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_0.15Ni_0.15Mn_0.7]O₂ ionic exchanged from Na_0.75[Li_0.15Ni_0.15Mn_0.7]O₂. 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 O²⁻/O₂ⁿ⁻ 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.