Xianglan Wu

Synthesis and Electrochemical Properties of Nanocrystalline Li [ Ni0.20Li0.20Mn0.60 ] O 2

A nanocrystalline Li[Ni 0 . 2 0 Li 0 . 2 0 Mn 0 . 6 0 ]O 2 powder was synthesized by a simple combustion method and investigated using X-ray diffraction, scanning electron microscopy, and galvanostatic charge/discharge cycling. The particle size of the powder was distributed in the range of 100-200 nm. Rietveld analysis revealed that Li[Ni 0 . 2 0 Li 0 . 2 0 Mn 0 . 6 0 ]O 2 is basically a layered rock-salt structure in which a small amount of Ni occupies the 3a sites. The initial discharge capacity of the Li/Li[Ni 0 . 2 0 Li 0 . 2 0 Mn 0 . 6 0 ]O 2 cell was about 288 mAh/g when it was cycled at a voltage range of 4.8-2.0 V with a specific current of 20 mA g - 1 . A very promising factor for high-rate capability applications was a reversible capacity of 200 mAh g - 1 at the 100th cycle with a high specific current of 400 mA g - 1 . The weight loss measurement for charged Li 1 - x [Ni 0 . 2 0 Li 0 . 2 0 Mn 0 . 6 0 ]O 2 electrodes gave indirect evidence that the long plateau at 4.5 V did not originate from the ejection of oxygen.

Electrochemical properties of layered Li–Cr–Mn oxides prepared at high temperature

Abstract The Li x Mn 0.91 Cr y O 4+δ material having α-NaFeO 2 structure was prepared by a solution method. This material was calcined at 900 °C to improve its structural stability. The high firing temperature also leads to materials having relatively high crystallinity that is beneficial for good capacity retention. Indeed, the layered Li 3.07 Mn 0.91 Cr 1.06 O 5.37 not only shows relatively good cycle performance but also exhibits an excellent discharge capacity of 191 mA h/g in the first cycle. Cyclic voltammetry and AC impedance spectroscopy were also employed to characterize the reversibility and reactions of lithium insertion and extraction in Li x Mn 0.91 Cr y O 4+δ electrodes.