Achieving Enhanced Reversible Anionic Redox Activity in Li-Rich Layered Oxides via LiCoMn₅ Superstructure Design.

Abstract

The Li-rich layered oxide (LRLO) cathode drives the development of low-cost and high-energy-density Li-based batteries, owing to its ultrahigh capacity contributed from cationic redox and extra oxygen anionic redox reaction (ARR). However, unlocking higher ARR activity without compromising reversibility remains challenging. Herein, a series of LRLO samples with varying Ni-Co-Mn compositions is designed to synergistically enhance ARR activity and reversibility. On the one hand, the absence of Co results in suppressed ARR activity for traditional Li_1.2Mn_0.6Ni_0.2O₂ with LiMn₆ superstructures, causing inferior O-related capacity and cycling stability. On the other hand, excessive Co/Mn atomic exchange within the honeycomb structure by forming LiCo_nMn_6-n (n ≥ 2) units activates more O-redox capacity for another typical Li_1.2Ni_0.13Mn_0.54Co_0.13O₂, but induces oxygen instability and low ARR reversibility. Notably, moderate incorporation of Co into LiMn₆ mainly produces LiCoMn₅ (n = 1) superstructures in Li_1.2(Mn_0.65Ni_0.25Co_0.1)_0.8O₂ (LRLO-Co10) with Li₃-O-LiCoMn coordination. This unique structure enables highly reversible ARR activity. Consequently, LRLO-Co10 exhibits a reversible capacity exceeding 300 mAh g^-1 at 0.1C and retains 95.7% of the initial capacity (271.1 mAh g^-1) after 300 cycles at 1C. These findings provide a valuable insight into compositional optimization and a strategy for achieving high-capacity Li-rich cathodes.