Electrochemical Performance Of Mo-based Nanocomposites For Lithium And Sodium Storage

Molybdenum compounds have been widely considered as promising materials for LIBs and SIBs for their unique physicochemical properties,such as conductivity,mechanical and thermal stability.This paper is focused on nanostructured Mo-based compounds,including oxides,carbides and sulfides.The preparation,structural control and the optimization of electrochemical performance for lithium and sodium storage of these nanocomposites are discussed.The main conclusions are as follows:1.MoO₂/Mo₂C/C HNWs.We develop a facile synthesis of hierarchical MoO₂/Mo₂C/C HNWs using Mo3O10?C6H5NH3?2·2H2O nanowires as a precursor and self-template via high temperature annealing process.Nanostructure can shorten ion diffusion instance,and carbon buffers volume expansion and keeps structure stable.With high conductivity and capacity,Mo₂ C nanocrystallines hybridizing with MoO₂ instead of carbon can avoid carbon materials with relatively low capacity brings down the overall capacity of the composites.Therefore,MoO₂/Mo₂C/C HNWs exhibit high capacity,high rate as well as long-term cycle stability.At a current density of 2000 mA g-1,the hybrid nanowires deliver a reversible capacity of 602 mA h g-1 after 500 cycles.2.Mo₂C/N-doped carbon heteronanowires.Mesoporous Mo₂C/N-doped carbon heteronanowires for high performance anode are obtained by controlling temperature and flow velocity using Mo3O10?C6H5NH3?2·2H2O nanowires as precursor and self-template.In this structure,Mo₂ C nanocrystallites with high capacity are embedded in a continuous 1D N-doped carbon matrix.Nanostructured shortens short paths for ion diffusion,1D N-doped carbon matrix facilitates charge transfer and buffers volume expansion of Mo₂ C during cycles.As anode for lithium storage,prominent capacitive behavior of Mo₂C/N-doped carbon heteronanowires shows its fast kinetics for Li+ storage,the keep of curves profiles after many cycles demonstrates its structure stability.At a current density of 2 A g-1,the reversible capacity for Li+ storage retains 732.9 mAh g-1 after 500 cycles.As anode for SIBs,Mo₂C/N-doped carbon heteronanowires exhibit greatly enhanced capacity compared with Mo₂ C MPs.3.MoS₂/C microfiber composites.By hydrothermal and high-temperature carbonation,we use cotton as a carbon source and bio-template to construct hierarchical structure in which MoS₂ nanosheets are vertically aligned on carbon fibers.Nanostructured carbon fibers provide paths for fast electron transport and as robust scaffold for the support of MoS₂ nanosheets.And they greatly improve the structural stability of the composite during the reversible Li+ and Na+ storage cycles.So,comparing with bare MoS₂,the cyclic stability of MoS₂/CDCFs is enhanced evidently.Moreover,the content of carbon fiber has a remarkable effect on capacity,cycle performance and rate capacity of the composites.We further optimize electrochemical performance of composites by tuning carbon fiber content.4.MoS₂@C flower-like nanosheets.MoS₂@C composite is synthesized by hydrothermal and subsequent CVD technology route using ethanol as carbon source.Carbon coated improves conductivity of composites and effectively stable the structure,which enhances the cycling performance.We can control the thickness of carbon layer by adjusting the deposition temperature.After contrast and optimization,MoS₂@C-700 shows the superior electrochemical performance for Na+ storage.At a current density of 1 A g-1,MoS₂@C-700 maintains a reversible capacity of 304.1 mAh g-1 after 230 cycles,which is much more than MoS₂ with a capacity of 129.4 mAh g-1.This method is extended to prepare SnS@C microplate to improve cyclic stability for Na+ storage.