Preparation method of ball-flower-shaped MoSSe-coated NC material used as negative electrode of sodium-ion battery

Abstract

The invention discloses a preparation method of a flower-ball-shaped MoSe-coated NC material used as a sodium-ion battery negative electrode, and relates to a preparation method of a sulfide composite material used as a sodium-ion battery negative electrode. The invention aims to solve the technical problems of low electronic conductivity, volume expansion, damage of electrochemical reaction products to the material structure and easy accumulation, agglomeration and even pulverization of the material in the charge-discharge cycle process of the current metal sulfide in the aspect of sodium storage. The invention provides the preparation method of the sodium-ion battery negative electrode material, the preparation method has the characteristics of simplicity and convenience in operation, good process repeatability, clear control parameters, stable product quality and the like, and the prepared negative electrode material has excellent sodium ion intercalation and deintercalation capability; the specific capacity, the cycling stability, the coulombic efficiency and the rate capability of the sodium ion secondary battery can be effectively improved, the requirements of different conditions can be met, and the application prospect is wide.

Description

Technical Field

[0001] The invention relates to a method for preparing a sulfide composite material used as a negative electrode of a sodium ion battery. Background Art

[0002] With the popularization of consumer electronics and portable mobile devices, the demand for lithium-ion batteries continues to increase. However, the shortage of lithium resources, high prices, and complex recycling procedures for lithium-ion batteries limit their large-scale development in the future. Sodium-ion batteries, which have similar storage mechanisms to lithium-ion batteries, have the advantages of abundant resources, low cost, high energy density, and superior safety performance, making them the most likely next-generation secondary batteries to replace lithium-ion batteries. However, the radius of sodium ions is Compared with lithium ion This makes it difficult for ions to be deintercalated from the electrode material during charge and discharge, ultimately resulting in a decrease in reversible capacity. In the early stages of sodium-ion battery research, researchers used metallic sodium as the negative electrode material. Although sodium metal has a high specific capacity, there is a risk of dendrite formation during the electrochemical charge and discharge cycle. In addition, the melting point of sodium metal is about 97.7°C, which poses a great risk during use and limits its application in high-temperature fields. Graphite, an important negative electrode material for the successful commercialization of lithium-ion batteries, is not ideal for use as a negative electrode material in sodium-ion batteries (SIBs). During the charge and discharge process, NaC x Due to reaction thermodynamics, the specific capacity is only about 37 mAh g -1 Therefore, there is an urgent need to seek negative electrode materials with high specific capacity.

[0003] Metal sulfides have many advantages, such as a wide variety, rich phases, adjustable band gap, and high theoretical capacity, and have been widely reported as negative electrode materials for sodium ion batteries. However, their own electrical conductivity is usually poor. During the electrochemical cycle, the electrode materials face problems such as volume expansion, surface cracking, electrode powdering and metal dissolution, which will seriously affect the battery's charge and discharge capacity, service life, and rate performance. Summary of the invention

[0004] The present invention aims to solve the technical problems of low electronic conductivity, volume expansion, destruction of material structure by electrochemical reaction products and easy accumulation, agglomeration and even pulverization of materials in the current metal sulfide sodium storage process, and provide a preparation method of flower ball-shaped MoSSe@NC material as the negative electrode of sodium ion battery.

[0005] The preparation method of the flower ball-shaped MoSSe@NC material as the negative electrode of the sodium ion battery of the present invention is carried out as follows:

[0006] 1. Add ammonium molybdate and thioacetamide into methanol together, and stir to form a uniform dispersed solution A;

[0007] The mass ratio of ammonium molybdate to thioacetamide is 1:1;

[0008] The mass ratio of the ammonium molybdate to the volume ratio of methanol is 1g:(0.3L-0.6L);

[0009] 2. Adding the nitrogen-containing organic small molecule material to the solution A prepared in step 1, stirring, and obtaining a solution B;

[0010] The mass ratio of the nitrogen-containing organic small molecule material to the ammonium molybdate in step 1 is (10-15):1;

[0011] 3. Transferring the solution B prepared in step 2 to a high pressure reactor for solvothermal reaction to obtain a black precursor powder;

[0012] Fourth, the black precursor powder prepared in step 3 and the selenium powder are placed at both ends of the same long porcelain boat with a distance between them, and tin foil is covered on the long porcelain boat. Then, the long porcelain boat is placed in a tube furnace and calcined in an inert atmosphere to obtain MoSSe@NC, where the selenium powder is located at one end of the long porcelain boat close to the air inlet, and the black precursor powder is located at one end of the long porcelain boat close to the air outlet;

[0013] The calcination temperature is 400°C to 500°C, and the calcination time is 1h to 3h;

[0014] The mass ratio of the black precursor powder to the selenium powder is 1:(1-3).

[0015] The role of the nitrogen-containing organic small molecule material (imidazole) in the present invention is:

[0016] Imidazole is the main source of carbon doped with N. The molecular structure of imidazole contains a five-membered aromatic heterocyclic compound with two meta-nitrogen atoms. The unshared electron pair of the 1-nitrogen atom in the imidazole ring participates in the cyclic conjugation, and the electron density of the nitrogen atom is reduced, making it easy for the hydrogen on this nitrogen atom to leave in the form of hydrogen ions. Imidazole can form complexes with coordinated transition metal ions. Transition metal ions have unfilled d orbitals or f orbitals and can accept electrons to form stable complexes. In organic synthesis, imidazole can be used as a ligand to bind to MoO4 through its nitrogen atom. 2- The precursor is formed by coordination, and decomposes to obtain N-doped carbon after the next calcination process.

[0017] The present invention replaces one S in MoS2 with Se, and prepares MoSSe@NC electrode material by solvent thermal reaction and tubular furnace calcination selenization. The carbon shell (N-doped carbon) modification can improve the intrinsic electronic conductivity of the material, alleviate the ability of volume change, expand the interlayer spacing of the material, increase the specific surface area of ​​the material, and create more defects. The spherical structure modified by the nanosheet can provide more active sites for electrochemical reactions, thereby improving the electrochemical performance of the material in the sodium storage process.

[0018] The beneficial effects of the present invention are:

[0019] The present invention provides a method for preparing a negative electrode material for a sodium ion battery, the preparation method has the characteristics of simple operation, good process repeatability, clear control parameters, stable product quality, etc., and the prepared negative electrode material has good cycle stability and rate performance. The MoSSe@NC electrode material prepared by the present invention has excellent ability to deintercalate and deintercalate sodium ions when used as a negative electrode material for a sodium ion secondary battery, can effectively improve the specific capacity, cycle stability, coulombic efficiency and rate performance of the sodium ion secondary battery, can meet the needs of different conditions, and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is the SEM image of the MoSSe@NC material prepared in experiment 1;

[0021] Figure 2 This is the Raman spectrum of the MoSSe@NC material prepared in Experiment 1;

[0022] Figure 3 is the GCD curve of the assembled battery in experiment 3;

[0023] Figure 4 This is the cycle performance diagram of the assembled battery in Experiment 3;

[0024] Figure 5 This is the rate performance diagram of the assembled battery at different current densities in Experiment 3;

[0025] Figure 6 This is the long cycle performance diagram of the assembled battery in Experiment 3;

[0026] Figure 7 This is the TEM image of MoSSe material prepared in the comparative experiment. DETAILED DESCRIPTION

[0027] Specific implementation method 1: This implementation method is a method for preparing a flower ball-shaped MoSSe@NC material as a negative electrode for a sodium ion battery, which is specifically carried out as follows:

[0028] 1. Add ammonium molybdate and thioacetamide into methanol together, and stir to form a uniform dispersed solution A;

[0029] The mass ratio of ammonium molybdate to thioacetamide is 1:1;

[0030] The mass ratio of the ammonium molybdate to the volume ratio of methanol is 1g:(0.3L-0.6L);

[0031] 2. Adding the nitrogen-containing organic small molecule material to the solution A prepared in step 1, stirring, and obtaining a solution B;

[0032] The mass ratio of the nitrogen-containing organic small molecule material to the ammonium molybdate in step 1 is (10-15):1;

[0033] 3. Transferring the solution B prepared in step 2 to a high pressure reactor for solvothermal reaction to obtain a black precursor powder;

[0034] Fourth, the black precursor powder prepared in step 3 and the selenium powder are placed at both ends of the same long porcelain boat with a distance between them, and tin foil is covered on the long porcelain boat. Then, the long porcelain boat is placed in a tube furnace and calcined in an inert atmosphere to obtain MoSSe@NC, where the selenium powder is located at one end of the long porcelain boat close to the air inlet, and the black precursor powder is located at one end of the long porcelain boat close to the air outlet;

[0035] The calcination temperature is 400°C to 500°C, and the calcination time is 1h to 3h;

[0036] The mass ratio of the black precursor powder to the selenium powder is 1:(1-3).

[0037] Specific embodiment 2: This embodiment is different from specific embodiment 1 in that the nitrogen-containing organic small molecule material in step 2 is one or a mixture of 2-methylimidazole, imidazole and benzimidazole. Others are the same as specific embodiment 1.

[0038] Specific embodiment 3: This embodiment is different from specific embodiment 1 or 2 in that the temperature of the solvent thermal reaction in step 3 is 180° C. to 220° C. The rest is the same as specific embodiment 1 or 2.

[0039] Specific embodiment 4: This embodiment is different from specific embodiment 3 in that the time of the solvent thermal reaction in step 3 is 12 hours to 36 hours. Other aspects are the same as those of specific embodiment 3.

[0040] Specific implementation example 5: This implementation example is different from specific implementation example 4 in that the inert atmosphere in step 4 is a mixture of one or both of nitrogen and argon. The rest is the same as specific implementation example 4.

[0041] The present invention is verified by the following tests:

[0042] Experiment 1: This experiment is a method for preparing a flower ball-shaped MoSSe@NC material as a negative electrode for a sodium ion battery, which is specifically carried out as follows:

[0043] 1. Add 20 mg of ammonium molybdate and 20 mg of thioacetamide into 8 mL of methanol and stir to form a uniform dispersed solution A;

[0044] 2. Add 240 mg of imidazole to the solution A prepared in step 1, stir and obtain solution B;

[0045] 3. Transfer the solution B prepared in step 2 to a high pressure reactor for solvothermal reaction at 180° C. for 24 h to obtain a black precursor powder;

[0046] 4. Place the black precursor powder and selenium powder prepared in step 3 at both ends of the same long porcelain boat with a distance between them, cover the long porcelain boat with tin foil, and then place the long porcelain boat in a tube furnace and calcine in argon to obtain MoSSe@NC, with the selenium powder located at one end of the long porcelain boat close to the air inlet and the black precursor powder located at one end of the long porcelain boat close to the air outlet; the calcination temperature is 400°C and the time is 3 hours; the mass ratio of the black precursor powder to the selenium powder is 1:1.

[0047] Figure 1 This is the SEM image of the MoSSe@NC material prepared in experiment 1. It can be seen from the figure that the MoSSe@NC material is in the shape of a flower ball, and the nanosheets are evenly loaded on the ball.

[0048] Figure 2 This is the Raman spectrum of the MoSSe@N material prepared in Experiment 1, which is used to confirm the phase composition of the material. In the Raman spectrum of the MoSSe@NC sample, 334.1 cm -1 and 374.5cm -1 The two obvious peaks at are the E 2g and A 1g mode. MoSSe@NC sample at 261.4 cm -1 and 277.9cm -1 Two new peaks appeared, namely the A peak of Mo-Se bond 1g and E 2g The other two at 1323 cm -1 and 1571cm -1 The nearby peaks belong to the D and G bands of carbon materials, indicating the presence of carbon in the product.

[0049] Experiment 2: This experiment is different from Experiment 1 in that the mass ratio of the black precursor powder to the selenium powder in step 4 is 1:2. The rest is the same as Experiment 1.

[0050] Experiment 3: Battery assembly process:

[0051] The MoSSe@NC prepared in Experiment 1 was used as the active material. It was mixed with a conductive agent (Super P) and a binder (PVDF) in a mass ratio of 7:2:1. Then, an appropriate amount of N-methylpyrrolidone was added as a solvent (NMP) for grinding. After grinding, it was coated on a copper foil. The coating amount of the active material was 1.05 mg / cm 2 , dried in a vacuum oven at 60°C for 6h; the copper foil coated with the slurry was punched into a pole piece with a diameter of 12mm as the negative electrode, a sodium sheet (diameter of 14mm) as the counter electrode, and glass fiber (Whatman GF / F) as the battery separator, and assembled into a button battery (CR2032 type) in an argon-filled glove box.

[0052] Figure 3 This is the GCD curve of the assembled battery in Experiment 3. It can be seen from the figure that the MoSSe@NC electrode exhibits the best initial discharge / charge capacity of 445.2 / 366.1 mAh g in the first cycle. -1 , the highest Coulombic efficiency is 82.2%. From the second cycle to the fifth cycle, the charge and discharge curves of MoSSe@NC electrode material overlap well, proving that MoSSe@NC electrode material has excellent electrochemical reversibility.

[0053] Figure 4 The cycling performance diagram of the assembled battery in Experiment 3 shows that the MoSSe@NC electrode exhibits high cycling stability at 2A g -1 After 500 cycles under the current density condition, its reversible capacity can reach 318.3 mAh g -1 .

[0054] Figure 5 The assembled battery in Experiment 3 is 1A g -1 To 8Ag -1 The rate performance diagram at different current densities shows that the MoSSe@NC electrode exhibits excellent rate performance at all current densities. -1 Under this condition, the discharge capacity is 392.3mAh g -1 、360.9mAh g -1 、337.2mAh g -1 、305.5mAhg -1 , 281.4mAh g-1 and 260.6mAh g -1 , even from 8A g -1 Back to 1Ag -1 , the specific capacity can also return to 341.3mAh g -1 , which indicates that the MoSSe@NC electrode has stable redox kinetics and structural integrity.

[0055] Figure 6 This is the long cycle performance diagram of the assembled battery in Experiment 3. It can be seen from the figure that at 4A g -1 Under the condition of high current density, the MoSSe@NC electrode exhibits high reversible capacity and remarkable cycling stability, and its discharge capacity can still reach 289.7 mAh g even after 1000 cycles. -1 .

[0056] Comparative test: This test is different from the first test in that imidazole is not added in step 2, that is, there is no step 2, and the solvent thermal reaction of step 3 is directly carried out after the first step, and the final product is MoSSe. The rest is the same as the first test.

[0057] Figure 7 This is the TEM image of the MoSSe material prepared in the comparative experiment. It can be seen from the figure that the morphology of the MoS / Se material is a solid sphere.

Claims

1. A method for preparing a flower ball-shaped MoSSe@NC material as a negative electrode for a sodium ion battery, characterized in that The preparation method of the flower ball-shaped MoSSe@NC material as the negative electrode of the sodium ion battery is carried out as follows:

1. Add ammonium molybdate and thioacetamide into methanol together, and stir to form a uniform dispersed solution A; The mass ratio of ammonium molybdate to thioacetamide is 1:1; The mass ratio of the ammonium molybdate to the volume ratio of methanol is 1g:(0.3L-0.6L); 2. Adding the nitrogen-containing organic small molecule material to the solution A prepared in step 1, stirring, and obtaining a solution B; The mass ratio of the nitrogen-containing organic small molecule material to the ammonium molybdate in step 1 is (10-15):1; 3. Transferring the solution B prepared in step 2 to a high pressure reactor for solvothermal reaction to obtain a black precursor powder; Fourth, the black precursor powder prepared in step 3 and the selenium powder are placed at both ends of the same long porcelain boat with a distance between them, and tin foil is covered on the long porcelain boat. Then, the long porcelain boat is placed in a tube furnace and calcined in an inert atmosphere to obtain MoSSe@NC, where the selenium powder is located at one end of the long porcelain boat close to the air inlet, and the black precursor powder is located at one end of the long porcelain boat close to the air outlet; The calcination temperature is 400°C to 500°C, and the calcination time is 1h to 3h; The mass ratio of the black precursor powder to the selenium powder is 1:(1-3).

2. The method for preparing a flower ball-shaped MoSSe@NC material as a negative electrode for a sodium ion battery according to claim 1, characterized in that The nitrogen-containing organic small molecule material in step 2 is one or a mixture of 2-methylimidazole, imidazole and benzimidazole.

3. The method for preparing a flower ball-shaped MoSSe@NC material as a negative electrode for a sodium ion battery according to claim 1, characterized in that The temperature of the solvent thermal reaction in step 3 is 180°C to 220°C.

4. The method for preparing a flower ball-shaped MoSSe@NC material as a negative electrode for a sodium ion battery according to claim 3, characterized in that The solvent thermal reaction time in step 3 is 12h to 36h.

5. The method for preparing a flower ball-shaped MoSSe@NC material as a negative electrode for a sodium ion battery according to claim 1, characterized in that The inert atmosphere described in step 4 is a mixture of one or both of nitrogen and argon.

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