A Multi‐Element Composition Modulation Strategy for Designing High‐Capacity and Stable O3‐Type Na‐Layered Oxide

Unstable high‐capacity cathodes remain a substantial barrier to enhancing the energy density of Na‐ion batteries (NIBs). While the high‐entropy strategy has demonstrated significant advantages in improving the performance of layered oxide cathodes, the specific capacities of reported high‐entropy oxides remain relatively low (<150 mAh g−1). This prompts a reconsideration toward leveraging not just high entropy, but also the synergy among multiple elements to meet the demands for higher energy density. Herein, a multi‐element composition modulation strategy is proposed to obtain cathodes without compromising on capacity, exemplified by LFANMT (NaLi0.05Fe0.04Al0.01Ni0.4Mn0.4Ti0.1O2), which achieves a remarkable specific capacity exceeding 180 mAh g−1 at 4.3 V. It is visualized that single‐crystal particles with surface compressive stress and bulk tensile stress exhibit superior surface lattice oxygen stability and crack resistance during cycling. Constructing an initial stress‐protective layer is beneficial for alleviating the internal and external stress differences caused by uneven Na+ extraction during the O3‐P3 phase transition. Through precise elemental modulation, cathodes exhibiting excellent cycling stability with negligible voltage decay under high voltage are successfully obtained. The work provides an effective approach for designing high‐capacity O3‐type layered oxides for NIBs, emphasizing the importance of synergistic effects among elements.