New Ion Substitution Method to Enhance Electrochemical Reversibility of Co-Rich Layered Materials for Li-Ion Batteries

摘要

The recent development of high-energy LiCoO_2 (LCO) and progress in thematerial recycling technology have brought Co-based materials under thelimelight, although their capacity still suffers from structural instability athighly delithiated states. Thus, in this study, a secondary doping ion substitutionmethod is proposed to improve the electrochemical reversibility of LCOmaterials for Li-ion batteries. To overcome the instability of LCO at highlydelithiated states, Na ions are utilized as functional dopants to exert the pillareffect at the Li sites. In addition, Fe-ion substitution (secondary dopant) isperformed to provide thermodynamically stable surroundings for the Na-iondoping. Density functional theory calculations reveal that the formationenergy for the Na-doped LCO is significantly reduced in the presence of Feions. Na and Fe doping improve the capacity retention as well as the averagevoltage decay at a cutoff voltage of 4.5 V. Furthermore, structural analysisindicates that the improved cycling stability results from the suppressed irreversiblephase transition in the Na- and Fe-doped LCO. This paper highlightsthe fabrication of high-energy Co-rich materials for high voltage operations,via a novel ion substitution method, indicating a new avenue for the manufacturingof layered cathode materials with a long cycle life.