Carbon Nanotubes Modified Metal Sulfides: Fabrication And Energy Storage Device Application

The ever increasing global demands for energy consumption and rapidly worsening environmental pollution have been receiving worldwide attention to develop clean-energy technologies.Supercapacitor,as a new type of energy storage device,has been applied to many fields because of its rapid charge/discharge rates,ultrahigh power densities,long cycle life and environment friendly.As portable electronic products become more flexible and lightweight,developing flexible all-solid-state supercapacitor has become research hotspot.For the flexible all-solid-state supercapacitors,their electrochemical performance and mechanical property are strongly relied on the structures and properties of the electrode materials.Transition metal sulfide has been widely used due to its high theoretical capacity and good electrical conductivity.CNT has been extensively used as conductive substrates to construct miscellaneous hybrid structures due to their reasonable remarkable flexibility and chemical stability.Therefore,combining the CNT with transition metal sulfides effectively can not only improve flexibility of the device,but improve the specific capacitance.In this paper,basing o n CuS,ZnS,MnS and CNT,different morphologies of electrode composite materials were synthesized via a simple hydrothermal approach,when used as electrode materials of flexible all-solid-state supercapacitors,they showed remarkable electrochemical performance.The main results in this paper are as follows:(1)Hierarchical-structured CuS nanoneedles are grown on multi-walled CNT as electrodes for supercapacitors via a simple two-step hydrothermal conversion approach,the electrodes deliver a high specific capacitance up to 566.4 F g-1 at a current density of 1 A g-1.Further by simply impregnating sulfur into CuS@CNT to construct S@CuS@CNT composites as electrodes for Li-S batteries.The electrode shows excellent capacity of 1019 mA h g-1 at 0.1 C.(2)The multi-walled CNT decorated with hierarchically ultrathin ZnS nanosheets(ZnS@CNT)are synthesized via a simple template-based hydrothermal method.B y changing the concentration of Zn(NO3)2 and the hydrothermal reaction time,demonstrates the formation process of ultra-thin ZnS nanosheets.ZnS@CNT shows better electrochemical performance than the pure ZnS nanoparticles,because the large specific surface area is advantageous to the ion diffusion in the electrolyte.Further the flexible symmetric all-solid-state supercapacitors are fabricated with ZnS@CNT electrodes,and the device delivers a high specific capacitance with 159.6 F g-1 at 1 A g-1,tandem supercapacitor assembled by four devices in series can light up LEDs.(3)The ?-MnS@CNT nanocomposites are successfully fabricated through a facile hydrothermal method.First growing a layer of Si O2 around the CNT is advantageous to the vertical growth of ?-MnS along the longitudinal axis CNT,finally Na2 S provides sulfur source and removes Si O2 interlayer.Change the hydrothermal reaction time,has realized the controllable synthesis of ?-MnS@CNT with different morphologies.Whe n used as the electrode materials of supercapacitor,the electrode shows high specific capacitance with 641.9 F g-1 at 0.5 A g-1 and excellent retention with 94.6 % after 3000 charge/discharge cycles.In addition,the as fabricated all-solid-state supercapacitors deliver good electrochemical performance.