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

Abstract

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: Li0.75[Li0.15Ni0.15Mn0.7]O2 ionic exchanged from Na0.75[Li0.15Ni0.15Mn0.7]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.