Construction Of Titanium Carbide Nano-composite For Energy Storage Application

Titanium carbide is one of typical transition metal carbide.It has been widely used in many fields（such as cutting tool materials,ceramic materials,refractories,hard alloy and so on）because of its outstanding properties: high strength,high hardness,wear resistance,high melting temperature,acid and alkali corrosion resistance,high electrical conductivity and other excellent performance.In this work,the materials of mesoporous carbon/titanium carbide and titanium carbide nanorods were synthesized by supercritical carbon dioxide fluid deposition technology and bio-template method combined with high temperature carbothermal reduction.The two kinds of structure of the titanium carbide materials were combined with sulfur and niobium pentoxide as mesoporous carbon/titanium carbide-sulfur lithium-sulfur battery material and titanium carbide/niobium pentoxide supercapacitor material,respectively.The relationship between the microstructure and electrochemical performance has been well discussed,which provides the experimental basis and theoretical basis for the application of titanium carbide in the field of new energy storage.The main results obtained in this work are as follows:（1）The TiC/C composites were synthesized by introducing tetrabutyl titanate into the mesoporous carbon material via supercritical CO₂ fluid and then combined with high temperature carbothermal reduction reaction.The composites were characterized by X-ray diffraction（XRD）,scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,specific surface area test（BET）and other materials analysis test means.It was found that TiC nanocrystals were embedded in the mesoporous carbon material to form a mesoporous structure with mesoporous carbon/titanium carbide.Compared with the traditional synthesis method,titanium carbide is relatively pure and the particle size is nano-level in this work.The material has a unique titanium carbide-mesoporous structure with a specific surface area of 760 m2 g-1.（2）TiC/C-S composite with up to 74 wt.% sulfur content was synthesized by thermal diffusion method.The XRD,SEM,TEM and X-ray energy dispersive spectroscopy（EDS）were used to analyze the microstructure of TiC/C material.Elemental sulfur is well integrated and distributed into the TiC/C material.The electrochemical test showed that the electrochemical performance of TiC/C-S is super to CMK-3-S and TiO₂/C-S.After small current activation,the TiC/C-S electrode achieves a capacity of 821 mAh g-1 at a current density of 0.2 A g-1,and the capacity rate remained above 73% after 200 cycles.The excellent electrochemical performances of TiC/C-S electrode can be attributed to the following reasons.Firstly,the polar titanium carbide particles have a chemical force on the polysulfide,which could slow down lithium-sulfur battery shuttle;Secondly,the addition of conductive titanium carbide can improve the conductivity of elemental sulfur,promote the charge transfer,accelerate the electrode reaction kinetics;Finally,the outward migration of polysulfides upon cycling may be limited by the mesoporous structure of CMK-3 so that the material has excellent cycling and rate performance.（3）TiC nanowires were synthesized by bio-template method and high temperature carbothermal reduction reaction.And then,the synthesis of TiC/Nb₂O₅ composites with core/shell Structure via sol-gel method and supercritical CO₂ drying technology.The microstructures of TiC/Nb₂O₅ were systematically analyzed by XRD and SEM.The results show that the diameter of TiC nanowires is 50-200 nm and the length is between several and several tens of micrometers.The niobium pentoxide particles directly grow on the surface of TiC nanowires.Electrochemical tests show that the as-constructed TiC/Nb₂O₅（75 wt.%）offers best reversible capacity,retaining 129 mAh g-1 at 0.1 A g-1 current density after 200 cycles.It’s matches with AC activated carbon in 1: 2 mass ratio,as the lithium-ion capacitor positive and negative electrode,respectively.The device TiC/Nb₂O₅∥AC exhibits a maximum energy density of 43.8 Wh kg-1,at a power density of 52.5 W kg-1 and a maximum power density is 3500 W kg-1（discharging time about 15 s）at an energy density of 14.5 Wh kg-1.The excellent electrochemical performances of composites electrode can be attributed to the following reasons.Firstly,the structure of nano core/shell structure which improve the electrical conductivity of Nb₂O₅,facilitate the full penetration of the electrolyte,and promote the electrode reaction;Secondly,intrinsic high electrical conductivity and chemical stability of TiC can maintain the nanowire integrity well,and promote the Li+ deintercalation speed during repeated cycling.