Preparation method of supercapacitor negative electrode material

Abstract

The invention discloses a preparation method of a supercapacitor negative electrode material, and belongs to the field of nanometer materials and electrochemical energy storage. A simple one-step hydrothermal method is adopted, nickel chloride hexahydrate, thioacetamide and ammonia water are selected as reaction raw materials, a certain amount of aluminum source is added, and reaction is performed in a high-pressure kettle at 160-220 DEG C for 8-14 hours to construct the electrode material. According to the electrode material constructed through the method, Al 3s-S 3p orbital hybridization with higher bonding strength is introduced, the stability of the Ni3S4 structure is enhanced, the Ni3S4 structure cannot collapse in the large-current and long-time charging and discharging process, the d band center of matrix metal Ni moves upwards, adsorption to electrolyte ions is greatly improved, and the oxidation-reduction activity of the Ni3S4 structure is enhanced. When the constructed Ni3S4 material is used as the negative electrode of the supercapacitor, the specific capacity is ultrahigh, and the rate capability and the cycling stability are excellent. When the current density is 1A / g, the specific capacity can reach 2124F / g, when the current density is increased to 20A / g, the specific capacity can still reach about 1360F / g, and the capacity can still be kept at 93.1% of the initial capacity after 10000 times of charge-discharge cycles, so that the preparation method has a very good application prospect.

Description

Technical Field

[0001] The invention relates to a method for preparing a supercapacitor negative electrode material, and belongs to the field of nanomaterials and electrochemical energy storage. Background Art

[0002] Supercapacitors have the characteristics of high power density, long cycle life, and wide operating temperature range, and are widely favored by researchers. At present, limited energy density is the crux of the development of supercapacitors, and the key to solving this problem lies in electrode materials (Adv. Funct. Mater. 2023, 33, 2300149). Double-layer electrode materials based on carbon-based materials cannot solve this problem due to their limited specific surface area and low specific capacity. Although pseudocapacitive electrode materials based on transition metal oxides or polymers such as MnO2, RuO2, and PPy show higher capacitance than double-layer electrode materials, their practical application is also limited due to their lower conductivity. In recent years, battery-type electrode materials based on transition metal sulfides have received widespread attention due to their high redox reaction activity and large theoretical capacity, and are expected to solve the bottleneck problem of supercapacitors. However, due to the instability of its structure during the electrochemical cycle, its rate performance and cycle stability are also limited.

[0003] Structurally, transition metal compounds are composed of a metal-nonmetal framework structure consisting of nonmetal ions shared by adjacent polyhedrons and metal cations at the center of the polyhedron. The framework is a channel for ion diffusion, and its stability determines the stability of the supercapacitor performance. The type of interstitial metal cations and changes in the electronic structure will affect the stability of the structure. For example, when the metal in the compound is Fe with a high spin configuration, 4+ (3d4, t 2g 3e g 1), Mn 3+ (3d4, t 2g 3e g 1) and low-spin Ni 3+ (3d7, t 2g 6e g 1), Co 2+ (3d7, t 2g 6e g1) and other compositions, due to the degeneracy of 3d orbitals, they always show a strong Jan-Taylor distortion effect (Chem. Mater. 2016, 28, 6575). This severe deformation will affect the electronic conductivity and ion diffusion kinetics of the electrode material, and lead to severe structural deformation, resulting in poor cycle stability. In order to stabilize the structure, replacing a part of the Jan-Taylor effect active elements with Jan-Taylor effect inactive transition metal elements can stabilize the framework structure for long-term cycling. Therefore, doping metal atoms has become an effective strategy to stabilize the metal-non-metal framework structure. However, the elements currently doped are all nd elements (n=3, 4), such as 3d Cr 3+ ,3d Co 3+ , 4d Ru 4+ and 4dRh 4+ , they always interact with non-metallic elements in the form of dp orbital hybridization. Although the cyclic stability can be improved to a certain extent, the results are not satisfactory enough. According to molecular orbital theory and the corresponding molecular orbital energy distribution of compounds, the energy of molecular orbitals formed by s orbitals and p orbitals or by p orbitals and p orbitals is significantly lower than that of orbitals formed by d orbital and p orbital hybridization (Angew. Chem. Int. Edit. 2022, 61, 202201969). Lower energy corresponds to more stable orbital interactions and lattice structures, which inspires us to stabilize the structural framework of the compound by constructing sp or pp orbital interactions. Summary of the invention

[0004] The technical problem to be solved by the present invention is the structural stability problem of Ni3S4. A method for stabilizing the Ni-S structural framework is provided through an orbital hybridization strategy, and the method is applied to supercapacitors.

[0005] The technical solution adopted by the present invention is as follows:

[0006] (1) Nickel chloride hexahydrate and thioacetamide are selected as reaction raw materials, dispersed in 50 mL of deionized water solution, and then a certain amount of aluminum source is added, stirred by magnetic force until completely dissolved, and then a small amount of ammonia water is added.

[0007] (2) The above solution is transferred to a reaction kettle, placed in an oven, heated to a certain temperature, and kept warm for a certain period of time. After the reaction is completed, it is naturally cooled to room temperature, washed, and dried to obtain the electrode material.

[0008] The advantages and beneficial effects of the present invention are:

[0009] 1. The present invention adopts a one-step hydrothermal method to achieve the preparation and structural modification of Ni3S4, which is simple to operate, low in cost and pollution-free.

[0010] 2. The electrode material constructed by the method of the present invention introduces Al 3s-S 3p orbital hybridization with higher bonding strength, which enhances the stability of the Ni3S4 structure and prevents its structure from collapsing during high current and long-term charging and discharging.

[0011] 3. The electrode material constructed by the method of the present invention not only has a stable structure, but also has the d-band center of the base metal Ni moved upward, which greatly increases the adsorption of electrolyte ions and enhances its redox activity.

[0012] 4. When the material constructed by the present invention is used as the negative electrode of supercapacitor, it has ultra-high specific capacity, excellent rate performance and cycle stability. When the current density is 1A / g, its specific capacity can reach 2124F / g, and when the current density increases to 20A / g, its specific capacity can still reach nearly 1360F / g, and after 10,000 charge and discharge cycles, the capacity can still be maintained at 93.1% of the initial capacity.

[0013] The present invention will be further described below in conjunction with the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 Scanning electron microscope (SEM) images of Ni3S4 (left) and Al-doped Ni3S4 (right);

[0015] Figure 2 is the X-ray photoelectron (XPS) spectrum of Al 2p;

[0016] Figure 3 The relationship between the capacity and current density of Ni3S4 and Al-doped Ni3S4;

[0017] Figure 4 The capacity retention curve of Ni3S4 and Al-doped Ni3S4 after 10,000 cycles measured at a current density of 20 A / g. DETAILED DESCRIPTION

[0018] Example 1

[0019] (1) Weigh 3 mmol of nickel chloride hexahydrate and 4 mmol of thioacetamide, disperse them in 50 mL of deionized water solution, then add 0.15 mmol of aluminum nitrate nonahydrate, stir magnetically for 0.5 hour until completely dissolved, and then add 1 mL of ammonia water.

[0020] (2) The above solution was transferred to a reaction kettle, placed in an oven and heated to 180°C for 12 hours. After the reaction was completed, the solution was naturally cooled to room temperature, washed and dried to obtain Al-doped Ni3S4 electrode material.

[0021] The above-obtained materials were characterized by SEM. The results showed that ( Figure 1 ), the morphology of Ni3S4 prepared without aluminum nitrate is irregular and there are many large particles, while the Al-doped Ni3S4 is a regular nanoflower morphology, in which the nanoflower is made of nanosheets with a diameter of about 200 to 400 nm, which exposes more active sites and is conducive to the migration and diffusion of electrolyte ions. From the XPS spectrum of Al 2p ( Figure 2 ) It can be seen that the binding energy of Al in Ni3S4 is located between the metal Al and the Al from Al2O3 3+ The binding energy is between 100 and 100A, which indicates that Al exists in Ni3S4 in the +2 state. DFT calculation results show that the energy of the molecular orbital formed by the hybridization of Al 3s orbital and S 3p orbital is significantly lower than the energy of the orbital formed by the hybridization of Ni 3d orbital and S3p orbital, which will improve the stability of the Ni3S4 structure. The constructed material was prepared into a supercapacitor electrode for cyclic voltammetry test. The results showed that when the current density was 1A / g, its specific capacity could reach 2124F / g (303mAh / g). When the current density increased to 20A / g, its specific capacity could still reach nearly 1360F / g (194mAh / g), which is much larger than Ni3S4 prepared without adding aluminum nitrate ( Figure 3 ), and after 10,000 charge and discharge cycles at a current density of 20 A / g, the capacity can still be maintained at 93.1% of the initial capacity ( Figure 4 ).

[0022] Embodiment 2:

[0023] The difference between this embodiment and embodiment 1 is that the holding temperature is adjusted to 200° C. in step (2). The obtained product is used for constant current charge and discharge test of supercapacitor electrode material. The results show that when the current density is 1A / g, its specific capacity can reach 1744F / g; when the current is increased to 20A / g, its specific capacity can still reach 1042F / g.

Claims

1. A method for preparing a supercapacitor negative electrode material, characterized in that: The steps include: (1) Nickel chloride hexahydrate and thioacetamide are selected as reaction raw materials, dispersed into 50 mL of deionized water solution, and then a certain amount of aluminum source is added, stirred by magnetic force until completely dissolved, and then a small amount of ammonia water is added; (2) Transfer the above solution to a reaction kettle, place it in an oven, heat it to a certain temperature, and keep it warm for a certain period of time. After the reaction is completed, naturally cool it to room temperature, wash it, and dry it to obtain the electrode material; The molar ratio of aluminum nitrate nonahydrate to nickel chloride hexahydrate in step (1) is 1:10-50. In step (2), a hydrothermal treatment is performed in an oven at a temperature of 160 to 220° C. In step (2), an oven is used for hydrothermal treatment, and the hydrothermal treatment time is 8 to 14 hours.

2. The method for preparing a supercapacitor negative electrode material according to claim 1, characterized in that: The aluminum source in step (1) is one of aluminum chloride and aluminum nitrate.

3. The method for constructing a supercapacitor negative electrode material according to claim 1, characterized in that: The negative electrode material exhibits large specific capacity, high rate performance and cycle stability. When the current density is 1A / g, its specific capacity can reach 2124F / g. When the current density increases to 20A / g, its specific capacity can still reach nearly 1360F / g, and after 10,000 charge and discharge cycles, the capacity can still be maintained at 93.1% of the initial capacity.

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