Zelang Jian

Atomic-scale investigation on lithium storage mechanism in TiNb2O7,

Titanium niobium oxide (TiNb2O7) with a monoclinic layered structure has been synthesized by a solid state reaction method as an anode candidate for Li-ion batteries. The TiNb2O7 electrode shows a lithium storage capacity of 281 mAh g−1with an initial coulombic efficiency as high as 93% at a current density of 30 mA g−1 (ca. 0.1C). The average lithium insertion voltage is about 1.64 V vs.Li/Li+ at a voltage range of 0.8–3.0 V. The electrodes exhibit small voltage hysteresis (c.a. 0.1 V at 30 mA g−1) and good capacity retention. Such superior electrochemical performance of TiNb2O7 makes it one of the most promising anode materials to replace spinel Li4Ti5O12 for applications in hybrid vehicles and large scale stationary Li-ion batteries. In addition, we demonstrate crystal structures of TiNb2O7 and lithiated TiNb2O7 using advanced spherical-aberration-corrected scanning transmission electron microscopy (STEM), to picture the lattice sites occupied by the Li, Ti, Nb and O atoms at atomic-scale. Possible lithiation/delithiation processes and reaction mechanisms are revealed in consistence with first-principles prediction.

New Insight into the Atomic Structure of Electrochemically Delithiated O3-Li(1–x)CoO2 (0 ≤ x ≤ 0.5) Nanoparticles

Direct observation of delithiated structures of LiCoO(2) at atomic scale has been achieved using spherical aberration-corrected scanning transmission electron microscopy (STEM) with high-angle annular-dark-field (HAADF) and annular-bright-field (ABF) techniques. The ordered Li, Co, and O columns for LiCoO(2) nanoparticles are clearly identified in ABF micrographs. Upon the Li ions extraction from LiCoO(2), the Co-contained (003) planes distort from the bulk to the surface region and the c-axis is expanded significantly. Ordering of lithium ions and lithium vacancies has been observed directly and explained by first-principles simulation. On the basis of HAADF micrographs, it is found that the phase irreversibly changes from O3-type in pristine LiCoO(2) to O1-type Li(x)CoO(2) (x ≈ 0.50) after the first electrochemical Li extraction and back to O2-type Li(x)CoO(2) (x ≈ 0.93) rather than to O3-stacking after the first electrochemical lithiation. This is the first report of finding O2-Li(x)CoO(2) in the phase diagram of O3-LiCoO(2), through which the two previously separated LiCoO(2) phases, i.e. O2 and O3 systems, are connected. These new investigations shed new insight into the lithium storage mechanism in this important cathode material for Li-ion batteries.

The low-temperature (400 °C) coating of few-layer graphene on porous Li4Ti5O12viaC28H16Br2 pyrolysis for lithium-ion batteries

Porous Li4Ti5O12 coated with few-layer graphene was prepared via the low-temperature pyrolysis of C28H16Br2 at 400 °C. The coating layer was very thin and uniform. The coated sample shows superior Li storage performance compared with the as-prepared sample. Capacities of 131 and 104 mA h g−1 can be reached at current rates of 5 and 10 C, respectively. Moreover, cyclic performance is significantly improved after coating. The capacity decreases from 144.6 to 124.4 mA h g−1 after 2400 cycles at a current rate of 2 C in a half cellversusLi/Li+, with high capacity retention of 86%.

Monodisperse Iron Phosphate Nanospheres: Preparation and Application in Energy Storage

An approach to synthesize monodisperse nanospheres with nanoporous structure through a solvent extraction route using an acid-base-coupled extractant has been developed. The nanospheres form through self-assembly and templating by reverse micelles in the organic solvent extraction systems. More importantly, the used extractant in this route can be recycled. The power of this approach is demonstrated by the synthesis of monodisperse iron phosphate nanospheres, exhibiting promising applications in energy storage. The synthetic parameters have been optimized. Based on this, a possible formation mechanism is also proposed. The synthetic procedure is relatively simple and could be extended to synthesize other water-insoluble inorganic metal salts.