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

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 sigma-pi-sigma 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.