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

• Published in: Scientific reports 2019-09, Vol.9 (1), p.13180-10, Article 13180
• Main Authors: Lee, Si Yeol, Park, Yong Joon
• Format: Article
• Language: English
• Subjects: 639/301/299/891; 639/4077/4079/891; Batteries; Catalysts; Cathodes; Heat treatment; Humanities and Social Sciences; multidisciplinary; Nanocomposites; Oxides; Oxygen; Phase transitions; Redox reactions; Science; Science (multidisciplinary)
• ISSN: 2045-2322; 2045-2322
• DOI: 10.1038/s41598-019-49806-6

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 Li 2 O 2 during cycling, lithia-based cathodes demand efficient catalysts (dopants). In this study, Ir based materials (Ir and Li 2 IrO 3 ) were introduced as catalysts (dopants) for nanolithia composites. Oxide types (Li 2 IrO 3 ) were used as source materials of catalyst because ductile metal (Ir) can hardly be pulverized during the milling process. Two types of Li 2 IrO 3 were prepared and used for catalyst-sources. They were named ‘1-step Li 2 IrO 3 ’ and ‘2-step Li 2 IrO 3 ’, respectively, since they were prepared by ‘1-step’ or ‘2-step’ heat treatment. The nanocomposites prepared using lithia & 2-step Li 2 IrO 3 presented a higher capacity, more stable cyclic performance, and lower overpotential than those of the nanocomposites prepared using lithia & 1-step Li 2 IrO 3 . The voltage profiles of the nanocomposites prepared using lithia & 2-step Li 2 IrO 3 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.