.7 )9S8@Ti3C2T x ); Its synthesis method is similar to (Co 0.5 Ni 0.5 )9S8@Ti3C2T x Similarly, only the ratio of nickel and cobalt metals is adjusted, and other conditions remain unchanged.

[0013] Step 5: For comparison, single metal Co9S8 nanoparticles and Ti3C2T x MXene nanosheet composite materials, the typical synthesis process is: 10mL Ti3C2T x The MXene aqueous solution was centrifuged and washed with ethylene glycol to obtain anhydrous Ti3C2T x MXene solution, the volume ratio of ethylene glycol to dimethylformamide was always kept at 1:4 during the reaction, a certain amount of CoSO4·7H2O, thiourea and PVP were dissolved in the above mixed solvent to form a uniform solution, which was transferred to a high-pressure reactor and reacted at 160-180℃ for 10-15 hours. It was naturally cooled to room temperature and centrifuged and washed and freeze-dried to obtain Co9S8@Ti3C2T x Composite materials.

[0014] As a cubic phase cobalt nickel sulfide and few-layer Ti3C2T for room temperature sodium sulfur battery described in the present invention x The preparation method of the MXene nanosheet composite material further comprises the steps of: x MXene, (Co 0.5 Ni 0.5 )9S8@Ti3C2T x 、(Co 0.8 Ni0.2 )9S8@Ti3C2T x 、(Co 0.3 Ni 0.7 )9S8@Ti3C2T x and Co9S8@Ti3C2T x The composite material and sublimed sulfur were ground in a mortar at a mass ratio of 1:2 or 1:3 for 10-30 minutes and transferred to a polytetrafluoroethylene-lined reactor. The reactor was sealed in a glove box and then transferred to a blast drying oven. The reaction was carried out at 150-170 ° C for 10-15 hours and naturally cooled to room temperature to obtain S@Ti3C2T x 、S@(Co 0.5 Ni 0.5 )9S8@Ti3C2T x 、S@(Co 0.8 Ni 0.2 )9S8@Ti3C2T x 、S@(Co 0.3 Ni 0.7 )9S8@Ti3C2T x and S@Co9S8@Ti3C2T x Composite positive electrode materials.

[0015] As a cubic phase cobalt nickel sulfide and few-layer Ti3C2T for room temperature sodium sulfur battery described in the present invention x A preferred embodiment of the method for preparing the MXene nanosheet composite material further includes grinding the above-mentioned composite positive electrode material, carbon nanotube conductive agent and polyacrylic acid binder in a mass ratio of 7:2:1 for 10-30 minutes to form a slurry, coating the slurry on a clean copper foil, and drying the slurry at 45-65°C for 8-15 hours to form a room temperature sodium-sulfur battery positive electrode sheet. The positive electrode sheet is cut into discs with a diameter of 12 mm, metallic sodium is used as the negative electrode, and 1M NaSO3CF3 is dissolved in DEGDME solvent as the electrolyte. In particular, GF / D and Celgard2325 are used as double-layer separators, and CR2032 button batteries are assembled in a glove box to evaluate their electrochemical performance.

[0016] As a cubic phase cobalt nickel sulfide and few-layer Ti3C2T for room temperature sodium sulfur battery described in the present invention x The preferred method for preparing the MXene nanosheet composite material also includes the study of the catalytic activity of the composite material. Specifically, a Na2S6 cathode electrolyte with a concentration of 0.05-5M is prepared and mixed with a 1M NaSO3CF3 / DEGDME electrolyte in a volume ratio of 1:1 to form a symmetrical battery electrolyte. The freeze-dried Ti3C2T prepared in steps 1, 3, 4 and 5 is added. x MXene, (Co 0.5 Ni 0.5)9S8@Ti3C2T x 、(Co 0.8 Ni 0.2 )9S8@Ti3C2T x 、(Co 0.3 Ni 0.7 )9S8@Ti3C2T x and Co9S8@Ti3C2T x Take 10-20 mg of each powder, mix it with 500 μL of deionized water, 480 μL of ethanol and 20 μL of naphthol to make a slurry, and apply it on hydrophilic carbon paper as an electrode sheet. The positive and negative electrodes are the same electrode sheets. Assemble a CR2032 symmetrical battery and assemble it into a symmetrical battery. Study the catalytic effect of each material by changing the CV curve.

[0017] Preferably, the size of the cubic cobalt-nickel bimetallic sulfide obtained in step 3 is about 200-300 nm, and the Ti3C2T x The number of MXene layers is 3-5.

[0018] The size of the sulfide nanomaterials with different cobalt-nickel ratios obtained in step 4 is 200-300 nm and is uniformly dispersed in the Ti3C2T x MXene on-chip.

[0019] The size of the Co9S8 nanoparticles obtained in step 5 is 200-300 nm and is evenly dispersed in the Ti3C2T x MXene on-chip.

[0020] In the preparation process of the composite positive electrode material of the sodium-sulfur battery, the present invention uses commercial carbon nanotubes with a diameter of 8-15 nm as a conductive agent, and uses Celgard 2325 and GF / D as separators. The room-temperature sodium-sulfur battery is assembled in a glove box filled with Ar gas.

[0021] In the present invention, a few-layer Ti3C2T x MXene nanosheets, as the synthetic substrate of cobalt-nickel sulfide nanomaterials, can effectively improve the dispersibility of metal sulfide nanomaterials, increase the contact area with polysulfides, enhance the adsorption catalytic effect, and improve the conductivity of electrode materials and battery reaction kinetics. Selecting carbon nanotubes as a conductive agent can not only adsorb soluble sodium polysulfide molecules to prevent the shuttle effect, but also improve the conductivity and enhance the battery reaction kinetics.

[0022] The present invention selects cubic cobalt-nickel bimetallic sulfide as the catalytic material because of its optimal nickel-cobalt ratio and unique electronic structure, which can increase the adsorption catalytic sites, promote the conversion of sodium polysulfide, and improve the specific capacity, rate performance and cycle life of room-temperature sodium-sulfur batteries.

[0023] In the existing room temperature sodium-sulfur battery related technology, the beneficial effects of the present invention are as follows:

[0024] The present invention prepares an efficient room-temperature sodium-sulfur battery composite cathode material, which is mainly composed of a highly catalytically active cubic phase cobalt-nickel bimetallic sulfide loaded with a two-dimensional highly conductive and flexible Ti3C2T x The active sulfur host catalytic material composed of MXene, the combination of this three-dimensional open structure and two-dimensional highly conductive nanosheets increases the sulfur loading and the utilization rate of active sulfur. At the same time, the well-dispersed bimetallic sulfide has more adsorption catalytic sites, which can form bonds with soluble sodium polysulfide to prevent the shuttle effect. The rich electronic structure can promote the conversion of soluble long-chain sodium polysulfide to short-chain Na2S, effectively improving the battery reaction kinetics and enhancing the cycle life. The room temperature sodium sulfur battery positive electrode material ((Co 0.5 Ni 0.5 )9S8@Ti3C2T x ) after 500 cycles (1401.5mAh / g) at 1.0A / g, the specific capacities were approximately 0.8 Ni 0.2 )9S8@Ti3C2T x (834.1mAh / g), (Co 0.3 Ni 0.7 )9S8@Ti3C2T x (792mAh / g), Co9S8@Ti3C2T x (793.6 mAh / g) and S@Ti3C2T x The results are 1.68, 1.76, 1.77 and 2.51 times that of (557.3 mAh / g).

[0025] The room temperature sodium sulfur battery sulfur positive electrode prepared by the present invention (Co 0.5 Ni 0.5 )9S8@Ti3C2T x The catalytic material has better catalytic activity than all the comparative materials; this is mainly manifested in the symmetrical battery CV curve having a large response current (1.29mA) and a small symmetrical voltage (-0.11 / 0.11V), which can effectively promote the conversion of sodium polysulfide, improve the cycle life of room-temperature sodium-sulfur batteries and obtain a higher sodium storage capacity.

[0026] The preparation method of the bimetallic sulfide composite catalytic material provided by the present invention is simple and controllable, which can provide ideas for the design and preparation of this high-efficiency room-temperature sodium-sulfur battery catalytic material and make large-scale application possible. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is the Ti3C2T obtained by etching and stripping in Example 1x Transmission electron microscopy image of MXene nanosheets and its corresponding selected area electron diffraction pattern;

[0028] Figure 2 The intermediate product Co prepared in Example 2 0.5 Ni 0.5 @Ti3C2T x Scanning electron microscope images of the composite material;

[0029] Figure 3 The intermediate product Co prepared in Example 2 0.5 Ni 0.5 @Ti3C2T x X-ray diffraction patterns of composite materials;

[0030] Figure 4 The (Co 0.5 Ni 0.5 )9S8@Ti3C2T x Scanning electron microscope images of the composite material;

[0031] Figure 5 Example 3 preparation (Co 0.5 Ni 0.5 )9S8@Ti3C2T x and the X-ray diffraction spectrum after molten sulfur mixing in Example 5;

[0032] Figure 6 The (Co 0.8 Ni 0.2 )9S8@Ti3C2T x Scanning electron microscope images of the composite material;

[0033] Figure 7 The (Co 0.3 Ni 0.7 )9S8@Ti3C2T x Scanning electron microscope images of the composite material;

[0034] Figure 8 The Co9S8@Ti3C2T synthesized in Comparative Example 2 x Scanning electron microscope images of the composite material;

[0035] Figure 9 The (Co 0.8 Ni 0.2 )9S8@Ti3C2T x 、(Co 0.3 Ni 0.7 )9S8@Ti3C2T xand Co9S8@Ti3C2T x X-ray diffraction patterns of composite materials;

[0036] Figure 10 The S@(Co prepared in Example 4 0.5 Ni 0.5 )9S8@Ti3C2T x Rate performance diagram of the positive electrode and comparative electrode materials at current densities of 0.2, 0.5, 1.0, 2.0 and 5.0 A / g;

[0037] Figure 11 The S@(Co prepared in Example 5 0.5 Ni 0.5 )9S8@Ti3C2T x Cycling performance diagram of the positive electrode and the comparative electrode materials after 500 cycles at a current density of 1.0 A / g;

[0038] Figure 12 The S@(Co prepared in Example 5 0.5 Ni 0.5 )9S8@Ti3C2T x Cycling performance diagram of the positive electrode material after 2000 cycles at a current density of 2.0 A / g;

[0039] Figure 13 The (Co 0.5 Ni 0.5 )9S8@Ti3C2T x CV curves of -Na2S6 and various comparative materials -Na2S6 symmetric batteries at a scan rate of 5.0 mV / s. DETAILED DESCRIPTION

[0040] In order to make the above-mentioned objects and advantages of the present invention clear and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with specific embodiments. The following embodiments are only some specific operations in the process of the present invention, and are only for a full understanding of the present invention. However, the present invention can also be implemented in other ways different from those described herein. Those skilled in the art can make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0041] Example 1

[0042] This Example 1 provides a highly conductive, flexible substrate for the synthesis of a sulfur cathode host material for a room-temperature sodium-sulfur battery. Bimetallic sulfide nanomaterials are uniformly grown on this substrate. This substrate is obtained by acid-etching and exfoliating a two-dimensional layered Ti3AlC2 MAX material, with an interlayer spacing of approximately 1.3 nm. The specific experimental preparation process is as follows:

[0043] S1: Measure 5 or 10 mL of deionized water and inject it into a 100 mL plastic beaker. Use a pipette to draw 15 or 30 mL of 12 M hydrochloric acid solution and inject it into the plastic beaker containing deionized water. Seal the beaker with plastic wrap and stir rapidly on a magnetic stirrer to prevent splashing to form a 9 M HCl solution.

[0044] S2: Weigh 1 or 2 g of LiF powder, remove the plastic wrap, and quickly pour the LiF powder into the 9 M hydrochloric acid prepared in step S1. Seal the mixture with plastic wrap and continue stirring for 5 minutes to form an HF solution.

[0045] S3: Weigh 1 or 2 g of the reserved 400 mesh Ti3AlC2 MAX powder and slowly add it to the HF solution prepared in step S2 using a small spoon.

[0046] S4: Seal the plastic beaker after completing the above steps, transfer it to a constant temperature water bath with a magnetic stirrer at a temperature of 24-40°C, and react at the constant temperature for 24-40 hours.

[0047] S5: Pour the solution after the reaction in step S4 into a 100 mL plastic centrifuge tube in a fume hood, rinse once with deionized water, and pour the sediment at the bottom of the beaker into the centrifuge tube. Centrifuge at 3500 rpm for 6 minutes in a high-speed centrifuge, and rinse with deionized water and centrifuge 6 times.

[0048] S6: Add 50 mL of deionized water to the centrifuge tube containing the precipitate obtained in step S5, shake it on a shaker for 5 minutes to form a uniform dispersion, then pour it into a glass beaker with a volume of 500 mL, and add 75 or 200 mL of deionized water to form Ti3C2T x The MXene aqueous solution was sonicated under Ar atmosphere for 1 h.

[0049] S7: Pour the aqueous solution after ultrasonic treatment in step S6 into a centrifuge tube, centrifuge it at 2000 rpm for 1 hour, and collect the supernatant to obtain the exfoliated Ti3C2T x The MXene solution was stored in a refrigerator at a temperature of approximately 3°C until ready for use.

[0050] Example 2

[0051] This Example 2 provides a synthesis and characterization analysis of an intermediate in the synthesis process of a host catalytic material for a sulfur cathode of a room temperature sodium-sulfur battery - a bimetallic sulfide. The intermediate is Co 0.5 Ni 0.5 Nanoparticles loaded on Ti3C2T x On the MXene sheet, the particle size is about 200-300nm. The specific synthesis process is as follows:

[0052] S1: Weigh CoCl2·6H2O and NiCl2·6H2O metal salt powders in a molar ratio of 1:1 and place them in a three-necked flask pre-installed with a magnetic stirrer. Use a graduated cylinder to measure 100 mL of ethylene glycol solvent and pour it into the three-necked flask. Stir on a strong magnetic stirrer until the metal salts are completely dissolved to form a uniform cobalt-nickel salt solution.

[0053] S2: Take 5-20 mL of the Ti3C2T exfoliated in Example 1 x The MXene aqueous solution was placed in a centrifuge tube, and 10 mL of the CoNi solution in step S1 was measured with a pipette, ultrasonically dispersed evenly, centrifuged at 8000 rpm in a high-speed centrifuge for 5 minutes, and the supernatant was poured out to obtain a precipitate, which was ultrasonically dispersed in 20 mL of ethylene glycol. After uniform dispersion, the precipitate was centrifuged again.

[0054] S3: Weigh 300 mg of PVP and add it to the cobalt-nickel salt solution obtained in step S1, stir it magnetically until it is completely dissolved to form a mixed solution, and add the precipitate in step S2 to the mixed solution, and sonicate it until it is completely dissolved to form a uniform mixed solution.

[0055] S4: The three-necked flask containing the uniformly mixed solution in step S3 was fixed on a constant temperature oil bath at 160-180°C, the oil bath stirrer was turned on for stirring, and the condensing reflux device was turned on. After reacting for 5 minutes, 2 mL of 80 wt% hydrazine hydrate solution was measured and added to the three-necked flask. After the reduction reaction for 1-2 hours, the mixture was naturally cooled to room temperature.

[0056] S5: The mixture obtained in step S4 was poured into a centrifuge tube, centrifuged at 8000 rpm and washed with deionized water and ethanol 6 times to obtain a precipitated product, which was freeze-dried to obtain Co 0.5 Ni 0.5 Precursor deposited on Ti3C2T x Mixed powder on MXene sheet (Co 0.5 Ni 0.5 @Ti3C2T x ).

[0057] Example 3

[0058] In this Example 3, a room temperature sodium-sulfur battery sulfur cathode host catalytic material - cubic cobalt-nickel bimetallic sulfide was synthesized. 0.5 Ni 0.5 )9S8 nanobowls loaded on Ti3C2T x On the MXene sheet, the size of the nanobowl is about 200-300nm. The specific synthesis process is as follows:

[0059] S1: Weigh 533 mg of thiourea powder and dissolve it in 40 mL of ethylene glycol solvent. Ultrasonic dispersion is performed and the mixture is set aside.

[0060] S2: Pour the thiourea solution obtained in step S1 into a constant pressure separatory funnel, and slowly drip it into the three-necked flask where the reduction reaction in step S4 in Example 2 is completed, and then react at a constant temperature (160-180°C) for 2 hours;

[0061] After the reaction of steps S1 to S4 in Example 2 was completed, the thiourea solution was added dropwise and the reaction was continued for 2 hours while maintaining the same temperature.

[0062] S3: After the reaction in step S2 is completed, turn off the heating device, lift the three-necked flask, and cool it naturally to room temperature. Pour the reaction product into a centrifuge tube and rinse it with deionized water. Place it in a high-speed centrifuge and centrifuge it at 8000 rpm for 5 minutes. Pour out the supernatant and rinse it with deionized water and centrifuge it. Repeat four times, then rinse it with anhydrous ethanol and centrifuge it twice to obtain the final product.

[0063] S4: The black product obtained in step S3 was collected in a centrifuge tube and dispersed in 10 mL of deionized water, cooled with liquid nitrogen, and dried in a freeze dryer under vacuum for 24 hours to obtain the final product (Co 0.5 Ni 0.5 )9S8@Ti3C2T x Powder, package and set aside.

[0064] Example 4

[0065] This Example 4 provides a preparation process for a room-temperature sodium-sulfur battery composite cathode material. The composite electrode material exhibits excellent rate capacity and excellent cycle life in room-temperature sodium-sulfur battery tests. After 500 and 2000 cycles at current densities of 1.0 and 2.0 A / g, respectively, the specific capacity can be maintained at 1401.5 and 1159.1 mAh / g. The specific preparation process is as follows:

[0066] S1: The (Co 0.5 Ni 0.5 )9S8@Ti3C2T x The dry powder and sublimed sulfur powder were ground in a mortar at a mass ratio of 1:2 or 1:3 for 10-30 minutes, transferred to a reactor, sealed in a glove box filled with Ar, and then transferred to a blast drying oven at 150-170 ° C for 10-15 hours. After cooling to room temperature, S@(Co 0.5 Ni 0.5 )9S8@Ti3C2T x Dry powder.

[0067] S2: In the preparation of electrode material slurry, S@(Co 0.5 Ni 0.5 )9S8@Ti3C2Tx Dry powder as active material, carbon nanotubes as high conductivity agent, and polyacrylic acid as aqueous binder are mixed and ground evenly in a mass ratio of 7:2:1, and deionized water is used as solvent to prepare a viscous slurry.

[0068] S3: Cut the highly conductive copper foil into pieces slightly larger than the width of the coating machine, stick them to a smooth glass plate with alcohol, wipe them clean, and use a coating machine to scrape the slurry prepared in step S2 into a membrane electrode. Dry it in an oven at 45-65°C for 8-15 hours to obtain an electrode sheet, which is cut into discs with a diameter of 12 mm. Weigh the mass of the electrode sheet and subtract the mass of the copper foil to convert the mass of the sulfur active material proportionally.

[0069] S4: Assemble the battery in the glove box. The electrolyte is 1M NaSO3CF3 dissolved in DEGDME. GF / D and Celgard 2325 membranes are used as battery separators, and metallic sodium is used as the negative electrode.

[0070] S5: The button battery assembled in step S4 is subjected to a performance test in a battery testing system. Figure 10 , 11 and 12 are the rate performance of the room temperature battery prepared by the present invention, and the cycle performance of 500 and 2000 cycles at current densities of 1.0 A / g and 2.0 A / g, respectively.

[0071] Example 5

[0072] This Example 5 provides evidence of the catalytic effect of bimetallic sulfide, a sulfur cathode host catalytic material for room-temperature sodium-sulfur batteries. The study found that the catalytic material prepared by the present invention has the highest response current (1.29 mA) and the smallest reversible voltage (-0.11 / 0.11 V), showing excellent catalytic activity. The specific research process is as follows:

[0073] S1: In a glove box, weigh Na2S and sulfur powder in a molar ratio of 1:5 into a clean glass bottle. Add 10 mL of diethylene glycol dimethyl ether solvent to the bottle. After sealing, place the glass bottle on a heated magnetic stirrer and stir at 50-80°C for 40-60 hours. The prepared Na2S6 solution has a concentration of 0.05-5 M and is stored in the glove box for later use.

[0074] S2: Cut the hydrophilic carbon paper into discs with a diameter of 12 mm and place them in a centrifuge tube. Add ethanol and ultrasonically clean them, then dry them in a vacuum oven for later use.

[0075] S3: Weigh 10-20 mg (Co 0.5 Ni 0.5 )9S8@Ti3C2T xThe powder was placed in a clean small centrifuge tube, and 500 μL of deionized water, 480 μL of anhydrous ethanol and 20 μL of naphthol were added, and ultrasonic dispersion was performed to obtain a slurry.

[0076] S4: The slurry obtained in step S3 is drop-coated on the carbon paper treated in step S1, maintaining a constant coating amount (the mass of the active material is 0.8 mg), and finally dried in an oven at 45-65°C to obtain an electrode sheet.

[0077] S5: Assemble the electrode obtained in step S4 into a symmetrical battery in a glove box, use the GF / F membrane as the battery separator, and use the Na2S6 and 1M NaSO3CF3 / DEGDME electrolyte prepared in step S1 in a volume ratio of 1:1 as the electrolyte to assemble into a CR2032 button-type symmetrical battery.

[0078] S6: Cyclic voltammetry curve test conditions are: scan rate 5.0 mV / s, voltage range -1.0-1.0; Figure 13 is the corresponding cyclic voltammetry curve.

[0079] Comparative Example 1

[0080] The synthesis and electrochemical performance characterization of sulfides with different cobalt-nickel ratios are provided as comparative materials for sulfur cathode host catalytic materials of room temperature sodium-sulfur batteries. The materials are sulfide nanoparticles with different cobalt-nickel ratios loaded on Ti3C2T x On the MXene sheet, the specific synthesis process is as follows:

[0081] During the synthesis process, the total amount of cobalt and nickel is kept constant (Co 0.5 Ni 0.5 )9S8@Ti3C2T x The same as in Example 1-5, only the proportion of CoCl2·6H2O was adjusted to 80% and 30% respectively, and the other conditions were exactly the same as in Example 1-5. 0.8 Ni 0.2 )9S8@Ti3C2T x and (Co 0.3 Ni 0.7 )9S8@Ti3C2T x of contrasting materials.

[0082] Comparative Example 2

[0083] The synthesis and characterization of a comparative material for the sulfur cathode host catalytic material of a room temperature sodium-sulfur battery—a single metal sulfide—is provided. The material is Co9S8 nanoparticles loaded on Ti3C2T x On the MXene sheet, the particle size is about 200-300nm. The specific synthesis process is as follows:

[0084] S1: Dissolve 1.4 mmol of CoSO4·7H2O powder and 300 mg of PVP powder in a mixed solvent (the volume ratio of ethylene glycol to N,N-dimethylformamide is 1:4), and ultrasonically disperse to form a homogeneous solution.

[0085] S2: Measure 5 - 20 mL of the Ti3C2T x MXene aqueous solution prepared in Example 1 into a centrifuge tube, add 10 mL of the homogeneous solution obtained in step S1, centrifuge at 8000 rpm for 5 minutes, pour off the supernatant, then add 20 mL of ethylene glycol and ultrasonically disperse evenly. After centrifugation, pour off the supernatant and disperse it in 20 mL of the mixed solution in step S1. After ultrasonically dispersing evenly, an anhydrous Ti3C2T x MXene solution is obtained.

[0086] S3: Weigh 533 mg of thiourea powder and disperse and dissolve it together with the anhydrous Ti3C2T x MXene solution in the solution in step S1. After ultrasonic dissolution, a homogeneous mixture is formed.

[0087] S4:分装 the homogeneous mixture obtained in step S3 into a 50 mL stainless steel autoclave, then transfer it to a forced-air drying oven, react at 160 - 180 °C for 10 - 15 hours, and then naturally cool to room temperature to obtain a reaction product.

[0088] S5: Pour the reaction product obtained in step S4 into a centrifuge tube, rinse it with deionized water, centrifuge at 8000 rpm for 5 minutes, pour out the supernatant, and then disperse it in deionized water again for centrifugation. Repeat four times, then change to rinse and disperse with absolute ethanol, and centrifuge twice to obtain a black product.

[0089] S6: Disperse the black product obtained in step S5 in a centrifuge tube containing 10 mL of deionized water, and freeze-dry to obtain the final comparative sample Co9S8@Ti3C2T x powder.

[0090] Comparative Example 3:

[0091] S1:分别将实施例4步骤S1中的(Co 0.5 Ni 0.5 )9S8@Ti3C2T x 干燥粉末换成冻干的Ti3C2T[[ID=3​​​​​​​​​​​​)9S8@Ti3C2T x After powder melting, diffusion, and sulfur mixing, it is used as a composite reference cathode material.

[0092] S2: Replace the active materials in step S2 of Example 4 with S@Ti3C2T x , S@Co9S8@Ti3C2T x , S@(Co 0.8 Ni 0.2 )9S8@Ti3C2T x and S@(Co 0.3 Ni 0.8 )9S8@Ti3C2T x cathode materials, and the remaining steps are the same as those in Example 4 to obtain the corresponding control sample batteries. Figure 9 and 10 are the rate performance and cycling performance curves at 1.0 A / g of the corresponding batteries.

[0093] Comparative Example 4:

[0094] S1: Replace the (Co 0.5 Ni 0.5 )9S8@Ti3C2T x powders in step S3 of Example 5 with freeze-dried Ti3C2T x MXene, Co9S8@Ti3C2T x , (Co 0.8 Ni 0.2 )9S8@Ti3C2T x , and (Co 0.3 Ni 0.7 )9S8@Ti3C2T x powders, and the remaining steps are the same as those in Example 5 to obtain the corresponding symmetric batteries of the comparative samples. Figure 13 is the CV curve of the corresponding symmetric battery. The symmetric battery of the (Co 0.5 ))9S8@Ti3C2T Ni 0.5 )9S8@Ti3C2T x (-0.11 / 0.11 V, 1.29 mA) material shows a smaller symmetric voltage compared with the symmetric battery of the comparative material (Ti3C2T x MXene: -0.69 / 0.69 V; Co9S8@Ti3C2T x : -0.19 / 0.19 V; (Co 0.8 Ni 0.2 )9S8@Ti3C2T x : -0.28 / 0.28 V; (Co 0.3 Ni 0.7 )9S8@Ti3C2T x:-0.31 / 0.31V) and larger response current (Ti3C2T x MXene: 0.16 mA; Co9S8@Ti3C2T x :0.84mA;(Co 0.8 Ni 0.2 )9S8@Ti3C2T x :0.78mA;(Co 0.3 Ni 0.7 )9S8@Ti3C2T x :0.88mA).

[0095] Matters not covered by the present invention are known technologies.

[0096] The above embodiments are intended only to illustrate the technical concepts and features of the present invention. Their purpose is to enable those skilled in the art to understand the contents of the present invention and implement them accordingly. They are not intended to limit the scope of protection of the present invention. Any equivalent changes or modifications made in accordance with the spirit of the present invention are intended to be covered by the scope of protection of the present invention.

Claims

1. A cubic phase cobalt nickel sulfide and few-layer Ti3C2T for room temperature sodium-sulfur batteries x The preparation method of MXene nanosheet composite material is characterized in that: The following steps are involved: Step 1: Etch the two-dimensional layered Ti3AlC2 MAX powder to obtain highly conductive few-layer Ti3C2T x MXene nanosheet aqueous solution; the etching is performed by adding the two-dimensional layered Ti3AlC2 MAX powder into a hydrochloric acid solution dissolved with LiF; Step 2: Dissolve CoCl2·6H2O and NiCl2·6H2O in a molar ratio of 1:1 in a three-necked flask containing ethylene glycol to obtain a uniform cobalt-nickel salt solution; Ultrasonic dispersion of 5-20 mL of the MXene aqueous solution obtained in step 1 and 10 mL of the cobalt-nickel salt solution was performed, and the precipitate was obtained after centrifugation. The precipitate was ultrasonically dispersed in a three-necked flask with ethylene glycol solvent, and the final precipitate was obtained by centrifugation again after uniform dispersion. Weighing 300 mg of polyvinyl pyrrolidone surface modifier and adding it to the cobalt nickel salt solution to obtain a mixed solution, and adding the final precipitate to the mixed solution, and sonicating until it is completely dissolved to obtain a uniform mixed solution; The three-necked flask containing the uniform mixed solution was transferred to a constant temperature oil bath at 160-180°C, and 80 wt% of hydrazine hydrate reducing agent was added thereto to react and obtain Co 0.5 Ni 0.5 @MXene precursor solution; Step 3: A certain amount of thiourea is dissolved in ethylene glycol to form a uniform solution and then added dropwise to the precursor solution obtained in step 2. After the sulfurization reaction, it is naturally cooled to room temperature, centrifuged, washed and freeze-dried to obtain a cubic phase cobalt nickel sulfide and few-layer Ti3C2T x MXene nanosheet composite material; wherein the cubic phase cobalt nickel sulfide is (Co 0.5 Ni 0.5 )9S8 nano bowl; Among them, in step 1, the highly conductive few-layer Ti3C2T x MXene nanosheets as a substrate for the synthesis of cubic cobalt nickel sulfide.

2. The cubic cobalt nickel sulfide and the few-layer Ti3C2T according to claim 1 x The preparation method of MXene nanosheet composite material is characterized in that: In step 1, an appropriate amount of 9 M HCl solution is mixed with 1 g or 2 g of LiF to obtain an HF solution, and 1 g or 2 g of two-dimensional layered Ti3AlC2MAX powder is slowly added. The etching temperature is 30-40 °C and the etching time is 24-40 hours. The powder after centrifugal washing is dispersed in deionized water and continuously shaken for 5 minutes to obtain a few-layer Ti3C2T x MXene dispersion solution; ultrasonicated for one hour under Ar atmosphere, and then centrifuged to obtain Ti3C2T x MXene nanosheet aqueous solution.

3. The cubic cobalt nickel sulfide and the few-layer Ti3C2T according to claim 1 x The preparation method of MXene nanosheet composite material is characterized in that: In step 2, 2 mL of hydrazine hydrate was used for reduction at 160-180 ° C for 1-2 hours; in step 3, 533 mg of thiourea was used for sulfurization to obtain cubic cobalt nickel sulfide (Co 0.5 Ni 0.5 )9S8 nanobowl, the size of the nanobowl is 200-300 nm.

4. A room temperature sodium-sulfur battery composite cathode material, characterized in that: Combining a cubic phase cobalt nickel sulfide for room temperature sodium sulfur battery according to any one of claims 1 to 3 with a few-layer Ti3C2T x Preparation method of MXene nanosheet composite material: The prepared composite material is mixed with sulfur in a certain proportion, ground in an agate mortar for 10-30 minutes, placed in a reactor with a polytetrafluoroethylene liner and sealed, the reactor is filled with inert gas, and melt-diffused and cooled to obtain S@(Co 0.5 Ni 0.5 )9S8@Ti3C2T x Composite positive electrode materials.

5. A room temperature sodium-sulfur battery composite positive electrode material according to claim 4, characterized in that: Cubic Cobalt Nickel Sulfide and Few-layer Ti3C2T for Room-temperature Na-S Batteries x The mass ratio of the MXene nanosheet composite material to sulfur was 1:2 or 1:

3. The reactor was sealed in a glove box filled with Ar gas. The melting and diffusion temperature is 150-170°C and the time is 10-15 hours.

6. A composite positive electrode sheet, characterized in that: The room temperature sodium-sulfur battery composite positive electrode material according to claim 5 is mixed with a conductive agent carbon nanotube and a polyacrylic acid binder in a mass ratio of 7:2:1, and vigorously ground in a mortar for 10-30 minutes. Deionized water is added dropwise to form a slurry with a certain viscosity, which is coated on a dry copper foil and dried at a temperature range of 45-65°C for 8-15 hours to obtain a uniform composite positive electrode sheet.

7. A room temperature sodium-sulfur battery, characterized in that: The composite positive electrode sheet according to claim 6 is cut into discs with a diameter of 12 mm, metallic sodium is used as the negative electrode, NaSO3CF3 is dissolved in DEGDME solvent with a concentration of 1 M as the electrolyte, GF / D and Celgard2325 are used as double-layer separators, and CR2032 button batteries are assembled. The prepared composite positive electrode material has a specific capacity of 1401.5 mAh / g and 1159.1 mAh / g after 500 and 2000 cycles at current densities of 1.0 A / g and 2.0 A / g, respectively.

8. Cubic cobalt nickel sulfide and few-layer Ti3C2T3 for room temperature sodium-sulfur battery prepared by the method of claim 3 x The application of MXene nanosheet composite materials is characterized by: The catalytic activity of the composite material was studied by symmetrical cell. The specific operation was as follows: first, a Na2S6 electrolyte with a concentration of 0.05-5 M was prepared and mixed with a 1M NaSO3CF3 / DEGDEM electrolyte in a volume ratio of 1:1 as the symmetrical cell electrolyte; the obtained (Co 0.5 Ni 0.5 )9S8@Ti3C2T x 10-20 mg of powder was mixed with 500 μL of deionized water, 480 μL of ethanol, and 20 μL of naphthol to form a slurry, which was then coated on hydrophilic carbon paper as an electrode sheet. The same electrode sheet was used for the positive and negative electrodes to assemble a CR2032 symmetrical battery.

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