Conformal Construction Of M(Mn Or Sn)S_x @Nanoreactor Composites And Their Properties Of Lithium/Sodium Storage

With the development and utilization of green energy yielded from wind,ocean and tidal,it is urgent to develop efficient energy storage systems.The secondary lithium/sodium ion batteries are considered as most promising power sources because of their high energy density,theoretical capacity and environmental friendliness.As the increase of environmental problems and demands in electronic devices,more stringent requirements are put forward for battery systems.In order to meet the ever-growing energy storage requirements,researchers urgently need to develop novel anode materials with higher energy density and more safety to replace traditional graphite.Metal sulfide materials?such as MnS,SnS₂,ZnS,etc.?are believed to be one of the most promising candidates.However,metal sulfides are confronted with such problems due to actives volume expansions,dissolution/diffusion of polysulfides?intermediate products?and instability of“electrolyte-electrode”interface,which lead to the rapid degradation of electrode performance.From perspectives of material innovation,electrode design and interface optimization,how to improve the battery performance has become a key scientific problem that needs to be explored.In this paper,taking metal sulfide as a case study,a functionalized nanoreactor was constructed on the outside of sulfide anode nanounit by St?ber and chemical vapor deposition methods.The working mechanisms of such nanoreactors that endow sulfide anodes with greatly enhanced cyclic behaviors were also investigated systematically.The main research contents are as follows:1.MnO₂ nanowires were synthesized by a liquid-phase method at room temperature using low-cost MnSO₄ salts as raw materials;Then,the modified layer of carbon nanoreactor with a thickness of¹0 nm was coated on the surface of MnO₂ nanowires with dopamine molecules and calcination treatment,leading to the formation of MnO@carbon nanocomposites.Next,MnS@carbon nanoreactors with an intact and conformal core-shell configurations were fabricated via a simple sulfuration procedure,where the displacement reaction between MnO@carbon composite and sulfur powder took place under vacuum conditions.Such one-dimensional carbon nanoreactors not only effectively buffer the electrode volume expansion,but also provide direct charge transfer pathways.This is favorable to improve the structural stability,enhance the cycle life and rate capability of MnS@carbon electrode.When used as anodes for lithium/sodium ion batteries,MnS@carbon hybrids exhibit a high reversible capacity,good rate capability and stable cyclic ability.In order to prove its potential in practical usage,we further assembled full cells?for lithium storage:MnS@carbon//LiFePO₄;for sodium storage:MnS@carbon//Na₃V₂?PO₄?₃@carbon?.Both battery devices show high working voltage and energy density.2.Hollow SnO₂ nanosphere precursors were synthesized by a hydrothermal method using SnCl₂?2H₂O salt as the raw material;Then,the intermediate products of SnO₂@SiO₂ nanosphere were fabricated by a St?ber method using the waste glass as silicon sources.Next,hollow SnO₂@SiO₂/carbon nanospheres with core-shell structure were synthesized by the chemical vapor deposition method using ethylene glycol as carbon source.Later,SnS₂@SiO₂/carbon nanoreactors were formed by a simple sulfuration reaction in vacuum conditions.The SiO₂/carbon nanoreactor has good mechanical stability,easily doped with group I elements?such as Li,Na and K?and excellent physical/chemical stability in organic electrolytes.As a result,when used as the anode for sodium storage,SnS₂@SiO₂/carbon composites can exhibit excellent electrochemical properties,including good rate capabilities,high reversible specific capacity and remarkable cyclic behaviors.Further,we have assembled full cells of SnS₂@SiO₂/carbon//Na₃V₂?PO₄?₃@carbon,which can output a high voltage of³.10 V and light the high-power blue LED.