Anamolously High Lithium Storage in Mesoporous Nanoparticulate Aggregation of Fe3+ Doped Anatase Titania

Abstract

Implications of iron (Fe 3+ ) doping on lithium insertion/de-insertion capacity of anatase TiO 2 is discussed here. Iron doped anatase TiO 2 mesoporous nanoparticulate aggregated at various Fe 3+ doping concentrations was synthesized by an optimized sol-gel method. The electrochemistry and lithium storage capacities of anatase TiO 2 exhibited strong function of dopant iron (Fe 3+ ) concentration. A very high first discharge cycle capacity of 704 mAhg −1 corresponding to approximately 2.1 mol of Li was observed for 5% iron (Fe 3+ ) doped TiO 2 at a current density of 75 mAg −1 . At the 30th discharge cycle, the capacity was remarkably high at 272 mAhg −1 (0.81 mol of Li) with coulombic efficiency greater than 96%. Increase in the iron (Fe 3+ ) concentration beyond 5% resulted in deterioration of lithium storage in TiO 2 . An improvement in lithium storage of more than 50% is noticed for 5% iron (Fe 3+ ) doped TiO 2 compared to pure anatase TiO 2 which shows an initial discharge capacity of 279 mAhg −1 . The anomalous lithium storage behavior in all the iron (Fe 3+ ) doped TiO 2 samples has been accounted, in addition to homogeneous Li insertion in the octahedral sites, via local conversion reaction and heterogeneous interfacial storage at Fe and Li 2 O.The demand for lithium ion batteries (LIBs) for diverse applications such as mobile electronics, electric vehicles with wide variation in specifications (especially with respect to energy/power density, configurations) have resulted in an upsurge in research activity worldwide. 1, 2 The present commercial LIBs employ LiCoO 2 as the positive electrode and graphite as the negative electrode. Although graphite shows a stable capacity of over 300 mAhg −1 (theoretical capacity of Li x C 6 : 372 mAhg −1 ), safety is a major concern with it since lithium insertion voltage in graphite is in the close proximity to lithium plating voltage (∼100 mV). 2 Employment of nanoparticulate graphite and lesser dimensional (< 3-D) carbonaceous materials (e.g. carbon nanotubes) further depreciates battery safety. 3 To overcome the problem of safety, efforts are on to find alternative high lithium storage capacity anodes. Storage of lithium via alloying reaction (e.g. Sn, Si) have received considerable attention 4-6 however, widespread practical realization has still not been possible. The materials exhibit poor cyclability due to enormous volume changes occurring during successive charging and discharging cycles resulting in both mechanical failure and loss of electrical contact at the electrode. Recently, TiO 2 (and TiO 2 based materials such as Li 4 Ti 5 O 12 ) have been demonstrated as promising anodes in LIBs. 7-12 TiO 2 do not exhibit any volume expansion during lithium insertion/de-insertion and is chemically stable, environmentally benign and cost effective. Additionally, in comparison to conventional carbonaceous anode materials, TiO 2 has a lithium insertion voltage at approximately 1.5 V 7 which is far above the lithium plating voltage (∼100 mV) and expectedly safer LIBs. The m...

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