Controllable Synthesis Of Transitional Metal Nanomatcrials And Its Applications In Rechargeable Batteries

During the past two decades,Lithium-Ion Batteries(LIBs)have played an important role in portable electronic devices.However,due to its high cost and limited resources of LIBs,we have to develop new-type batteries,like Sodium-Ion Batteries(SIBs)and Lithium Sulfur Batteries,in order to compensate or replace the present LIBs market.In this study,we focus on SIBs(low cost)and Li-S battery(high energy density).The main research contents are listed as follows:(1)Metal sulfides are one of the promising anode materials for SIBs.In this chapter,we synthesized NbS4 nanorods with uniform sizes by a high-temperature solution method.These colloidal nanorods readily self-assemble side by side,then form microsized superstructures.To this end,we further introduce two-dimensional graphene nanosheets as the spacer to interrupt nanorods self-assembly.Resultant composite presents a marked advantage toward electrochemical storage of Na+ ions.We demonstrate that in half-cells it exhibits large reversible specific capacity in excess of 600 mAh/g,high rate capability with>300 mAh/g retained at 4 A/g,and great cycle life(>200 cycles)at 1 A/g.This anode material can also be combined with the NASICON-type Na3V2(PO4)3 cathode in full cells to enable large capacity and good cyclability.(2)In order to realize the high-performance battery with high theoretical energy density but low-cost,we focused on Li-S battery which has 10 times of energy density(2500 Wh/kg)larger than LIBs.However,the shuttle effect is the main demerit that restricts practical industrialization.Thus,in this chapter,we developed a facile two-step preparation method for～3 nm α-MoC nanopartieles uniformly dispersed on micro-scale nano carbon flowers(α-MoC/NCF),which services as a catalyst in Li-S battery.Electrochemical results indicate that the presence of α-MoC/NCF can fast the transform of long-chain lithium polysulfides to lithium sulfide,improve sulfur utilization,enhance the cycling performance and upgrade the rate capability.It can still maintain high capacity of 873 mAh/g after 500 cycles at the current density of 0.5 C.In high sulfur mass loading experiments,these batteries can normally charge and discharge with little capacity loss after 100 cycles.We believe the extraordinary electrochemical performance of batteries mainly because of the α-MoC/NCF’s chemical anchoring to lithium polysulfides and catalytic effect in the transform of lithium polusufides.