Surface-Engineered Li4Ti5O12 Nanostructures for High-Power Li-Ion Batteries

Materials with high-power charge–discharge capabilities are of interest to overcome the power limitations of conventional Li-ion batteries.In this study,a unique solvothermal synthesis of Li4Ti5O12 nanoparticles is proposed by using an off-stoichiometric precursor ratio.A Li-deficient off-stoichiometry leads to the coexistence of phaseseparated crystalline nanoparticles of Li4Ti5O12 and TiO2 exhibiting reasonable high-rate performances.However,after the solvothermal process,an extended aging of the hydrolyzed solution leads to the formation of a Li4Ti5O12 nanoplate-like structure with a self-assembled disordered surface layer without crystalline TiO2.The Li4Ti5O12 nanoplates with the disordered surface layer deliver ultrahighrate performances for both charging and discharging in the range of 50–300C and reversible capacities of 156 and 113 mAh g−1 at these two rates,respectively.Furthermore,the electrode exhibits an ultrahigh-charging-rate capability up to 1200C(60 mAh g−1;discharge limited to 100C).Unlike previously reported high-rate half cells,we demonstrate a high-power Li-ion battery by coupling Li4Ti5O12 with a high-rate LiMn2O4 cathode.The full cell exhibits ultrafast charging/discharging for 140 and 12 s while retaining 97 and 66% of the anode theoretical capacity,respectively.Room-(25℃),low-(−10℃),and high-(55℃)temperature cycling data show the wide temperature operation range of the cell at a high rate of 100C.

WO_(3) passivation layer-coated nanostructured TiO_(2): An efficient defect engineered photoelectrode for dye sensitized solar cell

Major loss factors for photo-generated electrons due to the presence of surface defects in titanium dioxide(Ti O_2)were controlled by RF-sputtered tungsten trioxide(WO_3) passivation. X-ray photoelectron spectroscopy assured the coating of WO3 on the Ti O_2 nanoparticle layer by showing Ti 2 p, W 4 f and O 1 s characteristic peaks and were further confirmed by X-ray diffraction studies. The coating of WO_3 on the Ti O_2 nanoparticle layer did not affect dye adsorption significantly. Dye sensitized solar cells(DSSCs) fabricated using WO_3-coated Ti O_2 showed an enhancement of ~10% compared to DSSCs fabricated using pristine Ti O_2-based photo-electrodes. It is attributed to the WO_3 passivation on Ti O_2 that creates an energy barrier which favored photo-electron injection by tunneling but blocked reverse electron recombination pathways towards holes available in highest occupied molecular orbital of the dye molecules. It was further evidenced that there is an optimum thickness(duration of coating) of WO_3 to improve the DSSC performance and longer duration of WO_3 suppressed photo-electron injection from dye to Ti O_2 as inferred from the detrimental effect in short circuit current density values. RF-sputtering yields pinhole-free,highly uniform and conformal coating of WO_3 onto any area of interest, which can be considered for an effective surface passivation for nanostructured photovoltaic devices.

Conducting polymer PEDOT:PSS coated Co_(3)O_(4) nanoparticles as the anode for sodium-ion battery applications

Metal oxides are considered as potential anodes for sodium-ion batteries(SIBs).Nevertheless,they suffer from poor cycling and rate capability.Here,we investigate conductive polymer coating on Co_(3)O_(4)nanoparticles varying with different percentages.X-ray diffraction,electron microscopy and surface chemical analysis were adopted to analyze coated and uncoated Co_(3)O_(4)nanoparticles.Conducting polymer,poly(3,4-ethylene dioxythiophene)polystyrene sulfonate(PEDOT:PSS),has been utilized for coating.Improved specific capacity and rate capability for an optimal coating of 0.5 wt.%were observed.The 0.5 wt.%coated sample outperformed the uncoated one in terms of capacity,rate capability and coulombic efficiency.It delivered a reversible capacity of 561 mAh·g^(−1)at 100 mA·g^(−1)and maintained a capacity of 318 mAh·g^(−1)at a high rate of 1 A·g^(−1).Increasing the PEDOT:PSS coating percentage led to lower performance due to the thicker coating induced kinetic issues.Ex-situ analysis of the 0.5 wt.%coated sample after 100 cycles at 1 A·g^(−1)was characterized for performance correlation.Such a simple,cost-effective and wet-chemical approach has not been employed before for Co_(3)O_(4)as the SIB anode.