SnS2-based negative electrode construction method based on lithium ion capacitor

Abstract

The invention relates to the technical field of lithium ion capacitors, and discloses a SnS2 (at) C (at) MoS2 composite material negative electrode structure. SnS2 and MoS2 are two typical two-dimensional materials, the interiors of the materials are layered structures beneficial to intercalation and deintercalation of lithium ions, and the materials have rapid ion transmission channels and rich lithium ion active sites. Dopamine hydrochloride serves as a carbon source, volume expansion of internal SnS2 is effectively limited, structural integrity is maintained, dopamine hydrochloride serves as a high-conductivity material to accelerate matrix electron transmission, and a good substrate is provided for growth of MoS2 nanosheets. After SnS2 / MoS2 is optimized in the amount-of-substance proportion, not only is the hollow structure of SnS2 reserved, but also MoS2 nanosheets uniformly grow on the cubic surface, the specific surface area of the material is effectively increased while electrolyte permeation is performed, electrochemical reaction active sites are increased, and excellent electrochemical performance is shown.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion capacitors, and is particularly concerned with a SnS 2 @C@MoS 2 Construction method of composite material negative electrode structure. Background Art

[0002] With the depletion of fossil energy and the continuous deterioration of the environment, the storage and use of renewable clean energy is of vital importance. Therefore, the research on energy storage devices has attracted the attention of many researchers. Traditional energy storage devices, high energy density lithium-ion batteries (LIBs) and high power density supercapacitors (SCs), have been widely used in life. In recent years, a new type of energy storage device, lithium-ion capacitors (LICs), has been developed and studied, hoping to achieve the purpose of combining the advantages of both, that is, having both high power density and high energy density.

[0003] Lithium-ion capacitors are usually composed of a battery-type negative electrode and a capacitor-type positive electrode, which means that there is a huge kinetic difference between the positive and negative electrodes. The capacitor-type positive electrode is mainly a carbonaceous material with fast ion adsorption / desorption capabilities. Therefore, the development of high-capacity negative electrode materials with fast electrochemical kinetics is particularly important for improving the application performance of LICs.

[0004] Two-dimensional materials benefit from their large specific surface area and wide interlayer spacing, and have fast ion transport channels and abundant lithium ion active sites. 2 It is a typical two-dimensional material with a layered structure that is conducive to the insertion and extraction of lithium ions. However, it has the defects of large volume strain during lithium insertion / extraction and poor conductivity. It usually needs to be compounded with other conductive materials and the structural design is optimized to make SnS 2 To achieve the best electrochemical performance. MoS 2 It also has a layered structure, and the weaker van der Waals force between the layers is conducive to the intercalation and deintercalation of lithium ions, making it an excellent lithium storage material. 2 Poor conductivity, easy agglomeration, and large volume strain during discharge / charge cycles have led to the 2 The actual electrochemical performance of MoS is poor. The conductivity can be effectively enhanced by compounding with highly conductive materials, and the MoS 2 structure and distribution, thereby improving agglomeration and alleviating volume change. Summary of the invention

[0005] In view of the shortcomings of the prior art, the present invention provides a SnS 2 @C@MoS 2 The construction method of composite material negative electrode structure overcomes the SnS 2The serious volume expansion changes and poor conductivity of the base negative electrode material reflect the excellent structural stability and electrochemical performance.

[0006] To achieve the above object, the present invention provides the following technical solution: SnS 2 @C@MoS 2 Method for constructing composite material negative electrode structure, the SnS 2 @C@MoS 2 The preparation method of the composite material negative electrode is as follows: S1. A certain amount of zinc source and sodium citrate are prepared into solution A, and a certain amount of tin source is dispersed in ethanol to obtain solution B, and then solution B is added to solution A and continuously stirred to obtain a uniform dispersion; S2, adding sodium hydroxide solution to the uniform dispersion, stirring continuously to obtain a white turbid precipitate, washing multiple times and then freeze-drying to obtain ZnSn(OH) 6 Hollow microcubes; S3, take a certain amount of ZnSn(OH) 6 The hollow microcubes were dispersed in Tris buffer, and then a certain amount of dopamine hydrochloride was added. After the reaction, the ZnSn(OH) was obtained by multiple washings and vacuum freeze drying. 6 @PDA powder; S4, a certain amount of ZnSn(OH) 6 @PDA powder and ethylenediaminetetraacetic acid (EDTA) are prepared into a uniform dispersion. Then a certain amount of sulfur source is added to the solution and stirred to obtain a uniform dispersion; S5. The dispersion is transferred to a hydrothermal reactor for a simple hydrothermal reaction. After the hydrothermal reaction, the dispersion is washed several times and vacuum freeze-dried to obtain a powder sample, that is, SnS 2 @PDA cube; S6, the prepared SnS 2 @PDA cubes are annealed to produce SnS 2 @C Composite materials; S7, take a certain amount of SnS 2 @C composite material was added into the mixed solution of ethylene glycol and water, and SnS 2 @C The composite material is further evenly dispersed in the solution; S8, after the ultrasonic treatment, adding a certain amount of molybdenum source, sulfur source and cetyltrimethylammonium bromide (CTAB) to the dispersion to stir into a mixed solution, and then performing a hydrothermal reaction; S9. After the hydrothermal reaction is completed, SnS can be obtained by multiple washings and vacuum freeze drying. 2 @C@MoS 2 Composite materials; S10, SnS 2 @C@MoS 2 The composite material, conductive carbon black Super P and polyvinylidene fluoride (PVDF) were mixed uniformly in a mass ratio of 8:1:1 to prepare a slurry with appropriate viscosity. After drying, it was cut into discs (with a diameter of 12 mm) using a punching machine to obtain SnS 2 @C@MoS 2 Composite material negative electrode.

[0007] Specifically, the zinc source in step S1 is zinc nitrate hexahydrate (Zn(NO 3 ) 2 6H 2 O), zinc chloride (ZnCl 2 )、Zn(CH 3 COO 2 )

[0008] Specifically, the tin source described in step S1 is tin acetate (Sn(CH 3 COO 2 ), tin chloride pentahydrate (SnCl 2 ·5H 2 O), tin nitrate (Sn(NO 3 ) 4 )

[0009] Specifically, the sulfur source in step S4 is thiourea (CH 4 N 2 S), sodium thiosulfate (Na 2 S 2 O 3 ), sodium sulfide (Na 2 S), thioacetamide (C 2 H 5 NS), ammonium sulfide (NH 4 ) 2 S), potassium sulfide (K 2 S).

[0010] Specifically, the hydrothermal reaction temperature in step S5 is 180-200° C., and the insulation time is 2-5 hours.

[0011] Specifically, the annealing atmosphere in step S6 is a nitrogen atmosphere, the annealing temperature is 400-600° C., and the holding time is 2-5 hours.

[0012] Specifically, the molybdenum source in step S7 is sodium molybdate dihydrate (Na 2 MoO 4 ·2H 2 O), ammonium molybdate (NH4 ) 2 MoO 4 、Potassium molybdate(K 2 MoO 4 ), molybdenum trioxide (MoO 3 )

[0013] Specifically, the sulfur source in step S7 is thiourea (CH 4 N 2 S), sodium thiosulfate (Na 2 S 2 O 3 ), sodium sulfide (Na 2 S), thioacetamide (C 2 H 5 NS), ammonium sulfide (NH 4 ) 2 S), potassium sulfide (K 2 S).

[0014] Specifically, the hydrothermal reaction temperature in step S8 is 180-200° C., and the insulation time is 12-24 hours.

[0015] Compared with the prior art, the present invention has the following outstanding features and beneficial effects: MoS 2 The uniform growth of nanosheets and the construction of hollow structures significantly increase the specific surface area of ​​the composite material and increase the active sites for electrochemical reactions, thereby improving the specific capacity and energy storage efficiency of the material. The carbon layer as an intermediate layer not only significantly improves the conductivity of the matrix, accelerates electron transport and reaction kinetics, but also acts as a SnS 2 With MoS 2 The carbon layer effectively inhibits the internal SnS 2 The volume expansion during the charge and discharge process maintains the structural integrity of the material, thus significantly improving the stability of the composite material. 2 @C@MoS 2 The multi-level structure composite material is conducive to the full contact between the electrolyte and the active material, making SnS 2 @C@MoS 2 The composite material exhibits excellent rate capability, cycling performance and pseudocapacitive energy storage properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 SnS in Example 2 2 @C@MoS 2 Morphology of the composite material.

[0018] Figure 2SnS in Example 2 2 @C@MoS 2 TEM images and HRTEM images.

[0019] Figure 3 The XRD patterns of Example 2 and Comparative Example 1 in Example 2 are shown in FIG.

[0020] Figure 4 Example 2 in Example 4, Comparative Example 1 and Comparative Example 2 at 1.0 A g -1 Cycle performance under .

[0021] Figure 5 This is a comparison chart of the rate performance of Example 2, Comparative Example 1 and Comparative Example 2 materials in Example 4.

[0022] Figure 6 SnS in Example 5 2 @C@MoS 2 / / CV curves of AC lithium-ion capacitors in different voltage ranges and their electrochemical performance under different active material mass ratios.

[0023] Figure 7 SnS in Example 5 2 @C@MoS 2 / / AC Lithium Ion Capacitors at 1.0 A g -1 Cycling performance diagram at different current densities. DETAILED DESCRIPTION

[0025] In order to better understand the present invention, the present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the scope of protection of the present invention.

[0026] Example 1 - SnS 2 The preparation of the composite material includes the following steps: S1. A certain amount of zinc source and sodium citrate are prepared into solution A, and a certain amount of tin source is dispersed in ethanol to obtain solution B, which is then added to solution A and stirred for 30 minutes to obtain a uniform dispersion; S2, adding sodium hydroxide solution to the stirred mixture, stirring for 1 hour to obtain a white turbid precipitate, washing it several times and then freeze-drying it in vacuum to obtain ZnSn(OH) 6 Hollow microcubes; S3, take a certain amount of ZnSn(OH) 6 The hollow microcubes were dispersed in Tris buffer, and then a certain amount of dopamine hydrochloride was added. After the reaction, the ZnSn(OH) was obtained by multiple washings and vacuum freeze drying.6 @PDA powder; S3, a certain amount of ZnSn(OH) 6 @PDA powder and ethylenediaminetetraacetic acid (EDTA) are prepared into a uniform dispersion. Then a certain amount of sulfur source is added to the solution and stirred to obtain a uniform dispersion; the dispersion is transferred to an 80 mL hydrothermal kettle and kept at 180-200 °C for 2-5 hours. After the solution is cooled to room temperature naturally, it is washed several times and vacuum freeze-dried to obtain a powder sample, that is, SnS 2 @PDA cube; for the prepared SnS 2 @PDA cubes are annealed to produce SnS 2 @C composite material (referred to as comparative example 2 sample); Example 2 - SnS 2 @C@MoS 2 The construction of the composite material includes the following steps: S1. Take a certain amount of SnS 2 The composite material was added to a mixed solution of ethylene glycol and water and ultrasonicated for 30 minutes to make SnS 2 @C The composite material is further evenly dispersed in the solution; after the ultrasonic treatment, a certain amount of molybdenum source, sulfur source and hexadecyltrimethylammonium bromide (CTAB) are added to the dispersion and stirred for 30 minutes to obtain a uniform mixed solution; S2. The mixed solution was transferred to a hydrothermal reactor for hydrothermal reaction and kept at 180-200 °C for 12-24 hours. After the solution was cooled to room temperature naturally, it was centrifuged and washed with deionized water several times, and then freeze-dried in a freeze dryer to obtain SnS 2 @C@MoS 2 Composite materials; (In order to explore the influence of the middle carbon layer on the morphology and properties of the composite, SnS 2 @MoS 2 Composite material (referred to as Comparative Example 1 sample). 2 @C@MoS 2 The preparation process is to replace the SnS 2 @C replaced by SnS 2 Cube (SnS 2 The cube is made of ZnSn(OH) in step S3 of Example 1. 6 @PDA precursor replaced with ZnSn(OH) 6 And no annealing is required)).

[0027] from Figure 1 It can be seen that the damaged SnS 2 @C@MoS 2The cubic image shows an obvious hollow structure, and MoS 2 The nanosheets completely cover the cube and are evenly distributed without agglomeration. The hollow structure is beneficial to alleviate the SnS 2 The larger volume strain during the cycle further increases the overall specific surface area of ​​the material and improves the penetration of the electrolyte between the active substances, thereby effectively enhancing the electrochemical performance.

[0028] In order to understand the microstructure of the composite more intuitively, SnS 2 @C@MoS 2 The samples were characterized by TEM, and the images are shown in Figure 2 shown. Figure 2 (a) and (b) show SnS 2 @C@MoS 2 From the microscopic morphology of the sample, it can be observed that the cube has a hollow structure. Figure 2 The single sample in (c) more intuitively shows the structural characteristics of the interior being hollow, proving that the outer shell is composed of carbon material and hierarchical nanosheets. Figure 3 .4 (d) shows high-resolution transmission electron microscopy (HRTEM) images taken at the edge and center of the sample, respectively confirming the surface MoS 2 and internal SnS 2 existence.

[0029] The phase and crystal structure of Example 2 and Comparative Example 2 were characterized by XRD. Figure 3 First, the sample of comparative example 2 was tested and analyzed, and it can be seen that its diffraction peak is similar to that of the standard card SnS 2 (JCPDS No.23-0677) and there are no other impurity peaks. The sharp diffraction peaks at 14.91°, 28.16°, 32.08°, 41.88° and 49.96° correspond to SnS 2 In the spectrum of Example 2, broad peaks are generated at 8.78°, 33.24°, and 58.34°, and SnS 2 and MoS 2 The coexistence of characteristic peaks indicates the successful preparation of the composite material.

[0030] Example 3 - SnS 2 @C@MoS 2 The preparation of the negative electrode material includes the following steps: S1: SnS 2 @C@MoS 2The composite material, conductive carbon black Super P and polyvinylidene fluoride (PVDF) were mixed evenly in a mass ratio of 8:1:1, diluted with N-methyl-2-pyrrolidone (NMP) to a slurry with appropriate viscosity, and sealed and stirred at room temperature for 10 h.

[0031] S2: After the slurry is fully stirred and mixed, different thicknesses are selected according to the coater, and it is coated on the copper foil with an automatic coater. It is then placed in a vacuum oven and dried at a constant temperature of 100 °C for 12 h to allow the NMP organic solvent to fully evaporate (the loading amount of the active substance is changed by controlling the thickness of the coated slurry).

[0032] S3: After the temperature dropped to room temperature, the copper foil was taken out and cut into discs (12 mm in diameter) using a punching machine to obtain SnS with different loading amounts. 2 @C@MoS 2 Composite negative electrode.

[0033] Example 4 - SnS 2 @C@MoS 2 The assembly and testing of the half-cell includes the following steps: The entire process of half-cell assembly for testing the electrochemical properties of materials is completed in a glove box filled with argon (the water and oxygen values ​​in the glove box must be less than 0.1 ppm), and the battery used is a CR2032 battery. It is assembled in the order of negative electrode shell, spring, gasket, metal lithium sheet, diaphragm, pole piece, and positive electrode shell, and packaged with a suitable pressure by a buckle sealing machine. Among them, after putting in the lithium sheet and pole piece, it is necessary to drip several drops of electrolyte before proceeding to the next step. The electrolyte used in the battery is 1 M LiPF 6 Solution, the solvent is a liquid mixed with ethylene carbonate (EC), diethyl carbonate (DEC) and dimethyl carbonate (DMC) in a volume ratio of 1:1:1.

[0034] The assembled half-cells were subjected to long cycle tests and rate performance tests at different current densities. Figure 4 Example 2, Comparative Example 1 and Comparative Example 2 are shown at 1.0 A g -1 The capacity of Example 2 gradually decreased in the initial 60 cycles, then increased slowly, and basically stabilized at 710 mAh g after 400 cycles. -1 After 700 cycles, it can maintain about 570 mAh g -1 The phenomenon of capacity decreasing first and then increasing is related to the activation process of the electrode material. For the samples of Comparative Example 1 and Comparative Example 2, after 700 charge and discharge cycles, the capacity remained at 415 mAh g -1 and 95 mAh g -1 , which is quite different from Example 2.

[0035] Figure 5 Example 2, Comparative Example 1 and Comparative Example 2 show that the -1 The rate performance under 0.1 A g is shown in Example 2, among which Example 2 shows the best electrochemical performance, which is significantly better than that of Comparative Example 1 and Comparative Example 2. -1 It can provide about 1168 mAh g -1 The capacity of the -1 When the capacity is still maintained at 960, 810, 665 mAh g -1 When the current density is gradually reduced to 0.5, 0.2 and 0.1 A g -1 When the capacity increases slowly to the level of the first 30 cycles, it is 832, 1045, and 1150 mAh g -1 In addition, it is noted that the sample of Comparative Example 1 has an excellent rate performance during the first 10 cycles (current density of 0.1 A g -1 When the specific capacity drops sharply, the capacity of comparative example 2 is always low. In contrast, example 2 has excellent rate performance.

[0036] Example 5 - SnS 2 @C@MoS 2 The assembly of a lithium ion capacitor with the composite material as a negative electrode comprises the following steps: Before assembling the full battery of lithium-ion capacitor, the negative electrode material needs to be pre-embedded with lithium. The battery used for pre-embedded lithium is CR2016 type battery, and its assembly process is basically the same as CR2032 type battery, but without adding springs and gaskets. The assembled CR2016 type battery is charged at 0.1 A g -1 The battery was charged and discharged for 10 cycles at a current density of 1000 V, and then discharged to 0.01 V to complete the pre-lithium embedding process. The battery was then moved to the glove box for disassembly and the negative electrode sheet was taken out. The full battery of the lithium-ion capacitor is a CR2032 type battery. The assembly order is negative electrode shell, spring, gasket, negative electrode sheet, diaphragm, electrode sheet, positive electrode shell. After filling with sufficient electrolyte, it is sealed with a button sealing machine at a suitable pressure. 2 @C@MoS 2 The composite material was used as the negative electrode, commercial activated carbon (AC) was used as the positive electrode, and 1M LiPF 6 The organic solution is used as the electrolyte to assemble a lithium ion capacitor.

[0037] The selection and optimization of the voltage window and the mass ratio of the positive and negative active materials are crucial steps to achieve the best performance of LICs devices. In this chapter, the CV curves of the assembled devices in different voltage ranges (scan rate of 100 mV s -1 ), the measured results are as follows Figure 6 (a). The test results clearly show that SnS 2 @C@MoS 2 / / AC LICs can still show stable capacitance characteristics in the voltage range of 0-4.5 V, and no obvious polarization phenomenon occurs, so the voltage range of the full battery in subsequent tests is determined to be 0-4.5 V. The difference in reaction kinetics between the positive and negative electrodes is another major factor restricting the performance of LICs devices, so it is necessary to determine the optimal mass ratio of electrode active materials. Based on the above analysis, the performance of LICs under different mass ratios of electrode active materials was tested. Figure 6 As shown in (b), when the mass ratio of the active material of the negative electrode to the positive electrode is 1:3, SnS 2 @C@MoS 2 / / The AC LICs device has the best performance. Therefore, subsequent tests will be conducted based on this quality ratio.

[0038] Cyclic stability is an important indicator for evaluating the application performance of devices. -1 At a current density of 2 @C@MoS 2 / / The cycling stability of AC LICs was evaluated and the results are shown in Figure 7 As shown in the figure. After 6500 charge / discharge cycles, the device has a capacity of 76.1% of the initial capacity, and the Coulomb efficiency is stable (close to 100%), with excellent cycle performance. In addition, the assembled lithium-ion capacitor can drive the calculator to work normally, indicating that the device has good practical application capabilities.

[0039] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the techniques and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for constructing a SnS2-based negative electrode for a lithium ion capacitor, characterized in that: The steps include: S1. A certain amount of zinc source and sodium citrate are prepared into solution A, and a certain amount of tin source is dispersed in ethanol to obtain solution B, and then solution B is added to solution A and continuously stirred to obtain a uniform dispersion; S2, adding sodium hydroxide solution to the uniform dispersion obtained in step S1, continuously stirring to obtain a white turbid precipitate, washing multiple times, and then vacuum freeze-drying to obtain ZnSn(OH)6 hollow microcubes; S3, taking a certain amount of ZnSn(OH)6 hollow microcubes prepared in step S2 and dispersing them in Tris buffer, then adding a certain amount of dopamine hydrochloride, and gradually polymerizing dopamine to generate polydopamine (PDA). After the reaction is completed, washing multiple times and vacuum freeze drying are performed to obtain ZnSn(OH)6@PDA powder; S4, prepare a certain amount of ZnSn(OH)6@PDA powder prepared in step S3 and ethylenediaminetetraacetic acid (EDTA) into a uniform dispersion. Then add a certain amount of sulfur source to the solution and continue stirring; S5, transferring the dispersion obtained in S4 to a hydrothermal reactor for a simple hydrothermal reaction. After the hydrothermal reaction, washing multiple times and vacuum freeze drying are performed to obtain a powder sample, that is, SnS2@PDA cubes are obtained; S6, annealing the SnS2@PDA cube obtained in step S5 to obtain a SnS2@C composite material; S7, taking a certain amount of the SnS2@C composite material prepared in step S6 and adding it to a mixed solution of ethylene glycol and water, and further uniformly dispersing the SnS2@C composite material in the solution by ultrasound; S8, after the ultrasonic treatment in step S7 is completed, a certain amount of molybdenum source, sulfur source and cetyltrimethylammonium bromide (CTAB) are added to the dispersion and stirred into a mixed solution, followed by a hydrothermal reaction; S9. After the hydrothermal reaction described in step S8 is completed, the SnS2@C@MoS2 composite material can be obtained by washing multiple times and then vacuum freeze-drying.

2. According to claim 1, the zinc source described in step S1 is one of zinc nitrate hexahydrate (Zn(NO3)2·6H2O), zinc chloride (ZnCl2), and zinc acetate (Zn(CH3COO)2).

3. According to claim 1, the tin source in step S1 is one of tin acetate (Sn(CH3COO)2), tin chloride pentahydrate (SnCl2·5H2O), and tin nitrate (Sn(NO3)4).

4. The sulfur source described in step S4 of claim 1 is one of thiourea (CH4N2S), sodium thiosulfate (Na2S2O3), sodium sulfide (Na2S), thioacetamide (C2H5NS), ammonium sulfide ((NH4)2S), and potassium sulfide (K2S).

5. According to step S5 of claim 1, the hydrothermal reaction temperature is 180-200°C and the insulation time is 2-5 hours.

6. According to step S6 of claim 1, the annealing atmosphere is a nitrogen atmosphere, the annealing temperature is 400-600°C, and the holding time is 2-5 hours.

7. The molybdenum source described in step S8 of claim 1 is one of sodium molybdate dihydrate (Na2MoO4·2H2O), ammonium molybdate (NH4)2MoO4, potassium molybdate (K2MoO4), and molybdenum trioxide (MoO3).

8. The sulfur source in step S8 of claim 1 is one of thiourea (CH4N2S), sodium thiosulfate (Na2S2O3), sodium sulfide (Na2S), thioacetamide (C2H5NS), ammonium sulfide ((NH4)2S), and potassium sulfide (K2S).

9. The hydrothermal reaction temperature of step S8 according to claim 1 is 180-200°C and the insulation time is 12-24 hours.

10. A lithium ion capacitor, characterized in that: It comprises a SnS2@C@MoS2 composite material negative electrode obtained according to the preparation method according to any one of claims 1-9.

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