Synthesis Of Titaniun Carbide/Transition Metal Oxide Composites For Energy Storage

Energy storage devices with high energy density can satisfy the need of large-scale electric vehicle and gird-storage applications.Therefore it has become a hot topic to search new energy storage devices with remarkably improved performance.Among them,transition metal oxides?TMO?with the advantages of high specific capacity and environmental friendliness have been extensively explored in supercapacitors and Li-ion batteries.Herein,we have been devoted to improving the electrochemical properties of TMO by constructing a core-shell nanostructure,which is composed of transition metal oxides and titanium carbide?TiC?nanowires.It is expected to solve the poor cyclic performance and rate capability of these materials.With the optimizing processes,the electrochemical properties of TMO have been efficiently improved.The main results are listed as follows:In this work,carbothermal reduction method has been employed to systhesize TiC nanowires.Afterwards,nickel oxide nanosheets directly grow on the surface of TiC nanowires by chemical bath depositon,thus forming an interesting core-shell structure.The as-obtained TiC@NiO composite exhibits noticeable pseudocapacitive performance with a specific capacity of 560 F/g at the current density of 1 A/g.With increasing the current density,the specific capacity remains 425 F/g at 20 A/g with a capacity retention of 76%,as well as excellent structural stability.Moreover,the capacity keeps 312 F/g after 5000 cycles,which is much higher than that of the Ni O electrode prepared under similar conditions.The TiC@Co₃O₄ core-shell nanostucture has been systhesized by hydrothermal method.The effects of hydrothermal reaction time on the electrochemical properties of the samples have been discussed.Compared with pure Co₃O₄,it is found that the specific capacity and the cylic performance of Ti C@Co₃O₄ are much better than that of Co₃O₄.Even after 5000 cycles at 20 A/g,it still delivers a discharge capacity of 450 F/g,accompanying with a capacity retention of more than 93.2%.When the current density is increased to 50 A/g,the as-synthesized sample with hydrothermal reaction for 6 hours shows the best cycling stability with a capacity retention of 90.8%.In addition,the lithium storage properties of the TiC@Co₃O₄ core-shell structure synthesized by hydrothermal method have been studied.It exhibits the improved cyclic performance and rate capability as compared to pure Co₃O₄.When charged and discharged for 100 cycles at 100 mA/g,the Co₃O₄ electrode keeps a capacity retentionof 46%.By comparison,the TiC@Co₃O₄ composite electrode shows excellent cycling performance without an obvious capacity decline.The excellent performances of TiC@NiO and TiC@Co₃O₄ composites including favorable cyclic performance and rate capability can be attributed to their outstanding core-shell structure.On the one hand,TiC nanowires with chemical stability and high conductivity gurantee the stability of structure.on the other hand,nanosheet structure improves the specific surface area which is beneficial to tight contact between the electrode and the electrolyte due to its short diffusion channel.Furthermore,it would suppress the volumetic expansion of TMO during the electrochemical reaction.