Preparation Of Metal Sulfide Electrode Materials And Research On Electrochemical Energy Storage Devices

Energy strategy is an important topic in the sustainable development of society,and energy storage devices play a crucial role in the energy field.Supercapacitors（SCs）,also known as double-layer capacitors or electrochemical capacitors,are a new kinds of green energy storage devices,which have become the most promising candidates for next-generation energy storage devices in recent years because of their some certain advantages,such as fast charge-discharge rate,higher power density,longer cycle life and safer operation.The properties of energy storage devices depend sensitively on the structures and properties of electrode materials.High efficiency energy storage devices require electrode materials that integrate high specific capacitance,excellent rate capability and long lifespan.Composition design and morphology control of the electrode materials are effective strategies to achieve high performance for energy storage devices.Nanoscale design of the structure and chemistry of electrode materials may enable us to develop a new generation of devices that approach the theoretical limit for electrochemical storage and deliver electrical energy rapidly and efficiently.Nanomaterials and hybrid nanomaterials may enable us to build energy storage devices with the energy densities of the best batteries but with the fast charging,high power,and long lifespan features of electrochemical capacitors.Remarkably,as a field,we are still missing comprehensive understanding of how the local electronic structure of the electrode material,electrostatic interactions,and charge transfer between the electrode and electrolyte govern the charge storage mechanism and ionic transport.Understanding charge transfer and storage at electrochemical interfaces at the nanoscale is essential to uncover the underlying mechanisms.In this paper,we chose transition metal sulfide（KCu₇S₄ and Ni_xS_y）nanomaterials as the research object,with the aim to explore new methods for researching the synthesis of the nanoscale metal sulfide materials and study the electrochemical performance of the prepared nanmaterials for energy storage.The main contents of this paper can be summarized as follows:The novel KCu₇S₄ nanowires with average length of 100 μm have been prepared by a simple and controlled hydrothermal method.The morphology and composition of the as-prepared KCu₇S₄ sample are characterized by X-ray diffraction,field-emission electron scanning microscopy,energy dispersive X-ray spectroscopy,and X-ray photoelectron spectroscopy.The as-prepared KCu₇S₄ nanomaterial is used to fabricate solid-state supercapacitor in which the thin film of the electrodes are made with pressure of 10 MPa,and its electrochemical properties are tested using a two-electrode configuration.It is found that the KCu₇S₄ supercapacitor displays a good electrochemical performance,and its specific capacitance is 301 F g-1 at the scan rate of 1 mV s-1.To further improve the electrochemical performance of the KCu₇S₄ electrode,MnO₂@KCu₇S₄ hybrid electrode has been prepared by a simple coating method.Subsequently,the MnO₂/KCu₇S₄ hybrid electrodes are used to fabricate solid-state supercapacitor and its electrochemical properties are studied.The results demonstrate that the MnO₂/KCu₇S₄ hybrid supercapacitor shows a larger specific capacitance of 533 F g-1 at the scan rate of 1 mV s-1,and its maximum energy density is about 12.3 Wh kg-1 at a power density of 878.9 W kg-1.Moreover,two MnO₂@KCu₇S₄ hybrid supercapacitors in series can light 41 LEDs for about 4 min,revealing its viability and potential for practical applications.A graphene paper（GP）with highly flexible and mechanical strength has been successfully fabricated at a pressure of 5 MPa by a simple suction filtration method.The KCu₇S₄/CP electrode has also been fabricated by using a microsyringe,then the KCu₇S₄/CP electrodes are used to fabricate solid-state supercapacitors using the LiCl-PVA,KCl-PVA and H3PO4-PVA as electrolytes,respectively.Their electrochemical properties are tested using a two-electrode configuration,and the detailed mechanism of ions insertion competition reactions of tunnel structure KCu₇S₄ are studied.The diffusion paths of K+,Li+ and H+ in the KCu₇S₄ tunnels has been studied based on the density functional theory,thermodynamic analysis and nudged elastic band method.The results show that the intercalation/deintercalation of K+ plays a crucial role in the process of charging storage.Meanwhile,it is found that the intercalation of H+ makes great contribution to charge storage.But the proton is easy to be bound to sulfur ions,forming relatively stronger H-S covalent bonds,thus the stability of the KCu₇S₄ electrode will gradually decrease with the number of cycles.Furthermore,three KCu₇S₄/GP supercapacitors in series can power 6 LEDs for about 15 min,revealing its potential applications in energy storage.We report our findings in controlled synthesis and characterization of nickel sulfide nanostructures as battery-type electrode for hybrid energy storage device,where the phase structure and morphology is tuned by changing the initial NiCl2:S mole ratio and hydrothermal synthesis conditions.In particular,three-phase nickel sulfide（NiS-Ni3S2-Ni3S4,denoted as TP-Ni_xS_y）nanoflakes have been successfully prepared,delivering a high specific capacity of 724 C g-1 at a current density of 1 A g-1.Moreover,we has also further prepared the TP-Ni_xS_y/r GO nanoflakes by introducing GO,which demonstrates enhanced electrochemical performance compared to that of the TP-Ni_xS_y.The TP-Ni_xS_y/r GO nanoflake electrode exhibits an excellent specific capacity of 807 C g-1 at a current density of 1 A g-1,and it can still retain about 72%（581 C g-1）of the capacity when the current density is increased from 1 to 20 A g-1,which is higher than that of TP-Ni_xS_y nanoflakes（67%,484 C g-1）.More importantly,a TP-Ni_xS_y/r GO//G hybrid supercapacitor device has also been fabricated,and the device demonstrates a high energy density（46 Wh kg-1）and good cycling stability.Furthermore,two hybrid supercapacitor devices connected in series can well power 37 commercial LEDs,revealing its great potential application in energy storage systems.An all-solid-state wearable fiber-tybe supercapacitor is prepared based on a pen ink-carbon-fiber（Ink-CF）thread structure.This supercapacitor not only exhibits high electrochemical performance,but also shows flexible and wearble characteristics.By integrating it with a triboelectric nanogenarator,the supercapacitors could be charged and power 8 commercial LEDs,demonstrating its feasibility as an efficient storage component for energy storage.