A Se-vacancy-rich NiSe2@CoSe2 semi-coherent heterojunction composite cathode material for supercapacitors

Abstract

The present invention discloses a Se-vacancy-rich NiSe2@CoSe2 semi-coherent heterojunction supercapacitor composite positive electrode material, which belongs to the field of new energy storage. The present invention adopts simple electrodeposition and reduction treatment to prepare a Se-vacancy-rich NiSe2@CoSe2 heterojunction, and there is a specific interface semi-coherent matching relationship between them; the Vr-NiSe2@CoSe2 composite material prepared by the present invention exhibits ultra-high rate performance, and the current density is increased to 250A g ‑1 , its specific capacity can still maintain 60.4% of the original specific capacitance, which provides a high-quality candidate positive electrode material for building a new generation of high-performance supercapacitors.

Description

Technical Field

[0001] The present invention relates to the field of new energy storage, and in particular to a Se-vacancy-rich NiSe2@CoSe2 semi-coherent heterojunction supercapacitor composite positive electrode material. Technical Background

[0002] Supercapacitors are a new type of energy storage device developed in recent years. They have the advantages of high power density, fast charging speed, long cycle life, wide operating temperature range, good safety performance and environmental protection. They have broad application prospects in new energy vehicles, micro-communication equipment, heavy machinery, aerospace and other fields (Chinese invention patent, application number 201810202685.6). As we all know, the performance of supercapacitors depends entirely on their electrode materials. However, compared with rechargeable batteries, supercapacitors currently still lack high-performance electrode materials, which seriously restricts their industrial production process (Energy & Environmental Science, 2016, 9, 102-106. Advanced Energy Materials, 2019, 9, 1802928). Therefore, designing and constructing a new type of electrode material with excellent electrochemical properties is of great significance to improving the energy density of supercapacitors.

[0003] In recent years, researchers have often designed new cathode materials to improve the charge storage capacity of supercapacitors. They have tried to use transition metal compounds such as NiMoO4, CoNi-MOF, NiCoP / NiCo-OH, MoS2, Fe2O3, NiCoSe2 as cathode materials, mainly because they have high theoretical specific capacitance, excellent redox characteristics and electrochemical activity, and advantages such as abundant raw materials, environmental friendliness and low price (Nature Communications, 2017, 8, 14264. Advanced Energy Materials, 2017, 7, 1700294. Advanced Functional Materials, 2018, 28, 1800036. Nature Nanotechnology, 2015, 10, 313-318. Chinese invention patent, application number 201310058911.5; Chinese invention patent, application number 201611200095.7). However, these compounds have the disadvantages of poor electron transfer capacity and low rate. In order to overcome the above problems, researchers often use carbon materials with good conductivity and large specific surface area as the skeleton to compound with it, or compound two or more transition metal compounds (Advanced Energy Materials, 2018, 8, 1702247. Nano Energy, 2017, 35, 331-340. Energy & Environmental Science, 2016, 9, 1299-1307. Adv. Energy Mater. 2016, 6, 1600341). Although the above-prepared composite electrode material has a higher specific capacitance than a single active material, its rate performance still cannot meet the needs of new high-performance supercapacitors, which greatly hinders its practical application in supercapacitors. The reason may be that the composite of the above-mentioned skeleton and active material is a simple physical adsorption effect. During the high-current charge and discharge process, the rapid insertion / extraction of ions in the electrolyte causes the composite electrode material to expand / contract significantly. At the same time, the large alternating stress cycle can cause stress concentration, which leads to the pulverization of the active material or even falling off the skeleton surface, causing serious collapse of the entire electrode structure. Moreover, for the previously reported constructed transition metal compound composite electrode materials, due to anisotropic crystal growth and inherent lattice mismatch, this type of heterogeneous interface is unstable, which leads to the peeling of active materials or the interruption of ion transmission paths during the discharge / charge process.Therefore, how to construct a composite electrode material with high internal activity, strong electron transport capability and specific interface lattice matching relationship, and systematically explore its influence on the rate performance of the electrode material, is a huge challenge facing this field and a bottleneck problem that must be overcome for the future large-scale application of supercapacitors.

[0004] Studies have found that transition metal compounds with different energy levels will lead to changes in the electronic structure of the interface, and then generate a built-in electric field and two opposite charge distribution areas on their heterogeneous interfaces. The generated built-in field greatly accelerates the ion migration rate, which helps to fast reaction kinetics and reduce the ion diffusion barrier, thereby leading to improved rate performance; at the same time, the specific spatial charge area generated is also conducive to ion adsorption, so that redox reactions can be carried out more easily (Adv. Energy Mater. 2017, 8, 1. Chem. Sci. 2021, 12, 6048701228). Vacancy engineering is considered to be an ideal technology for improving the electrochemical performance of transition metal compounds. On the one hand, the introduction of vacancies in transition metal compounds can generate defect energy levels in the bandgap region, resulting in a reduction of the bandgap and a shift of the Fermi level. Therefore, anion vacancies can act as shallow donors to effectively regulate the electronic structure and enhance the conductivity of transition metal compounds [Adv. Mater. 2020, 32, 1905923, ACS Nano 2018, 12, 1894]. On the other hand, the presence of vacancy defects interferes with the surrounding atoms to a certain extent, resulting in a reduction in their coordination number, and inevitably generates a large number of exposed unsaturated dangling bonds in the vacancy part, which can serve as a strong adsorption site for foreign ions or intermediate species to achieve a more stable state of the system; at the same time, a large number of group VI element vacancy defects (i.e., sulfur or selenium vacancies) can be found, all of which carry a positive charge (proton state), which can also smoothly capture abundant anions [Adv. Mater. 2020, 32, 1905923]. Therefore, vacancies are more likely to capture electrolyte ions, and then provide a broad space for ion storage, thereby further promoting redox reactions. In addition, vacancy defects can have a profound effect on ion intercalation / deintercalation in active materials, reduce stress concentration and electrostatic repulsion between adjacent layers, directly act as a "highway" channel to accelerate ion migration, and effectively overcome its diffusion barriers during charge / discharge. Therefore, it greatly improves the reaction kinetics and rate performance of electrode materials. In addition, these generated vacancy defects can increase the surface energy of the system, thereby generating a large number of active centers, allowing more electrode materials to contact electrolyte ions for redox reactions, thereby improving their specific capacity. Therefore, constructing a NiSe2@CoSe2 heterojunction with abundant Se vacancies and semi-coherent interfaces is expected to significantly improve the specific capacity and rate performance of this composite cathode material. Summary of the invention

[0005] The purpose of the present invention is to solve the shortcomings of NiSe2@CoSe2 supercapacitor composite positive electrode material such as poor rate performance.

[0006] The objective of the present invention is achieved through the following technical solutions:

[0007] (1) Preparation of NiSe2@CoSe2 composite electrode materials rich in Se vacancies:

[0008] 10mmol L -1 NiCl2·6H2O, 5mmol L -1 CoCl2·6H2O, 30mmol L -1 SeO2 and 0.1 mol L - 1 LiCl was uniformly mixed and used as the electrolyte, and deposited at -0.8 V for 10 min to obtain a NiSe2@CoSe2 heterojunction. -1 After soaking in KBH4 solution for 10 min, a NiSe2@CoSe2 composite electrode material (Vr-NiSe2@CoSe2) containing abundant Se vacancies was obtained.

[0009] (2) Electrochemical performance test of Vr-NiSe2@CoSe2 composite material:

[0010] Firstly, a 2M KOH solution was prepared as the electrolyte solution. Then, a Vr-NiSe2@CoSe2 composite electrode material, a Pt electrode and a calomel electrode were used as the working electrode, the counter electrode and the reference electrode, respectively. The constant current charge and discharge (GCD) of the composite electrode material was tested by an electrochemical workstation to obtain its rate characteristics.

[0011] Compared with existing electrode materials, the Vr-NiSe2@CoSe2 composite electrode material disclosed in the present invention has the following advantages:

[0012] (1) In the present invention, a new type of NiSe2@CoSe2 composite electrode material prepared has a semi-coherent interface characteristic (interface mismatch is 13.5%), which can not only generate a built-in electric field and two opposite charge distribution regions, greatly accelerating the ion migration rate and reducing the ion diffusion barrier, but also during the charge and discharge process, the semi-coherent interface can make the composite electrode material not easy to fall off under current, ensuring the integration of the structure and promoting its rate performance.

[0013] (2) In the present invention, NiSe2@CoSe2 introduces a large number of Se vacancies, which not only regulates its electronic structure and improves its conductivity, but also increases its ion adsorption capacity, provides a fast channel for ion diffusion, and greatly improves the reaction kinetics and rate performance of the electrode material; in addition, these generated vacancy defects can increase the surface energy of the system, thereby generating a large number of active centers, allowing more electrode materials to contact electrolyte ions for redox reactions, thereby improving their specific capacity. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0015] Figure 1 SEM photo of Vr-NiSe2@CoSe2 composite material.

[0016] Figure 2 XRD patterns of Vr-NiSe2@CoSe2 and NiSe2@CoSe2 composites.

[0017] Figure 3 Se 3d XPS spectra of NiSe2@CoSe2, pure NiSe2 and CoSe2.

[0018] Figure 4 EPR spectra of Vr-NiSe2@CoSe2 and NiSe2@CoSe2 composites.

[0019] Figure 5 This is the curve of the specific capacity of Vr-NiSe2@CoSe2 composite material changing with current density. DETAILED DESCRIPTION

[0020] Example 1

[0021] Preparation of Vr-NiSe2@CoSe2 composite materials

[0022] First, 10 mmol L -1 NiCl2·6H2O, 5mmol L -1 CoCl2·6H2O, 30mmol L -1 SeO2 and 0.1 molL -1 LiCl is evenly mixed as the electrolyte, and then 1 cm -2 The graphite substrate, Pt wire electrode and saturated calomel were used as working electrode, counter electrode and reference electrode respectively. The deposition voltage was controlled at -0.8 V and the deposition time was 10 min to obtain the NiSe2@CoSe2 heterojunction. Finally, it was placed in 0.1 mol L -1After soaking in KBH4 solution for 10 min, it was taken out and dried at 60 °C for 12 h to obtain NiSe2@CoSe2 composite electrode material (Vr-NiSe2@CoSe2) containing abundant Se vacancies. At the same time, NiSe2@CoSe2, pure NiSe2 and CoSe2 were obtained by the same process. The SEM photo of Vr-NiSe2@CoSe2 composite material is shown in Figure 1 ; XRD, Se 3d XPS and EPR characterization results of Vr-NiSe2@CoSe2 and NiSe2@CoSe2 composites are shown in Figure 2 , Figure 3 and Figure 4 .

[0023] Electrochemical performance test of Vr-NiSe2@CoSe2 composite material

[0024] The three-electrode system was composed of Vr-NiSe2@CoSe2 composite electrode material as working electrode, saturated calomel electrode as reference electrode and platinum wire electrode as counter electrode. -1 The specific capacity was measured in KOH solution with the change of current density. When the current density increased to 250A g -1 After addition, its specific capacity can still maintain 60.4% of the original specific capacity, which shows that this electrode material has ultra-high rate performance.

Claims

1. A method for preparing a supercapacitor composite cathode material NiSe2@CoSe2 with ultra-high rate, wherein a NiSe2@CoSe2 supercapacitor composite cathode material with abundant Se vacancies is obtained by a one-step electrodeposition method and reduction treatment, and their interface is a typical semi-coherent interface and is bonded by chemical bonds; The specific method of the electrodeposition method and reduction treatment is: prepare 10mmol·L -1 NiCl2·6H2O, 5mmol·L - 1 CoCl2·6H2O, 30mmol·L -1 SeO2 and 0.1 mol·L -1 LiCl mixed electrolyte was deposited at -0.8V for 10min to obtain NiSe2@CoSe2 heterojunction; then it was placed in 0.1mol·L -1 After soaking in KBH4 solution for 10 min, NiSe2@CoSe2 containing abundant Se vacancies was obtained; The composite cathode material exhibits ultra-high rate characteristics, with a rate of 250 A·g -1 Its specific capacitance can still maintain 60.4% of the original specific capacitance.

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