Structurat Engineering And Sodium Storage Properties Of Metal Chalcogenides/Carbon Nanocomposites

With sodium sources available everywhere as carriers,sodium ion batteries?SIBs?possess compatible industrial facility with lithium ion batteries?LIBs?,exhibiting promising cost efficiency and application potential.However,due to larger ionic radius and mass,electrode materials for SIBs feature higher requirements on structural stability and electrochemical dynamics.Currently,energy density and power density of SIBs remain inferior to LIBs,which are the main bottlenecks in practical applications.Developing anode materials with high energy/power density is crucial to resolve them.In this dissertation,we present series of metal chalcognides/carbon nanohybrids?M_xC_y/C?with optimized architectures and phase interfaces for superior sodium storage via various routes such as electrostatic assembly,solvothermal-assisted intercalation modification,gas/solid Kirkendall effect,ion exchange-induced self-assembly,etc.The main contents are as follows:?1?Template-assisted construction of few-layer MoS₂ nanosheets/porous carbon nanohybrids?MoS₂@NHPC?for sodium storage.With ammonium tetrathiomolybdate and chitosan as precursors,and polysterene nanospheres as templates,we obtained MoS₂@NHPC via an electrostatic assembly-lyophilization-annealing strategy.The abundant MoS₂/C contact interfaces and three-dimensional interconnected pores in MoS₂@NHPC facilitate the charge transfer,electrolyte permeation;while ultrasmall MoS₂ shortens the ion diffusion pathways,beneficial for boosting electrochemical dynamics.When applied in SIBs,MoS₂@NHPC anodes show remarkably enhanced rate capability(330 mA h g^-1 @ 5 A g^-1)and long-life cyclability over 550 loops(340 mA h g^-1 @ ? A g^-1)with 72.5%capacity retention.?2?Construction of carbon-stabilized interlayer-expanded few-layer MoSe₂ nanosheets?MoSe₂@C?for sodium storage.With sodium molybdate and commercial selenium powders dissolved in hydrazine hydrate as precursors,and oleic aicd as solvent,we obtained MoSe₂@C via an oleic aicd intercalation/capping-amidation modification-annealing strategy.The substantial MoSe₂/C contact interfaces improve the conductivity,while interlayer-expanded few-layer architecture affords shortened ion diffusion and facilitated sodiation/sodiation,leading to enhanced electrochemical dynamics in the MoSe₂@C.Benefiting from the unique architecture,MoSe₂@C anodes exhibit overwhelming rate capability(367 mA h g^-1 @ 5 A g^-1)compared with bare MoSe₂,and can be cycled over 100 loops with 83.7%capacity retention(445 mA h g^-1 @ 1 A g^-1).?3?Construction of MOF-derived CoSe₂@C/CNTs hollow nanocages for sodium storage.When annealed under inert atmosphere,via a similar diffusion to Kirkendall effect,ZIF-67 particles?carbon/cobalt sources?are converted to polyhedral nanocages built from CNTs-bridged carbon-coated Co nanoparticles,which are subsequently selenized to CoSe₂,resulting in the formation of CoSe₂@C/CNTs.The numereous CoSe₂/C contact interfaces promote fast charge transfer,nanocage architecture facilitates the electrolyte permeation,and nanosized CoSe₂ shortens ion diffusion length,affording high-proportion pseudocapacitive effect in the CoSe₂@C/CNTs.As a result,CoSe₂@C/CNTs anodes deliver excellent rate capability(373 mA h g^-1 @ 10 A g^-1)and long-term cycle lifespan over 1000 loops with negligible capacity decay from 70th cycle(390 mA h g^-1 @ 1 A g^-1)??4?Construction of cellular carbon-wrapped ultrathin-wall multi-room FeSe₂ nanocavities?h-FeSez@PC?for sodium storage.With polyvinylpyrrolidone?PVP?-chelated ferric nitrate as precursor,cellular carbon embedded by carbon-coated metastable Fe₃C nanoparticles are obtained via a chemical blowing process.Subsequently,such Fe₃C nanoparticles are selenized to ultrathin-wall multi-room via an unusual stress-induced cracking-hollowing reassembly mechanism,obtaing the h-FeSe₂@PC.The abundant FeSe₂/C contact interfaces promote the charge transfer,three-dimensional cellular framework facilitates the electrolyte permeation,and ultrathin-wall multi-room nanocavities shorten the ion diffusion length,resulting in more than 93%pseudocapacitve proportion.As such,h-FeSe₂@PC anodes display 9.5%ultralow-decay rate capability,and can b cycled over 2000 loops with 98.5%capacity retention(381 mA h g^-1 @ 5 A g^-1),overwhelming other chalcogenides-based anode materials.?5?Construction of CNTs-stringed multi-level CoS₂/SnS₂ heteroassemblies?CoS₂@SnS₂/CNTs?for sodium storage.With acidized CNTs-stringed ZIF-67 and ammonium thiostanante solution as precursors,we obtained CoS₂@SnS₂/CNTs via a facile ion exchange-induced self-assembly-annealing strategy.Different from usual heterostructure,CoS₂@SnS₂/CNTs shows unique core/shell configuration,where the shells consist of vertical CoS₂/SnS₂ heterosheets,and the cores are carbon-cohered CoS₂/SnS₂ heteroparticles.Such architecture endows the CoS₂@SnS₂/CNTs with rich CoS₂/SnS₂ interfaces with increased active sites and shortened ion diffusion.Moreover,CNTs avert the CoS₂@SnS₂ agglomeration,and act as electron highway.Such properties afford CoS₂@SnS₂/CNTs remarkably boosted electrochemical dynamics,which is 1.64 time as high as CoS₂@SnS₂.As a result.CoS₂@SnS₂/CNTs anodes show outstanding high-rate capability at 20 A g^-1,and good long-life cyclability over 500 loops with 96.5%capacity retention(405 mA h g^-1 @ 10 Ag^-1).