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 (NaLi_0.05Fe_0.04Al_0.01Ni_0.4Mn_0.4Ti_0.1O₂), 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.