Mechanochemical coating with nano-VOPO4: Over lithiated layered oxide with high coulombic efficiency and good thermal stability
Journal
J POWER SOURCES
Date
2018.06.13
Abstract
Multi-functional coating of VOPO4 accommodating the additional lithiation and stabilizing the surface has been introduced onto the over-lithiated layered oxide (OLO). The prepared cathode OLO powder is mechano-chemically coated by multi-functional VOPO4, in which lithium ions can be reversibly inserted/extracted at 3.8 V vs. Li/Li+. Therefore, it is found that impregnation of VOPO4 improves the poor initial Coulombic efficiency of OLO because the initial fully de-lithiated structure of VOPO4 successfully provides the extra lithium storage sites which enables compensating the unavoidable irreversible charging capacity of OLO during the 1st cycle. As the amount of the blended VOPO4 increases to 20 wt.％, the initial Coulombic efficiency of the prepared OLOs is dramatically improves from 86.8 to 93.1 ％. VOPO4 also contributes the lithium ion accommodations at the subsequent cycles and has a high operating potential without consuming a lot of energy density of OLOs. The ball milled nano-size VOPO4 coating is performed on the OLO for high surface stability of OLO. This coating improves cycleability, whereas the total amount of VOPO4 should be limited under 1 wt.％ to detour unfavorable kinetic hindrances. Additionally, thermal stability of the VOPO4 coated sample also highly improves by reducing the heat generation and suppressing the on-set temperature for thermal runaways. The effect of multi-functional VOPO4 coating is studied by systematic analyses comprising structural investigation, electrochemical methods and thermal analyses.