Lithia/(Ir, Li₂IrO₃) nanocomposites for new cathode materials based on pure anionic redox reaction.

ABSTRACT: Anionic redox reactions attributed to oxygen have attracted much attention as a new approach to overcoming the energy-density limits of cathode materials. Several oxides have been suggested as new cathode materials with high capacities based on anionic (oxygen) redox reactions. Although most still have a large portion of their capacity based on the cationic redox reaction, lithia-based cathodes present high capacities that are purely dependent upon oxygen redox. Contrary to Li-air batteries, other systems using pure oxygen redox reactions, lithia-based cathodes charge and discharge without a phase transition between gas and condensed forms. This leads to a more stable cyclic performance and lower overpotential compared with those of Li-air systems. However, to activate nanolithia and stabilize reaction products such as Li₂O₂ during cycling, lithia-based cathodes demand efficient catalysts (dopants). In this study, Ir based materials (Ir and Li₂IrO₃) were introduced as catalysts (dopants) for nanolithia composites. Oxide types (Li₂IrO₃) were used as source materials of catalyst because ductile metal (Ir) can hardly be pulverized during the milling process. Two types of Li₂IrO₃ were prepared and used for catalyst-sources. They were named '1-step Li₂IrO₃' and '2-step Li₂IrO₃', respectively, since they were prepared by '1-step' or '2-step' heat treatment. The nanocomposites prepared using lithia & 2-step Li₂IrO₃ presented a higher capacity, more stable cyclic performance, and lower overpotential than those of the nanocomposites prepared using lithia & 1-step Li₂IrO₃. The voltage profiles of the nanocomposites prepared using lithia & 2-step Li₂IrO₃ were stable up to a limited capacity of 600 mAh·g^-1, and the capacity was maintained during 100 cycles. XPS analysis confirmed that the capacity of our lithia-based compounds is attributable to the oxygen redox reaction, whereas the cationic redox related to the Ir barely contributes to their discharge capacity.

SUBMITTER: Lee SY 

PROVIDER: S-EPMC6742652 | biostudies-literature | 2019 Sep

REPOSITORIES: biostudies-literature