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Sigdel S.,South Dakota State University | Elbohy H.,South Dakota State University | Gong J.,South Dakota State University | Gong J.,North Dakota State University | And 8 more authors.
IEEE Transactions on Electron Devices | Year: 2015

Porous hollow tin oxide (SnO2) nanofibers and their composite with titanium dioxide (TiTiO2) particles (Degussa P25) were investigated as a photoanode for dye-sensitized solar cells. Incorporation of TiTiO2 particles in porous hollow SnO2 fibers enhanced the power conversion efficiency (η) from 4.06% to 5.72% under 100-mW/cm2 light intensity. The enhancement of efficiency was mainly attributed to increase in current density ( Jsc) and improvement in fill factor (FF). Increase in Jsc was caused by higher dye loading as indicated by UV-Vis absorption spectra and the improvement in FF was attributed to faster charge transport time as obtained from transient analysis. The microstructure of SnO2 fibers was studied using transmission electron microscope, scanning electron microscope, and X-ray diffraction. The electron transfer and recombination life times were studied using transient analysis, whereas interfacial charge transfer was studied using electrochemical impedance spectroscopy. © 2015 IEEE. Source

Qu L.,Shanghai JiaoTong University | Luo D.,Shanghai JiaoTong University | Fang S.,Shanghai JiaoTong University | Fang S.,Shanghai Electrochemical Energy Devices Research Center | And 5 more authors.
Journal of Power Sources | Year: 2016

Mg-doped Li2FeSiO4/C is synthesized by using Fe2O3 nanoparticle as iron source. Through Rietveld refinement of X-ray diffraction data, it is confirmed that Mg-doped Li2FeSiO4 owns monoclinic P21/n structure and Mg occupies in Fe site in the lattice. Through energy dispersive X-ray measurement, it is detected that Mg element is distributed homogenously in the resulting product. The results of transmission electron microscopy measurement reveal that the effect of Mg-doping on Li2FeSiO4 crystallite size is not obvious. As a cathode material for lithium-ion battery, this Mg-doped Li2FeSiO4/C delivers high discharge capacity of 190 mAh g-1 (the capacity was with respect to the mass of Li2FeSiO4) at 0.1C and its capacity retention of 100 charge-discharge cycles reaches 96% at 0.1C. By the analysis of electrochemical impedance spectroscopy, it is concluded that Mg-doping can help to decrease the charge-transfer resistance and increase the Li+ diffusion capability. © 2016 Published by Elsevier B.V. Source

Luo D.,Shanghai JiaoTong University | Fang S.,Shanghai JiaoTong University | Fang S.,Shanghai Electrochemical Energy Devices Research Center | Yang L.,Shanghai JiaoTong University | And 2 more authors.
Journal of Materials Chemistry A | Year: 2016

As promising cathodes for high-energy Li-ion batteries, the commercial application of layered Li-rich transition-metal oxides (LROs) is significantly prevented by their non-ideal cycling stability and rate capability. In this work, Li1.23Mn0.46Ni0.15Co0.16O2 samples are prepared by combining a solvothermal process and a Li2CO3 molten-salt method. When the molar ratio of Li2CO3 to transition-metal ions is 4 : 1, the obtained sample has the best electrochemical performance. Its initial discharge capacities at 20 and 300 mA g-1 are larger than 307.8 and 232.2 mA h g-1, respectively. After 200 cycles, the capacity retention ratio at 300 mA g-1 is still as large as 85.3%. In addition, we discovered that the relative content of lithium on the particle surface of the samples is more than that in the particle interior, and this distribution behavior of lithium is adjustable. In particular, we demonstrate for the first time that the overmuch enrichment of lithium on the particle surface will hinder the diffusion of Li-ions. This is the blockade effect of surface lithium, and this blockade effect can be alleviated by the Li2CO3 molten-salt method. This is the reason that the electrochemical performance of LROs can be greatly improved by the Li2CO3 molten-salt method. © The Royal Society of Chemistry 2016. Source

Li X.,Shanghai JiaoTong University | Zhang Z.,Shanghai JiaoTong University | Zhang Z.,Shanghai Electrochemical Energy Devices Research Center | Li S.,Shanghai JiaoTong University | And 3 more authors.
Journal of Power Sources | Year: 2016

In this work, composite polymer electrolytes (CPEs), that is, 80%[(1-x)PIL-(x)SN]-20%LiTFSI, are successfully prepared by using a pyrrolidinium-based polymeric ionic liquid (P(DADMA)TFSI) as a polymer host, succinonitrile (SN) as a plastic crystal, and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) as a lithium salt. XRD and DSC measurements confirm that the as-obtained CPEs have amorphous structures. The 80%[50%PIL-50%SN]-20%LiTFSI (50% SN) electrolyte reveals a high room temperature ionic conductivity of 5.74 × 10-4 S cm-1, a wide electrochemical window of 5.5 V, as well as good mechanical strength with a Young's modulus of 4.9 MPa. Li/LiFePO4 cells assembled with the 50% SN electrolyte at 0.1C rate can deliver a discharge capacity of about 150 mAh g-1 at 25°C, with excellent capacity retention. Furthermore, such cells are able to achieve stable discharge capacities of 131.8 and 121.2 mAh g-1 at 0.5C and 1.0C rate, respectively. The impressive findings demonstrate that the electrolyte system prepared in this work has great potential for application in lithium ion batteries. © 2016 Elsevier B.V. All rights reserved. Source

Tian Q.,Shanghai JiaoTong University | Luo D.,Shanghai JiaoTong University | Li X.,Shanghai JiaoTong University | Zhang Z.,Shanghai JiaoTong University | And 4 more authors.
Journal of Power Sources | Year: 2016

Titanium dioxide (TiO2) has been considered to be a promisingly alternative anode material for lithium-ion batteries and thus attracted wide research interest. But, its practical application in lithium-ion batteries is seriously impeded by low capacity and poor rate capability. In the present work, the electrochemical performance of TiO2 is significantly improved by elaborately fabricating hierarchical structures. These as-prepared four hierarchical structure TiO2 assembled by different building blocks (TO2-2 h, TO2-6 h, TO2-18 h and TO2-24 h) all exhibit impressed performance. More importantly, the TO2-6 h constructed by curved nanosheets exhibits the best performance, delivering a capacity of 231.6 mAh g-1 at 0.2C after 200 cycles, and capacities of 187.1 and 129.3 mAh g-1 at 1 and 10C after even 1200 cycles, respectively. The results indicated that design and fabrication of hierarchical structure is an effective strategy for significantly improving the electrochemical performance of TiO2 electrodes, and the electrochemical performance of hierarchical structure TiO2 is heavily dependent on its building blocks. It is suggested that thus excellent electrochemical performance may make TiO2-6 h a promising anode material for advanced lithium-ion batteries with high capacity, good rate capability and long life. © 2016 Elsevier B.V. All rights reserved. Source

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