Weak σ–π–σ interaction stabilizes oxygen redox towards high-performance Li–rich layered oxide cathodes

Abstract

The aggregation of Li2MnO3–like domains in Li-rich layered oxides (LLOs) causes severe capacity/voltage fading, which seriously impedes their commercial applications. Here, we design Co–free LLO models with well–dispersed Li2MnO3–like domains (D–LNMO) and aggregated Li2MnO3–like domains (A–LNMO) to investigate the oxygen redox process and structural stability. It is found that low oxygen partial pressure can disperse Li2MnO3–like domains by forming stable ONiMn4+Mn3+Li3 coordination configurations so that D-LNMO is predominant. Moreover, a novel oxygen oxidation mechanism involving a weak σ–π–σ interaction where oxygen redox in OTM2MnLi3 (TM = Ni, Mn) configurations is triggered by O in Li-O-Li configurations is revealed. Specifically, the lattice oxygen at the interface of Li2MnO3–like domains and LiTMO2 domains can be activated, which is beyond conventional Li-O-Li configuration. Due to the abundance of interfacial lattice oxygen in D–LNMO, more lattice oxygen participates in charge compensation, thereby relieving the oxidation load of oxygen ions, suppressing lattice oxygen release, and delaying irreversible structural transformation. Consequently, D-LNMO possesses highly reversible oxygen redox and exceptional structural stability, exhibiting superior cycling stability of high capacity. The findings provide new perspectives and concepts for designing high-energy Li-rich cathodes.