Highly Reversible Local Structural Transformation Enabled by Native Vacancies in O2-Type Li-Rich Layered Oxides with Anion Redox Activity.

A novel O2-phase Li 1.033 Ni 0.2 [□ 0.1 Mn 0.5 ]O 2 cathode with native vacancies (denoted as "□") was delicately designed. By a combination of noninvasive 7 Li pj-MATPASS NMR and electron paramagnetic resonance measurements, it is unequivocally shown that the reservation of native vacancies enables the fully reversible local structural transformation without the formation of Li in the Li layer (Li tet ) in Li 1.033 Ni 0.2 [□ 0.1 Mn 0.5 ]O 2 during the initial and subsequent cycling. In addition, the pernicious in-plane Mn migration that would result in the generation of trapped molecular O 2 is effectively mitigated in Li 1.033 Ni 0.2 [□ 0.1 Mn 0.5 ]O 2 . As a result, the cycle stability of Li 1.033 Ni 0.2 [□ 0.1 Mn 0.5 ]O 2 is significantly enhanced compared to that of the vacancy-free Li 1.033 Ni 0.2 Mn 0.6 O 2 , showing an extraordinary capacity retention of 102.31% after 50 cycles at a rate of 0.1C (1C = 100 mA g -1 ). This study defines an efficacious strategy for upgrading the structural stability of O2-type Li-rich layered oxide cathodes with reversible high-voltage anion redox activity.