Search

Nanosheets can be used as building blocks to fabricate versatile nanostructured materials. In this paper, morphology of the Cs4W11O36 and Nb3O8 and TaO3 sheets with different layers are analyzed by different field-emission scanning electron microscopes (FE-SEMs). Chemical composition of the single-layered Cs4W11O36 with thickness of about 2 nm, and multilayered Nb3O8 nanosheets with thickness of less than 14 nm are analyzed by both the Si(Li) solid-state detector and transition edge sensor (TES) microcalorimeter, successfully. The effects of energy resolution, accelerating voltage and substrate on the quantitative analysis are discussed briefly. [ABSTRACT FROM AUTHOR]

LiFePO4 is a well-known electrode material that is capable of high-rate charging and discharging despite a strong phase-separation tendency of the lithium-rich and poor end-member phases. X-ray diffraction measurements (XRD) with high time-resolution are conducted under battery operation conditions to reveal the phase-transition mechanism of LiFePO4 that leads to the high rate capability. We here propose a hidden two-step phase transition of LiFePO4 via a metastable phase. The existence of the metastable phase, not just a member of a transient solid solution, is evidenced by the operando XRD measurements. Our two-step phase-transition model explains the behavior of LiFePO4 under the battery operation conditions. It also explains asymmetric behavior during the charging and discharging at high rates and low temperatures, as well as apparent single-step two-phase reaction between the end members at low rates at room temperature. This model also suggests underlying, rate-dependent electrochemical processes that result from a competing disproportion reaction of the metastable phase. [ABSTRACT FROM AUTHOR]

Nickel-substituted manganese spinel LiNi0.5Mn1.5O4 (LNMO) is a promising 5 V class positive electrode material for lithium-ion batteries. As micronsized LNMO particles show high rate capability in its two-phase coexistence regions, the phase transition mechanism is of great interest in understanding the electrode behavior at high rates. Here, the phase transition dynamics of LixNi0.5Mn1.5O4 is elucidated on high rate charging-discharging using operando time-resolved X-ray diffraction (TR-XRD). The TR-XRD results indicate the existence of intermediate states, in addition to the thermodynamically stable phases, and it is shown that the origin of such intermediate states is ascribed to the solid-solution domains at the phase transition front, as supported by the analysis using transmission electron microscopy coupled with electron energy-loss spectroscopy. The phase transition pathways dependent on the reaction rate are shown, together with possible explanation for this unique transition behavior. [ABSTRACT FROM AUTHOR]