Hydrothermal Synthesis And Electrochemical Performance Of TiN-based Composites

Lithium ion battery cannot meet the further requirements arising from thedevelopment of new energy field especially electric vehicle and hybrid electric vehicle.The graphite anode has been to the limit due to the expectation of high specific energiesand energy densities. Tin-based anode materials for high specific capacity, goodelectrical conductivity and S-shape charge and discharge curve has already been the oneof most widely studied alloy anode. The carbon-coated nano-Sn was successfullysynthesized based on the chemical reduction method and subsequent hydrothermalmethod. On the other hand, the pomegranate-like SnO₂@C composite anode preparedby one-pot hydrothermal method. And through the corresponding physical andelectrochemical characterization of the two category composite anode material, thecontrollable factors in the preparation process and the mechanism of the capacity fadeof electrodes are put forward and reasonable analyzed.The carbon-coated nano-Sn was synthesized by facile hydrothermal method,30mlsolution contained2.0g glucose and3.0g nano-Sn, which exhibited the excellenceelectrochemical properties. The reversible lithiation/delithiation capacity is over480mAh/g with the capacity retention rate of60%, When discharge/charge at constantcurrent density of200mA/g after100cycles. Even the current density increases to1000mA/g, the reversible capacity can still maintain404.86mAh/g. The electrochemicalperformance compared to the nano-Sn is significantly improved. That is mainlyattributed to the carbon-coated layer on the surface of nano-Sn which can effectivelybuffer volume expansion in the alloy/de-alloy process, maintaining the stability of thestructure. In the optimization of the electrode preparation process, the electrochemicalperformance of Sn@C had no obvious improvement because of the good conductivityof the tin-based anode when using carbon nanotubes as conductive compared withacetylene black. From the results of electrochemical analysis, The performance ofNano-Sn has been failure in several cycles, mainly due to Sn pulverization and crackingduring cycling, and the reversible capacity of Sn@C is dedicated by lithium-poor alloy.Pomegranate-like SnO₂@C composite materials were prepared by one-pothydrothermal process. Nanoscale SnO₂evenly uniform dispersed in the amorphouscarbon ball, and on the surface of the carbon ball coated10nm carbon layer. theSnO₂@C which displayed excellence electrochemical performance when the content ofurea is0.2g. the reversible specific capacity is360.7mAh/g with capacity retention rateof67.5%when the charge and discharge current density of200mA/g, voltage ranged from0.01V to1.5V after100cycles. Increasing cut-off voltage to2.5V, the initialdelithiation specific capacity is1035.6mAh/g, coulombic efficiency is64.7%. After130cycles the delithiation specific capacity is751mAh/g, capacity remain at a rate of72.6%. Even if the current density increases to1000mA/g, the reversible capacity ofSnO₂@C is more than600mAh/g. Superior electrochemical performance owns to itsspecial structure, pomegranate-like SnO₂@C composite materials in the process oflithiation, ultrafine nanoscae SnO₂uniform distribution in the surrounding carbon whichcan buffer volume expansion, and can prevent nano-Sn aggregation and being coarse.This phenomenon is mainly due to reversibility of Li₂O in composite materials, theOxygen atom derived from Li₂O which form SnO or SnO₂with nano-Sn, theaggregation phenomenon of SnO or SnO₂is significantly weaker than nano-Sn duringcycling, the advantages of nanoscale active material can be perfect exhibit which meansthe pomegranate-like SnO₂@C composite materials can be used as the anode of nextgeneration Lithium ion batteries.