Elevating Li-ion battery paradigms: Sophisticated ionic architectures in lithium-excess layered oxides for unprecedented electrochemical performance

In exploring the frontier of high-energy-density cathode materials for lithium-ion batteries, substantial progress has been made by fine-tuning the composition of Ni-rich cathodes tailored for high-capacity operation. Equally promising are Li-rich cathode materials, which leverage the novel mechanism of oxygen-redox chemistry to achieve enhanced capacities. Nonetheless, the practical realization of these capacities remains elusive, falling short of the desired benchmarks. In this work, we pioneer a Mn-based, Co-free, reduced-nickel, high-capacity cathode material: Li 0.75 Li 0.15 Ni 0.15 Mn 0.7 O 2 ionic exchanged from Na 0.75 Li 0.15 Ni 0.15 Mn 0.7 O 2 . This material is an O2-type layered structure, distinguished by honeycomb ordering within the transition-metal layer, as confirmed by comprehensive neutron and X-ray studies and extensive electrostatic screening. The material's unique structural integrity facilitates the delivery of an exceptional quantity of Li + ions via O 2 − / O 2 n − redox, circumventing oxygen release and phase transition. The de/lithiation process enables the delivery of a substantial reversible capacity of ∼284 ​mAh ​(g-oxide) − 1 (956 ​Wh ​(kg-oxide) − 1 ). Moreover, this structural and chemical stability contributes to an acceptable cycling stability for 500 ​cycles in full cells, providing improved thermal stability with lower exothermic heat generation and thus highlighting the feasibility of a Mn-based, Co-free, reduced-nickel composition. This investigation marks a pivotal advancement in layered lithium cathode materials. • O2-type layered cathode Li 0.75 Li 0.15 Ni 0.15 Mn 0.7 O 2 is a promising cathode for lithium-ion batteries. • Li 0.75 Li 0.15 Ni 0.15 Mn 0.7 O 2 delivers a discharge capacity of 284 ​mAh ​g −1 and an energy density of 956 ​Wh ​kg −1 . • The structural integrity of this O2 structure enables reversible oxygen redox and suppresses phase transition. • Li 0.75 Li 0.15 Ni 0.15 Mn 0.7 O 2 || graphite full cell maintains ∼70 ​% of capacity for 500 cycles at 0.5C.