Synthesis Of New Nanostructured Titanates And Their Electrochemical Properties

Sodium-ion battery is one of the most promising energy storage systems due to the abundant storage of sodium and low cost.Generally,hard carbon is the most conventional anode material for sodium-ion batteries because of its high theoretical capacity.However,this kind of material cannot provide a good rate performance and cycling stability.Thus,it is important to find alternative anode materials for Na-ion batteries.Titanate is such a new kind of anode materials,with advantages such as non-toxic,high abundance,high safety and so on.The electrochemical properties of titanate are closely related to its crystalline phase,structure,composition,morphology,size,dimensions and electrode structure.Compared with traditional anode materials,new nanostructured titanate anode materials have larger development space since they possess advantages of fast charge transport,high electrochemical reactivity and good conductivity.In the present work,we synthesized a series of new nanostructured titanate via a simple hydrothermal method and investigated the influences of different reaction conditions on the structure and morphology of titanate.Afterwards,these titanates were tested as an anode for sodium-ion batteries,and the relationship between their intrinsic characteristics and their electrochemical properties was further studied.1.Na2Ti6O13 microspheres were synthesized using organic titanium source as raw materials and PVP as a template via a hydrothermal method.After calcined,Na2Ti6O13 microspheres composed of nanoparticles were successfully obtained.When used as an anode for Na-ion batteries for the first time,this material showed good reversible capacity and excellent cycling stability.The excellent electrochemical performance could be attributed to the porous structure which could facillated the diffusion of electrolyte solution and sodium ion,and the nanostructure particle could effectively shorten diffusion length.2.Using Ti foil as a substrate,we prepared Na2Ti7O15 titanate nanosheets by one step via an in-situ synthesis method.By regulating the reaction time,we successfully obtained uniform Na2Ti7O15 nanosheets,which had thickness of 1-2 nm.Further more,the Na2Ti7O15 nanosheets grown on Ti substrate were directly used as a binder-free anode for Na-ion batteries and exhibited good electrochemical performance.Using such a binder-free anode could eliminate the effects of binder and further improve the conductivity of electrode.On the other hand,the nanostructure Na2Ti7O15 electrode material could effectively shorten the transport path of Na-ion and improve the diffusion of ions.3.On the basis of in-situ synthesis system of Na2Ti7O15 titanate,we successfully synthesized Na2Ti7O15 nanotubes using porous Ti net as a substrate through adjusting the reaction conditions.The as-prepared Na2Ti7O 15 nanotubes were multi-layer structure with non-concentric and about 2 ?m in length.Besides,the inner diameter and wall thickness were 3-5 nm and 0.3-0.4 nm,respectively.Afterwards,we investigated the influences of different substrates and morphologies on the electrochemical properties and found that Na2Ti7O15 nanotubes grown on Ti net represented higher reversible capacity and better cycling stability.The excellent electrochemical performances were probably because the porous Ti net substrate could not only improve the conductivity of electrode but also promote the transformation and diffusion of electrolyte.