Phase transitions and related electrochemical performances of Li-Rich layered cathode materials for high-energy lithium ion batteries

Abstract

The present work systematically probes and tracks the phase transition of Li-rich layered Li[Li0.2Mn0.54Ni0.13Co0.13]O2 (marked as LMNCO) by using an ex-situ chemical activation that is realized through ion-exchange and post-annealing processes, in order to understand related electrochemical performances of Li-rich cathode materials for advanced lithium-ion batteries. Ion exchanges of H+-Li+ and subsequent TBA+-H+ (TBA: tetrabutylammonium) in LMNCO are carried out, resulting in its layered-to-spinel phase transition after optimal heat treatments. The resultant compound shows a Li4Mn5O12-type spinel structure. This converted spinel cathode material can deliver discharge capacities higher than 300 mAh/g at 0.1 C and 200 mAh/g at 1 C (1 C = 250 mA/g), respectively, and also exhibits better cycling stability and rate capability in comparison with pristine layered LMNCO and other derivatives. This work offers a feasible route to study all changes of morphologies, crystal structures, chemical compositions, surface areas and related electrochemical lithium storage behaviors during phase transitions of Li-rich layered cathode materials, and thus provides insights on optimizing electrochemical performances for high-energy and high-power lithium ion batteries.