Vapor-grown carbon fibers （VGCFs） were introduced as conductive additives for sulfur-multiwalled carbon nanotubes （S-MWCNTs） composite cathode of lithium-sulfur batteries. The performance of S-MWCNTs composite cat...Vapor-grown carbon fibers （VGCFs） were introduced as conductive additives for sulfur-multiwalled carbon nanotubes （S-MWCNTs） composite cathode of lithium-sulfur batteries. The performance of S-MWCNTs composite cathodes with carbon black and VGCFs as sole conductive additives was investigated using scanning electron microscopy （SEM）, galvanostatic charge-discharge tests and electrochemical impedance spectroscopy （EIS）. The results show that the S-MWCNTs composite cathode with VGCFs displays a network-like morphology and exhibits higher activity and better cycle durability compared with the composite cathode with carbon black, delivering an initial discharge capacity of 1254 mA＆#183;h/g and a capacity of 716 mA＆#183;h/g after 40 cycles at 335 mA/g. The interconnected VGCFs can provide a stable conductive network, suppress the aggregation of cathode materials and residual lithium sulfide and maintain the porosity of cathode, and therefore the electrochemical performance of S-MWCNTs composite cathode is enhanced.展开更多
WS2/carbon nanofibers （WS2/CNFs） are obtained by a simple electrospinning method in which few-/ single-layer WS2 is uniformly embedded in carbon fibers. When used as the active anode material for Li-ion cells, these...WS2/carbon nanofibers （WS2/CNFs） are obtained by a simple electrospinning method in which few-/ single-layer WS2 is uniformly embedded in carbon fibers. When used as the active anode material for Li-ion cells, these nanofibers exhibit a first-cycle discharge/charge capacity of 941/756 mAh/g at 100 mAJg and maintain a capacity of 458 mAh/g after 100 cycles at 1 A/g. The evolution of size and crystallinity of WS2 with heating treatment are system- atically studied, which are found to strongly influence the final electrochemical performance. Interestingly, the WS2 samples of lowest crystallinity show the highest performance among all studied samples, which could result from the large interfacial capacity for Li ions due to their large specific surface area. More interestingly, the inherent flexible attribute of electrospun nanofibers renders them a great potential in the utilization of binder-flee anodes. Similar high discharge/charge capacity of 761/604 mAh/g with a first coulombic efficiency of 79.4 % has been achieved in these binder-flee anodes. Considering the universal of such simple and scalable preparation strategy, it is very likely to extend this method to other similar two-dimensional layered materials besides WS2 and provides a promising candidate elec- trode for developing flexible battery devices.展开更多
The inherently low electrical conductivity of TiO2-based electrodes as well as the high electrical resistance between an electrode and a current collector represents a major obstacle to their use as an anode for lithi...The inherently low electrical conductivity of TiO2-based electrodes as well as the high electrical resistance between an electrode and a current collector represents a major obstacle to their use as an anode for lithium ion batteries. In this study, we report on high-density TiO2 nanotubes （NTs） branched onto a carbon nanofiber （CNF） ＂tree＂ that provide a low resistance current path between the current collector and the TiO2 NTs. Compared to a TiO2 NT array grown directly on the current collector, the branched TiO2 NTs tree, coupled with the CNF electrode, exhibited -10 times higher areal energy density and excellent rate capability （discharge capacity of -150 mA.h.g-1 at a current density of 1,000 mA·g-1）. Based on the detailed experimental results and associated theoretical analysis, we demonstrate that the introduction of CNFs with direct electric contact with the current collector enables a significant increase in areal capacity （mA·h·cm-2） as well as excellent rate capability.展开更多
MoO_2@N-doped C nanofibers（MoO_2@NC NFs）were synthesized by electrospinning with polyacrylonitrile as carbon source.The in situ formed MoO_2nanocrystals are completely embedded in the carbon nanofibers,which can not...MoO_2@N-doped C nanofibers（MoO_2@NC NFs）were synthesized by electrospinning with polyacrylonitrile as carbon source.The in situ formed MoO_2nanocrystals are completely embedded in the carbon nanofibers,which can not only accelerate ion transition,but also act as a buffer to avoid the mechanical degradation of active material due to the volume changes during charge/discharge cycling.When used as the anode material for both Li/Na-ion batteries,the as-synthesized MoO_2@NC NFs displayed excellent Li~＋/Na~＋storage properties.As the anode for Li-ion battery,the MoO_2@NC NFs display a high discharge capacity of 930 mA h g^（-1）at a current density of 200 mA g^（-1）for 100 cycles,and 720 mA h g^（-1）at a current density of 1 A g^（-1）for 600 cycles.Moreover,the discharge capacity of 350 mA h g^（-1）could be realized at a current density of 100 mA g^（-1）for 200 cycles for Na-ion battery.展开更多
基金Project(JCYJ20120618164543322)supported by Strategic Emerging Industries Program of Shenzhen,ChinaProject(2013JSJJ027)supported by the Teacher Research Fund of Central South University,China
文摘Vapor-grown carbon fibers （VGCFs） were introduced as conductive additives for sulfur-multiwalled carbon nanotubes （S-MWCNTs） composite cathode of lithium-sulfur batteries. The performance of S-MWCNTs composite cathodes with carbon black and VGCFs as sole conductive additives was investigated using scanning electron microscopy （SEM）, galvanostatic charge-discharge tests and electrochemical impedance spectroscopy （EIS）. The results show that the S-MWCNTs composite cathode with VGCFs displays a network-like morphology and exhibits higher activity and better cycle durability compared with the composite cathode with carbon black, delivering an initial discharge capacity of 1254 mA＆#183;h/g and a capacity of 716 mA＆#183;h/g after 40 cycles at 335 mA/g. The interconnected VGCFs can provide a stable conductive network, suppress the aggregation of cathode materials and residual lithium sulfide and maintain the porosity of cathode, and therefore the electrochemical performance of S-MWCNTs composite cathode is enhanced.
文摘WS2/carbon nanofibers （WS2/CNFs） are obtained by a simple electrospinning method in which few-/ single-layer WS2 is uniformly embedded in carbon fibers. When used as the active anode material for Li-ion cells, these nanofibers exhibit a first-cycle discharge/charge capacity of 941/756 mAh/g at 100 mAJg and maintain a capacity of 458 mAh/g after 100 cycles at 1 A/g. The evolution of size and crystallinity of WS2 with heating treatment are system- atically studied, which are found to strongly influence the final electrochemical performance. Interestingly, the WS2 samples of lowest crystallinity show the highest performance among all studied samples, which could result from the large interfacial capacity for Li ions due to their large specific surface area. More interestingly, the inherent flexible attribute of electrospun nanofibers renders them a great potential in the utilization of binder-flee anodes. Similar high discharge/charge capacity of 761/604 mAh/g with a first coulombic efficiency of 79.4 % has been achieved in these binder-flee anodes. Considering the universal of such simple and scalable preparation strategy, it is very likely to extend this method to other similar two-dimensional layered materials besides WS2 and provides a promising candidate elec- trode for developing flexible battery devices.
文摘The inherently low electrical conductivity of TiO2-based electrodes as well as the high electrical resistance between an electrode and a current collector represents a major obstacle to their use as an anode for lithium ion batteries. In this study, we report on high-density TiO2 nanotubes （NTs） branched onto a carbon nanofiber （CNF） ＂tree＂ that provide a low resistance current path between the current collector and the TiO2 NTs. Compared to a TiO2 NT array grown directly on the current collector, the branched TiO2 NTs tree, coupled with the CNF electrode, exhibited -10 times higher areal energy density and excellent rate capability （discharge capacity of -150 mA.h.g-1 at a current density of 1,000 mA·g-1）. Based on the detailed experimental results and associated theoretical analysis, we demonstrate that the introduction of CNFs with direct electric contact with the current collector enables a significant increase in areal capacity （mA·h·cm-2） as well as excellent rate capability.
基金supported by the National Natural Science Foundation of China (51302079)
文摘MoO_2@N-doped C nanofibers（MoO_2@NC NFs）were synthesized by electrospinning with polyacrylonitrile as carbon source.The in situ formed MoO_2nanocrystals are completely embedded in the carbon nanofibers,which can not only accelerate ion transition,but also act as a buffer to avoid the mechanical degradation of active material due to the volume changes during charge/discharge cycling.When used as the anode material for both Li/Na-ion batteries,the as-synthesized MoO_2@NC NFs displayed excellent Li~＋/Na~＋storage properties.As the anode for Li-ion battery,the MoO_2@NC NFs display a high discharge capacity of 930 mA h g^（-1）at a current density of 200 mA g^（-1）for 100 cycles,and 720 mA h g^（-1）at a current density of 1 A g^（-1）for 600 cycles.Moreover,the discharge capacity of 350 mA h g^（-1）could be realized at a current density of 100 mA g^（-1）for 200 cycles for Na-ion battery.
