On the structural integrity and electrochemical activity of a 0.5Li(2)MnO(3)center dot 0.5LiCoO(2) cathode material for lithium-ion batteries

Abstract

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.Structural changes in a 0.5Li2MnO3·0.5LiCoO2cathode material were investigated by X-ray absorption spectroscopy. It is observed that both Li2MnO3and LiCoO2components of the material exist as separate domains, however, with some exchange of transition metal (TM) ions in their slab layers. A large irreversible capacity observed during activation of the material in the 1stcycle can be attributed to an irreversible oxygen release from Li2MnO3domains during lithium extraction. The average valence state of manganese ions remains unchanged at 4+ during charge and discharge. In the absence of conventional redox processes, lithium extraction/reinsertion from/into Li2MnO3domains occurs with the participation of oxygen anions in redox reactions and most likely involves the ion-exchange process. In contrast, lithium deintercalation/intercalation from/into LiCoO2domains occurs topotactically, involving a conventional Co3+/Co4+redox reaction. The presence of Li2MnO3domains and their unusual participation in electrochemical processes enable LiCoO2domains of the material to sustain a higher cut-off voltage without undergoing irreversible structural changes.EC/EFRE/200720132-35/EU//BATMA