ABSTRACT
Lithium-rich, Mn-based layered oxides Li2 MnO3 -LiMO2 (M=Ni, Co) have been considered as promising cathode candidates owing to their high capacity. However, the resources shortage and high price of cobalt make it imperious to substitute cobalt with other high-abundance elements. Here, we synthesized a low-cost, cobalt-free, Fe-substituted oxide material, Li(Li0.16 Ni0.19 Fe0.18 Mn0.46 )O2 . It exhibited a high reversible capacity of 169.2â mAh g-1 after 100 cycles and maintained an extraordinarily high discharge potential during cycling. X-ray photoelectron spectroscopy and DFT calculations revealed that super iron FeIV exists in the delithiated state, and oxygen participates in the redox reaction in addition to the Ni2+ /Ni4+ and Fe3+ /Fe4+ redox couples. The anionic oxidation preferentially occurred on oxygen with a Li-O-Li configuration and with oxidized Fe and Ni coordination.
ABSTRACT
Monodispersed mesoporous iron fluorides were synthesized by a low-cost reversed micelle method. The as-prepared materials with hierarchical mesoporous structure exhibit excellent rate capability (115.6 mAh g-1 at 2000 mA g-1) which is superior to many other carbon-free iron fluorides. In addition, a high reversible capacity of 143.2 mAh g-1 can be retained after 100 cycles at 1000 mA g-1. The outstanding electrochemical features can be attributed to the particular hierarchical mesoporous structure, facilitating electrolyte penetration as well as rapid electronic and ionic transportation.
