Fabrication Of Composite Mo-Based Nanostructures And Their Lithium And Sodium Storage Properties

In21st century, the increasing environmental problems, such as global warming, resource shortage and environmentalpollution, pose a severe challenge to mankind. We should reduce dependence on fossil fuels, at the same time, be preferable to produce energy from renewable and sustainable resources (e.g., solar and wind) in order to make a sustainable development. The electricity generated from intermittent renewable sources need efficient energy storage systems (ESSs). Electrochemical ESSs are considered as the most environmentally friendly, feasible and sustainable among the clean renewable energy storage systems, such as:rechargeable batteries and supercapacitors, which have been widely used in portable electronics, electric vehicles, and smart electrical grids. Because of the advantage of no memory effct, no self-discharge and high energy density, lithium ion battery (LIB), becomes one of the most popular electrochemical energy for portable electronics, such as, laptops, mobile telephone and digital cameras anditcould become a candidate for hybrid vehicles (HEVs), electric vehicles (EVs) and Green Grid energy storageby large-scale development. Dramatic developments in electricaltransportation and large-scale ESSs for smart grids will require substantially greater amounts of materials to build large batteries. Li is not an abundant element. We also witness the increasing price of Li resource in recent years for more and more using of LIBs. In contrast, the low cost and abundance of Na in the earth will become advantageous when a large amount of materials are demanded for renewable energy solutions. Because of the similarities in electrochemistry between Li and Na, the advances in LIBs may be useful for developing sodium-ion batteries (SIBs). However, the intercalation and storage mechanisms of Na ion are still scientifically challenging, since Na ions are～50%larger in radius than Li ions. It is very desirable to find appropriate host materials to accommodate Na+ions and facilitate reversible insertion/extraction of Na+ions.Nanosized MoP with a hexagonal phase is synthesized by using a sol-gel method and its LIBs electrochemical performance has been investigaed. Sol-gel method is safe and simple, and the as-prepared MoP shows high capacity andsuperior ratecapability. It exhibits a initial charge capacity of664.8mAh g-1at a current density of100mA g-1, after discharge-charge30cycles, still holds a capacity of423mAh g-1and rate capacities of603.8,536,453.7,368.9,320.6,264.2,223.2and157mAh g-1at different currents densities of0.05,0.1,0.2,0.4,0.8,1.2,1.6and3Ag-1, when turn the currenback to0.1A g-1after c-rate cycle, the capacity still have391.2mAh g-1。CNFs, CNFs/CNTs, and MoO2/CNFs/CNTsnanofibers have been fabricated through a facile electrospinningroute combined with postcalcination. MoO2/CNFs/CNTs nanofibers exhibit most great capacity no matter cycle performance or rate performance among the as-prepared samples, because of the special sturcure of MoO2/CNFs/CNTs nanofibers. The nanofibers is composited of a ID continous net structure, inside the structure, MoO2coated by amorphous carbon and CNTs which could enhance the electronic and ionic transport. The amorphous carbon coating on MoO2nanoparticles and CNTs with hollow tubes prevents the MoO2nanoparticles from pulverizationand capacity fading cuased by the volumetic expansion during charging/discharging processes.The electrospinning method and post thermal treatment have been introduced synthesize three kinds of MoS2-CNFs compounds with different carbon contents. The as-prepared MoS2was encapsulated in the carbon nanofibers with a siglelayer or a fewlayers. The content of MoS2in1.6MoS2-CNFs nanofibers is the highest in the samples, which improves the performance of1.6MoS2-CNFs nanofibers. It exhibits a charge capacity of911.3,804.7,733.8,686.7,616and577.3mAh g-1at current densities of0.1,0.2,0.5,1,2and3A g-1. When the currenwas back to0.1A g-1after c-rate cycles, the capacity still exhibits897.7mAh g-1。A simple and scalable electrospinning method has been successfully developed to fabricate flexible MoS2-CNFs membranes as binder-free anodes for SIBs. The as-prepared MoS2-CNFs membranes with homogeneous few-layered MoS2distributed in the carbon nanofibers exhibit high capacity, superior rate capability (283.3,246.5and186.3mAh g-1at0.5,1and2A g-1, respectively), and outstanding cyclability. The present strategy may be extended to fabricate other flexible nanocomposite membranes serving as high-performance binder-free electrodes for future SIB applications.